34,342 research outputs found
Formulating Light Cone QCD on the Lattice
We present the near light cone Hamiltonian in lattice QCD depending on
the parameter , which gives the distance to the light cone. Since the
vacuum has zero momentum we can derive an effective Hamiltonian from
which is only quadratic in the momenta and therefore solvable by standard
methods. An approximate ground state wave functional is determined
variationally in the limit .Comment: 48 pages, 8 figure
The Spectral Evolution of Transient Anomalous X-ray Pulsar XTE J1810--197
(Abridged) We present a multi-epoch spectral study of the Transient Anomalous
X-ray Pulsar XTE J1810-197 obtained with the XMM X-ray telescope. Four
observations taken over the course of a year reveal strong spectral evolution
as the source fades from outburst. The origin of this is traced to the
individual decay rates of the pulsar's spectral components. A 2-T fit at each
epoch requires nearly constant temperatures of kT=0.25 & 0.67 keV while the
component luminosities decrease exponentially with tau=900 & 300d,
respectively. One possible interpretation is that the slowly decaying cooler
component is the radiation from a deep heating event that affected a large
fraction of the crust, while the hotter component is powered by external
surface heating at the foot-points of twisted magnetic field lines, by
magnetospheric currents that are decaying more rapidly. The energy-dependent
pulse profile of XTE J1810-197 is well modeled at all epochs by the sum of a
sine and triangle function. These profiles peak at the same phase, suggesting a
concentric surface emission geometry. The spectral and pulse evolution together
argue against the presence of a significant ``power-law'' contribution to the
X-ray spectrum below 8 keV. The extrapolated flux is projected to return to the
historic quiescent level, characterized by an even cooler blackbody spectrum,
by the year 2007.Comment: 12 pages, 6 Figures, Latex, emulateapj. To appear in the
Astrophysical Journa
Tritium trick
Large controlled amounts of helium in uniform concentration in thick samples can be obtained through the radioactive decay of dissolved tritium gas to He3. The term, tritium trick, applies to the case when helium, added by this method, is used to simulate (n,alpha) production of helium in simulated hard flux radiation damage studies
Spectral analysis and abundances of the post-HB star HD 76431
HD76431 is a slow rotating post-HB star that shows an underabundance of
helium by 0.5 dex relative to the solar value. These observational facts
suggest that atomic diffusion could be active in its atmosphere. We have used
the MMT and Bok spectra to estimate the atmospheric parameters of the target
star using the model atmospheres and synthetic spectra calculated with TLUSTY
and SYNSPEC. The derived values of the effective temperature, surface gravity,
helium abundance are consistent with those obtained by Ramspeck et al. (2001b).
It appears that NLTE effect are not important for HD76431. We have used Stokes
I spectra from ESPaDOnS at CFHT to perform an abundance analysis and a search
for observational evidence of vertical stratification of the abundance of
certain elements. The results of our abundance analysis are in good agreement
with previously published data with respect to average abundances. Our
numerical simulations show that carbon and nitrogen reveal signatures of
vertical abundance stratification in the atmosphere of HD76431. It appears that
the carbon abundance increases toward the deeper atmospheric layers. Nitrogen
also shows a similar behaviour, but in deeper atmospheric layers we obtain a
significant dispersion for the estimates of its abundance. To our knowledge,
this is the first demonstration of vertical abundance stratification of metals
in a post-HB star and up to now it is the hottest star to show such
stratification features. We also report the detection of two SiIII and one
TiIII emission lines in the spectra of HD76431 that were not detected in
previous studies.Comment: 7 pages, 5 figures, accepted for publication in MNRA
The String Coupling Accelerates the Expansion of the Universe
Generic cosmological models in non-critical string theory have a
time-dependent dilaton background at a late epoch. The cosmological
deceleration parameter Q_0 is given by the square of the string coupling,
g_s^2, up to a negative sign. Hence the expansion of the Universe must
accelerate eventually, and the observed value of Q_0 coresponds to g_s^2 ~ 0.6.
In this scenario, the string coupling is asymptotically free at large times,
but its present rate of change is imperceptibly small.Comment: 7 page
Imaging X-ray, Optical, and Infrared Observations of the Transient Anomalous X-ray Pulsar XTE J1810-197
We report X-ray imaging, timing, and spectral studies of XTE J1810-197, a
5.54s pulsar discovered by Ibrahim et al. (2003) in recent RXTE observations.
In a set of short exposures with the Chandra HRC camera we detect a strongly
modulated signal (55+/-4% pulsed fraction) with the expected period located at
(J2000) 18:09:51.08, -19:43:51.7, with a uncertainty radius of 0.6 arcsec (90%
C.L.). Spectra obtained with XMM-Newton are well fitted by a two-component
model that typically describes anomalous X-ray pulsars (AXPs), an absorbed
blackbody plus power law with parameters kT = 0.67+/-0.01 keV, Gamma=3.7+/-0.2,
N_H=(1.05+/-0.05)E22 cm^-2, and Fx(0.5-10 keV) = 3.98E-11 ergs/cm2/s.
Alternatively, a 2T blackbody fit is just as acceptable. The location of CXOU
J180951.1-194351 is consistent with a point source seen in archival Einstein,
Rosat, & ASCA images, when its flux was nearly two orders-of-magnitude fainter,
and from which no pulsations are found. The spectrum changed dramatically
between the "quiescent" and "active" states, the former can be modeled as a
softer blackbody. Using XMM timing data, we place an upper limit of 0.03 lt-s
on any orbital motion in the period range 10m-8hr. Optical and infrared images
obtained on the SMARTS 1.3m telescope at CTIO show no object in the Chandra
error circle to limits V=22.5, I=21.3, J=18.9, & K=17.5. Together, these
results argue that CXOU J180951.1-194351 is an isolated neutron star, one most
similar to the transient AXP AX J1844.8-0256. Continuing study of XTE J1810-197
in various states of luminosity is important for understanding and possibly
unifying a growing class of isolated, young neutron stars that are not powered
by rotation.Comment: 12 pages, 7 figures, AAS LaTex, uses emulateapj5.sty. Updated to
include additional archival data and a new HRC observation. To appear in The
Astrophysical Journa
High-resolution spectropolarimetric observations of hot subdwarfs
We report on high-resolution spectropolarimetric observations of the hot
subdwarf stars HD 76431 and Feige 66, using the ESPaDOnS echelle
spectropolarimeter at CFHT. We compute cross-correlation Stokes I and V line
profiles to enhance the signal-to-noise ratio. We then average all available
cross-correlation profiles of each star to further decrease the noise level.
Although both targets were previously reported to host kilo-gauss magnetic
fields, we do not derive any evidence of large-scale photospheric fields from
our sets of observations, in spite of tight error bars on the longitudinal
field of the order of 60 gauss for HD 76431 and 200 gauss for Feige 66. A new
analysis of FORS1 observations of HD 76431, which provided the basis for the
original claim of field detection, confirms the absence of any detectable
Zeeman signature, with an error bar of about 100 gauss on the longitudinal
magnetic field.Comment: Proceedings of the fifth meeting on hot subdwarf stars and related
object
A Womanist Supervision Framework for Promoting Anti-Racist Therapy with Black Women
A counselor’s anti-racist disposition is particularly needed for Black woman clients due to unique treatment needs. Womanist values and pedagogy are used to develop a culturally-responsive supervision framework encompassing key themes of anti-racist supervisee development such as critical consciousness development, awareness of power dynamics, social justice activism and honoring the cultural self. Womanist pedagogy, previously used in K-12 schools, prioritizes the community orientation of maternal care to promote the survival of Black people in oppressive systems. A call to action for counselor educators is introduced for the promotion of an anti-racist supervisee disposition. Keywords: anti-racist, supervision, Womanist, critical consciousnes
Semiclassical correlators of three states with large S^5 charges in string theory in AdS_5 x S^5
We consider semiclassical computation of 3-point correlation functions of
(BPS or non-BPS) string states represented by vertex operators carrying large
charges in S5. We argue that the AdS5 part of the construction of relevant
semiclassical solution involves the two basic ingredients: (i) configuration of
three glued geodesics in AdS2 suggested by Klose and McLoughlin in
arXiv:1106.0495 and (ii) a particular Schwarz-Christoffel map of the 3-geodesic
solution in cylindrical (tau, sigma) domain into the complex plane with three
marked points. This map is constructed using the expression for the AdS2 string
stress tensor which is uniquely determined by the 3 scaling dimensions as noted
by Janik and Wereszczynski in arXiv:1109.6262 (our solution, however, is
different from theirs). We also find the S5 part of the solution and thus the
full expression for the semiclassical part of the 3-point correlator for
several examples: extremal and non-extremal correlators of BPS states and a
particular correlator of "small" circular spinning strings in S3 part of S5. We
demonstrate that for the BPS correlators the results agree with the large
charge limit of the corresponding supergravity and free gauge theory
expressions.Comment: 43 pages, 4 figures; v2: minor corrections; v3: comments added at the
end of section 3 and in section 5; v4: minor corrections; v5: discussion in
subsection 3.3 correcte
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