15,407 research outputs found
Relative chronology of Martian volcanoes
Impact cratering is one of the major geological processes that has affected the Martian surface throughout the planet's history. The frequency of craters within particular size ranges provides information about the formation ages and obliterative episodes of Martian geologic units. The Barlow chronology was extended by measuring small craters on the volcanoes and a number of standard terrain units. Inclusions of smaller craters in units previously analyzed by Barlow allowed for a more direct comparison between the size-frequency distribution data for volcanoes and established chronology. During this study, 11,486 craters were mapped and identified in the 1.5 to 8 km diameter range in selected regions of Mars. The results are summarized in this three page report and give a more precise estimate of the relative chronology of the Martian volcanoes. Also, the results of this study lend further support to the increasing evidence that volcanism has been a dominant geologic force throughout Martian history
Modified Paouris inequality
The Paouris inequality gives the large deviation estimate for Euclidean norms
of log-concave vectors. We present a modified version of it and show how the
new inequality may be applied to derive tail estimates of l_r-norms and suprema
of norms of coordinate projections of isotropic log-concave vectors.Comment: 14 page
Electrophoretic separation of human kidney cells at zero gravity
Electrophoretic isolation of cells results in a loss of resolution power caused by the sedimentation of the cells in the media. The results of an experiment to extract urokinase from human embryos during the Apollo Soyuz mission are presented and discussed
Unravelling the chemical inhomogeneity of PNe with VLT FLAMES integral-field unit spectroscopy
Recent weak emission-line long-slit surveys and modelling studies of PNe have
convincingly argued in favour of the existence of an unknown component in the
planetary nebula plasma consisting of cold, hydrogen-deficient gas, as an
explanation for the long-standing recombination-line versus forbidden-line
temperature and abundance discrepancy problems. Here we describe the rationale
and initial results from a detailed spectroscopic study of three Galactic PNe
undertaken with the VLT FLAMES integral-field unit spectrograph, which advances
our knowledge about the small-scale physical properties, chemical abundances
and velocity structure of these objects across a two-dimensional field of view,
and opens up for exploration an uncharted territory in the study and modelling
of PNe and photoionized nebulae in general.Comment: 4 pages; 3 figures; invited paper to appear in proceedings of IAU
Symp. No. 234, 2006, Planetary Nebulae in our Galaxy and Beyond (held in
Hawaii, April 2006
Atomic and molecular interstellar absorption lines toward the high galactic latitude stars HD~141569 and HD~157841 at ultra-high resolution
We present ultra-high resolution (0.32 km/s) spectra obtained with the 3.9m
Anglo-Australian Telescope (AAT) and Ultra-High-Resolution Facility (UHRF), of
interstellar NaI D1, D2, Ca II K, K I and CH absorption toward two high
galactic latitude stars HD141569 and HD157841. We have compared our data with
21-cm observations obtained from the Leiden/Dwingeloo HI survey. We derive the
velocity structure, column densities of the clouds represented by the various
components and identify the clouds with ISM structures seen in the region at
other wavelengths. We further derive abundances, linear depletions and H2
fractional abundances for these clouds, wherever possible. Toward HD141569, we
detect two components in our UHRF spectra : a weak, broad component at - 15
km/s, seen only in CaII K absorption and another component at 0 km/s, seen in
NaI D1, D2, Ca II K, KI and CH absorption. In the case of the HD157841
sightline, a total of 6 components are seen on our UHRF spectra in NaI D1, D2
Ca II K, K I and CH absorption. 2 of these 6 components are seen only in a
single species.Comment: 16 pages, Latex, 4 figures, ps files Astrophysical Journal (in press
The dimension of loop-erased random walk in 3D
We measure the fractal dimension of loop-erased random walk (LERW) in 3
dimensions, and estimate that it is 1.62400 +- 0.00005. LERW is closely related
to the uniform spanning tree and the abelian sandpile model. We simulated LERW
on both the cubic and face-centered cubic lattices; the corrections to scaling
are slightly smaller for the face-centered cubic lattice.Comment: 4 pages, 4 figures. v2 has more data, minor additional change
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Complete Experimental Structure Determination of the p(3x2)pg Phase of Glycine on Cu{110}
We present a quantitative low energy electron diffraction (LEED) surface-crystallograpic
study of the complete adsorption geometry of glycine adsorbed on Cu{110} in the ordered
p(3Ă—2) phase. The glycine molecules form bonds to the surface through the N atoms of the
amino group and the two O atoms of the de-protonated carboxylate group, each with separate
Cu atoms such that every Cu atom in the first layer is involved in a bond. Laterally, N atoms are
nearest to the atop site (displacement 0.41 Ă…). The O atoms are asymmetrically displaced from
the atop site by 0.54 Ă… and 1.18 Ă… with two very different O-Cu bond lengths of 1.93 Ă… and
2.18 Ă…. The atom positions of the upper-most Cu layers show small relaxations within 0.07 Ă…
of the bulk-truncated surface geometry. The unit cell of the adsorbate layer consists of two
glycine molecules, which are related by a glide-line symmetry operation. This study clearly
shows that a significant coverage of adsorbate structures without this glide-line symmetry must
be rejected, both on the grounds of the energy dependence of the spot intensities (LEED-IV
curves) and of systematic absences in the LEED pattern
Warming Early Mars by Impact Degassing of Reduced Greenhouse Gases
Reducing greenhouse gases are once again the latest trend in finding solutions to the early Mars climate dilemma. In its current form collision induced absorptions (CIA) involving H2 and/or CH4 provide enough extra greenhouse power in a predominately CO2 atmosphere to raise global mean surface temperatures to the melting point of water provided the atmosphere is thick enough and the reduced gases are abundant enough. Surface pressures must be at least 500 mb and H2 and/or CH4 concentrations must be at or above the several percent level for CIA to be effective. Atmospheres with 1-2 bars of CO2 and 2- 10% H2 can sustain surface environments favorable for liquid water. Smaller concentrations of H2 are sufficient if CH4 is also present. If thick CO2 atmospheres with percent level concentrations of reduced gases are the solution to the faint young Sun paradox for Mars, then plausible mechanisms must be found to generate and sustain the gases. Possible sources of reducing gases include volcanic outgassing, serpentinization, and impact delivery; sinks include photolyis, oxidation, and escape to space. The viability of the reduced greenhouse hypothesis depends, therefore, on the strength of these sources and sinks. In this paper we focus on impact delivered reduced gases
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