Enhanced Nonlinear Response by Manipulating the Dirac Point at the (111) LaTiO_{3}/SrTiO_{3} Interface.

Tunable spin-orbit interaction (SOI) is an important feature for future spin-based devices. In the presence of a magnetic field, SOI induces an asymmetry in the energy bands, which can produce nonlinear transport effects (V∼I^{2}). Here, we focus on such effects to study the role of SOI in the (111) LaTiO_{3}/SrTiO_{3} interface. This system is a convenient platform for understanding the role of SOI since it exhibits a single-band Hall response through the entire gate-voltage range studied. We report a pronounced rise in the nonlinear longitudinal resistance at a critical in-plane field H_{cr}. This rise disappears when a small out-of-plane field component is present. We explain these results by considering the location of the Dirac point formed at the crossing of the spin-split energy bands. An in-plane magnetic field pushes this point outside of the Fermi contour, and consequently changes the symmetry of the Fermi contours and intensifies the nonlinear transport. An out-of-plane magnetic field opens a gap at the Dirac point, thereby significantly diminishing the nonlinear effects. We propose that magnetoresistance effects previously reported in interfaces with SOI could be comprehended within our suggested scenario.

Inelastic Scattering of a Photon by a Quantum Phase Slip.

Spontaneous decay of a single photon is a notoriously inefficient process in nature irrespective of the frequency range. We report that a quantum phase-slip fluctuation in high-impedance superconducting waveguides can split a single incident microwave photon into a large number of lower-energy photons with a near unit probability. The underlying inelastic photon-photon interaction has no analogs in nonlinear optics. Instead, the measured decay rates are explained without adjustable parameters in the framework of a new model of a quantum impurity in a Luttinger liquid. Our result connects circuit quantum electrodynamics to critical phenomena in two-dimensional boundary quantum field theories, important in the physics of strongly correlated systems. The photon lifetime data represent a rare example of verified and useful quantum many-body simulation.

Kinetics of exciplex formation/dissipation in reaction following Weller Scheme II.

Creation of exciplexes from the charged products of photoionization is considered by means of Integral Encounter Theory. The general kinetic equations of such a reaction following the Weller scheme II are developed. The special attention is given to the particular case of irreversible remote ionization of primary excited electron donor. Kinetics of exciplex formation is considered at fast biexponential geminate transformation of exciplexes in cage that gives way to subsequent bulk reaction of equilibrated reaction products controlled by power law recombination of ions. It is shown that the initial geminate stage of exciplex kinetics is observed only in diffusion controlled regime of the reaction and disappears with increasing mobility of ions in passing to kinetic regime. The quantum yield of exciplexes is studied along with their kinetics.

Screening of exciplex formation by distant electron transfer.

The excitation quenching by reversible exciplex formation, combined with irreversible but distant electron transfer, is considered by means of the integral encounter theory (IET). Assuming that the quenchers are in great excess, the set of IET equations for the excitations, free ions, and exciplexes is derived. Solving these equations gives the Laplace images of all these populations, and these are used to specify the quantum yields of the corresponding reaction products. It appears that diffusion facilitates the exciplex production and the electron transfer. On the other hand the stronger the electron transfer is, the weaker is the exciplex production. At slow diffusion the distant quenching of excitations by ionization prevents their reaching the contact where they can turn into exciplexes. This is a screening effect that is most pronounced when the ionization rate is large.

Reversible charge separation followed by exciplex formation.

The quenching of fluorescence by reversible bimolecular ionization, followed by reversible exciplex formation from an ion pair (Scheme II) subjected to spin-conversion and subsequent radical-ion recombination/separation, has been studied by means of integral encounter theory (IET) and fitted to the available experimental data. Using the incoherent (rate) model of spin-conversion, the ion recombination to the excited triplet products is also accounted for. All of the results are obtained and shown to be different for the pulse excitation of fluorescence and its stationary detection. The free-energy dependence of all of the calculated properties of the forward and backward electron transfer are specified and compared with the conventional free-energy gap (FEG) law.

Reversible exciplex formation followed charge separation.

The reversible exciplex formation followed by its decomposition into an ion pair is considered, taking into account the subsequent geminate and bulk ion recombination to the triplet and singlet products (in excited and ground states). The integral kinetic equations are derived for all state populations, assuming that the spin conversion is performed by the simplest incoherent (rate) mechanism. When the forward and backward electron transfer is in contact as well as all dissociation/association reactions of heavy particles, the kernels of integral equations are specified and expressed through numerous reaction constants and characteristics of encounter diffusion. The solutions of these equations are used to specify the quantum yields of the excited state and exciplex fluorescence induced by pulse or stationary pumping. In the former case, the yields of the free ions and triplet products are also found, while in the latter case their stationary concentrations are obtained.

Regenerative effect of neural-induced human mesenchymal stromal cells in rat models of Parkinson's disease.

BACKGROUND: Human bone marrow multipotent mesenchymal stromal cells (hMSC), because of their capacity of multipotency, may provide an unlimited cell source for cell replacement therapy. The purpose of this study was to assess the developmental potential of hMSC to replace the midbrain dopamine neurons selectively lost in Parkinson's disease. METHODS: Cells were isolated and characterized, then induced to differentiate toward the neural lineage. In vitro analysis of neural differentiation was achieved using various methods to evaluate the expression of neural and dopaminergic genes and proteins. Neural-induced cells were then transplanted into the striata of hemi-Parkinsonian rats; animals were tested for rotational behavior and, after killing, immunohistochemistry was performed. RESULTS: Following differentiation, cells displayed neuronal morphology and were found to express neural genes and proteins. Furthermore, some of the cells exhibited gene and protein profiles typical of dopaminergic precursors. Finally, transplantation of neural-induced cells into the striatum of hemi-Parkinsonian rats resulted in improvement of their behavioral deficits, as determined by apomorphine-induced rotational behavior. The transplanted induced cells proved to be of superior benefit compared with the transplantation of naive hMSC. Immunohistochemical analysis of grafted brains revealed that abundant induced cells survived the grafts and some displayed dopaminergic traits. DISCUSSION: Our results demonstrate that induced neural hMSC may serve as a new cell source for the treatment of neurodegenerative diseases and have potential for broad application. These results encourage further developments of the possible use of hMSC in the treatment of Parkinson's disease.

Intrastriatal transplantation of mouse bone marrow-derived stem cells improves motor behavior in a mouse model of Parkinson's disease.

Strategies of cell therapy for the treatment of Parkinson's disease (PD) are focused on replacing damaged neurons with cells to restore or improve function that is impaired due to cell population damage. In our studies, we used mesenchymal stromal cells (MSCs) from mouse bone marrow. Following our novel neuronal differentiation method, we found that the basic cellular phenotype changed to cells with neural morphology that express specific markers including those characteristic for dopaminergic neurons, such as tyrosine hydroxylase (TH). Intrastriatal transplantation of the differentiated MSCs in 6-hydroxydopamine-lesioned mice led to marked reduction in the amphetamine-induced rotations. Immunohistological analysis of the mice brains four months post transplantation, demonstrated that most of the transplanted cells survived in the striatum and expressed TH. Some of the TH positive cells migrated toward the substantia nigra. In conclusion, transplantation of bone marrow derived stem cells differentiated to dopaminergic-like cells, successfully improved behavior in an animal model of PD suggesting an accessible source of cells that may be used for autotransplantation in patient with PD.

Production of free radicals and triplets from contact radical pairs and from photochemically generated radical ions.

The quantum yields of triplets and free radicals (or radical ions) that escaped recombination in photochemically created primary radical pairs (or radical ion pairs) are calculated. As the products of monomolecular photodissociation, the neutral radicals appear at contact, while the ions are initially distributed over the space due to distant photoionization (bimolecular electron transfer) in the liquid solution. The diffusional dependence of the quantum yields is shown to be different when recombination starts from contact or from separated reactants. The experimental data for recombination of ionized perylene with aromatic amine counterions is well fitted with the noncontact initial distribution provided the recombination is also noncontact and even more distant than ionization.

Photoionization affected by chemical anisotropy.

The kinetic constants of rhodamine 3B quenching by N,N-dimethyl aniline were extracted from the very beginning of the quenching kinetics, recently studied in a few solvents of different viscosities. They were well fitted with the conventional kinetic constant definition, provided the radial distribution function of simple liquids was ascribed to the reactant pair distribution and the contact electron transfer rate was different in all the cases. This difference was attributed to the chemical anisotropy averaging by the rotation of reactants, which is the faster in solvents of lower viscosity. With the proper choice of a space dependent encounter diffusion, the whole quenching kinetics was well fitted with an encounter theory, using the Marcus [J. Chem. Phys. 24, 966 (1956); 43, 679 (1965)] transfer rate instead of the contact Collins-Kimball [J. Colloid. Sci. 4, 425 (1949)] approximation. Not only the beginning and middle part of the quenching were equally well fitted, but the long time (Markovian) rate constant was also found to be the same as previously obtained. Moreover, the concentration dependencies of the fluorescence quantum yield and the Stern-Volmer constant were specified and await their experimental verification.

Quenching of singlets and triplets by reversible ionization followed by charge recombination.

The reversible electron transfer from donor to excited molecule (acceptor of electron) is shown to be the irreversible energy quenching, if it is completed by subsequent irreversible recombination radical-ions which are produced. The Stern-Volmer constant of fluorescence as well as the Markovian rate constant of triplet quenching are calculated analytically, assuming the electron transfer is contact. The multiple Rehm-Weller effect is shown to be peculiar to both constants.

Double-channel contact recombination of radical pairs subjected to spin conversion via the Delta g mechanism.

The contact recombination from both singlet and triplet states of a radical pair is studied assuming that the spin conversion is carried out by the fast transversal relaxation and Delta g mechanism. The alternative HFI mechanism is neglected as being much weaker in rather large magnetic fields. The magnetic-field-dependent quantum yields of the singlet and triplet recombination products, as well as of the free radical production, are calculated for any initial spin state and arbitrary separation of radicals in a pair. The magnetic field effect is traced and its diffusional (viscosity) dependence is specified.

Singlet and triplet products of the geminate recombination of a radical pair with a single magnetic nucleus (I = 1/2).

The double-channel recombination and separation of the photochemically created singlet radical pair is investigated, taking into account the spin conversion in a zero magnetic field and the arbitrary initial distance between the radicals. The quantum yields of the singlet and triplet products and the free radicals production are found analytically, assuming that the recombination of the diffusing radicals occurs at contact. All the yields are related to the singlet and triplet populations of the recombining radical pair, subjected to spin conversion and contact exchange interaction. The general analytical expressions for the quantum yields are specified for the particular limits of the weak and strong exchange. They are greatly simplified in the case of polar solvents, especially at the contact start. A close similarity is obtained with the results of a previously developed incoherent model of spin conversion, provided that the conversion rate is appropriately related to the hyperfine coupling constant.

Integral encounter theory of strong electron transfer.

The integral encounter theory (IET) has been extended to the reactions limited by diffusion along the reaction coordinate to the level crossing points where either thermal or hot electron transfer occurs. IET describes the bimolecular ionization of the instantaneously excited electron donor D* followed by the hot geminate backward transfer which precedes the ion pair equilibration and its subsequent thermal recombination. We demonstrate that the fraction of ion pairs which avoids the hot recombination is much smaller than their initial number when the electron tunneling is strong.

Variation of the resonant transfer rate when passing from nonadiabatic to adiabatic electron transfer.

Two competing theories are used for bridging the gap between the nonadiabatic and the deeply adiabatic electron transfer between symmetric parabolic wells. For the high friction limit, a simple analytic interpolation is proposed as a reasonable alternative to them, well-fitted to the results of numerical simulations. It provides a continuous description of the electron transfer rate in the whole range of variation of the nonadiabatic coupling between the diabatic states. For lower friction, the original theories are used for the same goal. With an increase in coupling, the cusped barrier transforms into the parabolic one. Correspondingly, the pre-exponent of the Arrhenius transfer rate first increases with coupling, then levels off approaching the "dynamic solvent effect" plateau but finally reduces reaching the limit of the adiabatic Kramers theory for the parabolic barrier. These changes proceeding with a reduction in the particle separation affect significantly the spatial dependence of the total transfer rate. When approaching the contact distance, the exact rate becomes smaller than in the theory of dynamical solvent effects and much smaller than predicted by perturbation theory (golden rule), conventionally used in photochemistry and electrochemistry.

Tunneling of excess electron from free and trapped states.

The association of an excess electron with scavengers in nonpolar solvents is considered assuming that the free electron performs the free diffusion during the lifetime between sequential places of temporary localization. The reaction of a free electron during this motion is at first taken into account along with a tunneling of the localized electron. When the mean step length between sequential localizations is short the reaction of the excess electron is diffusional and the free state contribution to the total reaction rate is negligible. In the opposite case, when this reaction becomes essentially hopping, the corresponding rate is significantly accelerated due to a faster diffusion of the free electron.

[Traumatic asphyxia].

Traumatic asphyxia is a commonly used designation of a syndrome related to severe compressive trauma to the thorax. It is characterized by cranial cyanosis, subconjunctival hemorrhage, vascular engorgement of the head, mucosal petechiae, hemoptysis, esophageal and rectal hemorrhage, hematuria, and varying degrees of cerebral dysfunction. By 1985 approximately 210 cases had been reported world-wide. We present an illustrative case in a 24-year-old man.

[HLA antigens in juvenile rheumatoid arthritis]. / Antigeny sistemy HLA pri iuvenil'nom revmatoidnom artrite.

Antigens of I class HLA system (locus A and B) were investigated in 67 patients of Latvian nationality suffering from juvenile rheumatoid arthritis (JRA). Associations of HLA antigens with juvenile rheumatoid arthritis partially coincided with the ones revealed earlier. Typing established an increased incidence of antigen B27 (p less than 0.01) and gaplotype A2, B40 (p less than 0.01). Antigen B15 possessed a protective action with respect to JRA. Interlocus combinations demonstrated a closer association with the disease than a single antigen. The authors also revealed markers of various clinico-anatomical variants of JRA.

[The lymphocytotoxic test as a method of identifying subpopulations of T lymphocytes using monoclonal antibodies]. / Limfotsitotoksicheskii test kak metod identifikatsii subpopuliatsii T-limfotsitov monoklonal'nymi antitelami.

The authors analyse the findings of the lymphocytotoxicity test with monoclonal antibodies and the indirect immunofluorescence method used for the assays of T lymphocyte subpopulations. The mean values of the total count of T lymphocytes, T helpers, T suppressors, as well as the immunoregulation index obtained by both methods have proved practically the same. The lymphocytotoxicity data have been in good correlation with the findings of indirect immunofluorescence in tests with all the monoclonal OCT antisera.