5,189 research outputs found
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Beagle to the Moon: nn experiment package to measure polar ice and volatiles in permanently shadowed areas or beneath the lunar surface
The Beagle Science Package is a flight qualified set of instruments which should be deployed to the lunar surface to answer the questions about water and volatiles present in permanently shadowed regions and/or beneath the surface
Ultra-high energy neutrino scattering
Estimates are made of the ultra-high energy neutrino cross sections based on
an extrapolation to very small Bjorken x of the logarithmic Froissart
dependence in x shown previously to provide an excellent fit to the measured
proton structure function F_2^p(x,Q^2) over a broad range of the virtuality
Q^2. Expressions are obtained for both the neutral current and the charged
current cross sections. Comparison with an extrapolation based on perturbative
QCD shows good agreement for energies where both fit data, but our rates are as
much as a factor of 10 smaller for neutrino energies above 10^9 GeV, with
important implications for experiments searching for extra-galactic neutrinos.Comment: 4 pages, 1 figure, 1 table; Title, abstract and text changed,
conclusions unchanged. Version accepted for publication in Physical Review
Graphs Identified by Logics with Counting
We classify graphs and, more generally, finite relational structures that are
identified by C2, that is, two-variable first-order logic with counting. Using
this classification, we show that it can be decided in almost linear time
whether a structure is identified by C2. Our classification implies that for
every graph identified by this logic, all vertex-colored versions of it are
also identified. A similar statement is true for finite relational structures.
We provide constructions that solve the inversion problem for finite
structures in linear time. This problem has previously been shown to be
polynomial time solvable by Martin Otto. For graphs, we conclude that every
C2-equivalence class contains a graph whose orbits are exactly the classes of
the C2-partition of its vertex set and which has a single automorphism
witnessing this fact.
For general k, we show that such statements are not true by providing
examples of graphs of size linear in k which are identified by C3 but for which
the orbit partition is strictly finer than the Ck-partition. We also provide
identified graphs which have vertex-colored versions that are not identified by
Ck.Comment: 33 pages, 8 Figure
Inclusive Scholarship: Developing Black Studies in the United States
Brings together four reports commissioned between 1982 and 2000 that examine the history of African American Studies, its impact, and its institutionalization. Reviews Ford's grantmaking to African American Studies programs from 1982 to 2007
Persistence distributions for non gaussian markovian processes
We propose a systematic method to derive the asymptotic behaviour of the
persistence distribution, for a large class of stochastic processes described
by a general Fokker-Planck equation in one dimension. Theoretical predictions
are compared to simple solvable systems and to numerical calculations. The very
good agreement attests the validity of this approach.Comment: 7 pages, 1 figure, to be published in Europhysics Letter
Spectra of sparse non-Hermitian random matrices: an analytical solution
We present the exact analytical expression for the spectrum of a sparse
non-Hermitian random matrix ensemble, generalizing two classical results in
random-matrix theory: this analytical expression forms a non-Hermitian version
of the Kesten-Mckay law as well as a sparse realization of Girko's elliptic
law. Our exact result opens new perspectives in the study of several physical
problems modelled on sparse random graphs. In this context, we show
analytically that the convergence rate of a transport process on a very sparse
graph depends upon the degree of symmetry of the edges in a non-monotonous way.Comment: 5 pages, 5 figures, 12 pages supplemental materia
Lab-Scale Study of the Calcium Carbonate Dissolution and Deposition by Marine Cyanobacterium Phormidium subcapitatum
Suggestions that calcification in marine organisms changes in response to global variations in seawater chemistry continue to be advanced (Wilkinson, 1979; Degens et al. 1985; Kazmierczak et al. 1986; R. Riding 1992). However, the effect of [Na+] on calcification in marine cyanobacteria has not been discussed in detail although [Na+] fluctuations reflect both temperature and sea-level fluctuations. The goal of these lab-scale studies therefore was to study the effect of environmental pH and [Na+] on CaCO3 deposition and dissolution by marine cyanobacterium Phormidium subcapitatum. Marine cyanobacterium P. subcapitatum has been cultivated in ASN-III medium. [Ca2+] fluctuations were monitored with Ca(2+) probe. Na(+) concentrations were determined by the initial solution chemistry. It was found that the balance between CaCO3 dissolution and precipitation induced by P. subcapitatum grown in neutral ASN III medium is very close to zero. No CaCO3 precipitation induced by cyanobacterial growth occurred. Growth of P. subcapitatum in alkaline ASN III medium, however, was accompanied by significant oscillations in free Ca(2+) concentration within a Na(+) concentration range of 50-400 mM. Calcium carbonate precipitation occurred during the log phase of P. subcapitatum growth while carbonate dissolution was typical for the stationary phase of P. subcapitatum growth. The highest CaCO3 deposition was observed in the range of Na(+) concentrations between 200-400 mM. Alkaline pH also induced the clamping of P. subcapitatum filaments, which appeared to have a strong affinity to envelop particles of chemically deposited CaCO3 followed by enlargement of those particles size. EDS analysis revealed the presence of Mg-rich carbonate (or magnesium calcite) in the solution containing 10-100 mM Na(+); calcite in the solution containing 200 mM Na(+); and aragonite in the solution containing with 400 mM Na(+). Typical present-day seawater contains xxmM Na(+). Early (Archean) seawater was likely less saline. The division of marine cyanobacterium P. subcapitatum is associated with periodic deposition and dissolution of CaCO3, the rhythms and intensity of which are dependent on concentrations of both OH(-) and Na(+). Thus, the role of present-day marine cyanobacteria in the global carbonate cycle might be reduced to aggregation and recrystallization of available CaCO3 particles in marine water rather than long-term precipitation and accumulation of CaCO3 deposits. For lower Na(+) concentrations, precipitation of carbonates by cyanobacteria would be even less significant. These results suggest that the lack of calcified cyanobacteria in stromatalite-bearing Precambrian sequences can be explained not only by high dissolved inorganic carbon concentrations but also by lower salinity, as well as possible lower pH compared to present-day oceans
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Observation and analysis of in situ carbonaceous matter in Nakhla: Part I
New analyses of indigenous secondary material in the martian meteorite Nakhla reveal amorphous carbon-rich veins and dendrites. The texture and chemistry of this material resembles that of biogenically altered sub-ocean basaltic glasses
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Observation and analysis of in situ carbonaceous matter in Nakhla: part II
Analysis of in situ carbonaceous matter in the Nakhla SNC meteorite has been carried out using a variety of techniques. Laser raman data shows the carbonaceous matter to be highly complex and static mass spectrometry has shown it to have an isotopic composition of '18 to '20' C
All Teleportation and Dense Coding Schemes
We establish a one-to-one correspondence between (1) quantum teleportation
schemes, (2) dense coding schemes, (3) orthonormal bases of maximally entangled
vectors, (4) orthonormal bases of unitary operators with respect to the
Hilbert-Schmidt scalar product, and (5) depolarizing operations, whose Kraus
operators can be chosen to be unitary. The teleportation and dense coding
schemes are assumed to be ``tight'' in the sense that all Hilbert spaces
involved have the same finite dimension d, and the classical channel involved
distinguishes d^2 signals. A general construction procedure for orthonormal
bases of unitaries, involving Latin Squares and complex Hadamard Matrices is
also presented.Comment: 21 pages, LaTe
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