4,289 research outputs found
Experimental evidence of thermal fluctuations on the X-ray absorption near-edge structure at the aluminum K-edge
After a review of temperature-dependent experimental x-ray absorption
near-edge structure (XANES) and related theoretical developments, we present
the Al K-edge XANES spectra of corundum and beryl for temperature ranging from
300K to 930K. These experimental results provide a first evidence of the role
of thermal fluctuation in XANES at the Al K-edge especially in the pre-edge
region. The study is carried out by polarized XANES measurements of single
crystals. For any orientation of the sample with respect to the x-ray beam, the
pre-edge peak grows and shifts to lower energy with temperature. In addition
temperature induces modifications in the position and intensities of the main
XANES features. First-principles DFT calculations are performed for both
compounds. They show that the pre-edge peak originates from forbidden 1s to 3s
transitions induced by vibrations. Three existing theoretical models are used
to take vibrations into account in the absorption cross section calculations:
i) an average of the XANES spectra over the thermal displacements of the
absorbing atom around its equilibrium position, ii) a method based on the crude
Born-Oppenheimer approximation where only the initial state is averaged over
thermal displacements, iii) a convolution of the spectra obtained for the atoms
at the equilibrium positions with an approximate phonon spectral function. The
theoretical spectra so obtained permit to qualitatively understand the origin
of the spectral modifications induced by temperature. However the correct
treatment of thermal fluctuation in XANES spectroscopy requires more
sophisticated theoretical tools
Topology of event distribution as a generalized definition of phase transitions in finite systems
We propose a definition of phase transitions in finite systems based on
topology anomalies of the event distribution in the space of observations. This
generalizes all the definitions based on the curvature anomalies of
thermodynamical potentials and provides a natural definition of order
parameters. The proposed definition is directly operational from the
experimental point of view. It allows to study phase transitions in Gibbs
equilibria as well as in other ensembles such as the Tsallis ensemble.Comment: 4 pages, 3 figure
Review of tau lifetime measurements
The measurements of the mean lifetime of the tau lepton are reviewed. The
conditions for measuring the lifetime at various e+e- colliders are compared
and the analysis methods are briefly described. The new developments since the
previous Workshop on Tau Lepton Physics are listed. The world average is
tau_tau = 290.5 +- 1.0 fs. The LEP experiments dominate this average and have
analyzed nearly all of their data. In anticipation of the next era of precision
measurements at CLEO and the b factories, the important sources of systematic
errors and the treatment of systematic biases are discussed.Comment: Invited talk presented at the Fifth International Workshop on Tau
Lepton Physics, Santander, Spain, 14-17 September 1998; 10 pages, 8 figure
Preclinical Evaluation of Antitumor Efficacy of a New Radiopharmaceutical Based on Thermoresponsive Carrier and Samarium-153
This work is devoted to studying the in vivo antitumor efficacy of the new injection radiopharmaceutical based on thermoresponsive polymer and ÎČâ-emitting radionuclide samarium-153 (153Sm-KARP-CheM). The study of in vivo antitumor efficacy was performed using mice F1 and C57Bl/6 with transplanted subcutaneously sarcoma S37 and melanoma B16, respectively. The animals received single intratumoral bolus injections of 37 MBq (1 mCi), or 18.5 MBq (0.5 mCi) of 153Sm-KARP-CheM, or saline in a volume 0.1 ml. The efficacy of antitumortreatment was evaluated using tumor growth inhibition index (TGI, %) and increase of average life span (ILS, %). The most meaningful therapeutic efficacy after intratumoral injection of 153Sm-KARPCheM was observed in melanoma-bearing mice C57Bl/6. The highest values of TGI for melanoma B16 were 79.5% and 79.6% after treatment with 18.5 MBq or 37 MBq, respectively. An increase of average life span by 17.1% was found in group of melanoma-bearing mice treated with 37 MBq of 153Sm-KARP-CheM only. Tumor growth inhibition of sarcoma S37 was slightly lower as compared with melanoma B16: 62.5% and 59.0% in 37 MBq and 18.5 MBq groups, respectively. 153Sm-KARP-CheM didnât increase average life span of treated animals. In conclusion, 153Sm-KARP-CheM seems to be effective radiopharmaceutical for local tumor radiotherapy.
Keywords: thermoresponsive polymer, samarium-153, radionuclide therapy of cancer, sarcoma S37, melanoma B16, antitumor efficacy
Test of the Running of in Decays
The decay rate into hadrons of invariant mass smaller than
can be calculated in QCD assuming global
quark--hadron duality. It is shown that this assumption holds for
~GeV. From measurements of the hadronic mass distribution, the
running coupling constant is extracted in the range
0.7~GeV. At , the result is
. The running of is in good
agreement with the QCD prediction.Comment: 9 pages, 3 figures appended; shortened version with new figures, to
appear in Physical Review Letters (April 1996
Gamma-Ray Burst Sequences in Hardness Ratio-Peak Energy Plane
The narrowness of the distribution of the peak energy of
spectrum of gamma-ray bursts (GRBs) and the unification of GRB population are
great puzzles yet to be solved. We investigate the two puzzles based on the
global spectral behaviors of different GRB population in the
plane (HR the spectral hardness ratio) with BATSE and HETE-2 observations. It
is found that long GRBs and XRFs observed by HETE-2 seem to follow the same
sequence in the plane, with the XRFs at the low end of this
sequence. The long and short GRBs observed by BATSE follow significantly
different sequences in the plane, with most of the short GRBs
having a larger hardness ratio than the long GRBs at a given .
These results indicate that the global spectral behaviors of the long GRB
sample and the XRF sample are similar, while that of short GRBs is different.
The short GRBs seem to be a unique subclass of GRBs, and they are not the
higher energy extension of the long GRBs (abridged).Comment: 9 pages, 3 figure
The OSACA Database and a Kinematic Analysis of Stars in the Solar Neighborhood
We transformed radial velocities compiled from more than 1400 published
sources, including the Geneva--Copenhagen survey of the solar neighborhood
(CORAVEL-CfA), into a uniform system based on the radial velocities of 854
standard stars in our list. This enabled us to calculate the average weighted
radial velocities for more than 25~000 HIPPARCOS stars located in the local
Galactic spiral arm (Orion arm) with a median error of +-1 km/s. We use these
radial velocities together with the stars' coordinates, parallaxes, and proper
motions to determine their Galactic coordinates and space velocities. These
quantities, along with other parameters of the stars, are available from the
continuously updated Orion Spiral Arm CAtalogue (OSACA) and the associated
database. We perform a kinematic analysis of the stars by applying an
Ogorodnikov-Milne model to the OSACA data. The kinematics of the nearest single
and multiple main-sequence stars differ substantially. We used distant
(r\approx 0.2 kpc) stars of mixed spectral composition to estimate the angular
velocity of the Galactic rotation -25.7+-1.2 km/s/kpc, and the vertex
deviation,l=13+-2 degrees, and detect a negative K effect. This negative K
effect is most conspicuous in the motion of A0-A5 giants, and is equal to
K=-13.1+-2.0 km/s/kpc.Comment: 16 pages, 8 figure
The Structure of the Local Interstellar Medium. II. Observations of D I, C II, N I, O I, Al II, and Si II toward Stars within 100 parsecs
Moderate and high-resolution measurements (R ~ 40,000) of interstellar
resonance lines of D I, C II, N I, O I, Al II, and Si II (light ions) are
presented for all available observed targets located within 100 pc which also
have high-resolution observations of interstellar Fe II or Mg II (heavy ions)
lines. All spectra were obtained with the Goddard High Resolution Spectrograph
or the Space Telescope Imaging Spectrograph instruments aboard the Hubble Space
Telescope. Currently, there are 41 sightlines to targets within 100 pc with
observations that include a heavy ion at high resolution and at least one light
ion at moderate or high resolution. We present new measurements of light ions
along 33 of these sightlines, and collect from the literature results for the
remaining sightlines that have already been analyzed. We greatly increase the
number of sightlines with useful LISM absorption line measurements of light
ions by using knowledge of the kinematic structure along a line of sight
obtained from high resolution observations of intrinsically narrow absorption
lines, such as Fe II and Mg II. Because high resolution observations of heavy
ions are critical for understanding the kinematic structure of local absorbers
along the line of sight, we include 18 new measurements of Fe II and Mg II in
an appendix. We present a statistical analysis of the LISM absorption
measurements, which provides an overview of some physical characteristics of
warm clouds in the LISM, including temperature and turbulent velocity. This
complete collection and reduction of all available LISM absorption measurements
provides an important database for studying the structure of nearby warm
clouds, including ionization, abundances, and depletions.Comment: 50 pages, 21 figures; Accepted for publication in ApJ (vol. 602,
February 20, 2004
Radial velocities of early-type stars in the Perseus OB2 association
We present radial velocities for 29 B- and A-type stars in the field of the
nearby association Perseus OB2. The velocities are derived from spectra
obtained with AURELIE, via cross correlation with radial velocity standards
matched as closely as possible in spectral type. The resulting accuracy is ~2 -
3 km s. We use these measurements, together with published values for a
few other early-type stars, to study membership of the association. The mean
radial velocity (and measured velocity dispersion) of Per OB2 is 23.5 \pm 3.9
km s, and lies ~15 km s away from the mean velocity of the local
disk field stars. We identify a number of interlopers in the list of possible
late-B- and A-type members which was based on Hipparcos parallaxes and proper
motions, and discuss the colour-magnitude diagram of the association.Comment: 20 pages, 9 figures, accepted for publication in A&A, minor revision
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