1,375 research outputs found
Convergence of the Many-Body Expansion of Interaction Potentials: From van der Waals to Covalent and Metallic Systems
The many-body expansion of the interaction potential between atoms and molecules is analyzed in detail for different types of interactions involving up to seven atoms. Elementary clusters of Ar, Na, Si, and, in particular, Au are studied, using first-principles wave-function- and density-functional-based methods to obtain the individual n-body contributions to the interaction energies. With increasing atom number the many-body expansion converges rapidly only for long-range weak interactions. Large oscillatory behavior is observed for other types of interactions. This is consistent with the fact that Au clusters up to a certain size prefer planar structures over the more compact three-dimensional Lennard-Jones-type structures. Several Au model potentials and semi-empirical PM6 theory are investigated for their ability to reproduce the quantum results. We further investigate small water clusters as prototypes of hydrogen-bonded systems. Here, the many-body expansion converges rapidly, reflecting the localized nature of the hydrogen bond and justifying the use of two-body potentials to describe water-water interactions. The question of whether electron correlation contributions can be successfully modeled by a many-body interaction potential is also addressed
Report of the National Science Foundation-Sponsored GeoEngineering Extreme Events Reconnaissance (GEER) Team
The L’Aquila earthquake occurred on April 6 2009 at 03:32:39 local time. The
earthquake was located in the central Italy region of Abruzzo. Much of the damage
occurred in the capital city of L’Aquila, a city of approximate population 73000,
although many small villages in the surrounding regions were significantly damaged
including Paganica, Castelnuovo, and Onna. Collapsed and damaged structures in
L’Aquila included both older masonry buildings and relatively modern reinforced
concrete structures. At the time of this writing, 307 people are known to have died from the earthquake, most in collapsed structures, making this the deadliest earthquake to strike Italy since the 1980 Irpinia earthquake.
A number of reconnaissance teams were mobilized to the affected region in the
weeks following the earthquake. The national institute of geophysics and volcanology
(Istituto Nazionale di Geofisica e Vulcanologia, INGV) mobilized a team of geologists (EMERGEO Working Group) to look for evidence of surface rupture and other effects;
some of their findings are discussed in this report. The GEER team was assembled to
investigate geological, seismological, and geotechnical engineering aspects of the
event. The international GEER team is comprised of members from Italy, Austria,
Switzerland, Greece, and the United states. Team members were selected to provide
needed expertise in geology, engineering geology, GIS applications, earthquake
ground motions, and geotechnical earthquake engineering. The team includes
individuals highly experienced in post-earthquake reconnaissance and relatively young
professionals investigating their first earthquake.
The GEER team did not focus on structural engineering or lifeline aspects of the
event, which were investigated by an EERI team. The GEER and EERI activities were
closely coordinated to optimize resources in the documentation of the valuable,
perishable data associated with the earthquake effects.
The GEER team employed a number of innovative technologies to facilitate
effective reconnaissance. All teams mobilized for field work had a common GPS unit and laptop with a Google Earth (GE) GIS database activity maintained over the course
of the work. The GE database was used to keep track of visited locations, but also
contained maps of surface geology, locations of aftershocks, strong motion stations,
and other information relevant to investigators in the field. Another valuable use of
technology involved LIDAR mapping of a site having significant incidents of ground
failure (Lake Sinizzo).
This report presents the GEER findings. Following this introduction, Chapter 2
describes the geologic and tectonic setting, moment tensor solutions for the mainshock
and several triggered events, analysis of aftershock patterns, and analysis of GPS and
InSAR data. Included in Chapter 2 is a preliminary model of the ruptured fault. Chapter 3 describes the ground motions recorded during the mainshock by a digital instrument array. Metadata associated with the recordings is presented, trends in the recorded ground motions are presented, and preliminary comparisons to ground motion
prediction equations are made. Chapter 4 presents damage patterns, both within
L’Aquila and through comparisons of damage intensities in adjacent villages with similar
construction. The results provide valuable insights into possible site effects on ground
motion in regions where recordings are not available. Chapter 5 presents our findings
on ground failure, defined as permanent ground deformations induced by the
earthquake. Observed ground failure included several rockfalls, seismic compression of
fill materials, and apparent strength loss of soil materials leading to inward movement of the banks of a lake. Chapter 6 reviews the performance of earth dams and earth
retaining structures, both of which generally performed well
Electronic Structure and Heavy Fermion Behavior in LiV_2O_4
First principles density functional calculations of the electronic and
magnetic properties of spinel-structure LiVO have been performed
using the full potential linearized augmented planewave method. The
calculations show that the electronic structure near the Fermi energy consists
of a manifold of 12 bands derived from V states, weakly hybridized
with O p states. While the total width of this active manifold is approximately
2 eV, it may be roughly decomposed into two groups: high velocity bands and
flatter bands, although these mix in density functional calculations. The flat
bands, which are the more atomic-like lead to a high density of states and
magnetic instability of local moment character. The value of the on-site
exchange energy is sensitive to the exact exchange correlation parameterization
used in the calculations, but is much larger than the interaction between
neighboring spins, reflecting the weak coupling of the magnetic system with the
high velocity bands. A scenario for the observed heavy fermion behavior is
discussed in which conduction electrons in the dispersive bands are weakly
scattered by local moments associated with strongly correlated electrons in the
heavy bands.This is analogous to that in conventional Kondo type heavy
fermions, but is unusual in that both the local moments and conduction
electrons come from the same d-manifold.Comment: 6 Revtex pages, Postscript figs embedded. Revision: figure 4 replaced
with a better version, showing the band character explicitel
Power Spectrum in Krein Space Quantization
The power spectrum of scalar field and space-time metric perturbations
produced in the process of inflation of universe, have been presented in this
paper by an alternative approach to field quantization namely, Krein space
quantization [1,2]. Auxiliary negative norm states, the modes of which do not
interact with the physical world, have been utilized in this method. Presence
of negative norm states play the role of an automatic renormalization device
for the theory.Comment: 8 pages, appear in Int. J. Theor. Phy
Detecting Current Noise with a Josephson Junction in the Macroscopic Quantum Tunneling Regime
We discuss the use of a hysteretic Josephson junction to detect current
fluctuations with frequencies below the plasma frequency of the junction. These
adiabatic fluctuations are probed by switching measurements observing the
noise-affected average rate of macroscopic quantum tunneling of the detector
junction out of its zero-voltage state. In a proposed experimental scheme,
frequencies of the noise are limited by an on-chip filtering circuit. The third
cumulant of current fluctuations at the detector is related to an asymmetry of
the switching rates.Comment: 26 pages, 10 figures. To appear in Journal of Low Temperature Physics
in the proceedings of the ULTI conference organized in Lammi, Finland (2006
Gammaherpesvirus infection modulates the temporal and spatial expression of SCGB1A1 (CCSP) and BPIFA1 (SPLUNC1) in the respiratory tract
Murine γ-herpesvirus 68 (MHV-68) infection of Mus musculus-derived strains of mice is an established model of γ-herpesvirus infection. We have previously developed an alternative system using a natural host, the wood mouse (Apodemus sylvaticus), and shown that the MHV-68 M3 chemokine-binding protein contributes significantly to MHV-68 pathogenesis. Here we demonstrate in A. sylvaticus using high-density micro-arrays that M3 influences the expression of genes involved in the host response including Scgb1a1 and Bpifa1 that encode potential innate defense proteins secreted into the respiratory tract. Further analysis of MHV-68-infected animals showed that the levels of both protein and RNA for SCGB1A1 and BPIFA1 were decreased at day 7 post infection (p.i.) but increased at day 14 p.i. as compared with M3-deficient and mock-infected animals. The modulation of expression was most pronounced in bronchioles but was also present in the bronchi and trachea. Double staining using RNA in situ hybridization and immunohistology demonstrated that much of the BPIFA1 expression occurs in club cells along with SCGB1A1 and that BPIFA1 is stored within granules in these cells. The increase in SCGB1A1 and BPIFA1 expression at day 14 p.i. was associated with the differentiation of club cells into mucus-secreting cells. Our data highlight the role of club cells and the potential of SCGB1A1 and BPIFA1 as innate defense mediators during respiratory virus infection
A general T-matrix approach applied to two-body and three-body problems in cold atomic gases
We propose a systematic T-matrix approach to solve few-body problems with
s-wave contact interactions in ultracold atomic gases. The problem is generally
reduced to a matrix equation expanded by a set of orthogonal molecular states,
describing external center-of-mass motions of pairs of interacting particles;
while each matrix element is guaranteed to be finite by a proper
renormalization for internal relative motions. This approach is able to
incorporate various scattering problems and the calculations of related
physical quantities in a single framework, and also provides a physically
transparent way to understand the mechanism of resonance scattering. For
applications, we study two-body effective scattering in 2D-3D mixed dimensions,
where the resonance position and width are determined with high precision from
only a few number of matrix elements. We also study three fermions in a
(rotating) harmonic trap, where exotic scattering properties in terms of mass
ratios and angular momenta are uniquely identified in the framework of
T-matrix.Comment: 14 pages, 4 figure
Increased risk of lower limb osteoarthritis among former professional soccer (football) players
Background: Soccer is a high-speed contact sport with risk of injury. Despite long-standing concern, evidence to date remains inconsistent as to the association between playing professional-level soccer and lifelong musculoskeletal consequences.
Aims: The objectives were to assess risk of osteoarthritis in former professional soccer players compared to matched general population controls, and subsequently assess associated musculoskeletal disorders which may contribute to, or result from, osteoarthritis—specifically meniscal injury and joint replacement.
Methods: We conducted a retrospective cohort study using national electronic health records (EHRs) on a cohort of 7676 former professional soccer players aged 40 or over at recruitment, matched on year of birth, sex (all male) and socio-economic status with 23 028 general population controls. Outcomes of interest were obtained by utilizing individual-level record linkage to EHRs from general hospital inpatient and day-case admissions. Results: Compared to controls, former soccer players showed a greater risk of hospital admission for osteoarthritis (hazard ratio [HR] 3.01; 95% confidence interval [CI] 2.80–3.25; P < 0.001). This increased risk appeared age dependant, normalizing over age 80 years and reflective of increased risk of lower limb osteoarthritis. Further, risk of hospital admissions for meniscal injury (HR 2.73; 95% CI 2.42–3.08; P &lt; 0.001) and joint replacement (HR 2.82; 95% CI 2.23–3.57; P &lt; 0.001) were greater among former soccer players. Conclusions: We report an increased risk of lower limb osteoarthritis in former soccer players when compared with matched population controls. The results of this research add data in support of lower limb osteoarthritis among former soccer players representing a potential industrial injury
Exploring leadership in multi-sectoral partnerships
This article explores some critical aspects of leadership in the context of multi-sectoral partnerships. It focuses on leadership in practice and asks the question, `How do managers experience and perceive leadership in such partnerships?' The study contributes to the debate on whether leadership in a multi-sectoral partnership context differs from that within a single organization. It is based on the accounts of practising managers working in complex partnerships. The article highlights a number of leadership challenges faced by those working in multi-sectoral partnerships. Partnership practitioners were clear that leadership in partnerships was more complex than in single organizations. However, it was more difficult for them to agree a consensus on the essential nature of leadership in partnership. We suggest that a first-, second- and third-person approach might be a way of better interpreting leadership in the context of partnerships
- …