793 research outputs found
Characterization of elastic scattering near a Feshbach resonance in rubidium 87
The s-wave scattering length for elastic collisions between 87Rb atoms in the
state |f,m_f>=|1,1> is measured in the vicinity of a Feshbach resonance near
1007 G. Experimentally, the scattering length is determined from the mean-field
driven expansion of a Bose-Einstein condensate in a homogeneous magnetic field.
The scattering length is measured as a function of the magnetic field and
agrees with the theoretical expectation. The position and the width of the
resonance are determined to be 1007.40 G and 0.20 G, respectively.Comment: 4 pages, 2 figures minor revisions: added Ref.6, included error bar
Electron transport through interacting quantum dots
We present a detailed theoretical investigation of the effect of Coulomb
interactions on electron transport through quantum dots and double barrier
structures connected to a voltage source via an arbitrary linear impedance.
Combining real time path integral techniques with the scattering matrix
approach we derive the effective action and evaluate the current-voltage
characteristics of quantum dots at sufficiently large conductances. Our
analysis reveals a reach variety of different regimes which we specify in
details for the case of chaotic quantum dots. At sufficiently low energies the
interaction correction to the current depends logarithmically on temperature
and voltage. We identify two different logarithmic regimes with the crossover
between them occurring at energies of order of the inverse dwell time of
electrons in the dot. We also analyze the frequency-dependent shot noise in
chaotic quantum dots and elucidate its direct relation to interaction effects
in mesoscopic electron transport.Comment: 21 pages, 4 figures. References added, discussion slightly extende
Recommended from our members
A multilevel neo-institutional analysis of infection prevention and control in English hospitals: coerced safety culture change?
Despite committed policy, regulative and professional efforts on healthcare safety, little is known about how such macro-interventions permeate organisations and shape culture over time. Informed by neo-institutional theory, we examined how inter-organisational influences shaped safety practices and inter-subjective meanings following efforts for coerced culture change. We traced macro-influences from 2000 to 2015 in infection prevention and control (IPC). Safety perceptions and meanings were inductively analysed from 130 in-depth qualitative interviews with senior- and middle-level managers from 30 English hospitals. A total of 869 institutional interventions were identified; 69% had a regulative component. In this context of forced implementation of safety practices, staff experienced inherent tensions concerning the scope of safety, their ability to be open and prioritisation of external mandates over local need. These tensions stemmed from conflicts among three co-existing institutional logics prevalent in the NHS. In response to requests for change, staff flexibly drew from a repertoire of cognitive, material and symbolic resources within and outside their organisations. They crafted 'strategies of action', guided by a situated assessment of first-hand practice experiences complementing collective evaluations of interventions such as 'pragmatic', 'sensible' and also 'legitimate'. Macro-institutional forces exerted influence either directly on individuals or indirectly by enriching the organisational cultural repertoire
Bloodstream infections in community hospitals in the 21st century: A multicenter cohort study
Background: While the majority of healthcare in the US is provided in community hospitals, the epidemiology and treatment of bloodstream infections in this setting is unknown. Methods and Findings: We undertook this multicenter, retrospective cohort study to 1) describe the epidemiology of bloodstream infections (BSI) in a network of community hospitals and 2) determine risk factors for inappropriate therapy for bloodstream infections in community hospitals. 1,470 patients were identified as having a BSI in 9 community hospitals in the southeastern US from 2003 through 2006. The majority of BSIs were community-onset, healthcare associated (n = 823, 56%); 432 (29%) patients had community-acquired BSI, and 215 (15%) had hospital-onset, healthcare-associated BSI. BSIs due to multidrug-resistant pathogens occurred in 340 patients (23%). Overall, the three most common pathogens were S. aureus (n = 428, 28%), E. coli (n = 359, 24%), coagulase-negative Staphylococci (n = 148, 10%), though type of infecting orgaism varied by location of acquisition (e.g., community-acquired). Inappropriate empiric antimicrobial therapy was given to 542 (38%) patients. Proportions of inappropriate therapy varied by hospital (median = 33%, range 21-71%). Multivariate logistic regression identified the following factors independently associated with failure to receive appropriate empiric antimicrobial therapy: hospital where the patient received care (p,0.001), assistance with $3 ADLs (p = 0.005), Charlson score (p = 0.05), community-onset, healthcare-associated infection (p = 0.01), and hospital-onset, healthcareassociated infection (p = 0.02). Important interaction was observed between Charlson score and location of acquisition. Conclusions: Our large, multicenter study provides the most complete picture of BSIs in community hospitals in the US to date. The epidemiology of BSIs in community hospitals has changed: community-onset, healthcare-associated BSI is most common, S. aureus is the most common cause, and 1 of 3 patients with a SI receives inappropriate empiric antimicrobial therapy. Our data suggest that appropriateness of empiric antimicrobial therapy is an important and needed performance metric for physicians and hospital stewardship programs in community hospitals
Making sense of leadership development: Developing a community of education leaders
In education literature there is a distinct lack of scholarly work on issues of leadership other than on functional leadership at lower levels or high-level individual leadership activity which dominates existing studies. This empirical research is based on the result of a merger of education providers within the North East of England. A crucial aspiration of the newly merged organisation was to provide an overarching innovative leadership structure to facilitate integrated leadership. The specific focus of this article is participants of a bespoke postgraduate learning intervention. The authors apply sense-making theory to identify how student-leaders undertaking a leadership development
intervention developed to become a community of education leaders. The reflective accounts of the student-leaders indicated a combined approach of distributed, shared and collaborative leadership. Whilst the study was conducted in the UK, the concepts and ideas are likely to have international application
Current Fluctuations and Electron-Electron Interactions in Coherent Conductors
We analyze current fluctuations in mesoscopic coherent conductors in the
presence of electron-electron interactions. In a wide range of parameters we
obtain explicit universal dependencies of the current noise on temperature,
voltage and frequency. We demonstrate that Coulomb interaction decreases the
Nyquist noise. In this case the interaction correction to the noise spectrum is
governed by the combination , where is the transmission
of the -th conducting mode. The effect of electron-electron interactions on
the shot noise is more complicated. At sufficiently large voltages we recover
two different interaction corrections entering with opposite signs. The net
result is proportional to , i.e. Coulomb interaction
decreases the shot noise at low transmissions and increases it at high
transmissions.Comment: 16 pages, 2 figure
POU5F1 (OCT3/4) identifies cells with pluripotent potential in human germ cell tumors
Human germ cell tumors (GCTs) may have variable histology and clinical
behavior, depending on factors such as sex of the patient, age at clinical
diagnosis, and anatomical site of the tumor. Some types of GCT, i.e., the
seminomas/germinomas/dysgerminomas and embryonal carcinomas (the stem cell
component of nonseminomas), have pluripotent potential, which is
demonstrated by their capacity to differentiate into somatic and/or
extraembryonic elements. Although embryonal carcinoma cells are
intrinsically pluripotent, seminoma/germinoma/dysgerminoma cells, as well
as their precursor carcinoma in situ/gonadoblastoma cells, have the
phenotype of early germ cells that can be activated to pluripotency. The
other types of GCT (teratomas and yolk sac tumors of infants and newborn,
dermoid cyst of the ovary, and spermatocytic seminoma of elderly) are
composed of (fully) differentiated tissues and lack the appearance of
undifferentiated and pluripotent stem cells. OCT3/4, a transcription
factor also known as OTF3 and POU5F1, is involved in regulation of
pluripotency during normal development and is detectable in embryonic stem
and germ cells. We analyzed the presence of POU5F1 in GCT and other tumor
types using immunohistochemistry. The protein was consistently detected in
carcinoma in situ/gonadoblasto
Nonperturbative renormalization group approach to frustrated magnets
This article is devoted to the study of the critical properties of classical
XY and Heisenberg frustrated magnets in three dimensions. We first analyze the
experimental and numerical situations. We show that the unusual behaviors
encountered in these systems, typically nonuniversal scaling, are hardly
compatible with the hypothesis of a second order phase transition. We then
review the various perturbative and early nonperturbative approaches used to
investigate these systems. We argue that none of them provides a completely
satisfactory description of the three-dimensional critical behavior. We then
recall the principles of the nonperturbative approach - the effective average
action method - that we have used to investigate the physics of frustrated
magnets. First, we recall the treatment of the unfrustrated - O(N) - case with
this method. This allows to introduce its technical aspects. Then, we show how
this method unables to clarify most of the problems encountered in the previous
theoretical descriptions of frustrated magnets. Firstly, we get an explanation
of the long-standing mismatch between different perturbative approaches which
consists in a nonperturbative mechanism of annihilation of fixed points between
two and three dimensions. Secondly, we get a coherent picture of the physics of
frustrated magnets in qualitative and (semi-) quantitative agreement with the
numerical and experimental results. The central feature that emerges from our
approach is the existence of scaling behaviors without fixed or pseudo-fixed
point and that relies on a slowing-down of the renormalization group flow in a
whole region in the coupling constants space. This phenomenon allows to explain
the occurence of generic weak first order behaviors and to understand the
absence of universality in the critical behavior of frustrated magnets.Comment: 58 pages, 15 PS figure
- âŠ