Who Was Alfred? A native gazing at Rhodes University from Makana’s Kop

No Abstrac

From random walk to single-file diffusion

We report an experimental study of diffusion in a quasi-one-dimensional (q1D) colloid suspension which behaves like a Tonks gas. The mean squared displacement as a function of time is described well with an ansatz encompassing a time regime that is both shorter and longer than the mean time between collisions. This ansatz asserts that the inverse mean squared displacement is the sum of the inverse mean squared displacement for short time normal diffusion (random walk) and the inverse mean squared displacement for asymptotic single-file diffusion (SFD). The dependence of the single-file 1D mobility on the concentration of the colloids agrees quantitatively with that derived for a hard rod model, which confirms for the first time the validity of the hard rod SFD theory. We also show that a recent SFD theory by Kollmann leads to the hard rod SFD theory for a Tonks gas.Comment: 4 pages, 4 figure

Surface Crystallization in a Liquid AuSi Alloy

X-ray measurements reveal a crystalline monolayer at the surface of the eutectic liquid Au_{82}Si_{18}, at temperatures above the alloy's melting point. Surface-induced atomic layering, the hallmark of liquid metals, is also found below the crystalline monolayer. The layering depth, however, is threefold greater than that of all liquid metals studied to date. The crystallinity of the surface monolayer is notable, considering that AuSi does not form stable bulk crystalline phases at any concentration and temperature and that no crystalline surface phase has been detected thus far in any pure liquid metal or nondilute alloy. These results are discussed in relation to recently suggested models of amorphous alloys.Comment: 12 pages, 3 figures, published in Science (2006

Purification and characterization of a milk-clotting protease from Mucor pusillus: Method comparison

Crude enzymatic extract obtained from five fermentations (300 g of wheat bran) was characterized by a clotting activity of 0.34 ± 0.08 UP/ml with a strength ratio of 1/1: 200. The comparative study of the summaries from 2 purification protocols showed that it is possible to recover 6% of the initial proteins with a 44.54% activity after gel filtration (protocol I), which appeared more technically sound when compared to ion-exchange (1.80% of total proteins with a 23% performance) (protocol II). The proteinhomogeneity (a single electrophoretic band) of the monomeric protease was confirmed by both methods after precipitation with 80% saturated ammonium sulphate. Moreover, the fractional precipitation technique with this salt (40 and 80%) was useless in the experimental conditionsemployed and an important loss of activity was observed (28.53%) with a 3-fold purification. In another part of the study, without ammonium sulphate precipitation, the gel filtration enabled the elimination of almost 97% of the inactive proteins and improved the activity performance by 55.13%, while multiplying the specific activity of the coagulant by a factor of 20.88 against a 6.75-fold purification with ionexchange and the appearance of a more or less 20 kDa peptide after electrophoresis. The proteolytic activity of the purified extracts had a similar appearance to a more pronounced kinetic when compared with the reference rennet. The purification protocols did not seem to have an impact on the isolatedprotease activity.Key words: Mucor pusillus, protease, purification, enzymatic performance, electrophoresis, milk clotting,rennet

Monovalent Ion Condensation at the Electrified Liquid/Liquid Interface

X-ray reflectivity studies demonstrate the condensation of a monovalent ion at the electrified interface between electrolyte solutions of water and 1,2-dichloroethane. Predictions of the ion distributions by standard Poisson-Boltzmann (Gouy-Chapman) theory are inconsistent with these data at higher applied interfacial electric potentials. Calculations from a Poisson-Boltzmann equation that incorporates a non-monotonic ion-specific potential of mean force are in good agreement with the data.Comment: 4 pages, 4 figure

Anomalous layering at the liquid Sn surface

X-ray reflectivity measurements on the free surface of liquid Sn are presented. They exhibit the high-angle peak, indicative of surface-induced layering, also found for other pure liquid metals (Hg, Ga and In). However, a low-angle peak, not hitherto observed for any pure liquid metal, is also found, indicating the presence of a high-density surface layer. Fluorescence and resonant reflectivity measurements rule out the assignment of this layer to surface-segregation of impurities. The reflectivity is modelled well by a 10% contraction of the spacing between the first and second atomic surface layers, relative to that of subsequent layers. Possible reasons for this are discussed.Comment: 8 pages, 9 figures; to be submitted to Phys. Rev. B; updated references, expanded discussio

Typology of dairy farming systems in the Mediterranean basin (case of Algeria)

Characterization of breeding dairy cattle systems from the Mediterranean basin was conducted on 16 farms in the north center region of Algeria through a survey. Results are highly variable both structurally and in techno- economic management terms. The principal component analysis and clusters analysis have identified four groups of farms that differ in feeding strategies. The first group contains four farms that promote the use of forages (61.8% of the total dry matter (DM) intake). The costs are above the general averages (cost of production: 38.4 DA / liter ≈ 0.34 € and cost of food in total production costs = 71.8%). The average annual productivity is about 4328.6 kg. Five farms of group 2 are characterized by milk yields below average (4146.5 kg). The concentrates represent only 39.3% of total DM intake. The cost of production (37.1 DA ≈ 0.33 €/ liter of milk) and food costs are the lowest (65.17% of total production costs). The third group contains 5 farms dominated by profitable farms (4833.4 kg) and the lower cost of production (35.2 DA ≈ 0.31 €). A relatively high proportion of DM is provided by forages (53.6%). Food accounts for 69.2% of the total production cost. The fourth group consists of two farms whose main characteristic is the total absence of forage production. This is associated with a significant contribution of concentrates in the global feed balance (48.8% of total DM intake). These concentrated foods were poorly converted into milk as recorded yields are the lowest (3561.2 kg). Production costs are highest (45.1 DA ≈ 0.40 €) and relation price of food/total cost of production is very high (79.3%). So there are areas for improvement via land restructuring and the adoption of healthy feeding practices in order to ensure the profitability and sustainability of farms identified in this study

Atomic-scale surface demixing in a eutectic liquid BiSn alloy

Resonant x-ray reflectivity of the surface of the liquid phase of the Bi$_{43}$Sn$_{57}$ eutectic alloy reveals atomic-scale demixing extending over three near-surface atomic layers. Due to the absence of underlying atomic lattice which typically defines adsorption in crystalline alloys, studies of adsorption in liquid alloys provide unique insight on interatomic interactions at the surface. The observed composition modulation could be accounted for quantitatively by the Defay-Prigogine and Strohl-King multilayer extensions of the single-layer Gibbs model, revealing a near-surface domination of the attractive Bi-Sn interaction over the entropy.Comment: 4 pages (two-column), 3 figures, 1 table; Added a figure, updated references, discussion; accepted at Phys. Rev. Let

Diagnostic utility of cytospin, cell block and immunocytochemistry in pleural effusion cytology

Background: With the introduction of cytospin, the sensitivity of diagnosing malignancies has increased mainly due to the increase in cellular yield. Cell block also gives the advantage of ancillary testing and allows for retrospective studies. Immunocytochemical markers are used to differentiate and subtype various malignancies in body effusions.Aim of the study was to compare the morphological features of both technique and to assess the diagnostic utility of cell block methods in the cytodiagnosis of pleural effusions.Methods: This was a Prospective observational comparative study of two cytopreparatory techniques. All samples were examined and processed by cytospin and cell block techniques. Continuous data were expressed as Mean±SD (standard deviation) while categorical data were expressed in number, percentage and compared by chi-square (χ2) test.Results: The final diagnosis of both cytospin (147 cases) and cell block (150 cases) techniques was divided into four broad categories: Inadequate, Benign, Suspicious and Malignant. The significant diagnostic cytospin (AUC=0.857, p<0.001) in discriminating positive and negative malignant cases with 75.00% sensitivity (95% CI=53.3-90.2) and 100.00% specificity (95% CI=86.7-100.0) and with 100.0% positive predictive value and 81.2% negative predictive value. In contrast, cell block also showed significant diagnostic but with higher accuracy (AUC=1.000, p<0.001) and sensitivity 100.00% (95% CI=86.7-100.0) and specificity 100.00% (95% CI=86.7-100.0) and 100.0% positive predictive value and 100.0% negative predictive value than cytospin technique.Conclusions: Cell block as a technique should be used in routine practice as it not only increases the diagnostic yield but ancillary test can also be done