176 research outputs found
Synthetic Aperture Radar (SAR) data processing
The available and optimal methods for generating SAR imagery for NASA applications were identified. The SAR image quality and data processing requirements associated with these applications were studied. Mathematical operations and algorithms required to process sensor data into SAR imagery were defined. The architecture of SAR image formation processors was discussed, and technology necessary to implement the SAR data processors used in both general purpose and dedicated imaging systems was addressed
Relativistic MHD with Adaptive Mesh Refinement
This paper presents a new computer code to solve the general relativistic
magnetohydrodynamics (GRMHD) equations using distributed parallel adaptive mesh
refinement (AMR). The fluid equations are solved using a finite difference
Convex ENO method (CENO) in 3+1 dimensions, and the AMR is Berger-Oliger.
Hyperbolic divergence cleaning is used to control the
constraint. We present results from three flat space tests, and examine the
accretion of a fluid onto a Schwarzschild black hole, reproducing the Michel
solution. The AMR simulations substantially improve performance while
reproducing the resolution equivalent unigrid simulation results. Finally, we
discuss strong scaling results for parallel unigrid and AMR runs.Comment: 24 pages, 14 figures, 3 table
Towards a unified theory of Sobolev inequalities
We discuss our work on pointwise inequalities for the gradient which are
connected with the isoperimetric profile associated to a given geometry. We
show how they can be used to unify certain aspects of the theory of Sobolev
inequalities. In particular, we discuss our recent papers on fractional order
inequalities, Coulhon type inequalities, transference and dimensionless
inequalities and our forthcoming work on sharp higher order Sobolev
inequalities that can be obtained by iteration.Comment: 39 pages, made some changes to section 1
Quantum-Mechanical Histories and the Uncertainty Principle: I.Information-Theoretic Inequalities
This paper is generally concerned with understanding how the uncertainty
principle arises in formulations of quantum mechanics, such as the decoherent
histories approach, whose central goal is the assignment of probabilities to
histories. We first consider histories characterized by position or momentum
projections at two moments of time. Both exact and approximate (Gaussian)
projections are studied. Shannon information is used as a measure of the
uncertainty expressed in the probabilities for these histories. We derive a
number of inequalities in which the uncertainty principle is expressed as a
lower bound on the information of phase space distributions derived from the
probabilities for two-time histories. We go on to consider histories
characterized by position samplings at moments of time. We derive a lower
bound on the information of the joint probability for position samplings.
Similar bounds are derived for histories characterized by samplings of other
variables. All lower bounds on the information of histories have the general
form , where is a volume element of
history space, which we define, and is the volume of that space probed by
the projections. We thus obtain a concise and general form of the uncertainty
principle referring directly to the histories description of the system, and
making no reference to notions of phase space.Comment: 40 pages (revised uncorrupted version), Imperial College Preprint IC
92-93/2
Clinicopathological and prognostic significance of HER-2/neu and VEGF expression in colon carcinomas
<p>Abstract</p> <p>Background</p> <p>HER-2/neu and VEGF expression is correlated with disease behaviors in various cancers. However, evidence for their expression in colon cancer is rather contradictory both for the protein expression status and prognostic value. HER-2/neu is found to participate in VEGF regulation, and has known correlation with VEGF expression in some tumors. In this study, we investigated HER-2/neu and VEGF expression in Chinese colon patients and explored whether there was any correlation between their expression patterns.</p> <p>Methods</p> <p>HER-2/neu and VEGF were investigated immunohistochemically using tumor samples obtained from 317 colon cancer patients with all tumor stages. Correlation of the degree of staining with clinicopathological parameters and survival was investigated.</p> <p>Results</p> <p>Positive expression rates of HER-2/neu and VEGF in colon cancer were 15.5% and 55.5% respectively. HER-2/neu expression was significantly correlated with tumor size and distant metastases (<it>P </it>< 0.05), but was not an independent prognostic marker of survival <it>(P > 0.05)</it>. Expression of VEGF was significantly correlated with tumor size, tumor stage, lymph node metastases, and distant metastases (<it>P </it>< 0.05). The 5-year survival rate in patients with negative and positive VEGF expression was 70.2% and 61.9% respectively; the difference was not statistically significant <it>(P = 0.146)</it>. No correlation between HER-2/neu and VEGF expression was detected (<it>P = </it>0.151).</p> <p>Conclusions</p> <p>HER-2/neu and VEGF are not important prognostic markers of colon cancer. The present results do not support any association between HER2/neu and VEGF expression in this setting.</p
Dynamic Models of Language Evolution: The Linguistic Perspective
Language is probably the key defining characteristic of humanity, an immensely powerful tool which provides its users with an infinitely expressive means of representing their complex thoughts and reflections, and of successfully communicating them to others. It is the foundation on which human societies have been built and the means through which humanity’s unparalleled intellectual and technological achievements have been realized. Although we have a natural intuitive understanding of what a language is, the specification of a particular language is nevertheless remarkably difficult, if not impossible, to pin down precisely. All languages contain many separate yet integral systems which work interdependently to allow the expression of our thoughts and the interpretation of others’ expressions: each has, for instance, a set of basic meaningless sounds (e.g. [e], [l], [s]) which can be combined to make different meaningful words and parts of words (e.g. else, less, sell, -less ); these meaningful units can be combined to make complex words (e.g. spinelessness, selling ), and the words themselves can then be combined in very many complex ways into phrases, clauses and an infinite number of meaningful sentences; finally each of these sentences can be interpreted in dramatically different ways, depending on the contexts in which it is uttered and on who is doing the interpretation. Languages can be analysed at any of these different levels, which make up many of the sub-fields of linguistics, and the primary job of linguistic theorists is to try to explain the rules which best explain these complex combinations
Measurement of the mass difference m(D-s(+))-m(D+) at CDF II
We present a measurement of the mass difference m(D-s(+))-m(D+), where both the D-s(+) and D+ are reconstructed in the phipi(+) decay channel. This measurement uses 11.6 pb(-1) of data collected by CDF II using the new displaced-track trigger. The mass difference is found to be m(D-s(+))-m(D+)=99.41+/-0.38(stat)+/-0.21(syst) MeV/c(2)
A guide to the Choquard equation
We survey old and recent results dealing with the existence and properties of
solutions to the Choquard type equations and some of its variants and extensions.Comment: 39 page
Context, cognition and communication in language
Questions pertaining to the unique structure and organisation of language have a
long history in the field of linguistics. In recent years, researchers have explored
cultural evolutionary explanations, showing how language structure emerges from
weak biases amplified over repeated patterns of learning and use. One outstanding
issue in these frameworks is accounting for the role of context. In particular,
many linguistic phenomena are said to to be context-dependent; interpretation
does not take place in a void, and requires enrichment from the current state
of the conversation, the physical situation, and common knowledge about the
world. Modelling the relationship between language structure and context is
therefore crucial for developing a cultural evolutionary approach to language.
One approach is to use statistical analyses to investigate large-scale, cross-cultural
datasets. However, due to the inherent limitations of statistical analyses, especially
with regards to the inadequacy of these methods to test hypotheses about
causal relationships, I argue that experiments are better suited to address questions
pertaining to language structure and context. From here, I present a series
of artificial language experiments, with the central aim being to test how
manipulations to context influence the structure and organisation of language.
Experiment 1 builds upon previous work in iterated learning and communication
games through demonstrating that the emergence of optimal communication systems
is contingent on the contexts in which languages are learned and used. The
results show that language systems gradually evolve to only encode information
that is informative for conveying the intended meaning of the speaker - resulting
in markedly different systems of communication. Whereas Experiment 1 focused
on how context influences the emergence of structure, Experiments 2 and 3 investigate
under what circumstances do manipulations to context result in the loss
of structure. While the results are inconclusive across these two experiments,
there is tentative evidence that manipulations to context can disrupt structure,
but only when interacting with other factors. Lastly, Experiment 4 investigates
whether the degree of signal autonomy (the capacity for a signal to be interpreted without recourse to contextual information) is shaped by manipulations
to contextual predictability: the extent to which a speaker can estimate and exploit
contextual information a hearer uses in interpreting an utterance. When
the context is predictable, speakers organise languages to be less autonomous
(more context-dependent) through combining linguistic signals with contextual
information to reduce effort in production and minimise uncertainty in comprehension.
By decreasing contextual predictability, speakers increasingly rely on
strategies that promote more autonomous signals, as these signals depend less on
contextual information to discriminate between possible meanings. Overall, these
experiments provide proof-of-concept for investigating the relationship between
language structure and context, showing that the organisational principles underpinning
language are the result of competing pressures from context, cognition,
and communication
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