A new approach to cosmological perturbations in f(R) models

We propose an analytic procedure that allows to determine quantitatively the deviation in the behavior of cosmological perturbations between a given f(R) modified gravity model and a LCDM reference model. Our method allows to study structure formation in these models from the largest scales, of the order of the Hubble horizon, down to scales deeply inside the Hubble radius, without employing the so-called "quasi-static" approximation. Although we restrict our analysis here to linear perturbations, our technique is completely general and can be extended to any perturbative order.Comment: 21 pages, 2 figures; Revised version according to reviewer's suggestions; Typos corrected; Added Reference

Effective interactions between inclusions in complex fluids driven out of equilibrium

The concept of fluctuation-induced effective interactions is extended to systems driven out of equilibrium. We compute the forces experienced by macroscopic objects immersed in a soft material driven by external shaking sources. We show that, in contrast with equilibrium Casimir forces induced by thermal fluctuations, their sign, range and amplitude depends on specifics of the shaking and can thus be tuned. We also comment upon the dispersion of these shaking-induced forces, and discuss their potential application to phase ordering in soft-materials.Comment: 10 pages, 8 figures, to appear in PR

A generalized Hamiltonian Constraint Operator in Loop Quantum Gravity and its simplest Euclidean Matrix Elements

We study a generalized version of the Hamiltonian constraint operator in nonperturbative loop quantum gravity. The generalization is based on admitting arbitrary irreducible SU(2) representations in the regularization of the operator, in contrast to the original definition where only the fundamental representation is taken. This leads to a quantization ambiguity and to a family of operators with the same classical limit. We calculate the action of the Euclidean part of the generalized Hamiltonian constraint on trivalent states, using the graphical notation of Temperley-Lieb recoupling theory. We discuss the relation between this generalization of the Hamiltonian constraint and crossing symmetry.Comment: 35 pp, 20 eps figures; minor corrections, references added; version to appear in Class. Quant. Gra

Fluctuations of Fluctuation-Induced "Casimir" Forces

The force experienced by objects embedded in a correlated medium undergoing thermal fluctuations--the so-called fluctuation--induced force--is actually itself a fluctuating quantity. We compute the corresponding probability distribution and show that it is a Gaussian centered on the well-known Casimir force, with a non-universal standard deviation that can be typically as large as the mean force itself. The relevance of these results to the experimental measurement of fluctuation-induced forces is discussed, as well as the influence of the finite temporal resolution of the measuring apparatus.Comment: 4 pages, 2 figure

Dopamine neuronal loss contributes to memory and reward dysfunction in a model of Alzheimer's disease

Alterations of the dopaminergic (DAergic) system are frequently reported in Alzheimer’s disease (AD) patients and are commonly linked to cognitive and non-cognitive symptoms. However, the cause of DAergic system dysfunction in AD remains to be elucidated. We investigated alterations of the midbrain DAergic system in the Tg2576 mouse model of AD, overexpressing a mutated human amyloid precursor protein (APPswe). Here, we found an age-dependent DAergic neuron loss in the ventral tegmental area (VTA) at pre-plaque stages, although substantia nigra pars compacta (SNpc) DAergic neurons were intact. The selective VTA DAergic neuron degeneration results in lower DA outflow in the hippocampus and nucleus accumbens (NAc) shell. The progression of DAergic cell death correlates with impairments in CA1 synaptic plasticity, memory performance and food reward processing. We conclude that in this mouse model of AD, degeneration of VTA DAergic neurons at pre-plaque stages contributes to memory deficits and dysfunction of reward processing

Uremic serum-induced calcification of human aortic smooth muscle cells is a regulated process involving Klotho and RUNX2

© 2019 The Author(s). This is an open access article published by Portland Press Limited on behalf of the Biochemical Society and distributed under the Creative Commons Attribution License 4.0 (CC BY).Vascular calcification (VC) is common in subjects with chronic kidney disease (CKD) and is associated with increased cardiovascular risk. It is an active process involving transdifferentiation of arterial smooth muscle cells (SMCs) into osteogenic phenotype. We investigated the ability of serum from CKD subjects to induce calcification in human SMCs in vitro (calcific potential of sera: CP), and associated changes in expression of Runt-related transcription factor 2 (RUNX2), SM22a, and Klotho. Sera from subjects with CKD (18 stage 3, 17 stage 4/5, and 29 stage 5D) and 20 controls were added to human cultured SMCs and CP quantified. The CP of CKD sera was greater (P>0.01) than that of controls, though not influenced by CKD stage. Modification of diet in renal disease estimated glomerular filtration rate (MDRD-4 eGFR) (P>0.001), serum phosphate (P=0.042), receptor activator of nuclear factor ?appa-B ligand (RANKL) (P=0.001), parathyroid hormone (PTH) (P=0.014), and high-density lipoprotein (HDL)/cholesterol ratio (P=0.026) were independent predictors of CP accounting for 45% of variation. Adding calcification buffer (CB: calcium chloride [7 mM] and β-glycerophosphate [7 mM]) increased the CP of control sera to approximate that of CKD sera. CP of CKD sera was unchanged. CKD sera increased RUNX2 expression (P>0.01) in human SMCs and decreased SM22a expression (P>0.05). Co-incubating control but not CKD serum with CB further increased RUNX2 expression (P>0.01). Both SM22a and Klotho expression decreased significantly (P>0.01) in the presence of CKD serum, and were virtually abolished with stage 5D sera. These findings support active regulation by CKD serum of in vitro VC by induction of RUNX2 and suppression of SM22a and Klotho.Peer reviewe

The CMB and the measure of the multiverse

In the context of eternal inflation, cosmological predictions depend on the choice of measure to regulate the diverging spacetime volume. The spectrum of inflationary perturbations is no exception, as we demonstrate by comparing the predictions of the fat geodesic and causal patch measures. To highlight the effect of the measure---as opposed to any effects related to a possible landscape of vacua---we take the cosmological model, including the model of inflation, to be fixed. We also condition on the average CMB temperature accompanying the measurement. Both measures predict a 1-point expectation value for the gauge-invariant Newtonian potential, which takes the form of a (scale-dependent) monopole, in addition to a related contribution to the 3-point correlation function, with the detailed form of these quantities differing between the measures. However, for both measures both effects are well within cosmic variance. Our results make clear the theoretical relevance of the measure, and at the same time validate the standard inflationary predictions in the context of eternal inflation.Comment: 28 pages; v2: reference added, some clarification

Transdimensional physics and inflation

Within the framework of a five-dimensional brane world with a stabilized radion, we compute the cosmological perturbations generated during inflation and show that the perturbations are a powerful tool to probe the physics of extra dimensions. While we find that the power spectrum of scalar perturbations is unchanged, we show that the existence of the fifth dimension is imprinted on the spectrum of gravitational waves generated during inflation. In particular, we find that the tensor perturbations receive a correction proportional to $(HR)^2$, where $H$ is the Hubble expansion rate during inflation and $R$ is the size of the extra dimension. We also generalize our findings to the case of several extra dimensions as well as to warped geometries.Comment: RevTeX file, 30 pages, 1 figure. Final version to appear in PR

New Zinc-Based Active Chitosan Films: Physicochemical Characterization, Antioxidant, and Antimicrobial Properties

The improvement of the antioxidant and antimicrobial activities of chitosan (CS) films can be realized by incorporating transition metal complexes as active components. In this context, bioactive films were prepared by embedding a newly synthesized acylpyrazolonate Zn(II) complex, [Zn(QPhtBu)2(MeOH)2], into the eco-friendly biopolymer CS matrix. Homogeneous, amorphous, flexible, and transparent CS@Znn films were obtained through the solvent casting method in dilute acidic solution, using different weight ratios of the Zn(II) complex to CS and characterized by powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), Fourier transform infrared (FT-IR), Raman, and scanning electron microscopy (SEM) techniques. The X-ray single-crystal analysis of [Zn(QPhtBu)2(MeOH)2] and the evaluation of its intermolecular interactions with a protonated glucosamine fragment through hydrogen bond propensity (HBP) calculations are reported. The effects of the different contents of the [Zn(QPhtBu)2(MeOH)2] complex on the CS biological proprieties have been evaluated, proving that the new CS@Znn films show an improved antioxidant activity, tested according to the DPPH method, with respect to pure CS, related to the concentration of the incorporated Zn(II) complex. Finally, the CS@Znn films were tried out as antimicrobial agents, showing an increase in antimicrobial activity against Gram-positive bacteria (Staphylococcus aureus) with respect to pure CS, when detected by the agar disk-diffusion method

Non-Gaussianity from Instant and Tachyonic Preheating

We study non-Gaussianity in two distinct models of preheating: instant and tachyonic. In instant preheating non-Gaussianity is sourced by the local terms generated through the coupled perturbations of the two scalar fields. We find that the non-Gaussianity parameter is given by $f_{NL}^{\phi}\sim 2g < O(1)$, where $g$ is a coupling constant, so that instant preheating is unlikely to be constrained by WMAP or Planck. In the case of tachyonic preheating non-Gaussianity arises solely from the instability of the tachyon matter and is found to be large. We find that for single field inflation the present WMAP data implies a bound $V_{0}^{1/4}/M_{P}\leq 10^{-4}$ on the scale of tachyonic instability. We argue that the tachyonic preheating limits are useful also for string-motivated inflationary models.Comment: 12 pages, 1 figure, additional discussion, improved constraint on the scale of tachyonic preheatin