On the internal structure of weakly nonlinear bores in laminar high Reynolds number flow

The paper deals with the internal structure of hydraulic jumps in near-critical single-layer flows which replaces the discontinuities predicted by hydraulic theory if viscous effects acting inside a thin laminar boundary layer are properly accounted for. In the limit of large Reynolds number this leads to a structure problem formed by the classical triple-deck equations supplemented with a novel nonlinear interaction relationship which allows for the passage through the critical state. Hydraulic jumps are shown to represent eigensolutions of the structure problem where this passage is achieved by the local thickening of the boundary layer which acts as a viscous hump. The effects of detuning and dispersion due to streamline curvature and surface tension on the internal structure of hydraulic jumps are studied in detail. In addition, the interaction of hydraulic jumps with surface mounted obstacles is investigated.     

Leucine enkephalin—A mass spectrometry standard

The present article reviews the mass spectrometric fragmentation processes and fragmentation energetics of leucine enkephalin, a commonly used peptide, which has been studied in detail and has often been used as a standard or reference compound to test novel instrumentation, new methodologies, or to tune instruments. The main purpose of the article is to facilitate its use as a reference material; therefore, all available mass spectrometry‐related information on leucine enkephalin has been critically reviewed and summarized. The fragmentation mechanism of leucine enkephalin is typical for a small peptide; but is understood far better than that of most other compounds. Because ion ratios in the MS/MS spectra indicate the degree of excitation, leucine enkephalin is often used as a thermometer molecule in electrospray or matrix‐assisted laser desorption ionization (ESI or MALDI). Other parameters described for leucine enkephalin include collisional cross‐section and energy transfer; proton affinity and gas‐phase basicity; radiative cooling rate; and vibrational frequencies. The lowest‐energy fragmentation channel of leucine enkephalin is the MH⁺ → b₄ process. All available data for this process have been re‐evaluated. It was found that, although the published E_a values were significantly different, the corresponding Gibbs free energy change showed good agreement (1.32 ± 0.07 eV) in various studies. Temperature‐ and energy‐dependent rate constants were re‐evaluated with an Arrhenius plot. The plot showed good linear correlation among all data (R² = 0.97), spanned over a 9 orders of magnitude range in the rate constants and yielded 1.14 eV activation energy and 10^11.0 sec^?1 pre‐exponential factor. Accuracy (including random and systematic errors, with a 95% confidence interval) is ±0.05 eV and 10^±0.5 sec^?1, respectively. The activation entropy at 470 K that corresponds to this reaction is ?38.1 ± 9.6 J mol^?1 K^?1. We believe that these re‐evaluated values are by far the most accurate activation parameters available at present for a protonated peptide and can be considered as “consensus” values; results on other processes might be compared to this reference value. © 2010 Wiley Periodicals, Inc., Mass Spec Rev 30:298–320, 2011     

A comparison of formulas for the design of cumulative sum control charts

A conventional cumulative sum control chart has a V‐mask where each arm makes an angle θ with the horizontal and has a lead distance d. These parameters are usually related to h (=dA tan(?), A is a scaling factor) and k(=A tan(?)). Two systems of formulas are examined for deriving h and k for selected values of the in control and out of control average run lengths. This is the first time an exhaustive comparison has been made. Copyright © 2009 John Wiley & Sons, Ltd.     

Effects of externally-generated electrons on pressure measurements of inverted magnetron gauges at Diamond

Diamond Light Source (Diamond) utilises a large number of Inverted Magnetron Gauges (IMGs) for both monitoring the vacuum and as a source of interlocks for protection of the machine. During storage ring operation it has been found that, in the presence of the stored electron beam, charged particles, assumed to be electrons, impinging on some of the gauges cause the pressures indicated by the gauges to drop to zero which causes problems with the operation of the storage ring. Diamond has designed and fitted a magnetic filter at the neck of each affected gauge port to eliminate this problem. This paper reports on and discusses experiments and proposed experiments with an electron flood gun and IMGs from two different manufacturers (MKS Instruments and Pfeiffer Vacuum) aimed at obtaining a better understanding of the effect. Externally-generated electrons from the flood gun can cause serious errors in the pressures indicated by the gauges; the error can be positive or negative depending on the gauge current-measuring circuit. Methods aimed at eliminating these spurious pressure readings, such as magnetic filters, bias voltages within the gauges and the use of earth meshes and baffles are also discussed.     

Reliability assessment of 3D space frame structures applying stochastic finite element analysis

Throughout design development of satellite structure, stress engineer is usually challenged with randomness in applied loads and material properties. To overcome such problem, a risk-based design is applied which estimates satellite structure probability of failure under static and thermal loads. Determining probability of failure can help to update initially applied factors of safety that were used during structure preliminary design phase. These factors of safety are related to the satellite mission objective. Sensitivity-based analysis is to be implemented in the context of finite element analysis (probabilistic finite element method or stochastic finite element method (SFEM)) to determine the probability of failure for satellite structure or one of its components.     

Investigation of a Novel Condensation Aerosol Generator: Solute and Solvent Effects

Part I of this article presents results of an experimental study on gas-phase nucleation for three model solutes and their solvent, propylene glycol (PG), with variables being solute concentration and the nature of the solute substance. A single manifestation of an aerosol generator, which forms condensation aerosols by cooling of hot vapor issuing from an electrically heated, pumped capillary, is described and used for all experiments. The effects of solute concentration and solute type were studied for deoxycorticosterone (DOC), benzil (BZ), and phenyl salicylate (PhS). Suppression of homogeneous nucleation and occurrence of heterogeneous condensation of the solvent was observed at different solute concentrations for BZ, PhS, and DOC. The nature and concentration of the solute dissolved in the solvent was shown to determine the final particle size distribution of the condensed aerosol. In the case of the least volatile solute, DOC, solute aerosol and total aerosol size distributions were identical at low solute concentrations. A transitional concentration region then existed in which a bimodal solute aerosol was formed, followed at high concentrations by increasing separation of the solvent-dominated aerosol size distribution and that of the solute. In Part II of this article, the effect of DOC dissolution in different solvents was studied at fixed solute concentration. The effects of six glycol solvents--i.e., PG, ethylene glycol (EG), dipropylene glycol (DPG), diethylene glycol (DEG), triethylene glycol (TEG), and tetraethylene glycol (TetEG)--and three nonglycol solvents--i.e., dimethyl sulfoxide (DMSO), formamide (FORM), and oleyl alcohol (OA)--were studied, as these affected the resultant aerosol sizes. Suppression of total aerosol mass median aerodynamic diameter (MMAD) was observed on dissolution of 0.5% w/w DOC in each solvent, although suppression occurred to different extents. It was shown that the boiling point or volatility of the solvent used to dissolve the less volatile DOC had an effect on the final particle size distribution of the condensed aerosol and whether the aerodynamic size distributions for the solute and the total aerosol were the same or different.     

Low-Temperature Processing of PZT Thick Film by Seeding and High-Energy Ball Milling and Studies on Electrical Properties

Lead zirconate titanate thick film with molecular formula PbZr_0.52Ti_0.42O₃ (PZT) was prepared by a modified conventional sol–gel method through seeding and high-energy ball milling, resulting in perovskite phase formation at lower temperatures. The ball-milling time was optimized by keeping the seed particle loading (5 wt.%) constant in the sol–gel solution. This methodology helped in reduction of the crystalline phase formation temperature to 300°C, which is much lower than that reported in the literature (450°C). The well-established perovskite phase was confirmed by x-ray diffraction (XRD) analysis. Scanning electron microscopy (SEM) of PZT films revealed uniform and crystalline microstructure. Film prepared by this methodology showed higher spontaneous polarization (2.22 μC/cm²), higher capacitance (1.17 nF), and low leakage current density (18 μA/cm²). The results obtained from ferroelectric characterization showed a strong correlation with the XRD and SEM results.