Constraining Perturbative Early Dark Energy with Current Observations

In this work, we study a class of early dark energy (EDE) models, in which, unlike in standard DE models, a substantial amount of DE exists in the matter-dominated era, self-consistently including DE perturbations. Our analysis shows that, marginalizing over the non DE parameters such as $Omega_m, H_0, n_s$, current CMB observations alone can constrain the scale factor of transition from early DE to late time DE to $a_t \geq 0.44$ and width of transition to $Delta_t \leq 0.37$. The equation of state at present is somewhat weakly constrained to $w_0 \leq -0.6$, if we allow $H_0 < 60$ km/s/Mpc. Taken together with other observations, such as supernovae, HST, and SDSS LRGs, the constraints are tighter-- $w_0 \leq -0.9, a_t \leq 0.19, \Delta_t \leq 0.21$. The evolution of the equation of state for EDE models is thus close to $\Lambda$CDM at low redshifts. Incorrectly assuming DE perturbations to be negligible leads to different constraints on the equation of state parameters, thus highlighting the necessity of self-consistently including DE perturbations in the analysis. If we allow the spatial curvature to be a free parameter, then the constraints are relaxed to $w_0 \leq -0.77, a_t \leq 0.35, \Delta_t \leq 0.35$ with $-0.014 < \Omega_{\kappa} < 0.031$ for CMB+other observations. For perturbed EDE models, the $2\sigma$ lower limit on $\sigma_8$ ($\sigma_8 \geq 0.59$) is much lower than that in $\Lambda$CDM ($\sigma_8 \geq 0.72$), thus raising the interesting possibility of discriminating EDE from $\Lambda$CDM using future observations such as halo mass functions or the Sunyaev-Zeldovich power spectrum.Comment: 12 pages, 5 figures, references updated, accepted for publication in Ap

Financing behavior of R&D investments in the emerging markets : the role of alliance and financial system

This paper examines the financing behaviour of R&D investments in emerging markets. Drawing on institutional theory and using panel data of generalized methods of moment (GMM) estimation for a sample of 302 firms from 20 countries during the period 2003-2015, we find that emerging market firms tend to use internal funds for financing R&D investments. Interesting results emerged when the sample was divided as alliance and non-alliance firms, and bank-based and market-based financial systems. The results show that R&D financing behaves differently for alliance and non-alliance firms. Alliance firms use both internal and external funds for R&D investments, while non-alliance firms do not use external funds. We also document that a country’s financial system influences the choice of available sources of finance. Firms from countries that follow a bank-based financial system tend to rely on external funds while firms from countries that follow a market-based financial system depend more on internal funds for financing R&D investments. This study is important as it provides new evidence on financing R&D investments in emerging countries taking into account the institutional arguments of financing choices, and so should guide stakeholders about appropriate sources of R&D financing

Terahertz single pixel imaging based on a Nipkow disk

We describe a terahertz single pixel imaging system based on a Nipkow disk. Nipkow disks have been used for fast scanning imaging systems since the first experimental television was invented in 1926. In our work, a Nipkow disk with 24 scanning lines was used to provide an axial resolution of 2 mm/pixel. We also show that by implementing a microscanning technique the axial resolution can be further improved to 0.5 mm/pixel. Imaging of several objects was demonstrated to show that this simple scanning system is promising for fast and/or real time terahertz imaging applications

Baseline study in environmental risk assessment: Escalating need for computer models to be whole-system approach

This is the author accepted manuscript. The final version is available from the publisher via the DOI in this record.Accepted author version posted online: 12 Dec 2016Despite landfills having the potential to pollute the environment both during their operation and long after they have ceased to receive waste, they remain a dominant waste management option, particularly in the UK. In order to combat the environmental pollution caused by landfills, risk analysis is increasingly being employed through computer models. However, for a risk analysis process to be successful, its foundation has to be well established through a baseline study. This paper aims to identify knowledge gaps in software packages regarding environmental risk assessments in general, and especially those that have been developed specifically for landfills and landfill leachate. The research establishes that there is no holistic computer model for the baseline study of landfills, which risk assessors can use to conduct risk analyses specifically for landfill leachate. This paper also describes a number of factors and features that should be added to the baseline study system in order to render it more integrated—thereby enhancing quantitative risk analysis, and subsequently environmental risk management.The authors acknowledge the financial support of Dundee City Council in this project. We are additionally grateful for the discussion and help received from Mr Peter Goldie of the Environment & Consumer Protection Department, Dundee City Council. The support from Dr I. M. Spence (Consultant Environmental Geologist, Scotland), and colleagues at the University of Abertay Dundee, including Dr Kehinde O. K. Oduyemi and Mr Phillip Jenkins is also highly 39 appreciated. It must be noted that concepts and ideas presented in this article by the authors do not necessarily represent views that of their respective employer organization

Microstructural and mechanical properties analysis of extruded Sn–0.7Cu solder alloy

AbstractThe properties and performance of lead-free solder alloys such as fluidity and wettability are defined by the alloy composition and solidification microstructure. Rapid solidification of metallic alloys is known to result in refined microstructures with reduced microsegregation and improved mechanical properties of the final products as compared to normal castings. The rapidly solidified Sn-based solders by melt spinning were shown to be suitable for soldering with low temperature and short soldering duration. In the present study, rapidly solidified Sn–0.7wt.%Cu droplets generated by impulse atomization (IA) were achieved as well as directional solidification under transient conditions at lower cooling rate. This paper reports on a comparative study of the rapidly solidified and the directionally solidified samples. Different but complementary characterization techniques were used to fully analyze the solidification microstructures of the samples obtained under the two cooling regimes. These include X-ray diffractometry (XRD) and scanning electron microscopy (SEM). In order to compare the tensile strength and elongation to fracture of the directionally solidified ingot and strip castings with the atomized droplet, compaction and extrusion of the latter were carried out. It was shown that more balanced and superior tensile mechanical properties are available for the hot extruded samples from compacted as-atomized Sn–0.7wt.%Cu droplets. Further, elongation-to-fracture was 2–3× higher than that obtained for the directionally solidified samples

Reconstructing the potentials for the quintessence and tachyon dark energy, from the holographic principle

We propose an holographic quintessence and tachyon models of dark energy. The correspondence between the quintessence and tachyon energy densities with the holographic density, allows the reconstruction of the potentials and the dynamics for the quintessence and tachyon fields, in flat FRW background. The proposed infrared cut-off for the holographic energy density works for two cases of the constant $\alpha$: for $\alpha<1$ we reconstructed the holographic quintessence model in the region before the $\omega=-1$ crossing for the EoS parameter. The cosmological dynamics for $\alpha>1$ was also reconstructed for the holographic quintessence and tachyon models.Comment: 21 pages, 18 figures, 2 table

An improved optimization technique for estimation of solar photovoltaic parameters

The nonlinear current vs voltage (I-V) characteristics of solar PV make its modelling difficult. Optimization techniques are the best tool for identifying the parameters of nonlinear models. Even though, there are different optimization techniques used for parameter estimation of solar PV, still the best optimized results are not achieved to date. In this paper, Wind Driven Optimization (WDO) technique is proposed as the new method for identifying the parameters of solar PV. The accuracy and convergence time of the proposed method is compared with results of Pattern Search (PS), Genetic Algorithm (GA), and Simulated Annealing (SA) for single diode and double diode models of solar PV. Furthermore, for performance validation, the parameters obtained through WDO are compared with hybrid Bee Pollinator Flower Pollination Algorithm (BPFPA), Flower Pollination Algorithm (FPA), Generalized Oppositional Teaching Learning Based Optimization (GOTLBO), Artificial Bee Swarm Optimization (ABSO), and Harmony Search (HS). The obtained results clearly reveal that WDO algorithm can provide accurate optimized values with less number of iterations at different environmental conditions. Therefore, the WDO can be recommended as the best optimization algorithm for parameter estimation of solar PV

On Smooth Orthogonal and Octilinear Drawings: Relations, Complexity and Kandinsky Drawings

We study two variants of the well-known orthogonal drawing model: (i) the smooth orthogonal, and (ii) the octilinear. Both models form an extension of the orthogonal, by supporting one additional type of edge segments (circular arcs and diagonal segments, respectively). For planar graphs of max-degree 4, we analyze relationships between the graph classes that can be drawn bendless in the two models and we also prove NP-hardness for a restricted version of the bendless drawing problem for both models. For planar graphs of higher degree, we present an algorithm that produces bi-monotone smooth orthogonal drawings with at most two segments per edge, which also guarantees a linear number of edges with exactly one segment.Comment: Appears in the Proceedings of the 25th International Symposium on Graph Drawing and Network Visualization (GD 2017