Search results for "ion channel"
showing 10 items of 567 documents
A mathematical study on effective wavenumber, an operative computation procedure, and its use with radiance-temperature relationships
2003
In this paper we study the existence of effective wavenumber for any sensor by means of simple mathematics. We implement a numeric algorithm, based on the developed mathematical background, into a computer program named 'srf2radi', which is freely available via anonymous File Transfer Protocol (FTP) at ftp://ftp.uv.es/pub/src/. The number of effective wavenumbers for each temperature and their accuracy are also computed and studied for NOAA-16 Advanced Very High Resolution Radiometer Version 3 (AVHRR/3) channel 4. These effective wavenumbers can be used to obtain radiance-temperature relationships with physical meaning for any sensor in user-defined temperature intervals.
Bed Topography Reconstruction in a Large Amplitude Meandering Flume: Application of Close Range Photogrammetry
2014
Natural rivers are characterized by continuous variations in bed topography, especially along curved reaches. High resolution topographic data are necessary to analyze the mutual interactions between the downstream flow and the cross-stream flow, which determine the distribution of the bed-shear stress along the channel. Because of the difficulty in acquiring good and accurate data in rivers, the major part of studies have been conducted in laboratory flumes. This paper reports on a laboratory study in which the automatic digital photogrammetric survey was applied to derive the high-resolution Digital Surface Model (DSM) of the bed topography in a large amplitude meandering flume. In order …
An experimental investigation on natural convection of air in a vertical channel
1993
Abstract The free convection of air in a vertical channel is studied experimentally in a laboratory model of height H = 2.6 m and rectangular cross-section b × s , with b = 1.2 m and the channel width s variable. One of the channel walls is heated with a uniform heat flux. Tests are made with different values of channel gap and heating power ( s = 7.5, 12.5, 17 cm; q c = 48–317 W m −2 ). On the basis of the results two empirical formulae are found, giving Nu and Re as functions of Ra and the geometrical parameter s/H ; Nu = 0.9282 Ra 0.2035 (s/H) 0.8972 ; Re = 0.5014 Ra 0.3148 (s/H) 0.418 . The mathematical form of these relationships reproduces other previously published formulae, valid fo…
Modeling Bedload Transport Trajectories along a Sine-generated Channel
2019
This study explores the influences of flow discharge and particle size on bedload transport trajectory by applying a depth-averaged two-dimensional model to a 110° sine-generated laboratory flume with wide-and-shallow sections. Calculated results exhibit two erosion regions in a bend: Zone-1 ‒ foreside of the point bar near the convex bank and Zone-2 ‒ near the apex of the concave bank. Sediments eroded from Zone-1 are mainly transported along the same-side convex bank rather than crossing the channel centerline, indicating the crucial role of longitudinal flow in shaping point bars. Most particles from Zone-2, however, behave more complicated by changing their trajectories with the develop…
Wireless OFDM-OQAM with a small number of subcarriers
2008
Orthogonal frequency division multiplexing based on offset quadrature amplitude modulation (OFDM-OQAM) is a multicarrier signaling technique which trades off robustness for spectral efficiency when compared to conventional OFDM with a cyclic prefix. In this paper, a novel matrix model for passband OFDM-OQAM signaling with a small number of subcarriers over a multipath frequency selective fading channel is presented. Specifically, in OFDM-OQAM a frequency selective channel is divided into many smaller but still frequency selective overlapping channels, so approximating the frequency response of a subchannel by the channel frequency response sampled at the subcarrier frequency may be inadequa…
Design of Measurement-Based Stochastic Wideband MIMO Channel Simulators
2009
In this paper, we propose a method for designing measurement-based stochastic models for simulating wideband multiple-input multiple-output (MIMO) wireless channels. The proposed method allows synthesizing channel transfer functions with the spatial-temporal-frequency correlation properties approximating those of real-world radio channels. The parameters of a channel simulator are determined by fitting the space-timefrequency cross-correlation matrix of the simulation model to the estimated space-time-frequency cross-correlation matrix of a physical channel. For this purpose, an iterative parameter computation algorithm has been developed. The proposed design method is verified by creating …
UWB Channel Measurements for Hand-Portable Devices: A Comparative Study
2007
On-body UWB signal propagation is analyzed using two different types of UWB antennas. For the study, measurements of the frequency response by means of a VNA (vector network analyzer) are performed at 2001 discrete frequency points in the 3 to 6 GHz range. Separated measures are taken for four different transmitter positions on the head and six receiver positions on the body. Channel estimation parameters, such as mean excess delay, delay spread and path loss are obtained. Results are similar for both types of antennas regarding path loss exponent and average power delay profiles.
A simple joint estimation-detection technique for OFDM systems
2005
In this work a simple approach for the joint estimation-detection in a frequency selective severe fading environment of OFDM signals adopting PSK constellations is presented. A linear predictor of suitable order is adopted for the channel estimation in the frequency domain. The predictor coefficients are estimated on the basis of a sample estimation of the autocorrelation of the channel frequency response, aided by a preliminary differential decoding, in a blockwise manner. The detection technique proposed here is based on a simple tree search where a small number of best survivor paths are maintained at each step. Despite the simplicity of above detection approach, the simulation results s…
UWB Channel Measurements for Measures for Hand-Portable and Wearable Devices
2007
On-body UWB signal propagation is analyzed for propagation channels surrounding the body in an usual office environment for an application requiring the transmission of signals recorded from the head to a device such as a mobile phone or a PDA carried by the subject or also from the transmitter on the head to other devices located along the body. For the study, measurements of the frequency response by means of a VNA (Vector Network Analyzer) are performed at 2001 discrete frequency points in the 3 to 6 GHz range. Channel estimation parameters, such as mean excess delay, delay spread and path loss are obtained. Results show that for the transmitter located on top of the head best average pe…
Chapter 17 Muscarinic receptors and cell signalling
1996
Publisher Summary Cells have developed signal transduction mechanisms in order to communicate with the cell exterior. Acetylcholine as an external signal is recognized by nicotinic and muscarinic receptors. This chapter presents various muscarinic receptors belonging to the superfamily of G protein-coupled receptors consisting of seven transmembrane (TM) helices tightly packed in a ring-like structure and arranged in a counter-clockwise fashion. Agonist binding leads to a conformational change of the receptor, thereby activating associated G proteins. Muscarinic stimulation of G proteins leads to the activation or inhibition of ion channels, such as K + and Ca 2+ channels, the activation of…