More power needed to probe cloud systems.
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Atmosphere↗
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Results for “cloud computing”
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Family-based tests of association in the presence of linkage.
Linkage analysis may not provide the necessary resolution for identification of the genes underlying phenotypic variation. This is especially true for gene-mapping studies that focus on complex diseases that do not exhibit Mendelian inheritance patterns. One positional genomic strategy involves application of association methodology to areas of identified linkage. Detection of association in the presence of linkage localizes the gene(s) of interest to more-refined regions in the genome than is possible through linkage analysis alone. This strategy introduces a statistical complexity when family-based association tests are used: the marker genotypes among siblings are correlated in linked regions. Ignoring this correlation will compromise the size of the statistical hypothesis test, thus clouding the interpretation of test results. We present a method for computing the expectation of a wide range of association test statistics under the null hypothesis that there is linkage but no association. To standardize the test statistic, an empirical variance-covariance estimator that is robust to the sibling marker-genotype correlation is used. This method is widely applicable: any type of phenotypic measure or family configuration can be used. For example, we analyze a deletion in the A2M gene at the 5' splice site of "exon II" of the bait region in Alzheimer disease (AD) discordant sibships. Since the A2M gene lies in a chromosomal region (chromosome 12p) that consistently has been linked to AD, association tests should be conducted under the null hypothesis that there is linkage but no association.
Algorithms↗
Dissipative flow and vortex shedding in the Painlevé boundary layer of a Bose-Einstein condensate.
This paper addresses the drag force and formation of vortices in the boundary layer of a Bose-Einstein condensate stirred by a laser beam following the experiments of Phys. Rev. Lett. 83, 2502 (1999)]. We make our analysis in the frame moving at constant speed where the beam is fixed. We find that there is always a drag around the laser beam. We also analyze the mechanism of vortex nucleation. At low velocity, there are no vortices and the drag has its origin in a wakelike phenomenon: This is a particularity of trapped systems since the density gets small in an extended region. The shedding of vortices starts only at a threshold velocity and is responsible for a large increase in drag. This critical velocity for vortex nucleation is lower than the critical velocity computed for the corresponding 2D problem at the center of the cloud.
Journal Article↗
Equilibrium phase behavior of polydisperse hard spheres.
We calculate the phase behavior of hard spheres with size polydispersity, using accurate free energies for the fluid and solid phases. Cloud and shadow curves are found exactly by the moment free energy method, but we also compute the complete phase diagram, taking full account of fractionation. In contrast to earlier, simplified treatments we find no point of equal concentration between fluid and solid or reentrant melting at higher densities. Rather, the fluid cloud curve continues to the largest polydispersity that we study (14%); from the equilibrium phase behavior a terminal polydispersity can thus be defined only for the solid, where we find it to be around 7%. At sufficiently large polydispersity, fractionation into several solid phases can occur, consistent with previous approximate calculations; we find, in addition, that coexistence of several solids with a fluid phase is also possible.
Journal Article↗
Pseudohypoxic brain swelling: a newly defined complication after uneventful brain surgery, probably related to suction drainage.
OBJECTIVE: This is the first description of a severe and sometimes fatal complication after uneventful intracranial surgery. The clinical presentation and imaging features mimic those of global cerebral hypoxia. Extensive investigations were performed to discover the pathogenesis. METHODS: Seventeen cases of pseudohypoxic brain swelling (PHBS) were collected from our institution and from various other neurosurgical departments and were studied for common features. PHBS can occur in a mild, moderate, or severe degree. It is characterized by a very early postoperative onset of clinical deterioration (clouded or lost consciousness and pupillary abnormalities), in association with typical bilateral computed tomographic or magnetic resonance imaging changes (hypodensities or altered intensities in the basal ganglia and/or thalamus). The following variables were considered: age, primary pathological lesion and intracranial location, previous cranial surgery, anesthetic risk, type of anesthesia, approach and duration of surgery, intraoperative observations, technical monitoring results, and blood gas analyses. The results of postoperative computed tomography and various other imaging studies, intracranial pressure measurements, transcranial Doppler sonography, toxicological analyses, brain and muscle biopsies, and autopsies were also considered in the investigation. Several countermeasures were instituted and evaluated. RESULTS: Anoxemic and ischemic hypoxia was excluded as a cause of PHBS. No evidence was found for inhibition of the respiratory chain, mitochondriopathy, poisoning, or adverse effects of drugs. CONCLUSION: Indications of intracranial hypotension, induced by suction drainage, being the main pathomechanism of PHBS are discussed. A serious warning is issued regarding the use of suction drainage after intracranial surgery.
Adult↗
Meteorite nanoparticles as models for interstellar grains: synthesis and preliminary characterisation.
Dust particles and their interaction with gases play important roles in star formation and in solar nebulae. Appropriate model dust grains are needed for the laboratory simulation of gas-grain interactions. Nanoparticles formed from carbonaceous meteorites may be particularly suitable, as these particles are formed from materials that were formed originally from interstellar/nebula dust. Extending our previous studies with grounded meteorite powders, we demonstrate here the production of nanoparticles formed from meteorites using the laser desorption/controlled condensation method developed in our laboratory. The product nanoparticle aggregates have porous, web-like morphologies similar to interstellar dust grains, indicating that they can present large specific surface areas for gas/grain interactions. In this paper, we present polarisation modulation reflection-absorption infrared spectra (PM-RAIRS) of supported thin films and compare these spectra with the known silicate bands in the spectra of interstellar dust recorded during the ISO mission. We also report an ultrahigh vacuum (UHV) temperature programmed desorption (TPD) study of the adsorption of CO on the supported nanoparticle films. The latter allow us to estimate the CO binding energy on the meteorite nanoparticles as 13.5 +/- 3.0 kJ mol(-1), cf. a value of 9.8 +/- 0.2 kJ mol(-1) for CO binding to a water ice substrate. Such thermochemical data can be useful for computational modelling of gas-grain interactions under the diverse conditions in interstellar clouds and solar nebulae.
Journal Article↗
[Personal computer interactive algorithm for estimating radiologic contamination and doses after a nuclear accident in Europe].
The algorithm RANA (radiological assessment of nuclear accidents) is a tool which can be exploited to estimate the space and time structure of the radiological consequences of a radioactive release following a nuclear accident in Europe. The algorithm, formulated in the language of Mathematica, can be run on a personal computer. It uses simplified physical assumptions as for the the diffusion of the cloud and the transfer of the contamination to the food chain. The user gets the needed information by means of interactive windows that allow a fast evaluation of dose and contamination profiles. Calculations are performed either starting from the source terms or from the knowledge of experimental contamination data. Radiological consequences, such as individual or collective doses from several exposure paths, are parametrized in terms of the atmospheric diffusion categories.
Air Pollution, Radioactive↗
Light tunneling in clouds.
Solar radiation, traveling outside cloud water droplets, excites sharp resonances and surface waves by tunneling into the droplets. This effect contributes substantially to the total absorption (typically, of the order of 20%) and yields the major contribution to backscattering, producing the meteorological glory. Usual computational practices in atmospheric science misrepresent resonance contributions and cannot be relied on in the assessment of possible anomalies in cloud absorption.
Journal Article↗
Modeling of interaction between therapeutic ultrasound propagation and cavitation bubbles.
In medical applications of high intense focused ultrasound the mechanism of interaction between ultrasound waves and cavitation bubbles is responsible for several therapeutic effects as well as for undesired side effects. Based on a two-phase continuum approach for bubbly liquids, in this paper a numerical model is presented to simulate these interactions. The numerical results demonstrate the influence of the cavitation bubble cloud on ultrasound propagation. In the case of a lithotripter pulse an increased bubble density leads to significant changes in the tensile part of the pressure waveform. The calculations are verified by measurements with a fiber optical hydrophone and by experimental results of the bubble cloud dynamics.
Computer Simulation↗
Self-consistent proteomic field theory of stochastic gene switches.
We present a self-consistent field approximation approach to the problem of the genetic switch composed of two mutually repressing/activating genes. The protein and DNA state dynamics are treated stochastically and on an equal footing. In this approach the mean influence of the proteomic cloud created by one gene on the action of another is self-consistently computed. Within this approximation a broad range of stochastic genetic switches may be solved exactly in terms of finding the probability distribution and its moments. A much larger class of problems, such as genetic networks and cascades, also remain exactly solvable with this approximation. We discuss, in depth, certain specific types of basic switches used by biological systems and compare their behavior to the expectation for a deterministic switch.
Animals↗
Detection of the center of the hip joint in computer-assisted surgery: an evaluation study of the Surgetics algorithm.
OBJECTIVE: The aim of this paper is to assess the accuracy of an algorithm implemented by PRAXIM in the SURGETICS navigation station for detection of the hip center. This study will assess the robustness and accuracy of the algorithm in various clinical situations such as those involving non-sphericity of the femoral head, motion of the pelvis during hip center detection, and restricted range of motion. MATERIALS AND METHODS: The localization of the hip center, based on kinematics, relies on the recording of n successive positions of the femoral rigid body in the localizer reference system during a passive circumduction motion of the hip joint. Therefore, the shape of the clouds of points acquired may vary from one acquisition to the next. To allow a comprehensive study of the consequences of these variations for hip center detection, we developed a simulator to generate numerous clouds of points. Results given subsequently for each test are the values of the difference between the femoral mechanical axis computed with C(c), the computed hip center, and the same axis computed with C(o), the reference hip center. RESULTS: Test 1: Sensitivity to noise. The errors ranged from 3.33 E - 12 (SD 3.29E - 12) for a noise of 0 mm to 8.18E - 1 (SD - 7.05E - 1) for a noise of 15 mm. Test 2: Sensitivity to the shape of the acquisition motion. All trajectories gave an error < 1 degrees . Test 3: Sensitivity to restricted range of motion. No value > 1 degrees was found during this test. Test 4: Sensitivity to the distance between two points of the cloud. No value > 0.5 degrees was found during this test. Test 5: Sensitivity to the number of points included in the cloud. No value > 1 degrees was found during this test. CONCLUSIONS: The Surgetics algorithm is robust to noise, can compensate for pelvic motion, and can be used even in the case of restricted range of motion.
Algorithms↗
Probability calculus for quantitative HREM. Part I: Monte-Carlo and point cloud techniques.
A new approach to a central question of modern high-resolution electron microscopy (1-IREM) is presented: How precisely can we locate atom positions in crystal defects using computer-controlled structure retrieval algorithms? The purpose is not just to give error bars for the determined atomic column positions, but to derive estimations for the continuous probability functions. In the first part of this two-part paper, we present techniques which analyse point clouds of fluctuating fit-results for atom coordinates. The point clouds are obtained in a first approach from multiple input images differing in noise, commonly known as Monte-Carlo error estimation. Furthermore, we exploit the response obtained during a global optimisation-based refinement process for which all the trial structures are evaluated resulting in a second type of point cloud. In comparison, the Monte-Carlo-type technique turns out to be the most robust one. Using examples from current research on SrTiO3-bicrystals and Cu-Al2O3 interfaces, we study two largely different crystallographic and statistical situations.
Journal Article↗
A laboratory model for interstellar chemical evolution.
The chemistry in a supersonic plasma source flow was studied as a laboratory model for interstellar chemical evolution. It is important to match the similarity parameters for cosmic and laboratory conditions, which connect the temporal and spatial scales of the two cases. The apparatus simulated the conditions in a molecular cloud with respect to molecular-ionic reaction fraction, temperature, and non-equilibrium kinetics. The plasma flow was found to be cold enough, by the radical expansion, to produce polyatomic molecules. From the simple atomic plasma as reactant, cyanopolyyne and unsaturated hydrocarbons were synthesized in the present experiment. These molecules are also inherent in molecular clouds. The reaction mechanism is discussed.
Computer Simulation↗
High bubble concentrations produced by ultrasounds in binary mixtures.
It was discovered that simultaneous insonification and air blowing of different aqueous binary solutions such as water/sodium-dodecyl-sulphate (SDS), water/methanol or water/potassium-sulphate yields a very concentrated bubble cloud invading the whole vessel in a few seconds. After the end of insonification, this cloudiness remained in the solution for about 1 min. The phenomenon was investigated by computer-treatment of solution pictures recorded every second after the end of insonification. Turbidity appeared to increase with ultrasound power, and also with SDS concentration. During the disappearance of the cloud, a turbidity front appeared rising and spreading upward. This front was studied in the characteristic plane and interpreted as a spatial segregation of different bubble sizes rising with different terminal velocities. The bubble sizes involved were estimated to about 10 microns. Adsorption of surface active species are invoked to explain the cloud formation and its abnormally slow disappearance, but the occurrence of the phenomenon for potassium-sulphate salt remains unexplained.
Journal Article↗
Assessment of gamma-exposure due to a radioactive cloud released from a point source.
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Air Pollution, Radioactive↗
Theory of dust and dust-void structures in the presence of the ion diffusion.
A dust void is a dust-free region inside the dust cloud that often develops for conditions relevant to plasma processing discharges and complex plasma experiments. A distinctive feature of the void is a sharp boundary between the dust and dust-free regions; this is manifested especially clear when dissipation in the plasma is small and discontinuity of the dust number density appear. Here, the structure of the dust void boundary and the distribution of the dust and plasma parameters in the dust structure bordering the void is analyzed taking into account effects of dissipation due to the ion diffusion on plasma neutrals. The sharp boundary between the dust and void regions exists also in the presence of the ion diffusion; however, only derivatives of the dust density, dust charge, electron density and electric field are discontinuous at the void boundaries, while the functions themselves as well as derivatives of the ion drift velocity and the ion density are continuous. Numerical calculations demonstrate various sorts of diffusive dust void structures; the possibility of singularities in the balance equations caused by the diffusion process inside the dust structures is investigated. These singularities can be responsible for a new type of shocklike structures. Other structures are typically self-organized to eliminate the singularities. Numerical computations in this case demonstrate a set of thin dust layers separated by high density thin dust clouds similar to the multiple-layer dust structures observed in the laboratory and in the upper ionosphere. The possibility for existence of a few equilibrium positions of the void boundary is discussed.
Journal Article↗
Image analysis of the lens opacities induced in developing chick embryo by glucocorticoid.
Glucocorticoid-induced cataracts in chick embryos were monitored by an image analysis system. Opacities in the lens visually showed a complex pattern with significant changes in the cortical and nuclear regions. An electronic image analyser produced an image in which contrast represented different zones of lens opacification in the frontal plane and documented objective lens findings such as the precise topography of the opacities, density and opacity measurements, geometric measurements of boundary surfaces and of regional areas. Parameters of lens clouding were evaluated quantitatively by measuring the optical density index and the area of the zones of clouding outlined with equi-densities. The light intensity standard graded different morphological areas of the lens into up to 256 grey levels. The data were entered and stored quantitatively into a computer. The lens images thus picked up by the TV camera and digitally stored in a frame buffer of the measuring system could be reliably transformed into a 2-D or 3-D picture of lens clouding. The approach demonstrated by the current study provides a sensitive and meaningful measure of cataractous changes for lens laboratory research.
Animals↗
Leaflet geometry extraction and parametric representation of a pericardial artificial heart valve.
Reverse engineering technology was used to reconstruct the complex leaflet geometry of a commercial pericardial valve in our study. Results show that the three-dimensional computer-aided design model of the leaflet surface can be rendered by fitting the surface either to cloud points or by a group of B-splines fitted to a set of cloud points that had been obtained by the process of laser-scanning digitizing. However, an acceptable smooth surface is usually not guaranteed and additional manipulation is required. An alternative method is introduced in this paper, which involves the fitting of an equation to the leaflet geometry to create a smooth surface. The geometrical profile of a pericardial artificial heart valve was scanned using a laser digitizing system. The leaflet profile is represented as a set of cloud points. A quadric surface is fitted to a set of unique points, which were located on the set of cloud points. A mathematical equation is obtained by solving a least-squares fit. The geometry of the fitted leaflet surface has been proven to be closely represented by an elliptical hyperboloid. The quadratic equations of the leaflet curvatures, calculated along both the circumferential and the radial directions, resulted in simple hyperbolic curvatures. The advantages of using elliptical hyperboloid geometry for the leaflet surface are discussed and compared with other types of conicoid geometries. The concepts of parametric representation of the leaflet geometry and parametric design for leaflets are discussed. A smooth surface without inflection points and with an adjustable surface area suitable for a series of stent sizes with incremented diameters is created by this method of a single parametric design. Finally, a generic method to apply the geometry extraction and parametric representation to most pericardial heart valve prostheses was discussed. The application to valves with natural shape was introduced, challenges were identified, and a technical solution was proposed.
Algorithms↗