A bracket for photographing data from computer screen

The paper describes the construction of a bracket suitable for photographing data obtained by energy-dispersive X-ray analyzer and displayed on a computer screen. The device can substitute for a costly printer.     

The perception of moving comets at high retinal illuminance levels: A rod-cone interaction effect

A small circular target of high retinal illuminance level can have a comet-like appearance when presented moving continuously with a speed as low as 0.2 deg/s. This perceived lengthening of the circular target increases with the speed of movement and is only observed for target presentations outside the foveal region. Data on the parametric properties of the comet effect are presented together with related results on the time-course of recovery of retinal sensitivity following brief exposure to intense stimuli. Measurement of target spectral irradiance levels which are just sufficient to yield the comet effect suggests that the lengthening of the circular target reflects a rodcone interaction and therefore it may be due to unsuppressed, saturated rod responses at high retinal illuminance levels. The restriction of the comet effect to areas outside the foveal region is used to produce spatial maps of what appears to be the rod-free area of the retina. A model simulation by means of a computational approach shows that the predicted appearance of the moving target matches very closely the experimental observations on the comet effect. Model predictions based on psychophysical estimates of comet length for the stimulus conditions of these experiments yield an overall response time for the rod system of some 600 ms.     

A high sensitivity system for luminescence measurement of materials

A unique combined and multi‐disciplinary wavelength multiplexed spectrometer is described. It is furnished with high‐sensitivity imaging plate detectors, the power to which can be gated to provide time‐resolved data. The system is capable of collecting spectrally resolved luminescence data following X‐ray excitation [radioluminescence (RL) or X‐ray excited optical luminescence (XEOL)], electron irradiation [cathodoluminescence (CL)] and visible light from light emitting diodes (LEDs) [photoluminescence (PL)]. Time‐resolved PL and CL data can be collected to provide lifetime estimates with half‐lives from microsecond timeframes. There are temperature stages for the high and low temperature experiments providing temperature control from 20 to 673 K. Combining irradiation, time resolved (TR) and TR‐PL allows spectrally‐resolved thermoluminescence (TL) and optically stimulated luminescence (OSL). The design of two detectors with matched gratings gives optimum sensitivity for the system. Examples which show the advantages and multi‐use of the spectrometer are listed. Potential future experiments involving lifetime analysis as a function of irradiation, dose and temperature plus pump‐probe experiments are discussed.     

A rapid method for selecting fermentative yeasts at high temperatures

A rapid and efficient method for isolating and selecting thermotolerant and sugar-fermenting yeasts was developed. Several samples from sugar cane by-products could be analyzed at the same time. Yeast cultures could be isolated in about 3 d, in contrast to the conventional methods, and its fermentative ability was qualitatively maintained at the desired temperature. A broad spectrum of temperatures can be tested. Yeasts of generaSaccharomyces andKluyveromyces were easily identified.     

A system for performing high throughput assays of synaptic function

Unbiased, high-throughput screening has proven invaluable for dissecting complex biological processes. Application of this general approach to synaptic function would have a major impact on neuroscience research and drug discovery. However, existing techniques for studying synaptic physiology are labor intensive and low-throughput. Here, we describe a new high-throughput technology for performing assays of synaptic function in primary neurons cultured in microtiter plates. We show that this system can perform 96 synaptic vesicle cycling assays in parallel with high sensitivity, precision, uniformity, and reproducibility and can detect modulators of presynaptic function. By screening libraries of pharmacologically defined compounds on rat forebrain cultures, we have used this system to identify novel effects of compounds on specific aspects of presynaptic function. As a system for unbiased compound as well as genomic screening, this technology has significant applications for basic neuroscience research and for the discovery of novel, mechanism-based treatments for central nervous system disorders.     

Developing a methodology for estimating the drag in front-crawl swimming at various velocities

We aimed to develop a new method for evaluating the drag in front-crawl swimming at various velocities and at full stroke. In this study, we introduce the basic principle and apparatus for the new method, which estimates the drag in swimming using measured values of residual thrust (MRT). Furthermore, we applied the MRT to evaluate the active drag (Da) and compared it with the passive drag (Dp) measured for the same swimmers. Da was estimated in five-stages for velocities ranging from 1.0 to 1.4 m s⁻¹; Dp was measured at flow velocities ranging from 0.9 to 1.5 m s⁻¹ at intervals of 0.1 m s⁻¹. The variability in the values of Da at MRT was also investigated for two swimmers. According to the results, Da (Da = 32.3 v^3.3, N = 30, R² = 0.90) was larger than Dp (Dp = 23.5 v^2.0, N = 42, R² = 0.89) and the variability in Da for the two swimmers was 6.5% and 3.0%. MRT can be used to evaluate Da at various velocities and is special in that it can be applied to various swimming styles. Therefore, the evaluation of drag in swimming using MRT is expected to play a role in establishing the fundamental data for swimming.     

A self-calibrating telemetry system for measurement of ventricular pressure-volume relations in conscious, freely moving rats

Using Bluetooth wireless technology, we developed an implantable telemetry system for measurement of the left ventricular pressure-volume relation in conscious, freely moving rats. The telemetry system consisted of a pressure-conductance catheter (1.8-Fr) connected to a small (14-g) fully implantable signal transmitter. To make the system fully telemetric, calibrations such as blood resistivity and parallel conductance were also conducted telemetrically. To estimate blood resistivity, we used four electrodes arranged 0.2 mm apart on the pressure-conductance catheter. To estimate parallel conductance, we used a dual-frequency method. We examined the accuracy of calibrations, stroke volume (SV) measurements, and the reproducibility of the telemetry. The blood resistivity estimated telemetrically agreed with that measured using an ex vivo cuvette method (y=1.09x - 11.9, r2= 0.88, n=10). Parallel conductance estimated by the dual-frequency (2 and 20 kHz) method correlated well with that measured by a conventional saline injection method (y=1.59x - 1.77, r2= 0.87, n=13). The telemetric SV closely correlated with the flowmetric SV during inferior vena cava occlusions (y=0.96x + 7.5, r2=0.96, n=4). In six conscious rats, differences between the repeated telemetries on different days (3 days apart on average) were reasonably small: 13% for end-diastolic volume, 20% for end-systolic volume, 28% for end-diastolic pressure, and 6% for end-systolic pressure. We conclude that the developed telemetry system enables us to estimate the pressure-volume relation with reasonable accuracy and reproducibility in conscious, untethered rats.     

A modified cable formalism for modeling neuronal membranes at high frequencies

Intracellular recordings of cortical neurons in vivo display intense subthreshold membrane potential (V_m) activity. The power spectral density of the V_m displays a power-law structure at high frequencies (>50 Hz) with a slope of ∼−2.5. This type of frequency scaling cannot be accounted for by traditional models, as either single-compartment models or models based on reconstructed cell morphologies display a frequency scaling with a slope close to −4. This slope is due to the fact that the membrane resistance is short-circuited by the capacitance for high frequencies, a situation which may not be realistic. Here, we integrate nonideal capacitors in cable equations to reflect the fact that the capacitance cannot be charged instantaneously. We show that the resulting nonideal cable model can be solved analytically using Fourier transforms. Numerical simulations using a ball-and-stick model yield membrane potential activity with similar frequency scaling as in the experiments. We also discuss the consequences of using nonideal capacitors on other cellular properties such as the transmission of high frequencies, which is boosted in nonideal cables, or voltage attenuation in dendrites. These results suggest that cable equations based on nonideal capacitors should be used to capture the behavior of neuronal membranes at high frequencies.     

A method for determining kinetic parameters at high enzyme concentrations.

A graphical method is described which allows determination of kinetic parameters when substrate, inhibitor or activator concentrations must be in the vicinity of the enzyme concentration and a significant fraction of ligand is bound. Velocity is measured at several ligand: enzyme ratios at two or more enzyme concentrations. Results are obtained in terms of free and bound ligand corresponding to particular velocities. The relationship between velocity and bound and free ligand may then be analysed by any desired plotting technique. Preknowledge of the reaction mechanism or experimental determination of Vmax. is not required. The relationship between ligand bound and enzyme activity need not be linear and the method is equally suitable for analysing co-operative as well as simple kinetics. Application of the method is demonstrated by analysis of the inhibition of fructose, 1,6-bisphosphatase by AMP.     

A novel high resolution micro-radiotherapy system for small animal irradiation for cancer research

Micro-radiotherapy (micro-RT) system is specially designed for small animal (cancer cell) irradiation for basic and translational cancer research. We use carbon nanotube (CNT) field emission technology to develop a novel micro-RT system for image-guided high precision irradiation that is similar to the state of the art radiotherapy which our cancer patients receive today at mouse scale. Through the field emission control of its individually addressable x-ray pixel beams the micro-RT system electronically shapes the radiation field and forms intensity modulation pattern. In this paper, we present the development of a carbon nanotube field emission cathode array chip--a key component for our novel micro-RT system. The prototype micro-RT CNT field emission cathode array chip has 5 x 5 individually addressable cathode pixels that are 1 mm in diameter and 2 mm in pitch. An individual CNT cathode pixel is predicted to generate a dose rate in the order of 100 cGy/min at the center of the irradiated mouse based on our Monte Carlo simulation. The temporal and spatial resolutions of the micro-RT system are expected to be approximately ms level and < 2 mm respectively.     

A novel, high stringency selection system allows screening of few clones for high protein expression

To obtain highly productive mammalian cell lines, often large numbers of clones need to be screened. This is largely due to low selection stringencies, creating many, but low protein producing clones. To remedy this problem, a novel, very stringent selection system was designed, to create few, but high protein producing clones. In essence, a selection marker with a startcodon that confers attenuated translation initiation frequency was placed upstream of the gene of interest with a startcodon that confers optimal translation initiation. From the transcribed bicistronic mRNA, the selection marker is translated at a low frequency, and the protein of interest at a high frequency. This selection system is so stringent that clones form only rarely. However, application of anti-repressor elements, which increase promoter activity, did induce the formation of clones that expressed proteins at high levels. When combined with anti-repressor elements, this novel selection system can be a valuable tool to rapidly create few, but highly productive mammalian cell lines.     

Solution stability of salmon calcitonin at high concentration for delivery in an implantable system.

Salmon calcitonin solutions (50 mg/mL and 100 mg/mL) were placed on stability at 37 degrees C for 1 year in a variety of solvent systems including water, ethanol, glycerol, propylene glycol (PG) and dimethyl sulfoxide (DMSO). Calcitonin degradation was monitored by RP-HPLC and size-exclusion chromatography. DMSO and pH 3.3 solutions provided optimum stability. Conformational stability was also monitored by FTIR over the 1 year time course and compared with chemical and physical stability. After 12 months at 37 degrees C, four major conformations were observed: a beta-sheet conformation (pH 3.3, pH 5.0, 70% DMSO and 70% glycerol), an aggregate conformation (pH 7.0 water), a strong alpha-helical conformation (70% EtOH, 70% PG) and a weak alpha-helical conformation (100% DMSO). No correlation between structure and chemical stability was observed in which both the beta-sheet structure (pH 3.3, water) and a loose alpha-helical structure (100% DMSO) demonstrated good stability. However, some correlation was observed between structure and physical stability, where co-solvents inducing an alpha-helical structure resulted in a decrease in gelation. These two structural states associated with improved stability and minimal gelation, indicated that gelation can be reduced or eliminated by the use of pharmaceutically acceptable co-solvents. Finally, salmon calcitonin (50 mg/mL) was formulated in 100% DMSO and delivered from a DUROS implant over 4 months. Delivery at a target dose of 18 microg/day calcitonin at 37 degrees C was confirmed.     

A stochastic model for a closed biochemical system at equilibrium

This paper presents a stochastic model, a theoretical multi-variate probability function describing concentrations of reactants in a closed biochemical system at equilibrium. The theory applies to the complete range of biochemical systems from single enzyme reactions to combinations of reactions to complete pathways. Prior to examining the general system, probability functions are derived for the following systems as examples: a reaction with a competitive inhibitor, a bisubstrate reaction using the ping-pong mechanism and a series of two mono-substrate reactions. The theory of Markov processes is used to derive the probability functions for each of the example systems and then for the general system which includes the example systems as special cases. The probability function for any appropriate biochemical system proves to be the product of independent Poisson probabilities conditioned on the conservation equations. Finally, the implications of the theory are briefly discussed and possible extensions proposed.     

一种用于自由活动动物的微型多模式遥控刺激器

本文采用集成有射频功能的片上系统(nRF24E1),研制了一种用于自由活动小动物的微型多模式遥控刺激器。刺激参数的设置及结果分析均由10 m外的个人计算机进行。通过离体实验,即刺激蛙坐骨神经干时产生动作电位并可观察到伪迹;及在体大鼠的训练操作性条件反射的行为学实验,即在Y臂迷宫中训练大鼠听到不同声音完成左右运动,如果完成正确给予前脑内侧束以电刺激,我们观察到5 d内大鼠的正确率增加3倍,达到93．5％。上述实验都验证了该刺激器的有效性与稳定性。本系统具有体积小(18 mm×28 mm双层线路板)、重量轻(不含电池5 g)、简单、实用、可靠等特点,能有效地用于自由活动小动物的实验研究。为基于电刺激的小动物行为训练(动物机器人)及相关神经生理学实验研究,提供了新的实验条件和实验手段。