45,809 research outputs found
Recommended from our members
Rurality, productivity and skills in the East Midlands: final report
This report sets out the findings of research into the relationship between rurality, skills and productivity in the East Midlands. The report has been prepared by the Enterprise Research and Development Unit (ERDU) at the University of Lincoln on behalf of the East Midlands Development Agency (emda)
A two-dimensional model of the quasi biennial oscillation of ozone
The largest amplitudes of the observed Quasi Biennial Oscillation (QBO) in column ozone are found in high latitudes and this must be taken into account in any explanation of the increased depletion of ozone in the southern polar spring during the 1980's. A QBO in zonal wind, temperature and column ozone has been successfully modelled in a two-dimensional dynamical/chemical model by the introduction of a parameterization scheme to model the transfer of momentum to the zonal flow associated with the damping of vertically propagating Kelvin and Rossby-Gravity waves. The largest anomalies in column ozone of approximately 20 DU are present at high latitudes. The equatorial ozone QBO is out of phase with the mid- and high-latitude ozone QBO, in good agreement with observations
Recommended from our members
Idealised simulations of cyclones with robust symmetrically-unstable sting jets
Idealised simulations of Shapiro-Keyser cyclones developing a sting jet (SJ) are presented. Thanks to an improved and accurate implementation of thermal wind balance in the initial state, it has been possible to use more realistic environments than in previous idealised studies. As a consequence, this study provides further insight in SJ evolution and dynamics and explores SJ robustness to different environmental conditions, assessed via a wide range of sensitivity experiments.
The control simulation contains a cyclone that fits the Shapiro-Keyser conceptual model and develops a SJ whose dynamics are associated with the evolution of mesoscale instabilities along the airstream, including symmetric instability (SI). The SJ undergoes a strong descent while leaving the cloud-head banded tip and markedly accelerating towards the frontal-fracture region, revealed as an area of buckling of the already-sloped moist isentropes.
Dry instabilities, generated by vorticity tilting via slantwise frontal motions in the cloud head, exist in similar proportions to moist instabilities at the start of the SJ descent and are then released along the SJ. The observed evolution supports the role of SI in the airstream’s dynamics proposed in a conceptual model outlined in a previous study.
Sensitivity experiments illustrate that the SJ is a robust feature of intense Shapiro-Keyser cyclones, highlighting a range of different environmental conditions in which SI contributes to the evolution of this airstream, conditional on the model having adequate resolution.
The results reveal that several environmental factors can modulate the strength of the SJ. However, a positive relationship between the strength of the SJ, both in terms of peak speed and amount of descent, and the amount of instability occurring along it can still be identified.
In summary, the idealised simulations presented in this study show the robustness of SJ occurrence in intense Shapiro-Keyser cyclones and support and clarify the role of dry instabilities in SJ dynamics
AdS Strings with Torsion: Non-complex Heterotic Compactifications
Combining the effects of fluxes and gaugino condensation in heterotic
supergravity, we use a ten-dimensional approach to find a new class of
four-dimensional supersymmetric AdS compactifications on almost-Hermitian
manifolds of SU(3) structure. Computation of the torsion allows a
classification of the internal geometry, which for a particular combination of
fluxes and condensate, is nearly Kahler. We argue that all moduli are fixed,
and we show that the Kahler potential and superpotential proposed in the
literature yield the correct AdS radius. In the nearly Kahler case, we are able
to solve the H Bianchi using a nonstandard embedding. Finally, we point out
subtleties in deriving the effective superpotential and understanding the
heterotic supergravity in the presence of a gaugino condensate.Comment: 42 pages; v2. added refs, revised discussion of Bianchi for N
Prediction of span loading of straight-wing/propeller combinations up to stall
A method is presented for calculating the spanwise lift distribution on straight-wing/propeller combinations. The method combines a modified form of the Prandtl wing theory with a realistic representation of the propeller slipstream distribution. The slipstream analysis permits calculations of the nonuniform axial and rotational slipstream velocity field of propeller/nacelle combinations. This nonuniform field was then used to calculate the wing lift distribution by means of the modified Prandtl wing theory. The theory was developed for any number of nonoverlapping propellers, on a wing with partial or full-span flaps, and is applicable throughout an aspect ratio range from 2.0 and higher. A computer program was used to calculate slipstream characteristics and wing span load distributions for a number of configurations for which experimental data are available, and favorable comparisons are demonstrated between the theoretical predictions and the existing data
Texture transitions in the liquid crystalline alkyloxybenzoic acid 6OBAC
The 4,n-alkyloxybenzoic acid 6OBAC has a very rich variety of crystalline
structures and two nematic sub-phases, characterised by different textures. It
is a material belonging to a family of liquid crystals formed by hydrogen
bonded molecules, the 4,n-alkyloxybenzoic acids indicates the homologue
number). The homologues with n ranging from 7 to 13 display both smectic C and
N phases. In spite of the absence of a smectic phase, 6OBAC exhibits two
sub-phases with different textures, as it happens in other materials of the
homologue series which possess the smectic phase. This is the first material
that exhibits a texture transition in a nematic phase directly originated from
a crystal phase. Here we present the results of an image processing assisted
optical investigation to characterise the textures and the transitions between
textures. This processing is necessary to discriminate between crystal
modifications and nematic sub-phases.Comment: 12 pages, 10 figure
Emotional modulation of visual cortex activity: A functional nearinfrared spectroscopy study
Functional neuroimaging and electroencephalography reveal emotional effects in early visual cortex.
Here, we used fNIRS to examine haemodynamic responses evoked by neutral, positive and negative emotional pictures, matched for brightness, contrast, hue, saturation, spatial frequency and entropy.
Emotion content modulated amplitude and latency of oxy-, deoxy- and total haemoglobin response peaks, and induced peripheral autonomic reactions. The processing of positive and negative pictures enhanced haemodynamic response amplitude, and this effect was paralleled by blood pressure changes. The processing of positive pictures was reflected in reduced haemodynamic response peak latency. Together these data suggest early visual cortex holds amplitude-dependent representation of stimulus salience and latency-dependent information regarding stimulus valence, providing new insight into affective interaction with sensory processing
A quantum mechanical approach to establishing the magnetic field orientation from a maser Zeeman profile
Recent comparisons of magnetic field directions derived from maser Zeeman
splitting with those derived from continuum source rotation measures have
prompted new analysis of the propagation of the Zeeman split components, and
the inferred field orientation. In order to do this, we first review differing
electric field polarization conventions used in past studies. With these
clearly and consistently defined, we then show that for a given Zeeman
splitting spectrum, the magnetic field direction is fully determined and
predictable on theoretical grounds: when a magnetic field is oriented away from
the observer, the left-hand circular polarization is observed at higher
frequency and the right-hand polarization at lower frequency. This is
consistent with classical Lorentzian derivations. The consequent interpretation
of recent measurements then raises the possibility of a reversal between the
large-scale field (traced by rotation measures) and the small-scale field
(traced by maser Zeeman splitting).Comment: 10 pages, 5 Figures, accepted for publication in MNRA
New string vacua from twistor spaces
We find a new family of AdS_4 vacua in IIA string theory. The internal space
is topologically either the complex projective space CP^3 or the "flag
manifold" SU(3)/(U(1)xU(1)), but the metric is in general neither Einstein nor
Kaehler. All known moduli are stabilized by fluxes, without using quantum
effects or orientifold planes. The analysis is completely ten--dimensional and
does not rely on assumptions about Kaluza--Klein reduction.Comment: 19 pages. v3: published version, further minor correction
- …