11,771 research outputs found
Three-dimensional quasi-Tonks gas in a harmonic trap
We analyze the macroscopic dynamics of a Bose gas in a harmonic trap with a
superimposed two-dimensional optical lattice, assuming a weak coupling between
different lattice sites. We consider the situation in which the local chemical
potential at each lattice site can be considered as that provided by the
Lieb-Liniger solution. Due to the weak coupling between sites and the form of
the chemical potential, the three-dimensional ground-state density profile and
the excitation spectrum acquire remarkable properties different from both 1D
and 3D gases. We call this system a quasi-Tonks gas. We discuss the range of
applicability of this regime, as well as realistic experimental situations
where it can be observed.Comment: 4 pages, 3 figures, misprints correcte
The incidence of fragility hip fractures in a subpopulation of South Africa
Background. Fragility hip fractures (FHFs) are associated with significant morbidity, mortality and burden on the healthcare system. European and North American literature suggests that the worldwide incidence of FHFs is increasing, but very little is known about the incidence of FHFs in Africa and South Africa (SA). Historically FHFs were believed to be uncommon in black African populations, but recent studies have shown a marked increase in the incidence compared with the early literature.
Objectives. To investigate the age-, gender-and population group-specific incidences of FHFs in a subpopulation in Eastern Cape Province, SA.
Methods. A retrospective review of all patients presenting with FHFs was performed at a tertiary hospital in the Eastern Cape over a 1-year period. Age-, gender-and population group-specific incidence rates were calculated for 5-year age intervals using the age distribution data of the western region of the Eastern Cape (WREC) as a denominator for each age group. Overall crude incidence rates were calculated by using the sum total of FHFs, divided by the study population. All incidences were calculated as number of fractures per 100 000 people annually.
Results. A total of 253 patients with FHFs were included. The crude incidence rate of low-energy hip fractures in the WREC was 19.3 per 100 000 (males 14.6, females 23.4) over the study period. Population group-specific incidences were 15.1, 18.7, 19.9 and 46.6 per 100 000 for black, coloured, Indian and white population groups, respectively. The highest number of low-energy hip fractures in females occurred in the ≥85-year (19.6%) and 70 -74-year (16.5%) age groups, with the highest number of male cases observed in the 60 -64-year group (20.2%). The highest frequency distribution of FHFs was observed in black males aged 60 -64 years (5.5%; n=14) and black females aged 70 -74 years (6.3%; n=16).
Conclusions. The local incidence of FHFs is higher than initially reported, but when compared with other countries remains on the lower end of spectrum. A large proportion of FHFs are occurring in young patients (<65 years). These findings warrant further investigation that may prompt the development of preventive strategies and optimal treatment programmes
Understanding behaviour in problem structuring methods interventions with activity theory
This is the author accepted manuscript. The final version is available from the publisher via the DOI in this record.This article argues that OR interventions, particularly problem structuring methods (PSM), are complex events that cannot be understood by conventional methods alone. In this paper an alternative approach is introduced, where the units of analysis are the activity systems constituted by and constitutive of PSM interventions. The paper outlines the main theoretical and methodological concerns that need to be appreciated in studying PSM interventions. The paper then explores activity theory as an approach to study them. A case study describing the use of this approach is provided
Full Scale Proton Beam Impact Testing of new CERN Collimators and Validation of a Numerical Approach for Future Operation
New collimators are being produced at CERN in the framework of a large
particle accelerator upgrade project to protect beam lines against stray
particles. Their movable jaws hold low density absorbers with tight geometric
requirements, while being able to withstand direct proton beam impacts. Such
events induce considerable thermo-mechanical loads, leading to complex
structural responses, which make the numerical analysis challenging. Hence, an
experiment has been developed to validate the jaw design under representative
conditions and to acquire online results to enhance the numerical models. Two
jaws have been impacted by high-intensity proton beams in a dedicated facility
at CERN and have recreated the worst possible scenario in future operation. The
analysis of online results coupled to post-irradiation examinations have
demonstrated that the jaw response remains in the elastic domain. However, they
have also highlighted how sensitive the jaw geometry is to its mounting support
inside the collimator. Proton beam impacts, as well as handling activities, may
alter the jaw flatness tolerance value by 70 m, whereas the
flatness tolerance requirement is 200 m. In spite of having validated
the jaw design for this application, the study points out numerical limitations
caused by the difficulties in describing complex geometries and boundary
conditions with such unprecedented requirements.Comment: 22 pages, 17 figures, Prepared for submission to JINS
Absence of a Cell Membrane Alteration Function in Non-transforming Mutants of Polyoma Virus
Numerical Investigation of Light Scattering off Split-Ring Resonators
Recently, split ring-resonators (SRR's) have been realized experimentally in
the near infrared (NIR) and optical regime. In this contribution we numerically
investigate light propagation through an array of metallic SRR's in the NIR and
optical regime and compare our results to experimental results.
We find numerical solutions to the time-harmonic Maxwell's equations by using
advanced finite-element-methods (FEM). The geometry of the problem is
discretized with unstructured tetrahedral meshes. Higher order, vectorial
elements (edge elements) are used as ansatz functions. Transparent boundary
conditions and periodic boundary conditions are implemented, which allow to
treat light scattering problems off periodic structures.
This simulation tool enables us to obtain transmission and reflection spectra
of plane waves which are incident onto the SRR array under arbitrary angles of
incidence, with arbitrary polarization, and with arbitrary
wavelength-dependencies of the permittivity tensor. We compare the computed
spectra to experimental results and investigate resonances of the system.Comment: 9 pages, 8 figures (see original publication for images with a better
resolution
Mutual Event Observations of Io's Sodium Corona
We have measured the column density profile of Io's sodium corona using 10 mutual eclipses between the Galilean satellites. This approach circumvents the problem of spatially resolving Io's corona directly from Io's bright continuum in the presence of atmospheric seeing and telescopic scattering. The primary goal is to investigate the spatial and temporal variations of Io's corona. Spectra from the Keck Observatory and McDonald Observatory from 1997 reveal a corona that is only approximately spherically symmetric around Io. Comparing the globally averaged radial sodium column density profile in the corona with profiles measured in 1991 and 1985, we find that there has been no significant variation. However, there appears to be a previously undetected asymmetry: the corona above Io's sub-Jupiter hemisphere is consistently more dense than above the anti-Jupiter hemisphere
Expansion of a coherent array of Bose-Einstein condensates
We investigate the properties of a coherent array containing about 200
Bose-Einstein condensates produced in a far detuned 1D optical lattice. The
density profile of the gas, imaged after releasing the trap, provides
information about the coherence of the ground-state wavefunction. The measured
atomic distribution is characterized by interference peaks. The time evolution
of the peaks, their relative population as well as the radial size of the
expanding cloud are in good agreement with the predictions of theory. The 2D
nature of the trapped condensates and the conditions required to observe the
effects of coherence are also discussed.Comment: 4 pages, 3 figure
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