From Graphene constrictions to single carbon chains

We present an atomic-resolution observation and analysis of graphene constrictions and ribbons with sub-nanometer width. Graphene membranes are studied by imaging side spherical aberration-corrected transmission electron microscopy at 80 kV. Holes are formed in the honeycomb-like structure due to radiation damage. As the holes grow and two holes approach each other, the hexagonal structure that lies between them narrows down. Transitions and deviations from the hexagonal structure in this graphene ribbon occur as its width shrinks below one nanometer. Some reconstructions, involving more pentagons and heptagons than hexagons, turn out to be surprisingly stable. Finally, single carbon atom chain bridges between graphene contacts are observed. The dynamics are observed in real time at atomic resolution with enough sensitivity to detect every carbon atom that remains stable for a sufficient amount of time. The carbon chains appear reproducibly and in various configurations from graphene bridges, between adsorbates, or at open edges and seem to represent one of the most stable configurations that a few-atomic carbon system accomodates in the presence of continuous energy input from the electron beam.Comment: 12 pages, 4 figure

The transition between hole-pairs and four-hole clusters in four-leg tJ ladders

Holes weakly doped into a four-leg \tj ladder bind in pairs. At dopings exceeding a critical doping of $\delta_c\simeq {1/8}$ four hole clusters are observed to form in DMRG calculations. The symmetry of the ground state wavefunction does not change and we are able to reproduce this behavior qualitatively with an effective bosonic model in which the four-leg ladder is represented as two coupled two-leg ladders and hole-pairs are mapped on hard core bosons moving along and between these ladders. At lower dopings, $\delta<\delta_c$, a one dimensional bosonic representation for hole-pairs works and allows us to calculate accurately the Luttinger liquid parameter \krho, which takes the universal value \krho=1 as half-filling is approached

The role of glutathione in the development and release of rest on 'Redhaven' peaches

A rapid and sensitive HPLC method for quantifying both the reduced and oxidized forms of glutathione simultaneously in woody plant tissues was developed. This method was applicable to a variety of woody plant species and different tissues. Total glutathione content in the bark tissue of seven of the woody plant species tested were lower during active plant growth, and higher in the dormant stage. All tested tissues of peach plants contained glutathione. The highest and lowest content was found in the leaves and roots, respectively. 'Redhaven' peach trees acquired the onset of rest on 1 Oct, before any chilling had been experienced. Maximum rest was reached on 1 Nov after the plants were exposed to 320 CU, and 50% of the buds were broken at 860 CU on 1 Dec. Total budbreak and phytotoxicity induced by hydrogen cyanamide applied to 'Redhaven' peach trees was dependent on concentration and time of application. Phytotoxicity was evident at all application dates, but greatest at the highest concentrations. Plants were more resistant to hydrogen cyanamide at maximum rest. Hydrogen cyanamide induced budbreak was best during the post-rest period. Budbreak and phytotoxicity induced by hydrogen cyanamide applied during the quiescent stage were dependent on posttreatment temperature and concentration. All cyanamide treatments inhibited budbreak at all tested temperatures. The inhibition was greatest at the the lowest temperature and at the highest concentrations. Phytotoxicity was greater at 15C and 35C than at 25C, and increased with increased concentrations. The content of GSH and GSSG in the buds changed with the development of rest. During the early phases of rest, when rest intensity increased, the content of GSH and GSSG decreased (15 Oct) and then increased at maximum rest (1 Nov). Content of GSH continued to increase and peaked on 1 Dec at 860 CU. On 15 Dec when the buds were qxiiescent GSH content decreased. In contrast, contents of GSSG did not drop during cjuiescence and were highest on 15 Dec. GSH content induced by chilling was closely associated with the end of rest. Hydrogen cyanamide treatments caused a rapid decrease of GSH content within 12 hr followed by a large increase 24 hr after application. The changes of GSH induced were inversely proportional to cyanamide concentration. Non-treated plants showed at relatively constant GSH and GSSG content during this period of time. Hydrogen cyanamide treatments increased GSH contents at all application dates. The extent of GSH changes was dependent on the physiological status of the bud and cyanamide concentration. At maximum rest the plants were more resistant to cyanamide and this coincided with the highest induced GSH content as compared to all application dates

Adaptive Control Optimization of Cutting Parameters for High Quality Machining Operations Based on Neural Networks and Search Algorithms

This book chapter presents an Adaptive Control with Optimization (ACO) system for optimising a multi-objective function based on material removal rate, quality loss function related to surface roughness, and cutting-tool life subjected to surface roughness specifications constraint

Effect of several apple rootstocks on growth, yield components and leaf area estimates on "Starkspur Supreme Delicious" trees

Growth, yield components and leaf area were evaluated on 'Starkspur Supreme Delicious' apple on nine rootstocks: MAC 24, EMLA 7, EMLA 26, OAR 1, MAC 9, 0.3, EMLA 9, M 9, and EMLA 27. Estimates of planting density based on growth, estimates of leaf area based on four independent variables and the relationships among yield components, fruit quality, growth and leaf area were investigated during 1985. Tree height, tree spread and trunk cross sectional area were highest for trees on MAC 24 followed for EMLA 7 while trees on EMLA 26, OAR 1, MAC 9, 0.3, EMLA 9 and M 9 were less in these values in descending order, with the most dwarfing on EMLA 27. Estimates of planting densities indicated higher densities with tree canopy spread than TCSA based on standard trees of the age except on EMLA 27. The densities for trees on MAC 24 and EMLA 7 were estimated 426 and 496 trees/ha. respectively, while for the rootstocks with intermediate size ranged from 700 to 1000 trees/ha. The highest density was for EMLA 27 with 1824 trees/ha. Flower cluster, fruit number, yield and leaf area were highest in the least size controlling rootstocks MAC 24 and EMLA 7, and in general these were a function of tree size. MAC 9 had the highest flowering density, crop density and yield efficiency followed by 0.3, EMLA 26 and EMLA 9. Potential yields based on the estimated planting density were also highest for MAC 9. Fruit on OAR 1 had greatest soluble solids, firmest at harvest, but were the smallest. Fruit on EMLA 7 which had the lowest soluble solids were largest. A negative correlation between flowering density and fruit set among the rootstocks was found. Crop density influenced fruit size and weight. Fruit on EMLA 7, MAC 24 and EMLA 9 were the largest but these trees had the lowest crop density. There was a high correlation of fruit number with yield indicating this was the main component of yield. The leaf-fruit ratio was negatively correlated with flowering density, crop density and yield efficiency and the ratio was lowest on the more efficient rootstocks MAC 9, 0.3 and M 9 while those of MAC 24 and EMLA 7 were highest. No differences were seen among the regression lines of leaf area and 4 independent variables obtained from trees on various rootstocks and within rootstock. Fresh weight was the best estimate of leaf area but because of greater speed and simplicity, branch cross sectional area was chosen to predict leaf area. Total leaf area per tree decreased from the least size controlling rootstocks to the most dwarfing rootstocks. Tree leaf area index ranged from 1.69 in MAC 24 to 0.87 in 0.3, but it did not always increase proportionately to tree size. Orchard leaf area index from estimated planting densities showed low values in all rootstocks but a slight increase with the tree size. This indicated that trees at the estimated densities are not intercepting the maximum quantity of light

Feed rate modeling in circular–circular interpolation discontinuity for high-speed milling

In this paper, a modeling approach is presented in order to evaluate feed rate during a circular interpolation in high-speed milling. The developed model depends on the type of discontinuity and the kinematic performance of the machine tool. To begin with, a feed rate modeling for circular interpolation with continuity in tangency is developed. After, the discontinuity in tangency between two circular interpolations is replaced by discontinuity in curvature by adding a fillet which is in relation to the functional tolerance ε imposed in the part design. An experimental study has been carried out to validate the models

Source localisation on aircraft in flight - new measurements with the DLR research aircraft Airbus 320 ATRA

Fly-over measurements with a large microphone array were performed with the Airbus A320-232 research aircraft ATRA of DLR. A large multi-arm spiral array was set up on the end of the runway of the airport. The aircraft trajectory was estimated from the vertical distance and time delays measured with an array of vertically mounted laser distance meters and GNSS trajectories recorded on board of the aircraft. Source localisation maps were obtained from a hybrid deconvolution method. The source powers in different regions of the aircraft were calculated by integrating over the source regions. The total power in the whole interrogation area matches the power in the far-field spectra, apart from contributions from sources on the ground plane which are reduced by focusing the array on the aircraft. Results from fly-overs in the same or in different configurations can be compared on the basis of the integration results and the individual sources can be ranked according to their contribution to the overall sound pressure

Hole-doping effects on a frustrated spin ladder

Hole-doping effects are investigated on the {\it t-J} ladder model with the linked-tetrahedra structure. We discuss how a metal-insulator transition occurs upon hole doping with particular emphasis on the effects of geometrical frustration. By computing the electron density and the spin correlation function by the density matrix renormalization group, we show that strong frustration triggers a first-order transition to a metallic phase, when holes are doped into the plaquette-singlet phase. By examining spin excitations in a metallic case in detail, we discuss whether the spin-gap phase persists upon hole doping according to the strength of frustration. It is further shown that the lowest excited state in a spin-gap metallic phase can be described in two independent quasiparticles.Comment: 7 pages, 9 figure