Transport in correlated and uncorrelated random media, with applications to molecularly doped polymers

The commonly observed Poole-Frenkel field dependence; of the mobility of photo-injected charges in molecularly-doped polymers has been shown to arise from the spatially-correlated, Gaussian energy distribution of transport sites encountered by charges moving through the material. Experimental current-time transients obtained for molecularly-doped polymers exhibit universality with respect to electric field and a metal-insulator-like transition from non-dispersive to dispersive transport, features usually identified with multiple trapping models that assume an uncorrelated exponential distribution of trap energies. For materials that exhibit both sets of features the possibility arises that both kinds of disorder coexist. We study here, analytically and numerically, transport in a random medium containing two kinds of energetic disorder, i.e., a spatially correlated Gaussian component and a spatially uncorrelated exponential component associated with traps. The essential question addressed is the degree to which the uncorrelated component of disorder alters or destroys the Poole-Frenkel field dependence associated with the correlated component. In our hybrid model, the bulk mobility theoretically drops to zero when the typical trap depth exceeds the thermal energy, causing a metal-insulator-like transition. In a finite sample this corresponds to a transition to the dispersive transport regime, in which carriers can never equilibrate. For a finite 3D computational sample, the behavior above and below the transition point shows different finite size scaling with the number of sites in the lattice. In agreement with experimental observations, the Poole-Frenkel field dependence of the charge carrier mobility, and the associated temperature dependence observed in a trap-free sample, is unaffected as the transition to dispersive transport is approached from the conducting side --Abstract, page iii

Multiple cerebral cavernous malformations in association with a Dubowitz-like syndrome.

Cerebral cavernous malformations (CCMs) are proliferative sinusoidal vascular lesions and are the most common vascular malformations of the brain. They can occur sporadically or secondary to an underlying genetic predisposition where multiple lesions are commonly seen. Dubowitz syndrome is a clinically-diagnosed rare genetic disorder with an unknown molecular basis. An association between these conditions has not been reported previously. A 30-year-old woman with a Dubowitz-like syndrome presented with acute left leg weakness, gait ataxia and transient loss of consciousness. Imaging revealed five CCMs with recent hemorrhage in relation to one lesion in the left middle cerebellar peduncle. A recurrent hemorrhage from the same lesion occurred ten weeks later and she underwent microsurgical excision of this malformation. Genetic analysis revealed an unbalanced chromosomal rearrangement involving partial deletion of chromosome 7q21, the locus of the CCM1/KRIT1 gene known to be associated with familial CCMs. This is the first description of CCMs in association with the Dubowitz phenotype. The genetic basis of Dubowitz syndrome may be heterogeneous but, for the first time, overlap is demonstrated between this condition and multiple CCMs, with a possible common genetic etiology. Knowledge of this association may be of help in the management of acute neurological presentations in Dubowitz-like syndromes. Keywords: Hemangioma, Cavernous, Central nervous system, Dubowitz syndrome, Genetics

Molecular electronic environment from methyl torsion and 14n quadrupole coupling

Methyl rotors are sensitive indicators of the local and non-local electronic environment, so a study of methyl torsional barriers at different sites around the perimeter of a conjugated ring system may reveal electronic environment of the indole ring. Previously reported results$^{a}$ are limited to microwave spectroscopic identification of the 1-methylindole, 2-methylindole, 3-methylindole, and 5-methylindole. The new measurements of 4-methylindole, 6-methylindole, and 7-methylindole complete the series. Over one thousand transitions were assigned in the 10.5 – 21 GHz frequency range, resolving both nuclear quadrupole coupling and methyl internal rotation for all seven species. Electronic structure calculations at MP2/6-311++G(d,p) level, torsional barrier calculations and molecular electrostatic potential maps at $\omega$B97XD/6-311++G(d,p) level are used along with the experimental data. $^{14}$N nuclear quadrupole coupling tensor elements were used to determine the ionic character of the NH sigma bond, $\pi$ bonding character of the nitrogen p$_{z}$ orbital, and the amount of negative charge on the nitrogen of each methylindole. Fitted torsional barriers were compared with theoretical investigations of the origin of methyl torsional barriers to confirm that overall barrier arises from both hyperconjugative interactions and structural interactions of bonding and anti-bonding orbitals. \bigskip $^{a}$R. M. Gurusinghe, M. J. Tubergen. 69$^{th}$ International Symposium of Molecular Spectroscopy, Urbana-Champaign, IL, 2014, RJ03

Composition-Tunable Properties Of CdSxTe1-x Alloy Nanocrystals

Ternary CdSxTe1-x semiconductor quantum dots with both homogeneous and gradient composition have been fabricated via pyrolysis of organometallic precursors. The nanocrystal structure, size, and composition were characterized by UV-visible absorption and fluorescence spectroscopy, transmission electron microscopy, energy-dispersive X-ray elemental analysis, and X-ray diffractrometry. It was found that the band gap of homogeneously alloyed CdSxTe1-x is highly nonlinear with the crystalline composition, which was evidenced by a significant red-shift in the fluorescence of these nanocrystals with respect to the emission wavelength of their CdS and CdTe binary compounds. This effect, also known as optical bowing, seems to be enhanced in CdSxTe1-x nanocrystals because of large differences in atomic radii and electronegativities of S and Te chalcogens. Properties of gradient ternary alloys were found to be markedly different from those of homogeneous CdSxTe1-x. Their absorption and emission profiles, for instance, had a relatively low spectral overlap leading to large Stokes shifts of up to 150 nm. Other properties of fabricated CdSxTe1-x, nanocrystals and their significance to applications in areas of biomedical imaging, solar cells, and quantum dot-based LEDs are discussed

Blue-shifted Emission in CdTe/ZnSe Heterostructured Nanocrystals

Properties of colloidal heterostructured nanocrystals are largely determined by the spatial distribution of photogenerated carriers across the junction of semiconductor materials that form the heterostructure. The two known types of carrier distributions are identified based on whether both carriers reside within the same (type I) or opposite (type II) sides of the heterojunction. Here we demonstrate the existence of another type of spatial carrier distribution in heteronanocrystals, which corresponds to the localization of both charges along the material junction. Such localization. pattern was realized in novel CdTe/ZnSe heteronanocrystals, where the expected type I infrared emission was dominated by more intense photoluminescence in the 570-600 nm range, corresponding to the recombination of carriers within an interfacial alloy layer, formed by the cation and anion exchange between CdTe and ZnSe phases. Fabricated heteronanocrystals exhibit excellent optical characteristics including near-single-exponential lifetimes, enhanced emission stability, and fluorescence emission quantum yields of up to 24%

Fractionation of Heavy Metals by BCR Sequential Extraction in Coastal Marine Sediments around Colombo Harbour

Marine environment around the Colombo harbour is prone to heavy coastal marine pollutiondue to heavy ship traffic, spilled oils, maintenance and repair of ships. Land based marinepollution is prominent near the coast of Kelani river estuary due to the fact that the rivercarries land run-offs, urban and domestic debris, industrial effluents, and agricultural wastesdumped directly into it. Lead (Pb), chromium (Cr), nickel (Ni), copper (Cu) and zinc (Zn)are some of the heavy metals that have a tendency to accumulate in food chains originatefrom the sea. However, the heavy metal should be present in bioavailable forms to be enteredin to biological systems. Thus the fractionation of heavy metals into four fractions (water andacid soluble, reducible, oxidisable, and residual) by the modified BCR (European CommunityBureau of Reference) sequential extraction procedure prior to the analysis is a better way ofinterpreting heavy metal pollution in marine sediments.In this study, field sampling was carried out twice in six locations adjacent to Colombo portin October 2011 (batch 1) and in March 2012 (batch 2) at the depth of 9-20 m depending onthe location and the season. Metal fractionation was done according to modified BCRprocedure and five elements (Pb, Cr, Ni, Cu, and Zn) were analysed by flame atomicabsorption spectroscopy (FAAS).The sum of three steps of BCR and residue analysis were in good agreement with the totalmetal content obtained by aqua regia digestion followed by the FAAS analysis via standardaddition method. The results showed that the levels of heavy metals vary widely by metal, bysampling site as well as by batch. Obtained results were compared with U.S.EPA-Region V,sediment quality criteria for concentration limits of heavy metal contaminants in sediments.The total metal contents in sediments of all metals except for Pb were above moderatelypolluted or polluted levels. More than 50% of total Cu and Cr contents were in residual andoxidisable fractions. Distribution of Ni and Zn did not have a clear pattern. Bioavailablemetal contents of all five metals under investigation were below the risk levels provided byUS EPA sediment quality criteria, except for Ni in one location and Zn in two locations.Marine sediments, BCR Sequential extraction, Heavy metals, AAS

A COMPARISON OF BARRIER TO METHYL INTERNAL ROTATION OF METHYLSTYRENES: MICROWAVE SPECTROSCOPIC STUDY

Rotational spectra of $alpha$-Methylstyrene, cis-$beta$-Methylstyrene, and trans-$beta$-Methylstyrene were examined to investigate their intrinsic tunneling properties. Theoretical calculations at wB97XD/6-311++G(d,p) level predict only one stable conformer for each molecular system. Spectra were recorded in the frequency range of 10.5 - 22.0 GHz using a cavity based Fourier transform microwave spectrometer. A relaxed potential scan for the methyl torsion at wB97XD/6-311++G(d,p) level of theory was used to estimate the associated barrier for the hindered internal rotation. The program XIAM was used to fit the rotational constants, distortion constants and barrier to methyl internal rotation to the measured transition frequencies of the A and E internal rotation states

GAS PHASE CONFORMATIONS AND METHYL INTERNAL ROTATION FOR 2-PHENYLETHYL METHYL ETHER AND ITS ARGON VAN DER WAALS COMPLEX FROM FOURIER TRANSFORM MICROWAVE SPECTROSCOPY

A mini-cavity microwave spectrometer was used to record the rotational spectra arising from 2-phenylethyl methyl ether and its weakly bonded argon complex in the frequency range of 10.5 � 22 GHz. Rotational spectra were found for two stable conformations of the monomer: anti-anti and gauche-anti, which are 1.4 kJ mol$^{-1}$ apart in energy at wB97XD/6-311++G(d,p) level. Doubled rotational transitions, arising from internal motion of the methyl group, were observed for both conformers. The program XIAM was used to fit the rotational constants, centrifugal distortion constants, and barrier to internal rotation to the measured transition frequencies of the A and E internal rotation states. The best global fit values of the rotational constants for the anti-anti conformer are A= 3799.066(3) MHz, B= 577.95180(17) MHz, C= 544.7325(3) MHz and the A state rotational constants of the gauche-anti conformer are A= 2676.1202(7) MHz, B= 760.77250(2) MHz, C= 684.78901(2) MHz. The rotational spectrum of 2-phenylethyl methyl ether � argon complex is consistent with the geometry where argon atom lies above the plane of the benzene moiety of gauche-anti conformer. Tunneling splittings were too small to resolve within experimental accuracy, likely due to an increase in three fold potential barrier when the argon complex is formed. Fitted rotational constants are A= 1061.23373(16) MHz, B= 699.81754(7) MHz, C= 518.33553(7) MHz. The lowest energy solvated ether - water complex with strong intermolecular hydrogen bonding has been identified theoretically. Progress on the assignment of the water complex will also be presented

Combination of LiCs and EDLCs with Batteries: A New Paradigm of Hybrid Energy Storage for Application in EVs

The research presented in this paper proposes a hybrid energy storage system that combines both electrolytic double-layer capacitors (EDLCs) also known as supercapacitors (SCs) and lithium-ion capacitors (LiCs) also known as hybrid capacitors (HCs) with a battery through a multiple input converter. The proposal was verified in simulation and validated by implementing a laboratory prototype. A new hybridisation topology, which reduces the amount of resource requirement when compared to the conventional hybridisation topology, is introduced. An electric vehicle (EV) current profile from previous research was used to test the performance of the proposed topology. From the results obtained, the hybridisation topology proposed in this research had the lowest cost per unit power at 14.81 $/kW, the lowest cost per unit power to energy, and available power to energy ratio, both at 1:1.3, thus making it a more attractive hybridisation topology than the two conventional alternatives. The multiple input converter built had efficiency values in excess of 80%. The key take away from this paper is that using the proposed hybridisation topology, the battery is less often required to supply energy to the electric vehicle, and so, its cycle life is preserved. Furthermore, since the battery is not used for the repeated acceleration and deceleration in the entire driving cycle, the battery’s cycle life is further preserved. Furthermore, since the battery is not the only storage device in the energy storage system, it can be further downsized to best fit the required base load therefore, leading to a more optimized energy storage system by reducing the weight and volume of space occupied by the energy storage system, while also achieving better efficiencies. Document type: Articl