8,900 research outputs found
Gauge invariance of massless QED
A simple general proof of gauge invariance in QED is given in the framework
of causal perturbation theory. It illustrates a method which can also be used
in non-abelian gauge theories.Comment: 7 pages, TEX-file, Zuerich University Preprint ZU-TH-33/199
Developing automated text-image alignment to enhance access to heritage manuscript images
The proposed project aims to enhance access to primary cultural heritage materials of India by developing human-validated automated text-image alignment techniques in order to provide access to digital images via related machine-readable texts, lexical resources, linguistic software, and a sophisticated search interface. Digital images of manuscripts written in Sanskrit, one of the world's richest culture-bearing languages, will be integrated into a digital library of Sanskrit. This integration will allow generalized information extraction and search techniques to reach enormous reservoirs of Sanskrit manuscripts. Integrating primary cultural materials with the Sanskrit Library will thus enable broad use of Indic collections for research and education where Indic materials are grossly underrepresented. The result will be extendable to the collections of Sanskrit manuscripts housed in American libraries and throughout the world and to archives of scanned Sanskrit books
Reproductive Health Aid: A Delicate Balancing Act
In this contribution the authors show that development assistance targeting reproductive health overwhelmingly concentrates on HIV/AIDS at the expense of family planning elements. Data on financial contributions disbursed by governments and private foundations are used as collected by the Resource Flows project as initiated by UNFPA/NIDI. The current allocation of aid does not accord well with the plans made in Cairo at the International Conference on Population and Development in 1994. Part of the explanation is that future health needs are difficult to predict, but it also shows how strong the influence of one donor, i.e. the United States, is in this setup. The landscape of population assistance is a highly volatile one, brought about not only by political issues like the Global Gag Rule, but also issues of collective action design as assistance under the heading of the Millennium Development Goals crowds out family planning. A complicating factor is that development assistance for reproductive health is at some points ill-adjusted towards the needs of developing countries.health;development aid;AIDS;fertility
The Chandra Fornax Survey - I: The Cluster Environment
We present the first results of a deep Chandra survey of the inner 1 degree
of the Fornax cluster of galaxies. Ten 50 ksec pointings were obtained in a
mosaic centered on the giant elliptical galaxy NGC 1399 at the nominal cluster
center. Emission and temperature maps of Fornax are presented, and an initial
study of 771 detected X-ray point sources is made. Regions as small as 100pc
are resolved. The intra-cluster gas in Fornax exhibits a highly asymmetric
morphology and temperature structure, dominated by a 180 kpc extended ``plume''
of low surface brightness, cool, ~1 keV) gas to the North-East of NGC 1399 with
a sharper edge to the South West. The elliptical galaxy NGC 1404 also exhibits
a cool halo of X-ray gas within the cluster, with a highly sharpened leading
edge as it presumably falls into the cluster, and a cometary-like tail. We
estimate that some ~200-400 point sources are physically associated with
Fornax. Confirming earlier works, we find that the globular cluster population
in NGC 1399 is highly X-ray active, extending to globulars which may in fact be
intra-cluster systems. We have also found a remarkable correlation between the
location of giant and dwarf cluster galaxies and the presence of X-ray
counterparts, such that systems inhabiting regions of low gas density are more
likely to show X-ray activity. Not only does this correlate with the asymmetry
of the intra-cluster gas but also with the axis joining the center of Fornax to
an infalling group 1 Mpc to the South-West. We suggest that Fornax may be
experiencing an intergalactic ``headwind'' due to motion relative to the
surrounding large-scale structure.Comment: 35 pages, 15 figures, submitted to ApJ. Most figures not included
owing to severe compression degradation - we strongly recommend downloading
the full resolution paper from
http://www.astro.columbia.edu/~caleb/ms_highres.pdf (1.9Mb
Sanskrit Lexical Sources: Digital Synthesis and Revision
The proposed project aims to synthesize, extend, revise, and improve the principal lexical reference works of Sanskrit, one of the world's richest culture-bearing languages, and to provide wide public access to them in the digital Sanskrit library
The Standard Model and its Generalizations in Epstein-Glaser Approach to Renormalization Theory II: the Fermion Sector and the Axial Anomaly
We complete our study of non-Abelian gauge theories in the framework of
Epstein-Glaser approach to renormalization theory including in the model an
arbitrary number of Dirac Fermions. We consider the consistency of the model up
to the third order of the perturbation theory. In the second order we obtain
pure group theoretical relations expressing a representation property of the
numerical coefficients appearing in the left and right handed components of the
interaction Lagrangian. In the third order of the perturbation theory we obtain
the the condition of cancellation of the axial anomaly.Comment: 38 pages, LATEX 2e, extensive rewritting, some errors eliminate
On Gauge Invariance and Spontaneous Symmetry Breaking
We show how the widely used concept of spontaneous symmetry breaking can be
explained in causal perturbation theory by introducing a perturbative version
of quantum gauge invariance. Perturbative gauge invariance, formulated
exclusively by means of asymptotic fields, is discussed for the simple example
of Abelian U(1) gauge theory (Abelian Higgs model). Our findings are relevant
for the electroweak theory, as pointed out elsewhere.Comment: 13 pages, latex, no figure
Tuning Topological Superconductivity in Phase-Controlled Josephson Junctions with Rashba and Dresselhaus Spin-Orbit Coupling
Recently, topological superconductors based on Josephson junctions in
two-dimensional electron gases with strong Rashba spin-orbit coupling have been
proposed as attractive alternatives to wire-based setups. Here, we elucidate
how phase-controlled Josephson junctions based on quantum wells with [001]
growth direction and an arbitrary combination of Rashba and Dresselhaus
spin-orbit coupling can also host Majorana bound states for a wide range of
parameters as long as the magnetic field is oriented appropriately. Hence,
Majorana bound states based on Josephson junctions can appear in a wide class
of two-dimensional electron gases. We study the effect of spin-orbit coupling,
the Zeeman energies, and the superconducting phase difference to create a full
topological phase diagram and find the optimal stability region to observe
Majorana bound states in narrow junctions. Surprisingly, for equal Rashba and
Dresselhaus spin-orbit coupling, well localized Majorana bound states can
appear only for phase differences as the topological gap
protecting the Majorana bound states vanishes at . Our results show
that the ratio between Rashba and Dresselhaus spin-orbit coupling or the choice
of the in-plane crystallographic axis along which the superconducting phase
bias is applied offer additional tunable knobs to test Majorana bound states in
these systems. Finally, we discuss signatures of Majorana bound states that
could be probed experimentally by tunneling conductance measurements at the
edge of the junction.Comment: 21 pages, 12 figure
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