3,131 research outputs found
Beyond the Landau Criterion for Superfluidity
According to the Landau criterion for superfluidity, a Bose-Einstein
condensate flowing with a group velocity smaller than the sound velocity is
energetically stable to the presence of perturbing potentials. We found that
this is strictly correct only for vanishingly small perturbations. The
superfluid critical velocity strongly depends on the strength and shape of the
defect. We quantitatively study, both numerically and with an approximate
analytical model, the dynamical response of a one-dimensional condensate
flowing against an istantaneously raised spatially periodic defect. We found
that the critical velocity decreases by incresing the strength of the
defect , up to to a critical value of the defect intensity where the
critical velocity vanishes
Features in the Primordial Spectrum from WMAP: A Wavelet Analysis
Precise measurements of the anisotropies in the cosmic microwave background
enable us to do an accurate study on the form of the primordial power spectrum
for a given set of cosmological parameters. In a previous paper (Shafieloo and
Souradeep 2004), we implemented an improved (error sensitive) Richardson-Lucy
deconvolution algorithm on the measured angular power spectrum from the first
year of WMAP data to determine the primordial power spectrum assuming a
concordance cosmological model. This recovered spectrum has a likelihood far
better than a scale invariant, or, `best fit' scale free spectra (\Delta ln L =
25 w.r.t. Harrison Zeldovich, and, \Delta ln L = 11 w.r.t. power law with
n_s=0.95). In this paper we use Discrete Wavelet Transform (DWT) to decompose
the local features of the recovered spectrum individually to study their effect
and significance on the recovered angular power spectrum and hence the
likelihood. We show that besides the infra-red cut off at the horizon scale,
the associated features of the primordial power spectrum around the horizon
have a significant effect on improving the likelihood. The strong features are
localised at the horizon scale.Comment: 8 pages, 4 figures, uses Revtex4, matches version accepted to Phys.
Rev. D, main results and conclusions unchanged, references adde
Computerized Tomography Detects Pulmonary Lesions in Children with Normal Radiographs Diagnosed to have Tuberculosis
This report is based on observations during the conduct of a larger study to develop diagnostic
criteria for childhood tuberculosis (TB). Of 20l children confirmed to have pulmonary or lymph
node TB, 84 had normal chest radiographs. Computerized tomography (CT) of the chest was
performed in nine of them, seven of whom had normal chest radiographs while two had visible
calcification. Eight of the nine children had definitive lesions detected by computerized
tomography of the chest. While five children had primarily hilar lymph node enlargement, three
had pulmonary parenchymal lesions. The use of more sensitive diagnostic tests like computed
tomography helps to detect tuberculosis lesions not otherwise visualized on chest radiographs.
This report highlights the difficulty in excluding active tuberculosis in children. More studies are
required on the role of CT scans in the diagnosis of tuberculosis in children
Quantum Dynamics of Three Coupled Atomic Bose-Einstein Condensates
The simplest model of three coupled Bose-Einstein Condensates (BEC) is
investigated using a group theoretical method. The stationary solutions are
determined using the SU(3) group under the mean field approximation. This
semiclassical analysis using the system symmetries shows a transition in the
dynamics of the system from self trapping to delocalization at a critical value
for the coupling between the condensates. The global dynamics are investigated
by examination of the stable points and our analysis shows the structure of the
stable points depends on the ratio of the condensate coupling to the
particle-particle interaction, undergoes bifurcations as this ratio is varied.
This semiclassical model is compared to a full quantum treatment, which also
displays the dynamical transition. The quantum case has collapse and revival
sequences superposed on the semiclassical dynamics reflecting the underlying
discreteness of the spectrum. Non-zero circular current states are also
demonstrated as one of the higher dimensional effects displayed in this system.Comment: Accepted to PR
Spectral Properties of Coupled Bose-Einstein Condensates
We investigate the energy spectrum structure of a system of two (identical)
interacting bosonic wells occupied by N bosons within the Schwinger realization
of the angular momentum. This picture enables us to recognize the symmetry
properties of the system Hamiltonian H and to use them for characterizing the
energy eigenstates. Also, it allows for the derivation of the single-boson
picture which is shown to be the background picture naturally involved by the
secular equation for H. After deriving the corresponding eigenvalue equation,
we recast it in a recursive N-dependent form which suggests a way to generate
the level doublets (characterizing the H spectrum) via suitable inner
parameters. Finally, we show how the presence of doublets in the spectrum
allows to recover, in the classical limit, the symmetry breaking effect that
characterizes the system classically.Comment: 8 pages, 3 figures; submitted to Phys. Rev. A. The present extended
form replaces the first version in the letter forma
Synthesis and antiproliferative activity of novel homopiperazine derivatives in leukemia cells
A series of novel homopiperazine derivatives were synthesized and characterized using 1H NMR, LC MS, IR and elemental analysis data. These novel molecules were evaluated for their antiproliferative activity against Reh, leukemia cells using trypan blue and MTT assays. All the molecules showed cytotoxicity with IC50 values between 50-100 μM as calculated by trypan blue assay and greater than 100 μM as calculated by MTT assay. Compound 6b with 3,5-dinitro substituents on phenyl ring of the aryl carboxamide moiety attached to homopiperazine ring showed good activity with IC50 value of 41 μM
The evolution of classification systems: Ontogeny of the UDC
To classify is to put things in meaningful groups, but the criteria for doing
so can be problematic. Study of evolution of classification includes
ontogenetic analysis of change in classification over time. We present an
empirical analysis of the UDC over the entire period of its development. We
demonstrate stability in main classes, with major change driven by 20th century
scientific developments. But we also demonstrate a vast increase in the
complexity of auxiliaries. This study illustrates an alternative to Tennis'
"scheme-versioning" method.Comment: ISKO conference 201
Developing resources to facilitate culturally-sensitive service planning and delivery – doing research inclusively with people with learning disabilities
Background Black, Asian and minority ethnic people with learning disabilities face inequities in health and social care provision. Lower levels of service uptake and satisfaction with services have been reported, however, this is largely based on the views of carers. The ‘Access to Social Care: Learning Disabilities (ASC-LD)’ study sought to explore the views and experiences of social support services among adults with learning disabilities from Black, Asian and minority ethnic communities. Interviews with 32 Black, Asian and minority ethnic adults with learning disabilities were conducted to explore participants’ cultural identities, their understanding and experience of ‘support’. The views and experiences expressed in the ASC-LD study were used in the ‘Tools for Talking project’ to develop a suite of resources designed to facilitate culturally-sensitive communication and information-sharing, service planning and delivery through improved mutual understanding between providers and users of services. This paper describes the Tools for Talking project which sought to co-develop the resources through a partnership event. Methods An inclusive approach was adopted to address issues that are important to people with learning disabilities, to represent their views and experiences, and to involve Black, Asian and minority ethnic people with learning disabilities in the research process. Partnerships were developed with provider organisations and service users who were invited to a ‘Partnership Event’. Collaborators at the partnership event were asked to comment on and evaluate draft resources which included a series of videos and activities to explore topics that emerged as important in the ASC-LD study. Their comments were collated and the tools developed as they suggested. Results Using the results from the ASC-LD study helped to ensure that the draft resources were relevant to service users, addressing topics that were important to them. The partnership event was an effective method to collaborate with a relatively large number of stakeholders. However, the event was resource intensive and required substantial planning to ensure active and meaningful participation. Considerations, such as inviting stakeholders, developing the programme and selecting a venue are discussed. Conclusions The partnership approach has led to the development of a set of five illustrative videos and accompanying activities that address issues that emerged from the collaborative process including: culture, activities, support from staff, important people, choices and independence. These resources are freely available at: www.Toolsfortalking.co.uk. They are designed to be used by users and providers of services, but may also be useful in other settings
Gamow-Teller Strengths of the Inverse-Beta Transition 176Yb --> 176Lu for Spectroscopy of Proton-Proton and other sub-MeV Solar Neutrinos
Discrete Gamow-Teller (GT) transitions, 176Yb-->176Lu at low excitation
energies have been measured via the (3He,t) reaction at 450 MeV and at 0
degrees. For 176Yb, two low-lying states are observed, setting low thresholds
Q(neutrino)=301 and 445 keV for neutrino capture. Capture rates estimated from
the measured GT strengths, the simple two-state excitation structure, and the
low Q(neutrino) in Yb--Lu indicate that Yb-based neutrino-detectors are well
suited for a direct measurement of the complete sub-MeV solar electron-neutrino
spectrum (including pp neutrinos) where definitive effects of flavor conversion
are expected
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