10,248 research outputs found
Codimension One Branes
We study codimension one branes, i.e. p-branes in (p+2)-dimensions, in the
superembedding approach for the cases where the worldvolume superspace is
embedded in a minimal target superspace with half supersymmetry breaking. This
singles out the cases p=1,2,3,5,9. For p=3,5,9 the superembedding geometry
naturally involves a fundamental super 2-form potential on the worldvolume
whose generalised field strength obeys a constraint deducible from considering
an open supermembrane ending on the p-brane. This constraint, together with the
embedding constraint, puts the system on-shell for p=5 but overconstrains the
9-brane in D=11 such that the Goldstone superfield is frozen. For p=3 these two
constraints give rise to an off-shell linear multiplet on the worldvolume. An
alternative formulation of this case is given in which the linear multiplet is
dualised to an off-shell scalar multiplet. Actions are constructed for both
cases and are shown to give equivalent equations of motion. After gauge fixing
a local Sp(1) symmetry associated with shifts in the Sp(1)_R Goldstone modes,
we find that the auxiliary fields in the scalar multiplet parametrise a
two-sphere. For completeness we also discuss briefly the cases p=1,2 where the
equations of motion (for off-shell multiplets) are obtained from an action
principle.Comment: 38 pages, latex, cover page correcte
Evolving temporal fuzzy association rules from quantitative data with a multi-objective evolutionary algorithm
A novel method for mining association rules that are both quantitative and temporal using a multi-objective evolutionary algorithm is presented. This method successfully identifies numerous temporal association rules that occur more frequently in areas of a dataset with specific quantitative values represented with fuzzy sets. The novelty of this research lies in exploring the composition of quantitative and temporal fuzzy association rules and the approach of using a hybridisation of a multi-objective evolutionary algorithm with fuzzy sets. Results show the ability of a multi-objective evolutionary algorithm (NSGA-II) to evolve multiple target itemsets that have been augmented into synthetic datasets
The mode 3 crack problem in bonded materials with a nonhomogeneous interfacial zone
The mode 3 crack problem for two bonded homogeneous half planes was considered. The interfacial zone was modelled by a nonhomogeneous strip in such a way that the shear modulus is a continuous function throughout the composite medium and has discontinuous derivatives along the boundaries of the interfacial zone. The problem was formulated for cracks perpendicular to the nominal interface and was solved for various crack locations in and around the interfacial region. The asymptotic stress field near the tip of a crack terminating at an interface was examined and it was shown that, unlike the corresponding stress field in piecewise homogeneous materials, in this case the stresses have the standard square root singularity and their angular variation was identical to that of a crack in a homogeneous medium. With application to the subcritical crack growth process in mind, the results given include mostly the stress intensity factors for some typical crack geometries and various material combinations
The crack problem in bonded nonhomogeneous materials
The plane elasticity problem for two bonded half planes containing a crack perpendicular to the interface was considered. The effect of very steep variations in the material properties near the diffusion plane on the singular behavior of the stresses and stress intensity factors were studied. The two materials were thus, assumed to have the shear moduli mu(o) and mu(o) exp (Beta x), x=0 being the diffusion plane. Of particular interest was the examination of the nature of stress singularity near a crack tip terminating at the interface where the shear modulus has a discontinuous derivative. The results show that, unlike the crack problem in piecewise homogeneous materials for which the singularity is of the form r/alpha, 0 less than alpha less than 1, in this problem the stresses have a standard square-root singularity regardless of the location of the crack tip. The nonhomogeneity constant Beta has, however, considerable influence on the stress intensity factors
Evidence for a Mid-Atomic-Number Atmosphere in the Neutron Star 1E1207.4-5209
Recently Sanwal et al. (2002) reported the first clear detection of
absorption features in an isolated neutron star, 1E1207.4-5209. Remarkably
their spectral modeling demonstrates that the atmosphere cannot be Hydrogen.
They speculated that the neutron star atmosphere is indicative of ionized
Helium in an ultra-strong (~1.5x10^{14} G) magnetic field. We have applied our
recently developed atomic model (Mori & Hailey 2002) for strongly-magnetized
neutron star atmospheres to this problem. We find that this model, along with
some simp le atomic physics arguments, severely constrains the possible
composition of the atmosphere. In particular we find that the absorption
features are naturally associated with He-like Oxygen or Neon in a magnetic
field of ~10^{12} G, comparable to the magnetic field derived from the spin
parameters of the neutron star. This interpretation is consistent with the
relative line strengths and widths and is robust. Our model predicts possible
substructure in the spectral features, which has now been reported by
XMM-Newton (Mereghetti et al. 2002). However we show the Mereghetti et al.
claim that the atmosphere is Iron or some comparable high-Z element at ~
10^{12} G is easily ruled out by the Chandra and XMM-Newton data.Comment: 5 pages, AASTeX, Revised version. Accepted for publication in ApJ
Letter
Stabilization of Extra Dimensions and The Dimensionality of the Observed Space
We present a simple model for the late time stabilization of extra
dimensions. The basic idea is that brane solutions wrapped around extra
dimensions, which is allowed by string theory, will resist expansion due to
their winding mode. The momentum modes in principle work in the opposite way.
It is this interplay that leads to dynamical stabilization. We use the idea of
democratic wrapping \cite{art5}-\cite{art6}, where in a given decimation of
extra dimensions, all possible winding cases are considered. To simplify the
study further we assumed a symmetric decimation in which the total number of
extra dimensions is taken to be where N can be called the order of the
decimation. We also assumed that extra dimensions all have the topology of
tori. We show that with these rather conservative assumptions, there exists
solutions to the field equations in which the extra dimensions are stabilized
and that the conditions do not depend on . This fact means that there exists
at least one solution to the asymmetric decimation case. If we denote the
number of observed space dimensions (excluding time) by , the condition for
stabilization is for pure Einstein gravity and for dilaton
gravity massaged by string theory parameters.Comment: Final versio
Critical role of lay health cultural brokers in promoting the health of immigrants and refugees: A case study in the United States of America
The United States of America, a home to immigrants and refugees from various cultures and corners of the world continues to encounter waves of mass immigration. Some immigrated due to well-founded fears of persecution (i.e. religious, political, race, or social group) or economic hardships. Others immigrated to, reunite with family members, seek economic and education opportunities, and better standards of living. Notwithstanding their channels of admission or entry and their pivotal role in enriching the culture and the economy of the United States of America, many confront several health and lifestyle related challenges as they acculturate and integrate into the mainstream of American life and culture. Although many individuals and organizations have created numerous programs and activities to help ease these difficulties, minimal documentation is available on the involvement and engagement of the non-traditional work force, such as the lay health cultural brokers
Comparative assessment of freeform polynomials as optical surface descriptions
Slow-servo single-point diamond turning as well as advances in computer controlled small lap polishing enables the fabrication of freeform optics, or more specifically, optical surfaces for imaging applications that are not rotationally symmetric. Various forms of polynomials for describing freeform optical surfaces exist in optical design and to support fabrication. A popular method is to add orthogonal polynomials onto a conic section. In this paper, recently introduced gradient-orthogonal polynomials are investigated in a comparative manner with the widely known Zernike polynomials. In order to achieve numerical robustness when higher-order polynomials are required to describe freeform surfaces, recurrence relations are a key enabler. Results in this paper establish the equivalence of both polynomial sets in accurately describing freeform surfaces under stringent conditions. Quantifying the accuracy of these two freeform surface descriptions is a critical step in the future application of these tools in both advanced optical system design and optical fabrication
Food systems in depressed and contested agro-territories: Participatory Rural Appraisal in Odemira, Portugal
Farming regions in Europe, particularly in the South, are increasingly feeling
the eects of climate change due to factors such as drought, extreme weather
events, and desertification, with severe consequences for food security and
food sovereignty. Additionally, decades of rural mismanagement have left
countless of these farming territories severely depressed as well as at the
mercy of competition for their natural resources. This paper presents and
discusses the results of a Participatory Rural Appraisal conducted in the region
of Odemira, Southwest Portugal. Rooted in the frameworks of agroecology
and food democracy, this mixed methodology aims to support people in
multiply stressed agro-territories to diagnose the state of their food systems
and agroecosystems from a democratic and ecological point of view and
engage local actors in imagining fairer and healthier food futures for their
regions. Local food actors were invited to identify and qualify the main
problems in the region’s food systems, complemented by an agroecological
assessment of farm production systems. The results of the study confirm
the status of Odemira as a depressed and contested agro-territory, whose
social, economic, and ecological vulnerability is being compounded by the
clash between the model of traditional smallholder farming and that of largescale intensive agriculture. The study also shows the potential of sustainable
farming practices as well as collaboration between the dierent food actors to
support an agroecological transition in the region. However, to jointly realise
food democracy and food system sustainability, the tensions resulting from the
current political support for hyper-industrialisation and the lack of democratic,
institutional, and legal mechanisms available to local actors will need to be
addressed head-oninfo:eu-repo/semantics/publishedVersio
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