5,641 research outputs found
Kondo effect in quantum dots coupled to ferromagnetic leads
We study the Kondo effect in a quantum dot which is coupled to ferromagnetic
leads and analyse its properties as a function of the spin polarization of the
leads. Based on a scaling approach we predict that for parallel alignment of
the magnetizations in the leads the strong-coupling limit of the Kondo effect
is reached at a finite value of the magnetic field. Using an equation-of-motion
technique we study nonlinear transport through the dot. For parallel alignment
the zero-bias anomaly may be split even in the absence of an external magnetic
field. For antiparallel spin alignment and symmetric coupling, the peak is
split only in the presence of a magnetic field, but shows a characteristic
asymmetry in amplitude and position.Comment: 5 pages, 2 figure
Development of single-cell protectors for sealed silver-zinc cells
Three design approaches to cell-level protection were developed, fabricated, and tested. These systems are referred to as the single-cell protector (SCP), multiplexed-cell protector(MCP). To evaluate the systems 18-cell battery packs without cell level control were subjected to cycle life test. A total of five batteries were subjected to simulate synchronous orbit cycling at 40% depth of discharge at 22C. Batteries without cell-level protection failed between 345 and 255 cycles. Cell failure in the cell level protected batteries occurred between 412 and 540. It was determined that the cell-level monitoring and protection is necessary to attain the long cycle life of a AgZn battery. The best method of providing control and protection of the AgZn cells depends on the specific application and capability of the user
Exact solution for the stationary Kardar-Parisi-Zhang equation
We obtain the first exact solution for the stationary one-dimensional
Kardar-Parisi-Zhang equation. A formula for the distribution of the height is
given in terms of a Fredholm determinant, which is valid for any finite time
. The expression is explicit and compact enough so that it can be evaluated
numerically. Furthermore, by extending the same scheme, we find an exact
formula for the stationary two-point correlation function.Comment: 9 pages, 3 figure
Polynuclear growth model, GOE and random matrix with deterministic source
We present a random matrix interpretation of the distribution functions which
have appeared in the study of the one-dimensional polynuclear growth (PNG)
model with external sources. It is shown that the distribution, GOE, which
is defined as the square of the GOE Tracy-Widom distribution, can be obtained
as the scaled largest eigenvalue distribution of a special case of a random
matrix model with a deterministic source, which have been studied in a
different context previously. Compared to the original interpretation of the
GOE as ``the square of GOE'', ours has an advantage that it can also
describe the transition from the GUE Tracy-Widom distribution to the GOE.
We further demonstrate that our random matrix interpretation can be obtained
naturally by noting the similarity of the topology between a certain
non-colliding Brownian motion model and the multi-layer PNG model with an
external source. This provides us with a multi-matrix model interpretation of
the multi-point height distributions of the PNG model with an external source.Comment: 27pages, 4 figure
Interacting topological phases and modular invariance
We discuss a (2+1) dimensional topological superconductor with left-
and right-moving Majorana edge modes and a
symmetry. In the absence of interactions, these phases are distinguished by an
integral topological invariant . With interactions, the edge state in the
case is unstable against interactions, and a invariant mass gap can be generated dynamically. We show that
this phenomenon is closely related to the modular invariance of type II
superstring theory. More generally, we show that the global gravitational
anomaly of the non-chiral Majorana edge states is the physical manifestation of
the bulk topological superconductors classified by .Comment: 11 page
Development of single cell protectors for sealed silver-zinc cells, phase 1
A single cell protector (SCP) assembly capable of protecting a single silver-zinc (Ag Zn) battery cell was designed, fabricated, and tested. The SCP provides cell-level protection against overcharge and overdischarge by a bypass circuit. The bypass circuit consists of a magnetic-latching relay that is controlled by the high and low-voltage limit comparators. Although designed specifically for secondary Ag-Zn cells, the SCP is flexible enough to be adapted to other rechargeable cells. Eighteen SCPs were used in life testing of an 18-cell battery. The cells were sealed Ag-Zn system with inorganic separators. For comparison, another 18-cell battery was subjected to identical life test conditions, but with battery-level protection rather than cell-level. An alternative approach to the SCP design in the form of a microprocessor-based system was conceptually designed. The comparison of SCP and microprocessor approaches is also presented and a preferred approach for Ag-Zn battery protection is discussed
Vertically coupled double quantum dots in magnetic fields
Ground-state and excited-state properties of vertically coupled double
quantum dots are studied by exact diagonalization. Magic-number total angular
momenta that minimize the total energy are found to reflect a crossover between
electron configurations dominated by intra-layer correlation and ones dominated
by inter-layer correlation. The position of the crossover is governed by the
strength of the inter-layer electron tunneling and magnetic field. The magic
numbers should have an observable effect on the far infra-red optical
absorption spectrum, since Kohn's theorem does not hold when the confinement
potential is different for two dots. This is indeed confirmed here from a
numerical calculation that includes Landau level mixing. Our results take full
account of the effect of spin degrees of freedom. A key feature is that the
total spin, , of the system and the magic-number angular momentum are
intimately linked because of strong electron correlation. Thus jumps hand
in hand with the total angular momentum as the magnetic field is varied. One
important consequence of this is that the spin blockade (an inhibition of
single-electron tunneling) should occur in some magnetic field regions because
of a spin selection rule. Owing to the flexibility arising from the presence of
both intra-layer and inter-layer correlations, the spin blockade is easier to
realize in double dots than in single dots.Comment: to be published in Phys. Rev. B1
Index for three dimensional superconformal field theories with general R-charge assignments
We derive a general formula of an index for three dimensional N=2
superconformal field theories with general R-charge assignments to chiral
multiplets by using the localization method in S^2xS^1 background. As examples
we compute the index for theories in a few mirror pairs, and confirm the
agreement of the indices in each mirror pair.Comment: 22 pages, no figure; v2: refs added, the definition of the index
changed; v3: chemical potentials for monopole charges introduced, Sec. 5
improved, a reference adde
A note on the dyonic D6-brane
We study the dyon electric charge of D6-branes as eleven dimensional
KK-monopoles. We observe that the dyon charge is intimately related with the
existence of gauge connections and antisymmetric fields on the brane world
volume.Comment: 8 pages, Contribution to the 6th International Workshop on Conformal
Field Theory and Integrable Models, Landau Institute, Sept. 2002, to honour
A. Belavin on the occasion of his 60th birthda
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