12,432 research outputs found
Diffuse gamma-ray emission from galactic pulsars
Millisecond Pulsars are second most abundant source population discovered by
the Fermi-LAT. They might contribute non-negligibly to the diffuse emission
measured at high latitudes by Fermi-LAT, the IDGRB. Gamma-ray sources also
contribute to the anisotropy of the IDGRB measured on small scales by
Fermi-LAT. We aim to assess the contribution of the unresolved counterpart of
the detected MSPs population to the IDGRB and the maximal fraction of the
measured anisotropy produced by this source class. We model the MSPs spatial
distribution in the Galaxy and the gamma-ray emission parameters by considering
radio and gamma-ray observational constraints. By simulating a large number of
MSPs populations, we compute the average diffuse emission and the anisotropy
1-sigma upper limit. The emission from unresolved MSPs at 2 GeV, where the peak
of the spectrum is located, is at most 0.9% of the measured IDGRB above 10
degrees in latitude. The 1-sigma upper limit on the angular power for
unresolved MSP sources turns out to be about a factor of 60 smaller than
Fermi-LAT measurements above 30 degrees. Our results indicate that this
galactic source class represents a negligible contributor to the high-latitude
gamma-ray sky and confirm that most of the intensity and geometrical properties
of the measured diffuse emission are imputable to other extragalactic source
classes. Nevertheless, given the MSP distribution, we expect them to contribute
significantly to the gamma-ray diffuse emission at low latitudes. Since, along
the galactic disk, the population of young Pulsars overcomes in number the one
of MSPs, we compute the gamma-ray emission from the whole population of
unresolved Pulsars in two low-latitude regions: the inner Galaxy and the
galactic center.Comment: 19 pages, 26 figures. It matches the published version, minor changes
onl
Single Spin Asymmetry in Inclusive Pion Production
It is shown how the single spin asymmetry observed in inclusive pion
production is related, in the helicity basis, to the imaginary part of the
product of two different distribution amplitudes, rather than to the usual
quark and gluon distribution functions; there is then no reason why it should
be zero even in massless perturbative QCD, provided the quark intrinsic motion
is taken into account. A simple model is constructed which reproduces the main
features of the data.Comment: (To appear in the proceedings of the XI International Symposium on
High Energy Spin Physics, September 15-22, Bloomington, Indiana). 5 pages + 1
figure, LaTeX 2.09, report DFTT47/94, INFNCA-TH-94-21. (figure appended as
uuencoded, tar-compressed postscript file; uncompressed ps file available
under request from [email protected]
An extended solution space for Chern-Simons gravity: the slowly rotating Kerr black hole
In the Einstein-Cartan formulation, an iterative procedure to find solutions
in non-dynamical Chern-Simons (CS) gravity in vacuum is proposed. The
iterations, in powers of a small parameter which codifies the CS
coupling, start from an arbitrary torsionless solution of Einstein equations.
With Schwarzschild as the zeroth-order choice, we derive a second-order
differential equation for the corrections to the metric,
for an arbitrary zeroth-order embedding parameter. In particular, the slowly
rotating Kerr metric is an solution in either the
canonical or the axial embeddings.Comment: 5 pages, PRD accepte
Suitable classification of mortars from ancient roman and renaissance frescoes using thermal analysis and chemometrics
Background
Literature on mortars has mainly focused on the identification and characterization of their components in order to assign them to a specific historical period, after accurate classification. For this purpose, different analytical techniques have been proposed. Aim of the present study was to verify whether the combination of thermal analysis and chemometric methods could be used to obtain a fast but correct classification of ancient mortar samples of different ages (Roman era and Renaissance).
Results
Ancient Roman frescoes from Museo Nazionale Romano (Terme di Diocleziano, Rome, Italy) and Renaissance frescoes from Sistine Chapel and Old Vatican Rooms (Vatican City) were analyzed by thermogravimetry (TG) and differential thermal analysis (DTA). Principal Component analysis (PCA) on the main thermal data evidenced the presence of two clusters, ascribable to the two different ages. Inspection of the loadings allowed to interpret the observed differences in terms of the experimental variables.
Conclusions
PCA allowed differentiating the two kinds of mortars (Roman and Renaissance frescoes), and evidenced how the ancient Roman samples are richer in binder (calcium carbonate) and contain less filler (aggregate) than the Renaissance ones. It was also demonstrated how the coupling of thermoanalytical techniques and chemometric processing proves to be particularly advantageous when a rapid and correct differentiation and classification of cultural heritage samples of various kinds or ages has to be carried out
Interpretation of AMS-02 electrons and positrons data
We perform a combined analysis of the recent AMS-02 data on electrons,
positrons, electrons plus positrons and positron fraction, in a self-consistent
framework where we realize a theoretical modeling of all the astrophysical
components that can contribute to the observed fluxes in the whole energy
range. The primary electron contribution is modeled through the sum of an
average flux from distant sources and the fluxes from the local supernova
remnants in the Green catalog. The secondary electron and positron fluxes
originate from interactions on the interstellar medium of primary cosmic rays,
for which we derive a novel determination by using AMS-02 proton and helium
data. Primary positrons and electrons from pulsar wind nebulae in the ATNF
catalog are included and studied in terms of their most significant (while
loosely known) properties and under different assumptions (average contribution
from the whole catalog, single dominant pulsar, a few dominant pulsars). We
obtain a remarkable agreement between our various modeling and the AMS-02 data
for all types of analysis, demonstrating that the whole AMS-02 leptonic data
admit a self-consistent interpretation in terms of astrophysical contributions.Comment: 33 pages, 26 figures and 4 tables, v2: accepted for publication in
JCAP, minor changes relative to v
YF-12 cooperative airframe/propulsion control system program, volume 1
Several YF-12C airplane analog control systems were converted to a digital system. Included were the air data computer, autopilot, inlet control system, and autothrottle systems. This conversion was performed to allow assessment of digital technology applications to supersonic cruise aircraft. The digital system was composed of a digital computer and specialized interface unit. A large scale mathematical simulation of the airplane was used for integration testing and software checkout
Effect of the boundary condition on the vortex patterns in mesoscopic three-dimensional superconductors - disk and sphere
The vortex state of mesoscopic three-dimensional superconductors is
determined using a minimization procedure of the Ginzburg-Landau free energy.
We obtain the vortex pattern for a mesoscopic superconducting sphere and find
that vortex lines are naturally bent and are closest to each other at the
equatorial plane. For a superconducting disk with finite height, and under an
applied magnetic field perpendicular to its major surface, we find that our
method gives results consistent with previous calculations. The matching
fields, the magnetization and , are obtained for models that differ
according to their boundary properties. A change of the Ginzburg-Landau
parameters near the surface can substantially enhance as shown here.Comment: 7 pages, 4 figures (low resolution
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