725 research outputs found
A space station onboard scheduling assistant
One of the goals for the Space Station is to achieve greater autonomy, and have less reliance on ground commanding than previous space missions. This means that the crew will have to take an active role in scheduling and rescheduling their activities onboard, perhaps working from preliminary schedules generated on the ground. Scheduling is a time intensive task, whether performed manually or automatically, so the best approach to solving onboard scheduling problems may involve crew members working with an interactive software scheduling package. A project is described which investigates a system that uses knowledge based techniques for the rescheduling of experiments within the Materials Technology Laboratory of the Space Station. Particular attention is paid to: (1) methods for rapid response rescheduling to accommodate unplanned changes in resource availability, (2) the nature of the interface to the crew, (3) the representation of the many types of data within the knowledge base, and (4) the possibility of applying rule-based and constraint-based reasoning methods to onboard activity scheduling
P-31 magnetization transfer measurements of P-i -> ATP flux in exercising human muscle
Fundamental criticisms have been made over the use of (31)P magnetic resonance spectroscopy (MRS) magnetization transfer estimates of inorganic phosphate (P(i))→ATP flux (V(Pi-ATP)) in human resting skeletal muscle for assessing mitochondrial function. Although the discrepancy in the magnitude of V(Pi-ATP) is now acknowledged, little is known about its metabolic determinants. Here we use a novel protocol to measure V(Pi-ATP) in human exercising muscle for the first time. Steady-state V(Pi-ATP) was measured at rest and over a range of exercise intensities and compared with suprabasal oxidative ATP synthesis rates estimated from the initial rates of postexercise phosphocreatine resynthesis (V(ATP)). We define a surplus P(i)→ATP flux as the difference between V(Pi-ATP) and V(ATP). The coupled reactions catalyzed by the glycolytic enzymes GAPDH and phosphoglycerate kinase (PGK) have been shown to catalyze measurable exchange between ATP and P(i) in some systems and have been suggested to be responsible for this surplus flux. Surplus V(Pi-ATP) did not change between rest and exercise, even though the concentrations of P(i) and ADP, which are substrates for GAPDH and PGK, respectively, increased as expected. However, involvement of these enzymes is suggested by correlations between absolute and surplus P(i)→ATP flux, both at rest and during exercise, and the intensity of the phosphomonoester peak in the (31)P NMR spectrum. This peak includes contributions from sugar phosphates in the glycolytic pathway, and changes in its intensity may indicate changes in downstream glycolytic intermediates, including 3-phosphoglycerate, which has been shown to influence the exchange between ATP and P(i) catalyzed by GAPDH and PGK
Long-term optical variability of PKS 2155-304
Aims: The optical variability of the blazar PKS 2155-304 is investigated to
characterise the red noise behaviour at largely different time scales from 20
days to O(>10 yrs). Methods: The long-term optical light curve of PKS 2155-304
is assembled from archival data as well as from so-far unpublished observations
mostly carried out with the ROTSE-III and the ASAS robotic telescopes. A
forward folding technique is used to determine the best-fit parameters for a
model of a power law with a break in the power spectral density function (PSD).
The best-fit parameters are estimated using a maximum-likelihood method with
simulated light curves in conjunction with the Lomb Scargle Periodogram (LSP)
and the first-order Structure Function (SF). In addition, a new approach based
upon the so-called Multiple Fragments Variance Function (MFVF) is introduced
and compared to the other methods. Simulated light curves have been used to
confirm the reliability of these methods as well as to estimate the
uncertainties of the best-fit parameters. Results: The light curve is
consistent with the assumed broken power-law PSD. All three methods agree
within the estimated uncertainties with the MFVF providing the most accurate
results. The red-noise behaviour of the PSD in frequency f follows a power law
with f^-{\beta}, {\beta}=1.8 +0.1/-0.2 and a break towards f^0 at frequencies
lower than f_min=(2.7 +2.2/-1.6 yrs)^-1.Comment: 10 pages, 8 figures, the ROTSE-light curve can be downloaded from
http://vizier.cfa.harvard.edu/viz-bin/VizieR?-source=J/A+A/531/A12
Is it Round? Spectropolarimetry of the Type II-P Supernova 1999em
We present the first multi-epoch spectropolarimetry of a type II plateau
supernova (SN II-P), with optical observations of SN 1999em on days 7, 40, 49,
159, and 163 after discovery. These data are used to probe the geometry of the
electron-scattering atmosphere before, during, and after the plateau phase,
which ended roughly 90 days after discovery. Weak continuum polarization with
an unchanging polarization angle (theta ~ 160 deg) is detected at all epochs,
with p ~ 0.2% on day 7, p ~ 0.3% on days 40 and 49, and p ~ 0.5% in the final
observations. Distinct polarization modulations across strong line features are
present on days 40, 49, 159, and 163. Uncorrected for interstellar polarization
(which is believed to be quite small), polarization peaks are associated with
strong P Cygni absorption troughs and nearly complete depolarization is seen
across the H-alpha emission profile. The temporal evolution of the continuum
polarization and sharp changes across lines indicate polarization intrinsic to
SN 1999em. When modeled in terms of the oblate, electron-scattering atmospheres
of Hoeflich, the observed polarization implies anasphericity of at least 7%
during the period studied. The temporal polarization increase may indicate
greater asphericity deeper into the ejecta. We discuss the implications of
asphericity on the use of type II-P supernovae as primary extragalactic
distance indicators through the expanding photosphere method (EPM). If
asphericity produces directionally dependant flux and peculiar galaxy motions
are characterized by sigma_v_rec = 300 km/s, it is shown that the agreement
between previous EPM measurements of SNe II and distances to the host galaxies
predicted by a linear Hubble law restrict mean SN II asphericity to values less
than 30% (3-sigma) during the photospheric phase.Comment: 65 pages (29 Figures, 4 Tables), Accepted for publication in the June
1, 2001 edition of ApJ. Revised statistical analysis of scatter in Hubble
diagram of previous EPM distances and the implications for mean SN II
asphericit
Spectropolarimetry of the Luminous Narrow-Line Seyfert Galaxies IRAS 20181-2244 and IRAS 13224-3809
We observed the narrow-line Seyfert 1 galaxies IRAS 20181-2244 and IRAS
13324-3809 with a new spectropolarimeter on the RC spectrograph at the CTIO 4m
telescope. Previously it had been suggested that IRAS 20181-2244 was a Type 2
QSO and thus might contain an obscured broad-line region which could be
detected by the presence of broad Balmer lines in the polarized flux. We found
the object to be polarized at about 2%, and constant with wavelength, (unlike
most narrow-line Seyfert 1s), but with no evidence of broad Balmer lines in
polarized flux. The spectropolarimetry indicates that the scattering material
is inside the BLR. IRAS 13224-3809, notable for its high variability in X-ray
and UV wavelengths, has a low polarization consistent with a Galactic
interstellar origin.Comment: 19 pages using (AASTEX) aaspp4.sty and 5 postscript figures To be
published in the Astrophysical Journa
Effects of fasting on serial measurements of hyperpolarized [1-(13) C]pyruvate metabolism in tumors.
Imaging of the metabolism of hyperpolarized [1-(13) C]pyruvate has shown considerable promise in preclinical studies in oncology, particularly for the assessment of early treatment response. The repeatability of measurements of (13) C label exchange between pyruvate and lactate was determined in a murine lymphoma model in fasted and non-fasted animals. The fasted state showed lower intra-individual variability, although the [1-(13) C]lactate/[1-(13) C]pyruvate signal ratio was significantly greater in fasted than in non-fasted mice, which may be explained by the higher tumor lactate concentrations in fasted animals. These results indicate that the fasted state may be preferable for the measurement of (13) C label exchange between pyruvate and lactate, as it reduces the variability and therefore should make it easier to detect the effects of therapy. © 2016 The Authors. NMR in Biomedicine published by John Wiley & Sons Ltd.Cancer Research UK (Grant ID: 17242)This is the final version of the article. It first appeared from Wiley via https://doi.org/10.1002/nbm.356
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