60 research outputs found
Method of the Riemann-Hilbert Problem for the Solution of the Helmholtz Equation in a Semi-infinite Strip
In this dissertation, a new method is developed to study BVPs of the modified Helmholtz and Helmholtz equations in a semi-infinite strip subject to the Poincare type, impedance and higher order boundary conditions. The main machinery used here is the theory of Riemann Hilbert problems, the residue theory of complex variables and the theory of integral transforms. A special kind of interconnected Laplace transforms are introduced whose parameters are related through branch of a multi-valued function. In the chapter 1 a brief review of the unified transform method used to solve BVPs of linear and non-linear integrable PDEs in convex polygons is given. Then unified transform method is applied to the BVP of the modified Helmholtz equation in a semi-infinite strip subject to the Poincare type and impedance boundary conditions. In the case of BVP of the modified Helmholtz equation in a semi-infinite strip subject to the impedance boundary conditions, two scalar RHPs are derived, then the closed form solutions of the given BVP are derived. The difficulty in application of the unified transform method to BVP of the Helmholtz equation in a semi infinite strip is discussed later on. The chapter 2 contains application of the finite integral transform (FIT) method to study the BVP for the Helmholtz equation in a semi-infinite strip subject to the Poincare type and impedance boundary conditions. In the case of the impedance boundary conditions, a series representation of the solution of the BVP for the Helmholtz equation in a semi-infinite strip is derived. The Burniston-Siewert method to find integral representations of a certain transcendental equation is presented. The roots of this equation are required for both methods, the FIT method and the RHP based method. To implement the Burniston-Siewert method, we solve a scalar RHP on several segments of the real axis. In chapter 3, we have applied the new method to study the Poincare type and impedance BVPs for the Helmholtz equation in a semi-infinite strip. In the case of the Poincare type boundary conditions an order two vector RHP is derived. In general, it is not possible to find closed form solution of an order two vector RHP. In the case of the impedance boundary conditions two scalar RHPs are derived whose closed form solutions are found. Then the series representation for solution of the BVP of the Helmholtz equation in a semi-infinite strip subject to the impedance boundary conditions, is recovered using the inverse transform operator, and the residue theory of complex variables. The numerical results are presented for various values of the parameters involved. It is observed that the FIT method and the new method generate exactly the same solution of the BVP of the Helmholtz equation in a semi-infinite strip subject to the impedance boundary conditions. In chapter 4, we have applied the new method to study the acoustic scattering from a semi-infinite strip subject to higher order boundary conditions. Two scalar RHPs are derived whose closed form solutions are found. A unique solution of the problem is obtained
The development and applications of a system designed to quantify coronary arterial stenosis
The objective analysis of coronary artery stenosis is required for the assessment of interventions in the management of Coronary Artery Disease (CAD). This thesis presents a microcomputer-based system designed to meet this requirement which is easy to use and relatively cheap. The hardware consists of a standard 35 mm cine-projector (International General Electric Company), a rear projection graphics tablet (GTCO Corporation) and microcomputer (Vector Graphic Limited) with printer (Epson Limited). The graphics tablet and projector are mounted into a steel framework which allows an arteriographic image to be cast from the rear of the projector and focused, parallax free, onto the centre of the tablet. The tablet in turn communicates with the computer via a RS232 link. [Continues.
Designing sound : procedural audio research based on the book by Andy Farnell
In
procedural
media,
data
normally
acquired
by
measuring
something,
commonly
described
as
sampling,
is
replaced
by
a
set
of
computational
rules
(procedure)
that
defines
the
typical
structure
and/or
behaviour
of
that
thing.
Here,
a
general
approach
to
sound
as
a
definable
process,
rather
than
a
recording,
is
developed.
By
analysis
of
their
physical
and
perceptual
qualities,
natural
objects
or
processes
that
produce
sound
are
modelled
by
digital
Sounding
Objects
for
use
in
arts
and
entertainments.
This
Thesis
discusses
different
aspects
of
Procedural
Audio
introducing
several
new
approaches
and
solutions
to
this
emerging
field
of
Sound
Design.Em
Media
Procedimental,
os
dados
os
dados
normalmente
adquiridos
através
da
medição
de
algo
habitualmente
designado
como
amostragem,
são
substituídos
por
um
conjunto
de
regras
computacionais
(procedimento)
que
definem
a
estrutura
típica,
ou
comportamento,
desse
elemento.
Neste
caso
é
desenvolvida
uma
abordagem
ao
som
definível
como
um
procedimento
em
vez
de
uma
gravação.
Através
da
análise
das
suas
características
físicas
e
perceptuais
,
objetos
naturais
ou
processos
que
produzem
som,
são
modelados
como
objetos
sonoros
digitais
para
utilização
nas
Artes
e
Entretenimento.
Nesta
Tese
são
discutidos
diferentes
aspectos
de
Áudio
Procedimental,
sendo
introduzidas
várias
novas
abordagens
e
soluções
para
o
campo
emergente
do
Design
Sonoro
NASA thesaurus. Volume 3: Definitions
Publication of NASA Thesaurus definitions began with Supplement 1 to the 1985 NASA Thesaurus. The definitions given here represent the complete file of over 3,200 definitions, complimented by nearly 1,000 use references. Definitions of more common or general scientific terms are given a NASA slant if one exists. Certain terms are not defined as a matter of policy: common names, chemical elements, specific models of computers, and nontechnical terms. The NASA Thesaurus predates by a number of years the systematic effort to define terms, therefore not all Thesaurus terms have been defined. Nevertheless, definitions of older terms are continually being added. The following data are provided for each entry: term in uppercase/lowercase form, definition, source, and year the term (not the definition) was added to the NASA Thesaurus. The NASA History Office is the authority for capitalization in satellite and spacecraft names. Definitions with no source given were constructed by lexicographers at the NASA Scientific and Technical Information (STI) Facility who rely on the following sources for their information: experts in the field, literature searches from the NASA STI database, and specialized references
THE DEVELOPMENT OF A HOLISTIC EXPERT SYSTEM FOR INTEGRATED COASTAL ZONE MANAGEMENT
Coastal data and information comprise a massive and complex resource, which is vital
to the practice of Integrated Coastal Zone Management (ICZM), an increasingly
important application. ICZM is just as complex, but uses the holistic paradigm to deal
with the sophistication. The application domain and its resource require a tool of
matching characteristics, which is facilitated by the current wide availability of high
performance computing.
An object-oriented expert system, COAMES, has been constructed to prove this
concept. The application of expert systems to ICZM in particular has been flagged as
a viable challenge and yet very few have taken it up. COAMES uses the Dempster-
Shafer theory of evidence to reason with uncertainty and importantly introduces the
power of ignorance and integration to model the holistic approach. In addition, object
orientation enables a modular approach, embodied in the inference engine -
knowledge base separation. Two case studies have been developed to test COAMES.
In both case studies, knowledge has been successfully used to drive data and actions
using metadata. Thus a holism of data, information and knowledge has been achieved.
Also, a technological holism has been proved through the effective classification of
landforms on the rapidly eroding Holderness coast. A holism across disciplines and
CZM institutions has been effected by intelligent metadata management of a Fal
Estuary dataset. Finally, the differing spatial and temporal scales that the two case
studies operate at implicitly demonstrate a holism of scale, though explicit means of
managing scale were suggested. In all cases the same knowledge structure was used to
effectively manage and disseminate coastal data, information and knowledge
The role of computer-aided design in the learning of practical 3D-descriptive geometry: a case study
There are a number of problems surrounding the teaching of
practical 3-D descriptive geometry to children in secondary
education, notably the difficulty pupils have with visualising
an object's form from orthographic views, and the interpretation
of an object's geometric attributes into the descriptive
geometry representation.
The purpose of the current research is to evaluate the use of
computer-aided design in this area of the curriculum and is
based upon work undertaken in a North London comprehensive school. The school and its context is described and evaluated.
Theories of child development and educational psychology of
relevance to the study are reviewed, notably the work of Piaget, Bryant, Gagne, and Freeman.
The history and nature of 3-D descriptive geometry is reviewed
in practice and in education, with special reference to various
methods employed in instruction.
Dr. J. Vince's PICASO SYSTEM of computer subroutines and
functions written in FORTRAN for graphic applications is
explained as a means of teaching the subject, with special
reference to the researcher's own instructional material and
computer programs. The use and effectiveness of these teaching materials are related and evaluated in the light of students' performance and results.
The research concludes that the special benefits of computer
graphics in this field are: the economic production of
appropriate didactic material under the direct control of the
teacher, increased pupil motivation due to the use of better
illustration and the interest generated by computer-aided design project work. and an opportunity to employ analytic geometry to support learning. Its limitations include: the high cost of the computer and peripheral devices, and the lack of a facility for modelling objects by the removal of solid volumes in the existing software. Further research is recommended in the areas of computer graphics, descriptive geometry, and psychology
Modeling EMI Resulting from a Signal Via Transition Through Power/Ground Layers
Signal transitioning through layers on vias are very common in multi-layer printed circuit board (PCB) design. For a signal via transitioning through the internal power and ground planes, the return current must switch from one reference plane to another reference plane. The discontinuity of the return current at the via excites the power and ground planes, and results in noise on the power bus that can lead to signal integrity, as well as EMI problems. Numerical methods, such as the finite-difference time-domain (FDTD), Moment of Methods (MoM), and partial element equivalent circuit (PEEC) method, were employed herein to study this problem. The modeled results are supported by measurements. In addition, a common EMI mitigation approach of adding a decoupling capacitor was investigated with the FDTD method
Data security in photonic information systems using quantum based approaches
The last two decades has seen a revolution in how information is stored and transmitted
across the world. In this digital age, it is vital for banking systems, governments and
businesses that this information can be transmitted to authorised receivers quickly and
efficiently. Current classical cryptosystems rely on the computational difficulty of
calculating certain mathematical functions but with the advent of quantum computers,
implementing efficient quantum algorithms, these systems could be rendered insecure
overnight. Quantum mechanics thankfully also provides the solution, in which
information is transmitted on single-photons called qubits and any attempt by an
adversary to gain information on these qubits is limited by the laws of quantum
mechanics.
This thesis looks at three distinct different quantum information experiments. Two of
the systems describe the implementation of distributing quantum keys, in which the
presence of an eavesdropper introduces unavoidable errors by the laws of quantum
mechanics. The first scheme used a quantum dot in a micropillar cavity as a singlephoton
source. A polarisation encoding scheme was used for implementing the BB84,
quantum cryptographic protocol, which operated at a wavelength of 905 nm and a clock
frequency of 40 MHz. A second system implemented phase encoding using asymmetric
unbalanced Mach-Zehnder interferometers, with a weak coherent source, operating at a
wavelength of 850 nm and pulsed at a clock rate of 1 GHz. The system used
depolarised light propagating in the fibre quantum channel. This helps to eliminate the
random evolution of the state of polarisation of photons, as a result of stress induced
changes in the intrinsic birefringence of the fibre. The system operated completely
autonomously, using custom software to compensate for path length fluctuations in the
arms of the interferometer and used a variety of different single-photon detector
technologies. The final quantum information scheme looked at quantum digital
signatures, which allows a sender, Alice, to distribute quantum signatures to two parties,
Bob and Charlie, such that they are able to authenticate that the message originated
from Alice and that the message was not altered in transmission
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