410 research outputs found
New stable phase of non uniform black strings in
We consider the non uniform black string equations in arbitrary number
of dimension in a perturbative approach up to order 2 and in a non
perturbative. We restrict the study in the perturbative approach to the
backreacting modes, since they provide the first relevant corrections on the
thermodynamical quantities of the solutions. We also present some preliminary
results in the construction of non-perturbative solutions, in particular, we
present a first part of the non uniform - uniform black string phase diagram.
Our results suggests the existence of a new stable phase for non uniform
black strings, namely long non uniform black string, with the extra direction
length of the order of the curvature.Comment: Results extended. 14 pages, 5 figure
Goldstone models in D+1 dimensions, D=3,4,5, supporting stable and zero topological charge solutions
We study finite energy static solutions to a global symmetry breaking
Goldstone model described by an isovector scalar field in D+1 spacetime
dimensions. Both topologically stable multisolitons with arbitrary winding
numbers, and zero topological charge soliton--antisoliton solutions are
constructed numerically in D=3,4,5. We have explored the types of symmetries
the systems should be subjected to, for there to exist multisoliton and
soliton--antisoliton pairs in D=3,4,5,6. These findings are underpinned by
constructing numerical solutions in the examples. Subject to axial
symmetry, only multisolitons of all topological charges exist in even D, and in
odd D, only zero and unit topological charge solutions exist. Subjecting the
system to weaker than axial symmetries, results in the existence of all the
possibilities in all dimensions. Our findings apply also to finite 'energy'
solutions to Yang--Mills and Yang-Mills--Higgs systems, and in principle also
sigma models.Comment: 29 pages, 6 figure
Rotating nonuniform black string solutions
We explore via linearized perturbation theory the Gregory-Laflamme
instability of rotating black strings with equal magnitude angular momenta. Our
results indicate that the Gregory-Laflamme instability persists up to
extremality for all even dimensions between six and fourteen. We construct
rotating nonuniform black strings with two equal magnitude angular momenta in
six dimensions. We see a first indication for the occurrence of a topology
changing transition, associated with such rotating nonuniform black strings.
Charged nonuniform black string configurations in heterotic string theory are
also constructed by employing a solution generation technique.Comment: 36 pages, 10 figures, final versio
Harrison transformation and charged black objects in Kaluza-Klein theory
We generate charged black brane solutions in dimensions in a theory of
gravity coupled to a dilaton and an antisymmetric form, by using a
Harrison-type transformation. The seed vacuum solutions that we use correspond
to uplifted Kaluza-Klein black strings and black holes in -dimensions. A
generalization of the Marolf-Mann quasilocal formalism to the Kaluza-Klein
theory is also presented, the global charges of the black objects being
computed in this way. We argue that the thermodynamics of the charged solutions
can be derived from that of the vacuum configurations. Our results show that
all charged Kaluza-Klein solutions constructed by means of Harrison
transformations are thermodynamically unstable in a grand canonical ensemble.
The general formalism is applied to the case of nonuniform black strings and
caged black hole solutions in Einstein-Maxwell-dilaton gravity, whose
geometrical properties and thermodynamics are discussed. We argue that the
topology changing transition scenario, which was previously proposed in the
vacuum case, also holds in this case. Spinning generalizations of the charged
black strings are constructed in six dimensions in the slowly rotating limit.
We find that the gyromagnetic ratio of these solutions possesses a nontrivial
dependence on the nonuniformity parameter.Comment: 42 pages, 12 figure
Sunscreens - Which and what for?
It is well established that sun exposure is the main cause for the development of skin cancer. Chronic continuous UV radiation is believed to induce malignant melanoma, whereas intermittent high-dose UV exposure contributes to the occurrence of actinic keratosis as precursor lesions of squamous cell carcinoma as well as basal cell carcinoma. Not only photocarcinogenesis but also the mechanisms of photoaging have recently become apparent. In this respect the use of sunscreens seemed to prove to be more and more important and popular within the last decades. However, there is still inconsistency about the usefulness of sunscreens. Several studies show that inadequate use and incomplete UV spectrum efficacy may compromise protection more than previously expected. The sunscreen market is crowded by numerous products. Inorganic sunscreens such as zinc oxide and titanium oxide have a wide spectral range of activity compared to most of the organic sunscreen products. It is not uncommon for organic sunscreens to cause photocontact allergy, but their cosmetic acceptability is still superior to the one given by inorganic sunscreens. Recently, modern galenic approaches such as micronization and encapsulation allow the development of high-quality inorganic sunscreens. The potential systemic toxicity of organic sunscreens has lately primarily been discussed controversially in public, and several studies show contradictory results. Although a matter of debate, at present the sun protection factor (SPF) is the most reliable information for the consumer as a measure of sunscreen filter efficacy. In this context additional tests have been introduced for the evaluation of not only the protective effect against erythema but also protection against UV-induced immunological and mutational effects. Recently, combinations of UV filters with agents active in DNA repair have been introduced in order to improve photoprotection. This article reviews the efficacy of sunscreens in the prevention of epithelial and nonepithelial skin cancer, the effect on immunosuppression and the value of the SPF as well as new developments on the sunscreen market. Copyright (C) 2005 S. Karger AG, Basel
Ultraviolet Extinction and Visible Transparency by Ivy Nanoparticles
Though much research has been conducted for nanoparticles, naturally occurring nanoparticles have not yet been well explored for their diverse properties and potential applications. This paper reports the optical absorption and scattering properties of nanoparticles secreted by English ivy. Both experimental and theoretical studies have been conducted. Strong ultraviolet extinction and excellent visible transparency are observed, compared to the inorganic TiO2 and ZnO nanoparticles at similar concentrations. The contributions of absorption and scattering to the total extinction are quantified by simulation of the Mie scattering theory
Influence of quorum sensing signal molecules on biofilm formation in Proteus mirabilis O18
The influence of basis of quorum sensing molecules on Proteus strains is much less known as compared to Pseudomonas or Escherichia. We have previously shown that a series of acylated homoserine lactones (acyl-HSL) does not influence the ureolytic, proteolytic, or hemolytic abilities, and that the swarming motility of Proteus mirabilis rods is strain specific. The aim of the presented study was to find out if the presence of a series of acyl-HSL influences biofilm formation of P. mirabilis laboratory strain belonging to O18 serogroup. This serogroup is characterized by the presence of a unique non-carbohydrate component, namely phosphocholine. Escherichia coli and P. mirabilis O18 strains used in this work contains cloned plasmids encoding fluorescent protein genes with constitutive gene expression. In mixed biofilms in stationary and continuous flow conditions, P. mirabilis O18 overgrow whole culture. P. mirabilis O18 strain has genetically proved a presence of AI–2 quorum sensing system. Differences in biofilm structure were observed depending on the biofilm type and culture methods. From tested acylated homoserine lactones (BHL, HHL, OHL, DHL, dDHL, tDHL), a significant influence had BHL on thickness, structure, and the amount of exopolysaccharides produced by biofilms formed by P. mirabilis O18 pDsRed2
Research on eco-hydro-morphological river processes by combining field investigations, physical modeling and numerical simulations
Hydrodynamical, morphodynamical and ecological river processes and their multiple linkages occur in an infinity of different configurations and over a wide range of spatial and temporal scales. This paper illustrates a research methodology that consists in combining field investigations, physical modeling in the laboratory, and numerical simulations in order to develop generic insight and tools for engineering and management of the river environment. This combined methodology is illustrated in research on (i) the macroscale characteristics of the velocity distribution and their relation to long-term and large-scale planimetric river processes, (ii) the flow field in the vicinity of the river bank and its importance with respect to bank erosion and, (iii) linkages between the characteristics of the mean flow and the turbulence on the one hand, and the behavior of invertebrates on the other. The reported research strongly relies on the use of state-of-the-art measuring instruments as well as numerical techniques
Determination of Molecular Structures of HIV Envelope Glycoproteins using Cryo-Electron Tomography and Automated Sub-tomogram Averaging
Since its discovery nearly 30 years ago, more than 60 million people have been infected with the human immunodeficiency virus (HIV) (www.usaid.gov). The virus infects and destroys CD4+ T-cells thereby crippling the immune system, and causing an acquired immunodeficiency syndrome (AIDS) 2. Infection begins when the HIV Envelope glycoprotein "spike" makes contact with the CD4 receptor on the surface of the CD4+ T-cell. This interaction induces a conformational change in the spike, which promotes interaction with a second cell surface co-receptor 5,9. The significance of these protein interactions in the HIV infection pathway makes them of profound importance in fundamental HIV research, and in the pursuit of an HIV vaccine
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