535 research outputs found
ON THE ISSUE OF PLANNING SOWING AGRICULTURAL CROPS WITH THE MINIMUM RISK UNDER THE PRESENCE OF VARIOUS AGROCLIMATIC CONDITIONS
The present paper deals with one problem of quantitative controlling the seeding of the sown area by agricultural crops in different agroclimatic conditions. The considered problem is studied from the standpoint of three strategies: from the seeding planning perspective aiming at minimal risk associated with possible unfavourable agroclimatic conditions (a probabilistic approach is used); from the perspective of obtaining the maximum crops sales profit (a deterministic approach is used); from the perspective of obtaining the maximum crops harvest. For the considered problem, mathematical models are constructed (one probabilistic model and two deterministic models, respectively), their analytical solutions are found, and then, using a specific example, the application of the constructed and solved mathematical models is illustrated as well as the obtained numerical results are analysed.
Екологічний стан агроландшафтів території межиріччя Західного Бугу та Прип’ять
The results of the evaluation of the ecological status of the territory of agricultural landscapes between the rivers Western Bug and Pripyat are given in view the existing ecological-reclamation monitoring system. It is highlighted the need to control water flow and water supplies to prevent negative consequences from the possible anthropogenic impact on the underground hydrosphere of the region.Наведено результати оцінювання екологічного стану агроландшафтів території межиріччя Західного Бугу та Прип’яті з урахуванням існуючої системи еколого-меліоративного моніторингу. Відмічено необхідність контролю водотоків та водозапасів для уникнення негативних наслідків з боку можливого антропогенного втручання в підземну гідросферу регіон
Influence of randomly distributed magnetic nanoparticles on surface superconductivity in Nb films
We report on combined resistance and magnetic measurements in a hybrid
structure (HS) of randomly distributed anisotropic CoPt magnetic nanoparticles
(MN) embedded in a 160 nm Nb thick film. Our resistance measurements exhibited
a sharp increase at the magnetically determined bulk upper-critical fields
Hc2(T). Above these points the resistance curves are rounded, attaining the
normal state value at much higher fields identified as the surface
superconductivity fields Hc3(T). When plotted in reduced temperature units, the
characteristic field lines Hc3(T) of the HS and of a pure Nb film, prepared at
exactly the same conditions, coincide for H10 kOe
they strongly segregate. Interestingly, the characteristic value H=10 kOe is
equal to the saturation field of the MN. The behavior mentioned above is
observed only for the case where the field is normal to the HS, while is absent
when the field is parallel to the film. Our experimental results suggest that
the observed enhancement of surface superconductivity field Hc3(T) is possibly
due to the not uniform local reduction of the external magnetic field by the
dipolar fields of the MN.Comment: to be published in Phys. Rev.
Generalized Darboux transformations for the KP equation with self-consistent sources
The KP equation with self-consistent sources (KPESCS) is treated in the
framework of the constrained KP equation. This offers a natural way to obtain
the Lax representation for the KPESCS. Based on the conjugate Lax pairs, we
construct the generalized binary Darboux transformation with arbitrary
functions in time for the KPESCS which, in contrast with the binary Darboux
transformation of the KP equation, provides a non-auto-B\"{a}cklund
transformation between two KPESCSs with different degrees. The formula for
N-times repeated generalized binary Darboux transformation is proposed and
enables us to find the N-soliton solution and lump solution as well as some
other solutions of the KPESCS.Comment: 20 pages, no figure
Reentrant superconductivity in superconductor/ferromagnetic-alloy bilayers
We studied the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) like state
establishing due to the proximity effect in superconducting Nb/Cu41Ni59
bilayers. Using a special wedge-type deposition technique, series of 20-35
samples could be fabricated by magnetron sputtering during one run. The layer
thickness of only a few nanometers, the composition of the alloy, and the
quality of interfaces were controlled by Rutherford backscattering
spectrometry, high resolution transmission electron microscopy, and Auger
spectroscopy. The magnetic properties of the ferromagnetic alloy layer were
characterized with superconducting quantum interference device (SQUID)
magnetometry. These studies yield precise information about the thickness, and
demonstrate the homogeneity of the alloy composition and magnetic properties
along the sample series. The dependencies of the critical temperature on the Nb
and Cu41Ni59 layer thickness, Tc(dS) and Tc(dF), were investigated for constant
thickness dF of the magnetic alloy layer and dS of the superconducting layer,
respectively. All types of non-monotonic behaviors of Tc versus dF predicted by
the theory could be realized experimentally: from reentrant superconducting
behavior with a broad extinction region to a slight suppression of
superconductivity with a shallow minimum. Even a double extinction of
superconductivity was observed, giving evidence for the multiple reentrant
behavior predicted by theory. All critical temperature curves were fitted with
suitable sets of parameters. Then, Tc(dF) diagrams of a hypothetical F/S/F
spin-switch core structure were calculated using these parameters. Finally,
superconducting spin-switch fabrication issues are discussed in detail in view
of the achieved results.Comment: 34 pages, 9 figure
Genetic environment of the blaKPC-2 gene in a Klebsiella pneumoniae isolate that may have been imported to Russia from Southeast Asia
The nucleotide sequence of a blaKPC-2-harboring plasmid (pKPCAPSS) from Klebsiella pneumoniae ST273 isolated in Saint Petersburg, Russia, from a patient with history of recent travel to Vietnam is presented. This 127,970-bp plasmid possessed both IncFII and IncR replicons. blaKPC-2 was localized on a hypothetical mobile element. This element was flanked by 38-bp inverted Tn3 repeats and included a Tn3-specific transposase gene, macrolide resistance operon (mphA-mrx-mphR), and a fragment of blaTEM with unique polymorphisms. © 2017 American Society for Microbiology. All Rights Reserved
Experimental and theoretical analysis of the upper critical field in FSF trilayers
The upper critical magnetic field H_{c2} in thin-film FSF trilayer spin-valve
cores is studied experimentally and theoretically in geometries perpendicular
and parallel to the heterostructure surface. The series of samples with
variable thicknesses of the bottom and of the top Cu_{41}Ni_{59} F-layers are
prepared in a single run, utilizing a wedge deposition technique. The critical
field H_{c2} is measured in the temperature range K and for magnetic
fields up to 9 Tesla. A transition from oscillatory to reentrant behavior of
the superconducting transition temperature versus F-layers thickness, induced
by an external magnetic field, has been observed for the first time. In order
to properly interpret the experimental data, we develop a quasiclassical
theory, enabling one to evaluate the temperature dependence of the critical
field and the superconducting transition temperature for an arbitrary set of
the system parameters. A fairly good agreement between our experimental data
and theoretical predictions is demonstrated for all samples, using a single set
of fit parameters. This confirms adequacy of the
Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) physics in determining the unusual
superconducting properties of the studied Cu_{41}Ni_{59}/Nb/Cu_{41}Ni_{59}
spin-valve core trilayers.Comment: 16 pages, 7 figures; published versio
Molecular mechanisms of vascular tissue patterning in <i>Arabidopsis thaliana</i> L. roots
A vascular system in plants is a product of aromorphosis that enabled them to colonize land because it delivers water, mineral and organic compounds to plant organs and provides effective communications between organs and mechanical support. Vascular system development is a common object of fundamental research in plant development biology. In the model plant Arabidopsis thaliana, early stages of vascular tissue formation in the root are a bright example of the self-organization of a bisymmetric (having two planes of symmetry) pattern of hormone distribution, which determines vascular cell fates. In the root, vascular tissue development comprises four stages: (1) specification of progenitor cells for the provascular meristem in early embryonic stages, (2) the growth and patterning of the embryo provascular meristem, (3) postembryonic maintenance of the cell identity in the vascular tissue initials within the root apical meristem, and (4) differentiation of their descendants. Although the anatomical details of A. thaliana root vasculature development have long been known and described in detail, our knowledge of the underlying molecular and genetic mechanisms remains limited. In recent years, several important advances have been made, shedding light on the regulation of the earliest events in provascular cells specification. In this review, we summarize the latest data on the molecular and genetic mechanisms of vascular tissue patterning in A. thaliana root. The first part of the review describes the root vasculature ontogeny, and the second reconstructs the sequence of regulatory events that underlie this histogenesis and determine the development of the progenitors of the vascular initials in the embryo and organization of vascular initials in the seedling root
Location of the Energy Levels of the Rare-Earth Ion in BaF2 and CdF2
The location of the energy levels of rare-earth (RE) elements in the energy
band diagram of BaF2 and CdF2 crystals is determined. The role of RE3+ and RE2+
ions in the capture of charge carriers, luminescence, and the formation of
radiation defects is evaluated. It is shown that the substantial difference in
the luminescence properties of BaF2:RE and CdF2:RE is associated with the
location of the excited energy levels in the band diagram of the crystals
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