Cases controversy

The variety of life forms to be found near hydrothermal vents does not, of course, mean that life itself originated there these geological systems are much too unstable for that. The dynamics of tectonic plates cause the vents to disappear after some decades, or at most after a few hundred years. According to Nils Holm from the Department of Geology and Geochemistry at the University of Stockholm, the discovery of the hydrothermal vents led to intense, and in some cases controversial, discussions of the question as to whether hydrothermal systems were the birthplaces of life around four billion years ago. Many geologists believe that hydrothermal activity on the primeval Earth was probably stronger than it is today, as the thick... 

The determination of the atomic structure of surfaces is the cornerstone of surface science. Before the invention of STM, various diffraction methods are applied, such as low-energy electron diffraction (LEED) and atom beam scattering see Chapter 4. However, those methods can only provide the Fourier-transformed information of the atomic structure averaged over a relatively large area. Often, after a surface structure is observed by diffraction methods, conflicting models were proposed by different authors. Sometimes, a consensus can be reached. In many cases, controversy remains. Besides, the diffraction method can only provide information about structures of relatively simple and perfectly periodic surfaces. Large and complex structures are out of the reach of diffraction methods. On real surfaces, aperiodic structures such as defects and local variations always exist. Before the invention of the STM, there was no way to determine those aperiodic structures. 

To date, these types of biomass have not been shown as the most profitable sources of energy, although in some cases controversy has arisen that has resulted in negative attitudes towards the use of various types of biomass for energy production these points will be discussed in the following sections. 

When an electric potential is imposed across the skin, as in iontophoresis, ions will move along the pathways of lowest electrical resistance. Although the exact anatomical location of these low-resistance shunt pathways has not been well characterized, recent microscopy studies have shed mechanistic insight on the problem. Experimental variables of particular importance that have been shown to strongly influence the preferred iontophoretic transport pathways include (a) the physicochemical nature of the penetrant and (b) the penetrant s affinity for the different environments available (e.g., hair follicle, sweat duct, intercellular lipids). These unresolved and, in some cases, controversial issues will be discussed in the context of both classical and recent microscopy investigations. 

In Table 2 the major metabolites of the steroid sex hormones and some important related steroids are listed. Their relationships to their precursors are in some cases controversial at present and will be discussed in the next section of this article. Suffice it to say at the moment that simple relationships between the excretion rates of some of these metabolites and the secretion rates of their precursors are not easy to establish. On the other hand, it is fair to add that some of the complexities implied by recent work on the metabolism of testosterone and andros-tenedione, and on the metabolic activity of the placenta and fetus in pregnancy should not be allowed to obscure the relative simplicity of many aspects of the metabolism of progesterone and of estrogens. 

For a period of over 60 years, spanning 1850 to 1910, in spite of considerable experimental effort, there was much uncertainty and, in some cases, controversy as to how to describe the temperature-dependent behaviour of the kinetics of a chemical reaction. During this period a number of empirical relationships linking the experimental rate constant to temperature were proposed and championed by different groups of workers. The situation is aptly described in a famous textbook published in 1904. 

The last sessions of the workshop were specifically devoted to discussions with all the invited speakers and representatives participating. There were four separate sessions under different headings design and statistics, outcome measures, exposure assessment, and animal studies. These topics were chosen during the meeting as a result of the interest, and in some cases controversy, that had been apparent in these areas, and they also provided convenient headings under which to discuss future directions. The four sessions were summarized by Professor Yule who acted as rapporteur. 

Another reason for discussing the mechanism of nitration in these media separately from that in inert organic solvents is that, as indicated above, the nature of the electrophile is not established, and has been the subject of controversy. The cases for the involvement of acetyl nitrate, protonated acetyl nitrate, dinitrogen pentoxide and the nitronium ion have been advocated. 

Such is the case of 2-amino or 2-(monoalkyl or arylamino)-4-oxo-selenazolines. Thus because of this aminoc=iimino tautomerism. these compounds can be called 2-aminose enazo ines or 2-iminoselenazolidines and can be classed either as selenazolines or selenazolidines. This has been a source of controversy that has been resolved by recent spectroscopic studies (67. 68). 

Certain base adducts of borane, such as triethylamine borane [1722-26-5] (C2H )2N BH, dimethyl sulfide borane [13292-87-OJ, (CH2)2S BH, and tetrahydrofuran borane [14044-65-6] C HgO BH, are more easily and safely handled than B2H and are commercially available. These compounds find wide use as reducing agents and in hydroboration reactions (57). A wide variety of borane reducing agents and hydroborating agents is available from Aldrich Chemical Co., Milwaukee, Wisconsin. Base displacement reactions can be used to convert one adduct to another. The relative stabiUties of BH adducts as a function of Group 15 and 16 donor atoms are P > N and S > O. This order has sparked controversy because the trend opposes the normal order estabUshed by BF. In the case of anionic nucleophiles, base displacement leads to ionic hydroborate adducts (eqs. 20,21). 

States have made substantial recent progress in the adoption, and EPA approval, of toxic pollutant water-quahty standards. Furthermore, virtually all states have at least proposed new toxics criteria for priority toxic pollutants since Section 303 (c) (2) (B) was added to the CWA in February of 1987. Unfortunately, not all such state proposals address, in a comprehensive manner, the requirements or Section 303 (c) (2) (B). For example, some states have proposed to adopt criteria to protect aquatic hfe, but not human health other states have proposed human health criteria that do not address major exposure pathways (such as the combination of both fish consumption and drinking water). In addition, in some cases final adoption or proposed state toxics criteria that would be approved by EPA has been substantially delayed due to controversial and difficult issues associated with the toxic pollutant criteria adoption process. 

The specific protein-DNA interactions described in this book are all with DNA in its regular B-form, or, in some cases with distorted B-DNA. In biological systems DNA appears not to adopt the A conformation, although double-stranded RNA does preferentially adopt this conformation in vivo. Whether or not Z-DNA occurs in nature is a matter of controversy. However, the formation of A-DNA and Z-DNA in vitro does illustrate the large structural changes that DNA can be forced to undergo. 

When the seal maximum pressure is such that the gas test must be conducted well below rated discharge pressure, then another test, or substituted test, may be invoked in which the seals are removed. It may require removing the rotor however, with this procedure the joint makeup still remains a problem when the rotor is replaced. However, without the seals, the test described earlier is performed, using the rated discharge pressure rather than the maximum seal pressure. The acceptance test is the same also no leaks should be detected. The latter test should help to still controversy about minor joint leaks on a hydrostatic test, if the casing is proven at rated pressure on gas. 

This is one approach to the explanation of retention by polar interactions, but the subject, at this time, remains controversial. Doubtless, complexation can take place, and probably does so in cases like olefin retention on silver nitrate doped stationary phases in GC. However, if dispersive interactions (electrical interactions between randomly generated dipoles) can cause solute retention without the need to invoke the... 

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