1,700 research outputs found
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
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
Scalar Field Theory on Fuzzy S^4
Scalar fields are studied on fuzzy and a solution is found for the
elimination of the unwanted degrees of freedom that occur in the model. The
resulting theory can be interpreted as a Kaluza-Klein reduction of CP^3 to S^4
in the fuzzy context.Comment: 16 pages, LaTe
Nonlocal regularisation of noncommutative field theories
We study noncommutative field theories, which are inherently nonlocal, using
a Poincar\'e-invariant regularisation scheme which yields an effective,
nonlocal theory for energies below a cut-off scale. After discussing the
general features and the peculiar advantages of this regularisation scheme for
theories defined in noncommutative spaces, we focus our attention onto the
particular case when the noncommutativity parameter is inversely proportional
to the square of the cut-off, via a dimensionless parameter . We work out
the perturbative corrections at one-loop order for a scalar theory with quartic
interactions, where the signature of noncommutativity appears in
-dependent terms. The implications of this approach, which avoids the
problems related to UV-IR mixing, are discussed from the perspective of the
Wilson renormalisation program. Finally, we remark about the generality of the
method, arguing that it may lead to phenomenologically relevant predictions,
when applied to realistic field theories.Comment: 1+11 pages, 6 figures; v2: references added, typos corrected,
conclusions unchange
Scalar field theory on kappa-Minkowski spacetime and translation and Lorentz invariance
We investigate the properties of kappa-Minkowski spacetime by using
representations of the corresponding deformed algebra in terms of undeformed
Heisenberg-Weyl algebra. The deformed algebra consists of kappa-Poincare
algebra extended with the generators of the deformed Weyl algebra. The part of
deformed algebra, generated by rotation, boost and momentum generators, is
described by the Hopf algebra structure. The approach used in our
considerations is completely Lorentz covariant. We further use an adventages of
this approach to consistently construct a star product which has a property
that under integration sign it can be replaced by a standard pointwise
multiplication, a property that was since known to hold for Moyal, but not also
for kappa-Minkowski spacetime. This star product also has generalized trace and
cyclic properties and the construction alone is accomplished by considering a
classical Dirac operator representation of deformed algebra and by requiring it
to be hermitian. We find that the obtained star product is not translationally
invariant, leading to a conclusion that the classical Dirac operator
representation is the one where translation invariance cannot simultaneously be
implemented along with hermiticity. However, due to the integral property
satisfied by the star product, noncommutative free scalar field theory does not
have a problem with translation symmetry breaking and can be shown to reduce to
an ordinary free scalar field theory without nonlocal features and tachionic
modes and basicaly of the very same form. The issue of Lorentz invariance of
the theory is also discussed.Comment: 22 pages, no figures, revtex4, in new version comments regarding
translation invariance and few references are added, accepted for publication
in Int. J. Mod. Phys.
Noncommutative Chiral Anomaly and the Dirac-Ginsparg-Wilson Operator
It is shown that the local axial anomaly in dimensions emerges naturally
if one postulates an underlying noncommutative fuzzy structure of spacetime .
In particular the Dirac-Ginsparg-Wilson relation on is shown to
contain an edge effect which corresponds precisely to the ``fuzzy''
axial anomaly on the fuzzy sphere . We also derive a novel gauge-covariant
expansion of the quark propagator in the form where
is the lattice spacing on , is
the covariant noncommutative chirality and is an effective
Dirac operator which has essentially the same IR spectrum as
but differes from it on the UV modes. Most remarkably is the fact that both
operators share the same limit and thus the above covariant expansion is not
available in the continuum theory . The first bit in this expansion
although it vanishes as it stands in the continuum
limit, its contribution to the anomaly is exactly the canonical theta term. The
contribution of the propagator is on the other hand
equal to the toplogical Chern-Simons action which in two dimensions vanishes
identically .Comment: 26 pages, latex fil
Unitary Quantum Physics with Time-Space Noncommutativity
In this work quantum physics in noncommutative spacetime is developed. It is
based on the work of Doplicher et al. which allows for time-space
noncommutativity. The Moyal plane is treated in detail. In the context of
noncommutative quantum mechanics, some important points are explored, such as
the formal construction of the theory, symmetries, causality, simultaneity and
observables. The dynamics generated by a noncommutative Schrodinger equation is
studied. We prove in particular the following: suppose the Hamiltonian of a
quantum mechanical particle on spacetime has no explicit time dependence, and
the spatial coordinates commute in its noncommutative form (the only
noncommutativity being between time and a space coordinate). Then the
commutative and noncommutative versions of the Hamiltonian have identical
spectra.Comment: 18 pages, published versio
Boundary degrees of freedom in fractional quantum Hall effect: Excitations on common boundary of two samples
Using the Carlip's method we have derived the boundary action for the fermion
Chern-Simons theory of quantum Hall effects on a planar region with a boundary.
We have computed both the bulk and edge responses of currents to the external
electric field. From this we obtain the well-known anomaly relation and the
boundary Hall current without introducing any ad hoc assumptions such as the
chirality condition. In addition, the edge current on the common boundary of
two samples is found to be proportional to the difference between Chern-Simons
coupling strengths.Comment: 20 pages, uses revte
Housing Deprivations in the Underserved Settlements of Jaffna Municipality and Its Urban Fringe Using Slum Severity Index
Underserved settlements pose challenges to urban planning and development in developing countries, while they provide affordable shelter and a livelihood to a large proportion of the urban poor. Most definitions consider an underserved settlement to be a community of several housing units, failing to recognize that housing conditions vary by housing unit within the area. This study employed the criteria of structural quality, living area, land tenure, improved drinking water, and water for other purposes, improved sanitation, electricity, kitchen, and clean fuel to identify the underserved settlements and assess their housing deprivations. A housing unit-level field survey, field observation, focus group discussions with representatives of community-based organizations and ground-level officers, and interviews with administrative officers of government institutions, local authorities, academics, and social activists were employed to gather primary data for this study, while secondary data was gathered from government departments. The Slum Severity Index adopted in the study measured the degree of deprivation on a continuous scale. Arc GIS 10.4 was used to create maps that depict the spatial distribution and housing deprivation of underserved settlements. According to the findings, 100% of settlements lacked access to drinking water, 81.23% lacked adequate living space, 58.99% lacked land tenure, 42.35% lacked housing structure, 23.45% lacked water for other purposes, 15.70% lacked sanitation, and 0.76% lacked electricity. Overall, 42.35% of settlements lacked more than three of the aforementioned criteria, and 0.76% of settlements lacked all of them. The study's conclusion emphasized the importance of assessing multiple housing deprivations via the Slum Severity Index to attain sustainable development goals and establish cities free of underserved settlements.
DOI: http://doi.org/10.31357/fhss/vjhss.v08i01.1
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