325 research outputs found
Loudness of harmonic and inharmonic two-tone complexes.
Thesis. 1975. M.S.--Massachusetts Institute of Technology. Dept. of Aeronautics and Astronautics.Includes bibliographical references.M.S
Evolution of microflares associated with bright points in coronal holes and in quiet regions
We aim to find similarities and differences between microflares at coronal
bright points found in quiet regions and coronal holes, and to study their
relationship with large scale flares. Coronal bright points in quiet regions
and in coronal holes were observed with Hinode/EIS using the same sequence.
Microflares associated with bright points are identified from the X-ray
lightcurve. The temporal variation of physical properties was traced in the
course of microflares. The lightcurves of microflares indicated an impulsive
peak at hot emission followed by an enhancement at cool emission, which is
compatible with the cooling model of flare loops. The density was found to
increase at the rise of the impulsive peak, supporting chromospheric
evaporation models. A notable difference is found in the surroundings of
microflares; diffuse coronal jets are produced above microflares in coronal
holes while coronal dimmings are formed in quiet regions. The microflares
associated with bright points share common characteristics to active region
flares. The difference in the surroundings of microflares are caused by open
and closed configurations of the pre-existing magnetic field.Comment: 9 pages, 11 figures, accepted for publication in A&
What is the true nature of blinkers?
Aims.
The aim of this work is to identify the true nature of the transient EUV brightenings, called blinkers.
Methods.
Co-spatial and co-temporal multi-instrument data, including imaging (EUVI/STEREO, XRT and SOT/Hinode), spectroscopic (CDS/SoHO and EIS/Hinode) and magnetogram (SOT/Hinode) data, of an isolated equatorial coronal hole were used. An automatic program for identifying transient brightenings in CDS O v 629 Å, EUVI 171 Å and XRT was applied.
Results.
We identified 28 blinker groups in the CDS O v 629 Å raster images. All CDS O v 629 Å blinkers showed counterparts in EUVI 171 Å and 304 Å images. We classified these blinkers into two categories, one associated with coronal counterparts and other with no coronal counterparts as seen in XRT images and EIS Fe xii 195.12 Å raster images. Around two-thirds of the blinkers show coronal counterparts and correspond to various events like EUV/X-ray jets, brightenings in coronal bright points or foot-point brightenings of larger loops. These brightenings occur repetitively and have a lifetime of around 40 min at transition region temperatures. The remaining blinker groups with no coronal counterpart in XRT and EIS Fe xii 195.12 Å appear as point-like brightenings and have chromospheric/transition region origin. They take place only once and have a lifetime of around 20 min. In general, lifetimes of blinkers are different at different wavelengths, i.e. different temperatures, decreasing from the chromosphere to the corona.
Conclusions.
This work shows that the term blinker covers a range of phenomena. Blinkers are the EUV response of various transient events originating at coronal, transition region and chromospheric heights. Hence, events associated with blinkers contribute to the formation and maintenance of the temperature gradient in the transition region and the corona
Abelian Dominance in Chiral Symmetry Breaking
Calculations of the chiral condensate on
the lattice using staggered fermions and the Lanczos algorithm are presented.
Three gauge fields are considered: the quenched non-Abelian field, the Abelian
field projected in the maximal Abelian gauge, and the monopole field further
decomposed from the Abelian field. The results show that the Abelian monopoles
largely reproduce the chiral condensate values of the full non-Abelian theory,
both in SU(2) and in SU(3).Comment: 4 pages in Latex with 4 embedded Postscript figures, uses
espcrc2.sty, psfig.sty. All are uuencoded, gzipped in a self-extracting file.
Contribution to Lattice'95, Melbourne, Australi
Large-scale horizontal flows in the solar photosphere II: Long-term behaviour and magnetic activity response
Recently, we have developed a method useful for mapping large-scale
horizontal velocity fields in the solar photosphere. The method was developed,
tuned and calibrated using the synthetic data. Now, we applied the method to
the series of Michelson Doppler Imager (MDI) dopplergrams covering almost one
solar cycle in order to get the information about the long-term behaviour of
surface flows. We have found that our method clearly reproduces the widely
accepted properties of mean flow field components, such as torsional
oscillations and a pattern of meridional circulation. We also performed a
periodic analysis, however due to the data series length and large gaps we did
not detect any significant periods. The relation between the magnetic activity
influencing the mean zonal motion is studied. We found an evidence that the
emergence of compact magnetic regions locally accelerates the rotation of
supergranular pattern in their vicinity and that the presence of magnetic
fields generally decelerates the rotation in the equatorial region. Our results
show that active regions in the equatorial region emerge exhibiting a constant
velocity (faster by 60 +/- 9 m/s than Carrington rate) suggesting that they
emerge from the base of the surface radial shear at 0.95 R_sun, disconnect from
their magnetic roots, and slow down during their evolution.Comment: 9 pages, 8 figures, accepted for publication in Astronomy &
Astrophysic
Observations of a rotating macrospicule associated with an X-ray jet
We attempt to understand the driving mechanism of a macrospicule and its
relationship with a coronal jet. We study the dynamics of a macrospicule and an
associated coronal jet captured by multi-spacecraft observations. Doppler
velocities both in the macrospicule and the coronal jet are determined by EIS
and SUMER spectra. Their temporal evolution is studied using X-ray and He II
304 images. A blueshift of -120+/-15 km/s is detected on one side of the
macrospicule, while a redshift of 50+/-6 km/s is found at the base of the other
side. The inclination angle of the macrospicule inferred from a stereoscopic
analysis with STEREO suggests that the measured Doppler velocities can be
attributed to a rotating motion of the macrospicule rather than a radial flow
or an expansion. The macrospicule is driven by the unfolding motion of a
twisted magnetic flux rope, while the associated X-ray jet is a radial outflow.Comment: 4 pages, 3 figures, accepted for publication in A&
Majority Dynamics and Aggregation of Information in Social Networks
Consider n individuals who, by popular vote, choose among q >= 2
alternatives, one of which is "better" than the others. Assume that each
individual votes independently at random, and that the probability of voting
for the better alternative is larger than the probability of voting for any
other. It follows from the law of large numbers that a plurality vote among the
n individuals would result in the correct outcome, with probability approaching
one exponentially quickly as n tends to infinity. Our interest in this paper is
in a variant of the process above where, after forming their initial opinions,
the voters update their decisions based on some interaction with their
neighbors in a social network. Our main example is "majority dynamics", in
which each voter adopts the most popular opinion among its friends. The
interaction repeats for some number of rounds and is then followed by a
population-wide plurality vote.
The question we tackle is that of "efficient aggregation of information": in
which cases is the better alternative chosen with probability approaching one
as n tends to infinity? Conversely, for which sequences of growing graphs does
aggregation fail, so that the wrong alternative gets chosen with probability
bounded away from zero? We construct a family of examples in which interaction
prevents efficient aggregation of information, and give a condition on the
social network which ensures that aggregation occurs. For the case of majority
dynamics we also investigate the question of unanimity in the limit. In
particular, if the voters' social network is an expander graph, we show that if
the initial population is sufficiently biased towards a particular alternative
then that alternative will eventually become the unanimous preference of the
entire population.Comment: 22 page
Trends of and factors associated with live-birth and abortion rates among HIV-positive and HIV-negative women
Little is known about fertility choices and pregnancy outcome rates among HIV-infected women in the current combination ART era
Liver Fibrosis Linked to Cognitive Performance in HIV and Hepatitis C
Since HIV impairs gut barriers to pathogens, HIV-infected adults may be vulnerable to Minimal Hepatic Encephalopathy (MHE) in the absence of cirrhosis
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