Effect of reabsorbed recombination radiation on the saturation current of direct gap p-n junctions

The radiative transfer theory for semiconductors recently developed is applied to p-n junctions under conditions of low level injection. By virtue of the interaction of the radiation field with free carriers across the depletion layer or space charge region, the saturation current density j₀ in Shockley's expression j = j₀[exp (qV/kT) ? 1] for the diode current is reduced at high doping levels from the customary value which neglects radiation effects altogether. While the effect is insignificant in p-type material, it is noticeable in n-type material owing to the small magnitude of the electron effective mass in direct gap III–V compounds. At an equilibrium electron concentration of 2 × 10¹⁸ cm^?3 in GaAs, a reduction of j₀ by 15% is predicted.     

Analytical solution of the state-dependent Erlangian queue: M/Ej/1/N with balking

The objective of this paper is to derive the analytical solution of the truncated single-channel Erlangian queue M/E_j/1/N with balking and state-dependent service rate. The researcher deduces p_ns the probability of n units in the system (n = 1, 2, 3,…, N) and the customer in service being in phase backwards, i.e. j is the first phase of service and 1 is the last (a customer leaving phase 1 actually leaves the system). p₀ is the probability of an empty system by using the iterative method. At the end of this paper some special cases are obtained.     

A Low-Noise 230 GHz SIS Receiver for Radio Astronomy Employing Untuned Nb/AlOx/Nb Tunnel Junctions

A heterodyne receiver based on a ～1/3 reduced height rectangular waveguide SIS mixer with two mechanical tuners has been built for astronomical observations of molecular transitions in the 230 GHz frequency band. The mixer used an untuned array (ωR_nC_j≈3, R_n≈70 Ω) of four Nb/AIOx/Nb tunnel junctions in series as a nonlinear mixing element. A reasonable balance between the input and output coupling efficiencies has been obtained by choosing the junction number N=4. The receiver exhibits DSB (Double Side Band) noise temperature around 50 K over a frequency range of more than 10 GHz centered at 230 GHz. The lowest system noise temperature of 38 K has been recorded at 232.5 GHz. Mainly by adjusting the subwaveguide backshort, the SSB (Single Side Band) operation with image rejection of ≥ 15 dB is obtained with the noise temperature as low as 50 K. In addition, the noise contribution from each receiver component has been studied further. The minimum SIS mixer noise temperature is estimated as 15 K, pretty close to the quantum limit ?v/k～11 K at 230 GHz. It is believed that the receiver noise temperatures presented are the lowest yet reported for a 230 GHz receiver using untuned junctions.     

Analytical prediction for the optimum operating conditions of SIS mixers

Using Tucker's quantum theory of mixing and a quasi five-frequency approximation proposed by Kerr et al., this paper explores the optimum operating conditions of SIS mixers in the frequency region of 100 to 650 GHz. Four parameters (i.e., ΩR_nC_j product, normal state resistance R_n, RF source admittance (R_rf ^?+jB), and IF load resistance R_if) affecting the performance of an SIS mixer have been investigated. Our results indicate that, independent of the absolute value of R_n, the SIS mixer performance is dominated by R_rf/R_n and R_if/R_n; and that the mixer performance becomes quite insensitive to the ΩR_nC_j product, as the mixer operating frequency goes up to submillimeter wavelengths. Concerning all properties of an SIS mixer, the optimum R_rf/R_n value seems proportional to f^1/n (n≈2), and the optimum R_if/R_n and jB/G_n values are relatively independent of frequency, about 0.5 to 1.5 and ?j0.5 to ?j1.0 respectively.     

Ballistic conductance of a quantum wire at finite temperatures

The temperature-dependent ballistic conductance of a quantum wire is calculated without consideration of carrier scattering. The contribution to the conductance (G) from size-quantization subbands with E _j - μ ? kT is described by the Landauer-Büttiker formula G=2e ²/h, where e is the elementary charge, h is Planck’s constant, μ(T) is the electrochemical potential, E _j is the j-th subband bottom, T is temperature, and k is the Boltzmann constant. The contribution from other subbands decreases as their number increases, being exponentially small for higher subbands. The quantum staircase disappears when kT approaches the energy spacing between the size-quantization levels. Such temperature quenching of the quantum staircase at gate potentials corresponding to a stepwise change in the ballistic conductance is observed in studies of the quantized conductance of a silicon quantum wire.     

Light detector for camera using a GaAs1−xPx photo diode

We have developed a light detector for a camera. It is a photodiode with a shallow p-n junction in a n-GaAs_1?xP_x layer grown epitaxially from the vapor phase on a n⁺-GaAs substrate. By controlling the composition, the junction depth and the donor concentration, photodiodes having ΔEV less than 0.085 and typical dark current 0.2 pA/mm² for a reverse bias of 2 V are mass produced. ΔEV less than 0.085 means that the spectral response of the photodiode is very close to that of the human eye. The diode has also proved to be highly reliable, partly because an i.r. cut-off filter is not needed.     

Finite-Time H ∞ Inverse Optimal Control of Affine Nonlinear Systems

This paper is focused on the problem of the finite-time H _∞ inverse optimal control for affine nonlinear systems. Based on the finite-time control Lyapunov function, we derive a sufficient condition for the existence of time-invariant, continuous, finite-time stabilizing and inverse optimal state feedback control law, and propose a universal formula for constructing the finite-time H _∞ inverse optimal control law. We investigate the relationship between the finite-time stabilization and the finite-time H _∞ inverse optimal control. Finally, some examples are given to illustrate the effectiveness of the presented results.     

Characteristic temperature of a tunneling-injection quantum dot laser: Effect of out-tunneling from quantum dots

A laser structure is studied, which exploits tunneling-injection of electrons and holes into quantum dots (QDs) from two separate quantum wells (QWs). An extended theoretical model is developed allowing for out-tunneling leakage of carriers from QDs into the opposite-to-injection-side QWs (electrons into the p-side QW and holes into the n-side QW). Due to out-tunneling leakage, parasitic recombination of electron-hole pairs occurs outside QDs – in the QWs and optical confinement layer. The threshold current density j_th and the characteristic temperature T₀ are shown to be mainly controlled by the recombination in the QWs. Even in the presence of out-tunneling from QDs and recombination outside QDs, a tunneling-injection laser shows potential for significant improvement of temperature stability of j_th – the characteristic temperature T₀ remains very high (above 300 K at room temperature) and not significantly affected by the QD size fluctuations.     

Energy constraint clustering algorithms for wireless sensor networks

Using partitioning in sensor networks to create clusters for routing, data management, and for controlling communication has been proven as a way to ensure long range deployment and to deal with sensor network shortcomings such as limited energy and short communication ranges. Choosing a cluster head within each cluster is important because cluster heads use additional energy for their responsibilities and that burden needs to be carefully passed around among nodes in a cluster. Many existing protocols either choose cluster heads randomly or use nodes with the highest remaining energy. We present an Energy Constrained minimum Dominating Set based efficient clustering called ECDS to model the problem of optimally choosing cluster heads with energy constraints. Our proposed randomized distributed algorithm for the constrained dominating set runs in O(log n log Δ) rounds with high probability where Δ is the maximum degree of a node in the graph. We provide an approximation ratio for the ECDS algorithm of expected size 8H_Δ∣OPT∣ and with high probability a size of O(∣OPT∣log n) where n is the number of nodes, H is the harmonic function and OPT means the optimal size. We propose multiple extensions to the distributed algorithm for the energy constrained dominating set. We experimentally show that these extensions perform well in terms of energy usage, node lifetime, and clustering time in comparison and, thus, are very suitable for wireless sensor networks.     

Fault Detection for Nonlinear Networked Control Systems with Markov Data Transmission Pattern

This paper is concerned with the fault-detection problem of nonlinear multiple channels data transmission networked control systems (NCSs). Two irrelevant Markov chains are introduced to describe the data transmission characterization of nonlinear delayed NCSs with data loss in both from sensors to controller and from controller to actuators, and a nonlinear Markovian jump system model is established. Based on this novel model, employing a mode-dependent fault-detection filter as residual generator, a fault-detection filter design of nonlinear NCSs is formulated as a nonlinear H _∞-filtering problem. Then an appropriate Lyapunov functional is chosen to derive the sufficient condition which satisfies the stochastic stability and prescribes the H _∞ attenuation level simultaneously. Especially, the desired mode-dependent fault-detection filters are constructed in terms of certain linear matrix inequalities (LMIs), and explicit parameters are characterized if these LMIs are feasible. The effectiveness of the proposed method is demonstrated by a simulation example.     

Tuneable filter using voltage conveyors and current active elements

In this article a new structure of the multifunction second-order frequency filter working in current mode is presented. The circuit solution employs voltage conveyors and programmable current amplifiers. The advantage of the proposed circuit is the possibility of mutually independent control of the quality factor Q and pole frequency f ₀ using the active elements, current inputs at low-impedance and ground potential, realisation of the low-, high- and band-pass response without changing the circuit topology, low passive and active sensitivities. The frequency filter has been designed using the M-C signal flow graphs and its behaviour verified by OrCAD PSpice simulations.     

Asymptotic throughput for large-scale wireless networks with general node density

We study the asymptotic throughput for a large-scale wireless ad hoc network consisting of n nodes under the generalized physical model. We directly compute the throughput of multicast sessions to unify the unicast and broadcast throughputs. We design two multicast schemes based on the so-called ordinary arterial road system and parallel arterial road system, respectively. Correspondingly, we derive the achievable multicast throughput by taking account of all possible cases of n _s  = ω(1) and 1 ≤ n _d  ≤ n ? 1, rather than only the cases of $n_s=\Uptheta(n)$ as in most related works, where n _s and n _d denote the number of sessions and the number of destinations of each session, respectively. Furthermore, we consider the network with a general node density $\lambda \in [1,n]$ , while the models in most related works are either random dense network (RDN) or random extended network (REN) where the density is λ = n and λ = 1, respectively, which further enhances the generality of this work. Particularly, for the special case of our results by letting λ = 1 and $n_s=\Uptheta(n)$ , we show that for some regimes of n _d , the multicast throughputs achieved by our schemes are better than those derived by the well-known percolation-based schemes.     

H ∞ Filtering for Markovian Switching System with Mode-Dependent Time-Varying Delays

This paper deals with the problem of H _∞ filtering for Markovian switching systems. The system under consideration involves discrete and mode-dependent time-varying delays. The aim of this paper is to design a filter such that the filtering error system is stochastically stable with a prescribed H _∞ disturbance attenuation level. Sufficient conditions for the existence of H _∞ filters are expressed in terms of linear matrix inequalities (LMIs), which can be solved by using Matlab LMI control toolbox. Numerical examples are given by including a transmission control protocol (TCP) network model to illustrate the practical importance and effectiveness of the proposed main results.     

Varicap-tuned narrowband filters with extended rejection band based on U-shaped microstrip Resonators

A resonance equation for the first unwanted resonant frequency of tunable microwave U-shaped loop-type resonator with variable capacitance has been derived. This frequency does not depend on the variable capacitance value; it is invariable and proportional to λ-type oscillations. The ascertained feature makes it possible to determine the ratio of the first unwanted resonant frequency to the frequency of the main resonance and control the rejection bandwidth of tunable filters with U-shaped resonators. A narrowband (2%) varicap-tuned filter with extended rejection band has been built and its experimental data are presented. The experimental four-resonator filter could be tuned in the frequency range 225–400 MHz. The filter rejection band in terms of the attenuation level of –40 dB was located in the frequency range 420–1290 MHz, i.e., f _max /f _min = 3.07. Varicap-tuned filters with microstrip U-shaped resonators are shown to have a good potential for their practical use.     

Design of selective CIC filter functions

The aim of this letter is to provide graphs which can be used to design a novel class of selective CIC (Cascaded-Integrator–Comb) filters given insertion loss specification. The goal is to choose the free integer filter parameters such that the filter function yields a desired frequency response. To determine the filter parameters needed to satisfy the desired specifications, one can use the graphs of normalized passband and stopband cut-off frequencies versus filter order N. Two graphs, one for maximum attenuation in the passband and one for minimum attenuation in the stopband, are given here. Achieved improvement of performances of the novel class of CIC filter functions over the classical CIC filters is also given. In case of N = 7, the novel class of CIC filter functions gives improvements of 27.68 dB, 47.29 dB and 66.53 dB for different values 1, 2 and 3 of free parameter L, respectively.     

Study of Scintillation for Infrared Laser Beam Propagating in Atmospheric Turbulence on Earth-Space Paths

On earth-space paths, by applying a modification of the Rytov method that incorporates spatial frequency filter function under strong atmosphere fluctuation conditions, a tractable model is developed for the scintillation index of infrared laser Gaussian beam wave that is valid under moderate-to-strong irradiance fluctuations. At Infrared band, based on ITU-R C ² _n model, the scintillation indexes for collimation laser beam are predicted by this analytic model. The results agree with theoretic expected scintillation. This scintillation model can be converted into a plane or a sphere wave scintillation index model on earth-space paths, and also reduced to a Gaussian beam wave model on horizontal sight paths of invariable C ² _n.     

A Non-Pilot Aided Iterative Carrier Frequency Offset Estimator Using Optimal Filtering for an Interleaved OFDMA Uplink System

In an uplink transmission of a coded orthogonal frequency division multiple access (C-OFDMA) system, channel estimation, time and frequency synchronization has to be addressed. For this purpose a control data, i.e. a known training sequence called “preamble” and pilot sub-carriers are used. As an alternative to the classic scheme and in order to maximize the data rate, we propose a non-pilot aided estimator based on an iterative architecture that does not require pilot sub-carriers. Our approach combines 1/ the so-called minimum mean square error successive detector to estimate the signal sent by each user 2/ a recursive method estimating the CFOs. Various algorithms such as the extended Kalman filter, the sigma-point Kalman filters and the extended H _∞ filter are tested and their performances are compared in terms of convergence speed and estimation accuracy. When considering an interleaved OFDMA uplink system over a Rayleigh fading channel, simulation results clearly show the efficiency of the proposed algorithm in terms of CFO estimation and bit error rate performances.     

Nonequilibrium properties of MIS-capacitors

A model for the nonequilibrium properties of MIS-capacitors proposed in a recent paper has been examined experimentally. Therefore the nonequilibrium C, V-curves of an n-type Si-MOS-capacitor have been measured and compared with calculated curves taking into account the charging of interface states via the interaction with both bands as well as surface recombination.From the simultaneously measured LF- and HF-C, V-curves the density of interface states and from the plot of the generation current j_gen vs depletion layer width W the generation time constant τ₀ has been determined. Furthermore from j_gen vs W the width of the nonequilibrium region ΔW = W ? W₀ has been obtained. To determine ΔW in the range W ≈ W₀, i.e. ΔW ≈ 0, more precisely, a new method is applied, which also yields τ₀.     

Experimental investigation of turn-on spread in a thyristor

The dependence of the spreading velocity of the turned-on state in a thyristor on the load current density is measured in the presence of a turn-off gate current as well as without it. For the same thyristor the critical charge density n_c and the dependence of turn-on time constant τ₁ of turned-off parts of the thyristor on the load current density j_a flowing through the turned-on part are also measured. The data obtained make it possible to compare in detail the experimental results with the recently proposed phenomenological theory of the spreading of the turned-on state. Our investigations show that the theory describes well all the experimental results. The τ₁(j_a) dependence is of great importance in the spreading of the turned-on state. The inhomogeneities of the critical charge density n_c at different points of the structure have a considerable influence on the condition of the spread.The data obtained improve the understanding of the turn-on process and allow to calculate the spreading velocity of the turned-on state in thyristors.     

A Quasi-Optical System for Converting TE0n Mode Outputs of a Gyrotron into Gaussian Beams

In this paper we present a novel design of a quasi-optical system for conversion of gyrotron outputs into Gaussian-like beams. It consists of a quasi-optical antenna, two focusing mirrors and a filter which removes the side lobes of the beam. The system is appropriate as a transmission line for frequency tunable gyrotrons operating at TE_0n mode. As an illustration of our approach, we present results which demonstrate the applicability of the developed system for conversion of the radiation generated by the Gyrotron FU IVA. The examples include conversion of three TE_0n modes (TE₀₂, 223 GHz; TE₀₃, 323 GHz; TE₀₄, 423 GHz) into Gaussian- like beams.