7,597 research outputs found
Low Redshift Intergalactic Absorption Lines in the Spectrum of HE0226-4110
We present an analysis of the FUSE and STIS E140M spectra of HE0226-4110
(z=0.495). We detect 56 Lyman absorbers and 5 O VI absorbers. The number of
intervening O VI systems per unit redshift with W>50 m\AA is dN(O VI)/dz~ 11.
The O VI systems unambiguously trace hot gas only in one case. For the 4 other
O VI systems, photoionization and collisional ionization models are viable
options to explain the observed column densities of the O VI and the other
ions. If the O VI systems are mostly photoionized, only a fraction of the
observed O VI will contribute to the baryonic density of the warm-hot ionized
medium (WHIM) along this line of sight. Combining our results with previous
ones, we show that there is a general increase of N(O VI) with increasing b(O
VI). Cooling flow models can reproduce the N-b distribution but fail to
reproduce the observed ionic ratios. A comparison of the number of O I, O II, O
III, O IV, and O VI systems per unit redshift show that the low-z IGM is more
highly ionized than weakly ionized. We confirm that photoionized O VI systems
show a decreasing ionization parameter with increasing H I column density. O VI
absorbers with collisional ionization/photoionization degeneracy follow this
relation, possibly suggesting that they are principally photoionized. We find
that the photoionized O VI systems in the low redshift IGM have a median
abundance of 0.3 solar. We do not find additional Ne VIII systems other than
the one found by Savage et al., although our sensitivity should have allowed
the detection of Ne VIII in O VI systems at T~(0.6-1.3)x10^6 K (if CIE
applies). Since the bulk of the WHIM is believed to be at temperatures T>10^6
K, the hot part of the WHIM remains to be discovered with FUV--EUV metal-line
transitions.Comment: Accepted for publication in the ApJS. Full resolution figures
available at
http://www.journals.uchicago.edu/ApJ/journal/preprints/ApJS63975.preprint.pd
The Delta-Delta Intermediate State in 1S0 Nucleon-Nucleon Scattering From Effective Field Theory
We examine the role of the Delta-Delta intermediate state in low energy NN
scattering using effective field theory. Theories both with and without pions
are discussed. They are regulated with dimensional regularization and MSbar
subtraction. We find that the leading effects of the Delta-Delta state can be
absorbed by a redefinition of the contact terms in a theory with nucleons only.
It does not remove the requirement of a higher dimension operator to reproduce
data out to moderate momentum. The explicit decoupling of the Delta-Delta state
is shown for the theory without pions.Comment: 16 pages, 3 figures, uses harvma
Flavor changing interactions mediated by scalars at the weak scale
The quark and lepton mass matrices possess approximate flavor symmetries.
Several results follow if the interactions of new scalars possess these
approximate symmetries. Present experimental bounds allow these exotic scalars
to have a weak scale mass. The Glashow-Weinberg criterion is rendered
unnecessary. Finally, rare leptonic B meson decays provide powerful probes of
these scalars, especially if they are leptoquarks.Comment: 13 pages, report LBL-3234
The properties of highly luminous IRAS galaxies
From a complete sample of 154 galaxies identified with IRAS sources in a 304 sq deg area centered on the South Galactic Pole, a subsample of 58 galaxies with L sub IR/L sub B > 3 was chosen. Low resolution spectra were obtained for 30% of the subsample and redshifts and relative emission line intensities were derived. As a class these galaxies are very luminous with = 2.9 x 10 to the 11th power L sub 0 and (L sub IR) max = 1.3 x 10 to the 12th power L sub 0. CCD images and JHK photometry were obtained for many of the subsample. The galaxies are for the most part newly identified and are optically faint, with a majority showing evidence of a recent interaction. Radio continuum observations of all galaxies of the subsample were recently obtained at 20 cm VLA with about 75% being detected in a typical integration time of about 10 minutes
Sequential Extensions of Causal and Evidential Decision Theory
Moving beyond the dualistic view in AI where agent and environment are
separated incurs new challenges for decision making, as calculation of expected
utility is no longer straightforward. The non-dualistic decision theory
literature is split between causal decision theory and evidential decision
theory. We extend these decision algorithms to the sequential setting where the
agent alternates between taking actions and observing their consequences. We
find that evidential decision theory has two natural extensions while causal
decision theory only has one.Comment: ADT 201
Extracting Scattering Phase-Shifts in Higher Partial-Waves from Lattice QCD Calculations
L\"uscher's method is routinely used to determine meson-meson, meson-baryon
and baryon-baryon s-wave scattering amplitudes below inelastic thresholds from
Lattice QCD calculations - presently at unphysical light-quark masses. In this
work we review the formalism and develop the requisite expressions to extract
phase-shifts describing meson-meson scattering in partial-waves with
angular-momentum l<=6 and l=9. The implications of the underlying cubic
symmetry, and strategies for extracting the phase-shifts from Lattice QCD
calculations, are presented, along with a discussion of the signal-to-noise
problem that afflicts the higher partial-waves.Comment: 79 pages, 41 figure
Superradiant scattering from a hydrodynamic vortex
We show that sound waves scattered from a hydrodynamic vortex may be
amplified. Such superradiant scattering follows from the physical analogy
between spinning black holes and hydrodynamic vortices. However a sonic horizon
analogous to the black hole event horizon does not exist unless the vortex
possesses a central drain, which is challenging to produce experimentally. In
the astrophysical domain, superradiance can occur even in the absence of an
event horizon: we show that in the hydrodynamic analogue, a drain is not
required and a vortex scatters sound superradiantly. Possible experimental
realization in dilute gas Bose-Einstein condensates is discussed.Comment: 10 pages, 1 figur
Characterization of steady-state fluorescence properties of polystyrene latex spheres using off- and online spectroscopic methods
Fluorescent dyed polystyrene latex spheres (PSLs) are commonly used for
characterization and calibration of instruments detecting fluorescence
signals from particles suspended in the air and other fluids. Instruments
like the Ultraviolet Aerodynamic Particle Sizer (UV-APS) and the Waveband
Integrated Bioaerosol Sensor (WIBS) are widely used for bioaerosol research,
but these instruments present significant technical and physical challenges
requiring careful characterization with standard particles. Many other
research communities use flow cytometry and other instruments that
interrogate fluorescence from individual particles, and these also frequently
rely on fluorescent PSLs as standards. Nevertheless, information about
physical properties of commercially available PSLs provided by each
manufacturer is generally proprietary and rarely available, making their use
in fluorescence validation and calibration very difficult.
This technical note presents an overview of steady-state fluorescence
properties of fluorescent and non-fluorescent PSLs, as well as of
polystyrene-divinylbenzene (PS-DVB) particles, by using on- and offline
spectroscopic techniques. We show that the fluorescence landscape of
PSLs is more complex than the information typically provided by
manufacturers may imply, especially revealing multimodal emission patterns.
Furthermore, non-fluorescent PSLs also exhibit defined patterns of
fluorescent emission originating from a mixture of polystyrene and
detergents, which becomes a crucial point for fluorescence threshold
calibrations and qualitative comparison between instruments. By comparing
PSLs of different sizes, but doped with the same dye, changes in emission
spectra from bulk solutions are not immediately obvious. On a
single-particle scale, however, fluorescence intensity values increase with
increasing particle size. No significant effect in the fluorescence
signatures was detectable by comparing PSLs in dry vs. wet states,
indicating that solvent water may only play a minor role as a fluorescence
quencher.
Because information provided by manufacturers of commercially available PSLs
is generally very limited, we provide the steady-state excitation–emission
matrices (EEMs) of PSLs as open-access data within the Supplement. Detergent
and solvent effects are also discussed in order to provide information not
available elsewhere to researchers in the bioaerosol and other research
communities. These data are not meant to serve as a fundamental library of
PSL properties because of the variability of fluorescent properties between
batches and as a function of particle aging and agglomeration. The data
presented, however, provide a summary of spectral features which are
consistent across these widely used fluorescent standards. Using these
concepts, further checks will likely be required by individual researchers
using specific lots of standards.</p
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