3,688 research outputs found
The connection between entropy and the absorption spectra of Schwarzschild black holes for light and massless scalar fields
We present heuristic arguments suggesting that if EM waves with wavelengths
somewhat larger than the Schwarzschild radius of a black hole were fully
absorbed by it, the second law of thermodynamics would be violated, under the
Bekenstein interpretation of the area of a black hole as a measure of its
entropy. Thus, entropy considerations make the well known fact that large
wavelengths are only marginally absorbed by black holes, a natural consequence
of thermodynamics. We also study numerically the ingoing radial propagation of
a scalar field wave in a Schwarzschild metric, relaxing the standard assumption
which leads to the eikonal equation, that the wave has zero spatial extent. We
find that if these waves have wavelengths larger that the Schwarzschild radius,
they are very substantially reflected, fully to numerical accuracy.
Interestingly, this critical wavelength approximately coincides with the one
derived from entropy considerations of the EM field, and is consistent with
well known limit results of scattering in the Schwarzschild metric. The
propagation speed is also calculated and seen to differ from the value , for
wavelengths larger than , in the vicinity of . As in all
classical wave phenomena, whenever the wavelength is larger or comparable to
the physical size of elements in the system, in this case changes in the
metric, the zero extent 'particle' description fails, and the wave nature
becomes apparent.Comment: 14 Pages, 4 figures. Accepted for publication in the Journal Entrop
Early Outbreak of 2009 Influenza A (H1N1) in Mexico Prior to Identification of pH1N1 Virus
10.1371/journal.pone.0023853PLoS ONE68
Modelling the Effect of Treatment and Behavioral Change in HIV Transmission Dynamics
25 pages, 1 article*Modelling the Effect of Treatment and Behavioral Change in HIV Transmission Dynamics* (Hsieh, Ying-Hen; Velasco-Hernandez, Jorge X.) 25 page
Interplay between HIV/AIDS Epidemics and Demographic Structures Based on Sexual Contact Networks
In this article, we propose a network spread model for HIV epidemics, wherein
each individual is represented by a node of the transmission network and the
edges are the connections between individuals along which the infection may
spread. The sexual activity of each individual, measured by its degree, is not
homogeneous but obeys a power-law distribution. Due to the heterogeneity of
activity, the infection can persistently exist at a very low prevalence, which
has been observed in real data but can not be illuminated by previous models
with homogeneous mixing hypothesis. Furthermore, the model displays a clear
picture of hierarchical spread: In the early stage the infection is adhered to
these high-risk persons, and then, diffuses toward low-risk population. The
prediction results show that the development of epidemics can be roughly
categorized into three patterns for different countries, and the pattern of a
given country is mainly determined by the average sex-activity and transmission
probability per sexual partner. In most cases, the effect of HIV epidemics on
demographic structure is very small. However, for some extremely countries,
like Botswana, the number of sex-active people can be depressed to nearly a
half by AIDS.Comment: 23 pages, 12 figure
HIF1α drives chemokine factor pro-tumoral signaling pathways in acute myeloid leukemia
Approximately 80% of patients diagnosed with acute myeloid leukemia (AML) die as a consequence of failure to eradicate the tumor from the bone marrow microenvironment. We have recently shown that stroma-derived interleukin-8 (IL-8) promotes AML growth and survival in the bone marrow in response to AML-derived macrophage migration inhibitory factor (MIF). In the present study we show that high constitutive expression of MIF in AML blasts in the bone marrow is hypoxia-driven and, through knockdown of MIF, HIF1α and HIF2α, establish that hypoxia supports AML tumor proliferation through HIF1α signaling. In vivo targeting of leukemic cell HIF1α inhibits AML proliferation in the tumor microenvironment through transcriptional regulation of MIF, but inhibition of HIF2α had no measurable effect on AML blast survival. Functionally, targeted inhibition of MIF in vivo improves survival in models of AML. Here we present a mechanism linking HIF1α to a pro-tumoral chemokine factor signaling pathway and in doing so, we establish a potential strategy to target AML
Osteocyte deficiency in hip fractures
Osteocytes play a central role in the regulation of bone remodeling. The aim of this study was to explore osteocyte function, and particularly the expression of SOST, a Wnt inhibitor, in patients with hip fractures. Serum sclerostin levels were measured by ELISA. The expression of several osteocytic genes was studied by quantitative PCR in trabecular samples of the femoral head of patients with hip fractures, hip osteoarthritis and control subjects. The presence of sclerostin protein and activated caspase 3 was revealed by immunostaining. There were no significant differences in serum sclerostin between the three groups. Patients with fractures have fewer lacunae occupied by osteocytes (60 ± 5% vs. 64 ± 6% in control subjects, P = 0.014) and higher numbers of osteocytes expressing activated caspase 3, a marker of apoptosis. The proportion of sclerostin-positive lacunae was lower in patients with fractures than in control subjects (34 ± 11% vs. 69 ± 10%, P = 2 × 10(-8)). The proportion of sclerostin-positive osteocytes was also lower in patients. RNA transcripts of SOST, FGF23 and PHEX were also less abundant in fractures than in control bones (P = 0.002, 5 × 10(-6), and 0.04, respectively). On the contrary, in patients with osteoarthritis, there was a decreased expression of SOST and FGF23, without differences in PHEX transcripts or osteocyte numbers. Osteocyte activity is altered in patients with hip fractures, with increased osteocyte apoptosis and reduced osteocyte numbers, as well as decreased transcription of osteocytic genes. Therefore, these results suggest that an osteocyte deficiency may play a role in the propensity to hip fractures
Chitosan–Starch–Keratin composites: Improving thermo-mechanical and degradation properties through chemical modification
The lysozyme test shows an improved in the degradability rate, the weight loss of the films at 21 days is reduced from 73 % for chitosan-starch matrix up to 16 % for the composites with 5wt% of quill; but all films show a biodegradable character depending on keratin type and chemical modification. The outstanding properties related to the addition of treated keratin materials show that these natural composites are a remarkable alternative to potentiat-ing chitosan–starch films with sustainable featuresChitosan–starch polymers are reinforced with different keratin materials obtained from chicken feather. Keratin materials are treated with sodium hydroxide; the modified surfaces are rougher in comparison with untreated surfaces, observed by Scanning Electron Microscopy. The results obtained by Differential Scanning Calorimetry show an increase in the endothermic peak related to water evaporation of the films from 92 °C (matrix) up to 102–114 °C (reinforced composites). Glass transition temperature increases from 126 °C in the polymer matrix up to 170–200 °C for the composites. Additionally, the storage modulus in the composites is enhanced up to 1614 % for the composites with modified ground quill, 2522 % for composites with modified long fiber and 3206 % for the composites with modified short fiber. The lysozyme test shows an improved in the degradability rate, the weight loss of the films at 21 days is reduced from 73 % for chitosan-starch matrix up to 16 % for the composites with 5wt% of quill; but all films show a biodegradable character depending on keratin type and chemical modification. The outstanding properties related to the addition of treated keratin materials show that these natural composites are a remarkable alternative to potentiat-ing chitosan–starch films with sustainable featuresUniversidad Autónoma del Estado de México Tecnológico Nacional de México, Instituto Tecnológico de Querétaro Universidad Nacional Autónoma de México Tecnológico Nacional de México, Instituto Tecnológico de Celaya Universidad Autónoma de Cd. Juáre
VAMOS: a Pathfinder for the HAWC Gamma-Ray Observatory
VAMOS was a prototype detector built in 2011 at an altitude of 4100m a.s.l.
in the state of Puebla, Mexico. The aim of VAMOS was to finalize the design,
construction techniques and data acquisition system of the HAWC observatory.
HAWC is an air-shower array currently under construction at the same site of
VAMOS with the purpose to study the TeV sky. The VAMOS setup included six water
Cherenkov detectors and two different data acquisition systems. It was in
operation between October 2011 and May 2012 with an average live time of 30%.
Besides the scientific verification purposes, the eight months of data were
used to obtain the results presented in this paper: the detector response to
the Forbush decrease of March 2012, and the analysis of possible emission, at
energies above 30 GeV, for long gamma-ray bursts GRB111016B and GRB120328B.Comment: Accepted for pubblication in Astroparticle Physics Journal (20 pages,
10 figures). Corresponding authors: A.Marinelli and D.Zaboro
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