50 research outputs found
Fluctuation Effects in High Sheet Resistance Superconducting Films
As the normal state sheet resistance, , of a thin film superconductor
increases, its superconducting properties degrade. For
superconductivity disappears and a transition to a nonsuperconducting state
occurs. We present electron tunneling and transport measurements on ultrathin,
homogeneously disordered superconducting films in the vicinity of this
transition. The data provide strong evidence that fluctuations in the amplitude
of the superconducting order parameter dominate the tunneling density of states
and the resistive transitions in this regime. We briefly discuss possible
sources of these amplitude fluctuation effects. We also describe how the data
suggest a novel picture of the superconductor to nonsuperconductor transition
in homogeneous 2D systems.Comment: 11 pages, 5 figure
Observation of a subgap density of states in superconductor-normal metal bilayers in the Cooper limit
We present transport and tunneling measurements of Pb-Ag bilayers with
thicknesses, and , that are much less than the superconducting
coherence length. The transition temperature, , and energy gap, ,
in the tunneling Density of States (DOS) decrease exponentially with
at fixed . Simultaneously, a DOS that increases linearly from the Fermi
energy grows and fills nearly 40% of the gap as is 1/10 of of bulk
Pb. This behavior suggests that a growing fraction of quasiparticles decouple
from the superconductor as goes to 0. The linear dependence is consistent
with the quasiparticles becoming trapped on integrable trajectories in the
metal layer.Comment: 5 pages and 4 figures. This version is just the same as the old
version except that we try to cut the unnecessary white space in the figures
and make the whole paper look more compac
The interference effect of concurrent working memory task on visual inhibitory control
We examined the interference between inhibitory control of a saccadic eye movement and a working memory task. This study was motivated by the observation that people are suscep-tible to cognitive errors when they are preoccupied. Subjects were instructed to make an anti-saccade, or to look in the opposite direction of a visual stimulus, thereby exercising inhibito-ry control over the reflexive eye movement towards a salient object. At the same time, the subjects were instructed to memorize a random sequence of digits that were read out to them, thereby engaging their working memory. We measured the success of an eye movement by rapidly switching between images and asking the subjects what they saw. We found that these concurrent cognitive tasks significantly degraded anti-saccade performance.We examined the interference between inhibitory control of a saccadic eye movement and a working memory task. This study was motivated by the observation that people are susceptible to cognitive errors when they are preoccupied. Subjects were instructed to make an anti-saccade, or to look in the opposite direction of a visual stimulus, thereby exercising inhibitory control over the reflexive eye movement towards a salient object. At the same time, the subjects were instructed to memorize a random sequence of digits that were read out to them, thereby engaging their working memory. We measured the success of an eye movement by rapidly switching between images and asking the subjects what they saw. We found that these concurrent cognitive tasks significantly degraded anti-saccade performance
A Theory of Object Recognition: Computations and Circuits in the Feedforward Path of the Ventral Stream in Primate Visual Cortex
We describe a quantitative theory to account for the computations performed by the feedforward path of the ventral stream of visual cortex and the local circuits implementing them. We show that a model instantiating the theory is capable of performing recognition on datasets of complex images at the level of human observers in rapid categorization tasks. We also show that the theory is consistent with (and in some case has predicted) several properties of neurons in V1, V4, IT and PFC. The theory seems sufficiently comprehensive, detailed and satisfactory to represent an interesting challenge for physiologists and modelers: either disprove its basic features or propose alternative theories of equivalent scope. The theory suggests a number of open questions for visual physiology and psychophysics
Proximity effect in granular superconductor-normal metal structures
We fabricated three-dimensional disordered Pb-Cu granular structures, with
various metal compositions. The typical grain size of both metals is smaller
than the superconductor and normal metal coherence lengths, thus satisfying the
Cooper limit. The critical temperature of the samples was measured and compared
with the critical temperature of bilayers. We show how the proximity effect
theories, developed for bilayers, can be modified for random mixtures and we
demonstrate that our experimental data fit well the de Gennes weak coupling
limit theory in the Cooper limit. Our results indicate that, in granular
structures, the Cooper limit can be satisfied over a wide range of
concentrations.Comment: 15 pages, 4 figure
A New Hybrid Debugging Architecture for Eclipse
The final publication is available at Springer via http://dx.doi.org/10.1007/978-3-319-14125-1_11[EN] During many years, print debugging has been the most used
method for debugging. Nowadays, however, industrial languages come
with a trace debugger that allows programmers to trace computations
step by step using breakpoints and state viewers. Almost all modern
programming environments include a trace debugger that allows us to
inspect the state of a computation in any given point. Nevertheless,
this debugging method has been criticized for being completely manual
and time-consuming. Other debugging techniques have appeared to
solve some of the problems of Trace Debugging, but they suffer from
other problems such as scalability. In this work we present a new hybrid
debugging technique. It is based on a combination of Trace Debugging,
Algorithmic Debugging and Omniscient Debugging to produce a synergy
that exploits the best properties and strong points of each technique. We
describe the architecture of our hybrid debugger and our implementation
that has been integrated into Eclipse as a plugin.This work has been partially supported by the Spanish Ministerio de EconomÃa y Competitividad (Secretaria de Estado de Investigación, Desarrollo e Innovación) under grant TIN2008-06622-003-02 and by the Generalitat Valenciana
under grant PROMETEO/2011/052. David Insa was partially supported by the Spanish Ministerio de Educación under FPU grant AP2010-4415.González, J.; Insa Cabrera, D.; Silva Galiana, JF. (2013). A New Hybrid Debugging Architecture for Eclipse. En Logic-Based Program Synthesis and Transformation. Springer. 183-201. doi:10.1007/978-3-319-14125-1_11S183201Swi-prolog (1987). http://www.swi-prolog.org/Netbeans (1999). http://www.netbeans.org/Eclipse (2003). http://www.eclipse.org/Omnicore codeguide (2007). http://www.omnicore.com/en/codeguide.htmBorland JBuilder (2008). http://www.embarcadero.com/products/jbuilder/Sicstus prolog spider ide (2009). https://sicstus.sics.se/spider/Caballero, R.: A Declarative Debugger of Incorrect Answers for Constraint Functional-Logic Programs. In: Proceedings of the 2005 ACM-SIGPLAN Workshop on Curry and Functional Logic Programming (WCFLP 2005), pp. 8–13. ACM Press, New York (2005)Davie, T., Chitil, O.: Hat-delta: One Right Does Make a Wrong. In: Proceedings of the 7th Symposium on Trends in Functional Programming (TFP 2006) (April 2006)Gestwicki, P., Jayaraman, B.: JIVE: Java Interactive Visualization Environment. In: Companion to the 19th Annual ACM-SIGPLAN Conference on Object-Oriented Programming Systems, Languages, and Applications (OOPSLA 2004), pp. 226–228. ACM Press, New York (2004)Giammona, D.: ORACLE ADF - Putting It Together. Technical report, ADF Declarative Debugger Archives (November 2009)Girgis, H., Jayaraman, B.: JavaDD: a Declarative Debugger for Java. Technical report,University at Buffalo (2006)González, F., De Miguel, R., Serrano, S.: Depurador Declarativo de Programas Java. Technical report, Universidad Complutense de Madrid (2006). http://eprints.ucm.es/9114/Hermanns, C., Kuchen, H.: Hybrid Debugging of Java Programs. In: Escalona, M.J., Cordeiro, J., Shishkov, B. (eds.) ICSOFT 2011. CCIS, vol. 303, pp. 91–107. Springer, Heidelberg (2013)Montebello, M., Abela, C.: Design and Implementation of a Backward-In-Time. In: Chaudhri, A.B., Jeckle, M., Rahm, E., Unland, R. (eds.) NODe-WS 2002. LNCS, vol. 2593, pp. 46–58. Springer, Heidelberg (2003)Insa, D., Silva, J.: An Algorithmic Debugger for Java. In: Proceedings of the 26th IEEE International Conference on Software Maintenance (ICSM 2010), pp. 1–6 (2010)Insa, D., Silva, J.: Scaling Up Algorithmic Debugging with Virtual Execution Trees. In: Alpuente, M. (ed.) LOPSTR 2010. LNCS, vol. 6564, pp. 149–163. Springer, Heidelberg (2011)Insa, D., Silva, J.: loops2recursion Java Library (2013). http://www.dsic.upv.es/~jsilva/loops2recursion/Kouh, H.-J., Yoo, W.-H.: The Efficient Debugging System for Locating Logical Errors in Java Programs. In: Kumar, V., Gavrilova, M.L., Kenneth Tan, C.J., L’Ecuyer, P. (eds.) ICCSA 2003. LNCS, vol. 2667, pp. 684–693. Springer, Heidelberg (2003)B. Lewis. Debugging Backwards in Time. Available in the Computing Research Repository 2003, ( http://arxiv.org/abs/cs.SE/0310016 ), cs.SE/0310016Lienhard, A., Gîrba, T., Wang, J.: Practical Object-Oriented Back-in-Time Debugging. In: Vitek, J. (ed.) ECOOP 2008. LNCS, vol. 5142, pp. 592–615. Springer, Heidelberg (2008)S. Microsystems. Java Platform Debugger Architecture - JPDA (2010). http://java.sun.com/javase/technologies/core/toolsapis/jpda/Mirghasemi, S., Barton, J., Petitpierre, C.: Debugging by lastChange. Technical report (2011). http://people.epfl.ch/salman.mirghasemiNilsson, H.: Declarative Debugging for Lazy Functional Languages. PhD thesis, Linköping, Sweden (May 1998)Nilsson, H., Fritzson, P.: Algorithmic Debugging for Lazy Functional Languages. Journal of Functional Programming 4(3), 337–370 (1994)Pothier, G.: Towards Practical Omniscient Debugging. PhD thesis, University of Chile (June 2011)Shapiro, E.: Algorithmic Program Debugging. MIT Press (1982)Silva, J.: A Survey on Algorithmic Debugging Strategies. Advances in Engineering Software 42(11), 976–991 (2011
Early stage morphology of quench condensed Ag, Pb and Pb/Ag hybrid films
Scanning Tunneling Microscopy (STM) has been used to study the morphology of
Ag, Pb and Pb/Ag bilayer films fabricated by quench condensation of the
elements onto cold (T=77K), inert and atomically flat Highly Oriented Pyrolytic
Graphite (HOPG) substrates. All films are thinner than 10 nm and show a
granular structure that is consistent with earlier studies of QC films. The
average lateral diameter, , of the Ag grains, however, depends on
whether the Ag is deposited directly on HOPG ( = 13 nm) or on a Pb
film consisting of a single layer of Pb grains ( = 26.8 nm). In
addition, the critical thickness for electrical conduction () of Pb/Ag
films on inert glass substrates is substantially larger than for pure Ag films.
These results are evidence that the structure of the underlying substrate
exerts an influence on the size of the grains in QC films. We propose a
qualitative explanation for this previously unencountered phenomenon.Comment: 11 pages, 3 figures and one tabl
Coherent, mechanical control of a single electronic spin
The ability to control and manipulate spins via electrical, magnetic and
optical means has generated numerous applications in metrology and quantum
information science in recent years. A promising alternative method for spin
manipulation is the use of mechanical motion, where the oscillation of a
mechanical resonator can be magnetically coupled to a spins magnetic dipole,
which could enable scalable quantum information architectures9 and sensitive
nanoscale magnetometry. To date, however, only population control of spins has
been realized via classical motion of a mechanical resonator. Here, we
demonstrate coherent mechanical control of an individual spin under ambient
conditions using the driven motion of a mechanical resonator that is
magnetically coupled to the electronic spin of a single nitrogen-vacancy (NV)
color center in diamond. Coherent control of this hybrid mechanical/spin system
is achieved by synchronizing pulsed spin-addressing protocols (involving
optical and radiofrequency fields) to the motion of the driven oscillator,
which allows coherent mechanical manipulation of both the population and phase
of the spin via motion-induced Zeeman shifts of the NV spins energy. We
demonstrate applications of this coherent mechanical spin-control technique to
sensitive nanoscale scanning magnetometry.Comment: 6 pages, 4 figure
Approaching Zero-Temperature Metallic States in Mesoscopic Superconductor-Normal-Superconductor Arrays
Systems of superconducting islands placed on normal metal films offer tunable
realizations of two-dimensional (2D) superconductivity; they can thus elucidate
open questions regarding the nature of 2D superconductors and competing states.
In particular, island systems have been predicted to exhibit zero-temperature
metallic states. Although evidence exists for such metallic states in some 2D
systems, their character is not well understood: the conventional theory of
metals cannot explain them, and their properties are difficult to tune. Here,
we characterize the superconducting transitions in mesoscopic island-array
systems as a function of island thickness and spacing. We observe two
transitions in the progression to superconductivity; both transition
temperatures exhibit unexpectedly strong depression for widely spaced islands.
These depressions are consistent with the system approaching zero-temperature
metallic states. The nature of the transitions and the state between them is
explained using a phenomenological model involving the stabilization of
superconductivity on each island via a weak coupling to and feedback from its
neighbors.Comment: 15 pages, 5 figure