Attenuation intern

These investigations were aided substantially by use of the multiple attenuated internal reflection (MAIR) spectroscopic technique to record surface specific, infrared (IR) spectra in order to determine structure and monitor preparation and cleaning methods. 

Using contact angle measurements, Baier determined the critical surface tension of the spontaneously acquired films deposited on a clean inorganic solid placed in human mouths for periods of 30 sec, 2 min, and 15 min (14) see Table II). Concurrent determination of multiple attenuated internal refiection IR spectra of the adsorbed films provided evidence for the presence of protein material. While the spectra revealed... 

Only the methods used in this study (i, 2, 3) can detect and follow the initial events at the boundary between a solid substrate and the biological milieu. This extraordinary sensitivity derives from the ability to monitor events from within the substrate itself by making the substrate capable of supporting multiple attenuated internal reflection (MAIR) at a variety of useful spectroscopic wavelengths. In other studies, it was concluded that adsorbed protein on solid substrates is of essentially native i.e. solution or volume phase) conflguration and present in signiflcant thickness (6). Those studies used a different version of the internal reflection spectroscopic method wherein a prism element was forcefully... 

An illuminating experiment to perform, if your spectrometer is able to alter the output attenuation internally, is to determine the pulse width over a wide range of attenuations. A plot of pulse widths vs logio(attenuation) should yield a single straight line over the full range. Discontinuities in the plot may arise when different power amplifiers come into use or when large attenuators are switched in place of many smaller ones. 

Fig. 4. Removal of an organic fatty acid monolayer on a water surface by a rising hydrophilic plate after the method of Blodgett (1934,1935) and its analysis by multiple attenuated internal reflection (Baier, 1970). Reproduced with permission of the author.

Raman spectra of acidic aqueous solutions of M0C12-8H20 (M = Zr or Hf) have been examined in an effort to detect the zirconyl and hafnyl ions, M=0. No evidence for a v(M=0) Raman band in the region 800-1000 cm was found. A broad IR band centered at 1000 cm" is observed in the multiple attenuated internal reflectance spectrum of a concentrated ZrOCL solution. " However, this band shifts to lower frequency upon deuteriation, indicating that the solution species contains hydroxo bridges, and not zirconyl groups. Bands due to 6(ZrOH) in the 910-1030 cm region of the IR spectrum of crystalline... 

Due to the fundamental importance of the adsorbed protein film, many methods have been used to characterize its nature. These methods include ellipsometry (3,A), Fourier transform infrared spectroscopy (FTIR) (5,6), multiple attenuated internal reflection spectroscopy (MAIR) (7,8) immunological labeling techniques (9), radioisotope labeled binding studies (j ), calorimetric adsorption studies (jj ), circular dichroism spectroscopy (CDS) (12), electrophoresis (j ), electron spectroscopy for chemical analysis (ESCA) (1 ), scanning electron microscopy (SEM) (15,16,9), and transmission electron microscopy (TEM) (17-19). 

Attenuated Internal Reflection (ATIR) spectra were obtained for the untreated and treated polymer surfaces using a BIORAD FTS-4R infrared spectrometer and then the two spectra were compared to identify characteristic peaks which are associated with the bonds formed by the addition of the phosphonate side groups on the polymer backbone. 

Baier, R. E., and Zisman, W. A., Wettability and multiple attenuated internal reflection infrared spectroscopy of solvent-cast thin films of polyamides. Macromolecules, 3, 462-468 (1970). 

Fig. 13.9a-d. Hepatocellular carcinoma with internal mosaic architecture, intratu-moral septa and areas of necrosis. Spiral CT images obtained in the baseline (a), arterial phase (b), portal venous (c) and delayed phase (d) images. Different components of the tumor show various degrees of attenuation. Internal fibrous septa are depicted as they enhance in the portal venous phase... 

Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy. Attenuated total redectance (atr) ftir spectroscopy is based on the principle of total internal redection (40). Methods based on internal redection in the uv and visible regions of the spectmm are also common in addition to those in the ir region. The implementation of internal redection in the ir region of the spectmm provides a means of obtaining ir spectra of surfaces or interfaces, thus providing moleculady-specific vibrational information. 

Attenuated total reflection, on which atr—ftir is based, occurs when the rarer medium is absorbing and is characterized by a complex refractive index (40). The absorbing characteristics of this medium allow coupling to the evanescent field such that this field is attenuated to an extent dependent on k. The critical angle in the case of attenuated total reflection loses its meaning, but internal reflection still occurs. Thus, if the internally reflected beam is monitored, its intensity will reflect the loss associated with the internal reflection process at the interface with an absorbing medium. 

Fig. 24. Attenuated total reflectance of thin film of thickness d and refractive index on a substrate of refractive index at the surface of internal reflection element (IRE) of refractive index Decay of evanescent field beyond thickness of thin film indicated.

Attenuated total reflection (ATR), also called internal reflection, is based on the phenomenon of total internal reflection. In ATR the infrared beam is directed into an infrared-transmitting crystal so that it strikes the crystal surface at less than the critical angle and undergoes total internal reflection. 

Examples of nir analysis are polymer identification (126,127), pharmaceutical manufacturing (128), gasoline analysis (129,130), and on-line refinery process chemistry (131). Nir fiber optics have been used as immersion probes for monitoring pollutants in drainage waters by attenuated total internal reflectance (132). The usefulness of nir for aqueous systems has led to important biological and medical appHcations (133). 

Filters have a time constant r = R x C which increases the damping of the measuring instrument. The time constant depends on the required attenuation and the interfering frequency, but not on the internal resistance of the measuring instrument. The time constants of the shielding filter are in the same range as those of the electrochemical polarization, so that errors in the off potential are increased. Since the time constants of attenuation filters connected in tandem are added, but the attenuation factors are multiplied, it is better to have several small filters connected in series rather than one large filter. 

With nondestructive ultrasonic test back and forth scanning of a specimen is accomplished with ultrasonics. This NDT can be used to find voids, delaminations, defects in fiber distribution, etc. In ultrasonic testing the sound waves from a high frequency ultrasonic transducer are beamed into a material. Discontinuities in the material interrupt the sound beam and reflect the energy back to the transducer, providing data that can be used to detect and characterize flaws. It can locate internal flaws or structural discontinuities by the use of high frequency reflection or attenuation (ultrasonic beam). 

The following experimental details apply both to the determination of tungsten with bromine as internal standard, and to the experiments of Table 7-2. The solutions filled a 3-ml container made by sectioning a 10-ml beaker. To prevent" evaporation and to maintain a fixed distance between x-ray tube window and sample surface, the beaker-section was covered with Mylar film, 0.0025 cm thick, placed in a plastic sample holder and pressed firmly against the sample drawer. The Mylar film attenuated the x-rays uniformly enough so as not to affect the precision of the results. 

Desensitization describes the rapid signal attenuation in response to stimulation of cells by receptor agonists. Changes in the coupling efficiency of receptors to signal transduction pathways and receptor internalization can account for desensitization and the development of pharmacodynamic tolerance. 

Cross sectional area Coefficient matrix Chemical species Coefficient matrix Numerical coefficients Advanced silicon etching Internal surface area Attenuated total reflection Numerical coefficient... 

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