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1.
EPR spectroscopy is a powerful tool to identify at a molecular level, the different steps of catalyst preparation, and of catalytic reactions: - the distribution among the different sites in zeolites can be determined; - the dispersion of the active phase may be appreciated; - the unsaturation degree of the active site may be evaluated using probe molecules such as water or13C enriched carbon monoxide.
- Deposition of paramagnetic transition metal ions onto a support is monitored, and the coordination sphere of the metallic center is characterized by EPR.
- The catalyst is also characterized after activation (thermal oxidation or reduction):
- The catalytic mechanisms can be investigated by studying the elementary steps of the catalytic reaction, as illustrated for methanol oxidation over Mo/SiO2 catalysts whose EPR results have extended the reaction mechanism proposed on the basis of kinetic data. In addition, reaction intermediates may be isolated inquasi-in situ conditions as in the case of olefin oligomerization catalyzed by Ni/SiO2 systems.
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3.
A. Bar-Nun A. Lazcano-Araujo J. Oró 《Origins of life and evolution of the biosphere》1981,11(4):387-394
Hoyle and Wickramasinghe have recently suggested that life may have originated in cometary nuclei rather than directly on Earth. Even though comets are known to contain substantial amounts of organic compounds which may have contributed to the formation of biochemical molecules on the primitive Earth, it is doubtful that the process of chemical evolution has proceeded in comets beyond the stage that has occurred in carbonaceous chondrites. Some of the arguments which do not favor the occurrence of biopoesis in comets are:
- A large layer of cometary ices is ablated from the nucleus' surface each time the comet passes through perihelion, so that essentially most of the organic products on the surface would be sublimed, blown off or polymerized.
- Because of the low temperatures of the cometary ices, polymers formed on one perihelion passage would not migrate deep enough into the nucleus to be preserved before they would be ablated away by the next perihelion passage.
- In the absence of atmosphere, and discrete liquid and solid surfaces, it is difficult to visualize the synthesis of key life molecules, such as oligopeptides, oligonucleotides and phospholipids by condensation and dehydration reactions as is presumed to have occurred in the evaporating ponds of the primitive Earth.
- Observations suggest that cometary nuclei have a rather weak structure. Hence, the low central pressures in comets combined with the high vapor pressures of cometary ices at the melting point of water ice, suggest that a liquid core is not a tenable structure. Yet, even if a cometary nucleus is compact enough to hold a liquid core and a transient liquid water environment was provided by the decay of26Al, the continuous irradiation in water of most of the biologically relevant polymers would have hydrolyzed and degraded them.
- Needless to say that the effects of radiation on self-replicating systems would also have caused the demise of any life forms which may have appeared under any circumstances.
- Concerning viruses, the high specificity of host-parasite relationships and their coevolutionary lines of descent, rule out a cometary origin for them.
4.
Thomas H. Jukes 《Origins of life and evolution of the biosphere》1969,1(4):469-490
Evolution depends upon the occurrence of occasional changes, large or small, in hereditary characteristics. Molecular genetics gave rise to the new field of molecular evolution, which is currently exploring the changes that take place in proteins and nucleic acids over long periods of time. The following are some of the fundamental assumptions:
- The phenotypic characteristics of organisms depend directly on proteins.
- Proteins are synthesized in accordance with information carried in molecules of DNA as sequences of the four bases, adenine, guanine, cytosine, and thymine. The information is transcribed into molecules of messenger RNA and is translated into proteins by the intervention of the genetic code.
- Changes in the composition of the base sequences in DNA can take place in living organisms, and these changes can affect the phenotypic characteristics of the next generation.
- The process of natural selection favors the perpetuation of organisms which compete successfully in the struggle for existence. This process leads to the elimination of all but a small fraction of the astronomical number of possible protein molecules that could result from genetic translation of the possible variants of DNA. Furthermore, the number of protein molecules was originally much smaller than it is to-day, and it has increased by hereditary processes rather than by the chance appearance of entirely new proteins.
- The DNA present in any single cell contains the complete information for all the hereditary characteristics of the organism. The amount of DNA per cell may increase during evolution and this increase has produced modern organisms that are ‘higher’, more specialized, and more complex, from carlicr and simpler forms.
- Protein molecules are slowly and steadily differentiated during evolution if their genes are physically separated from each other, by allopatric speciation or even by duplication and translocation, whether or not the function of the proteins are changed.
- Mutations, together with recombination, contribute to changes in the genetic pool which provide the variability within populations that is necessary for evolution of species.
5.
Purpose
to determine diagnosis and prognosis value of MRI in Peyronie’s disease.Material and Methods
thirty one penile MR examinations have been performed in 28 patients aged between 21 and 73. (1 tesla; surface coil; sagittal SET1, axial SET2 weighted, T1 before and after Gadolinium)Results
Conclusion
MRI can be helpfull in the pretreatment assessment and int he follow-up of Peyronie’s disease. 相似文献6.
D. Bruce Campbell 《Molecular neurobiology》1995,11(1-3):193-216
Pharmacological and toxicological studies undertaken on drugs that affect the brain are frequently performed in disparate species under various experimental conditions, at doses often greatly in excess of those expected to be administered to humans, and the findings are extrapolated implicitly or explicitly with scant regard to differences in the biodisposition of the drugs. Such considerations are necessary since:
- Species;
- Strain;
- Gender;
- Route;
- Dose;
- Frequency and time of administration;
- Temperature;
- Coadministration of drugs; and
- Surgical manipulation
7.
U. H. Mane 《Hydrobiologia》1975,47(3-4):439-451
- The neutral red technique was employed to study the rate of filtration in Katelysia opima.
- The weight specific water filtration was found to be greater for younger clams compared to the older ones.
- The rate of water filtration increased with decreasing salinity.
- Water filtration was found to increase as temperature increased, reaching a maximum at 35°C. but then sharply decreasing at 39°C.
- Light had no significant effect on the rate of filtration.
- Suspended matter was found to affect the rate of water filtration.
- The rate of filtration was low at high pH and high in low pH.
- The rate of water filtration was found to be faster during high tide than during low tide.
- The presence of the parasitic crab, Pennotheris sp., in the mantle cavity of clams had a marked effect on the particle filtration.
- Accidental cut of the siphon tips had no effect on the rate of filtration.
8.
Prof. Dr. Jobst Wendt 《Facies》1982,6(1):185-201
The fauna of the upper Cassian Formation is composed mainly of reef-building and reef-dwelling organisms which occur as reeeposited material in basinal sediments, but have not been found as original reef bodies. Such bodies have now been discovered in the uppermost Cassian Formation of the central Dolomites from the Sella Group in the west to the Monti Cadini in the east. Generally they are small-scale patch reefs, not exceeding a few metres in thickness and lateral extent, which are intercalated in well-bedded detrital and micritic limestones. locally, larger biostromes spread out from the margins of the Cassian Dolomite buildups. Four types of faunal communities have been encountered in these reefs:
- The thrombolite-calcareous algae community, composed of small patchy cryptalgal structures binding poorly sorted debris and associated with other Cyanophyta, sessile formainifera and scattered calcareous sponges and corals. This type is the most common within the calcareous and marly-tuffaceous facies of the Cassian Formation.
- The calcareous sponge-coral community, composed mostly of calcareous sponges (stromatoporoids, some pharetronids) and, to a lesser extent, colonial corals and thrombolites. This community corre-sponds well to the Cassian reef fauna, best known from erratic blocks at Alpe di Specie, but has been found in situ only at one locality.
- The Spongiomorpha-Solenopora community, associated with scattered calcareous sponges and colonial corals, forming a thin biostrome at one locality.
- Coral communities, composed predominantly of colonial Scleractinia; found only in small or stratigraphically illdefined outcrops and in erratic blocks.
9.
- An ecological and physiological study ofI. chelipes from Lake Veere, The Netherlands, was made.
- Both osmoregulatory capacity and survival decrease with increasing temperature as well as with decreasing salinity.
- Respiration experiments suggest that the need of energy by osmoregulatory activity may be supplied at the cost of other physiological processes, at any rate at temperatures of 10°C and higher.
- It may be expected that, if temperatures higher than 15°C and salinities lower than 8‰ coincide, the population ofI. chelipes will be affected negatively.
10.
The following scheme lists the problems which have been and will continue to be encountered in grazing experiments on natural particle assemblages. In some cases there are solutions, but many of the problems listed below remain intractable. To solve them will require innovative approaches, most probably combining the use of particle counters with other techniques to approach the problem to be solved from several angles at once. Variance between samples due to - statistical causes (especially caused by large particles) and - differences between experimental bottles and between experimentals and controls at start of experiment. Shifts in particle distribution during experiment due to - increase in small particles - growth of bacteria and other organisms due to excretion of grazers and - breakage during handling by grazers into fragments. Processes, independent of grazing, leading to changes in particle size distribution due to - primary production - grazing by additional components and - bacterial growth on detrital particles and the formation of detrital flocs. 相似文献
11.
- A method for the direct recording of the PEP efflux from isolated mitochondria is described.
- This method has been used to show the stimulation of PEP efflux by externally added Mn++ ions.
- Valinomycin, uncoupler and oleate were also shown to stimulate PEP efflux.
- Valinomycin caused an increase in the internal concentration of both PEP and citrate.
- The results indicate that the major pathway of PEP synthesis in isolated mitochondria is via PEP carboxykinase and the results do not call for an unknown pathway of metabolism.
- Two interactions between PEP and citrate are described; competition for the mitochondrial interior and the stimulation of PEP production by citrate.
12.
The effect of feeding on the respiration rate of Brachionus plicatilis was studied. Oxygen consumption was determined under two feeding regimes, duplicate feeding and constant feeding. Oxygen consumption rate increased during feeding. The oxygen consumption profile is discussed in relation to the following processes:
- filtration, mastication, and locomotion during feeding
- specific dynamic action (SDA)
- egg formation and routine metabolism.
13.
S. Uchino M. Yamakawa S. Ichikawa M. Okubo Y. Nakamura A. Limura 《International Journal of Anthropology》1986,1(1):89-89
Observations of the outer layers and sections of an object are made by visible rays, but electromagnetic waves make it possible to observe things on the surface of an object that are not observable by visible rays. It may be because of some specific waves whose reflection toward or absorption by visible rays is different. Thus, we have observed the surfaces of objects by irradiating them with ultraviolet rays and taking photographs. The following are the characterstics of ultraviolet photographs which we have confirmed.
- Since every uneveness of the surface of an object is magnified in ultraviolet photographs, projections and depressions can be more clearly observed.
- It is possible to more accurately detect the extent of the existence of an object, depending on the substance, as their pictures are exaggerated.
14.
Cycling of phosphorus (P) at the sediment/water interface is generally considered to be an abiotic process. Sediment bacteria are assumed to play only an indirect role by accelerating the transfer of electron from electron donors to electron acceptors, thus providing the necessary conditions for redox-and pH-dependent, abiotic sorption/desorption or precipitation/dissolution reactions. Results summarized in this review suggest that
- in eutrophic lakes, sediment bacteria contain as much P as settles with organic detritus during one year
- in oligotrophic lakes, P incorporated in benthic bacterial biomass may exceed the yearly deposition of bioavailable P several times
- storage and release of P by sediment bacteria are redox-dependent processes
- an appreciable amount of P buried in the sediment is associated with the organic fraction
- sediment bacteria not only regenerate PO4, they also contribute to the production of refractory, organic P compounds, and
- in oligotrophic lakes, a larger fraction of the P settled with organic detritus is converted to refractory organic compounds by benthic microorganisms than in eutrophic lakes.
15.
Hilmar Brunn Rolf Bretz Peter Fankhauser Thomas Spengler Otto Rentz 《The International Journal of Life Cycle Assessment》1996,1(4):221-225
Synthetic sulfuric acid is used in a wide range of applications in fine chemical industry. Despite an already performed optimization of input amounts, used sulfuric acid is still a quantitatively important waste by-product. As a result, different utilization technologies for used sulfuric acid exist: ? the starting point for a comparative LCA of the above mentioned utilization technologies at a concrete situation is explained, in a work of Ciba-Geigy Corp. ? a short summary of the comparative LCA is presented ? lessons learned from performing the LCA and using it in a decision process are described. 相似文献
- production of gypsum
- thermal reductive cracking
- thermal cracking and oxidation
16.
O. Professor Dr.-Ing. H. Brauer 《Bioprocess and biosystems engineering》1987,2(4):149-159
The development and investigation of high-efficiency bioreactors is one of the primary problems bioprocess engineers have to solve. With increasing efficiency of the bioreactor the downstream processes will be much simplified, energy and costs will be substantially reduced. According to fundamental research on the properties of stirred tank bioreactors the following rules for the design of bioreactors should be observed:
- Prevent rotational motion of the biosuspension.
- Generate motion of the biosuspension in the radial and axial direction.
- Prevent fluid flow in big spaces.
17.
Forest regeneration in the vegetation complex of the submontane belt in the Southern Alps involves the active participation ofOstrya carpinifolia woods and their wood edge communities. The corresponding syndynamical processes are described by employing phytosociological, phytogeographical and ecological methods. It is concluded that:
- The communities of the grassland-wood transition are of major importance in the successional developments in this man-made vegetation complex.
- Many species occurring in the region of the deciduous forests of Eurasia find their refuge in such transitional communities and are supposed to play an important part in the succession.
- Ostrya carpinifolia is considered as an early successional tree species.
18.
The development and investigation of high-efficiency bioreactors is one of the primary problems bioprocess engineers have to solve. With increasing efficiency of the bioreactor the downstream processes will be much simplified, energy and costs will be substantially reduced. According to fundamental research on the properties of stirred tank bioreactors the following rules for the design of bioreactors should be observed:
- Prevent rotational motion of the biosuspension.
- Generate motion of the biosuspension in the radial and axial direction.
- Prevent fluid flow in big spaces.
19.
- All methods used to analyze amino acid composition of different enzymes agree well with each other.
- They lead to a relationship between amino acid composition and function of proteins.
- Cytochrome oxidase is in a class by itself; copper-containing oxidases are closely related as expected.
20.
G. Peres 《Andrologie》1995,5(3):326-331
Androgenic hormones seem to be of beneficial effects on sports performance: - they increase motivation, will, aggressiveness, resistance to the stress and to the fatigue, leading to an increase of the training quantity, - they increase bone mineralization and probably mechanical resistance, - they stimulate the bone marrow and so, with the erythropoietin, the erythropoiesis, - they increase the tendancy to hyperglycemia, but with a decrease of the tolerance to the glucose, - they stimulate the fatty acids mobilization from the adipose tissue, for their utilization in the muscle during the exercise, - they participate, for the trained sportmen, to a better gestion of the muscle glycogen storage: their utilization during exercise is decreased, - they increase the lean body mass, with an increase of the protein synthesis and a decrease of the protein catabolism, leading also to an increase of the muscle force under training. There is no beneficial effect upon the tendons, - they have an immunomodulation action. 相似文献