69 research outputs found
Quantum critical point in a periodic Anderson model
We investigate the symmetric Periodic Anderson Model (PAM) on a
three-dimensional cubic lattice with nearest-neighbor hopping and hybridization
matrix elements. Using Gutzwiller's variational method and the Hubbard-III
approximation (which corresponds to the exact solution of an appropriate
Falicov-Kimball model in infinite dimensions) we demonstrate the existence of a
quantum critical point at zero temperature. Below a critical value of the
hybridization (or above a critical interaction ) the system is an {\em
insulator} in Gutzwiller's and a {\em semi-metal} in Hubbard's approach,
whereas above (below ) it behaves like a metal in both
approximations. These predictions are compared with the density of states of
the - and -bands calculated from Quantum Monte Carlo and NRG
calculations. Our conclusion is that the half-filled symmetric PAM contains a
{\em metal-semimetal transition}, not a metal-insulator transition as has been
suggested previously.Comment: ReVteX, 10 pages, 2 EPS figures. Minor corrections made in the text
and in the figure captions from the first version. More references added.
Accepted for publication in Physical Review
Mental health academics in rural and remote Australia
Context: The significant impact of mental ill health in rural and remote Australia has been well documented. Included among innovative approaches undertaken to address this issue has been the Mental Health Academic (MHA) project, established in 2007. Funded by the Australian Government (Department of Health), this project was established as a component of the University Departments of Rural Health (UDRH) program. All 11 UDRHs appointed an MHA. Although widely geographically dispersed, the MHAs have collaborated in various ways. The MHA project encompasses a range of activities addressing four key performance indicators. These activities, undertaken in rural and remote Australia, aimed to increase access to mental health services, promote awareness of mental health issues, support students undertaking mental health training and improve health professionals' capacity to recognise and address mental health issues. MHAs were strategically placed within the UDRHs across the country, ensuring an established academic base for the MHAs' work was available immediately. Close association with each local rural community was recognised as important. For most MHAs this was facilitated by having an established clinical role in their local community and actively engaging with the community in which they worked. In common with other rural health initiatives, some difficulties were experienced in the recruitment of suitable MHAs, especially in more remote locations. The genesis of this article was a national meeting of the MHAs in 2014, to identify and map the different types of activities MHAs had undertaken in their regions. These activities were analysed and categorised by the MHAs. These categories have been used as a guiding framework for this article.
Issues: The challenge to increase community access to mental health services was addressed by (i) initiatives to address specific access barriers, (ii) supporting recruitment and retention of rural mental health staff, (iii) developing the skills of the existing workforce and (iv) developing innovative approaches to student placements. Strategies to promote awareness of mental health issues included workshops in rural and remote communities, specific suicide prevention initiatives and targeted initiatives to support the mental health needs of Indigenous Australians. The need for collaboration between the widely dispersed MHAs was identified as important to bridge the rural divide, to promote project cohesiveness and ensure new ideas in an emerging setting are readily shared and to provide professional support for one another as mental health academics are often isolated from academic colleagues with similar mental health interests.
Lessons learned: The MHA project suggests that an integrated approach can be taken to address the common difficulties of community awareness raising of mental health issues, increasing access to mental health services, workforce recruitment and retention (access), and skill development of existing health professionals (access and awareness). To address the specific needs and circumstances of their community, MHAs have customised their activities. As in other rural initiatives, one size was found not to fit all. The triad of flexibility, diversity and connectedness (both to local community and other MHAs) describes the response identified as appropriate by the MHAs. The breadth of the MHA role to provide university sponsored educational activities outside traditional student teaching meant that the broader health workforce benefited from access to mental health training that would not otherwise have occurred. Provision of these additional educational opportunities addressed not only the need for increased education regarding mental health but also reduced the barriers commonly faced by rural health professionals in accessing quality professional development
Doping-dependent study of the periodic Anderson model in three dimensions
We study a simple model for -electron systems, the three-dimensional
periodic Anderson model, in which localized states hybridize with
neighboring states. The states have a strong on-site repulsion which
suppresses the double occupancy and can lead to the formation of a Mott-Hubbard
insulator. When the hybridization between the and states increases, the
effects of these strong electron correlations gradually diminish, giving rise
to interesting phenomena on the way. We use the exact quantum Monte-Carlo,
approximate diagrammatic fluctuation-exchange approximation, and mean-field
Hartree-Fock methods to calculate the local moment, entropy, antiferromagnetic
structure factor, singlet-correlator, and internal energy as a function of the
hybridization for various dopings. Finally, we discuss the relevance of
this work to the volume-collapse phenomenon experimentally observed in
f-electron systems.Comment: 12 pages, 8 figure
Signatures of Spin and Charge Energy Scales in the Local Moment and Specific Heat of the Two-Dimensional Hubbard Model
Local moment formation driven by the on--site repulsion is one of the
most fundamental features in the Hubbard model. At the simplest level, the
temperature dependence of the local moment is expected to have a single
structure at , reflecting the suppression of the double occupancy. In
this paper we show new low temperature Quantum Monte Carlo data which emphasize
that the local moment also has a signature at a lower energy scale which
previously had been thought to characterize only the temperatures below which
moments on {\it different} sites begin to correlate locally. We discuss
implications of these results for the structure of the specific heat, and
connections to quasiparticle resonance and pseudogap formation in the density
of states.Comment: 13 pages, 19 figure
Proximity effect at superconducting Sn-Bi2Se3 interface
We have investigated the conductance spectra of Sn-Bi2Se3 interface junctions
down to 250 mK and in different magnetic fields. A number of conductance
anomalies were observed below the superconducting transition temperature of Sn,
including a small gap different from that of Sn, and a zero-bias conductance
peak growing up at lower temperatures. We discussed the possible origins of the
smaller gap and the zero-bias conductance peak. These phenomena support that a
proximity-effect-induced chiral superconducting phase is formed at the
interface between the superconducting Sn and the strong spin-orbit coupling
material Bi2Se3.Comment: 7 pages, 8 figure
Centrality Dependence of the High p_T Charged Hadron Suppression in Au+Au collisions at sqrt(s_NN) = 130 GeV
PHENIX has measured the centrality dependence of charged hadron p_T spectra
from central Au+Au collisions at sqrt(s_NN)=130 GeV. The truncated mean p_T
decreases with centrality for p_T > 2 GeV/c, indicating an apparent reduction
of the contribution from hard scattering to high p_T hadron production. For
central collisions the yield at high p_T is shown to be suppressed compared to
binary nucleon-nucleon collision scaling of p+p data. This suppression is
monotonically increasing with centrality, but most of the change occurs below
30% centrality, i.e. for collisions with less than about 140 participating
nucleons. The observed p_T and centrality dependence is consistent with the
particle production predicted by models including hard scattering and
subsequent energy loss of the scattered partons in the dense matter created in
the collisions.Comment: 7 pages text, LaTeX, 6 figures, 2 tables, 307 authors, resubmitted to
Phys. Lett. B. Revised to address referee concerns. Plain text data tables
for the points plotted in figures for this and previous PHENIX publications
are publicly available at
http://www.phenix.bnl.gov/phenix/WWW/run/phenix/papers.htm
Formation of dense partonic matter in relativistic nucleus-nucleus collisions at RHIC: Experimental evaluation by the PHENIX collaboration
Extensive experimental data from high-energy nucleus-nucleus collisions were
recorded using the PHENIX detector at the Relativistic Heavy Ion Collider
(RHIC). The comprehensive set of measurements from the first three years of
RHIC operation includes charged particle multiplicities, transverse energy,
yield ratios and spectra of identified hadrons in a wide range of transverse
momenta (p_T), elliptic flow, two-particle correlations, non-statistical
fluctuations, and suppression of particle production at high p_T. The results
are examined with an emphasis on implications for the formation of a new state
of dense matter. We find that the state of matter created at RHIC cannot be
described in terms of ordinary color neutral hadrons.Comment: 510 authors, 127 pages text, 56 figures, 1 tables, LaTeX. Submitted
to Nuclear Physics A as a regular article; v3 has minor changes in response
to referee comments. Plain text data tables for the points plotted in figures
for this and previous PHENIX publications are (or will be) publicly available
at http://www.phenix.bnl.gov/papers.htm
Measurement of e+e- -> pi+pi- cross section with CMD-2 around rho-meson
The cross section of the process e+e- -> pi+pi- has been measured using about
114000 events collected by the CMD-2 detector at the VEPP-2M e+e- collider in
the center-of-mass energy range from 0.61 to 0.96 GeV. Results of the pion form
factor determination with a 0.6% systematic uncertainty are presented.
Implications for the hadronic contribution to the muon anomalous magnetic
moment are discussed.Comment: 17 pages, 4 figures, submitted to PL
Fontes de energia em suplementos múltiplos para recria de novilhos mestiços em pastejo durante o período de transição seca/águas: desempenho produtivo e características nutricionais
The evolving SARS-CoV-2 epidemic in Africa: Insights from rapidly expanding genomic surveillance
INTRODUCTION
Investment in Africa over the past year with regard to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) sequencing has led to a massive increase in the number of sequences, which, to date, exceeds 100,000 sequences generated to track the pandemic on the continent. These sequences have profoundly affected how public health officials in Africa have navigated the COVID-19 pandemic.
RATIONALE
We demonstrate how the first 100,000 SARS-CoV-2 sequences from Africa have helped monitor the epidemic on the continent, how genomic surveillance expanded over the course of the pandemic, and how we adapted our sequencing methods to deal with an evolving virus. Finally, we also examine how viral lineages have spread across the continent in a phylogeographic framework to gain insights into the underlying temporal and spatial transmission dynamics for several variants of concern (VOCs).
RESULTS
Our results indicate that the number of countries in Africa that can sequence the virus within their own borders is growing and that this is coupled with a shorter turnaround time from the time of sampling to sequence submission. Ongoing evolution necessitated the continual updating of primer sets, and, as a result, eight primer sets were designed in tandem with viral evolution and used to ensure effective sequencing of the virus. The pandemic unfolded through multiple waves of infection that were each driven by distinct genetic lineages, with B.1-like ancestral strains associated with the first pandemic wave of infections in 2020. Successive waves on the continent were fueled by different VOCs, with Alpha and Beta cocirculating in distinct spatial patterns during the second wave and Delta and Omicron affecting the whole continent during the third and fourth waves, respectively. Phylogeographic reconstruction points toward distinct differences in viral importation and exportation patterns associated with the Alpha, Beta, Delta, and Omicron variants and subvariants, when considering both Africa versus the rest of the world and viral dissemination within the continent. Our epidemiological and phylogenetic inferences therefore underscore the heterogeneous nature of the pandemic on the continent and highlight key insights and challenges, for instance, recognizing the limitations of low testing proportions. We also highlight the early warning capacity that genomic surveillance in Africa has had for the rest of the world with the detection of new lineages and variants, the most recent being the characterization of various Omicron subvariants.
CONCLUSION
Sustained investment for diagnostics and genomic surveillance in Africa is needed as the virus continues to evolve. This is important not only to help combat SARS-CoV-2 on the continent but also because it can be used as a platform to help address the many emerging and reemerging infectious disease threats in Africa. In particular, capacity building for local sequencing within countries or within the continent should be prioritized because this is generally associated with shorter turnaround times, providing the most benefit to local public health authorities tasked with pandemic response and mitigation and allowing for the fastest reaction to localized outbreaks. These investments are crucial for pandemic preparedness and response and will serve the health of the continent well into the 21st century
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