1,043 research outputs found
Can We Improve the Preprocessing of Photospheric Vector Magnetograms by the Inclusion of Chromospheric Observations?
The solar magnetic field is key to understanding the physical processes in
the solar atmosphere. Nonlinear force-free codes have been shown to be useful
in extrapolating the coronal field upward from underlying vector boundary data.
However, we can only measure the magnetic field vector routinely with high
accuracy in the photosphere, and unfortunately these data do not fulfill the
force-free condition. We must therefore apply some transformations to these
data before nonlinear force-free extrapolation codes can be self-consistently
applied. To this end, we have developed a minimization procedure that yields a
more chromosphere-like field, using the measured photospheric field vectors as
input. The procedure includes force-free consistency integrals, spatial
smoothing, and -- newly included in the version presented here -- an improved
match to the field direction as inferred from fibrils as can be observed in,
e.g., chromospheric H images. We test the procedure using a model
active-region field that included buoyancy forces at the photospheric level.
The proposed preprocessing method allows us to approximate the chromospheric
vector field to within a few degrees and the free energy in the coronal field
to within one percent.Comment: 22 pages, 6 Figur
High Resolution Observations using Adaptive Optics: Achievements and Future Needs
Over the last few years, several interesting observations were obtained with
the help of solar Adaptive Optics (AO). In this paper, few observations made
using the solar AO are enlightened and briefly discussed. A list of
disadvantages with the current AO system are presented. With telescopes larger
than 1.5m are expected during the next decade, there is a need to develop the
existing AO technologies for large aperture telescopes. Some aspects of this
development are highlighted. Finally, the recent AO developments in India are
also presented
Euclid space mission: a cosmological challenge for the next 15 years
Euclid is the next ESA mission devoted to cosmology. It aims at observing
most of the extragalactic sky, studying both gravitational lensing and
clustering over 15,000 square degrees. The mission is expected to be
launched in year 2020 and to last six years. The sheer amount of data of
different kinds, the variety of (un)known systematic effects and the complexity
of measures require efforts both in sophisticated simulations and techniques of
data analysis. We review the mission main characteristics, some aspects of the
the survey and highlight some of the areas of interest to this meetingComment: to appear in Proceedings IAU Symposium No. 306, 2014, "Statistical
Challenges in 21st Century Cosmology", A.F. Heavens, J.-L. Starck & A.
Krone-Martins, ed
P04-45. Characterization of the plasma cell repertoire in acute HIV-1 infection (AHI)
Analysis of immunoglobulin (Ig) VH and VL genes
derived from sorted single B cells is a powerful technology
for definition of Ig repertoires to viral infections. The purpose
of this study was to characterize the Ig repertoire of
plasma cells/plasmablasts (PCs) in subjects early on after
HIV transmission
GW170104: Observation of a 50-Solar-Mass Binary Black Hole Coalescence at Redshift 0.2
We describe the observation of GW170104, a gravitational-wave signal produced by the coalescence of a pair of stellar-mass black holes. The signal was measured on January 4, 2017 at 10 11:58.6 UTC by the twin advanced detectors of the Laser Interferometer Gravitational-Wave Observatory during their second observing run, with a network signal-to-noise ratio of 13 and a false alarm rate less than 1 in 70 000 years. The inferred component black hole masses are 31.2-6.0+8.4M\u27 and 19.4-5.9+5.3M (at the 90% credible level). The black hole spins are best constrained through measurement of the effective inspiral spin parameter, a mass-weighted combination of the spin components perpendicular to the orbital plane, ĂâĄeff=-0.12-0.30+0.21. This result implies that spin configurations with both component spins positively aligned with the orbital angular momentum are disfavored. The source luminosity distance is 880-390+450 Mpc corresponding to a redshift of z=0.18-0.07+0.08. We constrain the magnitude of modifications to the gravitational-wave dispersion relation and perform null tests of general relativity. Assuming that gravitons are dispersed in vacuum like massive particles, we bound the graviton mass to mgĂąâ°Â€7.7Ăâ10-23 eV/c2. In all cases, we find that GW170104 is consistent with general relativity
Error Analysis regarding the calculation of NLFF Field
Field extrapolation is an alternative method to study chromospheric and
coronal magnetic fields. In this paper, two semi-analytical solutions of force-
free fields (Low and Lou, 1990) have been used to study the errors of nonlin-
ear force-free (NLFF) fields based on force-free factor alpha. Three NLFF
fields are extrapolated by approximate vertical integration (AVI) Song et al.
(2006), boundary integral equation (BIE) Yan and Sakurai (2000) and
optimization (Opt.) Wiegelmann (2004) methods. Compared with the first
semi-analytical field, it is found that the mean values of absolute relative
standard deviations (RSD) of alpha along field lines are about 0.96-1.05,
0.94-1.07 and 0.46-0.72 for AVI, BIE and Opt. fields, respectively. While for
the second semi-analytical field, they are about 0.80-1.02, 0.63-1.34 and
0.33-0.55 for AVI, BIE and Opt. fields, respectively. As for the analytical
field, the calculation error of hjRSDji is about 0.1 {\guillemotright} 0.2. It
is also found that RSD does not apparently depend on the length of field line.
These provide the basic estimation on the deviation of extrapolated field
obtained by proposed methods from the real force-free field.Comment: 22 pages, 13 figures, "Accepted for publication in Astrophysics &
Space Science
A Cryogenic Silicon Interferometer for Gravitational-wave Detection
The detection of gravitational waves from compact binary mergers by LIGO has opened the era of gravitational wave astronomy, revealing a previously hidden side of the cosmos. To maximize the reach of the existing LIGO observatory facilities, we have designed a new instrument that will have 5 times the range of Advanced LIGO, or greater than 100 times the event rate. Observations with this new instrument will make possible dramatic steps toward understanding the physics of the nearby universe, as well as observing the universe out to cosmological distances by the detection of binary black hole coalescences. This article presents the instrument design and a quantitative analysis of the anticipated noise floor
Gravitational Waves From Known Pulsars: Results From The Initial Detector Era
We present the results of searches for gravitational waves from a large selection of pulsars using data from the most recent science runs (S6, VSR2 and VSR4) of the initial generation of interferometric gravitational wave detectors LIGO (Laser Interferometric Gravitational-wave Observatory) and Virgo. We do not see evidence for gravitational wave emission from any of the targeted sources but produce upper limits on the emission amplitude. We highlight the results from seven young pulsars with large spin-down luminosities. We reach within a factor of five of the canonical spin-down limit for all seven of these, whilst for the Crab and Vela pulsars we further surpass their spin-down limits. We present new or updated limits for 172 other pulsars (including both young and millisecond pulsars). Now that the detectors are undergoing major upgrades, and, for completeness, we bring together all of the most up-to-date results from all pulsars searched for during the operations of the first-generation LIGO, Virgo and GEO600 detectors. This gives a total of 195 pulsars including the most recent results described in this paper.United States National Science FoundationScience and Technology Facilities Council of the United KingdomMax-Planck-SocietyState of Niedersachsen/GermanyAustralian Research CouncilInternational Science Linkages program of the Commonwealth of AustraliaCouncil of Scientific and Industrial Research of IndiaIstituto Nazionale di Fisica Nucleare of ItalySpanish Ministerio de Economia y CompetitividadConselleria d'Economia Hisenda i Innovacio of the Govern de les Illes BalearsNetherlands Organisation for Scientific ResearchPolish Ministry of Science and Higher EducationFOCUS Programme of Foundation for Polish ScienceRoyal SocietyScottish Funding CouncilScottish Universities Physics AllianceNational Aeronautics and Space AdministrationOTKA of HungaryLyon Institute of Origins (LIO)National Research Foundation of KoreaIndustry CanadaProvince of Ontario through the Ministry of Economic Development and InnovationNational Science and Engineering Research Council CanadaCarnegie TrustLeverhulme TrustDavid and Lucile Packard FoundationResearch CorporationAlfred P. Sloan FoundationAstronom
- âŠ