The DCU laser ion source

Laser ion sources are used to generate and deliver highly charged ions of various masses and energies. We present details on the design and basic parameters of the DCU laser ion source (LIS). The theoretical aspects of a high voltage (HV) linear LIS are presented and the main issues surrounding laser-plasma formation, ion extraction and modeling of beam transport in relation to the operation of a LIS are detailed. A range of laser power densities (I ∼ 108–1011 W cm−2) and fluences (F = 0.1–3.9 kJ cm−2) from a Q-switched ruby laser (full-width half-maximum pulse duration ∼ 35 ns, λ = 694 nm) were used to generate a copper plasma. In “basic operating mode,” laser generated plasma ions are electrostatically accelerated using a dc HV bias (5–18 kV). A traditional einzel electrostatic lens system is utilized to transport and collimate the extracted ion beam for detection via a Faraday cup. Peak currents of up to I ∼ 600 μA for Cu+ to Cu3+ ions were recorded. The maximum collected charge reached 94 pC (Cu2+). Hydrodynamic simulations and ion probe diagnostics were used to study the plasma plume within the extraction gap. The system measured performance and electrodynamic simulations indicated that the use of a short field-free (L = 48 mm) region results in rapid expansion of the injected ion beam in the drift tube. This severely limits the efficiency of the electrostatic lens system and consequently the sources performance. Simulations of ion beam dynamics in a “continuous einzel array” were performed and experimentally verified to counter the strong space-charge force present in the ion beam which results from plasma extraction close to the target surface. Ion beam acceleration and injection thus occur at “high pressure.” In “enhanced operating mode,” peak currents of 3.26 mA (Cu2+) were recorded. The collected currents of more highly charged ions (Cu4+–Cu6+) increased considerably in this mode of operation

The Bacterial Photosynthetic Reaction Center as a Model for Membrane Proteins

Membrane proteins participate in many fundamental cellular processes. Until recently, an understanding of the function and properties of membrane proteins was hampered by an absence of structural information at the atomic level. A landmark achievement toward understanding the structure of membrane proteins was the crystallization (1) and structure determination (2-5) the photosynthetic reaction center (RC) from the purple bacteria Rhodopseudomonas viridis, followed by that of the RC from Rhodobacter sphaeroides (6-17). The RC is an integral membrane protein-pigment complex, which carries out the initial steps of photosynthesis (reviewed in 18). RCs from the purple bacteria Rps. viridis and Rb. sphaeroides are composed of three membrane-associated protein subunits (designated L, M, and H), and the following cofactors: four bacteriochlorophylls (Bchl or B), two bacteriopheophytins (Bphe or [phi]), two quinones, and a nonheme iron. The cofactors are organized into two symmetrical branches that are approximately related by a twofold rotation axis (2, 8). A central feature of the structural organization of the RC is the presence of 11 hydrophobic [alpha]-helixes, approximately 20-30 residues long, which are believed to represent the membrane-spanning portion of the RC (3, 9). Five membrane-spanning helixes are present in both the L and M subunits, while a single helix is in the H subunit. The folding of the L and M subunits is similar, consistent with significant sequence similarity between the two chains (19-25). The L and M subunits are approximately related by the same twofold rotation axis that relates the two cofactor branches. RCs are the first membrane proteins to be described at atomic resolution; consequently they provide an important model for discussing the folding of membrane proteins. The structure demonstrates that [alpha]-helical structures may be adopted by integral membrane proteins, and provides confirmation of the utility of hydropathy plots in identifying nonpolar membrane-spanning regions from sequence data. An important distinction between the folding environments of water-soluble proteins and membrane proteins is the large difference in water concentration surrounding the proteins. As a result, hydrophobic interactions (26) play very different roles in stabilizing the tertiary structures of these two classes of proteins; this has important structural consequences. There is a striking difference in surface polarity of membrane and water-soluble proteins. However, the characteristic atomic packing and surface area appear quite similar. A computational method is described for defining the position of the RC in the membrane (10). After localization of the RC structure in the membrane, surface residues in contact with the lipid bilayer were identified. As has been found for soluble globular proteins, surface residues are less well conserved in homologous membrane proteins than the buried, interior residues. Methods based on the variability of residues between homologous proteins are described (13); they are useful (a) in defining surface helical regions of membrane and water-soluble proteins and (b) in assigning the side of these helixes that are exposed to the solvent. A unifying view of protein structure suggests that water-soluble proteins may be considered as modified membrane proteins with covalently attached polar groups that solubilize the proteins in aqueous solution

Sulphur nutrition of pastures and crops Phosphorus and potassium nutrition of pastures on deep sands in the high rainfall areas

CONTENTS A. SULPHUR 1. Sources, rates, time of application of sulphur to legume pastures (high rainfall) - 80AL1, 80AL4, 80MA1, 80KE1. 2. Sulphur soil test on pastures (high rainfall) - 80AL12, 80AL13, 80AL14, 80BY2, 80KE2. 3. Sulphur rundown on sulphur absorbing soils of the high rainfall areas - 80BY1. 4. Sulphur requirements of pasture in low rainfall areas - 80JE17, 80M020. 5. Residual value of 1979 applied sulphur. Rates of fine gypsum applied 1980 - 79AL2, 79AL18, 79AL22, 79AL23, 79AL25, 79AL41, 78BA8 B, 79BY3, 79BY4, 79HA2, 79KE3, 79KE7, 79M020. 6. Sulphur requirements of wheat - 80JE16, 80M09. B. PHOSPHORUS 7. Sources, rates, time of application of phosphorus to legume pastures - 80AL2, 80AL5, 80AL15, 80MA2. C. POTASSIUM 8. Sources, rates, time of application of potassium to legume pastures - 80AL3, 80AL6, 80MA3. D. SLOW RELEASE P,S,K FERTILIZERS - 1979 TRIALS 9. Phosphorus sulphur and potassium slow release fertilizers on pastures 1980 results - 79AL1, 79KE2, 79MA2. E. APPENDIX P.R.D./Albany Regional Office PKS collaborative trials, sulphur results. (sulphur soil test on pastures) - 80AL44, 80AL46, 80AL47, 80AL72

The effects on plant growth

The level of acidity of a soil reflects its chemical and sometimes its biological condition. Changes in acidity mean changes in the availability to plants of some soil elements, and modifications to the biological processes in the soil. Some elements become more available to plants in acis soils, and in some soils particular elements can reach toxic levels. Other elements can be effected in the opposite way: deficiencies can develop in acid conditions. It is important to realise, however, that the chemical nature of all soils varies. Beccause of these variations, acidity can affect each soil differently and thus influence plant growth differently

Sulphur nutrition of pastures and crops, Phosphorus and potassium nutrition of high rainfall pastures on deep sands, Soil acidity - high rainfall pastures

A. SULPHUR - HIGH RAINFALL 1. Rates and time of application of superphosphate to pastures. 79AK2, 79AL23, 79AL25, 79AL41, 81BY1, 81KE1. 2. Sulphur soil test calibration on pastures. 79AL18, 80BY2, 80KE2. 3. Sulphur soil test calibration on pastures: Co-operative PKS soil test project on pastures on duplex soils of the east Albany area (PRD/ARO). Sulphur results. 80 AL44, 46, 47, 48, 72, 73 81AL51, 53, 55 4. Sulphur on adsorbing soils receiving no current S input. 80BY1., 80AL16. 5. Sources, rates, time of application of sulphur on pastures. 80AL1, 80AL4, 81AL3, 81AL4, 80KE1, 80MA1 B. SULPHUR - LOW RAINFALL 1. Sulphur on pastures. 80JE17, 80M020. 2. Sulphur on cereals 80JE16, 80M09. C. PHOSPHORUS 1. Sources, rates time of application of phosphorus on high rainfall pastures on deep sands. 79AL1, 80AL2, 80AL5, 80AL15, 81AL5, 81AL6, 81KE2, 79MA2, 80MA2, 81MA4. D. POTASSIUM 1. Sources, rates, time of application of potassium on high rainfall pastures on deep sand. 80AL3, 80AL6, 81AL7, 81AL8, 81MA3. E. SOIL ACIDITY 1. High rainfall soil pH survey - 2. Lime on old lan·d pastures (high 81AL10, 81ALll, 81AL12, 81AL13, Albany Region - Summary rainfall) 81AL14, 81AL15, 81AL16 3. Topdressed vs incorporated lime on new land acid peat. 81AL9 4. Lime on new land pastures: 1981 results from 1979-80 commenced trials by Albany Regional Office staff. 79AL14, 79AL16, 80AL50, 80AL51, 80AL52, 80AL53, 80AL54

1979 Phosphorus and sulphur interactions on pastures. Sulphur nutrition of pastures

Contents: Phosphorus and sulphur interactions on pastures. Sulphur nutrition of pastures. (i) Phosphorus x sulphur x times of application on pastures 1979: 79AL2, 79BY1, 79KE3, 79KE4. (ii) Sulphur status/soil tests on pastures: 79AL18, 79AL22, 79AL25, 79AL41, .79BY2, 79BY3, 79BY4, 79HA1, 79HA2, 79HA3, 79KE7, 79M020. (iii) Time of application of sulphur to pastures: 79BU1,79KE6. (iv) Phosphorus, sulphur and potassium fertilisers on pastures on deep leaching sands: 79AL1, 79KE2, 79MA2, 79MA6. (v) Phosphorus x sulphur interaction trials 1978; 1979 treatments: 78A7, 78BA8, 73B4, 78BU3, 78C4, 78MA2, 78M08, 78N04

Sulphur nutrition of pastures. Potassium nutrition of high rainfall pastures on deep sands

A. Sulphur - High Rainfall – 80AL1, 80AL4 (1980), 80AL4 B (established 1983). Sulphur rundown on heavy soils - 80BY1. Sources, rates, time of application of sulphur to pastures - 80AL1, 80AL4, 80AL4B. Sources, rates, time of application of sulphur to legume pastures – 80AL1, 80AL4, 80AL4B. Sulphur nutrition of pastures. 83PE36. B. Sulphur - Low Rainfall – 82AL9, 80JE16/17 82KA4. Sulphur on pastures - 80JE16/17, 82AL9, 82KA4. Sulphur on absorbing soils receiving no current S input – 80BY1. C. Potassium. Sources, rates, time of application of potassium on high rainfall deep sand pastures - 80AL3, 80AL6