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Titanium dioxide ( TiO 2 , also known as titania) has attracted a great deal of attention since the discovery of photocatalytic splitting of water under ultraviolet light exposure by Fujishima and Honda. Three modifications of TiO 2 are known to occur in nature: rutile, brookite, and anatase, of which only the first is a stable polymorph of bulk titania. The contribution of the surface free energy, however, makes anatase a stable polymorph at the nanometer scale. Compared to rutile, anatase has a longer carrier lifetime and exciton diffusion length, higher electron mobility, and is an order of magnitude more efficient in photocatalysis, which makes it a material of choice for a variety of applications. Hydrogen is a common impurity in TiO 2 with a strong impact on its electrical and optical properties. In this Perspective, we discuss the application of IR absorption, Raman scattering, electron paramagnetic resonance, and ab initio theory to get insight into the properties of hydrogen in bulk single-crystalline anatase. In particular, interstitial hydrogen, hydrogen substituting for oxygen, the nature of "hidden" species, as well as complexes formed by hydrogen with acceptors are considered. [ABSTRACT FROM AUTHOR]

A study combining vibrational spectroscopy and first-principles theory is presented for a hydrogen-related defect in natural anatase TiO 2 that is characterized by an O–H vibrational mode at 3373 cm − 1 (10 K). Based on complementary Raman scattering, IR absorption, electron paramagnetic resonance, and secondary ion mass spectrometry data supported also by ab initio calculations, it is tentatively proposed that the defect responsible for the 3373 cm − 1 line includes two hydroxyl units located next to a substitutional iron atom, Fe Ti H 2. The defect may exist in at least two charge states, whereby the 3373 cm − 1 line is associated with the positive charge state of the complex. [ABSTRACT FROM AUTHOR]

The ability to separate proteins is desirable for many fields of study, and nanoporous membranes may offer a method for rapid protein filtration at high throughput volume, provided there is an understanding of the protein dynamics involved. In this work, we use Brownian dynamics simulations to study the motion of coarse-grained proteins insulin and ubiquitin in an electrically biased membrane. In our model, the protein is subjected to various biases applied to the silicon membrane equipped with a nanopore of different radii. The time each protein takes to find a cylindrical nanopore embedded in a thin silicon membrane, attempt to translocate it (waiting time), and successfully translocate it in a single attempt (translocation time) is calculated. We observe insulin finding the nanopore and translocating it faster than the electrically neutral ubiquitin due to insulin's slightly smaller size and net negative charge. While ubiquitin's dynamics is also affected by the size of the pore, surprisingly, its translocation process is also noticeably changed by the membrane bias. By investigating the protein's multipole moments, we demonstrate that this behavior is largely due to the protein's dipole and quadrupole interactions with the membrane potential. [ABSTRACT FROM AUTHOR]

Ion heat conductivity in deuterium plasma of the circular limiter tokamak T-10 is analyzed in more than 100 Ohmic shots. Four data scans: plasma density, effective charge, plasma current, and toroidal magnetic field are presented. Each scan is formed with the preservation of other parameters. It is shown that at the plasma periphery, r / a = 0.6 − 0.8 , the ion heat conductivity exceeds neoclassical values up to three to eight times. The anomalous part χ i a n increases with plasma density and effective charge, while it decreases with plasma current and does not depend on the toroidal magnetic field. The highest value of χ i a n is observed in high-density low-current regimes. More negative values of plasma electric potential correlate with higher values of χ i a n . The empirical scaling of χ i a n is derived. The transport model based on this scaling allows us to describe experimental profiles of ion temperature T i (r) within experimental error ± 15 %. [ABSTRACT FROM AUTHOR]

We study the movement of a polymer attached to a large protein inside a nanopore in a thin silicon dioxide membrane submerged in an electrolyte solution. We use Brownian dynamics to describe the motion of a negatively charged polymer chain of varying lengths attached to a neutral protein modeled as a spherical bead with a radius larger than that of the nanopore, allowing the chain to thread the nanopore but preventing it from translocating. The motion of the protein-polymer complex within the pore is also compared to that of a freely translocating polymer. Our results showthat the free polymer's standard deviations in the direction normal to the pore axis is greater than that of the protein-polymer complex. We find that restrictions imposed by the protein, bias, and neighboring chain segments aid in controlling the position of the chain in the pore. Understanding the behavior of the protein-polymer chain complex may lead to methods that improve molecule identification by increasing the resolution of ionic current measurements. [ABSTRACT FROM AUTHOR]

In this work, we theoretically study the interaction between a solid state membrane equipped with a nanopore and a tethered, negatively charged polymer chain subjected to a time-dependent applied electrolyte bias. In order to describe the movement of the chain in the biomolecule-membrane system immersed in an electrolyte solution, Brownian dynamics is used. We show that we can control the polymer's equilibrium position with various applied electrolyte biases: for a sufficiently positive bias, the chain extends inside the pore, and the removal of the bias causes the polymer to leave the pore. Corresponding to a driven process, we find that the time it takes for a biomolecular chain to enter and extend into a nanopore in a positive bias almost increases linearly with chain length while the amount of time it takes for a polymer chain to escape the nanopore is mainly governed by diffusion. [ABSTRACT FROM AUTHOR]

A theoretical study of the interstitial molecular hydrogen in the silicon single-crystal is reported. H2 and Si have been approximated as a rigid object and a static matrix, respectively. A fivedimensional numerical-analytical representation of an ab initio potential energy surface of the system has been constructed. This representation has been used to calculate rotational, translational, and roto-translational energy levels of the interstitial hydrogen, where three levels of theory, 2D, 3D, and 5D were considered. The potential energy surface, the band structure of energy levels, and the roto-translational states obtained are presented together with the symmetry analysis of the roto-translational wavefunctions. [ABSTRACT FROM AUTHOR]

We study Alfvén eigenmodes (AEs) in the TJ-II heliac in hydrogen plasmas heated by hydrogen co-field neutral beam injector. Taking advantage of the unique TJ-II flexibility in a varying plasma current, we have observed strong variation of the AE frequency from fAE ∼ 30 to ∼220 kHz for selected modes. An advanced heavy-ion beam probe diagnostic determines the spatial location and internal amplitudes of the modes. The modes satisfy a local AE dispersion relation including the geodesic acoustic frequency that represents the lowest frequency of the mode. Linear MHD modeling with STELLGAP and FAR3D codes shows that the calculated temporal evolution of the mode frequency reproduces the observed maxima and minima at the same time intervals with a similar frequency range, and the radial profile peaks near the outer edge of the observed one. [ABSTRACT FROM AUTHOR]

A gated oscillating power amplifier has been developed for high frequency biasing and real time turbulent feedback experiments in the Saskatchewan Torus-modified tokamak. This oscillator is capable of providing a peak to peak oscillating output voltage of around ±60 V with a current around 30 A within the frequency band 1 kHz–50 kHz without any distortions. The overall output power is amplified by a two-stage metal oxide semiconductor field-effect transistor power op-amp as well as nine identical push–pull amplifiers in the final stages. The power amplifier input signal, collected from the plasma floating potential during the tokamak discharge, is optically isolated from the tokamak vessel ground. The filtered floating potential fluctuations with a band width of 5 kHz–40 kHz were amplified and fed to an electrode inserted into the plasma edge to study the response of the plasma turbulence. We observe that magnetic fluctuations are suppressed due to real time feedback of the floating potential. [ABSTRACT FROM AUTHOR]

2D poloidal contour plots of plasma potential, plasma density, and their fluctuations have been measured in low density plasmas sustained by Electron Cyclotron Resonance Heating using a heavy ion beam probe (HIBP) system in the TJ-II stellarator. A HIBP has been used in the new energy scanning mode to obtain the measurements for a 2D poloidal cross section of the stellarator. The 2D map for the absolute plasma potential shows a local maximum in the plasma core as expected in low density plasma scenarios. Fluctuations in the HIBP secondary ion current, as a proxy of plasma density fluctuations, appear both in positive and negative density gradient regions, with a normalized level of density fluctuations higher in the negative density gradient region. The TJ-II innovative experimental setup developed using a dual HIBP diagnostic paves the way for model validation on core plasma potential asymmetries and particle transport and fluctuations under positive and negative density gradient scenarios. [ABSTRACT FROM AUTHOR]

An algorithm and a computer program implementing it are presented for calculation of the rovibronic intensities for a triatomic molecule in a “double-Renner-degenerate” electronic state. The program has been applied to investigate, by theoretical simulation, the absorption spectrum of HO2 in the X 2A″ and à 2A′ electronic states. The spectrum simulations are based on potential energy functions, electric dipole moment functions, and electric dipole transition moment functions constructed from ab initio values calculated at the core-valence MR-SDCI+Q/[cc-pVQZ (H), aug-cc-pCVQZ (O)] level of theory. [ABSTRACT FROM AUTHOR]

An algorithm and a computer program implementing it are presented for calculation of the rovibronic intensities for a triatomic molecule in a “double-Renner-degenerate” electronic state. The program has been applied to investigate, by theoretical simulation, the absorption spectrum of HO2 in the X 2A″ and à 2A′ electronic states. The spectrum simulations are based on potential energy functions, electric dipole moment functions, and electric dipole transition moment functions constructed from ab initio values calculated at the core-valence MR-SDCI+Q/[cc-pVQZ (H), aug-cc-pCVQZ (O)] level of theory. [ABSTRACT FROM AUTHOR]

The rotation-torsion energies in the electronic ground state of HSOH are obtained in variational calculations based on a newly computed ab initio CCSD(T)/aug-cc-pV(Q+d)Z potential energy surface. Using the concept of the reaction path Hamiltonian, as implemented in the program TROVE (theoretical rovibrational energies), the rotation-vibration Hamiltonian is expanded around geometries on the torsional minimum energy path of HSOH. The calculated values of the torsional splittings are in excellent agreement with experiment; the root-mean-square (rms) deviation is 0.0002 cm-1 for all experimentally derived splittings (with J≤40 and Ka≤4). The model provides reliable predictions for splittings not yet observed. The available experimentally derived torsion-rotation term values (with J≤40 and Ka≤4) are reproduced ab initio with an rms deviation of 1.2 cm-1 (0.7 cm-1 for J≤20), which is improved to 1.0 cm-1 (0.07 cm-1 for J≤20) in an empirical adjustment of the bond lengths at the planar trans configuration. The theoretical torsional splittings of HSOH are analyzed in terms of an existing semiempirical model for the rotation-torsion motion. The analysis explains the irregular variation of the torsional splittings with Ka that has been observed experimentally. [ABSTRACT FROM AUTHOR]

A theoretical investigation of the X 2A″ and à 2A′ electronic states of the HO2 radical is reported. Both electronic states have nonlinear equilibrium geometries and they correlate with a 2Π state at linear geometries so that they exhibit the Renner effect. In highly excited bending states, there is tunneling between two equivalent minima (with geometries where the H nucleus is bound to one, or the other, of the two O nuclei), and the two linear geometries H–O–O and O–O–H become accessible to the molecule. Thus, HO2 affords an example of the so-called double Renner effect. Three-dimensional potential energy surfaces for the X 2A″ and à 2A′ electronic states of HO2 have been calculated ab initio and the global potential energy surfaces for the states have been constructed. These surfaces have been used, in conjunction with the computer program DR [Odaka et al., J. Mol. Structure 795, 14 (2006); Odaka et al., J. Chem. Phys. 126, 094301 (2007)], for calculating HO2 rovibronic energies in the “double-Renner”-degenerate electronic states X 2A″ and à 2A′. The results of the ab initio calculations, the rovibronic energies obtained, and analyses of the wavefunctions for selected states are presented. [ABSTRACT FROM AUTHOR]

A theoretical investigation of the X 2A″ and à 2A′ electronic states of the HO2 radical is reported. Both electronic states have nonlinear equilibrium geometries and they correlate with a 2Π state at linear geometries so that they exhibit the Renner effect. In highly excited bending states, there is tunneling between two equivalent minima (with geometries where the H nucleus is bound to one, or the other, of the two O nuclei), and the two linear geometries H–O–O and O–O–H become accessible to the molecule. Thus, HO2 affords an example of the so-called double Renner effect. Three-dimensional potential energy surfaces for the X 2A″ and à 2A′ electronic states of HO2 have been calculated ab initio and the global potential energy surfaces for the states have been constructed. These surfaces have been used, in conjunction with the computer program DR [Odaka et al., J. Mol. Structure 795, 14 (2006); Odaka et al., J. Chem. Phys. 126, 094301 (2007)], for calculating HO2 rovibronic energies in the “double-Renner”-degenerate electronic states X 2A″ and à 2A′. The results of the ab initio calculations, the rovibronic energies obtained, and analyses of the wavefunctions for selected states are presented. [ABSTRACT FROM AUTHOR]

The authors report here the implementation of a newly developed, highly efficient matrix diagonalization routine in the DR program [T. E. Odaka et al., J. Mol. Struct. 795, 14 (2006)]. The DR program solves the rovibronic Schrödinger equation for a triatomic molecule with a double Renner effect, i.e., with two accessible linear arrangements of the nuclei at which the electronic energy is doubly degenerate. With the new routines, the authors can extend the DR calculations of rovibronic energies for à 2Π MgNC/MgCN by considering a much larger set of rovibronic states, in particular, states at higher J values, than the authors were able to access previously. [ABSTRACT FROM AUTHOR]

We study the hyperfine interaction in the Kane solid-state quantum computer device structure [Nature (London) 393, 133 (1998)] by solving self-consistently three-dimensional Poisson and Kohn-Sham equations and taking into account the nonisotropic effective mass at each of the six degenerate minima in the silicon conduction band. Specifically, we calculate the hyperfine interaction coefficient from the electron wave-function solution within the envelope function approximation and investigate its variations as a function of gate voltages and impurity position. In addition, we also consider the effect of the gate design on the hyperfine interaction modulation. We show that the hyperfine interaction between the donor electron and donor nucleus is extremely sensitive to all these parameters. [ABSTRACT FROM AUTHOR]

Experimental comparison of the m = 2, n = 1 mode and plasma rotation velocities at q = 2 magnetic surface in a wide range of the mode amplitudes is presented. Phase velocity of the mode rotation is measured with a set of poloidal magnetic field sensors located at the inner side of the vacuum vessel wall. Plasma rotation velocity at the q = 2 magnetic surface in the direction of the mode phase velocity is measured with the heavy ion beam probe diagnostics. In the presence of a static Resonant Magnetic Perturbation (RMP), the rotation is irregular that appears as cyclical variations of the mode and plasma instantaneous velocities. The period of these variations is equal to the period of the mode oscillations. In the case of high mode amplitude, the rotation irregularity of the mode is consistent with the rotation irregularity of the resonant plasma layer. On the contrary, the observed rise of the mode rotation irregularity in the case of low mode amplitude occurs without an increase of the rotation irregularity of the resonant plasma layer. The experimental results are simulated and analyzed with the TEAR code based on the two-fluid MHD approximation. Calculated irregularities of the mode and plasma rotation depend on the mode amplitude similar to the experimental data. For large islands, the rotation irregularity is attributed to oscillations of the electromagnetic torque applied to the resonant plasma layer. For small islands, the deviation of the mode rotation velocity from the plasma velocity occurs due to the effect of finite plasma resistivity. [ABSTRACT FROM AUTHOR]

By using the full electromagnetic drift kinetic equations for electrons and ions, the general dispersion relation for geodesic acoustic modes (GAMs) is derived incorporating the electromagnetic effects. It is shown that m = 1 harmonic of the GAM mode has a finite electromagnetic component. The electromagnetic corrections appear for finite values of the radial wave numbers and modify the GAM frequency. The effects of plasma pressure βe, the safety factor q, and the temperature ratio τ on GAM dispersion are analyzed. [ABSTRACT FROM AUTHOR]

Results of a kinetic treatment of Geodesic Acoustic Modes (GAMs) that fully takes into account ion parallel dynamics, including the magnetic field component, are presented. The finite-orbit-width (FOW) parameter is considered in the calculation of the second harmonic effect on GAMs. For larger values of the FOW parameter, it is shown that dispersive effects related to the m = 2 harmonics is the cause of the mode frequency splitting and the modes appear due to the interaction with the ion sound mode. Furthermore, the modes may have enhanced damping rates due to second harmonic Landau damping. [ABSTRACT FROM AUTHOR]

An investigation of the critical behavior of the specific heat of the manganites La1-xAgxMnO3 ×(x=0.1,0.15,0.2) near the Curie temperature is carried out. The behavior of the universal critical parameters near the phase transition point is established. All of the samples studied correspond to the ferromagnetic Heisenberg 3D universality class of critical behavior, with the critical exponent α=-0.115, -0.106, and -0.106 for La0.9Ag0.1MnO3, La0.85Ag0.15MnO3, and La0.8Ag0.2MnO3, respectively. It is shown that the universality class of the critical behavior of the specific heat of the manganites La1-xAgxMnO3 is independent of the silver concentration. [ABSTRACT FROM AUTHOR]

The low-temperature minimum of the resistivity of La0.85Ag0.15MnO3 is investigated in detail. Analysis of the experimental data shows that the observed low-temperature minimum of the zero-field resistivity and the large magnetoresistive effect, which increases with decreasing temperature, can be explained in a model of spin-polarized tunneling of charge carriers through grain boundaries. [ABSTRACT FROM AUTHOR]

A comprehensive investigation of the electro- and thermophysical properties of the manganite La0.8Ag0.15MnO3 is carried out over a wide temperature interval (4.2–350 K) and in magnetic fields up to 26 kOe. It is shown that the colossal magnetoresistance in a magnetic field of 11 kOe amounts to 57%, and the effect is maximum at room temperature. The dominant mechanisms of current carrier scattering in the ferromagnetic and paramagnetic phases are established. An analysis of the data on the low-temperature heat capacity provides estimates of the electronic density of states at the Fermi level, NF=6.82×1024 eV-1 mol-1, and of the Debye temperature, θD=370 K. The results of thermal expansion measurements are used to find the spontaneous magnetostriction. It is found that the phonon mechanism of heat transfer is dominant, and the local Jahn–Teller distortions are considered as the main mechanism of phonon scattering. [ABSTRACT FROM AUTHOR]

Proposes the heavy ion-beam probing (HIBP) project for the mega ampere spherical tokamak to establish systematic research of the radial electric field as an idea to investigate both the reactor-related physics and basic plasma physics. HIBP optimization; Types of probing trajectories; Crossover of the secondaries; Optimal detector grid.

Discusses the specific features of the application of heavy ion beam probe systems to tight aspect ratio tokamaks. Brief description of the observed tokamaks from the viewpoint of the probing beam pass; Optimization procedure; Three-dimensional case.

Develops a procedure of fast calibration of the heavy ion beam probe parallel plate analyzer using the gas target and reference beam. Test facility in vitro calibration; Gas target in situ calibration; Nonideal effects in calibration.