27 research outputs found
Study of one-dimensional nature of (Sr,Ba)_2Cu(PO_4)_2 and BaCuP_2O_7 via 31P NMR
The magnetic behavior of the low-dimensional phosphates (Sr,Ba)_2 Cu(PO_4)_2
and BaCuP_2O_7 was investigated by means of magnetic susceptibility and ^{31}P
nuclear magnetic resonance (NMR) measurements. We present here the NMR shift
K(T), the spin-lattice 1/T_1 and spin-spin 1/T_2 relaxation-rate data over a
wide temperature range 0.02 K < T < 300 K. The T-dependence of the NMR K(T) is
well described by the S=1/2 Heisenberg antiferromagnetic chain model with an
intrachain exchange of J/k_B = 165 K, 151 K, and 108 K in Sr_2Cu(PO_4)_2,
Ba_2Cu(PO_4)_2, and BaCuP_2O_7, respectively. Our measurements suggest the
presence of magnetic ordering at 0.8 K in BaCuP_2O_7 (J/k_B = 108 K). For all
the samples, we find that 1/T_1 is nearly T-independent at low-temperatures (1
K < T < 10 K), which is theoretically expected for 1D chains when relaxation is
dominated by fluctuations of the staggered susceptibility. At high
temperatures, 1/T_1 varies nearly linearly with temperature
Aspects of Strangeness -1 Meson-Baryon Scattering
We consider meson-baryon interactions in S-wave with strangeness -1. This is
a sector populated by plenty of resonances interacting in several two-body
coupled channels. We consider a large set of experimental data, where the
recent experiments are remarkably accurate. This requires a sound theoretical
description to account for all the data and we employ Unitary Chiral
Perturbation Theory up to and including O(p^2). The spectroscopy of our
solutions is studied within this approach, discussing the rise from the pole
content of two \Lambda(1405) resonances and of the \Lambda(1670),
\Lambda(1800), \Sigma(1480), \Sigma(1620) and \Sigma(1750). We finally argue
about our preferred fit.Comment: 6 figures, 3 figures, talk given in the IVth International Conference
on Quarks and Nuclear Physics (QNP06), Madrid June 5th and 10th, 2006. One
reference is update
Optimization of Pinned Photodiode Pixels for High-Speed Time of Flight Applications
We discuss optimizations of pinned photodiode (PPD) pixels for indirect time of flight sensors. We focus on the transfer-gate and dumping gate regions optimization, on the PPD dimension and shape to assure fast lateral charge transfer and on the epitaxial layer thickness for a good tradeoff between fast vertical charge transfer and high quantum efficiency at near infrared region. The overall performance of the pixel is quantified by the demodulation contrast of the pixel at specific frequencies. The operation frequency of the device is determined by the required ambiguity range of the application and the required distance noise. In order to reach a reasonable distance noise, the pixel needs to allow modulation frequencies up to 100 MHz. In this paper, we present TCAD simulation and experimental data on demodulation contrast, impulse response time, and quantum efficiency of pixels. We introduce a setup for impulse response measurement and we compare this to the demodulation contrast. We also discuss the optimization of the dump gate and dump diffusion. With the best pixel we measured a quantum efficiency of about 45% at 850 nm, a demodulation contrast of 47% at 80 MHz, and an impulse response time < 5 ns
Recommended from our members
Hyperon-nucleon interaction and meson exchange
We present first results of our general program which is to construct meson-exchange potentials for hadronic systems involving stange particles, i.e. for KN and AN. We proceed along the same guidelines which have been successfully applied in deriving the (latest version of the) Bonn NN potential, namely to keep the important recoil and nonlocal structure and to use a comprehensive set of diagrams without introducing any fictitious contribution. For KN we show that single vector-meson (..omega..,p) exchange already provides a fair description of the data except for the isospin-1 P/sub 3/2/ wave. This partial wave is remarkably improved by adding a specific higher-order process involving ..delta..K intermediate states. For the ..lambda..N system we demonstrate the inadequacy of a nonrelativistic treatment of the ..lambda..N interaction and point to the strong interplay between K and K*-exchange in the tensor channel, which is even stronger than for ..pi..- and p-exchange in the NN system