Search results for "absorptio"

Dipole moments of aminophthalimides determined by modified electro-optical absorption and emission measurements

1995

Modified electro-optical absorption and emission methods were used to measure the electric dipole moments of five aminophthalimides in their ground and excited states. The equilibrated ground and excited state dipole moments measured by these methods are in reasonable agreement with those derived from other measurement techniques, confirming the general validity of these methods. A difference is observed between the properties of 3-aminophthalimide (3AP) and 4-amino-N-methylphthalimide (4ANMP) in different solvents. The equilibrated dipole moment of 3AP in its excited state is practically independent of the solvent polarity in contrast with 4ANMP. The possible mechanism of this effect is di…

Structure of Dioxygen Binding Xerogels Incorporating Cyclams Complexed with CuCl2 Salts

2005

X-ray absorption/emission spectroscopies were combined in order to elucidate how hybrid xerogels complexed with CuCl2 could bind reversibly O2. Difference EXAFS analyses at the Cu K-edge revealed the existence of binuclear structures with long Cu...Cu distances, i.e. RCu–Cu ≈ 3.98 A and 3.87 A for the oxygenated and oxygen-free xerogels. In oxygenated xerogels, dioxygen would bridge two Cu atoms in a μ-η1 : η1 peroxo-like conformation. The Cu-O signal found at short distance (RCu−O1 = 1.85 ± 0.01 A) is fully consistent with 40% of O2 molecules being chemisorbed per Cu site. In oxygen-free xerogels, Cl K-edge EXAFS revealed the presence of CuI sites with short Cl-Cu bond lengths (RCl−Cu = 2.…

High-pressure x-ray absorption study of GaTe including polarization

2000

The evolution of the local structure in GaTe under pressure is studied by x-ray absorption spectroscopy experiments at the Ga K-edge (10.368 keV) on oriented single crystals. Taking advantage of the linearly polarized character of synchrotron radiation, the pressure evolution of both the Ga-Te and the in-plane Ga-Ga bond lengths could be determined, in spite of the small amplitude of the latter. Our measurements show that both distances are much less compressible than what could be inferred from the bulk compressibility, which evidences a strong variation of Ga-Ga-Te and Te-Ga-Te angles under pressure. The Te-Te intralayer distance perpendicular to the layers is observed to increase with in…

Do we need to change the guideline values for determining low bone mineral density in athletes? [Viewpoint]

2022

Comparison of ultrasound and bone mineral density assessment of the calcaneus with different regions of interest in healthy early menopausal women.

1998

This study investigated the effect of different sized regions of interest (ROIs) on quantitative ultrasound (QUS) variables of the calcaneus. The effect on QUS of using a fixed ROI as opposed to an ROI adjusted for foot length was also assessed. Eighty Caucasian women, aged 50-57 yr (mean 53 +/- 2) who were healthy and within 0. 5-5 yr of the onset of menopause participated in this study. Using the QUS-1(trade mark) Ultrasonometer (Metra Biosystems, Mountain View, CA), we assessed broadband ultrasound attenuation ([BUA] and UBI-4, dB/MHz), the average transit time through the heel ([TTH], mus) and a multiple-factor index (UBI-4T = UBI-4/TTH, dB/[MHz. mus]). The QUS measurement results were …

Periacetabular Cortical and Cancellous Bone Mineral Density Loss After Press-Fit Cup Fixation

2012

The impact of total hip arthroplasty on strain adaptive bone remodeling has been extensively analyzed by dual-energy x-ray absorptiometry. In this study, we present a prospective computed tomography-assisted study of periacetabular cortical and cancellous bone mineral density (in milligrams of calcium hydroxyapatite [CaHA] per milliliter, or mgCaHA/mL) changes 10 days and 1, 3, and 7 years after press-fit cup implantation for 38 hips in vivo. Cancellous bone mineral density decreased by O -63% ventral and O -85% dorsal to the cup; cortical bone mineral density, by O -22% ventral and O -18% dorsal to the cup. The presented periacetabular strain adaptive bone mineral density data are the most…

Bioaccessibility of Enniatins A, A1, B, and B1 in Different Commercial Breakfast Cereals, Cookies, and Breads of Spain

2013

Fusarotoxins enniatins (ENs) can represent a potential risk as natural contaminants of cereal commodities. However, only their bioaccessible fraction can exert a toxicity. The purpose of this study was to determine the ENs A, A₁, B, and B₁ bioaccessibility added in 1.5 and 3.0 μmol/g concentrations in breakfast cereals, cookies, and breads using a simulated in vitro gastrointestinal extraction model. Bioaccessibility values ranged between 40.4 ± 1.9 and 79.9 ± 2.8%. The lower values were 50.1, 40.4, 43.9, and 46.3% in wheat bran with fibers, and the higher values were 79.9, 64.2, 69.8, and 73.6% in white loaf bread for the ENs A, A₁, B, and B₁, respectively. Food composition, compounds stru…

Electronic and Functional Scope of Boronic Acid Derived Salicylidenehydrazone (BASHY) Complexes as Fluorescent Dyes

2017

[EN] A series of boronic acid derived salicylidenehydrazone (BASHY) complexes was prepared and photophysically characterized. The dye platform can be modified by (a) electronic tuning along the cyanine-type axis via modification of the donor-acceptor pair and (b) functional tuning via the boronic acid residue. On the one hand, approach (a) allows the control of photophysical parameters such as Stokes shift, emission color, and two-photon absorption (2PA) cross section. The resulting dyes show emission light-up behavior in nonpolar media and are characterized by high fluorescence quantum yields (ca. 0.5-0.7) and brightness (ca. 35000-40000 M-1 cm(-1)). Moreover, the 2PA cross sections reach …

Evidence for long-lived, optically generated quenchers of excitons in single-walled carbon nanotubes.

2011

The nonlinear dependence of near-infrared photoluminescence (PL) emission on excitation intensity has been measured for individual nanotubes representing six different (n,m) species. Significant deviations from linearity are observed for intensities as low as ~100 W/cm(2), and an approximate inverse correlation is found between nonlinearity and PL action cross section (brightness). A model in which all PL nonlinearity arises from exciton-exciton annihilation is insufficient to account for the experimental data using realistic parameters. It is proposed that additional nonlinear quenching arises from photoinduced quenching states or species with longer lifetimes than emissive excitons. Evide…

Nonlinear pressure dependence of the direct band gap in adamantine ordered-vacancy compounds

2010

A strong nonlinear pressure dependence of the optical absorption edge has been measured in defect chalcopyrites CdGa{sub 2}Se{sub 4} and HgGa{sub 2}Se{sub 4}. The behavior is due to the nonlinear pressure dependence of the direct band-gap energy in these compounds as confirmed by ab initio calculations. Our calculations for CdGa{sub 2}Se{sub 4}, HgGa{sub 2}Se{sub 4} and monoclinic {beta}-Ga{sub 2}Se{sub 3} provide evidence that the nonlinear pressure dependence of the direct band-gap energy is a general feature of adamantine ordered-vacancy compounds irrespective of their composition and crystalline structure. The nonlinear behavior is due to a conduction band anticrossing at the {Gamma} po…