Tensión, deformación y fisurabilidad en el hormigón
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Durabilidad del hormigón
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Specimen replication for electron microscopy using x rays and x-ray resist
We point out the advantages of the use of x-ray resist as the recording medium in contact x-ray micrography, with subsequent viewing under the scanning electron microscope. Untreated specimens may be replicated with a resolution better than 100 nm. Photographs of latex spheres obtained by this technique are presented.
BRACKISH WATER AND FRESHWATER SPECIES OF THE DIATOM GENUS SKELETONEMA. II. SKELETONEMA POTAMOS COMB. NOV.1
SUMMARY Electron microscope investigations of the siliceous frustule show that the diatom described by Hustedt as Stephanodiscus subsalsus (A. Cleve) Hust. is not Skeletonema subsalsum (A. Cleve) Bethge (Melosira subsalsa A. Cleve) but is Microsiphona potamos Weber. This species is so similar to Skeletonema costatum (…
An experimental study of the kinetics of polymer crystallization during shear flow
Abstract Some principles of rheology are applied to the study of the shear‐induced crystallization of molten polymers. A new technique is described for measuring crystallization kinetics during isothermal flow at constant shear rate in a parallel plate rheometer. The crystallization rate is characterized by the time e…
A study of the motion of oil films on surfaces in air flow, with application to the measurement of skin friction
An oil film on a solid surface moves under the action of gravity or of the pressure gradient and skin friction resulting from the flow of air over the oil surface. Such oil flows are studied experimentally and theoretically. If the film is thin enough, the dominant force is the skin friction, and a simple relation is…
Structures of Two Crystalline Forms of Poly(butylene terephthalate) and Reversible Transition between Them by Mechanical Deformation
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTStructures of Two Crystalline Forms of Poly(butylene terephthalate) and Reversible Transition between Them by Mechanical DeformationMitsuru Yokouchi, Yoshio Sakakibara, Yozo Chatani, Hiroyuki Tadokoro, Tamotsu Tanaka, and Kentaro YodaCite this: Macromolecules 1976, 9, 2, 266…
Determination of the Structure of Cellulose II
The structure of regenerated cellulose is shown by x-ray diffraction to be comprised of an array of antiparallel chain molecules. The determination was based on the intensity data from rayon fibers and utilized rigid-body least-squares refinement techniques. The unit cell is monoclinic with space group P2(1) and dimen…
Can X-ray data distinguish bonding effects from vibrational smearing?
The frequent practice of combining X-ray and neutron diffraction for distinguishing vibrational smearing from charge deformation due to chemical bonding is neither necessary nor completely satisfactory. The two effects occur principally in distinct regions of real and reciprocal space. They can be distinguished by X-r…
Theoretical and experimental studies on one-dimensional magnetic systems
The present situation in theoretical and experimental studies on one-dimensional magnetic systems is fully discussed. Equal-time as well as the dynamic properties are included with an emphasis on the latter. Four model systems are examined in detail: TMMC (Heisenberg antiferromagnet), CsNiF3 (planar ferromagnet), CoCl…
Low-Energy Electrons and Surface Chemistry
Share Icon Share Twitter Facebook Reddit LinkedIn Reprints and Permissions Cite Icon Cite Search Site Citation G. Ertl, J. Küppers, Robert L. Park; Low‐Energy Electrons and Surface Chemistry. Physics Today 1 March 1976; 29 (3): 57. https://doi.org/10.1063/1.3023372 Download citation file: Ris (Zotero) Reference Manage…
Cleavage of type II and III collagens with mammalian collagenase: site of cleavage and primary structure at the amino-terminal portion of the smaller fragment released from both collagens
Collagenase cleavage of human Type II and III collagens has been studied using a highly purified preparation of rabbit tumor collagenase. Progress of the reactions in solution was followed by viscometry and the results indicated that under the conditions employed Type III collagen molecules were cleaved at approximate…
Optical studies of the 1.945 eV vibronic band in diamond
Abstract The 1.945eV band is the dominant end product of annealing radiation damage in diamonds containing isolated substitutional nitrogen atoms. In this paper uniaxial stress experiments are described which show the band to be a transition between A1 (ground) and E (excited) electronic states of a trigonal centre, t…
Band Structure and Optical Properties of Silicon Dioxide
The mixed-basis method has been used to compute the energy bands of an idealized $\ensuremath{\beta}$-cristobalite form of silicon dioxide. A direct-forbidden optical-absorption edge is predicted. Peaks in observed x-ray emission and optical-absorption spectra identified with critical points in the densities of states.
Free rotation of NO2 radicals in NaNO2 crystal
Infrared absorption spectra of ferroelectric NaNO2 crystals are obtained in the frequency range 700 to 950 cm−1 with polarized infrared rays. Periodic fine structures with spacing 4.35 cm−1 are observed for c-polarized rays in some of the specimens. These fine structures are attributed to the summation band of the v2…
X-ray and magnetic investigations of the high-temperature phase in the Co-rich CoV alloy system
X-ray and magnetic studies have been carried out for the f.c.c. CoV alloys containing V up to 30.1 at%. The X-ray measurements showed that the lattice parameter does not obey Vegard's law in the whole composition range observed in this work. The composition dependence of the lattice parameter can be related to the ma…
Chemisorption-Induced Surface Umklapp Processes in Angle-Resolved Synchrotron Photoemission from W(001)
Angle-resolved photoemission, using synchrotron radiation, from the chemisorption system W(001) + H shows a very large doublet of peaks at initial energies -1.3 and -0.6 eV for quarter-monolayer coverage which disappear at higher coverage. The emission lobes are strongly peaked in the $〈110〉$ azimuths and are attribut…
Dielectric study on the phase transitions in triammonium hydrogen disulfate (NH4)3H(SO4)2
Phase transitions in triammonium hydrogen disulfate (NH4)3H(SO4)2 were studied by means of dielectric measurements and differential thermal analysis. Below room temperature three phase transitions were observed at −8, −132, and −140°C. The dielectric constant along the c*-direction shows breaks at the −8 and −132°C tr…
The α → β phase transition in quartz and AlPO4 as studied by electron microscopy and diffraction
The α → β phase transition in quartz and in the isostructural AlPO4 has been studied in situ in an electron microscope. A very high density of defects was observed close to the transition temperature. A diffraction contrast analysis allowed us to identify these defects as dauphiné twins. In the neighbourhood of the tr…
Phase diagram of ammonium iodide obtained by Raman spectroscopy under hydrostatic pressure
The Raman spectra of ammonium iodide have been measured under hydrostatic pressure up to 6.4 kbar and at temperatures between 130 and 300 K. The strong change of the Raman spectra of NH4I allows the determination of the phase diagram of NH4I. The triple point is found to be at 5.5±0.1 kbar and 170±2 K. The temperature…