An Extended Replication of an Experiment for Assessing Methods for Software Requirements Inspections

We have performed an extended replication of the Porter-Votta-Basili experiment comparing the Scenario method and the Checklist method for inspecting requirements specifications using identical instruments. The experiment has been conducted in our educational context represented by a more general definition of a defect compared to the original defect list. Our study involving 24 undergraduate students manipulated three independent variables: detection method, requirements specification, and the order of the inspections. The dependent variable measured is the defect detection rate. We found the requirements specification inspected and not the detection method to be the most probable explanation for the variance in defect detection rate. This suggests that it is important to gather knowledge of how a requirements specification can convey an understandable view of the product and to adapt inspection methods accordingly. Contrary to the original experiment, we can not significantly support the superiority of the Scenario method. This is in accordance with a replication conducted by Fusaro, Lanubile and Visaggio, and might be explained by the lack of individual defect detection skill of our less experienced subjects.     

Extraction technique for the determination of oxygen-18 in water using preevacuated glass vials

The need for a rapid, inexpensive technique for routine 18O/16O extraction from water has arisen recently through applications in the medical sciences and in hydrology. The traditional experimental technique for determining the oxygen isotope composition of water, the CO2-H2O equilibration method, is tedious, time consuming, and involves the use of custom-made glass apparatus. Furthermore, because of potential memory effects from one sample to the next, the glassware needs to be thoroughly cleaned between runs. A few attempts have been made to improve upon the method. Attempts to analyze water directly in the source of the mass spectrometer produced large memory effects and questionable results. Commercially available apparatus for automated extraction of 18O/16O from water is generally prohibitively expensive and often is designed to interface only with the manufacturer's own mass spectrometer. The method described in this paper utilizes inexpensive, off-the-shelf, preevacuated, glass vials. Preevacuated vials have been used by others for the isotopic analysis of breath CO2 and are well tested. The vials can be purchased in bulk from scientific apparatus suppliers at a relatively low cost. These are coupled with a simplified extraction line consisting of a stainless steel syringe needle and a glass cold trap. Vials are filled with CO2 and H2O and shaken in a constant-temperature water bath for at least 90 min. Since the vials are discarded after use, no cleaning is necessary, essentially eliminating any memory effect. Reproducibility is generally better than +/- 0.05%. The only reagents required are gaseous CO2 for equilibration, a dry ice/alcohol mixture for trapping water, and liquid nitrogen for transferring the CO2.     

Measurement of the particle movement in the fountain region of a Wurster type bed

A non-intrusive technique to follow single particles in the fountain region of a spouted bed with draft tube, the Wurster coater, is developed and tested. Compared to other techniques found in literature, the measurement technique presented here is easy to handle, inexpensive and suitable for particles with a diameter down to 500 μm. The measurements are performed in a laboratory scale Wurster bed constructed of Plexiglas to allow optical access to the flow. A small quantity of the particles in the bed are marked with fluorescence. A UV lamp is used to excite the fluorescence and the marked particles are followed with a high-speed video camera equipped with an optical filter. A single marked particle in the fountain can be followed in 5-30 images in sequence at a frame rate of 125 fps. The particle position and velocity are calculated. The distribution of the particle trajectories maximum height is studied for different particle loading, jet air velocity and position of the Wurster tube. The technique can be used for the characterization of differences in process dynamics due to different operating conditions.     

Controlled destruction of residual crosslinker in a silicone elastomer for drug delivery

In drug delivery systems that use silicone elastomers as a diffusion matrix for the active drug, it is common to crosslink the material by the hydrosilylation reaction. In this platinum‐catalyzed reaction, vinyl groups on a polymer add to the methyl siloxane hydride (MHS) groups on a low molecular mass crosslinker. With an excess of crosslinker, a fast curing is achieved and a fully crosslinked material is formed. Unreacted MHS groups were shown to remain in the elastomer after curing because of the excess crosslinker. In this work, a simple procedure was developed to eliminate the unreacted MHS groups from the final product. We found that storage of the product at +40°C and 75% relative humidity for a few weeks will effectively destroy the residual MHS groups in the elastomer. The effects of varying levels of humidity, oxygen, and temperature on this postcuring procedure were studied. The amount of MHS groups was measured with NMR and IR spectroscopy. We also found that the hardness of the material increased by approximately 25% as a consequence of this postcuring treatment. This increase is probably due to a secondary crosslinking reaction between MHS and silanol groups. Heat treatment at higher temperatures led to an even further increase in the hardness and compression modulus. Because no MHS groups remained in the elastomer when this heat treatment was started, it is apparent that another secondary crosslinking reaction is occurring, probably silanol condensation. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2254–2264, 2002     

Mass transport in a weakly stratified electrochemical cell

A study of natural convection in an electrochemical system with a Rayleigh number of the order 10¹⁰ is presented. Theoretical and experimental results for the unsteady behaviour of the concentration and velocity fields during electrolysis of an aqueous solution of a metal salt are given. The cell geometry is a vertical slot and the reaction kinetics is governed by a Butler-Volmer law. To reduce the effects of stratification, the flush mounted electrodes are located (symmetrically) in the middle parts of the vertical walls. It is demonstrated, both theoretically and experimentally, that a weak stratification develops after a short time, regardless of cell geometry, even in the central part of the cell. This stratification has a strong effect on the velocity field, which rapidly attains boundary layer character. Measured profiles of concentration and vertical velocity at and above the cathode are in good agreement with numerical predictions. For a constant cell voltage, numerical computations show that between the initial transient and the time when stronger stratification reaches the electrode area, the distribution of electric current is approximately steady.List of symbols a _i left hand side of equation system - b _i right hand side of equation system - c concentration (mol m^–3) - c dimensionless concentration - c _i concentration of species i' (mol m^–3) - c₀ initial cell concentration (300 mol m^–3) - c ₀ dimensionless initial cell concentration - c_wall concentration at electrode surface (mol m^–3) - dx increment solution vector in Newton's method - D _i diffusion coefficient of species i (m² s^–1) - D ₁ 0.38 × 10^–9 m² s^–1 - D ₂ 0.82 × 10^–9 m² s^–1 - D effective diffusion coefficient of the electrolyte (0.52 × 10^–9 m² s^–1) - _x unit vector in the vertical direction - _y unit vector in the horizontal direction - F Faraday's constant (96 487 A s mol^–1) - g acceleration of gravity (9.81 m s^–2) - i dummy referring to positive (i = 1) or negative (i = 2) ion - f current density (A m^–2) - f dimensionless current density - i₀ exchange current density (0.01 A m^–2) - J _ij Jacobian of system matrix - L length of electrode (0.03 m) - N _i transport flux density of ion i (mol m^–2 s^–1) - n unit normal vector - p pressure (Nm^–2) - p dimensionless pressure - R gas constant molar (8.31 J K^–1 mol^–1) - R _i residual of equation system - Ra Rayleigh number gL ³ c ₀/D (2.54 × 101¹⁰) - S _c Schmidt number /D (1730) - t time (s) - t dimensionless time - T temperature (293 K) - velocity vector (m s^–1) - dimensionless velocity vector - U characteristic velocity in the vertical direction - V _± potential of anode and cathode, respectively - x spatial coordinate in vertical direction (m) - x dimensionless spatial coordinate in vertical direction - x solution vector for c, and - y spatial coordinate in horizontal direction (m) - y dimensionless spatial coordinate in horizontal direction - z _i charge number of ion i Greek symbols symmetry factor of the electrode kinetics, 0.5 - volume expansion coefficient (1.24 × 10^–4 m³ mol^–1) - _s surface overpotential - constant in equation for the electric potential (–5.46) - _s diffusion layer thickness - scale of diffusion layer thickness - constant relating c/y to the Butler-Volmer law (0.00733) - kinematic viscosity (0.9 × 10^–6 m2 s^–1)     

Single-stage flowing liquid film impactor for continuous on-line particle analysis

A single-stage “wet impactor” is presented, where the impaction occurs on a regenerated water surface. The developed impactor is equipped with an impaction liquid support plate of etched glass and a drain spout providing a continuous liquid flow covering the impaction area. Subsequent transport of the impaction liquid makes an on-line determination possible. With multiple nozzles (74 holes, 0.3 mm i.d.) and an air flow of 101/min the cut-off was determined to 0.41 ± 0.02 μm. The impactor was also investigated for its particle loss. The cut-off function, regarding the consequences of letting impaction occur in a liquid film is discussed and compared to conventional impactors. The analysis technique was tested in an ambient air measurement study with an ion chromatograph attached to the sampling system.     

The influence of thermal annealing on residual stresses and mechanical properties of arc-evaporated TiCxN1−x (x=0, 0.15 and 0.45) thin films

We report the stress relaxation behavior of arc-evaporated TiC_xN_1−x thin films during isothermal annealing between 350 and 900°C. Films with x=0, 0.15, and 0.45, each having an initial compressive intrinsic stress σ_int=−5.4 GPa, were deposited by varying the substrate bias V_s and the gas composition. Annealing above the deposition temperature leads to a steep decrease in the magnitude of σ_int to a saturation stress value, which is a function of the annealing temperature. The corresponding apparent activation energies for stress relaxation are E_a=2.4, 2.9, and 3.1 eV, for x=0, 0.15, and 0.45, respectively. TiC_0.45N_0.55 films with a lower initial stress σ_int=−3 GPa, obtained using a high substrate bias, show a higher activation energy E_a=4.2 eV. In all the films, stress relaxation is accompanied by a decrease in defect density indicated by the decreased width of X-ray diffraction peaks and decreased strain contrast in transmission electron micrographs. Correlation of these results with film hardness and microstructure measurements indicates that the stress relaxation is a result of point-defect annihilation taking place both during short-lived metal-ion surface collision cascades during deposition, and during post-deposition annealing by thermally activated processes. The difference in E_a for the films of the same composition deposited at different V_s suggests the existence of different types of point-defect configurations and recombination mechanisms.     

Protein profiling of low-density lipoprotein from obese subjects

Although obesity and high levels of low-density lipoprotein (LDL) are well-known risk factors for cardiovascular disease, the precise role(s) of different LDL constituents in obesity has not been explored. In the present study, we compared the LDL proteome of healthy control adults (body mass index<25) and obese subjects (body mass index>30). LDL was isolated by density-gradient ultracentrifugation and proteins were separated with 2-D PAGE, quantified, and identified by peptide mass fingerprinting using MALDI-TOF MS. A new LDL-associated protein was identified as transthyretin and found to be significantly more abundant in LDL from the obese subjects. In addition, LDL from the obese subjects contained relatively more α(1) -antitrypsin, apo J, apo C-II, than LDL from controls, and also more of an acidic isoform (pI/Mr; 5.2/23 100) of apo A-I. On the other hand, the relative amounts of apo A-IV and the major isoform of apo A-I (pI/Mr; 5.3/23 100) were significantly less in LDL from the obese subjects. Apo E was less and non-sialylated apo C-III more abundant in LDL from obese men than control men, while there were no such differences between LDL from obese and control women. These findings illustrate that obesity is not only associated with increased LDL-cholesterol levels but also with alterations in the LDL protein composition. The presence of transthyretin in LDL from obese subjects may reflect over-nutrition and affect the lipid metabolism in obesity.     

Human immunodeficiency virus 1 (HIV-1)-specific reverse transcriptase (RT) inhibitors may suppress the replication of specific drug-resistant (E138K)RT HIV-1 mutants or select for highly resistant (Y181C-->C181I)RT HIV-1 mutants

Mutant HIV-1 that expresses a Glu138-->Lys substitution in its RT [(E138K)RT] is resistant to the HIV-1-specific RT inhibitor 2',5'-bis-O-(tert-butyldimethylsilyl)-3'-spiro-5"-(4"-amino-1",2"- oxathiole-2",2"-dioxide)pyrimidine (TSAO). However, cell cultures infected with this mutant were completely protected against virus-mediated destruction by micromolar concentrations of the HIV-1-specific RT inhibitors tetrahydroimidazo[4,5,1-jk][1,4]benzodiazepin-2(1H)-one and -thione (TIBO), nevirapine, and bis(heteroaryl)piperazine (BHAP). In contrast, cells infected with a virus mutant that expresses a Tyr181-->Cys substitution in its RT [(Y181C)RT] were not protected by nevirapine and TIBO and were only temporarily protected by BHAP. HIV-1 mutant that emerged under the latter conditions contained a Cys181-->Ile substitution in their RT [(LC181I)RT]. This mutant proved highly resistant to all HIV-1-specific RT inhibitors tested, except for several 1-(2-hydroxyethoxymethyl)-6-(phenylthio)thymine (HEPT) derivatives. When recombinant (C181I)RT was evaluated for susceptibility to the HIV-1-specific RT inhibitors, it was resistant to all inhibitors except the HEPT compounds. Since a (Y181F)RT HIV mutant strain was isolated from cells infected with (Y181C)RT HIV-1 and treated with BHAP, we postulate that the Ile codon was derived from a Cys-->Phe transversion mutation (TGT-->TTT), followed by a Phe-->Ile transversion mutation (TTT-->ATT).