190 research outputs found
Decompositions of ideals of minors meeting a submatrix
We compute the primary decomposition of certain ideals generated by subsets
of minors in a generic matrix or in a generic symmetric matrix, or subsets of
Pfaffians in a generic skew-symmetric matrix. Specifically, the ideals we
consider are generated by minors that have at least some given number of rows
and columns in certain submatrices.Comment: 10 pages. v2: minor corrections. v3: minor changes, final version to
appear in Comm. Al
Immigration and low birthweight in the US: The role of time and timing
The literature exploring the health consequences of immigration is largely dominated by efforts to replicate, across outcomes and populations, and explain two widely observed findings: that foreign nativity is protective (yielding the “healthy migrant effect” or “immigrant paradox”) and that the health advantage of immigrants diminishes over time in the host country. In this study, we focus on the second of these patterns and provide evidence that a lifecourse perspective can help to explain the apparent deterioration in health by incorporating attention to immigrants’ timing of arrival. We examine the role of immigrants’ exposure to the US, in terms of both age at immigration and length of residence, in shaping birthweight, a well measured and consequential marker of health, and maternal smoking, an important risk factor for low birthweight.
Higher Derivative Gravity and Torsion from the Geometry of C-spaces
We start from a new theory (discussed earlier) in which the arena for physics
is not spacetime, but its straightforward extension-the so called Clifford
space (-space), a manifold of points, lines, areas, etc..; physical
quantities are Clifford algebra valued objects, called polyvectors. This
provides a natural framework for description of supersymmetry, since spinors
are just left or right minimal ideals of Clifford algebra. The geometry of
curved -space is investigated. It is shown that the curvature in -space
contains higher orders of the curvature in the underlying ordinary space. A
-space is parametrized not only by 1-vector coordinates but also by
the 2-vector coordinates , 3-vector coordinates , etc., called also {\it holographic coordinates}, since they
describe the holographic projections of 1-lines, 2-loops, 3-loops, etc., onto
the coordinate planes. A remarkable relation between the "area" derivative \p/
\p \sigma^{\mu \nu} and the curvature and torsion is found: if a scalar valued
quantity depends on the coordinates this indicates the
presence of torsion, and if a vector valued quantity depends so, this implies
non vanishing curvature. We argue that such a deeper understanding of the
-space geometry is a prerequisite for a further development of this new
theory which in our opinion will lead us towards a natural and elegant
formulation of -theory.Comment: 19 pages; A section describing the main physical implications of
C-space is added, and the rest of the text is modified accordingl
Spin Gauge Theory of Gravity in Clifford Space
A theory in which 16-dimensional curved Clifford space (C-space) provides a
realization of Kaluza-Klein theory is investigated. No extra dimensions of
spacetime are needed: "extra dimensions" are in C-space. We explore the spin
gauge theory in C-space and show that the generalized spin connection contains
the usual 4-dimensional gravity and Yang-Mills fields of the U(1)xSU(2)xSU(3)
gauge group. The representation space for the latter group is provided by
16-component generalized spinors composed of four usual 4-component spinors,
defined geometrically as the members of four independent minimal left ideals of
Clifford algebra.Comment: 9 pages, talk presented at the QG05 conference, 12-16 September 2005,
Cala Gonone, Ital
Towards the Unification of Gravity and other Interactions: What has been Missed?
Faced with the persisting problem of the unification of gravity with other
fundamental interactions we investigate the possibility of a new paradigm,
according to which the basic space of physics is a multidimensional space
associated with matter configurations. We consider general
relativity in . In spacetime, which is a 4-dimensional subspace of
, we have not only the 4-dimensional gravity, but also other
interactions, just as in Kaluza-Klein theories. We then consider a finite
dimensional description of extended objects in terms of the center of mass,
area, and volume degrees of freedom, which altogether form a 16-dimensional
manifold whose tangent space at any point is Clifford algebra Cl(1,3). The
latter algebra is very promising for the unification, and it provides
description of fermions.Comment: 11 pages; Talk presented at "First Mediterranean Conference on
Classical and Quantum Gravity", Kolymbari, Crete, Greece, 14-18 September
200
Spin Gauge Theory of Gravity in Clifford Space: A Realization of Kaluza-Klein Theory in 4-Dimensional Spacetime
A theory in which 4-dimensional spacetime is generalized to a larger space,
namely a 16-dimensional Clifford space (C-space) is investigated. Curved
Clifford space can provide a realization of Kaluza-Klein theory. A covariant
Dirac equation in curved C-space is explored. The generalized Dirac field is
assumed to be a polyvector-valued object (a Clifford number) which can be
written as a superposition of four independent spinors, each spanning a
different left ideal of Clifford algebra. The general transformations of a
polyvector can act from the left and/or from the right, and form a large gauge
group which may contain the group U(1)xSU(2)xSU(3) of the standard model. The
generalized spin connection in C-space has the properties of Yang-Mills gauge
fields. It contains the ordinary spin connection related to gravity (with
torsion), and extra parts describing additional interactions, including those
described by the antisymmetric Kalb-Ramond fields.Comment: 57 pages; References added, section 2 rewritten and expande
A Novel View on the Physical Origin of E8
We consider a straightforward extension of the 4-dimensional spacetime
to the space of extended events associated with strings/branes, corresponding
to points, lines, areas, 3-volumes, and 4-volumes in . All those objects
can be elegantly represented by the Clifford numbers . This leads to the
concept of the so-called Clifford space , a 16-dimensional manifold
whose tangent space at every point is the Clifford algebra . The latter space besides an algebra is also a vector space whose
elements can be rotated into each other in two ways: (i) either by the action
of the rotation matrices of SO(8,8) on the components or (ii) by the left
and right action of the Clifford numbers exp [\alpha^A \gam_A] and
exp [\beta^A \gam_A] on . In the latter case, one does not recover all
possible rotations of the group SO(8,8). This discrepancy between the
transformations (i) and (ii) suggests that one should replace the tangent space
with a vector space whose basis elements are
generators of the Clifford algebra , which contains the Lie
algebra of the exceptional group E as a subspace. E thus arises from
the fact that, just as in the spacetime there are -volumes generated
by the tangent vectors of the spacetime, there are -volumes,
, in the Clifford space , generated by the tangent
vectors of .Comment: 14 page
The effects of socio-political context on tourism
Purpose: The purpose of this paper is to examine the effects of tourists’ perceptions of political and economic instability and risks of terrorism on their intentions to travel to countries associated with various risks. Design/methodology/approach: A total of 648 Greek, Israeli and Portuguese students completed a questionnaire focusing on their perceptions concerning factors that shape their travel decisions. Findings: The findings showed that among tourists from Greece and Portugal, the experience of economic crisis and the salience of economic and political hardships mitigated their intentions to travel to destinations with similar problems. These factors had no effect on Israelis, who have not experienced such problems in their country. Frequent terrorist incidents diminished the intentions of Greek tourists to travel to destinations marked by terrorism, such as Israel. Thus, different factors affect tourists’ travel-related decisions in each of the three countries. Originality/value: The study sheds light on how potential tourists construe the risks of traveling to specific destination countries based on hazards in their home countries, a topic that to date has received little research attention.info:eu-repo/semantics/acceptedVersio
Factors shaping young tourists' intentions to travel to Greece, Israel and Portugal: Universal or idisyncratic perceptions of young Greeks, Israelis and Portugese?
Tourism constitutes an important branch of economy, especially in countries experiencing economic crisis and harsh socio-political events. The current study compares the intention of young people from three different countries – Greece, Israel and Portugal - to travel to two selected destinations. For each country of origin the other two countries were the destination of interest.
This research examined the factors affecting young tourists' intention to travel to different destinations assuming that those determinants depend on the country of origin as well as on the destination country.
The sample comprised of 648 students: Israelis (277), Portuguese (200), Greeks (171). The research questionnaire was distributed in Israeli, Greek and Portuguese academic institutions in 2014.
The results indicate that over half of the Israelis intend to visit Greece or Portugal. The majority of the Portuguese anticipate visiting Greece, while only 32.5% expect to visit Israel. Among the Greeks nearly 50% intend to visit Portugal and do not intend to visit Israel.
The study showed that the main factors affecting the decisions of young Portuguese to travel to Israel were: the image of Israel, the perceived risk of traveling to a country with political unrest and the number of trips abroad. The main factors affecting the decisions of young Greeks were the perceived risk of traveling to a country with political unrest and Israel's image. Israelis' decision to travel to Greece was affected by their image of Greece; the Portuguese also took into account the perceived risk regarding economic situation. For Israelis, considering Portugal as a traveling destination was related to the destination's image. The Greeks were affected by the number of Facebook friends and the Innovation, Entrepreneurship and Digital Ecosystems perceived economic risk. This research suggests that the socio-economic, political context of the country of origin and of the tourist destination plays an important role in young tourists' travelling-related decision-making.info:eu-repo/semantics/publishedVersio
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