1,128 research outputs found
Measurement of the analyzing power of proton-carbon elastic scattering in the CNI region at RHIC
The single transverse spin asymmetry, A_N, of the p-carbon elastic scattering
process in the Coulomb Nuclear Interference (CNI) region was measured using an
ultra thin carbon target and polarized proton beam in the Relativistic Heavy
Ion Collider (RHIC) at Brookhaven National Laboratory (BNL). In 2004, data were
collected to calibrate the p-carbon process at two RHIC energies (24 GeV, 100
GeV). A_N was obtained as a function of momentum transfer -t. The results were
fit with theoretical models which allow us to assess the contribution from a
hadronic spin flip amplitude.Comment: Contribution to the proceedings of the 16th International Spin
Physics Symposium, spin2004 (Trieste
RHIC polarimetry
Polarimeters were developed to measure the polarization of the proton beam at RHIC in relative scale through the asymmetry measurement of the elastic proton-carbon scattering. Recoil carbon ions with kinetic energy of 400 †E †900 keV were detected by silicon strip detectors installed at 90° with respect to the beam. The absolute polarization is given by normalizing against another polarimeter implemented at RHIC, namely a polarized hydrogen gas jet polarimeter. In this report, the details of polarization measurements, data analysis, and systematic uncertainties are discussed based on the data taken during â«s = 200 GeV operation of Run 05 at RHIC
Study of the Largest Multiwavelength Campaign of the Microquasar GRS 1915+105
We present the results from a multiwavelength campaign of GRS 1915+105
performed from 2000 April 16 to 25. This is one of the largest coordinated set
of observations ever performed for this source, covering the wide energy band
in radio (13.3-0.3 cm), near-infrared (J-H-K), X-rays and Gamma-rays (from 1
keV to 10 MeV). During the campaign GRS 1915+105 was predominantly in the
"plateau" (or low/hard) state but sometimes showed soft X-ray oscillations:
before April 20.3, rapid, quasi-periodic (~= 45 min) flare-dip cycles were
observed. The radio flares observed on April 17 shows frequency- dependent peak
delay, consistent with an expansion of synchrotron-emitting region starting at
the transition from the hard-dip to the soft-flare states in X-rays. On the
other hand, infrared flares on April 20 appear to follow (or precede) the
beginning of X-ray oscillations with an inconstant time delay of ~= 5-30 min.
This implies that the infrared emitting region is located far from the black
hole by >~ 10E13 cm, while its size is <~ 10E12 cm constrained from the time
variability. We find a good correlation between the quasi-steady flux level in
the near-infrared band and in the X-ray band. From this we estimate that the
reprocessing of X-rays, probably occurring in the outer parts of the accretion
disk, accounts for about 20-30% of the observed K magnitude in the plateau
state. The OSSE spectrum in the 0.05-10 MeV band is represented by a single
power law with a photon index of 3.1 extending to ~1 MeV with no cutoff. The
power-law slope above ~30 keV is found to be very similar between different
states in spite of large flux variations in soft X-rays, implying that the
electron energy distribution is not affected by the change of the state in the
accretion disk.Comment: 31 pages, 11 figures. Accepted for publication in ApJ, vol. 571,
2002. Minor corrections. Figure 2 is revised (numbers on the top axis are
corrected). References are update
Understanding signaling cascades in melanoma
Understanding regulatory pathways involved in melanoma development and progression has advanced significantly in recent years. It is now appreciated that melanoma is the result of complex changes in multiple signaling pathways that affect growth control, metabolism, motility and the ability to escape cell death programs. Here we review the major signaling pathways currently known to be deregulated in melanoma with an implication to its development and progression. Among these pathways are Ras, B-Raf, MEK, PTEN, phosphatidylinositol-3 kinase (PI3Ks) and Akt which are constitutively activated in a significant number of melanoma tumors, in most cases due to genomic change. Other pathways discussed in this review include the [Janus kinase/signal transducer and activator of transcription (JAK/STAT), transforming growth factor-beta pathways which are also activated in melanoma, although the underlying mechanism is not yet clear. As a paradigm for remodeled signaling pathways, melanoma also offers a unique opportunity for targeted drug development.Fil: Lopez Bergami, Pablo Roberto. Sanford-burnham Medical Research Institute; Estados Unidos. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Instituto de BiologĂa y Medicina Experimental. FundaciĂłn de Instituto de BiologĂa y Medicina Experimental. Instituto de BiologĂa y Medicina Experimental; ArgentinaFil: Fitchmann, B. Sanford-burnham Medical Research Institute; Estados UnidosFil: Ronai, ZeÂŽev. Sanford-burnham Medical Research Institute; Estados Unido
Energy Dependence of a Low Frequency QPO in GRS 1915+105
We analyze a set of three RXTE Target of Opportunity observations of the
Galactic microquasar GRS 1915+105, observed on April 2000, during a
multi-wavelength campaign.
During the three observations, a strong, variable low frequency (2-9 Hz)
quasi periodic oscillation (hereafter QPO), often referred to as the ubiquitous
QPO, is detected together with its first harmonic. We study the spectral
properties of both features, and show that : 1) their frequency variations are
better correlated with the soft X-ray flux (2-5 keV), favoring thus the
location of the QPO in the accretion disk; 2) the QPO affects more the hard
X-rays, usually taken as the signature of an inverse compton scattering of the
soft photons in a corona; 3) the fundamental and its harmonic do not behave in
the same manner: the fundamental sees its power increase with the energy up to
40 keV, whereas the harmonic increases up to keV. The results
presented here could find an explanation in the context of the
Accretion-Ejection Instability, which could appear as a rotating spiral or hot
point located in the disk, between its innermost edge and the corotation
radius. The presence of the harmonic could then be a signature of the
non-linear behavior of the instability. The high-energy (>40 keV) decrease of
the fundamental would favor an interpretation where most or all of the
quasi-periodic modulation at high energies comes, not from the comptonized
corona as usually assumed, but from a hot point in the optically thick diskComment: 8 pages, 7 figures, accepted for publication in Astronomy and
Astrophysic
MOJAVE: Monitoring of Jets in Active Galactic Nuclei with VLBA Experiments. VI. Kinematics Analysis of a Complete Sample of Blazar Jets
We discuss the jet kinematics of a complete flux-density-limited sample of
135 radio-loud active galactic nuclei (AGN) resulting from a 13 year program to
investigate the structure and evolution of parsec-scale jet phenomena. Our
analysis is based on new 2 cm Very Long Baseline Array (VLBA) images obtained
between 2002 and 2007, but includes our previously published observations made
at the same wavelength, and is supplemented by VLBA archive data. In all, we
have used 2424 images spanning the years 1994-2007 to study and determine the
motions of 526 separate jet features in 127 jets. The data quality and temporal
coverage (a median of 15 epochs per source) of this complete AGN jet sample
represents a significant advance over previous kinematics surveys. In all but
five AGNs, the jets appear one-sided, most likely the result of differential
Doppler boosting. In general the observed motions are directed along the jet
ridge line, outward from the optically thick core feature. We directly observe
changes in speed and/or direction in one third of the well-sampled jet
components in our survey. While there is some spread in the apparent speeds of
separate features within an individual jet, the dispersion is about three times
smaller than the overall dispersion of speeds among all jets. This supports the
idea that there is a characteristic flow that describes each jet, which we have
characterized by the fastest observed component speed. The observed maximum
speed distribution is peaked at ~10c, with a tail that extends out to ~50c.
This requires a distribution of intrinsic Lorentz factors in the parent
population that range up to ~50. We also note the presence of some rare
low-pattern speeds or even stationary features in otherwise rapidly flowing
jets... (abridged)Comment: 19 pages, 10 figures, 2 tables, accepted by the Astronomical Journal;
online only material is available from
http://www.cv.nrao.edu/2cmVLBA/pub/MOJAVE_VI_suppl.zi
Measurement of the Pion Form Factor in the Energy Range 1.04-1.38 GeV with the CMD-2 Detector
The cross section for the process is measured in the
c.m. energy range 1.04-1.38 GeV from 995 000 selected collinear events
including 860000 events, 82000 events, and 33000
events. The systematic and statistical errors of measuring the
pion form factor are equal to 1.2-4.2 and 5-13%, respectively.Comment: 5 pages, 2 figure
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