753 research outputs found
Fermion production from preheating-amplified metric perturbations
We study gravitational creation of light fermions in the presence of
classical scalar metric perturbations about a flat Friedmann-Lemaitre-
Robertson-Walker (FLRW) background. These perturbations can be large during
preheating, breaking the conformal flatness of the background spacetime. We
compute numerically the total number of particles generated by the modes of the
metric perturbations which have grown sufficiently to become classical. In the
absence of inhomogeneities massless fermions are not gravitationally produced,
and then this effect may be relevant for abundance estimates of light
gravitational relics.Comment: 17 pages, 7 figures, accepted for publication in Nuclear Physics
Gravitational waves from fermion production during axion inflation
We present analytic results for the gravitational wave power spectrum induced
in models where the inflaton is coupled to a fermionic pseudocurrent. We show
that although such a coupling creates helically polarized fermions, the
polarized component of the resulting gravitational waves is parametrically
suppressed with respect to the non-polarized one. We also show that the
amplitude of the gravitational wave signal associated to this production cannot
exceed that generated by the standard mechanism of amplification of vacuum
fluctuations. We previously found that this model allows for a regime in which
the backreaction of the produced fermions allows for slow-roll inflation even
for a steep inflaton potential, and still leads to Gaussian primordial scalar
perturbations. The present analysis shows that this regime also results in a
gravitational wave signal compatible with the current bounds.Comment: 29 pages, 2 figure
Where in the String Landscape is Quintessence
We argue that quintessence may reside in certain corners of the string
landscape. It arises as a linear combination of internal space components of
higher rank forms, which are axion-like at low energies, and may mix with
4-forms after compactification of the Chern-Simons terms to 4D due to internal
space fluxes. The mixing induces an effective mass term, with an action which
{\it preserves} the axion shift symmetry, breaking it spontaneously after the
background selection. With several axions, several 4-forms, and a low string
scale, as in one of the setups already invoked for dynamically explaining a
tiny residual vacuum energy in string theory, the 4D mass matrix generated by
random fluxes may have ultralight eigenmodes over the landscape, which are
quintessence. We illustrate how this works in simplest cases, and outline how
to get the lightest mass to be comparable to the Hubble scale now, . The shift symmetry protects the smallest mass from
perturbative corrections in field theory. Further, if the ultralight eigenmode
does not couple directly to any sector strongly coupled at a high scale, the
non-perturbative field theory corrections to its potential will also be
suppressed. Finally, if the compactification length is larger than the string
length by more than an order of magnitude, the gravitational corrections may
remain small too, even when the field value approaches .Comment: 8 pages RevTeX; added references, matches published versio
Mechanical ventilation during acute lung injury: current recommendations and new concepts
Despite a very large body of investigations, no effective pharmacological therapies have been found to cure acute lung injury. Hence, supportive care with mechanical ventilation remains the cornerstone of treatment. However, several experimental and clinical studies showed that mechanical ventilation, especially at high tidal volumes and pressures, can cause or aggravate ALI. Therefore, current clinical recommendations are developed with the aim of avoiding ventilator-induced lung injury (VILI) by limiting tidal volume and distending ventilatory pressure according to the results of the ARDS Network trial, which has been to date the only intervention that has showed success in decreasing mortality in patients with ALI/ARDS. In the past decade, a very large body of investigations has determined significant achievements on the pathophysiological knowledge of VILI. Therefore, new perspectives, which will be reviewed in this article, have been defined in terms of the efficiency and efficacy of recognizing, monitoring and treating VILI, which will eventually lead to further significant improvement of outcome in patients with ARDS
Gasification of Densified Sludge and Wastepaper in a Downdraft Packed-Bed Gasifier
The co-disposal of densified sludge and wastepaper in a co-current flow packed bed gasifier represents new application of the thermal gasification process. Advantages of this technology include lower costs than other incineration or pyrolysis technologies, simple construction and operation, and the ability to use a variety of fuels including agricultural wastes and other biomass materials in addition to densified sludge and wastepaper
Biological Responses to Cadmium Stress in Liverwort Conocephalum conicum (Marchantiales)
Oxidative damage (production and localization of reactive oxygen species) and related response mechanisms (activity of antioxidant enzymes), and induction of Heat Shock Protein 70 expression, have been studied in the toxi-tolerant liverwort Conocephalum conicum (Marchantiales) in response to cadmium stress using two concentrations (36 and 360 ”M CdCl2). Cadmium dose-dependent production of reactive oxygen species (ROS) and related activity of antioxidant enzymes was observed. The expression level of heat shock protein (Hsp)70, instead, was higher at 36 ”M CdCl2 in comparison with the value obtained after exposure to 360 ”M CdCl2, suggesting a possible inhibition of the expression of this stress gene at higher cadmium exposure doses. Biological responses were related to cadmium bioaccumulation. Since C. conicum was able to respond to cadmium stress by modifying biological parameters, we discuss the data considering the possibility of using these biological changes as biomarkers of cadmium pollution
Phenomenology of fermion production during axion inflation
We study the production of fermions through a derivative coupling with a
pseudoscalar inflaton and the effects of the produced fermions on the scalar
primordial perturbations. We present analytic results for the modification of
the scalar power spectrum due to the produced fermions, and we estimate the
amplitude of the non-Gaussianities in the equilateral regime. Remarkably, we
find a regime where the effect of the fermions gives the dominant contribution
to the scalar spectrum while the amplitude of the bispectrum is small and in
agreement with observation. We also note the existence of a regime in which the
backreaction of the fermions on the evolution of the zero-mode of the inflaton
can lead to inflation even if the potential of the inflaton is steep and does
not satisfy the slow-roll conditions.Comment: 48 pages, 9 figures, minor changes, matches published version; v3:
added one subsection on spectral index, improved constraints leading to
larger parameter space in figure 5, and minor change
Ultrafast polarization of an electron beam in an intense bichromatic laser field
Here, we demonstrate the radiative polarization of high-energy electron beams in collisions with ultrashort pulsed bichromatic laser fields. Employing a Boltzmann kinetic approach for the electron distribution allows us to simulate the beam polarization over a wide range of parameters and determine the optimum conditions for maximum radiative polarization. Those results are contrasted with a Monte Carlo algorithm where photon emission and associated spin effects are treated fully quantum mechanically using spin-dependent photon emission rates. The latter method includes realistic focusing laser fields, which allows us to simulate a near-term experimentally feasible scenario of an 8 GeV electron beam scattering from a 1 PW laser pulse and provide a measurement that would verify the ultrafast radiative polarization in high-intensity laser pulses that we predict. Aspects of spin-dependent radiation reaction are also discussed, with spin polarization leading to a measurable (5%) splitting of the energies of spin-up and spin-down electrons
Smart magnetic nanovesicles for theranostic application: Preparation and characterization
Nanomedicines are submicrometer-sized carrier materials designed to improve the biodistribution of systemically administered (chemo)therapeutic agents. By delivering pharmacologically active agents more effectively and more
selectively to the pathological site nanomedicines aim to improve the balance between the efficacy and the toxicity of systemic (chemo)therapeutic administrations. Nanomedicine formulations have also been used for imaging applications and, in recent years, for theranostic approaches, that is, for systems and strategies in which
disease diagnosis and therapy are combined. On the one hand, âclassicalâ drug delivery systems are being co-loaded with both drugs and contrast agents. Actually, nanomaterials with an intrinsic ability to be used for imaging purposes, such as iron-oxideâbased magnetic nanoparticles (MNPs), are increasingly being loaded with
drugs or alone for combining disease diagnosis and therapy. In this study, non-ionic surfactant vesicles loaded with lipophilic and hydrophilic MNPs have been prepared.
Vesicles have been characterized in terms of dimensions, ζ-potential, time stability, bilayer characteristics and overall iron content. The encouraging obtained results
confirm that Tween 20 and Span 20 vesicles could be promising carriers for the delivery of hydrophilic and lipophilic MNPs, respectively, thereby prompting various
opportunities for the development of suitable theranostic strategies. The analyzed formulations confirm the importance of surfactant chemical-physical characteristics
in entrapping the MNPs of different polarity, highlighting the high versatility of niosomal bilayer and structure; property that make them so appealing among drug delivery nanocarriers
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