ADVANCED ENGINEERING MATERIALS, Issue 6 2009
Melissa A. Sharp
Abstract Small-angle neutron scattering (SANS) has over the years proved to be a popular technique to investigate a variety of problems in materials science, since the length scales probed by this technique (1,100,nm) are ideal for many systems. However, there are a number of problems where the length scale of interest is larger. In order to study such systems it is possible to combine SANS with ultra-small-angle neutron scattering (USANS). This allows the study of structures from a few nanometers up to 50,µm. Here it is shown how the combination of SANS and USANS has allowed for a wider range of problems within materials science and polymer science to be solved. [source]

Multi-scale Microstructure Characterization of Solid Oxide Fuel Cell Assemblies With Ultra Small-Angle X-Ray Scattering,

ADVANCED ENGINEERING MATERIALS, Issue 6 2009
Andrew J. Allen
Ultra small angle X-ray scattering with synchrotron radiation is applied to assess the pore space of a highly complex solid oxide fuel cell assembly. The instrument permits to record scattering curves covering a size range from 1,nm to several ,m in a fine step width of 15,,m. [source]

Waveguide Sensors: Use of Reversal Nanoimprinting of Nanoparticles to Prepare Flexible Waveguide Sensors Exhibiting Enhanced Scattering of the Surface Plasmon Resonance (Adv. Funct.

ADVANCED FUNCTIONAL MATERIALS, Issue 11 2010
Mater.
The image displays a flexible surface plasmon resonance (SPR)-based waveguide sensor prepared by directly imprinting metal nanoparticles onto flexible plates, as presented by H.-L. Chen et al. on page 1742. The metal nanoparticles could scatter the evanescent wave and the guiding mode waves from the SPR-based waveguide simultaneously. The scattering signal underwent a distinguishable red-shift when the target molecules bound to the particles. [source]

Use of Reversal Nanoimprinting of Nanoparticles to Prepare Flexible Waveguide Sensors Exhibiting Enhanced Scattering of the Surface Plasmon Resonance

ADVANCED FUNCTIONAL MATERIALS, Issue 11 2010
Dehui Wan
Abstract A flexible surface plasmon resonance (SPR)-based scattering waveguide sensor is prepared by directly imprinting hollow gold nanoparticles (NPs) and solid gold NPs onto flexible polycarbonate (PC) plates,without any surface modification,using a modified reversal nanoimprint lithography technology. Controlling the imprinting conditions, including temperature and pressure, allows for the fine adjustment of the depths of the embedded metal NPs and their SPR properties. This patterning approach exhibits a resolution down to the submicrometer level. A 3D finite-difference time domain simulation is used to examine the optical behavior of light propagating parallel to the air/substrate interface within the near-field regime. Consistent with the simulations, almost an order of magnitude enhancement in the scattering signal after transferring the metal NPs from the glass mold to the PC substrate is obtained experimentally. The enhanced signal is attributed to the particles' strong scattering of the guiding-mode waves (within the waveguide) and the evanescent wave (above the waveguide) simultaneously. Finally, the imprinting conditions are optimized to obtain a strongly scattering bio/chemical waveguide sensor. [source]

Scattering of charged tensor bosons in gauge and superstring theories

FORTSCHRITTE DER PHYSIK/PROGRESS OF PHYSICS, Issue 7-9 2010
I. Antoniadis
Abstract We calculate the leading-order scattering amplitude of one vector and two tensor gauge bosons in a recently proposed non-Abelian tensor gauge field theory and open superstring theory. The linear in momenta part of the superstring amplitude has identical Lorentz structure with the gauge theory, while its cubic in momenta part can be identified with an effective Lagrangian which is constructed using generalized non-Abelian field strength tensors. [source]

Fabrication of a Macroporous Microwell Array for Surface-Enhanced Raman Scattering

ADVANCED FUNCTIONAL MATERIALS, Issue 19 2009
Martina Zamuner
Abstract Here, a colloidal templating procedure for generating high-density arrays of gold macroporous microwells, which act as discrete sites for surface-enhanced Raman scattering (SERS), is reported. Development of such a novel array with discrete macroporous sites requires multiple fabrication steps. First, selective wet-chemical etching of the distal face of a coherent optical fiber bundle produces a microwell array. The microwells are then selectively filled with a macroporous structure by electroless template synthesis using self-assembled nanospheres. The fabricated arrays are structured at both the micrometer and nanometer scale on etched imaging bundles. Confocal Raman microscopy is used to detect a benzenethiol monolayer adsorbed on the macroporous gold and to map the spatial distribution of the SERS signal. The Raman enhancement factor of the modified wells is investigated and an average enhancement factor of 4,×,104 is measured. This demonstrates that such nanostructured wells can enhance the local electromagnetic field and lead to a platform of ordered SERS-active micrometer-sized spots defined by the initial shape of the etched optical fibers. Since the fabrication steps keep the initial architecture of the optical fiber bundle, such ordered SERS-active platforms fabricated onto an imaging waveguide open new applications in remote SERS imaging, plasmonic devices, and integrated electro-optical sensor arrays. [source]

Scattering of elastic waves in media with a random distribution of fluid-filled cavities: theory and numerical modelling

GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2004
Tae-Kyung Hong
SUMMARY The propagation of elastic waves is modelled in media with a random distribution of fluid-filled circular cavities, which display high physical impedance in contrast to background media. Theoretical attenuation expressions for media with circular cavities, which may be filled with any material (e.g. vacuum, fluid, elastic materials), are formulated using an ensemble treatment for first-order transmitted waves. Numerical estimates of scattering attenuation rates agree with the theoretical results well. The scattering attenuations (Q,1) are proportional to the scale of cavities and the number density (,, number of cavities per area in a medium). The decrease of primary energy with the size of cavities does not result in the increase of coda energy owing to the increase of both purely backscattered waves from cavities and the trapped waves inside cavities. Scattering properties (e.g. scattering attenuation, coda energy, phase fluctuation of primary waves) in media with randomly distributed cavities are very different from those in stochastic random media. It appears that heterogeneities with high impedance in the earth may not be well represented with stochastic random heterogeneities. [source]

Chemical Nanosensors Based on Composite Molecularly Imprinted Polymer Particles and Surface-Enhanced Raman Scattering

ADVANCED MATERIALS, Issue 21 2010
Marc Bompart
Chemical nanosensors with a submicrometer core,shell composite design, based on a polymer core, a molecularly imprinted polymer (MIP) shell for specific analyte recognition, and an interlayer of gold nanoparticles for signal amplification, are described. SERS measurements on single nanosensors yield detection limits of 10,7,M for the , -blocker propranolol, several orders of magnitude lower than on plain MIP spheres. [source]

Highly Surface-roughened "Flower-like" Silver Nanoparticles for Extremely Sensitive Substrates of Surface-enhanced Raman Scattering

ADVANCED MATERIALS, Issue 45 2009
Hongyan Liang
Abstract Surface-enhanced Raman scattering (SERS) is a new optical spectroscopic analysis technique with potential for highly sensitive detection of molecules. Recently, many efforts have been made to find SERS substrates with high sensitivity and reproducibility. In this Research News article, we provide a focused review on the synthesis of monodispersed silver particles with a novel, highly roughened, "flower-like" morphology by reducing silver nitrate with ascorbic acid in aqueous solutions. The nanometer-scale surface roughness of the particles can provide several hot spots on a single particle, which significantly increases SERS enhancement. The incident polarization-dependent SERS of individual particles is also studied. Although the different "hot spots" on a single particle can have a strong polarization dependency, the total Raman signals from an individual particle usually have no obvious polarization dependency. Moreover, these flower-like silver particles can be measured by SERS with high enhancement several times, which indicates the high stability of the hot spots. Hence, the flower-like silver particles here can serve as highly sensitive and reproducible SERS substrates. [source]

XIIIth International Conference on Small-Angle Scattering

JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2007
Yoshiyuki Amemiya
First page of article [source]

The new V12 ultra-small-angle neutron scattering and tomography instrument at the Hahn,Meitner Institut

JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2007
M. Strobl
The new V12 instrument at the Hahn,Meitner Institute in Berlin is a multiple setup combining several techniques to investigate the internal structure of bulk samples. It consists of two double-crystal diffractometers (DCDs) and an attenuation tomography device operating with monochromatic neutrons. The three instrument parts can be used independently at the same time. The DCDs are mainly used in the ultra-small-angle neutron scattering (USANS) regime, where they overlap the accessible range of small-angle neutron scattering instruments, while tomographic methods collect real-space information on a macroscopic scale. Together they enable structural investigations over six orders of magnitude (50,nm to 5,cm). Scattering and tomographic methods can even be combined by means of diffraction and scattering-enhanced imaging. The sample environment can be varied over a large range of temperatures and pressures for USANS measurements and a polarized USANS option is available. [source]

The International Conference on Small-Angle Scattering , past and future

JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3-1 2003
Aldo F. Craievich
First page of article [source]

XIIth International Conference on Small-Angle Scattering

JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3-1 2003
Alvise Benedetti
First page of article [source]

XIth International Conference on Small-Angle Scattering

JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3-1 2000
Dieter K. Schneider
First page of article [source]

Taphonomy of Child-Sized Remains: A Study of Scattering and Scavenging in Virginia, USA,

JOURNAL OF FORENSIC SCIENCES, Issue 3 2006
Robert J. Morton M.S.
ABSTRACT: Child-sized pig carcasses (Sus scrofa) were placed in surface deposit and buried scenarios in a wooded area of Virginia from May 1998 through December 2000, to examine the taphonomic effects of decompositional changes, predator scavenging, and the extent of remains scattering. Changes were observed through on-site examination, charting of remains, and recorded video imaging. Analysis of data revealed that utilization of corpses as food sources by vertebrates was dependent upon invertebrate colonization. Vertebrates avoided feeding on the corpses while invertebrate colonization was active, and would feed before invertebrates successfully colonized a corpse, or would wait until the invertebrate populations migrated away from the corpse. Among vertebrates, there was no apparent succession order for the animals utilizing the remains as a food source. Different vertebrates would feed at different times based upon diurnal or nocturnal predilection. Analysis noted an accidental cooperative relationship between the invertebrates and vertebrates scavenging on the corpses. Certain vertebrates gained access to the internal tissues by utilizing openings in the corpses caused by invertebrate and other vertebrate scavenging. Alternately, carrion-frequenting insects were afforded access to previously inaccessible colonization sites as a result of scavenging vertebrate activities. [source]

Overview and new developments in softer X-ray (2Å < , < 5Å) protein crystallography

JOURNAL OF SYNCHROTRON RADIATION, Issue 1 2004
John R. Helliwell
New methodologies with synchrotron radiation and X-ray free electron lasers (XFELs) in structural biology are being developed. Recent trends in harnessing softer X-rays in protein crystallography for phase determination are described. These include reference to a data-collection test at 2.6 Å wavelength with a lysozyme crystal on SRS station 7.2 (Helliwell, 1983) and also use of softer X-rays (2,Å wavelength) to optimise f," at the xenon L1 absorption edge in the Single Isomorphous Replacement Optimised Anomalous Scattering ('SIROAS') structure determination of apocrustacyanin A1 with four, partially occupied, xenon atoms (Cianci et al., 2001; Chayen et al., 2000). The hand of the protein was determined using the f," enhanced sulphur anomalous signal from six disulphides in the protein dimer of 40,kDa. In a follow-up study the single wavelength xenon L1 -edge f," optimised data set alone was used for phase determination and phase improvement by solvent flattening etc. (CCP4 DM) (Olczak et al., 2003). Auto-tracing of the protein was feasible but required additional diffraction data at higher resolution. This latter could be avoided in future by using improved tilted detector settings during use of softer X-rays, i.e. towards back-scattering recording (Helliwell, 2002). The Olczak et al. study has already led to optimisation of the new SRS beamline MPW,MAD,10 (see www.nwsgc.ac.uk) firstly involving the thinning of the beryllium windows as much as possible and planning for a MAR Research tilted detector `desk top beamline' geometry. Thus the use of softer, i.e. 2 to 3,Å wavelength range, X-rays will allow optimisation of xenon and iodine L -edge f," and enhancing of sulphur f," signals for higher throughput protein crystallography. Softer X-rays utilisation in protein crystallography includes work done on SRS bending-magnet station 7.2 in the early 1980s by the author as station scientist (Helliwell, 1984). In the future development of XFELs these softer X-ray wavelengths could also be harnessed and relax the demands to some extent on the complexity and cost of an XFEL. Thus, by use of say 4,Å XFEL radiation and use of a back-scattering geometry area detector the single molecule molecular transform could be sampled to a spatial resolution of 2,Å, sufficient, in principle, for protein model refinement (Miao et al., 1999). Meanwhile, Miao et al. (2003) report the first experimental recording of the diffraction pattern from intact Escherichia coli bacteria using coherent X-rays, with a wavelength of 2,Å, at a resolution of 30,nm and a real-space image constructed. The new single-particle X-ray diffraction-imaging era has commenced. [source]

Determination of Scattering and Absorption Coefficients for Plasma-Sprayed Yttria-Stabilized Zirconia Thermal Barrier Coatings

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2008
Jeffrey I. Eldridge
Prediction of radiative transport through translucent thermal barrier coatings (TBCs) can only be performed if the scattering and absorption coefficients and index of refraction of the TBC are known. To date, very limited information on these coefficients, which depend on both the coating composition and the microstructure, has been available for the very commonly utilized plasma-sprayed 8 wt% yttria-stabilized zirconia (8YSZ) TBCs. In this work, the scattering and absorption coefficients of freestanding plasma-sprayed 8YSZ coatings were determined from room-temperature normal-incidence directional-hemispherical reflectance and transmittance spectra over the wavelength range from 0.8 to 7.5 ,m. Spectra were collected over a wide range of coating thickness from 60 to almost 900 ,m. From the reflectance and transmittance spectra, the scattering and absorption coefficients as a function of wavelength were obtained by fitting the reflectance and transmittance values predicted by a four flux model to the experimentally measured values at all measured 8YSZ thicknesses. While the combined effects of absorption and scattering were shown in general to exhibit a nonexponential dependence of transmittance on specimen thickness, it was shown that for sufficiently high absorption and optical thickness, an exponential dependence becomes a good approximation. In addition, the implications of the wavelength dependence of the plasma-sprayed 8YSZ scattering and absorption coefficients on (1) obtaining accurate surface-temperature pyrometer measurements and on (2) applying mid-infrared reflectance to monitor TBC delamination are discussed. [source]

Time-Resolved Small-Angle Neutron Scattering as a Tool for Studying Controlled Release from Liposomes using Polymer-Enzyme Conjugates

MACROMOLECULAR RAPID COMMUNICATIONS, Issue 19 2010
Elaine L. Ferguson
Abstract The action of phospholipase A2 (PLA2) on 1,2-dipalmitoyl- sn -glycero-3-phosphocholine (DPPC) liposomes (vesicles) , an integral component in the polymer enzyme liposome therapy (PELT) mechanism (R. Duncan et al., J. Controlled Release2001, 74, 135) for the controlled delivery of poorly soluble therapeutic molecules within liposomes , may be "masked" by conjugation to the biodegradable polymer dextrin and subsequently regenerated by the endogenous enzyme , -amylase that degrades the dextrin; that is, incorporating the so-called polymer-unmasked-masked protein therapy (PUMPT) approach (R. Duncan, et al. Biomacromolecules2008, 9, 1146). Small-angle neutron scattering (SANS) has been used to quantify the detailed structure of DPPC liposomes and any perturbation in that structure induced by the presence of PLA2 in native, "masked" (dextrin,PLA2 conjugate) and an in situ , -amylase-unmasked form. A time-dependent degradation of the vesicular structure was observed for the two active PLA2 cases, but not for the masked case. This study demonstrates that the PLA2 -induced hydrolysis of the DPPC , and the associated rupture of the liposome and the release of the enclosed material , may be controlled through masking with dextrin. Accordingly, the viability of using such a combinatorial nanomedicine approach as a general route for the controlled delivery of poorly soluble therapeutic molecules is shown. [source]

Submicron Polymer Gratings: Optical Diffraction and Spontaneous Brillouin Scattering

MACROMOLECULAR RAPID COMMUNICATIONS, Issue 9 2006
Wei Cheng
Abstract Summary: Brillouin light scattering (BLS) from submicron-size patterned polyurethane (PU) films was found to display rich spectral features. Their identification allows the determination of the mechanical properties of the PU and the characterization of the periodicity and the coherence of the structure. A temperature-dependent study demonstrates that BLS is a sensitive tool to monitor changes of the mechanical properties and/or of the morphology. (a) Scheme of the sample structure and the scattering geometry, (b) SEM top view of the PU features. [source]

Polycaprolactone- b -Poly(ethylene oxide) Biocompatible Micelles as Drug Delivery Nanocarriers: Dynamic Light Scattering and Fluorescence Experiments

MACROMOLECULAR SYMPOSIA, Issue 1 2005
Cristiano Giacomelli
Abstract Summary: Dynamic light scattering (DLS) and fluorescence experiments were carried out to study PCL44 - b -PEO114 biocompatible micelles used as nanocarriers in drug delivery. Micelles prepared by a simple procedure (THF removal under nitrogen flow) exhibited a narrow size distribution with an average diameter of 100 nm. For micelles containing a hydrophobic model compound (pyrene) within the PCL core, a smaller average micellar size of 80 nm was observed, with a simultaneous broadening in the size distribution profile. In parallel to DLS results, fluorescence experiments showed evidence of pyrene encapsulation, and that the onset of the micellization process occurs at approximately 10/90 (v/v) THF/water mixtures in the case of PCL44 - b -PEO114 polymer. [source]

Correlations and Fluctuations of Charged Colloids as Determined by Anomalous Small-Angle X-Ray Scattering

MACROMOLECULAR THEORY AND SIMULATIONS, Issue 3 2006
Arben Jusufi
Abstract Summary: We performed molecular dynamics simulation of a charged colloidal particle with explicit counterions. Our work provides a direct comparison between simulations and ASAXS-experiments, offering insight into the counterion distribution of charged colloidal suspensions. We give a detailed constitution of the appearing scattering terms with their physical meaning. It is shown that the cross-correlation between a macroion and its counterions gives the meanfield approximation of the counterion density even if the counterion system is highly fluctuating. Furthermore, it is shown that cross-correlations can be negative due to oscillations of the density amplitudes of the macroion and counterions and, therefore, must be distinguished from other scattering contributions. These oscillations become more pronounced if the counterions exhibit a fixed shape and if the size of the macroion and that of the counterion system are different. Simulation sanpshot of a charged colloid (big central sphere) with counterions (small spheres). [source]

Scattering and absorption of electromagnetic waves on a plane with hemispherical bosses

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 11 2007
Xiaoxiong Gu
Abstract We apply multiple scattering equations to study the scattering of electromagnetic waves on a perfectly conducting plane surface with a random dense distribution of hemispherical bosses. We derive a multipole solution up to third order to analyze close range interactions between nearby bosses. Results show significant improvement of accuracy compared with the traditional dipole approximation solution. Absorption on a lossy embossed surface is obtained from the field solution for the perfectly conducting surface. The surface current and absorption enhancement factor are further computed numerically. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 2681,2686, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22855 [source]

Dynamic Light Scattering for the Characterization of Polydisperse Fractal Systems: I. Simulation of the Diffusional Behavior

PARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 1 2008
Uwe Kätzel
Abstract Dynamic light scattering (DLS) is a method used to size nanoscale and submicron particles by measuring their thermal motion (diffusion) in a liquid environment. The measured diffusion coefficients are related to the hydrodynamic particle size via the Stokes-Einstein equation. This paper addresses the application of DLS for the characterization of diluted suspensions of pyrogenic silica, which consist of polydisperse fractal-like aggregates composed of sintered spherical primary particles. Simulations are employed to establish a relationship between the structural properties of the aggregates and their diffusional behavior. Therefore, an algorithm is developed that enables the generation of aggregates with a tunable fractal dimension and an arbitrary number of primary particles. The results provide evidence that the hydrodynamic radii show a different scaling compared to the structural radius of gyration, which is of great relevance for the interpretation of DLS results. In addition, the influence of rotational diffusion has to be accounted for in the measurements. [source]

Determination of Size Distributions of Concentrated Polymer Particles Embedded in a Solid Polymer Matrix

PARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 1 2008
Ezequiel R. Soulé
Abstract In this work we present the results obtained from the size characterization of polymer particles embedded in a solid polymer matrix using Static Light Scattering (SLS) and Scanning Electron Microscopy (SEM). The analyzed samples are the result of the solution polymerization of isobornyl methacrylate (IBoMA) in polyisobutylene (PIB) at complete conversion. Induced by polymerization, the system undergoes phase separation. As a result, spherical micron sized particles rich in PIB are formed. At the end of the polymerization, the particles become trapped in a solid polymer matrix rich in Poly-IBoMA. Size, concentration, and refractive index, make the resulting particle system scatter light under the Rayleigh-Debye-Gans (RDG) regime with interparticle interference. For Light Scattering (LS) characterization the samples are measured with a Flat Cell Static Light Scattering (FCSLS) apparatus, in which the reaction takes place. The resulting SLS spectra are analyzed using the Percus-Yevick approximation to model the interference effects. The local monodisperse approximation is used to consider polydispersity in the particle sizes. The estimated particle size distributions agree well with the measurements from SEM. In this work a concentrated particle system that naturally scatters light according to the RDG regime has been fully characterized in terms of its particle size distribution. This work, against the opinion of other authors, shows the feasibility of measuring still particles using a one dimensional array of light detectors. [source]

Resolving Concentrated Particle Size Mixtures Using Dynamic Light Scattering

PARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 3 2007
Michael Kaszuba
Abstract Dynamic light scattering (DLS) is a technique used for measuring the size of molecules and particles undergoing Brownian motion by observing time-dependent fluctuations in the intensity of scattered light. The measurement of samples using conventional DLS instrumentation is limited to low concentrations due to the onset of a phenomenon called multiple scattering. The problems of multiple scattering have been addressed in a light scattering instrument incorporating non- invasive backscatter optics (NIBS). This novel optic arrangement maximizes the detection of scattered light while maintaining signal quality and allows for measurements of turbid samples. This paper discusses the ability of backscatter detection to accurately determine particle sizes at 1,%w/v sample concentrations and demonstrates the correct resolution of different size populations using a series of latex standard mixtures with known volume ratios. The concentration of 1,%w/v is much higher than can be measured on conventional dynamic light scattering instruments. [source]

Particle Size Distributions from Static Light Scattering with Regularized Non-Negative Least Squares Constraints

PARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 6 2006
Alejandro R. Roig
Abstract Simulated data from static light scattering produced by several particle size distributions (PSD) of spherical particles in dilute solution is analyzed with a regularized non-negative least squares method (r-NNLS). Strong fluctuations in broad PSD's obtained from direct application of NNLS are supressed through an averaging procedure, as introduced long ago in the inversion problem in dynamic light scattering. A positive correlation between the best PSD obtained from several averaging schemes and the condition number of the respective data transfer matrices was obtained. The performance of the method is found to be similar to that of constrained regularization (CONTIN), which uses also NNLS as a starting solution, but incorporates another regularizing strategy. [source]

Measurement of Lens Protein Aggregation in Vivo Using Dynamic Light Scattering in a Guinea Pig/UVA Model for Nuclear Cataract

PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 6 2008
M. Francis Simpanya
The role of UVA radiation in the formation of human nuclear cataract is not well understood. We have previously shown that exposing guinea pigs for 5 months to a chronic low level of UVA light produces increased lens nuclear light scattering and elevated levels of protein disulfide. Here we have used the technique of dynamic light scattering (DLS) to investigate lens protein aggregation in vivo in the guinea pig/UVA model. DLS size distribution analysis conducted at the same location in the lens nucleus of control and UVA-irradiated animals showed a 28% reduction in intensity of small diameter proteins in experimental lenses compared with controls (P < 0.05). In addition, large diameter proteins in UVA-exposed lens nuclei increased five-fold in intensity compared to controls (P < 0.05). The UVA-induced increase in apparent size of lens nuclear small diameter proteins was three-fold (P < 0.01), and the size of large diameter aggregates was more than four-fold in experimental lenses compared with controls. The diameter of crystallin aggregates in the UVA-irradiated lens nucleus was estimated to be 350 nm, a size able to scatter light. No significant changes in protein size were detected in the anterior cortex of UVA-irradiated lenses. It is presumed that the presence of a UVA chromophore in the guinea pig lens (NADPH bound to zeta crystallin), as well as traces of oxygen, contributed to UVA-induced crystallin aggregation. The results indicate a potentially harmful role for UVA light in the lens nucleus. A similar process of UVA-irradiated protein aggregation may take place in the older human lens nucleus, accelerating the formation of human nuclear cataract. [source]

Structural Studies of Bleached Melanin by Synchrotron Small-angle X-ray Scattering,

PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 2 2003
Kenneth C. Littrell
ABSTRACT Small-angle X-ray scattering was used to measure the effects of chemical bleaching on the size and morphology of tyrosine-derived synthetic melanin dispersed in aqueous media. The average size as measured by the radius of gyration of the melanin particles in solution, at neutral to mildly basic pH, decreases from 16.5 to 12.5 Å with increased bleaching. The melanin particles exhibit scattering characteristic of sheet-like structures with a thickness of approximately 11 Å at all but the highest levels of bleaching. The scattering data are well described by the form factor for scattering from a pancake-like circular cylinder. These data are consistent with the hypothesis that unbleached melanin, at neutral to mildly basic pH, is a planar aggregate of 6- to 10-nm-sized melanin protomolecules, hydrogen bonded through their quinone and phenolic perimeters. The observed decrease in melanin particle size with increased bleaching is interpreted as evidence for deaggregation, most probably the result of oxidative disruption of hydrogen bonds and an increase in the number of charged, carboxylic acid groups, whereby the melanin aggregates disassociate into units composed of decreasing numbers of protomolecules. [source]

Quasi-localized low-frequency vibrational modes of disordered solids: Study by single-molecule spectroscopy

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 15 2004
A. V. Naumov
Editor's Choice of this issue of physica status solidi (b) is the article [1] by Andrei V. Naumov et al. This paper is Part II (Part I see [2]) of a study on elementary excitations in glasses, presented at the 11th International Conference on Phonon Scattering in Condensed Matter, St. Petersburg, 25,30 July 2004. For his outstanding talk, Naumov received the new physica status solidi Young Researcher Award which was bestowed for the first time at this conference. The cover picture is a sketch of a glass with a single impurity molecule and one hypothetical quasi-localized vibrational mode. The broadening and shift of the chromophore spectral line are caused by the interaction with this mode. Andrei V. Naumov is senior scientific researcher and deputy head of the Molecular Spectroscopy Department of the Institute of Spectroscopy, Troitsk. His main research interests are experimental and theoretical studies of low-temperature dynamics of amorphous solids (glasses, polymers etc.) via high resolution laser selective spectroscopy techniques. The second Editor's Choice is an article by E. A. Eliseev and M. D. Glinchuk [3]. Eugene A. Eliseev is scientific researcher at the Frantsevich Institute for Problems of Materials Science of the Ukrainian National Academy of Sciences, Kiev. His research areas are the theory of size and correlation effects in ferroelectric materials as well as modelling of disordered ferroelectrics properties. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Spontaneous stratification of InGaN layers and its influence on optical properties

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2009
Z. Liliental-Weber
Abstract Transmission Electron Microscopy, high resolution X-ray diffraction and reciprocal space maps, Rutherford Back Scattering and photoluminescence were applied to study InGaN layers grown by MOCVD with increasing layer thickness (100 nm to 1000 nm) and nominally constant In concentration of 10%. Spontaneous stratification of the layer has been found. A strained layer with lower than nominal In content was found in direct contact with the underlying GaN followed by relaxed layers with a nominal or higher In concentration. A high density of randomly distributed stacking faults as well as domains with cubic structure and closely distributed stacking faults (polytype-like) were present in the thicker layers. Strong corrugation of the thicker sample surface was observed. The appearance of multiple photoluminescence line positions was related not only to the spontaneously formed layers with different In content, but also to the structural planar defects formed in the thicker layers. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]