The gauge including magnetically induced current method

An overview of applications of the recently developed gauge including magnetically induced current method (GIMIC) is presented. The GIMIC method is used to obtain magnetically induced current densities in molecules. It provides detailed information about electron delocalization, aromatic character, and current pathways in molecules. The method has been employed in aromaticity studies on hydrocarbons, complex multi-ring organic nanorings, M?bius twisted molecules, inorganic and all-metal molecular rings and open-shell species. Recent studies on hydrogen-bonded molecules indicate that GIMIC can also be used to estimate hydrogen-bond strengths without fragmentation of the system. Preliminary results are presented on the applicability of GIMIC for investigating current transport in molecules attached to clusters simulating molecular conductivity measurements. Advantages and limitations of the GIMIC method are reviewed and discussed.     

A theoretical and experimental study on translational and internal energies of H2O and OH from the 157 nm irradiation of amorphous solid water at 90 K

The photodesorption of H(2)O in its vibrational ground state, and of OH radicals in their ground and first excited vibrational states, following 157 nm photoexcitation of amorphous solid water has been studied using molecular dynamics simulations and detected experimentally by resonance-enhanced multiphoton ionization techniques. There is good agreement between the simulated and measured energy distributions. In addition, signals of H(+) and OH(+) were detected in the experiments. These are inferred to originate from vibrationally excited H(2)O molecules that are ejected from the surface by two distinct mechanisms: a direct desorption mechanism and desorption induced by secondary recombination of photoproducts at the ice surface. This is the first reported experimental evidence of photodesorption of vibrationally excited H(2)O molecules from water ice.     

Structure and dynamics of the fast lithium ion conductor "Li7La3Zr2O12"

The solid lithium-ion electrolyte "Li(7)La(3)Zr(2)O(12)" (LLZO) with a garnet-type structure has been prepared in the cubic and tetragonal modification following conventional ceramic syntheses routes. Without aluminium doping tetragonal LLZO was obtained, which shows a two orders of magnitude lower room temperature conductivity than the cubic modification. Small concentrations of Al in the order of 1 wt% were sufficient to stabilize the cubic phase, which is known as a fast lithium-ion conductor. The structure and ion dynamics of Al-doped cubic LLZO were studied by impedance spectroscopy, dc conductivity measurements, (6)Li and (7)Li NMR, XRD, neutron powder diffraction, and TEM precession electron diffraction. From the results we conclude that aluminium is incorporated in the garnet lattice on the tetrahedral 24d Li site, thus stabilizing the cubic LLZO modification. Simulations based on diffraction data show that even at the low temperature of 4 K the Li ions are blurred over various crystallographic sites. This strong Li ion disorder in cubic Al-stabilized LLZO contributes to the high conductivity observed. The Li jump rates and the activation energy probed by NMR are in very good agreement with the transport parameters obtained from electrical conductivity measurements. The activation energy E(a) characterizing long-range ion transport in the Al-stabilized cubic LLZO amounts to 0.34 eV. Total electric conductivities determined by ac impedance and a four point dc technique also agree very well and range from 1 × 10(-4) Scm(-1) to 4 × 10(-4) Scm(-1) depending on the Al content of the samples. The room temperature conductivity of Al-free tetragonal LLZO is about two orders of magnitude lower (2 × 10(-6) Scm(-1), E(a) = 0.49 eV activation energy). The electronic partial conductivity of cubic LLZO was measured using the Hebb-Wagner polarization technique. The electronic transference number t(e-) is of the order of 10(-7). Thus, cubic LLZO is an almost exclusive lithium ion conductor at ambient temperature.     

Surface induced changes in coumarin solvation and photochemistry at polar solid/liquid interfaces

Steady state and time-resolved fluorescence measurements compare the photophysical properties of Coumarin 152 (C152) and Coumarin 461 (C461) in bulk methanol solution and adsorbed to silica/vapor and silica/methanol interfaces. C152 and C461 share the same structure except for a -CF(3) (C152) or -CH(3) (C461) group at the molecule's 4-position. This modest structural difference leads to markedly different emission behavior in bulk solution and different organization when adsorbed to silica surfaces. Steady state emission spectra of C152 and C461 adsorbed to silica surfaces from bulk methanol solutions show that the two solutes have similar surface activities (ΔG(ads) of -29.0 kJ/mol and -30.8 kJ/mol for C152 and C461, respectively) and that the interface itself has a polarity similar to that of short chain alcohols. Both solutes appear to form multilayers at higher bulk concentrations given observed linear growth in fluorescence emission intensities. At higher C152 surface concentrations a second emissive state appears at longer wavelengths, whereas the emission of C461 remains dominated by a single feature. Time dependent emission of C152 and C461 adsorbed to the silica/methanol interface shows that the silica surface inhibits C152's fast, nonradiative pathway inferred from bulk solution measurements but the fluorescence lifetime of adsorbed C461 remains unchanged from bulk solution limits. These findings are discussed in terms of the interface's ability to restrict C152 isomerization into a nonradiative, twisted intramolecular charge-transfer (TICT) state, despite the fact that this conformation represents an energetic minimum in polar solvation environments.     

The fate of optical excitations in small hydrated ZnS clusters: a theoretical study into the effect of hydration on the excitation and localisation of electrons in Zn4S4 and Zn6S6

In this paper we explore the effect of water on the excited state properties of ZnS nanostructures by means of time-dependent density functional theory (TD-DFT) calculations. Using these TD-DFT calculations we show that the effect of water on the optical absorption spectra is primarily a small blue-shift and that a secondary effect is that spectroscopic features that correspond to dark excitations for the anhydrous nanostructures gain intensity and new absorption peaks are predicted to appear. The effect of adsorbed water on the localisation of excited states is to produce small shifts in the values of the excited stabilisation energies but, more importantly, it results in the formation of extra minima when compared with the case for anhydrous ZnS. Finally, the effect of water on photoluminescence (PL) energies is predicted to be small but the appearance of extra minima induced by the presence of adsorbed water is expected to lead to a splitting/broadening of the PL signal.     

Separation of parasites from human blood using deterministic lateral displacement

We present the use of a simple microfluidic technique to separate living parasites from human blood. Parasitic trypanosomatids cause a range of human and animal diseases. African trypanosomes, responsible for human African trypanosomiasis (sleeping sickness), live free in the blood and other tissue fluids. Diagnosis relies on detection and due to their often low numbers against an overwhelming background of predominantly red blood cells it is crucial to separate the parasites from the blood. By modifying the method of deterministic lateral displacement, confining parasites and red blood cells in channels of optimized depth which accentuates morphological differences, we were able to achieve separation thus offering a potential route to diagnostics.     

An instrumented vehicle for offroad dynamics testing

The paper presents an instrumented vehicle that was equipped with measuring systems to perform complete dynamics tests, especially in off-road conditions. The equipment consists of four wheel dynamometers, a steering robot, and a differential GPS system together with an inertial platform, a non-contact vehicle speed sensor, and an on-board computer with software to control the devices and collect experimental data. The four wheel dynamometers measure six elements; based on strain gage force transducers, it measures three orthogonal forces and three moments. The steering robot can control the steering wheel of the vehicle at a variety of excitation modes; it can carry out typical vehicle dynamics tests (ISO 7401, ISO 4138, ISO/TR3888, etc.) as well as custom engineered tests at a wide range of setting parameters (steer angle rate up to 1600 deg/s). The differential GPS system gives true time vehicle kinematics data (velocities, accelerations, angles, etc.) at 10-ns sample rate and 20-mm accuracy. The base vehicle, a Suzuki Vitara 4 × 4, required no special modifications or changes to install the measuring equipment. The paper also describes typical tests performed with the use of the instrumented vehicle together with sample results.