Search results for " Spectra"
showing 10 items of 709 documents
Optical Spectra and Direct Optical Transitions in Amorphous and Crystalline ZnO Thin Films and Powders
2010
Comparative studies of ZnO crystalline and amorphous thin films and nanocrystalline powders are reported. The UV-visible optical spectra were analyzed with special attention paid to the direct optical bandgap. Atmospheric radio-frequency barrier torch discharge and pulsed hollow cathode sputtering techniques for the film fabrication were used. For the crystalline films, similar values of the direct optical bandgap were found independent of the growth method used. The analysis of the amorphous films and powders revealed a pronounced Urbach-like exponential absorption tail approaching the bandedge. For the powders, the bandgap energies were larger than those for the crystalline and amorphous …
Contact probe pressure effects in skin multi-spectral photoplethysmography
2007
A novel technique ensuring parallel recording of reflection photoplethysmography signals in broad spectral range has been tested for assessment of pressure-induced vascular changes at various depths from the skin surface. PPG signals have been simultaneously detected at three combinations of the cw laser wavelengths 405 nm, 532 nm, 645 nm, 807 nm and 1064 nm. The PPG baseline responses to the probe-skin contact pressure changes and shapes of the PPG pulses originated from the same heartbeat but recorded at different wavelengths have been detected and analyzed.
On the blue phase structure of hydrogen-bonded liquid crystals via 19F NMR
2018
Abstract 19 F NMR spectra are simulated for blue phase I of FPHG( St 1.5 ∗ Ap 1.5 ) based on a model of a double-twisted substructure inside cylinders that form a body-centred cubic lattice. A kinetic matrix is included to describe jump processes over quarter pitch lengths. Though the lines in the NMR spectra are broad and featureless, changes in the widths and positions with temperature are well described by the blue phase model structure. The spectra in the chiral nematic N∗ phase are also simulated. Dynamics in the BP I are found to be slower than in the N∗ phase.
Transition from polarization disorder to antiphase polarization domains in a fiber laser
2014
Adjusting polarization coupling in a fiber ring laser may lead to anti-synchronization of spatio-temporal disorder into ordered laminar states of orthogonal polarization temporal domains, as well as stable lattices of soliton trains.
Transient absorption and luminescence of LiNbO3 and KNbO3
2001
Abstract The results of time-resolved optical absorption spectra in congruent and stoichiometric LiNbO3 as well as KNbO3 crystals are reported. The role of different polaron types in transient absoiption and luminescence spectra and decay kinetics are discussed.
Multi-spectral photoplethysmography technique for parallel monitoring of pulse shapes at different tissue depths
2011
A photoplethysmography (PPG) signal can provide very useful information about a subject's hemodynamic status in a hospital or home environment. A newly developed portable multi-spectral photoplethysmography device has been used for studies of 11 healthy subjects. Multi-spectral photoplethysmography (MS-PPG) biosensor intended for analysis of peripheral blood volume pulsations at different vascular depths has been designed and experimentally tested. Multi-spectral monitoring was performed by means of a three–wavelengths (405 nm, 660 nm and 780 nm) laser diode and a single photodiode with multi-channel signal output processing. The proposed methodology and potential clinical applications are …
Near-Infrared Spectra of Water Confined in Silica Hydrogels in the Temperature Interval 365−5 K
2002
We have used a sol−gel technique to obtain optically transparent hydrogels in which water is trapped within a tridimensional disordered silica matrix. A suitable aging of these hydrogels enables to have transparent noncracking samples down to cryogenic temperatures. We report the optical absorption spectra, in the near-infrared region, of water trapped in our silica hydrogels, measured in the temperature range 365−5 K, and we compare them with the same spectra of liquid water, measured in the temperature range 365−263 K. The data show that it is possible to have noncrystallizing water even at 5 K: indeed, the overtone bands at ∼1.41 μm and at ∼1.155 μmtypical of “weakly bonded” water molec…
Physico-chemical characterization of perlite of various origins
1985
Abstract Pearlstones (perlite) from Sardinia (Italy). Milos (Greece) and Siberia (USSR) have been evaluated in terms of chemical composition, phase analysis, iron distribution, morphology and thermal properties, for application as raw material in zeolite synthesis.
Colloidal plasmonic back reflectors for light trapping in solar cells.
2014
A novel type of plasmonic light trapping structure is presented in this paper, composed of metal nanoparticles synthesized in colloidal solution and self-assembled in uniform long-range arrays using a wet-coating method. The high monodispersion in size and spherical shape of the gold colloids used in this work allows a precise match between their measured optical properties and electromagnetic simulations performed with Mie theory, and enables the full exploitation of their collective resonant plasmonic behavior for light-scattering applications. The colloidal arrays are integrated in plasmonic back reflector (PBR) structures aimed for light trapping in thin film solar cells. The PBRs exhib…
Zirconia nanocrystals as submicron level biological label
2012
Inorganic nanocrystals are of increasing interest for their usage in biology and pharmacology research. Our interest was to justify ZrO2 nanocrystal usage as submicron level biological label in baker's yeast Saccharomyces cerevisia culture. For the first time (to our knowledge) images with sub micro up-conversion luminescent particles in biologic media were made. A set of undoped as well as Er and Yb doped ZrO2 samples at different concentrations were prepared by sol-gel method. The up-conversion luminescence for free standing and for nanocrystals with baker's yeast cells was studied and the differences in up-conversion luminescence spectra were analyzed. In vivo toxic effects of ZrO2 nanoc…