1,017 research outputs found
Feasibility of UV lasing without inversion in mercury vapor
We investigate the feasibility of UV lasing without inversion at a wavelength
of nm utilizing interacting dark resonances in mercury vapor. Our
theoretical analysis starts with radiation damped optical Bloch equations for
all relevant 13 atomic levels. These master equations are generalized by
considering technical phase noise of the driving lasers. From the Doppler
broadened complex susceptibility we obtain the stationary output power from
semiclassical laser theory. The finite overlap of the driving Gaussian laser
beams defines an ellipsoidal inhomogeneous gain distribution. Therefore, we
evaluate the intra-cavity field inside a ring laser self-consistently with
Fourier optics. This analysis confirms the feasibility of UV lasing and reveals
its dependence on experimental parameters.Comment: changes were made according to reviewer comments (accepted for
publication in JOSA B
Evidence of strong quasar feedback in the early Universe
Most theoretical models invoke quasar driven outflows to quench star
formation in massive galaxies, this feedback mechanism is required to account
for the population of old and passive galaxies observed in the local universe.
The discovery of massive, old and passive galaxies at z=2, implies that such
quasar feedback onto the host galaxy must have been at work very early on,
close to the reionization epoch. We have observed the [CII]158um transition in
SDSSJ114816.64+525150.3 that, at z=6.4189, is one of the most distant quasars
known. We detect broad wings of the line tracing a quasar-driven massive
outflow. This is the most distant massive outflow ever detected and is likely
tracing the long sought quasar feedback, already at work in the early Universe.
The outflow is marginally resolved on scales of about 16 kpc, implying that the
outflow can really affect the whole galaxy, as required by quasar feedback
models. The inferred outflow rate, dM/dt > 3500 Msun/yr, is the highest ever
found. At this rate the outflow can clean the gas in the host galaxy, and
therefore quench star formation, in a few million years.Comment: 5 pages, 3 figures, accepted for publication in MNRAS Letter
Detection of metastable electronic states by Penning trap mass spectrometry
State-of-the-art optical clocks achieve fractional precisions of
and below using ensembles of atoms in optical lattices or individual ions in
radio-frequency traps. Promising candidates for novel clocks are highly charged
ions (HCIs) and nuclear transitions, which are largely insensitive to external
perturbations and reach wavelengths beyond the optical range, now becoming
accessible to frequency combs. However, insufficiently accurate atomic
structure calculations still hinder the identification of suitable transitions
in HCIs. Here, we report on the discovery of a long-lived metastable electronic
state in a HCI by measuring the mass difference of the ground and the excited
state in Re, the first non-destructive, direct determination of an electronic
excitation energy. This result agrees with our advanced calculations, and we
confirmed them with an Os ion with the same electronic configuration. We used
the high-precision Penning-trap mass spectrometer PENTATRAP, unique in its
synchronous use of five individual traps for simultaneous mass measurements.
The cyclotron frequency ratio of the ion in the ground state to the
metastable state could be determined to a precision of , unprecedented in the heavy atom regime. With a lifetime of about 130
days, the potential soft x-ray frequency reference at has a linewidth of only , and one of the highest electronic quality factor
() ever seen in an experiment. Our low
uncertainty enables searching for more HCI soft x-ray clock transitions, needed
for promising precision studies of fundamental physics in a thus far unexplored
frontier
Rotating Nuclear Rings and Extreme Starbursts in Ultraluminous Galaxies
New high resolution interferometer data of 10 IR ultraluminous galaxies shows
the molecular gas is in rotating nuclear rings or disks with radii 300 to 800
pc. Most of the CO flux comes from a moderate-density, warm, intercloud medium
rather than self-gravitating clouds. Gas masses of ~ 5 x 10^9 Msun, 5 times
lower than the standard method are derived from a model of the molecular disks.
The ratio of molecular gas to dynamical mass, is M_gas/M_dyn ~ 1/6 with a
maximum ratio of gas to total mass surface density of 1/3. For the galaxies
VIIZw31, Arp193, and IRAS 10565+24, there is good evidence for rotating
molecular rings with a central gap. In addition to the rotating rings a new
class of star formation region is identified which we call an Extreme
Starburst. They have a characteristic size of only 100 pc., about 10^9 Msun of
gas and an IR luminosity of ~3 x 10^11 Lsun. Four extreme starbursts are
identified in the 3 closest galaxies in the sample Arp220, Arp193 and Mrk273.
They are the most prodigious star formation events in the local universe, each
representing about 1000 times as many OB stars as 30 Doradus. In Arp220, the CO
and 1.3 mm continuum maps show the two ``nuclei'' embedded in a central ring or
disk and a fainter structure extending 3 kpc to the east, normal to the nuclear
disk. There is no evidence that these sources really are the pre-merger nuclei.
They are compact, extreme starburst regions containing 10^9 Msun of dense
molecular gas and new stars, but no old stars. Most of the dust emission and
HCN emission arises in the two extreme starbursts. The entire bolometric
luminosity of Arp~220 comes from starbursts, not an AGN. In Mrk231, the disk
geometry shows that the molecular disk cannot be heated by the AGN; the far IR
luminosity of Mrk~231 is powered by a starburst, not the AGN. (Abridged)Comment: 97 pages Latex with aasms.sty, including 29 encapsulated Postscript
figures. Figs 18 and 23 are GIFs. 31 figures total. Text and higher quality
versions of figures available at
http://sbastk.ess.sunysb.edu/www/RINGS_ESB_PREPRINT.html To be published in
Ap. J., 10 Nov. 199
Genetic fingerprinting of salmon louse (Lepeophtheirus salmonis) populations in the North-East Atlantic using a random forest classification approach
Caligid sea lice represent a significant threat to salmonid aquaculture worldwide. Population genetic analyses have consistently shown minimal population genetic structure in North Atlantic Lepeophtheirus salmonis, frustrating efforts to track louse populations and improve targeted control measures. The aim of this study was to test the power of reduced representation library sequencing (IIb-RAD sequencing) coupled with random forest machine learning algorithms to define markers for fine-scale discrimination of louse populations. We identified 1286 robustly supported SNPs among four L. salmonis populations from Ireland, Scotland and Northern Norway. Only weak global structure was observed based on the full SNP dataset. The application of a random forest machine-learning algorithm identified 98 discriminatory SNPs that dramatically improved population assignment, increased global genetic structure and resulted in significant genetic population differentiation. A large proportion of SNPs found to be under directional selection were also identified to be highly discriminatory. Our data suggest that it is possible to discriminate between nearby L. salmonis populations given suitable marker selection approaches, and that such differences might have an adaptive basis. We discuss these data in light of sea lice adaption to anthropogenic and environmental pressures as well as novel approaches to track and predict sea louse dispersal
The demand for sports and exercise: Results from an illustrative survey
Funding from the Department of Health policy research programme was used in this study.There is a paucity of empirical evidence on the extent to which price and perceived benefits affect the level of participation in sports and exercise. Using an illustrative sample of 60 adults at Brunel University, West London, we investigate the determinants of demand for sports and exercise. The data were collected through face-to-face interviews that covered indicators of sports and exercise behaviour; money/time price and perceived benefits of participation; and socio- economic/demographic details. Count, linear and probit regression models were fitted as appropriate. Seventy eight per cent of the sample participated in sports and exercise and spent an average of £27 per month and an average of 20 min travelling per occasion of sports and exercise. The demand for sport and exercise was negatively associated with time (travel or access time) and ‘variable’ price and positively correlated with ‘fixed’ price. Demand was price inelastic, except in the case of meeting the UK government’s recommended level of participation, which is time price elastic (elasticity = −2.2). The implications of data from a larger nationally representative sample as well as the role of economic incentives in influencing uptake of sports and exercise are discussed.This article is available through the Brunel Open Access Publishing Fund
Mid-infrared spectral evidence for a luminous dust enshrouded source in Arp220
We have re-analyzed the 6-12 micron ISO spectrum of the ultra-luminous
infrared galaxy Arp220 with the conclusion that it is not consistent with that
of a scaled up version of a typical starburst. Instead, both template fitting
with spectra of the galaxies NGC4418 and M83 and with dust models suggest that
it is best represented by combinations of a typical starburst component,
exhibiting PAH emission features, and a heavily absorbed dust continuum which
contributes ~40% of the 6-12 micron flux and likely dominates the luminosity.
Of particular significance relative to previous studies of Arp220 is the fact
that the emission feature at 7.7 micron comprises both PAH emission and a
broader component resulting from ice and silicate absorption against a heavily
absorbed continuum. Extinction to the PAH emitting source, however, appears to
be relatively low. We tentatively associate the PAH emitting and heavily
dust/ice absorbed components with the diffuse emission region and the two
compact nuclei respectively identified by Soifer et al. (2002) in their higher
spatial resolution 10 micron study. Both the similarity of the absorbed
continuum with that of the embedded Galactic protostars and results of the dust
models imply that the embedded source(s) in Arp220 could be powered by, albeit
extremely dense, starburst activity. Due to the high extinction, it is not
possible with the available data to exclude that AGN(s) also contribute some or
all of the observed luminosity. In this case, however, the upper limit measured
for its hard X-ray emission would require Arp220 to be the most highly obscured
AGN known.Comment: 11 pages, 9 figures. Accepted for publication in A&A. Also available
at http://www.astro.rug.nl/~spoon/publications.htm
Non-Equilibrium Dynamics in Two-Color, Few-Photon Dissociative Excitation and Ionization of D
D molecules, excited by linearly cross-polarized femtosecond extreme
ultraviolet (XUV) and near-infrared (NIR) light pulses, reveal highly
structured D ion fragment momenta and angular distributions that originate
from two different 4-step dissociative ionization pathways after four photon
absorption (1 XUV + 3 NIR). We show that, even for very low dissociation
kinetic energy release ~240~meV, specific electronic excitation pathways
can be identified and isolated in the final ion momentum distributions. With
the aid of {\it ab initio} electronic structure and time-dependent
Schr\"odinger equation calculations, angular momentum, energy, and parity
conservation are used to identify the excited neutral molecular states and
molecular orientations relative to the polarization vectors in these different
photoexcitation and dissociation sequences of the neutral D molecule and
its D cation. In one sequential photodissociation pathway, molecules
aligned along either of the two light polarization vectors are excluded, while
another pathway selects molecules aligned parallel to the light propagation
direction. The evolution of the nuclear wave packet on the intermediate \Bstate
electronic state of the neutral D molecule is also probed in real time.Comment: 11 pages including 6 figure
Spitzer Quasar and ULIRG Evolution Study (QUEST). IV. Comparison of 1-Jy Ultraluminous Infrared Galaxies with Palomar-Green Quasars
We report the results from a comprehensive study of 74 ultraluminous infrared
galaxies (ULIRGs) and 34 Palomar-Green (PG) quasars within z ~ 0.3$ observed
with the Spitzer Infrared Spectrograph (IRS). The contribution of nuclear
activity to the bolometric luminosity in these systems is quantified using six
independent methods that span a range in wavelength and give consistent results
within ~ +/-10-15% on average. The average derived AGN contribution in ULIRGs
is ~35-40%, ranging from ~15-35% among "cool" (f_25/f_60 =< 0.2) optically
classified HII-like and LINER ULIRGs to ~50 and ~75% among warm Seyfert 2 and
Seyfert 1 ULIRGs, respectively. This number exceeds ~80% in PG QSOs. ULIRGs
fall in one of three distinct AGN classes: (1) objects with small extinctions
and large PAH equivalent widths are highly starburst-dominated; (2) systems
with large extinctions and modest PAH equivalent widths have larger AGN
contributions, but still tend to be starburst-dominated; and (3) ULIRGs with
both small extinctions and small PAH equivalent widths host AGN that are at
least as powerful as the starbursts. The AGN contributions in class 2 ULIRGs
are more uncertain than in the other objects, and we cannot formally rule out
the possibility that these objects represent a physically distinct type of
ULIRGs. A morphological trend is seen along the sequence (1)-(2)-(3), in
general agreement with the standard ULIRG - QSO evolution scenario and
suggestive of a broad peak in extinction during the intermediate stages of
merger evolution. However, the scatter in this sequence, implies that black
hole accretion, in addition to depending on the merger phase, also has a strong
chaotic/random component, as in local AGN. (abridged)Comment: 61 pages, 39 figures, 16 tables, accepted for publication in ApJS,
June 2009 issue. Unabbreviated version can be found at
http://www.astro.umd.edu/~veilleux/pubs/quest4.pd
Physical properties of Lyman-alpha emitters at from UV-to-FIR measurements
The analysis of the physical properties of low-redshift Ly emitters
(LAEs) can provide clues in the study of their high-redshift analogues. At , LAEs are bright enough to be detected over almost the entire
electromagnetic spectrum and it is possible to carry out a more precise and
complete study than at higher redshifts. In this study, we examine the UV and
IR emission, dust attenuation, SFR and morphology of a sample of 23
GALEX-discovered star-forming (SF) LAEs at with direct UV (GALEX),
optical (ACS) and FIR (PACS and MIPS) data. Using the same UV and IR limiting
luminosities, we find that LAEs at tend to be less dusty, have
slightly higher total SFRs, have bluer UV continuum slopes, and are much
smaller than other galaxies that do not exhibit Ly emission in their
spectrum (non-LAEs). These results suggest that at Ly
photons tend to escape from small galaxies with low dust attenuation. Regarding
their morphology, LAEs belong to Irr/merger classes, unlike non-LAEs. Size and
morphology represent the most noticeable difference between LAEs and non-LAEs
at . Furthermore, the comparison of our results with those obtained
at higher redshifts indicates that either the Ly technique picks up
different kind of galaxies at different redshifts or that the physical
properties of LAEs are evolving with redshift.Comment: Accepted for publication in Ap
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