1,493 research outputs found
Analysis, fabrication and properties of single-mode fibres exhibiting extremely low polarization birefringence
There is currently a great deal of interest in the development of single-mode fibres, capable of transmitting linearly-polarized light. Conventional monomode fibres exhibit linear birefringence; they therefore have an output state which is, in general, elliptically polarized and different from that at the input. Apart from the possible curtailment of the transmission bandwidth caused by this birefringence, the indeterminacy of the output polarization is a considerable disadvantage when coupling fibres to polarization-sensitive integrated-optics receivers. In addition, several interesting devices which utilise single-mode fibres have recently emerged and it has been found that the intrinsic retardance present in the fibres accompanied by the uncertainty in output polarization imposes a limitation on performance. Amongst these, the best known are the Faraday-effect current transducer, the fibre Raman laser and the fibre gyroscope
Diffuse Bauchschmerzen und Eosinophilie
Zusammenfassung: Die eosinophile Gastroenteritis ist eine relativ seltene Erkrankung unklarer Ătiologie mit einem heterogenen Krankheitsbild. Wichtige Differenzialdiagnosen stellen intestinale parasitĂ€re Infektionen, das hypereosinophile Syndrom, Lymphome und andere maligne und allergische Erkrankungen dar. Die Diagnose kann meist mittels Anamnese und Standardlabor, zusammen mit den Ergebnissen von Biopsien oder Parazentese gestellt werden. Milde Formen mit lediglich Diarrhö als klinischer Manifestation können symptombezogen behandelt werden. Die Therapie bei schwereren VerlĂ€ufen erfolgt initial mit Kortikosteroide
Closed String Tachyon Condensation on Twisted Circles
We study IIA/B string theory compactified on twisted circles. These models
possess closed string tachyons and reduce to type 0B/A theory in a special
limit. Using methods of gauged linear sigma models and mirror symmetry we
construct a conformal field theory which interpolates between these models and
flat space via an auxiliary Liouville direction. Interpreting motion in the
Liouville direction as renormalization group flow, we argue that the end point
of tachyon condensation in all these models (including 0B/A theory) is
supersymmetric type II theory. We also find a zero-slope limit of these models
which is best described in a T-dual picture as a type II NS-NS fluxbrane. In
this limit tachyon condensation is an interesting and well posed problem in
supergravity. We explicitly determine the tachyon as a fluctuation of
supergravity fields, and perform a rudimentary numerical analysis of the
relevant flows.Comment: 21 pages plus appendices (12 pages), harvmac, 1 fig, v2: minor
changes and references added, v3: minor changes version published in JHE
Momentum transfer using chirped standing wave fields: Bragg scattering
We consider momentum transfer using frequency-chirped standing wave fields.
Novel atom-beam splitter and mirror schemes based on Bragg scattering are
presented. It is shown that a predetermined number of photon momenta can be
transferred to the atoms in a single interaction zone.Comment: 4 pages, 3 figure
Closed Strings Tachyons and Non-Commutative Instabilities
We observe a relation between closed strings tachyons and one-loop
instabilities in non-supersymmetric non-commutative gauge theories. In
particular we analyze the spectra of type IIB string theory on C^3/Z_N orbifold
singularities and the non-commutative field theory that lives on D3 branes
located at the singularity. We find a surprising correspondence between the
existence or not of one-loop low-momentum instabilities in the non-commutative
field theory and the existence or not of tachyons in the closed string twisted
sectors. Moreover, the relevant piece of the non-commutative field theory
effective action is suggestive of an exchange of closed string modes. This
suggests that non-commutative field theories retain some information about the
dynamics of the underlying string configuration. Finally, we also comment on a
possible relation between closed string tachyon condensation and field theory
tachyon condensation.Comment: 27 pages, Latex. v2: Comment about anomalies and refs. added. Version
published in JHEP. v3: minor change
Spacetime Energy Decreases under World-sheet RG Flow
We study renormalization group flows in unitary two dimensional sigma models
with asymptotically flat target spaces. Applying an infrared cutoff to the
target space, we use the Zamolodchikov c-theorem to demonstrate that the target
space ADM energy of the UV fixed point is greater than that of the IR fixed
point: spacetime energy decreases under world-sheet RG flow. This result
mirrors the well understood decrease of spacetime Bondi energy in the time
evolution process of tachyon condensation.Comment: 25 pages, 4 figures, harvma
Axial anomaly in the reduced model: Higher representations
The axial anomaly arising from the fermion sector of \U(N) or \SU(N)
reduced model is studied under a certain restriction of gauge field
configurations (the ``\U(1) embedding'' with ). We use the
overlap-Dirac operator and consider how the anomaly changes as a function of a
gauge-group representation of the fermion. A simple argument shows that the
anomaly vanishes for an irreducible representation expressed by a Young tableau
whose number of boxes is a multiple of (such as the adjoint
representation) and for a tensor-product of them. We also evaluate the anomaly
for general gauge-group representations in the large limit. The large
limit exhibits expected algebraic properties as the axial anomaly.
Nevertheless, when the gauge group is \SU(N), it does not have a structure
such as the trace of a product of traceless gauge-group generators which is
expected from the corresponding gauge field theory.Comment: 21 pages, uses JHEP.cls and amsfonts.sty, the final version to appear
in JHE
Closed String Tachyon Condensation at c=1
The c=1 matrix model, with or without a type 0 hat, has an exact quantum
solution corresponding to closed string tachyon condensation along a null
surface. The condensation occurs, and spacetime dissolves, at a finite retarded
time on I^+. The outgoing quantum state of tachyon fluctuations in this
time-dependent background is computed using both the collective field and exact
fermion pictures. Perturbative particle production induced by the moving
tachyon wall is shown to be similar to that induced by a soft moving mirror.
Hence, despite the fact that I^+ for the tachyon is geodesicaly incomplete,
quantum correlations in the incoming state are unitarily transmitted to the
outgoing state in perturbation theory. It is also shown that,
non-perturbatively, information can leak across the tachyon wall, and tachyon
scattering is not unitary. Exact unitarity remains intact only in the free
fermion picture.Comment: Minor corrections; References added; 24 pages, 2 figures, harvma
Dangerous work: The gendered nature of bullying in the context of higher education
This paper discusses results from a research project which set out to investigate gender differences in the nature and experience of bullying within the higher education sector. Gender differences emerged in the form and perception of bullying as well as in target response. Results also indicate that, irrespective of gender, bullies can capture and subvert organizational structures and procedures (official hierarchies, mentoring systems, probationary reviews) to further their abuse of the target and to conceal aggressive intent. These outcomes are discussed in relation to gendered assumptions behind management practices and in relation to the masculinist ethic that underpins many higher education management initiatives. Overall, results indicate that bullying cannot be divorced from gender and that such behaviour needs to be seen in a gendered context
Closed-String Tachyons and the Hagedorn Transition in AdS Space
We discuss some aspects of the behaviour of a string gas at the Hagedorn
temperature from a Euclidean point of view. Using AdS space as an infrared
regulator, the Hagedorn tachyon can be effectively quasi-localized and its
dynamics controled by a finite energetic balance. We propose that the off-shell
RG flow matches to an Euclidean AdS black hole geometry in a generalization of
the string/black-hole correspondence principle. The final stage of the RG flow
can be interpreted semiclassically as the growth of a cool black hole in a
hotter radiation bath. The end-point of the condensation is the large Euclidean
AdS black hole, and the part of spacetime behind the horizon has been removed.
In the flat-space limit, holography is manifest by the system creating its own
transverse screen at infinity. This leads to an argument, based on the
energetics of the system, explaining why the non-supersymmetric type 0A string
theory decays into the supersymmetric type IIB vacuum. We also suggest a notion
of `boundary entropy', the value of which decreases along the line of flow.Comment: 24 pages, Harvmac. 2 Figures. Typos corrected and reference adde
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