9,495 research outputs found
E 0336-248 : A New BL Lac Object Found by an Old Einstein
We obtained new ROSAT HRI and optical observations in the field of the
Einstein X-ray source E 0336-248, which we use to identify it as a 19th
magnitude BL Lacertae object at z=0.251 with an X-ray luminosity of 10^45
erg/s. It is also a 14 mJy radio source at 20 cm. An emission-line galaxy at
z=0.043 that was previously considered a Seyfert identification for E 0336-248
is shown instead to be an unrelated, non-active H II region galaxy that lies 78
arcseconds from the X-ray source. The resolution of this historical case of
mistaken identity illustrates that discoveries of non-AGN emission-line
galaxies with high X-ray luminosity should be tested carefully. The properties
of E 0336-248 are similar to those of other X-ray selected BL Lacs, including
its location in an apparent group or cluster of galaxies. Somewhat unusual is
the weak contribution of nonstellar optical light relative to the starlight in
the spectrum of its host galaxy, which raises once again the possibility that
even high-luminosity BL Lac objects may be difficult to identify in X-ray
selected samples. We discuss a possible manifestation of this problem that
appeared in the recent literature.Comment: To appear in the Astronomical Journal. 8 pages including figures
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Stratospheric Variability and Trends in Models Used for the IPCC AR4
Atmosphere and ocean general circulation model (AOGCM) experiments for the Intergovernmental Panel on Climate Change Fourth Assessment Report (AR4) are analyzed to better understand model variability and assess the importance of various forcing mechanisms on stratospheric trends during the 20th century. While models represent the climatology of the stratosphere reasonably well in comparison with NCEP reanalysis, there are biases and large variability among models. In general, AOGCMs are cooler than NCEP throughout the stratosphere, with the largest differences in the tropics. Around half the AOGCMs have a top level beneath ~2 hPa and show a significant cold bias in their upper levels (~10 hPa) compared to NCEP, suggesting that these models may have compromised simulations near 10 hPa due to a low model top or insufficient stratospheric levels. In the lower stratosphere (50 hPa), the temperature variability associated with large volcanic eruptions is absent in about half of the models, and in the models that do include volcanic aerosols, half of those significantly overestimate the observed warming. There is general agreement on the vertical structure of temperature trends over the last few decades, differences between models are explained by the inclusion of different forcing mechanisms, such as stratospheric ozone depletion and volcanic aerosols. However, even when human and natural forcing agents are included in the simulations, significant differences remain between observations and model trends, particularly in the upper tropical troposphere (200 hPa–100 hPa), where, since 1979, models show a warming trend and the observations a cooling trend
Fractional Operators, Dirichlet Averages, and Splines
Fractional differential and integral operators, Dirichlet averages, and
splines of complex order are three seemingly distinct mathematical subject
areas addressing different questions and employing different methodologies. It
is the purpose of this paper to show that there are deep and interesting
relationships between these three areas. First a brief introduction to
fractional differential and integral operators defined on Lizorkin spaces is
presented and some of their main properties exhibited. This particular approach
has the advantage that several definitions of fractional derivatives and
integrals coincide. We then introduce Dirichlet averages and extend their
definition to an infinite-dimensional setting that is needed to exhibit the
relationships to splines of complex order. Finally, we focus on splines of
complex order and, in particular, on cardinal B-splines of complex order. The
fundamental connections to fractional derivatives and integrals as well as
Dirichlet averages are presented
Transport in Almost Integrable Models: Perturbed Heisenberg Chains
The heat conductivity kappa(T) of integrable models, like the one-dimensional
spin-1/2 nearest-neighbor Heisenberg model, is infinite even at finite
temperatures as a consequence of the conservation laws associated with
integrability. Small perturbations lead to finite but large transport
coefficients which we calculate perturbatively using exact diagonalization and
moment expansions. We show that there are two different classes of
perturbations. While an interchain coupling of strength J_perp leads to
kappa(T) propto 1/J_perp^2 as expected from simple golden-rule arguments, we
obtain a much larger kappa(T) propto 1/J'^4 for a weak next-nearest neighbor
interaction J'. This can be explained by a new approximate conservation law of
the J-J' Heisenberg chain.Comment: 4 pages, several minor modifications, title change
Finite Temperature Spectral Densities of Momentum and R-Charge Correlators in Yang Mills Theory
We compute spectral densities of momentum and R-charge correlators in thermal
Yang Mills at strong coupling using the AdS/CFT correspondence. For
and smaller, the spectral density differs markedly from
perturbation theory; there is no kinetic theory peak. For large , the
spectral density oscillates around the zero-temperature result with an
exponentially decreasing amplitude. Contrast this with QCD where the spectral
density of the current-current correlator approaches the zero temperature
result like . Despite these marked differences with perturbation
theory, in Euclidean space-time the correlators differ by only from
the free result. The implications for Lattice QCD measurements of transport are
discussed.Comment: 18 pages, 3 figure
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Doubled haploid ramets via embryogenesis of haploid tissue cultures
Tissue culture in the oil palm business is generally concerned with the multiplication
(clonal production) of dura, pisifera and tenera palms. These are all normal diploids
(2n=2x=36). Sumatra Bioscience has pioneered haploid tissue culture of oil palm
(n=x=18). Haploid oil palm is the first step in producing doubled haploid palms
which in turn provide parental lines for F1 hybrid production. Chromosome doubling
is known to occur during embryogenesis in other haploid cultures, e.g. barley anther
culture. Haploid tissue cultures in oil palm were therefore set up to investigate and
exploit spontaneous chromosome doubling during embryogenesis. Flow cytometry of
embryogenic tissue showed the presence of both haploid (n) and doubled haploid (2n)
cells indicating spontaneous doubling. Completely doubled haploid ramets were
regenerated suggesting that doubling occurred during the first mitoses of
embryogenesis. This is the first report of doubled haploid production in oil palm via
haploid tissue culture. The method provides a means of producing a range of doubled
haploids in oil palm from the 1,000 plus haploids available at Sumatra Bioscience, in
addition the method also produced doubled haploid (and haploid) clones.
1
Resting state correlates of subdimensions of anxious affect
Resting state fMRI may help identify markers of risk for affective disorder. Given the comorbidity of anxiety and depressive disorders and the heterogeneity of these disorders as defined by DSM, an important challenge is to identify alterations in resting state brain connectivity uniquely associated with distinct profiles of negative affect. The current study aimed to address this by identifying differences in brain connectivity specifically linked to cognitive and physiological profiles of anxiety, controlling for depressed affect. We adopted a two-stage multivariate approach. Hierarchical clustering was used to independently identify dimensions of negative affective style and resting state brain networks. Combining the clustering results, we examined individual differences in resting state connectivity uniquely associated with subdimensions of anxious affect, controlling for depressed affect. Physiological and cognitive subdimensions of anxious affect were identified. Physiological anxiety was associated with widespread alterations in insula connectivity, including decreased connectivity between insula subregions and between the insula and other medial frontal and subcortical networks. This is consistent with the insula facilitating communication between medial frontal and subcortical regions to enable control of physiological affective states. Meanwhile, increased connectivity within a frontoparietal-posterior cingulate cortex-precunous network was specifically associated with cognitive anxiety, potentially reflecting increased spontaneous negative cognition (e.g., worry). These findings suggest that physiological and cognitive anxiety comprise subdimensions of anxiety-related affect and reveal associated alterations in brain connectivity
Universality of One-Dimensional Heat Conductivity
We show analytically that the heat conductivity of oscillator chains diverges
with system size N as N^{1/3}, which is the same as for one-dimensional fluids.
For long cylinders, we use the hydrodynamic equations for a crystal in one
dimension. This is appropriate for stiff systems such as nanotubes, where the
eventual crossover to a fluid only sets in at unrealistically large N. Despite
the extra equation compared to a fluid, the scaling of the heat conductivity is
unchanged. For strictly one-dimensional chains, we show that the dynamic
equations are those of a fluid at all length scales even if the static order
extends to very large N. The discrepancy between our results and numerical
simulations on Fermi-Pasta-Ulam chains is discussed.Comment: 7 pages, 2 figure
The size-star formation relation of massive galaxies at 1.5<z<2.5
We study the relation between size and star formation activity in a complete
sample of 225 massive (M > 5 x 10^10 Msun) galaxies at 1.5<z<2.5, selected from
the FIREWORKS UV-IR catalog of the CDFS. Based on stellar population synthesis
model fits to the observed restframe UV-NIR SEDs, and independent MIPS 24
micron observations, 65% of galaxies are actively forming stars, while 35% are
quiescent. Using sizes derived from 2D surface brightness profile fits to high
resolution (FWHM_{PSF}~0.45 arcsec) groundbased ISAAC data, we confirm and
improve the significance of the relation between star formation activity and
compactness found in previous studies, using a large, complete mass-limited
sample. At z~2, massive quiescent galaxies are significantly smaller than
massive star forming galaxies, and a median factor of 0.34+/-0.02 smaller than
galaxies of similar mass in the local universe. 13% of the quiescent galaxies
are unresolved in the ISAAC data, corresponding to sizes <1 kpc, more than 5
times smaller than galaxies of similar mass locally. The quiescent galaxies
span a Kormendy relation which, compared to the relation for local early types,
is shifted to smaller sizes and brighter surface brightnesses and is
incompatible with passive evolution. The progenitors of the quiescent galaxies,
were likely dominated by highly concentrated, intense nuclear star bursts at
z~3-4, in contrast to star forming galaxies at z~2 which are extended and
dominated by distributed star formation.Comment: 6 pages, 4 figures, accepted for publication in Ap
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