1,651 research outputs found
A Constraint on the Organization of the Galactic Center Magnetic Field Using Faraday Rotation
We present new 6 and 20 cm Very Large Array (VLA) observations of polarized
continuum emission of roughly 0.5 square degrees of the Galactic center (GC)
region. The 6 cm observations detect diffuse linearly-polarized emission
throughout the region with a brightness of roughly 1 mJy per 15"x10" beam. The
Faraday rotation measure (RM) toward this polarized emission has structure on
degree size scales and ranges from roughly +330 rad/m2 east of the dynamical
center (Sgr A) to -880 rad/m2 west of the dynamical center. This RM structure
is also seen toward several nonthermal radio filaments, which implies that they
have a similar magnetic field orientation and constrains models for their
origin. Modeling shows that the RM and its change with Galactic longitude are
best explained by the high electron density and strong magnetic field of the GC
region. Considering the emissivity of the GC plasma shows that while the
absolute RM values are indirect measures of the GC magnetic field, the RM
longitude structure directly traces the magnetic field in the central
kiloparsec of the Galaxy. Combining this result with previous work reveals a
larger RM structure covering the central ~2 degrees of the Galaxy. This RM
structure is similar to that proposed by Novak and coworkers, but is shifted
roughly 50 pc west of the dynamical center of the Galaxy. If this RM structure
originates in the GC region, it shows that the GC magnetic field is organized
on ~300 pc size scales. The pattern is consistent with a predominantly poloidal
field geometry, pointing from south to north, that is perturbed by the motion
of gas in the Galactic disk.Comment: Accepted to ApJ. emulateapj style, 14 pages, 15 figure
Year in review 2008: Critical Care - sepsis
The present report highlights the most important papers appearing in Critical Care and other major journals about severe sepsis, the systemic inflammatory response and multiorgan dysfunction over the past year. A number of these clinical and laboratory studies will have a considerable impact on the sepsis research agenda for years to come. The steroid controversy, the debate over tight glycemic control, the colloid versus crystalloid issue, the value of selective decontamination of the digestive tract, the enlarging role of biomarkers, the value of genomics and rapid diagnostic techniques have all been prominently featured in recent publications. Basic research into novel predictive assays, genetic polymorphisms, and new molecular methods to risk-stratify and to determine treatment options for sepsis have occupied much of the Critical Care publications relating to sepsis pathophysiology in 2008. We will attempt to briefly summarize what we consider to be the most significant contributions to the sepsis literature over the last year, and their likely ramifications in the future, for critical care clinicians, clinical investigators and basic researchers alike
A New System of Parallel Isolated Nonthermal Filaments Near the Galactic Center: Evidence for a Local Magnetic Field Gradient
We report the discovery of a system of isolated nonthermal filaments
approximately 0.5 deg. northwest (75 pc in projection) of Sgr A. Unlike other
isolated nonthermal filaments which show subfilamentation, braiding of
subfilaments, and flaring at their ends, these filaments are simple linear
structures and more closely resemble the parallel bundled filaments in the
Galactic center radio arc. However, the most unusual feature of these filaments
is that the 20/90 cm spectral index uniformly decreases as a function of
length, in contrast to all other nonthermal filaments in the Galactic center.
This spectral gradient may not be due to simple particle aging but could be
explained by a curved electron energy spectrum embedded in a diverging magnetic
field. If so, the scale of the magnetic gradient is not consistent with a large
scale magnetic field centered on Sgr A* suggesting that this filament system is
tracing a local magnetic field.Comment: 10 pages, AASTeX 5.01 LaTeX2e; 7 figures in 9 PostScript files;
scheduled for publication in the 2001 December 10, v. 563 issue of Ap
Australia Telescope Compact Array Radio Continuum 1384 and 2368 Mhz Observations of Sagittarius B
We present images of the Sagittarius (Sgr) B giant molecular cloud at 2368
and 1384 MHz obtained using new, multi-configuration Australia Telescope
Compact Array (ATCA) observations. We have combined these observations with
archival single-dish observations yielding images at resolutions of 47" by 14"
and 27" by 8" at 1384 and 2368 MHz respectively. These observations were
motivated by our theoretical work (Protheroe et al. 2008) indicating the
possibility that synchrotron emission from secondary electrons and positrons
created in hadronic cosmic ray (CR) collisions with the ambient matter of the
Sgr B2 cloud could provide a detectable (and possibly linearly polarized)
non-thermal radio signal. We find that the only detectable non-thermal emission
from the Sgr B region is from a strong source to the south of Sgr B2, which we
label Sgr B2 Southern Complex (SC). We find Sgr B2(SC) integrated flux
densities of 1.2+/-0.2 Jy at 1384 MHz and 0.7+/-0.1 Jy at 2368 MHz for a source
of FWHM size at 1384 MHz of ~54". Despite its non-thermal nature, the
synchrotron emission from this source is unlikely to be dominantly due to
secondary electrons and positrons. We use polarization data to place 5-sigma
upper limits on the level of polarized intensity from the Sgr B2 cloud of 3.5
and 3 mJy/beam at 1384 and 2368 MHz respectively. We also use the angular
distribution of the total intensity of archival 330 MHz VLA and the total
intensity and polarized emission of our new 1384 MHz and 2368 MHz data to
constrain the diffusion coefficient for transport of the parent hadronic CRs
into the dense core of Sgr B2 to be no larger than about 1% of that in the
Galactic disk. Finally, we have also used the data to perform a spectral and
morphological study of the features of the Sgr B cloud and compare and contrast
these to previous studies.Comment: 7 pages, 4 figures, matches version published in the Astronomical
Journa
Assessing the Feasibility of Cosmic-Ray Acceleration by Magnetic Turbulence at the Galactic Center
The presence of relativistic particles at the center of our galaxy is
evidenced by the diffuse TeV emission detected from the inner
of the Galaxy. Although it is not yet entirely clear whether the origin of the
TeV photons is due to hadronic or leptonic interactions, the tight correlation
of the intensity distribution with the distribution of molecular gas along the
Galactic ridge strongly points to a pionic-decay process involving relativistic
protons. In earlier work, we concluded that point-source candidates, such as
the supermassive black hole Sagittarius A* (identified with the HESS source
J1745-290), or the pulsar wind nebulae dispersed along the Galactic plane,
could not account for the observed diffuse TeV emission from this region.
Motivated by this result, we consider here the feasibility that the cosmic rays
populating the Galactic Center (GC) region are accelerated in situ by magnetic
turbulence. Our results indicate that even in a highly conductive environment,
this mechanism is efficient enough to energize protons within the intercloud
medium to the \ga TeV energies required to produce the HESS emission.Comment: Accepted for publication in Ap
Identifikasi Sumberdaya Kepiting Bakau (Scylla SP.) Yang Didaratkan Di Tpi Kabupaten Tapanuli Tengah
Salah satu sumberdaya perikanan di wilayah perairan Indonesia adalah kepiting bakau namun informasi mengenai keberadaan kepiting bakau khususnya jenis–jenisnya masih terbatas begitu juga pada wilayah perairan Kabupaten Tapanuli Tengah. Untuk mengatasi permasalahan tersebut perlu dilakukan identifikasi jenis morfologi kepiting bakau.Penelitian yang dilaksanakan pada bulan Januari-Februari 2011 ini adalah untuk mengetahui jenis dan morfologi kepiting bakau, kelimpahan dan dominasi kepiting bakau, serta mengetahui nilai komersil kepiting bakau di wilayah Kabupaten Tapanuli Tengah Sumatera Utara. Sampel yang diteliti adalah kepiting bakau yang didaratkan di 3 (tiga) TPI yaitu Desa Hajoran, Desa Poriaha dan Desa Sijago-jago Kabupaten Tapanuli Tengah. Kepiting yang tertangkap oleh nelayan diidentifikasi dan dilakukan pengukuran morfometrik kemudian menganalisis data yang didapatkan, dan wawancara nelayan untuk mengetahui berat komersil dan kisaran harga kepiting bakau tersebut. Jumlah spesies kepiting bakau yang ditemukan adalah 3 (tiga) spesies yaitu Scylla serrata (63.41%), Scylla olivacea (26.22 %), dan Scylla tranquebarica (10.37 %) dari sampel yang berjumlah 164 individu. Kepiting yang mendominasi adalah Scylla serrata. Kepiting bakau yang biasanya dipasarkan adalah kepiting yang memiliki berat ≥250 gram per ekor dengan harga Rp. 35.000/kg
The Sound Emission Board of the KM3NeT Acoustic Positioning System
We describe the sound emission board proposed for installation in the
acoustic positioning system of the future KM3NeT underwater neutrino telescope.
The KM3NeT European consortium aims to build a multi-cubic kilometre underwater
neutrino telescope in the deep Mediterranean Sea. In this kind of telescope the
mechanical structures holding the optical sensors, which detect the Cherenkov
radiation produced by muons emanating from neutrino interactions, are not
completely rigid and can move up to dozens of meters in undersea currents.
Knowledge of the position of the optical sensors to an accuracy of about 10 cm
is needed for adequate muon track reconstruction. A positioning system based on
the acoustic triangulation of sound transit time differences between fixed
seabed emitters and receiving hydrophones attached to the kilometre-scale
vertical flexible structures carrying the optical sensors is being developed.
In this paper, we describe the sound emission board developed in the framework
of KM3NeT project, which is totally adapted to the chosen FFR SX30 ultrasonic
transducer and fulfils the requirements imposed by the collaboration in terms
of cost, high reliability, low power consumption, high acoustic emission power
for short signals, low intrinsic noise and capacity to use arbitrary signals in
emission mode.Comment: 9 pages, 4 figure
The magnetic environment in the central region of nearby galaxies
The central regions of galaxies harbor some of the most extreme physical
phenomena, including dense stellar clusters, non-circular motions of molecular
clouds and strong and pervasive magnetic field structures. In particular, radio
observations have shown that the central few hundred parsecs of our Galaxy has
a striking magnetic field configuration. It is not yet clear whether these
magnetic structures are unique to our Milky Way or a common feature of all
similar galaxies. Therefore, we report on (a) a new radio polarimetric survey
of the central 200 pc of the Galaxy to better characterize the magnetic field
structure and (b) a search for large-scale and organized magnetized structure
in the nuclear regions of nearby galaxies using data from the Very Large Array
(VLA) archive. The high angular resolution of the VLA allows us to study the
central 1 kpc of the nearest galaxies to search for magnetized nuclear features
similar to what is detected in our own Galactic center. Such magnetic features
play a important role in the nuclear regions of galaxies in terms of gas
transport and the physical conditions of the interstellar medium in this
unusual region of galaxies.Comment: 8 pages; Proceedings for "The Universe under the Microscope" (AHAR
2008), held in Bad Honnef (Germany) in April 2008, to be published in Journal
of Physics: Conference Series by Institute of Physics Publishing, R.
Schoedel, A. Eckart, S. Pfalzner, and E. Ros (eds.
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