479 research outputs found
On the reliability of the Autosub autonomous underwater vehicle
As autonomous underwater vehicles (AUVs) enter operational service an assessment of their reliability is timely. Using the Autosub AUV as an example, several design issues affecting reliability are discussed, followed by an analysis of recorded faults. Perhaps contrary to expectations, failures rarely involved the autonomous nature of the vehicle. Rather, faults were typical of those that occur with any complex item of marine electromechanical equipment. A statistical analysis showed that the failure rate decreased with distance travelled- an indicator that an AUV underway, submerged, is at less risk of a fault developing than during other phases of a mission. 1
Modulational instability of two pairs of counter-propagating waves and energy exchange in two-component media
The dynamics of two pairs of counter-propagating waves in two-component media
is considered within the framework of two generally nonintegrable coupled
Sine-Gordon equations. We consider the dynamics of weakly nonlinear wave
packets, and using an asymptotic multiple-scales expansion we obtain a suite of
evolution equations to describe energy exchange between the two components of
the system. Depending on the wave packet length-scale vis-a-vis the wave
amplitude scale, these evolution equations are either four non-dispersive and
nonlinearly coupled envelope equations, or four non-locally coupled nonlinear
Schroedinger equations. We also consider a set of fully coupled nonlinear
Schroedinger equations, even though this system contains small dispersive terms
which are strictly beyond the leading order of the asymptotic multiple-scales
expansion method. Using both the theoretical predictions following from these
asymptotic models and numerical simulations of the original unapproximated
equations, we investigate the stability of plane-wave solutions, and show that
they may be modulationally unstable. These instabilities can then lead to the
formation of localized structures, and to a modification of the energy exchange
between the components. When the system is close to being integrable, the
time-evolution is distinguished by a remarkable almost periodic sequence of
energy exchange scenarios, with spatial patterns alternating between
approximately uniform wavetrains and localized structures.Comment: 35 pages, 13 figure
Single stranded fully Modified-Phosphorothioate oligonucleotides can induce structured nuclear inclusions, alter nuclear protein localization and disturb the transcriptome In Vitro
Oligonucleotides and nucleic acid analogues that alter gene expression are now showing therapeutic promise in human disease. Whilst the modification of synthetic nucleic acids to protect against nuclease degradation and to influence drug function is common practice, such modifications may also confer unexpected physicochemical and biological properties. Gapmer mixed-modified and DNA oligonucleotides on a phosphorothioate backbone can bind non-specifically to intracellular proteins to form a variety of toxic inclusions, driven by the phosphorothioate linkages, but also influenced by the oligonucleotide sequence. Recently, the non-antisense or other off-target effects of 2′ O- fully modified phosphorothioate linkage oligonucleotides are becoming better understood. Here, we report chemistry-specific effects of oligonucleotides composed of modified or unmodified bases, with phosphorothioate linkages, on subnuclear organelles and show altered distribution of nuclear proteins, the appearance of highly stable and strikingly structured nuclear inclusions, and disturbed RNA processing in primary human fibroblasts and other cultured cells. Phosphodiester, phosphorodiamidate morpholino oligomers, and annealed complimentary phosphorothioate oligomer duplexes elicited no such consequences. Disruption of subnuclear structures and proteins elicit severe phenotypic disturbances, revealed by transcriptomic analysis of transfected fibroblasts exhibiting such disruption. Our data add to the growing body of evidence of off-target effects of some phosphorothioate nucleic acid drugs in primary cells and suggest alternative approaches to mitigate these effects
Improving Landsat predictions of rangeland fractional cover with multi-task learning and uncertainty
Low Q^2 Jet Production at HERA and Virtual Photon Structure
The transition between photoproduction and deep-inelastic scattering is
investigated in jet production at the HERA ep collider, using data collected by
the H1 experiment. Measurements of the differential inclusive jet
cross-sections dsigep/dEt* and dsigmep/deta*, where Et* and eta* are the
transverse energy and the pseudorapidity of the jets in the virtual
photon-proton centre of mass frame, are presented for 0 < Q2 < 49 GeV2 and 0.3
< y < 0.6. The interpretation of the results in terms of the structure of the
virtual photon is discussed. The data are best described by QCD calculations
which include a partonic structure of the virtual photon that evolves with Q2.Comment: 20 pages, 5 Figure
Hadron Production in Diffractive Deep-Inelastic Scattering
Characteristics of hadron production in diffractive deep-inelastic
positron-proton scattering are studied using data collected in 1994 by the H1
experiment at HERA. The following distributions are measured in the
centre-of-mass frame of the photon dissociation system: the hadronic energy
flow, the Feynman-x (x_F) variable for charged particles, the squared
transverse momentum of charged particles (p_T^{*2}), and the mean p_T^{*2} as a
function of x_F. These distributions are compared with results in the gamma^* p
centre-of-mass frame from inclusive deep-inelastic scattering in the
fixed-target experiment EMC, and also with the predictions of several Monte
Carlo calculations. The data are consistent with a picture in which the
partonic structure of the diffractive exchange is dominated at low Q^2 by hard
gluons.Comment: 16 pages, 6 figures, submitted to Phys. Lett.
Energy Flow in the Hadronic Final State of Diffractive and Non-Diffractive Deep-Inelastic Scattering at HERA
An investigation of the hadronic final state in diffractive and
non--diffractive deep--inelastic electron--proton scattering at HERA is
presented, where diffractive data are selected experimentally by demanding a
large gap in pseudo --rapidity around the proton remnant direction. The
transverse energy flow in the hadronic final state is evaluated using a set of
estimators which quantify topological properties. Using available Monte Carlo
QCD calculations, it is demonstrated that the final state in diffractive DIS
exhibits the features expected if the interaction is interpreted as the
scattering of an electron off a current quark with associated effects of
perturbative QCD. A model in which deep--inelastic diffraction is taken to be
the exchange of a pomeron with partonic structure is found to reproduce the
measurements well. Models for deep--inelastic scattering, in which a
sizeable diffractive contribution is present because of non--perturbative
effects in the production of the hadronic final state, reproduce the general
tendencies of the data but in all give a worse description.Comment: 22 pages, latex, 6 Figures appended as uuencoded fil
A Search for Selectrons and Squarks at HERA
Data from electron-proton collisions at a center-of-mass energy of 300 GeV
are used for a search for selectrons and squarks within the framework of the
minimal supersymmetric model. The decays of selectrons and squarks into the
lightest supersymmetric particle lead to final states with an electron and
hadrons accompanied by large missing energy and transverse momentum. No signal
is found and new bounds on the existence of these particles are derived. At 95%
confidence level the excluded region extends to 65 GeV for selectron and squark
masses, and to 40 GeV for the mass of the lightest supersymmetric particle.Comment: 13 pages, latex, 6 Figure
Measurement of D* Meson Cross Sections at HERA and Determination of the Gluon Density in the Proton using NLO QCD
With the H1 detector at the ep collider HERA, D* meson production cross
sections have been measured in deep inelastic scattering with four-momentum
transfers Q^2>2 GeV2 and in photoproduction at energies around W(gamma p)~ 88
GeV and 194 GeV. Next-to-Leading Order QCD calculations are found to describe
the differential cross sections within theoretical and experimental
uncertainties. Using these calculations, the NLO gluon momentum distribution in
the proton, x_g g(x_g), has been extracted in the momentum fraction range
7.5x10^{-4}< x_g <4x10^{-2} at average scales mu^2 =25 to 50 GeV2. The gluon
momentum fraction x_g has been obtained from the measured kinematics of the
scattered electron and the D* meson in the final state. The results compare
well with the gluon distribution obtained from the analysis of scaling
violations of the proton structure function F_2.Comment: 27 pages, 9 figures, 2 tables, submitted to Nucl. Phys.
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