Warm Dark Haloes Accretion Histories and their Gravitational Signatures

We study clusters in Warm Dark Matter (WDM) models of a thermally produced dark matter particle $0.5$ keV in mass. We show that, despite clusters in WDM cosmologies having similar density profiles as their Cold Dark Matter (CDM) counterparts, the internal properties, such as the amount of substructure, shows marked differences. This result is surprising as clusters are at mass scales that are {\em a thousand times greater} than that at which structure formation is suppressed. WDM clusters gain significantly more mass via smooth accretion and contain fewer substructures than their CDM brethren. The higher smooth mass accretion results in subhaloes which are physically more extended and less dense. These fine-scale differences can be probed by strong gravitational lensing. We find, unexpectedly, that WDM clusters have {\em higher} lensing efficiencies than those in CDM cosmologies, contrary to the naive expectation that WDM clusters should be less efficient due to the fewer substructures they contain. Despite being less dense, the larger WDM subhaloes are more likely to have larger lensing cross-sections than CDM ones. Additionally, WDM subhaloes typically reside at larger distances, which radially stretches the critical lines associated with strong gravitational lensing, resulting in excess in the number of clusters with large radial cross-sections at the $\sim2\sigma$ level. Though lensing profile for an individual cluster vary significantly with the line-of-sight, the radial arc distribution based on a sample of $\gtrsim100$ clusters may prove to be the crucial test for the presence of WDM.Comment: 13 pages, 14 figures, submitted to MNRA

Hidden from view: Coupled Dark Sector Physics and Small Scales

We study cluster mass dark matter haloes, their progenitors and surroundings in an coupled Dark Matter-Dark Energy model and compare it to quintessence and $\Lambda$CDM models with adiabatic zoom simulations. When comparing cosmologies with different expansions histories, growth functions & power spectra, care must be taken to identify unambiguous signatures of alternative cosmologies. Shared cosmological parameters, such as $\sigma_8$, need not be the same for optimal fits to observational data. We choose to set our parameters to $\Lambda$CDM $z=0$ values. We find that in coupled models, where DM decays into DE, haloes appear remarkably similar to $\Lambda$CDM haloes despite DM experiencing an additional frictional force. Density profiles are not systematically different and the subhalo populations have similar mass, spin, and spatial distributions, although (sub)haloes are less concentrated on average in coupled cosmologies. However, given the scatter in related observables ($V_{\rm max},R_{V_{\rm max}}$), this difference is unlikely to distinguish between coupled and uncoupled DM. Observations of satellites of MW and M31 indicate a significant subpopulation reside in a plane. Coupled models do produce planar arrangements of satellites of higher statistical significance than $\Lambda$CDM models, however, in all models these planes are dynamically unstable. In general, the nonlinear dynamics within and near large haloes masks the effects of a coupled dark sector. The sole environmental signature we find is that small haloes residing in the outskirts are more deficient in baryons than their $\Lambda$CDM counterparts. The lack of a pronounced signal for a coupled dark sector strongly suggests that such a phenomena would be effectively hidden from view.Comment: 13 pages, 14 figures, 2 tables, accepted for publication in MNRA

Impulse Photothermal Evaluation of Materials Via Frequency Modulated Optical Reflectance II: Experimental

Recently, a powerful method of photothermal detection was reported which enabled thermal wave imaging to be carried out on micron sized structures in semiconductors [1,2]. The new method utilized the photothermally induced modulation of the sample’s surface optical reflectivity to detect thermal wave phenomena at bandwidths exceeding 10 MHz. The wide bandwidth capabilities of the method enabled very shallow structures to be analyzed in semiconducting materials because of the relationship that exists between the modulation frequency of the excitation beam and the thermal diffusion length

CROP RESIDUE EFFECTS ON SOIL ENVIRONMENT AND DRYLAND MAIZE AND SOYA BEAN PRODUCTION

The research reported here provides data on the effects of crop residues on the surface of no-till soil upon the soil environment and resulting biological activity, including crop growth. For maize (Zea mays L.) and soya bean [Glycine max (L.) Merr.] production in eastern Nebraska, U.S.A. (4 years of data), increasing crop residue rate decreased maximum soil temperatures at the soil surface by at least 5°C, and generally increased soil water storage by at least 50 mm. Availability and uptake of nitrogen from the soil organic matter and applied fertilizers (and for soya bean from decomposition of crop residues) were increased by increasing the crop residue rate from 0 to 150% of the quantity left after grain harvest of the previous crop. Hardly any of the nitrogen in maize residues was used by the next crop. These changes in the soil environment resulted in less stress on crops produced on residue-covered soil than for those on bare soil. Consequently, each Mg ha-1 of crop residues on the soil surface increased grain and stover production by approximately 120 and 270 kg ha-1 for maize, and 90 and 300 kg ha-1 for soya bean, respectively. Results show that there are major direct crop growth benefits from leaving crop residues on the soil surface, in addition to cumulative benefits that may result from reduced erosion losses and enhanced soil organic-matter contents

Classifying Crises-Information Relevancy with Semantics

Social media platforms have become key portals for sharing and consuming information during crisis situations. However, humanitarian organisations and affected communities often struggle to sieve through the large volumes of data that are typically shared on such platforms during crises to determine which posts are truly relevant to the crisis, and which are not. Previous work on automatically classifying crisis information was mostly focused on using statistical features. However, such approaches tend to be inappropriate when processing data on a type of crisis that the model was not trained on, such as processing information about a train crash, whereas the classifier was trained on floods, earthquakes, and typhoons. In such cases, the model will need to be retrained, which is costly and time-consuming. In this paper, we explore the impact of semantics in classifying Twitter posts across same, and different, types of crises. We experiment with 26 crisis events, using a hybrid system that combines statistical features with various semantic features extracted from external knowledge bases. We show that adding semantic features has no noticeable benefit over statistical features when classifying same-type crises, whereas it enhances the classifier performance by up to 7.2% when classifying information about a new type of crisis

Gravitational Geons Revisited

A careful analysis of the gravitational geon solution found by Brill and Hartle is made. The gravitational wave expansion they used is shown to be consistent and to result in a gauge invariant wave equation. It also results in a gauge invariant effective stress-energy tensor for the gravitational waves provided that a generalized definition of a gauge transformation is used. To leading order this gauge transformation is the same as the usual one for gravitational waves. It is shown that the geon solution is a self-consistent solution to Einstein's equations and that, to leading order, the equations describing the geometry of the gravitational geon are identical to those derived by Wheeler for the electromagnetic geon. An appendix provides an existence proof for geon solutions to these equations.Comment: 18 pages, ReVTeX. To appear in Physical Review D. Significant changes include more details in the derivations of certain key equations and the addition of an appendix containing a proof of the existence of a geon solution to the equations derived by Wheeler. Also a reference has been added and various minor changes have been mad