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Form Factor (form + factor)

Distribution by Scientific Domains

Chemistry	46%
Polymers and Materials Science	10%
Physics and Astronomy	10%
Medical Sciences	10%
Information Science and Computing	10%
3 Other Domains	14%

Selected Abstracts

Form factors for core electrons useful for the application of quantum crystallography (QCr) to organic molecules

ACTA CRYSTALLOGRAPHICA SECTION A, Issue 4 2002
Lulu Huang
Form factors are calculated for the core electrons of the first-row atoms B, C, N, O and F. The form factors are presented in an analytical form, as appears in International Tables for X-ray Crystallography [Ibers & Hamilton (1974), Vol. IV, pp. 103,145. Birmingham: Kynoch Press; present distributor Kluwer Academic Publishers, Dordrecht]. Having such form factors for the core electrons reduces the number of parameters to be determined by the methods of quantum crystallography (QCr). It is shown that the form factors obtained are quite accurate. Thus, when they are used in QCr, they are expected to be consistent with accurate charge densities. [source]

Automatic Creation of Object Hierarchies for Radiosity Clustering

COMPUTER GRAPHICS FORUM, Issue 4 2000
Gordon Müller
Using object clusters for hierarchical radiosity greatly improves the efficiency and thus usability of radiosity computations. By eliminating the quadratic starting phase very large scenes containing about 100k polygons can be handled efficiently. Although the main algorithm extends rather easily to using object clusters, the creation of ,good' object hierarchies is a difficult task both in terms of construction time and in the way how surfaces or objects are grouped to clusters. The quality of an object hierarchy for clustering depends on its ability to accurately simulate the hierarchy of the energy flow in a given scene. Additionally it should support visibility computations by providing efficient ray acceleration techniques. In this paper we will present a new approach of building hierarchies of object clusters. Our hybrid structuring algorithm provides accuracy and speed by combining a highly optimized bounding volume hierarchy together with uniform spatial subdivisions for nodes with regular object densities. The algorithm works without user intervention and is well suited for a wide variety of scenes. First results of using these hierarchies in a radiosity clustering environment are very promising and will be presented here. The combination of very deep hierarchies (we use a binary tree) together with an efficient ray acceleration structure shifts the computational effort away from form factor and visibility calculation towards accurately propagating the energy through the hierarchy. We will show how an efficient single pass gathering can be used to minimize traversal costs. [source]

Influence of melt drawing on the morphology of one- and two-step processed LDPE/thermoplastic starch blends

ADVANCES IN POLYMER TECHNOLOGY, Issue 4 2003
F. J. Rodriguez-Gonzalez
Abstract In this study the morphology of LDPE/TPS blends prepared by a one-step extrusion process is compared to that obtained by reprocessing of the original blends. The influence of composition and melt drawing is examined. A novel methodology based on the form factor of the dispersed particle was used to estimate the equivalent spherical particle size of dispersed thermoplastic starch (TPS). This approach allows for the quantitative comparison of average dispersed phase particles regardless of their shape. Blends prepared in the one-step extrusion process show increased levels of anisotropy as a consequence of a combination of coalescence and particle deformation during melt drawing. Reprocessed materials demonstrate morphologies that are highly stable to a wide range of hot stretch ratio conditions. The TPS particles of reprocessed blends show no coalescence and a low degree of deformation. This phenomenon is explained by plasticizer evaporation resulting from the second processing step. The TPS is transformed from a highly deformable phase to one resembling a partially cross-linked material. These data indicate that the one-step processing of LDPE/TPS blends can be used to generate a wide range of highly elongated morphological structures. A two-step approach, analogous to typical compounding and shaping operations and involving controlled glycerol removal in the second step can be used to prepare a wide range of highly stable, more isotropic, dispersed particle morphologies. © 2003 Wiley Periodicals, Inc. Adv Polym Techn 22: 297,305, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.10057 [source]

Method of separated form factors for polydisperse vesicles

JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3 2006
Jeremy Pencer
Use of the Schulz or Gamma distribution in the description of particle sizes facilitates calculation of analytic polydisperse form factors using Laplace transforms, [f(u)]. Here, the Laplace transform approach is combined with the separated form factor (SFF) approximation [Kiselev et al. (2002). Appl. Phys. A, 74, S1654,S1656] to obtain expressions for form factors, P(q), for polydisperse spherical vesicles with various forms of membrane scattering length density (SLD) profile. The SFF approximation is tested against exact form factors that have been numerically integrated over the size distribution, and is shown to represent the vesicle form factor accurately for typical vesicle sizes and membrane thicknesses. Finally, various model SLD profiles are used with the SFF approximation to fit experimental small-angle neutron scattering (SANS) curves from extruded unilamellar vesicles. [source]

Contrast analysis of the composition of ribosomes extracted with different purification procedures

JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 4 2000
Giuseppe Briganti
The composition and hydration of E. coli ribosomes isolated with different purification protocols has been analysed by combining two experimental techniques: measurements of small-angle neutron scattering (SANS), for two different isotopic solvent compositions, and refractive index (RI) increments. From the contrast between the solvent and solute scattering densities and the molar polarizability, determined experimentally with SANS and RI measurements, three independent equations are obtained and three unknown quantities are determined: (i) the volume of the solute hydrated skeleton Vs, (ii) the material contained in it, namely the biological components, intrinsic (rRNA and proteins) and extrinsic, such as aminoacylsynthetase and elongation factors, (iii) the number of water molecules structurally bound to the ribosome and non-exchangeable with the solvent. From the form factor at infinite contrast, a second definition of the solute volume is obtained, , which represents the volume within the contour surface of the ribosome. This value is generally larger than Vs and can include a certain amount of water molecules, i.e. those inside the volume (,Vs). Considering the molar volume of this water to be equal to that of the bulk water, it is possible to evaluate its amount. The particle density calculated from the ribosome components in , including proteins, RNA, bound and unbound water molecules, corresponds to the buoyant density measured for E. coli 70S particles. The two ribosomal preparations display different performances in protein synthesis; hence the results indicate that the optimal condition corresponds to a wider skeleton and contour volume but containing a smaller amount of segregated water molecules. It is believed that the method provides a reliable technique to determine the composition of ribosomes under various experimental conditions. [source]

Standardized analysis of UHMWPE wear particles from failed total joint arthroplasties

JOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 5 2002
Jay D. Mabrey
Abstract Periprosthetic tissue obtained at revision surgery from eight total hip replacement cases was hydrolyzed, and polyethylene debris particles were isolated from each case. Individual particles were analyzed by scanning electron microscopy (SEM) and computerized image analysis in accordance with ASTM F1877-98, a standard for quantitative description of wear debris. For comparison, periprosthetic tissues from eight total knee revision and four total shoulder revision cases were processed and analyzed with identical methods. A total of 2599 hip, 4345 knee, and 1200 shoulder particles were analyzed. The morphologies of the isolated polyethylene particles from the total hip specimens were distinctly different from the total knee and total shoulder particles. The mean equivalent circle diameter (ECD) for hip particles was 0.694 ,m ± 0.005; knee particles measured 1.190 ,m ±0.009; and shoulder particles 1.183 ,m ± 0.017. The ECD was significantly different between hip particles and those from the shoulder and knee. The mean aspect ratio (AR) for the hip particles was 1.626 ± 0.015, compared to the knee particles at 1.935 ± 0.015 and shoulder particles at 2.082 ± 0.033. The AR was statistically different among all three groups. Other descriptors from the ASTM standard, elongation (E), form factor (FF), and roundness (R) were all significantly different among the three groups of joints. This study demonstrates the utility of ASTM F1877-98 in differentiating wear debris particles from different sources. © 2002 Wiley Periodicals, Inc. J Biomed Mater Res (Appl Biomater) 63: 475,483, 2002 [source]

Distinction between Mulloidichthys flavolineatus juveniles from Reunion Island and Mauritius Island (south-west Indian Ocean) based on otolith morphometrics

JOURNAL OF FISH BIOLOGY, Issue 1 2006
K. Pothin
Sagittal otoliths of the yellowstripe goatfish Mulloidichthys flavolineatus were analysed in order to compare Reunion Island fish stocks with those of Mauritius (south-west Indian Ocean). Conventional otolith morphometric variables (area, perimeter, length and width), shape indices (form factor, roundness, circularity, rectangularity, ellipticity and eccentricity) and Fourier shape analysis were compared between three sites; two in Reunion Island and one in Mauritius. Regional and site-specific differences were found for all the conventional otolith morphometric features. Regarding the shape indices, the differences between sites were best described by form factor, roundness, circularity and rectangularity. A classification by canonical discriminant analysis indicated significant differences between the three sampling sites. The combined use of morphometric variables (size and shape) and external outlines (shape analysis through Fourier series) showed the importance of otolith shape for intraspecific discrimination. [source]

Visual Tracking and LIDAR Relative Positioning for Automated Launch and Recovery of an Unmanned Rotorcraft from Ships at Sea

NAVAL ENGINEERS JOURNAL, Issue 2 2009
MATT GARRATT
Sensors and systems for a fully autonomous unmanned helicopter have been developed with the aim of completely automating the landing and launch of a small-unmanned helicopter from the deck of a ship. For our scheme, we have combined a laser rangefinder (LRF) system with a visual tracking sensor to construct a low-cost guidance system. Our novel LRF system determines both the distance to and the orientation of the deck in one cycle. We have constructed an optical sensor to complement the laser system, comprising a digital camera interfaced to a Field Programmable Gate Array (FPGA), which enables the entire target tracking computation to be achieved in a very small self-contained form factor. A narrowband light source on the deck is detected by the digital camera and tracked by an algorithm implemented on the FPGA to provide a relative bearing to the deck from the helicopter. By combining the optical sensor bearing with the information from the laser system, an accurate estimate of the helicopter position relative to the deck can be found. [source]

Low grade diffuse gliomas: Shared cellular composition and morphometric differences

NEUROPATHOLOGY, Issue 5 2008
Sawako Kinjo
Low grade diffuse gliomas arising in the brain are challenging to treat because of their ability to infiltrate adjacent tissue. We attempted to clarify the cellular composition and histopathological features of low grade gliomas by utilizing morphometric and immunohistochemical analyses. Seventy-eight cases of low grade gliomas were examined including 21 diffuse astrocytomas (DA), 36 oligodendrogliomas (OL), and 21 oligoastrocytomas (OA), based on the WHO classification system. Moreover, OL were subdivided into three types based on the morphological characteristics advocated by Daumas-Duport et al.: OL type I, OL type II, and OL type III. The cellularity, nuclear form factor, and conditional entropy corresponding to the nuclear pleomorphism were measured in each sample by the image analysis software "Gunmetry." Twenty-two cases were immunohistochemically analyzed for the expression of several antigens. Morphometric data indicated that the cellularity of OL type II was significantly higher than that of DA, and that the conditional entropy of OL type III was significantly lower than that of DA. Although the results of the immunohistochemical studies were almost consistent with previous reports, there were significant differences in the expression of GFAP, nestin and p53 between DA and OL. Double immunostaining revealed that expression of Olig2 and GFAP, and Olig2 and nestin was mutually exclusive in most glioma cells. Moreover, the coexpression of nestin and GFAP occurred in DA and OA, but not in OL. We conclude that each glioma include cells expressing GFAP, cells expressing nestin, and cells expressing Olig2 in a characteristic proportion for each tumor type. We suggest that diffuse gliomas share cellular compositions in different ratios and that they can be distinguished by morphometrical analysis. [source]

A new technique, which clearly distinguishes fibre types in fixed muscle tissue

NEUROPATHOLOGY & APPLIED NEUROBIOLOGY, Issue 2 2002
W. M. H. Behan
Aims:, A method of distinguishing between type 1 and 2 skeletal muscle fibres in wax-embedded tissue is needed. The ATPase method is the basis for fibre identification on frozen tissue and a new method should not give significantly different results. Isoforms of myosin and myofibrillar ATPase are known to correlate. Materials and methods:, We devised an immunohistochemical double-labelling (IHC) protocol using monoclonal antibodies to fast and slow myosin. We compared results in the two methods by morphometric analysis of frozen muscle and then applied the method to paraffin-embedded tissue. Results:, On frozen sections there were no significant differences (P = 0.57) in the percentages of type 1 (46% IHC method vs. 48% ATPase) or type 2 fibres (54% vs. 52%) and 2a and 2b subtypes were distinguished easily. Cross-sectional area (in µm2), diameter (µm) and form factor were all similar. Various diagnostic samples of wax embedded tissue were then examined. These gave excellent results with clear colour contrast: type 1 fibres, black and type 2 fibres, red (see examples). Conclusion:, An IHC method based on the fast and slow isoforms of myosin gives similar results to the ATPase method while providing an important advantage in its applicability to wax-embedded muscle. [source]

Selection of Descriptors for Particle Shape Characterization

PARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 1 2003

Abstract Conventional shape descriptors, formed from a ratio of two particle size measurements, are among the simplest of the many methods used for quantitative particle shape characterization. However, a significant limitation of using one of these shape descriptors is that its value is often not unique to a specific shape. Use of several different shape descriptors may circumvent this problem but, as particle size can be defined in a large number of ways, a similarly large number of shape descriptors can be defined. While some differ substantially, others are only subtly different, conveying similar information. Thus, it is not obvious which of the many possible descriptors should be utilized. In this paper, two-dimensional particle shape descriptors obtained by image analysis of six different commercially sourced powders were considered. Techniques of cluster and correlation analysis were applied to assist in identifying redundant descriptors for shape characterization of these powder particles, allowing for efficient description of shape using a reduced set. It was found that at least two descriptors are required: aspect ratio and the square root of form factor. Significantly, each descriptor is most sensitive to a different attribute of shape: elongation and ruggedness, respectively. [source]

Structural Studies of Bleached Melanin by Synchrotron Small-angle X-ray Scattering,

PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 2 2003
Kenneth C. Littrell
ABSTRACT Small-angle X-ray scattering was used to measure the effects of chemical bleaching on the size and morphology of tyrosine-derived synthetic melanin dispersed in aqueous media. The average size as measured by the radius of gyration of the melanin particles in solution, at neutral to mildly basic pH, decreases from 16.5 to 12.5 Å with increased bleaching. The melanin particles exhibit scattering characteristic of sheet-like structures with a thickness of approximately 11 Å at all but the highest levels of bleaching. The scattering data are well described by the form factor for scattering from a pancake-like circular cylinder. These data are consistent with the hypothesis that unbleached melanin, at neutral to mildly basic pH, is a planar aggregate of 6- to 10-nm-sized melanin protomolecules, hydrogen bonded through their quinone and phenolic perimeters. The observed decrease in melanin particle size with increased bleaching is interpreted as evidence for deaggregation, most probably the result of oxidative disruption of hydrogen bonds and an increase in the number of charged, carboxylic acid groups, whereby the melanin aggregates disassociate into units composed of decreasing numbers of protomolecules. [source]

Diffuse scattering from large-angle, thermally induced, orientational disorder in molecular crystals

ACTA CRYSTALLOGRAPHICA SECTION A, Issue 5 2007
John Reid
Large-angle rotational motion (libration) characteristic of molecular solids has not been properly included in many scattering calculations because of the need to develop scattering theory through small-angle approximations. A simple but effective approach to calculating the influence of large-angle librations on the thermal disorder scattering given by molecular solids is to treat the molecules as independent librators, each in a harmonic potential well, using the mathematics appropriate for large-angle rotations. The resulting probability distribution for angular misorientations is Gaussian and this distribution can be used to smear the molecular form factor, enabling the librational influence on the scattering to be calculated. It is shown how to apply this direct approach quite generally and by way of examples the technique is used with the molecular solids sulfur hexafluoride (SF6), adamantane (C10H16) and buckminsterfullerene (C60). For these materials, the molecular Fourier transform (i.e. the molecular form factor) have been calculated in selected planes in reciprocal space, followed by the separate effects of librational and translational smearing. It is found that the librational smearing produces a large effect on the form factor, particularly at larger scattering vectors, that is not sensitive to approximations in the argument. Additionally, the Debye,Waller effect of vibrational motion is included in the calculations, showing quantitatively the decreasing influence of vibrations on the scattering with increasing scattering vector. Both effects illustrate with pedagogic clarity how different processes modify the basic molecular scattering. [source]

Polarization anisotropy of X-ray atomic factors and `forbidden' resonant reflections

ACTA CRYSTALLOGRAPHICA SECTION A, Issue 5 2005
Vladimir E. Dmitrienko
Symmetry and physical aspects of `forbidden' reflections excited by a local polarization anisotropy of the X-ray susceptibility are surveyed. Such reflections are observed near absorption edges where the anisotropy is caused by distortions of the atomic electronic states owing to interaction with neighbouring atoms. As a consequence, they allow for extracting nontrivial information about the resonant atom's local environment and their physical conditions. The unusual polarization properties of the considered reflections are helpful to distinguish them from other types of `forbidden' reflections. When such reflections are excited, it is, for example, possible to determine not only the intrinsic anisotropy of an atomic form factor but also additional anisotropy induced by thermal motion, point defects and/or incommensurate modulations. Even the local `chirality' of atoms in centrosymmetric crystals is accessible. Unsolved key problems and possible future developments are addressed. [source]

Deep inside the pion.

ANNALEN DER PHYSIK, Issue 11-12 2004
Reconciling QCD theory with data
Abstract Recent developments in the QCD description of the pion structure are reviewed. The CLEO pion-photon transition data analysis favors a distribution amplitude for the pion that is double-humped but endpoint-suppressed. After a short outline of the derivation of this amplitude from QCD sum rules with nonlocal condensates, we present the fully fledged analysis of the CLEO data prefaced by predictions for the F,,, form factor and commenting on the inherent theoretical uncertainties due to higher twists and NNLO perturbative corrections. We supplement our discussion by considering within QCD factorization theory, the electromagnetic pion form factor at NLO accuracy on one hand, and diffractive di-jets production on the other, comparing our predictions with the respective experimental data from JLab and the Fermilab E791 collaboration. In all cases, the agreement is impressive. [source]

Case study: ITU-T recommendation X.805 applied to an enterprise environment,banking

BELL LABS TECHNICAL JOURNAL, Issue 3 2007
David Ramirez
Base station costs are dominated by the cost of radio frequency (RF) units, that is, the duplexers, the power amplifiers, and the radio cards. But Moore's law is not applicable to these components. It only applies to the digital processing units of a base station, such as the baseband processing, line interface, and central control cards. The continuous size reduction of features at the chip level allows for increasingly higher integration of digital functionality. But in RF units, form factor is often a function of wavelength, which prevents a higher level of integration. Significant form factor and cost reductions in RF, therefore, will not arise from ongoing incremental improvements. They will result only through architectural innovation. However, changes in architecture predominantly require certain key technologies that are not yet available. Within the context of European Union (EU) research funding, the key technologies that are necessary to turn future RF system architectural visions into reality are being developed. This paper elaborates on the RF system vision and the research framework into which Bell Labs Europe is embedded, for conducting collaborative research to acquire the missing technological assets. © 2007 Alcatel-Lucent. [source]

Scaling laws in hadronic processes and string theory

FORTSCHRITTE DER PHYSIK/PROGRESS OF PHYSICS, Issue 7-8 2003
O. Andreev
We briefly review a possible scheme for getting the known QCD scaling laws within string theory. In particular, we consider amplitudes for exclusive scattering of hadrons at large momentum transfer and hadronic form factors. [source]

The Role of Processing in the Fabrication and Optimization of Plastic Solar Cells

ADVANCED MATERIALS, Issue 14-15 2009
Jeffrey Peet
Abstract The development of high-efficiency plastic solar cells is rapidly accelerating as the need for economically viable alternative energy sources becomes evident. Polymer-based bulk-heterojunction (BHJ) solar cells are attractive in that they can be coated from solution onto flexible substrates by a variety of techniques and thus inexpensive large-volume manufacturing should be possible. Further, the inherent flexibility of the polymeric materials combined with thin photovoltaic active layers results in devices that can be adapted to a variety of unique aesthetics and form factors. Recent advances in key relationships between thin-film casting methods, bulk-heterojunction morphology, and device performance have occurred in tandem with the synthesis of novel polymer semiconductors that possess increased optical-absorption breadth and optoelectronic performance. This Research News article highlights a few techniques developed to optimize the BHJ nanomorphology and performance of solar cells fabricated by various solution-processing methods. [source]

Scattering from laterally heterogeneous vesicles.

JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3 2007

Despite growing interest in the formation of domains or `rafts' in cell and model membranes, there have been relatively few attempts to characterize such systems via scattering techniques. Previously [Pencer et al. (2006). J. Appl. Cryst.39, 293,303], it was demonstrated that the Porod invariant, Q, could be used to detect lateral segregation. Here, the general theory for scattering from laterally heterogeneous vesicles is outlined and form factors are derived for vesicles containing either single circular or annular domains. These form factors are then applied to the analysis of neutron scattering data from heterogeneous vesicles. Potential advantages and limitations of this technique are also discussed. [source]

Method of separated form factors for polydisperse vesicles

Comparison of academic, application form and social factors in predicting early performance on the medical course

MEDICAL EDUCATION, Issue 9 2004
Andrew B Lumb
Objectives, To compare the relative importance of social, academic and application form factors at admission in predicting performance in the first 3 years of a medicine course. Design, Retrospective cohort study. Setting, A single UK medical school. Participants, A total of 738 students who entered medical school between 1994 and 1997. Main outcome measure, Performance in Year 3 objective structured clinical examination (OSCE). Results, School-leaving grades were significant predictors of success in the OSCE. Non-academic activities as assessed from the application form were associated with poorer performance. Mature students performed extremely well, and male and ethnic minority students performed less well. Socioeconomic status and type of school attended were not found to affect performance on the course. Conclusions, The relatively poor performance of male and ethnic minority students urgently needs further investigation. Our results carry no suggestion that, other things being equal, widening access to medical school for mature students and those from less affluent backgrounds would result in poorer performance. [source]