Distribution of inorganic nitrogen in agricultural soils at different dates and scales

To avoid the leaching of nitrate from agricultural soils to groundwater, appropriate N-fertilization strategies aim at the depletion of the pool of soil inorganic nitrogen (N_min = NO₃-N + NH₄-N) during crop growth. Such strategies need a good knowledge of the spatial distribution of inorganic nitrogen pools at the field sites and its change over time. Therefore inorganic nitrogen in arable soils of a farm was determined after harvest in 1990, 1991 and 1992 and in the spring of 1991 and 1992 with a high areal resolution. One bulk sample of four corings was taken per 50x50-m grid cell (n=152-178) from 0-90cm soil depth. At all arable sites, winter wheat was grown in the first, and spring barley in the second year of this study. Results show a wide range of nitrogen contents at the farm level, at the field level and at the level of subdivisions of fields. Almost no spatial dependence of N_min contents could be found from calculated semivariograms. Because of this small-scale variation the subdivision of fields into fixed plots of homogenous N-fertilizer demand is difficult and can be seen as only a first step towards site specific farming.     

Crystal structure of farnesyl protein transferase complexed with a CaaX peptide and farnesyl diphosphate analogue

The crystallographic structure of acetyl-Cys-Val-Ile-selenoMet-COOH and alpha-hydroxyfarnesylphosphonic acid (alphaHFP) complexed with rat farnesyl protein transferase (FPT) (space group P61, a = b = 174. 13 A, c = 69.71 A, alpha = beta = 90 degrees, gamma = 120 degrees, Rfactor = 21.8%, Rfree = 29.2%, 2.5 A resolution) is reported. In the ternary complex, the bound substrates are within van der Waals contact of each other and the FPT enzyme. alphaHFP binds in an extended conformation in the active-site cavity where positively charged side chains and solvent molecules interact with the phosphate moiety and aromatic side chains pack adjacent to the isoprenoid chain. The backbone of the bound CaaX peptide adopts an extended conformation, and the side chains interact with both FPT and alphaHFP. The cysteine sulfur of the bound peptide coordinates the active-site zinc. Overall, peptide binding and recognition appear to be dominated by side-chain interactions. Comparison of the structures of the ternary complex and unliganded FPT [Park, H., Boduluri, S., Moomaw, J., Casey, P., and Beese, L. (1997) Science 275, 1800-1804] shows that major rearrangements of several active site side chains occur upon substrate binding.     

Protein farnesyltransferase

Changes in mice haemopoietic cellular populations and in the radiosensitivity of CFU-C and BFUe progenitors cells were determined in vivo for mixed field radiations composed of a gamma-ray component and a neutron component. Five Dgamma/Dtotal ratios (gamma-rays over total dose ratios, quoted as tau in this report) were obtained (tau = 0.95, 0.83, 0.67, 0.33 and 0.09). Myelogram changes were enlarged with the increase of the neutron component. Radiosensitivity of the two progenitor cell lineages were increased with lower tau values (excess of neutrons). The radiosensitivity of haemopoietic progenitor cells exposed in vivo varies with the ratio of the high- and low-LET components in the mixture. The D0 value varied from 3.3 +/- 0.22 to 0.85 +/- 0.04 Gy with the decrease of tau for CFU-C and from 2.08 +/- 0.22 to 0.64 +/- 0.07 Gy for BFUe. The obtained relative biologic efficiency (RBE) varied from 1.2 +/- 0.08 to 4.7 +/- 0.24 for CFU-C and from 1.1 +/- 0.1 to 3.6 +/- 0.16 for the BFUe. The relation between RBE and tau could be somewhat non-linear for CFU-C and seems to be close to linear for BFUe. The higher is the neutron component, the higher is the radiosensitivity. These results indicate that variations of the quality of the mixed field in the haemopoietic local territory are of great importance in terms of radiation damage and cell killing as well as in terms of the ability to restore the haemopoietic system.     

Note on contributors

It is generally accepted that one particular wear mechanism involved in rolling contact between two cylinders is basically that of fatigue. This mode of wear is influenced by the maximum Hertzian stresses occurring in the contact zone of the cylinders. The equations usually employed to calculate the magnitude of the Hertzian stresses and the corresponding allowable working loads are based on an assumption that the contours of the contacting surfaces are perfect. In general practice however the profiles of the cylinders are always imperfect in form.In this paper cases of imperfect contact between bodies of nominally cylindrical form are analysed.     

Lubrication of hot-strip-mill rolls

To improve hot-steel-strip rolling mill operations trial attempts at work roll surface lubrication have been made by various investigators throughout the world during the last decade.Some European tests are briefly described. Most of the investigations have been somewhat inconclusive, possibly because they were not undertaken with sufficient determination. Even so, it is apparent that improved wear life of work rolls can be achieved together with a decrease in the extent of surface defects in the rolled product. There could be a side advantage in a reduction in power requirements of the main drive motors.It has been suggested that it could be simpler and at least equally beneficial, to add a surface active agent to the roll cooling water, instead of applying oil to the roll surfaces.     

Chest X ray: routine indication in the follow-up of differentiated thyroid cancer?

Models of the bacterial ribosome based on recent structural analyses are beginning to provide new insights into the protein synthetic machinery. Central to evolving models are the high-resolution structures of individual ribosomal proteins, which represent detailed probes of their local RNA and protein environments. Ribosomal proteins are extremely ancient molecules; the structures therefore also provide a unique window into early protein evolution. Many of the proteins contain domains that are present in more recently evolved families of RNA- and DNA-binding proteins. Such structural homology can be used to predict mechanisms by which proteins interact with RNA in the ribosome.     

Impact of Interlayer Dwell Time on Microstructure and Mechanical Properties of Nickel and Titanium Alloys

Path planning in additive manufacturing (AM) processes has an impact on the thermal histories experienced at discrete locations in simple and complex AM structures. One component of path planning in directed energy deposition is the time required for the laser or heat source to return to a given location to add another layer of material. As structures become larger and more complex, the length of this interlayer dwell time can significantly impact the resulting thermal histories. The impact of varying dwell times between 0 and 40 seconds on the microstructural and mechanical properties of Inconel® 625 and Ti-6Al-4V builds has been characterized. Even though these materials display different microstructures and solid-state phase transformations, the addition of an interlayer dwell generally led to a finer microstructure in both materials that impacted the resulting mechanical properties. With the addition of interlayer dwell times up to 40 seconds in the Inconel® 625 builds, finer secondary dendrite arm spacing values, produced by changes in the thermal history, correspond to increased yield and tensile strengths. These mechanical properties did not appear to change significantly, however, for dwell times greater than 20 seconds in the Inconel® 625 builds, indicating that longer dwell times have a minimal impact. The addition of interlayer dwell times in Ti-6Al-4V builds resulted in a slight decrease in the measured alpha lath widths and a much more noticeable decrease in the width of prior beta grains. In addition, the yield and tensile values continued to increase, nearly reaching the values observed in the rolled plate substrate material with dwell times up to 40 seconds.