950,684 research outputs found
Book Review: Marmot, M. Status syndrome: how your social standing directly affects your health and life expectancy. ISBN 09598138
Canonical ``Loop'' Quantum Gravity and Spin Foam Models
The canonical ``loop'' formulation of quantum gravity is a mathematically
well defined, background independent, non perturbative standard quantization of
Einstein's theory of General Relativity. Some among the most meaningful results
of the theory are: 1) the complete calculation of the spectrum of geometric
quantities like the area and the volume and the consequent physical predictions
about the structure of the space-time at the Plank scale; 2) a microscopical
derivation of the Bekenstein-Hawking black-hole entropy formula. Unfortunately,
despite recent results, the dynamical aspect of the theory (imposition of the
Wheller-De Witt constraint) remains elusive.
After a short description of the basic ideas and the main results of loop
quantum gravity we show in which sence the exponential of the super Hamiltonian
constraint leads to the concept of spin foam and to a four dimensional
formulation of the theory. Moreover, we show that some topological field
theories as the BF theory in 3 and 4 dimension admits a spin foam formulation.
We argue that the spin-foams/spin-networks formalism it is the natural
framework to discuss loop quantum gravity and topological field theory.Comment: 17 pages, LaTeX2e, 7 figures. To appear in the proceeding of the
XXIII SIGRAV conference, Monopoli (ITALY), September 21st-25th, 1998. Minor
correction
Change, psychosocial stress and health in an era of globalization
In the last decades, globalization has produced an acceleration of social, economic and political
changes worldwide. These changes had a number of positive effects including enhancing political freedom,
living standards and health conditions. However, many of them have also produced adverse health
consequences, especially when they have been implemented in a sudden, rapid and unexpected way. This is
especially true among those populations whose ability to adjust to the new circumstances generated by
rapid change was limited. The aim of the present research project was to examine the health consequences
of rapid social, economic and political change following globalization as well as to investigate the role of
psychosocial factors in explaining these relationships. A theoretical framework proposing major
psychosocial pathways connecting rapid change with health-related outcomes has been developed. A series
of case studies from countries affected by rapid change supported the hypothesized relationships included
in the framework. Countries of interest were the former Soviet Union nations, China, Japan, Micronesia
Islands, New Zealand, Australia, Canada, and the United States. The limited ability of certain populations
to adjust to rapid changes induced by globalization as well as the pace of change of social, economic and
political reforms are discussed
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Differences in forecasting approaches between product firms and product-service systems (PSS)
This paper examines the forecasting implications for Product-Service Systems (PSS) applications in manufacturing firms. The approach taken is to identify the scope of operations for PSS applications by identifying all the activities associated with the total cost of ownership (TCO). The paper then develops a revenue model for manufacturing firms providing PSS applications. The revenue model identifies three generic revenue streams that provide the basis for discussion on the differences in forecasting approaches between product firms and Product-Service Systems (PSS) in manufacturing firms. The forecasting approaches are different due to the nature of customer involvement in the service aspect of PSS applications. This necessitates an understanding of the customer service experience and the factors affecting this such as the service profit chain which links profitability, customer loyalty and service value to employee satisfaction, capability and productivity. The forecasting approaches identified raises forecasting challenges for each of the three generic revenue sources. These challenges vary from the difficulty in obtaining the service user’s viewpoint through to difficulties in determining market acceptance of PSS applications
Stellar Distributions and NIR Colours of Normal Galaxies
We discuss some results of a morphological study of edge-on galaxies, based
on optical and especially near-infrared surface photometry. We find that the
vertical surface brightness distributions of galaxies are fitted very well by
exponential profiles, much better than by isothermal distributions. We find
that in general the vertical scale height increases when going outward. This
increase is strong for early-type spiral galaxies and very small for late
types. We argue that it can be due to the presence of thick discs with scale
lengths larger than the galaxy's main disc. Finally we discuss the
colour-magnitude relation in I-K for spiral galaxies. We find that it is a
tight relation, for which the scatter is similar to the observational
uncertainties, with a steeper slope than for elliptical galaxies.Comment: Invited review, to appear in "Extragalactic Astronomy in the
Infrared", eds. G.A. Mamon, Trinh Xuan Thuan, and J. Tran Thanh Van, Editions
Frontieres, Gif-sur-Yvette. LaTeX2e, 10 pages, 6 postscript figures and
moriond.sty included. See also
ftp://kapteyn.astro.rug.nl/peletier/lesarcs.ps.g
Spiral galaxy distance indicators based on near-infrared photometry
We compare two methods of distance determination to spiral galaxies using
optical/near-infrared (NIR) observations, the (I-K) versus M_K colour -
absolute magnitude (CM) relation and the I and K-band Tully-Fisher relation
(TFR). Dust-free colours and NIR absolute magnitudes greatly enhance the
usefulness of the NIR CM relation as a distance indicator for moderately to
highly inclined_spiral_ galaxies_in the field_ (inclinations between ~ 80 and
90 deg); by avoiding contamination by dust the scatter in the CM relation is
significantly reduced, compared to similar galaxy samples published previously.
The CM relation can be used to determine distances to field spiral galaxies
with M_K > -25.5, to at least M_K ~ -20. Our results, supplemented with
previously published observations for which we can - to some degree - control
the effects of extinction, are consistent with a universal nature of the CM
relation for field spiral galaxies. High-resolution observations done with the
Hubble Space Telescope can provide a powerful tool to calibrate the relation
and extend the useful distance range by more than a factor of 2 compared to
ground-based observations. The intrinsic scatter in the NIR CM relation in the
absolute K-band magnitudes is ~0.5 mag, yielding a lower limit to the accuracy
of distance determinations on the order of 25%. Although we find an unusually
low scatter in the TFR (probably a statistical accident), a typical scatter in
the TFR would yield distances to our sample galaxies with uncertainties of only
about 15%. However, one of the main advantages of the use of the NIR CM
relation is that_we only need photometric data_ to obtain distance estimates;
use of the TFR requires additional kinematic data, although it can be used to
significantly greater distances.Comment: 12 pages, incl. 5 postscript files, LaTeX, accepted for publication
in MNRA
The global structure of galactic discs
A statistical study of global galaxy parameters can help to improve our
understanding of galaxy formation processes. In this paper we present the
analysis of global galaxy parameters based on optical and near-infrared
observations of a large sample of edge-on disc galaxies. We found a correlation
between the ratio of the radial to vertical scale parameter and galaxy type:
galaxies become systematically thinner when going from S0's to Sc's, whereas
the distribution seems to level off for later types.
The observed scale length ratios (and thus the radial colour gradients)
largely represent the galaxies' dust content. On average the colour gradients
indicated by the scale length ratios increase from type Sa to at least type Sc.
For galaxy types later than Sc, the average colour gradient seems to decrease
again.
The distribution of K-band (edge-on) disc central surface brightnesses is
rather flat, although with a large scatter. However, the latest-type sample
galaxies (T > 6) show an indication that their average disc central surface
brightnesses may be fainter than those of the earlier types. This effect is
probably not the result of dust extinction.Comment: 17 pages, LaTex, 11 figures, accepted for publication in MNRA
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