3,558 research outputs found
Spectral distortions from the dissipation of tensor perturbations
Spectral distortions of the cosmic microwave background (CMB) may become a
powerful probe of primordial perturbations at small scales. Existing studies of
spectral distortions focus almost exclusively on primordial scalar metric
perturbations. Similarly, vector and tensor perturbations should source CMB
spectral distortions. In this paper, we give general expressions for the
effective heating rate caused by these types of perturbations, including
previously neglected contributions from polarization states and higher
multipoles. We then focus our discussion on the dissipation of tensors, showing
that for nearly scale invariant tensor power spectra, the overall distortion is
some six orders of magnitudes smaller than from the damping of adiabatic scalar
modes. We find simple analytic expressions describing the effective heating
rate from tensors using a quasi-tight coupling approximation. In contrast to
adiabatic modes, tensors cause heating without additional photon diffusion and
thus over a wider range of scales, as recently pointed out by Ota et. al 2014.
Our results are in broad agreement with their conclusions, but we find that
small-scale modes beyond k< 2x10^4 Mpc^{-1} cannot be neglected, leading to a
larger distortion, especially for very blue tensor power spectra. At small
scales, also the effect of neutrino damping on the tensor amplitude needs to be
included.Comment: 14 pages, 7 figures, accepted version (MNRAS
ScanComplete: Large-Scale Scene Completion and Semantic Segmentation for 3D Scans
We introduce ScanComplete, a novel data-driven approach for taking an
incomplete 3D scan of a scene as input and predicting a complete 3D model along
with per-voxel semantic labels. The key contribution of our method is its
ability to handle large scenes with varying spatial extent, managing the cubic
growth in data size as scene size increases. To this end, we devise a
fully-convolutional generative 3D CNN model whose filter kernels are invariant
to the overall scene size. The model can be trained on scene subvolumes but
deployed on arbitrarily large scenes at test time. In addition, we propose a
coarse-to-fine inference strategy in order to produce high-resolution output
while also leveraging large input context sizes. In an extensive series of
experiments, we carefully evaluate different model design choices, considering
both deterministic and probabilistic models for completion and semantic
inference. Our results show that we outperform other methods not only in the
size of the environments handled and processing efficiency, but also with
regard to completion quality and semantic segmentation performance by a
significant margin.Comment: Video: https://youtu.be/5s5s8iH0NF
Search for Compensated Isocurvature Perturbations with Planck Power Spectra
In the standard inflationary scenario, primordial perturbations are
adiabatic. The amplitudes of most types of isocurvature perturbations are
generally constrained by current data to be small. If, however, there is a
baryon-density perturbation that is compensated by a dark-matter perturbation
in such a way that the total matter density is unperturbed, then this
compensated isocurvature perturbation (CIP) has no observable consequence in
the cosmic microwave background (CMB) at linear order in the CIP amplitude.
Here we search for the effects of CIPs on CMB power spectra to quadratic order
in the CIP amplitude. An analysis of the Planck temperature data leads to an
upper bound , at the 68\% confidence
level, to the variance of the CIP amplitude. This is then
strengthened to if Planck
small-angle polarization data are included. A cosmic-variance-limited CMB
experiment could improve the sensitivity to CIPs to . It is also found that adding CIPs to the
standard CDM model can improve the fit of the observed smoothing of
CMB acoustic peaks just as much as adding a non-standard lensing amplitude.Comment: 9 Pages, 3 Tables, 6 Figures. Accepted in PR
Spatial aspects of the design and targeting of agricultural development strategies:
Two increasingly shared perspectives within the international development community are that (a) geography matters, and (b) many government interventions would be more successful if they were better targeted. This paper unites these two notions by exploring the opportunities for, and benefits of, bringing an explicitly spatial dimension to the tasks of formulating and evaluating agricultural development strategies. We first review the lingua franca of land fragility and find it lacking in its capacity to describe the dynamic interface between the biophysical and socioeconomic factors that help shape rural development options. Subsequently, we propose a two-phased approach. First, development strategy options are characterized to identify the desirable ranges of conditions that would most favor successful strategy implementation. Second, those conditions exhibiting important spatial dependency – such as agricultural potential, population density, and access to infrastructure and markets – are matched against a similarly characterized, spatially-referenced (GIS) database. This process generates both spatial (map) and tabular representations of strategy-specific development domains. An important benefit of a spatial (GIS) framework is that it provides a powerful means of organizing and integrating a very diverse range of disciplinary and data inputs. At a more conceptual level we propose that it is the characterization of location, not the narrowly-focused characterization of land, that is more properly the focus of attention from a development perspective. The paper includes appropriate examples of spatial analysis using data from East Africa and Burkina Faso, and concludes with an appendix describing and interpreting regional climate and soil data for Sub-Saharan Africa that was directly relevant to our original goal.Spatial analysis (Statistics), Agricultural development., Burkina Faso., Africa, Sub-Saharan.,
Inflating bacterial cells by increased protein synthesis.
Understanding how the homeostasis of cellular size and composition is accomplished by different organisms is an outstanding challenge in biology. For exponentially growing Escherichia coli cells, it is long known that the size of cells exhibits a strong positive relation with their growth rates in different nutrient conditions. Here, we characterized cell sizes in a set of orthogonal growth limitations. We report that cell size and mass exhibit positive or negative dependences with growth rate depending on the growth limitation applied. In particular, synthesizing large amounts of "useless" proteins led to an inversion of the canonical, positive relation, with slow growing cells enlarged 7- to 8-fold compared to cells growing at similar rates under nutrient limitation. Strikingly, this increase in cell size was accompanied by a 3- to 4-fold increase in cellular DNA content at slow growth, reaching up to an amount equivalent to ~8 chromosomes per cell. Despite drastic changes in cell mass and macromolecular composition, cellular dry mass density remained constant. Our findings reveal an important role of protein synthesis in cell division control
Inexact Proximal-Gradient Methods with Support Identification
We consider the proximal-gradient method for minimizing an objective function
that is the sum of a smooth function and a non-smooth convex function. A
feature that distinguishes our work from most in the literature is that we
assume that the associated proximal operator does not admit a closed-form
solution. To address this challenge, we study two adaptive and implementable
termination conditions that dictate how accurately the proximal-gradient
subproblem is solved. We prove that the number of iterations required for the
inexact proximal-gradient method to reach a approximate first-order
stationary point is , which matches the similar result
that holds when exact subproblem solutions are computed. Also, by focusing on
the overlapping group regularizer, we propose an algorithm for
approximately solving the proximal-gradient subproblem, and then prove that its
iterates identify (asymptotically) the support of an optimal solution. If one
imposes additional control over the accuracy to which each subproblem is
solved, we give an upper bound on the maximum number of iterations before the
support of an optimal solution is obtained
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