A Distributed Safety-Critical System for Real-Time Train Control
Anup K. Ghosh, Vikram Rana,
and Barry W. Johnson
Center for Semicustom Integrated Systems Department of Electrical Engineering
University of Virginia
Charlottesville, Virginia 22903
Joseph A. Profeta, III Union Switch and Signal, Incorporated
A Member of the Ansaldo Group
1000 Technology Drive
Pittsburgh, Pennsylvania 15237
tolerant applications, hardware redundancy is essential. In addition, the real-time requirements for the different train control applications vary from tens of milliseconds for car-borne functions to full seconds for wayside functions.
Current microprocessor-based train control systems employ different systems at the wayside and on-board trains that are usually incompatible. In addition, ad hoc methodologies to safety-critical design have been imple-mented in these systems to ensure safety and fault-tolerant operation, often without regard to analyzable safety or real-istic assumptions on the nature of faults in digital hardware. Section 2 summarizes current systems used in train control and their shortcomings.
A single open-systems architecture that supports both wayside and carborne train control functions using com-mercial off-the-shelf (COTS) components is presented in Section 3. The time-triggered executive used in this archi-tecture is discussed in Section 4. A concurrent veri?cation technique that enables calculable safety in a distributed system is described in Section 5. Results from modeling and simulating the architecture are presented in Section 6. The experimental prototype of the system architecture that executes a wayside train control application using the con-current veri?cation algorithm is described in Section 7 along with experimental results. The overall contributions of the paper are summarized in Section 8.
2. BACKGROUND
The railroad industry has been actively replacing elec-tromechanical relay-driven safety interlocking systems with microprocessor-controlled interlocking systems. Recent advances in train control applications have sophis-ticated processing requirements that demand fail-safe and sometimes fault-tolerant system architectures.
A safe failure occurs when the failure of a component in a processing system is detected and the effect of the fail-ure emerges as a safe-side operation [1]. In the railway application, the safe-side failures are de?ned for the out-puts of the controller. A safe-side failure for a switch is to leave it in the locked position. The safe-side failure of a sig-nal is to set it to red, so that a train will stop before entering a block. In carborne control applications, most failures can be made safe by stopping the train immediately. Unlike planes that are controlled by computers, stopping the train is a safe failure state. Safety is the probability that the train controller is working correctly or has failed in a safe state. Reliability is the probability that the train controller is operating correctly. In order to have a highly reliable sys-
tem, a fault-tolerant controller with hardware or software redundancy is necessary. A system designed strictly for safety, on the other hand, requires only a single processor architecture with concurrent error detection mechanisms that switch outputs into a safe state upon error detection.
Simplex processing systems for wayside applications are described in the literature [2] [3]. In the MICROLOK system [2], the safety of the controller is dependent upon the diagnostic checks that are executed. One major draw-back inherent in a diagnostic approach to safety is that the level of safety achieved by diagnostics is not easily quanti-?ed. Second, the amount of processing overhead necessary for the diagnostics can often be greater than the amount used for executing the application. This performance factor will ultimately limit its application. The VPI system [3] uses a coded-processor approach to checking the safety-critical interlocking equations of the wayside application. Under the assumption that errors are equally likely, the safety of the system can be quantitatively determined. Aside from this unrealistic assumption, another major drawback of this system is that it lacks a modular architec-ture to allow for expansion into a distributed system. Finally, no provision for fault-tolerance is designed in the architecture, which limits its application to the wayside problem.
Two multiprocessing architectures have also been developed for train control [1] [5] Both use hardware rep-lication for fault tolerance. Two drawbacks are inherent in hardware replication. First, the software is assumed to be correct. An error in the software will not be revealed by majority voting in hardware. Second, the expense of a hardware redundant strategy to safety-critical operation is many times the expense of a single processor solution.
The dependable computing system described in this paper employs information redundancy and a concurrent veri?cation technique to assure safety globally in a distrib-uted system. This approach reduces the hardware overhead associated with majority voting to achieve safety and per-mits quanti?able measures of safety. Furthermore, the modularity of the distributed system enables fault tolerant operation for applications that require high reliability and availability. The open-systems architecture is designed to maximize the use of commercial off the shelf (COTS) com-ponents to reduce developmental costs.
3. SYSTEM ARCHITECTURE
The architecture for the distributed system which exe-cutes a safety-critical train control application is depicted in Figure 1. The basic building blocks of this architecture are the processors, input/output modules, and the network interface unit (NIU), which are co-located in backplane card cages. The parallel bus backplane interconnects pro-cessors with local input/output modules. Processors com-municate with remote processors and I/O over the high-speed serial network via the network interface unit. The input modules are responsible for sensing data from the ?eld such as the state of a switch or presence of a train. The processors are responsible for executing the train control algorithm. Multiple processors can be placed in a single card cage to execute multiprocessing applications. Proces-sors may also be arranged in voting clusters to be used in for fault-tolerant operation.
The Fiber Distributed Data Interface (FDDI) network standard is used for inter-node communication. The latency and response time for data transmissions is bounded to sup-port real-time applications.The FDDI network protocol guarantees media access for all nodes connected to the net-work. In addition, the protocol enforces a bounded response time for each node connected to the network to ensure hang-ups do not disrupt operation.
4. I/O CYCLE CONSIDERATIONS
A software executive which resides on a controlling processor has been designed for this safety critical system [9]. The software executive implements a time-triggered paradigm for the system. System events such as writing outputs, writing input polls, and control equation evalua-tion are activated by the system executive at ?xed periodi-cal intervals of time. An input/output cycle is the basic unit of processing in the system, and the executive is designed around it. The executive is a single tasking kernal in which tasks are executed singly through procedural calls. Upon completing a task, control is returned to the executive ker-nel. The executive also runs non-critical routines until the end of a frame, at which time a context switch takes place, and the I/O cycle is repeated in the next frame [10].
The frame-based timing speci?cation used by the executive is typical in the avionics industry and elsewhere [11]. Tasks may need to execute every frame, every other frame, or at other frequencies. The system cycle represent-ing this scheduling approach for the train control applica-tion appears in Figure 2. Task P1 represents writing outputs and polling inputs at the beginning of each frame. In order to support deterministic updating of actuator devices, out-puts are written at the beginning of each frame. Input cards are also polled at the beginning of each frame. In this para-digm, the actuators and sensors are updated and sensed, respectively, at known periodic intervals. Task P2 repre-sents the time it takes for inputs to be read into the memory of the processor card. The processor begins executing the control equations at the beginning of P3. If all inputs have not arrived by this time, an error will be signaled, and safe shutdown will follow.Non-critical routines (P4) run in vari-able-length subframes determined by the amount of idle time in a frame and are the only processes that can be pre-empted or suspended. These routines include other non-critical functions such as passenger information, train scheduling, data processing, and diagnostic functions for maintenance. It should be noted that the diagram is only descriptive, not speci?c, and the number of frames and the number of tasks per frame vary based on the train control application.
In order to support determinism of system behavior, the system uses a static scheduling algorithm. Static sched-uling is simple to implement and its deterministic schedul-ing allows hard deadlines to be set and enforced through watchdog time-outs. One drawback of static scheduling is that it is not very ?exible in permitting new tasks to be included without re-design. However, the safety achieved from deterministic scheduling outweigh the bene?ts of ?exibility in scheduling.
5. GLOBAL SAFETY ASSURANCE
The primary dependability requirement in the wayside and carborne train control application is safety. In this sec-tion, we present a concept for global safety assurance in a distributed system to be used in safety-critical applications. This concept is currently implemented in an experimental test-bed prototype which is described brie?y in Section 7.
5.1Goals of Global Safety Assurance
A code-based approach to concurrent error detection and control algorithm veri?cation is employed in the sys-tem to implement global safety assurance. The goal of this method is to provide a quanti?able level of safety assur-ance over a distributed system. Unlike highly reliable sys-tems, safety-critical systems have the option of failing-safe, which in the case of this particular application means stopping the train. As a result, a desired approach to safety assurance could take advantage of a simplex controller without resorting to N-modular redundancy. A major dis-advantage of many N-modular redundant approaches, is that identical software is executed on all redundant com-puters. If the software is used for executing safety critical functions, or if it could introduce unsafe errors into the out-put of the system, then the software must be formally veri-?ed or assumed correct. Leveson [12] has concluded that it
is next to impossible to uncover all bugs in complex soft-ware. The safety assurance approach presented here uses a single control algorithm veri?cation methodology to detect errors arising from both hardware and software.
Since the set of all faults that can occur in hardware and software is considered in?nite, we check the manifes-tation of these faults as errors in the information domain [7]. The basic assumption of this approach is that all faults that can lead to system failure will manifest themselves as errors in the data that the computer processes. As a result, the system must be exercised frequently to minimize fault latency times and the data that is processed by the computer must be checked for errors before outputs are set.
5.2Concurrent Veri?cation of the Control Algorithm
Many error detection or voting systems implement bus-level voting mechanisms to vote on data every machine cycle [13]. This methodology requires tight syn-chronization of hardware and intimate knowledge of the hardware platform. V oting systems also assume that the software executing on redundant machines is correct and that design errors in processors that may cause simulta-neous errors do not exist.
In order to detect errors arising out of hardware and software for a generic computing platform, the problem of error detection is abstracted to the control application level. In the method presented here, the error checking mecha-nisms are not concerned with the speci?cs of the hardware platform, but rather with the control algorithm being exe-cuted Figure 3 depicts a distributed system composed of three main elements: inputs, a hardware/software (HW/ SW) computing platform, and outputs. An abstraction of the control algorithm is projected out from the hardware/ software computing platform in the lower box. A subset of the inputs into the system will consist of the input operands into the control algorithm. A subset of the outputs from the computing platform will also be output operands from the control algorithm.
The control algorithm can be described in the para-digm of a ?nite state machine (FSM). The outputs of the state machine which correspond to the outputs of the con-trol algorithm are a function of the input operands and internal state variables. The next states of the FSM are a function of the input operands and the current state of the FSM. For the wayside interlocking application, the control algorithm functions are Boolean operators. In most car-borne applications, the functions are arithmetic. The con-trol algorithm itself is a predetermined sequence of operations on the predetermined set of input operands and state variables. The a priori knowledge of which inputs and state variables are to be used in executing the pre-deter-mined equations permits concurrent veri?cation of algo-rithm execution. The safety assurance method is concerned only with the set of operands, next states, and outputs of the control algorithm. The set of all inputs, outputs and opera-tions in the computing platform is not of concern, unless errors in this superset manifest themselves as errors in the control algorithm subset.
5.3Checking in Safety Assurance Regions
A global approach to safety must consider errors that can arise in all parts of the system. These components include input modules, communication channels, processor units, and output modules. Each component in a distributed system is considered a safety assurance region. All errors that arise in a safety assurance region must be detected by error detection mechanisms and prevented from propagat-ing into other regions. The safety assurance region is anal-ogous to fault containment regions used in some highly reliable systems [13].
Using a code-based approach for error detection allows an upper bound on the probability for undetected errors to be calculated. This calculation is necessary for determining the coverage of all errors and ultimately the safety of the system. Input data to the control algorithm are read by input sensors at the input cards. The input sensor themselves must be vital according to railway standards. Once sensed, the ?eld data is encoded with an identity and time stamp in a cyclic code. The identity and time stamp are used by the concurrent veri?cation algorithm to detect referencing and timing errors. A cyclic code is used in order to assure good random and burst error detection capa-bility. Once encoded, this data can be checked before leav-ing the input module safety assurance region. Checking must be performed at the interfaces of the safety assurance regions.
The communication media of the architecture is also a safety assurance region. Data from input cards and proces-sors are encoded in a cyclic code before being transmitted over the network. Data is checked at the interface to the destination upon arrival. Loss of data is detected by incom-plete data sets and late data error conditions are detected watchdog time-outs. The output cards need only to verify that the output data codeword is uncorrupted, the time stamp is correct for the current cycle, and the identity of the codeword corresponds to the output channel.
Representing the control application as a ?nite state machine allows every state that is calculated by the algo-rithm to be checked concurrently. The concurrent veri?ca-tion algorithm knows a priori the identities of the inputs, the sequence of operations, and the identities of the state variables and outputs for the control algorithm. With this knowledge and the constraint that the processor execute the control algorithm in a predetermined sequential fashion, the control algorithm can verify that the correct input oper-ands for the current cycle were used and uncorrupted, that the correct operation was executed, and the correct output identity was encoded with the output operand. In addition, the concurrent veri?cation algorithm checker must be able to verify that the operation executed correctly. The algo-rithm checker is able to verify that the primary outputs and the next states were calculated correctly by diversely checking that the resulting output is a correct functional map from the inputs and operation type. Other train control applications such as input ?ltering, output ?ltering, and command feedback can be represented and checked simi-larly.
The concurrent veri?cation algorithm outlined for each of the safety assurance regions provides global safety assurance by detecting errors in hardware and software. Once an error is detected, a fail-safe shutdown is required. The safety assurance method is designed to check a single processor unit executing the control application. The checking algorithm can be implemented in a small number of semi-custom integrated circuit chips which will pas-sively monitor the processor-memory bus to capture the necessary operands. Alternatively, the algorithm can be programmed on another processor card which will execute the concurrent veri?cation algorithm on data received from the primary processor card. In these cases, the probability of an error occurring simultaneously in both the primary processor and the checker card that results in an unsafe fail-ure is analyzable through near-coincident fault analysis based on assumed failure rates for both cards.
to the overhead associated with delievering a packet for 256 I/O channels. Therefore, the performance of the I/O subsystem for remote calls will jump on packet boundaries. In this experiment, however, all packets are sent in pairs. As a result, the performance of the I/O subsystem jumps on pairs of packets which can hold enough data for 512 I/O channels. Therefore the I/O response time is approximately constant during each interval of 512 I/O channels and jumps at the next interval.
The main conclusion that can be drawn from this graph is that the I/O response time is much worse for remote transactions over the FDDI network than it is for local transactions over the VME backplane. A performance anal-ysis of the I/O transactions determined that the primary bottleneck in transmitting packets remotely is in the soft-ware driver for the FDDI network [16]. In contrast, local transactions on the VME backplane are performed through simple memory-mapped reads and writes to the local I/O devices.
A hardware fault-injection module for the prototype has been developed and is currently being integrated with the executive processor. The fault-injection unit will inject errors into the 68040 CPU concurrently with execution of the control application. The goal of fault injection is to experimentally determine the effectiveness of the safety assurance methodology in the presence of errors.
8. SUMMARY AND CONCLUSIONS
This paper presented an architecture and safety assur-ance methodology to be used in a distributed control sys-tem executing a safety-critical application. The architecture is designed to support train control applica-tions that require fail-safe and fault-tolerant operation. The architecture and safety assurance methodology de?ned in this paper overcomes many of the current limitations in existing train control systems. The architecture provides ?exibility in terms of expanding the system by adding COTS processors and I/O devices. The safety assurance methodology provides calculable safety for a distributed system controlled by a single processor. This method uses a deterministic timing paradigm for execution and a control algorithm veri?cation method to detect errors arising from hardware and software concurrently. The safety assurance methodology allows signi?cant savings in both redundant hardware costs and software veri?cation.
Results from simulating indicate the impact on net-work latency and response time for larger con?gurations of the system. The system architecture and safety assurance method is currently implemented in an experimental test-bed prototype. The experimental results showed the impact on the I/O response time due to the FDDI driver and pack-etization overhead. Future work will focus on simulated and experimental fault injection for dependability analysis.
9. ACKNOWLEDGMENTS
We would like to acknowledge the contributions of Douglass Lamb to Section 4 on I/O Cycle considerations and Paul Perrone to Section 5 on global safety assurance methodology.
10. REFERENCES
[1] A. Hachiga, “The Concepts and Technologies of Dependable and
Real-time Computer Systems for Shinkansen Train Con-
trol,”Dependable Computing and Fault-Tolerant Systems,
V ol.7, pp. 225- 252.
[2] D. Disk., “A Unique Application of a Microprocessor to Vital
Controls,” Prod. of the Int’l Conf. on Railway Safety Con-
trol and Automation, 1984, pp 97-104.
[3] D. Rutherford, “Fail-Safe Microprocessor Interlocking with
Safety Assurance Logic: Establishing a Vital Benchmark,”
Proc. of the Int’l Conf. on Railway Safety Control and Auto-
mation, 1984, pp 1-5.
[4] A. Cribbens, “The Solid State Interlocking System,”Proc. of the
Int’l Conf. on Railway Safety Control and Automation,Lon-
don, Sept. 1984, pp. 24-29.
[5]K. Akita, T. Watanabe, H.Nakamura, and I. Okumura, “Comput-
erized Interlocking System for Railway Signaling Control:
SMILE”,IEEE Trans.on Industry Applications, V ol. 1A-21,
No.4, May/June 1985, pp. 826-834.
[6]M. El Koursi and A. Stuparu, ”Safety Microprocessors in Guided
Ground Transport,” Transportation Technologies Applica-
tions,pp. 428-432.
[7] B.W. Johnson,Design and Analysis of Fault Tolerant Digital Sys-
tems,Addison Wesley Publishing Company, Reading MA,
1989.
[8]G. Vernazza and R. Zunino, “A distributed intelligence method-
ology for railway traf?c control,”IEEE Trans. on Vehicular
Technology,V ol. 39, No. 3, August 1990, pp. 263-270 [9] D.T. Lamb. and B.W. Johnson, “Next Generation Architecture
Executive Speci?cation,” Technical Report 930801.0, Cen-
ter for Semicustom Integrated Systems, University of Vir-
ginia, November, 1993.
[10]M.H. Klein and T. Ralya.An Analysis of Input/Output Paradigms
for Real-Time Systems. Tech. Report CMU/SEI-90-TR-19,
ESD-90-TR-220, July 1990.
[11] B.L. Di Vito, R.W. Butler, and J.L. Caldwell.Formal Design and
Veri?cation of a Reliable Computing Platform for Real-
Time Control. Phase 1 Results. NASA Tech. Mem. 102716.
Oct. 1990.
[12]N.G. Leveson, “Software Safety: Why, what, and how.”ACM
Comp. Surveys, June 1986
[13]J. Lala, R.E. Harper, and L. Alger, “A design approach for
ultrareliable real-time systems,”Computer,IEEE Computer
Society, V olume 24, May 1991, pp. 12-22.
[14]S. Kumar, R.H. Klenke, J.H. Aylor, B.W. Johnson, R.D. Will-
iams, and R. Waxman, “ADEPT: A Uni?ed System Level
Modeling Design Environment,”Proceedings of the 1st
Annual RASSP Conference, Arlington, V A, August 15-18,
1994, pp. 114-123.
[15]M.H. Klein, J.P. Lehoczky, an R.Rajkumar, “Rate-Monotonic
Analysis for Real-Time Industrial Computing,”Computer,
IEEE Computer Society, V ol.27, No.l 1, January 1994, pp.
24-33.
[16]V.S. Rana, “Application of FDDI in a Safety-Critical System,”
Master’s Thesis, University of Virginia, 1995.
一、选择题 1．I’d like to________the mall because it’s crowded and noisy. A．visit B．hang out C．walk D．go off 2．That path ________ directly to my house.You won't miss it. A．leads B．forms C．repairs D．controls 3．I don’t want to go. __________, I am too tired. A．However B．And C．Besides D．But 4．Some animals carry seeds from one place to another, ________ plants can spread to new places. A．so B．or C．but D．for 5．When I as well as my cousins __________ as a volunteer in Beijing, I saw the Water Cube twice. A．were treated B．treated C．was served D．served 6．He is wearing his sunglasses to himself from the strong sunlight. A．prevent B．stop C．keep D．protect 7．When you are________, you should listen to music to cheer you up. A．shy B．afraid C．strict D．down 8．Mr. Smith gave us some________on how to improve our speaking skills. A．advice B．news C．knowledge D．information 9．World Book Day takes place ________ April 23rd every year. A．at B．in C．on 10．More and more people have realized that clear waters and green mountains are as ________ as mountain of gold and silver. A．central B．harmful C．valuable D．careful 11．We loved the food so much, ________the fish dishes. A．special B．especial C．specially D．especially 12．—Oh, my God! I have ________ five pounds after the Spring Festival. —All of the girls want to lose weight, but easier said than done. A．given up B．put on C．got on D．grown up 13．—What do you think of the performance today? —Great! ________ but a musical genius could perform so successfully. A．All B．None C．Anybody D．Everybody 14．He ________ his homework________the morning of Sunday. A．doesn’t do; on B．doesn’t do; in C．doesn’t; on 15．Maria ________ speaks Chinese because she doesn’t know much Chinese. A．seldom B．always C．often D．usually 16．In 2018, trade between China and Hungary rose by 7.5 percent, and recently on Friday companies from China and Hungary________ several cooperation (合作) agreements under the
1.选购电压力锅可根据个人的喜好而定。机械式电压力锅和微电脑式电压力锅的控制方式不同，但使用效果完全一样，前者操作复杂，后者方便直观，但价格较高。 2.选购电压力锅的规格应考虑人口数量，2-3人的家庭宜选4升的，3-5人的家庭宜选5升的，6人以上的家庭宜选6升或8升的。 3.性能方面要着重检查内锅与电热盘接触是否良好、通电发热是否正常，此外还要检查功能开关、轻触式按钮是否正常。旋动调节器和定时器动作应自如，加热和保温指示灯相应亮灭，定时器倒计时完成后能自动关机等。电源线和电源插头绝缘要良好，无氧化锈蚀等。 4.电压力锅安全装置的性能很重要，因为安全性能的优劣直接影响其使用性能。首先检查锅盖的密封圈应无变形和龟裂，将锅盖嵌到锅体端口，顺时针旋转锅盖手柄至定位位置，锅盖应密封良好。查看浮子阀、排气阀、安全阀、防堵罩安装要牢固可靠，金属外表面光亮无氧化锈蚀等。最后，注水通电试锅，加热到预定温度，排气阀能正常排气，定时器能自动关机。 5.说明书、相关标识及安全提示详尽齐备与否代表了企业的责任心，并能保证消费者正确安全的使用。因此对此项检查也不可疏忽。 6.应选购通过3C认证的产品。通过认证的电压力锅质量有保证，电气性能合格，售后服务到位。 如何选购电压力锅？ １．可根据个人喜好而定。 机械式和微电脑式控制方式不同，但使用效果完全一样， 机械式操作简单，只有一个倒计时旋扭，适用于家中老人常用，（我妈就是年纪大了，眼有点花，电脑型的有些按钮多，显示的东西也多，有时难以看清楚），而倒计时旋扭式很简单，根据不同食物，调到不同的烹饪时间即可。如果家中老人常用，尽量选择防烫型。 微电脑式较高档，数码或液晶显示，较贵，操作复杂些。 ２．规格：２-３人的家庭４升，３-５人５升的，６人以上６-8升。 ３．性能方面：着重检查内锅与电热盘接触是否良好、通电发热是否正常，此外还要检查功能开关、轻触式按钮是否正常。旋动调节器和定时器动作应自如，加热和保温指示灯相应亮灭，定时器倒计时完成后能自动保温或关机等。电源线和电源插头绝缘要良好，无氧化锈蚀等。
螺纹通止规 定是:螺纹止规进入螺纹不能超过2.5圈,一般的要实际不得超过2圈,并且用得力度不能大,我们的经验是用拇指和食指轻轻夹持螺纹规以刚好能转动螺纹规的力度为准.力大了就相当于在使用丝锥或牙板了,那样规就用不了几次了. 螺纹通止规 螺纹通止规是适用于标准规定型号的灯头作为灯用附件电光源产品时候的设计和生产、检验的工具设备。 用途 一般用于检验螺纹灯头或灯座的尺寸是否符合标准要求，分别检验螺纹灯头的通规和止规尺寸或灯座的通规或止规尺寸。 工作原理 具体检验要求及介绍详见中国人民国国家标准：GB/T1483.1-2008或 IEC60061-3:2004标准规定容。 操作方法 具体检验要求及介绍详见中国人民国国家标准：GB/T1483.1-2008或 IEC60061-3:2004标准规定容。 通止规
通止规，是量规的一种。作为度量标准，用于大批量的检验产品。 通止规是量具的一种，在实际生产批量的产品若采取用计量量具（如游标卡尺，千分表等有刻度的量具）逐个测量很费事．我们知道合格的产品是有一个度量围的.在这个围的都合格，所以人们便采取通规和止规来测量． 通止规种类 （一）对统一英制螺纹，外螺纹有三种螺纹等级：1A、2A和3A级，螺纹有三种等级：1B、2B和3B级，全部都是间隙配合。等级数字越高，配合越紧。在英制螺纹中，偏差仅规定1A和2A级，3A级的偏差为零，而且1A和2A级的等级偏差是相等的等级数目越大公差越小，如图所示：1B 2B 3B 螺纹基本中径3A 外螺纹2A 1A 1、1A和1B级，非常松的公差等级，其适用于外螺纹的允差配合。 2、2A和2B级，是英制系列机械紧固件规定最通用的螺纹公差等级。 3、3A和3B级，旋合形成最紧的配合，适用于公差紧的紧固件，用于安全性的关键设计。 4、对外螺纹来说，1A和2A级有一个配合公差，3A级没有。1A级公差比2A级公差大50，比3A级大75，对螺纹来说，2B级公差比2A公差大30。1B级比2B级大50，比3B级大75。 （二）公制螺纹，外螺纹有三种螺纹等级：4h、6h和6g，螺纹有三种螺纹等级：5H、6 H、7H。（日标螺纹精度等级分为I、II、III三级，通常状况下为II级）在公制螺纹中，H 和h的基本偏差为零。G的基本偏差为正值，e、f和g的基本偏差为负值。如图所示：公差G H 螺纹偏差基本中径外螺纹f g h e 1、H是螺纹常用的公差带位置，一般不用作表面镀层，或用极薄的磷化层。G位置基本偏差用于特殊场合，如较厚的镀层，一般很少用。 2、g常用来镀6-9um的薄镀层，如产品图纸要6h的螺栓，其镀前螺纹采用6g的公差带。 3、螺纹配合最好组合成H/g、H/h或G/h，对于螺栓、螺母等精制紧固件螺纹，标准推荐采用6H/6g的配合。 （三）螺纹标记M10×1–5g 6g M10×1–6H 顶径公差代号中径和顶径公差代号（相同）中径公差代号。 通止规是两个量具分为通规和止规．举个例子：M6－7h的螺纹通止规一头为通规（T）如果能顺利旋进被测螺纹孔则为合格，反之不合格需返工（也就是孔小了）．然后用止规（Z）如果能顺利旋进被测螺纹孔2.5圈或以上则为不合格反之合格．且此时不合格的螺纹孔应报废，不能进行返工了．其中2.5圈为国家标准，若是出口件最多只能进1.5圈（国际标准）．总之通规过止规不过为合格，通规止规都不过或通规止规都过则为不合格。
boring 令人厌烦的，乏味的，无聊的 tedious 乏味的，单调的，冗长的 flat 单调的，沉闷的 dull 乏味的，单调的 troublesome 令人烦恼的，讨厌的，麻烦的 tired 疲劳的，累的 bored 无聊的，无趣的，烦人的 exhausted 极其疲倦的 weary 疲劳的 bright 聪敏的，机灵的 apt 聪明的，反应敏捷的 intelligent 聪明的，有才智的 shrewd 机灵的，敏锐的，精明的（表示生意上的精明） ingenious （人，头脑）灵巧的 alert 警觉的，留神的 cute 聪明伶俐的，精明的 acute/cute acute 指的是视力，感觉的敏锐 dull 愚钝的，笨的 awkward 笨拙的，不灵巧的 absurd 荒谬的 ridiculous 可笑的，荒谬的 idiotic 白痴般的 blunt 率直的，直言不讳的 clumsy 笨拙的，粗陋的 happy 快乐的，幸福的 cheerful 欢乐的，高兴的 content 满意的，满足的 merry 欢乐的，愉快的，快乐的 pleasure 高兴，愉快，满足 enjoyment 享乐，快乐，乐趣 cheer 喝彩 applause 鼓掌，掌声 optimism 乐观，乐观主义 delight 快乐，高兴 kick 极大的乐趣 paradise 天堂，乐园 instant 立即的，即刻的 instantaneous 瞬间的，即刻的 immediate 立即的，即刻的 simultaneous 同时发生的，同时存在的，同步的punctual 严守时刻的，准时的，正点的 pick 挑选，选择 select 选择，挑选 single 选出，挑出 elect 选举，推举 vote 投票，选举 appoint 任命，委派 nominate 提名，任命 propose 提名，推荐 recommend 推荐，举荐 designate 指派，委任 delegate 委派（或选举）…为代表 install(l) 使就职，任命 ballot 使投票表决 dub 把…称为 choice 选择（权） option 选择 selection 选择，挑选 alternative 取舍，供选择的东西 favorite 特别喜爱的人（或物） inclination 爱好 preference 喜爱，偏爱，优先 observe 注意到，察觉到 perceive 认识到，意识到，理解 detect 察觉，发现 appreciate （充分）意识到，领会，体会 alert 使认识到，使意识到 awake 意识到，醒，觉醒 scent 察觉 ancient 古代的，古老的 primitive 原始的 preliminary 预备的，初步的 preliminary trial初审 primary 最初的，初级的 initial 开始的，最初的 original 起初的 former 在前的，以前的 previous 先，前 prior 在前的，优先的 beforehand 预先，事先 medieval 中世纪的，中古（时代）的preceding 在先的，在前的，前面的 senior 资格较老的，地位较高的 following 接着的，下述的 attendant 伴随的 subsequent 随后的，后来的 succeeding 以后的，随后的 consequent 作为结果（或后果）的，随之发生的 resultant 作为结果的，因而发生的therefore 因此，所以 consequently 所以，因此 then 那么，因而 thus 因此，从而 hence 因此，所以 accordingly 因此，所以，于是 thereby 因此，从而
一、故事引入 杜牧的《清明》一诗“清明时节雨纷纷，路上行人欲断魂。借问酒家何处有，牧童遥指杏花村。”大家都很熟悉，但如果把标点符号改动一下，就成了另一作品。有人巧妙短句将其改成了一首词：“清明时节雨，纷纷路上，行人欲断魂。借问酒家何处？有牧童遥指，杏花村。”还有人改成了一首优美隽永的散文：“清明时节，雨纷纷。路上，行人欲断魂。借问酒家：“何处有牧童？”遥指杏花村。 又如，常有人在一路边大小便，有人就在那立了块牌子：过路人等不得在此大小便。立牌人的本意是：“过路人等，不得在此大小便。”可没有点标点符号，于是被人认为是：“过路人，等不得，在此大小便。” 类似的故事不胜枚举，诸如一客栈“下雨天留客天留我不留”的对联，祝枝山写给一财主的对联“今年正好晦气全无财富进门”。可见，标点符号的作用举足轻重。语文课程标准对小学各阶段学生应该掌握的标点符号作了明确的规定和说明。因此，作为小学语文教师，不但要咬文嚼字，教会学生正确使用标点符号也不容忽视。下面，我就简单谈谈一些易错的标点符号的用法。 二、易错标点符号的用法例谈 （一）问号 1、非疑问句误用问号 如：他问你明天去不去公园。虽然“明天去不去公园”是一个疑问，但这个问句在整个句子中已经作了“问”的宾语，而整个句
子是陈述的语气，句尾应该用句号。又如：“我不晓得经理的心里到底在想什么。”句尾也应该用句号。 2、选择问句，中间的停顿误用问号 比如：宴会上我是穿旗袍，还是穿晚礼服？这是个选择问句，中间“旗袍”的后面应该用逗号，而不用问号。再有：他是为剥削人民的人去死的，还是为人民的利益而死的？这个句中的停顿也应该用逗号。 3、倒装句中误把问号前置 像这样一个句子：到底该怎么办啊，这件事？原来的语序是：这件事到底该怎么办啊？ 倒装之后，主语放到了句末，像这种情况，一般问号还是要放在句末，表示全句的语气。 4、介于疑问和感叹语气之间的句子该如何使用标点符号 有的句子既有感叹语气，又有疑问的语气，这样的情况下，哪种语气强烈，就用哪个标点，如果确定两种语气的所占比重差不多，也可以同时使用问号和叹号。 （二）分号 1、句中未用逗号直接用分号 从标点符号的层次关系来看，应该是逗号之间的句子联系比较紧密，分号之间的句子则要差一个层次，这样看来，在一个句中，如果没有逗号径直用分号是错误的。比如：漓江的水真静啊，漓江的水真清啊，漓江的水真绿啊。这里句中的两处停顿就不能使用分号。再
美的电炖锅WBZH22A的介绍 煲汤，为粤港澳以至中国大陆、台湾地区常见的菜肴，由于岭南地区气候炎热潮湿，因此人们爱喝滋身补益效用的老火汤，通常用锅把各种蔬菜、水果、肉类或中药熬上数小时而成。老火汤有护肤、护心、明目、降胆及健骨等效果。老火汤已经成为粤菜的特色之一。而炖锅是煲汤的最佳厨具之一，不过有很多人说对电炖锅不是很了解。我个人是比较喜欢用电炖锅炖汤，所以特地买了个电炖锅，是美的WBZH22A电炖锅。今天我就以美的电炖锅WBZH22A 为例，给大家介绍一下电炖锅。 一、产品概述： 美的WBZH22A电炖锅是美的一款隔水白瓷电炖锅。它有一盅三胆，是白瓷电炖盅，煲汤煮粥可同时进行，一锅三胆，有易取防烫提手，可以防止烫伤，更有118MM大盘加热、4小时定时、带保温等功能，还有双层内盖设计。 二、产品特色： 1、易取防烫提手设计 附合人体工程学设计的易取防烫提手，解决传统炖盅拿取汤品时的困扰。最大厚度达 6mm,材质强度更高，高温不软化，保证使用安全，拿取炖盅更方便。
2、大炖盅双重内盖设计 大炖盅采用双重内盖设计，炖汤过程中，能减少炖品温度的散发，避免营养与食品香气的流失。汤汁受热到位，骨酥肉嫩，香气浓郁，口感更好。 3、机身水位显示窗设计 在机身外侧就能观察到机身水箱内的水位情况，能实时了解水箱内水位，更加方便直接。
4、隐藏提手设计 宽大的提手隐藏于底座，防滑设计，移动整机轻而易举，搬取整机更安全更舒适。 5、电源线分体设计 收纳电炖盅时，可将电源线拔下，没有牵绊烦恼，移动更轻松方便。 6、白瓷内胆 白瓷内胆天然、优质、釉质光滑、蓄热性好、受热均匀，这样更健康安全、易清洗、汤汁浓郁富有营养。
螺纹通止规要求螺纹通规通，止规止。 但是如果螺纹通规止，说明什么？ 螺纹止规通，又说明什么？ 我也来说两句查看全部回复 最新回复 ?wpc (2008-11-07 20:11:20) 在牙型正确的前提下螺纹通止规检测螺纹中径 ?lobont (2008-11-08 11:16:32) 对外螺纹而言，螺纹通规是做到中径上偏差，所以能通过就表示产品合格，通不过就表示螺纹做大了，要再修一刀； 螺纹止规做到中径下偏差，所以只能通过2～3牙，如果也通过，就表示外螺纹做小了，产品成为废品 ?qubin8512 (2008-11-18 15:36:05) 螺纹赛规与螺纹环规主要测量螺纹的中径。 ?datafield (2008-11-29 19:12:51) 检具不是万能的，只是方便而已。具体没什么的我有在哪本书上看过，是一本螺纹手册上的。 ?ZYC007 (2009-2-09 20:31:13) 在牙型正确的前提下螺纹通止规检测螺纹中径。 对外螺纹而言，但是如果螺纹通规止，说明螺纹中径大；螺纹止规通，又说明螺纹中径小。 ?WWCCJJ (2009-3-19 09:27:19) 检测的是螺纹的中径,螺纹检测规在检定时,也是检测其中径. ?tanjiren (2009-3-20 22:23:06) 螺纹通止规只能检测螺纹的作用中径,大径和底径等均无法准确测量出来. ?月夜(2009-4-01 21:47:13) 用来测量中径 ?丽萍(2009-4-02 10:11:41)
只能检测工件螺纹的中径 yg196733456 (2009-4-03 09:15:56)原来是测中径的知道了
不能片面说人做主语用ed，物做主语ing ing形式是修饰引起这种感觉的人或物；ed形式是描写人或物的感受。（当然物一般是动物） 翻译的话 ing形式的词译为“令人……的”；ed形式译为“……的” boring是令人感到厌烦的；bored是厌烦的。 a boring person 能够指一个了无情趣的人，让人觉得无趣的人 a bored person 则是说这个人自己感到很无趣 1.bore 1）vt.使厌烦；挖 e.g. I'm bored with this job. 这件工作厌烦了。 The oldier bore the sharp pain in the wound with great courage. 这士兵以巨大的勇气忍受着伤口的剧烈疼痛。 2）n.令人讨厌的人（或事） e.g. It's a bore having to go out again. 外出真是讨厌。 boredom n.厌倦，无趣 e.g. in infinite boredom 极其无趣 boring n. 钻(孔) adj. 令人厌烦的(事或物） e.g. The play was boring. 这部短剧很一点意思都没有。 bored adj. 无聊的, 无趣的, 烦人的 e.g. Jack is so bored. 杰克是个没有趣的人。 2.surprising 是针对事或物感到惊奇。 surprised 则是针对人。 3.pleasant adj. 愉快的, 快乐的, 舒适的, 合意的可爱的, 举止文雅的, 活泼的滑稽的, 有趣的 (天气)晴朗的, 美好的容易相处的, 友爱的 e.g. a pleasant voice 悦耳的声音 a pleasant companion 可爱的伴侣 a pleasant time 愉快地度过时光 pleasing adj. 舒适的, 使人愉快的; 满意的; 惹人喜欢的, 可爱的 e.g. a pleasing look 使人愉快的神情 a very well mannered and pleasing young man 彬彬有礼而令人喜爱的年轻人
编校一课丨连接号用法大全 《标点符号用法》新标准中，连接号删除长横线“——”，只保留三种形式：一字线“—”、半字线“-”、波纹线“～”。三种连接号的使用范围各不相同。一字线 一字线占一个字位置，比汉字“一”略长标示时间、地域等相 关项目间的起止或相关项之间递进式发展时使用一字线。例：1.沈括（1031—1095），宋朝人。 2.秦皇岛—沈阳将建成铁路客运专线。 3.人类的发展可以分为古猿—猿人—古人—新人这四个阶段半字线半字线也叫短横线，比汉字“一”略短，占半个字位置。用于产品型号、化合物名称、 代码及其他相关项目间的连接。例：1.铜-铁合金（化合物 名称） 2.见下图3-4（表格、插图编号） 3. 中关园3号院3-2-11室（门牌号） 4.010-********（电话号码） 5.1949-10-01（用阿拉伯数字表示年月日） 6.伏尔加河-顿河运河（复合名词）波纹线波纹线俗称波浪线，占一个字位置标示数值范围的起止时用波纹线，包括用阿拉伯数字表示的数值和由汉字数字构成的数值。例：1.10～30cm 2. 第七～九课常见问题1.在数值间使用连接号时，前后两个数值都需要加上计量单位吗？在标示数值范围时，用波纹线连接号。此时，在不引起歧义的情况下，只在后一数值后计量单位，用波纹线连接的两个
数值，其单位是一致的。例：500～1000公斤 2.“1996～现在”这样的用法对吗？不对。波纹线连接数字，“现在”不是数字，应改为“”到或“至”。“1996”后宜加“年”。 关注“木铎书声”，做优秀出版人木铎书声是北京师范大学出版科学研究院官方微信平台，致力于传播最新行业动态，促进出版职业人的发展。
职业营销人与业余营销人的区别有很多，本文则从对产品质量问题的看法上，介绍了职业营销人与业余营销人的区别，可供参考，希望对大家能有所启发。 商业社会，不做营销职业也许是一种幸福，但不懂职业营销，一定是人生最大的遗憾。业余营销选手把自己销售掉，职业营销选手把自己营销出去。一个人选择了营销这个职业，做一个职业营销选手是不二的选择。企业的营销不缺少卓越的战略，企业的营销更不缺少优秀的策略，企业营销真正缺少的是把战略和策略变为现实的职业营销选手。就算成为一名职业营销选手，其实也没有什麽好兴奋的，做一个职业营销选手本来就是营销者的天职。 2010年5月23日，央视《每周质量报告》栏目曝光了美的紫砂煲生产内幕，称紫砂煲产品中的天然紫砂基本都是以普通陶土甚至田土为原料，用化工制剂进行增色制造而成，而非真正紫砂。 央视曝光后，消费者一片哗然。接着美的公司为不实说法公开道歉，承诺在全国设退货点接受退货，各大卖场纷纷下架紫砂煲。城门失火殃及池鱼，美的作为行业的领导品牌遭此“横祸”，其它品牌纷纷遇难!本次事件，与奶粉行业的“三聚氰胺事件”颇多相似之处，难免波及整个电炖锅行业。 美的在产品宣传册中称：美的紫砂煲内胆叫“紫金风火内胆”，是“全部选用纯正紫砂烧制”，“表里如一，从里到外的好”，而且“富含丰富微量元素，补铁补血，有益身体健康”。然后央视的记者开始打破“紫砂锅”问到底! 美的的做法完全符合营销书上面讲的“FAB”法则。F.即产品特点：全部选用纯正紫砂烧制A.即产品优点：表里如一，从里到外的好B.即产品利益点：富含丰富微量元素，补铁补血，有益身体健康。 从专业的角度来看，美的电炖锅销售这几句话，简直是小家电产品卖点提炼的模板。而且美的将专业的术语变成简单化、通俗化、形象化的生活语言，即终端销售“话术”。难怪那么多的消费者愿意花高价钱，买这些高档产品。这似乎印证了一位营销高人的一句话，高档，高档，就是让消费者高高兴兴上当。 提炼产品卖点关键是拿捏得当。“太实在”是傻子，“不实在”是骗子。“太实在”老板和上司看了不高兴;“不实在”媒体和消费者不答应。美的、九阳把电炖锅宣传为紫砂煲，就是犯了“不实在”的大忌。我们走访市场发现，尽管美的、九阳双双撤出国美、苏宁等家电卖场，依立、三源等品牌的依然在正常销售，莫非后者是实实在在的紫砂制成?可惜受兄弟品牌影响，购买者依然寥寥无几。有时候劣币驱逐良币，劣币大显身手，有时候城门失火殃及池鱼，劣币良币同归于尽。好在不少媒体已经在为紫砂门推托责任，说紫砂煲缺失国家标准，亟待政府规范。 看来这提炼产品卖点还大有学问。弄好了，卖点是流通策略中的销售“点”，是竞争战略转败为胜的“机会点”;弄不好，卖点是媒体的导火点,是消费者忧心忡忡的“焦点”。
N P T螺纹以及检测方法详 解 Prepared on 22 November 2020
一、目的：规范公司技术员，检验员，操作员对NPT螺纹的了解。 二、适用范围：适用于公司任何NPT螺纹类产品，参考资料为通用管螺 纹和国家标准GB/T12716-2011。 三、目录 1、NPT和NPTF介绍 2、螺纹技术参数参数讲解 3、NPT与NPTF加工工艺 4、NPT和NPTF的检测方法 四、内容： NPT和NPTF螺纹介绍 NPT 是 National (American) Pipe Thread 的缩写，属於美国标准的 60 度锥管 密封螺纹，用於北美地区，美国标准为13)通用管螺纹．国家标准可查阅 GB/T12716-2011。NPTF：美制干密封圆锥管螺。NPTF = National Pipe Thread Fine 称之为一般用途的锥管螺纹，这也是我们以前称之为的布氏锥螺纹。NPTF 螺纹称之为干密封式锥管螺纹，它连接密封的原理是在没有润滑剂或密封填 料情况下完全依靠螺纹自身形成密封，设计意图是使内、外螺纹牙的侧面、 牙顶和牙底同时接触，来达到密封的目的。它们两者的牙型角、斜度等指标 都是相同的，关键是牙顶和牙底的削平高度不一样，所以，量规的设计也是 不一样的。NPTF干密封管螺纹的牙形精度比NPT螺纹高，旋合时不用任何 填料，完全依靠螺纹自身形成密封，螺纹间无任何密封介质。干密封管螺纹 规定有较为严格的公差，属精密型螺纹，仅用在特殊场合。这种螺纹有较高 的强度和良好的密封性，在具有薄截面的脆硬材料上采用此螺纹可以减少断 裂现象。NPTF内、外螺纹牙顶与牙底间没有间隙，是过盈配合，而NPT螺 纹是过渡配合。NPTF螺纹主要用于高温高压对密封要求严格的场所。NPT
通止规的用法及管理 1、止规 使用前：应经相关检验计量机构检验计量合格后，方可投入生产现场使用。 使用时：应注意被测螺纹公差等级及偏差代号与环规标识公差等级、偏差代号相同（如M24*1.5-6h与M24*1.5-5g两种环规外形相同，其螺纹公差带不相同，错用后将产生批量不合格品)。 检验测量过程：首先要清理干净被测螺纹油污及杂质，然后在环规与被测螺纹对正后，用大母指与食指转动环规，旋入螺纹长度在2个螺距之内为合格，否则判为不合格品。 2、通规 使用前：应经相关检验计量机构检验计量合格后，方可投入生产现场使用。 使用时：应注意被测螺纹公差等级及偏差代号与环规标识的公差等级、偏差代号相同（如M24*1.5-6h与M24*1.5-5g两种环规外形相同，其螺纹公差带不相同，错用后将产生批量不合格品)。 检验测量过程：首先要清理干净被测螺纹塞规油污及杂质，然后在环规与被测螺纹对正后，用大母指与食指转动环规，使其在自由状态下旋合通过螺纹全部长度判定合格，否则以不通判定。 3、注意事项 在用量具应在每个工作日用校对塞规计量一次。经校对塞规计量超差或者达到计量器具周检期限的环规，由计量管理人员收回、标识隔离并作相应的处理措施。 可调节螺纹环规经调整后，测量部位会产生失圆，此现象由计量修复人员经螺纹磨削加工后再次计量鉴定，各尺寸合格后方可投入使用。 报废环规应标识隔离并及时处理，不得流入生产现场。 4、维护与保养 量具（环规）使用完毕后，应及时清理干净测量部位附着物，存放在规定的量具盒内。生产现场在用量具应摆放在工艺定置位置，轻拿轻放，以防止磕碰而损坏测量表面。 严禁将量具作为切削工具强制旋入螺纹，避免造成早期磨损。可调节螺纹环规严禁非计量工作人员随意调整，确保量具的准确性。环规长时间不用，应交计量管理部门妥善保管。
一、选择题 1．Is this a photo of your son? He looks________ in the blue T-shirt. A．lovely B．quietly C．beautiful D．happily 2．—Jerry looks so tired. He works too hard. —He has to ________ a family of four on his own. A．offer B．support C．provide D．remain 3．— Mr. Wilson, can I ask you some questions about your speech? — Certainly, feel __________ to ask me. A．good B．patient C．free D．happy 4．Some animals carry seeds from one place to another, ________ plants can spread to new places. A．so B．or C．but D．for 5．— Can you tell us about our new teacher? —Oh, I’m sorry. I know________ about him because I haven’t seen him before. A．something B．anything C．nothing D．everything 6．—Help yourselves! The drinks are ________ me. —Thank you. You’re always so generous. A．above B．in C．on D．over 7．Gina didn’t study medicine. ________, she decided to become an actor. A．Instead B．Again C．Anyway D．Also 8．—Have you got Kathy’s________ for her concert? —Yes, I’d like to go and enjoy it. A．interview B．information C．invitation D．introduction 9．More and more people have realized that clear waters and green mountains are as ________ as mountain of gold and silver. A．central B．harmful C．valuable D．careful 10．Kangkang usually does her homework ________ it is very late at night. A．until B．when C．before D．after 11．He ________all the “No Smoking” signs and lit up a cigarette. A．requested B．attacked C．protected D．ignored 12．一Where is Mr. Brown? 一I think he's _____________ the music hall. A．on B．in C．over D．from 13．— Is your home close to the school, Tom? — No, it's a long way, but I am________ late for school because I get up early daily. A．always B．usually C．never D．sometimes 14．—Mum, I don’t want the trousers. They’re too long.
连接号用法之深入辨析 王曜卿 第二轮修志，各地都是衔接上届志书的下限编修续志，续志书名也是千篇一律：在书名下加上断限。书名下断限的书写格式，规范写法为―(19xx－2000)‖，但采用这种写法的却不成主流。不规范的书写格式中，常见的是―(19xx～2000)‖，此外还有―(19xx－2000年)‖、―(19xx～2000年)‖、―(19xx年－2000年)‖、―(19xx年～2000年)‖，加上―－‖、―～‖两种符号自身宽度变化所产生的变体，不规范的写法就更多了。 志书断限中的连接号，没有引起人们的高度重视，由此所反映出来的，则是标点符号规范化和表达概念准确性的大问题。准确地说，是正确、规范地使用连接号，准确地表述时空范围之概念，准确地表述数值量之关系(或幅度)的大问题。 一、连接号的多种形式 连接号有多种形式，各自的作用、用途也不同。中华人民共和国国家标准(简称―国标‖)《标点符号用法》(GB/T 15834－1995)对连接号的规定： 4.13 连接号 4.13.1 连接号的形式为?－‘。连接号还有另外三种形式，即长横?——‘、半字线?-‘和浪纹?～‘。 4.13.2 两个相关的名词构成一个意义单位，中间用连接号。例如： a) 我国秦岭－淮河以北地区属于温带季风气候区，夏季高温多雨，冬季寒冷干燥。 b) 复方氯化钠注射液，也称任-洛二氏溶液(Ringer-Locke solution)，用于医疗和哺乳动物生理学实验。 4.13.3 相关的时间、地点或数目之间用连接号，表示起止。例如： a) 鲁迅(1881－1936)中国现代伟大的文学家、思想家和革命家。 b) ?北京——广州‘直达快车 c) 梨园乡种植的巨峰葡萄今年已经进入了丰产期，亩产1000公斤～1500公斤。 4.13.4 相关的字母、阿拉伯数字等之间，用连接号，表示产品型号。例如： 在太平洋地区，除了已建成投入使用的HAW－4和TPC－3海底光缆之外，又有TPC －4海底光缆投入运营。 4.13.5 几个相关的项目表示递进式发展，中间用连接号。例如：
【英语】英语形容词常见题型及答题技巧及练习题(含答案)及解析 一、初中英语形容词 1．My deskmate is really _____．She likes to attend different activities after school． A. active B. quiet C. lazy D. honest 【答案】 A 【解析】【分析】我的同桌同学非常活跃，放学后喜欢参加很多不同的活动． 句中提到"She likes to attend different activities after school"放学后喜欢参加很多不同的活动，由此推测此人非常活跃，A积极的，活跃的；B安静的；C懒惰的，D诚实的，根据句意可知选择A． 2．Wang Wei speaks English as ________ as Yang Lan. They both study English hard. A. good B. well C. better D. best 【答案】 B 【解析】【分析】句意：王伟的英语讲的和杨澜的一样好。他们学习英语都努力。可知as…as中间用形容词或副词原级；此处是副词修饰动词speak。good好的，形容词原形；well好地，副词原形，better比较级；best最高级，故选B。 【点评】此题考查形容词原级。注意as...as中间跟形容词或副词原级。 3．—If there are ________ people driving, there will be ________ air pollution. —Yes, and the air will be fresher. A. less; less B. less; fewer C. fewer; fewer D. fewer; less 【答案】 D 【解析】【分析】句意：——如果开车的人越少，空气污染越少。——是的，空气将会更新鲜。little少的，形容词，其比较级是less，修饰不可数名词，few几乎没有，形容词，其比较级是fewer，更少，修饰可数名词，people，可数名词，用fewer修饰，air pollution，空气污染，不可数名词，用less修饰，故选D。 【点评】考查形容词的辨析。注意less和fewer意思和用法。 4．—Guess what? The university has accepted my application! —Wow! That's ________ new I've heard this year, Boris! Let's celebrate. A. a worse B. the worst C. a better D. the best 【答案】 D 【解析】【分析】句意：——猜猜什么？那所大学已经接受我的申请了。——哇喔，那是今年我听到的最好的消息，Boris，让我们庆祝一下。A.一个更糟的，比较级；B.最糟的，最高级；C.一个更好的，比较级；D.最好的，最高级。因为大学接受申请了，所以是好消息，排除A、B。根据 I've heard this year，今年我听到的，可知是最高级，故选D。 【点评】考查形容词辨析，注意平时识记最高级结构，理解句意。
“趣味钓虾欢乐时光”活动方案 一、活动目的 1、通过趣味摊位互动，营造现场人气，延长客户客户逗留时间，吸引客户 的参与热情，维护老业主满意度，进一步挖掘“老带新“成交，促进项目销售； 2、通过周末暖场主题活动，加强客户对项目的忠诚度。进而增强项目市场 影响力及新客户对项目的认知度，促进新客户成交； 二、活动主题 “趣味钓虾欢乐时光” 三、活动时间 2017年4月15日-16日（上午9:00-12:00，下午14:00-18:00） 四、活动场地布置图 五、活动地点 恒大御景半岛销售中心,老业主、意向客户、新上门客户均可参与； 六、活动内容 1.上门抽奖：客户凭盖了恒大活动专用章的抽奖劵，上门可获得抽奖一次， 以乒乓球抽奖的形式，任意抽取一个球，球上标有数字，可获得对应的礼品； 中奖编号： 客户凭盖了恒大活动专用章的抽奖劵，上门可获得抽奖一次，以乒乓球抽奖的形式，任意抽取一个球，球上标有数字，可获得对应的礼品（100%有
礼）； 中奖编号： 编号：888 三开门冰箱（噱头）； 编号：88 2g金条（合计1条，具体视现场情况为准）； 编号：8 美的搅拌机； 编号：28 恒大油1.8L； 编号：2、18 恒大绿色大米5kg； 编号：1、16、17 恒大玻璃杯； 编号：空白球精美小礼品一份（钥匙扣）； 2、乐趣钓真虾：在营销中心内准备一个大游泳圈，里面放满小虾，在工作人员的协助下，来访客户可钓虾；（150份/天）；数量有限，赠完截止； 3、沙漏DIY：在销售中心设置一个制作沙漏的DIY摊位，来访客户可自行制作沙漏，（150份/天）；数量有限，赠完截止；
4.甜心美食：现场设置美食摊位提供爆米花和可乐供客户品尝，美食不间断。 5. 魔术小丑表演：魔术小丑现场与客户互动。表演魔术； 6.准点抽奖：活动期间，每天准点抽奖时间为下午4:30；同时配合项目推介 会，奖品有（家电、金条等）；
通止规的用法及管理 令狐采学 1、止规 使用前：应经相关检验计量机构检验计量合格后，方可投入生产现场使用。 使用时：应注意被测螺纹公差等级及偏差代号与环规标识公差等级、偏差代号相同（如M24*1.56h与M24*1.55g两种环规外形相同，其螺纹公差带不相同，错用后将产生批量不合格品)。 检验测量过程：首先要清理干净被测螺纹油污及杂质，然后在环规与被测螺纹对正后，用大母指与食指转动环规，旋入螺纹长度在2个螺距之内为合格，否则判为不合格品。 2、通规 使用前：应经相关检验计量机构检验计量合格后，方可投入生
产现场使用。 使用时：应注意被测螺纹公差等级及偏差代号与环规标识的公差等级、偏差代号相同（如M24*1.56h与M24*1.55g两种环规外形相同，其螺纹公差带不相同，错用后将产生批量不合格品)。 检验测量过程：首先要清理干净被测螺纹塞规油污及杂质，然后在环规与被测螺纹对正后，用大母指与食指转动环规，使其在自由状态下旋合通过螺纹全部长度判定合格，否则以不通判定。 3、注意事项 在用量具应在每个工作日用校对塞规计量一次。经校对塞规计量超差或者达到计量器具周检期限的环规，由计量管理人员收回、标识隔离并作相应的处理措施。 可调节螺纹环规经调整后，测量部位会产生失圆，此现象由计量修复人员经螺纹磨削加工后再次计量鉴定，各尺寸合格后方
可投入使用。 报废环规应标识隔离并及时处理，不得流入生产现场。 4、维护与保养 量具（环规）使用完毕后，应及时清理干净测量部位附着物，存放在规定的量具盒内。生产现场在用量具应摆放在工艺定置位置，轻拿轻放，以防止磕碰而损坏测量表面。 严禁将量具作为切削工具强制旋入螺纹，避免造成早期磨损。可调节螺纹环规严禁非计量工作人员随意调整，确保量具的准确性。环规长时间不用，应交计量管理部门妥善保管。