The results of investigation of profiles formed by ion-beam etching of semiconductor structures through a photolithographic mask are presented. The minimum dimensions of unmasked regions on the ...surfaces of two studied structures are 2 and 5 μm, respectively. It is demonstrated that the etching rate reduces with reduction in the width of the unmasked gap. The effect of reflection of the ion beam from vertical walls formed during etching may be used for fabrication of submicron separating mesaregions.
Mesaelements of the focal plane array (FPA) of p-i-n diodes based on Al^sub x^Ga^sub 1-x^N for p-i-n heteroepitaxial structures (HESs) grown by the molecular-beam epitaxy and hydride epitaxy methods ...with the use of metalorganic compounds are formed. Elements of 320 × 256 FPAs with a pitch of 30 mum are separated by means of ion-beam etching through a photoresist mask in the argon ion stream produced by the Kaufmann ion source in a vacuum plant. To determine the required etching depth, contact profilometry and ultraviolet spectrophotometry methods allowing one to determine positions of the n-layer and sufficient etching depth of the sample are used. The thickness accuracy of the HES functional layers stated in manufacturer's certificates does not exceed 28%. Rates of ion-beam etching of Al^sub x^Ga^sub 1-x^N for p-i-n layers with different compositions are determined.
Mesaelements of the focal plane array (FPA) of
p
–
i
–
n
diodes based on Al
x
Ga
1–
x
N for
p–i–n
heteroepitaxial structures (HESs) grown by the molecular-beam epitaxy and hydride epitaxy methods ...with the use of metalorganic compounds are formed. Elements of 320 × 256 FPAs with a pitch of 30 μm are separated by means of ion-beam etching through a photoresist mask in the argon ion stream produced by the Kaufmann ion source in a vacuum plant. To determine the required etching depth, contact profilometry and ultraviolet spectrophotometry methods allowing one to determine positions of the
n
-layer and sufficient etching depth of the sample are used. The thickness accuracy of the HES functional layers stated in manufacturer’s certificates does not exceed 28%. Rates of ion-beam etching of Al
x
Ga
1–
x
N for
p–i–n
layers with different compositions are determined.
Spectral diversity of fluorescent proteins, crucial for multiparameter imaging, is based mainly on chemical diversity of their chromophores. Recently we have reported, to our knowledge, a new green ...fluorescent protein WasCFP—the first fluorescent protein with a tryptophan-based chromophore in the anionic state. However, only a small portion of WasCFP molecules exists in the anionic state at physiological conditions. In this study we report on an improved variant of WasCFP, named NowGFP, with the anionic form dominating at 37°C and neutral pH. It is 30% brighter than enhanced green fluorescent protein (EGFP) and exhibits a fluorescence lifetime of 5.1 ns. We demonstrated that signals of NowGFP and EGFP can be clearly distinguished by fluorescence lifetime in various models, including mammalian cells, mouse tumor xenograft, and Drosophila larvae. NowGFP thus provides an additional channel for multiparameter fluorescence lifetime imaging microscopy of green fluorescent proteins.
The elucidation of the reasons and character of the influence of nature substituent and solvent composition on the kinetic features and selectivity of liquid-phase catalytic hydrogenation of ...compounds containing several reactive capable groups is a theoretical and practically significant task. In the presented work the process of 2-nitroazobenzene derivatives hydrogenation with various substituents was investigated in order to obtain the corresponding benzotriazoles on a skeletal nickel catalyst in a neutral azeotropic aqueous solution of 2-propanol, and in the presence of acetic acid or sodium hydroxide. According to the data obtained, the solvent composition has a decisive influence on the selectivity of this process. The transformation of azo- and nitro groups, included in the initial compound, proceeds in parallel stages, and the introduction of acidic or basic additives leads to а change in the rate ratio of these stages. Appropriately, selectivity of 2-nitroazobenzene derivatives hydrogenation changes with respect to reaction products containing a triazole ring, in particular, with respect to N-oxides of substituted benzotriazoles, and also with respect to nitrohydrazo compounds. The greatest influence of substituent nature on the hydrogenation selectivity in a solvent with any composition is manifested for the group whose transformation rate in a given medium is higher. In the presence of acid the substituent variation is more strongly reflected in the hydrogenation rate of azo group, and in the basic medium – of nitro group. It was found that the change in the transformation rate of both reactive capable groups corresponds to the Hammett constant alteration. The electron acceptor substituent has a deactivating effect on the transformation rate of nitro as well azo group. To increase the selectivity of substituted 2-nitroazobenzenes hydrogenation with respect to compounds containing a triazole ring, it is recommended to introduce a base into the aqueous solution of 2-propanol.
Cytotoxins are positively charged polypeptides that constitute about 60% of all proteins in cobra venom; they have a wide spectrum of biological activities. By CD spectroscopy, cytotoxins CT1 and CT2 ...Naja oxiana, CT3 Naja kaouthia, and CT1 and CT2 Naja haje were shown to have similar secondary structure in an aqueous environment, with dominating beta-sheet structure, and to vary in the twisting angle of the beta-sheet and the conformation of disulfide groups. Using dodecylphosphocholine micelles and liposomes, CT1 and CT2 Naja oxiana were shown to incorporate into lipid structures without changes in the secondary structure of the peptides. The binding of CT1 and CT2 Naja oxiana with liposomes was associated with an increase in the beta-sheet twisting and a sign change of the dihedral angle of one disulfide group. The cytotoxins were considerably different in cytotoxicity and cooperativity of the effect on human promyelocytic leukemia cells HL60, mouse myelomonocytic cells WEHI-3, and human erythroleukemic cells K562. The most toxic CT2 Naja oxiana and CT3 Naja kaouthia possessed low cooperativity of interaction (Hill coefficient h = 0.6-0.8), unlike 10-20-fold less toxic CT1 and CT2 Naja haje (h = 1.2-1.7). CT1 Naja oxiana has an intermediate position on the cytotoxicity scale and is characterized by h = 0.5-0.8. The cytotoxins under study induced necrosis of HL60 cells and failed to activate apoptosis. The differences in cytotoxicity are supposed to be related not with features of the secondary structure of the peptides, but with interactions of side chains of variable amino acid residues with lipids and/or membrane proteins.
Resident cardiac stem cells, known as “cardiogenic progenitor cells” (CPCs), are a heterogeneous population of immature cells residing in the myocardium and capable of self-renewal and ...differentiation into cardiomyocyte-like and vascular-like cells. CPCs are usually isolated by long enzymatic digestion of heart tissue and selection with stem cell markers. However, long exposure to enzymatic digestion and the small size of a myocardial sample significantly hinder acquiring a large number of viable cells. To avoid these problems, we developed a method based on CPC growth ex vivo and subsequent immunomagnetic selection.
This is a study of the influence of contamination in an S-4800 scanning electron microscope at electron energies of 1 keV on the profile of the surface relief elements of an MShPS-2.0K standard ...gauge. The observed width of the upper base of the relief elements is found to increase with electron irradiation dose in different irradiation modes.
Results from studies of the influence of contamination in S-4800 scanning electron microscopes on the profile of relief elements in monocrystalline silicon are presented. It is shown that the form of ...the profile of relief elements varies as a result of irradiation by electrons with energy 20 keV. The dependences of the dimensional parameters of the relief elements on the electron irradiation dose for different irradiation regimes are also considered.
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