Clarification Of Aqueous Suspensions With A High Content Of Suspended Solids In Rapid Sand Filters

The presented work is devoted to solving the actual problem of increasing the efficiency of rapid sand filters with granular filling, which operate at a constant filtration rate when cleaning suspensions with a relatively high concentration of contaminants. The proposed mathematical model for clarifying the suspension by filtration consists of three interconnected blocks: clarified, filtration, and hydraulic. Convenient dimensionless mathematical dependencies are obtained for calculating the concentrations of contaminants and sediment from the height of the filter and suspension in the filtrate; head loss in the filter loading; the effective time of the filter (the duration of the filter cycle). The design of the experimental setup and the methodology for conducting experimental studies and mathematical processing of the results are valid. The results of experimental studies of the suspension filtering process through the granular loading are presented, and the obtained data is analyzed. Measurement of pressure losses in the filter loading is performed when a suspension is passed with a relatively high concentration of contaminants at various filtration rates. The nature of the change in the filtration rate with time and height (length) loading at various filtration rates and initial contamination concentrations is determined. Measured variable concentration of suspended matter in filtered water and retained contamination over time. As a result of the experiments, it is confirmed that an increase in the concentration of retained contaminants S leads to an increase in the parameter Δn/n. Upon reaching a certain value of the concentration of the retained sediment S (in our case S=30 g/dm3), an increase in the relative specific volume of the sediment greater than Δn/n0=0.65 is not observed. It is established that an important characteristic of the retained sediment is the ratio of the volume concentration of the sediment to the volume concentration of solid particles in this sediment γ=Csd/Сs. The values of the adhesion and detachment of particles of contaminant in the particles of the material loading =4,9; =0,009. The results of experimental studies in general confirm the correctness and reliability of the obtained analytical dependencies

Electronic properties of disclinated flexible membrane beyond the inextensional limit: Application to graphene

Gauge-theory approach to describe Dirac fermions on a disclinated flexible membrane beyond the inextensional limit is formulated. The elastic membrane is considered as an embedding of 2D surface into R^3. The disclination is incorporated through an SO(2) gauge vortex located at the origin, which results in a metric with a conical singularity. A smoothing of the conical singularity is accounted for by replacing a disclinated rigid plane membrane with a hyperboloid of near-zero curvature pierced at the tip by the SO(2) vortex. The embedding parameters are chosen to match the solution to the von Karman equations. A homogeneous part of that solution is shown to stabilize the theory. The modification of the Landau states and density of electronic states of the graphene membrane due to elasticity is discussed.Comment: 15 pages, Journal of Physics:Condensed Matter in pres

Effective approach to the Nagaoka regime of the two dimensional t-J model

We argue that the t-J model and the recently proposed Ising version of this model give the same physical picture of the Nagaoka regime for J/t << 1. In particular, both models are shown to give compatible results for a single Nagaoka polaron as well as for a Nagaoka bipolaron. When compared to the standard t-J or t-Jz models, the Ising version allows for a numerical analysis on much larger clusters by means of classical Monte Carlo simulations. Taking the advantage of this fact, we study the low doping regime of t-J model for J/t << 1 and show that the ground state exhibits phase separation into hole-rich ferromagnetic and hole-depleted antiferromagnetic regions. This picture holds true up to a threshold concentration of holes, \delta < \delta_t ~ 0.44 \sqrt{J/t}. Analytical calculations show that \delta_t=\sqrt{J/2\pi t}.Comment: 10 pages, 10 figures, revte

Plant cell wall and the mechanisms of resistance to pathogens

A huge variety of phytopathogens (viruses, bacteria, fungi) are potentially able to infect plant tissues and cause diseases. Numerous plant genes control a complex network of defense mechanisms based on both constitutive and inducible processes. The cell wall is a primary barrier the pathogens have to penetrate to start the infection process. However,it is able to block invasion by most non-specific potential pathogens. The cell wall structure may differ in various plant species. It is based on the net of cellulose microfibrils linked by hemicellulose molecules. Pectin and lignin are the other important cell wall constituents. Dozens of proteins inside the cell wall are involved in structural and metabolic processes as well as in signal transduction and regulatory circuits (more information is available in W allProtDB database). Each of these components contributes to resistance to pathogens. At the points of contact with potential pathogens cell wall structural changes and accumulation of metabolites with antimicrobial, antifungal or antiviral activities occur. Some pathogens could produce hydrolytic enzymes able to degrade cellulose and pectin to counteract these non-specific plant resistance mechanisms. In turn, plants developed the inhibitors of pathogen-related enzymes and this “arms race” is an important part of plant evolution and host-pathogen interaction mechanisms. Plants also can evaluate the cell wall state to compensate for imbalances and deficiencies. For instance, mutants with cellulose deficiency may have a higher lignification rate and a stronger stress response. The cell wall is also a source of signal molecules triggering the initiation of response mechanisms. In total, the plan cell wall is a complex dynamic structure able to prevent infection by most potential (non-specific) pathogens and switch on the mechanisms of plant immune response. The reconstruction of gene networks controlling the cell wall structural and functional organization during the growth, and under normal and stressful conditions is vitally important for understanding the basic molecular mechanisms of development and stress resistance. The mechanisms of specific and non- specific plant resistance to various phytopathogens connected to the cell wall structure are reviewed. The roles of the cell wall constituents in pathogen detection and the induction of defense mechanism are discusse

A database on genes increasing resistance of wheat and relative species against pathogenic fungi

Fungi belong to the major plant pathogens and investigation of plant resistance genes is a quite important task. During the last years many wheat resistance genes were identified. However, the sequencing of the Triticum aestivum L. genome is still going on and the nucleotide sequences of most resistance genes are not yet known. In addition, the study of allelic variants of resistance genes is important for better understanding of the molecular mechanisms of their action. In this paper we present an information resource for accumulation of data on sequenced genes of wheat and its relatives providing resistance against diseases caused by fungal pathogens. The database (Pathogenesis-Related Genes, PRG) contains information on gene chromosomal localizations and functional activities, nucleotide sequences and single nucleotide polymorphisms associated with their effects. PRG provides data on the proteins encoded, pathogens and diseases, as well as on the resistance gene expression patterns in response to pathogen inoculations, exposure to hormones and various external stimuli. It also has cross-references with related entries from the databases on nucleotide sequences (GenBank) and proteins (UniProt). Information entered into the database is a result of the annotation of scientific publications and manual curation. Currently PRG compiles data on 75 allelic variants of 66 resistance genes. The PRG database was developed on the basis of the SRS (Sequence Retrieval System) platform. This system allows the use of complex queries and visualization tools and automatically generates www-interface with the information in table or text formats. PRG may be useful for researchers studying plant biology or breeding new plant cultivars resistant to fungal diseases. It is available at the address: http://srs6.bionet.nsc.ru/srs6bin/cgi-bin/wgetz?-page+top+-newId

New genetic tools for plant defense against parasitic nematodes

Nematodes belong to economically important pests. Here we reviewed the recent data on molecular mechanisms of plant resistance to cyst and gall nematodes including the most devastating Globodera rostochiensis, G. pallida, Heterodera schachtii, Meloidogyne chitwoodi, and M. incognita. The Golden Potato Cyst Nematode (G. rostochiensis, GPCN) may be taken as an example of an economically important pest: in Russia, it occurs in 61 regions with a total area of 1.8 million ha and may cause the yield loss from 19 to 90 %. The biological characteristics of sedentary nematodes makes their agrotechnical control problematic, i.e. the GPCN cysts remain dormant in soil for many years until a susceptible host appears, whereas nematicides are either toxic or inefficient. Introgression of resistance genes (R-genes) from related cultivated or wild species is likely to be the most appropriate way for their biocontrol. The life cycle of sedentary nematodes is based on juveniles’ penetration into the host root where they reprogram plant cells into a syncytium or the so-called ‘giant cells’ and inhibit the plant defense response. Molecular mechanisms of plant-nematode interaction are unusual and this phenomenon provides a very interesting model for the investigation of plant morphogenesis control as well as for the development of new genetic instruments of biocontrol. Here we reviewed recent publications on plant parasitic nematode effectors used for hijacking of the plant immune system, data on R-genes and molecular mechanisms of their activities. In addition, host-induced gene silencing (HIGS) is discussed as a perspective mechanism for nematode biocontrol. HIGS is based on the RNA interference in the cells of the host plant addressed against the nematode genes important for their development and productivity. Several recent investigations demonstrated efficiency of HIGS against sedentary nematodes

Influence of allelic polymorphism in the 3’ untranslated region of the <i>StTCP23</i> gene on the tolerance of potato cultivars to the potato spindle tuber viroid

Background. It is known that the pathological phenotype of potato plants can be mediated by complementary interactions between the genomic RNA of PSTVd and mRNA of some regulatory genes, which consequently lead to RNA interference, the synthesis of small interfering RNAs (vd-sRNA PSTVd), and impaired morphogenesis. At the same time, symptoms caused by the viroid may vary in different potato cultivars. Here we predict the interactions between the 3’ UTRs of various alleles of the StTCP23 transcription factor gene and the complementary regions in PSTVd genomic RNA.Materials and methods. We selected eight commercial potato cultivars with different symptoms of viroid infection and disease. For each cultivar, six clones of each cDNA amplicon of StTCP23 with a 3’ UTR were identified, and the allelic compositions of the target regions within their 3’ UTRs were characterized.Results. In total, 11 types of alleles of the 3’ UTR StTCP23 segment complementary to the vd-sRNA PSTVd were identified. Cultivars with the A allele (‘Gala’, ‘Colomba’, ‘Favorit’, and ‘Fioletovy’) identical to the reference genome or a high dose of the C allele with a deletion of four nucleotides (cv. ‘Impala’) were characterized by high susceptibility already at the primary (firstyear) infection with the PSTVd. Cvs. ‘Krepysh’, ‘Labadia’ and ‘Riviera’, classified as tolerant during primary inoculation, on the contrary, were characterized by the absence of the A allele and the presence of cultivar-specific mutant alleles.Conclusion. A high degree of polymorphism in the target site (3’ UTR region) of StTCP23 indicates a possible selection pressure on this locus. It can be assumed that cultivars with shorter alleles, which have fewer bases complementary to vd-sRNA in hypothetical duplexes and therefore less likely to induce target gene silencing, are more tolerant to the PSTVd upon primary viroid infection