1,058 research outputs found
Nanofriction behavior of cluster-assembled carbon films
We have characterized the frictional properties of nanostructured (ns) carbon
films grown by Supersonic Cluster Beam Deposition (SCBD) via an Atomic
Force-Friction Force Microscope (AFM-FFM). The experimental data are discussed
on the basis of a modified Amonton's law for friction, stating a linear
dependence of friction on load plus an adhesive offset accounting for a finite
friction force in the limit of null total applied load. Molecular Dynamics
simulations of the interaction of the AFM tip with the nanostructured carbon
confirm the validity of the friction model used for this system. Experimental
results show that the friction coefficient is not influenced by the
nanostructure of the films nor by the relative humidity. On the other hand the
adhesion coefficient depends on these parameters.Comment: 22 pages, 6 figures, RevTex
Quantum Sensor Miniaturization
The classical bound on image resolution defined by the Rayleigh limit can be
beaten by exploiting the properties of quantum mechanical entanglement. If
entangled photons are used as signal states, the best possible resolution is
instead given by the Heisenberg limit, an improvement proportional to the
number of entangled photons in the signal. In this paper we present a novel
application of entanglement by showing that the resolution obtained by an
imaging system utilizing separable photons can be achieved by an imaging system
making use of entangled photons, but with the advantage of a smaller aperture,
thus resulting in a smaller and lighter system. This can be especially valuable
in satellite imaging where weight and size play a vital role.Comment: 3 pages, 1 figure. Accepted for publication in Photonics Technology
Letter
Polyamorphism of ice at low temperatures from constant-pressure simulations
We report results of MD simulations of amorphous ice in the pressure range 0
- 22.5 kbar. The high-density amorphous ice (HDA) prepared by compression of Ih
ice at T = 80 K is annealed to T = 170 K at intermediate pressures in order to
generate relaxed states. We confirm the existence of recently observed
phenomena, the very high-density amorphous ice and a continuum of HDA forms. We
suggest that both phenomena have their origin in the evolution of the network
topology of the annealed HDA phase with decreasing volume, resulting at low
temperatures in the metastability of a range of densities.Comment: 11 pages, 5 postscript figures. To be published in Physical Review
Letter
Canonical sampling through velocity-rescaling
We present a new molecular dynamics algorithm for sampling the canonical
distribution. In this approach the velocities of all the particles are rescaled
by a properly chosen random factor. The algorithm is formally justified and it
is shown that, in spite of its stochastic nature, a quantity can still be
defined that remains constant during the evolution. In numerical applications
this quantity can be used to measure the accuracy of the sampling. We
illustrate the properties of this new method on Lennard-Jones and TIP4P water
models in the solid and liquid phases. Its performance is excellent and largely
independent on the thermostat parameter also with regard to the dynamic
properties
Energy-Aware Weight Assignment Framework for Circuit Oriented GMPLS Networks
A branch of green networking research is consolidating. It aims at routing traffic with the goal of reducing the network energy consumption. It is usually referred to as Energy- Aware Routing. Previous works in this branch only focused on pure IP networks, e.g., assuming an Open Shortest Path First (OSPF) control plane, and best effort packet forwarding on the data plane. In this work, we consider instead Generalized Multi-Protocol Label Switching (GMPLS) backbone networks, where optical technologies allow to design "circuit switching" network management policies with strict bandwidth reservation policies. We define a simple and generic framework which generates a family of routing algorithms, based on an energy-aware weight assignment. In particular, routing weights are functions of both the energy consumption and the actual load of network devices. Using such weights, a simple minimum-cost routing allows finding the current least expensive circuit, minimising the additional energy cost. Results obtained on realistic case studies show that our weight assignment policy favours a consistent reduction of the network power consumption, without significantly affecting the network performance. Furthermore, the framework allows to trade energy efficiently and network performance, a desirable property at which ISPs are looking for. Simple and robust parameter settings allow reaching a win-win situation, with excellent performance in terms of both energy efficiency and network resource utilization
Photoelasticity of sodium silicate glass from first principles
Based on density-functional perturbation theory we have computed the
photoelastic tensor of a model of sodium silicate glass of composition
(NaO)(SiO) (NS3). The model (containig 84 atoms) is
obtained by quenching from the melt in combined classical and Car-Parrinello
molecular dynamics simulations. The calculated photoelastic coefficients are in
good agreement with experimental data. In particular, the calculation
reproduces quantitatively the decrease of the photoelastic response induced by
the insertion of Na, as measured experimentally.
The extension to NS3 of a phenomenological model developed in a previous work
for pure a-SiO indicates that the modulation upon strain of other
structural parameters besides the SiOSi angles must be invoked to explain the
change in the photoelstic response induced by Na
UNINEPHRECTOMY INCREASES KIDNEY β2-MICROGLOBULIN: CAN IT PLAY A ROLE IN THE PROGRESSION OF KIDNEY DAMAGE?
Beta2-microglobulin (beta2M) is highly accumulated by the kidneys of normal rats. The aim of this study was to verify if uninephrectomy can modify the renal uptake of labeled beta2M. For this purpose the radioactivity of plasma and those of the remaining kidney, liver and urine have been measured in uninephrectomized rats (NX) and in controls (C) at different times after the injection as i.v. bolus of 131I-beta2M. The experiments were performed in 114 Sprague-Dawley male rats. Fifty seven animals underwent right nephrectomy, the other animals being the C. NX and their C were divided in 3 groups, studied 2, 4 and 6 weeks after nephrectomy, respectively. Part of the animals were sacrificed 12 min after the injection of labeled beta2M (peak-time, i.e. time of highest kidney accumulation of 131I-beta2M in the normal rat) and part 10 min later. The results demonstrate that: - uninephrectomy increases plasma retention of 131I-beta2M - kidney uptake (total and per gram) is always higher in NX - liver uptake (much lower than that of kidney) is not influenced by uninephrectomy - urine excretion of radioactivity is minimal in both NX and C. The behavior of beta2M is similar to that we previously observed with alpha1-microglobulin and lysozyme. The higher kidney content of some low mw proteins after uninephrectomy could play a role in the progressive reduction of renal function determined by the reduction of renal mass
A Two-Component regulatory system with opposite effects on glycopeptide antibiotic biosynthesis and resistance
The glycopeptide A40926, produced by the actinomycete Nonomuraea gerenzanensis, is the precursor of dalbavancin, a second-generation glycopeptide antibiotic approved for clinical use in the USA and Europe in 2014 and 2015, respectively. The final product of the biosynthetic pathway is an O-acetylated form of A40926 (acA40926). Glycopeptide biosynthesis in N. gerenzanensis is dependent upon the dbv gene cluster that encodes, in addition to the two essential positive regulators Dbv3 and Dbv4, the putative members of a two-component signal transduction system, specifically the response regulator Dbv6 and the sensor kinase Dbv22. The aim of this work was to assign a role to these two genes. Our results demonstrate that deletion of dbv22 leads to an increased antibiotic production with a concomitant reduction in glycopeptide resistance. Deletion of dbv6 results in a similar phenotype, although the effects are not as strong as in the Δdbv22 mutant. Consistently, quantitative RT-PCR analysis showed that Dbv6 and Dbv22 negatively regulate the regulatory genes (dbv3 and dbv4), as well as some dbv biosynthetic genes (dbv23 and dbv24), whereas Dbv6 and Dbv22 positively regulate transcription of the single, cluster-associated resistance gene. Finally, we demonstrate that exogenously added acA40926 and its precursor A40926 can modulate transcription of dbv genes but with an opposite extent: A40926 strongly stimulates transcription of the Dbv6/Dbv22 target genes while acA40926 has a neutral or negative effect on transcription of those genes. We propose a model in which glycopeptide biosynthesis in N. gerenzanensis is modulated through a positive feedback by the biosynthetic precursor A40926 and a negative feedback by the final product acA40926. In addition to previously reported control systems, this sophisticated control loop might help the producing strain cope with the toxicity of its own product. This work, besides leading to improved glycopeptide producing strains, enlarges our knowledge on the regulation of glycopeptide biosynthesis in actinomycetes, setting N. gerenzanensis and its two-component system Dbv6-Dbv22 apart from other glycopeptide producers
Osteopontin expression in healing wounds of horses and in human keloids
REASONS FOR PERFORMING STUDY:
Convincing evidence shows that persistent or excessive expression of osteopontin (OPN) is linked to fibroproliferation of various organs in laboratory animals and in man, such that its downregulation is a logical therapeutic objective.
OBJECTIVES:
To investigate OPN expression in an equine model of wound healing and in clinical specimens of equine exuberant granulation tissue and human keloids in an effort to better understand the contribution of this protein to inflammation-associated skin fibrosis.
STUDY DESIGN:
Description of gene and protein expression in an experimental equine model of wound healing and clinical specimens in horse and man.
METHODS:
Osteopontin gene expression was evaluated by quantitative PCR, while protein expression was investigated by means of immunohistochemical staining.
RESULTS:
Quantitative PCR showed that the OPN gene is expressed in normal intact skin of horses and continues to be expressed during the wound-healing process. An increase in gene expression was observed throughout the phases of wound healing, with a final decrease at wound closure. The protein was not detected in normal skin. Keratinocytes in wound-edge samples did not express the protein, whereas dermal immunoreactivity was confined to inflammatory cells. Healed wounds were devoid of staining. Equine exuberant granulation tissue showed immunoreactivity of the surrounding epidermis, infiltrating neutrophils, mononuclear cells, endothelial cells and fibroblasts. Human keloids showed OPN immunoreactivity throughout the epidermis as well as in mononuclear cells and scattered fibroblasts.
CONCLUSIONS:
Immunohistochemical data show a different pattern of expression between normally healing and fibrotic wounds (exuberant granulation tissue and keloids), thus suggesting a role in fibroproliferation in horses and man
Efficient Anharmonic Lattice Dynamics Calculations of Thermal Transport in Crystalline and Disordered Solids
Understanding heat transport in semiconductors and insulators is of
fundamental importance because of its technological impact in electronics and
renewable energy harvesting and conversion. Anharmonic Lattice Dynamics
provides a powerful framework for the description of heat transport at the
nanoscale. One of the advantages of this method is that it naturally includes
quantum effects due to atoms vibrations, which are needed to compute the
thermal properties of semiconductors widely used in nanotechnology, like
silicon and carbon, even at room temperature. While the heat transport picture
substantially differs between amorphous and crystalline semiconductors from a
microscopic standpoint, a unified approach to simulate both crystals and
glasses has been devised. Here we introduce a unified workflow, which
implements both the Boltzmann Transport equation (BTE) and the Quasi Harmonic
Green-Kubo (QHGK) methods. We discuss how the theory can be optimized to
exploit modern parallel architectures, and how it is implemented in : a versatile and scalable open-source software to compute phonon
transport in solids. This approach is applied to crystalline and partially
disordered silicon-based systems, including bulk silicon and clathrates, and on
silicon-germanium alloy clathrates with largely reduced thermal conductivity.Comment: 11 pages, 5 figure
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