The Experts below are selected from a list of 83370 Experts worldwide ranked by ideXlab platform
E K Warburton - One of the best experts on this subject based on the ideXlab platform.
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first forbidden beta decay in the lead region and mesonic enhancement of the weak axial current
Physical Review C, 1991Co-Authors: E K WarburtonAbstract:A shell-model study is made of first-forbidden \ensuremath{\beta} decay and related processes in A=205--212 nuclei. The interactions used are modifications of the Kuo-Herling realistic effective interactions for particles above and holes below $^{208}\mathrm{Pb}$ and a cross-shell G-Matrix interaction connecting these two. Large-scale diagonalizations are made of 1p-1h excitations across the double-shell closure at $^{208}\mathrm{Pb}$. The calculations of the first-forbidden rates use effective single-particle Matrix elements which incorporate core polarization of the final state to first order. All first-order initial state 1p-1h admixtures are included explicitly in the diagonalization. A least-squares fit of theory to experiment for eighteen \ensuremath{\Delta}J=0 and 1 decay rates was made with two unknowns: (1) an enhancement factor ${\mathrm{\ensuremath{\epsilon}}}_{\mathrm{mec}}$ for the rank Zero Matrix element of ${\ensuremath{\gamma}}_{5}$, and (2) an overall scaling factor for the rank one component of the decay rate. A good fit is achieved yielding ${\mathrm{\ensuremath{\epsilon}}}_{\mathrm{mec}}$=2.01\ifmmode\pm\else\textpm\fi{}0.05 and a rank-one scaling factor of 0.97\ifmmode\pm\else\textpm\fi{}0.06. The agreement of the latter with unity indicates a satisfactory understanding of the rank-one component of the decay. The result ${\mathrm{\ensuremath{\epsilon}}}_{\mathrm{mec}}$=2.01\ifmmode\pm\else\textpm\fi{}0.05 indicates an enhancement of the Matrix element of ${\ensuremath{\gamma}}_{5}$ by 100% over the impulse approximation. A 40% effect is predicted from meson exchange. Thus, a deficiency in the meson-exchange calculation or some further as-yet-unforeseen contribution is suggested. Predictions for twenty other decays in A=205--211 nuclei are compared to experiment and found to be in good general agreement. A calculation of the capture of neutrinos by $^{205}\mathrm{Tl}$ is described in detail.
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mesonic enhancement of the weak axial vector current evaluated from beta decay in the lead region
Physical Review Letters, 1991Co-Authors: E K WarburtonAbstract:A shell-model study is made of first-forbidden {beta} decay in {ital A}=205--212 nuclei. A least-squares fit for eighteen {Delta}{ital J}=0 and 1 decays gave a scaling factor for the rank-one contributions of 0.97{plus minus}0.06, i.e., agreement with experiment, and an enhancement factor {epsilon}{sub MEC} for the rank-Zero Matrix element of {gamma}{sub 5} of 2.01{plus minus}0.05, indicating an enhancement by 100% over the impulse approximation. A 40% effect is predicted from meson exchange. Thus, a deficiency in the meson-exchange calculation or some further unforeseen effect is suggested.
Hsiechia Chang - One of the best experts on this subject based on the ideXlab platform.
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an ldpc decoder chip based on self routing network for ieee 802 16e applications
IEEE Journal of Solid-state Circuits, 2008Co-Authors: Chihlung Chen, Hsiechia ChangAbstract:An LDPC decoder chip fully compliant to IEEE 802.16e applications is presented. Since the parity check Matrix can be decomposed into sub-matrices which are either a Zero-Matrix or a cyclic shifted Matrix, a phase-overlapping message passing scheme is applied to update messages immediately, leading to enhance decoding throughput. With only one shifter-based permutation structure, a self-routing switch network is proposed to merge 19 different sub-Matrix sizes as defined in IEEE 802.16e and enable parallel message to be routed without congestion. Fabricated in the 90 nm 1P9M CMOS process, this chip achieves 105 Mb/s at 20 iterations while decoding the rate-5/6 2304-bit code at 150 MHz operation frequency. To meet the maximum data rate in IEEE 802.16e, this chip operates at 109 MHz frequency and dissipates 186 mW at 1.0 V supply.
Patrick Otto Ludl - One of the best experts on this subject based on the ideXlab platform.
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two parameter neutrino mass matrices with two texture Zeros
Journal of Physics G, 2013Co-Authors: W Grimus, Patrick Otto LudlAbstract:We reanalyze Majorana neutrino mass matrices with two texture Zeros, by searching for viable hybrid textures in which the non-Zero Matrix elements of have simple ratios. Referring to the classification scheme of Frampton, Glashow and Marfatia, we find that the mass Matrix denoted by A1 allows the ratios and . There are analogous ratios for texture A2. With these two hybrid textures, one obtains, for instance, good agreement with the data if one computes the three mixing angles in terms of the experimentally determined mass-squared differences and . We could not find viable hybrid textures based on mass matrices different from those of cases A1 and A2.
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two parameter neutrino mass matrices with two texture Zeros
arXiv: High Energy Physics - Phenomenology, 2012Co-Authors: W Grimus, Patrick Otto LudlAbstract:We reanalyse Majorana-neutrino mass matrices M_nu with two texture Zeros, by searching for viable hybrid textures in which the non-Zero Matrix elements of M_nu have simple ratios. Referring to the classification scheme of Frampton, Glashow and Marfatia, we find that the mass Matrix denoted by A1 allows the ratios (M_nu)_{mu mu} : (Mnu)_{tau tau} = 1:1 and (M_nu)_{e tau} : (Mnu)_{mu tau} = 1:2. There are analogous ratios for texture A2. With these two hybrid textures, one obtains, for instance, good agreement with the data if one computes the three mixing angles in terms of the experimentally determined mass-squared differences Delta m^2_21 and Delta m^2_31. We could not find viable hybrid textures based on mass matrices different from those of cases A1 and A2.
Clive Elphick - One of the best experts on this subject based on the ideXlab platform.
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New spectral bounds on the chromatic number encompassing all eigenvalues of the adjacency Matrix
The Electronic Journal of Combinatorics, 2013Co-Authors: Pawel Wocjan, Clive ElphickAbstract:The purpose of this article is to improve existing lower bounds on the chromatic number $\chi$. Let $\mu_1,\ldots,\mu_n$ be the eigenvalues of the adjacency Matrix sorted in non-increasing order. First, we prove the lower bound $\chi \ge 1 + \max_m\{\sum_{i=1}^m \mu_i / -\sum_{i=1}^m \mu_{n - i +1}\}$ for $m=1,\ldots,n-1$. This generalizes the Hoffman lower bound which only involves the maximum and minimum eigenvalues, i.e., the case $m=1$. We provide several examples for which the new bound exceeds the Hoffman lower bound. Second, we conjecture the lower bound $\chi \ge 1 + s^+ / s^-$, where $s^+$ and $s^-$ are the sums of the squares of positive and negative eigenvalues, respectively. To corroborate this conjecture, we prove the bound $\chi \ge s^+/s^-$. We show that the conjectured lower bound is true for several families of graphs. We also performed various searches for a counter-example, but none was found. Our proofs rely on a new technique of considering a family of conjugates of the adjacency Matrix, which add to the Zero Matrix, and use majorization of spectra of self-adjoint matrices. We also show that the above bounds are actually lower bounds on the normalized orthogonal rank of a graph, which is always less than or equal to the chromatic number. The normalized orthogonal rank is the minimum dimension making it possible to assign vectors with entries of modulus one to the vertices such that two such vectors are orthogonal if the corresponding vertices are connected. All these bounds are also valid when we replace the adjacency Matrix $A$ by $W * A$ where $W$ is an arbitrary self-adjoint Matrix and $*$ denotes the Schur product, that is, entrywise product of $W$ and $A$.
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New spectral bounds on the chromatic number encompassing all eigenvalues of the adjacency Matrix
arXiv: Combinatorics, 2012Co-Authors: Pawel Wocjan, Clive ElphickAbstract:The purpose of this article is to improve existing lower bounds on the chromatic number chi. Let mu_1,...,mu_n be the eigenvalues of the adjacency Matrix sorted in non-increasing order. First, we prove the lower bound chi >= 1 + max_m {sum_{i=1}^m mu_i / - sum_{i=1}^m mu_{n-i+1}} for m=1,...,n-1. This generalizes the Hoffman lower bound which only involves the maximum and minimum eigenvalues, i.e., the case $m=1$. We provide several examples for which the new bound exceeds the {\sc Hoffman} lower bound. Second, we conjecture the lower bound chi >= 1 + S^+ / S^-, where S^+ and S^- are the sums of the squares of positive and negative eigenvalues, respectively. To corroborate this conjecture, we prove the weaker bound chi >= S^+/S^-. We show that the conjectured lower bound is tight for several families of graphs. We also performed various searches for a counter-example, but none was found. Our proofs rely on a new technique of converting the adjacency Matrix into the Zero Matrix by conjugating with unitary matrices and use majorization of spectra of self-adjoint matrices. We also show that the above bounds are actually lower bounds on the normalized orthogonal rank of a graph, which is always less than or equal to the chromatic number. The normalized orthogonal rank is the minimum dimension making it possible to assign vectors with entries of modulus one to the vertices such that two such vectors are orthogonal if the corresponding vertices are connected. All these bounds are also valid when we replace the adjacency Matrix A by W * A where W is an arbitrary self-adjoint Matrix and * denotes the Schur product, that is, entrywise product of W and A.
Chihlung Chen - One of the best experts on this subject based on the ideXlab platform.
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an ldpc decoder chip based on self routing network for ieee 802 16e applications
IEEE Journal of Solid-state Circuits, 2008Co-Authors: Chihlung Chen, Hsiechia ChangAbstract:An LDPC decoder chip fully compliant to IEEE 802.16e applications is presented. Since the parity check Matrix can be decomposed into sub-matrices which are either a Zero-Matrix or a cyclic shifted Matrix, a phase-overlapping message passing scheme is applied to update messages immediately, leading to enhance decoding throughput. With only one shifter-based permutation structure, a self-routing switch network is proposed to merge 19 different sub-Matrix sizes as defined in IEEE 802.16e and enable parallel message to be routed without congestion. Fabricated in the 90 nm 1P9M CMOS process, this chip achieves 105 Mb/s at 20 iterations while decoding the rate-5/6 2304-bit code at 150 MHz operation frequency. To meet the maximum data rate in IEEE 802.16e, this chip operates at 109 MHz frequency and dissipates 186 mW at 1.0 V supply.
