IR spectra of CO adsorbed on PdSiO2 have been monitored as a function of θ(CO) and isotopic composition x, where x = 12CO(12CO + 13CO). The results show that on rough curved surfaces of small particles of Pd there is no tendency to clustering of CO. Results do not support the idea of chemical (competition) effects. An alternative explanation of the large shifts (Δvmax) observed on flat single crystal planes is suggested: with increasing θ(CO), CO molecules change their adsorption sites. The latter process is absent on small particles of Pd.

Infrared spectroscopy has been used to study the influence of C6H6 coadsorption and potassium compound promotion on the adsorption of CO on supported Pd catalysts. Benzene is found to have a significant influence on single coordinated CO provided small Pd particles are being used. The promotion by potassium compounds has little influence on the single coordinated CO, but one finds on promoted Pd a new peak with a singleton frequency of about 1740 cm−1. The possible nature of this peak is discussed.

Using field electron microscopy (FEM) and thermal desorption and reaction spectroscopy (TDS) the behaviour of various Rh single crystal surfaces towards reactions involving NO has been studied. If, after NO adsorption up to saturation at 77 K, the temperature is slowly raised the FEM results suggest that dissociation of NO starts at the (321), (331) and (533) surfaces. The reaction of NOads with hydrogen starts also at these surfaces (at about 360 K) suggesting that NO bond scission initiates the reaction. After initiation a surface explosion is observed. Depending on the heating rate either a clean surface or a Nads covered surface is obtained after completion of the reaction. Apparently, the reduction of adsorbed Nads by hydrogen can occur at a significant rate at this temperature. At a higher heating rate the formed N adatoms do not react with hydrogen and are readily desorbed as N2 at 600 K. The reaction of NOads with CO starts again on the (321) and (331) surfaces. The rate of the reaction with CO is, however, much lower than that with hydrogen. For the reaction of COads with NO, desorption of CO is the initiation step. The mechanisms of the reactions and the dependence of the reaction on the surface structure are discussed in relation to literature data.

Adsorption and IR spectra of CO have been monitored with Pd, Pd/Ag and Pd/Cu on Aerosil catalysts. By isotopic dilution technique the singleton frequencies [ν(CO) for θ(CO) → 0] have been determined. It has been established that the ligand effect of alloying is almost zero with Cu, but — although small — well measurable with Ag. The effect of coadsorbed benzene (“ligand effect of benzene”) on the singleton frequency does exist and it is more pronounced with small particles.

The aim of this clinical trial was to compare the frequency of duodenal ulcer healing under omeprazole therapy, giving 30 mg/day or 60 mg/day.

The adsorption, desorption and decomposition of NO on Rh surfaces have been investigated using field electron microscopy (FEM) and thermal desorption spectroscopy (TDS). At 77 K NO is molecularly adsorbed on all surfaces of Rh. At room temperature, however, about 30% of NO adsorbed on the rough surfaces is dissociated. The work function change Δφ due to NO adsorption increases as the surface becomes rougher. The results suggest the following order in Δφ: 0.93 eV = (100) < (111) < (511) < (410) < (331), (533) < (321) < (110) < (650) < (531), (210) = 1.4 eV. Upon heating the tip covered with molecular NO the FEM results suggest that the (321) surface is most active in the NO bond scission. The smooth surfaces are least effective in NO dissociation. The most likely interpretation of the FEM results is that the activity in NO bond scission increases in the following order: (111), (110) < (100), (511) < (650) < (410) < (210) < (331), (533) < (321). These results are discussed in relation to literature data concerning the dissociation of NO on the noble metals of Group VIII.

The adsorption and dissociation of CO2 on Rh has been investigated using field emission microscopy and thermal desorption spectroscopy. In addition, the influence of hydrogen on the interaction of CO2 with Rh has been examined. Two clearly distinguishable adsorption states exist, one of a chemical nature and an activation energy of desorption of 60 kJ/mol and a physically adsorbed species with an activation energy of desorption of 27 kJ/mol. The chemisorbed species desorbs to a small extent at 210 K and dissociates for the other part to COa + Oa. The heat of adsorption of chemisorbed CO2 is particularly high on the open crystal planes like (210), (320) and (531). In dissociation the stepped planes around (111) and (100) are most active. No evidence was found for dissociation on the smooth (110), (100) and (111) surfaces. These results are discussed in relation with the disagreement in the literature concerning dissociation of CO2 on Rh. Our results point to surface heterogeneity as a major effect explaining the controversy. In addition some investigations on the adsorption of CO and H2 on Rh starting at 78 K are reported.

The original Laplace deconvolution of luminescence data, obtained with pulsed systems, is reviewed. The system of equations from which the luminescence parameters can be determined is generalized for the case that describes the relaxation by a sum of exponentials. Artifacts such as scatter and time-shift can be taken into account. A modification of the original method that eliminates the iterative procedure in the estimation of the cut-off correction is suggested. This modified Laplace method is no longer restricted to the cases where the cut-off error is rather small and the exciting flash has a low tail. The possibility of the combination of several discrete experiments in a single Laplace deconvolution, without introducing new parameters or normalization factors, is shown. The merits of this combination method are demonstrated on a time-resolved depolarization experiment.

The adsorption of nitrogen on rhodium has been investigated on various single crystal surfaces with field emission probe-hole microscopy and thermal desorption spectroscopy. The results are compared to data of nitrogen on iridium and platinum surfaces. TDS reveals the presence of three adsorption states with heats of adsorption of 30, 45 and 60 kJ mol−1. The FEM results show that the adsorption of nitrogen is markedly structure sensitive. Differences in the initial heats of adsorption of 30% are found between the densely packed (111) and (100) surfaces and rough surfaces, like (210). The nature of the nitrogen-metal bond is briefly discussed. In addition to the molecularly adsorbed states evidence is found for dissociation of nitrogen on rhodium upon heating the Rh tip in a nitrogen atmosphere at 500 K.

The surface composition of Pd-Cu alloys has been studied by Auger electron spectroscopy, photoelectric work function measurements and by calculations based on a broken bond model of surface segregation. The measurements were performed on thin films with a bulk composition varying from 0% to 100% Pd. The films were prepared by sublimation of both metals in ultrahigh vacuum onto a Pyrex glass support. For the work function measurements both the absolute value of the work function and the change in work function due to hydrogen chemisorption were used for an estimate of the surface composition. The Auger spectra were evaluated in the way proposed by Gallon to calculate the surface composition of the alloys. The data derived from the experimental results are in good agreement with the calculated values. The results show that the surfaces of clean and equilibrated Pd-Cu alloys are only slightly enriched in copper.

Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter Facebook Reddit LinkedIn Tools Icon Tools Reprints and Permissions Cite Icon Cite Search Site Citation M. Ameloot, H. Hendrickx; Determination of the polarizing direction of polarizers. The Physics Teacher 1 December 1983; 21 (9): 590. https://doi.org/10.1119/1.2341421 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAmerican Association of Physics TeachersThe Physics Teacher Search Advanced Search |Citation Search

Increase of the external K+ concentration depolarises the ureteral muscle membrane and induces, after a transient period of increased spontaneous activity, a tonic contraction. Tetraethylammonium, in concentrations normally required for ganglion blocking activity, does not influence the ureteral activity, but in higher doses it prolonges the duration of the action potential several times and increases the intraluminal pressure. Ouabain has only an inhibitory effect on the guinea pig ureter.

In Sodium-deficient solutions both the electrical and mechanical activity of the ureter are reduced. The plateau component of the action potential in the smooth muscle cell of the guinea pig ureter is more affected than the oscillations. Tetrodotoxin, which blocks the action potential in nerves, does not influence activity or conduction in the ureter. This is an important argument for the myogenic conduction of activity in this tissue.

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. Quelques aspects de la détection des graisses étrangères dans la matière grasse butyrique H. Hendrickx, A. Huyghebaert

AbstractDans l'insaponifiable des graisses de substitution ou graisses semblables au beurre, des cétones ont été détectées, qui ne sont pas des méthylcétones provenant d'une oxydation. II a été constaté par chromatographie en phase gazeuse et spectroscopie infra‐rouge que cette fraction de cétones est consistée de deux séries homologues du type CnH2n+1COCnH2n+1et CnH2n+1COCnH2n–1′ dans lesquelles n varie principalement de 11 à 17. La concordance, qui existe entre la composition des acides gras et des cétones, indique que ces cétones sont formées pendant la fabrication des graisses de substitution.