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Search Results: 1 - 10 of 87709 matches for " I. Geresdi "
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Intercomparison of aerosol-cloud-precipitation interactions in stratiform orographic mixed-phase clouds
A. Muhlbauer, T. Hashino, L. Xue, A. Teller, U. Lohmann, R. M. Rasmussen, I. Geresdi,Z. Pan
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2010,
Abstract: Anthropogenic aerosols serve as a source of both cloud condensation nuclei (CCN) and ice nuclei (IN) and affect microphysical properties of clouds. Increasing aerosol number concentrations is hypothesized to retard the cloud droplet coalescence and the riming in mixed-phase clouds, thereby decreasing orographic precipitation. This study presents results from a model intercomparison of 2-D simulations of aerosol-cloud-precipitation interactions in stratiform orographic mixed-phase clouds. The sensitivity of orographic precipitation to changes in the aerosol number concentrations is analysed and compared for various dynamical and thermodynamical situations. Furthermore, the sensitivities of microphysical processes such as coalescence, aggregation, riming and diffusional growth to changes in the aerosol number concentrations are evaluated and compared. The participating numerical models are the model from the Consortium for Small-Scale Modeling (COSMO) with bulk microphysics, the Weather Research and Forecasting (WRF) model with bin microphysics and the University of Wisconsin modeling system (UWNMS) with a spectral ice habit prediction microphysics scheme. All models are operated on a cloud-resolving scale with 2 km horizontal grid spacing. The results of the model intercomparison suggest that the sensitivity of orographic precipitation to aerosol modifications varies greatly from case to case and from model to model. Neither a precipitation decrease nor a precipitation increase is found robustly in all simulations. Qualitative robust results can only be found for a subset of the simulations but even then quantitative agreement is scarce. Estimates of the aerosol effect on orographic precipitation are found to range from 19% to 0% depending on the simulated case and the model. Similarly, riming is shown to decrease in some cases and models whereas it increases in others, which implies that a decrease in riming with increasing aerosol load is not a robust result. Furthermore, it is found that neither a decrease in cloud droplet coalescence nor a decrease in riming necessarily implies a decrease in precipitation due to compensation effects by other microphysical pathways. The simulations suggest that mixed-phase conditions play an important role in buffering the effect of aerosol perturbations on cloud microphysics and reducing the overall susceptibility of clouds and precipitation to changes in the aerosol number concentrations. As a consequence the aerosol effect on precipitation is suggested to be less pronounced or even inverted in regions with high terrain (e.g., the Alps or Rocky Mountains) or in regions where mixed-phase microphysics is important for the climatology of orographic precipitation.
Transition from coherent mesoscopic single particle transport to proximity Josephson-current
A. Geresdi,A. Halbritter,G. Mihály
Physics , 2010, DOI: 10.1103/PhysRevB.82.212501
Abstract: The transport through a metal-superconductor interface is governed by a special charge conversion process, the Andreev reflection, where each incident electron drags another electron with itself to form a Cooper pair. At the normal side a hole is left behind dressed by superconducting correlations. For a low transparency interface the simultaneous transfer of two charges is strongly suppressed leading to a reduced conductance. Here we demonstrate that this reduced conductance can be turned to an infinite one by tuning the nanoscale geometry. Creating variable size nanojunctions between a thin metallic film and a superconducting tip we study how multiple phase-coherent scatterings enhance the superconducting correlations at the normal side. By increasing the coherent volume of carriers initially the transmission through the interface is continuously enhanced. However, as the phase-coherent volume reaches the opposite surface of the thin film a resonator is formed, and a robust transition is induced due to Cooper pair condensation.
1 minute parity lifetime of a NbTiN Cooper-pair transistor
David J. van Woerkom,Attila Geresdi,Leo P. Kouwenhoven
Physics , 2015,
Abstract: The parity modulation of the ground state of a superconducting island is a direct consequence of the presence of the Cooper pair condensate preferring an even number of charge carriers. The addition energy of an odd, unpaired quasiparticle equals to the superconducting gap, $\Delta$, suppressing single electron hopping in the low temperature limit. Controlling the quasiparticle occupation is of fundamental importance for superconducting qubits as single electron tunneling results in decoherence. In particular, topological quantum computation relies on the parity control and readout of Majorana bound states. Here we present parity modulation for the first time of a niobium titanite nitride (NbTiN) Cooper-pair transistor coupled to aluminium (Al) leads. We show that this circuit is compatible with the magnetic field requirement in the range of 100 mT of inducing topological superconductivity in spin-orbit coupled nanowires. Our observed parity lifetime exceeding 1 minute is several orders of magnitude higher than the required gate time of flux-controlled braiding of Majorana states. Our findings readily demonstrate that a NbTiN island can be parity-controlled and therefore provides a good platform for superconducting coherent circuits operating in a magnetic field.
GHz Operation of Nanometer-Scale Metallic Memristors: Highly Transparent Conductance Channels in Ag$_{2}$S Devices
A. Geresdi,M. Csontos,A. Gubicza,A. Halbritter,G. Mihály
Physics , 2013, DOI: 10.1039/c3nr05682a
Abstract: The nonlinear transport properties of nanometer-scale junctions formed between an inert metallic tip and an Ag film covered by a thin Ag$_{2}$S layer are investigated. Suitably prepared samples exhibit memristive behavior with technologically optimal ON and OFF state resistances yielding to resistive switching on the nanosecond time scale. Utilizing point contact Andreev reflection spectroscopy we studied the nature of electron transport in the active volume of the memristive junctions showing that both the ON and OFF states correspond to truly nanometer scale, highly transparent metallic channels. Our results demonstrate the merits of Ag$_{2}$S nanojunctions as nanometer-scale memory cells with GHz operation frequencies.
From stochastic single atomic switch to nanoscale resistive memory device
A. Geresdi,A. Halbritter,A. Gyenis,P. Makk,G. Mihály
Physics , 2010, DOI: 10.1039/C0NR00951B
Abstract: Solid state ionic conductors are good candidates for the next generation of nonvolatile computer memory elements. Such devices have to show reproducible resistance switching at reasonable voltage and current values even if scaled down to the nanometer sizes. Here we study the switching characteristics of nanoscale junctions created between a tungsten tip and a silver film covered by a thin ionic conductor layer. Atomic-sized junctions show spectacular current induced switching characteristics, but both the magnitude of the switching voltage and the direction of the switching vary randomly for different junctions. In contrast, for somewhat larger junctions with diameters of a few nanometers a well defined, reproducible switching behavior is observed which is associated with the formation and destruction of nanoscale channels in the ionic conductor surface layer. Our results define a low size limit of 3 nm for reliable ionic nano-switches, which is well below the resolution of recent lithographic techniques.
Ferromagnetic proximity effect in F-QDot-S device
L. Hofstetter,S. Csonka,A. Geresdi,M. Aagesen,J. Nygard,C. Schonenberger
Physics , 2009, DOI: 10.1103/PhysRevLett.104.246804
Abstract: Ferromagnetic proximity effect is studied in InAs nanowire (NW) based quantum dots (QD) strongly coupled to a ferromagnetic (F) and a superconducting (S) lead. The influence of the F lead is detected through the splitting of the spin-1/2 Kondo resonance. We show that the F lead induces a local exchange field on the QD, which has varying amplitude and a sign depending on the charge states. The interplay of the F and S correlations generates an exchange field related supgap feature. This novel mini-gap allows now the visualization of the exchange field also in even charge states
Nanoscale spin-polarization in dilute magnetic semiconductor (In,Mn)Sb
A. Geresdi,A. Halbritter,M. Csontos,Sz. Csonka,G. Mihaly,T. Wojtowicz,X. Liu,B. Janko,J. K. Furdyna
Physics , 2008, DOI: 10.1103/PhysRevB.77.233304
Abstract: Results of point contact Andreev reflection (PCAR) experiments on (In,Mn)Sb are presented and analyzed in terms of current models of charge conversion at a superconductor-ferromagnet interface. We investigate the influence of surface transparency, and study the crossover from ballistic to diffusive transport regime as contact size is varied. Application of a Nb tip to a (In,Mn)Sb sample with Curie temperature Tc of 5.4 K allowed the determination of spin-polarization when the ferromagnetic phase transition temperature is crossed. We find a striking difference between the temperature dependence of the local spin polarization and of the macroscopic magnetization, and demonstrate that nanoscale clusters with magnetization close to the saturated value are present even well above the magnetic phase transition temperature.
Realization of microwave quantum circuits using hybrid superconducting-semiconducting nanowire Josephson elements
G. de Lange,B. van Heck,A. Bruno,D. J. van Woerkom,A. Geresdi,S. R. Plissard,E. P. A. M. Bakkers,A. R. Akhmerov,L. DiCarlo
Physics , 2015, DOI: 10.1103/PhysRevLett.115.127002
Abstract: We report the realization of quantum microwave circuits using hybrid superconductor-semiconductor Josephson elements comprised of InAs nanowires contacted by NbTiN. Capacitively-shunted single elements behave as transmon qubits with electrically tunable transition frequencies. Two-element circuits also exhibit transmon-like behavior near zero applied flux, but behave as flux qubits at half the flux quantum, where non-sinusoidal current-phase relations in the elements produce a double-well Josephson potential. These hybrid Josephson elements are promising for applications requiring microwave superconducting circuits operating in magnetic field.
Strategy of Ukraine : Economics, Sociology, Law , 2011,
Abstract: The question of origin of failures is considered in a global market, influence of TNK on an origin and functioning of such processes. Analysis of redistribution of development of countries. Рассмотрены вопросы возникновения провалов в глобальном рынке, влияние ТНК на возникновение и функционирование таких процессов. Проанализированы перераспределение развития стран. Розглянуто питання виникнення провал в у глобальному ринку, вплив ТНК на виникнення та функц онування таких процес в. Проанал зовано перерозпод л розвитку кра н.
Strategy of Ukraine : Economics, Sociology, Law , 2011,
Abstract: Розглядаються питання розвитку нтеграц йних процес в в С, а саме основна увага прид лена процесам дез нтеграц , вид ленн основних геопол тичних центр в, та наростанню протир ч у диному економ чному простор м ж кра нами-учасницями. The questions of development of integration processes are examined in ES, namely basic attention is directed on the processes of disintegration, determination of geopolitical centers, to growth of contradictions in single economic space between countries-participants. Рассматриваются вопросы развития интеграционных процессов в ЕС, а именно основное внимание направлено на процессы дезинтеграции, определение геополитических центров, нарастанию проти-воречий в едином экономическом пространстве между странами-участницами.
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