1,030 research outputs found
Astrophysical Production of Microscopic Black Holes in a Low Planck-scale World
In the framework of brane-world models lowering the Planck scale to the TeV
range, it has recently been pointed out that small black holes could be formed
at particle colliders or by neutrinos interactions in the atmosphere. This
article aims at reviewing other places and epochs where microscopic black holes
could be formed : the interstellar medium and the early Universe. The related
decay channels and the propagation of the emitted particles are studied to
conclude that, in spite of the large creation rate for such black holes, the
amount of produced particles do not conflict with experimental data. This
shows, from the astronomical viewpoint, that models with large extra dimensions
making the gravity scale much lower are compatible with observations.Comment: To appear in Ap
A Message Passing Strategy for Decentralized Connectivity Maintenance in Agent Removal
In a multi-agent system, agents coordinate to achieve global tasks through
local communications. Coordination usually requires sufficient information
flow, which is usually depicted by the connectivity of the communication
network. In a networked system, removal of some agents may cause a
disconnection. In order to maintain connectivity in agent removal, one can
design a robust network topology that tolerates a finite number of agent
losses, and/or develop a control strategy that recovers connectivity. This
paper proposes a decentralized control scheme based on a sequence of
replacements, each of which occurs between an agent and one of its immediate
neighbors. The replacements always end with an agent, whose relocation does not
cause a disconnection. We show that such an agent can be reached by a local
rule utilizing only some local information available in agents' immediate
neighborhoods. As such, the proposed message passing strategy guarantees the
connectivity maintenance in arbitrary agent removal. Furthermore, we
significantly improve the optimality of the proposed scheme by incorporating
-criticality (i.e. the criticality of an agent in its
-neighborhood).Comment: 9 pages, 9 figure
Using Ground Transportation for Aviation System Disruption Alleviation
An investigation was made into whether passenger delays and airline costs due to disruptive events affecting European airports could be reduced by a coordinated strategy of using alternative flights and ground transportation to help stranded passengers reach their final destination using airport collaborative decision-making concepts. Optimizing for airline cost for hypothetical disruptive events suggests that, for airport closures of up to 10 h, airlines could benefit from up to a 20% reduction in passenger delay-related costs. The mean passenger delay could be reduced by up to 70%, mainly via a reduction in very long delays
Bone Marrow Microenvironment and Tumor Progression
The bone marrow constitutes an unique microenvironment for cancer cells in three specific aspects. First, the bone marrow actively recruits circulating tumor cells where they find a sanctuary rich in growth factors and cytokines that promote their proliferation and survival. When in the bone marrow, tumor cells profoundly affect the homeostasis of the bone and the balance between osteogenesis and osteolysis. As a consequence, growth and survival factors normally sequestered into the bone matrix are released, further fueling cancer progression. Second, tumor cells actively recruit bone marrow-derived precursor cells into their own microenvironment. When in the tumors, these bone marrow-derived cells contribute to an inflammatory reaction and to the formation of the tumor vasculature. Third, bone marrow-derived cells can home in distant organs, where they form niches that attract circulating tumor cells. Our understanding of the contribution of the bone marrow microenvironment to cancer progression has therefore dramatically improved over the last few years. The importance of this new knowledge cannot be underestimated considering that the vast majority of cancer treatments such as cytotoxic and myeloablative chemotherapy, bone marrow transplantation and radiation therapy inflict a trauma to the bone marrow microenvironment. How such trauma affects the influence that the bone marrow microenvironment exerts on cancer is still poorly understood. In this article, the reciprocal relationship between the bone marrow microenvironment and tumor cells is reviewed, and its potential impact on cancer therapy is discussed
Systematic study of aqueous monoethanolamine-based CO2 capture process: model development and process improvement
In this paper, we present improvements to postcombustion capture (PCC) processes based on aqueous monoethanolamine (MEA). First, a rigorous, rate-based model of the carbon dioxide (CO2) capture process from flue gas by aqueous MEA was developed using Aspen Plus, and validated against results from the PCC pilot plant trials located at the coal-fired Tarong power station in Queensland, Australia. The model satisfactorily predicted the comprehensive experimental results from CO2 absorption and CO2 stripping process. The model was then employed to guide the systematic study of the MEA-based CO2 capture process for the reduction in regeneration energy penalty through parameter optimization and process modification. Important process parameters such as MEA concentration, lean CO2 loading, lean temperature, and stripper pressure were optimized. The process modifications were investigated, which included the absorber intercooling, rich-split, and stripper interheating processes. The minimum regeneration energy obtained from the combined parameter optimization and process modification was 3.1 MJ/kg CO2. This study suggests that the combination of a validated rate-based model and process simulation can be used as an effective tool to guide sophisticated process plant, equipment design and process improvement
Antibacterial Activity of Calcium Hydroxide Combined with Chlrohexidine or Sodium Hypochlorite against Gram Positive and Gram Negative Bacteria
The most significant current goal in endodontology is the maximum reduction of the microorganisms because they play a fundamental role in the etiology of pulpo-periapical pathosis and may escape from tooth and circulate throughout the body to cause an infection in distant part. Numerous materials have been used to achieve this goal. Calcium hydroxide [Ca(OH)2]with its unique properties, need to be mixed with other agents to fulfill its antimicrobial requirement. However, to the best of authors knowledge , no report has been found so far investigates the antimicrobial efficacy of Calcium hydroxide / chlorhexidine [CHX ]combination against klebsiella spp..The aim of this study is to evaluation of the effect of adding CHX or sodium hypochlorite[NaOCl] on the antibacterial activity of Ca(OH)2 against gram positive and gram negative bacteria. The tested samples were grouped into 5 groups of 20 samples for each group: G1:Ca(OH)2 mixed with H2O. G2:2% CHX solution. G3: 2.5% NaOCl solution. G4: combination of Ca(OH)2 and 2% CHX. G5:combination of Ca(OH)2 and 2.5% NaOCl. 10 samples from each group had been inoculated with streptococcus spp. and the other 10 had been inoculated with klebsiella spp. Microbial growth was verified and number of plates which show growth or no growth for bacteria were counted and analyzed statistically. As a result Ca(OH)2 and 2.5% NaOCl had antibacterial effect on both tested bacteria while 2% CHX appeared to be less effective . Pastes of Ca(OH)2 and 2% CHX were effective on klebsiella spp., while mixing of Ca(OH)2 with 2.5% NaOCl had significant effect on both types of bacteria and it was more effective against streptococcus spp. Key words: Calcium hydroxide, Chlorhexidine, Sodium hypochlorite, klebsiella, Streptococcus
Modeling the Images of Relativistic Jets Lensed by Galaxies with Different Mass Surface Density Distributions
The images of relativistic jets from extragalactic sources produced by
gravitational lensing by galaxies with different mass surface density
distributions are modeled. In particular, the following models of the
gravitational lens mass distribution are considered: a singular isothermal
ellipsoid, an isothermal ellipsoid with a core, two- and three-component models
with a galactic disk, halo, and bulge. The modeled images are compared both
between themselves and with available observations. Different sets of
parameters are shown to exist for the gravitationally lensed system B0218+357
in multicomponent models. These sets allow the observed geometry of the system
and the intensity ratio of the compact core images to be obtained, but they
lead to a significant variety in the Hubble constant determined from the
modeling results.Comment: 26 pages, 9 figures, will be published in the Astronomy Letters,
2011, v.37, N4, pp. 233-24
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