18,423 research outputs found
The Apollo spacecraft: A chronology volume 4, 21 January 1966 - 13 July 1974
This final volume of the chronology is divided into three parts: (1) preparation for flight, the accident, and investigation; (2) recovery, spacecraft redefinition, and the first manned flight; and (3) man circles the moon, the Eagle lands, and manned space exploration. Congressional documents, official correspondence, government and contractor reports, memoranda, working papers, and minutes of meetings were used as primary sources. A relatively few entries are based on press releases and newspaper and magazine articles
Development of a carbon fibre composite active mirror: Design and testing
Carbon fibre composite technology for lightweight mirrors is gaining
increasing interest in the space- and ground-based astronomical communities for
its low weight, ease of manufacturing, excellent thermal qualities and
robustness. We present here first results of a project to design and produce a
27 cm diameter deformable carbon fibre composite mirror. The aim was to produce
a high surface form accuracy as well as low surface roughness. As part of this
programme, a passive mirror was developed to investigate stability and coating
issues. Results from the manufacturing and polishing process are reported here.
We also present results of a mechanical and thermal finite element analysis, as
well as early experimental findings of the deformable mirror. Possible
applications and future work are discussed.Comment: Accepted by Optical Engineering. Figures 1-7 on
http://www.star.ucl.ac.uk/~sk/OEpaper_files
On Auxiliary Fields in BF Theories
We discuss the structure of auxiliary fields for non-Abelian BF theories in
arbitrary dimensions. By modifying the classical BRST operator, we build the
on-shell invariant complete quantum action. Therefore, we introduce the
auxiliary fields which close the BRST algebra and lead to the invariant
extension of the classical action.Comment: 7 pages, minor changes, typos in equations corrected and
acknowledgements adde
Monitoring coastal dolphins within the Reef 2050 Integrated Monitoring and Reporting Program: final report of the dolphins team in the megafauna expert group
Three species of coastal dolphins are commonly found throughout the Great Barrier Reef (the Reef), the Australian snubfin dolphin, Orcaella heinsohni, the Australian humpback dolphin, Sousa sahulensis, and the Indo-Pacific bottlenose dolphin, Tursiops aduncus. This report focuses on these three species, acknowledging that many other cetacean species also inhabit the Reef. This report is a desktop study that includes current status of the relevant elements of the Reef, priority indicators for monitoring, potential sources of data, assessment of the adequacy of existing monitoring activities and recommendations for the design of an integrated monitoring program as a component of RIMReP
Medium Modifications of Hadron Properties and Partonic Processes
Chiral symmetry is one of the most fundamental symmetries in QCD. It is
closely connected to hadron properties in the nuclear medium via the reduction
of the quark condensate , manifesting the partial restoration of
chiral symmetry. To better understand this important issue, a number of
Jefferson Lab experiments over the past decade have focused on understanding
properties of mesons and nucleons in the nuclear medium, often benefiting from
the high polarization and luminosity of the CEBAF accelerator. In particular, a
novel, accurate, polarization transfer measurement technique revealed for the
first time a strong indication that the bound proton electromagnetic form
factors in 4He may be modified compared to those in the vacuum. Second, the
photoproduction of vector mesons on various nuclei has been measured via their
decay to e+e- to study possible in-medium effects on the properties of the rho
meson. In this experiment, no significant mass shift and some broadening
consistent with expected collisional broadening for the rho meson has been
observed, providing tight constraints on model calculations. Finally, processes
involving in-medium parton propagation have been studied. The medium
modifications of the quark fragmentation functions have been extracted with
much higher statistical accuracy than previously possible.Comment: to appear in J. Phys.: Conf. Proc. "New Insights into the Structure
of Matter: The First Decade of Science at Jefferson Lab", eds. D.
Higinbotham, W. Melnitchouk, A. Thomas; added reference
Quantum interference and sub-Poissonian statistics for time-modulated driven dissipative nonlinear oscillator
We show that quantum-interference phenomena can be realized for the
dissipative nonlinear systems exhibiting hysteresis-cycle behavior and quantum
chaos. Such results are obtained for a driven dissipative nonlinear oscillator
with time-dependent parameters and take place for the regimes of long time
intervals exceeding dissipation time and for macroscopic levels of oscillatory
excitation numbers. Two schemas of time modulation: (i) periodic variation of
the strength of the {\chi}(3) nonlinearity; (ii) periodic modulation of the
amplitude of the driving force, are considered. These effects are obtained
within the framework of phase-space quantum distributions. It is demonstrated
that the Wigner functions of oscillatory mode in both bistable and chaotic
regimes acquire negative values and interference patterns in parts of
phase-space due to appropriately time-modulation of the oscillatory nonlinear
dynamics. It is also shown that the time-modulation of the oscillatory
parameters essentially improves the degree of sub-Poissonian statistics of
excitation numbers
The Effects of High Liquid Water Content on Thunderstorm Charging
Charge transfer to a riming graupel target during interactions with ice crystals has been investigated in the laboratory. When liquid water contents sufficiently high to cause wet growth are achieved, the charge transfer falls to values which are insignificant to thunderstorm electrification. The implications of this null result to a recent analysis of thunderstorm-charging processes by Wiliams et al. (1991) are discussed
Discrete complex analysis on planar quad-graphs
We develop a linear theory of discrete complex analysis on general
quad-graphs, continuing and extending previous work of Duffin, Mercat, Kenyon,
Chelkak and Smirnov on discrete complex analysis on rhombic quad-graphs. Our
approach based on the medial graph yields more instructive proofs of discrete
analogs of several classical theorems and even new results. We provide discrete
counterparts of fundamental concepts in complex analysis such as holomorphic
functions, derivatives, the Laplacian, and exterior calculus. Also, we discuss
discrete versions of important basic theorems such as Green's identities and
Cauchy's integral formulae. For the first time, we discretize Green's first
identity and Cauchy's integral formula for the derivative of a holomorphic
function. In this paper, we focus on planar quad-graphs, but we would like to
mention that many notions and theorems can be adapted to discrete Riemann
surfaces in a straightforward way.
In the case of planar parallelogram-graphs with bounded interior angles and
bounded ratio of side lengths, we construct a discrete Green's function and
discrete Cauchy's kernels with asymptotics comparable to the smooth case.
Further restricting to the integer lattice of a two-dimensional skew coordinate
system yields appropriate discrete Cauchy's integral formulae for higher order
derivatives.Comment: 49 pages, 8 figure
UK membership(s) in the European Higher Education Area post-2020: a ‘Europeanisation’ agenda
The European Higher Education Area (EHEA) is an international initiative for the harmonisation of higher education (HE) systems in 49 countries. Literature about UK’s participation in the EHEA is limited, and the role of EHEA’s membership for the UK, particularly after the end of the Brexit transitional period, has not been researched. The originality of the study reported in this paper is in addressing this gap by exploring the perspectives of key UK HE actors on the strategic significance of UK’s memberships in the EHEA post-2020 for the UK. The paper draws on the theoretical ideas of rational choice neo-institutionalism, differentiated Europeanisation and internationalisation, and a thematic analysis of 19 official communications of key stakeholders and six in-depth interviews with their representatives. The findings contribute to filling in a significant gap in the literature about Bologna in the UK in making a distinction between its two memberships in the EHEA and the differences and complexities of the roles they play in constructing UK’s overarching agenda in HE particularly in the post-Brexit context. The article has also contributed to the literature about Bologna more widely, presenting an investigation into differentiated Europeanisation that has been taking place within one unique post-EU country
Diversity of Chironomidae (Diptera) breeding in the Great Stour, Kent: baseline results from the Westgate Parks non-biting midge project
Chalk rivers and streams are of conservation importance due their ecological diversity, historical relevance and economic value. With more than 200 chalk watercourses, England is considered unusual in having the most chalk rivers in the world. However, due to increasing anthropogenic activities, many English chalk rivers and streams are becoming badly degraded. The non-biting midges or chironomids (Diptera, Chironomidae) are considered key-stone taxa in aquatic food webs, and have been used as ecological indicators of freshwater quality and environmental stress. Here we determined the generic richness, diversity, and community structure of Chironomidae across six sites in the mid-section of the Great Stour in Kent, a chalk river for which concern has been expressed regarding both water and habitat quality. Based on the morphological identification of 1336 insect larvae from the six sites (four in Westgate Parks, Canterbury, and two at nearby locations upstream and downstream from Canterbury City), a total of 20 genera of Chironomidae were identified, including some taxa indicative of freshwater habitats with low levels of organic pollution. There were different levels of generic richness and diversity among sites, and while there was little variation in the community composition among the sites within Westgate Parks, there were noticeable generic differences among Westgate Parks sites compared with those upstream and downstream, showing the highest complementarity and Beta diversity values. Overall, the results were comparable with other studies on chironomids in chalk rivers and other river systems. Although spatially limited to a small stretch of river, this represents the first study on chironomids in the Great Stour and provides baseline information on the diversity and structure of this important insect group with aquatic larvae, useful for the objective interpretation of any future biological assessments and monitoring programmes on the Kentish Stour, and also for comparisons with other chalk rivers
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