56 research outputs found
Induction of dc voltage, proportional to the persistent current, by external ac current on system of inhomogeneous superconducting loops
A dc voltage induced by an external ac current is observed in system of
asymmetric mesoscopic superconducting loops. The value and sign of this dc
voltage, like the one of the persistent current, depend in a periodical way on
a magnetic field with period corresponded to the flux quantum within the loop.
The amplitude of the oscillations does not depend on the frequency of the
external ac current (in the investigated region 100 Hz - 1 MHz) and depends on
its amplitude. The latter dependence is not monotonous. The observed phenomenon
of rectification is interpreted as a consequence of a dynamic resistive state
induced by superposition of the external current and the persistent current. It
is shown that the dc voltage can be added in system of loops connected in
series: the dc voltage oscillations with amplitude up to 0.00001 V were
observed in single loop, up to 0.00004 V in a system of 3 loops and up to
0.0003 V in a system of 20 loops.Comment: 5 pages, 6 figure
Remanence effects in the electrical resistivity of spin glasses
We have measured the low temperature electrical resistivity of Ag : Mn
mesoscopic spin glasses prepared by ion implantation with a concentration of
700 ppm. As expected, we observe a clear maximum in the resistivity (T ) at a
temperature in good agreement with theoretical predictions. Moreover, we
observe remanence effects at very weak magnetic fields for the resistivity
below the freezing temperature Tsg: upon Field Cooling (fc), we observe clear
deviations of (T ) as compared with the Zero Field Cooling (zfc); such
deviations appear even for very small magnetic fields, typically in the Gauss
range. This onset of remanence for very weak magnetic fields is reminiscent of
the typical signature on magnetic susceptibility measurements of the spin glass
transition for this generic glassy system
Absence of Size Dependence of the Kondo Resistivity
We have measured the low temperature resistivity of AuFe wires in the dilute magnetic impurity limit as a function of wire width, temperature, and magnetic field. When the width dependence of the electron-electron interaction contribution to the resistivity is taken into account, the temperature dependence of the remaining Kondo contribution to the resistivity of all samples with the same impurity concentration is identical. Similar behavior is observed for the magnetic field dependent resistivity. Thus, the Kondo contribution to the resistivity is independent of width down to 38 nm, much smaller than the Kondo length ξK=ħvF/kBTK≊10 μm
Quantum Force in Superconductor
Transitions between states with continuous (called as classical state) and
discrete (called as quantum state) spectrum of permitted momentum values is
considered. The persistent current can exist along the ring circumference in
the quantum state in contrast to the classical state. Therefore the average
momentum can changes at the considered transitions. In order to describe the
reiterated switching into and out the quantum state an additional term is
introduced in the classical Boltzmann transport equation. The force inducing
the momentum change at the appearance of the persistent current is called as
quantum force. It is shown that dc potential difference is induced on ring
segments by the reiterated switching if the dissipation force is not
homogeneous along the ring circumference. The closing of the superconducting
state in the ring is considered as real example of the transition from
classical to quantum stateComment: 4 pages, RevTex, 0 figure
Giant vortex state in perforated aluminum microsquares
We investigate the nucleation of superconductivity in a uniform perpendicular
magnetic field H in aluminum microsquares containing a few (2 and 4) submicron
holes (antidots). The normal/superconducting phase boundary T_c(H) of these
structures shows a quite different behavior in low and high fields. In the low
magnetic field regime fluxoid quantization around each antidot leads to
oscillations in T_c(H), expected from the specific sample geometry, and
reminiscent of the network behavior. In high magnetic fields, the T_c(H)
boundaries of the perforated and a reference non-perforated microsquare reveal
cusps at the same values of Phi/Phi_0 (where Phi is the applied flux threading
the total square area and Phi_0 is the superconducting flux quantum), while the
background on T_c(H) becomes quasi-linear, indicating that a giant vortex state
is established. The influence of the actual geometries on T_c(H) is analyzed in
the framework of the linearized Ginzburg-Landau theory.Comment: 14 pages, 6 PS figures, RevTex, accepted for publication in Phys.
Rev.
Management control systems in innovation companies: A literature based framework
Past research has traditionally argued that management control systems (MCSs) may present a hindrance to the creativity of innovation companies. This theoretical paper surveys the literature to focus an investigation on the MCSs of innovation companies. Within the object of control paradigm the paper develops and presents a theoretical model of the impact of eleven external, organisational and innovation related contingency factors on the MCSs in companies that engage in innovation activities. We also suggest measures for further empirical research. By formulating hypotheses on 43 potential interactions the model predicts contradictory influences on two direct control categories, results and action control, but stresses the importance of two indirect categories, personnel and cultural control. More specifically, the high levels of technological complexity and innovation capability in this type of company are expected to be negatively associated with the application of results and action control, whereas personnel and cultural seem to be more appropriate. Furthermore, important sources of finance, venture capital and public funding, are both hypothesised to be positively associated with the application of results, action and personnel control; whereas only public funding is predicted to be positively related to the application of cultural control. The principal contribution of this paper lies in synthesising the literature to provide a model of the impact of a unique set of eleven contingency factors for innovation companies on a broad scope of controls. In addition, the contingency model, if empirically validated, would add value by inferring the particular forms of management control which would be beneficial in innovative company settings. © 2014 Springer-Verlag Berlin Heidelberg
#EEGManyLabs: Investigating the Replicability of Influential EEG Experiments
There is growing awareness across the neuroscience community that the replicability of findings about the relationship between brain activity and cognitive phenomena can be improved by conducting studies with high statistical power that adhere to well-defined and standardised analysis pipelines. Inspired by recent efforts from the psychological sciences, and with the desire to examine some of the foundational findings using electroencephalography (EEG), we have launched #EEGManyLabs, a large-scale international collaborative replication effort. Since its discovery in the early 20th century, EEG has had a profound influence on our understanding of human cognition, but there is limited evidence on the replicability of some of the most highly cited discoveries. After a systematic search and selection process, we have identified 27 of the most influential and continually cited studies in the field. We plan to directly test the replicability of key findings from 20 of these studies in teams of at least three independent laboratories. The design and protocol of each replication effort will be submitted as a Registered Report and peer-reviewed prior to data collection. Prediction markets, open to all EEG researchers, will be used as a forecasting tool to examine which findings the community expects to replicate. This project will update our confidence in some of the most influential EEG findings and generate a large open access database that can be used to inform future research practices. Finally, through this international effort, we hope to create a cultural shift towards inclusive, high-powered multi-laboratory collaborations. © 2021 The Authors
#EEGManyLabs: Investigating the replicability of influential EEG experiments
There is growing awareness across the neuroscience community that the replicability of findings about the relationship between brain activity and cognitive phenomena can be improved by conducting studies with high statistical power that adhere to well-defined and standardised analysis pipelines. Inspired by recent efforts from the psychological sciences, and with the desire to examine some of the foundational findings using electroencephalography (EEG), we have launched #EEGManyLabs, a large-scale international collaborative replication effort. Since its discovery in the early 20th century, EEG has had a profound influence on our understanding of human cognition, but there is limited evidence on the replicability of some of the most highly cited discoveries. After a systematic search and selection process, we have identified 27 of the most influential and continually cited studies in the field. We plan to directly test the replicability of key findings from 20 of these studies in teams of at least three independent laboratories. The design and protocol of each replication effort will be submitted as a Registered Report and peer-reviewed prior to data collection. Prediction markets, open to all EEG researchers, will be used as a forecasting tool to examine which findings the community expects to replicate. This project will update our confidence in some of the most influential EEG findings and generate a large open access database that can be used to inform future research practices. Finally, through this international effort, we hope to create a cultural shift towards inclusive, high-powered multi-laboratory collaborations
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