1,175 research outputs found
Corrigendum: Displacement/length scaling relationships for normal faults; a review, critique, and revised compilation
The multiple quantum NMR dynamics in systems of equivalent spins with the dipolar ordered initial state
The multiple quantum (MQ) NMR dynamics in the system of equivalent spins with
the dipolar ordered initial state is considered. The high symmetry of the MQ
Hamiltonian is used in order to develop the analytical and numerical methods
for an investigation of the MQ NMR dynamics in the systems consisting of
hundreds of spins from "the first principles". We obtain the dependence of the
intensities of the MQ NMR coherences on their orders (profiles of the MQ NMR
coherences) for the systems of spins. It is shown that these
profiles may be well approximated by the exponential distribution functions. We
also compare the MQ NMR dynamics in the systems of equivalent spins having two
different initial states, namely the dipolar ordered state and the thermal
equilibrium state in the strong external magnetic field.Comment: 11 pages 4 figure
Algorithm engineering for optimal alignment of protein structure distance matrices
Protein structural alignment is an important problem in computational
biology. In this paper, we present first successes on provably optimal pairwise
alignment of protein inter-residue distance matrices, using the popular Dali
scoring function. We introduce the structural alignment problem formally, which
enables us to express a variety of scoring functions used in previous work as
special cases in a unified framework. Further, we propose the first
mathematical model for computing optimal structural alignments based on dense
inter-residue distance matrices. We therefore reformulate the problem as a
special graph problem and give a tight integer linear programming model. We
then present algorithm engineering techniques to handle the huge integer linear
programs of real-life distance matrix alignment problems. Applying these
techniques, we can compute provably optimal Dali alignments for the very first
time
Environmental controls on observed spatial variability of soil pore water geochemistry in small headwater catchments underlain with permafrost
Soil pore water (SPW) chemistry can vary substantially across
multiple scales in Arctic permafrost landscapes. The magnitude of these
variations and their relationship to scale are critical considerations for
understanding current controls on geochemical cycling and for predicting
future changes. These aspects are especially important for Arctic change
modeling where accurate representation of sub-grid variability may be
necessary to predict watershed-scale behaviors. Our research goal is to
characterize intra- and inter-watershed soil water geochemical variations at
two contrasting locations in the Seward Peninsula of Alaska, USA. We then
attempt to identify the key factors controlling concentrations of important
pore water solutes in these systems. The SPW geochemistry of 18 locations
spanning two small Arctic catchments was examined for spatial variability
and its dominant environmental controls. The primary environmental controls
considered were vegetation, soil moisture and/or redox condition, water–soil
interactions and hydrologic transport, and mineral solubility. The sampling
locations varied in terms of vegetation type and canopy height, presence or
absence of near-surface permafrost, soil moisture, and hillslope position.
Vegetation was found to have a significant impact on SPW NO3-
concentrations, associated with the localized presence of nitrogen-fixing
alders and mineralization and nitrification of leaf litter from tall willow
shrubs. The elevated NO3- concentrations were, however, frequently
equipoised by increased microbial denitrification in regions with sufficient
moisture to support it. Vegetation also had an observable impact on soil-moisture-sensitive constituents, but the effect was less significant. The
redox conditions in both catchments were generally limited by Fe reduction,
seemingly well-buffered by a cache of amorphous Fe hydroxides, with the most
reducing conditions found at sampling locations with the highest soil
moisture content. Non-redox-sensitive cations were affected by a wide
variety of water–soil interactions that affect mineral solubility and
transport. Identification of the dominant controls on current SPW
hydrogeochemistry allows for qualitative prediction of future geochemical
trends in small Arctic catchments that are likely to experience warming and
permafrost thaw. As source areas for geochemical fluxes to the broader
Arctic hydrologic system, geochemical processes occurring in these
environments are particularly important to understand and predict with
regards to such environmental changes.</p
Elastic turbulence in curvilinear flows of polymer solutions
Following our first report (A. Groisman and V. Steinberg, \sl Nature , 53 (2000)) we present an extended account of experimental observations of
elasticity induced turbulence in three different systems: a swirling flow
between two plates, a Couette-Taylor (CT) flow between two cylinders, and a
flow in a curvilinear channel (Dean flow). All three set-ups had high ratio of
width of the region available for flow to radius of curvature of the
streamlines. The experiments were carried out with dilute solutions of high
molecular weight polyacrylamide in concentrated sugar syrups. High polymer
relaxation time and solution viscosity ensured prevalence of non-linear elastic
effects over inertial non-linearity, and development of purely elastic
instabilities at low Reynolds number (Re) in all three flows. Above the elastic
instability threshold, flows in all three systems exhibit features of developed
turbulence. Those include: (i)randomly fluctuating fluid motion excited in a
broad range of spatial and temporal scales; (ii) significant increase in the
rates of momentum and mass transfer (compared to those expected for a steady
flow with a smooth velocity profile). Phenomenology, driving mechanisms, and
parameter dependence of the elastic turbulence are compared with those of the
conventional high Re hydrodynamic turbulence in Newtonian fluids.Comment: 23 pages, 26 figure
Perfect-fluid cylinders and walls - sources for the Levi-Civita space-time
The diagonal metric tensor whose components are functions of one spatial
coordinate is considered. Einstein's field equations for a perfect-fluid source
are reduced to quadratures once a generating function, equal to the product of
two of the metric components, is chosen. The solutions are either static fluid
cylinders or walls depending on whether or not one of the spatial coordinates
is periodic. Cylinder and wall sources are generated and matched to the vacuum
(Levi--Civita) space--time. A match to a cylinder source is achieved for
-\frac{1}{2}<\si<\frac{1}{2}, where \si is the mass per unit length in the
Newtonian limit \si\to 0, and a match to a wall source is possible for
|\si|>\frac{1}{2}, this case being without a Newtonian limit; the positive
(negative) values of \si correspond to a positive (negative) fluid density.
The range of \si for which a source has previously been matched to the
Levi--Civita metric is 0\leq\si<\frac{1}{2} for a cylinder source.Comment: 22 pages, LaTeX, one included figure. Revised version: three
(non-perfect-fluid) interior solutions are added, one of which falsifies the
original conjecture in Sec. 4, and the circular geodesics of the Levi-Civita
space-time are discussed in a footnot
Polymorphisms in the WNK1 gene are asociated with blood pressure variation and urinary potassium excretion
WNK1 - a serine/threonine kinase involved in electrolyte homeostasis and blood pressure (BP) control - is an excellent candidate gene for essential hypertension (EH). We and others have previously reported association between WNK1 and BP variation. Using tag SNPs (tSNPs) that capture 100% of common WNK1 variation in HapMap, we aimed to replicate our findings with BP and to test for association with phenotypes relating to WNK1 function in the British Genetics of Hypertension (BRIGHT) study case-control resource (1700 hypertensive cases and 1700 normotensive controls). We found multiple variants to be associated with systolic blood pressure, SBP (7/28 tSNPs min-p = 0.0005), diastolic blood pressure, DBP (7/28 tSNPs min-p = 0.002) and 24 hour urinary potassium excretion (10/28 tSNPs min-p = 0.0004). Associations with SBP and urine potassium remained significant after correction for multiple testing (p = 0.02 and p = 0.01 respectively). The major allele (A) of rs765250, located in intron 1, demonstrated the strongest evidence for association with SBP, effect size 3.14 mmHg (95%CI:1.23–4.9), DBP 1.9 mmHg (95%CI:0.7–3.2) and hypertension, odds ratio (OR: 1.3 [95%CI: 1.0–1.7]).We genotyped this variant in six independent populations (n = 14,451) and replicated the association between rs765250 and SBP in a meta-analysis (p = 7×10−3, combined with BRIGHT data-set p = 2×10−4, n = 17,851). The associations of WNK1 with DBP and EH were not confirmed. Haplotype analysis revealed striking associations with hypertension and BP variation (global permutation p10 mmHg reduction) and risk for hypertension (OR<0.60). Our data indicates that multiple rare and common WNK1 variants contribute to BP variation and hypertension, and provide compelling evidence to initiate further genetic and functional studies to explore the role of WNK1 in BP regulation and EH
The ArgoNeuT Detector in the NuMI Low-Energy beam line at Fermilab
The ArgoNeuT liquid argon time projection chamber has collected thousands of
neutrino and antineutrino events during an extended run period in the NuMI
beam-line at Fermilab. This paper focuses on the main aspects of the detector
layout and related technical features, including the cryogenic equipment, time
projection chamber, read-out electronics, and off-line data treatment. The
detector commissioning phase, physics run, and first neutrino event displays
are also reported. The characterization of the main working parameters of the
detector during data-taking, the ionization electron drift velocity and
lifetime in liquid argon, as obtained from through-going muon data complete the
present report.Comment: 43 pages, 27 figures, 5 tables - update referenc
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