31,818 research outputs found
Ultrahigh energy neutrino scattering: an update
We update our estimates of charged and neutral current neutrino total cross
sections on isoscalar nucleons at ultrahigh energies using a global (x, Q^2)
fit, motivated by the Froissart bound, to the F_2 (electron-proton) structure
function utilizing the most recent analysis of the complete ZEUS and H1 data
sets from HERA I. Using the large Q^2, small Bjorken-x limits of the "wee"
parton model, we connect the ultrahigh energy neutrino cross sections directly
to the large Q^2, small-x extrapolation of our new fit, which we assume
saturates the Froissart bound. We compare both to our previous work, which
utilized only the smaller ZEUS data set, as well as to recent results of a
calculation using the ZEUS-S based global perturbative QCD parton distributions
using the combined HERA I results as input. Our new results substantiate our
previous conclusions, again predicting significantly smaller cross sections
than those predicted by extrapolating pQCD calculations to neutrino energies
above 10^9 GeV.Comment: 8 pages, 1 figure, 3 table
Interplay of charge, spin and lattice degrees of freedom on the spectral properties of the one-dimensional Hubbard-Holstein model
We calculate the spectral function of the one dimensional Hubbard-Holstein
model using the time dependent Density Matrix Renormalization Group (tDMRG),
focusing on the regime of large local Coulomb repulsion, and away from
electronic half-filling. We argue that, from weak to intermediate
electron-phonon coupling, phonons interact only with the electronic charge, and
not with the spin degrees of freedom. For strong electron-phonon interaction,
spinon and holon bands are not discernible anymore and the system is well
described by a spinless polaronic liquid. In this regime, we observe multiple
peaks in the spectrum with an energy separation corresponding to the energy of
the lattice vibrations (i.e., phonons). We support the numerical results by
introducing a well controlled analytical approach based on Ogata-Shiba's
factorized wave-function, showing that the spectrum can be understood as a
convolution of three contributions, originating from charge, spin, and lattice
sectors. We recognize and interpret these signatures in the spectral properties
and discuss the experimental implications.Comment: 8 pages, 7 figure
Modeling and experimental validation of a solar-assisted direct expansion air conditioning system
Continuous increase in global electricity consumption, environmental hazards of pollution and depletion of fossil fuel resources have brought about a paradigm shift in the development of eco-friendly and energy-efficient technologies. This paper reports on an experimental study to investigate the inherent operational characteristics of a new direct-expansion air conditioning system combined with a vacuum solar collector. Mathematical models of the system components are firstly derived and then validated against experimental results. To investigate the potential of energy savings, the hybrid solar-assisted air-conditioner is installed and extensively equipped with a number of sensors and instrumentation devices, for experimentation and data collection. The influence on the system energy usage of the average water temperature, storage tank size and room set-point temperature are then analyzed. Once the air-conditioned room has achieved its desired temperature, the compressor turns off while the cooling process still continues until the refrigerant pressure no longer maintains the desired temperature. The advantages of the proposed hybrid system rest with the fact that the compressor can remain off in a longer period by heat impartation into the refrigerant via the water storage tank. Results show an average monthly energy saving of about between 25% and 42%. © 2013 Elsevier B.V. All rights reserved
Floquet stroboscopic divisibility in non-Markovian dynamics
We provide a general discussion of the Liouvillian spectrum for a system
coupled to a non-Markovian bath using Floquet theory. This approach is suitable
when the system is described by a time-convolutionless master equation with
time-periodic rates. Surprisingly, the periodic nature of rates allow us to
have a stroboscopic divisible dynamical map at discrete times, which we refer
to as Floquet stroboscopic divisibility. We illustrate the general theory for a
Schr\"odinger cat which is roaming inside a non-Markovian bath, and demonstrate
the appearance of stroboscopic revival of the cat at later time after its
death. Our theory may have profound implications in entropy production in
non-equilibrium systems.Comment: We changed the title and explained in more detail the definition of
non-Markovian dynamics used in the manuscrip
Casimir Dispersion Forces and Orientational Pairwise Additivity
A path integral formulation is used to study the fluctuation-induced
interactions between manifolds of arbitrary shape at large separations. It is
shown that the form of the interactions crucially depends on the choice of the
boundary condition. In particular, whether or not the Casimir interaction is
pairwise additive is shown to depend on whether the ``metallic'' boundary
condition corresponds to a ``grounded'' or an ``isolated'' manifold.Comment: 6 pages, RevTe
Role of the cyclic lipopeptide massetolide A in biological control of Phytophthora infestans and in colonization of tomato plants by Pseudomonas fluorescens
Pseudomonas strains have shown promising results in biological control of late blight caused by Phytophthora infestans. However, the mechanism(s) and metabolites involved are in many cases poorly understood. Here, the role of the cyclic lipopeptide massetolide A of Pseudomonas fluorescens SS101 in biocontrol of tomato late blight was examined. Pseudomonas fluorescens SS101 was effective in preventing infection of tomato (Lycopersicon esculentum) leaves by P. infestans and significantly reduced the expansion of existing late blight lesions. Massetolide A was an important component of the activity of P. fluorescens SS101, since the massA-mutant was significantly less effective in biocontrol, and purified massetolide A provided significant control of P. infestans, both locally and systemically via induced resistance. Assays with nahG transgenic plants indicated that the systemic resistance response induced by SS101 or massetolide A was independent of salicylic acid signalling. Strain SS101 colonized the roots of tomato seedlings significantly better than its massA-mutant, indicating that massetolide A was an important trait in plant colonization. This study shows that the cyclic lipopeptide surfactant massetolide A is a metabolite with versatile functions in the ecology of P fluorescens SS101 and in interactions with tomato plants and the late blight pathogen P. infestans
Particle Dynamics in a Mass-Conserving Coalescence Process
We consider a fully asymmetric one-dimensional model with mass-conserving
coalescence. Particles of unit mass enter at one edge of the chain and
coalescence while performing a biased random walk towards the other edge where
they exit. The conserved particle mass acts as a passive scalar in the reaction
process , and allows an exact mapping to a restricted ballistic
surface deposition model for which exact results exist. In particular, the
mass- mass correlation function is exactly known. These results complement
earlier exact results for the process without mass. We introduce a
comprehensive scaling theory for this process. The exact anaytical and
numerical results confirm its validity.Comment: 5 pages, 6 figure
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