V. V. Karavaeva

Bio: V. V. Karavaeva is an academic researcher. The author has contributed to research in topics: Medicine & Modular design. The author has an hindex of 1, co-authored 1 publications receiving 6 citations.

A study of the disperse-particle hardening of EI702 steel

Abstract: A study was made of aging EI702 austenitic steel. It was shown that the nature of the changes in the mechanical properties (deformation resistance, coefficient of hardening) with duration of aging is determined by the initial state of the material and the temperature of aging, two factors which determine the mechanism of decomposition.

In Campylobacter jejuni, a new type of chaperone receives heme from ferrochelatase

Abstract: Intracellular heme formation and trafficking are fundamental processes in living organisms. Three biogenesis pathways are used by bacteria and archaea to produce iron protoporphyrin IX (heme b) that diverge after the formation of the common intermediate uroporphyrinogen III (uro’gen III). In this work, we identify and provide a detailed characterization of the enzymes involved in the transformation of uro’gen III into heme. We show that in this organism operates the protoporphyrin-dependent pathway (PPD pathway), in which the last reaction is the incorporation of ferrous iron into the porphyrin ring by the ferrochelatase enzyme. In general, following this final reaction, little is known about how the formed heme b reaches the target proteins. In particular, the chaperons that are thought to be required to traffic heme for incorporation into hemeproteins to avoid the cytotoxicity associated to free heme, remain largely unidentified. We identified in C. jejuni a chaperon-like protein, named CgdH2, that binds heme with a dissociation constant of 4.9 ± 1.0 µM, a binding that is impaired upon mutation of residues histidine 45 and 133. We show that C. jejuni CgdH2 establishes protein-protein interactions with ferrochelatase, which should enable for the observed transfer of heme from ferrochelatase to CgdH2. Phylogenetic analysis revealed that C. jejuni CgdH2 is evolutionarily distinct from the currently known chaperones. Therefore, CgdH2 is a novel chaperone and the first protein identified as an acceptor of the intracellularly formed heme, thus enlarging our understanding of bacterial heme homeostasis.

Transport properties of the II–V semiconductor ZnSb

Abstract: The intermetallic compound ZnSb is an electron poor (II–V) semiconductor with interesting thermoelectric properties. Electrical resistivity, thermopower and thermal conductivity were measured on single crystalline and various polycrystalline specimens. The work establishes the presence of impurity band conduction as an intrinsic phenomenon of ZnSb. The impurity band governs electrical transport properties at temperatures up to 300–400 K after which ZnSb becomes an intrinsic conductor. Furthermore this work establishes an inherently low lattice thermal conductivity of ZnSb, which is comparable to the state-of-the-art thermoelectric material PbTe. It is argued that the impurity band relates to the presence of Zn defects and the low thermal conductivity to the electron-poor bonding properties of ZnSb.

Influence of Ball-Milling, Nanostructuring, and Ag Inclusions on Thermoelectric Properties of ZnSb

Abstract: In the last few years much attention has been given to the promising thermoelectric material Zn4Sb3. The related ZnSb phase features a high Seebeck coefficient at room temperature. Its thermoelectric conversion efficiency, however, is low due to its relatively high thermal conductivity. ZnSb has potential as a thermoelectric material if this can be reduced. Nanostructuring of bulk materials and introducing extrinsic particles have been shown to lower lattice thermal conductivity. In this study we created the microstructure by ball-milling of bulk ZnSb and added Ag particles which attain sizes in the micrometer range in this milling process. Hot-pressing was used to obtain dense samples. Several techniques were used for structural characterization. Here we report on scanning electron microscopy, transmission electron microscopy, and x-ray diffraction analysis. Thermoelectrical measurements were conducted around room temperature. Thermal conductivity was reduced by up to 40% by the reported nanostructuring. However, the electrical conductivity and the Seebeck coefficient were adversely affected, leading to no overall improvement in performance.

Enhanced thermoelectric properties of Cu doped ZnSb based thin films

Abstract: Cu doped ZnSb based thin films were deposited by direct current magnetron co-sputtering. X-ray diffraction results show that the un-doped thin film reveals a single ZnSb phase and it transforms to Zn4Sb3 phase after Cu doped. The material with Zn4Sb3 phase which belongs to R-3c space group crystal will lead to lower thermal conductivity. The Hall effect measurement shows that the samples are P-type semiconductors. The electrical conductivity increasers after Cu doped due to the increase of carrier concentration and the improvement in crystallinity. Though the Seebeck coefficient decreases after Cu doped, the ZT value increases from 0.11 to 0.43 with higher electrical conductivity and lower thermal conductivity at room-temperature. The temperature-dependent of ZT value is estimated to be ∼1.35 for the thin film with Zn4Sb3 phase by using the bulk lattice thermal conductivity together with the thin film electrical thermal conductivity.

Enhanced thermoelectric properties of mixed zinc antimonide thin films via phase optimization

Abstract: A series of Zn-Sb thin films were deposited by direct current (DC) magnetron co-sputtering through fixing the sputtering power of Zn target while varying the sputtering power of Sb target. The deposited thin films were annealed at 673 K under Ar atmosphere for 1 h. X-ray diffraction (XRD) results show that the prepared thin film gradually transforms from β phase Zn 4 Sb 3 to ZnSb phase with increasing Sb sputtering power. It is found that the thermoelectric properties of the prepared Zn-Sb thin films are related to the phase transformation. Firstly, the carrier concentration decreases while the Hall mobility increases with increasing Sb sputtering power until 20 W, and then with further increasing Sb sputtering power, the carrier concentration increases while Hall mobility decreases. The thin films prepared by the Sb sputtering power of 20 W shows a mixed phase of ZnSb and Zn 4 Sb 3 and its Seebeck coefficient has a higher value than the samples with single β-Zn 4 Sb 3 or ZnSb phase. Through optimizing the ratio of β-Zn 4 Sb 3 to ZnSb phase in the mixed Zn-Sb thin film, an enhanced power factor of 1.91 × 10 −3 W/m K 2 can be obtained with a high Seebeck coefficient of 360 μV K −1 and a low resistivity of 6.79 × 10 −5 Ω m at 573 K. X-ray photoelectron spectroscopy (XPS) was used to investigate the binding energy of Zn and Sb in the thin film with a power factor of 1.91 × 10 −3 W/m K 2 and it is suggested that the weak bonding of the thin film could be one of the reasons resulting in enhanced thermoelectric performance.

Computational and experimental analysis on Te-doped ZnSb thermoelectric material

Abstract: We report a combined theoretical and experimental work on the tellurium doping of thermoelectric ZnSb. We investigated the influence of tellurium on the phase’s stabilities by DFT calculations. During experimental validation by SEM and EPMA characterization “needlelike” areas of Te-doped ZnSb were identified. The experimental results also highlight that for the compositions Zn0.5 Sb0.5-x Tex the system reaches a non-equilibrium state where ZnSb, ZnTe and Te-doped ZnSb are simultaneously present. The determination of the doping mechanism has demonstrated the formation of Te-doped Zn4Sb3 after quenching, leading to the formation of Te-doped ZnSb due to the zinc diffusion during annealing. Presumed from experimental observation oxygen prevents the tellurium diffusion. These results lead to the conclusion of an inert processing chain as a prerequisite for production of n-type ZnSb, which puts hurdles on a cheap and easily scalable tellurium doping for homogeneous and competitive products.