3,361 research outputs found
Dissipative Transport of a Bose-Einstein Condensate
We investigate the effects of impurities, either correlated disorder or a
single Gaussian defect, on the collective dipole motion of a Bose-Einstein
condensate of Li in an optical trap. We find that this motion is damped at
a rate dependent on the impurity strength, condensate center-of-mass velocity,
and interatomic interactions. Damping in the Thomas-Fermi regime depends
universally on the disordered potential strength scaled to the condensate
chemical potential and the condensate velocity scaled to the peak speed of
sound. The damping rate is comparatively small in the weakly interacting
regime, and the damping in this case is accompanied by strong condensate
fragmentation. \textit{In situ} and time-of-flight images of the atomic cloud
provide evidence that this fragmentation is driven by dark soliton formation.Comment: 14 pages, 20 figure
Success Despite Socioeconomics: A Case Study of a High-Achieving, High-Poverty School
Effective school leadership is becoming more difficult than ever with the challenges of increased accountability and high stakes testing that are components of federal No Child Left Behind (NCLB) legislation. These challenges are more pronounced in schools with high rates of poverty. This was a case study of a high performing, high poverty school that has consistently been one of the highest performing elementary schools in the state. The purpose of the study was to describe the leadership that exists at the school, the culture of the school, and programs that contribute to the school’s success. The researcher conducted observations at the school site and interviews with school personnel. School personnel also completed the School Culture Survey and the Vanderbilt Assessment of Leadership in Education (VAL-ED). The study revealed school leadership that had high expectations for staff members and emphasized small group instruction, collaboration, and continuous improvement in instructional practices. The culture of the school was that of excellence, continuous improvement, school pride, and collaboration
Pepducin-mediated cardioprotection via β-arrestin-biased β2-adrenergic receptor-specific signaling
Reperfusion as a therapeutic intervention for acute myocardial infarction-induced cardiac injury itself induces further cardiomyocyte death. β-arrestin (βarr)-biased β-adrenergic receptor (βAR) activation promotes survival signaling responses in vitro; thus, we hypothesize that this pathway can mitigate cardiomyocyte death at the time of reperfusion to better preserve function. However, a lack of efficacious βarr-biased orthosteric small molecules has prevented investigation into whether this pathway relays protection against ischemic injury in vivo. We recently demonstrated that the pepducin ICL1-9, a small lipidated peptide fragment designed from the first intracellular loop of β2AR, allosterically engaged pro-survival signaling cascades in a βarr-dependent manner in vitro. Thus, in this study we tested whether ICL1-9 relays cardioprotection against ischemia/reperfusion (I/R)-induced injury in vivo.
Methods: Wild-type (WT) C57BL/6, β2AR knockout (KO), βarr1KO and βarr2KO mice received intracardiac injections of either ICL1-9 or a scrambled control pepducin (Scr) at the time of ischemia (30 min) followed by reperfusion for either 24 h, to assess infarct size and cardiomyocyte death, or 4 weeks, to monitor the impact of ICL1-9 on long-term cardiac structure and function. Neonatal rat ventricular myocytes (NRVM) were used to assess the impact of ICL1-9 versus Scr pepducin on cardiomyocyte survival and mitochondrial superoxide formation in response to either serum deprivation or hypoxia/reoxygenation (H/R) in vitro and to investigate the associated mechanism(s).
Results: Intramyocardial injection of ICL1-9 at the time of I/R reduced infarct size, cardiomyocyte death and improved cardiac function in a β2AR- and βarr-dependent manner, which led to improved contractile function early and less fibrotic remodeling over time. Mechanistically, ICL1-9 attenuated mitochondrial superoxide production and promoted cardiomyocyte survival in a RhoA/ROCK-dependent manner. RhoA activation could be detected in cardiomyocytes and whole heart up to 24 h post-treatment, demonstrating the stability of ICL1-9 effects on βarr-dependent β2AR signaling.
Conclusion: Pepducin-based allosteric modulation of βarr-dependent β2AR signaling represents a novel therapeutic approach to reduce reperfusion-induced cardiac injury and relay long-term cardiac remodeling benefits
Direct measurement of quantum phase gradients in superfluid 4He flow
We report a new kind of experiment in which we generate a known superfluid
velocity in a straight tube and directly determine the phase difference across
the tube's ends using a superfluid matter wave interferometer. By so doing, we
quantitatively verify the relation between the superfluid velocity and the
phase gradient of the condensate macroscopic wave function. Within the
systematic error of the measurement (~10%) we find v_s=(hbar/m_4)*(grad phi)
A systematic review of tagging as a method to reduce theft in retail environments
Background: Retailers routinely use security tags to reduce theft. Presently, however, there has been no attempt to systematically review the literature on security tags. Guided by the acronym EMMIE, this paper set out to (1) examine the evidence that tags are effective at reducing theft, (2) identify the key mechanisms through which tags are expected to reduce theft and the conditions that moderate tag effectiveness, and (3) summarise information relevant to the implementation and economic costs of tagging. Methods: In this mixed-methods review, we performed systematic keyword searches of the published and unpublished literature, hand searched relevant journals, conducted forward and backward citation searches and consulted with four retailers. Studies were included if they reported an explicit goal of reducing the theft or shrinkage of items through the use of security tags in retail environments. Results: We identified 50 eligible studies, eight of which reported quantitative data on the effectiveness of tags in retail environments. Across these eight studies, five showed positive results associated with the introduction of tags, but heterogeneity in the type of tag and reported outcome measures precluded a meta-analysis. We identified three mechanisms through which tags might plausibly reduce theft-increase the risks, reduce the rewards, increase the effort-which were found to vary by tag type, and their activation dependent on five broad categories of moderator: retail store and staff, customers (including shoplifters), tag type, product type, and the involvement of the police and criminal justice system. Implementation challenges documented in the literature related mainly to staffing issues and tagging strategy. Finally, although estimates are available on the costs of tagging, our searches identified no highquality published economic evaluations of tagging. Conclusions: Through applying the EMMIE framework this review highlighted the complexity involved in security tagging in retail environments, whereby different kinds of tags are expected to reduce theft through different casual mechanisms which are dependent on a distinctive configuration of conditions. Based on the available evidence it is difficult to determine the effectiveness of tags as a theft reduction measure, albeit there is suggestive evidence that more visible tags are associated with greater reductions in theft than less visible tags
Theoretical current-voltage characteristics of ferroelectric tunnel junctions
We present the concept of ferroelectric tunnel junctions (FTJs). These
junctions consist of two metal electrodes separated by a nanometer-thick
ferroelectric barrier. The current-voltage characteristics of FTJs are analyzed
under the assumption that the direct electron tunneling represents the dominant
conduction mechanism. First, the influence of converse piezoelectric effect
inherent in ferroelectric materials on the tunnel current is described. The
calculations show that the lattice strains of piezoelectric origin modify the
current-voltage relationship owing to strain-induced changes of the barrier
thickness, electron effective mass, and position of the conduction-band edge.
Remarkably, the conductance minimum becomes shifted from zero voltage due to
the piezoelectric effect, and a strain-related resistive switching takes place
after the polarization reversal in a ferroelectric barrier. Second, we analyze
the influence of the internal electric field arising due to imperfect screening
of polarization charges by electrons in metal electrodes. It is shown that, for
asymmetric FTJs, this depolarizing-field effect also leads to a considerable
change of the barrier resistance after the polarization reversal. However, the
symmetry of the resulting current-voltage loop is different from that
characteristic of the strain-related resistive switching. The crossover from
one to another type of the hysteretic curve, which accompanies the increase of
FTJ asymmetry, is described taking into account both the strain and
depolarizing-field effects. It is noted that asymmetric FTJs with dissimilar
top and bottom electrodes are preferable for the non-volatile memory
applications because of a larger resistance on/off ratio.Comment: 14 pages, 8 figure
Beta-decay properties of Si and P
The -decay properties of the neutron-deficient nuclei Si and
P have been investigated at the GANIL/LISE3 facility by means of
charged-particle and -ray spectroscopy. The decay schemes obtained and
the Gamow-Teller strength distributions are compared to shell-model
calculations based on the USD interaction. B(GT) values derived from the
absolute measurement of the -decay branching ratios give rise to a
quenching factor of the Gamow-Teller strength of 0.6. A precise half-life of
43.7 (6) ms was determined for P, the - (2)p decay mode of which
is described
Bogomol'nyi Limit For Magnetic Vortices In Rotating Superconductor
This work is the sequel of a previous investigation of stationary and
cylindrically symmetric vortex configurations for simple models representing an
incompressible non-relativistic superconductor in a rigidly rotating
background. In the present paper, we carry out our analysis with a generalized
Ginzburg-Landau description of the superconductor, which provides a
prescription for the radial profile of the normal density within the vortex.
Within this framework, it is shown that the Bogomol'nyi limit condition marking
the boundary between type I and type II behavior is unaffected by the rotation
of the background.Comment: 7 pages, uses RevTeX, submitted to Phys.Rev.
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