A sample and hold device

Typical sample and hold devices (SHDs) are characterized by a number of drawbacks: zero offset at the SHD output caused mainly by the zero-offset voltage of the operational amplifiers that are parts of the SHD, significant sampling time due to the need to use a storage capacitor with the largest possible capacity to increase the storage time, and the uncertainty of the sampling time conditioned by the recharge mode of the storage capacitor, which is a commutation process with nonzero initial conditions of a random character. An attempt to stabilize the sampling time with simultaneous minimization resulted in the development of an accelerated recharging procedure for the SHD storage capacitor based on amplification of the input signal, forced recharging of the storage capacitor, and determination of the amplitude equity moment of the memorized analogue system and the SHD output signal.     

Bayesian Estimation of Density via Multiple Sequential Inversions of Two-Dimensional Images With Application to Electron Microscopy

We present a new Bayesian methodology to learn the unknown material density of a given sample by inverting its two-dimensional images that are taken with a scanning electron microscope. An image results from a sequence of projections of the convolution of the density function with the unknown microscopy correction function that we also learn from the data; thus, learning of the unknowns demands multiple inversions. We invoke a novel design of experiment, involving imaging at multiple values of the parameter that controls the subsurface depth from which information about the density structure is carried, to result in the image. Real-life material density functions are characterized by high-density contrasts and are highly discontinuous, implying that they exhibit correlation structures that do not vary smoothly. In the absence of training data, modeling such correlation structures of real material density functions is not possible. So we discretize the material sample and treat values of the density function at chosen locations inside it as independent and distribution-free parameters. Resolution of the available image dictates the discretization length of the model; three models pertaining to distinct resolution classes (at micrometer to nanometer scale lengths) are developed. We develop priors on the material density, such that these priors adapt to the sparsity inherent in the density function. The likelihood is defined in terms of the distance between the convolution of the unknown functions and the image data. The posterior probability density of the unknowns given the data is expressed using the developed priors on the density and priors on the microscopy correction function as elicited from the microscopy literature. We achieve posterior samples using an adaptive Metropolis-within-Gibbs inference scheme. The method is applied to learn the material density of a three-dimensional sample of a nano-structure, using real image data. Illustrations on simulated image data of alloy samples are also included.     

An interference method for measuring parallelism of miniature optical components

A method for measuring parallelism of transparent optical components with small aperture size is described. It uses a Haidinger-type laser interferometer adapted for the measurement of optical components with millimeter and sub-millimeter aperture size. The method is based on the measurement of the optical thickness variation when the plate under test is translated across a focused laser beam. Measurement results for optical parts with 0.8 mm–10 mm aperture size are presented.     

Yeast extract as an effective nitrogen source stimulating cell growth and enhancing hydrogen photoproduction by Rhodobacter sphaeroides strains from mineral springs

The suitability and limitation of yeast extract as nitrogen source to support cell growth and to enhance hydrogen photoproduction by Rhodobacter sphaeroides strains MDC6521 and MDC6522 isolated from mineral springs in Armenia was investigated during the anaerobic growth. Yeast extract (2 g L⁻¹) was indicated to be an effective nitrogen source for bacterial cell growth stimulation and enhanced H₂ production (compared to glutamate). Both strains followed similar growth patterns in medium with yeast extract as nitrogen source and succinate or malate as carbon source. The highest growth rate was obtained for bacterial cells with yeast extract: the latter added gave a stimulated (2–3.5 fold) growth rate than using glutamate. R. sphaeroides suspension oxidation–reduction potential (ORP), which was measured with a platinum electrode, decreased down to low negative values with nitrogen source for both strains. ORP decreased down to more negative values (−610 ± 25 mV) in the presence of yeast extract than when adding glutamate (−405 ± 15 mV) compared to the control (without nitrogen source addition): the significant decrease of ORP indicated enhanced (∼6 fold) H₂ yield. The noticeable ORP decrease measured with the titanium-silicate electrode and simultaneously the increase of extracellular pH ([pH]_out) were observed; ORP was more negative at alkaline [pH]_out. Thus, the optimal culture conditions with nitrogen and carbon sources for bacterial growth stimulation and enhanced H₂ production were established. The ORP decrease together with the increase of [pH]_out point out a significant role of reduction processes in cell growth and ability of bacteria to live.     

Bio-hydrogen production and the F0F1-ATPase activity of Rhodobacter sphaeroides: Effects of various heavy metal ions

Rhodobacter sphaeroides MDC 6521 isolated from Arzni mineral springs in Armenia is able to produce bio-hydrogen (H₂) in anaerobic conditions upon illumination in the presence of various metal ions. The significant aspect in regulation of H₂ production by these bacteria and its energetics is the requirement for F₀F₁-ATPase, the main membrane enzyme responsible for generation of proton motive force under anaerobic conditions. In order to determine the mediatory role of F₀F₁ in H₂ production, the effects of various metal ions (Mn²⁺, Mg²⁺, Fe²⁺, Ni²⁺, and Mo⁶⁺) on N,N′-dicyclohexylcarbodiimide inhibited ATPase activity of R. sphaeroides membrane vesicles were investigated. These ions in appropriate concentrations considerably enhanced H₂ production, which was not observed in the absence of Fe²⁺, indicate the requirement for Fe²⁺. The R. sphaeroides membrane vesicles demonstrated significant ATPase activity. In the absence of Fe²⁺ inhibition (∼80%) of ATPase activity was observed, which was increased by addition of metal ions. A higher ATPase activity was detected in the presence of Fe²⁺ (80 μM) and Mo⁶⁺ (16 μM). These results indicate a relationship between the F₀F₁-ATPase activity and H₂ production that might be a significant pathway to provide novel evidence of a requirement for F₀F₁-ATPase in H₂ production by R. sphaeroides.     

Ni (II) and Mg (II) ions as factors enhancing biohydrogen production by Rhodobacter sphaeroides from mineral springs

Various metal ions play a key role in biohydrogen (H₂) production by phototrophic bacteria through incorporation into or stimulating the responsible enzymes and/or related pathways. The Ni (II) and Mg (II) ions effects on growth and H₂ production by Rhodobacter sphaeroides strain MDC6521 isolated from mineral springs in Armenia were established. The highest growth specific rate was obtained with 4–6 μM Ni²⁺ and 5 mM Mg²⁺. pH of the growth medium changed from 7.0 to 9.2–9.4 during the bacterial growth up to 72 h in spite of Ni²⁺ added but pH increased in different manner with Mg²⁺. In the presence of 2–4 μM Ni²⁺ external oxidation-reduction potential (ORP) decreased to more negative values (−800 ± 15 mV). This decrease of ORP indicated ∼2.7-fold enhanced H₂ yield (9.80 mmol L⁻¹) with Ni²⁺ compared with the control (without Ni²⁺). The H₂ yield determined in the medium with Mg²⁺ was ∼2.2 fold higher than that with 1 mM Mg²⁺. These results reveal new regulatory ways to improve H₂ production by R. sphaeroides those were depending on Ni²⁺ and Mg²⁺ of different concentrations.