11,104 research outputs found
Three Dimensional Structure and Energy Balance of a Coronal Mass Ejection
The Ultraviolet Coronagraph Spectrometer (UVCS) observed Doppler shifted
material of a partial Halo Coronal Mass Ejection (CME) on December 13 2001. The
observed ratio of [O V]/O V] is a reliable density diagnostic important for
assessing the state of the plasma. Earlier UVCS observations of CMEs found
evidence that the ejected plasma is heated long after the eruption. We have
investigated the heating rates, which represent a significant fraction of the
CME energy budget. The parameterized heating and radiative and adiabatic
cooling have been used to evaluate the temperature evolution of the CME
material with a time dependent ionization state model. The functional form of a
flux rope model for interplanetary magnetic clouds was also used to
parameterize the heating. We find that continuous heating is required to match
the UVCS observations. To match the O VI-bright knots, a higher heating rate is
required such that the heating energy is greater than the kinetic energy. The
temperatures for the knots bright in Ly and C III emission indicate
that smaller heating rates are required for those regions. In the context of
the flux rope model, about 75% of the magnetic energy must go into heat in
order to match the O VI observations. We derive tighter constraints on the
heating than earlier analyses, and we show that thermal conduction with the
Spitzer conductivity is not sufficient to account for the heating at large
heights.Comment: 40 pages, 16 figures, accepted for publication in ApJ For associated
mpeg file, please see https://www.cora.nwra.com/~jylee/mpg/f5.mp
Dedication of the Palomar Observatory and the Hale Telescope
The dedication of the Palomar Observatory, if it were being held in England, would be accompanied by brilliant pageantry both of the state, with its knights, heralds, pursuivants, kings at arms, admirals and captains, and of the church with its bishops, priests and deacons, crucifiers and choirs; and I am sure that we feel the quality of religion in this ceremony. We would hear the choirs chanting in antiphony that great canticle which so delights the choir boys: Benedicite, omnia opera Domini
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A Self-Propelled Biological Process Plk1-Dependent Product-Activated, Feed-Forward Mechanism
Comment on: Park JE, et al. Proc Natl Acad Sci USA 2011; 108:8200-05.Molecular and Cellular Biolog
Metabolite essentiality elucidates robustness of Escherichia coli metabolism
Complex biological systems are very robust to genetic and environmental
changes at all levels of organization. Many biological functions of Escherichia
coli metabolism can be sustained against single-gene or even multiple-gene
mutations by using redundant or alternative pathways. Thus, only a limited
number of genes have been identified to be lethal to the cell. In this regard,
the reaction-centric gene deletion study has a limitation in understanding the
metabolic robustness. Here, we report the use of flux-sum, which is the
summation of all incoming or outgoing fluxes around a particular metabolite
under pseudo-steady state conditions, as a good conserved property for
elucidating such robustness of E. coli from the metabolite point of view. The
functional behavior, as well as the structural and evolutionary properties of
metabolites essential to the cell survival, was investigated by means of a
constraints-based flux analysis under perturbed conditions. The essential
metabolites are capable of maintaining a steady flux-sum even against severe
perturbation by actively redistributing the relevant fluxes. Disrupting the
flux-sum maintenance was found to suppress cell growth. This approach of
analyzing metabolite essentiality provides insight into cellular robustness and
concomitant fragility, which can be used for several applications, including
the development of new drugs for treating pathogens.Comment: Supplements available at
http://stat.kaist.ac.kr/publication/2007/PJKim_pnas_supplement.pd
The association between back pain and trunk posture of workers in a special school for the severe handicaps
<p>Abstract</p> <p>Background</p> <p>The present study aims to determine the time spent in different static trunk postures during a typical working day of workers in a special school for the severe handicaps.</p> <p>Methods</p> <p>Eighteen workers with low back pain (LBP) and fifteen asymptomatic workers were recruited. A cross-sectional design was employed to study the time spent in different static trunk postures which was recorded by a biaxial accelerometer attached to the T<sub>12 </sub>level of the back of the subjects.</p> <p>Results</p> <p>The results of ANCOVA revealed that subjects with LBP spent significantly longer percentage of time in static trunk posture when compared to normal (p < 0.05). It was also shown that they spent significantly longer time in trunk flexion for more than 10° (p < 0.0125).</p> <p>Conclusion</p> <p>An innovative method has been developed for continuous tracking of spinal posture, and this has potential for widespread applications in the workplace. The findings of the present investigation suggest that teachers in special schools are at increased risk of getting LBP. In order to minimise such risk, frequent postural change and awareness of work posture are recommended.</p
The Effect of Ca, Sr, and Ba Doping on the Ionic Conductivity and Cathode Performance of LaFeO\u3csub\u3e3\u3c/sub\u3e
The influence of ionic conductivity on the performance of solid oxide fuel cell cathodes was studied for electrodes prepared by infiltration of 40 wt % La0.8Ca0.2FeO3 (LCF) La0.8Sr0.2FeO3 (LSF) and La0.8Ba0.2FeO3 (LBF) into 65% porous yttria-stabilized zirconia (LSZ). The ionic conductivities of LCF, LSF, and LBF, measured between 923 and 1073 K using permeation rates in a membrane reactor, showed that LSF exhibited the highest ionic conductivities, followed by LBF and LCF. When electrodes were calcined to 1123 K, the performance characteristics of each composite were essentially identical, exhibiting current-independent impedances of 0.2 Ω cm2 at 973 K. When the composites were calcined to 1373 K, the open-circuit impedances were much larger and showed a strong dependence on current density. The open-circuit impedances followed the ionic conductivities, with LSF– YSZ electrodes showing the lowest impedance and LCF–YSZ electrodes the highest. Scanning electron microscopy images and Brunauer–Emmett–Teller surface areas indicate that calcination at 1373 K causes the perovskites to form dense layers over the YSZ pores. A model is proposed in which diffusion of ions through the perovskite film limits the performance of the composite electrodes calcined at 1373 K
First measurements of high frequency cross-spectra from a pair of large Michelson interferometers
Measurements are reported of the cross-correlation of spectra of differential
position signals from the Fermilab Holometer, a pair of co-located 39 m long,
high power Michelson interferometers with flat, broadband frequency response in
the MHz range. The instrument obtains sensitivity to high frequency correlated
signals far exceeding any previous measurement in a broad frequency band
extending beyond the 3.8 MHz inverse light crossing time of the apparatus. The
dominant but uncorrelated shot noise is averaged down over
independent spectral measurements with 381 Hz frequency resolution to obtain
sensitivity to stationary
signals. For signal bandwidths kHz, the sensitivity to strain
or shear power spectral density of classical or exotic origin surpasses a
milestone where
is the Planck time.Comment: 5 pages, 3 figure
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