382 research outputs found
Raytrace simulations and experimental studies of luminescent solar concentrators
The luminescent solar concentrator is a planar, non-tracking device. Originally introduced
more than three decades ago, it has yet to establish itself as a means of making
photovoltaic solar energy more cost effective. Advances in organic luminescent centres,
the emergence of inorganic nanocrystals and the development of new light trapping
techniques have created promising opportunities for the LSC.
This thesis investigates novel geometries and materials for the practical exploitation of
LSCs. The research is based on experimental measurements as well as computational
simulations using a Raytrace Model. It is shown both experimentally and computationally
that a thin- lm structure produces the same effciency as a homogeneously doped
LSC.
Two building integrated applications are examined. The rst one is a power generating
window employing a Lumogen Violet dye that absorbs short wavelength radiation and
is mostly transparent in the visible. Annual yields of over 23 kWh/m2 and a conversion
effciency of over 1% are predicted for a 50 cm by 50 cm device. The second BIPV
application is the light-bar, which is designed to act as the secondary concentrator in a
Venetian blind-like system. With linear Fresnel lenses producing a primary concentration
factor of 20, an optimised system could generate nearly 60W/m^2 of power at an
effciency of nearly 6% using direct sunlight only.
Two novel luminescent materials, nanorods and phycobilisomes have been tested for
their potential to reduce re-absorption losses. Despite current practical limitations,
these materials are found to be promising due to enhanced Stokes shifts.
LSCs with optical concentrations of 10 to 20 could be feasible by addressing the key
shortcomings in the form of unabsorbed light and escape cone losses. Their versatility
with regards to shape, colour and light absorption makes LSCs particularly relevant for
building integrated photovoltaics.Imperial Users Onl
Non Gaussian information of heterogeneity in Soft Matter
Heterogeneity in dynamics in the form of non-Gaussian molecular displacement
distributions appears ubiquitously in soft matter. We address the
quantification of such heterogeneity using an information-theoretic measure of
the distance between the actual displacement distribution and its nearest
Gaussian estimation. We explore the usefulness of this measure in two generic
scenarios of random walkers in heterogeneous media. We show that our proposed
measure leads to a better quantification of non-Gaussianity than the
conventional ones based on moment ratios
Functional outcome of patients presenting with isolated medial condyle fractures of femur in a tertiary care hospital
Isolated medial condyle fractures of the femur with an intact lateral condyle are a rare entity. These fractures require prompt diagnosis and anatomical restoration of joint surface to prevent post traumatic arthritis. Till date no suitable implant is available for fixation of these fractures. In this study we have used 4.5 recon plates and CC screws to fix these fractures. We aim to study the functional outcome of these fractures in a group of patients fixed with the above implants. The study was conducted in a group of patients presenting with isolated medial condyle fractures of femur in a tertiary care hospital. An ORIF was done and fractures were fixed with recon plates and lag screws and various parameters were evaluated such as range of motion of knee, average time to weight bearing, Lysholm knee scores, pain perception etc 20 patients were evaluated in the age group of 20-70 in a 5 year period. Majority of the patients had a very good functional range of motion of the knee and nearly 75% achieved union by 12-16 weeks. 70% of the patients had a low VAS score. Overall early diagnosis and prompt anatomical restoration of joint surface in isolated medial condyle fractures of femur led to favourable range of motion of knee, early radiological healing and low VAS score
An extension of Thwaites method for turbulent boundary layers
Thwaites (1949) developed an approximate method for determining the evolution
of laminar boundary layers. The approximation follows from an assumption that
the growth of a laminar boundary layer in the presence of pressure gradients
could be parameterized solely as a function of a flow parameter, , thus reducing the von Karman momentum integral
to a first-order ordinary differential equation. This method is useful for the
analysis of laminar flows, and in computational potential flow solvers to
account for the viscous effects. However, for turbulent flows, a similar
approximation for turbulent boundary layers subjected to pressure gradients
does not yet exist. In this work, an approximate method for determining the
momentum thickness of a two-dimensional, turbulent boundary layer is proposed.
It is shown that the method provides good estimates of the momentum thickness,
when compared to available high-fidelity simulation data, for multiple boundary
layers including both favorable and adverse pressure gradient effects, up to
the point of separation. In the limit of high Reynolds numbers, it is possible
to derive a criterion for the onset of separation from the proposed model which
is shown to be in agreement with prior empirical observations (Alber,
\textit{ Aerospace Sciences Meeting, 1971}). The sensitivity of the
separation location with respect to upstream perturbations is also analyzed
through this model for the NASA/Boeing speed bump and the transonic
Bachalo-Johnson bumpComment: 21 pages, 13 figures. Under consideration for publication in J. Fluid
Mec
Exact ground state and kink-like excitations of a two dimensional Heisenberg antiferromagnet
A rare example of a two dimensional Heisenberg model with an exact dimerized
ground state is presented. This model, which can be regarded as a variation on
the kagome lattice, has several features of interest: it has a highly (but not
macroscopically) degenerate ground state; it is closely related to spin chains
studied by earlier authors; in particular, it is probably the first genuinely
two-dimensional quantum system to exhibit domain-wall-like ``kink'' excitations
normally found only in one-dimensional systems. In some limits it decouples
into non-interacting chains, purely dynamically and not because of weakening of
interchain couplings: indeed, paradoxically, this happens in the limit of
strong coupling of the chains.Comment: 4 pages, revtex, 5 figures included via epsfi
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