5,878 research outputs found
Nonequilibrium Stefan-Boltzmann law
We study thermal radiation outside equilibrium. The situation considered
consists of two bodies emitting photons at two different temperatures. We show
that the system evolves to a stationary state characterized by an energy
current which satisfies a Stefan-Boltzmann-like law expressing it as the
difference of the temperatures to the fourth power of the emitters . The
results obtained show how the classical laws governing the thermal radiation at
equlibrium can be generalized away from equilibrium situations.Comment: 9 pages, 1 figure. To be published in J. Noneq. Ther
Massive envelopes and filaments in the NGC 3603 star forming region
The formation of massive stars and their arrival on the zero-age
main-sequence occurs hidden behind dense clouds of gas and dust. In the giant
Hii region NGC 3603, the radiation of a young cluster of OB stars has dispersed
dust and gas in its vicinity. At a projected distance of 2:5 pc from the
cluster, a bright mid-infrared (mid-IR) source (IRS 9A) had been identified as
a massive young stellar object (MYSO), located on the side of a molecular clump
(MM2) of gas facing the cluster. We investigated the physical conditions in
MM2, based on APEX sub-mm observations using the SABOCA and SHFI instruments,
and archival ATCA 3 mm continuum and CS spectral line data. We resolved MM2
into several compact cores, one of them closely associated with IRS 9A. These
are likely infrared dark clouds as they do not show the typical hot-core
emission lines and are mostly opaque against the mid-IR background. The compact
cores have masses of up to several hundred times the solar mass and gas
temperatures of about 50 K, without evidence of internal ionizing sources. We
speculate that IRS 9A is younger than the cluster stars, but is in an
evolutionary state after that of the compact cores
Effects of Liposomes Contained in Thermosensitive Hydrogels as Biomaterials Useful in Neural Tissue Engineering
Indexación: Scopus.Advances in the generation of suitable thermosensitive hydrogels for the delivery of cells in neural tissue engineering demonstrate a delicate relationship between physical properties and capabilities to promote cell proliferation and differentiation. To improve the properties of these materials, it is possible to add liposomes for the controlled release of bioactive elements, which in turn can affect the physical and biological properties of the hydrogels. In the present investigation, different hydrogels based on Pluronic F127 have been formulated with the incorporation of chitosan and two types of liposomes of two different sizes. The rheological and thermal properties and their relation with the neurite proliferation and growth of the PC12 cell line were evaluated. Our results show that the incorporation of liposomes modifies the properties of the hydrogels dependent on the concentration of chitosan and the lipid type in the liposomes, which directly affect the capabilities of the hydrogels to promote the viability and differentiation of PC12 cells. © 2017 by the authors.http://www.mdpi.com/1996-1944/10/10/112
A study of ignition phenomena of bulk metals by radiant heating
Early research on combustion of metals was motivated by the knowledge of the large heat release and corresponding high temperatures associated with metal-oxygen reactions. The advent of space flight brought about an increased interest in the ignition and combustion of metallic particles as additives in solid rocket propellants. More recently, attention has been given to the flammability properties of bulk, structural metals due to the number of accidental explosions of metal components in high-pressure oxygen systems. The following work represents a preliminary study that is part of a broader research effort aimed at providing further insight into the phenomena of bulk metal combustion by looking at the effects of gravity on the ignition behavior of metals. The scope of this preliminary experimental study includes the use of a non-coherent, continuous radiation ignition source, the measurement of temperature profiles of a variety of metals and a qualitative observation of the ignition phenomena at normal gravity. The specific objectives of the investigation include: (1) a feasibility study of the use of a continuous radiation source for metal ignition; (2) testing and characterization of the ignition behavior of a variety of metals; and (3) building a preliminary experimental database on ignition of metals under normal gravity conditions
Diversity of chemistry and excitation conditions in the high-mass star forming complex W33
The object W33 is a giant molecular cloud that contains star forming regions
at various evolutionary stages from quiescent clumps to developed H II regions.
Since its star forming regions are located at the same distance and the primary
material of the birth clouds is probably similar, we conducted a comparative
chemical study to trace the chemical footprint of the different phases of
evolution. We observed six clumps in W33 with the Atacama Pathfinder Experiment
(APEX) telescope at 280 GHz and the Submillimeter Array (SMA) at 230 GHz. We
detected 27 transitions of 10 different molecules in the APEX data and 52
transitions of 16 different molecules in the SMA data. The chemistry on scales
larger than 0.2 pc, which are traced by the APEX data, becomes more
complex and diverse the more evolved the star forming region is. On smaller
scales traced by the SMA data, the chemical complexity and diversity increase
up to the hot core stage. In the H II region phase, the SMA spectra resemble
the spectra of the protostellar phase. Either these more complex molecules are
destroyed or their emission is not compact enough to be detected with the SMA.
Synthetic spectra modelling of the HCO transitions, as detected with the
APEX telescope, shows that both a warm and a cold component are needed to
obtain a good fit to the emission for all sources except for W33 Main1. The
temperatures and column densities of the two components increase during the
evolution of the star forming regions. The integrated intensity ratios
NH(32)/CS(65) and
NH(32)/HCO(43) show clear trends as a
function of evolutionary stage, luminosity, luminosity-to-mass ratio, and
H peak column density of the clumps and might be usable as chemical
clocks.Comment: 66 pages, 28 figures, 8 tables, accepted for publication at A&
On the inconsistency of the Bohm-Gadella theory with quantum mechanics
The Bohm-Gadella theory, sometimes referred to as the Time Asymmetric Quantum
Theory of Scattering and Decay, is based on the Hardy axiom. The Hardy axiom
asserts that the solutions of the Lippmann-Schwinger equation are functionals
over spaces of Hardy functions. The preparation-registration arrow of time
provides the physical justification for the Hardy axiom. In this paper, it is
shown that the Hardy axiom is incorrect, because the solutions of the
Lippmann-Schwinger equation do not act on spaces of Hardy functions. It is also
shown that the derivation of the preparation-registration arrow of time is
flawed. Thus, Hardy functions neither appear when we solve the
Lippmann-Schwinger equation nor they should appear. It is also shown that the
Bohm-Gadella theory does not rest on the same physical principles as quantum
mechanics, and that it does not solve any problem that quantum mechanics cannot
solve. The Bohm-Gadella theory must therefore be abandoned.Comment: 16 page
New bounds for discrete lacunary spherical averages
We show that the discrete lacunary spherical maximal function is bounded on
for all . Our range is new in dimension
4, where it appears that little was previously known for general lacunary
radii. Our technique follows that of Kesler-Lacey-Mena, using the Kloosterman
refinement to improve the estimates in several places, which leads to an
overall improvement in dimension 4.Comment: Errors corrected. Proof is restructured, but main result remains the
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