6,157 research outputs found
The use of snowcovered area in runoff forecasts
Long-term snowcovered area data from aircraft and satellite observations have proven useful in reducing seasonal runoff forecast error on the Kern river watershed. Similar use of snowcovered area on the Kings river watershed produced results that were about equivalent to methods based solely on conventional data. Snowcovered area will be most effective in reducing forecast procedural error on watersheds with: (1) a substantial amount of area within a limited elevation range; (2) an erratic precipitation and/or snowpack accumulation pattern not strongly related to elevation; and (3) poor coverage by precipitation stations or snow courses restricting adequate indexing of water supply conditions. When satellite data acquisition and delivery problems are resolved, the derived snowcover information should provide a means for enhancing operational streamflow forecasts for areas that depend primarily on snowmelt for their water supply
A 475 years-old founder effect involving IL12RB1: a highly prevalent mutation conferring Mendelian susceptibility to mycobacterial diseases in European descendants
Mutations in IFNGR1, IFNGR2, IL12RB1, IL12B, STAT1 and NEMO result in a common clinical phenotype known as Mendelian Susceptibility to Mycobacterial Diseases (MSMD). Interleukin-12 receptor 01 (IL12R beta 1) deficiency is the most common genetic etiology for MSMD. Known mutations affecting IL12RB1 are recessively inherited and are associated with null response to both IL-12 and IL-23. Mutation IL12RB1 1623_1624delinsTT was originally described in 5 families from European origin (2 from Germany: I from Cyprus, France and Belgium). Interestingly, this same mutation was found in an unexpectedly high prevalence among IL-12R beta 1 deficient patients in Argentina: 5-out-of-6 individuals born to unrelated families carried this particular change. To determine whether mutation 1623_1624delinsTT represents a DNA mutational hotspot or a founder effect, 34 polymorphic markers internal or proximal to IL12RB1 were studied in the Argentinean and the Belgian patients. A common haplotype spanning 1.45-3.51 Mb was shared by all chromosomes carrying mutation 1623_1624delinsTT, and was not detected on 100 control chromosomes. Applying a modified likelihood-based method the age of the most recent common ancestor carrying mutation 1623_1624delinsTT was estimated in 475 years (95% CI, 175-1275), which is the time when the Spaniards initiated the colonization of the Americas. Mutation 1623_1624delinsTT represents the first founder effect described on IL-12R beta 1, the most frequently affected gene in MSMD, and affecting patients with European ancestors. The reason(s) behind the persistency of this mutation across multiple generations, its relative high prevalence, and any potential selective advantage are yet to be established
Transition from Poisson to gaussian unitary statistics: The two-point correlation function
We consider the Rosenzweig-Porter model of random matrix which interpolates
between Poisson and gaussian unitary statistics and compute exactly the
two-point correlation function. Asymptotic formulas for this function are given
near the Poisson and gaussian limit.Comment: 19 pages, no figure
Charge Screening, Large-N, and the Abelian Projection Model of Confinement
We point out that the abelian projection theory of quark confinement is in
conflict with certain large-N predictions. According to both large-N and
lattice strong-coupling arguments, the perimeter law behavior of adjoint Wilson
loops at large scales is due to charge-screening, and is suppressed relative to
the area term by a factor of . In the abelian projection theory,
however, the perimeter law is due to the fact that out of adjoint
quark degrees of freedom are (abelian) neutral and unconfined; the suppression
factor relative to the area law is thus only . We study numerically the
behavior of Wilson loops and Polyakov lines with insertions of (abelian) charge
projection operators, in maximal abelian gauge. It appears from our data that
the forces between abelian charged, and abelian neutral adjoint quarks are not
significantly different. We also show via the lattice strong-coupling expansion
that, at least at strong couplings, QCD flux tubes attract one another, whereas
vortices in type II superconductors repel.Comment: 20 pages (Latex), 8 figures, IFUP-TH 54/9
Structure and Metal Binding Properties of ZnuA, a Periplasmic Zinc Transporter from \u3cem\u3eEscherichia coli\u3c/em\u3e
ZnuA is the periplasmic Zn2+-binding protein associated with the high-affinity ATP-binding cassette ZnuABC transporter from Escherichia coli. Although several structures of ZnuA and its homologs have been determined, details regarding metal ion stoichiometry, affinity, and specificity as well as the mechanism of metal uptake and transfer remain unclear. The crystal structures of E. coli ZnuA (Eco-ZnuA) in the apo, Zn2+-bound, and Co2+-bound forms have been determined. ZnZnuA binds at least two metal ions. The first, observed previously in other structures, is coordinated tetrahedrally by Glu59, His60, His143, and His207. Replacement of Zn2+ with Co2+ results in almost identical coordination geometry at this site. The second metal binding site involves His224 and several yet to be identified residues from the His-rich loop that is unique to Zn2+ periplasmic metal binding receptors. Electron paramagnetic resonance and X-ray absorption spectroscopic data on CoZnuA provide additional insight into possible residues involved in this second site. The second site is also detected by metal analysis and circular dichroism (CD) titrations. Eco-ZnuA binds Zn2+ (estimated K d \u3c 20 nM), Co2+, Ni2+, Cu2+, Cu+, and Cd2+, but not Mn2+. Finally, conformational changes upon metal binding observed in the crystal structures together with fluorescence and CD data indicate that only Zn2+ substantially stabilizes ZnuA and might facilitate recognition of ZnuB and subsequent metal transfer
Tunable Electron Multibunch Production in Plasma Wakefield Accelerators
Synchronized, independently tunable and focused J-class laser pulses are
used to release multiple electron populations via photo-ionization inside an
electron-beam driven plasma wave. By varying the laser foci in the laboratory
frame and the position of the underdense photocathodes in the co-moving frame,
the delays between the produced bunches and their energies are adjusted. The
resulting multibunches have ultra-high quality and brightness, allowing for
hitherto impossible bunch configurations such as spatially overlapping bunch
populations with strictly separated energies, which opens up a new regime for
light sources such as free-electron-lasers
Biotic homogenization of oceanic islands depends on taxon, spatial scale and the quantification approach
n/
Energy Loss of a High Charge Bunched Electron Beam in Plasma
There has been much interest in the blowout regime of plasma wakefield
acceleration (PWFA), which features ultra-high fields and nonlinear plasma
motion. Using an exact analysis, we examine here a fundamental limit of
nonlinear PWFA excitation, by an infinitesimally short, relativistic electron
beam. The beam energy loss in this case is shown to be linear in charge even
for nonlinear plasma response, where a normalized, unitless charge exceeds
unity. The physical basis for this effect is discussed, as are deviations from
linear behavior observed in simulations with finite length beams.Comment: Submitted to Physical Review Letter
Radiative Losses in Plasma Accelerators
We investigate the dynamics of a relativistic electron in a strongly
nonlinear plasma wave in terms of classical mechanics by taking into account
the action of the radiative reaction force. The two limiting cases are
considered. In the first case where the energy of the accelerated electrons is
low, the electron makes many betatron oscillations during the acceleration. In
the second case where the energy of the accelerated electrons is high, the
betatron oscillation period is longer than the electron residence time in the
accelerating phase. We show that the force of radiative friction can severely
limit the rate of electron acceleration in a plasma accelerator.Comment: 17 pages, 5 figure
Non-universality of compact support probability distributions in random matrix theory
The two-point resolvent is calculated in the large-n limit for the generalized fixed and bounded trace ensembles. It is shown to disagree with that of the canonical Gaussian ensemble by a nonuniversal part that is given explicitly for all monomial potentials V(M)=M2p. Moreover, we prove that for the generalized fixed and bounded trace ensemble all k-point resolvents agree in the large-n limit, despite their nonuniversality
- …