48,178 research outputs found
The control network of Mars: April 1991
The modern geodetic control network of Mars was first established based on Mariner 9 images with 1-2 km/pixel resolutions and covered almost the entire Martian surface. The introduction of higher resolution (10-200 meter/pixel) Viking Orbiter images greatly improved the accuracy and density of points in the control network. Analysis of the Viking Lander radio tracking data led to more accurate measurements of Mars' rotation period, spin axis direction, and the lander coordinates relative to the inertial reference frame. The prime meridian on Mars was defined by the Geodesy/Cartography Group of the Mariner 9 Television Team as the crater Airy-0, located about 5 degrees south of the equator. The Viking 1 Lander site was identified on a high resolution Viking frame. The control point measurements form the basis of a least squares solution determined by analytical triangulation after the pixel measurements are corrected for geometric distortions and converted to millimeter coordinates in the camera focal plane. Photogrammetric strips encircling Mars at the equator and at 60 degree north south were used to strengthen the overall net and improve the accuracy of the coordinates of points. In addition, photogrammetric strips along 0, 90, 180, and 270 degrees longitude to the Viking 1 Lander site have all significantly strengthened the control network. Most recently, photogrammetric strips were added to the net along 30 degrees north latitude between 0 and 180 degrees, and along 30 degrees between 180 and 360 degrees. The Viking 1 Lander site and Airy-0 are linked through photogrammetric strips occurring along the 0 degree meridian from Airy-0 to 65 degrees north, from that point through the Viking 1 Lander site to the equator, and along the equator to 180 degrees longitude. The Viking 1 lander site is thus a well calibrated area with coordinates of points accurate to approximately 200 meters relative to the J2000 inertial coordinate system. This will be a useful calibration region for upcoming missions. The current status of the control network calculations is presented
On Conserved Current in Markovian Open Quantum Systems
We reexamine the markovian approximation of local current in open quantum
systems, discussed recently by Gebauer and Car. Our derivation is more
transparent, the proof of current conservation becomes explicit and easy.Comment: 3 page
Ablation of solids by femtosecond lasers: ablation mechanism and ablation thresholds for metals and dielectrics
The mechanism of ablation of solids by intense femtosecond laser pulses is
described in an explicit analytical form. It is shown that at high intensities
when the ionization of the target material is complete before the end of the
pulse, the ablation mechanism is the same for both metals and dielectrics. The
physics of this new ablation regime involves ion acceleration in the
electrostatic field caused by charge separation created by energetic electrons
escaping from the target. The formulae for ablation thresholds and ablation
rates for metals and dielectrics, combining the laser and target parameters,
are derived and compared to experimental data. The calculated dependence of the
ablation thresholds on the pulse duration is in agreement with the experimental
data in a femtosecond range, and it is linked to the dependence for nanosecond
pulses.Comment: 27 pages incl.3 figs; presented at CLEO-Europe'2000 11-15 Sept.2000;
papers QMD6 and CTuK11
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Implications of moderate altitude training for sea level endurance in elite distance runners
Elite distance runners participated in one of
two studies designed to investigate the e ects of mod-
erate altitude training (inspiratory partial pressure of
oxygen »115±125 mmHg) on submaximal, maximal and
supramaximal exercise performance following return to
sea-level. Study 1 (New Mexico, USA) involved 14
subjects who were assigned to a 4-week altitude training
camp (1500±2000 m) whilst 9 performance-matched
subjects continued with an identical training programme
at sea-level (CON). Ten EXP subjects who trained at
1640 m and 19 CON subjects also participated in study 2
(Krugersdorp, South Africa). Selected metabolic and
cardiorespiratory parameters were determined with the
subjects at rest and during exercise 21 days prior to
(PRE) and 10 and 20 days following their return to sea-
level (POST). Whole blood lactate decreased by 23%
(P < 0.05 vs PRE) during submaximal exercise in the
EXP group only after 20 days at sea-level (study 1).
However, the lactate threshold and other measures of
running economy remained unchanged. Similarly, su-
pramaximal performance during a standardised track
session did not change. Study 2 demonstrated that
hypoxia per se did not alter performance. In contrast, in
the EXP group supramaximal running velocity de-
creased by 2% (P < 0.05) after 20 days at sea-level.
Both studies were characterised by a 50% increase in the
frequency of upper respiratory and gastrointestinal tract
infections during the altitude sojourns, and two male
subjects were diagnosed with infectious mononucleosis
following their return to sea-level (study 1). Group mean
plasma glutamine concentrations at rest decreased by
19% or 143 (74) lM (P < 0.001) after 3 weeks at alti-
tude, which may have been implicated in the increased
incidence of infectious illness
FliPer: Checking the reliability of global seismic parameters from automatic pipelines
Our understanding of stars through asteroseismic data analysis is limited by
our ability to take advantage of the huge amount of observed stars provided by
space missions such as CoRoT, Kepler, K2, and soon TESS and PLATO. Global
seismic pipelines provide global stellar parameters such as mass and radius
using the mean seismic parameters, as well as the effective temperature. These
pipelines are commonly used automatically on thousands of stars observed by K2
for 3 months (and soon TESS for at least around 1 month). However, pipelines
are not immune from misidentifying noise peaks and stellar oscillations.
Therefore, new validation techniques are required to assess the quality of
these results. We present a new metric called FliPer (Flicker in Power), which
takes into account the average variability at all measured time scales. The
proper calibration of FliPer enables us to obtain good estimations of global
stellar parameters such as surface gravity that are robust against the
influence of noise peaks and hence are an excellent way to find faults in
asteroseismic pipelines.Comment: 4 pages, 3 figures, Proceedings for SF2A 2017 (Paris
Heavy meson masses and decay constants from relativistic heavy quarks in full lattice QCD
We determine masses and decay constants of heavy-heavy and heavy-charm
pseudoscalar mesons as a function of heavy quark mass using a fully
relativistic formalism known as Highly Improved Staggered Quarks for the heavy
quark. We are able to cover the region from the charm quark mass to the bottom
quark mass using MILC ensembles with lattice spacing values from 0.15 fm down
to 0.044 fm. We obtain f_{B_c} = 0.427(6) GeV; m_{B_c} = 6.285(10) GeV and
f_{\eta_b} = 0.667(6) GeV. Our value for f_{\eta_b} is within a few percent of
f_{\Upsilon} confirming that spin effects are surprisingly small for heavyonium
decay constants. Our value for f_{B_c} is significantly lower than potential
model values being used to estimate production rates at the LHC. We discuss the
changing physical heavy-quark mass dependence of decay constants from
heavy-heavy through heavy-charm to heavy-strange mesons. A comparison between
the three different systems confirms that the B_c system behaves in some ways
more like a heavy-light system than a heavy-heavy one. Finally we summarise
current results on decay constants of gold-plated mesons.Comment: 16 pages, 12 figure
Precise determination of the lattice spacing in full lattice QCD
We compare three different methods to determine the lattice spacing in
lattice QCD and give results from calculations on the MILC ensembles of
configurations that include the effect of , and sea quarks. It is
useful, for ensemble to ensemble comparison, to express the results as giving a
physical value for , a parameter from the heavy quark potential. Combining
the three methods gives a value for in the continuum limit of
0.3133(23)(3) fm. Using the MILC values for , this corresponds to a
value for the parameter of 0.4661(38) fm. We also discuss how to use the
for determining the lattice spacing and tuning the -quark mass
accurately, by giving values for (0.6858(40) GeV) and
(0.1815(10) GeV).Comment: 15 page
The Uniqueness Problem of Sequence Product on Operator Effect Algebra
A quantum effect is an operator on a complex Hilbert space that satisfies
. We denote the set of all quantum effects by . In
this paper we prove, Theorem 4.3, on the theory of sequential product on which shows, in fact, that there are sequential products on which are not of the generalized L\"{u}ders form. This result answers a
Gudder's open problem negatively
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