112,645 research outputs found
A Model for Star Formation, Gas Flows and Chemical Evolution in Galaxies at High Redshifts
Motivated by the increasing use of the Kennicutt-Schmidt (K-S) star formation
law to interpret observations of high redshift galaxies, the importance of gas
accretion to galaxy formation, and the recent observations of chemical
abundances in galaxies at z~2-3, I use simple analytical models to assess the
consistency of these processes of galaxy evolution with observations and with
each other. I derive the time dependence of star formation implied by the K-S
law, and show that the sustained high star formation rates observed in galaxies
at z~2-3 require the accretion of additional gas. A model in which the gas
accretion rate is approximately equal to the combined star formation and
outflow rates broadly reproduces the observed trends of star formation rate
with galaxy age. Using an analytical description of chemical evolution, I also
show that this model, further constrained to have an outflow rate roughly equal
to the star formation rate, reproduces the observed mass-metallicity relation
at z~2.Comment: 7 pages, 3 figures. Accepted for publication in Ap
Effective Low-Energy Model for f-Electron Delocalization
We consider a Periodic Anderson Model (PAM) with a momentum-dependent
inter-band hybridization that is strongly suppressed near the Fermi level.
Under these conditions, we reduce the PAM to an effective low-energy
Hamiltonian, , by expanding in the small parameter (
is the maximum inter-band hybridization amplitude and is the hopping
integral of the broad band). The resulting model consists of a t-J f-band
coupled via the Kondo exchange to the electrons in the broad band. allows for studying the f-electron delocalization transition. The result
is a doping-induced Mott transition for the f-electron delocalization, which we
demonstrate by density-matrix renormalization group (DMRG) calculations
Amplification by stochastic interference
A new method is introduced to obtain a strong signal by the interference of
weak signals in noisy channels. The method is based on the interference of 1/f
noise from parallel channels. One realization of stochastic interference is the
auditory nervous system. Stochastic interference may have broad potential
applications in the information transmission by parallel noisy channels
Public Involvement in research within care homes: Benefits and challenges in the APPROACH Study
Public involvement in research (PIR) can improve research design and recruitment. Less is known about how PIR enhances the experience of participation and enriches the data collection process. In a study to evaluate how UK care homes and primary health care services achieve integrated working to promote older people’s health, PIR was integrated throughout the research processes. Objectives This paper aims to present one way in which PIR has been integrated into the design and delivery of a multi-site research study based in care homes. Design A prospective case study design, with an embedded qualitative evaluation of PIR activity. Setting and Participants Data collection was undertaken in six care homes in three sites in England. Six PIR members participated: all had prior personal or work experience in care homes. Data Collection Qualitative data collection involved discussion groups, and site-specific meetings to review experiences of participation, benefits and challenges, and completion of structured fieldwork notes after each care home visit. Results PIR members supported: recruitment, resident and staff interviews and participated in data interpretation. Benefits of PIR work were resident engagement that minimised distress and made best use of limited research resources. Challenges concerned communication and scheduling. Researcher support for PIR involvement was resource intensive. Discussion and Conclusions Clearly defined roles with identified training and support facilitated involvement in different aspectsPublic Involvement in Research members of the research team: Gail Capstick, Marion Cowie, Derek Hope, Rita Hewitt, Alex Mendoza, John Willmott. Also the involvement of Steven Iliffe and Heather Gag
Temperature dependence of Andreev spectra in a superconducting carbon nanotube quantum dot
Tunneling spectroscopy of a Nb coupled carbon nanotube quantum dot reveals
the formation of pairs of Andreev bound states (ABS) within the superconducting
gap. A weak replica of the lower ABS is found, which is generated by
quasi-particle tunnelling from the ABS to the Al tunnel probe. An inversion of
the ABS-dispersion is observed at elevated temperatures, which signals the
thermal occupation of the upper ABS. Our experimental findings are well
supported by model calculations based on the superconducting Anderson model.Comment: 6 pages, 7 figure
Universality and itinerant ferromagnetism in rotating strongly interacting Fermi gases
We analytically determine the properties of three interacting fermions in a
harmonic trap subject to an external rotation. Thermodynamic quantities such as
the entropy and energy are calculated from the third order quantum virial
expansion. By parameterizing the solutions in the rotating frame we find that
the energy and entropy are universal for all rotations in the strongly
interacting regime. Additionally, we find that rotation suppresses the onset of
itinerant ferromagnetism in strongly interacting repulsive three-body systems.Comment: 5 pages with 3 figure
Fine-Structure FeII* Emission and Resonant MgII Emission in z = 1 Star-Forming Galaxies
We present a study of the prevalence, strength, and kinematics of ultraviolet
FeII and MgII emission lines in 212 star-forming galaxies at z = 1 selected
from the DEEP2 survey. We find FeII* emission in composite spectra assembled on
the basis of different galaxy properties, indicating that FeII* emission is
prevalent at z = 1. In these composites, FeII* emission is observed at roughly
the systemic velocity. At z = 1, we find that the strength of FeII* emission is
most strongly modulated by dust attenuation, and is additionally correlated
with redshift, star-formation rate, and [OII] equivalent width, such that
systems at higher redshifts with lower dust levels, lower star-formation rates,
and larger [OII] equivalent widths show stronger FeII* emission. We detect MgII
emission in at least 15% of the individual spectra and we find that objects
showing stronger MgII emission have higher specific star-formation rates,
smaller [OII] linewidths, larger [OII] equivalent widths, lower dust
attenuations, and lower stellar masses than the sample as a whole. MgII
emission strength exhibits the strongest correlation with specific
star-formation rate, although we find evidence that dust attenuation and
stellar mass also play roles in the regulation of MgII emission. Future
integral field unit observations of the spatial extent of FeII* and MgII
emission in galaxies with high specific star-formation rates, low dust
attenuations, and low stellar masses will be important for probing the
morphology of circumgalactic gas.Comment: 29 pages, 22 figures, 2 tables; accepted to Ap
Emission lines and optical continuum in low-luminosity radio galaxies
We present spectroscopic observations of a complete sub-sample of 13
low-luminosity radio galaxies selected from the 2Jy sample. The underlying
continuum in these sources is carefully modelled in order to make a much-needed
comparison between the emission line and continuum properties of FRIs with
those of other classes of radio sources. We find that 5 galaxies in the sample
show a measurable UV excess: 2 of the these sources are BL Lacs and in the
remaining 3 galaxies we argue that the most likely contributor to the UV excess
is a young stellar component. Excluding the BL Lacs, we therefore find that
\~30% of the sample show evidence for young stars, which is similar to the
results obtained for higher luminosity samples. We compare our results with
far-infrared measurements in order to investigate the far-infrared-starburst
link. The nature of the optical-radio correlations is investigated in light of
this new available data and, in contrast to previous studies, we find that the
FRI sources follow the correlations with a similar slope to that found for the
FRIIs. Finally, we compare the luminosity of the emission lines in the FRI and
BL Lac sources and find a significant difference in the [OIII] line
luminosities of the two groups. Our results are discussed in the context of the
unified schemes.Comment: 18 pages, 31 figures, MNRAS in press, (all enquiries to Clive
Tadhunter ([email protected])
Precise Variational Calculation For The Doubly Excited State (2p^2)^3P^e of Helium
Highly precise variational calculations of non-relativistic energies of the
(2p^2)^3P^e state of Helium atom are presented.We get an upper bound energy
E=-0.71050015565678 a.u.,the lowest yet obtained.Comment: 5 pages, 1 tabl
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