45,469 research outputs found
Activation analysis for selected elements in micrometeorites and hypervelocity projectiles Annual progress report, 1 Jul. 1969 - 1 Jul. 1970
Activation analysis to identify materials for use as catcher for micrometeoroid
Low Temperature Superfluid Response of High-Tc Superconductors
We have reviewed our theoretical and experimental results of the low
temperature superfluid response function of high temperature superconductors
(HTSC). In clean high-Tc materials the in-plane superfluid density rho_s^{ab}
varies linearly with temperature. The slope of this linear T term is found to
scale approximately with 1/Tc which, according to the weak coupling BCS theory
for a d-wave superconductor, implies that the gap amplitude scales
approximately with Tc. A T^5 behavior of the out-of-plane superfluid density
rho_s^c for clean tetragonal HTSC was predicted and observed experimentally in
the single layer Hg-compound HgBa_2CuO_{4+delta}. In other tetragonal high-Tc
compounds with relatively high anisotropy, such as Hg_2Ba_2Ca_2Cu_3O_{8+delta},
rho_s^c varies as T^2 due to disorder effects. In optimally doped
YBa_2Cu_3O_{7-delta}, rho_s^c varies linearly with temperature at low
temperatures, but in underdoped YBa_2Cu_3O_{7-delta}, rho_s^c varies as T^2 at
low temperatures; these results are consistent with our theoretical
calculations.Comment: 26 pages, 8 figure
Structural and electrostatic effects at the surfaces of size- and charge-selected aqueous nanodrops.
The effects of ion charge, polarity and size on the surface morphology of size-selected aqueous nanodrops containing a single ion and up to 550 water molecules are investigated with infrared photodissociation (IRPD) spectroscopy and theory. IRPD spectra of M(H2O) n where M = La3+, Ca2+, Na+, Li+, I-, SO42- and supporting molecular dynamics simulations indicate that strong interactions between multiply charged ions and water molecules can disrupt optimal hydrogen bonding (H-bonding) at the nanodrop surface. The IRPD spectra also reveal that "free" OH stretching frequencies of surface-bound water molecules are highly sensitive to the ion's identity and the OH bond's local H-bond environment. The measured frequency shifts are qualitatively reproduced by a computationally inexpensive point-charge model that shows the frequency shifts are consistent with a Stark shift from the ion's electric field. For multiply charged cations, pronounced Stark shifting is observed for clusters containing ∼100 or fewer water molecules. This is attributed to ion-induced solvent patterning that extends to the nanodrop surface, and serves as a spectroscopic signature for a cation's ability to influence the H-bond network of water located remotely from the ion. The Stark shifts measured for the larger nanodrops are extrapolated to infinite dilution to obtain the free OH stretching frequency of a surface-bound water molecule at the bulk air-water interface (3696.5-3701.0 cm-1), well within the relatively wide range of values obtained from SFG measurements. These cluster measurements also indicate that surface curvature effects can influence the free OH stretching frequency, and that even nanodrops without an ion have a surface potential that depends on cluster size
Target value design: using collaboration and a lean approach to reduce construction cost
Target Costing is an effective management technique that has been used in manufacturing for decades to achieve cost predictability during new products development. Adoption of this technique promises benefits for the construction industry as it struggles to raise the number of successful outcomes and certainty of project delivery in terms of cost, quality and time. Target Value Design is a management approach that takes the best features of Target Costing and adapts them to the peculiarities of construction. In this paper the concept of Target Value Design is introduced based on the results of action research carried out on 12 construction projects in the USA. It has been shown that systemic application of Target Value Design leads to significant improvement of project performance – the final cost of projects was on average 15% less than market cost. The construction industry already has approaches that have similarities with elements of the Target Value Design process or uses the same terminology, e.g. Partnering and Target Cost Contracts, Cost planning, etc. Following an exploration of the similarities and differences Target Value Design is positioned as a form of Target Costing for construction that offers a more reliable route to successful projects outcomes
Search for long lived charged massive particles in pp collisions at s-hat = 1.8TeV
We report a search for the production of long-lived charged massive particles in a data sample of 90 pb-1 of √s=1.8 TeV pp̅ collisions recorded by the Collider Detector at Fermilab. The search uses the muonlike penetration and anomalously high ionization energy loss signature expected for such a particle to discriminate it from backgrounds. The data are found to agree with background expectations, and cross section limits of O(1) pb are derived using two reference models, a stable quark and a stable scalar lepton
A Universal Intrinsic Scale of Hole Concentration for High-Tc Cuprates
We have measured thermoelectric power (TEP) as a function of hole
concentration per CuO2 layer, Ppl, in Y1-xCaxBa2Cu3O6 (Ppl = x/2) with no
oxygen in the Cu-O chain layer. The room-temperature TEP as a function of Ppl,
S290(Ppl), of Y1-xCaxBa2Cu3O6 behaves identically to that of La2-zSrzCuO4 (Ppl
= z). We argue that S290(Ppl) represents a measure of the intrinsic equilibrium
electronic states of doped holes and, therefore, can be used as a common scale
for the carrier concentrations of layered cuprates. We shows that the Ppl
determined by this new universal scale is consistent with both hole
concentration microscopically determined by NQR and the hole concentration
macroscopically determined by the Cu valency. We find two characteristic
scaling temperatures, TS* and TS2*, in the TEP vs. temperature curves that
change systematically with doping. Based on the universal scale, we uncover a
universal phase diagram in which almost all the experimentally determined
pseudogap temperatures as a function of Ppl fall on two common curves; upper
pseudogap temperature defined by the TS* versus Ppl curve and lower pseudogap
temperature defined by the TS2* versus Ppl curve. We find that while pseudogaps
are intrinsic properties of doped holes of a single CuO2 layer for all high-Tc
cuprates, Tc depends on the number of layers, therefore the inter-layer
coupling, in each individual system.Comment: 11 pages, 9 figures, accepted for publication in Physical Review
Nuclear magnetic resonance probes for the Kondo scenario for the 0.7 feature in semiconductor quantum point contact devices
We propose a probe based on nuclear relaxation and Knight shift measurements
for the Kondo scenario for the "0.7 feature" in semiconductor quantum point
contact (QPC) devices. We show that the presence of a bound electron in the QPC
would lead to a much higher rate of nuclear relaxation compared to nuclear
relaxation through exchange of spin with conduction electrons. Furthermore, we
show that the temperature dependence of this nuclear relaxation is very
non-monotonic as opposed to the linear-T relaxation from coupling with
conduction electrons. We present a qualitative analysis for the additional
relaxation due to nuclear spin diffusion (NSD) and study the extent to which
NSD affects the range of validity of our method. The conclusion is that nuclear
relaxation, in combination with Knight shift measurements, can be used to
verify whether the 0.7 feature is indeed due to the presence of a bound
electron in the QPC.Comment: Published version. Appears in a Special Section on the 0.7 Feature
and Interactions in One-Dimensional Systems. 16 page
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