Static versus dynamic predictions of protective stepping following waist-pull perturbations in young and older adults

The purposes of this study were: (1) to determine the frequency of protective stepping for balance recovery in subjects of different ages and fall-status, and (2) to compare predicted stepping based on a dynamic model (Pai and Patton, 1997. Journal of Biomechanics 30, 347 354) involving displacement and velocity combinations of the center of mass (COM) versus a static model based on displacement alone against experimentally induced stepping. Responses to three different magnitudes of forward waist pulls were recorded for 13 young, 18 older-non-fallers and 18 older-fallers. The COM phase plane trajectories derived from motion analysis were compared with the model-predicted threshold values for stepping. We found that the older fallers had the highest percentage of stepping trials (52%), followed by older-non-fallers (17.3%), and young (2.7%) at the lowest perturbation level. Younger subjects stepped less often than the elderly at the middle level. Everyone consistently stepped at the highest level of perturbation. Overall, the dynamic model showed better predictive capacity (65%) than the static model (5%) for estimating the initiation of stepping. Furthermore, the threshold for step initiation derived from the dynamic model could consistently predict when a step must occur. However, it was limited, especially among older fallers at the low perturbation level, in that it considered some steps 'unnecessary' that were presumably triggered by fear of falling or other factors.     

Photophysical investigations of Langmuir–Blodgett mono- and multilayer films of pheophorbide-a

Absorption, fluorescence and time-resolved fluorescence spectroscopy has been applied to quasi two-dimensional Langmuir–Blodgett monolayers and three-dimensional arrangements of Langmuir–Blodgett films with different numbers of layers. Pure dye films of pheophorbide-a and films in which pheophorbide-a molecules were embedded in a behenic acid matrix have been investigated. Optical spectroscopy is used in order to obtain evidence for intra- and interlayer interaction in the membrane-like environment and distinguish between these different types of interactions. Depending on how the dye molecule is embedded a broad range of π-system interactions occur. Optical band shifts as well as band shape changes and the formation of new bands are indicators for these molecular interactions [M.B. Grieve, A.J. Hudson, T. Richardson, Thin Solid Films, 1994, 243, 581.]. Among such interactions, exciton coupling and excimer formation are considered to be possible reasons for the observed major differences between spectra and kinetics of mono- and multilayer Langmuir–Blodgett films. Exciton coupling is indicated by red shifts of the Q-band of about 600 cm⁻¹ in the absorption spectra of monolayer films. The observed broad red shifted fluorescence in the near-infrared region and their short lifetimes (≤100 ps) are assigned to excimer formation. Time-resolved fluorescence spectra of bilayer films as well as polarization dependencies of the Langmuir–Blodgett film absorption are presented.     

科氏流量计信号处理中频率跟踪方法的研究

采用ＤＦＴ方法处理科氏质量流量计的信号是项新技术。本提出一种频率跟踪方法,可以在不过零开始采样的情况下,实现整周期采样,保证频率和相位差测量的精度,仿真结果说明了本方法的有效性。     

Scaffolds for Hard Tissue Engineering by Ionotropic Gelation of Alginate–Influence of Selected Preparation Parameters

Cylindrical constructs with parallel aligned pores were prepared by using ionotropic gelation of alginate/calcium phosphate hydroxyapatite (HAP) mixtures in regard to applications as scaffold for bone regeneration. The starting powder and stabilizing agents were characterized by measurement of electrosonic amplitude, particle size distribution, and specific surface. The shrinkage of the gels was investigated in dependence on the drying methods. The pore size relied on preparation conditions such as amount of HAP and concentrations of gelling agent or alginate sol. A wide field of pore sizes could be fabricated by varying the kind and concentration of additives. Micro computer tomography-investigations of freeze dried scaffolds demonstrated the pore progression over a length of 4 mm. The pore dimension and structure were adequate for cell seeding and blood capillary ingrowth. Biocompatibility was proven by in vitro experiments with human mesenchymal stem cells by fluorescence microscopy. A high stability of the wet gels was maintained under cell culture conditions for a period of 3 weeks.     

Crystallographic effects in the kinetic excitation of metal surfaces: A computational study

We present a statistical investigation of the kinetic excitation in atomic collision cascades induced by keV particle impact on metal surfaces. For the model system 5-keV Ag → Ag and a set of 120 impact points, we study the effect of the crystallographic orientation of the target on the average electron temperature evolution at the very surface. Results are discussed in view of secondary ion formation.     

640 Mbit/s waveguide transmitter at 38 GHz

The principle of a digital waveguide transmitter working at 38 GHz is given. A pulse-code-modulation simulator, with a bit rate of 640 Mbit/s, produces the modulation signal and also allows error-rate measurements. Typical switching times of the modulator are less than 500 ps. These results have been obtained by use of a varactor diode installed in a rectangular R band waveguide.     

A 1-MHz-bandwidth second-order continuous-time quadrature bandpass sigma-delta modulator for low-IF radio receivers

This paper presents a quadrature bandpass /spl Sigma//spl Delta/ modulator with continuous-time architecture. Due to the continuous-time architecture and the inherent anti-aliasing filter, the proposed /spl Sigma//spl Delta/ modulator needs no additional anti-aliasing filter in front of the modulator in contrast to quadrature bandpass /spl Sigma//spl Delta/ modulators with switched-capacitor architectures. The second-order /spl Sigma//spl Delta/ modulator digitizes complex analog I/Q input signals at 1-MHz intermediate frequency and operates within a clock frequency range of 25-100 MHz. The modulator chip achieves a peak signal-to-noise-distortion ratio (SNDR) of 56.7 dB and a dynamic range of 63.8 dB within a 1-MHz signal bandwidth and at a clock frequency of 100 MHz. Furthermore, it provides an image rejection of at least 40 dB. The 0.65-/spl mu/m BiCMOS chip consumes 21.8 mW at 2.7-V supply voltage.