983 research outputs found
Aspects of Boundary Conditions for Nonabelian Gauge Theories
The boundary values of the time-component of the gauge potential form
externally specifiable data characterizing a gauge theory. We point out some
consequences such as reduced symmetries, bulk currents for manifolds with
disjoint boundaries and some nuances of how the charge algebra is realized.Comment: 15 page
Lehmann-Symanzik-Zimmermann S-Matrix elements on the Moyal Plane
Field theories on the Groenewold-Moyal(GM) plane are studied using the
Lehmann-Symanzik-Zimmermann(LSZ) formalism. The example of real scalar fields
is treated in detail. The S-matrix elements in this non-perturbative approach
are shown to be equal to the interaction representation S-matrix elements. This
is a new non-trivial result: in both cases, the S-operator is independent of
the noncommutative deformation parameter and the change in
scattering amplitudes due to noncommutativity is just a time delay. This result
is verified in two different ways. But the off-shell Green's functions do
depend on . In the course of this analysis, unitarity of the
non-perturbative S-matrix is proved as well.Comment: 18 pages, minor corrections, To appear in Phys. Rev. D, 201
Bosonic Description of Spinning Strings in Dimensions
We write down a general action principle for spinning strings in 2+1
dimensional space-time without introducing Grassmann variables. The action is
written solely in terms of coordinates taking values in the 2+1 Poincare group,
and it has the usual string symmetries, i.e. it is invariant under a)
diffeomorphisms of the world sheet and b) Poincare transformations. The system
can be generalized to an arbitrary number of space-time dimensions, and also to
spinning membranes and p-branes.Comment: Latex, 12 page
Twisted Gauge and Gravity Theories on the Groenewold-Moyal Plane
Recent work [hep-th/0504183,hep-th/0508002] indicates an approach to the
formulation of diffeomorphism invariant quantum field theories (qft's) on the
Groenewold-Moyal (GM) plane. In this approach to the qft's, statistics gets
twisted and the S-matrix in the non-gauge qft's becomes independent of the
noncommutativity parameter theta^{\mu\nu}. Here we show that the noncommutative
algebra has a commutative spacetime algebra as a substructure: the Poincare,
diffeomorphism and gauge groups are based on this algebra in the twisted
approach as is known already from the earlier work of [hep-th/0510059]. It is
natural to base covariant derivatives for gauge and gravity fields as well on
this algebra. Such an approach will in particular introduce no additional gauge
fields as compared to the commutative case and also enable us to treat any
gauge group (and not just U(N)). Then classical gravity and gauge sectors are
the same as those for \theta^{\mu \nu}=0, but their interactions with matter
fields are sensitive to theta^{\mu \nu}. We construct quantum noncommutative
gauge theories (for arbitrary gauge groups) by requiring consistency of twisted
statistics and gauge invariance. In a subsequent paper (whose results are
summarized here), the locality and Lorentz invariance properties of the
S-matrices of these theories will be analyzed, and new non-trivial effects
coming from noncommutativity will be elaborated.
This paper contains further developments of [hep-th/0608138] and a new
formulation based on its approach.Comment: 17 pages, LaTeX, 1 figur
Abelian BF-Theory and Spherically Symmetric Electromagnetism
Three different methods to quantize the spherically symmetric sector of
electromagnetism are presented: First, it is shown that this sector is
equivalent to Abelian BF-theory in four spacetime dimensions with suitable
boundary conditions. This theory, in turn, is quantized by both a reduced phase
space quantization and a spin network quantization. Finally, the outcome is
compared with the results obtained in the recently proposed general quantum
symmetry reduction scheme. In the magnetically uncharged sector, where all
three approaches apply, they all lead to the same quantum theory.Comment: 21 pages, LaTeX2e, v2: minor corrections in some formulas and a new
referenc
Quantum Geons and Noncommutative Spacetimes
Physical considerations strongly indicate that spacetime at Planck scales is
noncommutative. A popular model for such a spacetime is the Moyal plane. The
Poincar\`e group algebra acts on it with a Drinfel'd-twisted coproduct. But the
latter is not appropriate for more complicated spacetimes such as those
containing the Friedman-Sorkin (topological) geons. They have rich
diffeomorphism groups and in particular mapping class groups, so that the
statistics groups for N identical geons is strikingly different from the
permutation group . We generalise the Drinfel'd twist to (essentially)
generic groups including to finite and discrete ones and use it to modify the
commutative spacetime algebras of geons as well to noncommutative algebras. The
latter support twisted actions of diffeos of geon spacetimes and associated
twisted statistics. The notion of covariant fields for geons is formulated and
their twisted versions are constructed from their untwisted versions.
Non-associative spacetime algebras arise naturally in our analysis. Physical
consequences, such as the violation of Pauli principle, seem to be the outcomes
of such nonassociativity.
The richness of the statistics groups of identical geons comes from the
nontrivial fundamental groups of their spatial slices. As discussed long ago,
extended objects like rings and D-branes also have similar rich fundamental
groups. This work is recalled and its relevance to the present quantum geon
context is pointed out.Comment: 41 page
Twisted Quantum Fields on Moyal and Wick-Voros Planes are Inequivalent
The Moyal and Wick-Voros planes A^{M,V}_{\theta} are *-isomorphic. On each of
these planes the Poincar\'e group acts as a Hopf algebra symmetry if its
coproducts are deformed by twist factors. We show that the *-isomorphism T:
A^M_{\theta} to A^V_{\theta} does not also map the corresponding twists of the
Poincar\'e group algebra. The quantum field theories on these planes with
twisted Poincar\'e-Hopf symmetries are thus inequivalent. We explicitly verify
this result by showing that a non-trivial dependence on the non-commutative
parameter is present for the Wick-Voros plane in a self-energy diagram whereas
it is known to be absent on the Moyal plane (in the absence of gauge fields).
Our results differ from these of (arXiv:0810.2095 [hep-th]) because of
differences in the treatments of quantum field theories.Comment: 12 page
Process of designing robust, dependable, safe and secure software for medical devices: Point of care testing device as a case study
This article has been made available through the Brunel Open Access Publishing Fund.Copyright © 2013 Sivanesan Tulasidas et al. This paper presents a holistic methodology for the design of medical device software, which encompasses of a new way of eliciting requirements, system design process, security design guideline, cloud architecture design, combinatorial testing process and agile project management. The paper uses point of care diagnostics as a case study where the software and hardware must be robust, reliable to provide accurate diagnosis of diseases. As software and software intensive systems are becoming increasingly complex, the impact of failures can lead to significant property damage, or damage to the environment. Within the medical diagnostic device software domain such failures can result in misdiagnosis leading to clinical complications and in some cases death. Software faults can arise due to the interaction among the software, the hardware, third party software and the operating environment. Unanticipated environmental changes and latent coding errors lead to operation faults despite of the fact that usually a significant effort has been expended in the design, verification and validation of the software system. It is becoming increasingly more apparent that one needs to adopt different approaches, which will guarantee that a complex software system meets all safety, security, and reliability requirements, in addition to complying with standards such as IEC 62304. There are many initiatives taken to develop safety and security critical systems, at different development phases and in different contexts, ranging from infrastructure design to device design. Different approaches are implemented to design error free software for safety critical systems. By adopting the strategies and processes presented in this paper one can overcome the challenges in developing error free software for medical devices (or safety critical systems).Brunel Open Access Publishing Fund
Phytoplankton
Investigations on phytoplankton of the Indian Seas has assumed
great significance during the last 5 decades. As these microscopic
organisms fluctuated in response to climatic changes,
water movements, seasonal variations, nutrient content of the water
etc. they form an important and convenient link in the assessment
of the stock of potential resources. The shelf and oceanic
waters of the Indian seas show fluctuations in the standing crop of
phytoplankton due to the effect of two monsoons. Available data
indicated that the waters along the west coast of India are more
fertile than that along the east coast mainly due to upwelling and
other favourable factors conducive to phytoplankton growth. Some
of the ecological factors contributing to the pattern of production of
phytoplankton are also briefly discussed
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