Normal Vibrations in Near-Conservative Self-Excited and Viscoelastic Nonlinear Systems

International audienceA perturbation methodology and power series are utilized to the analysis of nonlinear normal vibration modes in broad classes of finite-dimensional self-excited nonlinear systems close to conservative systems taking into account similar nonlinear normal modes. The analytical construction is presented for some concrete systems. Namely, two linearly connected Van der Pol oscillators with nonlinear elastic characteristics and a simplest two-degrees-of-freedom nonlinear model of plate vibrations in a gas flow are considered. Periodical quasinormal solutions of integro-differential equations corresponding to viscoelastic mechanical systems are constructed using a convergent iteration process. One assumes that conservative systems appropriate for the dominant elastic interactions admit similar nonlinear normal modes

ChemSpaceAL: An Efficient Active Learning Methodology Applied to Protein-Specific Molecular Generation

The incredible capabilities of generative artificial intelligence models have inevitably led to their application in the domain of drug discovery. Within this domain, the vastness of chemical space motivates the development of more efficient methods for identifying regions with molecules that exhibit desired characteristics. In this work, we present a computationally efficient active learning methodology that requires evaluation of only a subset of the generated data in the constructed sample space to successfully align a generative model with respect to a specified objective. We demonstrate the applicability of this methodology to targeted molecular generation by fine-tuning a GPT-based molecular generator toward a protein with FDA-approved small-molecule inhibitors, c-Abl kinase. Remarkably, the model learns to generate molecules similar to the inhibitors without prior knowledge of their existence, and even reproduces two of them exactly. We also show that the methodology is effective for a protein without any commercially available small-molecule inhibitors, the HNH domain of the CRISPR-associated protein 9 (Cas9) enzyme. We believe that the inherent generality of this method ensures that it will remain applicable as the exciting field of in silico molecular generation evolves. To facilitate implementation and reproducibility, we have made all of our software available through the open-source ChemSpaceAL Python package

Spectroscopy of Baryons Containing Two Heavy Quarks in Nonperturbative Quark Dynamics

We have studied the three quark systems in an Effective Hamiltonian approach in QCD. With only two parameters: the string tension sigma and the strong coupling constant alpha_s we obtain a good description of the ground state light and heavy baryons. The prediction of masses of the doubly heavy baryons not discovered yet are also given. In particular, a mass of 3620 MeV for the lightest (ccu) baryon is found by employing the hyperspherical formalism to the three quark confining potential with the string junction.Comment: 8 pages, LaTe

Ground-state baryons in nonperturbative quark dynamics

We review the results obtained in an Effective Hamiltonian (EH) approach for the three-quark systems. The EH is derived starting from the Feynman--Schwinger representation for the gauge-invariant Green function of the three quarks propagating in the nonperturbative QCD vacuum and assuming the minimal area law for the asymptotic of the Wilson loop. It furnishes the QCD consistent framework within which to study baryons. The EH has the form of the nonrelativistic three-quark Hamiltonian with the perturbative Coulomb-like and nonperturbative string interactions and the specific mass term. After outlining the approach, methods of calculations of the baryon eigenenergies and some simple applications are explained in details. With only two parameters: the string tension $\sigma=0.15 GeV^2$ and the strong coupling constant $\alpha_s=0.39$ a unified quantitative description of the ground state light and heavy baryons is achieved. The prediction of masses of the doubly heavy baryons not discovered yet are also given. In particular, a mass of $3660 MeV$ for the lightest $\Xi_{cc}$ baryon is found by employing the hyperspherical formalism to the three quark confining potential with the string junction.Comment: 25 pages, 4 figures included, LaTeX 2e; to be published in Phys. Atom. Nuc

Pentaquarks in the Jaffe-Wilczek approximation

The masses of $uudd\bar s$, $uudd\bar d$ and $uuss\bar d$ pentaquarks are evaluated in a framework of both the Effective Hamiltonian approach to QCD and spinless Salpeter using the Jaffe--Wilczek diquark approximation and the string interaction for the diquark--diquark--antiquark system. The pentaquark masses are found to be in the region above 2 GeV. That indicates that the Goldstone boson exchange effects may play an important role in the light pentaquarks. The same calculations yield the mass of $[ud]^2\bar c$ pentaquark $\sim$ 3250 MeV and $[ud]^2\bar b$ pentaquark $\sim$ 6509 MeV.Comment: 14 pages, 2 tables, LaTeX2e. References correcte

Comment on the proper QCD string dynamics in a heavy-light system

The string correction to the inter-quark interaction at large distances is derived using the field theory approach to a heavy-light quark-antiquark system in the modified Fock-Schwinger gauge.Comment: LaTeX2e, 6 pages, no figures, to appear in JETP Let

Biotehnološka primjena kvasca Yarrowia lipolytica uzgojenog u uvjetima nedostatka tiamina

During the cultivation of a thiamine-auxotrophic yeast strain Yarrowia lipolytica VKM Y-2412 on ethanol, the growth limitation by thiamine leads to the production of α-ketoglutaric acid. The α-ketoglutaric acid synthesis has been studied in dependence on pH, oxygen supply and ethanol, zinc and iron concentrations. Under optimal conditions, Y. lipolytica produced 88.7 g/L of α-ketoglutaric acid. The culture broth containing α-ketoglutaric acid was subjected to chemical treatment with hydrogen peroxide, which led to the formation of succinic acid in significant quantities (71.7 g/L). Further direct esterification of succinic acid with excess absolute ethanol yielded diethyl succinate. Biomass of Y. lipolytica, a superproducer of α-ketoglutaric acid, was characterized by a high content of protein and essential amino acids, free amino acids, and unusually large amount of γ-aminobutyric acid. The unique amino acid composition of the producer makes it possible to use this biomass as a component of parenteral nutrition mixtures and as a basis for neuroleptics.Auksotrofni kvasac Yarrowia lipolytica VKM Y-2412 uzgojen je na podlozi s etanolom u uvjetima nedostatka tiamina, što je dovelo do nastajanja α-ketoglutarne kiseline. Ispitana je ovisnost njezine sinteze o pH-vrijednosti, opskrbljenosti kisikom i etanolom, te koncentracijama cinka i željeza. U optimalnim je uvjetima kvasac Y. lipolytica proizveo 88,7 g/L α-ketoglutarne kiseline. Podloga za uzgoj koja je sadržavala α-ketoglutarnu kiselinu kemijski je obrađena vodikovim peroksidom, što je dovelo do nastajanja značajne koncentracije sukcinske kiseline (71,7 g/L). Daljnjom izravnom esterifikacijom sukcinske kiseline uz suvišak apsolutnog etanola dobiven je dietil sukcinat. Biomasu kvasca Y. lipolytica, koji proizvodi velike količine α-ketoglutarne kiseline, karakterizira veliki udjel proteina i esencijalnih aminokiselina, slobodnih aminokiselina i neuobičajeno velika količina γ-aminomaslačne kiseline. Jedinstveni aminokiselinski sastav kvasca omogućuje njegovu primjenu u intravenoznoj prehrani i pri liječenju pacijenata antipsihoticima

Vibrating the QCD string

The large distance behaviour of the adiabatic hybrid potentials is studied in the framework of the QCD string model. The calculated spectra are shown to be the result of interplay between potential-type longitudinal and string-type transverse vibrations.Comment: LaTeX2e, 9 pages, 2 Postscript figures, final version to appear in Yad.Fi

Yield performance and stability of modern breeding stock of spring durum wheat (Triticum durum Desf.) from Russia and Kazakhstan

Identifcation of adaptive responses of breeding material, developed in different breeding centers, helps to purposefully correct these traits where it is necessary. Thus, 42 modern breeding lines from eight institutions of Russia and Kazakhstan were studied in comparison with the historical standard Bezenchukskaya 139 in trails of 16-17 and 18 KASIB-SDW (Kazakhstan-Siberian net for wheat improvement, spring durum wheat) in 2015–2017. Field experiments and yield measurements in each ecological cite were similar. To solve these tasks of the experiment, two-factor ANOVA, methods for adaptability assessment cluster analysis and principle component method were applied. As a result, it was established that 1) genotype and genotype – environment interaction (overall 15.8–23.5 % of total dispersion) had signifcant effect on yield variability; 2) genotype – environment interactions were of linear nature and had no destabilizing effect; 3) all the genotypes tested can be distributed in three clusters, the frst one for locally adapted varieties, the third for varieties of a wide areal, the second included genotypes with intermediate characteristics; 4) breeding centers of the Federal Altai Scientifc Centre of Agro-Biotechnologies and of the Research Institute of Agriculture of South-East produced predominantly varieties of local importance, the Samara Research Institute of Agriculture – varieties of wide area; 5) a stable trend of increased mean yield compared to historical standard Bezenchukskaya 139 over ecological sites was observed only for Samara varieties; 6) varieties of all the breeding centers had no stable difference from Bezenchukskaya 139 concerning stability and responsiveness, which can be explained by an incomplete breeding process for these parameters and confrms the importance of the KASIB program; 7) a trend of yield increase compared to Bezenchukskaya 139 under testing in defnite local environments had more stable parameters with the largest progress observed in the Altai Research Institute of Agriculture (135.4 and 163.2 % to Bezenchukskaya 139), which can be explained by a high efciency of breeding of locally adapted varieties in the breeding center