Biomedical subjects

D Zakharov

Publications and source records attributed to D Zakharov.

4 recordsLinked to original sources

PubMed2004

Atomic structure of defects in GaN:Mg grown with Ga polarity.

The atomic structure of characteristic defects (Mg-rich hexagonal pyramids and truncated pyramids) in GaN:Mg thin films grown with Ga polarity was determined at atomic resolution by reconstruction of the scattered electron wave in a transmission electron microscope. Small cavities within the defects have inside walls covered by GaN of reverse polarity. We propose that lateral overgrowth of the cavities restores matrix polarity on the defect base. From matrix to defect, exchange of Ga and N sublattices leads to a 0.6+/-0.2 A displacement of Ga sublattices. We observe a [1100]/3 shift from matrix AB stacking to BC stacking for the entire pyramid. Electron energy loss spectroscopy detected changes in N edge and presence of oxygen on the defect walls. Our results explain commonly observed decrease of acceptor concentration in heavily doped GaN:Mg.

Journal Article↗

PubMed2004

Screw dislocations in GaN grown by different methods.

A study of screw dislocations in hydride-vapor-phase-epitaxy (HVPE) template and molecular-beam-epitaxy (MBE) overlayers was performed using transmission electron microscopy (TEM) in plan view and in cross section. It was observed that screw dislocations in the HVPE layers were decorated by small voids arranged along the screw axis. However, no voids were observed along screw dislocations in MBE overlayers. This was true both for MBE samples grown under Ga-lean and Ga-rich conditions. Dislocation core structures have been studied in these samples in the plan-view configuration. These experiments were supported by image simulation using the most recent models. A direct reconstruction of the phase and amplitude of the scattered electron wave from a focal series of high-resolution images was applied. It was shown that the core structures of screw dislocations in the studied materials were filled. The filed dislocation cores in an MBE samples were stoichiometric. However, in HVPE materials, single atomic columns show substantial differences in intensities and might indicate the possibility of higher Ga concentration in the core than in the matrix. A much lower intensity of the atomic column at the tip of the void was observed. This might suggest presence of lighter elements, such as oxygen, responsible for their formation.

Gallium↗

PubMed1996

Nested retrotransposons in the intergenic regions of the maize genome.

The relative organization of genes and repetitive DNAs in complex eukaryotic genomes is not well understood. Diagnostic sequencing indicated that a 280-kilobase region containing the maize Adh1-F and u22 genes is composed primarily of retrotransposons inserted within each other. Ten retroelement families were discovered, with reiteration frequencies ranging from 10 to 30,000 copies per haploid genome. These retrotransposons accounted for more than 60 percent of the Adh1-F region and at least 50 percent of the nuclear DNA of maize. These elements were largely intact and are dispersed throughout the gene-containing regions of the maize genome.

Chromosomes, Artificial, Yeast↗

PubMedDate not supplied

[Assessing the informative value of positron emission tomography with the new radiopharmaceutical Sodium 11C-butyrate versus small-dose dobutamine stress echocardiography in the diagnosis of myocardial viability in patients with coronary heart disease and left ventricular dysfunction].

Myocardial viability in patients with coronary artery disease and heart failure was assessed by echocardiography with low doses of dobutamine and positron emission tomography with Sodium 11C-butyrate. Sensitivity and specificity of those methods were compared. Positron emission tomography and Sodium 11C-butyrate had quite high sensitivity and specificity, which could be compared with positron emission tomography and fluorine-18-deoxyglucose. Echocardiography with low doses of dobutamine had high specificity and its sensitivity was lower that one of positron emission tomography and Sodium 11C-butyrate. Thus, it is necessary to use the protocol of stress dobutamine echocardiography with high doses to avoid this problem.

Adult↗