17,726 research outputs found
Geometrical and electronic structures of the (5, 3) single-walled gold nanotube from first-principles calculations
The geometrical and electronic structures of the 4 {\AA} diameter perfect and
deformed (5, 3) single-walled gold nanotube (SWGT) have been studied based upon
the density-functional theory in the local-density approximation (LDA). The
calculated relaxed geometries show clearly significant deviations from those of
the ideally rolled triangular gold sheet. It is found that the different
strains have different effects on the electronic structures and density of
states of the SWGTs. And the small shear strain can reduce the binding energy
per gold atom of the deformed SWGT, which is consistent with the experimentally
observed result. Finally, we found the finite SWGT can show the
metal-semiconductor transition.Comment: 11 pages, 4 figure
Self-assembling DNA-caged particles: nanoblocks for hierarchical self-assembly
DNA is an ideal candidate to organize matter on the nanoscale, primarily due
to the specificity and complexity of DNA based interactions. Recent advances in
this direction include the self-assembly of colloidal crystals using DNA
grafted particles. In this article we theoretically study the self-assembly of
DNA-caged particles. These nanoblocks combine DNA grafted particles with more
complicated purely DNA based constructs. Geometrically the nanoblock is a
sphere (DNA grafted particle) inscribed inside a polyhedron (DNA cage). The
faces of the DNA cage are open, and the edges are made from double stranded
DNA. The cage vertices are modified DNA junctions. We calculate the
equilibriuim yield of self-assembled, tetrahedrally caged particles, and
discuss their stability with respect to alternative structures. The
experimental feasability of the method is discussed. To conclude we indicate
the usefulness of DNA-caged particles as nanoblocks in a hierarchical
self-assembly strategy.Comment: v2: 21 pages, 8 figures; revised discussion in Sec. 2, replaced 2
figures, added new reference
Global mean sea surface computation based upon a combination of SEASAT and GEOS-3 satellite altimeter data
A mean sea surface map was computed for the global ocean areas between 70 deg N latitude and 62 deg S latitude based upon the 70 day SEASAT and 3.5 year GEOS-3 altimeter data sets. The mean sea surface is presented in the form of a global contour map and a 0.25 deg x 0.25 deg grid. A combination of regional adjustments based upon crossover techniques and the subsequent adjustment of the regional solutions into a global reference system was employed in order to minimize the effects of radial orbit error. A global map of the crossover residuals after the crossover adjustments are made is in good agreement with earlier mesoscale variability contour maps based upon the last month of SEASAT collinear data. This high level of agreement provides good evidence that relative orbit error was removed to the decimeter level on a regional basis. This represents a significant improvement over our previous maps which contained patterns, particularly in the central Pacific, which were due to radial orbit error. Long wavelength, basin scale errors are still present with a submeter amplitude due to errors in the PGS-S4 gravity model. Such errors can only be removed through the improvement of the Earth's gravity model and associated geodetic parameters
Role of HIV Subtype Diversity in the Development of Resistance to Antiviral Drugs
Despite the fact that over 90% of HIV-1 infected people worldwide harbor non-subtype B variants of HIV-1, knowledge of resistance mutations in non-B HIV-1 and their clinical relevance is limited. Due to historical delays in access to antiretroviral therapy (ART) on a worldwide basis, the vast majority of reports on drug resistance deal with subtype B infections in developed countries. However, both enzymatic and virological data support the concept that naturally occurring polymorphisms among different nonB subtypes can affect HIV-1 susceptibility to antiretroviral drugs (ARVs), the magnitude of resistance conferred by major mutations, and the propensity to acquire some resistance mutations. Tools need to be optimized to assure accurate measurements of drug susceptibility of non-B subtypes. Furthermore, there is a need to recognize that each subtype may have a distinct resistance profile and that differences in resistance pathways may also impact on cross-resistance and the selection of second-line regimens. It will be essential to pay attention to newer drug combinations in well designed long-term longitudinal studies involving patients infected by viruses of different subtypes
Consequences of wall stiffness for a beta-soft potential
Modifications of the infinite square well E(5) and X(5) descriptions of
transitional nuclear structure are considered. The eigenproblem for a potential
with linear sloped walls is solved. The consequences of the introduction of
sloped walls and of a quadratic transition operator are investigated.Comment: RevTeX 4, 8 pages, as published in Phys. Rev.
Generalized Incremental Mechanisms for Scheduling Games
We study the problem of devising truthful mechanisms for cooperative cost sharing
games that realize (approximate) budget balance and social cost. Recent negative
results show that group-strategyproof mechanisms can only achieve very poor approximation
guarantees for several fundamental cost sharing games. Driven by these limitations,
we consider cost sharing mechanisms that realize the weaker notion of weak groupstrategyproofness.
Mehta et al. [Games and Economic Behavior, 67:125–155, 2009] recently
introduced the broad class of weakly group-strategyproof acyclic mechanisms and
show that several primal-dual approximation algorithms naturally give rise to such mechanisms
with attractive approximation guarantees. In this paper, we provide a simple yet
powerful approach that enables us to turn any r-approximation algorithm into a r-budget
balanced acyclic mechanism. We demonstrate the applicability of our approach by deriving
weakly group-strategyproof mechanisms for several fundamental scheduling problems
that outperform the best possible approximation guarantees of Moulin mechanisms.
The mechanisms that we develop for completion time scheduling problems are the first
mechanisms that achieve constant budget balance and social cost approximation factors.
Interestingly, our mechanisms belong to the class of generalized incremental mechanisms
proposed by Moulin [Social Choice and Welfare, 16:279–320, 1999]
Encapsulation of phosphorus dopants in silicon for the fabrication of a quantum computer
The incorporation of phosphorus in silicon is studied by analyzing phosphorus
delta-doped layers using a combination of scanning tunneling microscopy,
secondary ion mass spectrometry and Hall effect measurements. The samples are
prepared by phosphine saturation dosing of a Si(100) surface at room
temperature, a critical annealing step to incorporate phosphorus atoms, and
subsequent epitaxial silicon overgrowth. We observe minimal dopant segregation
(5 nm), complete electrical activation at a silicon growth temperature of 250
degrees C and a high two-dimensional electron mobility of 100 cm2/Vs at a
temperature of 4.2 K. These results, along with preliminary studies aimed at
further minimizing dopant diffusion, bode well for the fabrication of
atomically precise dopant arrays in silicon such as those found in recent
solid-state quantum computer architectures.Comment: 3 pages, 4 figure
Caspase-generated fragment of the Met receptor favors apoptosis via the intrinsic pathway independently of its tyrosine kinase activity
The receptor tyrosine kinase Met and its ligand, the hepatocyte growth factor, are essential to embryonic development, whereas the deregulation of Met signaling is associated with tumorigenesis. While ligand-activated Met promotes survival, caspase-dependent generation of the p40 Met fragment leads to apoptosis induction – hallmark of the dependence receptor. Although the survival signaling pathways induced by Met are well described, the pro-apoptotic signaling pathways are unknown. We show that, although p40 Met contains the entire kinase domain, it accelerates apoptosis independently of kinase activity. In cell cultures undergoing apoptosis, the fragment shows a mitochondrial localization, required for p40 Met-induced cell death. Fulminant hepatic failure induced in mice leads to the generation of p40 Met localized also in the mitochondria, demonstrating caspase cleavage of Met in vivo. According to its localization, the fragment induces mitochondrial permeabilization, which is inhibited by Bak silencing and Bcl-xL overexpression. Moreover, Met silencing delays mitochondrial permeabilization induced by an apoptotic treatment. Thus, the Met-dependence receptor in addition to its well-known role in survival signaling mediated by its kinase activity, also participates in the intrinsic apoptosis pathway through the generation of p40 Met – a caspase-dependent fragment of Met implicated in the mitochondrial permeabilization process
Sonoluminescing air bubbles rectify argon
The dynamics of single bubble sonoluminescence (SBSL) strongly depends on the
percentage of inert gas within the bubble. We propose a theory for this
dependence, based on a combination of principles from sonochemistry and
hydrodynamic stability. The nitrogen and oxygen dissociation and subsequent
reaction to water soluble gases implies that strongly forced air bubbles
eventually consist of pure argon. Thus it is the partial argon (or any other
inert gas) pressure which is relevant for stability. The theory provides
quantitative explanations for many aspects of SBSL.Comment: 4 page
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