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Physical Principles (physical + principle)

Distribution by Scientific Domains

Medical Sciences	27%
Engineering	18%
Chemistry	18%

Selected Abstracts

Formation of Network and Cellular Structures by Viscoelastic Phase Separation

ADVANCED MATERIALS, Issue 18 2009
Hajime Tanaka
Abstract Network (sponge) and cellular structures are often seen in various types of materials. Materials with such structures are generally characterized by light weight and high mechanical strength. The usefulness of such materials is highlighted, for example, by the remarkable material properties of bone tissue, which often has a highly porous structure. In artificial materials, plastic and metallic foams and breads have such structures. Here, we describe a physical principle for producing network and cellular structures using phase separation, and its potential applications to the morphological control of materials spanning from soft to hard matter. [source]

Gauss-Green theorem for weakly differentiable vector fields, sets of finite perimeter, and balance laws

COMMUNICATIONS ON PURE & APPLIED MATHEMATICS, Issue 2 2009
Gui-Qiang Chen
We analyze a class of weakly differentiable vector fields F : ,n , ,n with the property that F , L, and div F is a (signed) Radon measure. These fields are called bounded divergence-measure fields. The primary focus of our investigation is to introduce a suitable notion of the normal trace of any divergence-measure field F over the boundary of an arbitrary set of finite perimeter that ensures the validity of the Gauss-Green theorem. To achieve this, we first establish a fundamental approximation theorem which states that, given a (signed) Radon measure , that is absolutely continuous with respect to ,N , 1 on ,N, any set of finite perimeter can be approximated by a family of sets with smooth boundary essentially from the measure-theoretic interior of the set with respect to the measure ||,||, the total variation measure. We employ this approximation theorem to derive the normal trace of F on the boundary of any set of finite perimeter E as the limit of the normal traces of F on the boundaries of the approximate sets with smooth boundary so that the Gauss-Green theorem for F holds on E. With these results, we analyze the Cauchy flux that is bounded by a nonnegative Radon measure over any oriented surface (i.e., an (N , 1)-dimensional surface that is a part of the boundary of a set of finite perimeter) and thereby develop a general mathematical formulation of the physical principle of the balance law through the Cauchy flux. Finally, we apply this framework to the derivation of systems of balance laws with measure-valued source terms from the formulation of the balance law. This framework also allows the recovery of Cauchy entropy flux through the Lax entropy inequality for entropy solutions of hyperbolic conservation laws. © 2008 Wiley Periodicals, Inc. [source]

Prospects for diffusion enhancement of signal and resolution in magnetic resonance microscopy

CONCEPTS IN MAGNETIC RESONANCE, Issue 2 2003
Charles H. Pennington
Abstract The prospects for and practical requirements of the "diffusion enhancement of signal and resolution" (DESIRE) scheme proposed by Lauterbur as a method to enhance the sensitivity, spatial resolution, and contrast in magnetic resonance (MR) microscopy and localized MR spectroscopy is assessed. The method, which still has not been implemented, promises signal enhancements of 1,2 orders of magnitude in imaging or localized spectroscopy on the scale of ,10 microns and requires magnetic field gradient strengths (,10 T/m) that are not unreasonable. I emphasize the development of an understanding of the physical principles involved in this unfamiliar, "real-space" imaging method. © 2003 Wiley Periodicals, Inc. Concepts Magn Reson Part A 19A: 71,79, 2003. [source]

Flavour encapsulation and controlled release , a review

INTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 1 2006
Atmane Madene
Summary Flavours can be among the most valuable ingredients in any food formula. Even small amounts of some aroma substance can be expensive, and because they are usually delicate and volatile, preserving them is often a top concern of food manufacturers. Encapsulation describes different processes to cover an active compound with a protective wall material and it can be employed to treat flavours so as to impart some degree of protection against evaporation, reaction, or migration in a food. Encapsulation of flavours has been attempted and commercialized using many different methods such as spray drying, spray chilling or spray cooling, extrusion, freeze drying, coacervation and molecular inclusion. The choice of appropriate microencapsulation technique depends upon the end use of the product and the processing conditions involved in the manufacturing product. This overview describes each method cited above in terms of the basic chemical and/or physical principles involved and covers mechanisms of flavour release from food matrices. [source]

Mesoscale simulations of atmospheric flow and tracer transport in Phoenix, Arizona

METEOROLOGICAL APPLICATIONS, Issue 3 2006
Ge Wang
Abstract Large urban centres located within confining rugged or complex terrain can frequently experience episodes of high concentrations of lower atmospheric pollution. Metropolitan Phoenix, Arizona (United States), is a good example, as the general population is occasionally subjected to high levels of lower atmospheric ozone, carbon monoxide and suspended particulate matter. As a result of dramatic but continuous increase in population, the accompanying environmental stresses and the local atmospheric circulation that dominates the background flow, an accurate simulation of the mesoscale pollutant transport across Phoenix and similar urban areas is becoming increasingly important. This is particularly the case in an airshed, such as that of Phoenix, where the local atmospheric circulation is complicated by the complex terrain of the area. Within the study presented here, a three-dimensional time-dependent mesoscale meteorological model (HOTMAC) is employed for simulation of lower-atmospheric flow in Phoenix, for both winter and summer case-study periods in 1998. The specific purpose of the work is to test the model's ability to replicate the atmospheric flow based on the actual observations of the lower-atmospheric wind profile and known physical principles. While a reasonable general agreement is found between the model-produced flow and the observed one, the simulation of near-surface wind direction produces a much less accurate representation of actual conditions, as does the simulation of wind speed over 1,000 metres above the surface. Using the wind and turbulence output from the mesoscale model, likely particle plume trajectories are simulated for the case-study periods using a puff dispersion model (RAPTAD). Overall, the results provide encouragement for the efforts towards accurately simulating the mesoscale transport of lower-atmospheric pollutants in environments of complex terrain. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Polarized light imaging of white matter architecture

MICROSCOPY RESEARCH AND TECHNIQUE, Issue 10 2007
Luiza Larsen
Abstract Polarized light imaging (PLI) is a method to image fiber orientation in gross histological brain sections based on the birefringent properties of the myelin sheaths. The method uses the transmission of polarized light to quantitatively estimate the fiber orientation and inclination angles at every point of the imaged section. Multiple sections can be assembled into a 3D volume, from which the 3D extent of fiber tracts can be extracted. This article describes the physical principles of PLI and describes two major applications of the method: the imaging of white matter orientation of the rat brain and the generation of fiber orientation maps of the human brain in white and gray matter. The strengths and weaknesses of the method are set out. Microsc. Res. Tech., 2007. © 2007 Wiley-Liss, Inc. [source]

RF stationary waves integrated Fourier transform spectrometer

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 5 2007
S. Hemour
Abstract We describe here a new type of analog correlators based on stationary waves recovery and spatial Fourier transformation. The theoretical basis of the stationary waves integrated Fourier transform spectrometer (SWIFTS) is first introduced. Based on robust physical principles validated by circuits type simulations, the spectrometer could be an interesting competitor to actual RF analog correlators. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1138,1142, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI.10.1002/mop.22375 [source]

Chemical natures and distributions of metal impurities in multicrystalline silicon materials

PROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 6 2006
T. Buonassisi
Abstract We present a comprehensive summary of our observations of metal-rich particles in multicrystalline silicon (mc-Si) solar cell materials from multiple vendors, including directionally-solidified ingot-grown, sheet, and ribbon, as well as multicrystalline float zone materials contaminated during growth. In each material, the elemental nature, chemical states, and distributions of metal-rich particles are assessed by synchrotron-based analytical x-ray microprobe techniques. Certain universal physical principles appear to govern the behavior of metals in nearly all materials: (a) Two types of metal-rich particles can be observed (metal silicide nanoprecipitates and metal-rich inclusions up to tens of microns in size, frequently oxidized), (b) spatial distributions of individual elements strongly depend on their solubility and diffusivity, and (c) strong interactions exist between metals and certain types of structural defects. Differences in the distribution and elemental nature of metal contamination between different mc-Si materials can largely be explained by variations in crystal growth parameters, structural defect types, and contamination sources. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Further Correspondences and Similarities of Shamanism and Cognitive Science: Mental Representation, Implicit Processing, and Cognitive Structures

ANTHROPOLOGY OF CONSCIOUSNESS, Issue 1 2003
Timothy L. Hubbard
Properties of mental representation are related to findings in cognitive science and ideas in shamanism. A selective review of research in cognitive science suggests visual images and spatial memory preserve important functional information regarding physical principles and the behavior of objects in the natural world, and notions of second-order isomorphism and the perceptual cycle developed to account for such findings are related to shamanic experience. Possible roles of implicit processes in shamanic cognition, and the idea that shamanic experience may involve normally unconscious information becoming temporarily available to consciousness, are considered. The existence of a cognitive module dedicated to processing information relevant to social knowledge and social interaction is consistent with cognitive science and with shamanism, and may help account for the extension of intentionality and meaning that characterize shamanic practice. Overall, findings from cognitive science and ideas from shamanism exhibit a number of correspondences and similarities regarding basic properties of cognition, and this suggests that shamanic and nonshamanic cognition may not be fundamentally different. [source]

Structure of the sporulation histidine kinase inhibitor Sda from Bacillus subtilis and insights into its solution state

ACTA CRYSTALLOGRAPHICA SECTION D, Issue 6 2009
David A. Jacques
The crystal structure of the DNA-damage checkpoint inhibitor of sporulation, Sda, from Bacillus subtilis, has been solved by the MAD technique using selenomethionine-substituted protein. The structure closely resembles that previously solved by NMR, as well as the structure of a homologue from Geobacillus stearothermophilus solved in complex with the histidine kinase KinB. The structure contains three molecules in the asymmetric unit. The unusual trimeric arrangement, which lacks simple internal symmetry, appears to be preserved in solution based on an essentially ideal fit to previously acquired scattering data for Sda in solution. This interpretation contradicts previous findings that Sda was monomeric or dimeric in solution. This study demonstrates the difficulties that can be associated with the characterization of small proteins and the value of combining multiple biophysical techniques. It also emphasizes the importance of understanding the physical principles behind these techniques and therefore their limitations. [source]

Modelling skin disease: Lessons from the worlds of mathematics, physics and computer science

AUSTRALASIAN JOURNAL OF DERMATOLOGY, Issue 2 2005
Stephen Gilmore
SUMMARY Theoretical biology is a field that attempts to understand the complex phenomena of life in terms of mathematical and physical principles. Likewise, theoretical medicine employs mathematical arguments and models as a methodology in approaching the complexities of human disease. Naturally, these concepts can be applied to dermatology. There are many possible methods available in the theoretical investigation of skin disease. A number of examples are presented briefly. These include the mathematical modelling of pattern formation in congenital naevi and erythema gyratum repens, an information-theoretic approach to the analysis of genetic networks in autoimmunity, and computer simulations of early melanoma growth. To conclude, an analogy is drawn between the behaviour of well-known physical processes, such as earthquakes, and the spatio-temporal evolution of skin disease. Creating models in skin disease can lead to predictions that can be investigated experimentally or by observation and offer the prospect of unexpected or important insights into pathogenesis. [source]