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Plasmids are extra-chromosomal genetic elements that encode a wide variety of phenotypes and can be maintained in bacterial populations through vertical and horizontal transmission, thus increasing bacterial adaptation to hostile environmental conditions like those imposed by antimicrobial sub-stances. To circumvent the segregational instability resulting from randomly distributing plasmids between daughter cells upon division, non-transmissible plasmids tend to be carried in multiple copies per cell, with the added benefit of exhibiting increased gene dosage and resistance levels. But carrying multiple copies also results in a high metabolic burden to the bacterial host, therefore reducing the overall fitness of the population. This trade-off poses an existential question for plasmids: What is the optimal plasmid copy number? In this manuscript, we address this question by postulating and analyzing a population genetics model to evaluate the interaction between selective pressure, the number of plasmid copies carried by each cell, and the metabolic burden associated with plasmid bearing in the absence of selection for plasmid-encoded traits. Parameter values of the model were estimated experimentally usingEscherichia coliK12 carrying a multicopy plasmid encoding for a fluorescent protein andblaTEM-1, a gene conferring resistance toβ-lactam antibiotics. By numerically determining the optimal plasmid copy number for constant and fluctuating selection regimes, we show that plasmid copy number is a highly optimized evolutionary trait that depends on the rate of environmental fluctuation and balances the benefit between increased stability in the absence of selection with the burden associated with carrying multiple copies of the plasmid.

Zn-doped YIG was prepared using the sol–gel method with TGA measurements showing the phase formation between 900 and 1000 °C. XRD analysis showed close to 1100 °C the formation of Franklinite phase, coexisting with the cubic YIG. Y3(Fe1–xZnx)5O12 samples with different Zn concentrations (x = 0, 0.01, 0.03, and 0.05) were prepared and analyzed for a magnetic study. A decrease in magnetic moment of the samples was confirmed on increasing the concentration of Zn ions. This decrease is due to the substitution of Fe ions by Zn. This also confirmed the results of XRD showing the linear increase in the lattice parameter. Fittings by Bloch's law shows results compared with those already reported in the literature. The exponent and constant for the Bloch law presented similar values to those reported for YIG doped with other ions. We obtained the parameter α ∼10−6 K−n with n close to 1.9 for all samples.

The photoluminescence (PL) of nonconjugated and bioconjugated core-shell CdSe/ZnS quantum dots (QDs) has been discussed in this paper. Commercial CdSe/ZnS QDs with the size of 3.6-4.0 nm covered by polymer with emission at 560-565 nm (2.19-2.22 eV) have been used. The QD bioconjugation is performed with the mouse anti PSA (Prostate-Specific Antigen) antibody (mab). PL spectra of nonconjugated QDs are characterized by a superposition of PL bands related to exciton emission in the CdSe core (2.19-2.22 eV) and to hot electron-hole emission via surface states (2.37, 2.73 and 3.06 eV) at the CdSe/ZnS or ZnS/polymer interfaces. The PL spectrum of bioconjugated QDs has changed dramatically, with essential decreasing of the hot electron-hole recombination flow via interface states. This effect is explained on the base of re-charging of QD interface states at the bioconjugation. It is shown that the CdSe/ZnS QDs with interface states are very promising for the study of bioconjugation effects to antibodies (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Photoluminescence (PL), Raman scattering and atomic force microscopy (AFM) investigations have been done for porous silicon (PSi) in as-prepared state. The Schottky barrier to porous silicon layer and ohmic electrical contact to p-type Si substrate have been created. Photocurrent spectral response and reverse current-voltage characteristics in the dark and with light exposition have been investigated for these structures. The photoelectric parameters of Schottky barrier have been discussed from the point of view of variation of the sizes of Si nanocrystallites. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The temperature-dependent photoluminescence (PL) spectra of highly uniform self-assembled InAs quantum dots (QDs) embedded in In 0.15 Ga 0.8 As/GaAs multi-quantum well (MQW) structures have been investigated. Spectral peak shift and PL temperature quenching for ground state (GS) and first excited state (1ES) optical transitions in the range 12-220 K are analyzed. Small FWHM values equal to 37 and 27 meV at 12 K characterize the GS and 1ES transitions, respectively. For the highly uniform QDs no unusual decrease of the FWHM at low temperatures was seen that would be connected with the redistribution of carriers between the QDs. The activation energies of the PL temperature quenching processes for GS and 1ES in InAs QDs are found to be the same, about 50-52 meV. The reasons for the same GS and 1ES thermal activation energies in InAs self-assembled QDs are discussed.

Measurements of the conductivity and the Hall effect of single crystals were performed on zinc oxide (ZnO) samples after a thermal diffusion of indium (In) and copper (Cu) with different time periods. Single crystals of ZnO were growth by hydrothermal method and annealed previously to diffusion process. Diffusion was carried out in ZnO at 1000 ΩC in N2 atmosphere for 3, 6, and 15 h. Hall effect measurements were carried out using the Van der Pauw configuration with a current of 1 mA and a magnetic field of 0.37 T at room temperature. Results showed an increase in donor concentration from 4.6x1014 cm–3 to 1.15×1017 cm–3 when In is diffused and up to 9.9×1015 cm–3 when Cu is introduced in ZnO. Mobility decreased from 134.9 (undoped ZnO) to 44.7 cm2/V s, in In-doped, and 101.9 cm2/V s, in Cu-doped. Resistivity decreased with time from 1.29x102 Ω cm to 1.26 Ω cm and 6.25 Ω cm, in the same order as described. Based on measurements, introduction of indium is faster than copper and the higher concentration of donors is result of substitution of Zn by an ion with a different valence. This is a relative simple method to control the conductivity and donor concentration in single crystals of ZnO. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Blends of poly(vinyl chloride) (PVC) with different copolymers have been studied to obtain a plasticized PVC with improved properties and the absence of plasticizer migration. The copolymers used as plasticizers in the blends were acrylonitrile butadiene rubber, ethylene vinyl acetate (EVA), and ethylene-acrylic copolymer (E-Acry). Blends were studied with regard to their processing, miscibility, and mechanical properties, as a function of blend and copolymer composition. The results obtained were compared with those of equivalent compositions in the PVC/dioctyl phthalate (DOP) system. Better results than PVC/DOP were obtained for PVC/acrylonitrile butadiene rubber blends. The plasticizing effect on PVC of EVA and E-Acry copolymers was similar to that of DOP. It is shown that crosslinking PVC/E-Acry blends or increasing the vinyl acetate content in PVC/EVA blends, are alternatives that can increase the compatibility and mechanical properties of these blends. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1303–1312, 2000

The photoluminescence and its temperature dependence have been investigated for the ensembles of InAs quantum dots embedded in symmetric In0.15Ga0.85As/GaAs quantum wells with different PL intensities. The solution of the set of rate equations for exciton dynamics was used to analyze the nature of thermal activation energies of the QD photoluminescence quenching. It is revealed two different stages of thermally activated quenching of the QD PL intensity caused by thermal escape of excitons from the In0.15Ga0.85As/GaAs QW into the GaAs barrier and from the QDs into the QWs with their subsequent nonradiative recombination. The variety of activation energies of PL thermal quenching is discussed as well. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

This paper presents the results of peculiarity analysis in PL spectra of CdSe/ZnS QDs of different sizes. Commercially available CdSe/ZnS core/shell QDs characterized by emission at 525 nm (2.36 eV), 560 nm (2.22 eV), 605 nm (2.05 eV) and 640 nm (1.94 eV) have been studied. PL spectra were measured at excitation by a He-Cd laser with the light wavelength of 325 nm at the temperatures 10 and 300K. PL spectra of different size QDs can be presented as a superposition of 3 elementary PL bands: (i) PL band deals with ground state exciton emission in a CdSe core and (ii) two PL bands (2.37 and 2.68 eV) assigned to the electron-hole recombination via interface defects. The spectral positions of defect-related PL bands did not change versus temperature or QD size. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The vibration–rotation levels for the diatomic RKR potential curve are solved using both perturbational and variational approaches. To obtain any-order correction of the energy from unperturbed parameters, an iterative scheme is formulated in the hypervirial framework. Variational calculations are carried out upon a rotationless Morse oscillator basis set and using a transformation technique to treat the effective potential energy function. Numerical results for the RbH X1Σ+ state are obtained. The accuracy of the energy levels is tested by solving the Schrodinger equation by a numerical procedure.

The effect of the berries extract of Schizundru chinensis on polo and race horses was studied. The concentration of plasmatic lactate and glucose as well as the respiratory and heart rates of these horses submitted to daerent physical effort were examined. Thirty adult horses were used for this experiment; 20 polo horses and 10 race horses. Ten polo horses were submitted to a 12 min gallop at a speed of 400 m/min, and 10 other polo horses to a 5 min gallop at a speed of 700 m/min. The race horses were submitted to a single run on a fixed distance of 800111 at maximum speed. Blood jugular samples from each polo horse (when they were in the stable) were collected for lactate and glucose analysis before the exercise and at 10 and 50 min after the exercise. Heart and respiratory rates were recorded. First each horse was given a single dose of 500 mL of saline half an hour before the race. A week later the same horses were given a single dose of 48 g of Schizundru chinemis berry extract. Treated polo horses showed a lower increase in heart rate at all moments of the exercise. They also showed a quicker recovery of respiratory frequency at the moments immediately after the race (time 0) and 5 min after the same race. The performance of the race horses was improved. In polo horses administration of Schizundru extract led to a significant reduction of the concentration of plasmatic lactate at 10, and 50min after exercise. Plasma glucose concentration in polo horses showed no significant difference between the saline treated and the Schizandru-treated animals (with the exception at 50 min after the race).

The energy levels and perturbation expansions for the expectation values of arbitrary powers of position for a perturbed Morse oscillator are obtained by application of the hypervirial and Hellmann–Feynman theorems, solely in terms of the unperturbed energy. We obtain expressions for the first-order corrections for (1 − e−aq )m for 4 ⩽ m ⩽ 8 and the expressions to second and third order for the quartic perturbation. A numerical application to the CO molecule is made.

The behavior of a rigid rotor perturbed by an electric field is studied. An hypervirial calculation, to obtain the perturbation series without calculation of the perturbed wavefunctions, is used to determine the Stark-shifted eigenvalues. A numerical estimation of the m equals; 0 m = 1 transition for the lowest vibrational state (v = 0) and the first rotational state (J = 1) for the HF and DF molecules using Pade approximants is made.