Objective function choice for control of a thermocapillary flow using an adjoint-based control strategy

The problem of suppressing flow oscillations in a thermocapillary flow is addressed using a gradient-based control strategy. The physical problem addressed is the “open boat” process of crystal growth, the flow in which is driven by thermocapillary and buoyancy effects. The problem is modeled by the two-dimensional unsteady incompressible Navier–Stokes and energy equations under the Boussinesq approximation. The goal of the control is to suppress flow oscillations which arise when the driving forces are such that the flow becomes unsteady. The control is a spatially and temporally varying temperature gradient boundary condition at the free surface. The control which minimizes the flow oscillations is found using a conjugate gradient method, where the gradient of the objective function with respect to the control variables is obtained from solving a set of adjoint equations. The issue of choosing an objective function that can be both optimized in a computationally efficient manner and optimization of which provides control that damps the flow oscillations is investigated. Almost complete suppression of the flow oscillations is obtained for certain choices of the objective function.     

Impurity fingerprints for the identification of counterfeit medicines--a feasibility study

Most of the counterfeit medicines are manufactured in non good manufacturing practices (GMP) conditions by uncontrolled or street laboratories. Their chemical composition and purity of raw materials may, therefore, change in the course of time. The public health problem of counterfeit drugs is mostly due to this qualitative and quantitative variability in their formulation and impurity profiles.In this study, impurity profiles were treated like fingerprints representing the quality of the samples. A total of 73 samples of counterfeit and imitations of Viagra^® and 44 samples of counterfeit and imitations of Cialis^® were analysed on a HPLC-UV system. A clear distinction has been obtained between genuine and illegal tablets by the mean of a discriminant partial least squares analysis of the log transformed chromatograms. Following exploratory analysis of the data, two classification algorithms were applied and compared. In our study, the k-nearest neighbour classifier offered the best performance in terms of correct classification rate obtained with cross-validation and during external validation. For Viagra^®, both cross-validation and external validation sets returned a 100% correct classification rate. For Cialis^® 92.3% and 100% correct classification rates were obtained from cross-validation and external validation, respectively.     

Enantiomeric separation of amlodipine and its two chiral impurities by nano‐liquid chromatography and capillary electrochromatography using a chiral stationary phase based on cellulose tris(4‐chloro‐3‐methylphenylcarbamate)

In this work, a novel polysaccharide‐based chiral stationary phase, cellulose tris(4‐chloro‐3‐methylphenylcarbamate), also called Sepapak 4 has been evaluated for the chiral separation of amlodipine (AML) and its two impurities. AML is a powerful vasodilatator drug used for the treatment of hypertension. Capillary columns of 100 μm id packed with the chiral stationary phase were used for both nano‐LC and CEC experiments. The optimization of the mobile phase composed of ACN/water, (90:10, v/v) containing 15 mM ammonium borate pH 10.0 in nano‐LC allowed the chiral separation of AML and the two impurities, but not in a single run. With the purpose to obtain the separation of the three pairs of enantiomers simultaneously, CEC analyses were performed in the same conditions achieving better enantioresolution and higher separation efficiencies for each compound. To fully resolve the mixture of six enantiomers, parameters such as buffer pH and concentration sample injection have been then investigated. A mixture of ACN/water (90:10, v/v) containing 5 mM ammonium borate buffer pH 9.0 enabled the complete separation of the three couples of enantiomers in less than 30 min. The optimized CEC method was therefore validated and applied to the analysis of pharmaceutical formulation declared to contain only AML racemate.     

Structural, electronic and magnetic properties of the 3d transition metal-doped GaN nanotubes

We have performed first-principles calculations on the structural, electronic and magnetic properties of seven different 3d transition-metal (TM) impurity (V, Cr, Mn, Fe, Co, Ni and Cu) doped armchair (5,0) and zigzag (8,0) gallium nitride nanotubes (GaNNTs). The results show that there is distortion around 3d TM impurities with respect to the pristine GaNNTs for 3d TM-doped (5,5) and (8,0) GaNNTs. The change of total magnetic moment follows Hund’s rule for 3d TM-doped (5,5) and (8,0) GaNNTs, respectively. The total density of states (DOS) indicates that Cr-, Mn-, Fe- and Ni-doped (5,5) GaNNTs as well as Cr-, Mn-, Ni- and Cu-doped (8,0) GaNNTs are all half-metals with 100% spin polarization. The study suggests that such TM-doped nanotubes may be useful in spintronics and nanomagnets.     

Influence of Tb incorporation on the structural and the optical properties of ZnO nanoparticles

Structural and optical properties of the Tb doped ZnO nanoparticles are systematically studied as a function of the Tb mole-fraction. Our study suggests that the Tb incorporates mostly on the surface and affects the optical properties of the ZnO nanoparticles by influencing the attachment of certain adsorbed groups, which are found to be responsible for the appearance of a broad green luminescence (GL) band in the photoluminescence spectra recorded for these nanoparticles. It has been found that the accumulation of Tb on the surface of the nanoparticles not only enhances the band edge to green luminescence intensity ratio under the vacuum condition but also increases the band gap energy by introducing a hydrostatic compressive strain in individual nanoparticles, which provides a unique opportunity to study the pressure dependence of the optical properties of nanoparticles without applying any external pressure. The hydrostatic compressive strain is explained in terms of the increase of the surface strain energy as a result of the Tb accumulation on the surface of the nanoparticles. The average value of the surface energy density for the particles has been estimated as a function of Tb mole-fraction. The pressure coefficient of the band gap which is obtained from the variation of the band gap energy with the hydrostatic strain has been found to decrease significantly with the particle size for the ZnO nanoparticles.     

电感耦合等离子体质谱法测定高纯氧化镧中稀土杂质的研究

本文报道了用电感耦合等离子体质谱法（ＩＣＰ－ＭＳ）测定高纯氧化镧中１２个痕量稀土杂质的方法。分析讨论了测定中的种种谱干扰和基体效应，研究了用Ｔｌ，Ｃｓ，Ｉ作内标补补基体抑制效应和灵敏度漂移。单个稀土元素的检出奶为０．０１－００．２６ｎｇ／ｍＬ，回收率为９１．２５－１０８．５％。精密度（ＲＳＤ）为２．８％－６．８５。本方法酸溶样品后可以直接测定，不需要预富集和分离。     

Application of HPLC mobile phase optimization methods to the detection of impurities in bulk drug steroids

Summary Some mobile phase optimization methods have been used in developing a Reversed-Phase High-Performance Liquid Chromatography methodology for the determination of related impurities in bulk pharmaceutical steroids. Using two different approaches with binary and ternary mobile phase, the complete separation of 9--fluoroprednisolone acetate and its main potential impurities, at low concentration levels, has been achieved. This methodology may be applicable to other steroidal drugs and it is presented as an alternative to the thin-layer chromatography currently prescribed in official methods.     

Tomographic analysis of dilute impurities in semiconductor nanostructures

We describe the application of pulsed-laser atom probe (PLAP) tomography to the analysis of dopants and unintentional impurities in Si and Ge nanowires grown by the vapor–liquid–solid mechanism. PLAP tomography was used to determine the concentration of phosphorous in Ge nanowires and B in Si nanowires, enabling comparisons of the atomic concentrations of the reactants with those of the reaction products. Oxygen impurities were also detected, but the contribution from background gas adsorption was not ruled out. Gold catalyst impurities were not detected, and an upper bound of 5 ppm was established. Intrinsic and extrinsic origins of the detection limits of dopants and other impurities are described in detail. A tapered nanowire geometry was found to improve the mass resolution and signal-to-noise ratio by increasing the tip cooling rate. Simulations of nanowire cooling under laser pulsing were used to validate this improved approach to PLAP analysis of nanowires.     

Quantitative analysis of ripasudil hydrochloride hydrate and its impurities by reversed‐phase high‐performance liquid chromatography after precolumn derivatization: Identification of four impurities

We report the development and validation of a stability‐indicating reversed‐phase high‐performance liquid chromatography method with precolumn derivatization for the separation and identification of the impurities of ripasudil hydrochloride hydrate, a novel protein kinase inhibitor. 2,3,4,6‐Tetra‐O‐acetyl‐β‐d ‐glucopyranosyl isothiocyanate was chosen as the derivatizing reagent and triethylamine was added as catalyst. 200 μL sample solution (1 mg/mL), 600 μL derivatizing reagent (1 mg/mL), and 200 μL triethylamine solution (1%, v/v) were mixed and reacted at 40°C for 30 min. The separation was achieved on an Inertsil C₁₈ ODS‐3 (250 mm × 4.6 mm, 5 μm) column using mobile phases including 10 mmol monopotassium phosphate buffer (pH 3.0) and methanol in gradient mode. The column temperature was adjusted at 25°C and the flow rate at 1 mL/min. The detection was carried out at 220 nm. Different precolumn derivatization conditions as well as the high‐performance liquid chromatography conditions were optimized. Ripasudil hydrochloride hydrate and its four impurities were detected and quantitated, among which two new compounds were characterized. The proposed method was validated and proven to be selective, accurate, and precise and suitable for the quantitative analysis of ripasudil hydrochloride hydrate.