Problems in studying

Sufficient evidence is available to indicate that atmospheric pollution in vaiying degrees does affect health adversely. [Amdur, Melvin, and Drinker, Effec t of Inhalation of Sulfur Dioxide by Man, Lancet, 2, 758 (1953) Barton, Corn, Gee, VassaUo, and Thomas, Response of Healthy Men to Inhaled Low Concentrations of Gas-Aerosol Mixtures, Arch. Lnviron. Health, 18, 681 (1969) Bates, Bell, Burnham, Hazucha, and Mantha, Problems in Studies of Human Exposure to Air Pollutants, Can. Med. A.s.soc. J., 103, 833 (1970) Ciocco and... 

One of the important and diffieult problems in studying the eomposition/ properties dependenee of eomplex oxide materials is oxygen steehiometry determination. 

A central problem in studying ion-molecule reactions is the dependence of the microscopic cross-section, a or the rate constant k upon the relative velocity of the ion and the molecule. Only from reliable, established data on this dependence can one choose among the various theoretical models advanced to account for the kinetics of these processes such as the polarization theory of Gioumousis and Stevenson (10) or the more recent phase-space treatment of Light (26). 

Effect of UV on Productivity of the Southern Ocean. Has ozone depletion over Antarctica affected the productivity of the Southern Ocean There is no easy answer. First, one has to take into account the fact that the drastic decrease of ozone over Antarctica has been reported as recently as 1976, a relatively short time in the evolution of the organisms to develop mechanisms to cope with elevated UV. One of the most vexing problems in studying the effects of UV radiation on productivity, is a dearth of historical data on the level of UV. Without these baselines, normal fluctuations could easily be interpreted as decline in productivity. Second, there is a host of biotic and abiotic factors that play significant roles in governing the productivity of the Southern Ocean (40). Ultraviolet radiation is but one more complicating factor to be considered in an already stressful environment. 

The chief problem in studying the chemical nature of AB cements is that many are essentially amorphous, so that the powerful tool of X-ray diffraction (XRD) analysis cannot be used. Some AB cements do exhibit a degree of crystallinity, but rarely in significant amounts indeed, complete crystallinity is usually a sign that the reaction product is not cementitious. The literature contains numerous examples of workers being misled by the results of XRD analysis into neglecting the presence and significance of the amorphous phase. 

They have been prepared with several anions,332-335 the tetrafluoroborate salt exhibits SA and Sc phases332,333 but the triflate shows a nematic phase 334 One of the problems in studying these complexes was the very high temperatures at which the phases existed and the fact that decomposition was often observed in the upper reaches of the SA phases. Reduction of these temperatures was achieved by changing the small anions for dodecyl sulfate that also make that more materials exhibit nematic SA and Sc phases, and another more viscous phase appeared, named cubic phase So- With the anion octyl sulfate336 the crystal structure of one of the complex with 4-metoxystilbazole could be achieved (20), with this anion the cubic phase was not present. 

Peters, K., and Richards, F.M. (1977) Chemical cross-linking reagents and problems in studies of membrane structure. Annu. Rev. Biochem. 46, 523-551. 

The study of shape and crystal structure of small metallic particles is of prime importance in modern catalysis science. The relation between reactivity and structure is still not well known. The main problem in studying small metallic particles is that conventional techniques fail in the manometer diameter range. However it is possible to overcome these difficulties by the application of non-conventional methods. It is the purpose of this paper to review some of these methods and to present some results on the characterization of gold and platinum particles. 

One of the major problems in studying polymers quantitatively is the absence of model compounds for the purpose of calibration. A method of obtaining spectra of the components of a mixture spectra is based on obtaining the ratio of absorbances. This method was first used by Hirschfeld 851 for mixtures of components differing in relative concentration. This approach was later generalized but is limited to a rather... 

The lack of or the insufficience of chromatographic data (RI, Rt) and reference compounds for most of the labdanes [159], present basic problems in studies concerning the qualitative and quantitative analysis of plant extracts using GC or/and GC-MS analysis. Also their use as chemotaxonomic markers within species where they occur is limited. GC... 

The variety of values obtained in earlier studies reflect some of the difficulty. The value at pH 2.1 and 30° from Ginsburg and Carroll (Table XXII, No. 5) does not agree well with that given above, but the effect of phosphate and sulfate in stabilizing the structure, even at acid pH, is clearly shown. Direct calorimetric results (Nos. 6 and 7) do not agree with each other and bracket the data of Brandts and Hunt. Aggregation may be a problem in studies with more concentrated solutions. The more... 

One of the problems in studying zinc enzymes is that the zinc is silent from both electronic and nuclear points of view, and so provides no information about site symmetry and ligand groups. Accordingly a dominant feature of work on zinc enzymes has been the use of probe metal ions to replace Zn. Co11 has been used with some success, while a more recent innovation is the use of 113Cd2+ as a probe, and the application of Cd NMR techniques. 

One of the greatest problems in studying consciousness and altered states of consciousness is an implicit prejudice that tends to make us distort all sorts of information about states of consciousness, when you know you have a prejudice you are not completely caught by it, for you can question whether the bias is really useful and possibly try to change it or compensate for it. But when a prejudice is implicit it controls you without your knowledge and you have little chance to do anything about it. 

One of the problems in studying the chemistry of wet processes for desulfurization and denitrification of flue gas in order to determine an optimum design and operating condition of scrubbers is the difficulty in quantitatively detecting all important species produced. Specifically, there was no methodology available for the convenient determination of the large number of N-S compounds that can be produced. 

CRITICAL ASSESSMENT OF THE METHOD A very critical item has been a tendency of ACTH to fluctuate widely and rapidly under conditions of stress (Meeran 1989, Lambert 1985, Goverde 1989). This is especially a problem in studies with dogs, where the experiments need to be performed under stress-free conditions and even then there will be the difficulty of rapidly fluctuating concentrations. 

It is important to remember that the splitting of the t2g orbitals also occurs, but the splitting is smaller than that of the eg orbitals. Although it might be expected that complexes of dl and d2 ions would undergo Jahn-Teller distortion, such distortion would be extremely small. In fact, there are some other problems in studying this type of distortion because of the short lifetimes of excited states and rearrangement of the complexes. 

The preceding statement should not invoke in the reader an idea about the intractability of the problem. In studies of polymerizations, even of the complicated ones, the necessary direct and indirect evidence is almost always accessible, although it may not be easy to obtain. 

The central problem in studying the conductivity is to find the energy and temperature dependence of ct( ) and the related p( ) and to understand the physical processes involved in the transport. The motion of the carriers at non-zero temperatures may be either in extended states or by hopping in localized states and the magnitude of the conductivity is determined by the elastic and inelastic scattering mechanisms. In addition, when there is any local inhomogeneity of the... 

A longstanding problem in studies of ACS are the heterogeneous composition of the protein, with only 20-30% activity, reflected in the intensity of the NiFeC EPR signal, described above. After recognition that the vulnerability of the proximal metal site in the A-Cluster to substitution with different metals underlies this heterogeneity, a protocol was developed in which a Cu+ -speciflc chelator is used to remove the Cu and Ni is added to reconstitute the di-Ni center. 

A significant problem in studies on photocatalysis is the definition of positive hole. Positive hole is defined as a defect of an electron (i.e., a positive hole must be included in a substance, while an electron is a real substance). Therefore, not only h produced by photoinduced band-to-band transition in solid materials but also a hydroxyl radical, which is a one-electron deficient hydroxyl anion, can be a positive hole. If this definition is accepted, there should be no difference in the photocatalsrtic oxidation mechanisms between direct hole transfer and surface-adsorbed hydroxyl radical reaction, since it is well known that the surface of a metal oxide is covered with chemically or physically adsorbed water and a positive hole passing through this water layer into a solution may be a hydroxyl radical or its protonated or deprotonated species (Fig. 4). Actually, hydroxyl... 

Under dilatational stresses and in contact with solvents, polymers exhibit a cavitational mode of plasticity called environmental crazing. This phenomenon occurs at small strains in the order of a few percent well below the yield point of the polymer. Environmental crazes are normally observed at the surface of a specimen where the penetrating solvent produces a polymer-solvent mixture. Environmental crazing has been extensively discussed in the literature (see e.g. However, one basic problem in studying this phenomenon arises from the fact that the macroscopic state of the sample at craze initiation may differ considerably from the local one which is, in general, poorly defined. 

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