Mauritius forms part of the Mascarene Islands of the Indian Ocean and is situated ca. 700 km to the east of Madagascar at latitude 20degrees S and longitude 57.5degrees E. Mauritius has jurisdiction over a proclaimed Exclusive Economic Zone that stretches over 1 900 000 km(2). This extensive area holds an immense potential for exploration and presents a wide range of scientific and industrial challenges and opportunities. At present, ocean-related activities are undertaken by various governmental and parastatal institutions as well as non-governmental organizations. Mauritius recognizes the need to coordinate all efforts in order to eliminate wasteful duplication and focus on potential for development, and this has seen the establishment of different forums and committees. This paper gives a brief overview of the different institutions involved in marine science and oceanography in Mauritius and lists the major projects that are being undertaken as well as some of the projects or new research initiatives that are in the pipeline.
This note examines the effects of climate variability on natural-resources management in East Africa. The bimodal rainfall regime in much of East Africa brings rainy seasons from March to May and October to December with greater interannual variability from October to December. We discuss the impacts of rainfall extremes in 1961 and 1997 and explore three examples of natural-resources management in the context of rainfall variability: inland fisheries in East and southern Africa; fluctuations in the level of Lake Victoria; and lake-shore communities around Lake Kyoga in Uganda. The discussion reflects the complexity of linkages between climate, environment and society in the region and highlights implications for natural-resources management. These range from benefits due to improved seasonal rainfall forecasting to reduce the damage of extremes, to improved understanding of existing climate-society interactions to provide insights into the region's vulnerability and adaptive capacity in relation to future climate change.
This paper presents results from a detailed hydrographic survey of the Mascarene Plateau and surrounding area undertaken by the RRS Charles Darwin in June–July 2002. We examine how the westward–flowing South Equatorial Current (SEC) crosses the plateau, and how the structure of the flow determines the supply of nutrients to the surface waters. We find that the flow of the SEC across the plateau is highly dependent on the complex structure of the banks which make up the plateau, and that a large part of the flow is channelled between the Saya de Malha and Nazareth Banks. Furthermore, the SEC forms a sharp boundary between subtropical water masses from further south, which are low in nutrients, and waters from further north, which are relatively nutrient rich. Overall, the SEC delivers relatively high levels of nutrients to the near–surface waters of the central and northern regions of the plateau, compared with the southern regions of the plateau. This is partly due to uplifting of density surfaces through Ekman suction on the northern side of the SEC, and partly due to the higher levels of nutrients on those density surfaces on the northern side of the SEC. This may drive increased production of phytoplankton in these areas, which would in turn be expected to fuel increased abundances of zooplankton and higher levels of the food chain.
Changes in reef benthos were assessed at Aldabra Atoll following the mass coral bleaching event of 1998. Video transects were used to survey the benthos and analysed using the Australian Institute of Marine Science five-dot method. Comparison of coral cover data collected by the Cambridge Southern Seychelles Atoll Research Programme with data collected during this study revealed that mortality of coral at Aldabra following the bleaching event was approximately 66% at 10 m depth and 38% at 20 m depth. Five years on, there are signs of hard coral recovery at some locations, but in spite of several years of high coral recruitment (7-9 recruits per m2 at 10 m depth, 4-6 recruits per m2 at 20 m depth, where recruits are defined as any colony under 5 cm maximum diameter), recovery of hard coral has not occurred at a significant level. There has been a considerable increase in soft coral cover at some locations, which was dominated by the genus Rhytisma. Macro algal cover did not increase following the bleaching event, although, as would be expected, dead corals have been colonized by coralline algae. There have been no further events leading to large-scale coral mortality at Aldabra since 1998.
A strong but variable western boundary current flows south along the east coast of Madagascar, and at the island's southern end it interacts with eddies propagating zonally from the east. These two routes of variability are compared using altimetric sea-surface-height data and dynamic height from a high-resolution numerical model. The effects on biological productivity are also discussed.
Hydrostatic pressure has been used as a physical parameter for studying the stability and energetics of biomolecular systems, such as lipid mesophases and proteins, but also because high pressure is an important feature of certain natural membrane environments and because the high–pressure phase behaviour of biomolecules is of biotechnological interest. By using spectroscopic and scattering techniques, the temperature– and pressure–dependent structure and phase behaviour of lipid systems, differing in chain configuration, headgroup structure and concentration, and proteins have been studied and are discussed. A thermodynamic approach is presented for studying the stability of proteins as a function of both temperature and pressure. The results demonstrate that combined temperature–pressure dependent studies can help delineate the free–energy landscape of proteins and hence help elucidate which features and thermodynamic parameters are essential in determining the stability of the native conformational state of proteins. We also introduce pressure as a kinetic variable. Applying the pressure jump relaxation technique in combination with time–resolved synchrotron X–ray diffraction and spectroscopic techniques, the kinetics of un/refolding of proteins has been studied. Finally, recent advances in using pressure for studying misfolding and aggregation of proteins will be discussed.
Living cells are a collection of molecular machines which carry out many of the functions essential for the cell's existence, differentiation and reproduction. Most, though not all, of these machines are made up of proteins. Because of their complexity, an understanding of how they work requires a synergistic combination of experimental and theoretical studies. In this paper we outline our studies of two such protein machines. One is GroEL, the chaperone from Escherichia coli, which aids in protein folding; the other is F-1-ATPase, a motor protein which synthesizes and hydrolyses ATP.
The Indian Ocean differs from the other two oceans in not possessing an eastern equatorial upwelling regime. Instead, the upwelling occurs dominantly in the northwestern Arabian Sea and, to a lesser degree, around the Indian subcontinent. Subduction, on the other hand, occurs dominantly in the Southern Hemisphere. The result is a shallow Cross–Equatorial Cell connecting both regimes. The northward flow at thermocline levels occurs as part of the Somali Current and the southward upper–layer return flow is carried by the Ekman transports that are directed southward in both hemispheres. The main forcing is by the Southwest Monsoon that overwhelms the effects of the Northeast Monsoon and is the cause for the annual mean Northern Hemisphere upwelling and southward Ekman transports. In the Southern Hemisphere, the annual mean upwelling at the northern rim of the Southeast Trades causes a zonally extended open–ocean upwelling regime that is apparent in isopycnal doming in the 3–12○ S band; it drives a shallow Subtropical Cell.
In this article we highlight recent developments of ultrafast electron diffraction and crystallography at Caltech. These developments have made it possible to resolve transient structures, both spatially (0.01 A) and temporally (picosecond and now femtosecond), in the gas phase and condensed media--surfaces, interfaces, and crystals--with wide-ranging applications. With the extension to ultrafast electron microscopy, discussed here and elsewhere, we present an overview of one major research area at our centre, the Laboratory for Molecular Sciences.
The break–up of Gondwanaland and dispersal of several of its component continental fragments, which eventually formed the margins of the Indian Ocean, have produced an ocean basin of enormous variety, both in relief and in origin of seafloor features. The western half of the Indian Ocean alone contains every type of tectonic plate boundary, both active and fossil, and, along with some of the deepest fracture zones, the most complex mid–ocean ridge configurations and some of the thickest sedimentary sequences in the world's ocean basins. This ocean is one of the most diverse on the face of the globe. We explore the evolution of the morphology of the Indian Ocean floor, and discuss the effect of its variations, maxima and minima, on the interconnectivity of the ocean's water masses.
Soft sedimentary biotopes are extensive in the shallow Western Indian Ocean, especially on the Seychelles Plateau and Mascarene Ridge, yet pro rata compared with coral reefs the research effort devoted to them has been minimal. In this study we examine the benthic mollusc and polychaete worm assemblages of the shallow waters (11-62 m) around Mahe, in the Seychelles, and make direct comparisons with the temperate Irish Sea area and subtropical waters of Hong Kong, China (using identical methodology). Two assemblages were recognized, characterized by depth and sediment type. Of these, assemblage A (in shallow carbonate sands) was the most diverse, with diversity and richness measures exceeding those from the Irish Sea or Hong Kong. Hong Kong generally had the poorest fauna. Considering the Bivalvia alone, estimates of taxonomic distinctness showed this to be least for Seychelles assemblage A. The degree of conformity of the results to the concept of the latitudinal gradient in species richness and the possible underlying causes are discussed. Comparisons with other data suggest that the Seychelles support a benthic fauna at least as diverse as any other described from the tropics. A tentative examination of total bivalve species richness suggests a total of 400-500 for the Seychelles. This is in keeping with other Indian Ocean localities, but higher than known figures for continental east Africa. The findings of this paper support the case for widespread ecological and taxonomic studies of the Western Indian Ocean benthic invertebrates.
The bulk properties of organic crystalline materials depend on their molecular and crystal structures but. as many of these materials cannot be prepared in a suitable form for conventional single-crystal diffraction studies, structural characterization and rationalization of these properties must be obtained from powder diffraction data. The recent development of direct-space structure solution methods has enabled the study of a wide range of organic materials using powder diffraction data, many of structural complexity only made tractable by these advances in methodology. These direct-space methods are based on a number of global optimization techniques including Monte Carlo. simulated annealing, genetic algorithm and differential evolution approaches. In this article, the implementation and relative efficiency and reliability, of these methods are discussed, and their impact on the structural study of organic materials is illustrated by examples of polymorphic systems, pharmaceutical, pigment and polypeptide structures and compounds used in the study of intermolecular networks.
Inelastic tunnelling electrons are a proper excitation source to induce chemical transformations on a single adsorbate. When their energy is tuned to that of molecular vibrational states, the modification may follow complex internal vibrational pathways. Here, we analyse our recent results on the selective excitation of ammonium stretching or bending modes to control the outcome of a simple bond–cleavage reaction. With the help of model calculations, we provide a detailed molecular–scale picture of the competing internal pathways leading to molecular movement. A mode–selective strategy, based on local excitations of specific reaction coordinates, has an important drawback when applied to adsorbate systems due to the problem of fast energy randomization. The success of such a mode–selective strategy is determined here by the ability of the scanning tunnelling microscope to study reactivity in the limit of very low yield and very low power irradiation, in a regime where vibrational heating of the adsorbate/surface system becomes negligible.
Using the molecular-dynamics technique, cluster emission for 5 keV Ar bombardment of a Cu (111) surface has been investigated using a many-body (tight binding) potential for the Cu-Cu interaction. The calculations allow us to analyse the basic processes underlying cluster emission. It is found that two distinct processes can be distinguished which lead to cluster emission under energetic ion bombardment. The first process causes the emission of small clusters, which are emitted by a collective motion during the development of the collision cascade within the first picosecond after impact. Thus, emission times of such clusters agree with the emission times of atoms in sputtering. Such a process can be envisioned if, for example, a few layers below the surface, an energetic recoil causes the development of a subcascade. Energy transferred by this event to the surface is strongly directional and can lead to the simultaneous emission of a group of neighbouring surface atoms, which in some cases will remain bounded and form a cluster after emission. Typically, clusters emitted by this mechanism consist of atoms, which are neighbouring in the target and are almost exclusively surface atoms, similar to all sputtered atoms. Emission of large clusters (cluster sizes of 10 or more atoms), as observed experimentally, is a puzzling phenomenon. From our calculations we conclude that the emission of such large clusters does not occur during the collisional phase of sputtering, but happens much later (5-10 ps after ion impact). Emission can occur for spike events, where all the energy of the impinging ion is deposited locally in a small volume near to the surface, and the sputtering yield is 3-5 times the average yield. Such events are rare, but we have found a few cases in our calculations where stable clusters consisting of more than 20 atoms were emitted. Melting of the spike volume occurs, and the high temperatures and pressures produced can cause emission of large fragments during the thermal phase. The composition of such large clusters is quite different from that of small clusters. They consist of atoms from different layers and the constituents are also generally not next-neighbour atoms. This change in origin of the cluster atoms reflects the mixing and diffusion processes occurring in the melted zone before emission. The calculations indicate that hydrodynamical phenomena might play a role in the emission of large fragments. Additional calculations, where the energy was distributed 'thermally' in a three-dimensional volume under the surface for 500 fs, give very similar results, even in such cases where the kinetic phase of the collision-cascade development was absent.
We report the development of a quantum cascade laser at the longest wavelength to date, /spl lambda/=87.2 m (3.44 THz), that uses longitudinal-optical phonon scattering for electron depopulation. Operating in pulsed mode, lasing is obtained up to sixty-four Kelvin.
Find the next term in the sequence 1, 1, 12, 620, 87304. This particular problem belongs to a branch of mathematics called enumerative geometry. This is concerned with curve-counting - counting the number of curves that can be drawn on a particular geometric object. The sequence above is easy to describe: each term represents the number of curves, with increasing complexity, one can draw though a certain number of points on a plane. Despite its simplicity, the problem remained unsolved for most of the twentieth century. The solution - a formula with which one may calculate any term in the series - was discovered only in the century's closing decade. This article will describe the above problem, and some of the unexpected mathematics and physics that was used in finding its solution [corrected]
It is well known that millimetre-wave systems can penetrate poor weather, dust and smoke far better than infrared or visible systems. Imaging in this band offers the opportunity to be able to navigate and perform surveillance in these conditions of poor visibility. Furthermore, the ability to penetrate dielectrics such as plastic and cloth has opened up the opportunity of detecting weapons and contraband hidden under people's clothing. The optical properties of materials have a direct impact on the applicability of imaging systems. In the terahertz band solids have absorptions which can be assigned to vibrational modes. Lattice modes occur at the lowest frequencies and polythene, for example, has a lattice mode at 2.4 THz. Solids have no such absorptions in the millimetre bands (30-300 GHz) and image contrast is produced by differences in transmission, reflection and absorption.A novel, real-time, mechanically scanned, passive millimetre-wave imager has been designed. The antenna elements are based on a combination of a Schmidt camera and a conical scanner, both of which have their origins in optical systems. Polarization techniques, which were developed for operation in the centimetric band, are used to fold the optics. Both 35 GHz and 94 GHz versions have been constructed.
A discrete particle model is described which simulates bedload transport over a flat bed of a unimodal mixed–sized distribution of particles. Simple physical rules are applied to large numbers of discrete sediment grains moving within a unidirectional flow. The modelling assumptions and main algorithms of the bedload transport model are presented and discussed. Sediment particles are represented by smooth spheres, which move under the drag forces of a simulated fluid flow. Bedload mass–transport rates calculated by the model exhibit a low sensitivity to chosen model parameters. Comparisons of the calculated mass–transport rates with well–established empirical relationships are good, strongly suggesting that the discrete particle model has captured the essential elements of the system physics. This performance provides strong justification for future interrogation of the model to investigate details of the small–scale constituent processes which have hitherto been outside the reach of previous experimental and modelling investigations.
The electronic or quantum control of individual molecules with the scanning tunnelling microscope offers exciting perspectives on operating molecular nanomachines. This implies the use of semiconductor surfaces rather than metallic surfaces which would rapidly quench the electronic excitations. We review recent results illustrating the state of the art and the main problems which need to be solved: the choice, design and properties of functionalized organic molecules on semiconductor surfaces; the control of the inelastic electronic channels through a single molecule; and the search for well-controlled atomic-scale wide-band-gap semiconductor surfaces.
