404 research outputs found
Direct observation of growth and collapse of a Bose-Einstein condensate with attractive interactions
The dynamical behavior of Bose-Einstein condensation (BEC) in a gas with
attractive interactions is striking. Quantum theory predicts that BEC of a
spatially homogeneous gas with attractive interactions is precluded by a
conventional phase transition into either a liquid or solid. When confined to a
trap, however, such a condensate can form provided that its occupation number
does not exceed a limiting value. The stability limit is determined by a
balance between self-attraction and a repulsion arising from position-momentum
uncertainty under conditions of spatial confinement. Near the stability limit,
self-attraction can overwhelm the repulsion, causing the condensate to
collapse. Growth of the condensate, therefore, is punctuated by intermittent
collapses, which are triggered either by macroscopic quantum tunneling or
thermal fluctuation. Previous observation of growth and collapse has been
hampered by the stochastic nature of these mechanisms. Here we reduce the
stochasticity by controlling the initial number of condensate atoms using a
two-photon transition to a diatomic molecular state. This enables us to obtain
the first direct observation of the growth of a condensate with attractive
interactions and its subsequent collapse.Comment: 10 PDF pages, 5 figures (2 color), 19 references, to appear in Nature
Dec. 7 200
Formation and Propagation of Matter Wave Soliton Trains
Attraction between atoms in a Bose-Einstein-Condensate renders the condensate
unstable to collapse. Confinement in an atom trap, however, can stabilize the
condensate for a limited number of atoms, as was observed with 7Li, but beyond
this number, the condensate collapses. Attractive condensates constrained to
one-dimensional motion are predicted to form stable solitons for which the
attractive interactions exactly compensate for the wave packet dispersion. Here
we report the formation or bright solitons of 7Li atoms created in a quasi-1D
optical trap. The solitons are created from a stable Bose-Einstein condensate
by magnetically tuning the interactions from repulsive to attractive. We
observe a soliton train, containing many solitons. The solitons are set in
motion by offsetting the optical potential and are observed to propagate in the
potential for many oscillatory cycles without spreading. Repulsive interactions
between neighboring solitons are inferred from their motion
How weeds emerge: a taxonomic and trait‐based examination using United States data
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106812/1/nph12698.pd
Spin-Imbalance in a One-Dimensional Fermi Gas
Superconductivity and magnetism generally do not coexist. Changing the
relative number of up and down spin electrons disrupts the basic mechanism of
superconductivity, where atoms of opposite momentum and spin form Cooper pairs.
Nearly forty years ago Fulde and Ferrell and Larkin and Ovchinnikov proposed an
exotic pairing mechanism (FFLO) where magnetism is accommodated by formation of
pairs with finite momentum. Despite intense theoretical and experimental
efforts, however, polarized superconductivity remains largely elusive. Here we
report experimental measurements of density profiles of a two spin mixture of
ultracold 6Li atoms trapped in an array of one dimensional (1D) tubes, a system
analogous to electrons in 1D wires. At finite spin imbalance, the system phase
separates with an inverted phase profile in comparison to the three-dimensional
case. In 1D we find a partially polarized core surrounded by wings composed of
either a completely paired BCS superfluid or a fully polarized Fermi gas,
depending on the degree of polarization. Our observations are in quantitative
agreement with theoretical calculations in which the partially polarized phase
is found to be a 1D analogue of the FFLO state. This study demonstrates how
ultracold atomic gases in 1D may be used to create non-trivial new phases of
matter, and also paves the way for direct observation and further study of the
FFLO phase.Comment: 30 pages, 7 figure
Professional Development
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68715/2/10.1177_014572179301900204.pd
Identification and characterization of a novel non-structural protein of bluetongue virus
Bluetongue virus (BTV) is the causative agent of a major disease of livestock (bluetongue). For over two decades, it has been widely accepted that the 10 segments of the dsRNA genome of BTV encode for 7 structural and 3 non-structural proteins. The non-structural proteins (NS1, NS2, NS3/NS3a) play different key roles during the viral replication cycle. In this study we show that BTV expresses a fourth non-structural protein (that we designated NS4) encoded by an open reading frame in segment 9 overlapping the open reading frame encoding VP6. NS4 is 77–79 amino acid residues in length and highly conserved among several BTV serotypes/strains. NS4 was expressed early post-infection and localized in the nucleoli of BTV infected cells. By reverse genetics, we showed that NS4 is dispensable for BTV replication in vitro, both in mammalian and insect cells, and does not affect viral virulence in murine models of bluetongue infection. Interestingly, NS4 conferred a replication advantage to BTV-8, but not to BTV-1, in cells in an interferon (IFN)-induced antiviral state. However, the BTV-1 NS4 conferred a replication advantage both to a BTV-8 reassortant containing the entire segment 9 of BTV-1 and to a BTV-8 mutant with the NS4 identical to the homologous BTV-1 protein. Collectively, this study suggests that NS4 plays an important role in virus-host interaction and is one of the mechanisms played, at least by BTV-8, to counteract the antiviral response of the host. In addition, the distinct nucleolar localization of NS4, being expressed by a virus that replicates exclusively in the cytoplasm, offers new avenues to investigate the multiple roles played by the nucleolus in the biology of the cell
Comparing counselling alone versus counselling supplemented with guided use of a well-being app for university students experiencing anxiety or depression (CASELOAD): protocol for a feasibility trial.
BACKGROUND: University counselling services face a unique challenge to offer short-term therapeutic support to students presenting with complex mental health needs and in a setting which suits the academic timetable. The recent availability of mobile phone applications (apps) offers an opportunity to supplement face-to-face therapy and has the potential to reach a wider audience, maintain engagement between therapy sessions, and enhance therapeutic outcomes. The present study, entitled Counselling plus Apps for Students Experiencing Levels of Anxiety or Depression (CASELOAD), aims to explore the feasibility of supplementing counselling with guided use of a well-being app. METHODS/DESIGN: Forty help-seeking university students (aged 18 years and over) with symptoms of moderate anxiety or depression will be recruited from a University Counselling Service (UCS) in the United Kingdom (UK). Participants will be recruited via counsellors who provide the initial clinical assessment and who determine treatment allocation to one of two treatments on the basis of client-treatment fit. The two conditions comprise (1) counselling alone (treatment as usual/TAU) or (2) counselling supplemented with guided use of a well-being app (enhanced intervention). Trained counsellors will deliver up to six counselling sessions in each treatment arm across a 6-month period, and the session frequency will be decided by client-counsellor discussion. Assessments will occur at baseline, every counselling session, post-intervention (3 months after consent) and follow-up (6 months after consent). Assessments will include clinical measures of anxiety, depression, psychological functioning, specific mental health concerns (e.g. academic distress and substance misuse), resilience and therapeutic alliance. The usage, acceptability, feasibility and potential implications of combining counselling with guided use of the well-being app will be assessed through audio recordings of counselling sessions, telephone interviews with participants, focus groups with counsellors and counsellor notes. DISCUSSION: This study will inform the design of a randomised pilot trial and a definitive trial which aim to improve therapy engagement, reduce dropout and enhance clinical outcomes of student counselling. TRIAL REGISTRATION: ISRCTN55102899
The Role of Individual Variables, Organizational Variables and Moral Intensity Dimensions in Libyan Management Accountants’ Ethical Decision Making
This study investigates the association of a broad set of variables with the ethical decision making of management accountants in Libya. Adopting a cross-sectional methodology, a questionnaire including four different ethical scenarios was used to gather data from 229 participants. For each scenario, ethical decision making was examined in terms of the recognition, judgment and intention stages of Rest’s model. A significant relationship was found between ethical recognition and ethical judgment and also between ethical judgment and ethical intention, but ethical recognition did not significantly predict ethical intention—thus providing support for Rest’s model. Organizational variables, age and educational level yielded few significant results. The lack of significance for codes of ethics might reflect their relative lack of development in Libya, in which case Libyan companies should pay attention to their content and how they are supported, especially in the light of the under-development of the accounting profession in Libya. Few significant results were also found for gender, but where they were found, males showed more ethical characteristics than females. This unusual result reinforces the dangers of gender stereotyping in business. Personal moral philosophy and moral intensity dimensions were generally found to be significant predictors of the three stages of ethical decision making studied. One implication of this is to give more attention to ethics in accounting education, making the connections between accounting practice and (in Libya) Islam. Overall, this study not only adds to the available empirical evidence on factors affecting ethical decision making, notably examining three stages of Rest’s model, but also offers rare insights into the ethical views of practising management accountants and provides a benchmark for future studies of ethical decision making in Muslim majority countries and other parts of the developing world
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Response of the North Atlantic storm track to climate change shaped by ocean–atmosphere coupling
A poleward shift of the mid-latitude storm tracks in response to anthropogenic greenhouse-gas forcing has been diagnosed in climate model simulations1, 2. Explanations of this effect have focused on atmospheric dynamics3, 4, 5, 6, 7. However, in contrast to storm tracks in other regions, the North Atlantic storm track responds by strengthening and extending farther east, in particular on its southern flank8. These adjustments are associated with an intensification and extension of the eddy-driven jet towards western Europe9 and are expected to have considerable societal impacts related to a rise in storminess in Europe10, 11, 12. Here, we apply a regression analysis to an ensemble of coupled climate model simulations to show that the coupling between ocean and atmosphere shapes the distinct storm-track response to greenhouse-gas forcing in the North Atlantic region. In the ensemble of simulations we analyse, at least half of the differences between the storm-track responses of different models are associated with uncertainties in ocean circulation changes. We compare the fully coupled simulations with both the associated slab model simulations and an ocean-forced experiment with one climate model to establish causality. We conclude that uncertainties in the response of the North Atlantic storm track to anthropogenic emissions could be reduced through tighter constraints on the future ocean circulation
Successful surgical excision of primary right atrial angiosarcoma
Primary cardiac angiosarcoma is a rare and aggressive tumor with a high incidence of metastatic spread (up to 89%) at the time of diagnosis, which restricts the indication for surgical resection to a small number of patients. We report the case of a 50-year old Caucasian woman with non-metastatic primary right atrial angiosarcoma, who underwent successful surgical excision of the tumor (with curative intent) and reconstruction of the right atrium with a porcine pericardial patch. However, after a symptom-free survival of five months the patient presented with bone and liver metastases without evidence of local tumor recurrence
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