12,465 research outputs found
Analytical Hartree-Fock gradients for periodic systems
We present the theory of analytical Hartree-Fock gradients for periodic
systems as implemented in the code CRYSTAL. We demonstrate how derivatives of
the integrals can be computed with the McMurchie-Davidson algorithm. Highly
accurate gradients with respect to nuclear coordinates are obtained for systems
periodic in 0,1,2 or 3 dimensions.Comment: accepted by International Journal of Quantum Chemistr
A new camera for high-resolution infrared imaging of works of art
A new camera – SIRIS (scanning infrared imaging system) – developed at the National Gallery in London allows high-resolution images to be made in the near infrared region (900–1700 nm). The camera is based on a commercially available 320 × 256 pixel indium gallium arsenide area array sensor. This relatively small sensor is moved across the focal plane of the camera using two orthogonal translation stages to give images of c. 5000 × 5000 pixels. The main advantages of the SIRIS camera over scanning infrared devices or sequential image capture and mosaic assembly are its comparative portability and rapid image acquisition – making a 5000 × 5000 pixel image takes less than 20 minutes. The SIRIS camera can operate at a range of resolutions; from around 2.5 pixels per millimetre over an area of up to 2 × 2 m to 10 pixels per millimetre when examining an area measuring 0.5 × 0.5 m. The development of the mechanical, optical and electronic components of the camera, including the design of a new lens, is described. The software used to control image capture and to assemble the individual frames into a seamless mosaic image is mentioned. The camera was designed primarily to examine underdrawings in paintings; preliminary results from test targets and paintings imaged in situ are presented and the quality of the images compared with those from other cameras currently used for this application
Design approaches to more energy efficient engines
The status of NASA's Energy Efficient Engine Project, a comparative government-industry effort aimed at advancing the technology base for the next generation of large turbofan engines for civil aircraft transports is summarized. Results of recently completed studies are reviewed. These studies involved selection of engine cycles and configurations that offer potential for at least 12% lower fuel consumption than current engines and also are economically attractive and environmentally acceptable. Emphasis is on the advancements required in component technologies and systems design concepts to permit future development of these more energy efficient engines
SIRIS: a high resolution scanning infrared camera for examining paintings
The new SIRIS (Scanning InfraRed Imaging System) camera developed at the National Gallery in London allows highresolution images of paintings to be made in the near infrared region (900–1700 nm). Images of 5000 × 5000 pixels are made by moving a 320 × 256 pixel InGaAs array across the focal plane of the camera using two orthogonal translation stages. The great advantages of this camera over scanning infrared devices are its relative portability and that image acquisition is comparatively rapid – a full 5000 × 5000 pixel image can be made in around 20 minutes. The paper describes the development of the mechanical, optical and electronic components of the camera, including the design of a new lens. The software routines used to control image capture and to assemble the individual 320 × 256 pixel frames into a seamless mosaic image are also mentioned. The optics of the SIRIS camera have been designed so that the camera can operate at a range of resolutions; from around 2.5 pixels per millimetre on large paintings of up to 2000 × 2000 mm to 10 pixels per millimetre on smaller paintings or details of paintings measuring 500 × 500 mm. The camera is primarily designed to examine underdrawings in paintings; preliminary results from test targets and paintings are presented and the quality of the images compared with those from other cameras currently used in this field
Optimal Extraction of Fibre Optic Spectroscopy
We report an optimal extraction methodology, for the reduction of
multi-object fibre spectroscopy data, operating in the regime of tightly packed
(and hence significantly overlapping) fibre profiles. The routine minimises
crosstalk between adjacent fibres and statistically weights the extraction to
reduce noise. As an example of the process we use simulations of the numerous
modes of operation of the AAOmega fibre spectrograph and observational data
from the SPIRAL Integral Field Unit at the Anglo-Australian Telescope.Comment: Accepted for publication in PAS
Luminosity Density of Galaxies and Cosmic Star Formation Rate from Lambda-CDM Hydrodynamical Simulations
We compute the cosmic star formation rate (SFR) and the rest-frame comoving
luminosity density in various pass-bands as a function of redshift using
large-scale \Lambda-CDM hydrodynamical simulations with the aim of
understanding their behavior as a function of redshift. To calculate the
luminosity density of galaxies, we use an updated isochrone synthesis model
which takes metallicity variations into account. The computed SFR and the
UV-luminosity density have a steep rise from z=0 to 1, a moderate plateau
between z=1 - 3, and a gradual decrease beyond z=3. The raw calculated results
are significantly above the observed luminosity density, which can be explained
either by dust extinction or the possibly inappropriate input parameters of the
simulation. We model the dust extinction by introducing a parameter f; the
fraction of the total stellar luminosity (not galaxy population) that is
heavily obscured and thus only appears in the far-infrared to sub-millimeter
wavelength range. When we correct our input parameters, and apply dust
extinction with f=0.65, the resulting luminosity density fits various
observations reasonably well, including the present stellar mass density, the
local B-band galaxy luminosity density, and the FIR-to-submm extragalactic
background. Our result is consistent with the picture that \sim 2/3 of the
total stellar emission is heavily obscured by dust and observed only in the
FIR. The rest of the emission is only moderately obscured which can be observed
in the optical to near-IR wavelength range. We also argue that the steep
falloff of the SFR from z=1 to 0 is partly due to the shock-heating of the
universe at late times, which produces gas which is too hot to easily condense
into star-forming regions.Comment: 25 pages, 6 figures. Accepted version in ApJ. Substantially revised
from the previous version. More emphasis on the comparison with various
observations and the hidden star formation by dust extinctio
Mentalization-based treatment in adolescent inpatients: a naturalistic multi-informant study of outcomes
The present era of major cutbacks in intensive treatment programs throughout Europe stresses the importance of evaluating the outcomes of such programs for adolescents with severe personality pathology and comorbidity. Personality pathology has proven to be a valid concept in adolescents, with relatively high prevalence, that needs to be targeted by evidence-based interventions. The present study focused on the evaluation of outcomes of a 12-month mentalization-based treatment for adolescents (MBT-A) program in 118 inpatient adolescents with personality pathology symptoms, using a multi-informant multidomain design. The results showed that during treatment, adolescents improved on general psychiatric symptoms, personality pathology dimensions, and health-related and generic quality of life. Improvement was not only statistically significant, but also clinically important, especially for internalizing domains. Implications for clinical practice and research are discussed
A physics-based life prediction methodology for thermal barrier coating systems
A novel mechanistic approach is proposed for the prediction of the life of
thermal barrier coating (TBC) systems. The life prediction methodology is based
on a criterion linked directly to the dominant failure mechanism. It relies on
a statistical treatment of the TBC's morphological characteristics,
non-destructive stress measurements and on a continuum mechanics framework to
quantify the stresses that promote the nucleation and growth of microcracks
within the TBC. The last of these accounts for the effects of TBC constituents'
elasto-visco-plastic properties, the stiffening of the ceramic due to sintering
and the oxidation at the interface between the thermally insulating yttria
stabilized zirconia (YSZ) layer and the metallic bond coat. The mechanistic
approach is used to investigate the effects on TBC life of the properties and
morphology of the top YSZ coating, metallic low-pressure plasma sprayed bond
coat and the thermally grown oxide. Its calibration is based on TBC damage
inferred from non-destructive fluorescence measurements using
piezo-spectroscopy and on the numerically predicted local TBC stresses
responsible for the initiation of such damage. The potential applicability of
the methodology to other types of TBC coatings and thermal loading conditions
is also discussed
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