Evaluation of command algorithms for control of upper-extremity neural prostheses

Five new command control algorithms were created to enable increased control over grasp force in upper-extremity neural prostheses. Most of these algorithms took advantage of the ability to lock or assign a steady command value to the hand neural prosthesis. Five able-bodied subjects tested the algorithms by using a shoulder controller that controlled a video-simulated hand to repeatedly complete a consistent evaluation task. A generalized estimating equations-based linear model was used to analyze the data. The algorithms were ranked via contrast analyses between the coefficient values from the linear model of the proportional control with lock algorithm, which is the algorithm presently used in neural prostheses, and each of the other algorithms. The algorithms that allowed adjustment of the command value after the hand was locked as well as algorithms that allowed a decrease in controller gain after the hand was locked performed better than the proportional control with lock algorithm. Algorithms that changed command as a function of time performed worse than the proportional control with lock algorithm. Further, the computer-based video simulator proved to be useful as a first-pass evaluation tool for neural prosthesis control.     

Towards an easy to use authoring tool for interactive non-linear video

With growing bandwidths in the Internet and seemingly unlimited storage capacities on web servers, media became more and more important in the daily use of the World Wide Web. While about ten years ago only text and images with small file sizes (and as a result small resolutions) could be used, it is possible to watch high quality multimedia presentations nowadays. But those rarely exist because of tedious to learn authoring tools. A specialization to one main medium, in our case video, allows creating efficient authoring tools using well known paradigms. This work introduces an authoring tool called SIVA Producer. An iterative process for improving the usability of the authoring tool is described. Furthermore, a distinction of the terms “interactive video”, “annotated video”, “non-linear video” and “hypervideo” is given.     

Prospects of three-dimensional high resolution electron microscopy of non-periodic structures

In the first part of the paper the general features of three-dimensional electron microscopy of non-periodic structures at high resolution are discussed. Such an analysis requires series of 20 or more exposures of mechanically moved specimens. It is fundamentally important that the integral radiation dose, however, need not be increased--three-dimensional analysis yields extra information without additional radiation loading. It is demonstrated that the constraints characteristic for atomic resolution can in future facilitate many difficulties like restricted tilting range (conical tilting), inaccuracies in the refinement of the origin determination etc. Data collection up to atomic resolution is possible with existing image reconstruction methods if the chromatic spread of the cathodes can be partially corrected. The relatively great radiation induced changes of "stable" specimens will require additional averaging in the experiment (quasi-simultaneous registration). The advantage of a time dependent analysis of radiation sensitive structures--especially the possibility of using redundancies in the analysis (trace structure analysis)--is discussed. The experimental part (studies of radiation damage and three-dimensional work on carbon foils) presents examples of such analyses. The main experimental difficulty consists in the collection of many exposures with no extra load of the specimen in the intervals between exposures.     

Spatial periodicity in molecular switching

The ultimate miniaturization of future devices will require the use of functional molecules at the nanoscale and their integration into larger architectures. Switches represent a prototype of such functional molecules because they exhibit characteristic states of different physical/chemical properties, which can be addressed reversibly. Recently, various switching entities have been studied and switching of single molecules on surfaces has been demonstrated. However, for functional molecules to be used in a future device, it will be necessary to selectively address individual molecules, preferentially in an ordered pattern. Here, we show that azobenzene derivatives in the trans form, adsorbed in a homogeneous two-dimensional layer, can be collectively switched with spatial selectivity, thus forming a periodic pattern of cis isomers. We find that the probability of a molecule switching is not equally distributed, but is strongly dependent on both the surrounding molecules and the supporting surface, which precisely determine the switching capability of each individual molecule. Consequently, exactly the same lattices of cis isomers are created in repeated erasing and re-switching cycles. Our results demonstrate a conceptually new approach to spatially addressing single functional molecules.     

Volume Imaging by Three Dimensional Scanning Acoustic Microscopy with Phase Contrast

Abstract

Three dimensional scanning is employed for scanning acoustic microscopy with phase contrast in reflection operated at a frequency of 1.2 GHz. For samples with sufficient transparency, such as biological tissue immersed in water, which is used as a coupling fluid, spatially resolved information of the acoustic properties can be obtained in the volume of the object. Different schemes of image processing are demonstrated and discussed with respect to the obtainable information. Examples are presented for biological samples with relatively hard and, therefore, mechanically well defined surfaces and for samples exhibiting non abrupt and less pronounced variations of the mechanical properties in the vicinity of the surface.     

The role of hydrogen on the friction mechanism of diamond-like carbon films

The structure, properties and tribological behavior of DLC films are dependent on the deposition process, the hydrogen concentration and chemical bondings in the films. The present paper reports selected tribological experiments on model DLC films with different hydrogen contents. The experiments were performed in ultrahigh vacuum or in an atmosphere of pure hydrogen or argon in order to elucidate various friction mechanisms. Two typical friction regimes are identified. High steady-state friction in UHV (friction coefficient of 0.6) is observed for the lowest hydrogenated and mostly sp²-bonded DLC film. Superlow steady-state friction (friction coefficient in the millirange) is observed both for the highest hydrogenated film in UHV, and for the lowest hydrogenated film in an atmosphere of hydrogen (10 hPa). The high steady-state friction in UHV, observed for the lowest hydrogenated film with a dominant sp² carbon hybridization, is associated with a –^* sub-band overlap responsible for an increased across-the-plane chemical bonding with a high shear strength similar to what is observed with unintercalated graphite in the same UHV conditions. Superlow friction is correlated with a hydrogen saturation across the shearing plane through weak van der Waals interactions between the polymer-like hydrocarbon top layers. This regime is observed during the steady-state period if the film contains enough hydrogen incorporated during deposition. If this condition is not satisfied (i.e., for the film with the lowest hydrogen content), the limited diffusion of hydrogen from the film network towards the sliding surfaces seems to be responsible for a superlow running-in period. The superlow friction level can be reached over longer time periods by suitable combinations of temperature and molecular hydrogen present in the surrounding atmosphere during friction.     

Modeling the effects of electric fields on nerve fibers: influenceof tissue electrical properties

The effects of anisotropy and inhomogeneity of the electrical conductivity of extracellular tissue on excitation of nerve fibers by an extracellular point source electrode were determined by computer simulation. Analytical solutions to Poison's equation were used to calculate potentials in anisotropic infinite homogeneous media and isotropic semi-infinite inhomogeneous media, and the net driving function was used to calculate excitation thresholds for nerve fibers. The slope and intercept of the current-distance curve in anisotropic media were power functions of the ratio and product of the orthogonal conductivities, respectively. Excitation thresholds in anisotropic media were also dependent on the orientation of the fibers, and in strongly anisotropic media (sigma z/sigma xy > 4) there were reversals in the recruitment order between different diameter fibers and between fibers at different distances from the electrode. In source-free regions of inhomogeneous media (two regions of differing conductivity separated by a plane boundary), the current-distance relationship of fibers parallel to the interface was dependent only on the average conductivity, whereas in regions containing the source the current-distance relationship was dependent on the individual values of conductivity. Reversals in recruitment order between fibers at different distances from the electrode and between fibers of differing diameter were found in inhomogeneous media. The results of this simulation study demonstrate that the electrical properties of the extracellular medium can have a strong influence on the pattern of neuronal excitation generated by extracellular electric fields, and indicate the importance of tissue electrical properties in interpreting results of studies employing electrical stimulation applied in complex biological volume conductors.     

Reduction of Inclusions in (CdZn)Te and CdTe:In Single Crystals by Post-Growth Annealing

(CdZn)Te with the composition of 3% Zn and In-doped CdTe single crystals were annealed at various annealing temperatures and under various Cd or Te pressures with the aim of eliminating Te or Cd inclusions. Te inclusions were reduced by Cd-saturated annealing at temperatures above 660°C. Only small (<1 μm) residual dark spots, located at the original position of as-grown inclusions, were observed after annealing. The size of Cd inclusions was reduced by Te-rich annealing at temperatures higher than 700°C. A specific cooling regime was used to eliminate new small Te precipitates (∼1 μm) concurrently formed on dislocations during Te-rich annealing. Poor infrared transmittance of samples with Cd inclusions was detected after Te-rich annealing; therefore, Cd-saturated re-annealing of annealed samples was used for increasing infrared transmittance to a value above 60%. Alternative models explaining the formation of star-shaped corona-surrounding inclusions are discussed.     

显示多个偏差边界的监控警报与指示灯

用一个低成本监控器可以目视指示一个有问题的过程,如一个失效的柜子风扇,或其它高低温特性.