1,678 research outputs found
Searching for tau neutrinos with Cherenkov telescopes
Cherenkov telescopes have the capability of detecting high energy tau
neutrinos in the energy range of 1--1000 PeV by searching for very inclined
showers. If a tau lepton, produced by a tau neutrino, escapes from the Earth or
a mountain, it will decay and initiate a shower in the air which can be
detected by an air shower fluorescence or Cherenkov telescope. In this paper,
we present detailed Monte Carlo simulations of corresponding event rates for
the VERITAS and two proposed Cherenkov Telescope Array sites: Meteor Crater and
Yavapai Ranch, which use representative AGN neutrino flux models and take into
account topographic conditions of the detector sites. The calculated neutrino
sensitivities depend on the observation time and the shape of the energy
spectrum, but in some cases are comparable or even better than corresponding
neutrino sensitivities of the IceCube detector. For VERITAS and the considered
Cherenkov Telescope Array sites the expected neutrino sensitivities are up to
factor 3 higher than for the MAGIC site because of the presence of surrounding
mountains.Comment: arXiv admin note: text overlap with arXiv:1308.019
Hydrogen molecule in a magnetic field: The lowest states of the Pi manifold and the global ground state of the parallel configuration
The electronic structure of the hydrogen molecule in a magnetic field is
investigated for parallel internuclear and magnetic field axes. The lowest
states of the manifold are studied for spin singlet and triplet as well as gerade and ungerade parity for a broad range of field
strengths For both states with gerade parity we
observe a monotonous decrease in the dissociation energy with increasing field
strength up to and metastable states with respect to the
dissociation into two H atoms occur for a certain range of field strengths. For
both states with ungerade parity we observe a strong increase in the
dissociation energy with increasing field strength above some critical field
strength . As a major result we determine the transition field strengths
for the crossings among the lowest , and
states. The global ground state for is the strongly
bound state. The crossings of the with the
and state occur at and , respectively. The transition between the and
state occurs at Therefore, the global ground state of the
hydrogen molecule for the parallel configuration is the unbound
state for The ground state for is the strongly bound state. This result is of great
relevance to the chemistry in the atmospheres of magnetic white dwarfs and
neutron stars.Comment: submitted to Physical Review
Exchange and correlation energies of ground states of atoms and molecules in strong magnetic fields
Using a Hartree-Fock mesh method and a configuration interaction approach
based on a generalized Gaussian basis set we investigate the behaviour of the
exchange and correlation energies of small atoms and molecules, namely th e
helium and lithium atom as well as the hydrogen molecule, in the presence of a
magnetic field covering the regime B=0-100a.u. In general the importance of the
exchange energy to the binding properties of at oms or molecules increases
strongly with increasing field strength. This is due to the spin-flip
transitions and in particular due to the contributions of the tightly bound
hydrogenic state s which are involved in the corresponding ground states of
different symmetries. In contrast to the exchange energy the correlation energy
becomes less relevant with increasing field strength. This holds for the
individual configurations constituting the ground state and for the crossovers
of the global ground state.Comment: 4 Figures acc.f.publ.in Phys.Rev.
Identification of a novel retroviral gene unique to human immunodeficiency virus type 2 and simian immunodeficiency virus SIVMAC
Human and simian immunodeficiency-associated retroviruses are extraordinarily complex, containing at least five genes, tat, art, sor, R, and 3' orf, in addition to the structural genes gag, pol, and env. Recently, nucleotide sequence analysis of human immunodeficiency virus type 2 (HIV-2) and simian immunodeficiency virus SIVMAC revealed the existence of still another open reading frame, termed X, which is highly conserved between these two viruses but absent from HIV-1. In this report, we demonstrate for the first time that the X open reading frame represents a functional retroviral gene in both HIV-2 and SIVMAC and that it encodes a virion-associated protein of 14 and 12 kilodaltons, respectively. We also describe the production of recombinant TrpE/X fusion proteins in Escherichia coli and show that sera from some HIV-2-infected individuals specifically recognize these proteins
DEK Regulates Hematopoietic Stem Engraftment and Progenitor Cell Proliferation
DEK is a biochemically distinct protein that is generally found in the nucleus, where it is vital to global heterochromatin integrity. However, DEK is also secreted by cells (eg, macrophages) and influences other adjacent cells (eg, acts as a chemoattractant for certain mature blood cells). We hypothesized that DEK may modulate functions of hematopoietic stem (HSCs) and progenitor (HPCs) cells. C57Bl/6 mice were used to demonstrate that absolute numbers and cycling status of HPCs (colony forming unit-granulocyte macrophage [CFU-GM], burst forming unit-erythroid [BFU-E], and colony forming unit-granulocyte erythroid macrophage megakaryocyte [CFU-GEMM]) in bone marrow (BM) and spleen were significantly enhanced in DEK -/- as compared with wild-type (WT) control mice. Moreover, purified recombinant DEK protein inhibited colony formation in vitro by CFU-GM, BFU-E, and CFU-GEMM from WT BM cells and human cord blood (CB) cells in a dose-dependent fashion, demonstrating that DEK plays a negative role in HPC proliferation in vitro and in vivo. Suppression was direct acting as determined by inhibition of proliferation of single isolated CD34+ CB cells in vitro. In contrast, DEK -/- BM cells significantly demonstrated reduced long term competitive and secondary mouse repopulating HSC capacity compared with WT BM cells, demonstrating that DEK positively regulates engrafting capability of self-renewing HSCs. This demonstrates that DEK has potent effects on HSCs, HPCs, and hematopoiesis, information of biological and potential clinical interest.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90478/1/scd-2E2011-2E0451.pd
Eficiência agronômica de tecnologias de tratamento da ureia na cultura do algodão.
A cultura do algodão utiliza grande quantidade de fertilizantes nitrogenadas no processo produtivo. O objetivo deste trabalho foi avaliar tecnologias de tratamento da ureia para aumento da sua eficiência, no algodão. Avaliou-se o efeito de cinco fertilizantes nitrogenados em três doses, sob delineamento fatorial, além de um tratamento controle sem adubação nitrogenada, em duas safras no Mato Grosso, no rendimento de algodão em caroço, no número de maças, no peso de capulhos, na altura final e população de plantas. As doses de N avaliadas foram 0, 60, 90 e 120 kg ha-1, correspondentes à 0, 50, 75 e 100% da dose recomendada, respectivamente. Os parâmetros avaliados foram alterados positivamente pelas doses, mas não pelas tecnologias de tratamento da ureia, em ambas as safras. As tecnologias de tratamento para aumento da eficiência da ureia não permitem reduzir a dose de N recomendada, mas aumenta a eficiência agronômica na dose recomendada, em comparação com a ureia comum
A Novel Convex Relaxation for Non-Binary Discrete Tomography
We present a novel convex relaxation and a corresponding inference algorithm
for the non-binary discrete tomography problem, that is, reconstructing
discrete-valued images from few linear measurements. In contrast to state of
the art approaches that split the problem into a continuous reconstruction
problem for the linear measurement constraints and a discrete labeling problem
to enforce discrete-valued reconstructions, we propose a joint formulation that
addresses both problems simultaneously, resulting in a tighter convex
relaxation. For this purpose a constrained graphical model is set up and
evaluated using a novel relaxation optimized by dual decomposition. We evaluate
our approach experimentally and show superior solutions both mathematically
(tighter relaxation) and experimentally in comparison to previously proposed
relaxations
The Role of Nickel in Low Alloy Steels exposed to H2S-containing environments. Part I: Trench Formation at the Open Circuit Potential
The nickel content in low alloy steels (LAS) for oil and gas exploration and production is limited to a maximum of 1 wt.% according to ANSI/NACE MR 0175/ISO 15156. This restriction is imposed to avoid sulfide stress cracking (SSC) in sour (H2S-containing) environments. In this work, the effect of Ni on SSC of LAS was studied independently of other alloying elements. For this purpose, quenched and tempered steels heat treated to a yield strength of 610 MPa with a Ni content below and above the 1 wt.% threshold were evaluated at the open circuit potential (OCP) in unstressed specimens, and in slow strain rate tests (SSRT) at room temperature. Thiosulfate was used as a surrogate of H2S, according to the Tsujikawa method. It is concluded that Ni contributes to the stabilization of the sulfide films that form on the steel´s surface at OCP. The rupture of this film due to tensile stress promotes the nucleation of elongated deep pits, referred to as trenches, which can act as sulfide stress crack initiators. Trenches were observed exclusively in stressed, Ni-containing specimens. Moreover, trenches´ morphology, dimensions, and distribution varied with the Ni content in the steels. For the steels studied in this work, the Ni effect on trenching persisted below the 1 wt.% threshold.Fil: Chalfoun, Dannisa Romina. Universidad Nacional de San MartÃn. Instituto Sabato; Argentina. Comisión Nacional de EnergÃa Atómica; Argentina. Consejo Nacional de Investigaciones CientÃficas y Técnicas; ArgentinaFil: Kappes, Mariano Alberto. Universidad Nacional de San MartÃn. Instituto Sabato; Argentina. Comisión Nacional de EnergÃa Atómica; Argentina. Consejo Nacional de Investigaciones CientÃficas y Técnicas; ArgentinaFil: Perez, Teresa E.. Universidad Nacional de San MartÃn. Instituto Sabato; ArgentinaFil: Otegui, José L.. Consejo Nacional de Investigaciones CientÃficas y Técnicas; ArgentinaFil: Iannuzzi, Mariano. Curtin University; Australi
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