当前位置:文档之家› Trail A Distance Sensitive Sensor Network Service For Distributed Object Tracking

Trail A Distance Sensitive Sensor Network Service For Distributed Object Tracking

Trail A Distance Sensitive Sensor Network Service For Distributed Object Tracking
Trail A Distance Sensitive Sensor Network Service For Distributed Object Tracking

Trail:A Distance Sensitive Sensor Network Service For Distributed Object Tracking

VINODKRISHNAN KULATHUMANI,ANISH ARORA,MUKUNDAN SRIDHARAN Dept.of Computer Science and Engineering

The Ohio State University

and

MURAT DEMIRBAS

Dept.of Computer Science and Engineering

University at Bu?alo,SUNY

2·Vinodkrishnan Kulathumani et al.

1.INTRODUCTION

Tracking of mobile objects has received signi?cant attention in the context of cel-lular telephony,mobile computing,and military applications[Abraham et al.2004; Dolev et al.1995;Awerbuch and Peleg1995;Demirbas et al.2004].In this paper, we focus on the tracking of mobile objects using a network of static wireless sen-sors.Examples of such applications include those that monitor objects[Arora et al. 2004;He et al.2006;Arora and Ramnath2004],as well as applications that“close the loop”by performing tracking-based control;an example is a pursuer-evader tracking application,where a controller’s objective is to minimize the catch time of evaders.

We are particularly interested in large scale WSN https://www.doczj.com/doc/2b18236151.html,rge networks motivate several tracking requirements.First,queries for locations of objects in a large network should not be answered from central locations as the source of the query may be close to the object itself but still have to communicate all the way to a central location.Such a centralized solution not only increases the latency but also depletes the intermediate nodes of their energy.Plus,answering queries locally may also be important for preserving the correctness of applications deployed in large WSNs.As a speci?c example,consider an intruder-interceptor application, where a large number of sensor nodes lie along the perimeter that surrounds a valuable asset.Intruders enter the perimeter with the intention of crossing over to the asset and the objective of the interceptors is to“catch”the intruders as far from the asset as possible.In this case,it has been shown[Cao et al.2006]that there exist Nash equilibrium conditions which imply that,for satisfying optimality constraints,the latency with which an interceptor requires information about the intruder it is tracking depends on the relative locations of the two:the closer the distance,the smaller the latency.This requirement is formalized by the property of distance sensitivity for querying,i.e.,the cost in terms of latency and number of messages for returning the location of a mobile object grows linearly in terms of the distance between the object and the querier.

Second,tracking services for large networks must eschew solutions with dispropor-tionate update costs that update object locations across the network even when the object moves only by a small distance.This requirement is formalized by the prop-erty of distance sensitivity for updates,i.e.,the cost of an update is proportional to the distance moved by the object.Querying,by itself,for events or information of interest in WSNs has received signi?cant attention[Intanogonwiwat et al.2003; Ratnasamy et al.2002;Liu et al.2004]and some of them focus on distance sensitive querying[Ratnasamy et al.2002;Sarkar et al.2006;Funke et al.2006].In those solutions,information from a source is published across the network in such a way that queries can be resolved in a distance sensitive manner but the solutions do not address the update of the published information when an object moves.The focus of our work is on the tracking of mobile objects and we additionally require that the update cost is distance sensitive.

Contributions:In this paper,we use geometric ideas to design an energy-e?cient, fault-tolerant and hierarchy-free WSN service,Trail,that supports tracking-based WSN applications.The speci?cation of Trail is to return the location of a particular The Ohio State University Technical Report,Vol.,No.,072006.

Trail:A Distance Sensitive Network Service For Distributed Object Tracking·3 object in response to an in-network subscriber issuing a?nd query regarding that object.Trail has a?nd cost that is linear(O(d f))in terms of the distance(d f)of the subscriber from the object.To this end,Trail maintains a tracking data structure by propagating mobile object information only locally,and satisfying the distance sensitivity requirement for the track updates.The amortized cost of updating a track when an object moves a distance d m is O(d m?log(d m)).

A basic Trail protocol can be re?ned by tuning certain parameters,thus resulting in a family of Trail protocols.Appropriate re?nements of the basic Trail protocol are well suited for di?erent network sizes and?nd/update frequency settings:One re?nement is to tighten its tracks by progressively increasing the rate at which the tracking structure is updated;while this results in updating a large part of the tracking structure per unit move,which is for large networks still update distance sensitive,it signi?cantly lowers the?nd costs for objects at larger distances.An-other re?nement increases the number of points along a track,i.e.,progressively loosens the tracking structure in order to decrease the?nd costs and be more?nd-centric when object updates are less frequent or objects are static.Moreover,Trail scales well to networks of all sizes.As network size decreases,Trail gradually es-chews local explorations and updates and thus increasingly centralizes update and ?nd.

We evaluate the performance of Trail by simulations in a90×90sensor network and experiments on105Mica2nodes in the Kansei testbed[Arora et al.2006].This implementation has been used to support a distributed intruder interceptor tracking application where the goal of the interceptor is to catch the intruders as far away from an asset as possible.

Overview of solution:Trail maintains tracks from each object to only one termi-nating point,namely,the center of the network C;these tracks are almost straight to the center,with a stretch factor of at most1.2times the distance to C.Note that if the track to an object P is required to be always a straight line from C to the current location of P resulting in a stretch factor equal to1,then every time the object moves,the track has to be updated starting from C,which would not be a distance sensitive approach.Therefore,we form the track as a set of trail segments and update only a portion of the structure depending upon the distance moved.Thus given a terminating point Trail maintains a track with lengths from the terminating point that is almost close to minimum.This is important because longer tracks have a higher cost of initialization and given that network nodes may fail due to energy depletion or hardware faults,longer tracks increase the proba-bility of a failed node along a track as well as increase the cost of detecting and correcting failures in the track.

Given the track to an object,a?nd operation explores along circles of exponentially increasing radii until the track is intersected and then follows the track to the current location of the object.The tracks maintained in Trail only contain pointers to the current location of an object and not the state information of the object. Publishing the current state(namely location)of the object along all points in track will violate distance sensitivity of updates because every move of the object will result in updating the entire track.Following the trail of an object from any

The Ohio State University Technical Report,Vol.,No.,072006.

4·Vinodkrishnan Kulathumani et al.

location leads to the current location of the object which contains the state of the object.Yet Trail is distance sensitive in terms of the?nd in the sense that the total cost of reaching the track for an object,and following the track to reach the object is proportional to the distance of the?nder from the object.Note that a ?nd explores along circles until a radii that is at most half the distance of the?nder to C and then searches at C where the track is certain to be found.Thus C serves as a worst case landmark for?nding objects in the network.

In our solution,we make some design decisions like choosing a single point to ter-minate tracks from all points in the network and avoiding hierarchy in maintaining the tracks.In Section7,we analyze these aspects of our solution and compare them with other possible approaches.

Organization of the paper:In Section2,we describe the system model and problem speci?cation.In Section3,we design the basic Trail protocol for a2-d real plane.Then,in Section4,we present an implementation of the basic Trail protocol for a2-d sensor network.In Section5,we discuss re?nements of the basic Trail protocol.In Section6,we present results of our performance evaluation.In Section7,we analyze some design decisions made in our solution and compare them with other possible approaches.In Section8,we discuss related work and,in Section9,we make concluding remarks and discuss future work.

2.MODEL AND SPECIFICATION

The system consists of a set of mobile objects,and a network of static nodes that each consist of a sensing component and a radio component.Tracking applications execute on the mobile objects and use the sensor network to track desired mobile objects.Object detection and association services execute on the nodes,as does the desired Trail network tracking service.

The object detection and association service assigns a unique id,P,to every object detected by nodes in the network and stores the state of P at the node j that is closest to the object P.This node is called the agent for P and can be regarded as the node where P resides.The problem of detecting objects in the network and uniquely associating them with previous detections is thus orthogonal to the tracking service that we discuss in this paper.Detection and association services can be implemented in a centralized[Sinopoli et al.2003]or distributed[Shin et al. 2003]fashion;the latter approach would suit integration with the tracking service that we discuss in this paper.As a network level service,we do not make any assumptions about the quality of these detections and leave the implications of false detections and associations to be dealt with at the application layer.

Trail Network Service:Trail maintains an in-network tracking structure,trail P, for every object P.Trail supports two functions:?nd(P,Q),that returns the state of the object P,including its location at the current location of the object Q issuing the query and move(P,p’,p)that updates the tracking structure when object P moves from location p to location p.

De?nition2.1?nd(P,Q)Cost.The cost of the?nd(P,Q)function is the total communication cost of reaching the current location of P starting from the current location of Q.

The Ohio State University Technical Report,Vol.,No.,072006.

Trail:A Distance Sensitive Network Service For Distributed Object Tracking·5 De?nition2.2move(P,p’,p)Cost.The cost of the move(P,p ,p)function is the total communication cost of updating trail P to the new location p and deleting the tracking structure to the old location p .

We note that our network service does not assume knowledge of the motion model of objects being tracked,in contrast to some query services[Lu et al.2005],and as such the scope of every query in our case is the entire network as opposed to a certain locality.Nor does it assume a bound on the number of querying objects in the network or any synchrony between concurrent queries.

Network Model:To simplify our presentation,we?rst describe Trail in a2-d real continuous plane.We then re?ne the Trail protocol to suitably implement in a random connected deployment of a wireless sensor network.In this model, we impose a virtual grid on the random deployment and snap each node to its nearest grid location(x,y).Each node is aware of this location.We refer to unit distance as the one hop communication distance.dist(i,j)now stands for distance between nodes i and j in these units.We describe this model in more detail and the implementation of Trail in this discrete model in Section4.

Fault Model:In the wireless sensor network,we assume that nodes can fail due to energy depletion or hardware faults or there could be insu?cient density at certain regions,thus leading to holes in the network.However,we assume that the network may not be partitioned;there exists a path between every pair of nodes in the network.

3.TRAIL

In this section,we use geometric ideas to design Trail for a bounded2-d real plane. Let C denote the center of this bounded plane.

3.1Tracking Data Structure

We maintain a tracking data structure for each object in the plane.Let P be an object being tracked,and p denote its location on the plane.We denote the tracking data structure for object P as trail P.Before we formally de?ne this tracking structure,we give a brief overview.

Overview:If trail P is de?ned as a straight line from C to P,then every time the object moves,trail P has to be updated starting from C.This would not be a distance sensitive approach.Hence we form trail P as a set of trail segments and update only a portion of the structure depending upon the distance moved.The number of trail segments in trail P increases as dist(p,C)increases.Rather,the end points of the trail segments serve as marker points to update the tracking structure when an object moves.The point from where the update is started depends on the distance moved.Only,when P moves a su?ciently large distance,trail P is updated all the way from C.We now formally de?ne trail P.

De?nition3.1trail P.The tracking data structure for object P,denoted by trail P,for dist(p,C)≥1is a path obtained by connecting any sequence of points (C,N mx,...,N k,...,N1,p)by line segments,where mx≥1,and there exist auxil-iary points c1..c mx that satisfy the properties(P1)to(P3)below.mx is de?ned as

The Ohio State University Technical Report,Vol.,No.,072006.

6·Vinodkrishnan Kulathumani et al.

(log 2(dist (C,p o ))) ?1,where p o is the location of p when trail P was initialized or updated starting from C .

For brevity,let N k be the level k vertex in trail P ;let the level k trail segment in trail P be the segment between N k and N k ?1;let Seg (x,y )be any line segment between points x and y in the plane.

—(P1):dist (c k ,N k )=2k ,(mx ≥k ≥1).

—(P2):N k ?1,(mx ≥k ≥1),lies on Seg (N k ,c k ?1);N mx lies on Seg (C,c mx ).—(P3):dist (p,c k )<2k ?b ,(mx ≥k ≥1)and b ≥1is a constant.

If (dist (p,C )=0),trail P is C ;and if (0≤dist (p,C )<1),trail P is Seg (C,p ).

(a)Initial

trail P

(b)P moves away from c 3(c)P moves back towards c 3Fig.1.Examples of Trail to an Object P

Observations about trail P :From the de?nition of trail P ,we note that the auxiliary points c 1..c mx are used to mark vertices N 1..N mx of trail P .P 1and P 2describe the relation between the auxiliary points and the vertices of trail P .Given trail P ,points c 1..c mx are uniquely determined using P 1and P 2.Similarly given p and c 1,..c mx ,trail P is uniquely determined.These properties are stated in the following Lemmas.

Lemma 3.2.Given trail P ,points c 1..c mx are uniquely determined.

Proof.Extend Seg (C,N mx )of trail P by a distance of 2mx to obtain c mx .Sim-ilarly extend Seg (N k ,N k ?1)by 2k ?1to obtain c k ?1for 0

Lemma 3.3.Given c 1,...c mx and p ,trail P is uniquely determined.

The Ohio State University Technical Report,Vol.,No.,072006.

Trail:A Distance Sensitive Network Service For Distributed Object Tracking·7 Proof.N mx lies on Seg(C,c mx)such that dist(c mx,N mx)=2mx.Similarly N k?1lies on Seg(N k,c k?1)such that dist(c k?1,N k?1)=2k?1for1

By property P3,the maximum separation between p and any auxiliary point c k decreases exponentially as k decreases from mx to1.When an object moves a certain distance away from its current location,trail P has to be updated from the smallest index k such that property P3holds at all levels.By changing parameter b in property P3,we can tune the rate at which the tracking structure is updated. We discuss these re?nements in Section5.

Note from the de?nition of trail P that mx is de?ned as (log2(dist(C,p o))) ?1 where p o was the location of the object when trail P was either created or up-dated from C.The value of mx which denotes the number of trail segments in trail P,depends on the distance of P from C.When trail P is?rst created, c1,...,c mx are initialized to location p o,the number of levels mx is initialized to (log2(dist(C,p o))) ?1and trail P is a straight line.The value of mx is updated when trail P has moved a su?cient distance to warrant an update of trail P all the way from C.The update(and create)procedure for trail P is described in more

detail in the following subsection.

We now show3examples of the tracking structure in Fig.1.In this?gure,b=1. Fig.1(a)shows trail P when c3,..c1are collocated.When P moves away from this location,trail P is updated and Fig.1(b)shows an example of trail P where c2,c1 are displaced from c3.In Fig.1(b),dist(c3,c2)=2units,dist(c2,c1)=1unit,and p and c1are collocated.Moreover,N3lies on Seg(C,c3),N2lies on Seg(N3,c2) and so on.In Fig.1(c)we show an example of a zigzag trail to an object P,when P moves away from c3and then moves back in the opposite direction.

3.2Updating the trail

We now describe a procedure to update the tracking structure when object P moves from location p to p such that the properties of the tracking structure are maintained and the cost of update is distance sensitive.

Overview:When an object moves distance d away,if the distance dist(c1,p)≤1,then the trail is updated by replacing segment(N1,p )with segment(N1,p). Otherwise,we?nd the minimal index m,along trail P such that dist(p,c j)<2j?b for all j such that mx≥j≥m and trail P is updated starting from N m.In order to update trail P starting from N m,we?nd new vertices N m?1...N1and a new set of auxiliary points c m?1...c1.Let N m?1...N 1and c m?1...c 1denote the old vertices and old auxiliary points respectively.Starting from N m,we follow a recursive procedure to update trail P.This procedure is stated below:

Update Algorithm:

(1)If dist(p,c1)>1,then let m be the minimal index on the trail such that

dist(p,c j)<2j?b for all j such that mx≥j≥m.

(2)k=m

(3)while k>1

The Ohio State University Technical Report,Vol.,No.,072006.

8·Vinodkrishnan Kulathumani et al.

Fig.2.Updating trail P

(a)c k?1=p;Now obtain N k?1using property P2as follows:the point on

segment N k,c k?1,that is2k?1away from c k?1.

(b)k=k?1

If no indices exist such that dist(c k,p)<2k?1,then the trail is created starting from C.This could happen if the object is new or if the object has moved a su?ciently large distance from its original position.In this case,mx is set to ( log2(dist(C,p)) )?1.c mx is set to p.N mx is marked on Seg(C,p)at distance 2mx from c mx.Step1is executed with k=mx.

Fig.2illustrates an update operation,when b=1.In Fig.2a,dist(p,p )is2 units.Hence update starts at N3.Initially c3,c 2,c 1are at p .We use the update algorithm to determine new c2,c1and thereby the new N2,https://www.doczj.com/doc/2b18236151.html,ing step(3a) of the update algorithm,the new c2and c1lie at p.The vertex N2then lies on Seg(N3,c2)and N1lies on Seg(N2,c1).In Fig.2b,P moves further one unit.Hence update now starts at https://www.doczj.com/doc/2b18236151.html,ing step(3a)of the update algorithm,the new c1lies at p and N1lies on Seg(N2,c1).

Lemma3.4.The update algorithm for Trail yields a path that satis?es trail P. Proof.(1)Let m be the index at which update starts.By the condition in step1,dist(c j,p)<2j?b for all mx≥j≥m.Now,for m>j≥1,c j=p.

Therefore for m>j≥1,dist(c j,p)<2j?b.Thus property P3is satis?ed. (2)Properties P2and P1are satis?ed because m≥k>1,we obtain N k?1as the

point on Seg(N k,c k?1),that is2k?1away from c k?1.

(3)mx is de?ned for trail P,when trail P is created or updated starting from C.

When mx is(re)de?ned for trail P,c mx is the position of the object and mx is set to( log2(dist(C,p)) )?1.

De?nition3.5Trail Stretch Factor.Given trail P to an object p,we de?ne the trail stretch factor for any point x on trail P as the ratio of the length along trail P from x to p,to the Euclidean distance dist(x,p).

Lemma3.6.The maximum Trail Stretch Factor for any point along trail P,de-noted as T S p is sec(α)?sec(α

).

2b

The Ohio State University Technical Report,Vol.,No.,072006.

Trail:A Distance Sensitive Network Service For Distributed Object Tracking ·9

(a)Max Angle in Trail

(b)Analyzing Stretch Fig.3.Analyzing Trail Stretch Factor

Proof.We prove Lemma 3.6by using the following steps.

(Maximum angle (

pN k c k is maximum when Seg (N k ,p )is tangent to a circle of radius 2k ?b and center c k .Therefore we have the following condition.

α

dist (x,p )=(sin (θ)+sin (φ))

pN k c k .Using this,we get Eq.3

(θ+φ)≤α

(3)

Let f (θ,φ)denote the following function.

f (θ,φ)=(sin (θ)+sin (φ))2.

We state this as Proposition B.1and prove it in Appendix B.

Substituting (θ=φ)in Eq.2,we get the following condition.

The Ohio State University Technical Report,Vol.,No.,072006.

10·Vinodkrishnan Kulathumani et al.

(dist (x,N k )+dist (N k ,p ))

2)(5)

Thus,we see that at a single level k the maximum stretch for trail P occurs when

pxN k =

pxN k =

dist (x,p )=(dist (N k ,p ))2)

pN j c j =αand N j pN j ?1for all k ≥j >1.In Fig.4,we show one such trail segment ,Seg (N j ,N j ?1)of trail P .

Fig.4.Analyzing Trail Stretch

Using Eq.6,we get the following equations:

dist (N j ?1,p )2)

dist (N j ,p )=sec (α2?j :k ≥j >1(8)

When the above con?guration is repeated at all levels of trail P ,we determine the ratio of the lengths of two successive trail segments ,Seg (N j ?1,N j ?2)and Seg (N j ,N j ?1).Using Eq.7and Eq.8,we get the following equation.

dist (N j ?1,N j ?2)2)

Trail:A Distance Sensitive Network Service For Distributed Object Tracking·11 Let L k denote the length along trail P from vertex N https://www.doczj.com/doc/2b18236151.html,ing Eq.9,we get:

L k=dist(N2,N1)?j=(k?2)

j=0

(2?cos(

α

dist(N k,p)

(11)

Upon simpli?cation using Eq.7,Eq.8and Eq.10,we get:

R k=

1

2)?1

+

1

2

))k?1?(1?

1

2

)?1

)(12)

Since,α<π

2

)?1≤1.Therefore we get:

R k≤1

2)?1

(13)

Since,cos(α)=2?cos2(α

2

)≤1and0<2?cos(α

cos(α)

(14)

(Maximum trail stretch factor from any point in trail P to p)Let x be any point on trail P which lies on a level k+1segment,i.e Seg(N k+1,N k),but is not a vertex point.Let L xp denote the length along trail P from x to https://www.doczj.com/doc/2b18236151.html,ing Eq.14 and Eq.5,we have the following inequalities:

L xp≤dist(x,N k)+dist(N k,p)?sec(α)

≤(dist(x,N k)+dist(N k,p))?sec(α)

≤sec(α

2

)whereα=arcsin(1

12·Vinodkrishnan Kulathumani et al.

update starting at the level k vertex.Thus,between any two successive updates starting from a level k vertex,the object must have moved at least a distance of 2k?1?b.The total cost to create a new path and delete the old path starting from a level k vertex costs at most2?L k.

When an object moves a distance d m where d m>1,it could involve multiple updates at smaller distances.The object could be detected at multiple instances over this distance d m.Therefore we calculate the upper bound on the amortized cost of update when the object moves distance d m.We consider the minimum distance to trigger an update to be1unit.Note that between any two successive updates starting from a level k vertex,the object must have moved at least a distance of 2k?1?b.Thus over a distance d m,update can start at level(b+1)vertex at most d m times,update can start at level(b+2)vertex can at most d m/2 times,and so on.The update can start at level( log2(d m) +b+1)vertex at most once.Adding the total cost,the result follows.

b Update Cost

1.2

1.05

Approaches1

Trail:A Distance Sensitive Network Service For Distributed Object Tracking·13

(a)?nd path(b)Farthest?nd point

Fig.6.Basic?nd algorithm in Trail

Now,when the trail is intersected by the circle of radius2 log(d f) ,the point s at which the trail is intersected can be at most3?d f away from the object p.This is illustrated in Fig.6(b).In this?gure,q is d f+?away from p.Hence the trail can be missed by circle of radius2log(d f).From Lemma3.6,we have that distance along the trail from s to p is at most3?T S p?d f.Thus,the cost of?nding an object P at point p from object Q at point q is O(d f)where d f is dist(p,q). Remark on update cost:Note that in Theorem3.8we have characterized the upper bound on the amortized cost of update when an object moves distance d m. This is because over a distance of d m,the object can be detected in multiple instances and consequently multiple update of the track can result over a distance d m.We consider the minimum distance to trigger an update to be1unit.We add the total cost resulting from each update and the sum of the cost of all these possible updates results in an upper bound on the amortized cost.

But we note that,when an object makes a discrete or direct jump of distance d m,the logarithmic factor in the cost disappears.In other words,when an object disappears at a certain location and is later detected at another location,the cost of individual updates need not be added.However there is an additional cost of exploring to?nd an existing trail because we do not assume memory of the previous location of an object.In the continuous setting we ignore the cost of?nding an existing trail P as it will exist within a distance of1unit.The cost of update when an object makes a discrete jump of distance d m is summarized below.

Theorem3.10.The cost of updating trail P when object P makes a discrete jump of distance d m is O(d m).

Proof.When P moves distance d m away,an existing trail P can be intersected at a cost of8?π?d m.This follows from the proof of Theorem3.9.The highest level at which the update can start is level( log2(d m) +b+1)vertex.The cost of modifying the trail pointers is then bounded by4?(2b+1)?T S p?d m.The result follows.

4.IMPLEMENTING TRAIL IN A WSN

In this section,we describe how to implement the Trail protocol in a WSN that is a discrete plane,as opposed to a continuous plane as described in the previous section.

The Ohio State University Technical Report,Vol.,No.,072006.

14·Vinodkrishnan Kulathumani et al.

Trail can be implemented in any random deployment of a WSN aided by some approximation for routing along a circle.We describe one such implementation below.

System model:Consider any random deployment of nodes in the WSN.We impose a virtual grid on this deployment and snap each node to its nearest grid location(x,y)and assume that each node is aware of this location.We refer to unit distance as the one hop communication distance.dist(i,j)now stands for distance between nodes i and j in these units.The separation along the grid is less than or equal to the unit distance.When the network is dense,the grid separation can be smaller.The neighbors of a node are a set of all nodes within unit distance of the node.Thus when the grid separation is unit distance,there are at most4 neighbors for each node.We also assume the existence of an underlying geographic routing protocol such as GPSR[Karp and Kung2000],aided by an underlying neighborhood service that maintains a list of neighbors at each node.

Note:We have implicitly assumed in the above model that each location on the grid is mapped to a unique node.This can be achieved by decreasing the size of the grid to be equal to the smallest separation between any2nodes in the network. However this assumption is not necessary.In other words,all nodes need not be necessarily assigned to some location on the grid.Nodes can take turns to play the role of a given location.But for ease of exposition,we have abstracted away these possibilities in our model.

Fault Model:We assume that nodes in the network can fail due to energy de-pletion or hardware faults,or there could be insu?cient density at certain regions, thus leading to holes in the network.However,we assume that the network may not be partitioned;there exists a path between every pair of nodes in the network.

A node may also transiently fail.But we assume that the failed nodes return in a clean or null state without any knowledge of tracks previously passing through them.We do not consider arbitrary state corruptions in the nodes.

When implementing on a WSN grid,Trail is a?ected by the following factors:(1) discretization of points to nearest grid location;(2)Overhead of routing between any two points on the grid;and(3)holes in the network.We discuss these issues in this section.

Routing stretch factor:When using geographic routing to route on a grid,the number of hops to communicate across a distance of d units will be more than d.We measure this stretch in terms of the routing stretch factor,de?ned as the ratio of the communication cost(number of transmissions)between any two grid locations,to the Euclidean distance d between two grid locations.It can be shown

√that the upper bound on the routing stretch factor for the WSN unit grid is

Trail:A Distance Sensitive Network Service For Distributed Object Tracking·15 around the?nder.However,in the grid model,we approximate this procedure and instead of exploring around a circle of radius r,we explore along a square of side 2?r.The perimeter of the square spans a distance8?r instead of2?π?r.Tighter approximations of circle are possible,but approximating with a square is simpler. We characterize the upper bound on the?nd cost in the following Lemma,whose proof can be found in Appendix C.

Lemma4.1.The upper bound on the cost of?nding an object P at point p from object Q at point q is(32+3?sec(α)?sec(α2)?d f where d f is dist(p,q)and α=arcsin(1

16·Vinodkrishnan Kulathumani et al.

4.3Fault-Tolerance

Due to energy depletion and faults,some nodes may fail leading to holes in the WSN.Trail supports a graceful degradation in performance in the presence of node failures.As the number of failures increase,there is only a proportional increase in ?nd and update costs as the tracking data structure and the ?nd path get dis-torted.This is especially good when there are a large number of small holes in the network that are uniformly distributed across the network as has been the case in our experiments with large scale wireless sensor networks [Bapat et al.2005].We discuss the robustness of Trail under three scenarios:during update ,during ?nd and maintaining an existing trail.

Tolerating node failures during update :A grow message is used to update a trail starting at a level k mote and is directed towards the center of circle k ?1.In the presence of holes,we use a right hand rule,such as in [Karp and Kung 2000],in order to route around the hole and reach the destination.As indicated in the update algorithm for WSN grid,during routing the node closest to,but outside a circle of radius 2k ?1around c k ?1is marked as N k ?1.Since we assume that the network cannot be partitioned,eventually such a node will be found.(If all nodes along the circle have failed,the network is essentially partitioned).

Tolerating failures during a ?nd :We now describe how the ?nd message explores in squares of increasing levels.When a ?nd message comes across a hole,it is rerouted around the hole using geographic routing only radially outwards of the current level square.If during the re-route,we reach a distance from the source of the ?nd corresponding to the next level of search,we continue the search at the next level and so on.Thus,in the presence of larger holes,we abandon the current level and move to the next level,instead of routing around the hole back to the current level of exploration.

(a)Find re-route along same level

(b)Find re-route to next level Fig.8.Tolerating failures during ?nd

Maintaining an existing trail:Nodes may fail after a trail has been created.In order to stabilize from these states,we use periodic heartbeat actions along the trail.We assume that if a node has a transient failure,the node returns in a null state.We do not handle arbitrary state corruptions in the nodes.

The Ohio State University Technical Report,Vol.,No.,072006.

Trail:A Distance Sensitive Network Service For Distributed Object Tracking·17 The heartbeat actions are sent by each node along trail P to its child.At any node r,if a heartbeat is not received from its child,a search message is sent using geographic routing tracing the boundary of the hole.trail P is reinforced starting from the?rst node where the search message intersects trail P using a reinforce message along the reverse path.(If the goal is to?nd trail P in the shortest time, the search should likely be enforced in both directions along the boundary of the hole).

Tolerating failure of C:The terminating point C provides a sense of direction to the trail and serves as a?nal landmark for the?nd operation.If C fails,the node that is closest to C will takeover the role of C.However,even in the transient stage when there is no C,the failure of C is tolerated locally.We describe this below.

Consider that C and all nodes in a contiguous region around C have failed.In this case,a search message will be initiated from the node closes to C that be-longs to trail P.Because a contiguous set of nodes surrounding C have failed,the search message eventually returns to the node initiating the search by following the boundary of the hole.Thus an existing trail P terminates at the node that belongs to trail p and is closest to C.Thus if a?nd message is unable to reach C, then routing along the boundary of the hole will intersect trail P.

When a new node takes over the role of C,we do not assume that the state of the original C is transferred.The new C has no knowledge of tracks passing through it. Eventually,the maintenance actions for Trail will result in all tracks terminating at C.

5.REFINEMENTS OF TRAIL

In Sections3and4,we have described the basic Trail protocol.In this section, we discuss two techniques to re?ne the basic Trail network protocol:(1)tuning how often to update a Trail tracking structure,and(2)tuning the shape of a Trail tracking structure.This yields a family of protocols.

In the?rst re?nement we alter the parameter b to values greater than1.By increasing b,we update the track of an object more often.This results in straighter tracks with smaller stretch factor.As tracks get straighter,the?nd pattern at higher levels of the search can follow a triangular pattern(as illustrated in Fig.9) as opposed to complete circles.In fact,as b increases circular explorations can be avoided at more levels of the?nd.Thus the average?nd cost in the network decreases as b increases.In sum by increasing b,we increase the cost of update and decrease the cost of?nd.This re?nement can be used when the rate of updates is small as compared to the rate of?nd.For example,as the speed of objects in the network decreases,we can increase the value of b.

In the second re?nement we change the length of each segment in Trail.In the basic protocol,the segment at each level is a straight line to the next lower level. In this re?nement,we modify the length of each segment to be a straight line to the next level plus an arc of length x×2k.As x increases the amount of update at each level increases,but the?nd exploration can now be smaller.Speci?cally when

The Ohio State University Technical Report,Vol.,No.,072006.

18·Vinodkrishnan Kulathumani et al.

x=2×π,the?nd is a straight line towards the center of the network.We call this particular parameterization,the?nd-centric Trail protocol.

5.1Tightness of Trail Tracking Structure

The frequency at which trail P is updated depends on parameter constant b in property P3of trail P.As seen in Section3,for values of b>1,trail P is updated more and more frequently,hence leading to larger update costs.However,trail P becomes tighter and tends to a straight line with the trail stretch factor approaching 1.We exploit this tightness of trail p to optimize the?nd strategy.

5.1.1Optimization of?nd.The intuition behind this optimization is that since the trail to any object P originates at C,the angle formed by p with C and the higher level vertices is small and bounded.Hence as the levels of explorations increase in ?nd,we can progressively decrease the size of exploration from full circles.We now describe the details of this optimization.

Lemma5.1.Given trail P,(

2b )),where

(mx≥k≥1).

The proof can be found in Appendix D.

From hereon,we let d pC denote the distance of any object P from C.After the value of mx is de?ned for a trail P,object P can move for a certain distance before mx is rede?ned.Therefore,given d pC,the value of mx in trail P cannot be uniquely determined;however,we note that the value of mx can be bounded given d pC and we de?ne?

mx p as the highest possible value of mx in trail P,given d pC.We now determine?

mx p.

Let R denote the network radius,de?ned as the maximum distance from C.Recall that mx denotes the number of levels in the track for an object P.mx is de?ned as (log(dist(C,p o))) ?1where p o is the position of the object when trail P was (re)created from C.Given network radius R,let be the highest number of levels possible for any object in the network.Thus in a given network, = (log(R)) ?1. Lemma5.2.Given d pC,?

mx p=minimum( log(d pC) , ).

The proof can be found in Appendix E.

Since given d pC,the index of highest level mx in trail p cannot be uniquely deter-mined,we state the maximum angle formed by

C,p,N k where1≤k≤mx is lower than the maximum angles stated in the following equation.

(

2b

))(15)

We note from the above properties that the angles formed by p with C and the higher level vertices are small and bounded.For example,the angle formed by p with C and N mx is less than(arcsin(1

Trail:A Distance Sensitive Network Service For Distributed Object Tracking·19 search,a?nd operation does not have to explore in circles and yet can be guaranteed to intersect the track for an object.In the analysis below,we characterize the minimum size of exploration required at each level of exploration given the distance of?nder object q from C.Only for ease of explanation,we assume that b=3.

mx q=minimum( log(d qC) , ). Let Q be the?nder at distance d qC from C.Thus?

Let P be an object which should be found at the level k exploration.At level k of the exploration,trail P for any location of P within the circle of radius2k around q should be intersected.A circular exploration of radius2k around q is su?cient to achieve this.We now characterize the necessary exploration.

mx q?7,circular explorations We show that,at levels of exploration k where k≥?

can be avoided and instead a pattern of exploration along the base of an isosceles triangle with apex q and length of base determined by Fig.10is su?cient to intersect the trails of all objects at distance2k from Q.The base of the isosceles triangle is such that segment(C,q)is the perpendicular and equal bisector of the base of the

mx q?7,exploration along the entire circle triangle.At levels of exploration k

is necessary.For reasons of exposition,we have moved the procedure to determine the necessary exploration at each level,to Appendix F.

Exploration level k Height of triangle

2?2k

mx q?22k

?

3.1?2k

mx q?42k

?

4.3?2k

?

mx q?62k

6.2?2k

20·Vinodkrishnan Kulathumani et al.

from the ?nder;and (2)lower average cost of find (p,q )over all possible locations of q and p .

As described earlier when b =3,circular explorations are avoided at the highest 7levels of the ?nd operation.As the value of b increases,the number of levels at which circular explorations can be avoided,increases.But by increasing b ,we update the track of an object more often.Thus by increasing b ,we increase the cost of update and decrease the cost of ?nd.

We note that there are limits to tuning the frequency of updates,because for extreme values of b distance sensitivity may be violated.For example,for large values of b ,that cause dist (p,c k )

5.2Modifying Trail Segments

The second re?nement to Trail is by varying the shape of the tracking structure by generalizing property P 2of trail P .Instead of trail segment k between vertex N k and N k ?1being a straight line,we relax the requirement on trail segment k to be of length at most (2?π+1)?2k .By publishing information of P along more points,the ?nd path can be more straight towards C .An extreme case is when trail segment k is a full circle of radius 2k centered at c k and Seg (N k ,N k ?1).We call this variation of Trail the ?nd-centric Trail

.

Fig.11.Find-centric Trail 5.2.1Find-centric Trail.In this re?nement,

the ?nd procedure eschews exploring the circles

(thus traversing only straight line segments)at

the expense of the update procedure doing more

work.This alternative data structure is used

when objects are static or when object updates

are less frequent than that of ?nd queries in a

system.Let trail P for object P consist of seg-

ments connecting C,N mx ,..,N 1,p as described

before and,additionally,let all points on the

circles Circ k of center c k and radius 2k con-

tain pointers to their respective centers,where

mx ≥k >0.Starting at q ,the ?nd path now is a straight line towards the center.If a circle with information about object P is intersected then,starting from this point,a line is drawn towards the center of the circle.Upon intersecting the immediate inner circle (if there is one),information about its respective center is found,with which a line is drawn to this center.Object P is reached by following this procedure recursively.We characterize the upper bound on the ?nd cost in the following Lemma,whose proof can be found in Appendix G.

The Ohio State University Technical Report,Vol.,No.,072006.

android课程介绍

1.课程基本信息 课程编号:M21F58D10 课程名称:Android应用与开发 开设学期:第3学期 总学时:60 总学分:4 课程类别:岗位能力课程课程性质:必修课 适用专业:软件技术(移动应用开发) 责任单位:计算机与软件学院 2.课程定位 《Android应用与开发》课程是软件技术(移动应用开发方向)专业的岗位能力课程,课程的开设依据是软件技术专业人才培养目标和相关职业岗位(群)的能力要求,对本专业所面向的手机软件开发与测试、软件开发与项目管理等岗位所需要的知识、技能和素质目标的达成起支撑作用。 在课程设置上,前导课程有《Java程序设计》(M21F1611),《数据结构》(M21F232),后续课程有《移动互联网开发综合实训》(M21J57B10)、《毕业实习》(M21J991)。 3.课程设计思路 首先依据专业人才培养方案中关于人才培养目标的阐述,明确课程目标;其次,结合职业教育课程观、教学观、能力观,基于软件工程的开发过程,以项目化教学来组织课程内容,在课程内容的选择与排序中,以软件项目研发的不同阶段、典型任务为载体,将课程内容划分为互相联系的学习情景;第三,通过对各学习情景中学习目标、主要内容、授课方式、师生要求等各项内容的描述,来规范课程所要求的内容;第四,通过对课程内容的选取和组合,以一个完整的项目为载体,完成课程的实施;最后,通过对项目实施过程中各个环节的考察和评价,来完成对课程的评鉴与考核。 本课程在设计上本着懂方法,重应用的总体思路,突出体现职业教育的技能型、应用性特色,着重培养学生的实践应用技能,力求达到理论方法够用,技术技能过硬的目的。 4.课程建设基本理念 本课程按照理论实践一体、课内外互补、课堂教学与培优工程相结合的课程设计指导思想,以任务或项目为载体组织教学内容,突出学生的主体地位,实现“教、学、做”的有机融合;通过班级讲授、团队学习、个体辅导、展示交流、技能大赛等手段,实现从模仿到应用到创新的高职学生递进式培养。 本课程强调对学生职业岗位能力的培养和职业素养的养成,针对不同环节,采用特定的教学方法,有意识、有步骤地将职业能力的训练和职业素养的形成融入到实际的教学过程中。

最新小学数学课程标准(完整解读).

小学数学课程标准 第一部分前言 数学是研究数量关系和空间形式的科学。数学与人类发展和社会进步息息相关,随着现代信息技术的飞速发展,数学更加广泛应用于社会生产和日常生活的各个方面。数学作为对于客观现象抽象概括而逐渐形成的科学语言与工具,不仅是自然科学和技术科学的基础,而且在人文科学与社会科学中发挥着越来越大的作用。特别是20世纪中叶以来,数学与计算机技术的结合在许多方面直接为社会创造价值,推动着社会生产力的发展。 数学是人类文化的重要组成部分,数学素养是现代社会每一个公民应该具备的基本素养。作为促进学生全面发展教育的重要组成部分,数学教育既要使学生掌握现代生活和学习中所需要的数学知识与技能,更要发挥数学在培养人的理性思维和创新能力方面的不可替代的作用。 一、课程性质 义务教育阶段的数学课程是培养公民素质的基础课程,具有基础性、普及性和发展性。数学课程能使学生掌握必备的基础知识和基本技能;培养学生的抽象思维和推理能力;培养学生的创新意识和实践能力;促进学生在情感、态度与价值观等方面的发展。义务教育的数学课程能为学生未来生活、工作和学习奠定重要的基础。 二、课程基本理念 1.数学课程应致力于实现义务教育阶段的培养目标,要面向全体学生,适应学生个性发展的需要,使得:人人都能获得良好的数学教育,不同的人在数学上得到不同的发展。 2.课程内容要反映社会的需要、数学的特点,要符合学生的认知规律。它不仅包括数学的结果,也包括数学结果的形成过程和蕴涵的数学思想方法。课程内容的选择要贴近学生的实际,有利于学生体验与理解、思考与探索。课程内容的组织要重视过程,处理好过程与结果的关系;要重视直观,处理好直观与抽象的关系;要重视直接经验,处理好直接经验与间接经验的关系。课程内容的呈现应注意层次性和多样性。 3.教学活动是师生积极参与、交往互动、共同发展的过程。有效的教学活动是学生学与教师教的统一,学生是学习的主体,教师是学习的组织者、引导者与合作者。 数学教学活动应激发学生兴趣,调动学生积极性,引发学生的数学思考,鼓励学生的创造性思维;要注重培养学生良好的数学学习习惯,使学生掌握恰当的数学学习方法。 学生学习应当是一个生动活泼的、主动的和富有个性的过程。除接受学习外,动手实践、自主探索与合作交流同样是学习数学的重要方式。学生应当有足够的时间和空间经历观察、实验、猜测、计算、推理、验证等活动过程。 教师教学应该以学生的认知发展水平和已有的经验为基础,面向全体学生,注重启发式和因材施教。教师要发挥主导作用,处理好讲授与学生自主学习的关系,引导学生独立思考、主动探索、合作交流,使学生理解和掌握基本的数学知识与技能、数学思想和方法,获得基本的数学活动经验。 4.学习评价的主要目的是为了全面了解学生数学学习的过程和结果,激励学生学习和改进教师教学。应建立目标多元、方法多样的评价体系。评价既要关注学生学习的结果,也要重视学习的过程;既要关注学生数学学习的水平,也要重视学生在数学活动中所表现出来的情感与态度,帮助学生认识自我、建立信心。 5.信息技术的发展对数学教育的价值、目标、内容以及教学方式产生了很大的影响。数学课程的设计与实施应根据实际情况合理地运用现代信息技术,要注意信息技术与课程内容的整合,注重实效。要充分考虑信息技术对数学学习内容和方式的影响,开发并向学生提供丰富的学习资源,把现代信息技术作为学生学习数学和解决问题的有力工具,有效地改进教与学的方式,使学生乐意并有可能投入到现实的、探索性的数学活动中去。 三、课程设计思路 义务教育阶段数学课程的设计,充分考虑本阶段学生数学学习的特点,符合学生的认知规律和心理特征,有利于激发学生的学习兴趣,引发数学思考;充分考虑数学本身的特点,体现数学的实质;在呈现作为知识与技能的数学结果的同时,重视学生已有的经验,使学生体验从实际背景中抽象出数学问题、构建数学模型、寻求结果、解决问题的过程。 按以上思路具体设计如下。

Android智能手机软件开发概述

第1章Android智能手机软件开发概述 随着移动设备的普及,其功能越来越完善,移动设备的系统平台也日渐火热。 本章首先介绍智能手机及其操作系统平台(如Symbian、Android、Windows Mobile、IOS等),并对学习Android手机软件开发的必要性进行阐述。之后, 介绍Android平台的总体架构,并对完成Android应用程序软件开发的SDK及 其组成进行简要说明。最后,对通过Android Market发布自己应用程序的方法 进行介绍。学习本章内容时,要求重点掌握如下内容: ●了解常见的智能手机操作系统平台。 ●了解Android的总体结构及主要功能。 ●了解Dalvik虚拟机、AVD等。 ●了解Android Market及发布应用程序的方法。 1.1 智能手机及其操作系统 据中国互联网络信息中心于2011年7月19日发布的统计《中国互联网络发展统计报告》显示,2011年上半年,我国手机网民规模继续稳步扩大。截至2011年6月底,我国手机网民达3.18亿,较2010年底增加1495万人(如图1.1所示)。可以说,智能手机正在快速走进人们的生活。就目前来看,已经有越来越多的人开始把智能手机当作日常看视频、办公的首选设备。随着A9架构、双核概念的问世,智能手机能更广泛、轻松地接管生活和工作中的大小事务[1]。因此,学习和研究智能手机软件开发,具有广阔的社会需求和工程实践意义。 图1.1 手机上网网民规模 智能手机一般指像个人电脑一样具有独立操作系统,可由用户自行安装软件等第三方服务商提供的程序,并且,用户能对手机功能进行扩充。目前,全球多数手机厂商都有智能手

小学数学新课标解读

小学数学新课标解读 《全日制义务教育数学课程标准(修定稿)》(以下简称《标准》)是针对我国义务教育阶段的数学教育制定的。根据《义务教育法》.《基础教育课程改革纲要(试行)》的要求,《标准》以全面推进素质教育,培养学生的创新精神和实践能力为宗旨,明确数学课程的性质和地位,阐述数学课程的基本理念和设计思路,提出数学课程目标与内容标准,并对课程实施(教学.评价.教材编写)提出建议。 《标准》提出的数学课程理念和目标对义务教育阶段的数学课程与教学具有指导作用,教学内容的选择和教学活动的组织应当遵循这些基本理念和目标。《标准》规定的课程目标和内容标准是义务教育阶段的每一个学生应当达到的基本要求。《标准》是教材编写.教学.评估.和考试命题的依据。在实施过程中,应当遵照《标准》的要求,充分考虑学生发展和在学习过程中表现出的个性差异,因材施教。为使教师更好地理解和把握有关的目标和内容,以利于教学活动的设计和组织,《标准》提供了一些有针对性的案例,供教师在实施过程中参考。 二、设计理念 数学是研究数量关系和空间形式的科学。数学与人类的活动息息相关,特别是随着计算机技术的飞速发展,数学更加广泛应用于社会生产和日常生活的各个方面。数学作为对客观现象抽象概括而逐渐形成的科学语言与工具,不仅是自然科学和技术科学的基础,而且在社会科学与人文科学中发挥着越来越大的作用。数学是人类文化的重要组成部分,数学素养是现代社会每一个公民所必备的基本素养。数学教育作

为促进学生全面发展教育的重要组成部分,一方面要使学生掌握现代生活和学习中所需要的数学知识与技能,一方面要充分发挥数学在培养人的科学推理和创新思维方面的功能。 义务教育阶段的数学课程具有公共基础的地位,要着眼于学生的整体素质的提高,促进学生全面.持续.和谐发展。课程设计要满足学生未来生活.工作和学习的需要,使学生掌握必需的数学基础知识和基本技能,发展学生抽象思维和推理能力,培养应用意识和创新意识,在情感.态度与价值观等方面都要得到发展;要符合数学科学本身的特点.体现数学科学的精神实质;要符合学生的认知规律和心理特征.有利于激发学生的学习兴趣;要在呈现作为知识与技能的数学结果的同时,重视学生已有的经验,让学生体验从实际背景中抽象出数学问题.构建数学模型.得到结果.解决问题的过程。为此,制定了《标准》的基本理念与设计思路。 基本理念 数学课程应致力于实现义务教育阶段的培养目标,体现基础性.普及性和发展性。义务教育阶段的数学课程要面向全体学生,适应学生个性发展的需要,使得:人人都能获得良好的数学教育,不同的人在数学上得到不同的发展。课程内容既要反映社会的需要.数学学科的特征,也要符合学生的认知规律。它不仅包括数学的结论,也应包括数学结论的形成过程和数学思想方法。课程内容要贴近学生的生活,有利于学生经验.思考与探索。内容的组织要处理好过程与结果的关系,直观与抽象的关系,生活化.情境化与知识系统性的关系。课程内容

Android平台介绍及使用指导

Android平台介绍及使用指导 二○一○年二月 版本 1.0

目录 Android平台介绍 ................................................................................... - 4 -基本名词...................................................................................................................... - 5 - 操作方法介绍 .......................................................................................... - 6 - 手机按键介绍.............................................................................................................. - 6 - 快捷键介绍.................................................................................................................. - 6 - 信息功能介绍.............................................................................................................. - 7 - 联系人功能介绍........................................................................................................ - 11 - 通话记录功能介绍.................................................................................................... - 14 - 文本粘贴/复制功能介绍.......................................................................................... - 14 - Push Email(Moxier)功能介绍............................................................................ - 15 - 电子邮件功能介绍.................................................................................................... - 16 - 桌面功能介绍............................................................................................................ - 19 - 蓝牙功能介绍............................................................................................................ - 23 - Wifi功能介绍........................................................................................................... - 23 - 飞行模式功能介绍.................................................................................................... - 23 - CDMA数据链接介绍................................................................................................... - 24 - 黑屏解锁功能............................................................................................................ - 25 - 回复出厂设置............................................................................................................ - 26 - 应用程序设置............................................................................................................ - 26 - GPS设置..................................................................................................................... - 27 - 手机中英文语言切换................................................................................................ - 28 - 更换手机输入法........................................................................................................ - 29 - 数据线链接Android手机........................................................................................ - 29 - 手机测试模式进入方法............................................................................................ - 30 - 横屏显示介绍............................................................................................................ - 30 - 浏览器功能介绍........................................................................................................ - 31 - RSS功能介绍............................................................................................................ - 32 - Q/A- 34 -

最新小学数学课程标准(完整解读)

小学数学课程标准 一、总目标 通过义务教育阶段的数学学习,学生能: 1. 获得适应社会生活和进一步发展所必需的数学的基础知识、基本技能、基本思想、基本活动经验。 2. 体会数学知识之间、数学与其他学科之间、数学与生活之间的联系,运用数学的思维方式进行思考,增强发现和提出问题的能力、分析和解决问题的能力。 3. 了解数学的价值,提高学习数学的兴趣,增强学好数学的信心,养成良好的学习习惯,具有初步的创新意识和实事求是的科学态度。 总目标从以下四个方面具体阐述: 知识技能 1.经历数与代数的抽象、运算与建模等过程,掌握数与代数的基础知识和基本技能。 2.经历图形的抽象、分类、性质探讨、运动、位置确定等过程,掌握图形与几何的基础知识和基本技能。 3.经历在实际问题中收集和处理数据、利用数据分析问题、获取信息的过程,掌握统计与概率的基础知识和基本技能。 4.参与综合实践活动,积累综合运用数学知识、技能和方法等解决简单问题的数学活动经验。 数学思考

1.建立数感、符号意识和空间观念,初步形成几何直观和运算能力,发展形象思维与抽象思维。 2.体会统计方法的意义,发展数据分析观念,感受随机现象。 3.在参与观察、实验、猜想、证明、综合实践等数学活动中,发展合情推理和演绎推理能力,清晰地表达自己的想法。 4.学会独立思考,体会数学的基本思想和思维方式。 问题解决 1.初步学会从数学的角度发现问题和提出问题,综合运用数学知识解决简单的实际问题,增强应用意识,提高实践能力。 2.获得分析问题和解决问题的一些基本方法,体验解决问题方法的多样性,发展创新意识。 3.学会与他人合作交流。 4.初步形成评价与反思的意识。 情感态度 1.积极参与数学活动,对数学有好奇心和求知欲。 2.在数学学习过程中,体验获得成功的乐趣,锻炼克服困难的意志,建立自信心。 3.体会数学的特点,了解数学的价值。 4.养成认真勤奋、独立思考、合作交流、反思质疑等学习习惯,形成实事求是的科学态度。 总目标的这四个方面,不是相互独立和割裂的,而是一个密切联系、相互交融的有机整体。在课程设计和教学活动组织中,应同时兼顾这四

OTDR(光时域反射仪)操作手册

CMA8800光时域反射测试仪 操 作 手 册 郑州维修中心

目录 第一章快速开始 第二章概览 第三章OTDR测量模式 第四章储存及打印功能 附录 CMA8800的特点及日常维护

第一章快速开始 1.1仪器供电 CMA8800是通过220VAC适配器/充电器从外部供电。 注意:CMA8800不能用内置电池供电! 电源开关位于上面板的右侧。按下开关即可启动。 1.2启动顺序 当该单元上电后,首先出现了一个开始画面,包括软件版本及日期,接着单元进行自检。结果显示如图1-2所示。 当自检结束后,按下PAUSE可以读屏幕上的信息。按下“继续”可以继续进行操作。 图1-2典型设备和自检屏幕 1.3操作模式选择屏幕 当上电完成后,将显示一个可供选择模式的屏幕,每一种可见的模式均位于相应软键的旁边,你只要按下相应的键就按相应的模式进行操作。这里为有经验的用户出了每一种模式的快速操作信息,详细的信息见于手册中后面的章节。

1.3.1故障定位模式 故障定位模式是一种快速确定光纤端/断点位置的方法。当你按下FAULT LOCATE,首先就开始一个光纤接口质量的检查(如果在附加设置中,光纤接口质量的检查功能已启动),这个检查会告诉你基于用户在快速设置菜单中所定义的背向散射系数的连接是不好的、一般的还是好的。当检查进行测试完成后,光纤端/断点显示如图1-4所示。 通过按下硬键TEST/STOP或者模式屏幕软键可使测试取消,

1.3.2配置模式 按“配置模式”键进入“快速设置菜单”屏,在这里设置自动测试功能及测量参数,参见3.1节和3.2关于快速设置和附加设置的信息 按“启动”键显示光纤存储信息屏幕(如图1-5所示),从这里你可以输入描述新的测试的信息,按“继续”就到达了连接光纤屏幕,接着再按“继续”就开始进行测试。 如需要,此时可按“模式屏”回到模式选择屏幕。 1.3.3专家模式 专家级的OTDR模式是为那些想应用CMA8800更先进功能的用户而设计的,所有的OTDR功能均见于这种模式。 按软键“专家模式”进入快速设置菜单(参见图3-1);在此处,你可以在测试之前设置所有的必要的参数;目前的设置决定了自动执行哪些操作功能,如果“全自动”设为开,则所有的操作均被认定为自动执行,如果“全自动”设为关,则你必须选择哪一种操作是自动执行的。 按下“启动”进入显示曲线屏幕,按下硬键“REAL TIME”开始运行实时扫描,再按下硬键“REAL TIME”可以终止实时扫描状态。按下硬键“TEST/STOP即可开始测试。 1.3.3.1曲线显示屏幕 从设置状态按GO就显示了一个与图6-1相似的曲线屏。 1、图标行 在曲线图形区上方的图标行,显示了对比曲线和背景曲线参考的曲线文件名和其他信息,包括该曲线是否已被滤波、是否被施加衰减、是否进行过曲线分析的,测试平均是否未完成等产,对比曲线的文件名在屏幕左边显示,背景曲线(如果存在)的文件名在网络上的屏幕右边显示。 光标行图标:有效结果表 平滑已经运行 正在行进数据采集 差值比较 光标锁定 曲线被施加衰减

1.android发展历程简介

android(Google公司开发的操作系统) Android是一种基于Linux的自由及开放源代码的操作系统,主要使用于移动设备,如智能手机和平板电脑,由Google公司和开放手机联盟领导及开发。尚未有统一中文名称,中国大陆地区较多人使用“安卓”或“安致”。Android操作系统最初由Andy Rubin开发,主要支持手机。2005年8月由Google收购注资。2007年11月,Google与84家硬件制造商、软件开发商及电信营运商组建开放手机联盟共同研发改良Android系统。随后Google以Apache 开源许可证的授权方式,发布了Android的源代码。第一部Android智能手机发布于2008年10月。Android逐渐扩展到平板电脑及其他领域上,如电视、数码相机、游戏机等。2011年第一季度,Android在全球的市场份额首次超过塞班系统,跃居全球第一。2013年的第四季度,Android平台手机的全球市场份额已经达到78.1%。[1] 2013年09月24日谷歌开发的操作系统Android在迎来了5岁生日,全世界采用这款系统的设备数量已经达到10亿台。2014第一季度Android平台已占所有移动广告流量来源的42.8%,首度超越iOS。但运营收入不及iOS。 编程语言 C/C++(底层)Java等(应用层) 系统家族 类Unix,Linux 源码模式 自由及开放源代码软件 内核类型 宏内核(Linux内核) 软件许可 Apache License、GPL等 1系统简介编辑 Android一词的本义指“机器人”,同时也是Google于2007年11月5日 Android logo相关图片(36张) 宣布的基于Linux平台的开源手机操作系统的名称,该平台由操作系统、中间件、用户界面和应用软件组成。 Android一词最早出现于法国作家利尔亚当(Auguste Villiers de l'Isle-Adam)在1886年发表的科幻小说《未来夏娃》(L'ève future)中。他将外表像人的机器起名为Android。Android的Logo是由Ascender公司设计的,诞生于2010年,其设计灵感源于男女厕所门上

小学数学新课程标准(修改稿——)解读

小学数学新课程标准(修改稿)解读 一、前言 《全日制义务教育数学课程标准(修改稿)》(以下简称《标准》)是针对我国义务教育阶段的数学教育制定的。根据《义务教育法》、《基础教育课程改革纲要(试行)》的要求,《标准》以全面推进素质教育,培养学生的创新精神和实践能力为宗旨,明确数学课程的性质和地位,阐述数学课程的基本理念和设计思路,提出数学课程目标与内容标准,并对课程实施(教学、评价、教材编写)提出建议。 《标准》提出的数学课程理念和目标对义务教育阶段的数学课程与教学具有指导作用,教学内容的选择和教学活动的组织应当遵循这些基本理念和目标。《标准》规定的课程目标和内容标准是义务教育阶段的每一个学生应当达到的基本要求。《标准》是教材编写、教学、评估、和考试命题的依据。在实施过程中,应当遵照《标准》的要求,充分考虑学生发展和在学习过程中表现出的个性差异,因材施教。为使教师更好地理解和把握有关的目标和内容,以利于教学活动的设计和组织,《标准》提供了一些有针对性的案例,供教师在实施过程中参考。 二、设计理念 数学是研究数量关系和空间形式的科学。数学与人类的活动息息相关,特别是随着计算机技术的飞速发展,数学更加广泛应用于社会生产和日常生活的各个方面。数学作为对客观现象抽象概括而逐渐形成的科学语言与工具,不仅是自然科学和技术科学的基础,而且在社会科学与人文科学中发挥着越来越大的作用。数学是人类文化的重要组成部分,数学素养是现代社会每一个公民所必备的基本素养。数学教育作为促进学生全面发展教育的重要组成部分,一方面要使学生掌握现代生活和学习中所需要的数学知识与技能,一方面要充分发挥数学在培养人的科学推理和创新思维方面的功能 义务教育阶段的数学课程具有公共基础的地位,要着眼于学生的整体素质的提高,促进学生全面、持续、和谐发展。课程设计要满足学生未来生活、工作和学习的需要,使学生掌握必需的数学基础知识和基本技能,发展学生抽象思维和推理能力,培养应用意识和创新意识,在情感、态度与价值观等方面都要得到发展;要符合数学科学本身的特点、体现数学科学的精神实质;要符合学生的认知规律和心理特征、有利于激发学生的学习兴趣;要在呈现作为知识与技能的数学结果的同时,重视学生已有的经验,让学生体验从实际背景中抽象出数学问题、构建数学模型、得到结果、解决问题的过程。为此,制定了《标准》的基本理念与设计思路基本理念。 (一)总:六大理念 1、人人学有价值的数学,人人都能获得必需的数学,不同的人在数学上得到不同的发展 2、数学是人们生活、劳动和学习必不可少的工具,数学是一切重大技术发展的基础,数学是一种文化。 3、数学学习的内容要有利于学生主动地进行观察、实验、猜测、验证、推理、与交流,动手实践、自主探索与合作交流是学生学习数学的重要方式。 4、学生是数学学习的主人,教师是数学学习的组织者、引导者、合作者。 5、评价的目的—了解学生的数学学习历程,改进教师的教学;目标多元,方法多样;重过程,轻结果;关注情感态度。 6、把现代信息技术作为学生学习数学和解决问题的强有力的工具。 (二)分六大理念的解读: 数学课程应致力于实现义务教育阶段的培养目标,体现基础性、普及性和发展性。义务教育阶段的数学课程要面向全体学生,适应学生个性发展的需要,使得:人人都能获得良好的数学教育,不同的人在数学上得到不同的发展。 1、关于数学课程的功能 (1)“人人学有价值的数学”是指作为教育内容的数学,应当是适合学生在有限的学习时间里接触、了解和掌握的数学。 怎样理解有价值的数学?

自我介绍,android

自我介绍,android 篇一:安卓应用软件个人简历 个人简历 篇二:面试时自我介绍整理合集 应聘面试自我介绍范文 尊敬的领导: 您好! 我是×××,毕业于××学校××专业,获得的是××学位 在学校期间,主修的专业课有×××(此处添加技术类专业课,尤其是和应聘工作相关的),根据所学的知识,也参加过一些具体项目的事实,比如××××项目,在其中负责××模块或者××工作,应用了×××计算机语言或者技术,取得了×××什么样的成果。并在实践中,加深了对××的认识,提高了软件设计(或其他技术)的实际操作能力。 另外,在学校中也参加过一些社团活动,比如××(此处最好说1-2样),在其中加强了和同学们的团队协作,并且有×××的感受和知识。个性上××××(此处copy简历里面的性格介绍,主要要有团队精神,个人踏实努力,有责任感之类的) 在这里应聘贵公司的××职位,是想将自己的所学得到充分发挥,并在这里学习成长。希望有这样的机会,能和诸位成为同事。 我的情况大概就是这样,请问您有什么其他方面想要了解的么?(主

体说完之后来句这个,可以直接话题过度给面试的人,省得最后冷场)文员面试自我介绍范文 经过长期的实践和研究,面试文员的朋友需要注意三项文员面试技巧。文员面试自我介绍范文下次奉上。 文员面试技巧一:文职岗位要求面试者有很好的亲和力,能与其他人进行充分的沟通,这就要求面试者必须要保持良好的心态来面对招聘人员。关键要做到八个字——顺其自然,不卑不亢。只有这样才能给招聘人员留下好印象,使其相信你有能力在将来进入公司后与同事和谐的相处。 要做到面带微笑,平视考官,避免情绪波动,走向两个极端:一是自卑感很重,觉得坐在对面的那人博学多才、回答错了会被笑话。所以,畏首畏尾,不敢畅快地表达自己的观点;另一种情况则是,很自信,压根不把招聘人员放在眼里,觉得对方还不如自己。这两种表现都要不得,最好的表现应是,平视对方,彬彬有礼,不卑不亢。 应树立两种心态:一.面试的目的是合作而不是竞争。招聘人员对考生的态度一般是比较友好的,他目的是把优秀的人才遴选进自己的公司增强公司的竞争力,而不是为与考生一比高低而来,所以考生在心理上不要定位谁强谁弱的问题,那不是面试的目的。二.面试中两者的地位是平等的,面试者是求职不是乞职。 面试者是在通过竞争,谋求职业,而不是向招聘人员乞求工作,成功的关键在于自己的才能以及临场发挥情况。 文员面试技巧二:面试者要注意自己在面试中的礼仪问题。因为文职

光时域反射仪OTDR的基本原理

OTDR的基本原理 OTDR勺基本原理 什么是OTDR? 基础 OTDR将激光光源和检测器组合在一起以提供光纤链路的内视图。激光光源发送信号到光纤中,检测器接收从链路的不同元素反射的光。激光光源发送信号到光纤中,检测器在光纤中接收从链路的不同元素反射的光。发送的信号是一个短脉冲,其携带有一定数量的能量。然后,时钟精确计算出脉冲传播的时间,然后将时间转换为距离,便可以得知该光纤的属性。当脉冲沿着光纤传播时,由于连接和光纤自身的反射,一小部分脉冲能量会返回检测器。当脉冲完全返回检测器时,发送第二个脉冲一直到取样时间结束。因此,会立刻执 行多次取样并平均化以提供链路元件的清晰特性图。取样结束后,执行信号处理,除了计算 总链路长度、总链路损耗、光回损(ORL)和光纤衰减外,还计算每个事件的距离、损耗和 反射。使用OTDR的主要优势在于单端测试,只需要一位操作人员和一台仪器来鉴定链路质 量或查找网络故障。图#1显示了OTDR的框图。 图1. OTDR框图 图1 OTOR框图* 反射是关键 如前文所述,OTDR通过读取从所发送脉冲返回的光级别以显示链路情况。请注意,有两种类型的反射光:光纤产生的连续低级别光称为Rayleigh 背向散射,连接点处的高反射 峰值称为Fresnel反射。Rayleigh背向散射用于作为距离的函数以计算光纤中的衰减级别(单位是dB/km),在OTDR轨迹中显示为直线斜率。该现象来源于光纤内部杂质固有的反射 和吸收。当光照射到杂质上时,一些杂质颗粒将光重定向到不同的方向,同时产生了信号衰减和背向散射。波长越长,衰减越少,因此,在标准光纤上传输相同距离所需的功率越小。 图2说明了Rayleigh 背向散射。 图2. Rayleigh 背向散射 -iOR Puuse GEhJERATOft Dlf Ei?Tl JNAL C OUPLER ? Waller —Distance range

android应用技术简介

Android技术应用简介 摘要:近几年来,Android逐渐成为便携设备上的主要操作系统。2011年Android 在全球的市场份额首次超过塞班系统,跃居全球第一。本文主要通过阐述Android的主要思想、发展状况以及核心技术来使读者对Android有一个初步的认识。 关键词:Android、linux、NDK、google 这学期我们开设了《Android应用程序开发》这门课程。这么课程开始的时候同学们都很兴奋。因为Android在现在是最为流行的操作系统。同学们大部分用的手机都是Android操作系统。所以对它的名字非常熟悉,但是对它的真正意义和具体是如何实现Android应用程序却十分陌生。同学们都希望了解到自己的手机上的应用程序到底是如何实现其功能的。所以对这门课程产生了极大的兴趣。 这门课程主要给我们介绍了Android开发环境、应用程序、生命周期、用户界面、组件通信与广播信息、后台服务、数据存储与访问、位置服务与地图应用、Android NDK开发这9个方面的内容。让我们对Android有一个初步的认知。这本书上的内容仅仅是Android程序开发的一小部分,是引导我们正确看待Android。在今后的学习中还需要我们多看关于Android的书籍,关注Android 各方面的消息,多做关于Android的实验和课题。这样才能进一步了解这个当今全球最为流行的操作系统。 1、Android简介 Android是一种以linux为基础的开放源代码操作系统,主要使用于便携设备。目前尚未有统一中文名称,中国大陆地区较多人使用“安卓”或“安致”。Android操作系统最初由Andy Rubin开发,最初主要支持手机。2005年由google 收购注资,并组建开放手机联盟开发改良,逐渐扩展到平板电脑及其他领域上。Android的主要竞争对手是苹果公司的iOS以及RIM的Blackberry OS。2011年第一季度,Android在全球的市场份额首次超过塞班系统,跃居全球第一。 2012年2月数据,Android占据全球智能手机操作系统市场52.5%的份额,中国市场占有率为68.4%。 Android的系统架构和其它操作系统一样,采用了分层的架构。android分为四个层,从高层到低层分别是应用程序层、应用程序框架层、系统运行库层和linux核心层。 Android是以Linux为核心的手机操作平台,作为一款开放式的操作系统,随着Android的快速发展,如今已允许开发者使用多种编程语言来开发Android 应用程序,而不再是以前只能使用Java开发Android应用程序的单一局面,因而受到众多开发者的欢迎,成为真正意义上的开放式操作系统。 在Android中,开发者可以使用Java作为编程语言来开发应用程序,也可以通过NDK使用C/C++作为编程语言来开发应用程序,也可使用SL4A来使用其他各种脚本语言进行编程(如:python、lua、tcl、php等等),还有其他诸如:QT(qt for android)、Mono(mono for android)等一些著名编程框架也开始

2011版小学数学课程标准解读(全)

解读《义务教育小学数学课程标准》(2011年版)一 【新旧课标比较】与旧课标相比,新课标从基本理念、课程目标、内容标准 到实施建议都更加准确、规范、明了和全面。具体变化如下: 一、总体框架结构的变化 2001年版分四个部分:前言、课程目标、内容标准和课程实施建议。 2011年版把其中的“内容标准”改为“课程内容”。前言部分由原来的基本理念和设计思路,改为课程基本性质、课程基本理念和课程设计思路三部分。 二、关于数学观的变化 2001年版: 数学是人们对客观世界定性把握和定量刻画、逐渐抽象概括、形成方法和理论,并进行广泛应用的过程。 数学作为一种普遍适用的技术,有助于人们收集、整理、描述信息,建立数学模型,进而解决问题,直接为社会创造价值。 2011年版: 数学是研究数量关系和空间形式的科学。 数学作为对于客观现象抽象概括而逐渐形成的科学语言与工具。 数学是人类文化的重要组成部分,数学素养是现代社会每一个公民应该具备的基本素养。 三、基本理念“三句”变“两句”,“6条”改“5条” 2001年版“三句话”: 人人学有价值的数学,人人都能获得必需的数学,不同的人在数学上得到不同的发展。 2011年版“两句话”: 人人都能获得良好的数学教育,不同的人在数学上得到不同的发展。 “6条”改“5条”: 在结构上由原来的6条改为5条,将2001年版的第2条关于对数学的认识整合到理念之前的文字之中,新增了对课程内容的认识,此外,将“数学教学”与“数学学习”合并为数学“教学活动”。 2001年版:数学课程——数学——数学学习——数学教学活动——评价——现代信息技术 2011年版:数学课程——课程内容——教学活动——学习评价——信息技术 四、理念中新增加了一些提法 要处理好四个关系 数学课程基本理念(两句话) 数学教学活动的本质要求 培养良好的数学学习习惯 注重启发式 正确看待教师的主导作用 处理好评价中的关系

(完整版)人教版四年级数学新课标解读

人教版小学数学四年级下册新课标解读 崔庙镇实验小学 四年级

人教版小学数学四年级下册新课标解读 一、教材的主要内容: 小数的意义与性质,小数的加法和减法,四则运算,运算定律与简便计算,三角形,位置与方向,折线统计图,数学广角和数学综合运用活动等。 其中小数的意义与性质,小数的加法和减法,运算定律与简便计算,以及三角形是本册的重点教学内容。 二、教材的学习目标 1、理解小数的意义和性质,体会小数在日常生活中的应用,进一步发展数感,掌握小数点位置移动引起小数大小变化的规律,掌握小数的加法和减法。 2、掌握四则混合运算的顺序,会进行简单的整数四则混合运算;探索和理解加法和乘法的运算定律,会应用它们进行一些简便运算,进一步提高计算能力。 3、认识三角形的特性,会根据三角形的边、角特点给三角形分类,知道三角形任意两边之和大于第三边以及三角形的内角和是 180°。 4、初步掌握确定物体位置的方法,能根据方向和距离确定物体的位置,能描述简单的路线图。 5、认识折线统计图,了解折线统计图的特点,初步学会根据统计图和数据进行数据变化趋势的分析,进一步体会统计在现实生活中的作用。

6、经历从实际生活中发现问题、提出问题、解决问题的过程,体会数学在日常生活中的作用,初步形成综合运用数学知识解决问题的能力。 7、了解解决植树问题的思想方法,培养从生活中发现数学问题的意识,初步培养探索解决问题有效方法的能力,初步形成观察、分析及推理的能力。 8、体会学习数学的乐趣,提高学习数学的兴趣,建立学好数学的信心。 9、养成认真作业、书写整洁的良好习惯。 三、教材的编写特点: 本册实验教材具有内容丰富、关注学生的经验与体验、体现知识的形成过程、鼓励算法多样化、改变学生的学习方式,体现开放性的教学方法等特点。同时,本实验教材还具有下面几个明显的特点。 1. 改进四则运算的编排,降低学习的难度,促进学生的思维水平的提高。 四则运算的知识和技能是小学生学习数学需要掌握的基础知识和基本技能。以往的小学数学教材在四年级时要对以前学习过的四则运算知识进行较为系统的概括和总结,如概括出四则运算的意义和运算定律等。对于这些相关的内容,本套实验教材在本册安排了“四则运算”和“运算定律与简便计算”两个单元。“四则运算”单元的教学内容主要包括四则混合运算和四则运算的顺序。而关于四则运算的意义没有进行概括,简化了教学内容,降低了学习的难度。

1 Android系统简介及开发环境的搭建

1了解Android系统 1.1 Android系统介绍 Android是Google 开发的基于Linux 平台的、开源的、智能手机操作系统。Android 包括操作系统、中间件和应用程序,由于源代码开放,Android 可被移植到不同的硬件平台上。 围绕在Google的Android 系统中,形成了移植开发和应用程序开发两个不同的开发方面。手机厂商从事移植开发工作,应用程序开发可以由任何单位和个人完成,开发的过程可以基于真实的硬件系统,还可以基于仿真器环境。 作为一个手机平台,Android 在技术上的优势主要有以下几点: ●全开放智能手机平台 ●多硬件平台的支持:应用程序可通过标准API访问核心移动设备功能。 ●使用众多的标准化技术:可以轻松的嵌入HTML、JavaScript等网络内容 ●核心技术完整,统一:应用程序是平等条件创建的,可被替换或扩展。 ●应用程序可以并行运行。Android是完整的多任务环境,在后台运行时,应用程 序可生成通知引起用户注意。 ●完善的SDK 和文档 ●完善的辅助开发工具 Android 的开发者可以在完备的开发环境中进行开发,Android 的官方网站也提供了丰富的文档、资料。这些都使得Android 系统的开发和运行在一个良好的生态环境中。 1.2 Android系统的软件结构 Android 是一个开放的软件系统,它包含了众多的源代码。从下至上,Android 系统分成4个层次: ●第1 层次:Linux 操作系统及驱动; ●第2 层次:本地代码框架,包含各种类库和运行环境; ●第3 层次:Java 框架; ●第4 层次:Java 应用程序。 Android 的第1 层次由C 语言实现,第2层次由C 和/C++实现,第3、4层次主要由Java代码实现。对于Android 应用程序的开发,主要关注第3层次和第4层次之间的接口。 Android 系统的架构如图所示:

相关主题
相关文档 最新文档