Effect of excitation wavelength on the Raman spectroscopy of the porcine photoreceptor layer from the area centralis.

Raman microscopy, based upon the inelastic scattering (Raman) of light by molecular species, has been applied as a specific structural probe in a wide range of biomedical samples. The purpose of the present investigation was to assess the potential of the technique for spectral characterization of the porcine outer retina derived from the area centralis, which contains the highest proportion of cone:rod cell ratio in the pig retina. METHODS: Retinal cross-sections, immersion-fixed in 4% (w/v) PFA and cryoprotected, were placed on salinized slides and air-dried prior to direct Raman microscopic analysis at three excitation wavelengths, 785 nm, 633 nm, and 514 nm. RESULTS: Raman spectra of each of the photoreceptor inner and outer segments (PIS, POS) and of the outer nuclear layer (ONL) of the retina acquired at 785 nm were dominated by vibrational features characteristic of proteins and lipids. There was a clear difference between the inner and outer domains in the spectroscopic regions, amide I and III, known to be sensitive to protein conformation. The spectra recorded with 633 nm excitation mirrored those observed at 785 nm excitation for the amide I region, but with an additional pattern of bands in the spectra of the PIS region, attributed to cytochrome c. The same features were even more enhanced in spectra recorded with 514 nm excitation. A significant nucleotide contribution was observed in the spectra recorded for the ONL at all three excitation wavelengths. A Raman map was constructed of the major spectral components found in the retinal outer segments, as predicted by principal component analysis of the data acquired using 633 nm excitation. Comparison of the Raman map with its histological counterpart revealed a strong correlation between the two images. CONCLUSIONS: It has been demonstrated that Raman spectroscopy offers a unique insight into the biochemical composition of the light-sensing cells of the retina following the application of standard histological protocols. The present study points to the considerable promise of Raman microscopy as a component-specific probe of retinal tissue.

Conformations, vibrational frequencies and Raman intensities of short-chain fatty acid methyl esters using DFT with 6-31G(d) and Sadlej pVTZ basis sets

Density functional calculations, using B3LPY/6-31G(d) methods, have been used to investigate the conformations and vibrational (Raman) spectra of three short-chain fatty acid methyl esters (FAMEs) with the formula CnH2nO2 (n = 3-5). In all three FAMEs, the lowest energy conformer has a simple 'all-trans' structure but there are other conformers, with different torsions about the backbone, which lie reasonably close in energy to the global minimum. One result of this is that the solid samples we studied do not appear to consist entirely of the lowest energy conformer. Indeed, to account for the 'extra' bands that were observed in the Raman data but were not predicted for the all-trans conformer, it was necessary to add-in contributions from other conformers before a complete set of vibrational assignments could be made. Provided this was done, the agreement between experimental Raman frequencies and 6-31G(d) values (after scaling) was excellent, RSD = 12.6 cm(-1). However, the agreement between predicted and observed intensities was much less satisfactory. To confirm the validity of the approach followed by the 6-3 1 G(d) basis set, we used a larger basis set, Sadlej pVTZ, and found that these calculations gave accurate Raman intensities and simulated spectra (summed from two different conformers) that were in quantitative agreement with experiment. In addition, the unscaled Sadlej pVTZ, and the scaled 6-3 1 G(d) calculations gave the same vibrational mode assignments for all bands in the experimental data. This work provides the foundation for calculations on longer-chain FAMEs (which are closer to those found as triglycerides in edible fats and oils) because it shows that scaled 6-3 1 G(d) calculations give equally accurate frequency predictions, and the same vibrational mode assignments, as the much more CPU-expensive Sadlej pVTZ basis set calculations.

Roche tomography of cataclysmic variables - IV. Star-spots and slingshot prominences on BV Cen

We present Roche tomograms of the G5-G8 IV/V secondary star in the long-period cataclysmic variable BV Cen reconstructed from Magellan Inamori Kyocera Echelle spectrograph echelle data taken on the Magellan Clay 6.5-m telescope. The tomograms show the presence of a number of large, cool star-spots on BV Cen for the first time. In particular, we find a large high-latitude spot which is deflected from the rotational axis in the same direction as seen on the K3-K5 IV/V secondary star in the cataclysmic variable AE Aqr. BV Cen also shows a similar relative paucity of spots at latitudes between 40° and 50° when compared with AE Aqr. Furthermore, we find evidence for an increased spot coverage around longitudes facing the white dwarf which supports models invoking star-spots at the L1 point to explain the low states observed in some cataclysmic variables. In total, we estimate that some 25 per cent of the Northern hemisphere of BV Cen is spotted. We also find evidence for a faint, narrow, transient emission line with characteristics reminiscent of the peculiar low-velocity emission features observed in some outbursting dwarf novae. We interpret this feature as a slingshot prominence from the secondary star and derive a maximum source size of 75000 km and a minimum altitude of 160000 km above the orbital plane for the prominence. The entropy landscape technique was applied to determine the system parameters of BV Cen. We find M1 = 1.18 +/-0.280.16Msolar and M2 = 1.05 +/-0.230.14Msolar and an orbital inclination of i = 53° +/- 4° at an optimal systemic velocity of ? = -22.3 km s-1. Finally, we also report on the previously unknown binarity of the G5IV star HD 220492.

Perturbed frequency-selective surfaces fabricated on large thin polymer membranes for multiband infrared applications

The design, fabrication, and characterization of single-screen perturbed frequency-selective surfaces (FSS) at infrared frequencies for single and multiband applications are reported. Single-band FSS based on parallel strips have been perturbed by decreasing the length of every second strip within the array in order to achieve dual band-stop responses. The same principle has been extended to design FSS exhibiting tri- and quadreflection bands. In addition, strip FSSs have been perturbed by replacing every second strip for a metallic ring, resulting in dual-band filters with different polarization responses of the bands. These designs have been fabricated on large thin polyimide membranes using sacrificial silicon wafers. An oxide interlayer between the sacrificial silicon wafer and the polyimide membrane is employed to stop the silicon etching and is wet etched subsequently by a solution of ammonium fluoride and acetic acid that does not attack either the polyimide membrane or the aluminium FSS elements. Fourier transform infrared spectroscopy measurements are presented to validate the predicted responses of the fabricated prototypes.

Two-colour pulsed Raman studies of the lowest excited singlet state of tetraphenylporphyrin: band assignments and electronic structure

The resonance Raman spectra of the lowest lying singlet (S-1) state of free-base tetraphenylporphyrin and seven of its isotopomers were recorded under pump-and-probe conditions with a time delay of -2 ns between pump and probe laser pulses, In the S-1 spectra of the isotopomers, as in the ground state, there are dramatic splittings of what appear to be single bands in the natural isotopic abundance spectrum. The most structurally significant bands of the S-1 state were assigned on the basis of the isotope data, In some cases it was necessary to curve fit unresolved bands in the excited-state spectra in order to account for observed intensity ratios and to rationalize isotope shifts, The changes in band positions on excitation to the S-1 state were compared with those from earlier studies on the T-1 state. The changes in band positions were found to be similar For both excited states. Most notable was the similar shift in nu(2), the most widely used marker band for orbital character. The data are interpreted as implying that the lowest lying singlet state is a configuration interaction admixture of b(1u)b(2g) + a(u)b(3g) configurations with the coefficients weighted heavily in favour of b(1n)b(2g), which Is the configuration of the T-1 state. Copyright (C) 2000 John Wiley & Sons, Ltd.

RESONANCE RAMAN-SPECTRA OF THE TRIPLET-STATE OF FREE-BASE TETRAPHENYLPORPHYRIN AND 6 OF ITS ISOTOPOMERS

The resonance Raman spectra of the ground state and the lowest excited tripler state of free-base tetraphenylporphyrin and six of its isotopomers have been obtained using two-color time-resolved techniques. Ground-state spectra were recorded using low-energy 447 nm probe laser pulses, and triplet-state spectra were probed, with similar pulses, 30 ns after high-energy excitation with 532 nm pump pulses. Polarization data on both the ground and triplet states are also reported. The resonance Raman spectrum of the triplet is very different from that of the ground state but the combination of extensive isotope substitution with polarization data allows bands in the ground state to be assigned and corresponding bands in the tripler state to be located. Isotope shifts of the same bands in the S-0 and T-1 states are similar, implying that the compositions of the vibrational modes do not change significantly on excitation. Two of the strongest bands in the T-1 spectra are associated with phenyl ring substituents; these are shifted less than 5 cm(-1) between the S-0 and T-1 states so that bonding in the phenyl substituents is barely affected by excitation to the T-1 state. The changes in position of the porphyrin ring bands are larger, but still only tens of cm(-1) or less, the main changes in the spectra being due to differences in relative band intensities in the two states. The relatively small shifts in the porphyrin ring band positions which are observed show that the excitation energy is not localized on a single small region of the molecule but is delocalized over the entire porphyrin skeleton. This picture of an excited species with high chemical reactivity, but with individual bonds only slightly perturbed from the ground state, is contrasted with molecules, such as benzophenone, where excitation causes a large perturbation in the bonding within a single functional group.

TIME-RESOLVED RESONANCE RAMAN-SPECTROSCOPY OF EXCITED SINGLET AND TRIPLET-STATES OF FREE-BASE MESO-TETRAPHENYLPORPHYRIN

Two-color time-resolved resonance Raman spectroscopy has been used to probe the lowest excited singlet (S1) and triplet (T1) states of free-base meso-tetraphenylporphyrin and meso-tetrakis(4-sulphonatophenyl)porphyrin in solution at room temperature. The spectra were recorded using 532-nm excitation pulses and time-delayed probe pulses (DELTAT = 0-30 ns, 447 and 460 nm) near lambda(max) of the S1 and T1 states. Significant shifts in frequency of the porphyrin core vibrations were observed upon excitation to either the S1 or T1 state. Several of the strongest polarized bands in the spectra of both excited states, including nu1, nu2, nu4, nu6, and phi4, are assigned, and the information they give on the differences in electron distribution in the ground, S1, and T1 states is discussed.

Comparative growth rates and internal banding periodicity of maerl species (Corallinales, Rhodophyta) from northern Europe

Maerl is a type of rhodolith, found in ecologically important beds of high conservation value; a major conservation objective is to establish growth rates. Maerl shows internal banding of controversial periodicity that may contain a high-resolution record of palaeoceanographic-palaeoclimatic data. To investigate growth rates and banding periodicity, we used the vital stain Alizarin Red in combination with scanning electron microscopy (SEM). Three maerl species, Phymatolithon calcareum, Lithothamnion corallioides and L. glaciale, were collected from maerl beds in Ireland. Following staining, maerl was grown in three controlled temperature treatments and at two depths in the field (P. calcareum only), with Corallina officinalis as a control for the stain. Alizarin Red was shown to be a suitable marker for growth in European maerl species and for C. officinalis. The average tip growth rate of P. calcareum from Northern Ireland at 10 m depth and under constant laboratory conditions was c. 0.9 mm yr(-1), double the rates observed at 5 m depth and in L. corallioides. Our measurements and re-examination of reported data allow us to conclude that the three most abundant maerl species in Europe grow about 1 (0.5-1.5) mm per tip per year under a wide range of field and artificial conditions. Internal banding in temperate European maerl revealed by SEM is a result of regular changes in wall thickness; the approximately monthly periodicity of bands in field-grown specimens is consistent with previous suggestions that they may be lunar. The potential for maerl banding to be a high-resolution record of palaeoclimatic and palaeoenvironmental change could be realized with this vital stain in conjunction with isotopic or microgeochemical analyses.

Theoretical and photoemission studies of the band structure of CdI

The band structure of CdI has been calculated using a modified semi-empirical tight-binding method and the results obtained have been compared with both angularly averaged and angularly resolved photoemission spectra. The theoretically computed density of states distribution is in excellent agreement with angularly averaged results and all the main features observed experimentally are reproduced in the theory. Angularly resolved spectra have been used to draw up energy band dispersion curves directly and agreement with calculated bands in both the Gamma M and Gamma K directions of the Brillouin zone is good.

A theoretical study of the effects of lithium intercalation on the electronic structure of TiS

The band structure of the intercalation complex of LiTiS has been computed using a semi-empirical tight-binding method and this is compared with the results of a revised TiS calculation. The results obtained confirm that changes in the basic electrical characteristics of TiS, which occur when it is intercalated with lithium, can be attributed to a rigid-band filling of its lowest unoccupied electron states as has previously been proposed. However, they also suggest that intercalation can act to alter the nature and the dispersion of some of the energy bands in the unintercalated crystal. The bands which are most affected by the process are those which derive from orbitals which have the same symmetry as the lithium 2s orbital, namely, the titanium 4s conduction level and the tightly bound sulphur 3s levels.

A Late Pleistocene record of climate and environmental change from the northern and southern Kelabit Highlands of Sarawak, Malaysian Borneo

A late Pleistocene vegetation record is presented, using multi-proxy analysis from three palaeochannels in the northern (Bario) and southern (Pa'Dalih) Kelabit Highlands of Sarawak, Malaysian Borneo. Before 50 000 cal a BP and until approximate to 47 700 cal a BP [marine isotope stage 3 (MIS3)], two of the sites were probably being influenced by energetic fluvial deposition, possibly associated with strong seasonality. Fluvial activity declines between 47 700 and 30 000 cal a BP (MIS3), and may be associated with a reduction in seasonality with overall stability in precipitation. The pollen record between 47 700 and 30 000 cal a BP generally shows much higher representation of upper-montane taxa compared with the Holocene, indicating often significantly reduced temperatures. After 35 000-30 000 cal a BP and until the mid-Holocene, hiatuses appear in two of the records, which could be linked to fluvial down-cutting during the late/mid Holocene. Despite the jump in ages, a pronounced representation of Ericaceae and upper-montane taxa, represented both at Bario and at Pa'Dalih, corresponds to a further lowering of temperatures during the Last Glacial Maximum (MIS2). Thick charcoal bands in the PDH 210 record also suggest periods of extreme aridity between 30 200 and 12 700 cal a BP. This is followed by energetic fluvial deposition of sands and gravels, and may reflect a significant increase in seasonality.

The effect of dust obscuration in RR Telescopii on optical and IR long-term photometry and FeII emission lines

Aims. Infrared and optical photometric and spectroscopic observations of the symbiotic nova RR Tel are used to study the effects and properties of dust in symbiotic binaries containing a cool Mira component, as well as showing "obscuration events" of increased absorption, which are typical for such Miras. Methods. A set of photometric observations of the symbiotic nova RR Tel in different wavelength bands - visual from 1949 to 2002 and near-infrared (JHKL) from 1975 to 2002 - are presented. The variability due to the normal Mira pulsation was removed from the JHKL data, which were then compared with the American Association of Variable Star Observers' (AAVSO) visual light curve. The changes of the Fe II emission line fluxes during the 1996-2000 obscuration episode were studied in the optical spectra taken with the Anglo-Australian telescope. Results. We discuss the three periods during which the Mira component was heavily obscured by dust as observed in the different wavelength bands. A change in the correlations of J with other infrared magnitudes was observed with the colour becoming redder after JD 2 446 600. Generally, J-K was comparable, while K-L was larger than typical values for singleMiras. A distance estimate of 2.5 kpc, based on the IR data, is given. A larger flux decrease for the permitted than for the forbidden Fe II lines, during the obscuration episode studied, has been found. There is no evidence for other correlations with line properties, in particular with wavelength, which suggests obscuration due to separate optically thick clouds in the outer layers. Conclusions.