49,981 research outputs found
A mechanical fastening technique development for application in space Final report
Mechanical fastening technique development for aerospace applicatio
A Tutorial and Comprehensive Bibliography on the Identification of Foreign Bodies Found in Food
The paper presents a philosophical approach to the investigation of foreign body incidents in food. The suggested procedure has similarities with key procedures used for taxonomy. However, the wide diversity of materials encountered and the need to determine something of the history of the offending item demands modifications to this process. The categorisation may be made on instinct or experience, and appropriate confirmatory tests will be applied in the light of the initial categorisation. Cardinal rules are proposed: firstly , the receipt of the items should be well documented; and secondly, the initial observations should be as non-destructive as possible. The stereo microscope is the major in strument used to reveal clues as to origin of foreign substances. Other microscopy and analytical techniques are used to supplement the stereo microscope. The paper includes suggested categories for foreign materials; lists of possible origins of forei,gn contamination; examples of specific recurrent foreign materials associated with foods and a bibliography of helpful sources of information
The Kinetic Activation-Relaxation Technique: A Powerful Off-lattice On-the-fly Kinetic Monte Carlo Algorithm
Many materials science phenomena, such as growth and self-organisation, are
dominated by activated diffusion processes and occur on timescales that are
well beyond the reach of standard-molecular dynamics simulations. Kinetic Monte
Carlo (KMC) schemes make it possible to overcome this limitation and achieve
experimental timescales. However, most KMC approaches proceed by discretizing
the problem in space in order to identify, from the outset, a fixed set of
barriers that are used throughout the simulations, limiting the range of
problems that can be addressed. Here, we propose a more flexible approach --
the kinetic activation-relaxation technique (k-ART) -- which lifts these
constraints. Our method is based on an off-lattice, self-learning, on-the-fly
identification and evaluation of activation barriers using ART and a
topological description of events. The validity and power of the method are
demonstrated through the study of vacancy diffusion in crystalline silicon.Comment: 5 pages, 4 figure
Static and dynamic properties of crystalline phases of two-dimensional electrons in a strong magnetic field
We study the cohesive energy and elastic properties as well as normal modes
of the Wigner and bubble crystals of the two-dimensional electron system (2DES)
in higher Landau levels. Using a simple Hartree-Fock approach, we show that the
shear moduli ('s) of these electronic crystals show a non-monotonic
behavior as a function of the partial filling factor at any given
Landau level, with increasing for small values of , before
reaching a maximum at some intermediate filling factor , and
monotonically decreasing for . We also go beyond previous
treatments, and study how the phase diagram and elastic properties of electron
solids are changed by the effects of screening by electrons in lower Landau
levels, and by a finite thickness of the experimental sample. The implications
of these results on microwave resonance experiments are briefly discussed.Comment: Discussion updated - 16 pages, 10 figures; version accepted for
publication in Phys. Rev.
Submillimetre observations of a sample of broad absorption line quasars
The broad absorption line (BAL) features seen in a small fraction of quasar
optical/UV spectra are attributed to bulk outflows away from the quasar core.
Observational evidence suggests that dust plays a key role in these systems,
although whether the inferred dust properties are a signature of orientation
effects or whether they are indicative of an evolutionary sequence remains an
outstanding issue. Submillimetre (submm) detections of BAL quasars (BALQSOs),
which would clearly help to resolve this issue, have so far been sparse. This
paper reports on new submm observations of seven BALQSOs. The strongest
influence on the observed flux is found to be the redshift, with the two
highest redshift sources appearing intrinsically more submm-luminous than the
lower redshift ones. Since this trend is also seen in other high redshift AGN,
including non-BAL quasars it implies that the dust emission properties of these
systems are no different from those of the general AGN population, which is
difficult to reconcile with the evolutionary interpretation of the BAL
phenomenon.Comment: 5 Pages, to appear in ApJ Letter
Modeling the evolution of infrared luminous galaxies: the influence of the Luminosity-Temperature distribution
The evolution of the luminous infrared galaxy population is explored using a
pure luminosity evolution model which incorporates the locally observed
luminosity-temperature distribution for IRAS galaxies. Pure luminosity
evolution models in a fixed CDM cosmology are fitted to submillimeter
(submm) and infrared counts, and backgrounds. It is found that the differences
between the locally determined bivariate model and the single variable
luminosity function (LF) do not manifest themselves in the observed counts, but
rather are primarily apparent in the dust temperatures of sources in flux
limited surveys. Statistically significant differences in the redshift
distributions are also observed. The bivariate model is used to predict the
counts, redshifts and temperature distributions of galaxies detectable by {\it
Spitzer}. The best fitting model is compared to the high-redshift submm galaxy
population, revealing a median redshift for the total submm population of
, in good agreement with recent spectroscopic studies of
submillimeter galaxies. The temperature distribution for the submm galaxies is
modeled to predict the radio/submm indices of the submm galaxies, revealing
that submm galaxies exhibit a broader spread in spectral energy distributions
than seen in the local IRAS galaxies.Comment: Accepted for publication in ApJ. Quality of several figures reduced
due to size restriction
Microlensing of Broad Absorption Line Quasars: Polarization Variability
Roughly 10% of all quasars exhibit Broad Absorption Line (BAL) features which
appear to arise in material outflowing at high velocity from the active
galactic nucleus (AGN). The details of this outflow are, however, very poorly
constrained and the particular nature of the BAL material is essentially
unknown. Recently, new clues have become available through polarimetric studies
which have found that BAL troughs are more polarized than the quasar continuum
radiation. To explain these observations, models where the BAL material
outflows equatorially across the surface of the dusty torus have been
developed. In these models, however, several sources of the BAL polarization
are possible. Here, we demonstrate how polarimetric monitoring of
gravitationally lensed quasars, such as H 1413+117, during microlensing events
can not only distinguish between two currently popular models, but can also
provide further insight into the structure at the cores of BAL quasars.Comment: 17 pages, 3 figures, accepted to PAS
Defect-Seeded Atomic Layer Deposition of Metal Oxides on the Basal Plane of 2D Layered Materials
Atomic layer deposition (ALD) on mechanically exfoliated 2D layered materials spontaneously produces network patterns of metal oxide nanoparticles in triangular and linear deposits on the basal surface. The network patterns formed under a range of ALD conditions and were independent of the orientation of the substrate in the ALD reactor. The patterns were produced on MoS2 or HOPG when either tetrakis(dimethylamido)titanium or bis(ethylcyclopentadienyl)manganese were used as precursors, suggesting that the phenomenon is general for 2D materials. Transmission electron microscopy revealed the presence, prior to deposition, of dislocation networks along the basal plane of mechanically exfoliated 2D flakes, indicating that periodical basal plane defects related to disruptions in the van der Waals stacking of layers, such as perfect line dislocations and triangular extended stacking faults networks, introduce a surface reactivity landscape that leads to the emergence of patterned deposition
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