3,352 research outputs found
Gravitational Waves in the Nonsymmetric Gravitational Theory
We prove that the flux of gravitational radiation from an isolated source in
the Nonsymmetric Gravitational Theory is identical to that found in Einstein's
General Theory of Relativity.Comment: 10 Page
The C291R Tau variant forms different types of protofibrils
Mutations in the MAPT gene can lead to disease-associated variants of tau. However, the pathological mechanisms behind these genetic tauopathies are poorly understood. Here, we characterized the aggregation stages and conformational changes of tau C291R, a recently described MAPT mutation with potential pathogenic functions. The C291R variant of the tau four-repeat domain (tau-K18; a functional fragment with increased aggregation propensity compared with the full-length protein), aggregated into a mix of granular oligomers, amorphous and annular pore-like aggregates, in native-state and heparin-treated reactions as observed using atomic force microscopy (AFM) and negative-stained electron microscopy. On extended incubation in the native-state, tau-K18 C291R oligomers, unlike wild type (WT) tau-K18, aggregated to form protofibrils of four different phenotypes: (1) spherical annular; (2) spherical annular encapsulating granular oligomers; (3) ring-like annular but non-spherical; and (4) linear protofibrils. The ring-like tau-K18 C291R aggregates shared key properties of annular protofibrils previously described for other amyloidogenic proteins, in addition to two unique features: irregular/non-spherical-shaped annular protofibrils, and spherical protofibrils encapsulating granular oligomers. Tau-K18 C291R monomers had a circular dichroism (CD) peak at ~210 nm compared with ~199 nm for tau-K18 WT. These data suggest mutation-enhanced β-sheet propensity. Together, we describe the characterization of tau-K18 C291R, the first genetic mutation substituting a cysteine residue. The aggregation mechanism of tau-K18 C291R appears to involve β-sheet-rich granular oligomers which rearrange to form unique protofibrillar structures
Micro-manufactured Rogowski coils for fault detection of aircraft electrical wiring and interconnect systems (EWIS)
Aircraft wiring failures have increased over the last few years resulting in arc faults and
high-energy flashover on the wiring bundle, which can propagate down through aircraft
Electrical Wiring and Interconnect Systems (EWIS). It is considered cost prohibitive to
completely rewire a plane in terms of man hours and operational time lost to do this,
and most faults are only detectable whilst the aircraft is in flight. Temperature, humidity
and vibration all accelerate ageing and failure effects on EWIS.
This research investigates methods of in-situ non-invasive testing of aircraft wiring
during fight. Failure Mode Effects and Analysis (FMEA) was performed on legacy
aircraft EWIS using data obtained from RAF Brize Norton. Micro-Electro-mechanical-
Systems (MEMS) were evaluated for use in a wire monitoring system that measures the
environmental parameters responsible for ageing and failure of EWIS. Such MEMS can
be developed into a Health and Usage Monitoring MicroSystem (HUMMS) by
incorporating advanced signal processing and prognostic software.
Current and humidity sensors were chosen for further investigation in this thesis. These
sensors can be positioned inside and outside cable connectors of EWIS so that arc faults
can be reliably detected and located. This thesis presents the design, manufacture and
test of micro-manufactured Rogowski sensors. The manufactured sensors were
benchmarked against commercial high frequency current transformers (HFCT), as these
devices can also detect high frequency current signature due to wire insulation failure.
Results indicate that these sensors possess superior voltage output compared to the
HFCT.
The design, manufacture and test of a polymer capacitive humidity sensor is also
presented. Two different types of polymer were reviewed as part of the evaluation. A
feature of the sensor design is recovery from exposure to chemicals found on wiring
bundles. Current and humidity sensors were demonstrated to be suitable for integrating
onto a common substrate with accelerometers, temperature sensors and pressure sensors
for health monitoring and prognostics of aircraft EWIS
Boundary Operators in Quantum Field Theory
The fundamental laws of physics can be derived from the requirement of
invariance under suitable classes of transformations on the one hand, and from
the need for a well-posed mathematical theory on the other hand. As a part of
this programme, the present paper shows under which conditions the introduction
of pseudo-differential boundary operators in one-loop Euclidean quantum gravity
is compatible both with their invariance under infinitesimal diffeomorphisms
and with the requirement of a strongly elliptic theory. Suitable assumptions on
the kernel of the boundary operator make it therefore possible to overcome
problems resulting from the choice of purely local boundary conditions.Comment: 23 pages, plain Tex. The revised version contains a new section, and
the presentation has been improve
Micro-manufactured Rogowski coils for fault detection of aircraft electrical wiring and interconnection systems (EWIS)
Aircraft wiring failures have increased over the last few years resulting in arc faults and
high-energy flashover on the wiring bundle, which can propagate down through aircraft
Electrical Wiring and Interconnect Systems (EWIS). It is considered cost prohibitive to
completely rewire a plane in terms of man hours and operational time lost to do this,
and most faults are only detectable whilst the aircraft is in flight. Temperature, humidity
and vibration all accelerate ageing and failure effects on EWIS.
This research investigates methods of in-situ non-invasive testing of aircraft wiring
during fight. Failure Mode Effects and Analysis (FMEA) was performed on legacy
aircraft EWIS using data obtained from RAF Brize Norton. Micro-Electro-mechanical-
Systems (MEMS) were evaluated for use in a wire monitoring system that measures the
environmental parameters responsible for ageing and failure of EWIS. Such MEMS can
be developed into a Health and Usage Monitoring MicroSystem (HUMMS) by
incorporating advanced signal processing and prognostic software.
Current and humidity sensors were chosen for further investigation in this thesis. These
sensors can be positioned inside and outside cable connectors of EWIS so that arc faults
can be reliably detected and located. This thesis presents the design, manufacture and
test of micro-manufactured Rogowski sensors. The manufactured sensors were
benchmarked against commercial high frequency current transformers (HFCT), as these
devices can also detect high frequency current signature due to wire insulation failure.
Results indicate that these sensors possess superior voltage output compared to the
HFCT.
The design, manufacture and test of a polymer capacitive humidity sensor is also
presented. Two different types of polymer were reviewed as part of the evaluation. A
feature of the sensor design is recovery from exposure to chemicals found on wiring
bundles. Current and humidity sensors were demonstrated to be suitable for integrating
onto a common substrate with accelerometers, temperature sensors and pressure sensors
for health monitoring and prognostics of aircraft EWIS.Engineering and Physical Sciences Research Council (EPSRC
Regulation of neuronal excitability through pumilio-dependent control of a sodium channel gene
Dynamic changes in synaptic connectivity and strength, which occur during both embryonic development and learning, have the tendency to destabilize neural circuits. To overcome this, neurons have developed a diversity of homeostatic mechanisms to maintain firing within physiologically defined limits. In this study, we show that activity-dependent control of mRNA for a specific voltage-gated Na+ channel [encoded by paralytic (para)] contributes to the regulation of membrane excitability in Drosophila motoneurons. Quantification of para mRNA, by real-time reverse-transcription PCR, shows that levels are significantly decreased in CNSs in which synaptic excitation is elevated, whereas, conversely, they are significantly increased when synaptic vesicle release is blocked. Quantification of mRNA encoding the translational repressor pumilio (pum) reveals a reciprocal regulation to that seen for para. Pumilio is sufficient to influence para mRNA. Thus, para mRNA is significantly elevated in a loss-of-function allele of pum (pumbemused), whereas expression of a full-length pum transgene is sufficient to reduce para mRNA. In the absence of pum, increased synaptic excitation fails to reduce para mRNA, showing that Pum is also necessary for activity-dependent regulation of para mRNA. Analysis of voltage-gated Na+ current (INa) mediated by para in two identified motoneurons (termed aCC and RP2) reveals that removal of pum is sufficient to increase one of two separable INa components (persistent INa), whereas overexpression of a pum transgene is sufficient to suppress both components (transient and persistent). We show, through use of anemone toxin (ATX II), that alteration in persistent INa is sufficient to regulate membrane excitability in these two motoneurons
Nonexistence theorems for traversable wormholes
Gauss-Bonnet formula is used to derive a new and simple theorem of
nonexistence of vacuum static nonsingular lorentzian wormholes. We also derive
simple proofs for the nonexistence of lorentzian wormhole solutions for some
classes of static matter such as, for instance, real scalar fields with a
generic potential obeying and massless fermions fields
Ultraviolet Complete Electroweak Model Without a Higgs Particle
An electroweak model with running coupling constants described by an energy
dependent entire function is utraviolet complete and avoids unitarity
violations for energies above 1 TeV. The action contains no physical scalar
fields and no Higgs particle and the physical electroweak model fields are
local and satisfy microcausality. The and masses are compatible with a
symmetry breaking , which
retains a massless photon. The vertex couplings possess an energy scale
TeV predicting scattering amplitudes that can be tested at the
LHC.Comment: 19 pages, no figures, LaTex file. Equation and text corrected.
Reference added. Results remain the same. Final version published in European
Physics Journal Plus, 126 (2011
Gravitational solution to the Pioneer 10/11 anomaly
A fully relativistic modified gravitational theory including a fifth force
skew symmetric field is fitted to the Pioneer 10/11 anomalous acceleration. The
theory allows for a variation with distance scales of the gravitational
constant G, the fifth force skew symmetric field coupling strength omega and
the mass of the skew symmetric field mu=1/lambda. A fit to the available
anomalous acceleration data for the Pioneer 10/11 spacecraft is obtained for a
phenomenological representation of the "running" constants and values of the
associated parameters are shown to exist that are consistent with fifth force
experimental bounds. The fit to the acceleration data is consistent with all
current satellite, laser ranging and observations for the inner planets.Comment: 14 pages, 3 figures, 3 tables. typo's were corrected at Equations (4)
and (12) and a third table including our predictions for the anomalous
perihelion advance of the planets was adde
Field Equations and Conservation Laws in the Nonsymmetric Gravitational Theory
The field equations in the nonsymmetric gravitational theory are derived from
a Lagrangian density using a first-order formalism. Using the general
covariance of the Lagrangian density, conservation laws and tensor identities
are derived. Among these are the generalized Bianchi identities and the law of
energy-momentum conservation. The Lagrangian density is expanded to
second-order, and treated as an ``Einstein plus fields'' theory. From this, it
is deduced that the energy is positive in the radiation zone.Comment: 16 pages, RevTeX. Additional equations supplie
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