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At least 613 records · Page 34Linked to original sources
PubMed2002

Public health, GIS, and the internet.

Internet access and use of georeferenced public health information for GIS application will be an important and exciting development for the nation's Department of Health and Human Services and other health agencies in this new millennium. Technological progress toward public health geospatial data integration, analysis, and visualization of space-time events using the Web portends eventual robust use of GIS by public health and other sectors of the economy. Increasing Web resources from distributed spatial data portals and global geospatial libraries, and a growing suite of Web integration tools, will provide new opportunities to advance disease surveillance, control, and prevention, and insure public access and community empowerment in public health decision making. Emerging supercomputing, data mining, compression, and transmission technologies will play increasingly critical roles in national emergency, catastrophic planning and response, and risk management. Web-enabled public health GIS will be guided by Federal Geographic Data Committee spatial metadata, OpenGIS Web interoperability, and GML/XML geospatial Web content standards. Public health will become a responsive and integral part of the National Spatial Data Infrastructure.

Geographic Information Systems↗
PubMed2005

Motor-maps, navigation and implicit space representation in the hippocampus.

Multiple sensory-motor maps located in the brainstem and the cortex are involved in spatial orientation. Guiding movements of eyes, head, neck and arms they provide an approximately linear relation between target distance and motor response. This involves especially the superior colliculus in the brainstem and the parietal cortex. There, the natural frame of reference follows from the retinal representation of the environment. A model of navigation is presented that is based on the modulation of activity in those sensory-motor maps. The actual mechanism chosen was gain-field modulation, a process of multimodal integration that has been demonstrated in the parietal cortex and superior colliculus, and was implemented as attraction to visual cues (colour). Dependent on the metric of the sensory-motor map, the relative attraction to these cues implemented as gain field modulation and their position define a fixed point attractor on the plane for locomotive behaviour. The actual implementation used Kohonen-networks in a variant of reinforcement learning that are well suited to generate such topographically organized sensory-motor maps with roughly linear visuo-motor response characteristics. In the following, it was investigated how such an implicit coding of target positions by gain-field parameters might be represented in the hippocampus formation and under what conditions a direction-invariant space representation can arise from such retinotopic representations of multiple cues. Information about the orientation in the plane--as could be provided by head direction cells--appeared to be necessary for unambiguous space representation in our model in agreement with physiological experiments. With this information, Gauss-shaped "place-cells" could be generated, however, the representation of the spatial environment was repetitive and clustered and single cells were always tuned to the gain-field parameters as well.

Algorithms↗
PubMed1995

Crystallisation and preliminary X-ray analysis of the 'common-type' acylphosphatase.

Single crystals of a 'common-type' acylphosphatase from bovine testis have been grown. Crystals belong to space group C2 and have cell dimensions a = 64.6 A, b = 36.5 A, c = 45.2 A and beta = 104.8 and contain one monomer per asymmetric unit. The crystals diffract better than 2.0 A resolution and are well suited for an X-ray structure determination.

Acid Anhydride Hydrolases↗
PubMed1988

Crystallization and preliminary analysis of crystals of apolipophorin III isolated from Locusta migratoria.

Crystals of apolipophorin III, isolated from the locust Locusta migratoria, have been reproducibly grown from ammonium sulfate solutions and are well suited for an x-ray crystallographic analysis. Locust apolipophorin III is a glycosylated protein with a molecular weight of 19,100 and interacts with lipophorin, the major lipoprotein complex in insects. The crystals belong to the space group P6122 or P6522 with unit cell dimensions of a = b = 67.5 A, c = 155.6 A and diffract to a nominal resolution of 2.5 A. They are physically robust and are stable in the x-ray beam for over a week. A complete native x-ray data set has been collected and processed to 3.0-A resolution.

Animals↗
PubMedDate not supplied

Real space refinement of acto-myosin structures from sectioned muscle.

We have adapted a real space refinement protocol originally developed for high-resolution crystallographic analysis for use in fitting atomic models of actin filaments and myosin subfragment 1 (S1) to 3-D images of thin-sectioned, plastic-embedded whole muscle. The rationale for this effort is to obtain a refinement protocol that will optimize the fit of the model to the density obtained by electron microscopy and correct for poor geometry introduced during the manual fitting of a high-resolution atomic model into a lower resolution 3-D image. The starting atomic model consisted of a rigor acto-S1 model obtained by X-ray crystallography and helical reconstruction of electron micrographs. This model was rebuilt to fit 3-D images of rigor insect flight muscle at a resolution of 7 nm obtained by electron tomography and image averaging. Our highly constrained real space refinement resulted in modest improvements in the agreement of model and reconstruction but reduced the number of conflicting atomic contacts by 70% without loss of fit to the 3-D density. The methodology seems to be well suited to the derivation of stereochemically reasonable atomic models that are consistent with experimentally determined 3-D reconstructions computed from electron micrographs.

Actins↗
PubMed2004

Fast initiation of chemical reactions with laser-induced breakdown of a nanoscale partition.

This letter describes a new strategy for initiating a chemical reaction that is based on the laser-induced breakdown of a nanoscopic barrier, which physically separates the reactants in space. Because the breakdown of the barrier is fast ( approximately 0.3 micros) and owing to the nanometer dimension of the barrier, the reactants can be brought together and the reaction can be initiated rapidly. The time scale most suited for this method (from microseconds to tens of milliseconds) bridges nicely between the faster time scales that are accessible mostly with laser-based triggering experiments and the slower time scales that are studied most frequently with flow-based devices.

Kinetics↗
PubMed2006

On the detection of simple points in higher dimensions using cubical homology.

Simple point detection is an important task for several problems in discrete geometry, such as topology preserving thinning in image processing to compute discrete skeletons. In this paper, the approach to simple point detection is based on techniques from cubical homology, a framework ideally suited for problems in image processing. A (d-dimensional) unitary cube (for a d-dimensional digital image) is associated with every discrete picture element, instead of a point in epsilon(d) (the d-dimensional Euclidean space) as has been done previously. A simple point in this setting then refers to the removal of a unitary cube without changing the topology of the cubical complex induced by the digital image. The main result is a characterization of a simple point p (i.e., simple unitary cube) in terms of the homology groups of the (3d - 1) neighborhood of p for arbitrary, finite dimensions

Algorithms↗
PubMed2005

In vitro assembly of mosaic hepatitis B virus capsid-like particles (CLPs): rescue into CLPs of assembly-deficient core protein fusions and FRET-suited CLPs.

Hepatitis B virus core protein self-assembles into icosahedral, highly immunogenic capsid-like particles (CLPs) that can serve as molecular platforms for heterologous proteins. Insertion into the centrally located c/e1 epitope leads to surface display, fusion to the C terminus to internal disposition of the foreign domains. However, symmetry-defined space restrictions on the surface and particularly inside the CLPs limit the size of usable heterologous fusion partners. Further, CLPs carrying differing foreign domains are desirable for applications such as multivalent vaccines, and for structure probing by distance sensitive interactions like fluorescence resonance energy transfer (FRET). Here, we report an in vitro co-assembly system for such mosaic-CLPs allowing successful CLP formation with a per se assembly-deficient fusion protein, and of CLPs from two different fluoroprotein-carrying fusions that exert FRET in an assembly-status dependent way.

Capsid↗
PubMed1985

Probing the three-dimensional structures of DNA and RNA oligonucleotides in solution by nuclear Overhauser enhancement measurements.

DNA and RNA oligonucleotides are ideally suited for high-resolution X-ray crystallographic and 1H-NMR studies. The solution structures of such oligonucleotides can potentially be solved using proton-proton nuclear Overhauser enhancement measurements to demonstrate the proximity of protons in space and to determine their separation, thereby enabling a comparison of the structure in the crystalline and solution states to be made. In this review we describe the general strategy for the sequential resonance assignments of oligonucleotide 1H-NMR spectra, the essential prerequisite for further structural work, the approach to obtaining interproton distances from pre-steady state nuclear Overhauser enhancement measurements, and the use of interproton distances in structure determination. This is illustrated by several examples including double- and single-stranded DNA oligonucleotides as well as RNA stem and loop structures.

Base Sequence↗
PubMedDate not supplied

Noise reduction for vocal pathologies.

A noise reduction scheme, particularly suited for the correction of vocal pathologies, is proposed. The filter makes use of concepts originated within the theory of dynamical systems and deterministic chaos. In particular, the idea of embedding scalar data in order to reconstruct a phase space is of fundamental importance here. Furthermore, the concept of an attractor as a result of dynamical constraints is exploited. In order to perform noise reduction one needs redundancy and the human voice provides it even within a phoneme, namely the smallest structural unit of speech. Due to several repetitions of a pattern called pitch inside a phoneme, separation between the pure voice signal and the noise is possible, provided the latter is uncorrelated with the former. With a proper parameter tuning, different kinds of noise can be removed. We describe the idea behind the noise reduction algorithm and present applications to vocal pathologies.

Algorithms↗
PubMed1996

Effects of character weighting and species sampling on phylogeny reconstruction: a case study based on DNA sequence data in cetaceans.

Different phylogenetic analyses of the same genetic data set can yield conflicting results, depending on the choice of parameter settings and included taxa. This is particularly true in studies involving data sets where levels of homoplasy are high and likely to obscure the phylogenetic signal. Filtering of this phylogenetic noise can be attempted, with varying degrees of success, by using different weighting schemes and ingroup/outgroup choices, but it can be difficult to decide objectively which approach is best. Using a cytochrome b data set from cetaceans and artiodactyls, we examined the effects of a suite of parameter settings on the outcome of phylogenetic analyses. We tested 2968 combinations among the seven parameters that most often vary among phylogenetic studies. It is our contention that this sensitivity analysis identifies portions of the multidimensional parameter space where phylogenetic signal is most reliably recovered, and simple rules are given to guide the choice of settings. Portions of this data set have been used in previous studies with conflicting results, namely the monophyly vs. paraphyly of one of the two major recognized cetacean suborders, the toothed whales. This analysis strongly supports the sister relationship between sperm whales and baleen whales.

Animals↗
PubMed2003

Genetic diversity as an objective in multi-objective evolutionary algorithms.

A key feature of an efficient and reliable multi-objective evolutionary algorithm is the ability to maintain genetic diversity within a population of solutions. In this paper, we present a new diversity-preserving mechanism, the Genetic Diversity Evaluation Method (GeDEM), which considers a distance-based measure of genetic diversity as a real objective in fitness assignment. This provides a dual selection pressure towards the exploitation of current non-dominated solutions and the exploration of the search space. We also introduce a new multi-objective evolutionary algorithm, the Genetic Diversity Evolutionary Algorithm (GDEA), strictly designed around GeDEM and then we compare it with other state-of-the-art algorithms on a well-established suite of test problems. Experimental results clearly indicate that the performance of GDEA is top-level.

Algorithms↗
PubMed1994

Methods of reconstruction.

This article discusses methods of reconstruction, ranging from simple free-hand skin grafts to microvascular tissue transfer. The simplest reconstructive option must be chosen to suit the defect and to achieve the least possible donor morbidity. The most suitable reconstructive choices are discussed for each of the following situations: to provide a large surface area, to provide hair-bearing tissue, to fill "dead space," to restore motor function, or to provide composite bone and soft-tissue structures.

Humans↗
PubMed2002

Mechanisms of microgravity induced orthostatic intolerance: implications for effective countermeasures.

The development of orthostatic hypotension and instability immediately after return from spaceflight has been a significant operational problem to astronauts for more than four decades. Significant reductions in stroke volume and peripheral vascular resistance contribute to ineffective maintenance of systemic arterial blood pressure during standing after spaceflight despite compensatory elevations in heart rate. The primary mechanism underlying reduced stroke volume appears to be a reduction in preload associated with reduced circulating blood volume, although cardiac atrophy might also contribute. Space flight and ground based experiments have demonstrated that an inability to provide adequate peripheral vasoconstriction in astronauts that become presyncopal may be associated with several mechanisms including reduced sympathetic nerve activity, arterial smooth muscle atrophy and/or hyporeactivity, hypersensitivity of beta-adrenergic receptors, etc. In addition, an inability to provide adequate tachycardia in presyncopal subjects may be associated with reduced carotid-cardiac baroreflex sensitivity. Based on the current knowledge and understanding of cardiovascular mechanisms that are altered during exposure to microgravity, a major focus of future research should be directed to the systematic evaluation of potential countermeasures that specifically target and restore the function of these mechanisms. Based on a preliminary systematic evaluation presented in this review, acute physical exercise designed to elicit maximal effort, G-suit inflation, artificial gravity, and specific pharmacological interventions, alone or in combination, have shown promise as successful countermeasures that provide protection against post-flight orthostatic intolerance.

Aerospace Medicine↗
PubMed2005

Dynamic three-dimensional undersampled data reconstruction employing temporal registration.

Dynamic 3D imaging is needed for many applications such as imaging of the heart, joints, and abdomen. For these, the contrast and resolution that magnetic resonance imaging (MRI) offers are desirable. Unfortunately, the long acquisition time of MRI limits its application. Several techniques have been proposed to shorten the scan time by undersampling the k-space. To recover the missing data they make assumptions about the object's motion, restricting it in space, spatial frequency, temporal frequency, or a combination of space and temporal frequency. These assumptions limit the applicability of each technique. In this work we propose a reconstruction technique based on a weaker complementary assumption that restricts the motion in time. The technique exploits the redundancy of information in the object domain by predicting time frames from frames where there is little motion. The proposed method is well suited for several applications, in particular for cardiac imaging, considering that the heart remains relatively still during an important fraction of the cardiac cycle, or joint imaging where the motion can easily be controlled. This paper presents the new technique and the results of applying it to knee and cardiac imaging. The results show that the new technique can effectively reconstruct dynamic images acquired with an undersampling factor of 5. The resulting images suffer from little temporal and spatial blurring, significantly better than a sliding window reconstruction. An important attraction of the technique is that it combines reconstruction and registration, thus providing not only the 3D images but also its motion quantification. The method can be adapted to non-Cartesian k-space trajectories and nonuniform undersampling patterns.

Algorithms↗
PubMed1993

Cellular automaton simulation of pulsed field gel electrophoresis.

We describe simulation techniques well suited to detailed investigation of the microscopic behavior of DNA during electrophoretic separation in the diffusive regime. Long polymers moving diffusively in a medium are simulated using microscopic Monte-Carlo steps. Simulations rely upon a recently introduced two-space abstract polymer that enables fine-grained massively parallel simulation. Tests of the two-space polymer dynamics are reviewed. The scaling with polymer length of the size and relaxation time of isolated polymers are shown to agree with universal scaling relations. The relaxation time is found to be significantly faster than the alternative bond-fluctuation method. Simplicity of implementation enables simulation on cellular automaton machines (CAM) including CAM-6, and a prototype of the new CAM-8, as well as other massively parallel architectures. Preliminary simulations of polymers migrating under an external field through a random medium of obstacles in two dimensions are described. Two sequences of simulations are performed, with different obstacle densities corresponding to pore sizes larger and smaller than the polymer radius of gyration. In the dilute medium polymers are characteristically draped on single obstacles. In the denser medium draping across multiple obstacles results in reduced orientation in the field direction. A demonstration of rapid 90 degrees field direction switching results in polymer motion toward the expected intermediate direction.

Algorithms↗