Nonresonant high frequency excitation of mechanical vibrations in graphene based nanoresonator

We theoretically analyse the dynamics of a suspended graphene membrane which is in tunnel contact with grounded metallic electrodes and subjected to ac-electrostatic potential induced by a gate electrode. It is shown that for such system the retardation effects in the electronic subsystem generate an effective pumping for the relatively slow mechanical vibrations if the driving frequency exceeds the inverse charge relax- ation time. Under this condition there is a critical value of the driving voltage ampli- tude above which the pumping overcomes the intrinsic damping of the mechanical resonator leading to a mechanical instability. This nonresonant instability is saturated by nonlinear damping and the system exhibits self-sustained oscillations of relatively large amplitude.Comment: Major revisio

Dynamics of viscous amphiphilic films supported by elastic solid substrates

The dynamics of amphiphilic films deposited on a solid surface is analyzed for the case when shear oscillations of the solid surface are excited. The two cases of surface- and bulk shear waves are studied with film exposed to gas or to a liquid. By solving the corresponding dispersion equation and the wave equation while maintaining the energy balance we are able to connect the surface density and the shear viscocity of a fluid amphiphilic overlayer with experimentally accessible damping coefficients, phase velocity, dissipation factor and resonant frequency shifts of shear waves.Comment: 19 pages, latex, 3 figures in eps-forma

Development of a combined surface plasmon resonance/surface acoustic wave device for the characterization of biomolecules

It is known that acoustic sensor devices, if operated in liquid phase, are sensitive not just to the mass of the analyte but also to various other parameters, such as size, shape, charge and elastic constants of the analyte as well as bound and viscously entrained water. This can be used to extract valuable information about a biomolecule, particularly if the acoustic device is combined with another sensor element which is sensitive to the mass or amount of analyte only. The latter is true in good approximation for various optical sensor techniques. This work reports on the development of a combined surface plasmon resonance/surface acoustic wave sensor system which is designed for the investigation of biomolecules such as proteins or DNA. Results for the deposition of neutravidin and DNA are reported

Shuttle Mechanism for Charge Transfer in Coulomb Blockade Nanostructures

Room-temperature Coulomb blockade of charge transport through composite nanostructures containing organic inter-links has recently been observed. A pronounced charging effect in combination with the softness of the molecular links implies that charge transfer gives rise to a significant deformation of these structures. For a simple model system containing one nanoscale metallic cluster connected by molecular links to two bulk metallic electrodes we show that self-excitation of periodic cluster oscillations in conjunction with sequential processes of cluster charging and decharging appears for a sufficiently large bias voltage. This new `electron shuttle' mechanism of discrete charge transfer gives rise to a current through the nanostructure, which is proportional to the cluster vibration frequency.Comment: 4 pages, 4 figure

Новый высокопродуктивный штамм Propionibacterium acidipropionici FL-48 с повышенной устойчивостью к пропионовой кислоте и масштабирование технологии его наработки в промышленных биореакторах

Propionic acid bacteria, including Propionibacterium acidipropionici, are widely used in the chemical industry to produce propionic acid and also for food and feed preservation. However, the efficiency of the industrial production of these bacteria is limited by their sensitivity to high concentrations of propionic acid excreted into the cultivation medium. Therefore, the development of new biotechnological processes and strains able to overcome this limitation and to improve the profitability of the microbiological production remains  a relevant problem. A new P. acidipropionici FL-48 strain characterized by an increased resistance to 10 g/L of propionic acid (the number of viable cells after 24-h cultivation reached 1.05 × 106) was developed by a two-step induced mutagenesis using UV and diethyl sulphate from the P. acidipropionici VKPM B-5723 strain. The mutant strain exceeded the parental strain in the biomass accumulation rate and the amount of produced propionic and acetic acids by 35%, 20%, and 16%, respectively. The stability of such important characteristics as the biomass accumulation rate and the viability on media containing heightened concentrations of propionic acid was confirmed by three sequential monoclonal subculturings on a medium supplemented with 10 g/L of propionic acid. The optimization of the cultivation technology made it possible to determine the optimum seed inoculum dose (10% of the fermentation medium volume) and the best pH level for the active growth stage (6.1 ± 0.1). The scaling up of the fermentation to a 100-L bioreactor under observance of optimum cultivation conditions demonstrated a high biomass growth rate with a sufficient reproducability; after 20 h of fermentation, the number of viable cells in the culture broth exceeded 1 × 1010 CFU/mL. The new strain could be interesting as the component of silage and haylage biopreservatives and also could be used as an efficient producer of propionic acid.Пропионовокислые бактерии, в том числе Propionibacterium acidipropionici, широко используются в химической промышленности для получения пропионовой кислоты, а также для консервирования пищи и заготовки зерна и зеленых кормов. Однако эффективность промышленного производства биомассы пропионовокислых бактерий ограничена их чувствительностью к высоким концентрациям в среде пропионовой кислоты. Таким образом, актуальной задачей является разработка новых биотехнологических процессов и штаммов, позволяющих преодолеть это ограничение и повысить рентабельность микробиологического производства. Методом двухступенчатого индуцированного мутагенеза с применением УФ-облучения и диэтилсульфата получен новый мутантный штамм P. acidipropionici ФЛ-48, обладающий повышенной резистентностью к 10 г/л пропионовой кислоты (количество жизнеспособных клеток через 24 ч культивирования достигало 1,05 × 106) и превосходящий родительский штамм P. acidipropionici ВКПМ В-5723 по скорости накопления биомассы и количеству продуцируемых пропионовой и уксусной кислот на 35%, 20% и 16%, соответственно. Стабильность характеристик нового штамма (скорость накопления биомассы и жизнеспособность на средах с повышенной концентрацией пропионовой кислоты) подтверждена трехкратным последовательным моноклональным рассевом на среду, содержащую 10 г/л пропионовой кислоты. Выполненная оптимизация технологии культивирования штамма позволила определить оптимальную дозу инокулюма для засева биореактора (10% от объема ферментационной среды) и поддерживаемый в течение первых 12 ч уровень рН среды, обеспечивающий максимальный прирост биомассы (6,1 ± 0,1). Проведенное масштабирование ферментации до 100-литрового биореактора с соблюдением оптимальных условий культивирования показало сохранение высокой скорости роста штамма в условиях пониженного рН; уже к 20-му часу ферментации количество жизнеспособных клеток в культуральной жидкости превышало 1 × 1010 КОЕ/мл. Полученные результаты показали хорошую воспроизводимость. Новый штамм представляет интерес в качестве компонента биоконсервантов для силоса и сенажа, а также может быть использован в качестве эффективного продуцента пропионовой кислоты. Пропионовокислые бактерии, в том числе Propionibacterium acidipropionici, широко используются в химической промышленности для получения пропионовой кислоты, а также для консервирования пищи и заготовки зерна и зеленых кормов. Однако эффективность промышленного производства биомассы пропионовокислых бактерий ограничена их чувствительностью к высоким концентрациям в среде пропионовой кислоты. Таким образом, актуальной задачей является разработка новых биотехнологических процессов и штаммов, позволяющих преодолеть это ограничение и повысить рентабельность микробиологического производства. Методом двухступенчатого индуцированного мутагенеза с применением УФ-облучения и диэтилсульфата получен новый мутантный штамм P. acidipropionici ФЛ-48, обладающий повышенной резистентностью к 10 г/л пропионовой кислоты (количество жизнеспособных клеток через 24 ч культивирования достигало 1,05 × 106) и превосходящий родительский штамм P. acidipropionici ВКПМ В-5723 по скорости накопления биомассы и количеству продуцируемых пропионовой и уксусной кислот на 35%, 20% и 16%, соответственно. Стабильность характеристик нового штамма (скорость накопления биомассы и жизнеспособность на средах с повышенной концентрацией пропионовой кислоты) подтверждена трехкратным последовательным моноклональным рассевом на среду, содержащую 10 г/л пропионовой кислоты. Выполненная оптимизация технологии культивирования штамма позволила определить оптимальную дозу инокулюма для засева биореактора (10% от объема ферментационной среды) и поддерживаемый в течение первых 12 ч уровень рН среды, обеспечивающий максимальный прирост биомассы (6,1 ± 0,1). Проведенное масштабирование ферментации до 100-литрового биореактора с соблюдением оптимальных условий культивирования показало сохранение высокой скорости роста штамма в условиях пониженного рН; уже к 20-му часу ферментации количество жизнеспособных клеток в культуральной жидкости превышало 1 × 1010 КОЕ/мл. Полученные результаты показали хорошую воспроизводимость. Новый штамм представляет интерес в качестве компонента биоконсервантов для силоса и сенажа, а также может быть использован в качестве эффективного продуцента пропионовой кислоты.

Outcomes of ROHs (runs of homozygosity)/ LCSHs (long contiguous stretches of homozygosity) spanning the imprinted loci of chromosomes 7, 11 and 15 among children with neurodevelopmental disorders

To describe the outcomes of ROHs/LCSHs spanning the imprinted loci of chromosomes 7, 11 and 15 among children with neurodevelopmental disorder

Electrospun magnetic composite poly-3-hydroxybutyrate/magnetite scaffolds for biomedical applications: composition, structure, magnetic properties, and biological performance

Magnetically responsive composite polymer scaffolds have good potential for a variety of biomedical applications. In this work, electrospun composite scaffolds made of polyhydroxybutyrate (PHB) and magnetite (Fe3O4) particles (MPs) were studied before and after degradation in either PBS or a lipase solution. MPs of different sizes with high saturation magnetization were synthesized by the coprecipitation method followed by coating with citric acid (CA). Nanosized MPs were prone to magnetite-maghemite phase transformation during scaffold fabrication, as revealed by Raman spectroscopy; however, for CA-functionalized nanoparticles, the main phase was found to be magnetite, with some traces of maghemite. Submicron MPs were resistant to the magnetite-maghemite phase transformation. MPs did not significantly affect the morphology and diameter of PHB fibers. The scaffolds containing CA-coated MPs lost 0.3 or 0.2% of mass in the lipase solution and PBS, respectively, whereas scaffolds doped with unmodified MPs showed no mass changes after 1 month of incubation in either medium. In all electrospun scaffolds, no alterations of the fiber morphology were observed. Possible mechanisms of the crystalline-lamellar-structure changes in hybrid PHB/Fe3O4 scaffolds during hydrolytic and enzymatic degradation are proposed. It was revealed that particle size and particle surface functionalization affect the mechanical properties of the hybrid scaffolds. The addition of unmodified MPs increased scaffolds' ultimate strength but reduced elongation at break after the biodegradation, whereas simultaneous increases in both parameters were observed for composite scaffolds doped with CA-coated MPs. The highest saturation magnetization-higher than that published in the literature-was registered for composite PHB scaffolds doped with submicron MPs. All PHB scaffolds proved to be biocompatible, and the ones doped with nanosized MPs yielded faster proliferation of rat mesenchymal stem cells. In addition, all electrospun scaffolds were able to support angiogenesis in vivo at 30 days after implantation in Wistar rats

Role of Caustic Addition in Bitumen-Clay Interactions

Coating of bitumen by clays, known as slime coating, is detrimental to bitumen recovery from oil sands using the warm slurry extn. process. Sodium hydroxide (caustic) is added to the extn. process to balance many competing processing challenges, which include undesirable slime coating. The current research aims at understanding the role of caustic addn. in controlling interactions of bitumen with various types of model clays. The interaction potential was studied by quartz crystal microbalance with dissipation monitoring (QCM-D). After confirming the slime coating potential of montmorillonite clays on bitumen in the presence of calcium ions, the interaction of kaolinite and illite with bitumen was studied. To represent more closely the industrial applications, tailings water from bitumen extn. tests at different caustic dosage was used. At caustic dosage up to 0.5 wt % oil sands ore, a negligible coating of kaolinite on the bitumen was detd. However, at a lower level of caustic addn., illite was shown to attach to the bitumen, with the interaction potential decreasing with increasing caustic dosage. Increasing concn. of humic acids as a result of increasing caustic dosage was identified to limit the interaction potential of illite with bitumen. This fundamental study clearly shows that the crit. role of caustics in modulating interactions of clays with bitumen depends upon the type of clays. Thus, clay type was identified as a key operational variable