Structural templating as a route to improved photovoltaic performance in copper phthalocyanine/fullerene (C60) heterojunctions

We have developed a method to improve the short circuit current density in copper phthalocyanine (CuPc)/fullerene (C60) organic solar cells by ~60% by modifying the CuPc crystal orientation through use of a molecular interlayer to maximize charge transport in the direction between the two electrodes. Powder x-ray diffraction and electronic absorption spectroscopy show that a thin 3,4,9,10-perylenetetracarboxylic dianhydride interlayer before CuPc growth templates the CuPc film structure, forcing the molecules to lie flat with respect to the substrate surface, although the intrastack orientation is unaffected. This modified stacking configuration facilitates charge transport and improves charge collection

The Conceptual Politics of Democracy Promotion: The Venezuela Case

In 1970 Giovanni Sartori articulated what he saw as the greatest challenge to political science in an increasingly globalized worldconceptual stretching. Sartori was referring to the traveling of western concepts eastward and proposed the use of a conceptual ladder to help inform the decisions political scientists make regarding the concepts they wish to travel. This paper seeks to push the boundaries of Sartori’s critique beyond academia to include policy; a subject where a dynamic and informative relationship between academia and policy should exist, but are instead faced with a one-dimensional arrangement. In that vein, this paper consists of three main parts. The first employs a brief historiography of the conceptual debate between, largely, Schumpeterian and Dahlian definitions of democracy where two main schools of thought will be sketched. The second evokes Venezuela's recent political history to illustrate how the United States Government has, at different times, employed various definitions, and standards, of democracy to describe the Venezuelan regime. The third seeks to establish how American oscillation between standards erodes the value reference point of democracy and draw out the implications of this. In particular, the third part unpacks what this erosion should mean moving forward for academics engaged in the conceptual politics of democracy. In sum, the instrumentalizing of the ambiguity of the concept—democracy—by oscillating between Schumpeterian and Dahlian standards devalues the concept. And unless the academic debate regarding democratic theory begins to account for this devaluation, democracy may well be emptied of its substance.

Application of the wave finite element method to reinforced concrete structures with damage

Vibration based methods are commonly deployed to detect structural damage using sensors placed remotely from potential damage sites. Whilst many such techniques are modal based there are advantages to adopting a wave approach, in which case it is essential to characterise wave propagation in the structure. The Wave Finite Element method (WFE) is an efficient approach to predicting the response of a composite waveguide using a conventional FE model of a just a short segment. The method has previously been applied to different structures such as laminated plates, thinwalled structures and fluid-filled pipes. In this paper, the WFE method is applied to a steel reinforced concrete beam. Dispersion curves and wave mode shapes are first presented from free wave solutions, and these are found to be insensitive to loss of thickness in a single reinforcing bar. A reinforced beam with localised damage is then considered by coupling an FE model of a short damaged segment into the WFE model of the undamaged beam. The fundamental bending, torsion and axial waves are unaffected by the damage but some higher order waves of the cross section are significantly reflected close to their cut-on frequencies. The potential of this approach for detecting corrosion and delamination in reinforced concrete beams will be investigated in future work

Crack growth of pre-preg laminate composite subjected to elevated temperature fatigue post ballistic impact

Please click Additional Files below to see the full abstrac

Wave propagation in reinforced and prestressed concrete structures with damage

Corrosion of the steel reinforcement bars in reinforced concrete is the most common cause of premature failure that must be pre-empted. In this respect, wave based techniques provide a potential detection approach. In this paper, wave propagation is modelled in a steel reinforced concrete beam with and without prestress. A short section of the beam is modelled in ANSYS. This model is then used in the wave finite element (WFE) framework, which assumes spatial periodicity along the waveguide, to model a beam of infinite extent. Corrosion of the reinforcement bars is represented by a local loss of thickness. Numerical case studies are presented to investigate the effects of various configurations and the severity of damage on the dispersion curves of the propagating waves. Scattering matrices are also calculated for the damage site, by coupling damaged and undamaged sections of the waveguide. Wave modes are subsequently identified for which the reflection coefficients are potentially sufficiently large to observe and use for damage identification

Characterization of s-SWCNT/PF-PD Dispersions and Networks

Single-Walled Carbon Nanotubes (SWCNTs) are being investigated for their use in a wide variety of renewable energy applications. Their unique physical properties contribute to desirable traits such as a high carrier mobility, strong optical absorption and tunable electronic band gap. Unfortunately, due to variability in certain parameters, SWCNTs are limited in their application. The major drawback is that SWCNTs are variable in size and type and typical synthetic methods are not selective. As a result, selective methods must be developed in order to sort these tubes and extract those which are desirable for a particular application. Though there are several enrichment strategies, polymer-wrapping was used to select semiconducting SWCNTs in this research. Some issues with polymer-wrapping include inability to remove polymer post-enrichment as well as difficulty re-dispersing SWCNTs post polymer removal. Polymer removal is necessary for certain applications and the presence of excess polymer in SWCNTs can decrease their efficiency. To address the first issue, a removable polymer, PF-PD was used in the dispersion making process. The second issue of re-dispersal was discovered to be specific to a particular batch of PF-PD and was combatted by altering the polymer removal step from a centrifuge run to a TFA vapor treatment. PF-PD is loosely linked by imine bonds which are degraded by the TFA and make it easier to remove. This process does require some refining, however, since a significant percentage of SWCNTs are lost during the treatment. Several other mini experiments were conducted throughout the course of this research to contribute to a better understanding of the quality of dispersions that could be made using PF-PD with unpurified SWCNTs. The results of these experiments are inconclusive but do lead to the need for further and more detailed research on SWCNTs

On the degree of varieties of sum of squares

We study the problem of how many different sums of squares decompositions a general polynomial $f$ with SOS-rank $k$ admits. We show that there is a link between the variety $\mathrm{SOS}_k(f)$ of all SOS-decompositions of $f$ and the orthogonal group $\mathrm{O}(k)$. We exploit this connection to obtain the dimension of $\mathrm{SOS}_k(f)$ and show that its degree is bounded from below by the degree of $\mathrm{O}(k)$. In particular, for $k=2$ we show that $\mathrm{SOS}_2(f)$ is isomorphic to $\mathrm{O}(2)$ and hence the degree bound becomes an equality. Moreover, we compute the dimension of the space of polynomials of SOS-rank $k$ and obtain the degree in the special case $k=2$

Paths to Recovery: Coordinated and Comprehensive Care for Landmine Survivors

By conducting interviews with survivors of landmine incidents, Landmine Survivors Network (LSN) has been able to learn a lot about rehabilitative needs from the perspective of the patients. This article describes how physical health, psychological well-being and socio-economic reintegration are all important components of a complete recovery for landmine victims

The dramatic size evolution of elliptical galaxies and the quasar feedback

Observations have evidenced that passively evolving massive galaxies at high redshift are much more compact than local galaxies with the same stellar mass. We argue that the observed strong evolution in size is directly related to the quasar feedback, which removes huge amounts of cold gas from the central regions in a Salpeter time, inducing an expansion of the stellar distribution. The new equilibrium configuration, with a size increased by a factor >~ 3, is attained after ~ 40 dynamical times, corresponding to ~ 2 Gyr. This means that massive galaxies observed at z >~ 1 will settle on the Fundamental Plane by z ~ 0.8-1. In less massive galaxies (M_star <~ 2 10^10 M_sun), the nuclear feedback is subdominant, and the mass loss is mainly due to stellar winds. In this case, the mass loss timescale is longer than the dynamical time and results in adiabatic expansion that may increase the effective radius by a factor of up to ~ 2 in 10 Gyr, although a growth by a factor of ~ 1.6 occurs within the first 0.5 Gyr. Since observations are focused on relatively old galaxies, with ages >~ 1 Gyr, the evolution for smaller galaxies is more difficult to perceive. Significant evolution of velocity dispersion is predicted for both small and large galaxies.Comment: 4 pages, 2 figures, uses REVTeX4 + emulateapj.cls and apjfonts.sty. Accepted by ApJ

Stellar Nucleosynthesis in the Hyades Open Cluster

We report a comprehensive light element (Li, C, N, O, Na, Mg, and Al) abundance analysis of three solar-type main sequence (MS) dwarfs and three red giant branch (RGB) clump stars in the Hyades open cluster using high-resolution and high signal-to-noise spectroscopy. For each group (MS or RGB), the CNO abundances are found to be in excellent star-to-star agreement. Our results confirm that the giants have undergone the first dredge-up and that material processed by the CN cycle has been mixed to the surface layers. The observed abundances are compared to predictions of a standard stellar model based on the Clemson-American University of Beirut (CAUB) stellar evolution code. The model reproduces the observed evolution of the N and O abundances, as well as the previously derived 12C/13C ratio, but it fails to predict by a factor of 1.5 the observed level of 12C depletion. Li abundances are derived to determine if non-canonical extra mixing has occurred in the Hyades giants. The Li abundance of the giant gamma Tau is in good accord with the predicted level of surface Li dilution, but a ~0.35 dex spread in the giant Li abundances is found and cannot be explained by the stellar model. Possible sources of the spread are discussed; however, it is apparent that the differential mechanism responsible for the Li dispersion must be unrelated to the uniformly low 12C abundances of the giants. Na, Mg, and Al abundances are derived as an additional test of our stellar model. All three elements are found to be overabundant by 0.2-0.5 dex in the giants relative to the dwarfs. Such large enhancements of these elements are not predicted by the stellar model, and non-LTE effects significantly larger (and, in some cases, of opposite sign) than those implied by extant literature calculations are the most likely cause.Comment: 40 pages, 6 figures, 6 tables; accepted by Ap