12,288 research outputs found
A NICMOS search for obscured Supernovae in starburst galaxies
The detection of obscured supernovae (SNe) in near-infrared monitoring campaigns of starburst galaxies has shown that a significant fraction of SNe is missed by optical surveys. However, the number of SNe detected in ground-based near-IR observations is still significantly lower than the number of SNe extrapolated from the FIR luminosity of the hosts. A possibility is that most SNe occur within the nuclear regions, where the limited angular resolution of ground-based observations prevents their detection. This issue prompted us to exploit the superior angular resolution of NICMOS-HST to search for obscured SNe within the first kpc from the nucleus of strong starbursting galaxies. A total of 17 galaxies were observed in SNAPSHOT mode. Based on their FIR luminosity, we expected to detect not less than ~12 SNe. However, no confirmed SN event was found. From our data we derive an observed nuclear SN rate 11; ii) most SNe occur within the first 0.5" (which corresponds in our sample to about 500pc) where even NICMOS is unable to detect SN events
D-term inflation and neutrino mass
We study a -term inflation scenario in a model extended from the minimal
supersymmetric standard model (MSSM) by two additional abelian factor groups
focussing on its particle physics aspects. Condensates of the fields related to
the inflation can naturally give a possible solution to both the -problem
in the MSSM and the neutrino mass through their nonrenormalizable couplings to
the MSSM fields. Mixings between neutrinos and neutralinos are also induced by
some of these condensates. Small neutrino masses are generated by a weak scale
seesaw mechanism as a result of these mixings. Moreover, the decay of the
condensates may be able to cause the leptogenesis. Usually known discrepancy
between both values of a Fayet-Iliopoulos -term which are predicted by the
COBE normalization and also by an anomalous U(1) in the weakly-coupled
superstring might be reconciled.Comment: 21 pages, LaTeX, small modifications, one reference adde
Quasi Harmonic Lattice Dynamics and Molecular Dynamics calculations for the Lennard-Jones solids
We present Molecular Dynamics (MD), Quasi Harmonic Lattice Dynamics (QHLD)
and Energy Minimization (EM) calculations for the crystal structure of Ne, Ar,
Kr and Xe as a function of pressure and temperature. New Lennard-Jones (LJ)
parameters are obtained for Ne, Kr and Xe to reproduce the experimental
pressure dependence of the density. We employ a simple method which combines
results of QHLD and MD calculations to achieve densities in good agreement with
experiment from 0 K to melting. Melting is discussed in connection with
intrinsic instability of the solid as given by the QHLD approximation. (See
http://www.fci.unibo.it/~valle for related papers)Comment: 7 pages, 5 figures, REVte
SN 2002lt and GRB 021211: a SN/GRB Connection at z = 1
We present spectroscopic and photometric observations of the afterglow of GRB
021211 and the discovery of its associated supernova, SN 2002lt. The spectrum
shows a broad feature (FWHM = 150 A), around 3770 A (in the rest-frame of the
GRB), which we interpret as Ca H+K blueshifted by 14400 km/s. Potential sources
of contamination due to the host galaxy and/or residuals of telluric absorption
have been analyzed and ruled out. Overall, the spectrum shows a suggestive
resemblance with the one of the prototypical type-Ic SN 1994I. This might
indicate that GRBs are produced also by standard type-Ic supernovae.Comment: 6 pages, 5 color figures. Proceedings of the 2003 GRB Conference
(Santa Fe, NM, 2003 Sep 8-12). Needs aipprocs LaTeX clas
Five supernova survey galaxies in the southern hemisphere. II. The supernova rates
Based on the database compiled in the first article of this series, with 56
SN events discovered in 3838 galaxies of the southern hemisphere, we compute
the rate of supernovae (SNe) of different types along the Hubble sequence
normalized to the optical and near-infrared luminosities as well as to the
stellar mass of the galaxies. We find that the rates of all SN types show a
dependence on both morphology and colors of the galaxies, and therefore, on the
star-formation activity. The rate of core-collapse (CC) SNe is confirmed to be
closely related to the Star Formation Rate (SFR) and only indirectly to the
total mass of the galaxies. The rate of SNe Ia can be explained by assuming
that at least 15% of Ia events in spiral galaxies originates in relatively
young stellar populations. We find that the rates show no modulation with
nuclear activity or environment. The ratio of SN rates between types Ib/c and
II shows no trend with spiral type.Comment: 13 pages, 2 figures, 5 tables, published in Astrophysics (English
translation of Astrofizika
Molar volume of solid isotopic helium mixtures
Solid isotopic helium mixtures have been studied by path-integral Monte Carlo
simulations in the isothermal-isobaric ensemble. This method allowed us to
study the molar volume as a function of temperature, pressure, and isotopic
composition. At 25 K and 0.2 GPa, the relative difference between molar volumes
of isotopically-pure crystals of 3He and 4He is found to be about 3%. This
difference decreases under pressure, and for 12 GPa it is smaller than 1%. For
isotopically-mixed crystals, a linear relation between lattice parameters and
concentrations of helium isotopes is found, in agreement with Vegard's law. The
virtual crystal approximation, valid for isotopic mixtures of heavier atoms,
does not give reliable results for solid solutions of helium isotopes.Comment: 7 pages, 5 figure
Left-Right Symmetry and Supersymmetric Unification
The existence of an SU(3) X SU(2)_L X SU(2)_R X U(1) gauge symmetry with g_L
= g_R at the TeV energy scale is shown to be consistent with supersymmetric
SO(10) grand unification at around 1O^{16} GeV if certain new particles are
assumed. The additional imposition of a discrete Z_2 symmetry leads to a
generalized definition of R parity as well as highly suppressed Majorana
neutrino masses. Another model based on SO(10) X SO(10) is also discussed.Comment: 11 pages, 2 figures not included, UCRHEP-T124, Apr 199
-term as the origin of baryon and lepton number asymmetry
We study a possibility of combining an origin of the -term and the
baryon and lepton number asymmetry. If we assume that the -term is
generated through a flat direction of a singlet scalar field, the coherent
oscillation of this condensate around its potential minimum can store the
global U(1) charge asymmetry. The decay of this condensate can distribute this
asymmetry into the lepton and baryon number asymmetry as far as its decay
occurs at an appropriate temperature. We examine the compatibility between this
scenario and the small neutrino mass generation based on both the ordinary
seesaw mechanism and the bilinear R-parity violating terms.Comment: 22 pages, published versio
Color conductivity and ladder summation in hot QCD
The color conductivity is computed at leading logarithmic order using a Kubo
formula. We show how to sum an infinite series of planar ladder diagrams,
assuming some approximations based on the dominance of soft scattering
processes between hard particles in the plasma. The result agrees with the one
obtained previously from a kinetical approach.Comment: 15 pages, 4 figures. Explanations enlarged, two figures and some refs
added, typos corrected. Final version to be published in Phys.Rev.
Application of different DNA extraction procedures, library preparation protocols and sequencing platforms: impact on sequencing results
In this study three DNA extraction procedures, two library preparation protocols and two sequencing platforms were applied to analyse six bacterial cultures and their corresponding DNA obtained as part of a proficiency test. The impact of each variable on sequencing results was assessed using the following parameters: reads quality, assembly and alignment statistics; number of single nucleotide polymorphisms (SNPs), detected applying assembly- and alignment-based strategies; antimicrobial resistance genes (ARGs), identified on de novo assemblies of all sequenced genomes. The investigated nucleic acid extraction procedures, library preparation kits and sequencing platforms do not significantly affect de novo assembly statistics and number of SNPs and ARGs. The only exception was observed for two duplicates, which were associated to one PCR-based library preparation kit. Results from this comparative study can support researchers in the choice toward the available pre-sequencing and sequencing options, and might suggest further comparisons to be performed
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