638 research outputs found
Reverse Transplant Tourism
In this article, we propose a novel form of kidney swap, which we label “Reverse Transplant Tourism.” This proposal has the potential to increase the number of successful transplants in the US at a time of great need, while reducing costs. It also will provide benefits to impoverished international patients with willing, compatible donors who otherwise would have no access to transplantation. Instead of non-US kidney donors being offered money through a black market middleman in exchange for one of their kidneys, Reverse Transplant Tourism would provide a legal and ethical exchange of living donor kidneys through kidney-paired donation. In this way, the donors will not receive money for their kidneys, but rather will receive a transplant for someone they love, while also helping a US pair who would otherwise be unable to transplant due to biological incompatibility
Geometric semantic genetic programming for recursive boolean programs
This is the author accepted manuscript. The final version is available from ACM via the DOI in this record.Geometric Semantic Genetic Programming (GSGP) induces a unimodal fitness landscape for any problem that consists in finding a function fitting given input/output examples. Most of the work around GSGP to date has focused on real-world applications and on improving the originally proposed search operators, rather than on broadening its theoretical framework to new domains. We extend GSGP to recursive programs, a notoriously challenging domain with highly discontinuous fitness landscapes. We focus on programs that map variable-length Boolean lists to Boolean values, and design search operators that are provably efficient in the training phase and attain perfect generalization. Computational experiments complement the theory and demonstrate the superiority of the new operators to the conventional ones. This work provides new insights into the relations between program syntax and semantics, search operators and fitness landscapes, also for more general recursive domains.© 2017 Copyright held by the owner/author(s). Permission to make digital or hard copies of all or part of this work for personal or
classroom use is granted without fee provided that copies are not made or distributed
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Thermoelectric phenomena in a quantum dot asymmetrically coupled to external leads
We study thermoelectric phenomena in a system consisting of strongly
correlated quantum dot coupled to external leads in the Kondo regime. We
calculate linear and nonlinear electrical and thermal conductance and
thermopower of the quantum dot and discuss the role of asymmetry in the
couplings to external electrodes. In the linear regime electrical and thermal
conductances are modified, while thermopower remains unchanged. In the
nonlinear regime the Kondo resonance in differential conductance develops at
non-zero source-drain voltage, which has important consequences on
thermoelectric properties of the system and the thermopower starts to depend on
the asymmetry. We also discuss Wiedemann-Franz relation, thermoelectric figure
of merit and validity of the Mott formula for thermopower.Comment: 6 pages, 7 figure
Low-temperature transport through a quantum dot between two superconductor leads
We consider a quantum dot coupled to two BCS superconductors with same gap
energies . The transport properties are investigated by means of
infinite- noncrossing approximation. In equilibrium density of states, Kondo
effect shows up as two sharp peaks around the gap bounds. Application of a
finite voltage bias leads these peaks to split, leaving suppressed peaks near
the edges of energy gap of each lead. The clearest signatures of the Kondo
effect in transport are three peaks in the nonlinear differential conductance:
one around zero bias, another two at biases . This result is
consistent with recent experiment. We also predict that with decreasing
temperature, the differential conductances at biases anomalously
increase, while the linear conductance descends.Comment: replaced with revised versio
Can the initial singularity be detected by cosmological tests?
In the present paper we raise the question whether initial cosmological
singularity can be proved from the cosmological tests. The classical general
relativity predict the existence of singularity in the past if only some energy
conditions are satisfied. On the other hand the latest quantum gravity
applications to cosmology suggest of possibility of avoiding the singularity
and replace it with the bounce. The distant type Ia supernovae data are used to
constraints on bouncing evolutional scenario where square of the Hubble
function is given by formulae
, where are density parameters and . We show that the on the
base of the SNIa data standard bouncing models can be ruled out on the
confidence level. If we add the cosmological constant to the standard
bouncing model then we obtain as the best-fit that the parameter
is equal zero which means that the SNIa data do not support the bouncing term
in the model. The bounce term is statistically insignificant the present epoch.
We also demonstrate that BBN offer the possibility of obtaining stringent
constraints of the extra term . The other observational test
methods like CMB and the age of oldest objects in the Universe are used. We
also use the Akaike informative criterion to select a model according to the
goodness of fit and we conclude that this term should be ruled out by Occam's
razor, which makes that the big bang is favored rather then bouncing scenario.Comment: 30 pages, 7 figures improved versio
Electron transport across a quantum wire in the presence of electron leakage to a substrate
We investigate electron transport through a mono-atomic wire which is tunnel
coupled to two electrodes and also to the underlying substrate. The setup is
modeled by a tight-binding Hamiltonian and can be realized with a scanning
tunnel microscope (STM). The transmission of the wire is obtained from the
corresponding Green's function. If the wire is scanned by the contacting STM
tip, the conductance as a function of the tip position exhibits oscillations
which may change significantly upon increasing the number of wire atoms. Our
numerical studies reveal that the conductance depends strongly on whether or
not the substrate electrons are localized. As a further ubiquitous feature, we
observe the formation of charge oscillations.Comment: 7 pages, 7 figure
Geometric Semantic Grammatical Evolution
This is the author accepted manuscript. The final version is available from Springer via the DOI in this record.Geometric Semantic Genetic Programming (GSGP) is a novel form of
Genetic Programming (GP), based on a geometric theory of evolutionary algorithms,
which directly searches the semantic space of programs. In this chapter,
we extend this framework to Grammatical Evolution (GE) and refer to the new
method as Geometric Semantic Grammatical Evolution (GSGE). We formally derive
new mutation and crossover operators for GE which are guaranteed to see a simple
unimodal fitness landscape. This surprising result shows that the GE genotypephenotype
mapping does not necessarily imply low genotype-fitness locality. To
complement the theory, we present extensive experimental results on three standard
domains (Boolean, Arithmetic and Classifier)
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