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  • Springer  (152,772)
  • Wiley  (57,833)
  • 2015-2019  (126,232)
  • 1995-1999  (84,373)
  • 2017  (126,232)
  • 1999  (84,373)
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  • 2015-2019  (126,232)
  • 1995-1999  (84,373)
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  • 101
    Electronic Resource
    Electronic Resource
    Formation of single- and double-strand breaks of pBR322 plasmid irradiated in the presence of scavengers (1999)
    Springer
    Radiation and environmental biophysics 38 (1999), S. 105-109 
    Details
    ISSN: 1432-2099
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract  By the method of gel electrophoresis, radiation-induced DNA single- and double-strand breaks (SSB, DSB) were studied with a model system of pBR322 solution in vitro in the presence of ·OH radical scavengers, mannitol and TE (10–2 mol dm–3 Tris and 10–3 mol dm–3 ethylene diamine tetra-acetic acid). Experiments showed that SSB resulted from one-hit events of radiation energy deposition and DSB resulted from both one-hit and two-hit energy deposition events and so were distinguished into two classes of αDSB and βDSB. Moreover, α/β, where α is the number of DSB per unit dose induced in one irradiation event and β the number of DSB per unit squared dose induced by the combination of two independent SSB, was related to the scavenging capacity, σ, and for σ〉108 s–1,αDSB predominate over DSB. On the other hand, if σ〈2×108 s–1, the measured G(αDSB) decreased in parallel with G(SSB), i.e., G(αDSB)/G(SSB) was a constant. When σ〉2×108 s–1, G(αDSB) decreased slightly so that the ratio of αDSB to SSB evidently increased. Therefore, αDSB could be induced by the radical transfer mechanism for σ〈2×108 s–1 and contrarily produced by the local multiply damaged sites (LMDS) mechanism for σ larger than this value. In addition, the distance for two independent complementary SSB forming a DSB was deduced, but no apparent variation of it was found in the wide σ range from ∼105 to ∼109 s–1, which shows that the DNA steric structure was not influenced by mannitol.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004110050145
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  • 102
    Electronic Resource
    Electronic Resource
    Repair of cellular radiation damage in space under microgravity conditions (1999)
    Springer
    Radiation and environmental biophysics 38 (1999), S. 133-138 
    Details
    ISSN: 1432-2099
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract  The influence of microgravity on the repair of x-ray-induced DNA double-strand breaks was studied in the temperature-conditional repair mutant rad54–3 of diploid yeast Saccharomyces cerevisiae. Cells were exposed on the ground and kept at a low temperature until microgravity conditions were achieved. In orbit, they were incubated at the permissive temperature to allow repair. Before re-entry they were again cooled down and kept at a low temperature until final analysis. The experiment, which was flown on the shuttle Atlantis on flight STS-76 (SMM-03), showed that repair of pre-formed DNA double-strand breaks in yeast is not impaired by microgravity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004110050149
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  • 103
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    Electronic Resource
    The track structures of ionizing particles and their application to radiation biophysics (1999)
    Springer
    Radiation and environmental biophysics 38 (1999), S. 175-184 
    Details
    ISSN: 1432-2099
    Keywords: Key words Alpha particle ; Deuteron ; Proton ; Biophysical modeling ; Radiation quality influence ; Bacillus subtilis ; DNA density ; Monte Carlo calculations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract  A new approach to the interpretation of the effects of radiation on cells is described, in which sample particle tracks are constructed using a Monte Carlo computer program and the exposure of cellular targets to these tracks is simulated using a second program known as BIOPHYS. Data on the shapes and DNA contents of the cell nuclei are obtained from the literature. It is assumed that the sensitive material is DNA, and that the target is divided into cubes of approximately 2 nm (the diameter of the DNA helix) per side; the numbers of these cubes containing different numbers of ionizations are derived. Two different methods of analysing the output of BIOPHYS are described. In the first, it is assumed that lethality is caused by the occurrence of a number of ionizations equal to or greater than a certain threshold in one cube; in the second method, it is assumed that only two ionizations are required, in different parts of the cube, but that only some fraction of the cube is sensitive. These models have been applied to the interpretation of the variation of radiosensitivity with a linear energy transfer (LET) of spores of Bacillus subtilis exposed wet and dry, and good fits to the published experimental data were obtained using both models. Fits to experimental data for a range of other cell lines will be presented in a second paper.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004110050153
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  • 104
    Electronic Resource
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    Practical aspects of Monte Carlo simulation of charged particle transport: Mixed algorithms and variance reduction techniques (1999)
    Springer
    Radiation and environmental biophysics 38 (1999), S. 15-22 
    Details
    ISSN: 1432-2099
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract This paper is concerned with the practical implementation of Monte Carlo simulation methods for charged particle transport. The emphasis is on light particles (electrons and positrons) because of the larger scattering and energy straggling effects. Differential cross sections (DCS) for the various interaction mechanisms are described. As the average number of interactions along the particle track increases with the initial energy, detailed simulation becomes unfeasible at high energies. We can then rely on mixed simulation algorithms: hard events (i.e. individual interactions with angular deflection or energy loss larger than given cutoff values) are sampled from the DCS whereas soft events are simulated by means of a multiple scattering approach. Too frequently, the statistical uncertainty of analogue simulation (i.e. strict simulation of the physical interaction process) is found to be so large that results are meaningless. This problem can be partially solved by applying simple variance reduction techniques.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004110050133
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  • 105
    Electronic Resource
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    Synthetic activity of rat blood lymphocytes under acute and continuous gamma-irradiation – fluorescent microspectral study (1999)
    Springer
    Radiation and environmental biophysics 38 (1999), S. 49-56 
    Details
    ISSN: 1432-2099
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract The effects of different doses of acute and continuous gamma-irradiation on the synthetic activity of rat blood lymphocytes stained with acridine orange were studied by fluorescent microspectrometry. Male rats were exposed to acute gamma-irradiation with doses of 7.5, 4 and 3 Gy, or to continuous irradiation with dose rates of 14.4, 2.1, 1.1 and 0.43 cGy/day, respectively. The changes of the synthetic activity of blood lymphocytes occurred in three main stages after acute gamma-irradiation and in four stages under continuous irradiation. The stages reflect the processes of depression and activation of the immune system under irradiation. Essential differences between the acute and continuous effects were observed in the first stage. After acute gamma-irradiation, the synthetic activity decreased sharply, indicating the predominant contribution of the damaging effect of irradiation, whereas under continuous irradiation, as a result of the stimulatory effect of low-dose irradiation, the synthetic activity increased during the first stage.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004110050137
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  • 106
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    Radon-induced lung cancer in smokers and non-smokers: risk implications using a two-mutation carcinogenesis model (1999)
    Springer
    Radiation and environmental biophysics 38 (1999), S. 57-71 
    Details
    ISSN: 1432-2099
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Three sets of data (population statistics in non-smokers, data from an investigation of the smoking habits of British doctors and a study of Colorado uranium miners) were used to analyse lung cancer in humans as a function of exposure to radon and smoking. One of the aims was to derive implications for radon risk estimates. The data were analysed using a two-mutation radiation carcinogenesis model and a stepwise determination of the model parameters. The basic model parameters for lung cancer were derived from the age dependence fit of the spontaneous lung cancer incidence in non-smokers. The effect of smoking was described by two additional parameters and, subsequently, the effect of radon by three other parameters; these five parameters define the dependence of the two mutation steps on smoking and exposure to radon. Using this approach, a consistent fit and comprehensive description of the three sets of data have been achieved, and the parameters could, at least partly, be related to cellular radiobiological data. The model results explain the different effect of radon on non-smokers and smokers as seen in epidemiological data. Although the analysis was only applied to a limited number of populations, lung cancer incidence as a result of radon exposure is estimated to be about ten times higher for people exposed at the age of about 15 than at about 50, although this effect is masked (especially for smokers) by the high lung cancer incidence from smoking. Using the model to calculate the lung cancer risks from lifetime exposure to radon, as is the case for indoor radon, higher risks were estimated than previously derived from epidemiological studies of the miners' data. The excess absolute risk per unit exposure of radon is about 1.7 times higher for smokers of 30 cigarettes per day than for non-smokers, even though, as a result of the low spontaneous tumour incidence in the non-smokers, the excess relative risk per unit exposure for the smokers is about 20 times lower than for the non-smokers. This prediction could have serious consequences for the transfer of risk estimates between populations. Although the solution of the model presented here is not unique but dependent on the model assumptions, the predictions and risk implications are sufficiently supported to justify a thorough investigation of the applicability of the model to other radon data sets.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004110050138
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  • 107
    Electronic Resource
    Electronic Resource
    A Monte Carlo code for positive ion track simulation (1999)
    Springer
    Radiation and environmental biophysics 38 (1999), S. 97-104 
    Details
    ISSN: 1432-2099
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract  An ion interaction model has been described for simulating positive ion tracks in a variety of media with the capability of interfacing with several secondary electron transport codes. Data are presented for single- and double-differential cross-sections, binding energies, probability density distribution for delocalisation parameters for conductors and tissue, branching ratios and ionisation efficiencies for water vapour and liquid water.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004110050144
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  • 108
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    Biological effects of ion beams in Nicotiana tabacum L. (1999)
    Springer
    Radiation and environmental biophysics 38 (1999), S. 111-115 
    Details
    ISSN: 1432-2099
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract  The biological effects of ion beams on Nicotiana tabacum L., particularly the induction of chromosome aberrations, were investigated. Dry seeds were exposed to 12C5+, 4He2+ and 1H+ beams with linear energy transfer (LET) ranging from 1 to 111 keV/µm and irradiated with gamma-rays. Ion beams were more effective in reducing germination and survival of the seeds than gamma-rays. The LD50 for 12C5+ beams, 4He2+ beams and gamma-rays were 35, 60 and 500 Gy, respectively. The frequencies of mitotic cells with chromosome aberrations, such as chromosome bridges, acentric fragments and lagging chromosomes in the root tip cells of the exposed seeds, increased linearly with increasing doses. Relative biological effectiveness (RBE) values, based on the doses that induced a survival inhibition of 50% and a 10% frequency of aberrant cells, were 14.3–17.5 for the 12C5+ beams, 7.0–8.3 for the 4He2+ beams and 7.8 for the 1H+ beams. Furthermore, the relative ratios of the chromosome aberration types were significantly different between the ion beam and the gamma-ray regimes: chromosome fragments were more frequent in the former, and chromosome bridges in the latter. Based on these results, we concluded that the repair process of initial lesions induced by ion beams may be different from that induced by low- LET radiation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004110050146
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  • 109
    Electronic Resource
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    Condensed-history Monte-Carlo simulation for charged particles: what can it do for us? (1999)
    Springer
    Radiation and environmental biophysics 38 (1999), S. 163-173 
    Details
    ISSN: 1432-2099
    Keywords: Key words Charged particles ; Electron transport scheme ; Microdosimetry ; Monte Carlo simulation ; Radiation dosimetry ; Radiotherapy ; Track structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract  Condensed-history (CH) Monte-Carlo (MC) groups together the vast number of individual charged-particle collisions using multiple scattering theory for elastic angular changes and stopping power for energy losses. CH codes such as EGS4 have been enormously successful in simulating the transport of electrons, for example, in radiotherapy. MC-derived values of the water-to-air stopping-power ratio, s w/air, are used in all modern codes of practice for absolute dose determination in radiotherapy clinics. MC can also directly yield the dose ratio D med/D det for a dosimeter in a medium, and Correlated Sampling has been exploited to increase the efficiency, e. g., the central electrode in an ion chamber (aluminium vs. graphite). The extremely low density of the gas in an ion chamber poses problems for CH codes. However, multiple scattering can now be combined with single scattering and is expected to finally resolve important chamber perturbation effects. An exciting application of CH MC in radiotherapy is the computation of dose distributions in patients. Currently one can achieve an uncertainty around 1% (1 SD) in mm-sized voxels in several minutes for an electron beam and in around an hour for a photon treatment plan on hardware costing less than $20,000, and thus avoid all the various approximations conventionally used to account for inhomogeneities. In the microdosimetry/track structure field, CH codes have shown that the fluence (dΦ/dE) per unit dose at low electron energies is virtually independent of incident particle energy or depth, which simply explains the negligible RBE variation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004110050152
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  • 110
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    Estimation of the target stem-cell population size in chronic myeloid leukemogenesis (1999)
    Springer
    Radiation and environmental biophysics 38 (1999), S. 201-206 
    Details
    ISSN: 1432-2099
    Keywords: Key words Cancer risk modelling ; Chronic myeloid leukemia (CML) incidence ; CML target stem cells ; genome translocation ; Low-dose exposure ; Radiation-induced CML
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract  Estimation of the number of hematopoietic stem cells capable of causing chronic myeloid leukemia (CML) is relevant to the development of biologically based risk models of radiation-induced CML. Through a comparison of the age structure of CML incidence data from the Surveillance, Epidemiology, and End Results (SEER) Program and the age structure of chromosomal translocations found in healthy subjects, the number of CML target stem cells is estimated for individuals above 20 years of age. The estimation involves three steps. First, CML incidence among adults is fit to an exponentially increasing function of age. Next, assuming a relatively short waiting time distribution between BCR-ABL induction and the appearance of CML, an exponential age function with rate constants fixed to the values found for CML is fitted to the translocation data. Finally, assuming that translocations are equally likely to occur between any two points in the genome, the parameter estimates found in the first two steps are used to estimate the number of target stem cells for CML. The population-averaged estimates of this number are found to be 1.86×108 for men and 1.21×108 for women; the 95% confidence intervals of these estimates are (1.34×108, 2.50×108) and (0.84×108, 1.83×108), respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004110050156
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  • 111
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    Announcement (1999)
    Springer
    Radiation and environmental biophysics 38 (1999), S. 219-219 
    Details
    ISSN: 1432-2099
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004110050161
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  • 112
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    Tumor therapy and track structure (1999)
    Springer
    Radiation and environmental biophysics 38 (1999), S. 229-237 
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    ISSN: 1432-2099
    Keywords: Key words Ions ; Tumor therapy ; RBE ; Track structure ; Treatment planning ; Carbon beam
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract  The elevated relative biological effectiveness (RBE) of heavy ions like carbon is the main reason for their use in radiotherapy and is due to the microscopic distribution of dose inside each particle track. High local doses produce lesions that are expected to have a diminished possibility of repair. Thus, RBE depends on track structure and on the biological repair capacity of the tissue that is affected by the irradiation. For tumor treatment planning with heavy ions, the beam quality and the tissue sensitivity have to be taken into account. Using the dependence of radial dose distribution on particle energy and atomic number on the physical side and x-ray dose response for the repair capacity on the biological side, the response to particle irradiation can be calculated in the local effect model (LEM) and used for treatment planning. This article traces the route from electron emission as the basis of track structure to the RBE calculation and the application in treatment planning.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004110050163
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  • 113
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    Effect of lithium on thyroidal 131iodine uptake, its clearance, and circulating levels of triiodothyronine and thyroxine in lead-treated rats (1999)
    Springer
    Radiation and environmental biophysics 38 (1999), S. 261-266 
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    ISSN: 1432-2099
    Keywords: Key words Iodine uptake ; Lead ; Lithium ; Rats ; Thyroid ; Thyroid hormones
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract  The influence of lead acetate (50 mg per kg body weight) on the 131iodine (131I) biokinetics (uptake and retention) in rat thyroid and serum levels of triiodothyronine (T3) as well as thyroxine (T4) was evaluated as a function of time and in combination with lithium treatment. The 2-h and 24-h uptake of 131I in the thyroid was stimulated significantly by lead treatment. The 24-h uptake showed a maximum stimulation after 4 months of lead treatment. Lithium supplementation, however, showed the opposite effect by reducing the iodine uptake, whereby the maximum decrease was noticed after 2 months of treatment. Further, simultaneous lead and lithium treatment resulted in an even more pronounced increase of 2-h 131I uptake with a maximum after 3 months. However, the 24-h uptake after 3 months and 4 months of treatment did not differ significantly from the lead treated reference groups. The thyroidal biological half-life of 131I (Tbiol) was found to have clearly increased following the lead/lithium treatment. Interestingly, the combined lead/lithium treatment applied for 4 months caused a further growth of Tbiol, thus reflecting an increased retention of 131I. A maximum increase of Tbiol was seen after 2 months of combined treatment. A progressive decline of the circulating T3 and T4 levels following lead or lithium treatment was noticed and was more pronounced after combined treatment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004110050166
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  • 114
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    A Parametric Estimation Approach for Groove Dimensioning Using Remote Field Eddy Current Inspection (1999)
    Springer
    Research in nondestructive evaluation 11 (1999), S. 39-57 
    Details
    ISSN: 1432-2110
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract. The remote field eddy current technique is used for dimensioning grooves that may occur in ferromagnetic pipes. We propose a method to estimate the depth and the length of corrosion grooves from the measurement of a pick-up coil signal phase at different positions close to the defect. Groove dimensioning needs the knowledge of the physical relation between measurements and defect dimensions; therefore, finite-element calculations are performed to obtain a parametric algebraic function of the physical phenomena. The parameters of this model function are obtained by an optimization technique. By means of this model and a previously defined general approach, an estimate of groove size may be given. In this approach, algebraic function parameters and groove dimensions are linked through a polynomial function. To validate this estimation procedure, a statistical study has been performed. The approach is proved to be suitable for real measurements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00003913
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  • 115
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    Nondestructive Evaluation of Microcracks in Ceramics with Controlled Probability of False Alarm (1999)
    Springer
    Research in nondestructive evaluation 11 (1999), S. 15-24 
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    ISSN: 1432-2110
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract. In this paper we present a complete detection scheme for ultrasonic crack detection in wet ceramics by means of ultrasonic nondestructive techniques. The detection scheme is based on a previous statistical characterization of the ultrasonic grain noise. In these previous works we obtained that the ultrasonic grain noise can be modeled as a K -noise [1, 2]. From this characterization we will prove that the expression of the probability of false alarm (PFA) obtained for a detector of Gaussian envelope pulses over K -noise using the Wigner-Ville Transform (WVT) proposed in reference [3] is valid for the real problem of ultrasonic microcrack detection in wet ceramics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00003911
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  • 116
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    Nondestructive Determination of the Elastic Anisotropy in Aluminum—SiC and —Al 2 O 3 Metal—Matrix Composites (1999)
    Springer
    Research in nondestructive evaluation 11 (1999), S. 1-13 
    Details
    ISSN: 1432-2110
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract. Process control is becoming increasingly important to the high performance applications of aluminum metal—matrix composites. Most processing conditions of metal—matrix composites introduce a degree of anisotropy that results in the directional dependence of material properties. Aluminum alloys reinforced with up to 20 volume % silicon-carbide or alumina particles are examined using ultrasonic velocity measurements. The measurements indicate that these composites are transversely isotropic and thus their elastic properties can be described by the five independent elastic constants C 11 , C 33 , C 44 , C 12 , and C 23 . Anisotropy parameters are determined assuming either a preferred alignment of the matrix crystallites or a preferred alignment of the reinforcement. Comparing measured and theoretical anisotropy parameters for partially aligned reinforcement or for texture shows that neither is the single contributor to anisotropy in the composite material.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00003910
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  • 117
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    Nondestructive Characterization of Adhesive Joint Durability Using Ultrasonic Reflection Measurements (1999)
    Springer
    Research in nondestructive evaluation 11 (1999), S. 81-95 
    Details
    ISSN: 1432-2110
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract. The present work investigates the durability of two commercial epoxy adhesives nondestructively using ultrasonic reflection measurements from the interfacial region between the adhesive and the adherend. This method, which is primarily sensitive to the interfacial properties, employs a new specimen geometry that overcomes the drawbacks of the conventional closed adhesive sandwich. The interfacial region was modeled using the spring boundary conditions. The normal and tangential spring constants were determined, as a function of degradation, from normal-incidence longitudinal and shear-wave measurements. Obliquely incident shear-wave measurements were also performed using a newly developed dual-element PVDF transducer. An efficient angular spectrum approach was developed to model the oblique-incidence measurement system, and the predictions of the model were compared with measurements for various levels of degradation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00003915
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  • 118
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    Ultrasonic Wave Scattering by a Line Crack in a Solder Joint (1999)
    Springer
    Research in nondestructive evaluation 11 (1999), S. 117-135 
    Details
    ISSN: 1432-2110
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract. A numerical procedure for the solution of a wave propagation problem in a solder joint with a line crack in its base layer is presented. The two-dimensional ``in-plane'' wave propagation problem for a finite, multilayered body with a line crack in one of the layers is solved by the combined usage of the displacement and the traction BIEM. The discretization of the boundary with parabolic elements far from the crack edge and with quarter-point crack-tip boundary elements containing the correct $O(\sqrt{r})$ behavior for displacement variations at the crack edge is used. Numerical results for a solder joint with real geometry and physical properties are presented. The relations between the wave scattering problems, the solder joint fatigue state estimation, and the reliability and quality of electronic packages is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00003917
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  • 119
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    Practical Shear Wave Lens Design for Improved Resolution with Acoustic Microscope (1999)
    Springer
    Research in nondestructive evaluation 11 (1999), S. 97-116 
    Details
    ISSN: 1432-2110
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract. This paper presents a practical new lens design for acoustic microscopy. The new lens provides a factor-of-2 higher resolution than currently available commercial lenses for acoustic microscopy, and a reduction in the influence of surface roughness on the image formation. Analysis, computer simulations, and demonstration examples provide convincing evidence that new lens design works efficiently. Whereas most current lens designs emphasize the use of longitudinal waves, the designs presented here focus on the use of transverse or shear waves. In the present study, two kinds of lens designs have been developed: One is a ``center-sealed'' acoustic lens used at the center frequency of 400 MHz and 1 GHz for use with acoustic tone bursts, and the other is a ``high-NA acoustic lens'' used in the center frequency of 30 MHz for use with short pulses. The center-sealed acoustic lens has its center area aperture sealed to prevent longitudinal waves from traveling into the sample so that the acoustic image is substantially composed of shear wave components. The ``high-NA'' acoustic lens has an aperture with a large aperture angle for exciting shear waves in the object. In this study, the mechanisms of image formation with both of these lenses are described and their features are evaluated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00003916
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  • 120
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    Semigroup Varieties and Semigroup Algebras (1999)
    Springer
    Semigroup forum 59 (1999), S. 461-466 
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    ISSN: 1432-2137
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002339900064
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  • 121
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    On Existence Varieties of E-solid Semigroups (1999)
    Springer
    Semigroup forum 59 (1999), S. 470-521 
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    ISSN: 1432-2137
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: E -solid semigroups, a theory of e-varieties including appropriate notions of biidentities and biinvariant congruences is presented, such that, together with bifree objects, these notions inherit the properties and interrelations well known from universial algebra. This theory generalizes the previously developed such theory for orthodox semigroups. As an application, the bifree objects in certain e-varieties of E-solid locally orthodox semigroups, which are constructed by means of Malcev products from a varities of bands, groups and completely simple semigroups, are described as subsemigroups in suitable Pastijn products of some bands by relatively bifree completely simple semigroups. As a consequence, it follows that every regular E-solid locally orthodox semigroup regularly divides a so-called solid Pastijn product of a band by a completely simple semigroup.
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    On equalizer-flat acts (1999)
    Springer
    Semigroup forum 58 (1999), S. 5-16 
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    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: S : a right S-act A is strongly flat if and only if the functor A\otimes- (from the category of left S-acts into the category of sets) preserves both pullbacks and equalizers. Stenström gave two interpolation-type conditions whose conjunction describes strong flatness. In 1986, P. Normak studied these conditions separately, lablelling them (P) and (E), and investigated their relation to different types of flatness. Bulman-Fleming, in 1991, showed that pullback flatness and strong flatness actually coincide, and several papers have appeared in which condition (P) is discussed. To date, little work has been done on equalizer flat acts. This paper gives some new results connecting condition (E) and equalizer flatness, concentrating on situations in which the two coincide. A description is given of the completely simple and completely 0-simple semigroups (with 1 adjoined) over which this occurs.
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    On existence varieties of E-solid semigroups (1999)
    Springer
    Semigroup forum 58 (1999), S. 17-68 
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    ISSN: 1432-2137
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: E -solid semigroups, a theory of e-varieties including appropriate notions of biidentities and biinvariant congruences is presented, such that, together with bifree objects, these notions inherit the properties and interrelations well known from universal algebra. This theory generalizes the previously developed such theory for orthodox semigroups. As an application, the bifree objects in certain e-varieties of E-solid locally orthodox semigroups, which are constructed by means of Malcev products from varieties of bands, groups and completely simple semigroups, are described as subsemigroups in suitable Pastijn products of some bands by relatively bifree completely simple semigroups. As a consequence, it follows that every regular E-solid locally orthodox semigroup regularly divides a so-called solid Pastijn product of a band by a completely simple semigroup.
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    Transitive actions of semigroups in semi-simple Lie groups (1999)
    Springer
    Semigroup forum 58 (1999), S. 142-151 
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    ISSN: 1432-2137
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: G be a connected semi-simple Lie group with finite center and S⊂G a semigroup with interior points. It is proved that S is transitive on a homogenous space G/L only if the action of L on B is minimal and contracting, where B=G/Pis the flag manifold of G asssociated with S. In [5, Thm.6.4] the authors claimed another necessary condition in case G is simple, namely, that L is discrete. It is shown by means of an example that this condition is wrong without the further assumption that G/L is compact.
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    Fundamentals of Semigroup Theory by John M. Howie (1999)
    Springer
    Semigroup forum 58 (1999), S. 156-158 
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    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
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    Spectral theory and generator property for one-sided coupled operator matrices (1999)
    Springer
    Semigroup forum 58 (1999), S. 267-295 
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    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: operator matrix . We introduce a new class of unbounded operator matrices corresponding to these equations and study the spectral theory, compute the adjoint and analyze the generator property of its elements. The abstract results arre illustrated by a series of applications.
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    Representation of Finite Lattices by Annihilators of Completely 0-Simple Semigroups (1999)
    Springer
    Semigroup forum 59 (1999), S. 121-125 
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    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: L the explicit construction of a 0-simple Rees matrix semigroup is suggested such that the lattice of left annihilators of this semigroup is isomorphic to L.
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    Are Simulation Models Ready for Agricultural Research in Developing Countries? (1999)
    Springer
    Semigroup forum 91 (1999), S. 1-4 
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    ISSN: 1432-2137
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Oryza sativa L.) research in Southeast Asia. The models successfully simulated crop growth as affected by canopy photosynthesis, sink capacity, and N nutrition. The rather crude plant physiology in these and similar models limits their usefulness in simulating the effect of morphological modifications and the response to various stress factors. Modeling skills developed by SARP in Asian research institutes cannot be maintained without continued coordination from advanced institutes. More basic knowledge on the plant's morphogenesis and feedback mechanisms is required for effective simulation of plant adaptation to complex growth environments, including intercropping, as found in many developing countries. A more rigorous modular approach to modeling is advocated, as well as standardization of modules for well-understood processes, as part of a toolkit for applied research for use in combination with other techniques, including statistical techniques.
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    Conservation Tillage Corn Production for a Semiarid, Subtropical Environment (1999)
    Springer
    Semigroup forum 91 (1999), S. 116-121 
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    ISSN: 1432-2137
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Zea mays L.) yields and production costs during the transition from conventional to reduced tillage provide farmers with guidelines for implementing conservation tillage in a subtropical, semiarid environment through evaluation of grain yield and production economics as affected by tillage. Conventional tillage (CT), reduced tillage with wide V-sweeps (RT), and preplant no-tillage (PPNT) were compared for both spring and fall corn production over three years. Grain yields for PPNT were lower than CT in the spring (-9%) and fall (-20%) of the first cropping year. Yields in PPNT were equivalent or up to 12% greater than CT yields in Years 2 and 3. Production costs were lower in the PPNT than in the CT, because of the reduced number of tillage trips over the field. A three-year average of net returns for corn grown in the PPNT spring treatment was $47 ha-1 greater than RT, and $104 ha-1 more than CT systems. Average net returns from PPNT for spring and fall cropping seasons over three years was $23 ha-1 greater than the RT and $104 ha-1 greater than the CT. Greater economic returns and lower production costs of PPNT compared with CT systems for all seasons and years were the result of reduced energy and operator time requirements. The conservation tillage systems (RT and PPNT) resulted in greater economic returns, compared with a CT tillage system, due to both greater yields in dry years and lower production costs in all years.
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    Acidic Soil Amendment with a Magnesium-Containing Fluidized Bed Combustion By-Product (1999)
    Springer
    Semigroup forum 91 (1999), S. 24-32 
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    ISSN: 1432-2137
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: 2 from the emissions of coal-fired boilers produces by-products that often consist of CaSO4, residual alkalinity, and coal ash. These by-products could be beneficial to acidic soils because of their alkalinity and the ability of gypsum (CaSO4·2H2O) to reduce Al toxicity in acidic subsoils. A 3-yr field experiment was conducted to determine the liming efficacy of a fluidized bed combustion boiler by-product (FBC) that contained 129 g Mg kg-1 as CaMg(CO3)2 and MgO and its effects on surface and subsurface soil chemistry. The FBC was mixed in the surface 10 cm of two acidic soils (Wooster silt loam, an Oxyaquic Fragiudalf, and Coshocton silt loam, an Aquultic Hapludalf) at rates of 0, 0.5, 1, and 2 times each soil's lime requirement (LR). Soils were sampled in 10-cm increments to depths ranging from 20 to 110 cm, and corn (Zea mays L.) and alfalfa (Medicago sativa L.) were grown. Application of Mg-FBC increased alfalfa yields in all six site-years, whereas it had no effect on corn grain yield in five site-years and decreased grain yield in one site-year. Plant tissue concentrations of Mg, S, and Mo were increased by Mg-FBC, while most trace elements were either unaffected or decreased. Application of Mg-FBC at one or two times LR increased surface soil pH to near 7 within 1wk. Although surface soil pH remained near 7 for 2 yr, there was minimal effect on subjacent soil pH. Application of Mg-FBC increased surface soil concentrations of Ca, Mg, and S, which promoted downward movement of Mg and SO4. This had different effects on subsoil chemistry in the two soils: in the high-Ca-status Wooster subsoil, exchangeable Ca was decreased and exchangeable Al was increased, whereas in the high-Al-status Coshocton subsoil, exchangeable Al was decreased and exchangeable Mg was increased. The Mg-FBC was an effective liming material and, because of the presence of both Mg and SO4 , may be more effective than gypsum in ameliorating subsoil Al phytotoxicity.
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    Methods of Simulating Freezing Damage during Sorghum Grain Fill (1999)
    Springer
    Semigroup forum 91 (1999), S. 46-53 
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    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Sorghum bicolor (L.) Moench] grain yields can be reduced if plants are exposed to freezing temperatures prior to reaching physiological maturity. Two field experiments were conducted to evaluate chemical desiccation and panicle removal as methods for simulating the loss of carbohydrate production associated with leaf death or transport tissue damage when sorghum is exposed to freezing temperatures during grain fill. In one experiment, both treatments were repeated at 3- to 4-d intervals during grain fill with a range of hybrid maturities and environments to establish a relationship between caryopsis weight or test weight with heat unit accumulation after anthesis. This relationship was best described as sigmoidal in shape. A second field experiment compared these two treatments with potted field-grown plants exposed to -2° C for 4h. Treatments were applied four different times during grain fill. Panicle removal produced caryopsis weights 5% greater than those from freeze treatments, whereas chemical desiccation resulted in caryopsis weights 13% greater than those from freeze treatments. Test weights followed similar trends. Caryopsis weights from each treatment were similar across experiments. Panicle removal accurately simulated caryopsis weight reductions caused by exposure to freezing temperatures throughout the grain-filling period. Chemical desiccation underestimated freeze damage during early grain fill but adequately simulated caryopsis reductions during late grain fill. Test weights from panicle removal treatments were similar in both experiments, while chemical desiccation was inconsistent across experiments. Test weight reductions caused by exposure to freezing temperatures were not adequately simulated by either treatment. The results of these experiments indicate that panicle removal is a more appropriate method for simulating freeze damage to maturing grain sorghum than is chemical dessication; however, chemical desiccation may be utilized if appropriate adjustments are made during early grain fill.
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    Soybean Weed Communities: Relationships with Cultural History and Crop Yield (1999)
    Springer
    Semigroup forum 91 (1999), S. 234-241 
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    Topics: Mathematics
    Notes: Glycine max (L.) Merr.] fields in the Rolling Pampa, Argentina, to identify floristic and functional (life cycles, origin, and morphotypes) structure in fields with different management practices and to explore the association between weed species, cultural history, and crop yield. We surveyed 18 and 42 different fields in 1994 and 1995, respectively, in soybean cropped with conventional and no-tillage practices. In 1994, we recorded presence of weed species and in 1995 we recorded weed presence and abundance, and management information (type of tillage, number of agricultural cycles, grain yield, planting date, and weed control). We used multivariate analysis to examine relationships among variables. We distinguished four communities and eight floristic groups, related to crop yield and tillage system. The presence of Floristic Groups II [Oxalis chrysantha (Kunth) Prog., Sonchus oleraceus L., and Veronica persica Poir.], VII [Carduus acanthoides L., Stellaria media (L.) Vill., Physalis viscosa L., Taraxacum officinale Weber, and coronopus didymus (L.) Sm.], and IV [Bidens subalternans DC., Cirsium vulgare (Savi) Ten., and Cyperus sp.L.] may be an indicator of high potential crop yield (low soil degradation), and their absence may be an indicator of low potential crop yield (increasing soil degradation). Functional structure (life cycles, origin, and morphotypes) was similar between communities, indicating that agroecosystems preserve function, despite management practices. The main variables explaining weed distribution in the surveyed region were tillage system, crop yield, planting date, and the number of agricultural cycles.
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    Vertical Phosphorus and Potassium Stratification in No-Till Cotton Soils (1999)
    Springer
    Semigroup forum 91 (1999), S. 266-269 
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    ISSN: 1432-2137
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Gossypium hirsutum L.). Rows were planted within a few centimeters of the rows from the previous year; a common practice in no-till agriculture. The selected soils were Memphis silt loam (fine-silty, mixed, active, thermic Typic Hapludalf), Lexington silt loam (fine-silty, mixed, Ultic Hapludalf), and Loring silt loam (fine-silty, mixed, active, thermic Oxyaquic Fragiudalf). Potassium rates of 0, 28, 56, and 112 kg ha-1 were broadcast annually beginning in 1991. Experimental design was a split plot with five replications. Samples were collected from individual plots in the planted row (IR) and between the row (BR) to a depth of 30 cm. The soil samples were divided into 0- to 8-cm, 8- to 15-cm, and 15- to 30-cm depths and Mehlich-1 P and K were evaluated. Mehlich-1 P varied with soils, sampling position, and soil depth. Differences in extractable P levels due to sampling position would not affect soil test ratings; however, additional years in no-till production may magnify position influences and so affect P fertilizer recommendation. Mehlich-1 K was greater for the IR sampling position of the 0- to 8-cm sampling depth for the three soils. Sampling only the BR position may in some instances give a lower soil test value, resulting in higher fertilizer applications. These differences varied with soil-applied K rates and may increase with additional time in no-till cotton.
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    Response of Spring Wheat to Nitrogen Fertilizers of Different Nitrification Rates (1999)
    Springer
    Semigroup forum 91 (1999), S. 287-293 
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    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Triticum aestivum L.) are maximized when the N supply contains a mixture of NH4 and NO3. Tillers per plant is the yield component most commonly increased by mixed N nutrition in greenhouse studies. The objective of this study was to evaluate, under field conditions, the response of 'Butte 86' spring wheat to N sources differing greatly in nitrification rate. Nitrogen was applied at 0 or 112 kg N ha-1; the N sources were calcium nitrate (CN), urea, urea-dicyandiamide (DCD), 0.1-g urea granules, and 0.1-g urea-DCD granules. Six field trials were performed. Topsoil (0-15 cm) analysis of fertilized plots during tillering indicated a wide range of mineral N contents (19-101 mg N kg-1) and of NH4;NO3 mole ratios (0.04-2.06). Correlation analyses suggested that tillering was sensitive to the total mineral N supply, but quite insensitive to the NH4;colon;NO3 ratio in the topsoil. Vegetative growth and N uptake were generally lower for CN than for the other N sources. At some locations, more heads per square meter at harvest were observed with the slower-nitrifying N sources. Grain yields were increased by N fertilization, but significant differences between N sources were not generally observed. For both years of the study, the 0.1-g urea-DCD granules gave the highest N uptake efficiency. However, the dramatic responses in growth, tillering, or grain yield routinely observed with mixed N nutrition in hydroponic or greenhouse studies could not be duplicated in the field.
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    Intrablock Variance among Duplicate Treatments for Nearest-Neighbor Analyses (1999)
    Springer
    Semigroup forum 91 (1999), S. 317-320 
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    Topics: Mathematics
    Notes: pure error as variation between plots that are treated alike within a block. Within each location, each genotype was randomly assigned to two plots within each block of an RCB design. The pure error of soybean [Glycine max (L.) Merr.] genotypes was evaluated at eight locations. Our objective was to compare the block × treatment and pure error mean squares for yield, physiological maturity, and plant height to determine whether the NNA or UNADJ analysis reduces intrablock variation. The NNA analysis always decreased the magnitude of the block × treatment interaction mean squares, compared with the UNADJ analysis. In some comparisons, the pure error mean square of the NNA analysis was significantly smaller than the pure error of the UNADJ analysis. The magnitude of the block × treatment mean square is not useful for comparing the relative precision of these two analyses. When the pure error mean square was used to measure precision, the NNA was at least as precise as the UNADJ analysis.
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    Fertility Gradients in Naturally Formed Terraces on Honduran Hillside Farms (1999)
    Springer
    Semigroup forum 91 (1999), S. 350-353 
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    Improving Nitrogen Use Efficiency for Cereal Production (1999)
    Springer
    Semigroup forum 91 (1999), S. 357-363 
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    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Triticum aestivum L.; corn, Zea mays L.; rice, Oryza sativa L. and O. glaberrima Steud.; barley, Hordeum vulgare L.; sorghum, Sorghum bicolor (L.) Moench; millet, Pennisetum glaucum (L.) R. Br.; oat, Avena sativa L.; and rye, Secale cereale L.) is approximately 33%. The unaccounted 67% represents a $15.9 billion annual loss of N fertilizer (assuming fertilizer-soil equilibrium). Loss of fertilizer N results from gaseous plant emission, soil denitrification, surface runoff, volatilization, and leaching. Increased cereal NUE is unlikely, unless a systems approach is implemented that uses varieties with high harvest index, incorporated NH4-N fertilizer, application of prescribed rates consistent with in-field variability using sensor-based systems within production fields, low N rates applied at flowering, and forage productions systems. Furthermore, increased cereal NUE must accompany increased yields needed to feed a growing world population that has yet to benefit from the promise of N2-fixing cereal crops. The Consultative Group on International Agricultural Research (CGIAR) linked with advanced research programs at universities and research institutes is uniquely positioned to refine fertilizer N use in the world via the extension of improved NUE hybrids and cultivars and management practices in both the developed and developing world.
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    Effects of Mechanical Conditioning on Wilting of Alfalfa and Italian Ryegrass for Ensiling (1999)
    Springer
    Semigroup forum 91 (1999), S. 457-463 
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    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Medicago sativa L.) and Italian ryegrass (Lolium multiflorum Lam.) when treated with different types of mower-conditioners (rubber rolls; plastic or steel flails). Drying was measured by calculating the water loss rate from two subsequent hourly weights of swath portions placed on trays. Dry matter (DM) losses were estimated on 1.2-m lengths of swaths immediately after cutting. The steel flail conditioner provided faster drying than the other conditioning types for both crops. The effect of the rubber roll conditioner was limited due to the swath structure, especially with forage surface densities higher than 0.7 kg DM m-2. Tedding positively interacted with the conditioning treatment to increase the drying rate, especially when forage was conditioned with the rubber roll machine. Shatter losses from alfalfa were higher for the flail conditioner, ranging from 3.6 to 10.2%, and with greater loss of crude protein. The DM losses were always lower than 2.5% for Italian ryegrass. The most severe conditioning (steel flails) followed by tedding is appropriate for grass, as it significantly reduces the wilting time without affecting DM loss. However, a less severe conditioning (rubber rolls) without tedding is more appropriate for wilting alfalfa, to avoid excessive leaf and protein loss.
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    Desiccation and Germination of Grain Sorghum As Affected by Glufosinate (1999)
    Springer
    Semigroup forum 91 (1999), S. 373-376 
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    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Sorghum bicolor (L.) Moench] for earlier harvest to preserve seed quality and quantity. Objectives of this study were (i) to examine the desiccant activity of glufosinate [2-amino-4-(hydroxy-methylphosphinyl)butanoic acid] applied at sever rates to grain sorghum at different seed moisture levels in contrasting environments and (ii) to determine the effect of glufosinate on germination and seedling growth of the treated crop. The soil at College Station (east-central Texas), was a Ships clay (very-fine, mixed, active, thermic, Chromic Hapludert); at Mayagüez, PR, a Coto clay (very-fine, kaolinitic, isohyperthermic Typic Hapludox). Glufosinate was evaluated because of its contact herbicidal properties and limited systemic activity. In both Texas and Puerto Rico, glufosinate was applied at 0, 0.56, 1.1, or 2.2 kg ha-1 to grain sorghum. Leaves and seed were sampled at 0, 1, 2, and 3 wk after treatment (WAT) for grain and leaf moisture. Seed was collected at 2 and 3 WAT for germination and growth studies. Glufosinate at all three treatment rates dried seed of the grain sorghum hybrid Atx638/Tx2783 in Texas from 〉 350 g kg-1 grain moisture at application to a storable moisture of 〈 120 g kg-1 at 2 WAT, at which time untreated grain moisture was 150 g kg-1. Glufosinate rate did not affect grain moisture except at the high glufosinate rate at 1 WAT. Leaf moisture reduction was glufosinate rate-dependent, but all treatments significantly reduced leaf moisture content at 1 WAT. Germination and seedling growth were not affected by glufosinate treatment. Grain desiccation rate under a tropical environment (Puerto Rico) was slightly slower than in Texas, but leaf moisture reduction was rapid and reached 〈 300 g kg-1 by 1 WAT from initial leaf moisture contents of 500 or 770 g kg-1. Germination was not adversely affected by glufosinate.
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    Soil Management and Supplemental Irrigation Effects on Potato: II. Root Growth (1999)
    Springer
    Semigroup forum 91 (1999), S. 426-431 
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    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Solanum tuberosum L.). Root length density (RLD) and root dry matter production of potato were studied under two levels of supplemental irrigation (nonirrigated check vs. moderate irrigation) and two levels of soil amendments [none vs. amended with compost and manure from beef cattle (Bos taurus L.)] during 1993 and 1994. Amendments significantly increased RLD during both growing seasons and these increases occurred consistently throughout each growing season. Irrigation effects were not observed in 1993, while irrigation significantly increased RLD during 1994. Approximately 85% of the root length was concentrated in the upper 30-cm layer of the soil. The supplemental irrigation and soil amendment treatments did not affect the proportional distribution of roots among the soil layers. Root-to-root ratio was not affected by irrigation or amendment during either growing season. The RLD and leaf area index (LAI) at all four sample dates during 1994 were significantly correlated with final tuber yields, indicating that growth patterns early in the season were important in establishing the productivity of the potato crop. Root length density tended to have a higher correlation with yields than did LAI (r = 0.58* to 0.88** vs. 0.51* to 0.68**).
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    Chicory Effects on Lamb Weight Gain and Rate of In Vitro Organic Matter and Fiber Disappearance (1999)
    Springer
    Semigroup forum 91 (1999), S. 445-450 
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    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Cichorium intybus L.; CHIC) as a component of hill-land pastures in Appalachia. In 1995, lamb (Ovis aries) gain was 56.1 kg ha-1 on orchardgrass (Dactylis glomerata L.; OG), while those grazing OG + CHIC lost 24.2 kg ha-1 during the 44-d midsummer grazing period (P 〈 0.05). In 1996, while weight gains were not different (P 〉 0.10), total lamb production per hectare was 14% less on OG + CHIC (258 kg ha-1) than on OG only (300 kg ha-1) for the 79-d grazing period. In 1997, total weight gained for the season was not different (P 〉 0.10); lambs grazed OG or CHIC for 110 d and production was 362 and 351 kg ha-1, respectively. Laboratory mixtures of 40∝60 or 60∝40 OG∝CHIC had higher (P & lt: 0.05) in vitro organic matter disappearance (IVOMD), compared with 100% OG or 100% CHIC. There was a synergism in mixtures with orchardgrass that increased IVOMD relative to pure samples. Another laboratory experiment suggested that as total N increased in chicory herbage, rate of in vitro neutral-detergent fiber (NDF) disappearance decreased. More information on the influence of soil type and management on chicory growth in pure stands and mixtures with other plant species is needed to optimize productivity of systems that include chicory.
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    Banded Wetting Agent and Compaction Improve Barley Production on a Water-Repellent Sand (1999)
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    Semigroup forum 91 (1999), S. 463-467 
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    Notes: Hordeum vulgare L.) establishment on a water-repellent sand: (i) spraying various rates of banded (2 cm wide) wetting agent while furrow seeding with press wheels, (ii) seed placement either in a furrow or in the side of a ridge, and (iii) compaction with press wheels or a Flexi-Coil land packer. The application of wetting agent increased seedling emergence from 110 to 170 plants m-2, dry matter production from 4.2 to 6.0 t ha-1 and grain yield from 1.96 to 2.60 t ha-1, despite more weeds occurring with increasing rate of banded wetting agent. Use of press wheels, which also resulted in a furrow sowing condition, increased seedling emergence from 72 to 101 plants m-2 and grain yield from 1.70 to 2.13 t ha-1. In the absence of heavy press wheel compaction, furrow sowing at 18-cm row spacings with full soil disturbance had no effect on seedling emergence or grain yield. The application of wetting agent increased topsoil wetting. Increased soil wetting may have increased plant nutrient availability (from fertilizer and soil), reduced soil water evaporation, and possibly reduced water loss to subsoil on this duplex soil. The optimum degree of compaction required on water-repellent soils is not known and needs further research.
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    Yield and Nitrogen Content of Corn under Different Tillage Practices (1999)
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    Semigroup forum 91 (1999), S. 631-636 
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    Notes: Zea mays L.) under nonlimiting soil N conditions. Nitrate leaching has been identified as a source of non-point-source pollution. By identifying tillage practices which maximize corn N uptake, recommendations can be based on how to minimize N loss. A 2-yr field study was conducted in southwestern Quebec on a 2.4-ha site of a Typic Endoaquent (Humic Gleysol) cropped to corn. Three types of tillage practice (conventional tillage, reduced tillage, and no-till) were combined with two residue levels (with and without) in a randomized complete block design. The effect of these practices on corn yield and corn N were studied. Seedling emergence rates in spring, and corn moisture content at harvest, were also monitored. Residues hindered initial plant emergence in the no-till plots. Corn N and moisture contents in 1996 and 1997 indicated that no-till with residue had a delayed maturity relative to the other treatments. However, total corn biomass and grain yields were not affected by tillage or residue treatments. No correlation between corn yield and corn N content was found.
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    Generalization of the d'Alembert formula and the Fourier method (1999)
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    Semigroup forum 58 (1999), S. 85-93 
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    Unary hyperidentities for varieties of inverse semigroups (1999)
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    Semigroup forum 58 (1999), S. 106-125 
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    Notes: Fa(x)=Fb(x) , for inverse semigroup varieties. In this paper, we give a complete analysis of all unary hyperiddentities for inverse semigroup varieties: for any such hyperidentity we describe the largest variety of inverse semigroups to satisfy it.
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    The monoid of orientation-preserving mappings on a chain (1999)
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    Semigroup forum 58 (1999), S. 190-206 
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    On the semigroup BetaS (1999)
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    Semigroup forum 58 (1999), S. 241-247 
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    Notes: S be an infinite, discrete, cancellative semigroup and let BetaS be the Stone-Cech compactification of S. Then BetaS is a semigroup with an operation which extends that of S and which is continous only in one variable. We generalize some algebraic properties known to hold for the additive semigroup of the integers.
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    On Radical Congruence Systems (1999)
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    Semigroup forum 59 (1999), S. 56-73 
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    On Radicals of Semigroup Algebras (1999)
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    Semigroup forum 59 (1999), S. 93-105 
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    Notes: p -separative semigroups. In particular, the coincidence of the Jacobson radical and the Baer radical of a nilpotent group algebra over a field of prime characteristic is established.
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    Random Partitions by Semigroup Methods (1999)
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    Semigroup forum 59 (1999), S. 126-140 
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    Notes: P of all partitions of {1,2,3,...}, or rather its distribution. There is a natural compact metrizable topology on P taking care of measurability questions. With respect to the maximum operation P becomes an abelian semigroup, and our first theorem characterizes random partitions as normalized positive definite functions on the subsemigroup of partitions "with finite support". We then present a new proof of Kingman's theorem stating that the exchangeable random partitions form a simplex whose extreme points are the so-called "paint-box distributions". An interesting moment problem which is still open arises in this connection.
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    The Endomorphism Structure of Simple Faithful S-acts (1999)
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    Semigroup forum 59 (1999), S. 179-182 
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    Extending Ideals in Regular Topological Semigroups (1999)
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    Semigroup forum 59 (1999), S. 175-178 
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    Combinatorially Factorizable Inverse Monoids (1999)
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    Semigroup forum 59 (1999), S. 220-232 
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    On the Finite Basis Problem for Completely 0-Simple Semigroup Identities (1999)
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    Semigroup forum 59 (1999), S. 197-219 
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    Certain Relations on the Congruence Lattice of a Completely Regular Semigroup (1999)
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    Semigroup forum 59 (1999), S. 264-281 
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    Book Review: Algebra in the Stone-Cech Compactification by Neil Hindman and Dona Strauss (De Gruyter Expositions in Mathematics 27, de Gruyter, Berlin, New York, 1998, xiii + 485 pp. ISBN 3-11-015420-X) (1999)
    Springer
    Semigroup forum 59 (1999), S. 310-314 
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    Principal-ideal Bands (1999)
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    Semigroup forum 59 (1999), S. 362-373 
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    Norm Discontinuity of Ornstein-Uhlenbeck Semigroups (1999)
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    Semigroup forum 59 (1999), S. 389-403 
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    Topological Properties of Inverse Limits of Free Abelian Monoids, with an Application to Inverse Limits of UFDs (1999)
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    Semigroup forum 59 (1999), S. 418-434 
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    Möbius Type Semigroups in SL(2,F) (1999)
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    Semigroup forum 59 (1999), S. 453-460 
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    Notes: F with an order P, the semigroup S of elements in SL(2,F) having entries in P can be factored into upper triangular, diagonal and lower triangular matrices. Moreover, we show that the semigroup ±S is maximal in SL(2,F).
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    Red Clover and Tillage Influence on Soil Temperature, Water Content, and Corn Emergence (1999)
    Springer
    Semigroup forum 91 (1999), S. 101-108 
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    Topics: Mathematics
    Notes: Zea mays L.) because of problems with excess water, lower temperatures, and residue management during the early stages of corn growth. This is a problem, as corn is commonly used in rotation with wheat (Triticum aestivum L.) and soybean [Glycine max (L.) Merr.]. Furthermore, when corn follows winter wheat there may be additional problems associated with residue management during the early stages of corn growth. Hence, the objectives of this study were to measure the effect of the red clover (Trifolium pratense L.) cover crop underseeded in wheat and no-tillage on soil temperature, water content, corn emergence, surface residue, and yields in a wheat-corn-soybean rotation in southwestern Ontario. Treatments included conventional vs. no-tillage both with and without underseeded red clover in a wheat-corn-soybean rotation in a clay loam soil. A no-tillage and red clover treatment that had the wheat straw baled was also included. No-tillage (with and without red clover) increased soil water content by 2 to 5% and reduced soil temperatures by 1 to 2°C during early corn emergence. Soil drying occurred along the planting slot of the no-tillage treatments, which enabled the soil seed furrow to open and the corn seedlings to become water stressed even though the no-tillage treatments were wetter in the spring. Corn emergence in the no-tillage treatment without red clover was delayed by 3 to 4 d and the final plant stand was reduced by 24% compared with the conventional tillage treatment. The no-tillage treatment without red clover had 13% lower corn grain yield than the conventional tillage treatment averaged over three years. However, when red clover was included with no-tillage, corn emergence was increased and corn grain yields were not significantly different from conventional tillage in both 1994 and 1996. There was also 15% less dry weight of surface plant residue present in the no-tillage treatments when red clover was included. Hence, red clover alleviated some of the problems of no-tillage for corn production.
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    Plant Determinants of Mycorrhizal Dependency in Soybean (1999)
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    Semigroup forum 91 (1999), S. 135-141 
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    Notes: Glycine soja Sieb. & Zucc. PI 468916; referred to hereafter as Soja), to intermediate [Glycine max (L.) Merr. cv. Mandarin] and low (G. max cv. Swift). Shoot weight, P percentage in shoot tissue, total shoot P uptake, P use efficiency, rate of growth, and root acid phosphatase activity were measured at three harvests when plants were grown at three relative P levels, each with and without mycorrhizal fungal (Gigaspora margarita Becker & Hall) colonization. Soja developed an active symbiosis more quickly than Swift or Mandarin, and mycorrhizae clearly aided in P uptake. When averaged across harvests at low P, mycorrhizal Soja had 7.8 times greater total shoot P than nonmycorrhizal Soja. Comparable values were 2.4 for Mandarin and 1.5 for Swift. Soja roots showed higher phosphatase activity and a higher percentage increase in phosphatase activity with mycorrhizal colonization than did the other two cultivars. Nonmycorrhizal Soja root lengths (avg. 1401 cm) at 5-wk growth were significantly shorter than Mandarin (2303 cm) and Swift (2236 cm) root lengths. The mean diameter of lateral roots of Soja (0.38 mm) was greater than that of Mandarin or Swift (≈ 0.26 mm). Root lengths and root surface areas were negatively correlated (P 〈 0.01) with MD.
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    Evaluation of Fine Root Length and Diameter Measurements Obtained Using RHIZO Image Analysis (1999)
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    Semigroup forum 91 (1999), S. 142-147 
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    Notes: -2 . For samples with higher values, however, the method underestimated total length by 〉5%. It is therefore recommended that users of image analysis systems determine this maximum length per unit area for accurate determinations of total root length. In samples that contained different string diameters, the total sample length and average string diameter could accurately be measured. However, the length per diameter class was underestimated by 〉20% when the string diameter was less than one pixel smaller than the upper limit of the diameter class. Adjustment of diameter intervals and increasing the scanner resolution are required to reduce this underestimation. Both the length and the angle of the short segments analyzed were found to influence diameter measurement. Similar sets of experiments are proposed for a rigorous evaluation of the performance of other image analysis systems on root measurements.
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    Soil Nitrate Accumulation and Corn Response to Preceding Small-Grain Fertilization and Cover Crops (1999)
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    Semigroup forum 91 (1999), S. 17-24 
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    Notes: 3 leaching risk and lower fertilizer N requirements for succeeding crops, will be fully realized only when the cover crop N contribution is accurately accounted for and availability is synchronous with succeeding crop N demands. The objectives of this study were to evaluate spring soil NO3-N accumulation patterns and N availability to corn (Zea mays L.) following annual ryegrass (Lolium multiflorum L.), oilseed radish [Raphanus sativus (L.) var. oleiferus (Stokes) Metzg.], red clover (Trifolium pratense L.), and no cover crop established after either winter wheat (Triticum aestivum L.) or barley (Hordeum vulgare L.). The wheat and barley were produced with 0.5, 1.0, and 2.0 times the amount of recommended N fertilizer. Six field trials were conducted on well-drained Typic Hapludalf soils in southwestern Ontario intermittently from 1989 to 1995. Corn was produced using a spring mulch-till system with only 10 kg ha-1 of fertilizer N, which was applied as part of the P starter fertilizer. Applying more fertilizer N to the previous year's small-grain crop rarely increased spring soil NO3-N concentrations or corn yields. Soil NO3-N concentration increases between the May and June sample dates following annual ryegrass and oilseed radish did not differ substantially from where a cover crop had not been established; following red clover, however, NO3-N increases were always at least 2.8 times greater than after no cover crop. Average aboveground corn biomass N at anthesis following annual ryegrass was 25.6 kg ha-1 less than when no cover crop was grown, whereas following red clover it was 40.4 kg ha-1 greater than with no cover crop. Corn yields were consistently the highest following red clover and often the lowest following annual ryegrass; yield response was positively correlated with June soil NO3-N concentrations (r= 0.61-0.93). These results suggest that N availability to succeeding corn differs among the cover crop treatments evaluated in the order red clover 〉 oilseed radish ≥ no cover crop 〉 annual ryegrass.
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    Harvest Management of Switchgrass for Biomass Feedstock and Forage Production (1999)
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    Semigroup forum 91 (1999), S. 5-10 
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    Notes: Panicum virgatum L.), a warm-season perennial grass native to North America, has potential as a biomass energy crop. Our objective was to develop harvest management recommendations for biomass feedstock and forage production. 'Alamo' switchgrass was established in 1992 at Stephenville and Dallas, TX. Four harvest frequencies (one to four cuts per year) and three final autumn harvests (Sept., Oct., or Nov.) were imposed from 1993 to 1996. Tiller densities were counted each spring. Neutral detergent fiber (NDF) and crude protein (CP) concentrations were measured in 1993 and 1994. Concentrations of NDF were lowest (avg. = 640 g kg-1) and of CP (avg. = 110 g kg-1) were highest in May-harvested biomass. Forage quality of regrowth decreased with age, reaching NDF concentrations of 790 g kg-1 and CP of 〈20 g kg-1. Total seasonal yields decreased as harvest frequency increased; however, a severe drought reversed this trend at Dallas in 1996. The highest yields (15-20 Mg ha-1) occurred with a single harvest in mid-September. Delaying the final harvest until November reduced yields. Harvest date and frequency did not affect tiller density, although tiller density decreased from 900 to 650 and 630 to 310 m-2 at Dallas and Stephenville, respectively, during 1994 to 1997. Thus, a single mid-September harvest should maximize biomass yields in the south-central USA〉 A two-cut (spring-autumn) system may allow a farmer to use initial growth as forage and the regrowth for biomass, but total yields would be reduced. More frequent harvests would reduce yields further.
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    Spatial Variation Affects Precision of Perennial Cool-Season Forage Grass Trials (1999)
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    Semigroup forum 91 (1999), S. 75-81 
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    Notes: Dactylis glomerata L.), ryegrasses [a group comprising perennial ryegrass, Lolium perenne L.; intermediate ryegrass, L. hybridum Hausskn.; and festulolium, ×Festulolium braunii (K. Richt.) A. Camus], smooth bromegrass (Bromus inermis Leyss.), reed canarygrass (Phalaris arundinacea L.), tall fescue (Festuca arundinacea Schreb.), and timothy (Phleum pratense L.). Dry matter forage yield was determined for 3 yr on each trial and expressed, for each plot, as mean annual yield. Yield data for each trial were analyzed by the RCB or lattice model, trend analysis, and two NNA models (one or two covariates). Three incremental improvements in precision of entry means were observed: an average of 15% due to the RCB design, an additional average of 17% due to the lattice design, and an additional average of 22 to 30% due to trend analysis or NNA. Trials were highly variable in the relative efficiency of both their experimental design and the spatial analyses, but this variability was not related to species, planting years, or plot size. The only useful predictor of trial efficiency was number of entries: three of five trials with eight or fewer entries failed to show significant differences among entries, regardless of the analysis. Spatial analysis methods cannot overcome lack of true differences among entries or failure to detect differences due to low degrees of freedom. Trend analysis of NNA appear to be useful mechanisms to account for intrablock variability in fields where it is impossible or uneconomical to predict proper blocking patterns.
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    Performance of Sweet and Forage Sorghum Grown Continuously, Double-Cropped with Winter Rye, or in Rotation with Soybean and Maize (1999)
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    Semigroup forum 91 (1999), S. 93-101 
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    Notes: Sorghum bicolor (L.) Moench] with winter rye (Secale cereale L.) could increase annual dry matter production in the North-Central region of the USA and reduce soil erosion and other environmental concerns. We conducted this study to compare yield, chemical composition, erosion potential, and economics of sorghum grown continuously (sole crop), in a 3-yr rotation with maize (Zea mays L.) and soybean [Glycine max (L.) Merr.], or double-cropped with winter rye (rye-sorghum). The experiment was on a Typic Calciaquoll soil in central Iowa with 2 to 7% slope. Applied N moderately affected sole-cropped sorghum, with yields of 13.5, 16.1, 16.9, and 15.9 t ha-1 when fertilized with 0, 70, 140, and 280 kg ha-1 N, respectively. Rye-sorghum was highly responsive to N, with combined yields at 72, 84, 95, and 110% of sole-cropped sorghum fertilized with the same annual rate of N. Drought dramatically reduced rye-sorghum yields. Sole-cropped sweet sorghum had yields similar to sweet sorghum grown in the 3-yr rotation. Environmental conditions associated with years and locations affected fiber components N, and total nonstructural carbohydrate concentrations of sorghum. Use of the Universal Soil Loss Equation revealed that planting rye before sorghum would reduce estimated soil loss at both locations, but the loss was still unacceptably high on the sloping soil in southern Iowa (22 t ha-1). An economic partial budget showed that rye-sorghum cost $147 ha-1 more to produce than sole-cropped sorghum. We conclude that, if winter rye is to be grown as a double crop with sorghum in the North-Central region, it will likely be because of its positive influence on the environment and not because of potential for improved yield.
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    Evaluation of the Root Zone Water Quality Model Using Field-Measured Data from the Missouri MSEA (1999)
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    Semigroup forum 91 (1999), S. 183-192 
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    Notes: Zea mays L.) and soybean [Glycine max (L.) Merr.] yield predictions were within 15 and 20%, respectively, of those measured. Using the macropore option, (constant cracking) greatly improved the prediction of chemical losses to seepage. Annual runoff simulated for corn and soybean under conventional and no-till systems was adequately predicted. The model underpredicted large runoff events and overpredicted runoff events that occurred after long dry periods when soil cracking was a dominant factor. The model overpredicted NO- 3N concentrations in runoff but underpredicted concentrations in near-surface soils. Predicted and measured atrazine [6-chloro-N-ethyl-N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine] and alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide) concentrations in surface runoff compared well, particularly when the computed runoff was close to that measured. In this study, the model was run using the option of constant cracking in the soil. To improve the predictions of agrichemical losses to runoff and seepage, RZWQM should include the capability to predict variable soil cracking based on soil moisture.
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    Plant Production Model Evaluation for the Root Zone Water Quality Model (RZWQM 3.2) in Ohio (1999)
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    Semigroup forum 91 (1999), S. 220-227 
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    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Zea mays L.) and soybean [Glycine max (L.) Merr.] biomass data collected at the Ohio MSEA from 1991 to 1993 were used for evaluation. Data from 1992 were used in calibrating RZWQM, and data from two other years (1991 and 1993) at the same site were used for validation. Crop growth predictions were compared with observed values of leaf, stem, and seed biomass collected throughout the growing season. Leaf and stem biomass predictions generally fell within 1 SD of the observed values, but for all years there were dates when predictions were outside of the observed range. RZWQM predicted seed biomass or yield adequately for all 3 years, with predictions falling within 1 SD of the observed values. Soil water content estimates for corn were higher than observed values late in the season, perhaps because of underestimates of evapotranspiration due to errors in leaf area predictions. The model overpredicted nitrate concentrations for the corn plot late in the season. Nitrate concentrations for the soybean plot were generally underpredicted. These differences may be due to underestimates of the fast humus pool of the nutrient model and of the N2 fixation rate for soybean. More evaluation is needed to refine the nitrate and soil water content predictions.
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    Testing CERES-Wheat with Free-Air Carbon Dioxide Enrichment (FACE) Experiment Data: CO2 and Water Interactions (1999)
    Springer
    Semigroup forum 91 (1999), S. 247-255 
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    ISSN: 1432-2137
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: 2 concentration and associated climate change on crop yields. Such model predictions are largely untested in the field, for lack of experimental data. We tested the CERES-Wheat model, modified to include leaf-level photosynthesis response to elevated CO2 using field data from 2 yr of Free-Air Carbon Dioxide Enrichment (FACE) experiments with spring wheat (Triticum aestivum L. cv. Yecora Rojo) in Maricopa, AZ. Two irrigation treatments (well-watered, WW; water-deficit stressed, WS) and two atmospheric CO2 concentrations (ambient, 350 μmol mol-1, elevated, 550 μmol mol-1) were simulated. The model was evaluated using measurements of crop phenology, aboveground dry matter (DM) production, grain yield, and evapotranspiration (ET). Model calculations of crop phenology were within 2 to 3 d of observed values under WW, ambient CO2 conditions in both years. The model did not simulate the accelerated crop phenology (5-8 d at physiological maturity) observed in the WW and elevated CO2 treatments, indicating the need to include effects of increased stomatal resistance on canopy temperature. Simulations of DM and grain yield were within 10% of measured values, except for a tendency to overcalculate DM response to CO2 by 10 to 15% in Year 1 for WS treatments. The model undercalculated cumulative ET under WW conditions by 15%; model sensitivity analyses suggest that simulation of potential evapotranspiration (PET) was too low for this arid site. The model reproduced measured dynamics of CO2-water interactions. Simulated reductions in water loss due to elevated CO2 were about 4%, in agreement with measurements. The model simulated larger increases in DM production and yield due to elevated CO2 under WS than under WW conditions. In Year 1, simulated crop response to CO2 was 2% larger (measured:3%) under WS than under WW conditions; in Year 2, it was 11% larger (measured: to be further evaluated with additional experimental datasets, is an important attribute of models used to project crop yields under elevated CO2 and climate change.
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  • 171
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    Soil Organic Matter and Wheat Productivity in the Semiarid Argentine Pampas (1999)
    Springer
    Semigroup forum 91 (1999), S. 276-279 
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    ISSN: 1432-2137
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Triticum aestivum L.) yields in response to SOM levels and related properties and to quantify the contribution of a unit increment of SOM content to soil productivity during 1991, 1992, and 1994 on a total of 134 production fields in the semiarid Argentine Pampas. Wheat yields were related to both soil water retention and total organic (TOC) contents in the top layers (0-20 cm) in years with low moisture availability (1992 [r= 0.51, P 〈0.01] and 1994 [r = 0.59, P 〈 0.01]), and were related to both total N and available P contents in a year without water deficit stress (1991 [r = 0.58, P 〈 0.01]). Wheat yields over all years were linearly related to TOC (r = 0.68, P 〈 0.01) when these contents were 〈17.5 g kg-1. Dependence of wheat yields on soil water retention and on TOC contents under water deficit was related to the positive effect of these soil components on plant-available water. In the absence of water deficit (1991), nutrient availability was the limiting factor. Losses of 1 Mg SOM ha-1 were associated with a decrease in wheat yield of approximately 40 kg ha-1. These results demonstrate the importance of using cultural practices that minimize losses of soil organic C in the semiarid Argentine Pampas.
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  • 172
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    Remobilization of Pre-Anthesis Assimilates to the Grain for Grain Only and Dual-Purpose (Forage and Grain) Triticale (1999)
    Springer
    Semigroup forum 91 (1999), S. 312-316 
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    ISSN: 1432-2137
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Triticosecale Wittmack). Field experiments were conducted in 1992 and 1993 in northeastern Spain. Two harvesting treatments were used: (i) grain production only and (ii) cutting the crop for forage at the beginning of jointing and harvesting the grain produced after regrowth. Pre-anthesis storage of carbohydrates was very important to grain filling in triticale, both for grain and for dual-purpose. Contribution of pre-anthesis assimilates to grain yield in the uncut plots was 46% in spring triticale genotypes and 65% in winter genotypes, as the later-maturity winter triticale genotypes were more affected by terminal abiotic stresses. Reductions in DM accumulated at anthesis after forage removal were more pronounced in winter genotypes (39%) than in spring genotypes (20%), where an earlier development allowed for a longer recovery period after cutting; DM reductions were similar to grain yield decreases. The effect of forage removal on translocation depended on the growth habit of the genotype and environmental conditions. Most differences were associated with changes in crop phenology. In spring types, with early jointing, DM translocation and the contribution of pre-anthesis assimilates to grain were not affected by forage removal, whereas both traits were drastically reduced in winter triticale. Most differences in 13C/12C carbon isotope discrimination (δ) in grains were also phenology driven.
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  • 173
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    Switchgrass Seedling Development as Affected by Seed Size (1999)
    Springer
    Semigroup forum 91 (1999), S. 335-338 
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    ISSN: 1432-2137
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: -1 ) and light seed (LS) (0.13 to 0.16 g 100 seed-1) of 'Blackwell' and 'Trailblazer' switchgrass (Panicum virgatum L.). The experiment was conducted in 1995 and 1996 at Lincoln, NE, on a Kennebee silt loam (fine-silty, mixed, superactive, mesic Cumulic Hapludolls). The experimental design was a randomized complete block with four replicates. Seed was separated into two sizes using a South Dakota seed blower. Seed was planted into rows at a rate of 100 pure live seed per meter of row. Plants were excavated and evaluated for shoot weight, leaf area, and root weight. Shoot and root systems were morphologically staged four times during the summer. Seed size differences in switchgrass appeared to produce only slight differences in morphological development of shoot and root systems, leaf area, shoot weight, and adventitious root weight from seedling emergence to 6 wk of growth. Adventitious roots formed more quickly on seedlings from heavier than lighter seed, but the advantage to seedling establishment was minimal even when soil moisture appeared to be lacking. By 8 to 10 wk after emergence, growth and development of LS seedlings were similar to HS seedlings. Once seedlings formed two or more adventitious roots, seed size no longer affected establishment and growth. Seed size in switchgrass appears to have a minimal long-term effect on growth and development of seedlings.
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  • 174
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    Chemical Dwarfing and the Response of Cool-Season Grass Seed Crops to Spring-Applied Nitrogen (1999)
    Springer
    Semigroup forum 91 (1999), S. 344-350 
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    ISSN: 1432-2137
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Festuca rubra L. subsp. fallax (Thuill.) Nyman; syn. F. rubra var. commutata Gaudin], tall fescue (Festuca arundinacea Schreb.), and orchardgrass (Dactylis glomerata L.) were established in September 1983 near Corvallis, OR. Treatments were all combinations of 90, 120, 150, 180, and 210 kg N ha-1 applied at the double-ridge stage of development, followed by paclobutrazol [2RS,3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1H-1,2,4-triazol-1-yl)-pentan-3-ol] at 0, 0.25, 0.5, and 1 kg a.i. ha-1 applied at floret initiation stage in 1985 and 1986. Averaged across years and N rates, the 1 kg ha-1 rate reduced Chewing's fescue height by 23% and tall fescue and orchardgrass heights by 30%. In the absence of paclobutrazol, Chewing's fescue and tall fescue seed yields were the greatest at 90 kg N ha-1. Paclobutrazol did not affect seed yield response of Chewing's fescue to N rates, but tall fescue seed yield in 1986 was the greatest at 150 kg N ha-1 when only 0.25 kg a.i. paclobutrazol ha-1 was applied. Averaged across N rates, the 0.5 kg ha-1 rate increased Chewing's fescue seed yield by 32% in 1985 and 18% in 1986, and also increased tall fescue seed yield by 32% in 1985 and 23% in 1986. Orchardgrass seed yield was the greatest at 180 kg N ha-1 in both years. Paclobutrazol did not affect orchardgrass seed yield in 1985, and the 1 kg ha-1 rate decreased seed yield in 1986. We concluded that in western Oregon paclobutrazol application at floret initiation does not improve seed yield response of these crops to spring-applied N, but it would significantly improve Chewing's fescue and tall fescue seed yield, regardless of the N rate applied. Results did not indicate any advantage for applying paclobutrazol on orchardgrass seed crop.
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  • 175
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    Wheat Grain Yield and Soil Profile Water Distribution in a No-Till Arid Environment (1999)
    Springer
    Semigroup forum 91 (1999), S. 368-373 
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    ISSN: 1432-2137
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Triticum aestivum L.) grown in a wheat-fallow (WF) rotation system (1 crop in 2 years) generally occupies the greatest area in the Israeli dryland region, more than the continuous wheat (CW) rotation system. To identify the optimal crop management for dryland farming where annual precipitation is 〈250 mm, we compared the effects of no-tillage (NT) and conventional tillage (CT) on wheat growth and water use efficiency (WUE) in both the WF and the CW rotation systems, and on water storage in fallow (F) plots. During the 4-year period from 1994 to 1997, experiments were conducted at Gilat Experimental Station, located in the south of Israel (average annual precipitation, 237 mm; soil type, sandy loam loess-Calcic Xerosol). In the fallow year, F-NT increased water infiltration and soil water content in comparison with F-CT. However, most of the water evaporated during the summer, especially from the upper soil layer (0-120 cm). During growth, uncultivated soil with straw mulch increased water content in the upper soil layer and also encouraged the development of a longer root system capable of utilizing deeper water. During 1995, similar grain yields were obtained with both NT and CT treatments, an average of 3.45 t ha-1 for WF and 2.9 t ha-1 for CW. In the last 2 drought years (1996 and 1997), NT management increased yields by 62 to 67% for WF and by 18 to 75% for CW, relative to CT management. During the 2 years when water deficiency occurred during the grain-filling stage (1994 and 1997), NT management increased to the 70 to 200% increase in the total grain yield, relative to CT management. Crop yield and WUE can be increased in arid zones with annual precipitation of 〈200 mm, through use of a wheat-fallow rotation system that is managed by NT.
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  • 176
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    Bermudagrass Response to High Nitrogen Rates, Source, and Season of Application (1999)
    Springer
    Semigroup forum 91 (1999), S. 438-444 
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    ISSN: 1432-2137
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Cynodon dactylon (L.) Pers.] forage production, but less is known concerning season of application and estimated fertilizer N recovery in these systems. Two field studies (Ardmore, OK: Wildon silt loam, Vertic Haplustalfs; Burneyville, OK: Minco fine sandy loam, Udic Haplustolls) were conducted at two locations over two years to evaluate the effects of rate, timing, and source of N on bermudagrass forage yield, total N, NO3 concentration, and estimated fertilizer N recovery. Nitrogen was applied at rates of 112, 224, 448, 672, and 1344 kg N ha-1 as NH4NO3 or urea in early spring (March) and late summer (August). Fertilizer N recovery can be maximized at rates of 112 and 224 kg N ha-1 applied in the early spring and late summer, respectively. Even when N rates of 1344 kg N ha-1 were applied annually, bermudagrass forage NO3-N was seldom above 2000 mg kg-1, which is below published toxic levels (2400-4500 mg kg-1) for cattle (Bos taurus) consumption. Early-spring applied N increased yields, N removal, and fertilizer recovery compared with late-summer applied N. Fertilizer N recovery was higher for NH4NO3 than for urea, especially when applied in late summer. Late-summer applications of urea should be avoided, due to increased NH3 volatilization losses. Nitrogen applied at 112 kg N ha-1 in early spring can result in fertilizer recoveries in excess of 85%. These high recoveries in forage production systems are possibly a result of continuous preanthesis forage harvesting when gaseous plant N losses are small, but which increase following anthesis.
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  • 177
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    Improved Pasture Establishment and Production on Water-Repellent Soils (1999)
    Springer
    Semigroup forum 91 (1999), S. 467-470 
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    ISSN: 1432-2137
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: -1 of wetting agent in the furrows. There was a large (up to sixfold) increase in early pasture production (330 to 2010 kg ha-1) and a large effect on pasture composition due to the residual effect of a wetting agent applied 2 years previously. The proportion of subterranean clover (Trifolium subterranean L.) in the pasture increased from 6 to 33% due to the use of a wetting agent. This study shows that the effect of water repellency on pasture emergence and productivity is severe and that these ameliorative techniques are useful tools for improving pasture emergence.
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    Decomposition of Surface Crop Residues in Long-Term Studies of Dryland Agroecosystems (1999)
    Springer
    Semigroup forum 91 (1999), S. 401-409 
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    ISSN: 1432-2137
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
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  • 179
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    Agronomics and Economics of Different Weed Management Systems in Corn and Soybean (1999)
    Springer
    Semigroup forum 91 (1999), S. 585-591 
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    ISSN: 1432-2137
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Zea mays L.) and soybean [Glycine max (L.) Merr.]. Chemical and chemical-mechanical weed management had similar corn net returns under moldboard plow ($370 and $355 ha-1, respectively) and chisel tillage ($282 and $287 ha-1). Mechanical weed management had less net returns in moldboard plow ($302 ha-1) and chisel tillage ($121 ha-1) because of 15% lesser corn densities and greater weed densities, especially in chisel tillage. In soybean, mechanical weed management in moldboard plow tillage had similar weed density (1.5 weeds m-2) lower yield (2.71 Mg ha-1), but similar net return ($107.50 ha-1) compared with chemical (1.3 weeds m-2, 2.92 Mg ha-1, and $85.60 ha-1, respectively) and chemical-management (1.0 weeds m-2, 2.78 Mg ha-1 and $99.35 ha-1, respectively). In chisel tillage, mechanical weed management had greater weed density (7.4 weeds m-2), lower yield (2.2 Mg ha-1), and lower net return (-$7.80 ha-1) compared with chemical (1.9 weeds m-2, 2.8 Mg ha-1, and $56.80 ha-1, respectively) and chemical-mechanical weed management (1.9 weeds m-2, 2.4 Mg ha-1, and $27.30 ha-1). Corn and soybean growers apparently can adopt chemical-mechanical weed management and maintain net returns. Soybean growers who use moldboard plow tillage can also adopt mechanical weed management and maintain net returns.
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    Surface Residue and Soil Moisture Affect Fertilizer Loss in Simulated Runoff on a Heavy Clay Soil (1999)
    Springer
    Semigroup forum 91 (1999), S. 606-612 
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    ISSN: 1432-2137
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: -1 for 3 h to an Austin (Udorthentic Haplustoll) clay soil. Soil surface residue treatments were chisel tillage with no added corn (Zea mays L.) residue (CT-NAR), chisel tillage with added corn residue (CT-AR), and bermudagrass [Cynodon dactylon (L.) Pers.] sod (sod). Rainfall simulation was made following fertilizer (16-9-0 N-P-K) applications to relatively dry (350 g kg-1 moisture) and relatively wet (500 g kg-1) soil on each of the residue treatments. Runoff samples collected from a 1-m2 area were analyzed for NO- 3-N,NH+ 4-N, and PO- 4-P concentration and amount (kg ha-1). When fertilizer was applied to relatively dry soil, nutrient losses from both wet and dry runs combined were less than the losses with fertilizer applied to relatively wet soil. For wet runs, the CT-AR treatment reduced total PO- 4 loss nearly sevenfold and NH+ 4-N loss fivefold compared with CT-NAR (1.2 vs. 8.0 kg PO- 4-P ha-1; 3.9 vs. 18.9 kg ha-1 NH+ 4-N), due to increases in time before initiation of runoff and lower nutrient concentrations in runoff. For our conditions, therefore, reduction in nutrient losses in runoff can be achieved by maintaining surface crop residue and applying N and P fertilizers to relatively dry soils. The largest loss of fertilizer nutrients occurred with sod treatments: losses of PO- 4-P for the relatively wet soil were ≈ 41% of PO- 4-P fertilizer applied (51.9 kg PO- 4-P ha-1). This indicates that granular fertilizer application to pastures on heavy clay soils with vertic properties may make a significant contribution to non-point-source pollution; careful management of granular fertilizer applications is thus called for, especially soil water content, when fertilizing sod.
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  • 181
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    Winter Rye Cover Crop Following Soybean Under Conservation Tillage: Residual Soil Nitrate (1999)
    Springer
    Semigroup forum 91 (1999), S. 643-649 
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    ISSN: 1432-2137
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Secale cereale L.) cover crop following soybean [Glycine max (L.) Merr.] has been shown to reduce the soil erosion potential in a corn (Zea mays L.)-soybean rotation system, but little is known about the effect of rye on residual soil NO3-N (RSN). An irrigated field study was conducted for 4 yr on a Sharpsburg silty clay loam (fine, smectitic, mesic Typic Argiudoll) to compare crop rotation and winter rye cover crop following soybean effects on RSN under several tillage practices and N fertilization rates. Treatments each year were (i) tillage: no-till or disk; (ii) rotation:: corn following soybean/rye (Cbr) or soybean/rye following corn (BRc), corn following soybean (Cb) or soybean following corn (Bc), and corn following corn (Cc); and (iii) N rate: 0, 100, and 300 kg N ha-1 (applied to corn). Rye in the Cbr/BRc rotation was planted in the fall following soybean harvest and chemically killed in the spring of the following year prior to corn planting. Each spring, before tillage and N application, RSN was determined to a depth of 1.5 m, at 30-cm intervals. The net spring-to-spring change in RSN between subsequent spring seasons was computed for each plot, and annual aboveground N uptake for rye, corn, and soybean were determined. Rye, rotation N rate, and tillage significantly influenced RSN in the top 1.5 m of soil. The presence of rye (BRc) reduced total spring RSN between 18 and 33% prior to corn planting in 2 or the 3 yr, compared with the no-rye system (Bc), as rye immobilized from 42 to 48 kg N ha-1 in aboveground dry matter. Recycling of N in high-yielding rye cover crop residues led to an increase in RSN accumulation after corn in the succeeding spring. Up to 277 kg RSN ha-1 accumulated at high rates of N following corn in the Cbr rotation, compared with 67 kg RSN ha-1 in the no-rye system (Cb) in 1992. Regardless of the presence of rye, significant accumulation of RSN occurred following corn in the rotation sequence, while RSN declined following soybean. Less RSN was found in the top 1.5 m of soil under continuous than rotation corn, and disking tended to increase NO- 3 accumulation in rotation systems at high rates of N application. Although RSN declines following a rye cover crop, the ready release of this immobilized N suggests that some N credit should be given, reducing N recommendation for corn following winter rye cover, to minimize potential NO- 3 leaching under corn-soybean/ rotations.
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    Physiological Changes from 58 Years of Genetic Improvement of Short-Season Soybean Cultivars in Canada (1999)
    Springer
    Semigroup forum 91 (1999), S. 685-689 
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    ISSN: 1432-2137
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Glycine max (L.) Merr.] cultivars has increased by approximately 0.5% per year since they were first cultivated in the early 1930s. Future yield gains may be dependent on an understanding of the changes made to soybean cultivars by breeding and selection. Our objective was to examine physiological differences associated with seed yield increase within a group of historical cultivars. At Ottawa, Ontario, we grew 14 cultivars representing seven decades of breeding and selection (1934-1992) in a randomized complete block design with four replications, across 4 years. Growth analysis provided data on leaf area and dry weight. Photosynthetic rate per leaf area was measured at several stages of development each year. Yield and harvest index were determined at maturity. The number of days to maturity and the total plant dry weight were not affected by the year of cultivar release. Seed yield, harvest index, and photosynthetic rate were found to have increased by 0.5% per year, while leaf area index decreased by 0.4% per year. The increase in seed yield with year of release was significantly correlated with an increase in harvest index, photosynthesis, and stomatal conductance and a decrease in leaf area index. Today's cultivars are more efficient at producing and allocating carbon resources to seeds than were their predecessors.
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    Validity and Efficiency of Neighbor Analyses in Comparison with Classical Complete and Incomplete Block Analyses of Field Experiments (1999)
    Springer
    Semigroup forum 91 (1999), S. 721-731 
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    ISSN: 1432-2137
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: 0 ) and increasing CV. When spatially structured variation is strong (i.e., NC0 〈 10%), highly rectangular plots must be preferred to nearly square plots in incomplete block and neighbor analyses. Considering validity and efficiency, the best method was FD-EV, which is thus a reliable alternative to classical block analysis when spatial autocorrelation is present.
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    Mitochondrial gene expression in developing male gametophytes of male-fertile and S male-sterile maize (1999)
    Springer
    Sexual plant reproduction 11 (1999), S. 323-330 
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    ISSN: 1432-2145
    Keywords: Key words Cytoplasmic male sterility ; Pollen development ; Zea mays ; mitochondria
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Mitochondria play a critical role in the normal development of the plant male gametophyte and in the disruption of normal gametophyte development associated with cytoplasmically inherited male sterility (CMS). To investigate the role of mitochondria in these processes, the accumulation of mitochondrial gene transcripts and the accumulation of nuclear gene transcripts encoding mitochondrial proteins were investigated through male gametophyte development in normal maize and through the course of pollen abortion in CMS-S maize. Male gametophytes differing in developmental stage were isolated from male-fertile or male-sterile plants by sucrose density gradient centrifugation. Mature pollen was collected from dehiscent anthers of male-fertile plants. Aborted pollen, which collapsed during starch accumulation, was isolated from emergent tassels of CMS-S male-sterile plants. Microspores, developing pollen and mature pollen exhibited striking differences in mitochondrial transcript accumulation. Mature pollen lacked detectable mitochondrial transcripts. Aborted pollen of CMS-S plants contained abundant, intact transcripts of all mitochondrial genes studied, but prematurely degraded transcripts of several nuclear genes. Transcripts of the CMS-S associated mitochondrial open reading frames (orf355 and orf77) were detected from the early stages of microspore development through the aborted pollen stage. The implications of these findings are discussed in terms of the mitochondrial requirements for pollen function and the mechanism of pollen abortion in CMS-S maize.
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    Effect of pollen source and pollen ploidy on endosperm formation and seed set in pseudogamous apomictic Paspalum notatum (1999)
    Springer
    Sexual plant reproduction 11 (1999), S. 331-335 
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    ISSN: 1432-2145
    Keywords: Key words Apomixis ; Pseudogamy ; Endosperm ; Endosperm balance number
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  It is generally accepted that most angiosperms require an accurate balance between maternal and paternal genome contribution for endosperm development. The endosperm balance number (EBN) hypothesis postulates that each species has an effective number which must be in a 2:1 maternal to paternal ratio for normal endosperm development and seed formation. The aim of this work was to investigate the effect of different sources and ploidy levels of pollen donors on endosperm formation and seed production of aposporous tetraploid (2n=4×=40) Paspalum notatum. Hand-emasculated spikelets of an apomictic 4× plant were dusted with pollen of 2×, 4×, 5×, 6× and 8× races of the same species; 3× and 4× races of a phylogenetically closely related species, P. cromyorrhizon; and 2× and 4× races of P. simplex, a species of a different subgenus. Experiments including self-pollination as well as emasculation without pollination were conducted for controls. Results indicated that apomictic 4×P. notatum is a pseudogamous species with effective fertilization of the two unreduced (2n) polar nuclei by a reduced (n) sperm. Endosperm development and seed production occurred independently of the species or the ploidy level of the pollen donor. However, seed germination rates were significantly lower than in the self-pollinated control when the pollen donor was 3×P. cromyorrhizon or 2× and 4×P. simplex. Aposporous embryo sacs in Paspalum contribute to endosperm formation with two unreduced (2n) polar nuclei, while the male contribution is the same as in sexual plants (n). Since sexual Paspalum plants fit the EBN hypothesis, the EBN insensitivity observed in apomictic plants might be a prerequisite for the spread of pseudogamous apomixis. The EBN insensitivity could have arisen as an imprinting consequence of a high maternal genome contribution.
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    Characterization of an anther-expressed protein kinase gene in the potato Solanum berthaultii and its antisense inhibition in transgenic plants (1999)
    Springer
    Sexual plant reproduction 11 (1999), S. 336-346 
    Details
    ISSN: 1432-2145
    Keywords: Key words Pollen germination ; cDNA library ; Solanum berthaultii ; Protein kinase ; Antisense inhibition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  A cDNA clone (1.7 kb) isolated from a cDNA library of in-vitro germinated pollen from the potato species Solanum berthaultii contains an open reading frame of 465 amino acid residues. The predicted protein sequence has typical sequence characteristics of the catalytic subunit of the cyclic-nucleotide dependent protein kinases isolated from yeasts and animals, and the gene has been provisionally termed SBPK, (Solanum berthaultii protein kinase) A transcript of about 1.9 kb was detected on a northern blot in developing anthers, mature pollen, and in-vitro germinated pollen, but not in other plant tissues. The expression in anthers corresponds to the late uninucleate stage of microspore development. Isolation and nucleotide sequencing of a SBPK genomic clone revealed the kinase transcribed region to be interrupted by two introns, both close to the 5′end of the open reading frame, one upstream and one downstream of the start codon. Chimeric genes were constructed by fusing the coding sequence in the antisense orientation to the promoter of a strong late-expressed pollen gene, LAT52, and introduced in potato. Transformants fell into two classes, one displaying a typical antisense phenotype, and a second type arising from a cosuppression event. Both types of transformant gave rise to increased proportions of defective pollen, although the cosuppression effect was more severe. The results indicate that this anther-expressed protein kinase is essential for pollen development in potato.
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    URL: http://dx.doi.org/10.1007/s004970050161
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    Sexual reproduction in the cork oak (Quercus suber L.). I. The progamic phase (1999)
    Springer
    Sexual plant reproduction 11 (1999), S. 347-353 
    Details
    ISSN: 1432-2145
    Keywords: Key words Quercussuber ; Cork oak ; Pollen tube arrest ; Pollen tube competition ; Ovule abortion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Cork oak (Quercus suber L.) is a monoecious wind-pollinated species with a protandrous system to ensure cross-pollination. To the best of our knowledge, this report provides the first insight into the sexual reproduction cycle in this species. The cork oak flowering season extends from April until the end of May. Our results show that, at anthesis, the pistillate flower is not completely formed and ovules are just starting to develop. Pollen reaching the dry stigmatic surface adheres to the receptive cells, germinates and penetrates the epidermis in aproximately 24 h, and grows through the intercellular spaces of a solid transmitting tissue. In cross-pollination, a sequential arrest of pollen tubes was observed along the style, providing preliminary evidence for a pollen tube competition mechanism. As a consequence, few pollen tubes reach the basal portion of the style. Furthermore, pollen tube growth is a discontinuous process since tubes are arrested in the basal portion of the style about 10–12 days after pollination. While tubes are latent, the ovarian loculus starts to develop from an emerging mass of sporogeneous cells which later will differentiate into the placenta and ovules. One and a half months after pollination ovules complete their differentiation, tubes resume growth and fertilisation occurs. Ovular abortion is frequent at this stage, and only one ovule will successfully mature during autumn into a monospermic seed.
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    URL: http://dx.doi.org/10.1007/s004970050162
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    Post-zygotic gametic selection due to endosperm balance number explains unusual chromosome numbers of 3×× 2× progeny in Solanum (1999)
    Springer
    Sexual plant reproduction 12 (1999), S. 27-31 
    Details
    ISSN: 1432-2145
    Keywords: Key words Endosperm breakdown ; Aneuploidy ; 3×× 2× crosses ; Solanum commersonii ; Solanum tuberosum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Crosses between triploid and diploid genotypes are usually the best sources of trisomics in potato as well as in several other crop species. However, 3×× 2× crosses between triploid (2n=3×=36; 2EBN) Solanum commersonii-S. tuberosum hybrids and diploid (2n= 2×=24; 2EBN) genotypes gave progenies with a high number of extra chromosomes, 29–36, suggesting that only eggs with 17–24 chromosomes produced embryos that reached full development. Our hypothesis is that although triploids produce eggs with a range of chromosome numbers, 3×× 2× crosses involving a 2×(2EBN) parent favor eggs with a high chromosome number. These eggs have higher probabilities of possessing the same endosperm balance number (EBN) value (i.e. 1) of gametes produced by the 2EBN diploid parent to give the required 2:1 maternal to paternal EBN ratio in the hybrid endosperm. Under this model, trisomics are produced only if the diploid parent has an EBN of 1. Based on our results and those reported in the literature, it is proposed that in 3×(2EBN) × 2×(2EBN) crosses the endosperm balance number exercises negative selection for gametes with a low chromosome number, and a corresponding low EBN, and positive selection for gametes with a high chromosome number and EBN.
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    URL: http://dx.doi.org/10.1007/s004970050168
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    Use of the APETALA1 promoter to assay the in vivo function of chimeric MADS box genes (1999)
    Springer
    Sexual plant reproduction 12 (1999), S. 14-26 
    Details
    ISSN: 1432-2145
    Keywords: Key words Arabidopsis ; Flower development ; MADS domain ; Functional specificity ; Domain swapping
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  The MADS domain proteins AP1, AP3, PI, and AG are required to specify the four classes of organs in an Arabidopsis flower. Each of these proteins is involved in specifying the identity of two different organs in two adjacent floral whorls. They all share a 56-amino acid MADS domain required for DNA binding and dimerization, a region (I or L) involved in dimerization specificity, the K domain named for its sequence similarity to the coiled-coil of keratin, and a variable carboxy terminal sequence. The abilities of these four related proteins to specify distinct organs presumably result from differential effects on transcriptional regulation. We have previously used chimeric MADS box genes, expressed under the constitutive 35S promoter, to map the regions of these proteins that are responsible for their different organ identity activities. In this paper, we extend these studies by characterizing the phenotypes of plants ectopically expressing chimeric genes under the control of the endogenous AP1 promoter. Similar results are obtained with the 35S and AP1 promoters, although the endogenous promoter does provide a more rigorous test of function. We also describe results from new chimeric gene constructs that show new in vivo functions for the K domain and the amino-terminal portion of the MADS domain.
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    URL: http://dx.doi.org/10.1007/s004970050167
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    Rethinking cytoskeleton in plant reproduction: toward a biotechnological future? (1999)
    Springer
    Sexual plant reproduction 12 (1999), S. 67-70 
    Details
    ISSN: 1432-2145
    Keywords: Key words Cytoskeleton ; Cytoskeleton proteins ; Cytoskeleton function ; Pollen tube ; Embryo sac
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Sexual reproduction in plants is intimately connected to the activity of the cytoskeletal apparatus in reproductive cells. Because of the ease with which the pollen tube can be studied, it has become a model for studying many aspects of cell physiology related to the cytoskeleton, such as movement of organelles and vesicles and cell division. However, information about cytoskeletal proteins is still insufficient for determining cytoskeletal functions during reproduction, especially in terms of cell-cell interactions. One reason may be that cytological and biochemical research on the cytoskeleton of pollen and the embryo sac has not been complemented by sufficient research activity at genetic and molecular levels, and few laboratories are currently involved in this work. This might be because of problems in identifying appropriate applied applications of the work that might attract more investigation.
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    URL: http://dx.doi.org/10.1007/s004970050173
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    Apomixis and sexuality in diploid and tetraploid accessions of Brachiaria decumbens (1999)
    Springer
    Sexual plant reproduction 12 (1999), S. 43-52 
    Details
    ISSN: 1432-2145
    Keywords: Key words Apomixis ; Sexuality ; Day length ; Embryology ; Brachiaria ; Agamic complexes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Meiotic and aposporous embryo sacs and the initial steps of parthenogenetic embryogenesis and endosperm formation were investigated in diploid and tetraploid accessions of Brachiaria decumbens in two environments, differing mainly in day length: early summer and late autumn. Both diploid and tetraploid accessions were facultative apomicts. Di(ha)ploids showed a much lower level of apomixis (10% to15%) than tetraploids (80% to 95%). No obligate sexual diploids were found; thus, their occurrence in natural populations is obscure. It is suggested that reproduction in B. decumbens, as in other agamic complexes of the Paniceae tribe, in general, approximates a diploid-tetraploid-(di)haploid reproductive cycle which does not involve triploids. The dihaploids were fertile and survived in nature. Development of the reproductive structures depended on the environment. In autumn, in contrast to early summer, many meiotic and aposporous embryo sacs degenerated during development, leading to a significant reduction in the proportion of parthenogenetic embryos. Whether this effect can be attributed to day length or simply to age remains to be investigated. The ratio of aposporous to sexual embryo sacs was relatively stable over the two seasons.
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    URL: http://dx.doi.org/10.1007/s004970050170
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    Mitochondrial orf107 transcription, editing, and nucleolytic cleavage conferred by the gene Rf3 are expressed in sorghum pollen (1999)
    Springer
    Sexual plant reproduction 12 (1999), S. 53-59 
    Details
    ISSN: 1432-2145
    Keywords: Key words Cytoplasmic male sterility ; Mitochondria ; Sorghum ; RNA editing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Restoration of male fertility in the A3, IS1112C source of cytoplasmic male sterility (cms) in sorghum is exacted in a gametophytic manner. One required nuclear gene, Rf3, regulates a nucleolytic transcript processing activity, cleaving sequences internal to the chimeric mitochondrial open reading frame orf107. We examined mitochondrial transcription, RNA editing, and action of Rf3 in developing pollen from a male-sterile line, the progenitor, a male-fertile line, and the fertile F1 to determine if these expression processes were manifested at the haploid pollen stage. Steady-state levels of orf107 transcripts and nucleolytic processing conferred by Rf3 were similar to observations from leaves, indicating comparable expression in pollen. RNA editing frequency at two of three sites in orf107 was differentially suppressed compared to leaves, but editing was higher in male-sterile plants than in fertile plants, consistent with the possibility that nucleolytic cleavage is enhanced by editing. The differential suppression of editing frequency at two sites in orf107 contrasts with near-complete editing of a third site in orf107, shared with atp9, indicating that factors influencing editing frequency of the chimeric transcript are temporally regulated and sequence-specific. Since action of the nuclear gene Rf3 is manifested at the diploid and haploid stages, pollen-specific expression of this fertility restoration gene is not required in the A3 gametophytic cms system.
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    URL: http://dx.doi.org/10.1007/s004970050171
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    Pollen-expressed S-RNases are not involved in self-incompatibility in Lycopersicon peruvianum (1999)
    Springer
    Sexual plant reproduction 12 (1999), S. 76-87 
    Details
    ISSN: 1432-2145
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Self-incompatibility in solanaceous plants is gametophytically controlled by a multiallelic S-locus. The only known S-locus product is a series of extracellular ribonucleases (the S-RNases) which are expressed in the mature style and determine its self-incompatibility phenotype. Potentially, S-RNases also determine the self-incompatibility phenotype of pollen as some solanaceous plants express this protein for a brief period during anther development. To test this, we first showed that the S3-RNase of Lycopersicon peruvianum is expressed during anther development. We then transformed L. peruvianum plants with sense and antisense versions of the S3-RNase coding region under the control of a pollen-specific promoter. Pollen from the transgenic plants accumulated S3-RNase transcripts and the S3-RNase protein was detected immunologically in the sense transgenic plants. However, neither the sense nor the antisense S3-RNase constructs altered the self-incompatibility phenotype of pollen from the transgenic plants, demonstrating the S3-RNase is not the pollen product of the S3-allele.
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    URL: http://dx.doi.org/10.1007/s004970050175
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    Comparison of an S-protein expression between self-compatible and -incompatible Japanese pear cultivars (1999)
    Springer
    Sexual plant reproduction 12 (1999), S. 88-93 
    Details
    ISSN: 1432-2145
    Keywords: Key words Japanese pear ; Pyrus serotina ; S-allele ; Self-incompatibility ; S-protein
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  An S4-allele-associated protein (S4-protein) was identified by both isoelectricfocusing (IEF) polyacrylamide-gel electrophoresis and N-terminal amino-acid sequences in self-incompatible Nijisseiki (self-in- compatibility genotype=S2S4) and self-compatible Osa-Nijisseiki (S2S4 SM, SM=stylar-part mutant) styles of the Japanese pear, Pyrus serotina Rehd. var. culta Rehd. Expression of the protein in the cultivars was compared during flower bud development and at post-transcriptional levels. In mature styles, S4-protein could be detected on IEF gel in both cultivars and the N-terminal amino acid sequences were identical, although Osa-Nijisseiki contained only one-third the amount contained in Nijisseiki. No difference was observed in S2-protien amounts. In Nijisseiki styles, S4-protein was already detectable 8 days before anthesis (DBA) and it was synthesized consistently until 2 days after anthesis (DAA); the amount increased 4.7-fold during these 10 days. In contrast, S4-protein in Osa-Nijisseiki was not detected earlier than 6 DBA; a small amount was found at 4 DBA, and it increased gradually as flowers developed. Thus, expression of Osa-Nijisseiki S4-protein is developmentally controlled in the same way as that of Nijisseiki S4-protein, but with a time lag of several days; the protein level at 2 DAA corresponded to that of Nijisseiki earlier than 4 DBA. S4-proteins from both Nijisseiki and Osa- Nijisseiki showed RNase activity and the activity was also developmentally controlled; it increased about fourfold during the interval from 8 DBA to 2 DAA in Nijisseiki, and 3.3-fold during the interval from 4 DBA to 2 DAA in Osa-Nijisseiki. Activity at 2 DAA, however, was twice as high in Nijisseiki. In vitro protein synthesis showed that poly(A)+ from mature Osa-Nijisseiki styles could form S4-like protein in a manner similar to that of Nijisseiki. These results suggest that the self-compatibility of Osa-Nijisseiki is due to a low level of S4-protein expression, a mechanism very similar to the low level of S-protein and weak incompatibility in immature styles of self-incompatible Nijisseiki. Part of this protein repression may be regulated during post-transcriptional events.
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    URL: http://dx.doi.org/10.1007/s004970050176
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    Megasporogenesis in Arabidopsis thaliana L.: an ultrastructural study (1999)
    Springer
    Sexual plant reproduction 12 (1999), S. 99-109 
    Details
    ISSN: 1432-2145
    Keywords: Key words Arabidopsis thaliana ; Megasporogenesis ; Meiosis ; Ultrastructure ; Cellular polarity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  In this study, megasporogenesis of the plant model Arabidopsis thaliana was investigated by electron microscopy for the first time. The data described here could constitute a reference for future investigations of Arabidopsis mutants. During the beginning of meiosis the megaspore mother cell shows a polarity created by unequal distribution of organelles in the cytoplasm. Plastids accumulate in the chalazal region and long parallel saccules of endoplasmic reticulum, small vacuoles and some dictyosomes are found in the micropylar region. Plasmodesmata are abundant in the chalazal cell wall. The nucleus is almost centrally localized and contains a prominent excentric nucleolus and numerous typical synaptonemal complexes. After the second division of meiosis the four megaspores are separated by thin cell walls crossed by numerous plasmodesmata and do not show significant cellular organization. The young functional megaspore is characterized by a large nucleus and a large granular nucleolus. The cytoplasm is very electron dense due to the abundance of free ribosomes and contains the following randomly distributed organelles: mitochondria, a few short saccules of endoplasmic reticulum, dictyosomes and undifferentiated plastids. However, there is no apparent polarity, except for the distribution of some small vacuoles which are more abundant in the micropylar region of the cell. The degenerating megaspores are extremely electron dense and do not show any substructure.
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    URL: http://dx.doi.org/10.1007/s004970050178
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    Promoter region of Ory s 1, the major rice pollen allergen gene (1999)
    Springer
    Sexual plant reproduction 12 (1999), S. 125-126 
    Details
    ISSN: 1432-2145
    Keywords: Key words Gene regulation ; Ory s 1 ; Oryza sativa ; Pollen allergen ; Promoter ; Rice
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
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    URL: http://dx.doi.org/10.1007/s004970050182
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    Successful first and second backcrosses of S. nigrum (+) S. tuberosum somatic hybrids with both Solanum parents (1999)
    Springer
    Sexual plant reproduction 12 (1999), S. 144-151 
    Details
    ISSN: 1432-2145
    Keywords: Key words Solanum tuberosum ; Solanum nigrum ; Somatic hybrids ; Backcross experiments ; Phytophthora infestans
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Somatic hybrids of Solanum nigrum (+) 2× potato were successfully crossed with S. nigrum and with potato. First and second backcross progeny with S. nigrum could easily be obtained. One of the BC1 genotypes was already self-fertile. Backcrosses with potato had a much lower success rate. Only pollinations with tetraploid potato resulted in seed-containing berries. Two BC1 genotypes were obtained after 4362 pollinations from which 505 ovules were cultured. The first BC1 genotype grew vigorously in vitro and in the greenhouse and flowered abundantly. The second BC1 showed many abnormalities and dropped its flowers before anthesis. The first BC1 was again crossed with tetraploid potato and in this generation also the success rate was low. Over 5000 pollinations resulted in 1750 berries from which over 3000 ovules were obtained. Twelve plants germinated from these ovules and they were not as vigorous in vitro and in vivo as the BC1 parent. Some of the BC2 genotypes were used for further backcrosses but no BC3 plants were obtained. BC1 and BC2 genotypes that resulted from the backcross program with potato were tested for resistance to Phytophthora infestans. The BC1 genotype was as resistant as the S. nigrum fusion parent, but among the eight BC2 genotypes scored six were resistant, whereas two genotypes showing lesions were susceptible.
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    Isolation and osmotic relations of developing megagametophytes of Torenia fournieri (1999)
    Springer
    Sexual plant reproduction 12 (1999), S. 152-157 
    Details
    ISSN: 1432-2145
    Keywords: Keywords Megagametophyte ; Embryo sac ; Osmotic potential ; Protoplast ; Torenia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  A new method is reported to isolate and handle living megagametophytes of Torenia fournieri at any developmental stage. The stages were determined using light microscopy and delimited by correlating floral morphological traits. When significant changes in the osmotic pressure were found during development, enzyme solutions contained different concentrations of osmoticum. Osmotic pressure is lowest in the megaspore, increases until the four-nucleate stage and then gradually decreases until complete embryo sac formation. In enzymatic solutions containing appropriate concentrations of osmoticum, protoplasts of megaspores, two-, four-, eight-nucleate embryo sacs, egg cells, synergids and central cells were successfully isolated. The living protoplasts were collected by micromanipulator, transferred into microdroplets and tested for viability.
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    URL: http://dx.doi.org/10.1007/s004970050186
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    Gametic behavior in a marine green alga, Monostroma angicava: an effect of phototaxis on mating efficiency (1999)
    Springer
    Sexual plant reproduction 12 (1999), S. 158-163 
    Details
    ISSN: 1432-2145
    Keywords: Key words  Evolution of anisogamy ; Mating behavior ; Mating efficiency ; Monostroma angicava ; Phototaxis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. The role of phototactic behavior of gametes was tested experimentally in the slightly anisogamous marine green alga Monostroma angicava Kjellman, and the effect of phototaxis on mating efficiency was discovered. Both male and female gametes showed positive phototaxis in response to a white light source. In contrast, they did not respond to a red light source. Their swimming velocity did not differ between these two illuminating light sources. It was, therefore, suggested that the search ability of the gamete itself might not vary between phototactic and non-phototactic conditions. The number of zygotes formed during the mating process may be expressed as the product of the number of encounters between male and female gametes and the fraction of encounters that result in sexual fusion. In this study, with high densities of male and female gametes mixed in test tubes, almost all minor (fewer in number) gametes fused sexually within 10 min. After dilution of the gamete suspensions by half, mating efficiency in test tubes illuminated by white light from above was higher than that in dark controls. This suggests that male and female gametes gathered at the water surface through their positive phototaxis, thus increasing the rate of encounters. Mating efficiency also decreased if the test tubes were illuminated from above by white light and also shaken. Since negative phototaxis is clearly shown in planozygotes, we suggest that positive phototaxis of male and female gametes in M. angicava is an adaptive trait for increasing the rate of gametic encounters rather than for the dispersal of zygotes as previously reported for zoospores of some marine algae.
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    URL: http://dx.doi.org/10.1007/s004970050187
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    Pollen sporopollenin: degradation and structural elucidation (1999)
    Springer
    Sexual plant reproduction 12 (1999), S. 171-178 
    Details
    ISSN: 1432-2145
    Keywords: Key words Pollen ; Exine ; Sporopollenin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  We report the isolation of purified sporopollenin from pollen grains of different species and its complete solubilization. Exine from Pinus pinaster, Betula alba, Ambrosia elatior and Capsicum annuum was extracted by treatment with hydrogen fluoride in pyridine. These exines were purified from their aromatic moieties and from fatty acids linked by ester bonds using acidolysis and saponification treatments. The biopolymer obtained retains almost completely the shape of the original pollen grain. Fourier-transform infrared spectroscopy analysis of the isolated sporopollenin showed the absence of polysaccharide and phenolic material and the presence of carboxylic acid groups joined to unsaturations and ether linkages. Sporopollenin samples were successfully degraded by exhaustive 24-h ozonolysis at room temperature. Gentle ozonolysis (3 h at 0°C) did not completely degrade the biopolymer. The compounds obtained after exhaustive ozonolysis were analysed by gas chromatography-mass spectrometry. Dicarboxylic acids with a low number of carbon atoms were identified as major components of sporopollenin from P. pinaster, A. elatior and C. annuum, representing 28.8%, 63.2% and 88.5%, respectively, of the total compounds obtained. Fatty acids and n-alkanes also were identified in P. pinaster, A. elatior and B. alba sporopollenin. From the data obtained, an hypothesis about the chemical nature and structural arrangement of the sporopollenin is proposed.
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    URL: http://dx.doi.org/10.1007/s004970050189
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