Concentration polarisation in tubular membranes —a numerical approach

A theoretical investigation ofparticle deposition onto a permeable surface of a tubular membrane is presented. Themass transport mechanisms are mathematically expressed using the two-dimensional convective diffusion equation. A numerical scheme is presented to solve the two-dimensional convective diffusion equation at the steady state for the case of nonuniform permeation velocity. This equation is solved numerically using a finite difference method. The numerical prediction of mass transfer in the mass boundary requires the use of a very dense grid. The concentration profiles along the membrane surface and the mass boundary layer are predicted. The effect of the Reynolds number, the wall Reynolds number and the Schmidt number were investigated. Correlations for the concentration boundary layer thickness δ_c/D=2(z/D)^0.33(ReSc)^{− 0.33} Re_w^−0.3 (1-0.4377 Sc^−0.0018 Re_w^−0.1551), and for the Sherwood number Sh =1.230 [(D/z) ReSc] ^0.33 (1 + 0.010 Re^−0.125Sc^1.055 Re_w.^1.132) based on the predicted values of the solute concentration profiles, are proposed, in the operating condition ranges 300 < Re < 1000, 0.02 < Re_w < 0.3 and 600 < Sc < 3200.     

Argon plasma treatment of glass surfaces

The effect of argon plasma treatment of glass surfaces is studied by FTIR and SEM. The argon plasma on cleaned glass surfaces resulted in increased surface area due to microetching and surface rearrangement of the silicate network as indicated by the observed changes in the Si-O stretching infrared absorption. The result was a relative increase in surface hydrophilicity which could be optimized by the plasma reaction conditions. The etching action of the argon plasma on the substrate surfaces facilitated the removal of the micrometre thick sizing from the commercial fibres accompanied by little loss in tensile strength. Plasma was also used to graft selected monomers to the surface of glass fibres for enhancement of bond compatibility in a composite system. This grafting treatment was followed by an argon etching step. The argon plasma action on the coated surfaces improved the wettability further and increased the sur face area. Changes in surface chemistry that accompanied the argon etching treatment were very subtle in the case of the plasma polymer of allylamine, but proved significant in the case of the plasma polymer of hexamethyldisiloxane. On the latter surfaces, rearrangement of the siloxane (Si-O-Si) bonds to silylmethylene (Si-(CH₂) _n -Si) groups is suggested.     

Cryptosporidiosis among HIV positive intravenous drug users in Malaysia

A study conducted at the Tampin Drug Rehabilitation Center in Malaysia established a high prevalence (23%) of asymptomatic carriers of Cryptosporidium among exposed HIV positive intravenous drug users (IVDUs). A majority of them were young adults and among the ethnic groups, the Malay HIV positive inmates had the highest prevalence of Cryptosporidium infection.     

The distribution of kth nearest neighbours and its application to cluster settling in dispersions of equal spheres

The spatial distribution of spheres in a very dilute suspension is described approximately by a Poison distribution, but much better approximations result when the volume of the spheres is taken into account. For solids fractions up to 0.32, the distribution of kth nearest neighbours calculated from the radial distribution function for a hard-sphere gas agreed closely with that determined from a computer simulation. This distribution provides insight into the concentration threshold for cluster settling and the increase in sedimentation rate with time in dilute dispersions. Two models provide rough explanations for the maintenance of cluster velocities greater than the Stokes velocity.     

An analysis of BioHashing and its variants

As a result of the growing demand for accurate and reliable personal authentication, biometric recognition, a substitute for or complement to existing authentication technologies, has attracted considerable attention. It has recently been reported that, along with its variants, BioHashing, a new technique that combines biometric features and a tokenized (pseudo-) random number (TRN), has achieved perfect accuracy, having zero equal error rates (EER) for faces, fingerprints and palmprints. There are, however, anomalies in this approach. These are identified in this paper, in which we systematically analyze the details of the approach and conclude that the claim of having achieved a zero EER is based upon an impractical hidden assumption. We simulate the claimants’ experiments and find that it is not possible to achieve their reported performance without the hidden assumption and that, indeed, the results are worse than when using the biometric alone.     

Corrosion of tin in aqueous solutions of mono-, Di- and trichloroacetic acids

The corrosion behaviour of tin in stagnant mono-, di- and trichloroacetic acids solutions in the pH range 1–6 and at concentrations 4.0 to 5 × 10^?4 M was investigated. The results indicate behaviour that is generally the same but there is some dependence on the acid concentration and the pH value. In 4.0 to 10^?2 M solutions, the corrosion rate (W) increased with increasing acid concentration and decreasing pH value from 1 to 4 as follows: log W=a+b log C, where b=0.70, 0.42 and 0.35 for tri-, di- and mono-chloroacetic acids respectively. At high concentrations 4.0 to 10^?2 M and in the pH range 1–6, the steady state corrosion potential shifted in the negative direction with increase of acid concentration accompanied by an increase in the corrosion rate, indicating that the corrosion process becomes anodically controlled by the complexing of Sn²⁺ ions with organic acid anions and that the order of aggressiveness is mono-<di-<trichloroacetic acids. In dilute solutions (10^?2 to 5.10^?4 M) in the pH range 1–6 the steady state potential shifted in the noble direction with increase of acid concentration (accompanied by a remarkable decrease in the corrosion rate). Corrosion inhibition in dilute solutions was attributed to film formation on the surface of tin which may result from the hydrolysis of tin species.     

Absence of human herpesvirus 8 and Epstein-Barr virus genome sequences in cutaneous epithelial neoplasms arising in immunosuppressed organ-transplant patients

Recent studies have implicated herpesvirus 8 and Epstein-Barr virus in the development of cutaneous malignancies in immunosuppressed patients. In order to examine the strength of this association, we examined 37 malignant, pre-malignant and benign cutaneous epithelial neoplasms removed from immunosuppressed organ recipients for the presence of human herpesvirus 8 and Epstein-Barr viral genome sequences using polymerase chain reaction (PCR) and in situ hybridization. We examined 2 actinic keratoses, 1 benign keratosis, 11 invasive squamous cell carcinomas, 17 squamous cell carcinomas in situ and 6 basal cell carcinomas. We also examined 4 basal cell carcinomas, 1 invasive squamous cell carcinoma and 3 squamous cell carcinomas in immunocompetent hosts. In contrast to findings reported by other investigators, we were unable to detect viral genome sequences in any of the biopsies examined. Our findings suggest that human herpesvirus 8 and Epstein-Barr virus likely do not play an etiologic role in cutaneous epithelial oncogenesis in immunocompromised patients.