Numerical modeling of parasitic barrier formation at the SiGe/Si heterojunction due to p–n junction displacement

The formation and characteristics of a parasitic conduction band barrier located at a SiGe/Si heterojunction have been investigated using a commercial numerical simulator and a simple, three-region model of a heterojunction with a nearby p–n junction. The barrier’s formation is examined as a function of the displacement of the p–n junction from the heterojunction, but also found to depend on the germanium concentration, junction doping and the applied bias. The phenomenon is of interest for understanding the performance of SiGe/Si heterojunction bipolar transistors, where the p–n junction is intentionally displaced from the heterojunction at either the emitter or collector junctions or where boron outdiffusion from the base produces p–n junction displacement. The barrier is found to scale with the germanium mole fraction and to be significantly larger when the heterojunction is displaced into the p-side of the p–n junction. Beyond some minimum separation of the junctions, the barrier height rises with junction displacement and saturates. For a given displacement, the barrier’s height can be suppressed with reverse bias or enhanced by forward bias of the p–n junction. The results of the numerical simulations are compared with those from a simple analytical model as an aid in understanding the barrier’s formation and characteristics.     

Generation of chromophore Tyr-containing mutants of the ribosomal protein L7/L12 from Escherichia coli by site-directed mutagenesis and characterization

1. The effects of tachykinins and capsaicin were studied by means of intracellular membrane potential and isometric tension recordings in the isolated trachea of the guinea-pig. 2. The basal membrane potential averaged -51 mV, and most preparations demonstrated spontaneous slow waves. Tetraethylammonium (TEA), a potassium channel blocker (8 x 10(-3) M), depolarized the membrane potential to -44 mV and induced a rhythmic activity. 3. In control solution, substance P (10(-8)-10(-6) M), [Nle10]-neurokinin A(4-10) (10(-8)-10(-6) M) and capsaicin (10(-7)-10(-6) M) induced concentration-dependent depolarizations which were statistically significant at the highest concentration tested (depolarization by 10(-6) M: 8, 11 and 16 mV for the NK1 agonist, the NK2 agonist and capsaicin, respectively). 4. In the presence of TEA (8 x 10(-3) M), the three substances induced depolarizations which were statistically significant at the highest concentration tested for substance P (10(-6) M) and at 10(-7) and 10(-6) M for both [Nle10]-neurokinin A(4-10) and capsaicin (depolarization by 10(-6) M: 11, 17 and 10 mV for substance P, [Nle10]neurokinin A(4-10) and capsaicin, respectively). 5. In the presence or absence of tetraethylammonium, [MePhe7]-neurokinin B (10(-8)-10(-6) M) did not induce any significant changes in membrane potential. 6. The depolarizing effects of substance P (10(-6) M) and [Nle10]-neurokinin A(4-10) (10(-6) M) were blocked only by the specific antagonists for NK1 and NK2 receptors, SR 140333 (10(-7) M) and SR 48968 (10(-7) M), respectively. The effects of capsaicin (10(-6) M) were partially inhibited by each antagonist and fully blocked by their combination. 7. Substance P (10(-9) to 10(-4) M), [Nle10]-neurokinin A(4-10) (10(-10) to 10(-5) M), [MePhe7]-neurokinin B and capsaicin (10(-7) to 10(-5) M) evoked concentration-dependent contractions. 8. The contractions to substance P were significantly inhibited by SR 140333 (10(-8) to 10(-6) M) but unaffected by SR 48968 (10(-8) to 10(-6) M). Furthermore, the response to [Nle10]-neurokinin A(4-10) was significantly inhibited by SR 48968 and unaffected by SR 140333 at the same concentrations. Although SR 48968 (10(-7) M) alone did not influence the effects of substance P, it potentiated the inhibitory effect of SR 140333 (10(-7) M). A similar synergetic effect of these two compounds was observed in the inhibition of the contractile response to [Nle10]-neurokinin A(4-10). 9. Neither SR 140333 (10(-7) M) nor SR 48968 (10(-7) M) alone influenced the contractions to [MePhe7]-neurokinin B and capsaicin. However, the combination of the two antagonists abolished the contractions to either peptide. 10. These results demonstrate that the stimulation of both NK1 and NK2 tachykinin-receptors induced contraction and depolarization of the guinea-pig tracheal smooth muscle and that both receptors were stimulated during the endogenous release of tachykinins by capsaicin. There was no evidence for a major role of NK3 receptors in the contractile and electrical activity of the guinea-pig isolated trachea.     

Simultaneous copper, cobalt and phenol removal from aqueous solutions by alternating biosorption and biodegradation

A strategy for removal of heavy metals and phenol from wastewaters is proposed. It involves consecutive cation biosorption by fungi, phenol biodegradation by the yeast association Candida sp. 2326 + Candida sp. 2327 and regeneration. Copper and cobalt removal from aqueous solutions containing 80-120 mg/L phenol by biosorption, using Rhizopus archizus cells immobilized onto poly (vinyl alcohol), was investigated by conducting a series of batch experiments. The removal efficiencies were 81% for Cu and 5% for Co. The residual concentrations of Cu (1.9 mg/L) and of Co (9.5 mg/L) did not change the biodegradation dynamics of phenol. A quantitative biodegradation of 120 mg/L phenol proceeded within 22 h. After biodegradation of phenol, the removal efficiencies achieved by biosorption after regeneration were 90% for Cu and 44% for Co. It was found that copper and cobalt form positively charged complexes with phenol. This complex formation hinders the retention of Cu and Co by the biosorbent and reduces the uptake of their cations.     

Materials from Nanosized ZnO and Polyacrylonitrile: Properties Depending on the Design of Fibers (Electrospinning or Electrospinning/Electrospraying)

New hybrid fibrous materials from polyacrylonitrile (PAN) and nanosized zinc oxide have been prepared by electrospinning or by combining electrospinning and electrospraying techniques. Electrospinning of PAN/nanosized zinc oxide dispersion leads to the production of mats with nanofiller distributed mainly in the bulk of the fibers. Electrospinning of PAN solution performed in conjunction with electrospraying of nanosized zinc oxide dispersion enables the preparation of fibers decorated with zinc oxide particles. The incorporation of zinc oxide in the fibers leads to enhancement of the mechanical properties of the mats. The fibrous materials having zinc oxide particles situated on the fibers surface exhibit better photocatalytic activity in respect to photo-induced degradation of the model dye methylene blue and greater antibacterial activity against the pathogenic microorganism Staphylococcus aureus.     

Analytical solution of gas lubricated slider microbearing

The analytical solution of a two-dimensional, isothermal, compressible gas flow in a slider microbearing is presented. A higher order accuracy of the solution is achieved by applying the boundary condition of Kn ² order for the velocity slip on the wall, together with the momentum equation of the same order (known as the Burnett equation). The analytical solution is obtained by the perturbation analysis. The order of all terms in continuum and momentum equations and in boundary conditions is evaluated by incorporating the exact relation between the Mach, Reynolds and Knudsen numbers in the modelling procedure. Low Mach number flows in microbearing with slowly varying cross-sections are considered, and it is shown that under these conditions the Burnett equation has the same form as the Navier–Stokes equation. Obtained analytical results for pressure distribution, load capacity and velocity field are compared with numerical solutions of the Boltzmann equation and some semi-analytical results, and excellent agreement is achieved. The model presented in this paper is a useful tool for the prediction of flow conditions in the microbearings. Also, its results are the benchmark test for the verifications of various numerical procedures.     

Production of Antioxidant Egg White Hydrolysates in a Continuous Stirred Tank Enzyme Reactor Coupled with Membrane Separation Unit

Food and Bioprocess Technology - The objective of this research was to design an efficient continuously operated membrane reactor with a separation unit for egg white protein (EWP) hydrolysis and...     

Compositional dependence of the optical properties of new quaternary chalcogenide glasses of Ge–Sb–(S,Te) system

New quaternary telluride glassy materials with composition of Ge_xSb_40−xS₅₀Te₁₀ and Ge_xSb_40−xS₅₅Te₅ (x = 10, 20, and 27) have been synthesized and their optical properties have been studied by means of spectroscopic ellipsometry in the range of 400–820 nm. The optical constants, i.e. the refractive index, extinction coefficient, absorption coefficient, and the optical band gap energy are determined and their compositional dependence is considered. These parameters are characteristics for amorphous structure of the synthesized glasses, revealed from the neutron diffraction measurements.     

Administration of a β-glucan-enriched extract activates beneficial hepatic antioxidant and anti-inflammatory mechanisms in streptozotocin-induced diabetic rats

The beneficial effect of a commercially available β-glucan-enriched extract (BGEE) from cereal grain, against a diabetes-induced hepatic redox imbalance and inflammatory response in streptozotocin-induced diabetic rats was evaluated. Diabetic rats that were treated with BGEE exhibited lower hyperglycaemia and improved biochemical parameters of liver damage. BGEE attenuated hepatic oxidative stress, revealed by a decreased concentration of thiobarbituric acid reactive substances and a restored GSH/GSSG ratio. BGEE also exerted an anti-inflammatory effect on the liver, evidenced by the normalization of the serum concentrations of the “positive” and “negative” acute-phase proteins, α₂-macroglobulin and albumin, respectively, as well as by upregulation of anti-inflammatory cytokine IL-10 and IL-4 mRNA expression, and inhibition of RAGE/NF-κB signaling. These findings suggest that BGEE application exerts a beneficial effect in the liver of streptozotocin-induced diabetic rats via its antioxidant and anti-inflammatory activities, and that it therefore possesses an important potential in diabetes management.     

Composite hydroxyapatite/TiO2 materials for photocatalytic oxidation of NOx

Hydroxyapatite/TiO₂ composite photocatalysts were obtained from sol–gel prepared TiO₂ and commercial hydroxyapatite (HA) powders. Composites with different HA/TiO₂ ratio were studied to assess the influence of HA on the morphology and the photocatalytic behavior of the materials. Morphological SEM analysis revealed that the presence of HA diminishes the aggregation of TiO₂ particles and leads to their higher dispersion in the composites that was confirmed by the N₂ adsorption–desorption isotherms and Barret–Joyner–Halenda analysis. The photocatalytic activity of the prepared catalysts was examined by monitoring photocatalytic oxidation of NO_x model gases over catalysts under UV illumination. The NO_x oxidation over the composite catalysts was improved in comparison with pure TiO₂ powder. Moreover, the decrease of the TiO₂ content, which is the photocatalytically active component in the composites, resulted in enhanced NO_x removal. Maximum activity was recorded for composites with HA/TiO₂ ratios 1 and 2 that was related to improved TiO₂ dispersion and NO₂ trapping by the composite materials.