17,424 research outputs found
Skewed Factor Models Using Selection Mechanisms
Traditional factor models explicitly or implicitly assume that the factors follow a multivariate normal distribution; that is, only moments up to order two are involved. However, it may happen in real data problems that the first two moments cannot explain the factors. Based on this motivation, here we devise three new skewed factor models, the skew-normal, the skew-t, and the generalized skew-normal factor models depending on a selection mechanism on the factors. The ECME algorithms are adopted to estimate related parameters for statistical inference. Monte Carlo simulations validate our new models and we demonstrate the need for skewed factor models using the classic open/closed book exam scores dataset
Improved TPB-coated Light Guides for Liquid Argon TPC Light Detection Systems
Scintillation light produced in liquid argon (LAr) must be shifted from 128
nm to visible wavelengths in light detection systems used for liquid argon
time-projection chambers (LArTPCs). To date, LArTPC light collection systems
have employed tetraphenyl butadiene (TPB) coatings on photomultiplier tubes
(PMTs) or plates placed in front of the PMTs. Recently, a new approach using
TPB-coated light guides was proposed. In this paper, we report on light guides
with improved attenuation lengths above 100 cm when measured in air. This is an
important step in the development of meter-scale light guides for future
LArTPCs. Improvements come from using a new acrylic-based coating,
diamond-polished cast UV transmitting acrylic bars, and a hand-dipping
technique to coat the bars. We discuss a model for connecting bar response in
air to response in liquid argon and compare this to data taken in liquid argon.
The good agreement between the prediction of the model and the measured
response in liquid argon demonstrates that characterization in air is
sufficient for quality control of bar production. This model can be used in
simulations of light guides for future experiments.Comment: 25 pages, 20 figure
Planar Superconductor-Normal-Superconductor Josephson Junctions in MgB2
Since the discovery of superconductivity in MgB2 considerable progress has
been made in determining the physical properties of the material, which are
promising for bulk conductors. Tunneling studies show that the material is
reasonably isotropic and has a well-developed s-wave energy gap (∆),
implying that electronic devices based on MgB2 could operate close to 30K.
Although a number of groups have reported the formation of thin films by
post-reaction of precursors, heterostructure growth is likely to require
considerable technological development, making single-layer device structures
of most immediate interest. MgB2 is unlike the cuprate superconductors in that
grain boundaries do not form good Josephson junctions, and although a SQUID
based on MgB2 nanobridges has been fabricated, the nanobridges themselves do
not show junction-like properties. Here we report the successful creation of
planar MgB2 junctions by localised ion damage in thin films. The critical
current (IC) of these devices is strongly modulated by applied microwave
radiation and magnetic field. The product of the critical current and normal
state resistance (ICRN) is remarkably high, implying a potential for very high
frequency applications.Comment: 7 pages including 4 figure
Jamming transition in a highly dense granular system under vertical vibration
The dynamics of the jamming transition in a three-dimensional granular system
under vertical vibration is studied using diffusing-wave spectroscopy. When the
maximum acceleration of the external vibration is large, the granular system
behaves like a fluid, with the dynamic correlation function G(t) relaxing
rapidly. As the acceleration of vibration approaches the gravitational
acceleration g, the relaxation of G(t) slows down dramatically, and eventually
stops. Thus the system undergoes a phase transition and behaves like a solid.
Near the transition point, we find that the structural relaxation shows a
stretched exponential behavior. This behavior is analogous to the behavior of
supercooled liquids close to the glass transition.Comment: 5 pages, 5 figures, accepted by Phys. Rev.
Influence of compressing pressure on macro void formation of carbon monolith for methane adsorption
Carbon monoliths for adsorbed natural gas (ANG) storage were prepared from Mongolian anthracite-based activated carbons using carboxy-methyl cellulose as a binder under different compressing pressures. Nitrogen adsorption/desorption experiments were carried out to obtain the specific surface area, pore volume, and pore size distribution of the monoliths. Methane adsorption experiments on the carbon monoliths were conducted at different temperatures and pressures up to around 3.5 MPa in a high pressure volumetric adsorption apparatus. As expected, adsorption results indicated that the methane adsorption capacity of the carbon monoliths increased with increasing specific surface area and packing density. The maximum volumetric adsorption of methane was observed as 163 V/V at 293 K and 3.5 MPa on a carbon monolith sample, PMAC1/2-3-65, that does not have the highest specific surface area but relatively high packing density comparing with other monoliths, which implies that two physical properties contribute contradictorily to the methane adsorption capacity. Based on experimental results, the carbon monoliths prepared from Mongolian anthracite-based activated carbons can be promising media for ANG storage application
Retraction notice: Influence of compressing pressure on macro void formation carbon monolith for methane adsorption
RETRACTION NOTICEOn 21rd February 2019, the Editorial Board of the Mongolian Journal of Chemistry decided to retract this article entitled "Influence of compressing pressure on macro void formation of carbon monolith for methane adsorption" because of an authorship dispute. The article was originally published in Vol.18 No.44 2017 pp.24-35. doi: https://doi.org/10.5564/mjc.v18i44.93
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Flame Retardant Intumescent Polyamide 11 Nanocomposites – Further Study
The objective of this research is to develop improved polyamide 11 and 12 polymers with
enhanced flame retardancy, thermal, and mechanical properties for selective laser sintering
(SLS) rapid manufacturing (RM). In the present study, a nanophase was introduced into the
polyamide 11 and combine with a conventional intumescent flame retardant (FR) additive via
twin screw extrusion. Arkema Rilsan® polyamide 11 molding polymer pellets were used with
two types of nanoparticles such as: chemically modified montmorillonite (MMT) organoclays
and carbon nanofibers (CNFs). Two types of Clariant’s Exolit® OP 1311 and 1312 intumescent
FR additives were used to generate a family of FR intumescent polyamide 11 nanocomposites
with anticipated synergism.Mechanical Engineerin
Chaotic Interaction of Langmuir Solitons and Long Wavelength Radiation
In this work we analyze the interaction of isolated solitary structures and
ion-acoustic radiation. If the radiation amplitude is small solitary structures
persists, but when the amplitude grows energy transfer towards small spatial
scales occurs. We show that transfer is particularly fast when a fixed point of
a low dimensional model is destroyed.Comment: LaTex + 4 eps file
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