A century of Zoology and Entomology at Rhodes University, 1905 to 2005

The history of the Department of Zoology & Entomology at Rhodes University is traced from its origin with a single staff member, through the era of permanent heads of department to the present day staff. Significant achievements and developments in teaching and research are highlighted, and some anecdotal material is included

Mesoporous matrices for quantum computation with improved response through redundance

We present a solid state implementation of quantum computation, which improves previously proposed optically driven schemes. Our proposal is based on vertical arrays of quantum dots embedded in a mesoporous material which can be fabricated with present technology. The redundant encoding typical of the chosen hardware protects the computation against gate errors and the effects of measurement induced noise. The system parameters required for quantum computation applications are calculated for II-VI and III-V materials and found to be within the experimental range. The proposed hardware may help minimize errors due to polydispersity of dot sizes, which is at present one of the main problems in relation to quantum dot-based quantum computation. (c) 2007 American Institute of Physics

Sperm morphology in five species of cicadettine cicadas (Hemiptera: Cicadomorpha: Cicadidae)

Mature spermatozoa from five species of cicadas of the subfamily Cicadettinae (Quintilia wealei, Melampsalta leucoptera, Stagira simplex, Xosopsaltria thunbergi and Monomatapa matoposa) were examined by light and electron microscopy. In each species sperm are elongate, aggregated into organized bundles with their heads embedded in a homogenous matrix to form spermatodesmata, and exhibit polymegaly. The head of the sperm consist of an anteriorly positioned conical acrosome that has a tubular substructure and a deep, posterior invagination that forms the subacrosomal space (eccentrically positioned anteriorly). The acrosome is flattened anteriorly; posteriorly it extends along either side of the nucleus as two tubular processes that gradually decrease in diameter. The filiform nucleus tapers anteriorly and intrudes into the subscrosomal space. Posteriorly the nucleus has a lateral invagination that houses material of the so-called centriolar adjunct. Posterior to the centriolar adjuct and the nucleus are two crystalline mitochondrial derivatives and a centriole, respectively, the latter giving rise to the axoneme, which has a 9 + 9 + 2 arrangement of microtubules. In these respects the sperm are similar to those of platypleurine cicadas. However, some features seem unique to cicadettines, including the structural organization of an enlarged centriolar adjunct and the dimensions of the tails. The enlarged centriolar adjunct has a lamella-like substructure and can be considered a synapomorphic character in the Cicadettinae. It is, therefore, potentially useful in the separation of this subfamily from the Cicadinae. In addition, the great length of the sperm nucleus of long-headed sperm in M. matoposa could be a synapomorphy of this genus and related taphurine and cicadettine species

Sperm morphology in four species of African platypleurine cicadas (Hemiptera: Cicadomorpha: Cicadidae)

Mature spermatozoa from four species of platypleurine cicadas (Albanycada albigera, Azanicada zuluensis, Platypleura capensis and P. hirtipennis) were examined by light and electron microscopy. The filiform sperm have a similar ultrastructure in all species but notable variations were found in sperm dimensions. All species produce more than one discrete length of nucleated, motile sperm, a form of polymorphism termed polymegaly. Polymegaly is expressed in two ways: sperm have bi- or trimodal head and tail lengths. The anterior parts of sperm heads are embedded in an elongate homogenous matrix forming a spermatodesm. The conical acrosome is deeply invaginated posteriorly, and sits on top of the nucleus. The acrosomal contents are differentiated internally with an electron-lucent central medulla and a denser cortex. The homogenously electron-dense nucleus is pointed anteriorly and is generally cylindrical, although posteriorly there is a lateral invagination that extends part-way along the nucleus. This invagination houses fine granular material of the centriolar adjunct. Vesicle-like elements that are associated with both the posterior nucleus and the centriolar adjunct are also found within the invagination. Immediately posterior of and adjoining the centriolar adjunct is a pair of mitochondrial derivatives that are elongated and extend for almost the entire length of the tail. The absence of accessory bodies in cicada sperm suggests that within the Cicadomorpha, the families Cicadidae and Cercopidae are closely affiliated

Nucleon momentum distribution in deuteron and other nuclei within the light-front dynamics method

The relativistic light-front dynamics (LFD) method has been shown to give a correct description of the most recent data for the deuteron monopole and quadrupole charge form factors obtained at the Jefferson Laboratory for elastic electron-deuteron scattering for six values of the squared momentum transfer between 0.66 and 1.7 (GeV/c)$^{2}$. The good agreement with the data is in contrast with the results of the existing non-relativistic approaches. In this work we firstly make a complementary test of the LFD applying it to calculate another important characteristic, the nucleon momentum distribution $n(q)$ of the deuteron using six invariant functions $f_{i}$ $(i=1,...,6)$ instead of two ($S$- and $D$-waves) in the nonrelativistic case. The comparison with the $y$-scaling data shows the decisive role of the function $f_{5}$ which at $q\geq$ 500 MeV/c exceeds all other $f$-functions (as well as the $S$- and $D$-waves) for the correct description of $n(q)$ of the deuteron in the high-momentum region. Comparison with other calculations using $S$- and $D$-waves corresponding to various nucleon-nucleon potentials is made. Secondly, using clear indications that the high-momentum components of $n(q)$ in heavier nuclei are related to those in the deuteron, we develop an approach within the natural orbital representation to calculate $n(q)$ in $(A,Z)$-nuclei on the basis of the deuteron momentum distribution. As examples, $n(q)$ in $^{4}$He, $^{12}$C and $^{56}$Fe are calculated and good agreement with the $y$-scaling data is obtained.Comment: 16 pages, 6 figures, corrected, to appear in Phys. Rev. C in February 200

The exploitation of Upogebia africana (Crustacea: Thalassinidae) for bait in the Knysna Estuary

The activities of people collecting Upogebia africana for bait at six popular collecting sites in the Knysna Estuary were monitored from February 1995 until April 1996. Three groups of bait harvesters were identified on the basis of their source of income: subsistence fishers who rely on bait collecting and fishing for their income; supplementary fishers who catch fish to supplement their income; leisure anglers who draw no income from fishing. Two groups of collectors were identified based on methods of collecting bait and fishing: leisure anglers who collect bait using a prawn pusher or pump and fish using a rod and tackle; non-leisure fishers who collect using tin cans and fish with hand or planted lines. The average harvest of bait per collecting trip by leisure anglers was 59 mud prawns, whereas non-leisure fishers took 101 animals, twice the legal limit. The numbers of bait collectors present per mud bank were found to be highest on public holidays ([horizontal bar over]X = 43.5) and higher during the summer holidays ([horizontal bar over]X = 16.5) than during the spring/summer ([horizontal bar over]X = 8.6) and autumn/winter ([horizontal bar over]X = 4.6) periods. Most collectors spent 11-30 minutes on the mud banks. It was estimated that 1.86 x 10[superscript 6] U. africana or about 740 kg (dry mass) was removed by bait collectors annually from the six bait-collecting sites studied. This represented about 8.5% of the mud prawn stocks at these sites and about 0.9% of the entire estuary stock. 85% of the mud prawns taken as bait was removed by 77% of the bait collectors who were the non-leisure fishers

An estimation of the standing stock and population structure of Upogebia africana (Crustacea: Thalassinidae) in the Knysna Estuary

Within the Knysna Estuary Upogebia africana has an extensive distribution from north of Leisure Isle to the Red Bridge, occupying 62% of the available intertidal zone. Six sites were surveyed within the above distributional range. U. africana was found from the high-water level (Spartina zone) to the shallow subtidal zone (to about 1.5 m depth). The density, biomass and population structure of the mud prawns were found to be highly variable within the estuary. Only small animals (carapace length –× = 10.9 mm) were found in the upper estuary at the Red Bridge. Although large animals were present, the Invertebrate Reserve had a low density and biomass of U. africana (– × = 11.7 m–2; 3.9 g.m–2 dry weight). By contrast a relatively inaccessible centre mud bank (Oyster Bank) in the middle reaches of the estuary had much larger populations (–× = 176.5 m–2; 65.3 g.m–2 dry weight). This site is, therefore, a natural mud prawn reserve. Within the intertidal zone, mud prawn density (74–76 m–2) and biomass (26–27 g.m–2 dry weight) was usually greatest in the Spartina and lower Zostera zones. Sex ratios throughout the estuary did not deviate significantly from 1:1

Simulation of dynamic recrystallization using irregular cellular automata

Computer simulation is a powerful tool to predict microstructure and its evolution during dynamic recrystallization. Cellular Automata (CA), as one of the most efficient methods proposed to simulate recrystallization and grain growth. In this work, recrystallization and grain growth phenomena were modelled by using a two dimensional irregular CA method. Initial grain size, nuclei density and orientation of each grain were variables which have been used as entering data to the CA model. Final grain size, orientation of each grain, dislocation density and stress-strain curve were the results which have been resulted to validate the current model. Considering the model assumptions, it is shown that the CA can successfully simulate dynamic recrystallization

Effects of temperature and salinity on the standard metabolic rate (SMR) of the caridean shrimp Palaemon peringueyi

The standard metabolic rate (SMR) of the caridean shrimp Palaemon peringueyi to changes in temperature (15–30 °C), salinity (0–45‰) and a combination thereof was investigated. The rate of oxygen consumption of the shrimp was determined using a YSI oxygen meter. At a constant salinity of 35‰ the respiration rate of P. peringueyi increased with an increase in temperature and ranged between 0.260 and 0.982 μl O[subscript 2] mg wwt[superscript −1] h[superscript −1]. The Q[subscript 10] value over the temperature range 15–25 °C was estimated at 3.13. At a constant temperature of 15 °C the respiration rate of P. peringueyi also increased with an increase in salinity and ranged between 0.231 and 0.860 μl O[subscript 2] mg wwt[superscript −1] h[superscript −1]. For combination experiments the absence of any significant difference in the respiration rate of P. peringueyi at the four temperatures over the salinity range 15–35‰ suggests that the shrimp is well adapted to inhabiting environments characterised by variations in salinity and temperature such as those encountered within the middle and lower reaches of permanently open estuaries with substantial freshwater inflow. On the other hand, the total mortality of the shrimp recorded at salinities 35‰ suggests that the shrimp may experience osmotic stress in freshwater deprived permanently open and intermittently open estuaries where hypersaline conditions may develop

Chiral segregation driven by a dynamical response of the adsorption footprint to the local adsorption environment: Bitartrate on Cu(110)

Local or global ordering of chiral molecules at a surface is a key step in both chiral separation and heterogeneous enantioselective catalysis. Using density functional theory and scanning probe microscopy results, we find that the accepted structural model for the well known bitartrate on Cu(110) chiral system cannot account for the chiral segregation observed. Instead, we show that this strongly bound, chiral adsorbate changes its adsorption footprint in response to the local environment. The flexible adsorption geometry allows bitartrate to form stable homochiral trimer chains in which the central molecule restructures from a rectangular to an oblique footprint, breaking its internal hydrogen bonds in order to form strong intermolecular hydrogen bonds to neighbouring adsorbates. Racemic structures containing mixed enantiomers do not form strong hydrogen bonds, providing the thermodynamic driving force for the chiral separation that is observed experimentally. This result shows the importance of considering the dynamical response of molecular adsorption footprints at the surface in directing chiral assembly and segregation. The ability of strongly-chemisorbed enantiomers to change footprint depending on the local adsorption environment indicates that supramolecular assemblies at surfaces may exhibit more complex dynamical behaviour than hitherto suspected, which, ultimately, could be tailored to lead to environment and stimuli-responsive chiral surfaces