1,183 research outputs found
Controlling the Sign of Magnetoconductance in Andreev Quantum Dots
We construct a theory of coherent transport through a ballistic quantum dot
coupled to a superconductor. We show that the leading-order quantum correction
to the two-terminal conductance of these Andreev quantum dots may change sign
depending on (i) the number of channels carried by the normal leads or (ii) the
magnetic flux threading the dot. In contrast, spin-orbit interaction may affect
the magnitude of the correction, but not always its sign. Experimental
signatures of the effect include a non-monotonic magnetoconductance curve and a
transition from an insulator-like to a metal-like temperature dependence of the
conductance. Our results are applicable to ballistic or disordered dots.Comment: Final version (4pages 3figs)- improved presentation and fig 3, and
updated reference
Optimization of admittances on parameters of radio electronic circles by method of tolerance of ellipsoid evaluation
Розглянуто метод допускового еліпсоїдального оцінювання параметрів радіоелектронних кіл з урахуванням технологічної області розсіювання. Даний метод, у порівнянні з існуючими, забезпечує більше покриття області допусків. Із використанням розробленого методу розв’язано задачу оцінювання допусків параметрів широкосмугового фільтра.In this work the method of ellipsoidal tolerance in the estimation of radio electronic circles parameters REC is considered taking into account the technological area of dispersion. This method, compared with existing, provide more coverage tolerance region. Using the developed method solves the problem of estimation parameters tolerances broadband filter
Stereotypical risks and threats in the youth’s opinion (diachronic comparative aspect)
The paper reveals the structure of associative fields of words-stimuli "danger", "risk", "threat", fixed in 1988-90 (the materials of "Russian Association Dictionary") and in 2015 (the results of authors’ associative experiment). The obtained results demonstrate the structural stability of these fields diachronically on the one hand and explicit redistribution of "association vectors" within them on the other on
Towards a Java Subtyping Operad
The subtyping relation in Java exhibits self-similarity. The self-similarity
in Java subtyping is interesting and intricate due to the existence of wildcard
types and, accordingly, the existence of three subtyping rules for generic
types: covariant subtyping, contravariant subtyping and invariant subtyping.
Supporting bounded type variables also adds to the complexity of the subtyping
relation in Java and in other generic nominally-typed OO languages such as C#
and Scala. In this paper we explore defining an operad to model the
construction of the subtyping relation in Java and in similar generic
nominally-typed OO programming languages. Operads, from category theory, are
frequently used to model self-similar phenomena. The Java subtyping operad, we
hope, will shed more light on understanding the type systems of generic
nominally-typed OO languages.Comment: 13 page
Theory of quantum metal to superconductor transitions in highly conducting systems
We derive the theory of the quantum (zero temperature) superconductor to
metal transition in disordered materials when the resistance of the normal
metal near criticality is small compared to the quantum of resistivity. This
can occur most readily in situations in which ``Anderson's theorem'' does not
apply. We explicitly study the transition in superconductor-metal composites,
in an s-wave superconducting film in the presence of a magnetic field, and in a
low temperature disordered d-wave superconductor. Near the point of the
transition, the distribution of the superconducting order parameter is highly
inhomogeneous. To describe this situation we employ a procedure which is
similar to that introduced by Mott for description of the temperature
dependence of the variable range hopping conduction. As the system approaches
the point of the transition from the metal to the superconductor, the
conductivity of the system diverges, and the Wiedemann-Franz law is violated.
In the case of d-wave (or other exotic) superconductors we predict the
existence of (at least) two sequential transitions as a function of increasing
disorder: a d-wave to s-wave, and then an s-wave to metal transition
Topologies of nodal sets of random band limited functions
It is shown that the topologies and nestings of the zero and nodal sets of
random (Gaussian) band limited functions have universal laws of distribution.
Qualitative features of the supports of these distributions are determined. In
particular the results apply to random monochromatic waves and to random real
algebraic hyper-surfaces in projective space.Comment: 62 pages. Major revision following referee repor
Magnetic fluctuations in 2D metals close to the Stoner instability
We consider the effect of potential disorder on magnetic properties of a
two-dimensional metallic system (with conductance ) when interaction in
the triplet channel is so strong that the system is close to the threshold of
the Stoner instability. We show, that under these conditions there is an
exponentially small probability for the system to form local spin droplets
which are local regions with non zero spin density. Using a non-local version
of the optimal fluctuation method we find analytically the probability
distribution and the typical spin of a local spin droplet (LSD). In particular,
we show that both the probability to form a LSD and its typical spin are
independent of the size of the droplet (within the exponential accuracy). The
LSDs manifest themselves in temperature dependence of observable quantities. We
show, that below certain cross-over temperature the paramagnetic susceptibility
acquires the Curie-like temperature dependence, while the dephasing time
(extracted from magneto-resistance measurements) saturates.Comment: 15 pages, 4 figure
Mesoscopic mechanism of adiabatic charge transport
We consider adiabatic charge transport through mesoscopic metallic samples
caused by a periodically changing external potential. We find that both the
amplitude and the sign of the charge transferred through a sample per period
are random sample specific quantities. The characteristic magnitude of the
charge is determined by the quantum interference.Comment: 4 pages, 2 figure
Mesoscopic mechanism of exchange interaction in magnetic multilayers
We discuss a mesoscopic mechanism of exchange interaction in
ferromagnet-normal metal-ferromagnet multilayers. We show that in the case when
the metal's thickness is larger than the electron mean free path, the relative
orientation of magnetizations in the ferromagnets is perpendicular. The
exchange energy between ferromagnets decays with the metal thickness as a power
law
On the Nature of Infrared Singularities in Disordered Interacting Systems
We address the problem of infrared singularities in the perturbation theory
for disordered interacting systems in . We show that a typical,
sufficiently large interacting system exhibits a linear instability in the spin
triplet channel. In a density-density channel, although stability is preserved,
a large number of soft modes is accumulated. These phenomena are responsible
for the instability of the weak-interacting fixed point. Although generic, the
unstable direction and soft modes are highly sample specific and can not be
effectively captured by conventional techniques based on an averaging
procedure. Rather, the instability is determined by the largest eigenvalues of
the polarization operator. We propose to employ the optimal fluctuation method
for evaluating the probability of such events.Comment: 4 pages, RevTeX. References added, minor change
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