7,684 research outputs found
Addendum to "Coherent radio pulses from GEANT generated electromagnetic showers in ice"
We reevaluate our published calculations of electromagnetic showers generated
by GEANT 3.21 and the radio frequency pulses they produce in ice. We are
prompted by a recent report showing that GEANT 3.21-modeled showers are
sensitive to internal settings in the electron tracking subroutine. We report
the shower and pulse characteristics obtained with different settings of GEANT
3.21 and with GEANT 4. The default setting of electron tracking in GEANT 3.21
we used in previous work speeds up the shower simulation at the cost of
information near the end of the tracks. We find that settings tracking electron
and positron to lower energy yield a more accurate calculation, a more intense
shower, and proportionately stronger radio pulses at low frequencies. At high
frequencies the relation between shower tracking algorithm and pulse spectrum
is more complex. We obtain radial distributions of shower particles and phase
distributions of pulses from 100 GeV showers that are consistent with our
published results.Comment: 4 pages, 3 figure
Growth diagram of La0.7Sr0.3MnO3 thin films using pulsed laser deposition
An experimental study was conducted on controlling the growth mode of
La0.7Sr0.3MnO3 thin films on SrTiO3 substrates using pulsed laser deposition
(PLD) by tuning growth temperature, pressure and laser fluence. Different thin
film morphology, crystallinity and stoichiometry have been observed depending
on growth parameters. To understand the microscopic origin, the adatom
nucleation, step advance processes and their relationship to film growth were
theoretically analyzed and a growth diagram was constructed. Three boundaries
between highly and poorly crystallized growth, 2D and 3D growth, stoichiometric
and non-stoichiometric growth were identified in the growth diagram. A good fit
of our experimental observation with the growth diagram was found. This case
study demonstrates that a more comprehensive understanding of the growth mode
in PLD is possible
Development Of Reciptures Of Canned Smothies Made From Zucchini And Fruits
Rational nutrition for a whole year is possible with a well-established system of storage and processing of plant raw materials. Products with vegetable and fruit raw materials due to their availability and nutritional value are in demand among the population. There is a constant interest in new products with increased biological value. The preservation of ascorbic acid, the main source of which is vegetables and fruits, is also affected by the technology of production. Despite the damaging effect of the heat treatment temperature of canned products on thermolabile components, the sterilization regimes should be relaxed. To this end, it has been proposed to produce beverages from vegetables and fruits for scientifically-based recipes, which allows them to be processed at a temperature of 100 °C, as well as juices with pulp and sugar. Smoothie, made on the basis of zucchini with the addition of gooseberries and blackcurrant puree contain respectively 13.3 and 41.8 mg/100 g of ascorbic acid, have an optimal for good perception of the sugar-acid index 21,4-21,5 compared with juices from soft pulp and sugar from gooseberry and black currant, which produces industry. The latter is explained by the fact that instead of sugar syrup, natural juice from zucchini was used in the recipe
IceCube-Plus: An Ultra-High Energy Neutrino Telescope
While the first kilometer-scale neutrino telescope, IceCube, is under
construction, alternative plans exist to build even larger detectors that will,
however, b e limited by a much higher neutrino energy threshold of 10 PeV or
higher rather than 10 to 100 GeV. These future projects detect radio and
acoustic pulses as w ell as air showers initiated by ultra-high energy
neutrinos. As an alternative, we here propose an expansion of IceCube, using
the same strings, placed on a gri d with a spacing of order 500 m. Unlike other
proposals, the expanded detector uses methods that are understood and
calibrated on atmospheric neutrinos. Atmosp heric neutrinos represent the only
background at the energies under consideratio n and is totally negligible.
Also, the cost of such a detector is understood. We conclude that supplementing
the 81 IceCube strings with a modest number of addi tional strings spaced at
large distances can almost double the effective volume of the detector.
Doubling the number of strings on a 800 m grid can deliver a d etector that
this a factor of 5 larger for horizontal muons at modest cost.Comment: Version to be published in JCA
Disappearance of integer quantum Hall effect
The disappearance of integer quantum Hall effect (IQHE) at strong disorder
and weak magnetic field is studied in a lattice model. A generic sequence by
which the IQHE plateaus disappear is revealed: higher IQHE plateaus always
vanish earlier than lower ones, and extended levels between those plateaus do
not float up in energy but keep merging together after the destruction of
plateaus. All of these features remain to be true in the weak-field limit as
shown by the thermodynamic-localization-length calculation. Topological
characterization in terms of Chern integers provides a simple physical
explanation and suggests a qualitative difference between the lattice and
continuum models.Comment: Revtex, four pages; four figures, postscript fil
Universal scaling, beta function, and metal-insulator transitions
We demonstrate a universal scaling form of longitudinal resistance in the
quantum critical region of metal-insulator transitions, based on numerical
results of three-dimensional Anderson transitions (with and without magnetic
field), two-dimensional quantum Hall plateau to insulator transition, as well
as experimental data of the recently discovered two-dimensional metal-insulator
transition. The associated reflection symmetry and a peculiar logarithmic form
of the beta function exist over a wide range in which the resistance can change
by more than one order of magnitude. Interesting implications for the
two-dimensional metal-insulator transition are discussed.Comment: 4 pages, REVTEX, 4 embedded figures; minor corrections to figures and
tex
RICE Limits on the Diffuse Ultra-High Energy Neutrino Flux
We present new limits on ultra-high energy neutrino fluxes above 100 PeV
based on data collected by the Radio Ice Cherenkov Experiment (RICE) at the
South Pole from 1999-2005. We discuss estimation of backgrounds, calibration
and data analysis algorithms (both on-line and off-line), procedures used for
the dedicated neutrino search, and refinements in our Monte Carlo (MC)
simulation, including recent in situ measurements of the complex ice dielectric
constant. An enlarged data set and a more detailed study of hadronic showers
results in a sensitivity improvement of more than one order of magnitude
compared to our previously published results. Examination of the full RICE data
set yields zero acceptable neutrino candidates, resulting in 95%
confidence-level model dependent limits on the flux
(E_\nu)^2(d\phi/dE_\nu)<10^{-6} GeV/(cm^2s~sr}) in the energy range 10^{17}<
E_\nu< 10^{20} eV. The new RICE results rule out the most intense flux model
projections at 95% confidence level.Comment: Submitted to Astropart. Phy
Bulk Tunneling at Integer Quantum Hall Transitions
The tunneling into the {\em bulk} of a 2D electron system (2DES) in strong
magnetic field is studied near the integer quantum Hall transitions. We present
a nonperturbative calculation of the tunneling density of states (TDOS) for
both Coulomb and short-ranged electron-electron interactions. In the case of
Coulomb interaction, the TDOS exhibits a 2D quantum Coulomb gap behavior,
\nu(\ve)=C_Q\ave/e^4, with a nonuniversal coefficient of quantum
mechanical origin. For short-ranged interactions, we find that the TDOS at low
bias follows \nu(\ve)/\nu (0)=1+(\ave/\ve_0)^\gamma, where is a
universal exponent determined by the scaling dimension of short-ranged
interactions.Comment: 4 pages, revtex, final version to appear in Phys. Rev. Let
Two-dimensional Anderson-Hubbard model in DMFT+Sigma approximation
Density of states, dynamic (optical) conductivity and phase diagram of
paramagnetic two-dimensional Anderson-Hubbard model with strong correlations
and disorder are analyzed within the generalized dynamical mean-field theory
(DMFT+Sigma approximation). Strong correlations are accounted by DMFT, while
disorder is taken into account via the appropriate generalization of the
self-consistent theory of localization. We consider the two-dimensional system
with the rectangular "bare" density of states (DOS). The DMFT effective single
impurity problem is solved by numerical renormalization group (NRG). Phases of
"correlated metal", Mott insulator and correlated Anderson insulator are
identified from the evolution of density of states, optical conductivity and
localization length, demonstrating both Mott-Hubbard and Anderson
metal-insulator transitions in two-dimensional systems of the finite size,
allowing us to construct the complete zero-temperature phase diagram of
paramagnetic Anderson-Hubbard model. Localization length in our approximation
is practically independent of the strength of Hubbard correlations. However,
the divergence of localization length in finite size two-dimensional system at
small disorder signifies the existence of an effective Anderson transition.Comment: 10 pages, 10 figures, improve phase diagra
Weak Field Phase Diagram for an Integer Quantum Hall Liquid
We study the localization properties in the transition from a two-dimensional
electron gas at zero magnetic field into an integer quantum Hall (QH) liquid.
By carrying out a direct calculation of the localization length for a finite
size sample using a transfer matrix technique, we systematically investigate
the field and disorder dependences of the metal-insulator transition in the
weak field QH regime. We obtain a different phase diagram from the one
conjectured in previous theoretical studies. In particular, we find that: (1)
the extended state energy for each Landau level (LL) is {\it always}
linear in magnetic field; (2) for a given Landau level and disorder
configuration there exists a critical magnetic field below which the
extended state disappears; (3) the lower LLs are more robust to the
metal-insulator transition with smaller . We attribute the above results
to strong LL coupling effect. Experimental implications of our work are
discussed.Comment: 4 pages, ReVTeX 3.0, 4 figures (available upon request
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