Tensor Trains Approximation Estimates in the Chebyshev Norm

Computational Mathematics and Mathematical Physics - A new elementwise bound on the cross approximation error used for approximating multi-index arrays (tensors) in the format of a tensor train is...     

Redox-active cobalt complexes as promising antitumor agents

Cobalt(iii) complexes with tetradentate aliphatic Schiff"s bases containing also compounds of the vitamin PP series or their analogs as axial ligands were synthesized as potential antitumor agents. The behavior of these redox-active complexes in chemical processes that presumably govern their biological action was studied. These processes include aquation and subsequent decomposition, electrode and homogeneous redox reactions, and catalytic activity in autooxidation of biosubstrates, especially at the stages of generation and consumption of reactive oxygen species (ROS). The antitumor action of these complexes in vivo was studied. Changes in the organisms of laboratory animals characteristic of processes involving ROS were followed at the cellular and molecular levels. The tumor-selective action of the complexes is due to specific features of microenvironment of tumor cells. Some of them exhibit a strong antimetastatic effect, which exceeds that for a number of drugs used in clinical practice. A complex with nicotinamide was recommended for preclinical studies. The scope of application of the redox-active transition metal complexes in oncology is discussed.     

New accuracy estimates for pseudoskeleton approximations of matrices

A priori accuracy estimates for low-rank approximations using a small number of rows and columns of the initial matrix are proposed. Unlike in the existing methods of pseudoskeleton approximation, this number is larger than the rank of approximation, but the estimates are substantially more accurate than those known previously.     

High‐gain Zn1–xMgx O‐based ultraviolet photodetectors on Al2O3 and LiGaO2 substrates

We report the fabrication and characterization of highly responsive ZnMgO‐based ultraviolet (UV) photodetectors in the metal–semiconductor–metal (MSM) configuration for solar‐blind/visible‐blind optoelectronic application. MSM devices were fabricated from wurtzite Zn_1–xMg_x O/ZnO (x ～ 0.44) thin‐film heterostructures grown on sapphire (α‐Al₂O₃) substrates and w‐Zn_1–xMg_x O (x ～ 0.08), grown on nearly lattice‐matched lithium gallate (LiGaO₂) substrates, both by radio‐frequency plasma‐assisted molecular beam epitaxy (PAMBE). Thin film properties were studied by AFM, XRD, and optical transmission spectra, while MSM device performance was analyzed by spectral photoresponse and current–voltage techniques. Under biased conditions, α‐Al₂O₃ grown devices exhibit peak responsivity of ～7.6 A/W at 280 nm while LiGaO₂ grown samples demonstrate peak performance of ～119.3 A/W, albeit in the UV‐A regime (～324 nm). High photoconductive gains (76, 525) and spectral rejection ratios (～10³, ～10⁴) were obtained for devices grown on α‐Al₂O₃ and LiGaO₂, respectively. Exemplary device performance was ascribed to high material quality and in the case of lattice‐matched LiGaO₂ films, decreased photocarrier trapping probability, presumably due to low‐density of dislocation defects. To the best of our knowledge, these results represent the highest performing ZnO‐based photodetectors on LiGaO₂ yet fabricated, and demonstrate both the feasibility and substantial enhancement of photodetector device performance via growth on lattice‐matched substrates. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Thermal stability of Ti/Al/Pt/Au and Ti/Au Ohmic contacts on n-type ZnCdO

The specific contact resistivity and chemical intermixing of Ti/Au and Ti/Al/Pt/Au Ohmic contacts on n-type Zn_0.05Cd_0.95O layers grown on ZnO buffer layers on GaN/sapphire templates is reported as a function of annealing temperature in the range 200-600 °C. A minimum contact resistivity of 2.3 × 10⁻⁴ Ω cm² was obtained at 500 °C for Ti/Al/Pt/Au and 1.6 × 10⁻⁴ Ω cm² was obtained at 450 °C for Ti/Al. These values also correspond to the minima in transfer resistance for the contacts. The Ti/Al/Pt/Au contacts show far smoother morphologies after annealing even at 600 °C, whereas the Ti/Au contacts show a reacted appearance after 350 °C anneals. In the former case, Pt and Al outdiffusion is significant at 450 °C, whereas in the latter case the onset of Ti and Zn outdiffusion is evident at the same temperature. The improvement in contact resistance with annealing is suggested to occur through formation of TiO_x phases that induce oxygen vacancies in the ZnCdO.