Influence of non-P region domains on selectivity filter properties in voltage-gated K+ channels

The selectivity filter in voltage-gated K+ channels is formed at the interface of the pore loops (S5-S6 loop) from four channel subunits. Whereas most K+ channels are essentially impermeable to Na+, the Kv2.1 K+ channel conducts Na+ relatively well in the absence of K+ and selects for K+ over Na+ at least partially by an affinity-based competition mechanism. To examine whether the ability of Kv2.1 to conduct Na+ reflected unique properties of either its S5-S6 loop or channel domains that held the S5-S6 loop in place (the scaffolding), we studied chimeras made from Kv1.3 (which is completely impermeable to Na+) and Kv2.1. Chimeras that contained either the S5-S6 loop from Kv1.3 inserted into the Kv2.1 scaffolding or vice versa both made highly selective K+ channels that conducted Na+ and displayed competition between Na+ and K+ for conduction through the pore: In channels that contained the S5-S6 loop from Kv2.1, concentration-dependent block of Na+ current by either external or internal K+ differed depending on whether Kv2.1 or Kv1.3 donated the scaffolding. These results indicate that neither the S5-S6 loop nor the scaffolding from Kv2.1 possess unique attributes that permit Na+ to conduct through the channel. Furthermore, these results indicate that the competitive interaction between K+ and Na+ at the selectivity filter is determined not only by the S5-S6 loop but also by the scaffolding that holds the S5-S6 loop.     

Simple Expression for Interchannel and Intersymbol Interference Degradation in MSK Systems with Application to Systems with Gaussian Filters

In this paper, we derive a simple expression for the degradation in signal-to-noise ratio caused by intersymbol and adjacent channel interference in MSK systems for which the total response is nonnegative and the response is such that only two intersymbol and one adjacent channel terms are dominant. An MSK system with Gaussian filters in transmitter and receiver satisfy this condition. The resulting expression is simple because we simultaneously maximize the signal value from the main channel (by selecting the sampling time) and the degradation caused by the signals in the interfering channels. For such systems we derive the relation between the optimal filter bandwidth and channel frequency separation. Numerical results are presented for the case of Gaussian filters in both transmitter and receiver or receiver only and either one or two adjacent interfering channels.     

Review of procedures involving separation and preconcentration for the determination of cadmium using spectrometric techniques

Spectrometric techniques for the analysis of trace cadmium have developed rapidly due to the increasing need for accurate measurements at extremely low levels of this element in diverse matrices. This review covers separation and preconcentration procedures, such as electrochemical deposition, precipitation, coprecipitation, solid phase extraction, liquid-liquid extraction (LLE) and cloud point extraction (CPE), and consider the features of the their application with several spectrometric techniques.     

A Propsed Method for Simpliofied Microcomputer Programming*

A key obstacle to wider application of the new microprocessors is the need to program in assembly language with fairly cumbersome instruction sets. We propose a new technique which will make it easy for applications-oriented non-programmers to generate efficient microcomputer programs without any need to learn assembly language. The user merely specifies an analog-computer-like block diagram whose intuitively meaningful block-operators specify standard mathematical operations (addition, multiplication, integration, etc.) and input/output operations (e.g., analog/digital conversion, switching, sensing). These standard operations are implemented as subroutines in the microcomputer read-only memory (ROM). An interactive editor/translator program running on a small minicomputer translates block-diagram specifications into a simple address table and loads it into the microcomputer memory (RAM, PROM, or ROM). This address table represents the block-diagram operation sequence and specifies successive jumps to the correct standard subroutines in ROM and data fetching/storing operations in the random-access memory.     

Process layout for driving workings in burst-prone areas

Institute of Nonferrous Metallurgy, Ust'-Kamenogorsk. Translated from Fiziko-Tekhnicheskie Problemy Razrabotki Poleznykh Iskopaemykh, No. 6, pp. 81-88, November-December, 1991.     

Physiological properties of the Mauthner system in the adult zebrafish

We investigated the morphological and electrophysiological properties of the Mauthner (M-) cell and its networks in the adult zebrafish (Danio rerio) in comparison with those in the goldfish (Carassius auratus). The zebrafish M-cell has an axon cap, a high resistivity structure which surrounds the initial segment of the M-axon, and accounts for an unusual amplification of the fields generated within and around it. Second, extra- and intracellular recordings were performed with microelectrodes. The resting potential was approximately -80 mV with an input resistance of approximately 0.42 M omega. The M-cell extracellular field was large (10-20 mV), close to the axon hillock, and the latency of antidromic spikes short (approximately 0.4 milliseconds), confirming a high conduction velocity in the M-axon. The extrinsic hyperpolarizing potential (EHP), which signals firing of presynaptic cells and collateral inhibition, was markedly lower at frequencies of spinal stimulation > approximately 5/second, suggesting an organization of the recurrent collateral network similar to that in the goldfish. Inhibitory postsynaptic potentials (IPSPs) were highly voltage-dependent; their decay time constant was increased by depolarizations. The presynaptic neurons which are numerous could be identified by their passive hyperpolarizing potential (PHP) produced by the M-spike current. Auditory responses, mediated via mixed synapses (electrical and chemical), had short delays and hence are well suited to trigger the escape reaction. The similarities of their properties indicate that the wealth of information generated over decades in the goldfish can be extrapolated to the zebrafish.     

Adjacent-Channel and Quadrature-Channel Interference in Minimum Shift Keying

In this paper we present formulas for the computation of error probability in the presence of quadrature-channel or adjacentchannel interference in addition to intersymbol interference in a minimum shift keying system. The filters in the receiver and transmitter are arbitrary but with a finite number of poles. The effect of phase jitter in the main channel, phase and symbol timing misalignment in the interfering channels, and sampling time jitter is taken into account. The probability of error is averaged over the phase and symbol timing misalignment. Numerical results are presented for Butterworth filters in the receiver and transmitter with two, three, and four poles. Curves of error probability as a function of various variables (signal-to-noise ratio, bandwidth of receiver and transmitter filters, number of poles, channel frequency separation, phase jitter, sampling time, and symbol timing and phase misalignment) are presented. The method of this paper can readily be applied to other filters; hence, it can be used in the design and prediction of the performance of digital communication systems.