578 research outputs found
Temperature limited fed-batch technique for control of proteolysis in Pichia pastoris bioreactor cultures
BACKGROUND: A temperature limited fed-batch (TLFB) technique is described and used for Pichia pastoris Mut(+ )strain cultures and compared with the traditional methanol limited fed-batch (MLFB) technique. A recombinant fusion protein composed of a cellulose-binding module (CBM) from Neocallimastix patriciarum cellulase 6A and lipase B from Candida antarctica (CALB), was produced and secreted by this strain. RESULTS: A protein concentration of about 1 g L(-1 )was produced in the MLFB process. However, this product was considerably degraded by protease(s). By applying the TLFB process, the yield was increased to 2 g L(-1 )full-length product and no proteolytic degradation was observed. Flow cytometry analysis showed that the percentage of dead cells increased rapidly during the initial methanol feed phase in the MLFB process and reached a maximum of about 12% after about 40â70 hours of methanol feeding. In the TLFB process, cell death rate was low and constant and reached 4% dead cells at the end of cultivation (about 150 hours methanol feeding time). The lower cell death rate in the TLFB correlated with a lower protease activity in the culture supernatant. The specific alcohol oxidase (AOX) activity in the TLFB process was 3.5 times higher than in the MLFB process. CONCLUSION: Three mechanisms that may contribute to the much higher accumulation of product in the TLFB process are: 1) reduced proteolysis due to lower temperature, 2) reduced proteolysis due to lower cell death and protease release to the medium, 3) increased synthesis rate due to higher AOX activity
From Heisenberg matrix mechanics to EBK quantization: theory and first applications
Despite the seminal connection between classical multiply-periodic motion and
Heisenberg matrix mechanics and the massive amount of work done on the
associated problem of semiclassical (EBK) quantization of bound states, we show
that there are, nevertheless, a number of previously unexploited aspects of
this relationship that bear on the quantum-classical correspondence. In
particular, we emphasize a quantum variational principle that implies the
classical variational principle for invariant tori. We also expose the more
indirect connection between commutation relations and quantization of action
variables. With the help of several standard models with one or two degrees of
freedom, we then illustrate how the methods of Heisenberg matrix mechanics
described in this paper may be used to obtain quantum solutions with a modest
increase in effort compared to semiclassical calculations. We also describe and
apply a method for obtaining leading quantum corrections to EBK results.
Finally, we suggest several new or modified applications of EBK quantization.Comment: 37 pages including 3 poscript figures, submitted to Phys. Rev.
Hybrid Natural Low Scale Inflation
We discuss the phenomenological implications of hybrid natural inflation
models in which the inflaton is a pseudo-Goldstone boson but inflation is
terminated by a second scalar field. A feature of the scheme is that the scale
of breaking of the Goldstone symmetry can be lower than the Planck scale and so
gravitational corrections are under control. We show that, for supersymmetric
models, the scale of inflation can be chosen anywhere between the Lyth upper
bound and a value close to the electroweak breaking scale. Unlike previous
models of low scale inflation the observed density perturbations and spectral
index are readily obtained by the choice of the free parameters
A large stellar evolution database for population synthesis studies: VI. White dwarf cooling sequences
We present a new set of cooling models and isochrones for both H- and
He-atmosphere white dwarfs, incorporating accurate boundary conditions from
detailed model atmosphere calculations, and carbon-oxygen chemical abundance
profiles based on updated stellar evolution calculations from the BaSTI stellar
evolution archive - a theoretical data center for the Virtual Observatory. We
discuss and quantify the uncertainties in the cooling times predicted by the
models, arising from the treatment of mixing during the central H- and
He-burning phases, number of thermal pulses experienced by the progenitors,
progenitor metallicity and the reaction rate. The
largest sources of uncertainty turn out to be related to the treatment of
convection during the last stages of the progenitor central He-burning phase,
and the reaction rate. We compare our new models
to previous calculations performed with the same stellar evolution code, and
discuss their application to the estimate of the age of the solar neighborhood,
and the interpretation of the observed number ratios between H- and
He-atmosphere white dwarfs. The new white dwarf sequences and an extensive set
of white dwarf isochrones that cover a large range of ages and progenitor
metallicities are made publicly available at the official BaSTI website.Comment: 34 pages, 13 figures, The Astrophysical Journal, in pres
Optimized clustering estimators for BAO measurements accounting for significant redshift uncertainty
We determine an optimized clustering statistic to be used for galaxy samples with significant redshift uncertainty, such as those that rely on photometric redshifts. To do so, we study the baryon acoustic oscillation (BAO) information content as a function of the orientation of galaxy clustering modes with respect to their angle to the line of sight (LOS). The clustering along the LOS, as observed in a redshift-space with significant redshift uncertainty, has contributions from clustering modes with a range of orientations with respect to the true LOS. For redshift uncertainty Ïz â„ 0.02(1 + z), we find that while the BAO information is confined to transverse clustering modes in the true space, it is spread nearly evenly in the observed space. Thus, measuring clustering in terms of the projected separation (regardless of the LOS) is an efficient and nearly lossless compression of the signal for Ïz â„ 0.02(1 + z). For reduced redshift uncertainty, a more careful consideration is required. We then use more than 1700 realizations (combining two separate sets) of galaxy simulations mimicking the Dark Energy Survey Year 1 (DES Y1) sample to validate our analytic results and optimized analysis procedure. We find that using the correlation function binned in projected separation, we can achieve uncertainties that are within 10âper cent of those predicted by Fisher matrix forecasts. We predict that DES Y1 should achieve a 5âper cent distance measurement using our optimized methods. We expect the results presented here to be important for any future BAO measurements made using photometric redshift data.Please visit publisher's website for further information
Clarifying the effects of interacting dark energy on linear and nonlinear structure formation processes
We present a detailed numerical study of the impact that cosmological models
featuring a direct interaction between the Dark Energy component that drives
the accelerated expansion of the Universe and Cold Dark Matter can have on the
linear and nonlinear stages of structure formation. By means of a series of
collisionless N-body simulations we study the influence that each of the
different effects characterizing these cosmological models - which include
among others a fifth force, a time variation of particle masses, and a
velocity-dependent acceleration - separately have on the growth of density
perturbations and on a series of observable quantities related to linear and
nonlinear cosmic structures, as the matter power spectrum, the gravitational
bias between baryons and Cold Dark Matter, the halo mass function and the halo
density profiles. We perform our analysis applying and comparing different
numerical approaches previously adopted in the literature, and we address the
partial discrepancies recently claimed in a similar study by Li & Barrow
(2010b) with respect to the first outcomes of Baldi et al. (2010), which are
found to be related to the specific numerical approach adopted in the former
work. Our results fully confirm the conclusions of Baldi et al. (2010) and show
that when linear and nonlinear effects of the interaction between Dark Energy
and Cold Dark Matter are properly disentangled, the velocity-dependent
acceleration is the leading effect acting at nonlinear scales, and in
particular is the most important mechanism in lowering the concentration of
Cold Dark Matter halos.Comment: 14 pages, 1 Table, 6 Figures. MNRAS accepte
CFHTLS weak-lensing constraints on the neutrino masses
We use measurements of cosmic shear from CFHTLS, combined with WMAP-5 cosmic
microwave background anisotropy data, baryonic acoustic oscillations from SDSS
and 2dFGRS and supernovae data from SNLS and Gold-set, to constrain the
neutrino mass. We obtain a 95% confidence level upper limit of 0.54 eV for the
sum of the neutrino masses, and a lower limit of 0.03 eV. The preference for
massive neutrinos vanishes when shear-measurement systematics are included in
the analysis.Comment: 10 pages. Published versio
The Impact of an Extra Background of Relativistic Particles on the Cosmological Parameters derived from Microwave Background Anisotropies
Recent estimates of cosmological parameters derived from Cosmic Microwave
Background (CMB) anisotropies are based on the assumption that we know the
precise amount of energy density in relativistic particles in the universe,
, at all times. There are, however, many possible mechanisms that
can undermine this assumption. In this paper we investigate the effect that
removing this assumption has on the determination of the various cosmological
parameters. We obtain fairly general bounds on the redshift of equality,
. We show that
is nearly degenerate with the amount of energy in matter,
, and that its inclusion in CMB parameter estimation also affects the
present constraints on other parameters such as the curvature or the scalar
spectral index of primordial fluctuations. This degeneracy has the effect of
limiting the precision of parameter estimation from the MAP satellite, but it
can be broken by measurements on smaller scales such as those provided by the
Planck satellite mission.Comment: 9 pages, 6 figures, Submitted to MNRAS. High resolution colour
pictures can be obtained on request from the author
Tests of model predictions for the responses of stellar spectra and absorption-line indices to element abundance variations. Tests of model predictions for the responses of stellar spectra and absorption-line indices to element abundance variations.
A method that is widely used to analyse stellar populations in galaxies is to apply the theoretically derived responses of stellar spectra and line indices to element abundance variations, which are hereafter referred to as response functions. These are applied in a differential way, to base models, in order to generate spectra or indices with different abundance patterns. In this paper, sets of such response functions for three different stellar evolutionary stages are tested with new empirical [Mg/Fe] abundance data for the medium-resolution Isaac Newton Telescope library of empirical spectra (MILES). Recent theoretical models and observations are used to investigate the effects of [Fe/H], [Mg/H] and overall [Z/H] on spectra, via ratios of spectra for similar stars. The global effects of changes in abundance patterns are investigated empirically through direct comparisons of similar stars from MILES, highlighting the impact of abundance effects in the blue part of the spectrum, particularly for lower temperature stars. It is found that the relative behaviour of iron-sensitive line indices are generally well predicted by response functions, whereas Balmer line indices are not. Other indices tend to show large scatter about the predicted mean relations. Implications for element abundance and age studies in stellar populations are discussed and ways forward are suggested to improve the match with the behaviour of spectra and line-strength indices observed in real stars
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