511 research outputs found
On Some Stability Properties of Compactified D=11 Supermembranes
We desribe the minimal configurations of the bosonic membrane potential, when
the membrane wraps up in an irreducible way over . The
membrane 2-dimensional spatial world volume is taken as a Riemann Surface of
genus with an arbitrary metric over it. All the minimal solutions are
obtained and described in terms of 1-forms over an associated U(1) fiber
bundle, extending previous results. It is shown that there are no infinite
dimensional valleys at the minima.Comment: 12 pages,Latex2e lamuphys, Invited talk at International Seminar
"Supersymetry and Quantum Symmetries", Dubn
Super Five Brane Hamiltonian and the Chiral Degrees of Freedom
We construct the Hamiltonian of the super five brane in terms of its physical
degrees of freedom. It does not depend on the inverse of the induced metric.
Consequently, some singular configurations are physically admissible, implying
an interpretation of the theory as a multiparticle one. The symmetries of the
theory are analyzed from the canonical point of view in terms of the first and
second class constraints. In particular it is shown how the chiral sector may
be canonically reduced to its physical degrees of freedom.Comment: 16 pages, typos correcte
Fracture of the pancreas in two patients after a goâkart accident
BackgroundAfter blunt abdominal trauma, an isolated injury to the pancreatic duct is uncommon. Physical signs and laboratory parameters are often inaccurate, and missing this diagnosis can cause serious clinical problems.Case outlinesTwo young women (aged 18 and 20 years) are reported who sustained isolated trauma to the pancreatic duct in goâkart accidents. Each patient sustained a fracture of the pancreas. This injury was diagnosed only after a period of clinical observation with repeated laboratory parameters, ultrasound and CT scan. Pancreatic tissue was conserved by performing a pancreaticojejunostomy.DiscussionAfter any episode of blunt abdominal trauma, isolated injury to the pancreatic duct should be considered. Serum analysis, ultrasonography and CT scanning can be helpful in early diagnosis. Preservation of pancreatic tissue can be achieved with a good clinical outcome
Haematidrosis: The Rare Phenomenon of Sweating Blood
Objectives: Haematidrosis, also known as haematohidrosis, is a very rare condition where blood is excreted with sweat. As only a few cases have been described in the literature, we present guidelines on management of this rare phenomenon.
Case: A 44-year-old man presented with self-limited and spontaneous bleeding episodes from different parts of his body. This had started 2 weeks before admission after an episode of extreme emotional stress. Medical history and laboratory tests were normal. The microscopic examination of a sample of the fluid excreted confirmed all blood elements.
Conclusion: The disorder is thought to be related to activation of the sympathetic nervous system. The use of benzodiazepines and beta blockers may be helpful in controlling the bleeding episodes and give some comfort to the patient
STU Black Holes and String Triality
We find double-extreme black holes associated with the special geometry of
the Calabi-Yau moduli space with the prepotential F=STU. The area formula is
STU-moduli independent and has symmetry in space of charges.
The dual version of this theory without prepotential treats the dilaton S
asymmetric versus T,U-moduli. We display the dual relation between new (STU)
black holes and stringy (S|TU) black holes using particular Sp(8, Z)
transformation. The area formula of one theory equals that of the dual theory
when expressed in terms of dual charges. We analyse the relation between (STU)
black holes to string triality of black holes: (S|TU), (T|US), (U|ST)
solutions. In the democratic STU-symmetric version we find that all three S and
T and U duality symmetries are non-perturbative and mix electric and magnetic
charges.Comment: 12 pages, 2 Postscript figures, ref.added, minor corrections, version
to appear in Phys. Rev.
Supermembranes and Super Matrix Models
We review recent developments in the theory of supermembranes and their
relation to matrix models.Comment: Invited lecture presented at the Corfu Workshop, September 20 - 26,
1998, of the TMR Project "Quantum Aspects of Gauge Theories, Supersymmetry
and Unification" (ERBFMRXCT96-0045), to appear in the proceedings. Latex 41
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An evaluation for harnessing low-enthalpy geothermal energy in the Limpopo Province, South Africa
South Africa generates most of its energy requirements from coal, and is now the leading carbon emitter in Africa, and has one of the highest rates of emissions of all nations in the world. In an attempt to decrease its CO2 emissions, South Africa continues to research and develop alternative forms of energy, expand on the development of nuclear and has began to explore potentially vast shale gas reserves. In this mix, geothermal has not been considered to date as an alternative energy source. This omission appears to stem largely from the popular belief that South Africa is tectonically too stable. In this study, we investigated low-enthalpy geothermal energy from one of a number of anomalously elevated heat flow regions in South Africa. Here, we consider a 75-MW enhanced geothermal systems plant in the Limpopo Province, sustainable over a 30-year period. All parameters were inculcated within a levelised cost of electricity model that calculates the single unit cost of electricity and tests its viability and potential impact toward South Africa's future energy security and CO2 reduction. The cost of electricity produced is estimated at 14 USc/KWh, almost double that of coal-generated energy. However, a USD25/MWh renewable energy tax incentive has the potential of making enhanced geothermal systems comparable with other renewable energy sources. It also has the potential of CO2 mitigation by up to 1.5 gCO2/KWh. Considering the aggressive nature of the global climate change combat and South Africa's need for a larger renewable energy base, low-enthalpy geothermal energy could potentially form another energy option in South Africa's alternative energy basket
Anti-de Sitter Black Holes in Gauged N=8 Supergravity
We present new anti-de Sitter black hole solutions of gauged N=8, SO(8)
supergravity, which is the massless sector of the AdS_4\times S^7 vacuum of
M-theory. By focusing on the U(1)^4 Cartan subgroup, we find non-extremal 1, 2,
3 and 4 charge solutions. In the extremal limit, they may preserve up to 1/2,
1/4, 1/8 and 1/8 of the supersymmetry, respectively. In the limit of vanishing
SO(8) coupling constant, the solutions reduce to the familiar black holes of
the M_4\times T^7 vacuum, but have very different interpretation since there
are no winding states on S^7 and no U-duality. In contrast to the T^7
compactification, moreover, we find no static multi-center solutions. Also in
contrast, the S^7 fields appear "already dualized" so that the 4 charges may be
all electric or all magnetic rather than 2 electric and 2 magnetic. Curiously,
however, the magnetic solutions preserve no supersymmetries. We conjecture that
a subset of the extreme electric black holes preserving 1/2 the supersymmetry
may be identified with the S^7 Kaluza-Klein spectrum, with the non-abelian
SO(8) quantum numbers provided by the fermionic zero modes.Comment: 18 pages, Latex, minor notation improvements and references adde
Training telescope operators and support astronomers at Paranal
The operations model of the Paranal Observatory relies on the work of
efficient staff to carry out all the daytime and nighttime tasks. This is
highly dependent on adequate training. The Paranal Science Operations
department (PSO) has a training group that devises a well-defined and
continuously evolving training plan for new staff, in addition to broadening
and reinforcing courses for the whole department. This paper presents the
training activities for and by PSO, including recent astronomical and quality
control training for operators, as well as adaptive optics and interferometry
training of all staff. We also present some future plans.Comment: Paper 9910-123 presented at SPIE 201
(p,q)-string in matrix-regularized membrane and type IIB duality
We consider a lightcone wrapped supermembrane compactified on 2-torus in the
matrix regularization. We examine the double dimensional reduction technique
and deduce the free matrix string of (p,q)-string in type IIB superstring
theory explicitly from the matrix-regularized wrapped supermembrane. In
addition we obtain the (2+1)-dimensional super Yang-Mills action in curved
background. We also examine the duality.Comment: 25 page
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