附录一英文科技文献翻译
英文原文：
Experimental investigation of laser surface textured parallel thrust bearings
Performance enhancements by laser surface texturing (LST) of parallel-thrust bearings is experimentally investigated. Test
results are compared with a theoretical model and good correlation is found over the relevant operating conditions. A compari-
son of the performance of unidirectional and bi-directional partial-LST bearings with that of a baseline, untextured bearing is
presented showing the bene?ts of LST in terms of increased clearance and reduced friction.
KEY WORDS: ?uid ?lm bearings, slider bearings, surface texturing
1. Introduction
The classical theory of hydrodynamic lubrication yields linear (Couette) velocity distribution with zero pressure gradients between smooth parallel surfaces under steady-state sliding. This results in an unstable hydrodynamic ?lm that would collapse under any external force acting normal to the surfaces. However, experience shows that stable lubricating ?lms can develop between parallel sliding surfaces, generally because of some mechanism that relaxes one or more of the assumptions of the classical theory.
A stable ?uid ?lm with su?cient load-carrying capacity in parallel sliding surfaces can be obtained, for example, with macro or micro surface structure of di?erent types. These include waviness [1] and protruding microasperities [2–4]. A good literature review on the subject can be found in Ref. [5]. More recently, laser surface texturing (LST) [6–8], as well as inlet roughening by longitudinal or transverse grooves [9] were suggested to provide load capacity in parallel sliding. The inlet roughness concept of Tonder [9] is based on ??e?ective clearance‘‘ reduction in the sliding direction and in this respect it is identical to the par- tial-LST concept described in ref.
[10] for generating hydrostatic e?ect in high-pressure mechanical seals.
Very recently Wang et al. [11] demonstrated experimentally a doubling of the load-carrying capacity for the surface- texture design by reactive ion etching of SiC
parallel-thrust bearings sliding in water. These simple parallel thrust bearings are usually found in seal-less pumps where the pumped ?uid is used as the lu bricant for the bearings. Due to the parallel sliding their performance is poorer than more sophisticated tapered or stepped bearings. Brizmer et al. [12] demon-strated the potential of laser surface texturing in the form of regular micro-dimples for providing load-carrying capacity with parallel-thrust bearings. A model of a textured parallel
slider was developed and the e?ect of surface texturing on load-carrying capacity
was analyzed. The optimum parameters of the dimples were found in order to obtain
maximum load-carrying capacity. A micro-dimple ??collective e?ect‘‘ was identi-
?ed that is capable of generating substantial load-carrying capacity, approaching that of optimumconventional thrust bearings. The purpose of the present paper is to investigate experimentally the validity of the model described in Ref. [12] by testing practical thrust bearings and comparing the performance of LST bearings with that of the theoretical predictions and with the performance of standard non-textured bearings
2. Background
A cross section of the basic model that was analyzed in Ref. [12] is shown in figure
1. A slider having a width B is partially textured over a portion Bp =αB of its width.
The textured surface consists of multiple dimples with a diameter，depth and area density Sp. As a result of the hydrodynamic pressure generated by the dimples
the sliding surfaces will be separated by a clearance depending on the sliding
velocity U, the ?uid viscosity l and the external load It was found in Ref. [12] that
an optimum ratio exists for the parameter that provides maximum
dimensionless load-carrying capacity where L is
the bearing length, and this optimum value is hp=1.25. It was further found in Ref. [12] that an optimum value exists for the textured portion a depending onthe bearing aspect ratio L/B. This behavior is shown in ?gure 2 for a bearing with L/B = 0.75 at various values of the area density Sp. As can be seen in the range of Sp values from 0.18 to 0.72 the optimum a value varies from 0.7 to 0.55, respectively. It can also be seen from ?gure 2 that for a < 0.85 no optimum value exists for Sp and the maximum load W increases with increasing Sp. Hence, the largest area density that can be practically obtained with the laser texturing is desired. It is also interesting to note from ?gure 2 the advantage of partial-LST (a < 1) over the full LST (a = 1) for bearing applications. At Sp= 0.5, for example, the load W at a = 0.6 is about three times higher than its value at a = 1. A full account of this behavior is given in Ref. [12].
3. Experimental
The tested bearings consist of sintered SiC disks 10 mm thick, having 85 mm outer diameter and 40 mm inner diameter. Each bearing (see ?gure 3) comprises a ?at rotor (a) and a six-pad stator (b). The bearings were pro vided with an original surface ?nish by lapping to a roughness average Ra= 0.03 lm. Each pad has an aspect ratio of 0.75 when its width is measured along the mean diameter of the stator. The photographs of two partial-LST stators are shown in ?gure 4 where the textured areas appear as brighter matt surfaces. The ?rst stator indicated (a) is a unidirectional bearing with the partial-LST adjacent to the leading edge of each pad, similar to the model shown in ?gure 1. The second stator (b) is a bi-directional version of a partial-LST bearing having two equal textured portions, a/2, on each of the pad ends. The laser texturing
parameters were the following; dimple depth, dimple
diameter and dimple area density Sp= 0.60.03. These dimple dimensions were obtained with 4 pulses of 30 ns duration and 4 mJ each using a 5 kHz pulsating Nd:YAG laser. The textured portion of the unidirectional bearing was a= 0.73 and that of the bi-directional bearing was a= 0.63. As can be seen from ?gure 2 both these a values should produce load-carrying capacity vary close to the maximum theoretical value.The test rig is shown schematically in ?gure 5. An electrical motor turns a spindle to which an upper holder of the rotor is attached. A second lower holder of the stator is ?xed to a housing, which rests on a journal bearing and an axial loading mechanism that can freely move in the axial direction
. An arm that presses against a load cell and thereby permits friction torque measurements prevents the free rotation of this housing. Axial loading is provided by means of dead weights on a lever and is measured with a second load cell. A proximity probe that is attached to the lower holder of the stator allows on-line measurements of the clearance change between rotor and stator as the hydrodynamic
e?ects cause axial movement of the housing to which the stator holder is ?xed. Tap
water is supplied by gravity from a large tank to the center of the bearing and the leakage from the bearing is collected and re-circulated. A thermocouple adjacent to the outer diameter of the bearing allows monitoring of the water temperature as the water exit the bearing. A PC is used to collect and process data on-line. Hence,the
instantaneous clearance, friction coe?cient, bearing speed and exit water temperature
can be monitored constantly.
The test protocol includes identifying a reference ―zero‖ point for the clearance measurements by ?rst loading and then unloading a stationary bearing over the full load range. Then the lowest axial load is applied, the water supply valve is opened and the motor turned on. Axial loading is increased by steps of 40 N and each load step is maintained for 5 min following the stabilization of the friction coe?cient at
a steady-state value. The bearing speed and water temperature are monitored throughout the test for any irregularities. The test ends when a maximum axial load of 460 N is reached or if the friction coe?cient exceeds a value of 0.35. At the end of
the last load step the motor and water supply are turned o? and the reference for the clearance measurements is rechecked. Tests are performed at two speeds of 1500
and 3000 rpm corresponding to average sliding velocities of 4.9 and 9.8 m/s, respectively and each test is repeated at least three times.
4. Results and discussion
As a ?rst step the validity of the theoretical model in Ref. [12] was examined by comparing the theoretical and experimental results of bearing clearance versus bearing load for a unidirectional partial-LST bearing. The results are shown in ?gu re 6 for the two speeds of 1500 and 3000 rpm where the solid and dashed lines correspond to the model and experiment, respectively. As can be seen, the agreement between the model and the experiment is good, with di?erences of less than 10%, as
long as the load is above 150 N. At lower loads the measured experimental clearances are much larger than the model predictions, particularly at the higher speed of 3000 rpm where at 120 N the measured clearance is 20 lm, which is about 60% higher than the predicted value. It turns out that the combination of such large clearances and relatively low viscosity of the water may result in turbulent ?uid ?lm. Hence, the assumption of laminar ?ow on which the solution of the Reynolds equation in Ref.
[12] is based may be violated making the model invalid especially at the higher speed and lowest load. In order to be consistent with the model of Ref. [12] it was decided to limit further comparisons to loads above 150 N.
It should be noted here that the ?rst attempts to test the baseline untextured bearing with the original surface ?nish of Ra= 0.03 lm on both the stator and rotor failed due to extremely high friction even at the lower loads. On the other hand the partial-LST bearing ran smoothly throughout the load range. It was found that the post-LST lapping to completely remove about 2 lm height bulges, which are formed during texturing around the rims of the dimples, resulted in a slightly rougher surface with Ra= 0.04 lm. Hence, the baseline untextured stator was also lapped to the same rough- ness of the partial-LST stator and all subsequent tests were performed with the same Ra value of 0.04 lm for all the tested stators. The rotor surface roughness remained, the original one namely, 0.03 lm. Figure 7 presents the experimental results
for the clearance as a function of the load for a partial-LST unidirectional bearing (see stator in ?gure 4(a)) and a baseline untextured bearing. The comparison is made at the two speeds of 1500 and 3000 rpm. The area density of the dimples in the partial-LST bearing is Sp= 0.6 and the textured portion is a ? 0:734. The load range extends from 160 to 460 N. The upper load was determined by the test-rig limitation that did not permit higher loading. It is clear from ?gure 7 that the par tial-LST bearing operates at substantially larger clearances than the untextured bearing. At the maximum load of 460 N and speed of 1500 rpm the partial-LST bearing has a clearance of 6 lm while the untextured bearing clearance is only 1.7 lm. At 3000 rpm the clearances are 6.6 and 2.2 lm for the LST and untextured bearings, respectively. As can be seen from ?gure 7 this ratio of about 3 in favor of the partial-LST bearing is maintained over the entire load range.
Figure 8 presents the results for the bi-d irectionalbearing (see stator in ?gure 4(b)). In this case the LST parameters are Sp ? 0:614 and a ? 0:633. The clearances of the bi-directional partial-LST bearing are lower compared to these of the unidirectional bearing at the same load. At 460 N load the clearance for the 1500 rpm is 4.1 lm and for the 3000 rpm it is 6 lm. These values represent a reduction of clearance between 33 and 10% compared to the unidirectional case. However, as can be seen from ?gure 8 the performance of the partial-LST bi-directional bearing is still substantially better than that of the untextured bearing.
The friction coe?cient of partial-LST unidirectional and bi-directional bearings was compared with that of the untextured bearing in ?gures 9 and 10 for the two spee ds of 1500 and 3000 rpm, respectively. As can be seen the friction coe?cient of the two partial-LST bearings is very similar with slightly lower values in the case of the more e?cient unidirectional bearing. The friction coe?cient of the untextured bearing is much larger compared to that of the LST bearings. At 1500 rpm (?gure 9) and the highest load of 460 N the friction coe?cient of the untextured bearing is about 0.025 compared to about 0.01 for the LST bearings.
At the lowest load of 160 N the values are about 0.06 for the untextured bearing and around 0.02 for the LST bearings. Hence, the friction values of the untextured bearing are between 2.5 and 3 times higher than the corresponding values for the partial-LST bearings over the entire load range. Similar results were obtained at the velocity of
3000 rpm (?gure 10) but the level of the friction coe?cients is somewhat higher
due to the higher speed. The much higher friction of the untextured bearing is due to the much smaller clearances of this b earing (see ?gures 7 and 8) that result in higher viscous shear.
Bearings fail for a number of reasons，but the most common are misapplication，contamination，improper lubricant，shipping or handling damage，and misalignment. The problem is often not difficult to diagnose because a failed bearing usually leaves telltale signs about what went wrong．
However，while a postmortem yields good information，it is better to avoid the process altogether by specifying the bearing correctly in The first place．To do this，it is useful to review the manufacturers sizing guidelines and operating characteristics for the selected bearing.
Equally critical is a study of requirements for noise, torque, and runout, as well as possible exposure to contaminants, hostile liquids, and temperature extremes. This can provide further clues as to whether a bearing is right for a job.
1 Why bearings fail
About 40% of ball bearing failures are caused by contamination from dust, dirt, shavings, and corrosion. Contamination also causes torque and noise problems, and is
often the result of improper handling or the application environment．Fortunately, a bearing failure caused by environment or handling contamination is preventable，and a simple visual examination can easily identify the cause．
Conducting a postmortem il1ustrates what to look for on a failed or failing bearing．Then，understanding the mechanism behind the failure, such as brinelling or fatigue, helps eliminate the source of the problem.
Brinelling is one type of bearing failure easily avoided by proper handing and assembly. It is characterized by indentations in the bearing raceway caused by shock loading－such as when a bearing is dropped-or incorrect assembly. Brinelling usually occurs when loads exceed the material yield point(350,000 psi in SAE 52100 chrome steel)．It may also be caused by improper assembly, Which places a load across the races．Raceway dents also produce noise，vibration，and increased torque.
A similar defect is a pattern of elliptical dents caused by balls vibrating between raceways while the bearing is not turning．This problem is called false brinelling. It occurs on equipment in transit or that vibrates when not in operation. In addition, debris created by false brinelling acts like an abrasive, further contaminating the bearing. Unlike brinelling, false binelling is often indicated by a reddish color from fretting corrosion in the lubricant.
False brinelling is prevented by eliminating vibration sources and keeping the bearing well lubricated. Isolation pads on the equipment or a separate foundation may be required to reduce environmental vibration. Also a light preload on the bearing helps keep the balls and raceway in tight contact. Preloading also helps prevent false brinelling during transit.
Seizures can be caused by a lack of internal clearance, improper lubrication, or excessive loading. Before seizing, excessive, friction and heat softens the bearing steel. Overheated bearings often change color，usually to blue-black or straw colored．Friction also causes stress in the retainer，which can break and hasten bearing failure．
Premature material fatigue is caused by a high load or excessive preload．When these conditions are unavoidable，bearing life should be carefully calculated so that a maintenance scheme can be worked out．
Another solution for fighting premature fatigue is changing material．When standard bearing materials，such as 440C or SAE 52100，do not guarantee sufficient life，specialty materials can be recommended. In addition，when the problem is traced
back to excessive loading，a higher capacity bearing or different configuration may be used．
Creep is less common than premature fatigue．In bearings．it is caused by excessive clearance between bore and shaft that allows the bore to rotate on the shaft．Creep can be expensive because it causes damage to other components in addition to the bearing．
0ther more likely creep indicators are scratches，scuff marks，or discoloration to shaft and bore．To prevent creep damage，the bearing housing and shaft fittings should be visually checked．
Misalignment is related to creep in that it is mounting related．If races are misaligned or cocked．The balls track in a noncircumferencial path．The problem is incorrect mounting or tolerancing，or insufficient squareness of the bearing mounting site．Misalignment of more than 1/4·can cause an early failure．
Contaminated lubricant is often more difficult to detect than misalignment or creep．Contamination shows as premature wear．Solid contaminants become an abrasive in the lubricant．In addition。insufficient lubrication between ball and retainer wears and weakens the retainer．In this situation，lubrication is critical if the retainer is a fully machined type．Ribbon or crown retainers，in contrast，allow lubricants to more easily reach all surfaces．
Rust is a form of moisture contamination and often indicates the wrong material for the application．If the material checks out for the job，the easiest way to prevent rust is to keep bearings in their packaging，until just before installation．
2 Avoiding failures
The best way to handle bearing failures is to avoid them．This can be done in the selection process by recognizing critical performance characteristics．These include noise，starting and running torque，stiffness，nonrepetitive runout，and radial and axial play．In some applications, these items are so critical that specifying an ABEC level alone is not sufficient．
Torque requirements are determined by the lubricant，retainer，raceway quality(roundness cross curvature and surface finish)，and whether seals or shields are used．Lubricant viscosity must be selected carefully because inappropriate lubricant，especially in miniature bearings，causes excessive torque．Also，different lubricants have varying noise characteristics that should be matched to the application. For example，greases produce more noise than oil．
Nonrepetitive runout(NRR)occurs during rotation as a random eccentricity between the inner and outer races，much like a cam action．NRR can be caused by retainer tolerance or eccentricities of the raceways and balls．Unlike repetitive runout, no compensation can be made for NRR.
NRR is reflected in the cost of the bearing．It is common in the industry to provide different bearing types and grades for specific applications．For example，a bearing with an NRR of less than 0.3um is used when minimal runout is needed，such as in disk—drive spindle motors．Similarly，machine—tool spindles tolerate only minimal deflections to maintain precision cuts．Consequently, bearings are manufactured with low NRR just for machine-tool applications．
Contamination is unavoidable in many industrial products，and shields and seals are commonly used to protect bearings from dust and dirt．However，a perfect bearing seal is not possible because of the movement between inner and outer races．Consequently，lubrication migration and contamination are always problems．Once a bearing is contaminated, its lubricant deteriorates and operation becomes noisier．If it overheats，the bearing can seize．At the very least，contamination causes wear as it works between balls and the raceway，becoming imbedded in the races and acting as an abrasive between metal surfaces．Fending off dirt with seals and shields illustrates some methods for controlling contamination．
Noise is as an indicator of bearing quality．Various noise grades have been developed to classify bearing performance capabilities．
Noise analysis is done with an Anderonmeter, which is used for quality control in bearing production and also when failed bearings are returned for analysis. A transducer is attached to the outer ring and the inner race is turned at 1,800rpm on an air spindle. Noise is measured in andirons, which represent ball displacement in μm/rad.
With experience, inspectors can identify the smallest flaw from their sound. Dust, for example, makes an irregular crackling. Ball scratches make a consistent popping and are the most difficult to identify. Inner-race damage is normally a constant high-pitched noise, while a damaged outer race makes an intermittent sound as it rotates.
Bearing defects are further identified by their frequencies. Generally, defects are separated into low, medium, and high wavelengths. Defects are also referenced to the number of irregularities per revolution.
Low-band noise is the effect of long-wavelength irregularities that occur about 1.6 to 10 times per revolution. These are caused by a variety of inconsistencies, such as pockets in the race. Detectable pockets are manufacturing flaws and result when the race is mounted too tightly in multiplejaw chucks.
Medium-hand noise is characterized by irregularities that occur 10 to 60 times per revolution. It is caused by vibration in the grinding operation that produces balls and raceways. High-hand irregularities occur at 60 to 300 times per revolution and indicate closely spaced chatter marks or widely spaced, rough irregularities.
Classifying bearings by their noise characteristics allows users to specify a noise grade in addition to the ABEC standards used by most manufacturers. ABEC defines physical tolerances such as bore, outer diameter, and runout. As the ABEC class number increase (from 3 to 9), tolerances are tightened. ABEC class, however, does not specify other bearing characteristics such as raceway quality, finish, or noise. Hence, a noise classification helps improve on the industry standard.
5. Conclusion
The idea of partial-LST to enhance performance of the parallel thrust bearing was evaluated experimentally. Good correlation was found with a theoretical model as long as the basic assumption of laminar ?ow in the ?uid ?lm is valid. At low loads with relatively large clearances, where turbulence may occur, the experimental clearance is larger than the prediction of the model.The performance of both unidirectional and bidirectional partial-LST bearings in terms of clearance
and friction coe?cient was compared with that of a baseline untextured bearing over a load range in which the theoretical model is valid. A dramatic increase, of
about three times, in the clearance of the partial-LST bearings compared to that of the untextured bearing was obtained over the entire load range. Consequently the friction coe?cient of the partial-LST bearings is much lower, representing more than 50% reduction in friction compared to the untextured bearing.
The larger clearance and lower friction make the partial-LST simple parallel thrust bearing concept much more reliable and e?cient especially in seal-less pumps and similar applications where the process ?uid, which is often a poor lubricant, is the only available lubricant for the bearings.
Acknowledgments
The authors would like to thank Mr. J. Boylan of Morgan AM&T for providing the bearing specimens and Mr. N. Barazani of Surface Technologies Ltd. For providing the laser surface texturing.
实验研究激光加工表面微观造型平行的推力轴承实验是研究激光处理的表面微观造型平行的推力轴承增强的某些性能。测试结果与理论模型进行了比较,，发现在有关的运行条件之外有着别的关系。突出表现在，单向和双向定向部分反演轴承与一个基线的关系，激光表面微观造型与无微观造型轴承的比较显示好处在于，增加了清理和减少摩擦。
关键词：油膜轴承，滑块，轴承，表面微观造型
第一章绪论
经典理论的流体动力润滑产生线性（couette ）的速度分布与零压力梯度之间的顺利进行平行表面下的稳定状态滑动。这个结果在不稳定的润滑膜在任何外部力在表面起作用的情况下会破裂。不过，经验表明，稳定的润滑膜可以扩大他们之间的平行滑动面，一般由于某些机制，放宽一种或一种以上的对经典理论的假设。
在平行滑动面可以得到一个稳定的，有足够的承载能力的油膜，例如，宏观或微观表面结构就是不同类型。这些措施包括波纹形[ 1 ]和凸起微粗糙面[ 2-4 ]。一个好的工艺系统就是一个标准[ 5 ] 。最近，激光表面纹理[ 6-8 ] ，就是开口粗糙的纵向或横向的凹槽[ 9 ]在平行滑动提供承载能力。开口粗糙度的概念既[ 9 ]是基于有效地清除，减少在滑动方向和在这方面是相同的部分激光表面微造型概念所描述的标准。[ 10 ]产生静压力对高压力的机械密封影响。最近，王等人。[ 11 ]实验表明，增加一倍的承载能力为表面纹理设计的反应离子刻蚀碳化硅平行推力轴承滑动在水中。这些简单的平行推力轴承，通常发现，在密封泵少的地方抽液是用来作为润滑剂的轴承。由于平行滑动他们的表现较差，比更先进的锥形或加强轴承。brizmer等人。[ 12 ]表现出的潜力，激光表面纹理在的形式，定期微量波纹提供承载能力与平行推力轴承。模型的纹理平行滑块是发达国家和作用的表面纹理对承载能力进行了分析。最佳参数的微波被发现，以取得最大的承载能力。微蜂窝集体效应被鉴定是能产生可观的承载能力，接近的最佳的传统推力轴承。该本文件的目的是调查实验模型的有效性所描述的档号。[ 12 ]通过测试的实际推力轴承且与没有表面微观造型的轴承比较，表现反演轴承与该理论预测与性能标准的差异。
第二章背景
基本模型的横截面用标准分析了[ 12 ]是表现在图1。滑块有一个宽度B是部分微观造型BP = αB的宽度。该纹理的表面组成众多波纹同一的直径为深度为分布密度为自身属性。人们发现，有着微观表面造型的滑动面的油压被分开是与滑动速度U、液体粘度1和外部负载W有关[ 12 ]认为，有一个最佳的比例参数存在能使微观表面造型提供最大的无量纲负载
。其中L是轴承的长度，且最浩的动力是HP=1.25.
这是进一步发现，[ 12 ]认为，部分的表面微观造型存在一个最佳值为轴承长宽比L/B这种行为是如图2所示为轴承 b = 0.75在不同的价值观该地区的密度藻可以看出，在从0.18至0.72范围内发现SP值的最佳值不同，分别从0.7至0.55 。它也可以从图2 ，对于一个0.85<密度是没有最优值的SP存在且最高负荷瓦特与SP同步增加，因此，最大的面积密度，可以得到几乎与激光毛化是理想的。这亦是有趣地注意到，从图2，我们看到用软件仿真的部分表面微观造型的优势。举例说明，在SP=0.5比例α=0.6时是α=1时的三倍的的承载能力。
第三章实验
测试轴承组成烧结碳化硅磁盘10毫米厚，有八十五毫米外径和40毫米内径。每个轴承（见图3 ）组成一个单位，转子（ a ）和6垫定子（ b ）款。轴承提供了一个原始的表面光洁度
由研磨到平均粗糙度在Ra = 0.03的LM 。每个垫有一个长宽比0.75时，其宽度是衡量沿线平均直径定子。照片2部分第1定子是如图4所示的地方纹理地区出现更加美好的亚光表面。第一定子表示，（ a ）是单向轴承与局部反演毗邻的领先地位，每个垫，类似的模型如图1所示。第二定子（二）是一个双向定向版本的部分反演轴承有两个平等的纹理部分1/2，对每一项垫结束。该激光毛化参数以下;压痕深度，压痕直径和压痕面积密度sp = 0.6 0.03 。这些压痕的尺寸，获得了与4脉冲30的NS的时间长短和4兆焦耳每使用1 5千赫的脉动Nd ：YAG激光。该纹理部分单向轴承是一个= 0.73和该双向定向轴承是一个= 0.63 。可以看出，从图2这两种价值观应产生承载能力不同，接近最高的理论value.the试验台是显示schematically在图5 。电机轮流主轴，以其中一上持有转子重视。第二个较低的持有人的定子是固定的房屋，在于对滑动轴承和一个轴向加载机制，在轴线方向可以自由走动。
一个单臂反应压力与负载单元相互作用，从而许可证的摩擦力矩测量阻止自由旋转这个机架。轴向载荷是所提供的手段，对绝对的权重杠杆作用，是衡量一个第二负荷单元。感应探头是附加到较低的持有人的定子，让上线的测量清拆变化之间的转子和定子由于水动力影响的原因轴向运动的房屋，其中定子持有人，这是
一个固定的。自来水供应的重心从一个大罐的中心轴承和渗漏从轴承是收集和重新分发。1热电偶毗邻
外径轴承允许监测水温，作为水出口轴承。电脑是用来收集和处理数据上线。因此，瞬时关，摩擦系数，轴承的速度和开槽的温度可不断监测。
测试草案包括确定一个参考“零”点为清除测量第一有负载和无负载，然后固定轴承超过满负荷的范围。然后最低的轴向载荷应用，供水阀打开及汽车开启。轴向负荷增加的步骤40 N和每个负载的步骤是维持5分钟之后，稳定的摩擦系数在一稳定状态的价值。轴承的速度和水温监测整个测试的任何违规行为。试验结束时，最大轴向负荷460 N是达到或如果摩擦系数超过了价值0.35 。在年底的最后一步负荷电机及食水供应关掉，并参考有关清拆测量是复查。测试是在两种速度的1500 和3000 RPM的相应的平均滑动速度4.9和9.8米/秒，分别和每个测试重复至少3次
第四章成果与讨论
作为第一步的有效性的理论模型。[ 12 ]研究并比较，理论和实验结果的轴承间隙银两轴承载荷为单向局部反演轴承。结果表明，在图6为两种速度的1500和3000 rpm的情况下固体和虚线对应到模型和实验，分别。可以看出，双方间的协议模型和实验是好的，与不同的不到10 ％，只要负荷是150以上的12月31日在较低载荷测量的实验清拆要远远大于模型预测，尤其是在较高的速度，3000 rpm的情况下，在120 n实测关是20的LM ，这是约60 ％，高于预测值。结果表明，该组合，如此庞大的间隙和相对低粘度的水可能会导致湍流流体膜。因此，假设油膜上，解决这一雷诺方程的标准形式。[ 12 ]是基于可能违反决策模型无效特别是在较高的速度和最低的负荷。[ 12 ]这是决定进一步限制比较负荷以上150 N
它这里应该指出，第一，企图测试基线无微观造型轴承与原来的表面光洁度的RA = 0.03的LM上都定子和转子失败，由于极高的摩擦，甚至在较低的负荷。在另一方面部分-第1轴承，整个负荷范围顺利。结果发现，后反演研磨完全移除约2的LM高度凸出部分，这是中形成的纹理周围的轮辋的波纹，导致在一个稍微粗糙的表面粗糙度= 0.04的LM 。因此，基线与无造型的定子重叠，以同一粗糙性的部分-第1定子和其后所有测试的表现与定子同在Ra值为0.04的LM 的所有测试。转子表面粗糙度仍然存在，原因，即0.03的LM 。图7给出了实
验结果为清除作为一个功能负荷为局部反演单向轴承（见定子在图4 （ a ））和基线无微观造型轴承。比较是在两种速度的1500和3000 RPM的。面密度的波纹在部分-第1轴承是sp = 0.6和纹理部分是一个6.3 0:734 。该负荷范围扩大，从160至460 12月31日上负载检测试验台的限制，不容许较高的负荷。很显然，从图7部分-第1轴承运转大幅清拆比无微观造型轴承。在最高负荷460 N和速度1500 RPM的部分-第1轴承已清拆6的LM ，而无微观造型轴承间隙是只有1.7的LM 。在3000 RPM的清拆是6.6 和2.2的LM为第1和无微观造型轴承，分别。可以看出，从图7 ，这个比例约三倍，赞成部分-第1轴承是保持在整个负荷范围。
图8给出的结果为双向轴承（见定子在图4 （ b ）款）。在这种情况下，反演参数sp=6.3 α=0.614和0.633 6.3 。清拆的双向定向部分反演轴承相比，降低这些的单向轴承在同一负荷。在460 n负载清拆为1500 rpm的是4.1 LM和为3000 rpm的，这是6月的LM 。这些价值观所代表的减少之间的关
33和10 ％相比，单向的情况。不过，可以看出，从图8的表现，部分-第1双向定向轴承仍是大大优于该无微观造型轴承。
图10为两种速度分别是1500和3000 rpm。可以看出，摩擦系数的两个部分反演轴承是非常类似的与略低的价值观，在部件较有高效率的单向轴承。无微观造型的的摩擦系数大得多比他们大的多，即第1轴承。在1500 RPM的（图9 ）和最高负荷460 n摩擦系数的untextured轴承是约0.025相比，约为第1轴承0.01。
在最低负荷160 n值约0.06为无微观造型轴承的为第1轴承的0.02左右。因此，无微观造型轴承摩擦值，高于相应值为局部反演轴承在整个负荷范围的2.5和3倍。，在速度上获得了类似的结果，3000每分钟转速（图10 ），但水平的摩擦系数是有点高，由于较高的速度。无微观造型轴承的摩擦高得多，是因为无小槽清理磨砂（见图7和图8），导致较高的粘性剪切。
导致轴承失效的原因很多，但常见的是不正确的使用、污染、润滑剂使用不当、装卸或搬运时的损伤及安装误差等。诊断失效的原因并不困难，因为根据轴承上留下的痕迹可以确定轴承失效的原因。
然而，当事后的调查分析提供出宝贵的信息时，最好首先通过正确地选定轴承来完全避免失效的发生。为了做到这一点，再考察一下制造厂商的尺寸定位指南和所选轴承的使用特点是非常重要的。
吉林化工学院理学院 毕业论文外文翻译English Title（Times New Roman ，三号） 学生学号：08810219 学生姓名：袁庚文 专业班级：信息与计算科学0802 指导教师：赵瑛 职称副教授 起止日期：2012.2.27～2012.3.14 吉林化工学院 Jilin Institute of Chemical Technology
1 外文翻译的基本内容 应选择与本课题密切相关的外文文献（学术期刊网上的），译成中文，与原文装订在一起并独立成册。在毕业答辩前，同论文一起上交。译文字数不应少于3000个汉字。 2 书写规范 2.1 外文翻译的正文格式 正文版心设置为：上边距：3.5厘米，下边距：2.5厘米，左边距：3.5厘米，右边距：2厘米，页眉：2.5厘米，页脚：2厘米。 中文部分正文选用模板中的样式所定义的“正文”，每段落首行缩进2字；或者手动设置成每段落首行缩进2字，字体：宋体，字号：小四，行距：多倍行距1.3，间距：前段、后段均为0行。 这部分工作模板中已经自动设置为缺省值。 2.2标题格式 特别注意：各级标题的具体形式可参照外文原文确定。 1．第一级标题（如：第1章绪论）选用模板中的样式所定义的“标题1”，居左；或者手动设置成字体：黑体，居左，字号：三号，1.5倍行距，段后11磅，段前为11磅。 2．第二级标题（如：1.2 摘要与关键词）选用模板中的样式所定义的“标题2”，居左；或者手动设置成字体：黑体，居左，字号：四号，1.5倍行距，段后为0，段前0.5行。 3．第三级标题（如：1.2.1 摘要）选用模板中的样式所定义的“标题3”，居左；或者手动设置成字体：黑体，居左，字号：小四，1.5倍行距，段后为0，段前0.5行。 标题和后面文字之间空一格（半角）。 3 图表及公式等的格式说明 图表、公式、参考文献等的格式详见《吉林化工学院本科学生毕业设计说明书（论文）撰写规范及标准模版》中相关的说明。
Inventory management Inventory Control On the so-called "inventory control", many people will interpret it as a "storage management", which is actually a big distortion. The traditional narrow view, mainly for warehouse inventory control of materials for inventory, data processing, storage, distribution, etc., through the implementation of anti-corrosion, temperature and humidity control means, to make the custody of the physical inventory to maintain optimum purposes. This is just a form of inventory control, or can be defined as the physical inventory control. How, then, from a broad perspective to understand inventory control? Inventory control should be related to the company's financial and operational objectives, in particular operating cash flow by optimizing the entire demand and supply chain management processes (DSCM), a reasonable set of ERP control strategy, and supported by appropriate information processing tools, tools to achieved in ensuring the timely delivery of the premise, as far as possible to reduce inventory levels, reducing inventory and obsolescence, the risk of devaluation. In this sense, the physical inventory control to achieve financial goals is just a means to control the entire inventory or just a necessary part; from the perspective of organizational functions, physical inventory control, warehouse management is mainly the responsibility of The broad inventory control is the demand and supply chain management, and the whole company's responsibility. Why until now many people's understanding of inventory control, limited physical inventory control? The following two reasons can not be ignored: First, our enterprises do not attach importance to inventory control. Especially those who benefit relatively good business, as long as there is money on the few people to consider the problem of inventory turnover. Inventory control is simply interpreted as warehouse management, unless the time to spend money, it may have been to see the inventory problem, and see the results are often very simple procurement to buy more, or did not do warehouse departments . Second, ERP misleading. Invoicing software is simple audacity to call it ERP, companies on their so-called ERP can reduce the number of inventory, inventory control, seems to rely on their small software can get. Even as SAP, BAAN ERP world, the field of
Statistical hypothesis testing Adriana Albu，Loredana Ungureanu Politehnica University Timisoara,adrianaa@aut.utt.ro Politehnica University Timisoara,loredanau@aut.utt.ro Abstract In this article,we present a Bayesian statistical hypothesis testing inspection, testing theory and the process Mentioned hypothesis testing in the real world and the importance of, and successful test of the Notes. Key words Bayesian hypothesis testing; Bayesian inference;Test of significance Introduction A statistical hypothesis test is a method of making decisions using data, whether from a controlled experiment or an observational study (not controlled). In statistics, a result is called statistically significant if it is unlikely to have occurred by chance alone, according to a pre-determined threshold probability, the significance level. The phrase "test of significance" was coined by Ronald Fisher: "Critical tests of this kind may be called tests of significance, and when such tests are available we may discover whether a second sample is or is not significantly different from the first."[1] Hypothesis testing is sometimes called confirmatory data analysis, in contrast to exploratory data analysis. In frequency probability,these decisions are almost always made using null-hypothesis tests. These are tests that answer the question Assuming that the null hypothesis is true, what is the probability of observing a value for the test statistic that is at [] least as extreme as the value that was actually observed?) 2 More formally, they represent answers to the question, posed before undertaking an experiment,of what outcomes of the experiment would lead to rejection of the null hypothesis for a pre-specified probability of an incorrect rejection. One use of hypothesis testing is deciding whether experimental results contain enough information to cast doubt on conventional wisdom. Statistical hypothesis testing is a key technique of frequentist statistical inference. The Bayesian approach to hypothesis testing is to base rejection of the hypothesis on the posterior probability.[3][4]Other approaches to reaching a decision based on data are available via decision theory and optimal decisions. The critical region of a hypothesis test is the set of all outcomes which cause the null hypothesis to be rejected in favor of the alternative hypothesis. The critical region is usually denoted by the letter C. One-sample tests are appropriate when a sample is being compared to the population from a hypothesis. The population characteristics are known from theory or are calculated from the population.
毕业论文（设计）外文翻译 题目：中国上市公司偏好股权融资：非制度性因素 系部名称：经济管理系专业班级:会计082班 学生姓名：任民学号： 200880444228 指导教师：冯银波教师职称:讲师 年月日
译文： 中国上市公司偏好股权融资：非制度性因素 国际商业管理杂志 2009.10 摘要：本文把重点集中于中国上市公司的融资活动，运用西方融资理论，从非制度性因素方面，如融资成本、企业资产类型和质量、盈利能力、行业因素、股权结构因素、财务管理水平和社会文化，分析了中国上市公司倾向于股权融资的原因，并得出结论，股权融资偏好是上市公司根据中国融资环境的一种合理的选择。最后，针对公司的股权融资偏好提出了一些简明的建议。 关键词：股权融资，非制度性因素，融资成本 一、前言 中国上市公司偏好于股权融资，根据中国证券报的数据显示，1997年上市公司在资本市场的融资金额为95.87亿美元，其中股票融资的比例是72.5％，，在1998年和1999年比例分别为72.6％和72.3％，另一方面，债券融资的比例分别是17.8％，24.9％和25.1％。在这三年，股票融资的比例，在比中国发达的资本市场中却在下跌。以美国为例，当美国企业需要的资金在资本市场上，于股权融资相比他们宁愿选择债券融资。统计数据显示，从1970年到1985年，美日企业债券融资占了境外融资的91.7％，比股权融资高很多。阎达五等发现，大约中国3/4的上市公司偏好于股权融资。许多研究的学者认为，上市公司按以下顺序进行外部融资：第一个是股票基金，第二个是可转换债券，三是短期债务，最后一个是长期负债。许多研究人员通常分析我国上市公司偏好股权是由于我们国家的经济改革所带来的制度性因素。他们认为，上市公司的融资活动违背了西方古典融资理论只是因为那些制度性原因。例如，优序融资理论认为，当企业需要资金时，他们首先应该转向内部资金（折旧和留存收益），然后再进行债权融资，最后的选择是股票融资。在这篇文章中，笔者认为，这是因为具体的金融环境激活了企业的这种偏好，并结合了非制度性因素和西方金融理论，尝试解释股权融资偏好的原因。
农村社会养老保险的现状、问题与对策研究社会保障对国家安定和经济发展具有重要作用，“城乡二元经济”现象日益凸现，农村社会保障问题客观上成为社会保障体系中极为重要的部分。建立和完善农村社会保障制度关系到农村乃至整个社会的经济发展，并且对我国和谐社会的构建至关重要。我国农村社会保障制度尚不完善，因此有必要加强对农村独立社会保障制度的构建，尤其对农村养老制度的改革，建立健全我国社会保障体系。从户籍制度上看，我国居民养老问题可分为城市居民养老和农村居民养老两部分。对于城市居民我国政府已有比较充足的政策与资金投人，使他们在物质和精神方面都能得到较好地照顾，基本实现了社会化养老。而农村居民的养老问题却日益突出，成为摆在我国政府面前的一个紧迫而又棘手的问题。 一、我国农村社会养老保险的现状 关于农村养老，许多地区还没有建立农村社会养老体系，已建立的地区也存在很多缺陷，运行中出现了很多问题，所以完善农村社会养老保险体系的必要性与紧迫性日益体现出来。 （一）人口老龄化加快 随着城市化步伐的加快和农村劳动力的输出，越来越多的农村青壮年人口进入城市，年龄结构出现“两头大，中间小”的局面。中国农村进入老龄社会的步伐日渐加快。第五次人口普查显示：中国65岁以上的人中农村为5938万，占老龄总人口的67.4%.在这种严峻的现实面前，农村社会养老保险的徘徊显得极其不协调。 （二）农村社会养老保险覆盖面太小 中国拥有世界上数量最多的老年人口，且大多在农村。据统计，未纳入社会保障的农村人口还很多，截止2000年底，全国7400多万农村居民参加了保险，占全部农村居民的11.18%，占成年农村居民的11.59%.另外，据国家统计局统计，我国进城务工者已从改革开放之初的不到200万人增加到2003年的1.14亿人。而基本方案中没有体现出对留在农村的农民和进城务工的农民给予区别对待。进城务工的农民既没被纳入到农村养老保险体系中，也没被纳入到城市养老保险体系中，处于法律保护的空白地带。所以很有必要考虑这个特殊群体的养老保险问题。
软件专业毕业论文外文文献中英文翻译 Object landscapes and lifetimes Tech nically, OOP is just about abstract data typing, in herita nee, and polymorphism, but other issues can be at least as importa nt. The rema in der of this sect ion will cover these issues. One of the most importa nt factors is the way objects are created and destroyed. Where is the data for an object and how is the lifetime of the object con trolled? There are differe nt philosophies at work here. C++ takes the approach that con trol of efficie ncy is the most importa nt issue, so it gives the programmer a choice. For maximum run-time speed, the storage and lifetime can be determined while the program is being written, by placing the objects on the stack (these are sometimes called automatic or scoped variables) or in the static storage area. This places a priority on the speed of storage allocatio n and release, and con trol of these can be very valuable in some situati ons. However, you sacrifice flexibility because you must know the exact qua ntity, lifetime, and type of objects while you're writing the program. If you are trying to solve a more general problem such as computer-aided desig n, warehouse man ageme nt, or air-traffic con trol, this is too restrictive. The sec ond approach is to create objects dyn amically in a pool of memory called the heap. In this approach, you don't know un til run-time how many objects you n eed, what their lifetime is, or what their exact type is. Those are determined at the spur of the moment while the program is runnin g. If you n eed a new object, you simply make it on the heap at the point that you n eed it. Because the storage is man aged dyn amically, at run-time, the amount of time required to allocate storage on the heap is sig ni fica ntly Ion ger tha n the time to create storage on the stack. (Creat ing storage on the stack is ofte n a si ngle assembly in structio n to move the stack poin ter dow n, and ano ther to move it back up.) The dyn amic approach makes the gen erally logical assumpti on that objects tend to be complicated, so the extra overhead of finding storage and releas ing that storage will not have an importa nt impact on the creati on of an object .In additi on, the greater flexibility is esse ntial to solve the gen eral program ming problem. Java uses the sec ond approach, exclusive". Every time you want to create an object, you use the new keyword to build a dyn amic in sta nee of that object. There's ano ther issue, however, and that's the lifetime of an object. With Ian guages that allow objects to be created on the stack, the compiler determines how long the object lasts and can automatically destroy it. However, if you create it on the heap the compiler has no kno wledge of its lifetime. In a Ianguage like C++, you must determine programmatically when to destroy the
本科毕业设计（论文）中英文对照翻译 院（系部）电气工程与自动化 专业名称电子信息工程 年级班级 04级7班 学生姓名 指导老师
Infrared Remote Control System Abstract Red outside data correspondence the technique be currently within the scope of world drive extensive usage of a kind of wireless conjunction technique,drive numerous hardware and software platform support. Red outside the transceiver product have cost low, small scaled turn, the baud rate be quick, point to point SSL, be free from electromagnetism thousand Raos etc.characteristics, can realization information at dissimilarity of the product fast, convenience, safely exchange and transmission, at short distance wireless deliver aspect to own very obvious of advantage.Along with red outside the data deliver a technique more and more mature, the cost descend, red outside the transceiver necessarily will get at the short distance communication realm more extensive of application. The purpose that design this system is transmit cu stomer’s operation information with infrared rays for transmit media, then demodulate original signal with receive circuit. It use coding chip to modulate signal and use decoding chip to demodulate signal. The coding chip is PT2262 and decoding chip is PT2272. Both chips are made in Taiwan. Main work principle is that we provide to input the information for the PT2262 with coding keyboard. The input information was coded by PT2262 and loading to high frequent load wave whose frequent is 38 kHz, then modulate infrared transmit dioxide and radiate space outside when it attian enough power. The receive circuit receive the signal and demodulate original information. The original signal was decoded by PT2272, so as to drive some circuit to accomplish
毕业论文外文资料翻译题目(宋体三号，居中) 学院(全称，宋体三号，居中) 专业(全称，宋体三号，居中) 班级(宋体三号，居中) 学生(宋体三号，居中) 学号(宋体三号，居中) 指导教师(宋体三号，居中) 二〇一〇年月日(宋体三号，居中，时间与开题时间一致)
（英文原文装订在前）
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Real-time interactive optical micromanipulation of a mixture of high- and low-index particles Peter John Rodrigo, Vincent Ricardo Daria and Jesper Glückstad Optics and Plasma Research Department, Ris? National Laboratory, DK-4000 Roskilde, Denmark jesper.gluckstad@risoe.dk http://www.risoe.dk/ofd/competence/ppo.htm Abstract: We demonstrate real-time interactive optical micromanipulation of a colloidal mixture consisting of particles with both lower (n L < n0) and higher (n H > n0) refractive indices than that of the suspending medium (n0). Spherical high- and low-index particles are trapped in the transverse plane by an array of confining optical potentials created by trapping beams with top-hat and annular cross-sectional intensity profiles, respectively. The applied method offers extensive reconfigurability in the spatial distribution and individual geometry of the optical traps. We experimentally demonstrate this unique feature by simultaneously trapping and independently manipulating various sizes of spherical soda lime micro- shells (n L≈ 1.2) and polystyrene micro-beads (n H = 1.57) suspended in water (n0 = 1.33). ?2004 Optical Society of America OCIS codes: (140.7010) Trapping, (170.4520) Optical confinement and manipulation and (230.6120) Spatial Light Modulators. References and links 1. A. Ashkin, “Optical trapping and manipulation of neutral particles using lasers,” Proc. Natl. Acad. Sci. USA 94, 4853-4860 (1997). 2. K. Svoboda and S. M. Block, “Biological applications of optical forces,” Annu. Rev. Biophys. Biomol. Struct. 23, 247-285 (1994). 3. D. G. Grier, “A revolution in optical manipulation,” Nature 424, 810-816 (2003). 4. M. P. MacDonald, G. C. Spalding and K. Dholakia, “Microfluidic sorting in an optical lattice,” Nature 426, 421-424 (2003). 5. J. Glückstad, “Microfluidics: Sorting particles with light,” Nature Materials 3, 9-10 (2004). 6. A. Ashkin, “Acceleration and trapping of particles by radiation-pressure,”Phys. Rev. Lett. 24, 156-159 (1970). 7. A. Ashkin, J. M. Dziedzic, J. E. Bjorkholm and S. Chu, “Observation of a single-beam gradient force optical trap for dielectric particles,” Opt. Lett. 11, 288-290 (1986). 8. K. Sasaki, M. Koshioka, H. Misawa, N. Kitamura, and H. Masuhara, “Optical trapping of a metal particle and a water droplet by a scanning laser beam,” Appl. Phys. Lett. 60, 807-809 (1992). 9. K. T. Gahagan and G. A. Swartzlander, “Trapping of low-index microparticles in an optical vortex,” J. Opt. Soc. Am. B 15, 524-533 (1998). 10. K. T. Gahagan and G. A. Swartzlander, “Simultaneous trapping of low-index and high-index microparticles observed with an optical-vortex trap,” J. Opt. Soc. Am. B 16, 533 (1999). 11. M. P. MacDonald, L. Paterson, W. Sibbett, K. Dholakia, P. Bryant, “Trapping and manipulation of low-index particles in a two-dimensional interferometric optical trap,” Opt. Lett. 26, 863-865 (2001). 12. R. L. Eriksen, V. R. Daria and J. Glückstad, “Fully dynamic multiple-beam optical tweezers,” Opt. Express 10, 597-602 (2002), https://www.doczj.com/doc/1214891394.html,/abstract.cfm?URI=OPEX-10-14-597. 13. P. J. Rodrigo, R. L. Eriksen, V. R. Daria and J. Glückstad, “Interactive light-driven and parallel manipulation of inhomogeneous particles,” Opt. Express 10, 1550-1556 (2002), https://www.doczj.com/doc/1214891394.html,/abstract.cfm?URI=OPEX-10-26-1550. 14. V. Daria, P. J. Rodrigo and J. Glückstad, “Dynamic array of dark optical traps,” Appl. Phys. Lett. 84, 323-325 (2004). 15. J. Glückstad and P. C. Mogensen, “Optimal phase contrast in common-path interferometry,” Appl. Opt. 40, 268-282 (2001). 16. S. Maruo, K. Ikuta and H. Korogi, “Submicron manipulation tools driven by light in a liquid,” Appl. Phys. Lett. 82, 133-135 (2003). #3781 - $15.00 US Received 4 February 2004; revised 29 March 2004; accepted 29 March 2004 (C) 2004 OSA 5 April 2004 / Vol. 12, No. 7 / OPTICS EXPRESS 1417
本科毕业设计 外文文献及译文 文献、资料题目：Designing Stable Control Loops 文献、资料来源：期刊 文献、资料发表（出版）日期：2010.3.25 院（部）：信息与电气工程学院 专班姓学业：电气工程与自动化级： 名： 号： 指导教师：翻译日期：2011.3.10
外文文献： Designing Stable Control Loops The objective of this topic is to provide the designer with a practical review of loop compensation techniques applied to switching power supply feedback control. A top-down system approach is taken starting with basic feedback control concepts and leading to step-by-step design procedures,initially applied to a simple buck regulator and then expanded to other topologies and control algorithms. Sample designs are demonstrated with Math cad simulations to illustrate gain and phase margins and their impact on performance analysis. I. I NTRODUCTION Insuring stability of a proposed power supply solution is often one of the more challenging aspects of the design process. Nothing is more disconcerting than to have your lovingly crafted breadboard break into wild oscillations just as its being demonstrated to the boss or customer, but insuring against this unfortunate event takes some analysis which many designers view as formidable. Paths taken by design engineers often emphasize either cut-and-try empirical testing in the laboratory or computer simulations looking for numerical solutions based on complex mathematical models.While both of these approach a basic understanding of feedback theory will usually allow the definition of an acceptable compensation network with a minimum of computational effort. II. S TABILITY D EFINED Fig. 1.Definition of stability Fig. 1 gives a quick illustration of at least one definition of stability. In its simplest terms, a system is stable if, when subjected to a perturbation from some source, its response to that