1,108 research outputs found
Modelización de la variabilidad horaria de los contenidos de humedad en hojarasca de Eucalyptus globulus
Fuel moisture content is a basic parameter of the present fire danger rating systems and fire behaviour simulation programs. Diurnal Eucalyptus globulus litter fuel moisture content variation patterns in rain free periods are shown in this document. Several situations in relation to sun exposition, wind and nocturnal dead organic fuels dew are considered and the capacity of prediction models which are available in literature in order to follows the patterns is evaluated. It is concluded by emphasizing the good behaviour of a physically based model in the different conditions considered and the appropriate behaviour of particular empirical models to specific situations. Fuel moisture nocturnal latent heat effect is remarked together with the fast sun effect drying up litter which make possible to pass, in a very short time step, from a non inflammable fuel to a situation clearly well-disposed to fire propagation.La humedad de los combustibles es variable fundamental de los sistemas de predicción del riesgo meteorológico de incendio forestal y de simulación del comportamiento de fuego actuales. En este trabajo se muestran patrones de variación de la humedad de la hojarasca de Eucalyptus globulus a lo largo del día en períodos libres de lluvia. Se analizan situaciones diversas en cuanto a exposición al sol, viento y condensación nocturna sobre los restos orgánicos vegetales, y se evalúa la capacidad de modelos de estimación disponibles en la literatura para seguir las tendencias. Se concluye resaltando el buen funcionamiento de un modelo de base física en las distintas condiciones planteadas así como la adecuación de determinados modelos empíricos a situaciones concretas. Se resalta la importancia de la condensación de humedad sobre el combustible así como el rápido efecto desecante del sol que permite pasar, en un br evísimo intervalo de tiempo, de un combustible no inflamable a una situación claramente favorecedora de la propagación
A Singular Conformal Spacetime
The infinite cosmological "constant" limit of the de Sitter solutions to
Einstein's equation is studied. The corresponding spacetime is a singular,
four-dimensional cone-space, transitive under proper conformal transformations,
which constitutes a new example of maximally-symmetric spacetime. Grounded on
its geometric and thermodynamic properties, some speculations are made in
connection with the primordial universe.Comment: RevTeX4, 10 pages, 1 eps figure. Presentation changes, including a
new title; section II.E, on the thermodynamic properties of the de Sitter
horizon, completely revised. Version to be published in Journal of Geometry
and Physic
Prospects for observations of high-energy cosmic tau neutrinos
We study prospects for the observations of high-energy cosmic tau neutrinos
(E \geq 10^6 GeV) originating from proton acceleration in the cores of active
galactic nuclei. We consider the possibility that vacuum flavor neutrino
oscillations induce a tau to muon neutrino flux ratio greatly exceeding the
rather small value expected from intrinsic production. The criterias and event
rates for under water/ice light Cerenkov neutrino telescopes are given by
considering the possible detection of downgoing high-energy cosmic tau
neutrinos through characteristic double shower events.Comment: 10 pages, Revtex, 3 figures included with eps
Measuring the Spectra of High Energy Neutrinos with a Kilometer-Scale Neutrino Telescope
We investigate the potential of a future kilometer-scale neutrino telescope
such as the proposed IceCube detector in the South Pole, to measure and
disentangle the yet unknown components of the cosmic neutrino flux, the prompt
atmospheric neutrinos coming from the decay of charmed particles and the
extra-galactic neutrinos, in the 10 TeV to 1 EeV energy range.
Assuming a power law type spectra,
, we quantify the discriminating
power of the IceCube detector and discuss how well we can determine magnitude
() as well as slope () of these two components of the high
energy neutrino spectrum, taking into account the background coming from the
conventional atmospheric neutrinos.Comment: 21 pages, 7 figure
A regulatory cascade involving retinoic acid, Cbfa1, and matrix metalloproteinases is coupled to the development of a process of perichondrial invasion and osteogenic differentiation during bone formation
Tissue-remodeling processes are largely mediated by members of the matrix metalloproteinase (MMP) family of endopeptidases whose expression is strictly controlled both spatially and temporally. In this article, we have examined the molecular mechanisms that could contribute to modulate the expression of MMPs like collagenase-3 and MT1-MMP during bone formation. We have found that all-trans retinoic acid (RA), which usually downregulates MMPs, strongly induces collagenase-3 expression in cultures of embryonic metatarsal cartilage rudiments and in chondrocytic cells. This effect is dose and time dependent, requires the de novo synthesis of proteins, and is mediated by RAR-RXR heterodimers. Analysis of the signal transduction mechanisms underlying the upregulating effect of RA on collagenase-3 expression demonstrated that this factor acts through a signaling pathway involving p38 mitogen-activated protein kinase. RA treatment of chondrocytic cells also induces the production of MT1-MMP, a membrane-bound metalloproteinase essential for skeletal formation, which participates in a proteolytic cascade with collagenase-3. The production of these MMPs is concomitant with the development of an RA-induced differentiation program characterized by formation of a mineralized bone matrix, downregulation of chondrocyte markers like type II collagen, and upregulation of osteoblastic markers such as osteocalcin. These effects are attenuated in metatarsal rudiments in which RA induces the invasion of perichondrial osteogenic cells from the perichondrium into the cartilage rudiment. RA treatment also resulted in the upregulation of Cbfa1, a transcription factor responsible for collagenase-3 and osteocalcin induction in osteoblastic cells. The dynamics of Cbfa1, MMPs, and osteocalcin expression is consistent with the fact that these genes could be part of a regulatory cascade initiated by RA and leading to the induction of Cbfa1, which in turn would upregulate the expression of some of their target genes like collagenase-3 and osteocalcin
Energy and Flux Measurements of Ultra-High Energy Cosmic Rays Observed During the First ANITA Flight
The first flight of the Antarctic Impulsive Transient Antenna (ANITA)
experiment recorded 16 radio signals that were emitted by cosmic-ray induced
air showers. For 14 of these events, this radiation was reflected from the ice.
The dominant contribution to the radiation from the deflection of positrons and
electrons in the geomagnetic field, which is beamed in the direction of motion
of the air shower. This radiation is reflected from the ice and subsequently
detected by the ANITA experiment at a flight altitude of 36km. In this paper,
we estimate the energy of the 14 individual events and find that the mean
energy of the cosmic-ray sample is 2.9 EeV. By simulating the ANITA flight, we
calculate its exposure for ultra-high energy cosmic rays. We estimate for the
first time the cosmic-ray flux derived only from radio observations. In
addition, we find that the Monte Carlo simulation of the ANITA data set is in
agreement with the total number of observed events and with the properties of
those events.Comment: Added more explanation of the experimental setup and textual
improvement
Thermodynamic behavior of IIA string theory on a pp-wave
We obtain the thermal one loop free energy and the Hagedorn temperature of
IIA superstring theory on the pp-wave geometry which comes from the circle
compactification of the maximally supersymmetric eleven dimensional one. We use
both operator and path integral methods and find the complete agreement between
them in the free energy expression. In particular, the free energy in the limit is shown to be identical with that of IIB string theory on
maximally supersymmetric pp-wave, which indicates the universal thermal
behavior of strings in the large class of pp-wave backgrounds. We show that the
zero point energy and the modular properties of the free energy are naturally
incorporated into the path integral formalism.Comment: 25 pages, Latex, JHEP style, v4: revised for clarity without change
in main contents, version to appear in JHE
Magnetic flux tube models in superstring theory
Superstring models describing curved 4-dimensional magnetic flux tube
backgrounds are exactly solvable in terms of free fields. We first consider the
simplest model of this type (corresponding to `Kaluza-Klein' Melvin
background). Its 2d action has a flat but topologically non-trivial
10-dimensional target space (there is a mixing of angular coordinate of the
2-plane with an internal compact coordinate). We demonstrate that this theory
has broken supersymmetry but is perturbatively stable if the radius R of the
internal coordinate is larger than R_0=\sqrt{2\a'}. In the Green-Schwarz
formulation the supersymmetry breaking is a consequence of the presence of a
flat but non-trivial connection in the fermionic terms in the action. For R <
R_0 and the magnetic field strength parameter q > R/2\a' there appear
instabilities corresponding to tachyonic winding states. The torus partition
function Z(q,R) is finite for R > R_0 (and vanishes for qR=2n, n=integer). At
the special points qR=2n (2n+1) the model is equivalent to the free superstring
theory compactified on a circle with periodic (antiperiodic) boundary condition
for space-time fermions. Analogous results are obtained for a more general
class of static magnetic flux tube geometries including the a=1 Melvin model.Comment: 28 pages, harvmac. Minor changes, final version to appear in NP
Sensors based on polymer modified electrodes
This paper will review the recent results that we have obtained using novel ruthenium-containing polymers, and on the further studies on the incorporation of proteins into polymeric matrices
Cosmic Neutrinos and the Energy Budget of Galactic and Extragalactic Cosmic Rays
Although kilometer-scale neutrino detectors such as IceCube are discovery
instruments, their conceptual design is very much anchored to the observational
fact that Nature produces protons and photons with energies in excess of
10^{20} eV and 10^{13} eV, respectively. The puzzle of where and how Nature
accelerates the highest energy cosmic particles is unresolved almost a century
after their discovery. We will discuss how the cosmic ray connection sets the
scale of the anticipated cosmic neutrino fluxes. In this context, we discuss
the first results of the completed AMANDA detector and the science reach of its
extension, IceCube.Comment: 13 pages, Latex2e, 3 postscript figures included. Talk presented at
the International Workshop on Energy Budget in the High Energy Universe,
Kashiwa, Japan, February 200
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