4,405 research outputs found
Effects of Rotationally-Induced Mixing in Compact Binary Systems with Low-Mass Secondaries and in Single Solar-Type Stars
Many population synthesis and stellar evolution studies have addressed the
evolution of close binary systems in which the primary is a compact remnant and
the secondary is filling its Roche lobe, thus triggering mass transfer.
Although tidal locking is expected in such systems, most studies have neglected
the rotationally-induced mixing that may occur. Here we study the possible
effects of mixing in the mass-losing stars for a range in secondary star masses
and metallicities. We find that tidal locking can induce rotational mixing
prior to contact and thus affect the evolution of the secondary star if the
effects of the Spruit-Tayler dynamo are included both for angular momentum and
chemical transport. Once contact is made, the effect of mass transfer tends to
be more rapid than the evolutionary time scale, so the effects of mixing are no
longer directly important, but the mass transfer strips matter to inner layers
that may have been affected by the mixing. These effects are enhanced for
secondaries of 1-1.2 Msun and for lower metallicities. We discuss the possible
implications for the paucity of carbon in the secondaries of the cataclysmic
variable SS Cyg and the black hole candidate XTE J1118+480 and for the
progenitor evolution of Type Ia supernovae. We also address the issue of the
origin of blue straggler stars in globular and open clusters. We find that for
models that include rotation consistent with that observed for some blue
straggler stars, evolution is chemically homogeneous. This leads to tracks in
the HR diagram that are brighter and bluer than the non-rotating main-sequence
turn-off point. Rotational mixing could thus be one of the factors that
contribute to the formation of blue stragglers.Comment: 46 pages, 18 figure
Optimisation of Bluetooth wireless personal area networks
In recent years there has been a marked growth in the use of wireless cellular telephones, PCs and the Internet. This proliferation of information technology has hastened the advent of wireless networks which aim to increase the accessibility and reach of communications devices. Ambient Intelligence (Ami) is a vision of the future of computing in which all kinds of everyday objects will contain intelligence. To be effective, Ami requires Ubiquitous Computing and Communication, the latter being enabled by wireless networking. The IEEE's 802.11 task group has developed a series of radio based replacements for the familiar wired ethernet LAN. At the same time another IEEE standards task group, 802.15, together with a number of industry consortia, has introduced a new level of wireless networking based upon short range, ad-hoc connections. Currently, the most significant of these new Wireless Personal Area Network (WPAN) standards is Bluetooth, one of the first of the enabling technologies of Ami to be commercially available. Bluetooth operates in the internationally unlicensed Industrial, Scientific and Medical (ISM) band at 2.4 GHz. unfortunately, this spectrum is particularly crowded. It is also used by: WiFi (IEEE 802.11); a new WPAN standard called Zig- Bee; many types of simple devices such as garage door openers; and is polluted by unintentional radiators. The success of a radio specification for ubiquitous wireless communications is, therefore, dependant upon a robust tolerance to high levels of electromagnetic noise. This thesis addresses the optimisation of low power WPANs in this context, with particular reference to the physical layer radio specification of the Bluetooth system
Containerless low gravity processing of glass forming and immiscible alloys
Under normal one-g conditions immiscible alloys segregate extensively during solidification due to sedimentation of the more dense of the immiscible liquid phases. Immiscible (hypermonotectic) gold-rhodium alloys were processed in the 100 meter drop tube under low gravity, containerless conditions to determine the feasibility of producing dispersed structures. Three alloy compositions were utilized. Alloys containing 10 percent by volume of the gold-rich hypermonotectic phase exhibited a tendency for the gold-rich liquid to wet the outer surface of the samples. This wetting tendency led to extensive segregation in several cases. Alloys containing 80 and 90 percent by volume of the gold-rich phase possessed completely different microstructures from the 10 percent samples when processed under low-g, containerless conditions. Several samples exhibited microstructures consisting of well dispersed 2 to 3 microns diameter rhodium-rich spheres in a gold-rich matrix
An exploration of external environmental scanning and the strategy process
This thesis is concerned with ways in which organisations scan their external
environments and how this scanning is related to the process by which they make and
implement strategy. The aim of this thesis is to use a qualitative approach to elaborate
on existing theory relating to external environmental scanning and to consider its
relationship with the strategy process.
Prior academic literature bases for strategy process and for environmental scanning
were reviewed and synthesised. From this an integrated conceptual framework
incorporating strategy process, environmental scanning and the external environment
was proposed.
Seven case studies, encompassing small, medium and large businesses, were selected
for empirical study using a theoretical sampling approach. Qualitative data from
interviews and secondary sources were collected and in-case analyses conducted for
each organisation, the final outcome of which was a causal network of factors that
resulted in scanning of the environment in each organisation. A validation exercise that
involved feeding back parts of the analysis to selected respondents suggested that the
analysis was robust.
The cross-case analysis revealed that size of organisation had a significant impact on
various aspects of scanning activity, including scope, mode and formality of scanning.
The impact of perceived environmental uncertainty on scanning was affected by both
company size and type of uncertainty. The research uncovered six drivers of scanning
activity that were present in different ways depending on the strategic approach of the
organisation. Finally, with the integrated conceptual framework as a foundation, a
model of environmental scanning and the strategy process was developed using
empirical evidence from the seven causal networks.
This research contributes an understanding of how and why environmental scanning
activity relates to the strategy process in organisations. In addition, this research
contributes to knowledge of environmental scanning through its qualitative, multiplecase
study approach and its perspective on scanning as an organisational rather than an
individual activity
Overview of Environmental Durability Coatings and Test Capabilities
Overview of LME organizations capabilities including the Analytical and experimental capabilities of the Environmental Effects and Coatings Branch (LME), Case Studies - Past Hypersonics related work, and current capabilities relevant for future hypersonic work with multi-layer coatings concepts and unique testing capabilities
CAPTURING PANORAMA IMAGES
A panorama imaging system can be used to reduce parallax errors when capturing high quality panoramas. The panorama imaging system includes a panorama guidance apparatus and an image capturing device. A user of the system attaches the panorama guidance apparatus to the image capturing device and captures a panorama image with the image capturing device while maintaining a stable position of the panorama guidance apparatus
A representation of odd Sugihara chains via weakening relations
We present a relational representation of odd Sugihara chains. The elements
of the algebra are represented as weakening relations over a particular poset
which consists of two densely embedded copies of the rationals. Our
construction mimics that of Maddux (2010) where a relational representation of
the even Sugihara chains is given. An order automorphism between the two copies
of the rationals is the key to ensuring that the identity element of the monoid
is fixed by the involution.Comment: 14 pages, 1 figur
Representable distributive quasi relation algebras
We give a definition of representability for distributive quasi relation
algebras (DqRAs). These algebras are a generalisation of relation algebras and
were first described by Galatos and Jipsen (2013). Our definition uses a
construction that starts with a poset. The algebra is concretely constructed as
the lattice of upsets of a partially ordered equivalence relation. The key to
defining the three negation-like unary operations is to impose certain symmetry
requirements on the partial order. Our definition of representable distributive
quasi relation algebras is easily seen to be a generalisation of the definition
of representable relations algebras by Jonsson and Tarski (1948). We give
examples of representable DqRAs and give a necessary condition for an algebra
to be finitely representable. We leave open the questions of whether every DqRA
is representable, and also whether the class of representable DqRAs forms a
variety. Moreover, our definition provides many other opportunities for
investigations in the spirit of those carried out for representable relation
algebras
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