43,528 research outputs found
Leptonic Electroweak Spin-Torsion Interactions
In this paper we consider the most general field equations for a system of
two fermions of which one single-handed, showing that the spin-torsion
interactions among these spinors have a structure identical to that of the
electroweak forces among leptons; possible extensions are discussed.Comment: 7 page
On the use of Gaia magnitudes and new tables of bolometric corrections
The availability of reliable bolometric corrections and reddening estimates,
rather than the quality of parallaxes will be one of the main limiting factors
in determining the luminosities of a large fraction of Gaia stars. With this
goal in mind, we provide Gaia G, BP and RP synthetic photometry for the entire
MARCS grid, and test the performance of our synthetic colours and bolometric
corrections against space-borne absolute spectrophotometry. We find indication
of a magnitude-dependent offset in Gaia DR2 G magnitudes, which must be taken
into account in high accuracy investigations. Our interpolation routines are
easily used to derive bolometric corrections at desired stellar parameters, and
to explore the dependence of Gaia photometry on Teff, log(g), [Fe/H],
alpha-enhancement and E(B-V). Gaia colours for the Sun and Vega, and
Teff-dependent extinction coefficients, are also provided.Comment: MNRAS Letter. Solar colours: BP-G = 0.33, G-RP = 0.49, BP-RP = 0.82.
Mean extinction coefficients at turn-off: R_G = 2.740 , R_BP = 3.374, R_RP =
2.035. Interpolation routines available at
https://github.com/casaluca/bolometric-correction
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Protein evolution speed depends on its stability and abundance and on chaperone concentrations.
Proteins evolve at different rates. What drives the speed of protein sequence changes? Two main factors are a protein's folding stability and aggregation propensity. By combining the hydrophobic-polar (HP) model with the Zwanzig-Szabo-Bagchi rate theory, we find that: (i) Adaptation is strongly accelerated by selection pressure, explaining the broad variation from days to thousands of years over which organisms adapt to new environments. (ii) The proteins that adapt fastest are those that are not very stably folded, because their fitness landscapes are steepest. And because heating destabilizes folded proteins, we predict that cells should adapt faster when put into warmer rather than cooler environments. (iii) Increasing protein abundance slows down evolution (the substitution rate of the sequence) because a typical protein is not perfectly fit, so increasing its number of copies reduces the cell's fitness. (iv) However, chaperones can mitigate this abundance effect and accelerate evolution (also called evolutionary capacitance) by effectively enhancing protein stability. This model explains key observations about protein evolution rates
On the FĆ¼rstenberg closure of a class of binary recurrences
In this paper, we determine the closure in the full topology over Z of the set {un: nā„0}, where (un)nā„0 is a nondegenerate binary recurrent sequence with integer coefficients whose characteristic roots are quadratic units. This generalizes the result for the case when un=Fn was the nth Fibonacci number
Synthetic Stellar Photometry - I. General considerations and new transformations for broad-band systems
After a pedagogical introduction to the main concepts of synthetic
photometry, colours and bolometric corrections in the Johnson-Cousins, 2MASS,
and HST-ACS/WFC3 photometric systems are generated from MARCS synthetic fluxes
for various [Fe/H] and [alpha/Fe] combinations, and virtually any value of
reddening E(B-V) < 0.7. The successes and failures of model fluxes in
reproducing the observed magnitudes are highlighted. Overall, extant synthetic
fluxes predict quite realistic broad-band colours and bolometric corrections,
especially at optical and longer wavelengths: further improvements of the
predictions for the blue and ultraviolet spectral regions await the use of
hydrodynamic models where the microturbulent velocity is not treated as a free
parameter. We show how the morphology of the colour-magnitude diagram (CMD)
changes for different values of [Fe/H] and [alpha/Fe]; in particular, how
suitable colour combinations can easily discriminate between red giant branch
and lower main sequence populations with different [alpha/Fe], due to the
concomitant loops and swings in the CMD. We also provide computer programs to
produce tables of synthetic bolometric corrections as well as routines to
interpolate in them. These colour-Teff-metallicity relations may be used to
convert isochrones for different chemical compositions to various bandpasses
assuming observed reddening values, thus bypassing the standard assumption of a
constant colour excess for stars of different spectral type. We also show how
such an assumption can lead to significant systematic errors. The MARCS
transformations presented in this study promise to provide important
constraints on our understanding of the multiple stellar populations found in
globular clusters (e.g., the colours of lower main sequence stars are predicted
to depend strongly on [alpha/Fe]) and of those located towards/in the Galactic
bulge.Comment: MNRAS, accepted. Tables and programs to generate synthetic colours
and bolometric corrections in various photometric systems and for different
combination of E(B-V), [Fe/H], [alpha/Fe], Teff and logg available via CDS at
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/MNRAS/444/39
Generalized Magnetofluid Connections in Relativistic Magnetohydrodynamics
The concept of magnetic connections is extended to non-ideal relativistic
magnetohydrodynamical plasmas. Adopting a general set of equations for
relativistic magnetohydrodynamics including thermal-inertial, thermal
electromotive, Hall and current-inertia effects, we derive a new covariant
connection equation showing the existence of generalized magnetofluid
connections that are preserved during the dissipationless plasma dynamics.
These connections are intimately linked to a general antisymmetric tensor that
unifies the electromagnetic and fluid fields, allowing the extension of the
magnetic connection notion to a much broader concept.Comment: Accepted for publication in Physical Review Letter
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