Compact Channel Research Articles

Micro-channel plates and vacuum detectors

A micro-channel plate is an array of miniature electron multipliers that are each acting as a continuous dynode chain. The compact channel structure results in high spatial and time resolutions and robustness to magnetic fields. Micro-channel plates have been originally developed for night vision applications and integrated as an amplification element in image intensifiers. These devices show single-photon sensitivity with very low noise and have been used as such for scintillating fiber tracker readout in high-energy physics experiments. Given their very short transit time spread, micro-channel plate photomultiplier tubes are also being used in time-of-flight and particle identification detectors. The present paper will cover the history of the micro-channel plate development, basic features, and some of their applications. Emphasis will be put on various new manufacturing processes that have been developed over the last few years, and that result in a significant improvement in terms of efficiency, noise, and lifetime performance.

Nd^3+-doped ion-exchanged aluminum germanate glass channel waveguide

K+–Na+ ion-exchanged channel waveguide has been fabricated in Nd3+ doped aluminum germanate (NMAG) glasses with potential photosensitive property. The channel waveguide exhibits single mode at 1.3μm and the mode field diameters were measured to be horizontally 10.1μm and vertically 5.3μm, respectively. Amplified spontaneous emissions (ASE) of 905, 1060, 1334 and 1816nm originating from the 4F3/2 level were recorded under ~800nm diode laser pumping and the maximum stimulated emission cross-sections for the 4F3/2→4I11/2 and 4F3/2→4I13/2 transitions are derived to be 21.5 × 10−21 and 7.6 × 10−21cm2, respectively. In addition, with 71.8% quantum efficiency and the largest emission intensity among various Nd3+ doping cases, 2wt% Nd2O3 is considered as the optimized doping concentration for the compact channel waveguide. The ion-exchanged Nd3+-doped NMAG glass channel waveguides offer favorable prospects for the development of optical waveguide amplifiers, broadband light sources and infrared UV-written grating waveguide lasers.

Exact analysis of downlink capacity employing opportunistic feedback and maximal ratio transmission in Rayleigh fading environments

The downlink throughput of opportunistic-feedback multiuser wireless systems with capture effects employing maximal ratio transmission (MRT) in a Rayleigh fading environment is studied. To the best of the authors’ knowledge, MRT has not been employed to improve multiuser system throughput with capture effects. Employing MRT means that the channel fading gains between the base station (BS) and users are a chi-square distribution with 2L degrees of freedom, where L is the diversity order, as opposed to Rayleigh distribution which has been examined in detail in the literature. Thus, the main challenge is to obtain a new and compact channel capacity expression for the system in which the roles of BS and users are reversed to make it practically sound. The new downlink throughput expression is derived as a function of L, fading-gain threshold η, capture ratio z and other parameters. For large η, the capture effects are not as effective as when η is small. Effects of the capture ratio z on system throughput are also obtained. The new findings are validated using available results in the open literature.

Digital Interferometric Measurement of Forced Convection Fields in Compact Channels

The application of digital interferometric techniques in the measurement of forced convection in compact channels is examined. Michelson Interferometry and Mach–Zehnder Interferometry have been compared and contrasted, in terms of the suitability for temperature measurements. A wedge-fringe setting parallel to the heated surface has been utilized as the basis of the fringe analysis, for effective measurement in small dimension channels. Michelson interferometry was found to provide a larger number of data points in the visualization field, thus proving to be a better method of measurement in compact passages. Heat transfer parameters, useful in heat sink design, were also calculated.

Compact 3D Microfluidic Channel Structures Embedded in Glass Fabricated by Femtosecond Laser Direct Writing

Compact 3D Microfluidic Channel Structures Embedded in Glass Fabricated by Femtosecond Laser Direct Writing

PH-Dependent Conformation, Dynamics, and Aromatic Interaction of the Gating Tryptophan Residue of the Influenza M2 Proton Channel from Solid-State NMR

The M2 protein of the influenza virus conducts protons into the virion under external acidic pH. The proton selectivity of the tetrameric channel is controlled by a single histidine (His37), whereas channel gating is accomplished by a single tryptophan (Trp41) in the transmembrane domain of the protein. Aromatic interaction between these two functional residues has been previously observed in Raman spectra, but atomic-resolution evidence for this interaction remains scarce. Here we use high-resolution solid-state NMR spectroscopy to determine the side-chain conformation and dynamics of Trp41 in the M2 transmembrane peptide by measuring the Trp chemical shifts, His37-Trp41 distances, and indole dynamics at high and low pH. The interatomic distances constrain the Trp41 side-chain conformation to trans for χ1 and 120–135° for χ2. This t90 rotamer points the Nε1-Cε2-Cζ2 side of the indole toward the aqueous pore. The precise χ1 and χ2 angles differ by ∼20° between high and low pH. These differences, together with the known changes in the helix tilt angle between high and low pH, push the imidazole and indole rings closer together at low pH. Moreover, the measured order parameters indicate that the indole rings undergo simultaneous χ1 and χ2 torsional fluctuations at acidic pH, but only restricted χ1 fluctuations at high pH. As a result, the Trp41 side chain periodically experiences strong cation-π interactions with His37 at low pH as the indole sweeps through its trajectory, whereas at high pH the indole ring is further away from the imidazole. These results provide the structural basis for understanding how the His37-water proton exchange rate measured by NMR is reduced to the small proton flux measured in biochemical experiments. The indole dynamics, together with the known motion of the imidazolium, indicate that this compact ion channel uses economical side-chain dynamics to regulate proton conduction and gating.

Investigations on Forced Convection in Compact Passages With Surface Irregularities

Two-dimensional, fully developed, convective heat transfer in compact passages is investigated numerically, incorporating the effects of the surface irregularities, to analyze the influence of these irregularities on fluid flow and heat transfer. This analysis helps to bring out the differences in the performance evaluation if regular cross sections are assumed in analyzing compact and mini channels. Forced convection in compact passages with an apparent rectangular shape is analyzed using a finite-difference method. The calculation is validated experimentally using Michelson interferometry. The numerical results for the channel, incorporating surface irregularities, are compared with those assuming a regular cross-sectional geometry. The results indicate that the coefficient of friction and the Nusselt number calculated for channels, considering the irregular cross section, are less than those predicted using an assumption of regular geometry. The results provide some insight into the reasons for the observed deviations in the comparisons. The observations are attributed to the influence of the surface irregularities on the relative dominance of the surface area to the cross-sectional area, which gets pronounced in compact passages. The findings suggest that some of the observed deviations in the performance of compact passages, compared to theoretical results, may be due to the use of regular geometries to define domain shapes while performing theoretical analysis.

Design and modeling of a low-power multi-channel integrated circuit for infrared gas recognition

The design and high-level modeling of a multi-channel integrated circuit for infrared gas recognition suitable for low-power consumption are presented. The thermal compensation and independent programmability methods are used in all the main channel stages: sensor biasing, high-pass filtering and pre-amplification, blind cancellation, lock-in demodulation and A/D conversion. CMOS transistor subthreshold operation and circuit reuse techniques are widely applied in order to obtain a low-power and compact channel realization. Experimental results are presented for a 340×880μm channel integrated in 0.35μm CMOS technology reporting good agreement with electrical and higher level simulations.

Transient Simulation of Complex High-Speed Channels via Waveform Relaxation

This paper presents a class of numerical schemes for fast transient simulation of electrically long and complex linear channels terminated by linear or nonlinear networks. The common denominator of all schemes is waveform relaxation. Domain decomposition approaches based on longitudinal and transverse partitioning are pursued, leading to various iterative methods characterized by different properties and numerical efficiency. For each scheme, we present a detailed convergence analysis and a set of numerical results obtained on industrial benchmarks. The main contribution of this paper is a novel theoretical framework based on a combination of longitudinal and transverse relaxation, leading to particularly efficient simulations when combined with compact channel representations based on delay-rational macromodels. Our prototypal implementation outperforms SPICE solvers, with speedup of up to two orders of magnitude.

Single-field programmable gate array simulator for geometric multiple-input multiple-output fading channel models

The authors propose a compact and fast fading channel simulator for the baseband verification and prototyping of multiple-input multiple-output (MIMO) wireless communication systems. The simulator accurately and efficiently implements models of both single-bounce and multiple-bounce geometric propagation conditions. Fading samples are generated at a low rate, comparable to the Doppler frequency, and then interpolated to match the desired sample rate. Bit-true simulations verify the accuracy of the hardware simulator. As an example, when implemented on a Xilinx XC5VLX110 field-programmable gate array (FPGA), the 4×4 MIMO geometric fading channel simulator occupies only 6.6% of the configurable slices while generating more than 16×324 million samples per second. The geometric MIMO fading channel simulator is well suited for use in an FPGA-based error rate performance verification system.

Experimental Demo for Small Scale MHD Plasma Accelerator

The objective of the current MHD acceleration study is to thoroughly explain the compact experimental demo of MHD accelerator and to clarify some significant plasma variables both within and at the exit of the newly introduced mullite ceramic compact channel. The significant challenge of the current study is to use the 0.4-tesla neodymium magnetic as an MHD source, while the model rocket engine (C6-0, ESTES) is introduced and employed as a gas (plasma) source. The results of present demonstrations reveal that the highest gas velocity was calculated at 117.2 m/s using the gas pressure measurement through the pitot tube. The TOF method using two photo diodes showed the slowest speed of 50 m/s.

The gas diffusion layer in polymer electrolyte membrane fuel cells: A process model of the two-phase flow

A two-phase flow process model for the gas diffusion layer (GDL) of a polymer electrolyte membrane fuel cell, considering also the cathode catalyst layer (CL), is presented. For this purpose, a systematic analysis of the factors affecting flooding and drying, including the liquid accumulation in the gas channel (CH), was performed using a one-dimensional reference model for the GDL and a compact channel model. The treatment proposed for the CH–GDL interface was compared with other boundary conditions in the literature. It was concluded that the liquid accumulation in the channel is determinant for estimating the steady state and transient GDL flooding, but that predicting the saturation level in the CL can help for determining operation policies for precluding flooding in the GDL–CL composite, in the absence of an adequate channel model. Bifurcation behavior, associated with the water phase change, was identified by means of the compact model.

Design method for area-efficient and uniform channel DACs

A current-mode driving scheme has significant advantages over other competing driving method, and the scheme does not require the time-consuming threshold voltage sampling process used in recent voltage-mode driving methods. Design considerations for compact and uniform channel DACs in current-mode AMOLED display data drivers are addressed in detail. Furthermore, an 8 bit area-efficient cascaded-dividing DAC and a 9 bit segmented DAC are designed in accordance with the suggested DAC design method. The presented DACs perform outstandingly when compared in terms of a composite DAC performance that comprises chip area, power consumption, sampling frequency, and DAC bit resolution.

Degrees of Freedom of a Communication Channel: Using DOF Singular Values

A fundamental problem in any communication system is: given a communication channel between a transmitter and a receiver, how many ?independent? signals can be exchanged between them? Arbitrary communication channels that can be described by linear compact channel operators mapping between normed spaces are examined in this paper. The (well-known) notions of degrees of freedom (DOF) at level ? and essential dimension of such channels are developed in this general setting. We argue that the DOF at level ? and the essential dimension fundamentally limit the number of independent signals that can be exchanged between the transmitter and the receiver. We also generalize the concept of singular values of compact operators to be applicable to compact operators defined on arbitrary normed spaces which do not necessarily carry a Hilbert space structure. We show how these generalized singular values, which we call DOF singular values, can be used to calculate the DOF at level ? and the essential dimension of compact operators that describe communication channels. We describe physically realistic channels that require such general channel models.

MIMO channel estimation in correlated fading environments

This paper presents two analytic correlated multiple-input multiple-output (MIMO) block fading channel models and their time-variant extensions that encompass the popular Kronecker model and the more general Weichselberger model as special cases. Both static and time-variant models offer compact representations of spatial- and/or time-correlated channels. When the transmit antenna array is such that the associated MIMO channel has a small angle spread (AS), which occurs quite often in a cellular downlink, our models admit reduced-rank channel representations. They also provide compact channel state information (CSI) descriptions which are needed in feedback systems and in many post channel estimation applications. The latter has the important implication of reduced feedback channel bandwidth requirement and lower post-processing complexity. Based on one of the proposed channel models we present novel iterative algorithms for estimating static and time-variant MIMO channels. The proposed models make it natural to decompose each iteration of our algorithms into two successive stages that are responsible for estimating the correlation coefficients and the signal direction, respectively. Using popular industry-approved standard channel models, we verify through simulations that our algorithms yield good MSE performance which, in many practical cases, is better than that achievable by a conventional least-square estimator. The mean-squared error (MSE) performance of our estimators are analyzed and the resulting predictions are consistent with those estimated by simulations.

Compact Channel Noise Models for Deep-Submicron MOSFETs

In this paper, compact channel noise models valid in all regions of operation for deep-submicron MOSFETs have been developed and experimentally verified. The physics-based expressions for thermal noise and flicker noise and corner frequency constitute compact channel noise models. The carrier heating, channel-length modulation, and mobility degradation due to the lateral electric field have been incorporated in the models. The effect of the mobility and carrier number fluctuations on the flicker noise, as well as the dependence of the mobility limited by Coulomb scattering on the inversion carrier density, have been considered in the flicker noise model. The measurement results validate the proposed models.

Application of the Compact Channel Thermal Noise Model of Short Channel MOSFETs to CMOS RFIC Design

In this paper, a compact channel thermal noise model for short-channel MOSFETs is presented and applied to the radio frequency integrated circuit (RFIC) design. Based on the analysis of the relationship among different short-channel effects such as velocity saturation effect (VSE), channel-length modulation (CLM), and carrier heating effect (CHE), the compact model for the channel thermal noise was analytically derived as a simple form. In order to simulate MOSFET's noise characteristics in circuit simulators, an appropriate methodology is proposed. The used compact noise model is verified by comparing simulated results to the measured data at device and circuit level by using 65nm and 130nm CMOS technologies, respectively.

Features of the development of extrusion granulation of biofuel based on wood and plant waste products

The problem is considered of using granulated fuel from sawdust as a replacement for traditional energy sources, and the advantages of wood granules over other types of fuel are demonstrated. Results are provided for a study of the behavior of sawdust in a channel during continuous compaction. Results are given for a study of the effect of temperature on the change in plastic strength of the original raw material. It is shown that use of heating leads to a reduction in the specific compaction pressure, and this makes it possible to reduce energy expenditure and to increase the efficiency of preparing the final product. Operating principles are considered for rotary presses and also forces that operate on the compacted mass at a deformation site. A series of equations is provided describing material behavior in an extrusion compaction channel, and also the connection of channel geometric parameters and reprocessed material properties.

Compact tunable three-dimensional polymer optical waveguide comb filter

A compact channel spacing tunable polymeric three-dimensional (3D) comb filter has been designed and fabricated. This comb filter is made of three waveguides laid in two different but parallel layers: one is in the lower layer and the other two are in the upper layer. These two waveguides in upper layer do not cross each other but instead each twice cross over the waveguide in the lower layer. At each crossing point an electrode heater is deposited on the top surface to adjust the coupling ratio between these guides. By supplying power to each heater pair, respectively, the channel spacing can be selected to be either 1.6nm or 0.8nm; in addition a flat-top spectral response may be obtained at the 1.6nm channel spacing if power is supplied to both the heater pairs simultaneously.

Microstructured Surfaces for Drag Reduction Purposes: Experiments and Simulations on Rectangular 2D Riblets

AbstractIt is well established that properly structured surface exhibits a lower friction drag, when exposed to a turbulent boundary layer, than a smooth surface under the same flow conditions. The observed drag decrease is usually attributed to an increased thickness of the viscous sublayer. In this work we examine the friction drag reducing mechanism. Two parallel approaches towards achieving this goal are presented. Photolithography was used to manufacture rectangular riblets in the 10∝m range on a standard 4” silicon wafer. A special compact plane channel system was designed and used for measurements of the frictional drag on structured surfaces in the turbulent flow covering a wide Reynolds number range. Navier-Stokes equation, for the examined drag reducing geometry, was solved in the laminar regime with appropriate boundary conditions. The resulting velocity field was used to extract the protrusion heights difference for streamwise and spanwise flows over the structured surface. The latter was then related to the experimentally measured drag reduction slope. We show that in case of a rectangular riblet, with a size of the order of one wall unit, the observed drag reduction can be accounted for within the above model.