Search results for "Spectroscopy"
showing 10 items of 10293 documents
Synchrotron Mössbauer Reflectometry in Materials Science
1999
57Fe nuclear resonant scattering experiments are reported on iron-containing thin films using 14.41 keV synchrotron radiation at angles of grazing incidence around and slightly above the critical angle of the electronic total reflection. In partially oxidised α–Fe films of 20 nm original thickness various oxide and oxihydroxide phases are identified at different depth. In a [Fe/FeSi]10multilayer grown on Zerodur®substrate the Fe—Fe interlayer coupling varies with the distance from the substrate. The antiferromagnetic order of the top layers of this multilayer can be suppressed by external magnetic field. These examples demonstrate the efficiency of synchrotron Mossbauer reflectometry (SMR),…
Achromatic linear retarder with tunable retardance
2018
We present a universal design and proof-of-concept of a tunable linear retarder of uniform wavelength response in a broad spectral range. It consists of two half-wave retarders (HWR) between two quarter-wave retarders (QWRs), where the uniform retardance can be tuned continuously by simply rotating one of the HWRs. A proof-of-concept of this design is built by using commercially available Fresnel rhomb retarders that provide retardation with almost wavelength uniformity in the visible and near infrared from 450 to 1550 nm. The design is universal, since other achromatic QWRs and HWRs could also be employed. The system is experimentally demonstrated to control the state of polarization of a …
Comparison of total-reflection X-ray fluorescence, static and portable energy dispersive X-ray fluorescence spectrometers for art and archeometry stu…
2004
Abstract In this paper, a Total-reflection X-ray Fluorescence (TXRF), a static and a portable Energy Dispersive X-ray Fluorescence (EDXRF) spectrometers are described. Both the equipments and the techniques employed in the field of the art and archeometry are compared. Some applications in this area are presented as well. The aim of the work is to know which spectrometer is the best suited depending on the work of art and the problem treated. The conclusion reached from the experience is that the portable EDXRF spectrometer is advisable to make “in situ” and online analysis in a multidisciplinary environment, the static EDXRF equipment is good to perform analysis on paper and metal pieces a…
Sample–tip coupling efficiencies of the photon-scanning tunneling microscope
1991
The photon-scanning tunneling microscope is the photon analog to the electron-scanning tunneling microscope. It uses the evanescent field due to the total internal reflection of a light beam in a prism, modulated by a sample attached to the prism. The exponential decay of the evanescent field is characterized by the penetration depth dp and depends on the angle of incidence θ, the wavelength, and the polarization of the incident beam. The 1/e decay lengths range from 150 to 265 nm as deduced from the expression of the electric-field intensity in the rarer medium for θ = π/2. If we place another optically transparent medium near the surface, frustrated total reflection occurs. It is shown th…
Recent Experimental Results with the PSTM: - Observation of a Step on a Quartz Surface. - Spatial Spectroscopy of Microwaveguides
1993
The Photon Scanning Tunneling Microscope (PSTM) is based on the frustration of the total internal reflected beam by the end of an optical fiber. Till today it has been used to obtain topographic information generally for smooth samples. In this paper we report two different kinds of experimental results. First, when the sample is in the form of a step, our measurements demonstrate how the images, obtained in the constant intensity mode, depend on the orientation of the incident beam of light with respect to the step. Next, we show that the first derivative of the collected intensity with respect to the probe-sample distance at each point of the sample yields to a new kind of image named her…
Resolution of the photon scanning tunneling microscope: influence of physical parameters
1992
Abstract The photon scanning tunneling microscope (PSTM) is the photon analogue of the electron scanning tunneling microscope (ESTM). It uses the evanescent field due to total internal reflection (TIR) of a light beam in a prism modulated by a sample placed on the base of the prism. Our experimental results shown details which present a lateral size as small as 200 A. The PSTM axial resolution is more difficult to evaluate. It is a function of the roughness of the sample. For very smooth samples, images shown an axial resolution of about 10 A. At last we discuss how both lateral and axial resolution can be affected by several parameters such as the tip surface distance and the roughness of …
Prediction of organic carbon and total nitrogen contents in organic wastes and their composts by Infrared spectroscopy and partial least square regre…
2017
Middle and near infrared (MIR and NIR) were employed to determine organic carbon (OC) and total nitrogen (TN) in different soil organic amendments including wastes, composts and mixtures of composts and organic wastes. Prediction models based on partial least squares (PLS) regression from the spectra of untreated samples were built. Different spectra preprocessing strategies were adopted and the best number of latent variable was evaluated using leave-one-out cross-validation. Attenuated total reflectance (PLS-ATR-MIR) and diffuse reflectance (PLS-DR-NIR) models were built and evaluated from root mean square error of cross validation and prediction (RMSECV and RMSEP), coefficients of determ…
Development of accurate mass spectrometric routine and reference methods for the determination of trace amounts of iridium and rhodium in photographi…
1999
For the determination of trace amounts of iridium and rhodium in photographic emulsions different sample treatment procedures were coupled with inductively coupled plasma mass spectrometry (ICP-MS) and, for iridium, also with negative thermal ionisation isotope dilution mass spectrometry (NTI-IDMS) and ICP-IDMS. IDMS determinations of iridium were carried out using an enriched 191Ir spike solution. Elimination of the silver matrix was established for both mass spectrometric methods, which prevents corresponding memory effects in the ICP-MS system and is essential for the formation of IrO2 - thermal ions, respectively. For NTI-MS measurements, the gelatine matrix of the emulsion must also be…
Cytotoxic neo-clerodane diterpenes from Stachys aegyptiaca
2018
Abstract Two new E/Z neo-clerodane diterpene isomers, trivially named stachaegyptin D (1) and E (2), together with known compounds, stachysolon monoacetate (3) and stachysolon diacetate (4), were isolated from an organic-solvent extract of the medicinal herb Stachys aegyptiaca. Structures were elucidated by a combination of spectroscopic methods, including HREIMS, 1H, 13C, DEPT, and 2D NMR analysis, as well as, first time X-ray analysis for stachysolone (3). All isolated metabolites showed some activity against the human hepatocellular cell line, HepG2. Compound 4 was the most active with an IC50 of 59.5 μM.
mTOR Driven Gene Transcription Is Required for Cholesterol Production in Neurons of the Developing Cerebral Cortex
2021
AbstractDysregulated mammalian target of rapamycin (mTOR) activity is associated with various neurodevelopmental disorders ranging from idiopathic autism spectrum disorders to syndromes caused by single gene defects. This suggests that maintaining mTOR activity levels in a physiological range is essential for brain development and functioning. Upon activation, mTOR regulates a variety of cellular processes such as cell growth, autophagy and metabolism. On a molecular level, however, the consequences of mTOR activation in the brain are not well understood.Low levels of cholesterol are associated with a wide variety of neurodevelopmental disorders. We here describe numerous genes of the stero…