5,228 results for 2012

  • The role of crowding in contextual influences on contour integration

    Robol, V; Casco, C; Dakin, Steven (2012-07)

    Journal article
    The University of Auckland Library

    Dakin and Baruch (2009) investigated how context influences contour integration, specifically reporting that nearperpendicular surrounding-elements reduced the exposure-duration observers required to localize and determine the shape of contours (compared to performance with randomly oriented surrounds) while near-parallel surrounds increased this time. Here, we ask if this effect might be a manifestation of visual crowding (the disruptive influence of ''visual clutter'' on object recognition). We first report that the effect generalizes to simple contour-localization (without explicit shape-discrimination) and influences tolerance to orientation jitter in the same way it affects threshold exposure-duration. We next directly examined the role of crowding by quantifying observers' local uncertainty (about the orientation of the elements that comprised our contours), showing that this largely accounts for the effects of context on global contour integration. These findings support the idea that context influences contour integration at a predominantly local stage of processing and that the local effects of crowding eventually influence downstream stages in the cortical processing of visual form.

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  • Number and density discrimination rely on a common metric: Similar psychophysical effects of size, contrast, and divided attention

    Tibber, MS; Greenwood, JA; Dakin, Steven (2012-06)

    Journal article
    The University of Auckland Library

    While observers are adept at judging the density of elements (e.g., in a random-dot image), it has recently been proposed that they also have an independent visual sense of number. To test the independence of number and density discrimination, we examined the effects of manipulating stimulus structure (patch size, element size, contrast, and contrast-polarity) and available attentional resources on both judgments. Five observers made a series of two-alternative, forced-choice discriminations based on the relative numerosity/density of two simultaneously presented patches containing 16???1,024 Gaussian blobs. Mismatches of patch size and element size (across reference and test) led to bias and reduced sensitivity in both tasks, whereas manipulations of contrast and contrast-polarity had varied effects on observers, implying differing strategies. Nonetheless, the effects reported were consistent across density and number judgments, the only exception being when luminance cues were made available. Finally, density and number judgment were similarly impaired by attentional load in a dual-task experiment. These results are consistent with a common underlying metric to density and number judgments, with the caveat that additional cues may be exploited when they are available.

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  • The path to MetalSVM: Shared virtual memory for the SCC

    Lankes, S; Reble, P; Clauss, C; Sinnen, Oliver (2012)

    Conference item
    The University of Auckland Library

    In this paper, we present first successes with building an SCC-related shared virtual memory management system, called MetalSVM, that is implemented using a bare-metal hypervisor, located within a virtualization layer between the SCC's hardware and the operating system. The basic concept is based on a small kernel developed from scratch by the authors: A separate kernel instance runs on each core and together they build the virtualization layer. High performance is reached by the realization of a scalable inter-kernel communication layer for MetalSVM. In this paper we present the employed concepts and technologies. We briefly describe the current state of the developed components and their interactions leading to the realization of a Shared Virtual Memory system on top of our kernels. First performance results of the SVM system are presented in this work.

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  • Bi-linear reductions for the Multiprocessor Scheduling Problem with Communication Delays using Integer Linear Programming

    Venugopalan, Sarad; Sinnen, Oliver (2012)

    Conference item
    The University of Auckland Library

    With computer processors running at speeds closer to their theoretical limit, the recent focus has turned to the use of parallelism in hardware by the use of multicore processors for speedup. However, duplicating processors do not automatically translate to faster task execution. The tasks are to be carefully assigned and scheduled so that their total execution time on the multiple processors is minimal. We propose an optimal Integer Linear Programming formulation for the Multiprocessor Scheduling Problem with Communication Delays (MSPCD). The formulations use an effective method to linearise the bi-linear forms arising out of communication delays and introduce new overlap constraints to ensure that no two tasks running on the same processor overlap in time. The proposed formulation is compared with known ILP formulations that solve the MSPCD problem.

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  • Optimal linear programming solutions for multiprocessor scheduling with communication delays

    Venugopalan, S; Sinnen, Oliver (2012)

    Conference item
    The University of Auckland Library

    Task parallelism does not automatically scale with the use of parallel processors. Optimised scheduling of tasks is necessary to maximise the utilisation of each available processor. It is common to use heuristics to find solutions for task scheduling problem instances. However, there is no guarantee that the heuristic solution is close to the optimal solution. The outcome of this work is to provide optimal solutions for small and medium sized instances of the task scheduling problem. Two optimal scheduling formulations using Integer Linear Programming (ILP) are proposed for the Multiprocessor Scheduling Problem with Communication Delays: ILP-RevisedBoolean Logic and ILP-Transitivity Clause. ILP-RevisedBooleanLogic is designed to work efficiently when the number of processors available to be scheduled on is small. ILP-TransitivityClause is efficient when a larger number of processors are available to be scheduled on. Each formulation uses a different linearisation of the Integer Bilinear Programming formulation and is tested on CPLEX using known benchmark graphs for task scheduling.

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  • Revisiting shared virtual memory systems for non-coherent memory-coupled cores

    Lankes, S; Reble, P; Sinnen, Oliver; Clauss, C (2012)

    Conference item
    The University of Auckland Library

    The growing number of cores per chip implies an increasing chip complexity, especially with respect to hardware-implemented cache coherence protocols. An attractive alternative for future many-core systems is to waive the hardware-based cache coherency and to introduce a software-oriented approach instead: a so-called Cluster-on-Chip architecture. The Single-chip Cloud Computer (SCC) is a recent research processor of such architectures. This paper presents an approach to deal with the missing cache coherence protocol by using a software managed cache coherence system, which is based on the well-established concept of a shared virtual memory (SVM) management system. Through SCC's unique features like a new memory type, which is directly integrated on the processor die, new and capable options exist to realize an SVM system. The convincing performance results presented in this paper show that nearly forgotten concepts will become attractive again for future many-core systems.

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  • Crystallographic studies on Ru and Ir-based SrB1-xMxO3-type perovskites

    Qasim, Ilyas; Kennedy, BJ; Avdeev, M (2012-11-22)

    Conference poster
    The University of Auckland Library

    Strontium ruthenate and iridate perovskites are of great interest due to their potential technological importance related to their exotic physical properties. Despite the chemical simplicity of the perovskite structure there are a number of examples where the precise structure is unknown or where different researchers have proposed different structures for the sample material. Understanding the relationship between the structure and physical properties is a significant barrier to the development of these types of materials. Two series of oxides of the type SrRu1-xBx03 and Srlr1-xBxO3- (?? = transition metals) have been synthesized using solid state methods, and selected members of these have been structurally characterized using combination of synchrotron X-ray and neutron diffraction methods and their physical properties investigated. Neutron data were critical to establish precise and accurate structures of a number of these materials including Sr2FeIr06 SrRu0.8Ni0.2O3 and Srlr0.8Ni0.203.

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  • High versus low altitude hot spring settings and associated sinter textures from El Tatio, Chile, and the Taupo Volcanic Zone, New Zealand

    Lynne, Bridget; Morata, D; Reich, M (2012)

    Conference item
    The University of Auckland Library

    Hot alkali chloride fluids ascend from deep geothermal reservoirs and discharge at the surface as hot springs. As the silica-rich fluid discharges and cools to below 100??C, the silica carried in solution precipitates and accumulates to form a rock referred to as siliceous sinter. Hot springs display broad temperature gradients from high temperature vent to low-temperature distal-apron areas. Distinctive sinter textures form, depending on environmental conditions such as flow rate or water temperature. These textures are preserved over time and throughout diagenesis. As sinters and deep geothermal reservoirs remain long after hot spring discharge ceases, sinter textures can be used to create maps of paleo-flow conditions and to establish the locations of historic hot up-flow zones. But does altitude make a difference? Can our knowledge of preserved low altitude sinter textures be applied to high altitude sinters? This study compares the modern high altitude hot springs of El Tatio, Chile with the modern low altitude hot springs of Orakei Korako, New Zealand. If we are to use textural recognition in paleo-sinter outcrops from different elevations to establish hot spring paleo-flow conditions, it is important to understand both hot spring environments, and how altitude influences sinter textures. By identifying the modern high and low altitude hot spring settings and associated microbial communities, we can recognize preserved sinter textures in high and low altitude ancient sinters. From accurate textural sinter mapping, high temperature locations could be targeted as sites for further exploration with more advanced exploration techniques such as geophysical methods.

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  • The relation between the physico-chemical characteristics of thermal water and the nature of their siliceous sinter deposits

    Nicolau del Roure, C; Reich, M; Lynne, Bridget (2012-08-08)

    Conference poster
    The University of Auckland Library

    Siliceous sinters (hot spring rocks) form by evaporation of near-neutral, alkali-chloride silica-rich thermal waters. Their importance resides in their capacity for recording environmental conditions and their relation to the existence of a geothermal reservoir at depth. Previous studies have shown that sinter textures are commonly controlled by hydrodynamic conditions, whereas their mineralogy and chemistry is controlled by chemical composition of thermal waters. However, the effect of altitude, wind velocity and discharge rate are still poorly constrained. Here we present preliminary data of an experiment developed at the El Tatio geothermal field in northern Chile, designed to determine silica accumulation rates and textures developed in sinter, and their relationship to environmental and hydrodynamic conditions.

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  • A comparison of the mineralogy and morphology of travertine from the USA and NZ

    Channel, K; Lynne, Bridget; Zarrouk, Sadiq (2012)

    Conference item
    The University of Auckland Library

    Travertine is a common geothermal surface feature that forms by the deposition of carbonate from discharging bicarbonate thermal water. Travertine samples from two sites: Silver Peak, Nevada, USA, and Waikite, New Zealand, were examined to contrast their mineralogy, morphology, and chemical composition. These sites were chosen as they provided examples of travertine formed in different countries and in different geothermal settings. Travertine formed at Silver Peak is related to a deep-reaching heat-sweep system, travertine at Waikite contains silica and is related to a flat terrain geothermal system where the heat source appears to be extensive, hot rhyolitic crustal rock. X-ray Powder Diffraction (XRPD) determined differences in the travertine mineralogy of Silver Peak samples were calcite, whereas samples from Waikite consisted of calcite with some samples also conteining silica (opal-A). Based on the XRPD trace samples from Waikite were slightly more crystalline than those from Silver Peak. The crystal size (>100 ??m) of Waikite???s samples is larger than Silver Peak???s samples (~ 100 ??m) while some samples have no obvious crystal shape. Different morphologies exist between the Silver Peak and Waikite calcite. Also calcite/silica samples from Waikite show that amorphous silica is deposited above the water level. The depositional and hydrological conditions of these geothermal fields differs which influences the mineralogy, morphology, and chemical composition of their associated travertine deposits. Therefore, fine-scale examination of travertine enables us to better understand the hydrological setting (i.e. no hot intrusion Vs hot intrusion) and how the setting effects the formation of travertine.

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  • The successful application of ground penetrating radar to image trace element-rich and trace element-poor siliceous sinters

    Lynne, Bridget; Sim, CY (2012)

    Conference item
    The University of Auckland Library

    In the early stages of geothermal exploration, with the help of ground-truthing via outcrop or coring examination, Ground Penetrating Radar (GPR) has proven a successful technique in mapping the lateral and vertical extent of hot spring siliceous sinter deposits up to depths of 10 meters. Alkali chloride fluid is the fluid we seek for our geothermal power plants, making sinters important in geothermal exploration. Sinters are important as they provide evidence of sites where alkali chloride fluid discharged at the surface. They are preserved for thousands of years after hot spring flow discharge ceases. Sinter samples were collected from Opal Mound, and Steamboat Springs, USA, and from Pukemoremore and Horohoro, New Zealand. Samples were specifically chosen to represent the opal-A to opal-A/CT to opal-CT ?? opal-C to quartz silica phase diagenetic sequence and to include both trace element-poor and trace element-rich sinters. GPR was conducted over the sample sites in order to test the suitability of GPR in imaging sinters with different silica phases, density and porosity values and trace element compositions. The GPR imaging revealed that despite the differences in these sinters they were capable of reflecting the emitted high-frequency electromagnetic wave to produce clear GPR profiles. We therefore conclude that GPR can be used for imaging all types of sinters. The new application of GPR to image sinters provides a technique whereby we can map the subsurface extent of a sinter and are no longer limited to outcrop examination. This provides us with new information on the volume of sinter present at any one site which can be directly related to the amount of fluid discharged in an area, as well as a tool that enables mapping buried sinters that could cap a blind geothermal resource.

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  • Infrared imaging of thermal areas

    Lynne, Bridget; Yag??e, R (2012)

    Conference item
    The University of Auckland Library

    Heat discharges at the surface from thermal features such as hot springs, fumaroles and steaming ground. An understanding of discharging heat is important for geothermal exploration, as it provides a guide to the geothermal power potential of the reservoir. One way to determine the amount of heat discharging in active thermal areas is to measure the temperature of the surface features. In three New Zealand geothermal fields, we measured temperatures of surface manifestations using: 1) a temperature probe, 2) an infrared thermometer, and 3) an infrared camera. Using all three techniques we documented the temperatures in 12 alkali chloride hot springs and channels, six acid sulfate hot springs, six mud pools, nine areas of steaming ground and seven fumaroles. This enabled a direct comparison of the temperatures obtained using the different techniques for each feature type. Our study revealed that regardless of which measuring device was used, the temperatures measured in hot spring pools and channels showed minimal variation. In fumaroles and steaming ground areas, the correlation between temperature measuring devices was not as consistent. However, there was minimal temperature variation when we were within one meter of the steam features and when we altered the emissivity value to account for the higher reflectance due to the discharging steam. Our infrared camera enabled the quick identification of sites with increased temperature that were not easily accessible. It was also ideally suited for mapping the location of micro-fractures and vents that discharged heat and were not otherwise visible. Infrared imaging enables the mapping of subtle temperature differences establishing surface thermal gradients profiles. Alignment and orientation of areas discharging a higher-than-ambient temperature are also easily mapped. Infrared imaging of heat flow migration pathways contributes to the development of a conceptual model of a geothermal system.

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  • Patient-specific modeling of breast biomechanics with applications to breast cancer detection and treatment

    Babarenda Gamage, Thiranja; Rajagopal, Vijayaraghavan; Nielsen, Poul; Nash, Martyn (2012)

    Book item
    The University of Auckland Library

    There are many challenges clinicians are faced with when diagnosing and treating breast cancer. Biomechanical modeling of the breast is a field of research that aims to assist clinicians by providing a physics based approach to addressing some of these challenges. This review describes the state of the art in the field, from aiding co-location of information between various medical imaging modalities used to identify tumours; to providing the ability to predict the location of these tumors during different biopsy or surgical procedures; to aiding temporal registration of follow-up medical images used to review the progress of suspicious lesions and therefore evaluate effectiveness of breast cancer treatments; to aiding implant selection for breast augmentation procedures and the subsequent prediction of the resulting appearance following such procedures. Significant technical challenges remain in terms of improving the accuracy of such biomechanical models. These include the precise determination and application of loading and boundary constraints applied during different clinical procedures, and accurate characterization of individual-specific mechanical properties of the different breast tissues. In addition to these more technical challenges, a number of practical challenges exist when translating biomechanical models from research based environments into clinical workflows, which demand general applicability, and ease and speed of use. This review outlines such challenges and provides an overview of the steps researchers are taking to address them. Once these challenges have been met, there is potential for extending the use of biomechanics to simulate more complex clinical procedures, from modeling needle insertions into breast tissue during real-time biopsy procedures, to simulating and predicting the outcome of different surgical procedures such as tumorectomies. Clinical adoption of such state-of-the-art modeling techniques has significant potential for reducing the number of misdiagnosed breast cancers while also helping improve clinical treatment of patients.

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  • St. Thomas' Chapel in St Matthew-in-the-City Church

    Mulla, Sarosh; Salmond Reed Architects (2012)

    Design
    The University of Auckland Library

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  • Mapping vent to distal-apron hot spring paleo-flow pathways using siliceous sinter architecture

    Lynne, Bridget (2012-07)

    Journal article
    The University of Auckland Library

    Environmentally significant textural components of sinters from New Zealand and the U.S.A. were examined using X-ray powder diffraction, petrographic microscopy, scanning electron microscopy, and 14C accelerated mass spectroscopy (AMS). Sinter samples from five New Zealand sites; Waiotapu, Orakei Korako, Wairakei, Tahunataara, Broken Hill, and two USA sites; Opal Mound, Utah, and Steamboat Springs, Nevada, revealed, textures are preserved in pristine condition in sinters of varying silica phases and ages. The distinctive macro-textures that relate to temperature-pH gradients and the hydrodynamics of hot spring environments enabled the identification of paleo-hot spring settings. Sinter textures observed include: (1) low-temperature biotic textures; (2) mid-temperature biotic textures; (3) high-temperature abiotic textures; and (4) flow-rate indicative textures. Mapping the paleo-hydrology of extinct hot spring locations based on sinter architecture established the location of historic high- versus low-temperature hot spring flow paths. This information is particularly useful in the early phases of geothermal exploration, especially for hidden geothermal systems and epithermal mineralization, where establishing the location of hot up-flow zones and high temperature discharge vents is favorable. Sinter textural mapping combined with AMS 14C dating provides a spatial and temporal context of discharging reservoir fluid, enables the tracking of alkali chloride fluid flow to the surface, establishes hot spring migration pathways, and contributes to the development of a geothermal hydrologic model.

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  • The growth of siliceous sinter deposits around high-temperature eruptive hot springs

    Boudreau, AE; Lynne, Bridget (2012-12-01)

    Journal article
    The University of Auckland Library

    Siliceous hot spring deposits (sinter) are of interest as they are indicative of hydrothermal resources at depth and may provide evidence for early life on Earth and possibly Mars. Numeric models of concurrent evaporation and opal-A precipitation around high temperature ( > 73. ??C), eruptive hot spring vents such as geysers show that silica is most efficiently precipitated by complete evaporation owing to very sluggish growth kinetics for silica precipitation from supersaturated hydrothermal water. Where evaporation is complete between geyser events, areas of initially deeper water precipitate more silica that, over time, fill in topographic lows to produce a smooth surface. In contrast, incomplete evaporation, in which water is left in low areas prior to being washed away by the next geyser event (or equivalently where there is continuous surface flow in topographic low areas), tends to enhance the growth of minor topographic highs and leads to an increase in surface roughness such as seen in the development of "knobby" geyserite sinter texture around vents.

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  • Infiltration of Martian outflow channel floodwaters into lowland cavernous systems

    Rodriquez, A; Bourke, M; Tanaka, K; Miyamoto, H; Kargel, J; Baker, V; Fairen, A; Davies, R; Lynne, Bridget; Hernandes, M; Linares, R; Berman, D (2012)

    Journal article
    The University of Auckland Library

    [1] The hydrosphere of Mars has remained mostly concealed within the subsurface for the past ???3.5 Gyr. Localized rupturing of the permafrost-capped crust led to voluminous groundwater discharges that carved some of the largest known channels in the solar system. However, our knowledge of the nature of the flows and their ultimate fate remains incomplete, partly because diagnostic landforms at outflow channel termini have been largely destroyed or buried. The Hebrus Valles outflow channels were excavated by fluid discharges that emanated from two point sources, and they mostly terminate in systems of fractures and depressions within the northern plains. Our investigation indicates that outflow channel floodwaters were captured and reabsorbed into the subsurface in zones where caverns developed within the northern plains. These findings imply that the study region comprises the only known location in the Martian northern lowlands where the fate of outflow channel discharges can be assessed with confidence. We propose that evacuation of subsurface materials via mud volcanism was an important process in cavern formation. Our conceptual model provides a hypothesis to account for the fate of sediments and fluids from some of the Martian outflow channels. It also reveals a mechanism for lowland cavern formation and upper crustal volatile enrichment after the development of the Martian global cryosphere.

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  • Native bird abundance after Australian magpie (Gymnorhina tibicen) removal from localised areas of high resource availability

    Morgan, Dai K.J.; Waas, Joseph R.; Innes, John G.; Arnold, Greg (2012)

    Journal article
    University of Waikato

    Many reports exist of Australian magpies (Gymnorhina tibicen) attacking and sometimes killing other birds. One study concluded that magpies had little impact on the abundance of other birds at landscape scales, but another found that birds (mainly exotic species) avoided flying or landing close to them. We assessed whether continuously removing magpies for 6 weeks from localised areas of high resource availability (e.g. bush remnants or private gardens with fruit- or nectar-producing trees) in rural areas increased visitations by native birds compared with similar sites where magpies were not removed. Three count methods were used to estimate bird abundance: five-minute bird counts and ‘slow-walk’ transects in bush remnants, and five-minute bird counts and ‘snapshot’ counts in gardens. Generally, the abundance of native birds did not increase in treatment areas after magpie removal. In bush remnants, transect counts were typically better at detecting the presence of most species compared with five-minute bird counts. In gardens, snapshot counts were better at detecting tui (Prosthemadera novaeseelandiae) while five-minute bird counts were better at detecting magpies. Despite these differences, the different bird counting methods were generally in agreement and revealed that magpies had little impact on native birds at the scale we examined.

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  • Synthesis and antimalarial and antituberculosis activities of a series of natural and unnatural 4-methoxy-6-styryl-pyran-2-ones, dihydro analogues and photo-dimers

    McCracken, ST; Kaiser, M; Boshoff, HI; Boyd, Peter; Copp, Brent (2012-02-15)

    Journal article
    The University of Auckland Library

    Previous studies have identified the 3,6-dialkyl-4-hydroxy-pyran-2-one marine microbial metabolites pseudopyronines A and B to be modest growth inhibitors of Mycobacterium tuberculosis and a range of tropical diseases including Plasmodium falciparum and Leishmania donovani. In an effort to expand the structure-activity relationship of this compound class towards infectious diseases, a library of natural product and natural product-like 4-methoxy-6-styryl-pyran-2-ones and a subset of catalytically reduced examples were synthesized. In addition, the photochemical reactivity of several of the 4-methoxy-6-styryl-pyran-2-ones were investigated yielding head-to-head and head-to-tail cyclobutane dimers as well as examples of asymmetric aniba-dimer A-type dimers. All compounds were evaluated for cytotoxicity and activity against M. tuberculosis, P. falciparum, L. donovani, Trypanosoma brucei rhodesiense and Trypanosoma cruzi. Of the styryl-pyranones, natural product 3 and non-natural styrene and naphthalene substituted examples 13, 18, 21, 22 and 23 exhibited antimalarial activity (IC(50) 10. ??(7) Dihydro analogues were typically less active or lacked selectivity. Head-to-head and head-to-tail photodimers 5 and 34 exhibited moderate IC(50)s of 2.3 to 17 ??M towards several of the parasitic organisms, while the aniba-dimer-type asymmetric dimers 31 and 33 were identified as being moderately active towards P. falciparum (IC(50) 1.5 and 1.7 ??M) with good selectivity (SI ~80). The 4-tert-butyl aniba-dimer A analogue 33 also exhibited activity towards L. donovani (IC(50) 4.5 ??M), suggesting further elaboration of this latter scaffold could lead to the identification of new leads for the dual treatment of malaria and leishmaniasis.

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  • Marine natural products

    Blunt, JW; Copp, Brent; Keyzers, RA; Munro, MHG; Prinsep, MR (2012-02-01)

    Journal article
    The University of Auckland Library

    This review covers the literature published in 2010 for marine natural products, with 895 citations (590 for the period January to December 2010) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms. The emphasis is on new compounds (1003 for 2010), together with the relevant biological activities, source organisms and country of origin. Biosynthetic studies, first syntheses, and syntheses that lead to the revision of structures or stereochemistries, have been included.

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