2,579 research outputs found
A Design for Additive Manufacturing Ontology
Design for additive manufacturing (DFAM) gives designers new freedoms to create complex geometries and combine parts into one. However, it has its own limitations, and more importantly, requires a shift in thinking from traditional design for subtractive manufacturing. There is a lack of formal and structured guidelines, especially for novice designers. To formalize knowledge of DFAM, we have developed an ontology using formal web ontology language (OWL)/resource description framework (RDF) representations in the Prot eg e tool. The description logic formalism facilitates expressing domain knowledge as well as capturing information from benchmark studies. This is demonstrated in a case study with three design features: revolute joint, threaded assembly (screw connection), and slider-crank. How multiple instances (build events) are stored and retrieved in the knowledge base is discussed in light of modeling requirements for the DFAM knowledge base: knowledge capture and reuse, supporting a tutoring system, integration into CAD tools. A set of competency questions are described to evaluate knowledge retrieval. Examples are given with SPARQL queries. Reasoning with semantic web rule language (SWRL) is exemplified for manufacturability analysis. Knowledge documentation is the main objective of the current ontology. However, description logic creates multiple opportunities for future work, including representing and reasoning about DFAM rules in a structured modular hierarchy, discovering new rules with induction, and recognizing patterns with classification, e.g., what leads to "successful" versus "unsuccessful" fabrications
The structure of the Au(111)/methylthiolate interface : new insights from near-edge X-ray absorption spectroscopy and X-ray standing waves
The local structure of the Au(111)([square root of]3×[square root of]3)R30°-methylthiolate surface phase has been investigated by S K-edge near-edge s-ray absorption fine structure (NEXAFS) both experimentally and theoretically and by experimental normal-incidence x-ray standing waves (NIXSW) at both the C and S atomic sites. NEXAFS shows not only excitation into the intramolecular sigma* S–C resonance but also into a sigma* S–Au orbital perpendicular to the surface, clearly identifying the local S headgroup site as atop a Au atom. Simulations show that it is not possible, however, to distinguish between the two possible adatom reconstruction models; a single thiolate species atop a hollow-site Au adatom or a dithiolate moiety comprising two thiolate species bonded to a bridge-bonded Au adatom. Within this dithiolate moiety a second sigma* S–Au orbital that lies near parallel to the surface has a higher energy that overlaps that of the sigma* S–C resonance. The new NIXSW data show the S–C bond to be tilted by 61° relative to the surface normal, with a preferred azimuthal orientation in , corresponding to the intermolecular nearest-neighbor directions. This azimuthal orientation is consistent with the thiolate being atop a hollow-site Au adatom, but not consistent with the originally proposed Au-adatom-dithiolate moiety. However, internal conformational changes within this species could, perhaps, render this model also consistent with the experimental data
The Keck Aperture Masking Experiment: spectro-interferometry of 3 Mira Variables from 1.1 to 3.8 microns
We present results from a spectro-interferometric study of the Miras o Cet, R
Leo and W Hya obtained with the Keck Aperture Masking Experiment from 1998 Sep
to 2002 Jul. The spectrally dispersed visibility data permit fitting with
circularly symmetric brightness profiles such as a simple uniform disk. The
stellar angular diameter obtained over up to ~ 450 spectral channels spaning
the region 1.1-3.8 microns is presented. Use of a simple uniform disk
brightness model facilitates comparison between epochs and with existing data
and theoretical models. Strong size variations with wavelength were recorded
for all stars, probing zones of H2O, CO, OH, and dust formation. Comparison
with contemporaneous spectra extracted from our data show a strong
anti-correlation between the observed angular diameter and flux. These
variations consolidate the notion of a complex stellar atmosphere consisting of
molecular shells with time-dependent densities and temperatures. Our findings
are compared with existing data and pulsation models. The models were found to
reproduce the functional form of the wavelength vs. angular diameter curve
well, although some departures are noted in the 2.8-3.5 micron range.Comment: 10 pages, 10 figures Accepted to Ap
The role of religiosity types in the phenomenology of hallucinations:A large cross-sectional community-based study in a predominantly Muslim society
Religiosity is a multidimensional construct known to influence the occurrence of hallucinations. However, it remains unknown how different religiosity types affect clinically relevant phenomenological features of hallucinations. Therefore, we wished to explore associations between intrinsic and extrinsic (non-organizational and organizational) religiosity and hallucinations severity, distress or impact on daily function in a non-clinical Muslim population. We recruited a representative sample of full-time students at Qatar's only national university via systematic random sampling and administered the Questionnaire of Psychotic Experiences online. The study design was cross-sectional. Using structural equation modeling, we estimated effects of the religiosity types on hallucinations severity, distress or impact on daily function in the past week while accounting for sociodemographic variables, anxiety, depressive symptoms, and, delusions. Extrinsic non-organizational religiosity (ENORG) was associated with experiencing reduced distress or impact on daily function from hallucinations both directly and indirectly through intrinsic religiosity. In contrast, extrinsic non-organizational religiosity (EORG) was associated with increased hallucinations distress or impact albeit only through higher intrinsic religiosity. We found no association between any religiosity types and hallucinations severity. Younger and married participants from lower socio-economic class had comparatively more severe hallucinations and more distress from them. Qatari nationality was positively associated EORG and negatively associated with hallucinations distress or impact. Evidence of differential associations between the religiosity types, socioeconomic and cultural groups, and distress or impact from past week's hallucinations supports the importance of alignment between religious, mental health, and well-being education
Direct calculation of the hard-sphere crystal/melt interfacial free energy
We present a direct calculation by molecular-dynamics computer simulation of
the crystal/melt interfacial free energy, , for a system of hard
spheres of diameter . The calculation is performed by thermodynamic
integration along a reversible path defined by cleaving, using specially
constructed movable hard-sphere walls, separate bulk crystal and fluid systems,
which are then merged to form an interface. We find the interfacial free energy
to be slightly anisotropic with = 0.62, 0.64 and
0.58 for the (100), (110) and (111) fcc crystal/fluid
interfaces, respectively. These values are consistent with earlier density
functional calculations and recent experiments measuring the crystal nucleation
rates from colloidal fluids of polystyrene spheres that have been interpreted
[Marr and Gast, Langmuir {\bf 10}, 1348 (1994)] to give an estimate of
for the hard-sphere system of , slightly lower
than the directly determined value reported here.Comment: 4 pages, 4 figures, submitted to Physical Review Letter
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Large Differences in Small RNA Composition Between Human Biofluids.
Extracellular microRNAs (miRNAs) and other small RNAs are implicated in cellular communication and may be useful as disease biomarkers. We systematically compared small RNAs in 12 human biofluid types using RNA sequencing (RNA-seq). miRNAs and tRNA-derived RNAs (tDRs) accounted for the majority of mapped reads in all biofluids, but the ratio of miRNA to tDR reads varied from 72 in plasma to 0.004 in bile. miRNA levels were highly correlated across all biofluids, but levels of some miRNAs differed markedly between biofluids. tDR populations differed extensively between biofluids. Y RNA fragments were seen in all biofluids and accounted for >10% of reads in blood plasma, serum, and cerebrospinal fluid (CSF). Reads mapping exclusively to Piwi-interacting RNAs (piRNAs) were very rare, except in seminal plasma. These results demonstrate extensive differences in small RNAs between human biofluids and provide a useful resource for investigating extracellular RNA biology and developing biomarkers
IMECE2002-33575 COHESIVE FINITE ELEMENT BASED MODELING OF DAMAGE IN COMPOSITE MATERIALS
ABSTRACT Damage in composite laminates affects its overall viscoelastic response. Constitutive equations have been developed for composite laminates considering a fixed damage state. A complete description, however, requires suitable damage evolution laws. This paper is focused on studying damage evolution in viscoelastic laminates using a cohesive finite element approach. A two dimensional, four nodded finite element is developed incorporating a rate-independent tractiondisplacement cohesive law. This element is used in conjunction with plane strain bulk elements behaving in a linear viscoelastic manner to simulate crack evolution between two existing transverse cracks in symmetric cross-ply laminates. The effects of loading strain-rate, ply constraint and initial crack density are studied. This study shows expected trends in the behavior and indicates the suitability of cohesive zone modeling to study damage evolution in viscoelastic composite materials
Renormalisation-theoretic analysis of non-equilibrium phase transitions I: The Becker-Doring equations with power law rate coefficients
We study in detail the application of renormalisation theory to models of
cluster aggregation and fragmentation of relevance to nucleation and growth
processes. We investigate the Becker-Dorging equations, originally formulated
to describe and analyse non-equilibrium phase transitions, and more recently
generalised to describe a wide range of physicochemical problems. In the
present paper we analyse how the systematic coarse-graining renormalisation of
the \BD system of equations affects the aggregation and fragmentation rate
coefficients. We consider the case of power-law size-dependent cluster rate
coefficients which we show lead to only three classes of system that require
analysis: coagulation-dominated systems, fragmentation-dominated systems and
those where coagulation and fragmentation are exactly balanced. We analyse the
late-time asymptotics associated with each class.Comment: 18 pages, to appear in J Phys A Math Ge
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