183 research outputs found
Trialogue on the number of fundamental constants
This paper consists of three separate articles on the number of fundamental
dimensionful constants in physics. We started our debate in summer 1992 on the
terrace of the famous CERN cafeteria. In the summer of 2001 we returned to the
subject to find that our views still diverged and decided to explain our
current positions. LBO develops the traditional approach with three constants,
GV argues in favor of at most two (within superstring theory), while MJD
advocates zero.Comment: Version appearing in JHEP; 31 pages late
Charge conservation and time-varying speed of light
It has been recently claimed that cosmologies with time dependent speed of
light might solve some of the problems of the standard cosmological scenario,
as well as inflationary scenarios. In this letter we show that most of these
models, when analyzed in a consistent way, lead to large violations of charge
conservation. Thus, they are severly constrained by experiment, including those
where is a power of the scale factor and those whose source term is the
trace of the energy-momentum tensor. In addition, early Universe scenarios with
a sudden change of related to baryogenesis are discarded.Comment: 4 page
Sum rules and energy scales in the high-temperature superconductor YBa2Cu3O6+x
The Ferrell-Glover-Tinkham (FGT) sum rule has been applied to the temperature
dependence of the in-plane optical conductivity of optimally-doped
YBa_2Cu_3O_{6.95} and underdoped YBa_2Cu_3O_{6.60}. Within the accuracy of the
experiment, the sum rule is obeyed in both materials. However, the energy scale
\omega_c required to recover the full strength of the superfluid \rho_s in the
two materials is dramatically different; \omega_c \simeq 800 cm^{-1} in the
optimally doped system (close to twice the maximum of the superconducting gap,
2\Delta_0), but \omega_c \gtrsim 5000 cm^{-1} in the underdoped system. In both
materials, the normal-state scattering rate close to the critical temperature
is small, \Gamma < 2\Delta_0, so that the materials are not in the dirty limit
and the relevant energy scale for \rho_s in a BCS material should be twice the
energy gap. The FGT sum rule in the optimally-doped material suggests that the
majority of the spectral weight of the condensate comes from energies below
2\Delta_0, which is consistent with a BCS material in which the condensate
originates from a Fermi liquid normal state. In the underdoped material the
larger energy scale may be a result of the non-Fermi liquid nature of the
normal state. The dramatically different energy scales suggest that the nature
of the normal state creates specific conditions for observing the different
aspects of what is presumably a central mechanism for superconductivity in
these materials.Comment: RevTeX 4 file, 9 pages with 7 embedded eps figure
A Kinematical Approach to Conformal Cosmology
We present an alternative cosmology based on conformal gravity, as originally
introduced by H. Weyl and recently revisited by P. Mannheim and D. Kazanas.
Unlike past similar attempts our approach is a purely kinematical application
of the conformal symmetry to the Universe, through a critical reanalysis of
fundamental astrophysical observations, such as the cosmological redshift and
others. As a result of this novel approach we obtain a closed-form expression
for the cosmic scale factor R(t) and a revised interpretation of the space-time
coordinates usually employed in cosmology. New fundamental cosmological
parameters are introduced and evaluated. This emerging new cosmology does not
seem to possess any of the controversial features of the current standard
model, such as the presence of dark matter, dark energy or of a cosmological
constant, the existence of the horizon problem or of an inflationary phase.
Comparing our results with current conformal cosmologies in the literature, we
note that our kinematic cosmology is equivalent to conformal gravity with a
cosmological constant at late (or early) cosmological times. The cosmic scale
factor and the evolution of the Universe are described in terms of several
dimensionless quantities, among which a new cosmological variable delta emerges
as a natural cosmic time. The mathematical connections between all these
quantities are described in details and a relationship is established with the
original kinematic cosmology by L. Infeld and A. Schild. The mathematical
foundations of our kinematical conformal cosmology will need to be checked
against current astrophysical experimental data, before this new model can
become a viable alternative to the standard theory.Comment: Improved version, with minor changes. 58 pages, including 7 figures
and one table. Accepted for publication in General Relativity and Gravitation
(GERG
Necessidades térmicas de videiras na região da Campanha do Rio Grande do Sul - Brasil
A compendium of multi-omics data illuminating host responses to lethal human virus infections
Human infections caused by viral pathogens trigger a complex gamut of host responses that limit disease, resolve infection, generate immunity, and contribute to severe disease or death. Here, we present experimental methods and multi-omics data capture approaches representing the global host response to infection generated from 45 individual experiments involving human viruses from the Orthomyxoviridae, Filoviridae, Flaviviridae, and Coronaviridae families. Analogous experimental designs were implemented across human or mouse host model systems, longitudinal samples were collected over defined time courses, and global multi-omics data (transcriptomics, proteomics, metabolomics, and lipidomics) were acquired by microarray, RNA sequencing, or mass spectrometry analyses. For comparison, we have included transcriptomics datasets from cells treated with type I and type II human interferon. Raw multi-omics data and metadata were deposited in public repositories, and we provide a central location linking the raw data with experimental metadata and ready-to-use, quality-controlled, statistically processed multi-omics datasets not previously available in any public repository. This compendium of infection-induced host response data for reuse will be useful for those endeavouring to understand viral disease pathophysiology and network biology
Physical Processes in Star Formation
© 2020 Springer-Verlag. The final publication is available at Springer via https://doi.org/10.1007/s11214-020-00693-8.Star formation is a complex multi-scale phenomenon that is of significant importance for astrophysics in general. Stars and star formation are key pillars in observational astronomy from local star forming regions in the Milky Way up to high-redshift galaxies. From a theoretical perspective, star formation and feedback processes (radiation, winds, and supernovae) play a pivotal role in advancing our understanding of the physical processes at work, both individually and of their interactions. In this review we will give an overview of the main processes that are important for the understanding of star formation. We start with an observationally motivated view on star formation from a global perspective and outline the general paradigm of the life-cycle of molecular clouds, in which star formation is the key process to close the cycle. After that we focus on the thermal and chemical aspects in star forming regions, discuss turbulence and magnetic fields as well as gravitational forces. Finally, we review the most important stellar feedback mechanisms.Peer reviewedFinal Accepted Versio
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