1,398 research outputs found
Design of a welded joint for robotic, on-orbit assembly of space trusses
A preliminary design for a weldable truss joint for on-orbit assembly of large space structures is described. The joint was designed for ease of assembly, for structural efficiency, and to allow passage of fluid (for active cooling or other purposes) along the member through the joint. The truss members were assumed to consist of graphite/epoxy tubes to which were bonded 2219-T87 aluminum alloy end fittings for welding on-orbit to truss nodes of the same alloy. A modified form of gas tungsten arc welding was assumed to be the welding process. The joint was designed to withstand the thermal and structural loading associated with a 120-ft diameter tetrahedral truss intended as an aerobrake for a mission to Mars
Commensurate Fluctuations in the Pseudogap and Incommensurate spin-Peierls Phases of TiOCl
X-ray scattering measurements on single crystals of TiOCl reveal the presence
of commensurate dimerization peaks within both the incommensurate spin-Peierls
phase and the so-called pseudogap phase above T_c2. This scattering is
relatively narrow in Q-space indicating long correlation lengths exceeding ~
100 A below T* ~ 130 K. It is also slightly shifted in Q relative to that of
the commensurate long range ordered state at the lowest temperatures, and it
coexists with the incommensurate Bragg peaks below T_c2. The integrated
scattering over both commensurate and incommensurate positions evolves
continuously with decreasing temperature for all temperatures below T* ~ 130 K.Comment: To appear in Physical Review B: Rapid Communications. 5 page
Agroforestry- Growing Crops, Livestock, and Trees on Iowa Farms and the Midwest
Agroforestry is formally defined as a land-use system that intentionally combines trees or shrubs with annual plants and/or animals on the same land area. The combination may exist at the same time or in a sequential fashion (Agroforestry Systems, 1982). The production of diverse agronomic and forestry outputs (hence agro-forestry ) on the same land area is an important feature that may be very practical in trying to strengthen and diversify the primarily agricultural economy of Iowa. While agroforestry is still an emerging food, fiber, and industrial material production system in the American Midwest, it has been proven to be a sustainable system of land use in many parts of the world. Sustainability implies that this land use system is a healthy, economically viable, and environmentally protective technology
Kinetics and Penetration into Inflammatory Tissue Cage Fluid of Cefepime Administered to Rabbits
The kinetics and penetration of cefepime into inflammatory tissue cage fluid were determined in rabbits. Ten adult healthy rabbits were used. Concentrations of cefepime were measured in serum and induced inflammatory exudate by biological methods. The kinetic analysis was performed by mean of a non-compartmental model. Pharmacokinetic results in serum (S) and inflammatory tissue cage fluid (ITCF) (means ± standard error) were: half life of elimination [t1\2 (S) ]= 1.6 ± 0.2 and (ITCF) 3.7 ± 0.3 h; area under the curve [AUC (S)]= 225.3 ± 21.4 and (ITCF) 208.0 ± 13.6 (μg/ml/h]; maximum concentration [Cmax (ITCF)]= 37.7 ± 3.6 μg/ml and time to reach Cmax [tmax (ITCF)]= 1.8 ± 0.4 h and the penetration into inflammatory tissue cage fluid [P (ITCF)] = 92.3 ± 8.7 %. In conclusion, the cefepime administered to rabbits penetrate rapidly and nearly completely into inflammatory tissue cage fluid.
Suppression of the commensurate spin-Peierls state in Sc-doped TiOCl
We have performed x-ray scattering measurements on single crystals of the
doped spin-Peierls compound Ti(1-x)Sc(x)OCl (x = 0, 0.01, 0.03). These
measurements reveal that the presence of non-magnetic dopants has a profound
effect on the unconventional spin-Peierls behavior of this system, even at
concentrations as low as 1%. Sc-doping suppresses commensurate fluctuations in
the pseudogap and incommensurate spin-Peierls phases of TiOCl, and prevents the
formation of a long-range ordered spin-Peierls state. Broad incommensurate
scattering develops in the doped compounds near Tc2 ~ 93 K, and persists down
to base temperature (~ 7 K) with no evidence of a lock-in transition. The width
of the incommensurate dimerization peaks indicates short correlation lengths on
the order of ~ 12 angstroms below Tc2. The intensity of the incommensurate
scattering is significantly reduced at higher Sc concentrations, indicating
that the size of the associated lattice displacement decreases rapidly as a
function of doping.Comment: 7 pages, 5 figure
Structural Fluctuations in the Spin Liquid State of Tb2Ti2O7
High resolution X-ray scattering measurements on single crystal Tb2Ti2O7
reveal finite structural correlations at low temperatures. This geometrically
frustrated pyrochlore is known to exhibit a spin liquid, or cooperative
paramagnetic state, at temperatures below ~ 20 K. Parametric studies of
structural Bragg peaks appropriate to the Fdm space group of Tb2Ti2O7
reveal substantial broadening and peak intensity reduction in the temperature
regime 20 K to 300 mK. We also observe a small, anomalous lattice expansion on
cooling below a density maximum at ~ 18 K. These measurements are consistent
with the development of fluctuations above a cooperative Jahn-Teller,
cubic-tetragonal phase transition at very low temperatures.Comment: 5 pages, 4 figures, submitted for publicatio
Critical X-ray Scattering Studies of Jahn-Teller Phase Transitions in TbVAsO
The critical behaviour associated with cooperative Jahn-Teller phase
transitions in TbVAsO (where \textit{x} = 0, 0.17, 1)
single crystals have been studied using high resolution x-ray scattering. These
materials undergo continuous tetragonal orthorhombic structural phase
transitions driven by Jahn-Teller physics at T = 33.26(2) K, 30.32(2) K and
27.30(2) K for \textit{x} = 0, 0.17 and 1 respectively. The orthorhombic strain
was measured close to the phase transition and is shown to display mean field
behavior in all three samples. Pronounced fluctuation effects are manifest in
the longitudinal width of the Bragg scattering, which diverges as a power law,
with an exponent given by , on approaching the transition from
either above or below. All samples exhibited twinning; however the disordered x
= 0.17 sample showed a broad distribution of twins which were stable to
relatively low temperatures, well below T. This indicates that while the
orthorhombic strain continues to develop in a conventional mean field manner in
the presence of disorder, twin domains are easily pinned by the quenched
impurities and their associated random strains.Comment: 8 pages, 6 figure
Magnetic soft modes in the locally distorted triangular antiferromagnet alpha-CaCr2O4
In this paper we explore the phase diagram and excitations of a distorted
triangular lattice antiferromagnet. The unique two-dimensional distortion
considered here is very different from the 'isosceles'-type distortion that has
been extensively investigated. We show that it is able to stabilize a 120{\deg}
spin structure for a large range of exchange interaction values, while new
structures are found for extreme distortions. A physical realization of this
model is \alpha-CaCr2O4 which has 120{\deg} structure but lies very close to
the phase boundary. This is verified by inelastic neutron scattering which
reveals unusual roton-like minima at reciprocal space points different from
those corresponding to the magnetic order.Comment: 5 pages, 3 figures and lots of spin-wave
Evaluation of cefepime kinetic variables and milk production volume in goats
The objective of the present work was to investigate the correlation between the kinetic variables, and the volume of milk production, with and without a local inflammatory reaction induced by subcutaneous implants of a device for collecting tissue fluid.\n\n(Párrafo extraÃdo del texto a modo de resumen)</i
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