8,074 research outputs found
A polarised QCD condensate: nu p elastic scattering as a probe of U_A(1) dynamics
U_A(1) dynamics have the potential to induce a polarised condensate inside a
nucleon. The formation of this condensate is related to the realisation of
U_A(1) symmetry breaking by tunneling processes such as instantons. If it is
present, the polarised condensate induces a term in g_1 which has support only
at x=0. Tunneling processes then induce a net transfer of ``spin'' from finite
x to x=0. The polarised condensate may be measured by comparing the
flavour-singlet axial charges which are extracted from polarised deep inelastic
and nu p elastic scattering experiments.Comment: 13 pages LaTeX, Section 3 improved to include discussion of the 3
flavour quark instanton interaction; to appear in Mod. Phys. Lett.
Electron and Phonon Thermal Waves in Semiconductors: an Application to Photothermal Effects
The electron and phonon temperature distribution function are calculated in
semiconductors. We solved the coupled one-dimensional heat-diffussion equations
in the linear approximation in which the physical parameters on the sample are
independent of the temperature. We also consider the heat flux at the surface
of the semiconductor as a boundary condition for each electron and phonon
systems instead of using a fixed temperature. From this, we obtain an
expression for electron and phonon temperature respectively. The
characterization of the thermal waves properties is duscussed and some
practical procedures for this purpose provide us information about the electron
and phonon thermal parameters.Comment: 12 pages, amstex and amssymb macro package (LaTeX2e edition
Jet Modification in a Brick of QGP Matter
We have implemented the LPM effect into a microscopic transport model with
partonic degrees of freedom by following the algorithm of Zapp & Wiedemann. The
Landau-Pomeranchuk-Migdal (LPM) effect is a quantum interference process that
modifies the emission of radiation in the presence of a dense medium. In QCD
this results in a quadratic length dependence for radiative energy loss. This
is an important effect for the modification of jets by their passage through
the QGP.
We verify the leading parton energy loss in the model against the leading
order Baier-Dokshitzer-Mueller-Peigne-Schiff-Zakharov (BDMPS-Z) result.
We apply our model to the recent observations of the modification of di-jets
at the LHC.Comment: Presented at Panic 1
Towards an understanding of nucleon spin structure: from hard to soft scales
The workshop "The Helicity Structure of the Nucleon" (BNL June 5, 2006) was
organized as part of the 2006 RHIC & AGS Users' Meeting to review the status of
the spin problem and future directions. The presentations can be found at
http://www.phenix.bnl.gov/WWW/publish/caidala/UsersHelicityWorkshop2006/ .
Recent data suggests small polarized glue and strangeness in the proton. Here
we present a personal summary of the main results and presentations. What is
new and exciting in the data, and what might this tell us about the structure
of the proton ?Comment: 20 pages, to appear in Int. J. Mod. Phys.
Slow imbalance relaxation and thermoelectric transport in graphene
We compute the electronic component of the thermal conductivity (TC) and the
thermoelectric power (TEP) of monolayer graphene, within the hydrodynamic
regime, taking into account the slow rate of carrier population imbalance
relaxation. Interband electron-hole generation and recombination processes are
inefficient due to the non-decaying nature of the relativistic energy spectrum.
As a result, a population imbalance of the conduction and valence bands is
generically induced upon the application of a thermal gradient. We show that
the thermoelectric response of a graphene monolayer depends upon the ratio of
the sample length to an intrinsic length scale l_Q, set by the imbalance
relaxation rate. At the same time, we incorporate the crucial influence of the
metallic contacts required for the thermopower measurement (under open circuit
boundary conditions), since carrier exchange with the contacts also relaxes the
imbalance. These effects are especially pronounced for clean graphene, where
the thermoelectric transport is limited exclusively by intercarrier collisions.
For specimens shorter than l_Q, the population imbalance extends throughout the
sample; the TC and TEP asymptote toward their zero imbalance relaxation limits.
In the opposite limit of a graphene slab longer than l_Q, at non-zero doping
the TC and TEP approach intrinsic values characteristic of the infinite
imbalance relaxation limit. Samples of intermediate (long) length in the doped
(undoped) case are predicted to exhibit an inhomogeneous temperature profile,
whilst the TC and TEP grow linearly with the system size. In all cases except
for the shortest devices, we develop a picture of bulk electron and hole number
currents that flow between thermally conductive leads, where steady-state
recombination and generation processes relax the accumulating imbalance.Comment: 14 pages, 4 figure
Sensitivity of Ag/Al Interface Specific Resistances to Interfacial Intermixing
We have measured an Ag/Al interface specific resistance, 2AR(Ag/Al)(111) =
1.4 fOhm-m^2, that is twice that predicted for a perfect interface, 50% larger
than for a 2 ML 50%-50% alloy, and even larger than our newly predicted 1.3
fOhmm^2 for a 4 ML 50%-50% alloy. Such a large value of 2ARAg/Al(111) confirms
a predicted sensitivity to interfacial disorder and suggests an interface
greater than or equal to 4 ML thick. From our calculations, a predicted
anisotropy ratio, 2AR(Ag/Al)(001)/2AR(Ag/Al)(111), of more then 4 for a perfect
interface, should be reduced to less than 2 for a 4 ML interface, making it
harder to detect any such anisotropy.Comment: 3 pages, 2 figures, 1 table. In Press: Journal of Applied Physic
Beat-wave generation of plasmons in semiconductor plasmas
It is shown that in semiconductor plasmas, it is possible to generate large
amplitude plasma waves by the beating of two laser beams with frequency
difference close to the plasma frequency. For narrow gap semiconductors (for
example n-type InSb), the system can simulate the physics underlying beat wave
generation in relativistic gaseous plasmas.Comment: 11 pages, LaTex, no figures, no macro
The Tower Building Challenge: Introducing Stakeholder Management to MBA Students
The ability to consider and analyze different stakeholder interests is a skill required of today’s business students. This paper describes a 35-minute experiential exercise using Tinkertoys® or Legos® to demonstrate and reinforce the concept of stakeholder management. The exercise, the Tower Building Challenge (TBC), is targeted toward classes in business ethics, strategy, or decision-making and requires students to work in groups to build a tower with the underpinning challenge that each group member has a different interest in how the tower should be built. Student feedback reflects on the difficulty of satisfying all stakeholders when making business decisions, the importance of making the interests of stakeholders transparent to enhance cooperation and the effectiveness of the decision-making process, and the need for stakeholder management when considering business decisions that impact stakeholders. Following this experiential exercise, students’ preliminary understanding presents an opportunity for a deeper discussion of stakeholder management. Specifically, students are prompted to consider stakeholder interests as joint, rather than opposed, when engaged in stakeholder management
Particle and light fragment emission in peripheral heavy ion collisions at Fermi energies
A systematic investigation of the average multiplicities of light charged
particles and intermediate mass fragments emitted in peripheral and
semiperipheral collisions is presented as a function of the beam energy,
violence of the collision and mass of the system.
The data have been collected with the "Fiasco" setup in the reactions
93Nb+93Nb at 17, 23, 30, 38AMeV and 116Sn+116Sn at 30, 38AMeV.
The midvelocity emission has been separated from the emission of the
projectile-like fragment. This last component appears to be compatible with an
evaporation from an equilibrated source at normal density, as described by the
statistical code Gemini at the appropriate excitation energy.
On the contrary, the midvelocity emission presents remarkable differences for
what concerns both the dependence of the multiplicities on the energy deposited
in the midvelocity region and the isotopic composition of the emitted light
charged particles.Comment: 18 pages, 17 figures, Revtex
Quantum and Boltzmann transport in the quasi-one-dimensional wire with rough edges
We study quantum transport in Q1D wires made of a 2D conductor of width W and
length L>>W. Our aim is to compare an impurity-free wire with rough edges with
a smooth wire with impurity disorder. We calculate the electron transmission
through the wires by the scattering-matrix method, and we find the Landauer
conductance for a large ensemble of disordered wires. We study the
impurity-free wire whose edges have a roughness correlation length comparable
with the Fermi wave length. The mean resistance and inverse mean
conductance 1/ are evaluated in dependence on L. For L -> 0 we observe the
quasi-ballistic dependence 1/ = = 1/N_c + \rho_{qb} L/W, where 1/N_c
is the fundamental contact resistance and \rho_{qb} is the quasi-ballistic
resistivity. As L increases, we observe crossover to the diffusive dependence
1/ = = 1/N^{eff}_c + \rho_{dif} L/W, where \rho_{dif} is the
resistivity and 1/N^{eff}_c is the effective contact resistance corresponding
to the N^{eff}_c open channels. We find the universal results
\rho_{qb}/\rho_{dif} = 0.6N_c and N^{eff}_c = 6 for N_c >> 1. As L exceeds the
localization length \xi, the resistance shows onset of localization while the
conductance shows the diffusive dependence 1/ = 1/N^{eff}_c + \rho_{dif} L/W
up to L = 2\xi and the localization for L > 2\xi only. On the contrary, for the
impurity disorder we find a standard diffusive behavior, namely 1/ =
= 1/N_c + \rho_{dif} L/W for L < \xi. We also derive the wire conductivity from
the semiclassical Boltzmann equation, and we compare the semiclassical electron
mean-free path with the mean free path obtained from the quantum resistivity
\rho_{dif}. They coincide for the impurity disorder, however, for the edge
roughness they strongly differ, i.e., the diffusive transport is not
semiclassical. It becomes semiclassical for the edge roughness with large
correlation length
- …