5,263 research outputs found
Universality in Blow-Up for Nonlinear Heat Equations
We consider the classical problem of the blowing-up of solutions of the
nonlinear heat equation. We show that there exist infinitely many profiles
around the blow-up point, and for each integer , we construct a set of
codimension in the space of initial data giving rise to solutions that
blow-up according to the given profile.Comment: 38 page
New accurate measurement of 36ArH+ and 38ArH+ ro-vibrational transitions by high resolution IR absorption spectroscopy
The protonated Argon ion, ArH, has been identified recently in
the Crab Nebula (Barlow et al. 2013) from Herschel spectra. Given the
atmospheric opacity at the frequency of its =1-0 and =2-1 rotational
transitions (617.5 and 1234.6 GHz, respectively), and the current lack of
appropriate space observatories after the recent end of the Herschel mission,
future studies on this molecule will rely on mid-infrared observations. We
report on accurate wavenumber measurements of ArH and
ArH rotation-vibration transitions in the =1-0 band in the
range 4.1-3.7 m (2450-2715 cm). The wavenumbers of the (0)
transitions of the =1-0 band are 2612.501350.00033 and
2610.701770.00042 cm () for ArH and
ArH, respectively. The calculated opacity for a gas thermalized at
a temperature of 100 K and a linewidth of 1 km.s of the (0) line is
(ArH). For column densities of
ArH larger than cm, significant absorption
by the (0) line can be expected against bright mid-IR sources
Analyzing the external social capital of family firms
We examine an important yet overlooked aspect in research on social capital: the familial bonding that interorganizational relations may hold. We argue that the social identity of a family member is likely to reframe how they behave within social relations and towards actors outside the firm that are within or not within the family, changing the conditions for trust, knowledge exchange, and value creation. Drawing on a family and nonfamily classification of interorganizational relations, we examine: 1) theoretically and empirically the extent to which relationships with family members located in other related firms, which we define as external family social capital (EFSC), affect firm performance; (2) its interaction with relationships with members of other firms not bearing a family connection, referred to as external organizational social capital (EOSC); and (3) the varying levels of trust required to extract value from EFSC and EOSC
Improved determination of the 1(0)-0(0) rotational frequency of NH3D+ from the high resolution spectrum of the v4 infrared band
The high resolution spectrum of the v4 band of NH3D+ has been measured by
difference frequency IR laser spectroscopy in a multipass hollow cathode
discharge cell. From the set of molecular constants obtained from the analysis
of the spectrum, a value of 262817(6) MHz (3sigma) has been derived for the
frequency of the 1(0)-0(0) rotational transition. This value supports the
assignment to NH3D+ of lines at 262816.7 MHz recorded in radio astronomy
observations in Orion-IRc2 and the cold prestellar core B1-bS.Comment: Accepted for publication in the Astrophysical Journal Letters 04 June
201
Testing Supersymmetry with Lepton Flavor Violating tau and mu decays
In this work the following lepton flavor violating and decays
are studied: , , , , and . We work in a supersymmetric scenario consisting of the minimal
supersymmetric standard model particle content, extended by the addition of
three heavy right handed Majorana neutrinos and their supersymmetric partners,
and where the generation of neutrino masses is done via the seesaw mechanism.
Within this context, a significant lepton flavor mixing is generated in the
slepton sector due to the Yukawa neutrino couplings, which is transmited from
the high to the low energies via the renormalization group equations. This
slepton mixing then generates via loops of supersymmetric particles significant
contributions to the rates of and the correlated decays. We analize here in full detail these rates in terms of the
relevant input parameters, which are the usual minimal supergravity parameters
and the seesaw parameters. For the decays, a full one-loop
analytical computation of all the contributing supersymmetric loops is
presented. This completes and corrects previous computations in the literature.
In the numerical analysis compatibility with the most recent experimental upper
bounds on all these and decays, with the neutrino data, and with
the present lower bounds on the supersymmetric particle masses are required.
Two typical scenarios with degenerate and hierarchical heavy neutrinos are
considered. We will show here that the minimal supergravity and seesaw
parameters do get important restrictions from these and decays in
the hierarchical neutrino case.Comment: Version to appear in Physical Review
Hydrogen and muonium in diamond: A path-integral molecular dynamics simulation
Isolated hydrogen, deuterium, and muonium in diamond have been studied by
path-integral molecular dynamics simulations in the canonical ensemble.
Finite-temperature properties of these point defects were analyzed in the range
from 100 to 800 K. Interatomic interactions were modeled by a tight-binding
potential fitted to density-functional calculations. The most stable position
for these hydrogenic impurities is found at the C-C bond center. Vibrational
frequencies have been obtained from a linear-response approach, based on
correlations of atom displacements at finite temperatures. The results show a
large anharmonic effect in impurity vibrations at the bond center site, which
hardens the vibrational modes with respect to a harmonic approximation.
Zero-point motion causes an appreciable shift of the defect level in the
electronic gap, as a consequence of electron-phonon interaction. This defect
level goes down by 70 meV when replacing hydrogen by muonium.Comment: 11 pages, 8 figure
Outflows of hot molecular gas in ultra-luminous infra-red galaxies mapped with VLT-SINFONI
We present the detection and morphological characterization of hot molecular
gas outflows in nearby ultra-luminous infrared galaxies, using the near-IR
integral-field spectrograph SINFONI on the VLT. We detect outflows observed in
the 2.12 micron H 1-0 S(1) line for three out of four ULIRGs analyzed;
IRAS 12112+0305, 14348-1447, and 22491-1808. The outflows are mapped on scales
of 0.7-1.6 kpc, show typical outflow velocities of 300-500 km/s, and appear to
originate from the nuclear region. The outflows comprise hot molecular gas
masses of ~6-8x10 M(sun). Assuming a hot-to-cold molecular gas mass ratio
of 6x10, as found in nearby luminous IR galaxies, the total (hot+cold)
molecular gas mass in these outflows is expected to be ~1x10 M(sun). This
translates into molecular mass outflow rates of ~30-85 M(sun)/yr, which is a
factor of a few lower than the star formation rate in these ULIRGs. In
addition, most of the outflowing molecular gas does not reach the escape
velocity of these merger systems, which implies that the bulk of the outflowing
molecular gas is re-distributed within the system and thus remains available
for future star formation. The fastest H outflow is seen in the
Compton-thick AGN of IRAS 14348-1447, reaching a maximum outflow velocity of
~900 km/s. Another ULIRG, IRAS 17208-0014, shows asymmetric H line
profiles different from the outflows seen in the other three ULIRGs. We discuss
several alternative explanations for its line asymmetries, including a very
gentle galactic wind, internal gas dynamics, low-velocity gas outside the disk,
or two superposed gas disks. We do not detect the hot molecular counterpart to
the outflow previously detected in CO(2-1) in IRAS 17208-0014, but we note that
our SINFONI data are not sensitive enough to detect this outflow if it has a
small hot-to-cold molecular gas mass ratio of < 9x10.Comment: Accepted for publication in A&A (11 pages, 10 figures
Kinetic growth walks on complex networks
Kinetically grown self-avoiding walks on various types of generalized random
networks have been studied. Networks with short- and long-tailed degree
distributions were considered (, degree or connectivity), including
scale-free networks with . The long-range behaviour of
self-avoiding walks on random networks is found to be determined by finite-size
effects. The mean self-intersection length of non-reversal random walks, ,
scales as a power of the system size $N$: $ \sim N^{\beta}$, with an
exponent $\beta = 0.5$ for short-tailed degree distributions and $\beta < 0.5$
for scale-free networks with $\gamma < 3$. The mean attrition length of kinetic
growth walks, , scales as , with an exponent
which depends on the lowest degree in the network. Results of
approximate probabilistic calculations are supported by those derived from
simulations of various kinds of networks. The efficiency of kinetic growth
walks to explore networks is largely reduced by inhomogeneity in the degree
distribution, as happens for scale-free networks.Comment: 10 pages, 8 figure
Detection of the Ammonium Ion in Space
We report on the detection of a narrow feature at 262816.73 MHz towards Orion
and the cold prestellar core B1-bS, that we attribute to the 1(0)-0(0) line of
the deuterated Ammonium ion, NH3D+. The observations were performed with the
IRAM 30m radio telescope. The carrier has to be a light molecular species as it
is the only feature detected over 3.6 GHz of bandwidth. The hyperfine structure
is not resolved indicating a very low value for the electric quadrupolar
coupling constant of Nitrogen which is expected for NH3D+ as the electric field
over the N nucleus is practically zero. Moreover, the feature is right at the
predicted frequency for the 1(0)-0(0) transition of the Ammonium ion, 262817(6)
MHz (3sigma), using rotational constants derived from new infrared data
obtained in our laboratory in Madrid. The estimated column density is
1.1(0.2)e12 cm-2. Assuming a deuterium enhancement similar to that of NH2D, we
derive N(NH4+) sim 2.6e13 cm-2, i.e., an abundance for Ammonium of a few
1e(-11).Comment: Accepted for publication in the Astrophysical Journal Letters 04 June
201
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