3,885 research outputs found
Static dielectric response and Born effective charge of BN nanotubes from {\it ab initio} finite electric field calculations
{\it Ab initio} investigations of the full static dielectric response and
Born effective charge of BN nanotubes (BN-NTs) have been performed for the
first time using finite electric field method. It is found that the ionic
contribution to the static dielectric response of BN-NTs is substantial and
also that a pronounced chirality-dependent oscillation is superimposed on the
otherwise linear relation between the longitudinal electric polarizability and
the tube diameter (), as for a thin dielectric cylinderical shell. In
contrast, the transverse dielectric response of the BN-NTs resemble the
behavior of a thin (non-ideal) conducting cylindrical shell of a diameter of
\AA, with a screening factor of 2 for the inner electric field. The
medium principal component of the Born effective charge corresponding
to the transverse atomic displacement tangential to the BN-NT surface, has a
pronounced -dependence (but independent of chirality), while the large
longitudinal component exhibits a clear chirality dependence (but
nearly -independent), suggesting a powerful way to characterize the diameter
and chirality of a BN-NT.Comment: submitted to PR
Graphitic-BN Based Metal-free Molecular Magnets From A First Principle Study
We perform a first principle calculation on the electronic properties of
carbon doped graphitic boron nitride graphitic BN. It was found that carbon
substitution for either boron or nitrogen atom in graphitic BN can induce
spontaneous magnetization. Calculations based on density functional theory with
the local spin density approximation on the electronic band structure revealed
a spin polarized, dispersionless band near the Fermi energy. Spin density
contours showed that the magnetization density originates from the carbon atom.
The magnetization can be attributed to the carbon 2p electron. Charge density
distribution shows that the carbon atom forms covalent bonds with its three
nearest neighbourhood. The spontaneous magnetization survives the curvature
effect in BN nanotubes, suggesting the possibility of molecular magnets made
from BN. Compared to other theoretical models of light-element or metal-free
magnetic materials, the carbon-doped BN are more experimentally accessible and
can be potentially useful.Comment: 8 pages, 4 figure
An integrated approach to supply chain risk analysis
Despite the increasing attention that supply chain risk management is receiving by both researchers and practitioners, companies still lack a risk culture. Moreover, risk management approaches are either too general or require pieces of information not regularly recorded by organisations. This work develops a risk identification and analysis methodology that integrates widely adopted supply chain and risk management tools. In particular, process analysis is performed by means of the standard framework provided by the Supply Chain Operations Reference Model, the risk identification and analysis tasks are accomplished by applying the Risk Breakdown Structure and the Risk Breakdown Matrix, and the effects of risk occurrence on activities are assessed by indicators that are already measured by companies in order to monitor their performances. In such a way, the framework contributes to increase companies' awareness and communication about risk, which are essential components of the management of modern supply chains. A base case has been developed by applying the proposed approach to a hypothetical manufacturing supply chain. An in-depth validation will be carried out to improve the methodology and further demonstrate its benefits and limitations. Future research will extend the framework to include the understanding of the multiple effects of risky events on different processe
Cognitive bias modification training in adolescents reduces anxiety to a psychological challenge
Many anxiety disorders begin in adolescence. Early interventions that target adolescent anxiety may prevent later disabling consequences. Previous studies show that cognitive bias modification training can generate positive interpretative styles of ambiguous information in adolescents but effects on anxious mood reduction are less clear. Adult studies suggest more consistent training effects on mood when assessed in response to a psychological challenge. Here, we assess whether positive training reduces adolescent anxious responses to a laboratory stressor. A total of 40 adolescents were randomly assigned to positive or negative computerised training. During training, ambiguous scenarios were resolved positively or negatively. After training, adolescents completed a test of interpretation bias and a difficult mental arithmetic task while believing that they were being videotaped for teaching purposes. First, positively-trained adolescents endorsed more positive and fewer negative interpretations of new ambiguous situations than negatively-trained adolescents. Second, positively-trained adolescents also showed attenuated anxiety levels after but not before the challenge. Induced positive interpretations via computerised cognitive training may modify anxious responsivity. Although there some caveats to these data, in general they justify extensions of computerised training to adolescents with clinical anxiety, to reduce anxious responsivity
To Recognize the Use of International Standards for Making Harmonized Regulation of Medical Devices in Asia-Pacific
‘Medical Devices’ include everything from highly sophisticated, computerized, medical equipment, right down to simple wooden tongue depressors. Regulations embody the public expectations for how buildings and facilities are expected to perform and as such represent public policy. Regulators, who develop and enforce regulations, are empowered to act in the public’s interest to set this policy and are ultimately responsible to the public in this regard. Standardization contributes to the basic infrastructure that underpins society including health and environment, while promoting sustainability and good regulatory practice. The international organizations that produce International Standards are the International Electrotechnical Commission (IEC), the International Organization for Standardization (ISO), and the International Telecommunication Union (ITU). With the increasing globalization of markets, International Standards (as opposed to regional or national standards) have become critical to the trading process, ensuring a level playing field for exports, and ensuring that imports meet the internationally recognized levels of performance and safety. The development of standards is done in response to sectors and stakeholders that express a clearly established need for them. An industry sector or other stakeholder group typically communicates its requirement for standards to one of the national members. To be accepted for development, a proposed work item must receive a majority support of the participating members, who verify the global relevance of the proposed item. The regulatory authority (RA) should provide a method for the recognition of international voluntary standards and for public notification of such recognition. The process of recognition may vary from country to country. Recognition may occur by periodic publication of lists of standards that a regulatory authority has found will meet the Essential Principles. In conclusion, International standards, such as, basic standards, group standards, and product standards, are a tool for harmonizing regulatory processes, to assure the safety, quality, and performance of medical devices. Standards represent the opinion of experts from all interested parties, including industry, regulators, users, and others
A low‐cost, sensitive and specific PCR ‐based tool for rapid clinical detection of HLA‐B*35 alleles associated with delayed drug hypersensitivity reactions
HLA (HLA) alleles are risk factors for CD8+ T-cell-mediated drug hypersensitivity reactions. However, as most HLA associations are incompletely predictive and/or involve risk alleles at low frequency, costly sequence-based typing can elude an economically productive cost: benefit ratio for clinical validation studies and diagnostic and/or preventative screening. Hence rapid and low-cost detection assays are now required, both for single alleles but also across risk loci associated with broader multi-disease risk; exemplified by associations with diverse alleles in HLA-B*35, including HLA-B*35:01 and green tea- or co-trimoxazole-induced liver injury. Here, we developed a cost-effective (<$10USD) qPCR assay for rapid (<2.5 h) clinical detection of HLA-B*35 alleles. The assay was validated using 430 DNA samples with previous American society for histocompatibility and immunogenetics-accredited sequence-based high-resolution HLA typing, positively detecting all HLA-B*35 allelic variants in our cohort, and as expected by primer design, the six samples that expressed low-frequency B*78:01. The assay did not result in positive detection for any negative control allele. With expected detection of B*35 and B*78, our assay sensitivity (95% CI, 95.07%–100.00%) and specificity (95% CI, 98.97%–100.00%) of 100% using as low as 10 ng of DNA provides a reliable HLA-B*35 screening tool for clinical validation and HLA–risk-based prevention and diagnostics
Isomorphs in model molecular liquids
Isomorphs are curves in the phase diagram along which a number of static and
dynamic quantities are invariant in reduced units. A liquid has good isomorphs
if and only if it is strongly correlating, i.e., the equilibrium
virial/potential energy fluctuations are more than 90% correlated in the NVT
ensemble. This paper generalizes isomorphs to liquids composed of rigid
molecules and study the isomorphs of two systems of small rigid molecules, the
asymmetric dumbbell model and the Lewis-Wahnstrom OTP model. In particular, for
both systems we find that the isochoric heat capacity, the excess entropy, the
reduced molecular center-of-mass self part of the intermediate scattering
function, the reduced molecular center-of-mass radial distribution function to
a good approximation are invariant along an isomorph. In agreement with theory,
we also find that an instantaneous change of temperature and density from an
equilibrated state point to another isomorphic state point leads to no
relaxation. The isomorphs of the Lewis-Wahnstrom OTP model were found to be
more approximative than those of the asymmetric dumbbell model, which is
consistent with the OTP model being less strongly correlating. For both models
we find "master isomorphs", i.e., isomorphs have identical shape in the
virial/potential energy phase diagram.Comment: 20 page
Modeling seismic wave propagation and amplification in 1D/2D/3D linear and nonlinear unbounded media
To analyze seismic wave propagation in geological structures, it is possible
to consider various numerical approaches: the finite difference method, the
spectral element method, the boundary element method, the finite element
method, the finite volume method, etc. All these methods have various
advantages and drawbacks. The amplification of seismic waves in surface soil
layers is mainly due to the velocity contrast between these layers and,
possibly, to topographic effects around crests and hills. The influence of the
geometry of alluvial basins on the amplification process is also know to be
large. Nevertheless, strong heterogeneities and complex geometries are not easy
to take into account with all numerical methods. 2D/3D models are needed in
many situations and the efficiency/accuracy of the numerical methods in such
cases is in question. Furthermore, the radiation conditions at infinity are not
easy to handle with finite differences or finite/spectral elements whereas it
is explicitely accounted in the Boundary Element Method. Various absorbing
layer methods (e.g. F-PML, M-PML) were recently proposed to attenuate the
spurious wave reflections especially in some difficult cases such as shallow
numerical models or grazing incidences. Finally, strong earthquakes involve
nonlinear effects in surficial soil layers. To model strong ground motion, it
is thus necessary to consider the nonlinear dynamic behaviour of soils and
simultaneously investigate seismic wave propagation in complex 2D/3D geological
structures! Recent advances in numerical formulations and constitutive models
in such complex situations are presented and discussed in this paper. A crucial
issue is the availability of the field/laboratory data to feed and validate
such models.Comment: of International Journal Geomechanics (2010) 1-1
Theoretical Study of One-dimensional Chains of Metal Atoms in Nanotubes
Using first-principles total-energy pseudopotential calculations, we have
studied the properties of chains of potassium and aluminum in nanotubes. For BN
tubes, there is little interaction between the metal chains and the tubes, and
the conductivity of these tubes is through carriers located at the inner part
of the tube. In contrast, for small radius carbon nanotubes, there are two
types of interactions: charge-transfer (dominant for alkali atoms) leading to
strong ionic cohesion, and hybridization (for multivalent metal atoms)
resulting in a smaller cohesion. For Al-atomic chains in carbon tubes, we show
that both effects contribute. New electronic properties related to these
confined atomic chains of metal are analyzed.Comment: 12 pages + 3 figure
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