107 research outputs found
Proximity and Josephson effects in superconductor - two dimensional electron gas planar junctions
The DC Josephson effect is theoretically studied in a planar junction in
which a two dimensional electron gas (2DEG) infinite in lateral directions is
in contact with two superconducting electrodes placed on top of the 2DEG. An
energy gap in the excitation spectrum is created in the 2DEG due to the
proximity effect. It is shown that under certain conditions, the region of the
2DEG underneath the superconductors is analogous to a superconducting region
with an order parameter \/, where
\/ depends on the interface transmittance
and the Fermi velocity mismatch between the superconductors and the 2DEG.Comment: 9 pages REVTeX, 5 figures available on reques
Administration Launches Next Chapter of Education Reform
Background: Although the recovery of patients suffering from low back pain is highly context dependent, patient preferences about treatment options are seldom incorporated into the therapeutic plan. Shared decision-making (SDM) offers a tool to overcome this deficiency. The reinforcement by the general practitioner (GP) of a 'shared' chosen therapy might increase patients' expectations of favourable outcomes and thus contribute to recovery. Methods: In the Netherlands, a clustered randomised controlled trial was performed to assess the effectiveness of shared decision-making followed by positive reinforcement of the chosen therapy (SDM&PR) on patient-related clinical outcomes. Overall, 68 GPs included 226 patients visiting their GP for a new episode of non-chronic low back pain. GPs in the intervention group were trained in implementing SDM&PR using a structured training programme with a focus on patient preferences in reaching treatment decisions. GPs in the control group provided care as usual. The primary outcome was the change in physical disability measured with the Roland-Morris disability questionnaire (RMD) during the six-month follow-up after the first consultation. Physical disability (RMD), pain, adequate relief, absenteeism and healthcare consumption at 2, 6, 12 and 26 weeks were secondary outcomes. A multivariate analysis with a mixed model was used to estimate the differences in outcomes. Results: Of the patients in the intervention and the control groups, 66 and 62%, respectively, completed the follow-up. Most patients (77%) recovered to no functional restrictions due to back pain within 26 weeks. No significant differences in the mean scores for any outcome were observed between intervention patients and controls during the follow-up, and in multivariate analysis, there was no significant difference in the main outcome during the six-month follow-up. Patients in the intervention group reported more involvement in decision-making. Conclusion: This study did not detect any improvement in clinical outcome or in health care consumption of patients with non-chronic low back pain after the training of GPs in SDM&PR. The implementation of SDM merely introduces task-oriented communication. The training of the GPs may have been more effective if it had focused more on patient-oriented communication techniques and on stressing the expectation of favourable outcomes. Trial registration: The Netherlands National Trial Register (NTR) number: NTR1960. The trial was registered in the NTR on August 20, 2009
Experimental determination of the quasi-particle decay length in a superconducting quantum well
We have investigated experimentally the electronic transport properties of a
two-dimensional electron gas (2DEG) present in an AlSb/InAs/AlSb quantum well,
where part of the toplayer has been replaced by a superconducting Nb strip,
with an energy gap . By measuring the lateral electronic transport
underneath the superconductor, and comparing the experimental results with a
model based on the Bogoliubov-de Gennes equation and the Landauer-B\"uttiker
formalism, we obtain a decay length for
electrons. This decay length corresponds to an interface transparency
between the Nb and InAs. Using this value, we infer an
energy gap in the excitation spectrum of the SQW of .Comment: Revtex, 3 PostScript figure
Multisensory Integration and Attention in Autism Spectrum Disorder: Evidence from Event-Related Potentials
Successful integration of various simultaneously perceived perceptual signals is crucial for social behavior. Recent findings indicate that this multisensory integration (MSI) can be modulated by attention. Theories of Autism Spectrum Disorders (ASDs) suggest that MSI is affected in this population while it remains unclear to what extent this is related to impairments in attentional capacity. In the present study Event-related potentials (ERPs) following emotionally congruent and incongruent face-voice pairs were measured in 23 high-functioning, adult ASD individuals and 24 age- and IQ-matched controls. MSI was studied while the attention of the participants was manipulated. ERPs were measured at typical auditory and visual processing peaks, namely, P2 and N170. While controls showed MSI during divided attention and easy selective attention tasks, individuals with ASD showed MSI during easy selective attention tasks only. It was concluded that individuals with ASD are able to process multisensory emotional stimuli, but this is differently modulated by attention mechanisms in these participants, especially those associated with divided attention. This atypical interaction between attention and MSI is also relevant to treatment strategies, with training of multisensory attentional control possibly being more beneficial than conventional sensory integration therapy
Proline and COMT Status Affect Visual Connectivity in Children with 22q11.2 Deletion Syndrome
Background Individuals with the 22q11.2 deletion syndrome (22q11DS) are at increased risk for schizophrenia and Autism Spectrum Disorders (ASDs). Given the prevalence of visual processing deficits in these three disorders, a causal relationship between genes in the deleted region of chromosome 22 and visual processing is likely. Therefore, 22q11DS may represent a unique model to understand the neurobiology of visual processing deficits related with ASD and psychosis. Methodology We measured Event-Related Potentials (ERPs) during a texture segregation task in 58 children with 22q11DS and 100 age-matched controls. The C1 component was used to index afferent activity of visual cortex area V1; the texture negativity wave provided a measure for the integrity of recurrent connections in the visual cortical system. COMT genotype and plasma proline levels were assessed in 22q11DS individuals. Principal Findings Children with 22q11DS showed enhanced feedforward activity starting from 70 ms after visual presentation. ERP activity related to visual feedback activity was reduced in the 22q11DS group, which was seen as less texture negativity around 150 ms post presentation. Within the 22q11DS group we further demonstrated an association between high plasma proline levels and aberrant feedback/feedforward ratios, which was moderated by the COMT158 genotype. Conclusions These findings confirm the presence of early visual processing deficits in 22q11DS. We discuss these in terms of dysfunctional synaptic plasticity in early visual processing areas, possibly associated with deviant dopaminergic and glutamatergic transmission. As such, our findings may serve as a promising biomarker related to the development of schizophrenia among 22q11DS individuals
Mesoscopic proximity effect in double barrier Superconductor/Normal Metal junctions
We report transport measurements down to T=60mK of SININ and SNIN structures
in the diffusive limit. We fabricated Al-AlOx/Cu/AlOx/Cu (SININ) and
Al/Cu/AlOx/Cu (SNIN) vertical junctions. For the first time, a zero bias
anomaly was observed in a metallic SININ structure. We attribute this peak of
conductance to coherent multi-reflections of electrons between the two tunnel
barriers. This conductance maximum is quantitatively fitted by the relevant
theory of mesoscopic SININ structures. When the barrier at the SN interface is
removed (SNIN structure), we observe a peak of conductance at finite voltage
accompagnied by an excess of sub-gap conductance.Comment: 4 pages, 4 figures, editorially approved for publication in Phys.
Rev. B Rapid Com
Extraordinary Temperature Dependence of the Resonant Andreev Reflection
An extraordinary temperature dependence of the resonant Andreev reflection
via discrete energy level in a normal-metal / quantum-dot / superconductor
(N-QD-S) system is predicted theoretically by using Green function technique.
The width of zero bias conductance peak in N-QD-S is about and does not exhibit thermal broadening, where and
are the coupling strength between QD and leads. Considering the
intra-dot Coulomb interaction, the Coulomb blockade oscillations conducted by
Andreev reflection differs dramatically from that in N-QD-N. Instead of thermal
broadening, finite temperature induces more resonant peaks around the
oscillation peaks of zero temperature. This effect can be applied to determine
the coupling strength and QD level spacing in N-QD-S.Comment: 11 pages, 3 figures, LaTe
Nonlinearity in NS transport: scattering matrix approach
A general formula for the current through a disordered
normal--superconducting junction is derived, which is valid at finite
temperature and includes the full voltage dependence. The result depends on a
multichannel scattering matrix, which describes elastic scattering in the
normal region, and accounts for the Andreev scattering at the NS interface. The
symmetry of the current with respect to sign reversal in the subgap regime is
discussed. The Andreev approximation is used to derive a spectral conductance
formula, which applies to voltages both below and above the gap. In a case
study the spectral conductance formula is applied to the problem of an NINIS
double barrier junction.Comment: 26 pages, 4 Postscript figures, Latex, to be published in Phys. Rev.
Experiential peer support and its effects on desistance from delinquent behavior: protocol paper for a systematic realist literature review
Background
Experiential peers are increasingly involved in the development and delivery of interventions for individuals who are engaged in delinquent behavior. Experiential peer support, which is the provision of support to an individual engaged in delinquent behavior by someone who has previously also practiced such behavior, is one such application. Little is known, however, about its effects on desistance, or the mechanisms that explain these effects. On the basis of theoretical papers, program descriptions, and interviews with experts, we developed an initial program theory. We propose seven mechanisms that might play a role in the (potential) effects of support by experiential peers: (1) empathy and acceptance, (2) social learning, (3) social bonding, (4) social control, (5) narrative and identity formation, (6) hope and perspective, and (7) translation and connection. In addition, in this protocol paper, we describe the methods of a systematic realist literature review that will be conducted in order to investigate the evidence base for this program theory.
Methods
The study described in this protocol paper is a realist review, which is a suitable approach to study complex interventions and fits the explanatory purpose of the study. We outline the steps to be taken for the systematic realist review, including the selection and assessment of studies and the methods for synthesizing the findings.
Discussion
Investigating the effects and the underlying mechanisms of support by experiential peers for individuals with delinquent behavior is relevant because the forensic setting has some unique features, and the involvement of service users might create even more tension than in other settings due to stigma and perceived risks. The findings that will be reported in the realist review will contribute to the knowledge of the effects of support by experiential peers and will provide insight into which aspects remain to be studied. It might also provide formal care institutions with guidance on whether to involve experiential peers in the delivery of their services and the conditions under which these interventions are likely to lead to positive results
Effect of transport-induced charge inhomogeneity on point-contact Andreev reflection spectra at ferromagnet-superconductor interfaces
We investigate the transport properties of a ferromagnet-superconductor
interface within the framework of a modified three-dimensional
Blonder-Tinkham-Klapwijk formalism. In particular, we propose that charge
inhomogeneity forms via two unique transport mechanisms, namely, evanescent
Andreev reflection and evanescent quasiparticle transmission. Furthermore, we
take into account the influence of charge inhomogeneity on the interfacial
barrier potential and calculate the conductance as a function of bias voltage.
Point-contact Andreev reflection (PCAR) spectra often show dip structures,
large zero-bias conductance enhancement, and additional zero-bias conductance
peak. Our results indicate that transport-induced charge inhomogeneity could be
a source of all these anomalous characteristics of the PCAR spectra.Comment: 9 pages, 6 figure
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