28,317 research outputs found
Concentration and energy fluctuations in a critical polymer mixture
A semi-grand-canonical Monte Carlo algorithm is employed in conjunction with
the bond fluctuation model to investigate the critical properties of an
asymmetric binary (AB) polymer mixture. By applying the equal peak-weight
criterion to the concentration distribution, the coexistence curve separating
the A-rich and B-rich phases is identified as a function of temperature and
chemical potential. To locate the critical point of the model, the cumulant
intersection method is used. The accuracy of this approach for determining the
critical parameters of fluids is assessed. Attention is then focused on the
joint distribution function of the critical concentration and energy, which is
analysed using a mixed-field finite-size-scaling theory that takes due account
of the lack of symmetry between the coexisting phases. The essential Ising
character of the binary polymer critical point is confirmed by mapping the
critical scaling operator distributions onto independently known forms
appropriate to the 3D Ising universality class. In the process, estimates are
obtained for the field mixing parameters of the model which are compared both
with those yielded by a previous method, and with the predictions of a mean
field calculation.Comment: 17 pages Latex, 9 figures appended as uuencoded .gz tar fil
Wigner Crystallization in inhomogeneous one dimensional wires
We explore the theory of electrons confined by one dimensional power law
potentials. We calculate the density profile in the high density electron gas,
the low density Wigner crystal, and the intermediate regime. We extract the
momentum space wavefunction of the electron at the Fermi surface, which can be
measured in experiments on tunneling between parallel wires. The onset of
localization leads to a dramatic broadening of the momentum space wavefunction
together with pronounced sharpening (in energy) of the tunneling spectrum.Comment: 11 pages, 10 figures, RevTeX4: v2. Revised+Expande
Mobile Phone Power Amplifier Linearity and Efficiency Enhancement Using Digital Predistortion
The new generation mobile communication systems using spectrum efficient linear modulation schemes (QPSK,8PSK,QAM)need linear power amplifiers in the transmission path to have good ACPR and EVM values. Linearization methods can be used to increase the linearity of the power amplifiers (PA).However,it is not reasonable o use complicated,power consuming and high cost systems. This paper presents a digital predistortion implementation for WCDMA signals using an FPGA (Field Programmable Gate Array)as DSP and investigates the application of this system in handsets.The method applied requires minimum change in the conventional transmitter path configuration but considerable PAE improvement can be achieved
Performance results of a 300-degree linear phase modulator for spaceborne communications applications
A phase modulator capable of large linear phase deviation, low loss, and wide band operation with good thermal stability was developed for deep space spacecraft transponder (DST) applications at X-band (8.415 GHz) and Ka-band (32 GHz) downlinks. The design uses a two-stage circulator-coupled reflection phase shifter with constant gamma hyperabrupt varactors and an efficient modulator driver circuit to obtain a phase deviation of +/-2.5 rad with better than 8 percent linearity. The measured insertion loss is 6.6 dB +/- 0.35 dB at 8415 MHz. Measured carrier and relative sideband amplitudes resulting from phase modulation by sine wave and square modulating functions agree well with the predicted results
The Boltzmann Equation in Classical Yang-Mills Theory
We give a detailed derivation of the Boltzmann equation, and in particular
its collision integral, in classical field theory. We first carry this out in a
scalar theory with both cubic and quartic interactions and subsequently in a
Yang-Mills theory. Our method is not relied on a doubling of the fields, rather
it is based on a diagrammatic approach representing the classical solution to
the problem.Comment: 24 pages, 7 figures; v2: typos corrected, reference added, published
in Eur. Phys. J.
Interference of Mycobacterium tuberculosis with macrophage responses
Tuberculosis, caused by Mycobacterium tuberculosis, has become an important health and economic burden, with more than four thousand people succumbing to the disease every day. Thus, there is an urgent need to understand the molecular basis of this pathogen's success in causing disease in humans, in order to develop new drugs superior to conventional drugs available at present. One reason why M. tuberculosis is such a dangerous microbe lies within its ability to survive within infected hosts, thereby efficiently circumventing host immune responses. Over the past few years, a number of mechanisms have been unravelled that are utilized by M. tuberculosis to survive within hosts and to avoid immune defence mechanisms. Several of these mechanisms have been described in this communication that may be useful for the development of novel compounds to treat tuberculosis
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