23,502 research outputs found
Cenozoic extension and magmatism in Arizona
The Basin and Range Province of Arizona was the site of two episodes of Cenozoic extension that can be distinguished on the basis of timing, direction and style of extension, and associated magmatism. The first episode of extension occurred during Oligocene to mid-Miocene time and resulted in the formation of low-angle detachment faults, ductile shear zones (metamorphic core complexes), and regional domains of tilted fault blocks. Evidence for extreme middle Tertiary crustal extension in a NE to SW to SW to ENE to WSW direction has been recognized in various parts of the Basin and Range of Arizona, especially in the Lake Mead area and along the belf of metamorphic core complexes that crosses southern Arizona from Parker to Tucson. New geologic mapping and scrutiny of published geologic maps indicates that significant middle Tertiary extension is more widely distributed than previously thought. The state can be subdivided into regional tilt-block domains in which middle Tertiary rocks dip consistently in one direction. The dip direction in any tilt-block domain is generally toward the breakaway of a low-angle detachment fault that underlies the tilt-block domain; we interpret this an indicating that normal faults in the upper plate of a detechment fault are generally synthetic, rather than antithetic, with respect to the detachment fault
The sign problem in full configuration interaction quantum Monte Carlo: Linear and sub-linear representation regimes for the exact wave function
We investigate the sign problem for full configuration interaction quantum
Monte Carlo (FCIQMC), a stochastic algorithm for finding the ground state
solution of the Schr\"odinger equation with substantially reduced computational
cost compared with exact diagonalisation. We find -space Hubbard models for
which the solution is yielded with storage that grows sub-linearly in the size
of the many-body Hilbert space, in spite of using a wave function that is
simply linear combination of states. The FCIQMC algorithm is able to find this
sub-linear scaling regime without bias and with only a choice of Hamiltonian
basis. By means of a demonstration we solve for the energy of a 70-site
half-filled system (with a space of determinants) in 250 core hours,
substantially quicker than the 10 core hours that would be
required by exact diagonalisation. This is the largest space that has been
sampled in an unbiased fashion. The challenge for the recently-developed FCIQMC
method is made clear: expand the sub-linear scaling regime whilst retaining
exact on average accuracy. This result rationalizes the success of the
initiator adaptation (i-FCIQMC) and offers clues to improve it. We argue that
our results changes the landscape for development of FCIQMC and related
methods.Comment: 6 pages, 4 figures. The mentioned supplementary material is included
as "Ancillary files". Comments welcom
Increased Adenine Nucleotide Degradation in Skeletal Muscle Atrophy
Adenine nucleotides (AdNs: ATP, ADP, AMP) are essential biological compounds that facilitate many necessary cellular processes by providing chemical energy, mediating intracellular signaling, and regulating protein metabolism and solubilization. A dramatic reduction in total AdNs is observed in atrophic skeletal muscle across numerous disease states and conditions, such as cancer, diabetes, chronic kidney disease, heart failure, COPD, sepsis, muscular dystrophy, denervation, disuse, and sarcopenia. The reduced AdNs in atrophic skeletal muscle are accompanied by increased expression/activities of AdN degrading enzymes and the accumulation of degradation products (IMP, hypoxanthine, xanthine, uric acid), suggesting that the lower AdN content is largely the result of increased nucleotide degradation. Furthermore, this characteristic decrease of AdNs suggests that increased nucleotide degradation contributes to the general pathophysiology of skeletal muscle atrophy. In view of the numerous energetic, and non-energetic, roles of AdNs in skeletal muscle, investigations into the physiological consequences of AdN degradation may provide valuable insight into the mechanisms of muscle atrophy
Evaluation of the ADVIA (R) Centaur (TM) TSH-3 assay
An analytical evaluation of the thyroid stimulating hormone (TSH-3) assay on the Sayer ADVIA(R) Centaur(TM) immunoassay system was performed. General analytical requirements (linearity, resistance to typical interferences, absence of a carry-over effect) were fulfilled and reproducibility was satisfactory. Inter-assay coefficient of variation (CV) of a human serum pool with a concentration of 0.014 mU/l was 22.3%; at concentrations between 0.26 and 83 mU/l CV was below 6%. Method comparison study demonstrated close agreement of TSH results compared to those obtained with the Roche Elecsys(R) 2010 TSH assay (ADVIA Centaur = 1.08 x Elecsys - 0.18 mU/l; r = 0.987; n = 324). Handling and practicability of the ADVIA Centaur system proved to be convenient with a very high sample throughput. We conclude that the ADVIA Centaur TSH-3 assay meets requirements for clinical use
Minimising biases in Full Configuration Interaction Quantum Monte Carlo
We show that Full Configuration Interaction Quantum Monte Carlo (FCIQMC) is a
Markov Chain in its present form. We construct the Markov matrix of FCIQMC for
a two determinant system and hence compute the stationary distribution. These
solutions are used to quantify the dependence of the population dynamics on the
parameters defining the Markov chain. Despite the simplicity of a system with
only two determinants, it still reveals a population control bias inherent to
the FCIQMC algorithm. We investigate the effect of simulation parameters on the
population control bias for the neon atom and suggest simulation setups to in
general minimise the bias. We show a reweighting scheme to remove the bias
caused by population control commonly used in Diffusion Monte Carlo [J. Chem.
Phys. 99, 2865 (1993)] is effective and recommend its use as a post processing
step.Comment: Supplementary material available as 'Ancillary Files
Radicals in carbonaceous residue deposited on mordenite from methanol
It is shown that control of the degree of coking can lead to the observation of hyperfine structures in the carbonaceous residues deposited from methanol over mordenite (H-MOR) at temperatures relevant to the conversion of methanol to hydrocarbons. EPR measurements of the catalyst samples at various times on stream have been recorded, with a rich hyperfine splitting pattern observed in the early stages of the reaction. Interpretation of the EPR data with the aid of density functional theoretical calculations has afforded the first definitive assignment of the radical cations formed in high temperature coke. The results detail a shortlist of six species: 2,3/2,6/2,7-dimethylnaphthalenium, 2,3,6-trimethylnaphthalenium, 2,3,6,7-tetramethylnaphthalenium, and anthracenium radical cations whose proton hyperfine splitting profiles match the experimental spectra; 2,3,6,7-tetramethylnaphthalenium showed the best agreement. The observation of these particular isomers of polymethylnaphthalene suggest the formation of more highly branched polyaromatic species is less likely within the confines of the H-MOR 12-membered ring channel. These radicals formed when the catalyst is active may constitute key intermediates in the conversion of methanol to light olefins
A Matrix Hyperbolic Cosine Algorithm and Applications
In this paper, we generalize Spencer's hyperbolic cosine algorithm to the
matrix-valued setting. We apply the proposed algorithm to several problems by
analyzing its computational efficiency under two special cases of matrices; one
in which the matrices have a group structure and an other in which they have
rank-one. As an application of the former case, we present a deterministic
algorithm that, given the multiplication table of a finite group of size ,
it constructs an expanding Cayley graph of logarithmic degree in near-optimal
O(n^2 log^3 n) time. For the latter case, we present a fast deterministic
algorithm for spectral sparsification of positive semi-definite matrices, which
implies an improved deterministic algorithm for spectral graph sparsification
of dense graphs. In addition, we give an elementary connection between spectral
sparsification of positive semi-definite matrices and element-wise matrix
sparsification. As a consequence, we obtain improved element-wise
sparsification algorithms for diagonally dominant-like matrices.Comment: 16 pages, simplified proof and corrected acknowledging of prior work
in (current) Section
Compact steep-spectrum sources from the S4 sample
We present the results of 5-GHz observations with the VLA A-array of a sample
of candidate Compact Steep Spectrum sources (CSSs) selected from the S4 survey.
We also estimate the symmetry parameters of high-luminosity CSSs selected from
different samples of radio sources, and compare these with the larger sources
of similar luminosity to understand their evolution and the consistency of the
CSSs with the unified scheme for radio galaxies and quasars. The majority of
CSSs are likely to be young sources advancing outwards through a dense
asymmetric environment. The radio properties of CSSs are found to be consistent
with the unified scheme, in which the axes of the quasars are observed close to
the line of sight, while radio galaxies are observed close to the plane of the
sky.Comment: accepted for publication in mnras; 8 pages, figure 1 with 21 images,
and two additional figures; 2 table
- …