257 research outputs found
Scale Invariance without Inflation?
We propose a new alternative mechanism to seed a scale invariant spectrum of
primordial density perturbations that does not rely on inflation. In our
scenario, a perfect fluid dominates the early stages of an expanding,
non-inflating universe. Because the speed of sound of the fluid decays,
perturbations are left frozen behind the sound horizon, with a spectral index
that depends on the fluid equation of state. We explore here a toy model that
realizes this idea. Although the model can explain an adiabatic, Gaussian,
scale invariant spectrum of primordial perturbations, it turns out that in its
simplest form it cannot account for the observed amplitude of the primordial
density perturbations.Comment: 6 two-column pages, 1 figure. Uses RevTeX4. v2: References added and
number of required e-folds refine
Vacuum Choices and the Predictions of Inflation
In the presence of a short-distance cutoff, the choice of a vacuum state in
an inflating, non-de Sitter universe is unavoidably ambiguous. The ambiguity is
related to the time at which initial conditions for the mode functions are
specified and to the way the expansion of the universe affects those initial
conditions. In this paper we study the imprint of these uncertainties on the
predictions of inflation. We parametrize the most general set of possible
vacuum initial conditions by two phenomenological variables. We find that the
generated power spectrum receives oscillatory corrections whose amplitude is
proportional to the Hubble parameter over the cutoff scale. In order to further
constrain the phenomenological parameters that characterize the vacuum
definition, we study gravitational particle production during different
cosmological epochs.Comment: 10 two-column pages, 1 figure; uses RevTeX
Neural predictive control of broiler chicken and pig growth
Active control of the growth of broiler chickens and pigs has potential benefits for farmers in terms of improved production efficiency, as well as for animal welfare in terms of improved leg health in broiler chickens. In this work, a differential recurrent neural network (DRNN) was identified from experimental data to represent animal growth using a nonlinear system identification algorithm. The DRNN model was then used as the internal model for nonlinear model predictive control (NMPC) to achieve a group of desired growth curves. The experimental results demonstrated that the DRNN model captured the underlying dynamics of the broiler and pig growth process reasonably well. The DRNN based NMPC was able to specify feed intakes in real time so that the broiler and pig weights accurately followed the desired growth curves ranging from to +12% and to +20% of the standard curve for broiler chickens and pigs, respectively. The overall mean relative error between the desired and achieved broiler or pig weight was 1.8% for the period from day 12 to day 51 and 10.5% for the period from week 5 to week 21, respectively
Metabolic and Innate Immune Cues Merge into a Specific Inflammatory Response via the UPR
Erratum in : Metabolic and Innate Immune Cues Merge into a Specific Inflammatory Response via the UPR. [Cell. 2019]International audienceInnate immune responses are intricately linked with intracellular metabolism of myeloid cells. Toll-likereceptor (TLR) stimulation shifts intracellular metabolism toward glycolysis, while anti-inflammatorysignals depend on enhanced mitochondrial respiration. How exogenous metabolic signals affect theimmune response is unknown. We demonstrate that TLR-dependent responses of dendritic cells (DC)are exacerbated by a high fatty acid (FA) metabolic environment. FA suppress the TLR-inducedhexokinase activity and perturb tricarboxylic acid cycle metabolism. These metabolic changesenhance mitochondrial reactive oxygen species (mtROS) production and, in turn, the unfolded proteinresponse (UPR) leading to a distinct transcriptomic signature, with IL-23 as hallmark. Interestingly,chemical or genetic suppression of glycolysis was sufficient to induce this specific immune response.Conversely, reducing mtROS production or DC-specific deficiency in XBP1 attenuated IL-23expression and skin inflammation in an IL-23-dependent model of psoriasis. Thus, fine-tuning of innateimmunity depends on optimization of metabolic demands and minimization of mtROS-induced UPR
Adjustment for time-invariant and time-varying confounders in ‘unexplained residuals’ models for longitudinal data within a causal framework and associated challenges
‘Unexplained residuals’ models have been used within lifecourse epidemiology to model an exposure measured longitudinally at several time points in relation to a distal outcome. It has been claimed that these models have several advantages, including: the ability to estimate multiple total causal effects in a single model, and additional insight into the effect on the outcome of greater-than-expected increases in the exposure compared to traditional regression methods. We evaluate these properties and prove mathematically how adjustment for confounding variables must be made within this modelling framework. Importantly, we explicitly place unexplained residual models in a causal framework using directed acyclic graphs. This allows for theoretical justification of appropriate confounder adjustment and provides a framework for extending our results to more complex scenarios than those examined in this paper. We also discuss several interpretational issues relating to unexplained residual models within a causal framework. We argue that unexplained residual models offer no additional insights compared to traditional regression methods, and, in fact, are more challenging to implement; moreover, they artificially reduce estimated standard errors. Consequently, we conclude that unexplained residual models, if used, must be implemented with great care
Statefinder diagnostic and analysis for interacting polytropic gas dark energy model
The interacting polytropic gas dark energy model is investigated from the
viewpoint of statefinder diagnostic tool and analysis. The
dependency of the statefinder parameters on the parameter of the model as well
as the interaction parameter between dark matter and dark energy is calculated.
We show that different values of the parameters of model and different values
of interaction parameter result different evolutionary trajectories in
and planes. The polytropic gas model of dark energy mimics the
standard CDM model at the early time.Comment: 17 pages, 4 figures, ijtp accepte
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