627 research outputs found
Second Harmonic Operation at 460 GHz and Broadband Continuous Frequency Tuning of a Gyrotron Oscillator
The First Measurement of Spectral Lines in a Short-Period Star Bound to the Galaxy's Central Black Hole: A Paradox of Youth
We have obtained the first detection of spectral absorption lines in one of
the high-velocity stars in the vicinity of the Galaxy's central supermassive
black hole. Both Brgamma (2.1661 micron) and He I (2.1126 micron) are seen in
absorption in S0-2 with equivalent widths (2.8+-0.3 Ang & 1.7+-0.4 Ang) and an
inferred stellar rotational velocity (220+-40 km/s) that are consistent with
that of an O8-B0 dwarf, which suggests that it is a massive (~15 Msun), young
(<10 Myr) main sequence star. This presents a major challenge to star formation
theories, given the strong tidal forces that prevail over all distances reached
by S0-2 in its current orbit (130 - 1900 AU) and the difficulty in migrating
this star inward during its lifetime from further out where tidal forces should
no longer preclude star formation. The radial velocity measurements (-510+-40
km/s) and our reported proper motions for S0-2 strongly constrain its orbit,
providing a direct measure of the black hole mass of 4.1(+-0.6)x10^6(Ro/8kpc)^3
Msun. The Keplerian orbit parameters have uncertainities that are reduced by a
factor of 2-3 compared to previously reported values and include, for the first
time, an independent solution for the dynamical center; this location, while
consistent with the nominal infrared position of Sgr A*, is localized to a
factor of 5 more precisely (+-2 milli-arcsec). Furthermore, the ambiguity in
the inclination of the orbit is resolved with the addition of the radial
velocity measurement, indicating that the star is behind the black hole at the
time of closest approach and counter-revolving against the Galaxy. With further
radial velocity measurements in the next few years, the orbit of S0-2 will
provide the most robust estimate of the distance to the Galactic Center.Comment: 14 pages, Latex, Accepted for Publication in ApJ Letter
Accretion models of Sgr A*
The supermassive black hole in the center of our Galaxy, Sgr A*, is unique
because the angular size of the black hole is the largest in the sky thus
providing detailed boundary conditions on, and much less freedom for, accretion
flow models. In this paper I review advection-dominated accretion flow (ADAF;
another name is radiatively inefficient accretion flow) models for Sgr A*. This
includes the developments and dynamics of ADAFs, and how to explain
observational results including the multi-waveband spectrum, radio
polarization, IR and X-ray flares, and the size measurements at radio
wavebands.Comment: 9 pages, 6 figures; invited talk presented at the "Galactic Center
Workshop 2006: From the Center of the Milky Way to Nearby Low-Luminosity
Galactic Nuclei", April 18-22, 2006; Bad Honnef, German
Circulating miR-181 is a prognostic biomarker for amyotrophic lateral sclerosis
Amyotrophic lateral sclerosis (ALS) is a relentless neurodegenerative disease of the human motor neuron system, where variability in progression rate limits clinical trial efficacy. Therefore, better prognostication will facilitate therapeutic progress. In this study, we investigated the potential of plasma cell-free microRNAs (miRNAs) as ALS prognostication biomarkers in 252 patients with detailed clinical phenotyping. First, we identified, in a longitudinal cohort, miRNAs whose plasma levels remain stable over the course of disease. Next, we showed that high levels of miR-181, a miRNA enriched in neurons, predicts a greater than two-fold risk of death in independent discovery and replication cohorts (126 and 122 patients, respectively). miR-181 performance is similar to neurofilament light chain (NfL), and when combined together, miR-181 + NfL establish a novel RNA–protein biomarker pair with superior prognostication capacity. Therefore, plasma miR-181 alone and a novel miRNA–protein biomarker approach, based on miR-181 + NfL, boost precision of patient stratification. miR-181-based ALS biomarkers encourage additional validation and might enhance the power of clinical trials
An evolving hot spot orbiting around Sgr A*
Here we report on recent near-infrared observations of the Sgr A* counterpart
associated with the super-massive ~ 4x10^6 M_sun black hole at the Galactic
Center. We find that the May 2007 flare shows the highest sub-flare contrast
observed until now, as well as evidence for variations in the profile of
consecutive sub-flares. We modeled the flare profile variations according to
the elongation and change of the shape of a spot due to differential rotation
within the accretion disk.Comment: 7 pages, 5 figures, contribution for the conference "The Universe
under the Microscope" (AHAR 2008), to be published in Journal of Physics:
Conference Series by Institute of Physics Publishin
Overtly anaphoric control in type logical grammar
In this paper we analyse anaphoric pronouns in control sentences and we investigate the implications of these kinds of sentences in relation to the Propositional Theory versus Property Theory question. For these purposes, we invoke the categorial calculus with limited contraction, a conservative extension of Lambek calculus that builds contraction into the logical rules for a customized slash type-constructor.Peer ReviewedPostprint (author's final draft
Evaluation of Methodologies for Microrna Biomarker Detection by Next Generation Sequencing
In recent years, microRNAs (miRNAs) in tissues and biofluids have emerged as a new class of promising biomarkers for numerous diseases. Blood-based biomarkers are particularly desirable since serum or plasma is easily accessible and can be sampled repeatedly. To comprehensively explore the biomarker potential of miRNAs, sensitive, accurate and cost-efficient miRNA profiling techniques are required. Next generation sequencing (NGS) is emerging as the preferred method for miRNA profiling; offering high sensitivity, single-nucleotide resolution and the possibility to profile a considerable number of samples in parallel. Despite the excitement about miRNA biomarkers, challenges associated with insufficient characterization of the sequencing library preparation efficacy, precision and method-related quantification bias have not been addressed in detail and are generally underappreciated in the wider research community.
Here, we have tested in parallel four commercially available small RNA sequencing kits against a cohort of samples comprised of human plasma, human serum, murine brain tissue and a reference library containing ~ 950 synthetic miRNAs. We discuss the advantages and limits of these methodologies for massive parallel microRNAs profiling. This work can serve as guideline for choosing an adequate library preparation method, based on sensitivity, specificity and accuracy of miRNA quantification, workflow convenience and potential for automation
Influence of the re-scattering process on polarization observables in reaction gamma + d --> p + p + pi- in Delta - resonance region
Influence of the effects of the pion-nucleon and nucleon-nucleon
re-scattering on the polarization observables of the reaction gamma + d = p + p
+ pi- in Delta - isobar region is investigated. Pion-nucleon and
nucleon-nucleon re-scattering are studied in the diagrammatic approach.
Relativistic-invariant forms of the pion photoproduction and pion-nucleon
scattering operators are used. The unitarization procedure in K-matrix approach
is applied for the resonance partial amplitudes. It is shown a considerable
influence of the re-scattering effects on the polarization observables of this
reaction in the Delta - resonance region for the large momenta of the final
protons.Comment: 16 pages, 5 Postscript figure
Passives and Se Constructions
In this chapter we discuss some of the main properties of constructions involving participial passives, passive se, and impersonal se in Portuguese, focusing on its two main varieties, European and Brazilian Portuguese (henceforth EP and BP, respectively).1 When the two dialects differ, we will provide the relevant judgments each dialect assigns to the data under discussion by using the abbreviations EP and BP.
The chapter is organized in five sections. Section 2 deals with participial passives, distinguishing between adjectival and verbal passives and between the participial forms of passives and compound tenses. Section 3 focuses on passive se and impersonal se constructions, comparing them with verbal passives when appropriate. Section 4 concludes the paper.info:eu-repo/semantics/publishedVersio
- …