Experiment hardness

Constipation can be due to primary and secondary causes (Table 18-1). Primary or idiopathic constipation is typified by normal-transit constipation, slow-transit constipation, and dyssynergic defecation. In the normal-transit type, colonic motility is unchanged and patients tend to experience hard stools despite normal movements. In the slow-transit type, motility is decreased leading to infrequent harder, drier stools. In dyssynergic defecation (also known as pelvic floor dysfunction), patients have lost the ability to relax the anal sphincter while coordinating muscle contractions of the pelvic floor. Some causes of secondary constipation are listed in Table 18-1. 

Patients report a history of abdominal pain or discomfort that is relieved with defecation. Symptom onset is associated with change in frequency or appearance of stool. Some persons experience hard, dry stools whereas others experience loose or watery stools. Some stools may be small and pellet-like in appearance while others may be narrow and pencil-like. 

Fig. 3.1. Left visible pump/X-ray probe scheme for femtosecond TRXRD experiments. Hard X-ray pulses are generated by shining intense femtosecond laser pulses on a metal target (laser plasma X-ray source). Right geometrical structure factor of bismuth as a function of inter-atomic distance for diffraction from (111) and (222) lattice planes. From [1] and [2]...

In this experiment hard water is made by dissolving Epsom salt in water. Epsom salt contains magnesium ions. 

Feller and Peterson, op. cit. They state, Straightforward increases in the size of the one-particle basis set of Gaussian functions or the use of more sophisticated levels of theory can frequently lead to a seemingly paradoxical deterioration in the agreement with experiment. Hardly a characteristic for a mature theory. 

For shorter chains an approximate expression for any solvency may be derived using the Flory excluded-volume parameter v, which is unity when the segments experience hard-core repulsion and vanishes in case of a -solvent. Based on Flory s result [37] for the expansion coefficient, the coil size can be written as [39] ... 

The high energies of the K p lines (33-35 keV) favor the K-emission spectroscopy for use in high-pressure experiments. Hard X-rays easily penetrate most of the high pressure window or anvil materials. The pressure dependence of the K p emission line shifts was measured in Ce, SmS (Shaburov et al. 1974) and in CeNij, CeCoj (Shaburov et al. 1981) up to 12kbar. 

The simulation results for this model that will be discussed in the following section were obtained by multithreaded, multicanonical, and parallel tempering Monte Carlo simulations imder the assumption that the peptide only interacts with the surface layer (/= 1). A simulation box of dimension [50 A] with periodic boundary conditions parallel to the substrate was used. In perpendicular direction, peptide mobility is restricted by the Si substrate residing by definition atz = 0. The influence of the wall parallel to the substrate is simply steric, i.e., the atoms experience hard-wall repulsion atz = Zmax = 50 A [340]. 

The numerical illustration given above is so highly idealized that any agreement with experiment could hardly be more than coincidental. A number of caveats have been mentioned, including the inadequacies of theoretical calculations, the various surface distortions and reconstructions expected, surface... 

Understanding VER in condensed phases has proven difficult. The experiments are hard. The stmcturally simple systems (diatomic molecules) involve complicated relaxation mechanisms. The stmctures of polyatomic molecules are obviously more complex, but polyatomic systems are tractable because the VER mechanisms are somewhat simpler. 

Such water, and also that containing salts of multipositive metals, (usually sulphates), is said to be hard since it does not readily produce a lather with soap. Experiments with alkali metal salts can be performed to verify that the hardness is due to the presence of the multipositive metal ions and not to any of the anions present. The hardness due to calcium and magnesium hydrogencarbonates is said to be temporary since it can be removed by boiling ... 

The preparation of synthetic polymers is hardly suitable for the ordinary organic laboratory. However, a few simple demonstration experiments are described below which, it is hoped, will provide an elementary introduction to the subject. 

An interesting example of a large specific surface which is wholly external in nature is provided by a dispersed aerosol composed of fine particles free of cracks and fissures. As soon as the aerosol settles out, of course, its particles come into contact with one another and form aggregates but if the particles are spherical, more particularly if the material is hard, the particle-to-particle contacts will be very small in area the interparticulate junctions will then be so weak that many of them will become broken apart during mechanical handling, or be prized open by the film of adsorbate during an adsorption experiment. In favourable cases the flocculated specimen may have so open a structure that it behaves, as far as its adsorptive properties are concerned, as a completely non-porous material. Solids of this kind are of importance because of their relevance to standard adsorption isotherms (cf. Section 2.12) which play a fundamental role in procedures for the evaluation of specific surface area and pore size distribution by adsorption methods. 

The hysteresis loops to be found in the literature are of various shapes. The classification originally put forward by de Boer S in 1958 has proved useful, but subsequent experience has shown that his Types C and D hardly ever occur in practice. Moreover in Type B the closure of the loop is never characterized by the vertical branch at saturation pressure, shown in the de Boer diagrams. In the revised classification presented in Fig. 3.5, therefore. Types C and D have been omitted and Type B redrawn at the high-pressure end. The designation E is so well established in the literature that it is retained here, despite the interruption in the sequence of lettering. 

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