743 research outputs found
Instability tests for air-jet textured yarns
The air-jet texturing process is briefly introduced and its advantages over other texturing processes are summarized. Characteristics of air-jet textured yarns are stated with special reference to the stability of the yarns. Test methods used in industry and research to determine the "stability" or "instability" of air-jet textured yarns are critically reviewed. These methods involve different basic principles and therefore inevitably give different results. There is no consensus on a standard method. Effects of various test parameters, such as specimen length, test duration, and the alternatives of using a single yarn, a hank, or a skein as a test specimen are investigated. An improved test method is suggested as a standard instability test, and various existing methods are compared with it. Results of all the methods show similar trends for varying values of air pressure. Other yarn characteristics such as linear density, breaking elongation, and tenacity are also determined, and their indications of yarn quality are compared with the indications of instability tests. Stability test results alone provide misleading information regarding air-jet textured yarn quality
Diffractive Phenomena and Shadowing in Deep-Inelastic Scattering
Shadowing effects in deep-inelastic lepton-nucleus scattering probe the mass
spectrum of diffractive leptoproduction from individual nucleons. We explore
this relationship using current experimental information on both processes. In
recent data from the NMC and E665 collaboration, taken at small x << 0.1 and
Q^2 < 1 GeV^2, shadowing is dominated by the diffractive excitation and
coherent interaction of low mass vector mesons. If shadowing is explored at
small x > 1 GeV^2 as discussed at HERA, the situation is
different. Here dominant contributions come from the coherent interaction of
diffractively produced heavy mass states. Furthermore we observe that the
energy dependence of shadowing is directly related to the mass dependence of
the diffractive production cross section for free nucleon targets.Comment: 12 pages Latex, 8 figure
Extension of the generalized multipole technique to three-dimensional anisotropic scatterers
New expansions are derived for the simulation of three-dimensional anisotropic scatterers with the generalized multipole technique (GMT). This extension of the GMT makes possible the investigation of subtle phenomena such as the interaction of light with realistic crystals or magneto-optic materials. (C) 1998 Optical Society of America
Electromagnetic scattering in polarizable backgrounds
We develop a fully vectorial formalism for the investigation of electromagnetic scattering in polarizable backgrounds, i.e., where the scatterers are not in vacuum but situated in a medium with a dielectric permittivity different from unity. Our approach is based on the Green's tensor technique and the corresponding Green's tensors for two-dimensional (2D) and three-dimensional (3D) systems are developed. The analysis of 2D systems is not restricted to the case where transverse electric (TE) and transverse magnetic (TM) modes are decoupled, but treated in a general manner. Practical examples illustrate the application of the method: scattering by a microcavity for two dimensions and color formation in opal for three dimensions
Increasing the performance of the coupled-dipole approximation: A spectral approach
We show that it is possible to increase the performance of the coupled-dipole approximation (CDA) for scattering by using concepts from the sampling theory. In standard CDA, the source in each discretized cell is represented by a point dipole and the corresponding scattered field given by Green's tensor. In the present approach, the source has a certain spatial extension, and the corresponding Green's tensor must be redefined. We derive these so-called filtered Green's tensors for one-dimensional (1-D), two-dimensional (2-D), and three-dimensional (3-D) systems, which forms the basis of our new scheme: the filtered coupled-dipole technique (FCD)
Nuclear shadowing at low Q^2
We re-examine the role of vector meson dominance in nuclear shadowing at low
Q^2. We find that models which incorporate both vector meson and partonic
mechanisms are consistent with both the magnitude and the Q^2 slope of the
shadowing data.Comment: 7 pages, 2 figures; to appear in Phys. Rev.
Psychometric Evaluation of the Parent Effort Scale
ObjectiveThe Parent Effort Scale (PES) is a parent report questionnaire designed to quantify the level of effort required of caregivers to assist their children in developmentally appropriate home- and community-based activities. This manuscript describes the psychometric evaluation of the PES.MethodData collected from 304 parents of children ages 2–7 years (167 parents of a children with autism spectrum disorder and 137 parents of neurotypical children) were factor analyzed, calibrated using item response theory, and evaluated for construct validity.ResultsThe final PES scales are reliable and valid measures of the level of parental effort required to assist children in dressing, personal hygiene, sleep, socialization at home, participation in community events, and access to healthcare. A total score reflects overall parental effort.ConclusionThe PES can be used to plan and evaluate the effectiveness of interventions that aim to help parents enhance children's participation opportunities and thus, support their cognitive and social development
Shadowing, Binding and Off-Shell Effects in Nuclear Deep Inelastic Scattering
We present a unified description of nuclear deep inelastic scattering (DIS)
over the whole region of the Bjorken variable. Our approach is based on
a relativistically covariant formalism which uses analytical properties of
quark correlators. In the laboratory frame it naturally incorporates two
mechanisms of DIS: (I) scattering from quarks and antiquarks in the target and
(II) production of quark-antiquark pairs followed by interactions with the
target. We first calculate structure functions of the free nucleon and develop
a model for the quark spectral functions. We show that mechanism (II) is
responsible for the sea quark content of the nucleon while mechanism (I)
governs the valence part of the nucleon structure functions. We find that the
coherent interaction of pairs with nucleons in the nucleus leads to
shadowing at small and discuss this effect in detail. In the large
region DIS takes place mainly on a single nucleon. There we focus on the
derivation of the convolution model. We point out that the off-shell properties
of the bound nucleon structure function give rise to sizable nuclear effects.Comment: 29 pages (and 10 figures available as hard copies from Authors),
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