3,787 research outputs found
Topological Kondo effect with Majorana fermions
The Kondo effect is a striking consequence of the coupling of itinerant
electrons to a quantum spin with degenerate energy levels. While degeneracies
are commonly thought to arise from symmetries or fine-tuning of parameters, the
recent emergence of Majorana fermions has brought to the fore an entirely
different possibility: a "topological degeneracy" which arises from the
nonlocal character of Majorana fermions. Here we show that nonlocal quantum
spins formed from these degrees of freedom give rise to a novel "topological
Kondo effect". This leads to a robust non-Fermi liquid behavior, known to be
difficult to achieve in the conventional Kondo context. Focusing on mesoscopic
superconductor devices, we predict several unique transport signatures of this
Kondo effect, which would demonstrate the non-local quantum dynamics of
Majorana fermions, and validate their potential for topological quantum
computation
Lopsidedness in dwarf irregular galaxies
We quantify the amplitude of the lopsidedness, the azimuthal angular
asymmetry index, and the concentration of star forming regions, as represented
by the distribution of the H emission, in a sample of 78 late-type
irregular galaxies. We bin the observed galaxies in two groups representing
blue compact galaxies (BCDs) and low surface brightness dwarf galaxies (LSBs).
The light distribution is analysed with a novel algorithm, which allows
detection of details in the light distribution pattern.
We find that while the asymmetry of the underlying continuum light,
representing the older stellar generations, is relatively small, the H
emission is very asymmetric and is correlated in position angle with the
continuum light.
We test a model of random star formation over the extent of a galaxy by
simulating HII regions in artificial dwarf galaxies. The implication is that
random star formation over the full extent of a galaxy may be generated in LSB
dwarf-irregular galaxies but not in BCD galaxies.Comment: 42 pages, LaTex. Accepted by: MNRAS, 13 Mar 200
Possible Local Spiral Counterparts to Compact Blue Galaxies at Intermediate Redshift
We identify nearby disk galaxies with optical structural parameters similar
to those of intermediate-redshift compact blue galaxies. By comparing HI and
optical emission-line widths, we show that the optical widths substantially
underestimate the true kinematic widths of the local galaxies. By analogy,
optical emission-line widths may underrepresent the masses of intermediate-z
compact objects. For the nearby galaxies, the compact blue morphology is the
result of tidally-triggered central star formation: we argue that interactions
and minor mergers may cause apparently compact morphology at higher redshift.Comment: 5 pages, uses emulateapj5 and psfig. To appear in ApJ
Preconception Care: Concepts and Perceptions: An ethical perspective
General individual preconception care is a new strategy to improve the health of future
children and their mothers –and to a lesser extent the prospective fathers’ health- through
primary intervention. Improving their health through preconception care comprises two
component actions. The first is to impart relevant information to prospective parents, thereby
improving knowledge. The second is to modify individual behaviour based on the knowledge
gained. General individual preconception care anticipates on both these components and
entails risk assessment, health promotion, counselling, and interventions. Risk assessment is
the systematic identification and evaluation of risk factors for so-called adverse ‘pregnancy
outcomes’. Risk factors vary widely and include not taking folic acid supplements, using
medication that can cause malformations or functional damage to an embryo, overweight,
smoking, diabetes or having an inheritable disease. Health promotion means informing and
educating couples on how to improve their health in order to improve the future child’s health,
including avoiding alcohol and tobacco, and the importance of proper nutrition and exercise.
Prospective parents are counselled about additional screening, diagnostic tests, and specialist
consultations that may be necessary if risks are identified. Intervention refers to efforts to
modify or eliminate risk factors
Specifying Reusable Components
Reusable software components need expressive specifications. This paper
outlines a rigorous foundation to model-based contracts, a method to equip
classes with strong contracts that support accurate design, implementation, and
formal verification of reusable components. Model-based contracts
conservatively extend the classic Design by Contract with a notion of model,
which underpins the precise definitions of such concepts as abstract
equivalence and specification completeness. Experiments applying model-based
contracts to libraries of data structures suggest that the method enables
accurate specification of practical software
Segmentation and texture analysis with multimodel inference for the automatic detection of exudates in early diabetic retinopathy
published_or_final_versio
Giant Magnetic Moments of Nitrogen Stabilized Mn Clusters and Their Relevance to Ferromagnetism in Mn Doped GaN
Using first principles calculations based on density functional theory, we
show that the stability and magnetic properties of small Mn clusters can be
fundamentally altered by the presence of nitrogen. Not only are their binding
energies substantially enhanced, but also the coupling between the magnetic
moments at Mn sites remains ferromagnetic irrespective of their size or shape.
In addition, these nitrogen stabilized Mn clusters carry giant magnetic moments
ranging from 4 Bohr magnetons in MnN to 22 Bohr magnetons in Mn_5N. It is
suggested that the giant magnetic moments of Mn_xN clusters may play a key role
in the ferromagnetism of Mn doped GaN which exhibit a wide range (10K - 940K)
of Curie temperatures
Coulomb Screening of 2D Massive Dirac Fermions
A model of 2D massive Dirac fermions, interacting with a instantaneous
Coulomb interaction, is presented to mimic the physics of gapped graphene. The
static polarization function is calculated explicitly to analyze screening
effect at the finite temperature and density. Results are compared with the
massless case . We also show that various other works can be reproduced within
our model in a straightforward and unified manner
Vacuum energies due to delta-like currents: simulating classical objects along branes with arbitrary codimensions
In this paper we investigate the vacuum energies of several models of quantum
fields interacting with static external currents (linear couplings)
concentrated along parallel branes with an arbitrary number of codimensions. We
show that we can simulate the presence of static charges distributions as well
as the presence of classical static dipoles in any dimension for massive and
massless fields. We also show that we can produce confining potentials with
massless self interacting scalar fields as well as long range anisotropic
potentials.Comment: 18 latex page
Abelian gauge theories on compact manifolds and the Gribov ambiguity
We study the quantization of abelian gauge theories of principal torus
bundles over compact manifolds with and without boundary. It is shown that
these gauge theories suffer from a Gribov ambiguity originating in the
non-triviality of the bundle of connections whose geometrical structure will be
analyzed in detail. Motivated by the stochastic quantization approach we
propose a modified functional integral measure on the space of connections that
takes the Gribov problem into account. This functional integral measure is used
to calculate the partition function, the Greens functions and the field
strength correlating functions in any dimension using the fact that the space
of inequivalent connections itself admits the structure of a bundle over a
finite dimensional torus. The Greens functions are shown to be affected by the
non-trivial topology, giving rise to non-vanishing vacuum expectation values
for the gauge fields.Comment: 33 page
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