Quantum theory of electric polarization nonlinearity in metal nanofilms

We develop a quantum theory of electron confinement in metal nanofilms. The theory is used to compute the nonlinear response of the film to a static or low-frequency external electric field and to investigate the role of boundary conditions imposed on the metal surface. We find that the sign and magnitude of the nonlinear polarizability depends dramatically on the type of boundary condition used.Comment: Accepted to PRB in this for

Spectroscopic studies of fractal aggregates of silver nanospheres undergoing local restructuring

We present an experimental spectroscopic study of large random colloidal aggregates of silver nanoparticles undergoing local restructuring. We argue that such well-known phenomena as strong fluctuation of local electromagnetic fields, appearance of "hot spots" and enhancement of nonlinear optical responses depend on the local structure on the scales of several nanosphere diameters, rather that the large-scale fractal geometry of the sample.Comment: 3.5 pages, submitted to J. Chem. Phy

Study of acute and subacute action of iron-molybdenum nanocluster polyoxometalates

There were no significant deviations from the norm in the functional state of the liver, kidneys, and pancreas in the study of the acute toxicity of iron-molybdenum buckyballs intended for targeted drug delivery. No accumulation of nanoparticles or deviation from the norm in any investigated parameter was detected in the study of subacute toxicity. © 2013 Pleiades Publishing, Ltd

Biosafety model of adenovirus infection: Effects of bacterial proteases for infection of human cells in vitro

To determine the antiviral activity of various biologically active compounds, the model of adenovirus infection on the basis of cell cultures of human HEK293A and recombinant adenovirus Ad-EGFP, expressing green fluorescent protein EGFP. Adenoviruses have a capsid size of 70-90 nm and are able to infect dividing and nondividing cells in vitro and in vivo. Recombinant adenoviruses are the replicative defect in the cells of humans and animals. The developed model allowed us to determine the effect of bacterial proteases in the infected cell cultures with adenovirus. This model can also be used for screening drugs with potential protivivovirusnoy activity

Gamma irradiation impact on electronic carrier transport in AlGaN/GaN high electron mobility transistors

AlGaN/GaN high electron mobility transistors were irradiated with Co-60 gamma-rays to doses up to 1000 Gy, in order to analyze the effects of irradiation on the devices\u27 transport properties. Temperature-dependent electron beam-induced current measurements, conducted on the devices before and after exposure to gamma-irradiation, allowed for the obtaining of activation energies related to radiation-induced defects due to nitrogen vacancies. DC current-voltage measurements were also conducted on the transistors to assess the impact of gamma-irradiation on transfer, gate, and drain characteristics

Main directions of the study of plant invasions in Russia

This article is focused on the analysis of major approaches to plant invasion research used by Russian researchers. Multivariate statistical methods allow for the visualization of various data, including those on alien species group structures in various region

Plant invasion research in Russia: basic projects and scientific fields

This paper represents a review of comprehensive research into invasion biology done by Russian scholars for four decades. Invasion biology is a relatively new field of research focused on the study of alien plants, their behavior in new habitats and risks they pose to indigenous species. It is shown that over 40 years, single finds of alien plant species have transformed into a check-list of invasive species in Russi

Local anisotropy and giant enhancement of local electromagnetic fields in fractal aggregates of metal nanoparticles

We have shown within the quasistatic approximation that the giant fluctuations of local electromagnetic field in random fractal aggregates of silver nanospheres are strongly correlated with a local anisotropy factor S which is defined in this paper. The latter is a purely geometrical parameter which characterizes the deviation of local environment of a given nanosphere in an aggregate from spherical symmetry. Therefore, it is possible to predict the sites with anomalously large local fields in an aggregate without explicitly solving the electromagnetic problem. We have also demonstrated that the average (over nanospheres) value of S does not depend noticeably on the fractal dimension D, except when D approaches the trivial limit D=3. In this case, as one can expect, the average local environment becomes spherically symmetrical and S approaches zero. This corresponds to the well-known fact that in trivial aggregates fluctuations of local electromagnetic fields are much weaker than in fractal aggregates. Thus, we find that, within the quasistatics, the large-scale geometry does not have a significant impact on local electromagnetic responses in nanoaggregates in a wide range of fractal dimensions. However, this prediction is expected to be not correct in aggregates which are sufficiently large for the intermediate- and radiation-zone interaction of individual nanospheres to become important.Comment: 9 pages 9 figures. No revisions from previous version; only figure layout is change

Bacterial enzymes effectively digest Alzheimer's β-amyloid peptide

© 2014 Elsevier Inc. Aggregated β-amyloid peptides play key roles in the development of Alzheimer's disease, and recent evidence suggests that microbial particles, among others, can facilitate their polymerization. Bacterial enzymes, however, have been proved to be beneficial in degrading pathological fibrillar structures in clinical settings, such as strepto-kinases in resolving blood-clots. The purpose of this study was to investigate the ability of bacterial substances to effectively hydrolyze β-amyloid peptides. Degrading products of several proteinases from Bacillus pumilus were evaluated using MALDI-TOF mass-spectrometry, and their toxicity was assessed in vitro using cell-culture assays and morphological studies. These enzymes have proved to be non-toxic and were demonstrated to cleave through the functional domains of β-amyloid peptide. By yielding inactive fragments, proteinases of Bacillus pumilus may be used as candidate anti-amyloid agents

Design principles for riboswitch function

Scientific and technological advances that enable the tuning of integrated regulatory components to match network and system requirements are critical to reliably control the function of biological systems. RNA provides a promising building block for the construction of tunable regulatory components based on its rich regulatory capacity and our current understanding of the sequence–function relationship. One prominent example of RNA-based regulatory components is riboswitches, genetic elements that mediate ligand control of gene expression through diverse regulatory mechanisms. While characterization of natural and synthetic riboswitches has revealed that riboswitch function can be modulated through sequence alteration, no quantitative frameworks exist to investigate or guide riboswitch tuning. Here, we combined mathematical modeling and experimental approaches to investigate the relationship between riboswitch function and performance. Model results demonstrated that the competition between reversible and irreversible rate constants dictates performance for different regulatory mechanisms. We also found that practical system restrictions, such as an upper limit on ligand concentration, can significantly alter the requirements for riboswitch performance, necessitating alternative tuning strategies. Previous experimental data for natural and synthetic riboswitches as well as experiments conducted in this work support model predictions. From our results, we developed a set of general design principles for synthetic riboswitches. Our results also provide a foundation from which to investigate how natural riboswitches are tuned to meet systems-level regulatory demands