286 research outputs found
Magnetic Evolution and Temperature Variation in a Coronal Hole
We have explored the magnetic flux evolution and temperature variation in a
coronal-hole region, using Big Bear Solar Observatory (BBSO) deep magnetograms
and {\it SOHO}/EIT images observed from 2005 October 10 to 14. For comparison,
we also investigated a neighboring quiet region of the Sun. The coronal hole
evolved from its mature stage to its disappearance during the observing period.
We have obtained the following results: (1) When the coronal hole was well
developed on October 10, about 60 % of the magnetic flux was positive. The EUV
brightness was 420 counts pixel, and the coronal temperature, estimated
from the line ratio of the EIT 195 {\AA} and 171 {\AA} images, was 1.07 MK. (2)
On October 14, when the coronal hole had almost disappeared, 51 % of the
magnetic flux was positive, the EUV radiance was 530 counts pixel, and
the temperature was 1.10 MK. (3) In the neighboring quiet region, the fraction
of positive flux varied between 0.49 and 0.47. The EUV brightness displayed an
irregular variation, with a mean value of 870 counts pixel. The
temperature was almost constant at 1.11 MK during the five-day observation. Our
results demonstrate that in a coronal hole less imbalance of the magnetic flux
in opposite polarities leads to stronger EUV brightness and higher coronal
temperatures
The G-O Rule and Waldmeier Effect in the Variations of the Numbers of Large and Small Sunspot Groups
We have analysed the combined Greenwich and Solar Optical Observing Network
(SOON) sunspot group data during the period of 1874-2011 and determined
variations in the annual numbers (counts) of the small, large and big sunspot
groups (these classifications are made on the basis of the maximum areas of the
sunspot groups). We found that the amplitude of an even-numbered cycle of the
number of large groups is smaller than that of its immediately following
odd-numbered cycle. This is consistent with the well known Gnevyshev and Ohl
rule or G-O rule of solar cycles, generally described by using the Zurich
sunspot number (Rz). During cycles 12-21 the G-O rule holds good for the
variation in the number of small groups also, but it is violated by cycle pair
(22, 23) as in the case of Rz. This behaviour of the variations in the small
groups is largely responsible for the anomalous behaviour of Rz in cycle pair
(22, 23). It is also found that the amplitude of an odd-numbered cycle of the
number of small groups is larger than that of its immediately following
even-numbered cycle. This can be called as `reverse G-O rule'. In the case of
the number of the big groups, both cycle pairs (12, 13) and (22, 23) violated
the G-O rule. In many cycles the positions of the peaks of the small, large,
and big groups are different and considerably differ with respect to the
corresponding positions of the Rz peaks. In the case of cycle 23, the
corresponding cycles of the small and large groups are largely symmetric/less
asymmetric (Waldmeier effect is weak/absent) with their maxima taking place two
years later than that of Rz. The corresponding cycle of the big groups is more
asymmetric (strong Waldmeier effect) with its maximum epoch taking place at the
same time as that of Rz.Comment: 13 pages, 5 figures, 1 table, accepted by Solar Physic
MOST detects corotating bright spots on the mid-O type giant {\xi} Persei
We have used the MOST (Microvariability and Oscillations of STars)
microsatellite to obtain four weeks of contiguous high-precision broadband
visual photometry of the O7.5III(n)((f)) star {\xi} Persei in November 2011.
This star is well known from previous work to show prominent DACs (Discrete
Absorption Components) on time-scales of about 2 d from UV spectroscopy and NRP
(Non Radial Pulsation) with one (l = 3) p-mode oscillation with a period of 3.5
h from optical spectroscopy. Our MOST-orbit (101.4 min) binned photometry fails
to reveal any periodic light variations above the 0.1 mmag 3-sigma noise level
for periods of hours, while several prominent Fourier peaks emerge at the 1
mmag level in the two-day period range. These longer-period variations are
unlikely due to pulsations, including gravity modes. From our simulations based
upon a simple spot model, we deduce that we are seeing the photometric
modulation of several co-rotating bright spots on the stellar surface. In our
model, the starting times (random) and lifetimes (up to several rotations) vary
from one spot to another yet all spots rotate at the same period of 4.18 d, the
best-estimated rotation period of the star. This is the first convincing
reported case of co-rotating bright spots on an O star, with important
implications for drivers of the DACs (resulting from CIRs - Corotating
Interaction Regions) with possible bright-spot generation via a breakout at the
surface of a global magnetic field generated by a subsurface convection zone.Comment: 9 pages, 4 figures, 2 tables, MNRAS in pres
A Bayesian Analysis of the Correlations Among Sunspot Cycles
Sunspot numbers form a comprehensive, long-duration proxy of solar activity
and have been used numerous times to empirically investigate the properties of
the solar cycle. A number of correlations have been discovered over the 24
cycles for which observational records are available. Here we carry out a
sophisticated statistical analysis of the sunspot record that reaffirms these
correlations, and sets up an empirical predictive framework for future cycles.
An advantage of our approach is that it allows for rigorous assessment of both
the statistical significance of various cycle features and the uncertainty
associated with predictions. We summarize the data into three sequential
relations that estimate the amplitude, duration, and time of rise to maximum
for any cycle, given the values from the previous cycle. We find that there is
no indication of a persistence in predictive power beyond one cycle, and
conclude that the dynamo does not retain memory beyond one cycle. Based on
sunspot records up to October 2011, we obtain, for Cycle 24, an estimated
maximum smoothed monthly sunspot number of 97 +- 15, to occur in
January--February 2014 +- 6 months.Comment: Accepted for publication in Solar Physic
The fluctuating \alpha-effect and Waldmeier relations in the nonlinear dynamo models
We study the possibility to reproduce the statistical relations of the
sunspot activity cycle, like the so-called Waldmeier relations, the cycle
period - amplitude and the cycle rise rate - amplitude relations, by means of
the mean field dynamo models with the fluctuating \alpha-effect. The dynamo
model includes the long-term fluctuations of the \alpha-effect and two types of
the nonlinear feedback of the mean-field on the \alpha-effect including the
algebraic quenching and the dynamic quenching due to the magnetic helicity
generation. We found that the models are able to reproduce qualitatively and
quantitatively the inclination and dispersion across the Waldmeier relations
with the 20% fluctuations of the \alpha-effect. The models with the dynamic
quenching are in a better agreement with observations than the models with the
algebraic \alpha-quenching. We compare the statistical distributions of the
modeled parameters, like the amplitude, period, the rise and decay rates of the
sunspot cycles, with observations.Comment: revision, (add comment about effect of nonlinear diffusivity): 18
pages, 7 Figures, submitted to Physica Script
Protons in near earth orbit
The proton spectrum in the kinetic energy range 0.1 to 200 GeV was measured
by the Alpha Magnetic Spectrometer (AMS) during space shuttle flight STS-91 at
an altitude of 380 km. Above the geomagnetic cutoff the observed spectrum is
parameterized by a power law. Below the geomagnetic cutoff a substantial second
spectrum was observed concentrated at equatorial latitudes with a flux ~ 70
m^-2 sec^-1 sr^-1. Most of these second spectrum protons follow a complicated
trajectory and originate from a restricted geographic region.Comment: 19 pages, Latex, 7 .eps figure
Isotopic Composition of Light Nuclei in Cosmic Rays: Results from AMS-01
The variety of isotopes in cosmic rays allows us to study different aspects
of the processes that cosmic rays undergo between the time they are produced
and the time of their arrival in the heliosphere. In this paper we present
measurements of the isotopic ratios 2H/4He, 3He/4He, 6Li/7Li, 7Be/(9Be+10Be)
and 10B/11B in the range 0.2-1.4 GeV of kinetic energy per nucleon. The
measurements are based on the data collected by the Alpha Magnetic
Spectrometer, AMS-01, during the STS-91 flight in 1998 June.Comment: To appear in ApJ. 12 pages, 11 figures, 6 table
A Study of Cosmic Ray Secondaries Induced by the Mir Space Station Using AMS-01
The Alpha Magnetic Spectrometer (AMS-02) is a high energy particle physics
experiment that will study cosmic rays in the to range and will be installed on the International Space Station
(ISS) for at least 3 years. A first version of AMS-02, AMS-01, flew aboard the
space shuttle \emph{Discovery} from June 2 to June 12, 1998, and collected
cosmic ray triggers. Part of the \emph{Mir} space station was within the
AMS-01 field of view during the four day \emph{Mir} docking phase of this
flight. We have reconstructed an image of this part of the \emph{Mir} space
station using secondary and emissions from primary cosmic rays
interacting with \emph{Mir}. This is the first time this reconstruction was
performed in AMS-01, and it is important for understanding potential
backgrounds during the 3 year AMS-02 mission.Comment: To be submitted to NIM B Added material requested by referee. Minor
stylistic and grammer change
Cyclosporin A Associated Helicase-Like Protein Facilitates the Association of Hepatitis C Virus RNA Polymerase with Its Cellular Cyclophilin B
BACKGROUND: Cyclosporin A (CsA) is well known as an immunosuppressive drug useful for allogeneic transplantation. It has been reported that CsA inhibits hepatitis C virus (HCV) genome replication, which indicates that cellular targets of CsA regulate the viral replication. However, the regulation mechanisms of HCV replication governed by CsA target proteins have not been fully understood. PRINCIPAL FINDINGS: Here we show a chemical biology approach that elucidates a novel mechanism of HCV replication. We developed a phage display screening to investigate compound-peptide interaction and identified a novel cellular target molecule of CsA. This protein, named CsA associated helicase-like protein (CAHL), possessed RNA-dependent ATPase activity that was negated by treatment with CsA. The downregulation of CAHL in the cells resulted in a decrease of HCV genome replication. CAHL formed a complex with HCV-derived RNA polymerase NS5B and host-derived cyclophilin B (CyPB), known as a cellular cofactor for HCV replication, to regulate NS5B-CyPB interaction. CONCLUSIONS: We found a cellular factor, CAHL, as CsA associated helicase-like protein, which would form trimer complex with CyPB and NS5B of HCV. The strategy using a chemical compound and identifying its target molecule by our phage display analysis is useful to reveal a novel mechanism underlying cellular and viral physiology
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