159 research outputs found
Analytical modeling of light transport in scattering materials with strong absorption
We have investigated the transport of light through slabs that both scatter
and strongly absorb, a situation that occurs in diverse application fields
ranging from biomedical optics, powder technology, to solid-state lighting. In
particular, we study the transport of light in the visible wavelength range
between and nm through silicone plates filled with YAG:Ce
phosphor particles, that even re-emit absorbed light at different wavelengths.
We measure the total transmission, the total reflection, and the ballistic
transmission of light through these plates. We obtain average single particle
properties namely the scattering cross-section , the absorption
cross-section , and the anisotropy factor using an analytical
approach, namely the P3 approximation to the radiative transfer equation. We
verify the extracted transport parameters using Monte-Carlo simulations of the
light transport. Our approach fully describes the light propagation in phosphor
diffuser plates that are used in white LEDs and that reveal a strong absorption
() up to , where is the
slab thickness, is the absorption mean free path. In
contrast, the widely used diffusion theory fails to describe this parameter
range. Our approach is a suitable analytical tool for industry, since it
provides a fast yet accurate determination of key transport parameters, and
since it introduces predictive power into the design process of white light
emitting diodes
Theory of Electric Field-Induced Photoluminescence Quenching in Disordered Molecular Solids
The dynamics of excitons in disordered molecular solids is studied
theoretically, taking into account migration between different sites,
recombination, and dissociation into free charge carriers in the presence of an
electric field. The theory is applied to interpret the results of electric
field-induced photoluminescence (PL) quenching experiments on molecularly doped
polymers by Deussen et al. [Chem. Phys. 207, 147 (1996)]. Using an
intermolecular dissociation mechanism, the dependence of the PL quenching on
the electric field strength and the dopant concentration, and the time
evolution of the transient PL quenching can be well described. The results
constitute additional proof of the distinct exciton dissociation mechanisms in
conjugated polymer blends and molecularly doped polymers.Comment: 4 pages RevTeX, 3 Postscript figure
Intrinsic hole mobility and trapping in a regio-regular poly(thiophene)
The transport properties of high-performance thin-film transistors (TFT) made
with a regio-regular poly(thiophene) semiconductor (PQT-12) are reported. The
room-temperature field-effect mobility of the devices varied between 0.004
cm2/V s and 0.1 cm2/V s and was controlled through thermal processing of the
material, which modified the structural order. The transport properties of TFTs
were studied as a function of temperature. The field-effect mobility is
thermally activated in all films at T<200 K and the activation energy depends
on the charge density in the channel. The experimental data is compared to
theoretical models for transport, and we argue that a model based on the
existence of a mobility edge and an exponential distribution of traps provides
the best interpretation of the data. The differences in room-temperature
mobility are attributed to different widths of the shallow localized state
distribution at the edge of the valence band due to structural disorder in the
film. The free carrier mobility of the mobile states in the ordered regions of
the film is the same in all structural modifications and is estimated to be
between 1 and 4 cm2/V s.Comment: 20 pages, 8 figure
Orientability and energy minimization in liquid crystal models
Uniaxial nematic liquid crystals are modelled in the Oseen-Frank theory
through a unit vector field . This theory has the apparent drawback that it
does not respect the head-to-tail symmetry in which should be equivalent to
-. This symmetry is preserved in the constrained Landau-de Gennes theory
that works with the tensor .We study
the differences and the overlaps between the two theories. These depend on the
regularity class used as well as on the topology of the underlying domain. We
show that for simply-connected domains and in the natural energy class
the two theories coincide, but otherwise there can be differences
between the two theories, which we identify. In the case of planar domains we
completely characterise the instances in which the predictions of the
constrained Landau-de Gennes theory differ from those of the Oseen-Frank
theory
Computation of Electrostatic Field near Three-Dimensional Corners and Edges
Theoretically, the electric field becomes infinite at corners of two and
three dimensions and edges of three dimensions. Conventional finite-element and
boundary element methods do not yield satisfactory results at close proximity
to these singular locations. In this paper, we describe the application of a
fast and accurate BEM solver (which usesexact analytic expressions to compute
the effect of source distributions on flatsurfaces) to compute the electric
field near three-dimensional corners and edges. Results have been obtained for
distances as close as 1 near the corner/edge and good agreement has been
observed between the present results and existing analytical solutions.Comment: Presented in International Conference on Computational and
Experimental Engineering and Sciences held at IIT Madras, Chennai, India,
during 1-6 December, 200
Dopant-induced crossover from 1D to 3D charge transport in conjugated polymers
The interplay between inter- and intra-chain charge transport in bulk
polythiophene in the hopping regime has been clarified by studying the
conductivity as a function of frequency (up to 3 THz), temperature and doping
level. We present a model which quantitatively explains the observed crossover
from quasi-one-dimensional transport to three-dimensional hopping conduction
with increasing doping level. At high frequencies the conductivity is dominated
by charge transport on one-dimensional conducting chains.Comment: 4 pages, 2 figure
AXY3 encodes a α-xylosidase that impacts the structure and accessibility of the hemicellulose xyloglucan in Arabidopsis plant cell walls
Xyloglucan is the most abundant hemicellulose in the walls of dicots such as Arabidopsis. It is part of the load-bearing structure of a plant cell and its metabolism is thought to play a major role in cell elongation. However, the molecular mechanism by which xyloglucan carries out this and other functions in planta is not well understood. We performed a forward genetic screen utilizing xyloglucan oligosaccharide mass profiling on chemically mutagenized Arabidopsis seedlings to identify mutants with altered xyloglucan structures termed axy-mutants. One of the identified mutants, axy3.1, contains xyloglucan with a higher proportion of non-fucosylated xyloglucan subunits. Mapping revealed that axy3.1 contains a point mutation in XYLOSIDASE1 (XYL1) known to encode for an apoplastic glycoside hydrolase releasing xylosyl residues from xyloglucan oligosaccharides at the non-reducing end. The data support the hypothesis that AXY3/XYL1 is an essential component of the apoplastic xyloglucan degradation machinery and as a result of the lack of function in the various axy3-alleles leads not only to an altered xyloglucan structure but also a xyloglucan that is less tightly associated with other wall components. However, the plant can cope with the excess xyloglucan relatively well as the mutant does not display any visible growth or morphological phenotypes with the notable exception of shorter siliques and reduced fitness. Taken together, these results demonstrate that plant apoplastic hydrolases have a larger impact on wall polymer structure and function than previously thought
The DISC (Diabetes in Social Context) Study-evaluation of a culturally sensitive social network intervention for diabetic patients in lower socioeconomic groups: a study protocol
<p>Abstract</p> <p>Background</p> <p>Compared to those in higher socioeconomic groups, diabetic patients in lower socioeconomic groups have less favourable metabolic control and experience more diabetes-related complications. They encounter specific barriers that hinder optimal diabetes self-management, including a lack of social support and other psychosocial mechanisms in their immediate social environments. <it>Powerful Together with Diabetes </it>is a culturally sensitive social network intervention specifically targeted to ethnic Dutch, Moroccan, Turkish, and Surinamese diabetic patients in lower socioeconomic groups. For ten months, patients will participate in peer support groups in which they will share experiences, support each other in maintaining healthy lifestyles, and learn skills to resist social pressure. At the same time, their significant others will also receive an intervention, aimed at maximizing support for and minimizing the negative social influences on diabetes self-management. This study aims to test the effectiveness of <it>Powerful Together with Diabetes</it>.</p> <p>Methods/Design</p> <p>We will use a quasi-experimental design with an intervention group (Group 1) and two comparison groups (Groups 2 and 3), N = 128 in each group. Group 1 will receive <it>Powerful Together with Diabetes</it>. Group 2 will receive <it>Know your Sugar</it>, a six-week group intervention that does not focus on the participants' social environments. Group 3 receives standard care only. Participants in Groups 1 and 2 will be interviewed and physically examined at baseline, 3, 10, and 16 months. We will compare their haemoglobin A1C levels with the haemoglobin A1C levels of Group 3. Main outcome measures are haemoglobin A1C, diabetes-related quality of life, diabetes self-management, health-related, and intermediate outcome measures. We will conduct a process evaluation and a qualitative study to gain more insights into the intervention fidelity, feasibility, and changes in the psychosocial mechanism in the participants' immediate social environments.</p> <p>Discussion</p> <p>With this study, we will assess the feasibility and effectiveness of a culturally sensitive social network intervention for lower socioeconomic groups. Furthermore, we will study how to enable these patients to optimally manage their diabetes. This trial is registered in the Dutch Trial Register: NTR1886</p
Discovery of small molecule inhibitors of xyloglucan endotransglucosylase (XET) activity by high-throughput screening
AbstractSmall molecules (xenobiotics) that inhibit cell-wall-localised enzymes are valuable for elucidating the enzymes’ biological roles. We applied a high-throughput fluorescent dot-blot screen to search for inhibitors of Petroselinum xyloglucan endotransglucosylase (XET) activity in vitro. Of 4216 xenobiotics tested, with cellulose-bound xyloglucan as donor-substrate, 18 inhibited XET activity and 18 promoted it (especially anthraquinones and flavonoids). No compounds promoted XET in quantitative assays with (cellulose-free) soluble xyloglucan as substrate, suggesting that promotion was dependent on enzyme–cellulose interactions. With cellulose-free xyloglucan as substrate, we found 22 XET-inhibitors – especially compounds that generate singlet oxygen (1O2) e.g., riboflavin (IC50 29μM), retinoic acid, eosin (IC50 27μM) and erythrosin (IC50 36μM). The riboflavin effect was light-dependent, supporting 1O2 involvement. Other inhibitors included tannins, sulphydryl reagents and triphenylmethanes. Some inhibitors (vulpinic acid and brilliant blue G) were relatively specific to XET, affecting only two or three, respectively, of nine other wall-enzyme activities tested; others [e.g. (−)-epigallocatechin gallate and riboflavin] were non-specific. In vivo, out of eight XET-inhibitors bioassayed, erythrosin (1μM) inhibited cell expansion in Rosa and Zea cell-suspension cultures, and 40μM mycophenolic acid and (−)-epigallocatechin gallate inhibited Zea culture growth. Our work showcases a general high-throughput strategy for discovering wall-enzyme inhibitors, some being plant growth inhibitors potentially valuable as physiological tools or herbicide leads
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