Smart Antennas Implementation for MIMO

MIMO systems place the same requirements on the RF link as do the receive diversity systems that are in place for current cellular networks, that is, there must be de-correlation between the channels received at the antenna. This de-correlation is provided by space diversity when achieved by the separation of the antennas, or by the use of polarization diversity when implemented by the use of orthogonal antenna elements. However, for dual-pole antennas, cross-polar discrimination and port-to-port isolations can affect the diversity or MIMO performance of the system by introducing correlation between the channels. MIMO systems employing smart antennas are a promising candidate for future mobile communications due to their tremendous spectral efficiency. RF engineers have to find new antenna solutions for MIMO applications, especially the integration of MIMO antennas into small handsets is a challenging task. Smart antenna systems may revolutionize future communications systems. So far, only the spectrum, the time and the code domain are exploited for communications systems. The resources spectrum and code are very limited. Smart antennas exploit the spatial domain, which has been almost completely unused so far. For multiplex transmission within one communications link, i.e. a parallel transmission of several data streams at the same time and frequency only separated by the spatial domain, multiple transmit and multiple receive antennas (multiple input multiple output - MIMO) are required. MIMO systems promise to reach very large data rates and therewith high spectral efficiencies. The proposed research work states smart antennas for mimo’s and related for wireless systems. Keywords:MIMO,SISO,DIVERSIT

Statistics of finite-time Lyapunov exponents in the Ulam map

The statistical properties of finite-time Lyapunov exponents at the Ulam point of the logistic map are investigated. The exact analytical expression for the autocorrelation function of one-step Lyapunov exponents is obtained, allowing the calculation of the variance of exponents computed over time intervals of length $n$. The variance anomalously decays as $1/n^2$. The probability density of finite-time exponents noticeably deviates from the Gaussian shape, decaying with exponential tails and presenting $2^{n-1}$ spikes that narrow and accumulate close to the mean value with increasing $n$. The asymptotic expression for this probability distribution function is derived. It provides an adequate smooth approximation to describe numerical histograms built for not too small $n$, where the finiteness of bin size trimmes the sharp peaks.Comment: 6 pages, 4 figures, to appear in Phys. Rev.

Manipulation of exciton and trion quasiparticles in monolayer WS2 via charge transfer

Charge doping in transition metal dichalcogenide is currently a subject of high importance for future electronic and optoelectronic applications. Here, we demonstrate chemical doping in the CVD-grown monolayer (1L) of WS2 by a few commonly used laboratory solvents by investigating the room temperature photoluminescence (PL). The appearance of distinct trionic emission in the PL spectra and quenched PL intensities suggests n-type doping in WS2. The temperature-dependent PL spectra of the doped 1L-WS2 reveal a significant enhancement of trions emission intensity over the excitonic emission at low temperature, indicating the stability of trion at low temperature. The temperature-dependent exciton-trion population dynamic has been modeled using the law of mass action of trion formation. These results shed light on the solution-based chemical doping in 1L-WS2 and its profound effect on the photoluminescence which is essential for the control of optical and electrical properties for optoelectronic applications

Criteria for performance evaluation of RC building frames using non-linear time history analysis for performance-based design

Displacement-based design (DBD) is emerging as the new trend for seismic design of buildings. Several displacement-based design procedures have been developed in recent times. The performances of buildings designed using these methods are usually evaluated by conducting non-linear time history analysis (NLTHA). The efficiency of performance assessment depends on proper non-linear material modelling, selection of proper earthquake records and their scaling and appropriate setting up of limit states (acceptance criteria). The present paper discusses the provisions in various seismic guidelines including ATC 63, FEMA P695 (2009) and PEER Centre report No.2010/05 and recent research findings regarding the above parameters. According to FEMA P695, only the far-field record set is required for collapse assessment as there are many unresolved issues concerning the characterization of near-fault hazard and ground motion effects. To verify this, the response spectra are plotted for 10 selected far-field and near-field ground motions and found that there is considerable increase in the response of long period structures when they are subjected to near-field pulses. Time history analysis done on a 15-storeyed frame (which is designed as per DBD) shows an increase in roof displacement of the order of two and inter-storey drift amplification of about 2.7 near the base, when near-field ground motions are used for performance assessment

Simulating the dynamic responses of Highway bridges for multiple vehicle presence effects

The paper investigates the dynamic amplification factors to be applied for critical loading events involving multiple vehicles in bridge design. Numerical simulation of dynamic responses of two typical highway bridges, a short span one and a medium to large span one, reported in the literature as part of the DIVINE research program was carried out for the purpose. During DIVINE field investigations, these bridges had responded very heavily to single truck passage to the extent that the current dynamic amplification factors in bridge design codes were exceeded. From the simulation studies it is observed that vehicles with air suspensions, generally supposed to induce lower dynamic loads compared to those with steel suspensions, are capable of generating amplified bridge responses whenever the combination of road profile and vehicle speed is capable of exciting the critical frequencies and there is condition of frequency matching between bridge and vehicle. Also, it was observed in the case of short span bridge that there can be many cycles of amplified bridge oscillations even when the vehicle is over the bridge, which may have implications in its fatigue life. Presence of multiple vehicles in bridge span reduced the dynamic amplification factors in case of both short span and medium span bridges, with the reduction being more pronounced near vehicle speeds capable of exciting critical vehicle frequencies. The reduction was more pronounced in the case of medium to large span bridge than for the one with short span

Imaginary Potential as a Counter of Delay Time for Wave Reflection from a 1D Random Potential

We show that the delay time distribution for wave reflection from a one-dimensional random potential is related directly to that of the reflection coefficient, derived with an arbitrarily small but uniform imaginary part added to the random potential. Physically, the reflection coefficient, being exponential in the time dwelt in the presence of the imaginary part, provides a natural counter for it. The delay time distribution then follows straightforwardly from our earlier results for the reflection coefficient, and coincides with the distribution obtained recently by Texier and Comtet [C.Texier and A. Comtet, Phys.Rev.Lett. {\bf 82}, 4220 (1999)],with all moments infinite. Delay time distribution for a random amplifying medium is then derived . In this case, however, all moments work out to be finite.Comment: 4 pages, RevTeX, replaced with added proof, figure and references. To appear in Phys. Rev. B Jan01 200

Cold cathode emission studies on topographically modified few layer and single layer MoS2 films

Nanostructured materials, such as carbon nanotubes, are excellent cold cathode emitters. Here, we report comparative field emission (FE) studies on topographically tailored few layer MoS2films consisting of ⟨0001⟩ plane perpendicular (⊥) to c-axis (i.e., edge terminated vertically aligned) along with planar few layer and monolayer (1L) MoS2films. FE measurements exhibited lower turn-on field Eto (defined as required applied electric field to emit current density of 10 μA/cm2) ∼4.5 V/μm and higher current density ∼1 mA/cm2, for edge terminated vertically aligned (ETVA) MoS2films. However, Eto magnitude for planar few layer and 1L MoS2films increased further to 5.7 and 11 V/μm, respectively, with one order decrease in emission current density. The observed differences in emission behavior, particularly for ETVA MoS2 is attributed to the high value of geometrical field enhancement factor (β), found to be ∼1064, resulting from the large confinement of localized electric field at edge exposed nanograins. Emission behavior of planar few layers and 1L MoS2films are explained under a two step emission mechanism. Our studies suggest that with further tailoring the microstructure of ultra thin ETVA MoS2films would result in elegant FE properties

Anomalous synchronization threshold in coupled logistic maps

We consider regular lattices of coupled chaotic maps. Depending on lattice size, there may exist a window in parameter space where complete synchronization is eventually attained after a transient regime. Close outside this window, an intermittent transition to synchronization occurs. While asymptotic transversal Lyapunov exponents allow to determine the synchronization threshold, the distribution of finite-time Lyapunov exponents, in the vicinity of the critical frontier, is expected to provide relevant information on phenomena such as intermittency. In this work we scrutinize the distribution of finite-time exponents when the local dynamics is ruled by the logistic map $x \mapsto 4x(1-x)$. We obtain a theoretical estimate for the distribution of finite-time exponents, that is markedly non-Gaussian. The existence of correlations, that spoil the central limit approximation, is shown to modify the typical intermittent bursting behavior. The present scenario could apply to a wider class of systems with different local dynamics and coupling schemes.Comment: 6 pages, 6 figure

A modular focal plane detector system for the heavy ion reaction analyzer at NSC, New Delhi

A detector system has been developed for the focal plane of the HIRA. It consists of two independent detectors, a low-pressure multiwire proportional counter (LP-MWPC) followed by a split-anode ionization detector. Details of the design and test results are presented. Using slow preamplifiers, the position resolution is ≥1 mm and the time resolution is estimated to be 1.5 ns for the LP-MWPC. The ionization detector gives 2.4% energy resolution for 150 MeV 28Si scattered off a gold target and the ΔZ/Z obtained for 28Si+27Al is 1/42 for Z=14. Some results for fusion and transfer studies for the 48Ti+58Ni and 28Si+68Zn systems, respectively, at energies around the Coulomb barrier, are presented to highlight the performance of the detector system

Dyons in N=4 Gauged Supergravity

We study monopole and dyon solutions to the equations of motion of the bosonic sector of N = 4 gauged supergravity in four dimensional space-time. A static, spherically symmetric ansatz for the metric, gauge fields, dilaton and axion leads to soliton solutions which, in the electrically charged case, have compact spatial sections. Both analytical and numerical results for the solutions are presented.Comment: 12 pages, 7 figures. Minor changes, references adde