257 research outputs found
On the completeness of impulsive gravitational wave space-times
We consider a class of impulsive gravitational wave space-times, which
generalize impulsive pp-waves. They are of the form ,
where is a Riemannian manifold of arbitrary dimension and carries
the line element with the line
element of and the Dirac measure. We prove a completeness result
for such space-times with complete Riemannian part .Comment: 13 pages, minor changes suggested by the referee
Overexpression of melanoma inhibitory activity (MIA) enhances extravasation and metastasis of A-mel 3 melanoma cells in vivo
The secreted MIA protein is strongly expressed by advanced primary and metastatic melanomas but not in normal melanocytes. Previous studies have shown that MIA serum levels correlate with clinical tumour progression in melanoma patients. To provide direct evidence that MIA plays a role in metastasis of malignant melanomas, A-mel 3 hamster melanoma cells were transfected with sense- and antisense rhMIA cDNA and analysed subsequently for changes in their tumorigenic and metastatic potential. Enforced expression of MIA in A-mel 3 cells significantly increased their metastatic potential without affecting primary tumour growth, cell proliferation or apoptosis rate in hamsters, compared with control or antisense transfected cells. Additionally, MIA overexpressing transfectants showed a higher rate of both tumour cell invasion and extravasation. Cells transfected with MIA antisense generally exerted an opposite response. The above changes in function attributed to the expression of MIA may underlie the contribution of MIA to the malignant phenotype. © 2000 Cancer Research Campaig
An experimental investigation of a novel iron chelating protoporphyrin IX prodrug for the enhancement of photodynamic therapy (article)
This is the author accepted manuscript. The final version is available from Wiley via the DOI in this recordThe dataset associated with this article is located in ORE at: http://hdl.handle.net/10871/32090Objectives: Non-melanoma skin cancers are the most frequently occurring type of cancer
worldwide. They can be effectively treated using topical dermatological photodynamic therapy
(PDT) employing protoporphyrin IX (PpIX) as the active photosensitising agent as long as the disease
remains superficial. Novel iron chelating agents are being investigated to enhance the effectiveness
and extend the applications of this treatment modality, as limiting free iron increases the
accumulation of PpIX available for light activation and thus cell kill.
Methods: Human lung fibroblasts (MRC-5) and epithelial squamous carcinoma (A431) cells were
treated with PpIX precursors (aminolaevulinic acid (ALA) or methyl-aminolevulinate (MAL)) with or
without the separate hydroxypyridinone iron chelating agent (CP94) or alternatively, the new
combined iron chelator and PpIX producing agent, AP2-18. PpIX fluorescence was monitored hourly
for 6 hours prior to irradiation. PDT effectiveness was then assessed the following day using the
lactate dehydrogenase and neutral red assays.
Results: Generally, iron chelation achieved via CP94 or AP2-18 administration significantly increased
PpIX fluorescence. ALA was more effective as a PpIX-prodrug than MAL in A431 cells, corresponding
with the lower PpIX accumulation observed with the latter congener in this cell type. Addition of
either iron chelating agent consistently increased PpIX accumulation but did not always convey an
extra beneficial effect on PpIX-PDT cell kill when using the already highly effective higher dose of
ALA. However, these adjuvants were highly beneficial in the skin cancer cells when compared with
MAL administration alone. AP2-18 was also at least as effective as CP94 + ALA/MAL coadministration
throughout and significantly better than CP94 supplementation at increasing PpIX
fluorescence in MRC5 cells as well as at lower doses where PpIX accumulation was observed to be
more limited.
Conclusions: PpIX fluorescence levels, as well as PDT cell kill effects on irradiation can be
significantly increased by pyridinone iron chelation, either via the addition of CP94 to the
administration of a PpIX precursor or alternatively via the newly synthesised combined PpIX prodrug
and siderophore, AP2-18. The effect of the latter compound appears to be at least equivalent to, if
not better than, the separate administration of its constituent parts, particularly when employing
MAL to destroy skin cancer cells. AP2-18 therefore warrants further detailed analysis, as it may have
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the potential to improve dermatological PDT outcomes in applications currently requiring
enhancement.The authors wish to thank Professor Hider (King’s College London, UK) for synthesising CP94. The
financial support of the Medical Research Council (MRC, UK) and Killing Cancer (UK) is very gratefully
acknowledged
Geodesic deviation in pp-wave spacetimes of quadratic curvature gravity
We write the equation of geodesic deviations in the spacetime of -waves
in terms of the Newman-Penrose scalars and apply it to study gravitational
waves in quadratic curvature gravity. We show that quadratic curvature gravity
-waves can have a transverse helicity-0 polarization mode and two
transverse helicity-2 general relativity-like wave polarizations. A concrete
example is given in which we analyze the wave polarizations of an exact
impulsive gravitational wave solution to quadratic curvature gravity.Comment: 16 pages, no figures, accepted in Physical Review
Coupling a Point-Like Mass to Quantum Gravity with Causal Dynamical Triangulations
We present a possibility of coupling a point-like, non-singular, mass
distribution to four-dimensional quantum gravity in the nonperturbative setting
of causal dynamical triangulations (CDT). In order to provide a point of
comparison for the classical limit of the matter-coupled CDT model, we derive
the spatial volume profile of the Euclidean Schwarzschild-de Sitter space glued
to an interior matter solution. The volume profile is calculated with respect
to a specific proper-time foliation matching the global time slicing present in
CDT. It deviates in a characteristic manner from that of the pure-gravity
model. The appearance of coordinate caustics and the compactness of the mass
distribution in lattice units put an upper bound on the total mass for which
these calculations are expected to be valid. We also discuss some of the
implementation details for numerically measuring the expectation value of the
volume profiles in the framework of CDT when coupled appropriately to the
matter source.Comment: 26 pages, 9 figures, updated published versio
Space-time extensions II
The global extendibility of smooth causal geodesically incomplete spacetimes
is investigated. Denote by one of the incomplete non-extendible causal
geodesics of a causal geodesically incomplete spacetime . First, it
is shown that it is always possible to select a synchronised family of causal
geodesics and an open neighbourhood of a final segment
of in such that is comprised by members of ,
and suitable local coordinates can be defined everywhere on
provided that does not terminate either on a tidal force tensor
singularity or on a topological singularity. It is also shown that if, in
addition, the spacetime, , is globally hyperbolic, and the
components of the curvature tensor, and its covariant derivatives up to order
are bounded on , and also the line integrals of the
components of the -order covariant derivatives are finite along the
members of ---where all the components are meant to be registered with
respect to a synchronised frame field on ---then there exists a
extension so that for each , which
is inextendible in , the image, , is
extendible in . Finally, it is also proved that
whenever does terminate on a topological singularity
cannot be generic.Comment: 42 pages, no figures, small changes to match the published versio
Deflection of Highly Relativistic Particles in a Gravitational Field
A novel approach to the calculation of the deflection of highly relativistic
test particles in gravitational fields is described. We make use of the
light-like boosts of the gravitational fields of the sources. Examples are
given of the deflection of highly relativistic particles in the Schwarzschild
and Kerr gravitational fields, in the field of a static, axially symmetric,
multipole source and in the field of a cosmic string. The deflection of
spinning particles is also discussed.Comment: 18 pages, 2 figures, accepted for publication in Classical and
Quantum Gravit
Using automated vegetation cover estimation from close-range photogrammetric point clouds to compare vegetation location properties in mountain terrain
In this paper we present a low-cost approach to mapping vegetation cover by means of high-resolution close-range terrestrial photogrammetry. A total of 249 clusters of nine 1 m2 plots each, arranged in a 3 × 3 grid, were set up on 18 summits in Mediterranean mountain regions and in the Alps to capture images for photogrammetric processing and in-situ vegetation cover estimates. This was done with a hand-held pole-mounted digital single-lens reflex (DSLR) camera. Low-growing vegetation was automatically segmented using high-resolution point clouds. For classifying vegetation we used a two-step semi-supervised Random Forest approach. First, we applied an expert-based rule set using the Excess Green index (ExG) to predefine non-vegetation and vegetation points. Second, we applied a Random Forest classifier to further enhance the classification of vegetation points using selected topographic parameters (elevation, slope, aspect, roughness, potential solar irradiation) and additional vegetation indices (Excess Green Minus Excess Red (ExGR) and the vegetation index VEG). For ground cover estimation the photogrammetric point clouds were meshed using Screened Poisson Reconstruction. The relative influence of the topographic parameters on the vegetation cover was determined with linear mixed-effects models (LMMs). Analysis of the LMMs revealed a high impact of elevation, aspect, solar irradiation, and standard deviation of slope. The presented approach goes beyond vegetation cover values based on conventional orthoimages and in-situ vegetation cover estimates from field surveys in that it is able to differentiate complete 3D surface areas, including overhangs, and can distinguish between vegetation-covered and other surfaces in an automated manner. The results of the Random Forest classification confirmed it as suitable for vegetation classification, but the relative feature importance values indicate that the classifier did not leverage the potential of the included topographic parameters. In contrast, our application of LMMs utilized the topographic parameters and was able to reveal dependencies in the two biomes, such as elevation and aspect, which were able to explain between 87% and 92.5% of variance
Estimation of the solubility parameters of model plant surfaces and agrochemicals: a valuable tool for understanding plant surface interactions
Background
Most aerial plant parts are covered with a hydrophobic lipid-rich cuticle, which is the interface between the plant organs and the surrounding environment. Plant surfaces may have a high degree of hydrophobicity because of the combined effects of surface chemistry and roughness. The physical and chemical complexity of the plant cuticle limits the development of models that explain its internal structure and interactions with surface-applied agrochemicals. In this article we introduce a thermodynamic method for estimating the solubilities of model plant surface constituents and relating them to the effects of agrochemicals.
Results
Following the van Krevelen and Hoftyzer method, we calculated the solubility parameters of three model plant species and eight compounds that differ in hydrophobicity and polarity. In addition, intact tissues were examined by scanning electron microscopy and the surface free energy, polarity, solubility parameter and work of adhesion of each were calculated from contact angle measurements of three liquids with different polarities. By comparing the affinities between plant surface constituents and agrochemicals derived from (a) theoretical calculations and (b) contact angle measurements we were able to distinguish the physical effect of surface roughness from the effect of the chemical nature of the epicuticular waxes. A solubility parameter model for plant surfaces is proposed on the basis of an increasing gradient from the cuticular surface towards the underlying cell wall.
Conclusions
The procedure enabled us to predict the interactions among agrochemicals, plant surfaces, and cuticular and cell wall components, and promises to be a useful tool for improving our understanding of biological surface interactions
Ecological Indicator Values for Europe (EIVE) 1.0
Aims: To develop a consistent ecological indicator value system for Europe for five of the main plant niche dimensions: soil moisture (M), soil nitrogen (N), soil reaction (R), light (L) and temperature (T). Study area: Europe (and closely adjacent regions). Methods: We identified 31 indicator value systems for vascular plants in Europe that contained assessments on at least one of the five aforementioned niche dimensions. We rescaled the indicator values of each dimension to a continuous scale, in which 0 represents the minimum and 10 the maximum value present in Europe. Taxon names were harmonised to the Euro+Med Plantbase. For each of the five dimensions, we calculated European values for niche position and niche width by combining the values from the individual EIV systems. Using T values as an example, we externally validated our European indicator values against the median of bioclimatic conditions for global occurrence data of the taxa. Results: In total, we derived European indicator values of niche position and niche width for 14,835 taxa (14,714 for M, 13,748 for N, 14,254 for R, 14,054 for L, 14,496 for T). Relating the obtained values for temperature niche position to the bioclimatic data of species yielded a higher correlation than any of the original EIV systems (r = 0.859). The database: The newly developed Ecological Indicator Values for Europe (EIVE) 1.0, together with all source systems, is available in a flexible, harmonised open access database. Conclusions: EIVE is the most comprehensive ecological indicator value system for European vascular plants to date. The uniform interval scales for niche position and niche width provide new possibilities for ecological and macroecological analyses of vegetation patterns. The developed workflow and documentation will facilitate the future release of updated and expanded versions of EIVE, which may for example include the addition of further taxonomic groups, additional niche dimensions, external validation or regionalisation
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