3,546 research outputs found
Dirac and Klein-Gordon particles in one-dimensional periodic potentials
We evaluate the dispersion relation for massless fermions, described by the
Dirac equation, and for zero-spin bosons, described by the Klein-Gordon
equation, moving in two dimensions and in the presence of a one-dimensional
periodic potential. For massless fermions the dispersion relation shows a zero
gap for carriers with zero momentum in the direction parallel to the barriers
in agreement with the well-known "Klein paradox". Numerical results for the
energy spectrum and the density of states are presented. Those for fermions are
appropriate to graphene in which carriers behave relativistically with the
"light speed" replaced by the Fermi velocity. In addition, we evaluate the
transmission through a finite number of barriers for fermions and zero-spin
bosons and relate it with that through a superlattice.Comment: 9 pages, 12 figure
PULSED ELECTRON BEAM ANNEALING OF As AND B IMPLANTED SILICON
p-type (100) silicon wafers have been implanted either by As or B ions at 20 and 200 keV energies and doses of 1016cm-2. Pulsed electron beam annealing has been performed with fluences of 1.1 and 1.4 J/cm2 using a mean electron energy of 15 keV. The pulse duration was 50 ns. The annealed layers have been investigated by Rutherford backscattering under random and channeling conditions and by S.I.M.S. profiling. Good crystal regrowth and high dopant activation occur in all cases except for the 200 keV Boron implant. Impurities redistribution is observed but no significant segregation effects appear. The experimental profiles are in good agreement with a diffusion model using a modified green function solution and taking into account dopant diffusion in liquid phase and the computed melt front location. The deduced diffusion coefficient are in the 5.10-5cm2/s range for boron and 2.10-4cm2/s range for arsenic
Single chargino production via gluon-gluon fusion in a supersymmetric theory with an explicit R-parity violation
We studied the production of single chargino
accompanied by lepton via gluon-gluon fusion at the LHC. The
numerical analysis of their production rates is carried out in the mSUGRA
scenario with some typical parameter sets. The results show that the cross
sections of the productions via gluon-gluon
collision are in the order of femto barn quantitatively at the
CERN LHC, and can be competitive with production mechanism via quark-antiquark
annihilation process.Comment: LaTex file, 18 pages, 4 EPS file
Two-loop neutrino masses with large R-parity violating interactions in supersymmetry
We attempt to reconcile large trilinear R-parity violating interactions in a
supersymmetric (SUSY) theory with the observed pattern of neutrino masses and
mixing. We show that, with a restricted number of such interaction terms with
the -type couplings in the range (0.1-1.0), it is possible to forbid
one-loop contributions to the neutrino mass matrix. This is illustrated with
the help of a `working example' where an econnomic choice of SUSY parameters is
made, with three non-vanishing and `large' R-parity violating terms in the
superpotential. The two-loop contributions in such a case can not only generate
the masses in the requisite order but can also lead us to specific allowed
regions of the parameter space.Comment: Revised version, 25 pages, 16 figure
Confirmation of the \eps -- \eiso (Amati) relation from the X-ray flash XRF 050416A observed by Swift/BAT
We report Swift Burst Alert Telescope (BAT) observations of the X-ray Flash
(XRF) XRF 050416A. The fluence ratio between the 15-25 keV and 25-50 keV energy
bands of this event is 1.5, thus making it the softest gamma-ray burst (GRB)
observed by BAT so far. The spectrum is well fitted by the Band function with
E^{\rm obs}_{\rm peak} of 15.0_{-2.7}^{+2.3} keV. Assuming the redshift of the
host galaxy (z = 0.6535), the isotropic-equivalent radiated energy E_{\rm iso}
and the peak energy at the GRB rest frame (E^{\rm src}_{\rm peak}) of XRF
050416A are not only consistent with the correlation found by Amati et al. and
extended to XRFs by Sakamoto et al., but also fill-in the gap of this relation
around the 30 - 80 keV range of E^{\rm src}_{\rm peak}. This result tightens
the validity of the E^{\rm src}_{\rm peak} - E_{\rm iso} relation from XRFs to
GRBs.
We also find that the jet break time estimated using the empirical relation
between E^{\rm src}_{\rm peak} and the collimation corrected energy E_{\gamma}
is inconsistent with the afterglow observation by Swift X-ray Telescope. This
could be due to the extra external shock emission overlaid around the jet break
time or to the non existence of a jet break feature for XRF, which might be a
further challenging for GRB jet emission, models and XRF/GRB unification
scenarios.Comment: 16 pages, 4 figures; accepted for publication in ApJ
Constraining R-parity violating couplings from B --> PP decays using QCD improved factorization method
We investigate the role of R-parity violating interaction in the non-leptonic
decays of B mesons into two light mesons B --> PP. The decay amplitudes are
calculated using the QCD improved factorization method. Using the combined data
on B decays from BaBar, Belle and CLEO, we obtain strong constraints on the
various products of R-parity violating couplings. Many of these new constraints
are stronger than the existing bounds.Comment: 19 pages including two eps figure
A Policy Maker’s Guide to Designing Payments for Ecosystem Services
Over the past five years, there has been increasing interest around the globe in payment schemes for the provision of ecosystem services, such as water purification, carbon sequestration, flood control, etc. Written for an Asian Development Bank project in China, this report provides a user-friendly guide to designing payments for the provision of ecosystem services. Part I explains the different types of ecosystem services, different ways of assessing their value, and why they are traditionally under-protected by law and policy. This is followed by an analysis of when payments for services are a preferable approach to other policy instruments. Part II explains the design issues underlying payments for services. These include identification of the service as well as potential buyers and sellers, the level of service needed, payment timing, payment type, and risk allocation. Part II contains a detailed analysis of the different types of payment mechanisms, ranging from general subsidy and certification to mitigation and offset payments. Part III explores the challenges to designing a payment scheme. These include the ability to monitor service provision, secure property rights, perverse incentives, supporting institutions, and poverty alleviation
Autocorrelation analysis for the unbiased determination of power-law exponents in single-quantum-dot blinking
We present an unbiased and robust analysis method for power-law blinking
statistics in the photoluminescence of single nano-emitters, allowing us to
extract both the bright- and dark-state power-law exponents from the emitters'
intensity autocorrelation functions. As opposed to the widely-used threshold
method, our technique therefore does not require discriminating the emission
levels of bright and dark states in the experimental intensity timetraces. We
rely on the simultaneous recording of 450 emission timetraces of single
CdSe/CdS core/shell quantum dots at a frame rate of 250 Hz with single photon
sensitivity. Under these conditions, our approach can determine ON and OFF
power-law exponents with a precision of 3% from a comparison to numerical
simulations, even for shot-noise-dominated emission signals with an average
intensity below 1 photon per frame and per quantum dot. These capabilities pave
the way for the unbiased, threshold-free determination of blinking power-law
exponents at the micro-second timescale
Experimental study of a liquid Xenon PET prototype module
A detector using liquid Xenon in the scintillation mode is studied for
Positron Emission Tomography (PET). The specific design aims at taking full
advantage of the liquid Xenon properties. It does feature a promising
insensitive to any parallax effect. This work reports on the performances of
the first LXe prototype module, equipped with a position sensitive PMT
operating in the VUV range (178 nm).Comment: Proc. of the 7th International Workshops on Radiation Imaging
Detectors (IWORID-7), Grenoble, France 4-7 July 200
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