Search Results - (Author, Cooperation:M. Simek)

2011-08-13

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

AIDS Vaccines ; Amino Acid Sequence ; Antibodies, Neutralizing/*chemistry/genetics/*immunology/isolation & purification ; Antibody Affinity ; Antibody Specificity ; Antigens, CD4/metabolism ; Base Sequence ; Binding Sites ; Binding Sites, Antibody ; Complementarity Determining Regions/genetics ; Crystallography, X-Ray ; Epitopes ; *Evolution, Molecular ; Genes, Immunoglobulin Heavy Chain ; HIV Antibodies/*chemistry/genetics/*immunology/isolation & purification ; HIV Envelope Protein gp120/chemistry/*immunology/metabolism ; HIV Infections/immunology ; HIV-1/chemistry/*immunology ; High-Throughput Nucleotide Sequencing ; Humans ; Immunoglobulin Fab Fragments/chemistry/immunology ; Immunoglobulin Heavy Chains/chemistry/immunology ; Immunoglobulin J-Chains/genetics ; Immunoglobulin Light Chains/chemistry/immunology ; Models, Molecular ; Molecular Sequence Data ; Mutation ; Sequence Analysis, DNA

1365-2389

Blackwell Publishing Journal Backfiles 1879-2005

Geosciences

Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Results from the pioneering research on the interactions between pH and denitrification in soil from the 1950s to the present are reviewed, the changing perceptions of this complex relationship are discussed, and the current status of the subject is assessed. Facets of this relationship that are analysed in detail include the direct or indirect influence of pH on overall denitrification rates in soils, changes in the composition of gaseous products that depend on pH, methods for measuring the process, the concept of an optimum pH for denitrification, and the adaptation of microbial denitrifying communities to acidic environments. The main conclusions to be drawn are as follows. Total gaseous emissions to the atmosphere (N2O, NO and N2) have repeatedly been shown to be less in acidic than in neutral or slightly alkaline soils. This may be attributable to smaller amounts of organic carbon and mineral nitrogen available to the denitrifying population under acid conditions rather than a direct effect of low pH on denitrification enzymes. Numerous laboratory and field studies have demonstrated that the ratio N2O:N2 is increased when the pH of soils is reduced. The relation between soil pH and potential denitrification as determined by various incubation methods remains unclear, results being influenced both by original conditions in soil samples and by unknown changes during incubation. The concept of an optimum pH for denitrification has been frequently proposed, but such a term has little or no meaning without reference to specific attributes of the process.

Electronic Resource

1467-8586

Blackwell Publishing Journal Backfiles 1879-2005

Economics

In contrast to the other countries in eastern and central Europe, unemployment has so far increased only modestly in the Czech Republic. Results are reported from a panel survey of a sample of initially unemployed workers in the industrial centre of Ostrava, interviewed in three rounds during 1993. Results are reported regarding the wage in the former job, the reservation wage, the wage in a new job and the minimum acceptable wage in another job for those who have become employed during the panel study. Finally, results from estimating a hazard function for leaving unemployment are reported.

Electronic Resource

1089-7690

AIP Digital Archive

Physics

Chemistry and Pharmacology

The vibrational excitation and decay of N2(B 3Πg) state has been investigated in a N2 pulsed rf discharge. The effect of the pulsing frequency and the duty cycle on the N2 (B,v=1–12) vibrational distribution, obtained from the 1PG spectra taken at different times in discharge and afterglow, has been examined in the N2 pressure range 2.4 mTorr–1.5 Torr. The measured (B,v) distributions have been analyzed by a steady-state kinetic model taking into account the main excitation processes, like the electron impact from N2(X 1Σg+,v) and N2(A 3Σu+,v) states, the associative excitation of N2(X,v) with N2(A,v), the pooling by N2(A,v) molecules, the atomic recombination of N(4S), as well as the quenching processes. For the various processes, experimental state-to-state rate coefficients from the literature and/or calculated data sets have been used. Measured N2(A,v) and electron energy distribution functions, and estimated N2(X,v) distributions have been used as input data for the model. The model satisfactorily reproduces almost all the measured distributions. The kinetic analysis evidences that the shape of the (B,v=1–12) distribution depends on the competition between the different processes and in turn on the time variation of both density and the degree of internal excitation of the reaction species with discharge repetition rate, duty cycle, and pressure. In general, in the discharge the electron impact is always the predominant excitation mechanism, while the processes involving long-lived species: N2(A,v) and N2(X,v) are important in the postdischarge regime. Under conditions of high metastable density, the associative collision processes contribute to (B,v) excitation in the discharge, and the electron impact process from the A and X states gives a non-negligible contribution to the low v levels in the millisecond time scale afterglow. An analysis of the B quenching is carried out. © 1999 American Institute of Physics.

Electronic Resource

0021-9673

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Chemistry and Pharmacology

Electronic Resource

0032-0633

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Geosciences

Physics

Electronic Resource

0301-0104

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Chemistry and Pharmacology

Physics

Electronic Resource

1435-1536

Springer Online Journal Archives 1860-2000

Chemistry and Pharmacology

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Electronic Resource

1435-1536

Springer Online Journal Archives 1860-2000

Chemistry and Pharmacology

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Electronic Resource

1435-1536

Springer Online Journal Archives 1860-2000

Chemistry and Pharmacology

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Electronic Resource

1435-1536

Springer Online Journal Archives 1860-2000

Chemistry and Pharmacology

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Electronic Resource

1435-1536

Springer Online Journal Archives 1860-2000

Chemistry and Pharmacology

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Electronic Resource

1572-8838

Springer Online Journal Archives 1860-2000

Chemistry and Pharmacology

Electrical Engineering, Measurement and Control Technology

Abstract Limiting currents and volume flow rates in the self pumping regime were measured on a model rotating electrolyzer with a variable geometry. The volume flow rate depends not only on the radius of the inlet orifice, outer disc radius, and angular velocity, but also on the interelectrode distance. Experimental mean current densities are compared with those calculated by the finite-element method, from an equation based on the theory of similarity of the diffusion layer, and from the theory of the rotating disc electrode with a ring.

Electronic Resource

1572-8838

Springer Online Journal Archives 1860-2000

Chemistry and Pharmacology

Electrical Engineering, Measurement and Control Technology

Abstract The distribution of local current densities in a rotating electrolyser with axial electrolyte inlet in a laminar flow regime was studied by the autoradiographic method. With all systems studied, the local current density decreased monotonically from a maximum value at the inner to a minimum at the outer boundary of the electrode. Experimental results are compared with the numerical solution of the convective diffusion equation by the finite element method.

Electronic Resource

1572-8838

Springer Online Journal Archives 1860-2000

Chemistry and Pharmacology

Electrical Engineering, Measurement and Control Technology

Abstract A theoretical relationship for mass transfer in the laminar flow region of streaming in a rotating electrolyser was derived by the method of similarity of the diffusion layer for electrodes placed sufficiently far from the rotation axis. The obtained relationship was compared with the known equations valid for systems with axial symmetry. The mean current densities were found from the numerical solution of the convective diffusion equation by the finite-element method and were compared with experimental results.

Electronic Resource

1432-0789

Key words Carbon dioxide ; Microbial biomass ; Microbial growth ; Soil respiration ; Glucose ; mineralization rate ; Chloroform fumigation extraction method

Springer Online Journal Archives 1860-2000

Biology

Geosciences

Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Abstract The effect of increasing soil CO2 concentration was studied in six different soils. The soils were incubated in ambient air (0.05 vol.% CO2) or in air enriched with CO2 (up to 5.0 vol.% CO2). Carbon dioxide evolution, microbial biomass, growth or death rate quotients and glucose decay rate were measured at 6, 12 and 24 h of CO2 exposure. The decrease in soil respiration ranged from 7% to 78% and was followed by a decrease in microbial biomass by 10–60% in most cases. High CO2 treatments did not affect glucose decay rate but the portion of Cgluc mineralized to CO2 was lowered and a larger portion of Cgluc remained in soils. This carbon was not utilized by soil microorganisms.

Electronic Resource

1432-0789

Key words Long-term fertilization ; Microbial biomass ; Dehydrogenase activity ; Denitrification potential ; Denitrifying enzyme activity

Springer Online Journal Archives 1860-2000

Biology

Geosciences

Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Abstract  Using soils from field plots in four different arable crop experiments that have received combinations of manure, lime and inorganic N, P and K for up to 20 years, the effects of these fertilizers on soil chemical properties and estimates of soil microbial community size and activity were studied. The soil pH was increased or unaffected by the addition of organic manure plus inorganic fertilizers applied in conjunction with lime, but decreased in the absence of liming. The soil C and N contents were greater for all fertilized treatments compared to the control, yet in all cases the soil samples from fertilized plots had smaller C:N ratios than soil from the unfertilized plots. The soil concentrations of all the other inorganic nutrients measured were greater following fertilizer applications compared with the unfertilized plots, and this effect was most marked for P and K in soils from plots that had received the largest amounts of these nutrients as fertilizers. Both biomass C determined by chloroform fumigation and glucose-induced respiration tended to increase as a result of manure and inorganic fertilizer applications, although soils which received the largest additions of inorganic fertilizers in the absence of lime contained less biomass C than those to which lime had been added. Dehydrogenase activity was lower in soils that had received the largest amounts of fertilizers, and was further decreased in the absence of lime. This suggests that dehydrogenase activity was highly sensitive to the inhibitory effects associated with large fertilizer additions. Potential denitrification and anaerobic respiration determined in one soil were increased by fertilizer application but, as with both the microbial biomass and dehydrogenase activity, there were significant reductions in both N2O and CO2 production in soils which received the largest additions of inorganic fertilizers in the absence of lime. In contrast, the size of the denitrifying component of the soil microbial community, as indicated by denitrifying enzyme activity, was unaffected by the absence of lime at the largest rate of inorganic fertilizer applications. The results indicated differences in the composition or function of microbial communities in the soils in response to long-term organic and inorganic fertilization, especially when the soils were not limited.

Electronic Resource

1432-0789

Key words Denitrification potential ; Denitrifying enzyme activity ; Soil reaction ; Respiration ; Fertilizers

Springer Online Journal Archives 1860-2000

Biology

Geosciences

Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Abstract  The denitrifying enzyme activity (DEA), denitrification potential (DP) and anaerobic respiration (RESP) together with chemical characteristics were measured in three contrasting soils collected from experimental arable plots that had been subjected to long-term (21–23 years) fertilizer treatments. The plots sampled were either unfertilized or had received either annual inorganic NPK, manure and lime, or inorganic NPK and manure treatments. Addition of inorganic NPK, manure and lime led to large increases in the DEA for two of the three soils, but in the absence of lime, inorganic NPK and manure caused only small increases in DEA compared to unfertilized soils. Both DP and RESP were increased by the addition of inorganic NPK, manure and lime, but were substantially decreased by fertilizer treatments without lime. In most cases there was a simple relationship between soil pH and either DEA and DP, with those treatments that reduced soil pH also leading to reduced denitrification and vice versa. The effects of artificially increasing the pH to a value close to the pH in unfertilized soils (6.3) by addition of NaOH to the soils that had received inorganic NPK, and which had the lowest soil pH values, were to increase substantially DEA, DP and RESP. In soil from one of the sites that had been stored for 5 weeks, the DP values responded differently between the fertilizer treatments. The DP value was lowest in the soil that had inorganic NPK and manure, higher in the soil that received inorganic NPK, manure and lime and it was the highest in unfertilized (control) soil. The soil pH values for these treatments were 4.47, 5.79 and 6.58, respectively. However, when the soil pHs were adjusted by addition of either H2SO4 or NaOH to give a range between pH 2 and 12, the DP values from all three fertilizer treatments showed almost identical responses. The optimum pH value for DP was between 7 and 8 for all three fertilizer treatments. Substrate-induced respiration values from all fertilizer treatments showed a similar trend to DP when the soil pHs were modified. The results show that soil pH was an important factor which in the studied soils controls the microbial community in general and the community of denitrifiers in particular. However, denitrifiers showed a high pH resilience leading to no marked change of the pH optimum for potential denitrification.

Electronic Resource

1432-0789

Key words Aeration status ; Glucose ; Microbial biomass ; Redox potential ; Anoxic conditions

Springer Online Journal Archives 1860-2000

Biology

Geosciences

Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Abstract  The response of the microbial community to changes in aeration status, from oxic to anoxic and from anoxic to oxic, was determined in arable soil incubated in a continuous flow incubation apparatus. Soil incubated in permanently oxic (air) and/or anoxic (O2-free N2) conditions was used as the control. Before experiments soil was preincubated for 6 days, then aeration status was changed and glucose added. Glucose concentration, extractable C, CO2 production, microbial biomass, pH and redox potential were determined 0, 4, 8, 12, 16, 24, 36 and 48 h after change of aeration status. If oxic conditions were changed to anoxic, the amount of glucose consumed was reduced by about 60%, and CO2 production was 10 times lower at the end of incubation compared to the control (permanently oxic conditions). Microbial biomass increased by 114% in glucose-amended soil but did not change in unamended soil. C immobilization prevailed over C mineralization. Redox potential decreased from +627 mV to –306 mV. If anoxic conditions were changed to oxic, consumption of glucose and CO2 evolution significantly increased, compared to permanently anoxic conditions. Microbial biomass did not change in glucose-amended soil, but decreased by 78% in unamended soil. C mineralization was accelerated. Redox potential increased from +238 to +541 mV. The rate of glucose consumption was low in anoxic conditions if soil was incubated in pure N2 but increased significantly when incubation was carried out in a CO2/N2 mixture.

Electronic Resource

1432-0789

Nitrogenase activity ; Earthworm casts ; Soil ; Aporrectodea caliginosa ; Lumbricus rubellus ; Acetylene reduction assay

Springer Online Journal Archives 1860-2000

Biology

Geosciences

Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Summary Nitrogenase activity associated with earthworms, their faeces and activity in soil was measured by the acetylene reduction technique. A clear increase in nitrogenase activity was found in field-deposited casts of Aporrectodea caliginosa in comparison with surrounding soil, although potential nitrogenase activity was significantly higher in soil than in casts. Nitrogenase activity associated directly with earthworms (Lumbricus rubellus ) was detected, indicating the presence of active N2-fixing bacteria on the body surface and/or in the gut. Laboratory experiments showed that nitrogenase activity in the casts of L. rubellus was higher than in unmodified soil, and that nitrogenase activity in soil was significantly increased by the burrowing and feeding activity of these worms. This paper discusses the possible causes of these earthworm effects on soil nitrogenase activity and some methodological problems of determining the nitrogenase activity.

Electronic Resource