Applied nuclear physics at Yerevan Physics Institute

A number of areas of development of applied studies at the Yerevan Physics Institute (YerPhI) are viewed. The main area is research into possibilities to produce radio nuclides for nuclear medicine on the linear accelerator of electrons at YerPhI. We consider also the methods for employment of neutron beams obtained from photonuclear reactions for boron-capture neutron therapy and for nondestructive detection of fission materials.     

A Single Enzyme Transforms a Carboxylic Acid into a Nitrile through an Amide Intermediate

The biosynthesis of nitriles is known to occur through specialized pathways involving multiple enzymes; however, in bacterial and archeal biosynthesis of 7‐deazapurines, a single enzyme, ToyM, catalyzes the conversion of the carboxylic acid containing 7‐carboxy‐7‐deazaguanine (CDG) into its corresponding nitrile, 7‐cyano‐7‐deazaguanine (preQ₀). The mechanism of this unusual direct transformation was shown to proceed via the adenylation of CDG, which activates it to form the newly discovered amide intermediate 7‐amido‐7‐deazaguanine (ADG). This is subsequently dehydrated to form the nitrile in a process that consumes a second equivalent of ATP. The authentic amide intermediate is shown to be chemically and kinetically competent. The ability of ToyM to activate two different substrates, an acid and an amide, accounts for this unprecedented one‐enzyme catalysis of nitrile synthesis, and the differential rates of these two half reactions suggest that this catalytic ability is derived from an amide synthetase that gained a new function.     

On multiplicity of intersection point of two plane algebraic curves

The paper studies the multiplicity of intersecting point of two plane algebraic curves. The multiplicity is characterized by means of operators with partial derivatives. It is proved that if A is a point of multiplicity m for one of the curves and, a point of multiplicity n for the other curve, then the arithmetical multiplicity of the intersection (or the number of intersections) of the curves in A, is not less than mn and is equal to mn when the curves do not have common tangents at the point A.     

Synthesis of New Derivatives of 4-(1,4-Benzodioxan-2-yl)thiophene

Russian Journal of Organic Chemistry - thyl 2-amino-4-(1,4-benzodioxan-2-yl)thiophene-3-carboxylate was synthesized by the Gewald reaction of 2-acetyl-1,4-benzodioxane with ethyl 2-cyanoacetate and...     

Synthesis and Some Transformations of 5-(1,4-Benzodioxan-2-yl)-4-phenyl-4H-1,2,4-triazole-3-thiol

Russian Journal of Organic Chemistry - The title compound was synthesized by reaction of 1,4-benzodioxane-2-carbohydrazide with phenyl isothiocyanate, followed by cyclization of the...     

Influence of ultrasound on nanostructural iron formed by electrochemical reduction

A method for control of particle dimensions of nanostructural amorphous iron powder obtained by electrochemical reduction under the effect of ultrasonic oscillations in reaction medium is described in this paper. Depending on the character of ultrasonic oscillations nanostructural powders were obtained differing both in average dimension and distribution of particle dimensions. In the case of simultaneous sonocation using ultrasonic vibrations with frequencies differing from each other by a factor of ten (20 and 200 kHz), the effect is complex, but includes narrowing of the average particle dimension.     

Deciphering deazapurine biosynthesis: pathway for pyrrolopyrimidine nucleosides toyocamycin and sangivamycin

Pyrrolopyrimidine nucleosides analogs, collectively referred to as deazapurines, are an important class of structurally diverse compounds found in a wide variety of biological niches. In this report, a cluster of genes from Streptomyces rimosus (ATCC 14673) involved in production of the deazapurine antibiotics sangivamycin and toyocamycin was identified. The cluster includes toyocamycin nitrile hydratase, an enzyme that catalyzes the conversion of toyocamycin to sangivamycin. In addition to this rare nitrile hydratase, the cluster encodes a GTP cyclohydrolase I, linking the biosynthesis of deazapurines to folate biosynthesis, and a set of purine salvage/biosynthesis genes, which presumably convert the guanine moiety from GTP to the adenine-like deazapurine base found in toyocamycin and sangivamycin. The gene cluster presented here could potentially serve as a model to allow identification of deazapurine biosynthetic pathways in other bacterial species.     

Improving the Graphical Lasso Estimation for the Precision Matrix Through Roots of the Sample Covariance Matrix

In this article, we focus on the estimation of a high-dimensional inverse covariance (i.e., precision) matrix. We propose a simple improvement of the graphical Lasso (glasso) framework that is able to attain better statistical performance without increasing significantly the computational cost. The proposed improvement is based on computing a root of the sample covariance matrix to reduce the spread of the associated eigenvalues. Through extensive numerical results, using both simulated and real datasets, we show that the proposed modification improves the glasso procedure. Our results reveal that the square-root improvement can be a reasonable choice in practice. Supplementary material for this article is available online.     

Reply to “A comment on “A test of general relativity using the LARES and LAGEOS satellites and a GRACE Earth gravity model,by I. Ciufolini et al.””

In 2016, we published “A test of general relativity using the LARES and LAGEOS satellites and a GRACE Earth’s gravity model. Measurement of Earth’s dragging of inertial frames [1]”, a measurement of frame-dragging, a fundamental prediction of Einstein’s theory of General Relativity, using the laser-ranged satellites LARES, LAGEOS and LAGEOS 2. The formal error, or precision, of our test was about 0.2% of frame-dragging, whereas the systematic error was estimated to be about 5%. In the 2017 paper “A comment on “A test of general relativity using the LARES and LAGEOS satellites and a GRACE Earth’s gravity model by I. Ciufolini et al.”” by L. Iorio [2] (called I2017 in the following), it was incorrectly claimed that, when comparing different Earth’s gravity field models, the systematic error in our test due to the Earth’s even zonal harmonics of degree 6, 8, 10 could be as large as 15%, 6% and 36%, respectively. Furthermore, I2017 contains other, also incorrect, claims about the number of necessary significant decimal digits of the coefficients used in our test (claimed to be nine), in order to eliminate the largest uncertainties in the even zonals of degree 2 and 4, and about the non-repeatability of our test. Here we analyze and rebut those claims in I2017.