32 research outputs found
Optimisation of ascent and descent trajectories for lifting body space access vehicles
One of the forerunners for future space access vehicles is the spaceplane, a lifting body vehicle capable of powered horizontal take-off and landing. Employing strategies from multidisciplinary design optimisation, this paper outlines the approaches and models used towards developing an integrated design platform to assess the preliminary design and performance of a spaceplane. The trajectory and control is optimised, based on different mission objectives and constraints, for the ascent and descent mission segments of a conceptual single stage to orbit vehicle, to a circular low Earth orbits from different take-off and landing sites. A modular approach is employed, dividing the mission into phases based on model discontinuities, changes in the operating environment or vehicle operation, mission objectives or constraints. The problem is reformulated by direct transcription using multiple shooting into a constrained NLP problem, and solved by a combination of genetic algorithms for a global search, and SQP plus interior point methods for local refinement with hard constraints
Cataloguing cowries: a standardised strategy to record six key species of cowrie shell from the West African archaeological record
Two species of cowrie shell, Monetaria moneta (Linnaeus 1758) and Monetaria annulus (Linnaeus 1758), occur repeatedly in archaeological contexts across West Africa. Despite their archaeological and ethnographic importance, these shells remain poorly and inconsistently reported in the archaeological literature. The absence of standardised data on species composition, size and condition of cowrie assemblages, and whether and how the shells were modified, make it difficult to examine their significance in a regional and/or chronological framework. To address this, we propose a standardisation of the criteria and coding used to systematically record cowrie assemblages – in particular species, size, condition and state of modification. We aim to enable non-shell specialists within the wider archaeological community to securely identify intact or intact but modified specimens of M. annulus and M. moneta, showing how these can be distinguished from four cowries native to West Africa (specifically Luria lurida (Linnaeus 1758), Zonaria zonaria (Gmelin 1791), Zonaria sanguinolenta (Gmelin 1791) and Trona stercoraria (Linnaeus 1758)) that occur in assemblages from West African sites. We demonstrate how accurate species identification and the assessment of proportions of different sizes of shells within suitably large assemblages can provide insight into their provenance, and through this enhance our appreciation of the exchange networks within which these shells moved. We also identify five different strategies documented in the archaeological record that were used to modify cowries, detailing how these can be differentiated and classified. The aim here is to suggest a recording strategy that will enable comparisons of the use and value of cowries in West Africa and more widely
Coastal Subsistence, Maritime Trade, and the Colonization of Small Offshore Islands in Eastern African Prehistory
Recent archaeological research has firmly established eastern Africa's offshore islands as important localities for understanding the region's pre-Swahili maritime adaptations and early Indian Ocean trade connections. While the importance of the sea and small offshore islands to the development of urbanized and mercantile Swahili societies has long been recognized, the formative stages of island colonization—and in particular the processes by which migrating Iron Age groups essentially became “maritime”—are still relatively poorly understood. Here we present the results of recent archaeological fieldwork in the Mafia Archipelago, which aims to understand these early adaptations and situate them within a longer-term trajectory of island settlement and pre-Swahili cultural developments. We focus on the results of zooarchaeological, archaeobotanical, and material culture studies relating to early subsistence and trade on this island to explore the changing significance of marine resources to the local economy. We also discuss the implications of these maritime adaptations for the development of local and long-distance Indian Ocean trade networks
Archaeological Assessment of Second World War Anti-Torpedo Close Protection Pontoons in Scapa Flow, Orkney
This paper presents the outcomes of sidescan sonar and archaeological diving surveys in 2015 of two wrecked vessels located off Flotta Island, Orkney, North Scotland. Archival research indicates these are the remains of Anti-Torpedo Close Protection Pontoons (ATCPP), an experimental protection device used for close protection of naval vessels at anchor in Scapa Flow from attack by aircraft-launch torpedoes. The pontoons were only in operation in Scapa Flow for 13 months (March 1941-April 1942) and few were brought into service. As such they represent a rare heritage resource, for which very little is known about their operation
Cowries in the archaeology of West Africa: the present picture
Despite the perceived importance of cowrie shells as indicators of long-distance connections in the West African past, their distribution and consumption patterns in archaeological contexts remain surprisingly underexplored, a gap that is only partly explicable by the sparse distribution of archaeological sites within the sub-continent. General writings on the timeline of importation of cowries into West Africa often fail to take into account the latest archaeological evidence and rely instead on accounts drawn from historical or ethnographic documents. This paper is based on a first-hand assessment of over 4500 shells from 78 sites across West Africa, examining chronology, shell species and processes of modification to assess what distribution patterns can tell us about the history of importation and usage of cowries. These first-hand analyses are paralleled by a consideration of published materials. We re-examine the default assumption that two distinct routes of entry existed — one overland from North Africa before the fifteenth century, another coming into use from the time sea links were established with the East African coast and becoming predominant by the middle of the nineteenth century. We focus on the eastern part of West Africa, where the importance of imported cowries to local communities in relatively recent periods is well known and from where we have a good archaeological sample. The conclusion is that on suitably large assemblages shell size can be an indication of provenance and that, while the present archaeological picture seems largely to confirm historical sources, much of this may be due to the discrepancy in archaeological data available from the Sahara/Sahel zone compared to the more forested regions of the sub-continent. Future archaeological work will clarify this matter
Determining the neurotransmitter concentration profile at active synapses
Establishing the temporal and concentration profiles of neurotransmitters during synaptic release is an essential step towards understanding the basic properties of inter-neuronal communication in the central nervous system. A variety of ingenious attempts has been made to gain insights into this process, but the general inaccessibility of central synapses, intrinsic limitations of the techniques used, and natural variety of different synaptic environments have hindered a comprehensive description of this fundamental phenomenon. Here, we describe a number of experimental and theoretical findings that has been instrumental for advancing our knowledge of various features of neurotransmitter release, as well as newly developed tools that could overcome some limits of traditional pharmacological approaches and bring new impetus to the description of the complex mechanisms of synaptic transmission
Coastal subsistence, maritime trade, and the colonization of small offshore islands in eastern African prehistory
Recent archaeological research has firmly established eastern Africa’s
offshore islands as important localities for understanding the region’s
pre-Swahili maritime adaptations and early Indian Ocean trade connections.
While the importance of the sea and small offshore islands
to the development of urbanized and mercantile Swahili societies has
long been recognized, the formative stages of island colonization—and
in particular the processes by which migrating Iron Age groups essentially
became “maritime”—are still relatively poorly understood. Here
we present the results of recent archaeological fieldwork in the Mafia
Archipelago, which aims to understand these early adaptations and
situate them within a longer-term trajectory of island settlement and
pre-Swahili cultural developments. We focus on the results of zooarchaeological,
archaeobotanical, and material culture studies relating
to early subsistence and trade on this island to explore the changing
significance of marine resources to the local economy. We also discuss
the implications of these maritime adaptations for the development of
local and long-distance Indian Ocean trade networks.The Sealinks Project is funded through a
grant toNicole Boivin from the European Research
Council (StarterGrant 206148) under
the “Ideas” specific Programme of the 7th
Framework Programme (FP7). Additional
funding includes: postdoctoral fellowships
from the British Academy (2010–2013) and
the University of Queensland (2015–2017)
to Alison Crowther; a Fondation Fyssen Postdoctoral
Grant toEr´endira Quintana Morales;
and a postdoctoral fellowship from the Government
of the Balearic Islands (Conselleria
d’Educaci´o) and the European Social Fund
to Llorenc¸ Picornell-Gelabert. Fieldwork was
carried out under COSTECH Research Permit
no. 2012-303-ER-2011-85 and the Division
of Antiquities (Ministry of Natural Resources
and Tourism, Tanzania) excavation
license no. EA.402/605/01 issued to Alison
Crowther, and with the support and permission
of theRegionalAdministrative Secretary
(Dar es Salaam andCoast/Pwani), the District
Administrative Secretary (Mafia), and the Village
Executive Officer (Mtendaji wa Kijiji,
Juani).http://www.tandfonline.com/loi/uica20hb2016Anthropology and Archaeolog
Coastal subsistence, maritime trade, and the colonization of small offshore islands in eastern African prehistory
Recent archaeological research has firmly established eastern Africa’s
offshore islands as important localities for understanding the region’s
pre-Swahili maritime adaptations and early Indian Ocean trade connections.
While the importance of the sea and small offshore islands
to the development of urbanized and mercantile Swahili societies has
long been recognized, the formative stages of island colonization—and
in particular the processes by which migrating Iron Age groups essentially
became “maritime”—are still relatively poorly understood. Here
we present the results of recent archaeological fieldwork in the Mafia
Archipelago, which aims to understand these early adaptations and
situate them within a longer-term trajectory of island settlement and
pre-Swahili cultural developments. We focus on the results of zooarchaeological,
archaeobotanical, and material culture studies relating
to early subsistence and trade on this island to explore the changing
significance of marine resources to the local economy. We also discuss
the implications of these maritime adaptations for the development of
local and long-distance Indian Ocean trade networks.The Sealinks Project is funded through a
grant toNicole Boivin from the European Research
Council (StarterGrant 206148) under
the “Ideas” specific Programme of the 7th
Framework Programme (FP7). Additional
funding includes: postdoctoral fellowships
from the British Academy (2010–2013) and
the University of Queensland (2015–2017)
to Alison Crowther; a Fondation Fyssen Postdoctoral
Grant toEr´endira Quintana Morales;
and a postdoctoral fellowship from the Government
of the Balearic Islands (Conselleria
d’Educaci´o) and the European Social Fund
to Llorenc¸ Picornell-Gelabert. Fieldwork was
carried out under COSTECH Research Permit
no. 2012-303-ER-2011-85 and the Division
of Antiquities (Ministry of Natural Resources
and Tourism, Tanzania) excavation
license no. EA.402/605/01 issued to Alison
Crowther, and with the support and permission
of theRegionalAdministrative Secretary
(Dar es Salaam andCoast/Pwani), the District
Administrative Secretary (Mafia), and the Village
Executive Officer (Mtendaji wa Kijiji,
Juani).http://www.tandfonline.com/loi/uica20hb2016Anthropology and Archaeolog