2,688 research outputs found
A Study of Meteoroid Impact Phenomena
Process of crater formation resulting from impact of hypervelocity projectile - meteoroid impac
Quantifying new water fractions and transit time distributions using ensemble hydrograph separation: theory and benchmark tests
Decades of hydrograph separation studies have estimated the proportions of
recent precipitation in streamflow using end-member mixing of chemical or
isotopic tracers. Here I propose an ensemble approach to hydrograph
separation that uses regressions between tracer fluctuations in precipitation
and discharge to estimate the average fraction of new water (e.g., same-day
or same-week precipitation) in streamflow across an ensemble of time steps.
The points comprising this ensemble can be selected to isolate conditions of
particular interest, making it possible to study how the new water fraction
varies as a function of catchment and storm characteristics. Even when new
water fractions are highly variable over time, one can show mathematically
(and confirm with benchmark tests) that ensemble hydrograph separation will
accurately estimate their average. Because ensemble hydrograph separation is
based on correlations between tracer fluctuations rather than on tracer mass
balances, it does not require that the end-member signatures are constant
over time, or that all the end-members are sampled or even known, and it is
relatively unaffected by evaporative isotopic fractionation.Ensemble hydrograph separation can also be extended to a multiple regression
that estimates the average (or marginal) transit time distribution (TTD)
directly from observational data. This approach can estimate both
backward transit time distributions (the fraction of streamflow that originated as
rainfall at different lag times) and forward transit time distributions
(the fraction of rainfall that will become future streamflow at different
lag times), with and without volume-weighting, up to a user-determined
maximum time lag. The approach makes no assumption about the shapes of the
transit time distributions, nor does it assume that they are time-invariant,
and it does not require continuous time series of tracer measurements.
Benchmark tests with a nonlinear, nonstationary catchment model confirm that
ensemble hydrograph separation reliably quantifies both new water fractions
and transit time distributions across widely varying catchment behaviors,
using either daily or weekly tracer concentrations as input. Numerical
experiments with the benchmark model also illustrate how ensemble hydrograph
separation can be used to quantify the effects of rainfall intensity, flow
regime, and antecedent wetness on new water fractions and transit time
distributions.</p
Novel structural features of the ripple phase of phospholipids
We have calculated the electron density maps of the ripple phase of
dimyristoylphosphatidylcholine (DMPC) and palmitoyl-oleoyl phosphatidylcholine
(POPC) multibilayers at different temperatures and fixed relative humidity. Our
analysis establishes, for the first time, the existence of an average tilt of
the hydrocarbon chains of the lipid molecules along the direction of the ripple
wave vector, which we believe is responsible for the occurrence of asymmetric
ripples in these systems
Data compression for the Cassini radio and plasma wave instrument
The Cassini Radio and Plasma Wave Science experiment will employ data compression to make effective use of the available data telemetry bandwidth. Some compression will be achieved by use of a lossless data compression chip and some by software in a dedicated 80C85 processor. A description of the instrument and data compression system are included in this report. Also, the selection of data compression systems and acceptability of data degradation is addressed
edgeRun: an R package for sensitive, functionally relevant differential expression discovery using an unconditional exact test.
UNLABELLED: Next-generation sequencing platforms for measuring digital expression such as RNA-Seq are displacing traditional microarray-based methods in biological experiments. The detection of differentially expressed genes between groups of biological conditions has led to the development of numerous bioinformatics tools, but so far, few exploit the expanded dynamic range afforded by the new technologies. We present edgeRun, an R package that implements an unconditional exact test that is a more powerful version of the exact test in edgeR. This increase in power is especially pronounced for experiments with as few as two replicates per condition, for genes with low total expression and with large biological coefficient of variation. In comparison with a panel of other tools, edgeRun consistently captures functionally similar differentially expressed genes. AVAILABILITY AND IMPLEMENTATION: The package is freely available under the MIT license from CRAN (http://cran.r-project.org/web/packages/edgeRun). CONTACT: [email protected] SUPPLEMENTARY INFORMATION: Supplementary data are available at Bioinformatics online
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Branching geometry of valley networks on mars and earth and its implications for early martian climate
Mars’ surface bears the imprint of valley networks formed billions of years ago. Whether these networks were formed by groundwater sapping, ice melt, or fluvial runoff has been debated for decades. These different scenarios have profoundly different implications for Mars’ climatic history and thus for its habitability in the distant past. Recent studies on Earth revealed that valley networks in arid landscapes with more surface runoff branch at narrower angles, while in humid environments with more groundwater flow, branching angles are much wider. We find that valley networks on Mars generally tend to branch at narrow angles similar to those found in arid landscapes on Earth. This result supports the inference that Mars once had an active hydrologic cycle and that Mars’ valley networks were formed primarily by overland flow erosion, with groundwater seepage playing only a minor role
Variation after Particle-Number Projection for the HFB Method with the Skyrme Energy Density Functional
Variation after particle-number restoration is incorporated for the first
time into the Hartree-Fock-Bogoliubov framework employing the Skyrme energy
density functional with zero-range pairing. The resulting projected HFB
equations can be expressed in terms of the local gauge-angle-dependent
densities. Results of projected calculations are compared with those obtained
within the Lipkin-Nogami method in the standard version and with the
Lipkin-Nogami method followed by exact particle-number projection.Comment: 11 pages, 6 figure
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