bluuebunny/crossref_metadata_2025 huggingface dataset:
Asthma and Suicidal Ideation Among Youth in the Community
Authors: Goodwin Renee D. , Marušič Andrej
Published: August 2004

Summary: Objective: To determine the association between asthma and suicidal ideation among youth in the community. Method: Data were drawn from the MECA (n = 1285), a community-based study of youth aged 9-17 in the United States. Multiple logistic regression analyses were used to determine the association between asthma and suicidal ideation, adjusting for differences in sociodemographic characteristics and mental disorders. Results: Asthma was associated with a significantly increased likelihood of suicidal ideation (OR = 3.25 ‘1.04, 10.1’), compared to youth without asthma. Conclusions: These data suggest that youth who are hospitalized for asthma may have higher than expected levels of suicidal ideation, compared with youth without asthma in the community. This association appears to persist after controlling for the effects of comorbid mental disorders. These findings are consistent with previous clinical reports of an association between physical illness and suicidal ideation, as well as with links between asthma and suicidal ideation among adults. More in-depth evaluation of the mental health of youth hospitalized for asthma may be indicated if these results are replicated.
Mantle dynamics and genesis of mafic magmatism in the intermontane Pacific Northwest
Authors: Camp Victor E. , Ross Martin E.
Published: August 2004

The Columbia Plateau, Oregon Plateau, Snake River Plain, and Northern Nevada Rift compose a single magmatic system containing all the essential characteristics ascribed to a mantle plume genesis. A mobile mantle is delineated by volcanic migrations, divisible into two types: (1) Rapid, radial migrations (∼10–100 cm/yr) are associated with impingement and spreading of the Yellowstone plume head along the Chief Joseph, Steens Mountain–Picture Gorge, and Northern Nevada Rift magmatic trends from ∼16.6 to 15.0 Ma. (2) Subsequent (post‐15.0 Ma), slower migrations (1–5 cm/yr) are associated with shearing off of the plume head, generating the Snake River Plain hot spot track above the plume tail, and with westward asthenospheric drag of the plume head beneath the Oregon Plateau. The plume head provided a melt component to Imnaha and Grande Ronde Basalts. Depleted mantle lithosphere lying above the plume head provided a melt component to Steens Basalt and Picture Gorge Basalt and to younger eruptions of high‐alumina olivine tholeiite. The plume head currently resides beneath a broad lithospheric swell, marked by young volcanism, high heat flow, and slow P wave travel times. The periphery of the plume head is delineated by the cratonic margin to the east, a gravity discontinuity and a set of wrinkle ridges to the north, and a prominent belt of young high‐alumina olivine tholeiites and active volcanoes adjacent to the Cascade volcanic arc to the west.
Statistical simulation of the influence of the NAO on European winter surface temperatures: Applications to phenological modeling
Authors: Cook Benjamin I. , Mann Michael E. , D'Odorico Paolo , Smith Thomas M.
Published: August 2004

We develop a modeling framework to investigate the influence of the North Atlantic Oscillation (NAO) on phenological variability in Europe through its influence on the distribution of wintertime synoptic‐scale surface temperature variability. The approach employs an eigendecomposition of NCEP daily winter surface temperature estimates from the latter twentieth century to represent the spatial structure in the surface temperature field. The subset of statistically significant principal components are modeled as first‐order autoregressive AR(1) processes, while the residual variance is modeled as spatially uncorrelated AR(1) noise. For those principal component time series that exhibit a statistically significant seasonal relationship with the NAO index, the parameters of the AR(1) model are conditioned on the phase (“high,” “neutral,” or “low”) of the NAO. This allows for realistic simulations of synoptic scale surface temperature variability over Europe as it is influenced by the NAO index. The model is applied to the simulation of trends in growing degree days (GDD) over Europe where simulated GDD variations are shown to agree well with growing degrees days from the data and evidence from available phenological records. Preliminary application of this model to a climate change scenario involving an increasing NAO 50 years into the future suggests the potential for a continued advancement of the start of the growing season.
Magmatic evolution of impact‐induced Martian mantle plumes and the origin of Tharsis
Authors: Reese C. C. , Solomatov V. S. , Baumgardner J. R. , Stegman D. R. , Vezolainen A. V.
Published: August 2004

Tharsis province is a major center of Martian volcanic activity characterized by large gravity and topography anomalies. The origin of Tharsis is debated. One hypothesis is that the province was produced by melting associated with a mantle plume from the core‐mantle boundary. An alternative hypothesis is that Tharsis formed by a plume associated with an impact. Recent studies have shown that this hypothesis is plausible from a geodynamical point of view and that long‐lived impact plumes might play a role in areoid evolution. In this study, the magmatic evolution of impact‐induced thermochemical mantle plumes is investigated with fully three‐dimensional spherical shell simulations of mantle convection. Melt volumes and emplacement rates predicted by the model can satisfy observational constraints on Tharsis development.
An approximate approach to predict multiple screen diffraction in the case of grazing incidence
Authors: Beyer Jürgen
Published: August 2004

An approximate approach is derived to enable a computer time‐efficient prediction of multiple screen diffraction for grazing incidence. Comprehensive computations of multiple screen diffraction at up to ten randomly arranged screens were carried out using the Vogler method. On the basis of these numerical results, a suitable polynomial approximation is derived. In order to verify the approximation, the computations are repeated with different random screen distribution, and the deviation between the Vogler method and polynomial approximation is statistically evaluated.
Tectonostratigraphic subdivisions of the Himalaya: A view from the west
Authors: DiPietro Joseph A. , Pogue Kevin R.
Published: September 2004

Indian plate rocks in the central Himalaya have traditionally been divided into orogen‐parallel, fault‐bound tectonostratigraphic zones. A straightforward westward extrapolation of these zones has proved problematic in part because of a lack of consensus on the existence or significance of major faults within the metamorphic zone of the Indian plate in Pakistan where more than 10 locations for the Main Central thrust (MCT) have been proposed. We address this ambiguity by systematically tracing established central Himalayan tectonostratigraphy around the western Himalayan syntaxis and across Pakistan. This exercise reveals the following stratigraphic and structural relationships: (1) There is a westward decrease in Neogene shortening across the Himalayan fold and thrust belt such that there is no age equivalent thrust in Pakistan with displacement and metamorphic juxtaposition equivalent to the central Himalayan MCT. (2) Shortening across the fold and thrust belt in western Pakistan is concentrated in the unmetamorphosed foreland as opposed to the metamorphic zone in the central Himalaya. (3) Lesser Himalayan, Higher Himalayan, and Tethyan rocks are in stratigraphic order within the metamorphic zone of Pakistan which appears to be the metamorphic equivalent of Kashmir Tethyan stratigraphy. (4) The combination of early Paleozoic and late Paleozoic tectonism in Pakistan has locally eliminated Upper Proterozoic Higher Himalayan rock and lower to middle Paleozoic Tethyan rock from the metamorphic zone of Pakistan. (5) Late Cretaceous and/or early Paleocene proto‐Himalayan deformation in the Pakistan foreland telescoped and eroded stratigraphy prior to the main phase of Himalayan orogeny. (6) Tectonostratigraphic zones are offset in eastern Pakistan by the transverse Jhelum‐Balakot fault. (7) There is no evidence within the Indian plate of Pakistan for a large‐scale normal fault system comparable to the South Tibetan detachment system. (8) Stratigraphy, as well as the age and tectonic setting of deformation and metamorphism, must be taken into account when drawing tectonostratigraphic zones.
Modelling of rift propagation on Ronne Ice Shelf, Antarctica, and sensitivity to climate change
Authors: Larour E. , Rignot E. , Aubry D.
Published: August 2004

The calving of icebergs from large Antarctic ice shelves is controlled mainly by the formation and propagation of rifts originating from the side margins of the ice shelf and local areas of grounding. Using InSAR, we observe the evolution of rifts along Hemmen Ice Rise, on Ronne Ice Shelf, Antarctica prior to the large calving event of October 1998. We couple these observations with a computer model combining the viscous flow of an ice shelf with a linear elastic fracture mechanics description of the propagation of rifts. The model reveals that the ice melange trapped in between the rifts exerts a major control on the propagation of rifts, and in turn on ice shelf stability. Melting of the ice melange from oceanic or atmospheric warming would significantly increase the propagation rate of rifts and threaten the ice‐shelf stability.
Online versus offline air quality modeling on cloud‐resolving scales
Authors: Grell Georg A. , Knoche Richard , Peckham Steven E. , McKeen Stuart A.
Published: August 2004

Computational advances now allow air quality forecast models to fully couple the meteorology with chemical constituents within a unified modeling system –online– that allows two‐way interactions. The more common approach is theofflinesystem, which only allows one‐way coupling from the meteorology – sampled at fixed time intervals – to the chemistry. To study the information loss between online and offline numerical forecasts, a next‐generation nonhydrostatic air quality modeling system has been developed that can be used both offline or online. First, a control online air quality simulation is conducted and the meteorology and chemical data are saved at a 10 s time interval. Subsequently, three offline simulations are conducted with meteorological data updates at 10, 30, and 60 min time intervals. Analysis of the wind velocity power spectrum and chemical profiles indicate that the offline simulations are susceptible to large errors in the vertical mass distribution.
Wind shear effects on cloud‐radiation feedback in the western Pacific warm pool
Authors: Lin Jia‐Lin , Mapes Brian
Published: August 2004

Upper tropospheric stratiform clouds associated with deep convection are important to global radiation budgets and to cloud‐radiation feedbacks on climate variability and change. Several recent observational studies indicate that vertical wind shear is an important factor affecting stratiform cloud fraction and cloud overlap. This study further examines wind shear effects on cloud properties (including cloud fraction and cloud optical depth) and associated top of atmosphere (TOA) and surface radiative fluxes, using observations from the Tropical Ocean Global Atmosphere program's Coupled Ocean Atmosphere Response Experiment (TOGA COARE) experiment and long‐term satellite measurements. Wind shear affects cloud‐radiative fluxes, through both the cloud fraction and optical thickness, in a strong and systematic way. In typical convecting conditions, shear‐induced additional cloudiness can reduce outgoing longwave radiation (OLR) by 10s of Wm−2, implying longwave radiative changes on the order of 10% of the total latent heating. Such cloud also reflects shortwave radiation, reducing surface downward flux (energy input to the ocean) by 10s of Wm−2. Current climate models lack these effects.
The timing of snow melt controls the annual CO2 balance in a subarctic fen
Authors: Aurela Mika , Laurila Tuomas , Tuovinen Juha‐Pekka
Published: August 2004

The first continuous multi‐year measurements of the CO2 exchange between a subarctic fen and the atmosphere were conducted at Kaamanen in northern Finland (69°N). According to our six‐year data‐set, the fen is presently a sink of atmospheric CO2 with a mean rate of −22 g C m−2 yr−1. The interannual variation of the CO2 balances originates almost completely from the variations during the snow‐free period, but the efflux in the wintertime constitutes a significant part of the annual balance. The snow melt timing is the most important single determinant of the annual carbon balance. In contrast to a commonly‐held view, the hydrometeorological conditions during the growing season had only a minor effect on the annual balance, emphasizing the importance of year‐round measurements. This study indicates that climate warming may increase the length of the growing season and thus benefit rather than threaten the carbon pool of subarctic peatlands.
Impact of cooling on the water mass exchange of Agulhas rings in a high resolution ocean model
Authors: Donners J. , Drijfhout S. S. , Coward A. C.
Published: August 2004

The leakage of water from three Agulhas rings has been studied in a high resolution global ocean model using a Lagrangian particle following technique. A bowl shaped ring boundary that reaches a radius of 140 km and a depth of 800 m separates regions of fast and slow leakage. The dilution of Agulhas ring water generally increases with depth, but a shallow secondary circulation enhances leakage in the upper 150 m. Strong surface cooling upsets the horizonal pressure gradient which is balanced by subinertial motions that act to form this shallow overturning cell.
Effects of a perovskite‐post perovskite phase change near core‐mantle boundary in compressible mantle convection
Authors: Nakagawa Takashi , Tackley Paul J.
Published: August 2004

Numerical simulations of compressible, isochemical mantle convection are used to investigate the effect of the perovskite to post‐perovskite phase transition at around 2700 km depth, which has recently been discovered by high‐pressure experiments and ab initio calculations, on the convective planform, temperature, and heat transport characteristics of the mantle. The usual phase transitions at 410 km (olivine‐spinel) and 660 km (spinel‐perovskite) are also included. The exothermic post‐perovskite phase change at 2700 km depth destabilizes the lower thermal boundary layer, increasing the heat flow, increasing interior mantle temperature, and increasing the number and time‐dependence of upwelling plumes. The resulting weak, highly time‐dependent upwellings also have a smaller horizontal spacing than the plumes that occur in the absence of the phase transition. While the influence of post‐perovskite phase change may be smaller than that of some other complexities, such as compositional stratification, it appears to have an important enough effect that it should not be ignored in dynamical studies of mantle convection.
Multiple ions resonant heating and acceleration by Alfvén/cyclotron fluctuations in the corona and the solar wind
Authors: Xie Hong , Ofman Leon , Viñas Adolfo
Published: August 2004

We study the interaction between protons, multiple minor ions (O5+, He++), and a given Alfvén/cyclotron fluctuation spectra in the corona and the solar wind. One‐dimensional hybrid simulations are performed in initially homogeneous, collisionless, magnetized plasma with waves propagating parallel to the background magnetic field. The self‐consistent hybrid simulations and linear Vlasov theory are used to study the effect of the driving spectrum, ion drift velocity, and microinstabilities on the coronal plasma and solar wind heating. The simulation results provide a clear picture of wave‐particle interaction and successfully explain (1) how the driving spectrum frequency range and the power law index affect the resonant heating, (2) how ion double‐peak distribution is formed and how differential flows affect the resonant interaction via the change of the resonant wave dispersion relation, and (3) how local microinstabilities affect minor ion heating and constraint the values of plasma parameters observed in the solar wind.
Statistical analysis of total ozone measurements in Oslo, Norway, 1978–1998
Authors: Svendby T. M. , Dahlback A.
Published: August 2004

The total ozone series from Dobson spectrophotometer 56 (D56) operating at the University of Oslo (59.9°N, 10.7°E), Norway, from March 1978 to May 1998 has recently been reevaluated. Ozone trends for the time series are calculated using multiple regression models with explanatory variables for the 11 year solar cycle (lagged 22 months), the 2.5 year Quasi‐Biennial Oscillation (QBO) cycle, stratospheric aerosol loading from volcanoes, detrended temperatures at 100 hPa and 500 hPa levels, El Niño–Southern Oscillation (ENSO) events, and various teleconnection patterns. Six of the teleconnection explanatory variables examined are significant to a 95% confidence level in describing the observed total ozone variations. The year‐round total ozone trend in Oslo (±SD) is estimated to −4.2 ± 0.4 % per decade, whereas the winter and summer trends amount to −6.2 ± 0.9 % per decade and −2.4 ± 0.5 % per decade, respectively. The analyses imply that climatic and dynamical changes account for up to a 20% increase in winter ozone trend and a 40% decrease in summer ozone trend. The East Atlantic Jet is the single most dominating teleconnection pattern in Oslo and contributes to about 0.7 percentage points per decade change in summer total ozone trend. The regression analyses demonstrate that the start and termination dates of the ozone record are highly important for the trend results: The summer and winter ozone trend can change by 0.9 percentage points per decade if 1 year is included or omitted from the analyses.
Visualising Changes in Fund Manager Holdings in Two and a Half-Dimensions
Authors: Dwyer Tim , Gallagher David R.
Published: August 2004

We explore a multiple view, or overview and detail, method for visualising a high-dimensional portfolio holdings data set with attributes that change over time. The method employs techniques from multidimensional scaling and graph visualisation to find a two-dimensional mapping for high-dimensional data. In both the overview and detail views, time is mapped to the third dimension providing a two and a half-dimensional view of changes in the data. We demonstrate the utility of the paradigm with a prototype system for visualisation of movements within a large set of UK fund managers’ stock portfolios.
Spontaneous and persistent currents in superconductive and mesoscopic structures (Review)
Authors: Kulik I. O.
Published: August 2004

We briefly review aspects of superconductive persistent currents in Josephson junctions of the S/I/S, S/O/S and S/N/S types, focusing on the origin of jumps in the current versus phase dependences, and discuss in more detail the persistent and the “spontaneous” currents in Aharonov–Bohm mesoscopic and nanoscopic (macromolecular) structures. A fixed-number-of-electrons mesoscopic or macromolecular conducting ring is shown to be unstable against structural transformation removing spatial symmetry (in particular, azimuthal periodicity) of its electron–lattice Hamiltonian. In the case when the transformation is blocked by strong coupling to an external azimuthally symmetric environment, the system becomes bistable in its electronic configuration at a certain number of electrons. Under such a condition, the persistent current has a nonzero value even at an (almost) zero applied Aharonov–Bohm flux and results in very high magnetic susceptibility dM/dH at small nonzero fields, followed by an oscillatory dependence at larger fields. We tentatively assume that previously observed oscillatory magnetization in cyclic metallo-organic molecules by Gatteschi et al. can be attributed to persistent currents. If this proves correct, it may present an opportunity for (and, more generally, macromolecular cyclic structures may suggest the possibility of) engineering quantum computational tools based on the Aharonov–Bohm effect in ballistic nanostructures and macromolecular cyclic aggregates.
Spontaneous currents in Josephson junctions between unconventional superconductors and d-wave qubits (Review)
Authors: Kolesnichenko Yu. A. , Omelyanchouk A. N. , Zagoskin A. M.
Published: August 2004

The modern physics of superconductivity can be called the physics of unconventional superconductivity. The discovery of the d-wave symmetry of the order parameter in high-temperature superconductors and the triplet superconductivity in compound Sr2RuO4 has caused a huge stream of theoretical and experimental investigations of unconventional superconductors. In this review we discuss some novel aspects of the Josephson effect which are related to the symmetry of the order parameter. The most intriguing of them is spontaneous current generation in an unconventional weak link. The example of a Josephson junction in the form of a grain boundary between two disorientated d-wave or f-wave superconductors is considered in detail. Josephson current–phase relations and the phase dependences of the spontaneous current that flows along the interface are analyzed. The spontaneous current and spontaneous phase difference are manifestations of the time-reversal symmetry (𝒯 ) breaking states in the system. We analyzed the region of appearance of 𝒯-breaking states as function of temperature and mismatch angle. A review of the basics of superconducting qubits with emphasis on specific properties of d-wave qubits is given. Recent results in the problem of decoherence in d-wave qubits, which is the major concern for any qubit realization, are presented.
Charge and spin effects in mesoscopic Josephson junctions (Review)
Authors: Krive I. V. , Kulinich S. I. , Shekhter R. I. , Jonson M.
Published: August 2004

We consider the charge and spin effects in low-dimensional superconducting weak links. The first part of the review deals with the effects of electron–electron interaction in Superconductor/Luttinger liquid/Superconductor junctions. The experimental realization of this mesoscopic hybrid system can be an individual single-wall carbon nanotube that bridges a gap between two bulk superconductors. The dc Josephson current through a Luttinger liquid is evaluated in the limits of perfectly and poorly transmitting junctions. The relationship between the Josephson effect in a long SNS junction and the Casimir effect is discussed. In the second part of the paper we review the recent results concerning the influence of the Zeeman and Rashba interactions on the thermodynamic properties of ballistic S–QW–S junction fabricated in a two-dimensional electron gas. It is shown that in a magnetically controlled junction there are conditions for a resonant Cooper pair transition which results in a giant supercurrent through a tunnel junction and a giant magnetic response of a multichannel SNS junction. The supercurrent induced by the joint action of the Zeeman and Rashba interactions in 1D quantum wires connected to bulk superconductors is predicted.
The ac Josephson effect: observation of electromagnetic radiation (Review)
Authors: Yanson I. K.
Published: August 2004

An historical review of the discovery and the early period of research on the Josephson effect is given. Experiments on the tunneling effect in superconductors done in the 1960s at the Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine, Kharkov (ILTPE), which led to the observation of Josephson electromagnetic radiation are described in detail. The experimental data are illustrated by the original curves, and the dates they were taken are indicated. The physical mechanism for the generation of rf radiation in superconducting tunnel junctions is examined, and some of the more promising applications of the ac Josephson effect are briefly listed.
Experimental studies of weakly coupled superconductors (Review)
Authors: Dmitrenko I. M.
Published: August 2004

A review is given of the main experimental results obtained in research on weakly coupled superconductors after 1964 at the Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine, Kharkov (ILTPE).
Some novel effects in superconducting nanojunctions
Authors: Zaikin A. D.
Published: August 2004

In this paper we address several new developments in the theory of the dc Josephson effect in superconducting weak links. We analyze the interplay between quantum interference effects and Andreev reflection in SNS nanojunctions with insulating barriers and demonstrate that these effects may qualitatively modify the Josephson current in such structures. We also investigate the impact of the parity effect on persistent currents in superconducting nanorings interrupted by a quantum point contact (QPC). In the limit of zero temperature and for an odd number of electrons in the ring we predict complete suppression of the supercurrent across a QPC with one conducting mode. In nanorings with SNS junctions a π-state can occur for an odd number of electrons. Changing this number from even to odd yields spontaneous supercurrent in the ground state of such rings without any externally applied magnetic flux.
Impurity scattering effect on charge transport in high-Tc cuprate junctions
Authors: Tanaka Y. , Asano Y. , Kashiwaya S.
Published: August 2004

It is known that the zero-bias conductance peak (ZBCP) is expected in tunneling spectra of normal-metal/high-Tc cuprate junctions because of the formation of the midgap Andreev resonant states (MARS) at junction interfaces. In the present review, we report the recent theoretical study of impurity scattering effects on the tunneling spectroscopy. In the former part of the present paper, we discuss impurity effects in the normal metal. We calculate tunneling conductance for diffusive normal metal (DN)/high-Tc cuprate junctions based on the Keldysh Green function technique. Besides the ZBCP due to the MARS, we can expect ZBCP of a different origin, i.e., caused by coherent Andreev reflection (CAR) assisted by the proximity effect in DN. Their relative importance depends on the angle α between the interface normal and the crystal axis of high-Tc superconductors. At α=0 we find the ZBCP by the CAR for low-transparency junctions with small Thouless energies in DN; this is similar to the case of diffusive normal metal/insulator/s-wave superconductor junctions. Under increase of α from zero to π/4, the contribution of MARS to ZBCP becomes more prominent and the effect of the CAR is gradually suppressed. Such complex spectral features would be observable in conductance spectra of high-Tc junctions at very low temperatures. In the latter part of our paper, we study impurity effects in superconductors. We consider impurities near the junction interface on the superconductor side. The conductance is calculated from the Andreev and the normal reflection coefficients, which are estimated by using the single-site approximation in an analytic calculation and by the recursive Green function method in a numerical simulation. We find splitting of the ZBCP in the presence of the time reversal symmetry. Thus the zero-field splitting of ZBCP in the experiment does not perfectly prove the existence of a broken time reversal symmetry state.
Advances in high-Tc grain-boundary junctions
Authors: Tafuri F. , Kirtley J. R. , Lombardi F. , Medaglia P. G. , Orgiani P. , Balestrino G.
Published: August 2004

We review results on two novel types of grain-boundary Josephson junctions in the high-critical-temperature cuprate superconductors. The quality of YBa2Cu3O7−δ biepitaxial grain-boundary Josephson junctions has been improved using a new growth geometry to the point that “tunnel-like” characteristics are reproducibly obtained. The consequent low barrier transmission probabilities are apparently favorable for isolating intrinsic d-wave induced effects. We also focus on peculiar aspects of spontaneous currents in HTS Josephson junctions, which are unique and reflect the intimate relation between vortex matter and the Josephson effect. Bicrystal grain-boundary Josephson junctions have also been fabricated using artificial superlattice films with as few as six superconducting copper–oxygen planes. Extrinsic and intrinsic d-wave effects in these junctions are discussed within the framework of novel designs for π-circuitry and qubits.
Electron transport in metal oxide superconducting heterojunctions
Authors: Komissinski F. V. , Constantinian K. I. , Kislinskii Yu. , Ovsyannikov G. A.
Published: August 2004

Research results on electron transport in Au/YBa2Cu3Ox and Nb/Au/YBa2Cu3Ox thin-film heterojunctions are reviewed. The experimental current–phase relations of Nb/Au/YBa2Cu3Ox heterojunctions on c-oriented YBCO films exhibit a second harmonic, temperature dependence, and a phase shift that is explained in terms of a combined symmetry dx2−y2+s of the superconducting order parameter of YBa2Cu3Ox. The current–voltage characteristics of Au/YBa2Cu3Ox and Nb/Au/YBa2Cu3Ox heterojunctions on (1 1 20)YBa2Cu3Ox thin films with an inclined crystallographic c axis display an anomaly of the conductance at low voltages, the behavior of which is studied at various temperatures and magnetic fields. The experimental results are analyzed in the framework of a model for the appearance of bound states caused by multiple Andreev reflection in junctions containing a superconductor with dx2−y2 symmetry of the superconducting order parameter. Studies of the noise characteristics of Nb/Au/(1 1 20)YBa2Cu3Ox heterojunctions at T=4.2 K reveal the presence of thermal and shot components. However, enhancement of the shot noise due to multiple Andreev reflection is not observed in the experiment.
On the nonmonotonic temperature dependence of the magnetization of YBCO single crystals at low fields
Authors: Timofeev V. P. , Bondarenko A. V.
Published: August 2004

The results of experiments on the low-field dc magnetic response of YBa2Cu3O7−x single crystals having unidirectional twinning planes are presented. The nonmonotonicity observed in the temperature dependence of the magnetization of the samples is interpreted in the framework of a possible model for the existence of a system of Josephson weak links on the twinning planes and of anisotropy of the order parameter.
Fractional ac Josephson effect in unconventional superconductors
Authors: Kwon H.-J. , Yakovenko V. M. , Sengupta K.
Published: August 2004

For certain orientations of Josephson junctions between two px-wave or two d-wave superconductors, the subgap Andreev bound states produce a 4π-periodic relation between the Josephson current I and the phase difference φ: I∝sin(φ/2). Consequently, the ac Josephson current has the fractional frequency eV/ℏ, where V is the dc voltage. In the tunneling limit, the Josephson current is proportional to the first power (and not the square) of the electron tunneling amplitude. Thus, the Josephson current between unconventional superconductors is carried by single electrons, rather than by Cooper pairs. The fractional ac Josephson effect can be observed experimentally by measuring the frequency spectrum of microwave radiation from the junction.
Radio-frequency method for investigation of quantum properties of superconducting structures
Authors: Il’ichev E. , Oukhanski N. , Wagner Th. , Meyer H.-G. , Smirnov A. Yu. , Grajcar M. , Izmalkov A. , Born D. , Krech W. , Zagoskin A.
Published: August 2004

We implement the impedance measurement technique (IMT) for characterization of interferometer-type superconducting qubits. In the framework of this method, the interferometer loop is inductively coupled to a high-quality tank circuit. We show that the IMT is a powerful tool for studying the response of an externally controlled two-level system to different types of excitations. Conclusive information about the qubits is obtained from a readout of the tank properties.
Spin and current variations in Josephson junctions
Authors: Shnirman A. , Nussinov Z. , Zhu Jian-Xin , Balatsky A. V. , Makhlin Yu.
Published: August 2004

We study the dynamics of a single spin embedded in the tunneling barrier between two superconductors. As a consequence of pair correlations in the superconducting state, the spin displays rich and unusual dynamics. To properly describe the time evolution of the spin we derive the effective Keldysh action for the spin. The superconducting correlations lead to an effective spin action, which is nonlocal in time, leading to unconventional precession. We further illustrate how the current is modulated by this novel spin dynamics.
Topologically protected quantum states and quantum computing in Josephson junctions arrays
Authors: Ioffe L. B. , Feigel’man M. V. , Douçot B.
Published: August 2004

We review recent results on a new class of Josephson arrays which have nontrivial topology and exhibit novel quantum states at low temperatures. One of these states is characterized by long-range order in a two-Cooper-pair condensate and by a discrete topological order parameter. The second state is insulating and can be considered as being the result of an evolution of the former state due to Bose-condensation of usual superconductive vortices with a flux quantum Φ0. The quantum phase transition between these two states is controlled by variation of the external magnetic field. Both the superconductive and insulating states are characterized by the presence of 2K-degenerate ground states, with K being the number of topologically different cycles existing in the plane of the array. This degeneracy is “protected” from the external perturbations (and noise) by the topological order parameter and spectral gap. We show that under ideal conditions the low-order effect of the external perturbations on this degeneracy is exactly zero and that deviations from ideality lead to only exponentially small effects of perturbations. We argue that this system provides a physical implementation of an ideal quantum computer with a built-in error correction. A number of relatively simple “echo-like” experiments possible on small-size arrays are discussed.
Topological solitons of the Lawrence–Doniach model as equilibrium Josephson vortices in layered superconductors
Authors: Kuplevakhsky S. V.
Published: August 2004

We present a complete, exact solution of the problem of the magnetic properties of layered superconductors with an infinite number of superconducting layers in parallel fields H>0. Based on a new exact variational method, we determine the type of all stationary points of both the Gibbs and Helmholtz free-energy functionals. For the Gibbs free-energy functional, they are either points of strict, strong minima or saddle points. All stationary points of the Helmholtz free-energy functional are those of strict, strong minima. The only minimizers of both the functionals are the Meissner (0-soliton) solution and soliton solutions. The latter represent equilibrium Josephson vortices. In contrast, nonsoliton configurations (interpreted in some previous publications as “isolated fluxons” and “fluxon lattices”) are shown to be saddle points of the Gibbs free-energy functional: They violate the conservation law for the flux and the stationarity condition for the Helmholtz free-energy functional. For stable solutions, we give a topological classification and establish a one-to-one correspondence with Abrikosov vortices in type-II superconductors. In the limit of weak interlayer coupling, exact, closed-form expressions for all stable solutions are derived: They are nothing but the “vacuum state” and topological solitons of the coupled static sine-Gordon equations for the phase differences. The stable solutions cover the whole field range 0⩽H<∞ and their stability regions overlap. Soliton solutions exist for arbitrary small transverse dimensions of the system, provided the field H is sufficiently high. Aside from their importance for weak superconductivity, the new soliton solutions can find applications in different fields of nonlinear physics and applied mathematics.
Wigner distribution function formalism for superconductors and collisionless dynamics of the superconducting order parameter
Authors: Amin M. H. S. , Bezuglyi E. V. , Kijko A. S. , Omelyanchouk A. N.
Published: August 2004

A technique for studying collisionless dynamics of a homogeneous superconducting system is developed which is based on Riccati parametrization of the Wigner distribution function. The quantum evolution of the superconducting order parameter, initially deviating from the equilibrium value, is calculated using this technique. The effect of a time-dependent BCS paring interaction on the dynamics of the order parameter is also studied.
Membrane insertion of anthrax protective antigen and cytoplasmic delivery of lethal factor occur at different stages of the endocytic pathway
Authors: Abrami Laurence , Lindsay Margaret , Parton Robert G. , Leppla Stephen H. , van der Goot F. Gisou
Published: August 2004

The protective antigen (PA) of anthrax toxin binds to a cell surface receptor, undergoes heptamerization, and binds the enzymatic subunits, the lethal factor (LF) and the edema factor (EF). The resulting complex is then endocytosed. Via mechanisms that depend on the vacuolar ATPase and require membrane insertion of PA, LF and EF are ultimately delivered to the cytoplasm where their targets reside. Here, we show that membrane insertion of PA already occurs in early endosomes, possibly only in the multivesicular regions, but that subsequent delivery of LF to the cytoplasm occurs preferentially later in the endocytic pathway and relies on the dynamics of internal vesicles of multivesicular late endosomes.
Kazrin, a novel periplakin-interacting protein associated with desmosomes and the keratinocyte plasma membrane
Authors: Groot Karen R. , Sevilla Lisa M. , Nishi Kazunori , DiColandrea Teresa , Watt Fiona M.
Published: August 2004

Periplakin forms part of the scaffold onto which the epidermal cornified envelope is assembled. The NH2-terminal 133 amino acids mediate association with the plasma membrane and bind a novel protein, kazrin. Kazrin is highly conserved and lacks homology to any known protein. There are four alternatively spliced transcripts, encoding three proteins with different NH2 termini. Kazrin is expressed in all layers of stratified squamous epithelia; it becomes membrane associated in the suprabasal layers, coincident with up-regulation of periplakin, and is incorporated into the cornified envelope of cultured keratinocytes. Kazrin colocalizes with periplakin and desmoplakin at desmosomes and with periplakin at the interdesmosomal plasma membrane, but its subcellular distribution is independent of periplakin. On transfection, all three kazrin isoforms have similar subcellular distributions. We conclude that kazrin is a novel component of desmosomes that associates with periplakin.
Sonic hedgehog regulates the proliferation, differentiation, and migration of enteric neural crest cells in gut
Authors: Fu Ming , Lui Vincent Chi Hang , Sham Mai Har , Pachnis Vassilis , Tam Paul Kwong Hang
Published: August 2004

Enteric neural crest cells (NCCs) migrate and colonize the entire gut and proliferate and differentiate into neurons and glia of the enteric nervous system in vertebrate embryos. We have investigated the mitogenic and morphogenic functions of Sonic hedgehog (Shh) on enteric NCCs in cell and organ culture. Enteric NCCs expressed Shh receptor Patched and transcripts encoding the Shh signal transducer (Gli1). Shh promoted the proliferation and inhibited the differentiation of NCCs. The pro-neurogenic effect of glial cell line–derived neurotrophic factor (GDNF) on NCCs was abolished by Shh. In gut explants, NCCs migrated from the explants onto the adjacent substratum if GDNF was added, whereas addition of Shh abolished this migration. Neuronal differentiation and coalescence of neural crest–derived cells into myenteric plexuses in explants was repressed by the addition of Shh. Our data suggest that Shh controls the proliferation and differentiation of NCCs and modulates the responsiveness of NCCs toward GDNF inductions.
Yeast actin patches are networks of branched actin filaments
Authors: Young Michael E. , Cooper John A. , Bridgman Paul C.
Published: August 2004

Cortical actin patches are the most prominent actin structure in budding and fission yeast. Patches assemble, move, and disassemble rapidly. We investigated the mechanisms underlying patch actin assembly and motility by studying actin filament ultrastructure within a patch. Actin patches were partially purified from Saccharomyces cerevisiae and examined by negative-stain electron microscopy (EM). To identify patches in the EM, we correlated fluorescence and EM images of GFP-labeled patches. Patches contained a network of actin filaments with branches characteristic of Arp2/3 complex. An average patch contained 85 filaments. The average filament was only 50-nm (20 actin subunits) long, and the filament to branch ratio was 3:1. Patches lacking Sac6/fimbrin were unstable, and patches lacking capping protein were relatively normal. Our results are consistent with Arp2/3 complex-mediated actin polymerization driving yeast actin patch assembly and motility, as described by a variation of the dendritic nucleation model.
Pericentrin forms a complex with intraflagellar transport proteins and polycystin-2 and is required for primary cilia assembly
Authors: Jurczyk Agata , Gromley Adam , Redick Sambra , Agustin Jovenal San , Witman George , Pazour Gregory J. , Peters Dorien J.M. , Doxsey Stephen
Published: August 2004

Primary cilia are nonmotile microtubule structures that assemble from basal bodies by a process called intraflagellar transport (IFT) and are associated with several human diseases. Here, we show that the centrosome protein pericentrin (Pcnt) colocalizes with IFT proteins to the base of primary and motile cilia. Immunogold electron microscopy demonstrates that Pcnt is on or near basal bodies at the base of cilia. Pcnt depletion by RNA interference disrupts basal body localization of IFT proteins and the cation channel polycystin-2 (PC2), and inhibits primary cilia assembly in human epithelial cells. Conversely, silencing of IFT20 mislocalizes Pcnt from basal bodies and inhibits primary cilia assembly. Pcnt is found in spermatocyte IFT fractions, and IFT proteins are found in isolated centrosome fractions. Pcnt antibodies coimmunoprecipitate IFT proteins and PC2 from several cell lines and tissues. We conclude that Pcnt, IFTs, and PC2 form a complex in vertebrate cells that is required for assembly of primary cilia and possibly motile cilia and flagella.
Phospholipase C and cofilin are required for carcinoma cell directionality in response to EGF stimulation
Authors: Mouneimne Ghassan , Soon Lilian , DesMarais Vera , Sidani Mazen , Song Xiaoyan , Yip Shu-Chin , Ghosh Mousumi , Eddy Robert , Backer Jonathan M. , Condeelis John
Published: August 2004

The epidermal growth factor (EGF)–induced increase in free barbed ends, resulting in actin polymerization at the leading edge of the lamellipodium in carcinoma cells, occurs as two transients: an early one at 1 min and a late one at 3 min. Our results reveal that phospholipase (PLC) is required for triggering the early barbed end transient. Phosphoinositide-3 kinase selectively regulates the late barbed end transient. Inhibition of PLC inhibits cofilin activity in cells during the early transient, delays the initiation of protrusions, and inhibits the ability of cells to sense a gradient of EGF. Suppression of cofilin, using either small interfering RNA silencing or function-blocking antibodies, selectively inhibits the early transient. Therefore, our results demonstrate that the early PLC and cofilin-dependent barbed end transient is required for the initiation of protrusions and is involved in setting the direction of cell movement in response to EGF.
Role of lipid rafts in E-cadherin– and HGF-R/Met–mediated entry of Listeria monocytogenes into host cells
Authors: Seveau Stéphanie , Bierne Hélène , Giroux Stéphanie , Prévost Marie-Christine , Cossart Pascale
Published: August 2004

Listeria monocytogenes uptake by nonphagocytic cells is promoted by the bacterial invasion proteins internalin and InlB, which bind to their host receptors E-cadherin and hepatocyte growth factor receptor (HGF-R)/Met, respectively. Here, we present evidence that plasma membrane organization in lipid domains is critical for Listeria uptake. Cholesterol depletion by methyl-β-cyclodextrin reversibly inhibited Listeria entry. Lipid raft markers, such as glycosylphosphatidylinositol-linked proteins, a myristoylated and palmitoylated peptide and the ganglioside GM1 were recruited at the bacterial entry site. We analyzed which molecular events require membrane cholesterol and found that the presence of E-cadherin in lipid domains was necessary for initial interaction with internalin to promote bacterial entry. In contrast, the initial interaction of InlB with HGF-R did not require membrane cholesterol, whereas downstream signaling leading to F-actin polymerization was cholesterol dependent. Our work, in addition to documenting for the first time the role of lipid rafts in Listeria entry, provides the first evidence that E-cadherin and HGF-R require lipid domain integrity for their full activity.
The raft-associated protein MAL is required for maintenance of proper axon–glia interactions in the central nervous system
Authors: Schaeren-Wiemers Nicole , Bonnet Annick , Erb Michael , Erne Beat , Bartsch Udo , Kern Frances , Mantei Ned , Sherman Diane , Suter Ueli
Published: August 2004

The myelin and lymphocyte protein (MAL) is a tetraspan raft-associated proteolipid predominantly expressed by oligodendrocytes and Schwann cells. We show that genetic ablation of mal resulted in cytoplasmic inclusions within compact myelin, paranodal loops that are everted away from the axon, and disorganized transverse bands at the paranode–axon interface in the adult central nervous system. These structural changes were accompanied by a marked reduction of contactin-associated protein/paranodin, neurofascin 155 (NF155), and the potassium channel Kv1.2, whereas nodal clusters of sodium channels were unaltered. Initial formation of paranodal regions appeared normal, but abnormalities became detectable when MAL started to be expressed. Biochemical analysis revealed reduced myelin-associated glycoprotein, myelin basic protein, and NF155 protein levels in myelin and myelin-derived rafts. Our results demonstrate a critical role for MAL in the maintenance of central nervous system paranodes, likely by controlling the trafficking and/or sorting of NF155 and other membrane components in oligodendrocytes.
Bend propagation drives central pair rotation in Chlamydomonas reinhardtii flagella
Authors: Mitchell David R. , Nakatsugawa Masako
Published: August 2004

Regulation of motile 9+2 cilia and flagella depends on interactions between radial spokes and a central pair apparatus. Although the central pair rotates during bend propagation in flagella of many organisms and rotation correlates with a twisted central pair structure, propulsive forces for central pair rotation and twist are unknown. Here we compared central pair conformation in straight, quiescent flagella to that in actively beating flagella using wild-type Chlamydomonas reinhardtii and mutants that lack radial spoke heads. Twists occur in quiescent flagella in both the presence and absence of spoke heads, indicating that spoke–central pair interactions are not needed to generate torque for twisting. Central pair orientation in propagating bends was also similar in wild type and spoke head mutant strains, thus orientation is a passive response to bend formation. These results indicate that bend propagation drives central pair rotation and suggest that dynein regulation by central pair–radial spoke interactions involves passive central pair reorientation to changes in bend plane.