Parametric and Parametrically Smoothed Distribution-Free Proportional Hazard Models with Discrete Data

This paper discusses discrete time proportional hazard models and suggests a new class of flexible hazard functions. Explicitly modeling the discreteness of data is important since standard continuous models are biased; allowing for flexibility in the hazard estimation is desirable since strong parametric restrictions are likely to be similarly misleading. Simulation compare continuous and discrete models when data are generated by grouping and demonstrate that simple approximations recover underlying hazards well and outperform nonparametric maximum likelihood estimates in term of mean squared error.     

SAR measurement due to mobile phone exposure in a simulated biological media

The specific absorption rate (SAR) measurements are carried out for compliance testing of personal 3G Mobile phone. The accuracy of this experimental setup has been checked by comparing the SAR in 10 gm of simulated tissue and an arbitrary shaped box. This has been carried out using a 3G mobile Phone at 1718.5 MHz, in a medium simulating brain and muscle phantom. The SAR measurement system consists of a stepper motor to move a monopole E-field probe in two dimensions inside an arbitrary shaped box. The phantom is filled with appropriate frequency-specific fluids with measured electrical properties (dielectric constant and conductivity). That is close to the average for gray and white matters of the brain at the frequencies of interest (1718.5 MHz). Induced fields are measured using a specially designed monopole probe in its close vicinity. The probe is immersed in the phantom material. The measured data for induced fields are used to compute SAR values at various locations with respect to the mobile phone location. It is concluded that these SAR values are position dependent and well below the safety criteria prescribed for human exposure.     

Arm lengths and arm reaches: some interrelationships of structural and functional body dimensions

Structural measurements of the human body have for the most part been of little practical use as indicators of such functional body dimensions as arm reaches. These dimensions, which define the area around the body to which a person can reach given certain specified conditions and constraints are often critical for the design and layout of workspaces. However, they are relatively difficult and time-consuming to obtain, usually requiring specially constructed measuring systems for each differing design situation, as well as resurveys for each physically distinct population. An alternate approach, described here, investigates the interrelationships between these two classes of measurements with the aim of predicting functional reaches from structural body dimensions. In the present study traditional structural measurements and 117 functional arm reaches were obtained on 100 subjects. Correlations between the two types of measures are reported. Regression equations are presented which can predict functional arm reaches from two structural body dimensions on anthropometrically differing populations under a fixed set of workspace conditions.     

Assessment of Data Quality: Errors of Measurement and Errors of Process

As projects progress from pilot studies with few simple variables and small samples, the research process as a whole becomes qualitatively more complex and subject to an array of contamination by errors and mistakes. Data usually undergo a series of manipulations (e.g., recording, computer entry, transmission) prior to final statistical analysis. The process, then, consists of numerous operations only ending with eventual statistical analysis and write-up. We present a means of estimating the impact of process error in the same terms as psychometric reliability and discuss the implications for reducing the impact of errors on overall data quality.     

A Bayesian Approach to Joint Mixed‐Effects Models with a Skew‐Normal Distribution and Measurement Errors in Covariates

Summary In recent years, nonlinear mixed‐effects (NLME) models have been proposed for modeling complex longitudinal data. Covariates are usually introduced in the models to partially explain intersubject variations. However, one often assumes that both model random error and random effects are normally distributed, which may not always give reliable results if the data exhibit skewness. Moreover, some covariates such as CD4 cell count may be often measured with substantial errors. In this article, we address these issues simultaneously by jointly modeling the response and covariate processes using a Bayesian approach to NLME models with covariate measurement errors and a skew‐normal distribution. A real data example is offered to illustrate the methodologies by comparing various potential models with different distribution specifications. It is showed that the models with skew‐normality assumption may provide more reasonable results if the data exhibit skewness and the results may be important for HIV/AIDS studies in providing quantitative guidance to better understand the virologic responses to antiretroviral treatment.     

Binary Regression Analysis with Pooled Exposure Measurements: A Regression Calibration Approach

Summary It has become increasingly common in epidemiological studies to pool specimens across subjects to achieve accurate quantitation of biomarkers and certain environmental chemicals. In this article, we consider the problem of fitting a binary regression model when an important exposure is subject to pooling. We take a regression calibration approach and derive several methods, including plug‐in methods that use a pooled measurement and other covariate information to predict the exposure level of an individual subject, and normality‐based methods that make further adjustments by assuming normality of calibration errors. Within each class we propose two ways to perform the calibration (covariate augmentation and imputation). These methods are shown in simulation experiments to effectively reduce the bias associated with the naive method that simply substitutes a pooled measurement for all individual measurements in the pool. In particular, the normality‐based imputation method performs reasonably well in a variety of settings, even under skewed distributions of calibration errors. The methods are illustrated using data from the Collaborative Perinatal Project.     

Application of a multi-cylinder evapotranspirometer method for evapotranspiration measurements in wetlands

This paper introduces a multi-cylinder evapotranspirometer method, which can directly measure evapotranspiration (ET) from emergent plants in different species and states as well as simultaneously measure evaporation (E_W) from an open water surface. Values of daily ET from three contrasting reed (Phragmites australis) stands, with different leaf area indexes (LAI), were obtained through in situ measurements of the Baiyangdian wetland using this method during the growing seasons in 2008 and 2009. The results showed that the ET rate of the reed belt was very high, even exceeding 20 mm d⁻¹ under extreme weather conditions. Depending on the LAI change, the annual ET from the different reed canopies ranged from 970 to 2035 mm, whereas the ET/E_W ratios ranged from 2.05 to 3.98. Accuracy analysis results showed that the errors of the measurement from this method were no more than 2 mm. The relative errors of the measurement were correspondingly from 0.04% to 0.33%. It is indicated that the accuracy of our measurement is good enough for the requirements of the ET measurement.     

颧根与侧颅底重要结构的解剖学测量

目的：通过测量颧根与侧颅底各重要结构间的距离关系,为临床侧颅底外科手术治疗提供定位参考。方法：取成人颅骨标本50例（去颅盖标本8例,整颅42例）100侧,用游标卡尺、圆规和直尺测量颧根与侧颅底重要结构的距离。结果：实验测得左右侧颧根与外耳门前缘中点、乳突尖、茎突、翼突外侧板根部、舌下神经管外口、茎乳孔、颈静脉孔外缘、颈动脉管外口后缘、棘孔、卵圆孔、破裂孔的距离分别为22.30±2.84mm和22.02±3.27mm、40.37±3.21mm和40.56±3.54mm、32.53±2.78mm和32.92±2.68mm、35.13±3.14mm和35.19±2.74mm、49.29±2.88mm和48.98±2.87mm、32.92±2.44mm和33.05±2.61mm、35.15±2.86mm和34.68±3.13mm、33.17±2.78mm和33.17±2.72mm、28.83±2.62mm和28.68±2.63mm、31.15±2.76mm和31.49±2.73mm、43.67±3.32mm和44.15±3.02mm,左右侧数据无差异（P〉0.05）。结论：颧根可以作为侧颅底外科手术的定位标志,为直视条件下经颞下等入路的侧颅底外科手术提供解剖学依据。     

EMG gait data from indwelling electrodes is attenuated over time and changes independent of any experimental effect

The effect of time on the validity of electromyography (EMG) signals from indwelling fine-wire electrodes has not been explored. This is important because experiments using intramuscular electrodes are often long and biochemical and mechanical factors, may impair measurement accuracy over time. Measures over extended periods might therefore be erroneous. Twelve healthy participants (age = 33 ± 8 years) walked for 50 min at a controlled speed. Fine-wire electrodes were inserted into tibialis anterior and a surface EMG sensor attached near the fine-wire insertion site. EMG signals progressively and significantly decreased with time with the fine-wire electrode, but not the surface electrode. For the fine-wire electrode, after 25 min mean amplitude had reduced by 11% (p < 0.001) and after 50 min by 16% (p < 0.001), and peak amplitude reduced 22% at 20 min (p = 0.006) and 37% at 50 min (p < 0.001). Reduced amplitude with indwelling EMG without concurrent changes in surface EMG signal suggests an important inconsistency in data from fine-wire EMG electrodes. Changes in EMG signal will occur over time independent of the experimental condition and this questions their use in experiments of more than 30 min. These results should impact on experimental study design. They also invite reinterpretation of prior literature and sensor innovation to improve measurement performance.     

髋骨闭孔沟的临床解剖学测量

目的：对闭孔沟进行解剖学观察和测量,为相关应用提供临床解剖学依据和丰富人类学数据。方法：选取结构完整、解剖标志清晰的髋骨108例,其中男性髋骨59例（左侧36例,右侧23例）,女性髋骨49例（其中左侧20例,右侧29例）,对闭孔沟进行观察并测量其长度和闭孔沟中点宽度。结果：试验测得男性左、右侧闭孔沟长度分别为31．4±3．4mm、32．1±2．4min,女性左、右侧闭孔沟长度分别为19．4±2．2mm、20．8±2．7mm;统计学分析显示同性别左、右侧差异无统计学意义（P〉0．05）,男、女性之间差异有统计学意义（P〈0．05）。男性左、右侧闭孔沟中点宽度分别为9．7±1．6mm、10．7±1．5mm,女性左、右侧闭孔沟中点宽度分别为12．1±1．7mm、11．6±2．0mm;同性别左、右侧及男、女间差异均无统计学意义（P〉0．05）。结论：男、女性闭孔沟测量数据可为闭孔处疾病的诊断和治疗提供应用解剖学的考虑依据并丰富人类学数据。