10,431 research outputs found
Topological Quantum Field Theory and Seiberg-Witten Monopoles
A topological quantum field theory is introduced which reproduces the
Seiberg-Witten invariants of four-manifolds. Dimensional reduction of this
topological field theory leads to a new one in three dimensions. Its partition
function yields a three-manifold invariant, which can be regarded as the
Seiberg-Witten version of Casson's invariant. A Geometrical interpretation of
the three dimensional quantum field theory is also given.Comment: 15 pages, Latex file, no figure
The spectral shift function and spectral flow
This paper extends Krein's spectral shift function theory to the setting of
semifinite spectral triples. We define the spectral shift function under these
hypotheses via Birman-Solomyak spectral averaging formula and show that it
computes spectral flow.Comment: 47 page
Spinor Parallel Propagator and Green's Function in Maximally Symmetric Spaces
We introduce the spinor parallel propagator for maximally symmetric spaces in
any dimension. Then, the Dirac spinor Green's functions in the maximally
symmetric spaces R^n, S^n and H^n are calculated in terms of intrinsic
geometric objects. The results are covariant and coordinate-independent.Comment: 7 page
Malignancy within a tail gut cyst:a case of retrorectal carcinoid tumour
Purpose. Tailgut cysts with malignant transformation are rare entities. We discuss the diagnostic strategy and treatment of a malignancy within a tailgut cyst. Methods. In this study we report on the case of a 61-year-old man with a malignant neuroendocrine tumour arising within a tailgut cyst and an overview of the literature emphasising the histopathological characteristics and differential diagnosis. Results. Our patient presented with lower back pain, rectal pain, and increased urgency of defecation. MRI scan and CT-guided biopsy on histological analysis revealed a diagnosis of carcinoid tumour of the presacral space. The patient subsequently underwent an abdominoperineal excision of the rectum. Conclusions. This case highlights the importance of tailgut cysts as a differential diagnosis of presacral masses. It is a rare congenital lesion developing from remnants of the embryonic postanal gut and is predominantly benign in nature. Approximately half of cases remain asymptomatic; therefore, diagnosis is often delayed. Magnetic resonance imaging is the investigation of choice and an awareness of the possibility of malignant potential is critical to avoiding missed diagnosis and subsequent morbidity. Complete surgical excision allows accurate diagnosis, confirmation of oncological clearance, and prevention of mortality
Riding a Spiral Wave: Numerical Simulation of Spiral Waves in a Co-Moving Frame of Reference
We describe an approach to numerical simulation of spiral waves dynamics of
large spatial extent, using small computational grids.Comment: 15 pages, 14 figures, as accepted by Phys Rev E 2010/03/2
Effects of rf Current on Spin Transfer Torque Induced Dynamics
The impact of radiofrequency (rf) currents on the direct current (dc) driven
switching dynamics in current-perpendicular-to-plane nanoscale spin valves is
demonstrated. The rf currents dramatically alter the dc driven free layer
magnetization reversal dynamics as well as the dc switching level. This occurs
when the frequency of the rf current is tuned to a frequency range around the
dc driven magnetization precession frequencies. For these frequencies,
interactions between the dc driven precession and the injected rf induce
frequency locking and frequency pulling effects that lead to a measurable
dependence of the critical switching current on the frequency of the injected
rf. Based on macrospin simulations, including dc as well as rf spin torque
currents, we explain the origin of the observed effects.Comment: 5 pages, 4 figure
Regime-based TRMM and GV Microphysical Studies at MSFC and UAH
Differences in rain rate between TMI and PR vary systematically with PR Z-profile statistics, whose frequency of occurrence is modified to create seasonal biases in the sub-tropical Southeastern U.S. (and almost certainly elsewhere). Tropical (non-tropical) DSDs in N. Alabama exhibit larger (smaller) D(sub 0), and larger (smaller) N(sub 0) and mu. The formulation process for empirical retrievals of DSD using dual-pol radar is sensitive to D(sub max) assumptions used in the scattering model stage. 4. DSD retrievals from Parsivel disdrometers compare favorably to those of the 2DVD unless rain rates exceed 25 mm/hr and D(sub m) exceeds 2 mm (at which point the Parsivels overestimate D(sub m) and rain rate)
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