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Technology.     

Effects of low-voltage electrical stimulation during exsanguination on meat quality and display colour stability

Five steers from each of four slaughter groups were randomly assigned to a low-voltage electrical stimulation (LVES) treatment during exsanguination (within 5 min after stunning) and five served as controls (C). LVES consisted of 50V of 60 Hz alternating current (1 s on and 1 s off for 2 min).

At 28 h, LVES longissimus (LM) was lighter in colour, softer, coarser in texture and tended to have lower marbling estimates than C. LVES LM steaks were lighter red at 0 and 1 days, but more discoloured at 5 days, of display than C steaks. Both the deep (DSM) and superficial (SSM) portions of LVES semimembranosus (SM) steaks were lighter red at 0 and 1 days of display than C steaks. Water-holding capacity for LVES LM and DSM steaks was lower than for C steaks. A trained sensory panel found LVES LM steaks to be less juicy and less tender than C steaks. Also, LVES LM steaks had greater cooking losses than C steaks in two of the four slaughter groups. We conclude that LVES during exsanguination, coupled with relatively slow initial chilling, may be detrimental to muscle quality.     

Correlations between visible light scattering and CO2 laser damage to reflective and antireflective coatings

In this work, 10.6-microm pulsed laser damage studies were performed on reflective and antireflective coatings on Si, Ge, and ZnSe substrates. Single-pulse damage threshold determinations were conducted at two different laser spot sizes. A high-resolution TV system was used to perform visible light scattering studies, the results of which correlated with laser damage at 10.6 microm. Single-pulse damage determinations along with visible light scattering and multipulse damage determinations indicate that coating performance can be improved substantially by reducing the density of scattering centers present on the coatings.     

A Realistic Computer-Simulated Brain Phantom for Evaluation of PET Charactenstics

To evaluate accurately the imaging characteristics of positron emission tomography (PET), a realistic computer-simulated brain phantom was developed. A cross-sectional slice from a human cadaver brain was chosen for its combination of gray matter, white matter, and cerebrospinal fluid (CSF) regions. The slice was photographed and digitized into a gray-level image with a video digitizer, boundary edges were located around cerebral structures in the digitized image, and each structural region was assigned a uniform pixel value dependent on both the cerebral parameter (e.g., blood flow, oxygen uptake, metabolic rate) under investigation and the type of structure (gray matter, white matter, CSF). Line integrals through the regions were generated at various angular and transverse positions according to specific physical characteristics (such as detector line-spread function) of a tomographic scanner configuration to create a set of simulated but realistic projection measurements. The set of projection measurements can be processed with any standard reconstruction program to create a tomographic image to reveal the effects of various PET characteristics. Investigations with this computer-simulated brain phantom have demonstrated its usefulness for examining the interrelations among neuroanatomical structure volume, tomographic spatial resolution, partial volume effect, and nonlinear parameter estimation. Transportability of the simulated phantom and the procedure to other medical imaging environments is described, and limitations of this simulation procedure are discussed.     

Fiber optic sensing technology for detecting gas hydrate formation and decomposition

A fiber optic-based distributed sensing system (DSS) has been integrated with a large volume (72 l) pressure vessel providing high spatial resolution, time-resolved, 3D measurement of hybrid temperature-strain (TS) values within experimental sediment-gas hydrate systems. Areas of gas hydrate formation (exothermic) and decomposition (endothermic) can be characterized through this proxy by time series analysis of discrete data points collected along the length of optical fibers placed within a sediment system. Data are visualized as an animation of TS values along the length of each fiber over time. Experiments conducted in the Seafloor Process Simulator at Oak Ridge National Laboratory clearly indicate hydrate formation and dissociation events at expected pressure-temperature conditions given the thermodynamics of the CH(4)-H(2)O system. The high spatial resolution achieved with fiber optic technology makes the DSS a useful tool for visualizing time-resolved formation and dissociation of gas hydrates in large-scale sediment experiments.     

Computing linear approximations to nonlinear neuronal response

We present an approach to obtain nonlinear information about neuronal response by computing multiple linear approximations. By calculating local linear approximations centered around particular stimuli, one can obtain insight into stimulus features that drive the response of highly nonlinear neurons, such as neurons highly selective to a small set of stimuli. We implement this approach based on stimulus-spike correlation (i.e., reverse correlation or spike-triggered average) methods. We illustrate the benefits of these linear approximations with a simplified two-dimensional model and a model of an auditory neuron that is highly selective to particular features of a song.     

Ultrahigh-efficiency, very narrowpassband, tunable optical filter

Recently developed technologies have been uniquely integrated to produce optical filters with unprecedented performance. The precise design and fabrication of narrow-passband and high-efficiency optical filters with a central frequency of 532 nm are reported. Measurements with these filters demonstrate a performance that accurately mirrors the design specification, with one filter having a passband of 70 pm and an efficiency greater than 90% and the second filter having a passband of 7 pm and an efficiency greater than 80%.