Localized shear generates three-dimensional transport

Understanding the mechanisms that control three-dimensional (3D) fluid transport is central to many processes including mixing, chemical reaction and biological activity. Here a novel mechanism for 3D transport is uncovered where fluid particles are kicked between streamlines near a localized shear, which occurs in many flows and materials. This results in 3D transport similar to Resonance Induced Dispersion (RID); however, this new mechanism is more rapid and mutually incompatible with RID. We explore its governing impact with both an abstract 2-action flow and a model fluid flow. We show that transitions from one-dimensional (1D) to two-dimensional (2D) and 2D to 3D transport occur based on the relative magnitudes of streamline jumps in two transverse directions.Comment: Copyright 2017 AIP Publishing. This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishin

Performance of Electropun Polyacrylonitrile Nanofibrous Phases, Shown for the Separation of Water-Soluble Food Dyes via UTLC-Vis-ESI-MS

Research in the miniaturization of planar chromatography led to various approaches in manufacturing ultrathin-layer chromatography (UTLC) layers of reduced thickness (<50 µm) along with smaller instrumentation, as targeted in Office Chromatography. This novel concept merges 3D print & media technologies with miniaturized planar chromatography to realize an all-in-one instrument, in which all steps of UTLC are automated and integrated in the same tiny device. In this context, the development of electrospun polyacrylonitrile (PAN) nanofiber phases was investigated as well as its performance. A nanofibrous stationary phase with fiber diameters of 150–225 nm and a thickness of ca. 25 µm was manufactured. Mixtures of water-soluble food dyes were printed on it using a modified office printer, and successfully separated to illustrate the capabilities of such UTLC media. The separation took 8 min for 30 mm and was faster (up to a factor of 2) than on particulate layers. The mean hRF values ranging from 25 to 90 for the five food dyes were well spread over the migration distance, with an overall reproducibility of 7% (mean %RSD over 5 different plates for 5 dyes). The individual mean plate numbers over 5 plates ranged between 8286 and 22,885 (mean of 11,722 over all 5 dyes). The single mean resolutions RS were between 1.7 and 6.5 (for the 5 food dyes over 5 plates), with highly satisfying reproducibilities (0.3 as mean deviation of RS). Using videodensitometry, different amounts separated in parallel led to reliable linear calibrations for each dye (sdv of 3.1–9.1% for peak heights and 2.4–9.3% for peak areas). Coupling to mass spectrometry via an elution head-based interface was successfully demonstrated for such ultrathin layers, showing several advantages such as a reduced cleaning process and a minimum zone distance. All these results underline the potential of electrospun nanofibrous phases to succeed as affordable stationary phase for quantitative UTLC

Surface passivation of c-Si by atmospheric pressure chemical vapor deposition of Al2O3

Atmospheric pressure chemical vapor deposition of Al₂O₃ is shown to provide excellent passivation of crystalline silicon surfaces.Surface passivation,permittivity, and refractive index are investigated before and after annealing for deposition temperatures between 330 and 520 °C. Deposition temperatures >440 °C result in the best passivation, due to both a large negative fixed charge density (∼2 × 10¹² cm⁻²) and a relatively low interface defect density (∼1 × 10¹¹ eV⁻¹ cm⁻²), with or without an anneal. The influence of deposition temperature on film properties is found to persist after subsequent heat treatment. Correlations between surface passivation properties and the permittivity are discussed

On effective surface recombination parameters

This paper examines two effective surface recombination parameters: the effective surface recombination velocity Seff and the surface saturation current density J0 s . The dependence of Seff and J0 s on surface charge Q, surface dopant concentration Ns , and interface parameters is derived. It is shown that for crystalline silicon at 300 K in low-injection, Seff is independent of Ns only when Q²/Ns   1.5 × 10⁷ cm for accumulation and Q¹˙⁸⁵ /Ns  > 1.5 × 10⁶ cm for inversion. These conditions are commonly satisfied in undiffused wafers but rarely in diffused wafers. We conclude that for undiffused silicon, J0 s is superior to the conventional Seff as a metric for quantifying the surface passivation, whereas for diffused silicon, the merit in using J0 s or Seff (or neither) depends on the sample. Experimental examples are given that illustrate the merits and flaws of J0 s and Seff

Improving the optimization solution for a semi-analytical shallow water inversion model in the presence of spectrally correlated noise

In coastal regions, shallow water semi-analytical inversion algorithms may be used to derive geophysical parameters such as inherent optical properties (IOPs), water column depth, and bottom albedo coefficients by inverting sensor-derived sub-surface remote sensing reflectance, rrs. The uncertainties of these derived geophysical parameters due to instrumental and environmental noise can be estimated numerically via the addition of spectral noise to the sensor-derived rrs before inversion. Repeating this process multiple times allows the calculation of the standard error and average for each derived parameter. Apart from spectral non-uniqueness, the optimization algorithm employed in the inversion must converge onto a single minimum to obtain a true representation of the uncertainty for a given set of noise-perturbed rrs. Failure to do so inflates the uncertainty and affects the average retrieved value (accuracy). We show that the standard approach of seeding the optimization with an arbitrary, fixed initial guess, can lead to the convergence to multiple minima, each having substantially different centroids in multi-parameter solution space. We present the Update-Repeat Levenberg-Marquardt (UR-LM) and Latin Hypercube Sampling (LHS) routines that dynamically search the solution space for an optimal initial guess, that when applied to the optimization allows convergence to the best local minimum. We apply the UR-LM and LHS methods on HICO-derived and simulated rrs and demonstrate the improved computational efficiency, precision, and accuracy afforded from these methods compared with the standard approach. Conceptually, these methods are applicable to remote sensing based, shallow water or oceanic semi-analytical inversion algorithms requiring nonlinear least squares optimization

Resonant Cavity Modification of Ground State Chemical Kinetics

Recent experiments have suggested that ground state chemical kinetics can be suppressed or enhanced by coupling the vibrational degrees of freedom of a molecular system with a radiation mode inside an optical cavity. Experiments show that the chemical rate is strongly modified when the photon frequency is close to characteristic vibrational frequencies. The origin of this remarkable effect remains unknown. In this work, we develop an analytical rate theory for cavity-modified ground state chemical kinetics based on the Pollak-Grabert-H\"anggi rate theory. Unlike previous work, our theory covers the complete range of solvent friction values, from the energy-diffusion limited to the spatial-diffusion limited regimes. We show that the chemical reaction rate can either be enhanced or suppressed depending on the bath friction; when bath friction is weak chemical kinetics is enhanced as opposed to the case of strong bath friction, where chemical kinetics is suppressed. Further, we show that the photon frequency at which maximum modification of chemical rate is achieved is close to the reactant well, and hence resonant rate modification occurs. In the strong friction limit the {\it resonant} photon frequency is instead close to the barrier frequency, as obtained using the Grote-Hynes rate theory. Finally, we observe that the rate changes (as a function of photon frequency) are much sharper and more sizable in the weak friction limit than in the strong friction limit, and become increasingly sharp with decreasing well frequency

Effect of boron concentration on recombination at the p-Si–Al2O3 interface

We examine the surface passivation properties of Al₂O₃ deposited on boron-doped planar crystalline silicon surfaces as a function of the boron concentration. Both uniformly doped and diffused surfaces are studied, with surface boron concentrations ranging from 9.2 × 10¹⁵ to 5.2 × 10¹⁹ cm⁻³. Atmospheric pressure chemical vapor deposition and thermal atomic layer deposition are used to deposit the Al₂O₃ films. The surface recombination rate of each sample is determined from photoconductance measurements together with the measured dopant profiles via numerical simulation, using the latest physical models. These values are compared with calculations based on the interface properties determined from capacitance–voltage and conductance measurements. It is found that the fundamental surface recombination velocity of electrons, Sn 0 , which describes the chemical passivation of the interface, is independent of the surface boron concentration Ns for Ns  ≤ 3 × 10¹⁹ cm⁻³, and in excellent agreement with values calculated from the interface state density Dit and capture coefficients cn and cp measured on undiffused boron-doped surfaces. We conclude that the physical properties of the Si– Al₂O₃ interface are independent of the boron dopant concentration over this range

Isoniazid resistance in <i>Mycobacterium tuberculosis</i>

Drug resistant tuberculosis (TB) is increasing worldwide and it is now estimated by the World Health Organisation (WHO) that 7% of TB cases globally are resistant to isoniazid (INH). INH is a key drug for the treatment of TB, alongside rifampicin (RIF). Understanding factors which influence the emergence and propagation of INH resistance and the influence of INH resistance on TB treatment success are vital in improving global TB control efforts. Vietnam is ranked 12th of 22 high burden countries for TB and has a high prevalence of INH resistance (25%) with a relatively modest prevalence of TB resistant to both INH and RIF (multi-drug resistant, MDR TB) (2.7%). The first study in this thesis developed rapid screening tests for both RIF and INH resistance in Mycobacterium tuberculosis isolates which showed high accuracy. The specificity and the sensitivity of the MAS-PCR test for INH resistance compared to the conventional phenotypic DST were 100% [95% CI 92.9-100%] and 90% [95% CI 82.4-95.1 %], respectively. The second study demonstrated that the minimum inhibitory concentration (MIC) for INH is influenced by both the mutation responsible for resistance to INH and the lineage backbone of the M.tuberculosis isolate. A two-way ANOVA of MIC including both strain lineage (p=0.003) and resistance mutation (p<0.001) showed highly significant independent effects of both factors on MIC level. MIC to INH of isolates with a katG315 mutation (2ug/ml) was significantly higher compared to MIC to INH of isolates with an inhA-15 mutation (0.25p.g/ml) and wild-type isolates (0- 0.lug/ml) (p<0.00l). The independent effect of the strain lineage on INH MIC was predicted to correspond to a 2.68-fold (95% Cl 1.52-4.73, p<0.001) increase for Beijing lineage strains and a 1.40-fold (95% Cl 0.72-2.74, p=0.32) increase for EuroAmerican lineage strains in comparison with strains of the Indo-Oceanic lineage. The third study investigated the impact of INH resistance on outcome in patients with HIV-associated TB meningitis (HIV/TBM) and showed that HIV/TBM patients infected with INH resistant M.tuberculosis which remains susceptible to RIF have significantly worse outcomes than patients infected with fully susceptible strains. The adjusted hazard ratio for MDR patients in comparison with fully susceptible or streptomycin (STR)-monoresistant isolates was 5.21 [95% Cl 2.38-11.42], p<0.0001 compared with HR= 1.78 [95% Cl 1.18-2.66], p=0.005 for patients with INH resistant isolates (+/-STR resistance). The final study investigated the distribution of N-acetylator-2 (NAT2) phenotypes for INH metabolism in healthy volunteers from the Vietnamese Kinh population and correlated this with phenotypes using caffeine as a surrogate indicator for INH metabolism. This study showed that characterisation of 3 single nucleotide polymorphisms is sufficient to determine the acetylator status of individuals of Vietnamese Kinh ethnicity and that there is a predominance of fast acetylators (65%) in this popUlation. A simple PCR-RFLP test was developed to enable rapid determination of acetylator status for further studies. Collectively, these results contribute to our understanding of INH resistance in M.tuberculosis and provide molecular tools for further studies of this crucial drug