Field induced evolution of regular and random 2D domain structures and shape of isolated domains in LiNbO₃ and LiTaO₃

The shapes of isolated domains produced by application of the uniform external electric field in different experimental conditions were investigated experimentally in single crystalline lithium niobate LiNbO3 and lithium tantalate LiTaO3. The study of the domain kinetics by computer simulation and experimentally by polarization reversal of the model structure using two-dimensional regular electrode pattern confirms applicability of the kinetic approach to explanation of the experimentally observed evolution of the domain shape and geometry of the domain structure. It has been shown that the fast domain walls strictly oriented along X directions appear after domain merging

Shape of isolated domains in lithium tantalate single crystals at elevated temperatures

The shape of isolated domains has been investigated in congruent lithium tantalate (CLT) single crystals at elevated temperatures and analyzed in terms of kinetic approach. The obtained temperature dependence of the growing domain shape in CLT including circular shape at temperatures above 190 °C has been attributed to increase of relative input of isotropic ionic conductivity. The observed nonstop wall motion and independent domain growth after merging in CLT as opposed to stoichiometric lithium tantalate have been attributed to difference in wall orientation. The computer simulation has confirmed applicability of the kinetic approach to the domain shape explanation. © 2013 AIP Publishing LLC

Self-organized growth of dendrite domains in lithium niobate and lithium tantalate single crystals

The equipment of the Ural Center for Shared Use “Modern nanotechnology” UrFU was used. The research was made possible by Russian Science Foundation (Project №14-12-00826)

Spatial computing in structured spiking neural networks with a robotic embodiment

One of the challenges of modern neuroscience is creating a "living computer" based on neural networks grown in vitro. Such an artificial device is supposed to perform neurocomputational tasks and interact with the environment when embodied in a robot. Recent studies have identified the most critical challenge, the search for a neural network architecture to implement associative learning. This work proposes a model of modular architecture with spiking neural networks connected by unidirectional couplings. We show that the model enables training a neuro-robot according to Pavlovian conditioning. The robot's performance in obstacle avoidance depends on the ratio of the weights in inter-network couplings. We show that besides STDP, critical factors for successful learning are synaptic and neuronal competitions. We use the recently discovered shortest path rule to implement the synaptic competition. This method is ready for experimental testing. Strong inhibitory couplings implement the neuronal competition in the subnetwork responsible for the unconditional response. Empirical testing of this approach requires a technique for growing neural networks with a given ratio of excitatory and inhibitory neurons not available yet. An alternative is building a hybrid system with in vitro neural networks coupled through hardware memristive connections

Tip-induced domain growth on the non-polar cuts of lithium niobate single-crystals

Currently, ferroelectric materials with designed domain structures are considered as a perspective material for new generation of photonic, data storage, and data processing devices. Application of external electric field is the most convenient way of the domain structure formation. Lots of papers are devoted to the investigation of domain kinetics on polar surface of crystals while the forward growth remains one of the most mysterious stages due to lack of experimental methods allowing to study it. Here, we performed tip-induced polarization reversal on X- and Y-non-polar cuts in single-crystal of congruent lithium niobate which allows us to study the forward growth with high spatial resolution. The revealed difference in the shape and length of domains induced on X- and Y-cuts is beyond previously developed theoretical approaches used for the theoretical consideration of the domains growth at non-polar ferroelectric surfaces. To explain experimental results, we used kinetic approach with anisotropy of screening efficiency along different crystallographic directions. © 2015 AIP Publishing LLC

Field Induced Evolution of Regular and Random 2D Domain Structures and Shape of Isolated Domains in LiNbO3 and LiTaO3

The shapes of isolated domains produced by application of the uniform external electric field in different experimental conditions were investigated experimentally in single crystalline lithium niobate LiNbO3 and lithium tantalate LiTaO3. The study of the domain kinetics by computer simulation and experimentally by polarization reversal of the model structure using two-dimensional regular electrode pattern confirms applicability of the kinetic approach to explanation of the experimentally observed evolution of the domain shape and geometry of the domain structure. It has been shown that the fast domain walls strictly oriented along X directions appear after domain merging.The research was made possible in part by Grant 03-51-6562 of INTAS; by Grant 04-02-16770 of RFBR; by Grant 03-02-39004 of RFBR-NNSF; by Grant 04-02-04007 of RFBR-DFG and by Grants 48859, 49130 and RNP 2.1.1.8272 of Program ”Development of the Scientific Potential of High Education,” by Grant MK-2434.2005.2 of President Program of Federal Agency of Education; by PhD Award Y1-P-05-20/4146 of the U.S. CRDF BRHE and Federal Agency of Education, by Grant RUE1-5037-EK-04 of CRDF FSTM

Correlation of wall velocity and tip curvature radius of dendrite domain in lithium niobate

The research was made possible by Russian Science Foundation (Project № 19-12-00210). The equipment of the Ural Center for Shared Use “Modern nanotechnology” Ural Federal University was used

Role of stromal cell-mediated Notch signaling in CLL resistance to chemotherapy

Stromal cells are essential components of the bone marrow (BM) microenvironment that regulate and support the survival of different tumors, including chronic lymphocytic leukemia (CLL). In this study, we investigated the role of Notch signaling in the promotion of survival and chemoresistance of human CLL cells in coculture with human BM-mesenchymal stromal cells (hBM-MSCs) of both autologous and allogeneic origin. The presence of BM-MSCs rescued CLL cells from apoptosis both spontaneously and following induction with various drugs, including Fludarabine, Cyclophosphamide, Bendamustine, Prednisone and Hydrocortisone. The treatment with a combination of anti-Notch-1, Notch-2 and Notch-4 antibodies or γ-secretase inhibitor XII (GSI XII) reverted this protective effect by day 3, even in presence of the above-mentioned drugs. Overall, our findings show that stromal cell-mediated Notch-1, Notch-2 and Notch-4 signaling has a role in CLL survival and resistance to chemotherapy. Therefore, its blocking could be an additional tool to overcome drug resistance and improve the therapeutic strategies for CLL