Retardation effect of jojoba chain length on the chemical reactivity of the liquid wax

Jojoba wax and its derivatives are slow-reacting compounds. To elucidate the reasons for this phenomenon, we reacted jojoba mono- and bis-epoxide and trans-jojoba bis-epoxide (C₃₈–C₄₄ long-chain esters), as well as side chain esters of three steroid skeleton mono-epoxide derivatives with NaI under acidic conditions to yield the corresponding iodohydrins, which then formed the respective bis-keto (or mono-ketone) derivatives. The kinetics, activation energies, and thermodynamic parameters of activation of nucleophilic epoxide opening and pinacol rearrangement were determined for all these compounds. The reaction rates of the jojoba derivatives were similar to those of two of the epoxides derived from the steroid skeleton compounds, and in the third case the steroid derivative reacted somewhat faster than all the rest. This pattern of rate retardation could stem either from folding of the long jojoba chain, resulting in steric hindrance around the reaction centers, or from repeated unproductive collisions along the long hydrocarbon chain of the jojoba wax (statistical effect). Our results appear to suggest that the multiple unsuccessful collisions were the dominant factor, although steric hindrance cannot be ruled out.     

Ionic composition of rat airway surface liquid determined by X-ray microanalysis

The thin layer of liquid that lines the conducting airway epithelium, the airway surface liquid (ASL), is important for mucociliary clearance. Altered ionic composition and/ or volume of the ASL play a major role in the pathology of airway diseases such as cystic fibrosis. Since the ASL is a thin layer, it has been difficult to exactly determine its composition. The present paper describes two techniques that have been developed and used to study ASL composition: X-ray microanalysis of frozen hydrated rat trachea, and an ion-exchange (dextran) bead method, where dextran beads were placed on the airway epithelium to equilibrate with the ASL; the beads were then collected under silicone oil, dried and analyzed by X-ray microanalysis. The results from both frozen-hydrated specimens and from the dextran beads showed that ASL from rat trachea is hypotonic. Concentrations of Na, P, S, and K were higher in the frozen-hydrated ASL, in which mainly the mucus layer is analyzed, compared with the dextran bead method, in which mainly the periciliary liquid is sampled. Also the composition of rat nasal fluid was investigated by the dextran bead method. This fluid was somewhat hypertonic because of a high K concentration. The ionic composition of the nasal and tracheal fluid can be manipulated by cholinergic or alpha- or beta-adrenergic stimulation. Collecting ASL with dextran beads did not disturb the integrity of the airway epithelium. The ionic composition of the collected beads remained stable for several days during storage in silicone oil. It is concluded that X-ray microanalysis is a suitable method to determine the ionic composition of ASL.     

Noniterative Implementation of Pressure-Dependent Demands Using the Hydraulic Analysis Engine of EPANET 2

To analyze water distribution networks under pressure-deficient conditions, most of the available hydraulic simulators, including EPANET 2, must be either modified by embedding pressure-dependent demands in the governing network equations or run repeatedly with successive adjustments made to specific parameters until a sufficient hydraulic consistency is obtained. This paper presents and discusses a simple technique that implements the square root relationship between the nodal demand and the nodal pressure using EPANET 2 tools and allows a water distribution network with pressure-dependent demands to be solved in a single run of the unmodified snapshot hydraulic analysis engine of EPANET 2. In this technique, artificial strings made up of a flow control valve, a pipe with a check valve, and a reservoir are connected to the demand nodes before running the engine, and the pressure-dependent demands are determined as the flows in the strings. The resistance of the artificial pipes is chosen such that the demands are satisfied in full at a desired nodal pressure. The proposed technique shows reasonable convergence as evidenced by its testing on example networks.     

Desiliconization of Mullite Felt

High-temperature evaporation from 80% porous, rigid mullite (3Al₂O₃·2SiO₂) whisker felt was studied under vacuum and at various helium pressures using gravimetry, X-ray diffractometry, SEM, and EDS. Heat treatments at 1350° to 1550°C resulted in evaporation of SiO₂ from mullite with a rate strongly dependent on temperature and pressure. A concentration gradient of SiO₂ was observed through the cross section of samples after heating under vacuum, indicating that SiO₂ preferentially evaporated from whiskers on the periphery of the samples. The SiO₂ concentration gradient was accompanied by sharp microstructural changes across the specimens. The gradient was decreased by raising the ambient helium pressure during heat treatment. A mathematical model was developed to predict the SiO₂ concentration profile. The model agrees well with experimental results and demonstrates that the diffusivity of SiO₂ in the vapor phase controls the gradient of SiO₂ through the cross section of mullite felt.     

Complexity Evaluation of Computer-Based Tasks

In this work, task complexity is considered as a multidimensional, integral characteristic of a task. The more complex a task is, the higher the cognitive demands for performing the task. Components of task complexity impose demands on the mental efforts of users. This article proposes a general approach to evaluate the complexity of computer-based tasks. The proposed principles of complexity evaluation and measures of complexity provide a proper basis for optimization, modification, and enhancement of the software design process. Experimental results support the effectiveness of the proposed method for both the design of man–machine systems and human–computer interfaces. The suggested methods and principles of complexity assessment derive from systemic-structural activity theory.     

Oxidation Processes for Alloys in the Ni – Zr System. Part 2. Phase Composition of Scale Formed on Ni7Zr2

We have used x-ray and metallographic layer-by-layer phase analysis to study the structure and composition of scale formed on the alloy Ni₇Zr₂ during its oxidation in air over a period of 1 h and 10 h in the temperature range 500-1200°C. In the scale we find NiO, the cubic and monoclinic modifications of ZrO₂, and also Ni and Ni₅Zr. The phase components are nonuniformly distributed over the thickness of the scale. The outer scale consists of the oxides NiO and ZrO₂, while the composition of the inner scale includes Ni and Ni₅Zr in addition to monoclinic ZrO₂. Cubic ZrO₂ is formed on the surface of the specimen in the initial stages of its oxidation at 500-700°C. For T ≥ 900°C, on the surface of the scale we find both modifications of ZrO₂, while the nickel phase is itself a solid solution Ni(Zr). We note that the mechanisms for the formation of low-temperature (T ≤ 800°C) and high-temperature (T ≥ 900°C) scales are different. It is hypothesized that these differences are determined mainly by the fact that at high temperatures, diffusion of zirconium ions toward the outer boundary of the scale is superimposed on diffusion of oxygen toward the scale – alloy boundary.     

Processing of ZrC–Mo Cermets for High Temperature Applications, Part II: Pressureless Sintering and Mechanical Properties

Pressureless sintering of ZrC–Mo cermets was investigated in a He/H₂ atmosphere and under vacuum. A large density increase was observed for specimens with >20 vol% Mo after heating at 2150°C for 60 min in a He/H₂ atmosphere. The increase in density was attributed to the formation of Mo₂C during heating and its subsequent eutectic reaction with Mo, which produced rounded ZrC grains in a Mo–Mo₂C matrix. Sintering in vacuum did not produce the same increase in density, due to the lack of Mo₂C formation and subsequent lack of liquid formation, which resulted in a microstructure with irregular ZrC grains with isolated areas of Mo. Mechanical properties testing showed a decrease in Young's modulus with increasing Mo content that was consistent with the models presented. Flexure strength of ZrC–Mo cermets sintered in He/H₂ atmosphere materials increased with increasing Mo content from 320 MPa at 20 vol% Mo to 410 MPa at 40 vol% Mo. Strength was predicted by adapting theories developed previously for WC–Co cermets.     

Defeaturing: A posteriori error analysis via feature sensitivity

It is well known that small geometric features within a CAD model can significantly impact the computational cost, and often undermine the reliability, of finite element analysis. Engineers therefore resort to defeaturing or detail removal, wherein the offending features are suppressed prior to computational analysis. However, this results in a defeaturing‐induced analysis error. In this paper, we estimate this error in an a posteriori sense through the novel concept of feature sensitivity. The latter determines the first‐order change in quantities of interest when an arbitrary cluster of small geometric features is deleted from a model. A formal theory and a set of associated algorithms are provided to compute the feature sensitivity associated with a scalar elliptic partial differential equation. The theory is supported through numerical experiments in 2‐D, involving both internal and boundary features. Copyright © 2008 John Wiley & Sons, Ltd.     

Microbial degradation of the detoxification products of mustard from the Russian chemical weapons stockpile

This work was undertaken to examine the possibility of biodegradation of the organic components of the ‘reaction masses’ (detoxification products) generated by destruction of the chemical warfare agent mustard. The composition of these components was analysed by gas chromatography and mass spectrometry. The major components formed during chemical detoxification were identified as 1,4‐perhydrothiazine derivatives. N‐(2‐Hydroxyethyl)‐2‐methyl‐1,4‐perhydrothiazine hydrochloride and N‐(2‐hydroxyethyl)‐3‐methyl‐1,4‐perhydrothiazine hydrochloride were predominant (about 70% of total 1,4‐perhydrothiazine derivatives). Pseudomonas putida strains that used some organic components of the mustard reaction masses as carbon sources for growth were isolated and selected. Growth cessation in this medium (with organic carbon still available) was due to the depletion of bioutilisable substrates, primarily monoethanolamine and ethylene glycol (the residual components of the detoxifying mixture). 1,4‐Perhydrothiazine derivatives were not used as carbon sources for growth of P putida strain SH1, but their concentration decreased during bacterial growth with monoethanolamine and ethylene glycol as the carbon substrates. It is suggested that 1,4‐perhydrothiazines undergo transformation by the microbial cells under these conditions. Copyright © 2005 Society of Chemical Industry