41,825 research outputs found
Analytical Bit Error Rate Performance of DS-CDMA Ad Hoc Networks using Large Area Synchronous Spreading Sequences
The performance of large area synchronous (LAS) direct sequence code division multiple access (DS-CDMA) assisted ad hoc networks is investigated in the context of a single-hop infinite mesh of rectilinearly located ad hoc nodes. It is shown that LAS DS-CDMA exhibits a significantly better performance than the family of traditional spreading sequences used in a quasisynchronous DS-CDMA scenario having a low number of resolvable multipath components and a sufficiently high number of RAKE receiver branches. The benefits of LAS codes in ad hoc networks are multifold: (i) Their performance is noise-limited, rather than interference-limited, provided that the multipath and multi-user interference arrives within their interference free window. (ii) Under the same conditions LAS codes are robust against the ânearâfarâ effects imposed by ad hoc networks operating without base-station-aided power control, without accurate synchronisation and without implementationally complex interference cancellers
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Machine Learning Optimization of p-Type Transparent Conducting Films
p-Type transparent conducting materials (p-TCMs) are important components of optoelectronic devices including solar cells, photodetectors, displays, and flexible sensors. Cu-Zn-S thin films prepared by chemical bath deposition (CBD) can have both high transparency in the visible range (>80%) as well as excellent hole conductivity (>1000 S cm-1). However, the interplay between the deposition parameters in the CBD process (metal and sulfur precursor concentrations, temperature, pH, complexing agents, etc.) creates a multidimensional parameter space such that optimization for a specific application is challenging and time-consuming. Here we show that strategic design of experiment combined with machine learning (ML) allows for the efficient optimization of p-TCM performance. The approach is guided by a figure of merit (FOM) calculated from the film conductivity and optical transmission in the desired spectral range. A specific example is shown using two steps of optimization using a selected subset of four experimental CBD factors. The ML model is based on support vector regression employing a radial basis function as the kernel function. 10-fold cross-validation was performed to mitigate overfitting. After the first round of optimization, predicted areas in the parameter space with maximal FOMs were selected for a second round of optimization. Films with optimal FOMs were incorporated into heterojunction solar cells and transparent photodiodes. The optimization approach shown here will be generally applicable to any materials synthesis process with multiple parameters
Quantum state engineering with flux-biased Josephson phase qubits by Stark-chirped rapid adiabatic passages
In this paper, the scheme of quantum computing based on Stark chirped rapid
adiabatic passage (SCRAP) technique [L. F. Wei et al., Phys. Rev. Lett. 100,
113601 (2008)] is extensively applied to implement the quantum-state
manipulations in the flux-biased Josephson phase qubits. The broken-parity
symmetries of bound states in flux-biased Josephson junctions are utilized to
conveniently generate the desirable Stark-shifts. Then, assisted by various
transition pulses universal quantum logic gates as well as arbitrary
quantum-state preparations could be implemented. Compared with the usual
PI-pulses operations widely used in the experiments, the adiabatic population
passage proposed here is insensitive the details of the applied pulses and thus
the desirable population transfers could be satisfyingly implemented. The
experimental feasibility of the proposal is also discussed.Comment: 9 pages, 4 figure
Einstein Equations and MOND Theory from Debye Entropic Gravity
Verlinde's proposal on the entropic origin of gravity is based strongly on
the assumption that the equipartition law of energy holds on the holographic
screen induced by the mass distribution of the system. However, from the theory
of statistical mechanics we know that the equipartition law of energy does not
hold in the limit of very low temperature. Inspired by the Debye model for the
equipartition law of energy in statistical thermodynamics and adopting the
viewpoint that gravitational systems can be regarded as a thermodynamical
system, we modify Einstein field equations. We also perform the study for
Poisson equation and modified Newtonian dynamics (MOND). Interestingly enough,
we find that the origin of the MOND theory can be understood from Debye
entropic gravity perspective. Thus our study may fill in the gap existing in
the literature understanding the theoretical origin of MOND theory. In the
limit of high temperature our results reduce to their respective standard
gravitational equations.Comment: 8 pages, no figures. Accepted for publication in JCA
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