787 research outputs found
Bürgerinitiativen: politisches Engagement und moralisches Urteilen
No full textBürgerinitiativen : polit. Engagement u. moral. Urteilen / Michael Schenk ; Gerhard Bohm. - In: Moralisches Urteilen und soziale Umwelt / hrsg. von Georg Lind ... - Weinheim u.a. : Beltz, 1983. - S. 223-23
The Aharonov-Bohm effect: the role of tunneling and associated forces
No full textThrough tunneling, or barrier penetration, small wavefunction tails can enter a finitely shielded cylinder with a magnetic field inside. When the shielding increases to infinity, the Lorentz force goes to zero together with these tails. However, it is shown, by considering the radial derivative of the wavefunction on the cylinder surface, that a flux-dependent force remains. This force explains in a natural way the Aharonov-Bohm effect in the idealized case of infinite shielding
Emergent quantum mechanics : David Bohm Centennial perspectives
No full textEmergent quantum mechanics (EmQM) explores the possibility of an ontology for quantum mechanics. The resurgence of interest in realist approaches to quantum mechanics challenges the standard textbook view, which represents an operationalist approach. The possibility of an ontological, i.e., realist, quantum mechanics was first introduced with the original de Broglie-Bohm theory, which has also been developed in another context as Bohmian mechanics. This Editorial introduces a Special Issue featuring contributions which were invited as part of the David Bohm Centennial symposium of the EmQM conference series (www.emqm17.org). Questions directing the EmQM research agenda are: Is reality intrinsically random or fundamentally interconnected? Is the universe local or nonlocal? Might a radically new conception of reality include a form of quantum causality or quantum ontology? What is the role of the experimenter agent in ontological quantum mechanics? The Special Issue also includes research examining ontological propositions that are not based on the Bohm-type nonlocality. These include, for example, local, yet time-symmetric, ontologies, such as quantum models based upon retrocausality. This Editorial provides topical overviews of thirty-one contributions which are organized into seven categories to provide orientation.
Observation of Aharonov-Bohm conductance oscillations in a graphene ring
No full textWe investigate experimentally transport through ring-shaped devices etched in graphene and observe clear Aharonov-Bohm conductance oscillations. The temperature dependence of the oscillation amplitude indicates that below 1 K, the phase coherence length is comparable to or larger than the size of the ring. An increase in the amplitude is observed at high magnetic field, when the cyclotron diameter becomes comparable to the width of the arms of the ring. By measuring the dependence on gate voltage, we find that the Aharonov-Bohm effect vanishes at the charge neutrality point, and we observe an unexpected linear dependence of the oscillation amplitude on the ring conductance.Kavli Institute of NanoscienceApplied Science
Typicality and the Approach to Equilibrium in Boltzmannian Statistical Mechanics
No full textSystems prepared in a non-equilibrium state approach, and eventually reach, equilibrium. Why do they do so? An important contemporary version of the Boltzmannian approach to statistical mechanics answers this question in terms of typicality. The problem with this approach is that it comes in different versions, which are, however, not recognised as such and not clearly distinguished. The aim of this paper is to identify three different versions of typicality-based explanations of thermodynamic-like behaviour and evaluate their respective success. My conclusion is that the first two are unsuccessful because they fail to take the system’s dynamics into account. The third, however, is promising. I give a precise formulation of the proposal and present an argument in support of its central contention
Aharonov–Bohm oscillations of a tuneable quantum ring
No full textUsing an atomic force microscope a ring geometry with self-aligned in-plane gates was directly written into a GaAs/AlGaAs heterostructure, Transport measurements in the open regime show only one transmitting mode and Aharonov-Bohm oscillations with more than 50% modulation are observed in the conductance. The tuning via in-plane gates allows one to study the Aharonov-Bohm effect in the whole range from the open ring to the Coulomb-blockade regime
Effects of different inotropic interventions on myocardial function in the developing rabbit heart
No full textThe development of the mammalian heart is characterized by substantial changes in myocardial performance. We studied the ontogeny of myocardial function with and without various inotropic interventions in the developing isolated, antegrade-perfused rabbit heart (2d, 8d, 14d, 28d, n = 96). Myocardial function was related to the protein expression of the sarcolemmal Na+-Ca2+ exchanger and to the sarcoplasmic Ca2+-ATPase. In neonatal hearts an age-dependent increase in maximal developed pressure velocity (dP/dt(max)) by 45% and peak negative pressure velocity (dP/ dt(min)) by 75 % within days 2 to 8 were observed. In response to inotropic intervention with isoproterenol, ouabain, calcium and the Na+-channel modulator BDF 9148, dP/dt(max) and dP/dt(min) increased in a concentration dependent manner. Significant differences between neonatal, juvenile and adult hearts could be demonstrated in a repeated measurement ANOVA model on the concentration-response curves for BDF 9148 (dP/dt(max) and dP/dt(min)), ouabain (dP/dt(min)) and calcium (dP/dt(min)), but not for isoproterenol. At the maximum isoproterenol concentration of 1 mumol/l, the increase in dP/dt(max) and dP/dt(min) was significantly higher in adult compared to neonatal hearts (t-test, p < 0.01). The significant decline of the Na+-Ca2+ exchanger protein expression from neonatal (1822 +/- 171) to adult hearts (411 +/- 96 S.E.M. [units per 20 mug protein], p < 0.01) was related to an increase in myocardial function (dP/dt(max) r = 0.63, p < 0.01, dP/dt(min) r = 0.62, p < 0.01). Contractility, relaxation and the observed positive inotropic effects were in general significantly lower in neonatal compared to adult hearts. In the individual heart an increase in contractility and relaxation was related to a decrease in Na+-Ca2+ exchanger expression
Emergent Quantum Mechanics: David Bohm Centennial Perspectives
No full text544 p.Emergent quantum mechanics explores the possibility of an ontology for quantum mechanics. The resurgence of interest in "deeper-level" theories for quantum phenomena challenges the standard, textbook interpretation. The book presents expert views that critically evaluate the significance—for 21st century physics—of ontological quantum mechanics, an approach that David Bohm helped pioneer. The possibility of a deterministic quantum theory was first introduced with the original de Broglie-Bohm theory, which has also been developed as Bohmian mechanics. The wide range of perspectives that were contributed to this book on the occasion of David Bohm’s centennial celebration provide ample evidence for the physical consistency of ontological quantum mechanics. The book addresses deeper-level questions such as the following: Is reality intrinsically random or fundamentally interconnected? Is the universe local or nonlocal? Might a radically new conception of reality include a form of quantum causality or quantum ontology? What is the role of the experimenter agent? As the book demonstrates, the advancement of ‘quantum ontology’—as a scientific concept—marks a clear break with classical reality. The search for quantum reality entails unconventional causal structures and non-classical ontology, which can be fully consistent with the known record of quantum observations in the laboratory
Aharonov-Bohm–Type Effect for Vortices in Josephson-Junction Arrays
No full textThe dynamics of a single vortex present in a ring-shaped (Corbino geometry) two-dimensional array of low-capacity Josephson junctions is studied. The vortex is treated as a macroscopic quantum particle, whose energy levels En(Q0) are periodic functions of the externally induced gauge charge Q0 which is enclosed by the vortex, with a period 2e. This Aharonov-Bohm–type effect may manifest itself as a persistent voltage Vs = dE0(Q0)/dQ0 between interior and exterior contacts, or alternatively as Bloch oscillations. The relation with the Aharonov-Casher effect and the possibility for experimental observation are discussed.
Two-story frame residence of Robert A. and Anna Bohms Wolters, Summit and Upton Streets, Schulenburg, Texas
No full textPhotograph shows front and side of the house built for Gerhard and Augusta Bohm, parents of Mrs. Wolters. People on ground floor are perhaps Mr. and Mrs. Wolters and Augusta Bohm. Unidentified people on second floor may be the lodgers who rented rooms. Two men (employees?) outside fence, one beside wagon
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