Design of Fixed-Point Processing Based LDPC Codes Using EXIT Charts

Logarithmic representation of the variables processed by iterative decoding algorithms of Low-Density Parity-Check (LDPC) codes are attractive, since the resultant reduced dynamic range of its Logarithmic Likelihood Ratios (LLRs) allows a Fixed Point (FP) operand-representation to be used. This FP representation has a lower computational complexity than a floating point representation, allowing the decoder's hardware to have a low energy consumption, which depends on the Operand-Width (OW) of the LLRs. However, if the OW is too low, then an inevitable performance degradation will be introduced. Therefore it is desirable to determine the minimum OW that does not impose a significant performance degradation. Previous efforts have advocated different OWs based on results obtained using time-consuming Bit Error Ratio (BER) simulations. However, these simulations are extremely time consuming, owing to the requirement of considering a range of channel Signal-to-Noise Ratios (SNRs). Therefore, in this paper, we propose the employment of EXtrinsic Information Transfer (EXIT) charts to overcome this drawback. Furthermore, EXIT charts analysis has the additional benefit of offering insights into the specific causes of the performance degradations encountered. Finally, a FP scheme having an overall OW = 6 is proposed for the implementation of the Min-Sum Algorithm (MSA)

Ab-initio density functional studies of stepped TaC surfaces

We report on density functional total energy calculations of the step formation and interaction energies for vicinal TaC(001) surfaces. Our calculations show that double and triple-height steps are favored over single-height steps for a given vicinal orientation, which is in agreement with recent experimental observations. We provide a description of steps in terms of atomic displacements and charge localization and predict an experimentally observable rumpled structure of the step-edges, where the Ta atoms undergo larger displacements compared to the C atoms.Comment: 4 pages, 4 figure

Lambda polarization in pp -> p\Lambda K^+ \pi^+\pi^-\pi^+\pi^-

We show that there is a correlation between the invariant mass of the produced \Lambda K^+, \Lambda K^+\pi^+\pi^- or \Lambda K^+ \pi^+\pi^-\pi^+\pi^- system in the exclusive reaction pp\to p\Lambda K^+\pi^+\pi^-\pi^+\pi^- and the longitudinal or transverse momentum of $\Lambda$. Together with the longitudinal and transverse momentum dependence of Lambda polarization observed in inclusive reactions, such a correlation implies a dependence of Lambda polarization on these invariant masses. The qualitative features of this dependence are consistent with the recent observation by E766 collaboration at BNL. A quantitative estimation has been made using an event generator for $pp$ collisions. A detailed comparison with the data is made.Comment: 10 pages with 3 figures, submitted to J. Phys.

Microscopic three-body forces and kaon condensation in cold neutrino-trapped matter

We investigate the composition and the equation of state of the kaon condensed phase in neutrino-free and neutrino-trapped star matter within the framework of the Brueckner-Hartree-Fock approach with three-body forces. We find that neutrino trapping shifts the onset density of kaon condensation to a larger baryon density, and reduces considerably the kaon abundance. As a consequence, when kaons are allowed, the equation of state of neutrino-trapped star matter becomes stiffer than the one of neutrino free matter. The effects of different three-body forces are compared and discussed. Neutrino trapping turns out to weaken the role played by the symmetry energy in determining the composition of stellar matter, and thus reduces the difference between the results obtained by using different three-body forces.Comment: 9 pages, 7 figures, accepted in Phys. Rev.

Spin Polarized Asymmetric Nuclear Matter and Neutron Star Matter Within the Lowest Order Constrained Variational Method

In this paper, we calculate properties of the spin polarized asymmetrical nuclear matter and neutron star matter, using the lowest order constrained variational (LOCV) method with the $AV_{18}$, $Reid93$, $UV_{14}$ and $AV_{14}$ potentials. According to our results, the spontaneous phase transition to a ferromagnetic state in the asymmetrical nuclear matter as well as neutron star matter do not occur.Comment: 21 pages, 11 figure

Hot Nuclear Matter Equation of State with a Three-body Force

The finite temperature Brueckner-Hartree-Fock approach is extended by introducing a microscopic three-body force. In the framework of the extended model, the equation of state of hot asymmetric nuclear matter and its isospin dependence have been investigated. The critical temperature of liquid-gas phase transition for symmetric nuclear matter has been calculated and compared with other predictions. It turns out that the three-body force gives a repulsive contribution to the equation of state which is stronger at higher density and as a consequence reduces the critical temperature of liquid-gas phase transition. The calculated energy per nucleon of hot asymmetric nuclear matter is shown to satisfy a simple quadratic dependence on asymmetric parameter $\beta$ as in the zero-temperature case. The symmetry energy and its density dependence have been obtained and discussed. Our results show that the three-body force affects strongly the high-density behavior of the symmetry energy and makes the symmetry energy more sensitive to the variation of temperature. The temperature dependence and the isospin dependence of other physical quantities, such as the proton and neutron single particle potentials and effective masses are also studied. Due to the additional repulsion produced by the three-body force contribution, the proton and neutron single particle potentials are correspondingly enhanced as similar to the zero-temperature case.Comment: 16 pages, 8 figure

A method to find unstable periodic orbits for the diamagnetic Kepler Problem

A method to determine the admissibility of symbolic sequences and to find the unstable periodic orbits corresponding to allowed symbolic sequences for the diamagnetic Kepler problem is proposed by using the ordering of stable and unstable manifolds. By investigating the unstable periodic orbits up to length 6, a one to one correspondence between the unstable periodic orbits and their corresponding symbolic sequences is shown under the system symmetry decomposition