Universal Voltage Fluctuations in Disordered Superconductors.

The Aharonov-Casher effect is the analogue of the Aharonov-Bohm effect that applies to neutral particles carrying a magnetic moment. This effect can be manifested by vortices or fluxons flowing in trajectories that encompass an electric charge. These vortices have been predicted to result in a persistent voltage that fluctuates for different sample realizations. Here, we show that disordered superconductors exhibit reproducible voltage fluctuation, which is antisymmetrical with respect to the magnetic field, as a function of various parameters such as the magnetic field amplitude, field orientations, and gate voltage. These results are interpreted as the vortex equivalent of the universal conductance fluctuations typical of mesoscopic disordered metallic systems. We analyze the data in the framework of random matrix theory and show that the fluctuation correlation functions and curvature distributions exhibit behavior that is consistent with Aharonov-Casher physics. The results demonstrate the quantum nature of the vortices in highly disordered superconductors, both above and below T_{c}.

Multiple periodicity in a nanoparticle-based single-electron transistor.

A single-electron transistor is a nano-device with large potential for low-power applications that can be used as logic elements in integrated circuits. In this device, the conductance oscillates with a well-defined period due to the Coulomb blockade effect. By using a unique technique, we explore single-electron transistors based on a single metallic nanoparticle with tunable coupling to electric leads. We demonstrate a unique regime in which the transistor is characterized by multi-periodic oscillations of the conductance with gate voltage where the additional periods are harmonics of the basic periodicity of the Coulomb blockade and their relative strength can be controllably tuned. These harmonics correspond to a charge change on the dot by a fraction of the electron charge. The presence of multiple harmonics makes these transistors potential elements in future miniaturization of nano-sized circuit elements.Single-electron transistors are elements for nanoscale electronics. Employing single-electron transistors based on gold nanoparticles, Bitton et al., report a fabrication technique that allows precise control over the coupling between a nanodot and leads, resulting in new transport characteristics.

Coexistence of Coulomb blockade and zero bias anomaly in a strongly coupled nanodot.

The current-voltage characteristics through a metallic nanoparticle which is well coupled to a metallic lead are measured. It is shown that the I-V curves are composed of two contributions. One is a suppression of the tunneling conductivity at the Fermi level, and the second is an oscillating feature which shifts with gate voltage. The results indicate that zero-bias anomaly and Coulomb blockade phenomena coexist in an asymmetric strongly coupled zero-dimensional system.

Localization transition on complex networks via spectral statistics.

The spectral statistics of complex networks are numerically studied. The features of the Anderson metal-insulator transition are found to be similar for a wide range of different networks. A metal-insulator transition as a function of the disorder can be observed for different classes of complex networks for which the average connectivity is small. The critical index of the transition corresponds to the mean field expectation. When the connectivity is higher, the amount of disorder needed to reach a certain degree of localization is proportional to the average connectivity, though a precise transition cannot be identified. The absence of a clear transition at high connectivity is probably due to the very compact structure of the highly connected networks, resulting in a small diameter even for a large number of sites.

Coherent electron transport in a Si quantum dot dimer.

We show that the coherence of charge transfer through a weakly coupled double-dot dimer can be determined by analyzing the statistics of the conductance pattern, and does not require a large phase coherence length in the host material. We present an experimental study of the charge transport through a small Si nanostructure, which contains two quantum dots. The transport through the dimer is shown to be coherent. At the same time, one of the dots is strongly coupled to the leads, and the overall transport is dominated by inelastic cotunneling processes.

Conductance peak motion due to a magnetic field in weakly coupled chaotic quantum dots.

We study the influence of moderate exchange interactions on the behavior of the peaks in the conductance of single electron transistors. We numerically reproduce recently observed features of the magnetic field dependence of both the peak positions and heights. These features unambiguously identify the total spin S of each ground state. We evaluate the probability of each S as a function of the exchange strength J, and external magnetic field B. The expressions involve only J and the g factor as adjustable parameters. For a broad parameter range these probabilities are determined by a linear combination of J and gB.

Caustic injury of the oesophagus. Sixteen years experience, and introduction of a new model oesophageal stent.

Caustic ingestion can lead to oesophageal stenosis. We studied 251 patients, 205 of whom were children, in a sixteen-year period. Seventeen patients, of whom one was an adult, acquired deep burns in the oesophagus which had to be treated, to prevent the development of oesophageal strictures. These patients were treated with long-term stenting of the oesophagus with specially designed, silicone rubber stents, impregnated with silicone oil 20 cS, designed by one of us (R.N.P.B.) as the only treatment. Of all models, the twin-tube dilator was the most satisfactory. No corticosteroids were administered. Only one patient developed a mild stenosis. It is therefore our opinion that, when life-saving operations are not indicated, twin-tube stenting of the oesophagus is helpful in treating caustic lesions of the oesophagus and will prevent stricture formation. Corticosteroids were not given in this series, and should be abandoned in the treatment of caustic lesions.

Acquired laryngeal stenosis in infants and children treated by laryngofissure and stenting.

Thirty young patients with acquired laryngeal stenosis were treated by means of a laryngofissure and stenting. The age distribution suggested two subgroups: infants aged 0-2 years (n = 24), and children aged 6-16 years (n = 6). The causes of the stenosis and the treatment results were different in these subgroups. Treatment resulted in successful decannulation in 22 of 24 infants, and in 5 of 6 children. Treatment included a re-operation in two patients. In 1 patient the therapy failed, and 2 patients died after fatal complications. Decannulation rate, duration of the tracheotomy, and the number of re-operations compare favorably to the results of other centers. The longer duration of stenting, and the high mortality rate may be considered disadvantages.

Durational effects in final lengthening, gapping, and contrastive stress.

Lengthening in utterance-final position and in contrastive stress was examined in Hebrew, focusing on the distribution of the durational effect across syllables and within the final syllable. Initially-stressed and finally-stressed bisyllabic key words were read in sentence-final versus nonfinal position, and in contrastive stress versus nonstressed constructions. The results were compared with data from an earlier study of verb gapping. Contrastive stress showed a smaller effect than final lengthening and verb gapping, consistent with the claim that other acoustic parameters are more prominently involved in this process. Utterance-final lengthening and verb gapping principally affected the final syllable regardless of stress, whereas contrastive stress primarily lengthened the stressed syllable. The pattern of progressively greater lengthening within the utterance-final syllable, previously found for stressed syllables, applied to unstressed syllables as well. The finding that target syllables in sentence-final position are characterized by progressive lengthening, unlike those in contrastive stress and gapping, supports the suggestion that utterance-final lengthening is a reflection of deceleration at the end of motor activity. Durational measures of individual syllables within the key word, and of segments in addition to the vocalic portion of the final syllable, reveal differences in the acoustic implementation of different lengthening processes.