On modeling center of foot pressure distortion through a medium

The center of foot pressure (COP) is a commonly used output measure of the postural control system as it is indicative of the systems stability. A dense piece of foam, i.e., a sponge, can be used to emulate random environmental conditions that distort the ground reaction forces received and interpreted by the cutaneous sensors in the feet; thus introducing uncertainty into the control system. In this paper, the density and size of the sponge was selected such that a subject's weight did not cause full compression. In general, the COP is measured from the bottom of the sponge. As the sponge is used to distort ground reaction forces, it is reasonable then to assume that the COP signal would also be distorted. The use of other sensory information to identify state of balance, and compute necessary balance adjustments, is therefore required. In addition to a sponge, many different types of specialized footwear and inserts are used for people with peripheral neuropathy, such as diabetics. However, it is difficult to design diabetic footwear without a better understanding of the mechanical and physiological effects that different surfaces typical of outdoor terrains, such as a sponge, which cannot be predicted without the sense of the foot, have on balance. Therefore, the goal of this study was to investigate the change of the COP signal from the top and bottom of the sponge. Portable force sensing mats from Vista Medical were used to obtain the COP from the top and bottom of the sponge. The COP measured on the bottom of the sponge is not the same as the COP measured on the top, particularly in the medial-lateral direction. Several linear and nonlinear models were used to identify the unknown plant; i.e., the sponge. Overall, the nonlinear neural network method had superior performance when compared with the linear models. Thus, the results indicate that the signals from the top and bottom of the sponge are in fact different, and furthermore, they are nonlinearly related. A nonlinear mathematical model is proposed which describes COP distortion through a medium such as a sponge. Although the values for the model parameters determined were for a particular sponge, this study suggests that a neural network plant identification model may be applied to any medium other than the sponge; the information can then be used to determine how the balance control model is affected given the sensory information received.     

Application of cross time-frequency analysis to postural sway behavior: the effects of aging and visual systems

In this paper, the effects of visual feedback and aging on postural sway systems and signals are investigated by analyzing the transient phase difference between "input" and "output" which correspond to center of pressure (COP) and center of mass (COM), respectively. In order to analyze the transient phase difference characteristics of COP and COM, a relatively new cross time-frequency analysis technique that provides time- and frequency-localized phase difference information is utilized. The feedback control process in the postural sway is interpreted in terms of a feedback compensator which is characterized in terms of a phase difference. Using the experimental results of the transient phase difference obtained from the cross time-frequency distribution, it is demonstrated that the postural control of young persons are more stable and rely more on visual sensory feedback to stabilize postural control compared to that of the elderly persons.     

Characterization of human gait by means of body center of massoscillations derived from ground reaction forces

Ground reaction forces from two force plates are used to determine the cyclic oscillations of the body center of mass while walking at preferred speed. Good approximations to the oscillations may be obtained from formulae containing just the first-and second-order Fourier coefficients of the combined left-right ground reaction forces taken over a complete walking cycle. The symmetric components of the oscillations have consistent mutual phase relations for normal subjects, so that the amplitudes alone can be used as sufficient parameters to characterize the body center of mass oscillations. The analytical technique enables detection of small but consistent gait asymmetries     

Constraining LDPC degree distributions for improved error floor performance

The error floor performance of finite-length irregular low-density parity-check (LDPC) codes can be very poor if code degree distributions are chosen to optimize the threshold performance. In this paper we show that by constraining the optimization process, a balance between threshold and error floor' performance can be obtained. The resulting degree distributions give the best threshold performance subject to some minimum requirement on the error floor.     

用于声光移频的声表面波谐振器

针对一种喇曼型声表面波声光器件的设计需求,设计制作出一种能够满足喇曼-奈斯衍射要求的、低损耗、高Q值声表面波谐振器。利用耦合模(COM)理论仿真谐振器的性能,建立谐振器的COM模型,求解COM方程,提取出COM参数。利用COM软件仿真设计谐振器的结构参数,设计的谐振器中心频率为78.028MHz,Q值为10 428,插入损耗为-6.153dB。利用微加工技术加工制作出声表面波谐振器,用矢量网络分析仪对其性能进行测试,得到谐振器实际中心频率为78.34MHz,插入损耗为-11.273dB,Q值为6 465.7,该谐振器能够满足喇曼型声表面波声光器件的应用需求。     

天线回转中心偏离阵列球心对测向的影响

在微波暗室内进行射频仿真试验时,必须保证被试装备天线回转中心和天线阵列的球心重合,否则就会引起测向误差,从而影响对被试装备性能的科学评估.分析了对心不准对装备测向测试结果的影响,建立了测向误差的分析模型,并且结合实例详细分析了偏心距离和测向误差的关系.相关分析模型和结论可以作为对心设备建设中对对心精度的指标论证的依据,也可以为仿真试验战情的设计提供科学的借鉴.     

Center of mass approximation and prediction as a function of body acceleration

In order to maintain postural stability, the central nervous system must maintain equilibrium of the total center of body mass (COM) in relation to its base of support. Thus, the trajectory of the COM provides an important measure of postural stability. Three different models were developed to estimate the COM and the results tested on 16 subjects: namely a neural network, an adaptive fuzzy interface system and a hybrid genetic algorithm sum-of-sines model. The inputs to the models were acquired via two accelerometers, one representing the trunk segment placed on T2 and the second representing the limb segment placed on the shank below the knee joint. The portability, ease of use and low cost (compared with video motion analysis systems) of the accelerometers increases the range of clinics to which the system will be available. The subjects performed a multisegmental movement task on fixed and foam surfaces, thus covering a relatively wide dynamic scope. The results are encouraging for obtaining COM estimates that have clinical applications; the genetic sum-of-sines model was found to be superior when compared to the other two models.     

Exposure of fertile chicken eggs to microwave radiation (2.45 GHz, CW) during incubation: technique and evaluation.

A multi-mode cavity constructed of 22-gauge perforated galvanized steel with a horn irradiator was used to expose chicken embryos to microwave (MW) radiation during incubation. The MW exposure system was placed within an environmental chamber. Mean +/- standard error of mean (SEM) power level was 3.6 +/- 0.02 mW/cm2 and mean egg specific absorption rate was 0.8 mW/g per mW/cm2. Mean temperature of the MW-exposed eggs was 37.5 +/- 0.9 degrees C as monitored by a Luxtron fluoroptic thermometer. Non-irradiated eggs were incubated at 37.5 +/- 0.1 degrees C and 55% relative humidity. There was no significant different in percent fertile eggs hatched between eggs exposed to MW radiation during incubation or eggs incubated conventionally (82.9% and 87.7%, respectively).     

Error analysis of tissue resistivity measurement

We identified the error sources in a system for measuring tissue resistivity at eight frequencies from 1 Hz to 1 MHz using the four-terminal method. We expressed the measured resistivity with an analytical formula containing all error terms. We conducted practical error measurements with in-vivo and bench-top experiments. We averaged errors at all frequencies for all measurements. The standard deviations of error of the quantization error of the 8-bit digital oscilloscope with voltage averaging, the nonideality of the circuit, the in-vivo motion artifact and electrical interference combined to yield an error of +/- 1.19%. The dimension error in measuring the syringe tube for measuring the reference saline resistivity added +/- 1.32% error. The estimation of the working probe constant by interpolating a set of probe constants measured in reference saline solutions added +/- 0.48% error. The difference in the current magnitudes used during the probe calibration and that during the tissue resistivity measurement caused +/- 0.14% error. Variation of the electrode spacing, alignment, and electrode surface property due to the insertion of electrodes into the tissue caused +/- 0.61% error. We combined the above errors to yield an overall standard deviation error of the measured tissue resistivity of +/- 1.96%.     

Effects of radiofrequency energy on human chondromalacic cartilage: an assessment of insulation material properties

The objective of this study was to establish guidelines for the selection of an insulation material used to surround the electrode of radiofrequency energy (RFE) probes used for thermal chondroplasty. These guidelines were established by identifying which insulation materials resulted in the least amount of chondrocyte death while smoothing the surface of chondromalacic cartilage. RFE causes electrolyte oscillation and molecular friction in the tissue to heat it and subsequently smooth the surface. Material properties investigated included the coefficient of thermal expansion (CTE), thermal conductivity (TC), and volume resistivity (VR). Fresh human chondromalacic cartilage samples of Outerbridge grades II and III were obtained from patients undergoing total knee arthroplasty. Stiffness measurements were taken pretreatment and posttreatment. RFE was applied to a 1-cm2 area for 15 s in a paintbrush treatment pattern. The insulation materials evaluated included Macor (decrease CTE, decrease TC, increase VR; in relation to CTE = 10 x 10(-6)/degrees C at 20 degrees C, TC = 3 W/mK, VR=1 x 10(14) ohm x cm), zirconia toughened alumina (ZTA) and 99.5% alumina (decrease CTE, increase TC, increase VR), aluminum nitride (decrease CTE, increase TC, decrease VR), Teflon (PTFE) (increase CTE, decrease TC, increase VR), partially stabilized zirconia (YTZP) (decrease CTE, decrease TC, decrease VR), and Ultem (increase CTE, decrease TC, decrease VR). There were no significant differences between pretreatment and posttreatment stiffness of the cartilage for any material investigated. Subjectively scored scanning electron microscopy (SEM) images revealed that the surfaces of all samples treated with RFE were relatively smooth with melted fronds. Prototype probes made with Macor, 99.5% alumina, and ZTA had TC < or = 30 W/mol x K and resulted in a mean of 35% less cell death (176+/-56 microm, 130+/-48 microm, and 114+/-33 microm, respectively) than aluminum nitride, PTFE, and YTZP (246+/-68 microm, 231+/-108 microm, and 195+/-89 microm, respectively). Macor, 99.5% alumina, and ZTA prototype probes all had VR > or = 1 x 10(14) ohm x cm and resulted in a mean 37% less cell death than aluminum nitride or YTZP. There was no apparent relationship between CTE and the depth of chondrocyte death.     

ELAB:end-host-based congestion aware load balancing for data center network

A good load balance mechanism is the key to effectively use the network of the data center network.In current production data center,ECMP is the de facto load balancing scheme.However,it has two drawbacks.1) the load balance unit is too coarse-grained,2) it’s not congestion aware.To solve these problems,several fine-grained and congestion-aware load balancing works have emerged in recent years.These works either need to modify the switch hardware to collect congestion in various parts of the network in real time,and it is difficult to deploy; or only need to modify the end system,but the inaccurate sense of congestion cannot achieve a good load balancing effect.A novel edge-based load balancing scheme ELAB was proposed,which addresses above existing problems and improves the network performance up to 20%.     

The Accuracy of Electrical Transducers for the Measurement of Pressure Applied to the Skin

The accuracies of five commercially available small flat pressure transducers (~5 mm ×~1 mm) were evaluated for their ability to measure pressures applied to the body surface. The diaphragms of the transducer were loaded with rubber and cloth surfaces in an in vitro test and under a blood pressure cuff over the gastrocnemius muscle, 2 cm on the medial and lateral sides of the tibia and on the tibial crest of the leg. These areas offer varying amounts of underlying tissue compliance. The cuff was pumped up to 200 mmHg in 20 mmHg increments. The average error obtained with the transducers zeroed in air before placement on the leg varied from 20.4 to 64.9 mmHg depending on the hardness of the underlying surface. The averaged error obtained with the transducer zeroed after placing on the leg ranged from 9.5 to 47.9 mmHg.     

Frame-level traffic splitting for link aggregation in data center networks

Ethernet link aggregation, which provides an easy and cost-effective way to increase both bandwidth and link availability between a pair of devices, is well suited for data center networks. However, all the traffic splitting algorithms used in existing Ethernet link aggregation are flow-level which do not work well owing to the traffic characteristics of data centers. Though frame-level traffic splitting can achieve optimal load balance and the maximum benefits from aggregated capacity, it is generally deprecated in most cases because of frame disordering which can disrupt the operation of many Internet protocols, most notably transmission control protocol (TCP). To address this issue, we first investigate the causes of frame disordering in link aggregation and find that all of them either are no longer true or can be prevented in data centers. Then we present a byte-counter frame-level traffic splitting algorithm which achieves optimal performance while causes no frame disordering. The only requirement is that frames in a flow are the same size which can be easily met in data centers. Simulation results show that the proposed frame-level traffic splitting method could achieve higher throughput and optimal load balance. The average completion time of different sized flows is reduced by 24% on average and by up to 46%.     

Accurate object localization in gray level images using the center of gravity measure: accuracy versus precision

A widely used subpixel precision estimate of an object center is the weighted center of gravity (COG). We derive three maximum-likelihood estimators for the variance of the two-dimensional (2-D) COG as a function of the noise in the image. We assume that the noise is additive, Gaussian distributed and independent between neighboring pixels. Repeated experiments using 2500 generated 2-D bell-shaped markers superimposed with an increasing amount of Gaussian noise were performed, to compare the three approximations. The error of the most exact approximative variance estimate with respect to true variance was always less than 5% of the latter. This deviation decreases with increasing signal-to-noise ratio. Our second approximation to the variance estimate performed better than the third approximation, which was originally presented by Oron et al. by up to a factor /spl ap/10. The difference in performance between these two approximations increased with an increasing misplacement of the window in which the COG was calculated with respect to the real COG.     

The Importance of Accurate Skin Temperature in Assimilating Radiances From Satellite Sounding Instruments

An error analysis has been performed, which shows that skin temperature errors are important for sounding channels. An approach for estimating skin temperature and emissivity errors from the dependence of differences between observed and calculated radiances on surface-to-space transmittance is described. Estimates of emissivity and skin temperature error for the operational Met Office data assimilation system are presented as an example, and the implications are discussed, in terms of use of data over different surfaces and in different conditions (e.g., day/night). The results highlight the need for a better emissivity estimate over sea ice than that used at the Met Office and the inaccuracy of the land surface skin temperature that was derived from radiative flux balance at the surface.     

Coupling Between Guided Surface Waves, Lateral Waves, and the Radiation Fields by Rough Surfaces--Full-Wave Solutions

In this paper explicit expressions are presented for the guided surface waves and lateral waves that are excited when radiation fields are incident upon rough surfaces. Similarly, expressions are presented for the radiation fields scattered by rough surfaces that are excited by surface waves and lateral waves. In addition, coupling between the surface waves and the lateral waves due to surface irregularities is considered in detail. The solutions, which are based on a full-wave approach to the problem, are subject to the exact boundary conditions at the irregular interface. These are shown to be consistent with the reciprocity relationship in electromagnetic theory. The validity of the approximate impedance boundary condition is examined and consideration is given to excitation at the grazing incidence, the Brewster angle, and to waves incident at the critical angle for total internal reflection. Optimum conditions are determined for coupling between the radiation fields, the surface waves, and the Iateral waves incident upon irregular boundaries. Thus this work is applicable to problems of radio wave propagation near an irregular interface between two media and excitation of guided waves by irregular dielectric structures.     

位置敏感探测器光斑脱靶误差补偿方法研究

为了提高位置敏感探测器(PSD)的位置检测范围,解决光斑在探测器光敏面脱靶时无法准确定位光斑的问题,提出一种光斑脱靶误差补偿方法,分析了脱靶前后PSD检测光斑能量重心变化规律,建立了PSD光强信号与位置检测误差间的函数关系。实验结果表明:当PSD光敏面尺寸为12mm×12mm时,对于半径为5mm的高斯光斑,通过所提出的光斑补偿方案补偿后PSD的X轴检测范围提高了66.7%,位置检测平均相对误差不超过5%,该方法对提高PSD位置检测性能具有重要的意义。     

Determination of time-of-flight surfaces using the method of moments [US imaging

To produce an image from backscattered signals requires a knowledge of the time of flight from each source to each sensor in a transducer array. The authors reduced the determination of the rectangular coordinates of a new point on any time-of-flight surface, which requires finding the square root of the sum of squares, to the time of a single addition. To do this, the time-of-flight surface was represented by a two-dimensional, positive-integer-degree polynomial and then that polynomial was implemented in its forward-difference form. Two solutions for such a polynomial were found using the method of moments. A minimum-mean-square-error constraint yields polynomial coefficients from a numeric evaluation of the moments of arbitrary surfaces over rectangular regions, and an analytical solution for moments of time-of-flight surfaces over sector-shaped regions. For a 7x6-cm region at a minimum range of 4 cm centered in a 74 degrees sector, the maximum error for a second-degree polynomial was 0.30% of the average time of flight over the region for the numeric solution and 0.32% for the analytic solution, assuming a 1500-m/s background velocity.     

Correlation between structure and resistivity variations of the live human skull

A study on correlation between structure and resistivity variations was performed for live adult human skull. The resistivities of 388 skull samples, excised from 48 skull flaps of patients undergoing surgery, were measured at body temperature (36.5 degrees C) using the well-known four-electrode method in the frequency range of 1-4 MHz. According to different structures of the skull samples, all the 388 samples were classified into six categories and measured their resistivities: standard trilayer skull (7943 +/- 1752 ohm x cm, 58 samples), quasi-trilayer skull (14,471 +/- 3061 ohm x cm, 110 samples), standard compact skull (26,546 +/- 5374 ohm x cm, 62 samples), quasi-compact skull (19,824 +/- 3232 ohm x cm, 53 samples), dentate suture skull (5782 +/- 1778 ohm x cm, 41 samples), and squamous suture skull (12747 +/- 4120 ohm x cm, 64 samples). The results showed that the skull resistivities were not homogenous and were significantly influenced by local structural variations. The presence of sutures appeared to decrease the overall resistivity of particular regions largely and dentate suture decreased the resistivity more than squamous suture. The absence of diploe appeared to increase skull resistivity. The percentage on thickness of diploe would be the primary factor in determining the resistivity of the skull sample without suture. From resistivity spectra results, an inverse relationship between skull resistivity and signal frequency was found.     

Nonlinear transient chirp signal modeling of the aortic and pulmonary components of the second heart sound

This paper describes a new approach based on the time-frequency representation of transient nonlinear chirp signals for modeling the aortic (A2) and the pulmonary (P2) components of the second heart sound (S2). It is demonstrated that each component is a narrow-band signal with decreasing instantaneous frequency defined by its instantaneous amplitude and its instantaneous phase. Each component is also a polynomial phase signal, the instantaneous phase of which can be accurately represented by a polynomial having an order of thirty. A dechirping approach is used to obtain the instantaneous amplitude of each component while reducing the effect of the background noise. The analysis-synthesis procedure is applied to 32 isolated A2 and 32 isolated P2 components recorded in four pigs with pulmonary hypertension. The mean +/- standard deviation of the normalized root-mean-squared error (NRMSE) and the correlation coefficient (rho) between the original and the synthesized signal components were: NRMSE = 2.1 +/- 0.3% and rho = 0.97 +/- 0.02 for A2 and NRMSE = 2.52 +/- 0.5% and rho = 0.96 +/- 0.02 for P2. These results confirm that each component can be modeled as mono-component nonlinear chirp signals of short duration with energy distributions concentrated along its decreasing instantaneous frequency.