29,898 research outputs found
Processing of Cosmological Perturbations in a Cyclic Cosmology
The evolution of the spectrum of cosmological fluctuations from one cycle to
the next is studied. It is pointed out that each cycle leads to a reddening of
the spectrum. This opens up new ways to generate a scale-invariant spectrum of
curvature perturbations. The large increase in the amplitude of the
fluctuations quickly leads to a breakdown of the linear theory. More generaly,
we see that, after including linearized cosmological perturbations, a cyclic
universe cannot be truly cyclic.Comment: 5 pages, 1 figur
A New Redshift Interpretation
A nonhomogeneous universe with vacuum energy, but without spacetime
expansion, is utilized together with gravitational and Doppler redshifts as the
basis for proposing a new interpretation of the Hubble relation and the 2.7K
Cosmic Blackbody Radiation.Comment: 9 pages LaTeX, no figure
On the Spatial Correlations of Lyman Break Galaxies
Motivated by the observed discrepancy between the strong spatial correlations
of Lyman break galaxies (LBGs) and their velocity dispersions, we consider a
theoretical model in which these starbursting galaxies are associated with dark
matter halos that experience appreciable infall of material. We show using
numerical simulation that selecting halos that substantially increase in mass
within a fixed time interval introduces a ``temporal bias'' which boosts their
clustering above that of the underlying population. If time intervals
consistent with the observed LBGs star formation rates of 50 solar masses per
year are chosen, then spatial correlations are enhanced by up to a factor of
two. These values roughly correspond to the geometrical bias of objects three
times as massive. Thus, it is clear that temporal biasing must be taken into
account when interpreting the properties of Lyman break galaxies.Comment: 5 Pages, 2 Figures, Accepted for Publication in ApJ Letter
Functionalized hyperbranched polymers via olefin metathesis
Hyperbranched polymers are highly branched, three-dimensional
macromolecules which are closely related to dendrimers
and are typically prepared via a one-pot polycondensation of
AB_(n≥2) monomers.^1 Although hyperbranched macromolecules
lack the uniformity of monodisperse dendrimers, they still
possess many attractive dendritic features such as good solubility,
low solution viscosity, globular structure, and multiple end
groups.^1-3 Furthermore, the usually inexpensive, one-pot synthesis
of these polymers makes them particularly desirable
candidates for bulk-material and specialty applications. Toward
this end, hyperbranched polymers have been investigated as both
rheology-modifying additives to conventional polymers and as
substrate-carrying supports or multifunctional macroinitiators,
where a large number of functional sites within a compact space
becomes beneficial
A Radiation Bounce from the Lee-Wick Construction?
It was recently realized that matter modeled by the scalar field sector of
the Lee-Wick Standard Model yields, in the context of a homogeneous and
isotropic cosmological background, a bouncing cosmology. However, bouncing
cosmologies induced by pressure-less matter are in general unstable to the
addition of relativistic matter (i.e. radiation). Here we study the possibility
of obtaining a bouncing cosmology if we add not only radiation, but also its
Lee-Wick partner, to the matter sector. We find that, in general, no bounce
occurs. The only way to obtain a bounce is to choose initial conditions with
very special phases of the radiation field and its Lee-Wick partner.Comment: 11 page
Lung Circulation Modeling: Status and Prospect
Mathematical modeling has been used to interpret anatomical and physiological data obtained from metabolic and hemodynamic studies aimed at investigating structure-function relationships in the vasculature of the lung, and how these relationships are affected by lung injury and disease. The indicator dilution method was used to study the activity of redox processes within the lung. A steady-state model of the data was constructed and used to show that pulmonary endothelial cells may play an important role in reducing redox active compounds and that those reduction rates can be altered with oxidative stress induced by exposure to high oxygen environments. In addition, a morphometric model of the pulmonary vasculature was described and used to detect, describe,and predict changes in vascular morphology that occur in response to chronic exposure to low-oxygen environments, a common model of pulmonary hypertension. Finally, the model was used to construct simulated circulatory networks designed to aid in evaluation of competing hypotheses regarding the relative contribution of various morphological and biomechanical changes observed with hypoxia. These examples illustrate the role of mathematical modeling in the integration of the emerging metabolic, hemodynamic, and morphometric databases
Diquarks and Exotic Spectroscopy
We propose that the recently discovered \Theta baryon is a bound state of
four quarks and an antiquark, containing two highly correlated ud-pairs. If so,
the \Theta baryon has positive parity, and it lies in an near-ideally mixed
SU(3)_{f} \mathbf{\bar{10}}_{f} oplus \mathbf{8}_{f}. The Roper resonance and
the P_{11}(1710) fit naturally into this classification. We predict an isospin
3/2 multiplet of \Xi's (S=-2) with J^{\Pi}=\half^{+} around 1750 MeV. A search
for manifestly exotic \Xi^{+} and \Xi^{--} in this mass range could provide a
sharp test of our proposal. We predict that charm and bottom analogues of the
\Theta baryon are stable against strong decays.Comment: 5 pages, 2 figures, revtex 4, minor corrections and revisions for
journal publicatio
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