1,050 research outputs found
Evidence for Kosterlitz-Thouless type orientational ordering of CFBr monolayers physisorbed on graphite
Monolayers of the halomethane CFBr adsorbed on graphite have been
investigated by x-ray diffraction. The layers crystallize in a commensurate
triangular lattice. On cooling they approach a three-sublattice
antiferroelectric pattern of the in-plane components of the dipole moments. The
ordering is not consistent with a conventional phase transition, but points to
Kosterlitz-Thouless behavior. It is argued that the transition is described by
a 6-state clock model on a triangular lattice with antiferromagnetic nearest
neighbor interactions which is studied with Monte-Carlo simulations. A
finite-size scaling analysis shows that the ordering transition is indeed in
the KT universality class.Comment: 4 pages, 5 figure
BlinkML: Efficient Maximum Likelihood Estimation with Probabilistic Guarantees
The rising volume of datasets has made training machine learning (ML) models
a major computational cost in the enterprise. Given the iterative nature of
model and parameter tuning, many analysts use a small sample of their entire
data during their initial stage of analysis to make quick decisions (e.g., what
features or hyperparameters to use) and use the entire dataset only in later
stages (i.e., when they have converged to a specific model). This sampling,
however, is performed in an ad-hoc fashion. Most practitioners cannot precisely
capture the effect of sampling on the quality of their model, and eventually on
their decision-making process during the tuning phase. Moreover, without
systematic support for sampling operators, many optimizations and reuse
opportunities are lost.
In this paper, we introduce BlinkML, a system for fast, quality-guaranteed ML
training. BlinkML allows users to make error-computation tradeoffs: instead of
training a model on their full data (i.e., full model), BlinkML can quickly
train an approximate model with quality guarantees using a sample. The quality
guarantees ensure that, with high probability, the approximate model makes the
same predictions as the full model. BlinkML currently supports any ML model
that relies on maximum likelihood estimation (MLE), which includes Generalized
Linear Models (e.g., linear regression, logistic regression, max entropy
classifier, Poisson regression) as well as PPCA (Probabilistic Principal
Component Analysis). Our experiments show that BlinkML can speed up the
training of large-scale ML tasks by 6.26x-629x while guaranteeing the same
predictions, with 95% probability, as the full model.Comment: 22 pages, SIGMOD 201
Grasses and Legumes for Cellulosic Bioenergy
Human life has depended on renewable sources of bioenergy for many thousands of years, since the time humans fi rst learned to control fi re and utilize wood as the earliest source of bioenergy. The exploitation of forage crops constituted the next major technological breakthrough in renewable bioenergy, when our ancestors began to domesticate livestock about 6000 years ago. Horses, cattle, oxen, water buffalo, and camels have long been used as sources of mechanical and chemical energy. They perform tillage for crop production, provide leverage to collect and transport construction materials, supply transportation for trade and migratory routes, and create manure that is used to cook meals and heat homes. Forage cropsâmany of which form the basis of Grass: The 1948 Yearbook of Agriculture (Stefferud, 1948), as well as the other chapters of this volumeâhave composed the principal or only diet of these draft animals since the dawn of agriculture
Two-dimensional array of microtraps with atomic shift register on a chip
Arrays of trapped atoms are the ideal starting point for developing registers
comprising large numbers of physical qubits for storing and processing quantum
information. One very promising approach involves neutral atom traps produced
on microfabricated devices known as atom chips, as almost arbitrary trap
configurations can be realised in a robust and compact package. Until now,
however, atom chip experiments have focused on small systems incorporating
single or only a few individual traps. Here we report experiments on a
two-dimensional array of trapped ultracold atom clouds prepared using a simple
magnetic-film atom chip. We are able to load atoms into hundreds of tightly
confining and optically resolved array sites. We then cool the individual atom
clouds in parallel to the critical temperature required for quantum degeneracy.
Atoms are shuttled across the chip surface utilising the atom chip as an atomic
shift register and local manipulation of atoms is implemented using a focused
laser to rapidly empty individual traps.Comment: 6 pages, 4 figure
Strain analysis of a seismically imaged massâtransport complex, offshore Uruguay
Strain style, magnitude and distribution within massâtransport complexes (MTCs) are important for understanding the process evolution of submarine mass flows and for estimating their runout distances. Structural restoration and quantification of strain in gravitationally driven passive margins have been shown to approximately balance between updip extensional and downdip contractional domains; such an exercise has not yet been attempted for MTCs. We here interpret and structurally restore a shallowly buried (c. 1,500 mbsf) and wellâimaged MTC, offshore Uruguay using a highâresolution (12.5 m vertical and 15 Ă 12.5 m horizontal resolution) threeâdimensional seismicâreflection survey. This allows us to characterise and quantify vertical and lateral strain distribution within the deposit. Detailed seismic mapping and attribute analysis shows that the MTC is characterised by a complicated array of kinematic indicators, which vary spatially in style and concentration. Seismicâattribute extractions reveal several previously undocumented fabrics preserved in the MTC, including internal shearing in the form of subâorthogonal shear zones, and foldâthrust systems within the basal shear zone beneath raftedâblocks. These features suggest multiple transport directions and phases of flow during emplacement. The MTC is characterised by a broadly tripartite strain distribution, with extensional (e.g. normal faults), translational and contractional (e.g. folds and thrusts) domains, along with a radial frontally emergent zone. We also show how strain is preferentially concentrated around intraâMTC raftedâblocks due to their kinematic interactions with the underlying basal shear zone. Overall, and even when volume loss within the frontally emergent zone is included, a strain deficit between the extensional and contractional domains (c. 3%â14%) is calculated. We attribute this to a combination of distributed, subâseismic, âcrypticâ strain, likely related to deâwatering, grainâscale deformation and related changes in bulk sediment volume. This work has implications for assessing MTCs strain distribution and provides a practical approach for evaluating structural interpretations within such deposits
Theory of Hysteresis Loop in Ferromagnets
We consider three mechanisms of hysteresis phenomena in alternating magnetic
field: the domain wall motion in a random medium, the nucleation and the
retardation of magnetization due to slow (critical) fluctuations. We construct
quantitative theory for all these processes. The hysteresis is characterized by
two dynamic threshold fields, by coercive field and by the so-called reversal
field. Their ratios to the static threshold field is shown to be function of
two dimensionless variables constituted from the frequency and amplitude of the
ac field as well as from some characteristics of the magnet. The area and the
shape of the hysteresis loop are found. We consider different limiting cases in
which power dependencies are valid. Numerical simulations show the domain wall
formation and propagation and confirm the main theoretical predictions. Theory
is compared with available experimental data.Comment: RevTex, 13 pages, 8 figures (PostScript), acknowledgements adde
Dynamic pressure enhancements as a cause of largeâscale stormtime substorms
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94960/1/jgra19239.pd
Quantum kinetic Ising models
We introduce a quantum generalization of classical kinetic Ising models,
described by a certain class of quantum many body master equations. Similarly
to kinetic Ising models with detailed balance that are equivalent to certain
Hamiltonian systems, our models reduce to a set of Hamiltonian systems
determining the dynamics of the elements of the many body density matrix. The
ground states of these Hamiltonians are well described by matrix product, or
pair entangled projected states. We discuss critical properties of such
Hamiltonians, as well as entanglement properties of their low energy states.Comment: 20 pages, 4 figures, minor improvements, accepted in New Journal of
Physic
Harvest and storage of two perennial grasses as biomass feedstocks
ABSTRACT. Some perennial grasses, such as reed canarygrass (RCG) n North America, the main feedstock for fuel ethanol is currently corn grain. New enzyme hydrolysis and fermentation technologies are being developed to produce ethanol from cellulosic biomass such as grasses, straw, and wood. The energy balance for these materials has the potential to be much more favorable than with corn grain One production variable that needs to be considered with perennial grasses to be used as biomass feedstocks is cutting frequency. Since high forage quality for livestock production is not required, it may be more economical to harvest perennial grasses once per year
Global statistics of liquid water content and effective number concentration of water clouds over ocean derived from combined CALIPSO and MODIS measurements
This study presents an empirical relation that links the volume extinction coefficients of water clouds, the layer integrated depolarization ratios measured by lidar, and the effective radii of water clouds derived from collocated passive sensor observations. Based on Monte Carlo simulations of CALIPSO lidar observations, this method combines the cloud effective radius reported by MODIS with the lidar depolarization ratios measured by CALIPSO to estimate both the liquid water content and the effective number concentration of water clouds. The method is applied to collocated CALIPSO and MODIS measurements obtained during July and October of 2006, and January 2007. Global statistics of the cloud liquid water content and effective number concentration are presented
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