3,978 research outputs found
Calibration of the LOFAR low-band antennas using the Galaxy and a model of the signal chain
The LOw-Frequency ARray (LOFAR) is used to make precise measurements of radio
emission from extensive air showers, yielding information about the primary
cosmic ray. Interpreting the measured data requires an absolute and
frequency-dependent calibration of the LOFAR system response. This is
particularly important for spectral analyses, because the shape of the detected
signal holds information about the shower development. We revisit the
calibration of the LOFAR antennas in the range of 30 - 80 MHz. Using the
Galactic emission and a detailed model of the LOFAR signal chain, we find an
improved calibration that provides an absolute energy scale and allows for the
study of frequency-dependent features in measured signals. With the new
calibration, systematic uncertainties of 13% are reached, and comparisons of
the spectral shape of calibrated data with simulations show promising
agreement.Comment: 23 pages, 10 figure
Realtime processing of LOFAR data for the detection of nano-second pulses from the Moon
The low flux of the ultra-high energy cosmic rays (UHECR) at the highest
energies provides a challenge to answer the long standing question about their
origin and nature. Even lower fluxes of neutrinos with energies above
eV are predicted in certain Grand-Unifying-Theories (GUTs) and e.g.\ models for
super-heavy dark matter (SHDM). The significant increase in detector volume
required to detect these particles can be achieved by searching for the
nano-second radio pulses that are emitted when a particle interacts in Earth's
moon with current and future radio telescopes.
In this contribution we present the design of an online analysis and trigger
pipeline for the detection of nano-second pulses with the LOFAR radio
telescope. The most important steps of the processing pipeline are digital
focusing of the antennas towards the Moon, correction of the signal for
ionospheric dispersion, and synthesis of the time-domain signal from the
polyphased-filtered signal in frequency domain. The implementation of the
pipeline on a GPU/CPU cluster will be discussed together with the computing
performance of the prototype.Comment: Proceedings of the 22nd International Conference on Computing in High
Energy and Nuclear Physics (CHEP2016), US
Cosmic Ray Physics with the LOFAR Radio Telescope
The LOFAR radio telescope is able to measure the radio emission from cosmic
ray induced air showers with hundreds of individual antennas. This allows for
precision testing of the emission mechanisms for the radio signal as well as
determination of the depth of shower maximum , the shower observable
most sensitive to the mass of the primary cosmic ray, to better than 20
g/cm. With a densely instrumented circular area of roughly 320 m, LOFAR
is targeting for cosmic ray astrophysics in the energy range -
eV. In this contribution we give an overview of the status, recent
results, and future plans of cosmic ray detection with the LOFAR radio
telescope.Comment: Proceedings of the 26th Extended European Cosmic Ray Symposium
(ECRS), Barnaul/Belokurikha, 201
Condensation of Ideal Bose Gas Confined in a Box Within a Canonical Ensemble
We set up recursion relations for the partition function and the ground-state
occupancy for a fixed number of non-interacting bosons confined in a square box
potential and determine the temperature dependence of the specific heat and the
particle number in the ground state. A proper semiclassical treatment is set up
which yields the correct small-T-behavior in contrast to an earlier theory in
Feynman's textbook on Statistical Mechanics, in which the special role of the
ground state was ignored. The results are compared with an exact quantum
mechanical treatment. Furthermore, we derive the finite-size effect of the
system.Comment: 18 pages, 8 figure
Foundations of self-consistent particle-rotor models and of self-consistent cranking models
The Kerman-Klein formulation of the equations of motion for a nuclear shell
model and its associated variational principle are reviewed briefly. It is then
applied to the derivation of the self-consistent particle-rotor model and of
the self-consistent cranking model, for both axially symmetric and triaxial
nuclei. Two derivations of the particle-rotor model are given. One of these is
of a form that lends itself to an expansion of the result in powers of the
ratio of single-particle angular momentum to collective angular momentum, that
is essentual to reach the cranking limit. The derivation also requires a
distinct, angular-momentum violating, step. The structure of the result implies
the possibility of tilted-axis cranking for the axial case and full
three-dimensional cranking for the triaxial one. The final equations remain
number conserving. In an appendix, the Kerman-Klein method is developed in more
detail, and the outlines of several algorithms for obtaining solutions of the
associated non-linear formalism are suggested.Comment: 29 page
Off shell behaviour of the in medium nucleon-nucleon cross section
The properties of nucleon-nucleon scattering inside dense nuclear matter are
investigated. We use the relativistic Brueckner-Hartree-Fock model to determine
on-shell and half off-shell in-medium transition amplitudes and cross sections.
At finite densities the on-shell cross sections are generally suppressed. This
reduction is, however, less pronounced than found in previous works. In the
case that the outgoing momenta are allowed to be off energy shell the
amplitudes show a strong variation with momentum. This description allows to
determine in-medium cross sections beyond the quasi-particle approximation
accounting thereby for the finite width which nucleons acquire in the dense
nuclear medium. For reasonable choices of the in-medium nuclear spectral width,
i.e. MeV, the resulting total cross sections are, however,
reduced by not more than about 25% compared to the on-shell values. Off-shell
effect are generally more pronounced at large nuclear matter densities.Comment: 31 pages Revtex, 12 figures, typos corrected, to appear in Phys. Rev.
Molecular formations in ultracold mixtures of interacting and noninteracting atomic gases
Atom-molecule equilibrium for molecular formation processes is discussed for
boson-fermion, fermion-fermion, and boson-boson mixtures of ultracold atomic
gases in the framework of quasichemical equilibrium theory. After presentation
of the general formulation, zero-temperature phase diagrams of the
atom-molecule equilibrium states are calculated analytically; molecular, mixed,
and dissociated phases are shown to appear for the change of the binding energy
of the molecules. The temperature dependences of the atom or molecule densities
are calculated numerically, and finite-temperature phase structures are
obtained of the atom-molecule equilibrium in the mixtures. The transition
temperatures of the atom or molecule Bose-Einstein condensations are also
evaluated from these results. Quantum-statistical deviations of the law of mass
action in atom-molecule equilibrium, which should be satisfied in mixtures of
classical Maxwell-Boltzmann gases, are calculated, and the difference in the
different types of quantum-statistical effects is clarified. Mean-field
calculations with interparticle interactions (atom-atom, atom-molecule, and
molecule-molecule) are formulated, where interaction effects are found to give
the linear density-dependent term in the effective molecular binding energies.
This method is applied to calculations of zero-temperature phase diagrams,
where new phases with coexisting local-equilibrium states are shown to appear
in the case of strongly repulsive interactions.Comment: 35 pages, 14 figure
Towards Activity Context using Software Sensors
Service-Oriented Computing delivers the promise of configuring and
reconfiguring software systems to address user's needs in a dynamic way.
Context-aware computing promises to capture the user's needs and hence the
requirements they have on systems. The marriage of both can deliver ad-hoc
software solutions relevant to the user in the most current fashion. However,
here it is a key to gather information on the users' activity (that is what
they are doing). Traditionally any context sensing was conducted with hardware
sensors. However, software can also play the same role and in some situations
will be more useful to sense the activity of the user. Furthermore they can
make use of the fact that Service-oriented systems exchange information through
standard protocols. In this paper we discuss our proposed approach to sense the
activity of the user making use of software
Higgs bosons in the simplest SUSY models
Nowadays in the MSSM the moderate values of are almost excluded
by LEP II lower bound on the lightest Higgs boson mass. In the Next-to-Minimal
Supersymmetric Standard Model the theoretical upper bound on it increases and
reaches maximal value in the strong Yukawa coupling limit when all solutions of
renormalization group equations are concentrated near the quasi-fixed point.
For calculation of Higgs boson spectrum the perturbation theory method can be
applied. We investigate the particle spectrum in the framework of the modified
NMSSM which leads to the self-consistent solution in the strong Yukawa coupling
limit. This model allows one to get GeV at values of
. In the investigated model the lightest Higgs boson mass
does not exceed GeV. The upper bound on the lightest CP-even
Higgs boson mass in more complicated supersymmetric models is also discussed.Comment: 27 pages, 5 figures included, LaTeX 2e. Plenary talk at the
Conference of RAS Nuclear Physics Department 2000 in ITEP, Moscow, Russia; to
appear in Phys. Atom. Nuc
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