Effect of a gap opening on the conductance of graphene superlattices

The electronic transmission and conductance of a gapped graphene superlattice were calculated by means of the transfer-matrix method. The system that we study consists of a sequence of electron-doped graphene as wells and hole-doped graphene as barriers. We show that the transmission probability approaches unity at some critical value of the gap. We also find that there is a domain around the critical gap value for which the conductance of the system attains its maximum value.Comment: 14 pages, 5 figures. To appear in Solid State Communication

Dirac Spectrum in Piecewise Constant One-Dimensional Potentials

We study the electronic states of graphene in piecewise constant potentials using the continuum Dirac equation appropriate at low energies, and a transfer matrix method. For superlattice potentials, we identify patterns of induced Dirac points which are present throughout the band structure, and verify for the special case of a particle-hole symmetric potential their presence at zero energy. We also consider the cases of a single trench and a p-n junction embedded in neutral graphene, which are shown to support confined states. An analysis of conductance across these structures demonstrates that these confined states create quantum interference effects which evidence their presence.Comment: 10 pages, 12 figures, additional references adde

Graphene-based modulation-doped superlattice structures

The electronic transport properties of graphene-based superlattice structures are investigated. A graphene-based modulation-doped superlattice structure geometry is proposed and consist of periodically arranged alternate layers: InAs/graphene/GaAs/graphene/GaSb. Undoped graphene/GaAs/graphene structure displays relatively high conductance and enhanced mobilities at elevated temperatures unlike modulation-doped superlattice structure more steady and less sensitive to temperature and robust electrical tunable control on the screening length scale. Thermionic current density exhibits enhanced behaviour due to presence of metallic (graphene) mono-layers in superlattice structure. The proposed superlattice structure might become of great use for new types of wide-band energy gap quantum devices.Comment: 5 figure

Goos-H\"{a}nchen-like shifts for Dirac fermions in monolayer graphene barrier

We investigate the Goos-H\"{a}nchen-like shifts for Dirac fermions in transmission through a monolayer graphene barrier. The lateral shifts, as the functions of the barrier's width and the incidence angle, can be negative and positive in Klein tunneling and classical motion, respectively. Due to their relations to the transmission gap, the lateral shifts can be enhanced by the transmission resonances when the incidence angle is less than the critical angle for total reflection, while their magnitudes become only the order of Fermi wavelength when the incidence angle is larger than the critical angle. These tunable beam shifts can also be modulated by the height of potential barrier and the induced gap, which gives rise to the applications in graphene-based devices.Comment: 5 pages, 5 figure

Monitoring the initial pulmonary absorption of two different beclomethasone dipropionate aerosols employing a human lung reperfusion model

BACKGROUND: The pulmonary residence time of inhaled glucocorticoids as well as their rate and extend of absorption into systemic circulation are important facets of their efficacy-safety profile. We evaluated a novel approach to elucidate the pulmonary absorption of an inhaled glucocorticoid. Our objective was to monitor and compare the combined process of drug particle dissolution, pro-drug activation and time course of initial distribution from human lung tissue into plasma for two different glucocorticoid formulations. METHODS: We chose beclomethasone dipropionate (BDP) delivered by two different commercially available HFA-propelled metered dose inhalers (Sanasthmax(®)/Becloforte™ and Ventolair(®)/Qvar™). Initially we developed a simple dialysis model to assess the transfer of BDP and its active metabolite from human lung homogenate into human plasma. In a novel experimental setting we then administered the aerosols into the bronchus of an extracorporally ventilated and reperfused human lung lobe and monitored the concentrations of BDP and its metabolites in the reperfusion fluid. RESULTS: Unexpectedly, we observed differences between the two aerosol formulations Sanasthmax(®)/Becloforte™ and Ventolair(®)/Qvar™ in both the dialysis as well as in the human reperfusion model. The HFA-BDP formulated as Ventolair(®)/Qvar™ displayed a more rapid release from lung tissue compared to Sanasthmax(®)/Becloforte™. We succeeded to explain and illustrate the observed differences between the two aerosols with their unique particle topology and divergent dissolution behaviour in human bronchial fluid. CONCLUSION: We conclude that though the ultrafine particles of Ventolair(®)/Qvar™ are beneficial for high lung deposition, they also yield a less desired more rapid systemic drug delivery. While the differences between Sanasthmax(®)/Becloforte™ and Ventolair(®)/Qvar™ were obvious in both the dialysis and lung perfusion experiments, the latter allowed to record time courses of pro-drug activation and distribution that were more consistent with results of comparable clinical trials. Thus, the extracorporally reperfused and ventilated human lung is a highly valuable physiological model to explore the lung pharmacokinetics of inhaled drugs

In vitro metabolism of beclomethasone dipropionate, budesonide, ciclesonide, and fluticasone propionate in human lung precision-cut tissue slices

<p>Abstract</p> <p>Background</p> <p>The therapeutic effect of inhaled corticosteroids (ICS) may be affected by the metabolism of the drug in the target organ. We investigated the <it>in vitro </it>metabolism of beclomethasone dipropionate (BDP), budesonide (BUD), ciclesonide (CIC), and fluticasone propionate (FP) in human lung precision-cut tissue slices. CIC, a new generation ICS, is hydrolyzed by esterases in the upper and lower airways to its pharmacologically active metabolite desisobutyryl-ciclesonide (des-CIC).</p> <p>Methods</p> <p>Lung tissue slices were incubated with BDP, BUD, CIC, and FP (initial target concentration of 25 μM) for 2, 6, and 24 h. Cellular viability was assessed using adenosine 5'-triphosphate content and protein synthesis in lung slices. Metabolites and remaining parent compounds in the tissue samples were analyzed by HPLC with UV detection.</p> <p>Results</p> <p>BDP was hydrolyzed to the pharmacologically active metabolite beclomethasone-17-monopropionate (BMP) and, predominantly, to inactive beclomethasone (BOH). CIC was hydrolyzed initially to des-CIC with a slower rate compared to BDP. A distinctly smaller amount (approximately 10-fold less) of fatty acid esters were formed by BMP (and/or BOH) than by BUD or des-CIC. The highest relative amounts of fatty acid esters were detected for BUD. For FP, no metabolites were detected at any time point. The amount of drug-related material in lung tissue (based on initial concentrations) at 24 h was highest for CIC, followed by BUD and FP; the smallest amount was detected for BDP.</p> <p>Conclusion</p> <p>The <it>in vitro </it>metabolic pathways of the tested ICS in human lung tissue were differing. While FP was metabolically stable, the majority of BDP was converted to inactive polar metabolites. The formation of fatty acid conjugates was confirmed for BMP (and/or BOH), BUD, and des-CIC.</p

Absence of N-terminal acetyltransferase diversification during evolution of eukaryotic organisms

Protein N-terminal acetylation is an ancient and ubiquitous co-translational modification catalyzed by a highly conserved family of N-terminal acetyltransferases (NATs). Prokaryotes have at least 3 NATs, whereas humans have six distinct but highly conserved NATs, suggesting an increase in regulatory complexity of this modification during eukaryotic evolution. Despite this, and against our initial expectations, we determined that NAT diversification did not occur in the eukaryotes, as all six major human NATs were most likely present in the Last Eukaryotic Common Ancestor (LECA). Furthermore, we also observed that some NATs were actually secondarily lost during evolution of major eukaryotic lineages; therefore, the increased complexity of the higher eukaryotic proteome occurred without a concomitant diversification of NAT complexes

Impact of livestock manure, nitrogen and biofertilizer (Azotobacter) on yield and yield components of wheat (Triticum aestivum L.)

Integrated nutrient management strategies involving chemical and biologic fertilizer is a real challenge to stop using the high rates of agrochemicals and to enhance sustainability of crop production. In order to study the effects of livestock manure, chemical nitrogen, and biologic (Azotobacter) fertilizers on yield and yield components of wheat, an agricultural experiment in the form of split factorial design with three replications was conducted in Elam region, Iran. The aim of this research was assessment of the effects of these fertilizers separately and in integrated forms; and setting out the best fertilizer mixture. The results showed that treatment with livestock manure, Azotobacter and chemical nitrogen increased plant height, biological and grain yield. Using livestock manure and Azotobacter increased biologic yield through increase in plant height which cause to increase in grain yield without any significant changes in harvest index and other yield components, but the use of chemical nitrogen caused an increase in plant height, No. of spikelete/spike, No. of grain/spike, one thousand grain weight and harvest index, biologic and grain yield. In the light of the results achieved, we may conclude that using livestock manure and chemical nitrogen fertilizer together with the Azotobacter had the maximum impact on yield; and that we can decrease use of chemical fertilizers through using livestock manure and biologic fertilizers and to reach to the same yield when we use only chemical fertilizers

An improved model for estimating fractal structure of silica nano-agglomerates in a vibro-fluidized bed

A study has been conducted to determine the effects of operating conditions such as vibration frequency, vibration amplitude on the fractal structure of silica (SiO2) nanoparticle agglomerate in a vibro-fluidized bed. An improved model was proposed by assimilation of fractal theory, Richardson-Zaki equation and mass balance. This model has been developed to predict the properties of nanoparticle agglomerate, such as fractal dimension and its size. It has been found out the vibration intensity increase leads to a slight reduction in fractal dimension of agglomerate. This Paper is also indicated that the size of agglomerate has the same behavior as fractal dimension with respect to vibration intensity changes. This study demonstrated that the fractal dimension of Silica nanoparticle agglomerate is in the range of 2.61 to 2.69 and the number of primary particles in the agglomerate is in the order of 1010. The vibration frequency is more impressive than its amplitude on agglomerate size reduction. Calculated Minimum fluidization velocity by applying predicted agglomerate sizes and experimental data are acceptable fitted

Simulation of Drying Characteristics of Evaporation from a Wet Particle in a Turbulent Pulsed Opposing Jet Contactor

The motion and drying characteristics of a single particle in a novel two-dimensional pulsed opposing jet contactor (POJC) are modeled and discussed. Hot air is used as the drying medium. To simulate particle drying, the gas phase and dispersed phase conservation equations are considered in the Eulerian reference frame and the Lagrangian reference frame, respectively. The RNG turbulence model is used to determine the turbulent characteristics of the gas phase. The particle motion is described by the BBO (Basset-Boussinesq-Oseen) equation. The effects of the key parameters, such as the jet Reynolds number, amplitude of pulsation, frequency of pulsation, particle diameter, location of release of particle from one jet as well as velocity profile on residence time (RT) and particle penetration depth (PN) into the opposite jet, are examined. Results show that POJC has strong potential for particulate heat transfer as well as drying; it can improve evaporation rate relative to the corresponding steady OJC by up to 30% as a result of increased residence time in the impingement zone within the parameter ranges simulated. © 2013 Copyright Taylor and Francis Group, LLC