3,753 research outputs found
Signatures of the Youngest Starbursts: Optically-thick Thermal Bremsstrahlung Radio Sources in Henize 2-10
VLA radio continuum imaging reveals compact (<8 pc) ~1 mJy radio sources in
the central 5" starburst region of the blue compact galaxy Henize 2-10. We
interpret these radio knots as extremely young, ultra-dense HII regions. We
model their luminosities and spectral energy distributions, finding that they
are consistent with unusually dense HII regions having electron densities, 1500
cm^-3 < n_e < 5000 cm^-3, and sizes of 3-8 pc. Since these H II regions are not
visible in optical images, we propose that the radio data preferentially reveal
the youngest, densest, and most highly obscured starforming events. Energy
considerations imply that each of the five \HII regions contains ~750 O7V
equivalent stars, greater than the number found in 30 Doradus in the LMC. The
high densities imply an over-pressure compared to the typical interstellar
medium so that such objects must be short-lived (<0.5 Myr expansion
timescales). We conclude that the radio continuum maps reveal the very young
(<0.5 Myr) precursors of ``super starclusters'' or ``proto globular clusters''
which are prominent at optical and UV wavelengths in He 2-10. If the
ultra-dense HII regions are typical of those which we predict will be found in
other starbursting systems, then super starclusters spend 15% of their lifetime
in heavily-obscured environments, similar to Galactic ultra-compact HII
regions. This body of work leads us to propose that massive extragalactic star
clusters (i.e. proto globular clusters) with ages <10^6 yr may be most easily
identified by finding compact radio sources with optically-thick thermal
bremsstrahlung spectral signatures.Comment: AASTeX, 8 figures 2 included with psfig in text; other 6 in jpeg
format; Postscript versions of figures may be found at
http://zem.ucolick.org/chip/Research/young_clusters.html -- Accepted for
publication in the Astrophysical Journa
Untangling Source-To-Sink Geochemical Signals in a ~3.5 Ga Martian Lake: Sedimentology and Geochemistry of the Murray Formation
Sedimentary rocks are historical archives of planetary surface processes; their grains, textures, and chemistry integrate the effects of source terrains, paleoclimatic conditions, weathering and transport processes, authigenic mineral precipitation, and diagenesis, which records groundwater chemistry through time. Source to Sink basin analysis seeks to constrain the influence of each of these different signals through sedimentary and geochemical analyses. Here, we use Mars Science Laboratory (MSL) Curiosity rover images and geochemical and mineralogical data from a traverse across a portion of the Murray formationthe lowermost unit exposed in the Gale crater central moundto begin to constrain the aspects of the source to sink system that formed this Martian mudstone between 3.7 and 3.2 Ga
A multi-layer extension of the stochastic heat equation
Motivated by recent developments on solvable directed polymer models, we
define a 'multi-layer' extension of the stochastic heat equation involving
non-intersecting Brownian motions.Comment: v4: substantially extended and revised versio
Hydrogen atom in phase space. The Kirkwood-Rihaczek representation
We present a phase-space representation of the hydrogen atom using the
Kirkwood-Rikaczek distribution function. This distribution allows us to obtain
analytical results, which is quite unique because an exact analytical form of
the Wigner functions corresponding to the atom states is not known. We show how
the Kirkwood-Rihaczek distribution reflects properties of the hydrogen atom
wave functions in position and momentum representations.Comment: 5 pages (and 5 figures
A stochastic space-time rainfall forecasting system for real time flow forecasting II: Application of SHETRAN and ARNO rainfall runoff models to the Brue catchment
International audienceKey issues involved in converting MTB ensemble forecasts of rainfall into ensemble forecasts of runoff are addressed. The physically-based distributed modelling system, SHETRAN, is parameterised for the Brue catchment, and used to assess the impact of averaging spatially variable MTB rainfall inputs on the accuracy of simulated runoff response. Averaging is found to have little impact for wet antecedent conditions and to lead to some underestimation of peak discharge under dry catchment conditions. The simpler ARNO modelling system is also parameterised for the Brue and SHETRAN and ARNO calibration and validation results are found to be similar. Ensemble forecasts of runoff generated using both SHETRAN and the simpler ARNO modelling system are compared. The ensemble is more spread out with the SHETRAN model, and a likely explanation is that the ARNO model introduces too much smoothing. Nevertheless, the forecasting performance of the simpler model could be adequate for flood warning purposes. Keywords: SHETRAN, ARNO, HYREX, rainfall-runoff model, Brue, real-time flow forecasting</p
Time-Series Photometry of M67: W UMa Systems, Blue Stragglers, and Related Systems
We present an analysis of over 2200 V images taken on 14 nights at the Mt.
Laguna 1 m telescope of the open cluster M67. Our observations overlap but
extend beyond the field analyzed by Gilliland et al. (1991), and complement
data recently published by van den Berg et al. (2002) and Stassun et al.
(2002). We show variability in the light curves of all 4 of the known W UMa
variables on timescales ranging from a day to decades (for AH Cnc). We have
modeled the light curve of AH Cnc, and the total eclipses allow us to determine
q = 0.16 +0.03/-0.02 and i = 86 +4/-8 degrees. The position of this system near
the turnoff of M67 makes it useful for constraining the turnoff mass for the
cluster. We have also detected two unusual features in the light curve of AH
Cnc that may be caused by prominences. We have also monitored cluster blue
stragglers for variability, and we present evidence hinting at low level
variations in the stragglers S752, S968, and S1263, and we place limits on the
variability of a number of other cluster blue stragglers. Finally, we provide
photometry of the sub-subgiant branch star S1063 showing variability on
timescales similar to the orbital period, while the ``red straggler'' S1040
shows evidence of an unexplained drop in brightness at phases corresponding to
the passage of the white dwarf in front of the giant.Comment: 44 pages, 16 figures, AASTeX, accepted for A
Exciton-plasmon states in nanoscale materials: breakdown of the Tamm-Dancoff approximation
Within the Tamm-Dancoff approximation ab initio approaches describe excitons
as packets of electron-hole pairs propagating only forward in time. However, we
show that in nanoscale materials excitons and plasmons hybridize, creating
exciton--plasmon states where the electron-hole pairs oscillate back and forth
in time. Then, as exemplified by the trans-azobenzene molecule and carbon
nanotubes, the Tamm-Dancoff approximation yields errors as large as the
accuracy claimed in ab initio calculations. Instead, we propose a general and
efficient approach that avoids the Tamm--Dancoff approximation, and correctly
describes excitons, plasmons and exciton-plasmon states
Measurements of the magnetic field induced by a turbulent flow of liquid metal
Initial results from the Madison Dynamo Experiment provide details of the
inductive response of a turbulent flow of liquid sodium to an applied magnetic
field. The magnetic field structure is reconstructed from both internal and
external measurements. A mean toroidal magnetic field is induced by the flow
when an axial field is applied, thereby demonstrating the omega effect.
Poloidal magnetic flux is expelled from the fluid by the poloidal flow.
Small-scale magnetic field structures are generated by turbulence in the flow.
The resulting magnetic power spectrum exhibits a power-law scaling consistent
with the equipartition of the magnetic field with a turbulent velocity field.
The magnetic power spectrum has an apparent knee at the resistive dissipation
scale. Large-scale eddies in the flow cause significant changes to the
instantaneous flow profile resulting in intermittent bursts of non-axisymmetric
magnetic fields, demonstrating that the transition to a dynamo is not smooth
for a turbulent flow.Comment: 9 pages, 11 figures, invited talk by C. B. Forest at 2005 APS DPP
meeting, resubmitted to Physics of Plasma
Disrupted Maturation of the Microbiota and Metabolome among Extremely Preterm Infants with Postnatal Growth Failure
Growth failure during infancy is a major global problem that has adverse effects on long-term health and neurodevelopment. Preterm infants are disproportionately affected by growth failure and its effects. Herein we found that extremely preterm infants with postnatal growth failure have disrupted maturation of the intestinal microbiota, characterized by persistently low diversity, dominance of pathogenic bacteria within the Enterobacteriaceae family, and a paucity of strictly anaerobic taxa including Veillonella relative to infants with appropriate postnatal growth. Metabolomic profiling of infants with growth failure demonstrated elevated serum acylcarnitines, fatty acids, and other byproducts of lipolysis and fatty acid oxidation. Machine learning algorithms for normal maturation of the microbiota and metabolome among infants with appropriate growth revealed a pattern of delayed maturation of the microbiota and metabolome among infants with growth failure. Collectively, we identified novel microbial and metabolic features of growth failure in preterm infants and potentially modifiable targets for intervention
Quantum process tomography of two-qubit controlled-Z and controlled-NOT gates using superconducting phase qubits
We experimentally demonstrate quantum process tomography of controlled-Z and
controlled-NOT gates using capacitively-coupled superconducting phase qubits.
These gates are realized by using the state of the phase qubit. We
obtain a process fidelity of 0.70 for the controlled-phase and 0.56 for the
controlled-NOT gate, with the loss of fidelity mostly due to single-qubit
decoherence. The controlled-Z gate is also used to demonstrate a two-qubit
Deutsch-Jozsa algorithm with a single function query.Comment: 10 pages, 8 figures, including supplementary informatio
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