Search results for "Absorption"
showing 10 items of 2701 documents
Analysis of the atmospheric and emissivity influence on the splitwindow equation for sea surface temperature
1994
Abstract In this paper we have analysed the effects of the different atmospheric species (water vapour, fixed gases and aerosols) and the surface emissivity on the split-window method for determining the sea surface temperature. The widely used split-window method is based on the differential absorption of water vapour in the atmospheric window 10.5ndash;12.5 μm. Other atmospheric species with absorption coefficients different to that of water vapour can then have a large influence on the split-window. The effect of gases, such as C02, N20, CH4, CO and 03, and maritime aerosols is evaluated by comparing the effect of the water vapour alone. To do this we simulated AVHRR measurements in chan…
New insights into seismic absorption imaging
2020
Abstract In recent years, attenuation has been used as a marker for source and dynamic Earth processes due to its higher sensitivity to small variations of lithospheric properties compared to seismic velocity. From seismic hazard analysis to oil and gas exploration and rock physics, many fields need a better reconstruction of energy absorption, a constituent of seismic attenuation generally considered a reliable marker of fluid saturation in space. Here, we propose absorption tomography (AT), a technique grounded on the principles of scattering tomography and Multiple Lapse Time Window Analysis. We benchmark its efficiency to image absorption in space by comparing its results with those obt…
Structure determination and homogeneous optical properties of CdS/HgS quantum dots
1997
The structural and optical properties of heterogeneous semiconductor nanoparticles consisting of CdS and HgS are investigated by High Resolution Electron Microscopy (HRTEM) and selective spectroscopy like Hole Burning (HB) and Fluorescence Line Narrowing (FLN). The HRTEM study shows that epitaxy is possible in nanocrystals, provided the crystallites have well defined faceted shapes to begin with. From the HB- and FLN experiments homogeneous absorption and fluorescence spectra are calculated. It could be shown that the absorption is coupled to HgS-like phonons (250 cm -1 ) whereas the emission frequency is closer to the LO phonon frequency of CdS.
Total Absorption Spectroscopy Study ofRb92Decay: A Major Contributor to Reactor Antineutrino Spectrum Shape
2015
The antineutrino spectra measured in recent experiments at reactors are inconsistent with calculations based on the conversion of integral beta spectra recorded at the ILL reactor. (92)Rb makes the dominant contribution to the reactor antineutrino spectrum in the 5-8 MeV range but its decay properties are in question. We have studied (92)Rb decay with total absorption spectroscopy. Previously unobserved beta feeding was seen in the 4.5-5.5 region and the GS to GS feeding was found to be 87.5(25)%. The impact on the reactor antineutrino spectra calculated with the summation method is shown and discussed.
Magnesium homeostasis and aging.
2010
Aging is very often associated with magnesium (Mg) deficit. Total plasma magnesium concentrations are remarkably constant in healthy subjects throughout life, while total body Mg and Mg in the intracellular compartment tend to decrease with age. Dietary Mg deficiencies are common in the elderly population. Other frequent causes of Mg deficits in the elderly include reduced Mg intestinal absorption, reduced Mg bone stores, and excess urinary loss. Secondary Mg deficit in aging may result from different conditions and diseases often observed in the elderly (i.e. insulin resistance and/or type 2 diabetes mellitus) and drugs (i.e. use of hypermagnesuric diuretics). Chronic Mg deficits have been…
Isoelectronic series of twofold coordinated Si, Ge, and Sn atoms in glassy SiO2: a luminescence study
1992
Abstract Luminescence centers causing optical absorption bands in the 5 eV region in oxygen-deficient pure (‘Si-doped’), as well as in Ge- and Sn-doped glassy SiO2 were studied. The spectral and particularly kinetic data show that in all cases luminescence centers with closely similar properties exist which constitute an isoelectronic series. They are attributed to defects, formed by electrically neutral twofold coordinated Si, Ge, and Sn atoms (T20 centers) in glassy SiO2. Twofold coordinated Si causes the characteristic ‘B2’ optical absorption band at 5.03 eV. Upon reaction with atomic hydrogen, T20 centers convert to the well known ‘H(I)’, ‘H(II)’ and ‘H(III)’ ESR-active defects. The alt…
Vacuum-ultraviolet absorption of amorphous SiO2: intrinsic disorder and role of silanol groups
2008
We present a study on the vacuum-ultraviolet VUV absorption properties of amorphous SiO2 a-SiO2 with high concentrations of silanol groups Si-OH . We found that the absorption spectra are made up of a couple of exponential profiles. The first, in the range from 7.5 to 8.1 eV, was attributed to Si-OH group absorption, while the second, in the range from 8.1 to 8.25 eV, was ascribed to the intrinsic absorption. The VUV absorption cross section of Si-OH groups in a-SiO2 was determined as well. The intrinsic absorption was found to be affected by the Si-OH concentration: high silanol group contents allow lower values of the Urbach energy. This result is interpreted in terms of a reduction in th…
Sturctural disorder and silanol groups content in amorphous SiO2
2009
We present a study on the features of the Urbach edge in amorphous silicon dioxide a-SiO2 . The effects of temperature on the absorption edge in the range from 4 to 300 K were studied in both materials having negligible dry, 1017 cm−3 and significant wet, 1019 cm−3 silanol groups contents. Remarkable differences in the values and in the temperature dependence of the Urbach energy in the dry and wet samples were observed. These differences are interpreted as a consequence of a drastic reduction in the degree of disorder in wet materials, which turn out to be characterized by an electronic structure more similar to that of crystalline quartz. Furthermore, our results indicate that silanol gro…
Carbon nanotubes thin filters for x-ray detectors in space
2022
In this paper, we present the first results from an investigation performed on nanometric thin pellicles based on carbon nanotubes (CNT) of potential interest for manufacturing large area optical blocking filters to protect soft X-ray detectors in astrophysics space missions. In order to evaluate the effective capability of such materials to block UV/VIS/IR radiation, while being highly transparent in the soft X-rays and strong enough to withstand the severe launch stresses, we have performed a suite of characterization measurements. These include: UV/VIS/IR and X-ray absorption spectroscopy, X-ray Photoelectron Spectroscopy and Scanning Electron Microscopy on bare and Al coated small self-…
Synthetic and natural chromium bearing spinels: an optical spectroscopy study
2014
Four samples of synthetic chromium-bearing spinels of (Mg, Fe2+)(Cr, Fe3+)2O4 composition and four samples of natural spinels of predominantly (Mg, Fe2+)(Al, Cr)2O4 composition were studied at ambient conditions by means of optical absorption spectroscopy. Synthetic end-member MgCr2O4 spinel was also studied at pressures up to ca. 10 GPa. In both synthetic and natural samples, chromium is present predominantly as octahedral Cr3+ seen in the spectra as two broad intense absorption bands in the visible range caused by the electronic spin-allowed 4A2g → 4T2g and 4A2g → 4T1g transitions (U- and Y-band, respectively). A distinct doublet structure of the Y-band in both synthetic and natural spine…