1,862 research outputs found
Meter for use in detecting tension in straps having predetermined elastic characteristics
A meter for detecting tension in elastic bodies, especially in fabric straps employed as tie down straps for stowed objects is presented. The meter is characterized by a pair of elongated arms coupled together for pivotal motion about a common axis in a common plane and a strap receiver located at adjacent ends of the arms for receiving and securing adjacent portions of the strap. The receivers are supported by the arms for motion along intersecting arcs, and motion detection means is located at the opposite ends of the arms for detecting the magnitude of the motion imparted to the receivers as the strap is placed in tension
Germanium Detector with Internal Amplification for Investigation of Rare Processes
Device of new type is suggested - germanium detector with internal
amplification. Such detector having effective threshold about 10 eV opens up
fresh opportunity for investigation of dark matter, measurement of neutrino
magnetic moment, of neutrino coherent scattering at nuclei and for study of
solar neutrino problem. Construction of germanium detector with internal
amplification and perspectives of its use are described.Comment: 13 pages, latex, 3 figures, report at NANP-99, International
Conference on Non-Accelerator Physics, Dubna, Russia, June 29- July 3, 1999.
To be published in the Proceeding
Charge-based silicon quantum computer architectures using controlled single-ion implantation
We report a nanofabrication, control and measurement scheme for charge-based
silicon quantum computing which utilises a new technique of controlled single
ion implantation. Each qubit consists of two phosphorus dopant atoms ~50 nm
apart, one of which is singly ionized. The lowest two energy states of the
remaining electron form the logical states. Surface electrodes control the
qubit using voltage pulses and dual single electron transistors operating near
the quantum limit provide fast readout with spurious signal rejection. A low
energy (keV) ion beam is used to implant the phosphorus atoms in high-purity
Si. Single atom control during the implantation is achieved by monitoring
on-chip detector electrodes, integrated within the device structure, while
positional accuracy is provided by a nanomachined resist mask. We describe a
construction process for implanted single atom and atom cluster devices with
all components registered to better than 20 nm, together with electrical
characterisation of the readout circuitry. We also discuss universal one- and
two-qubit gate operations for this architecture, providing a possible path
towards quantum computing in silicon.Comment: 9 pages, 5 figure
Structure factor of polymers interacting via a short range repulsive potential: application to hairy wormlike micelles
We use the Random Phase Approximation (RPA) to compute the structure factor,
S(q), of a solution of chains interacting through a soft and short range
repulsive potential V. Above a threshold polymer concentration, whose magnitude
is essentially controlled by the range of the potential, S(q) exhibits a peak
whose position depends on the concentration. We take advantage of the close
analogy between polymers and wormlike micelles and apply our model, using a
Gaussian function for V, to quantitatively analyze experimental small angle
neutron scattering profiles of semi-dilute solutions of hairy wormlike
micelles. These samples, which consist in surfactant self-assembled flexible
cylinders decorated by amphiphilic copolymer, provide indeed an appropriate
experimental model system to study the structure of sterically interacting
polymer solutions
Doped Stripes in Models for the Cuprates Emerging from the One-hole Properties of the Insulator
The extended and standard t-J models are computationally studied on ladders
and planes, with emphasis on the small J/t region. At couplings compatible with
photoemission results for undoped cuprates, half-doped stripes separating
-shifted antiferromagnetic (AF) domains are found, as in Tranquada's
interpretation of neutron experiments. Our main result is that the elementary
stripe `"building-block" resembles the properties of hole at small J/t,
with robust AF correlations across-the-hole induced by the local tendency of
the charge to separate from the spin (G. Martins {\it et al.}, Phys. Rev. B{\bf
60}, R3716 (1999)). This suggests that the seed of half-doped stripes already
exists in the unusual properties of the insulating parent compound.Comment: 4 pages, LateX, 4 figures, to appear on Phys. Rev. Let
Magnetic Domains and Stripes in the Spin-Fermion Model for Cuprates
Monte Carlo simulations applied to the Spin-Fermion model for cuprates show
the existence of antiferromagnetic spin domains and charge stripes upon doping.
The stripes are partially filled, with a filling of approximately 1/2 hole per
site, and they separate spin domains with a phase shift among them. The
stripes observed run either along the x or y axes and they are separated by a
large energy barrier. No special boundary conditions or external fields are
needed to stabilize these structures at low temperatures. When magnetic
incommensurate peaks are observed at momentum and symmetrical
points, charge incommensurate peaks appear at and symmetrical
points, as experimentally observed. The strong charge fluctuations responsible
for the formation of the stripes also induce a pseudogap in the density of
states.Comment: Four pages with four figures embedded in tex
Indications of Spin-Charge Separation at Short Distance and Stripe Formation in the Extended t-J Model on Ladders and Planes
The recently discussed tendency of holes to generate nontrivial spin
environments in the extended two-dimensional t-J model (G. Martins, R. Eder,
and E. Dagotto, Phys. Rev. B{\bf 60}, R3716 (1999)) is here investigated using
computational techniques applied to ladders with several number of legs. This
tendency is studied also with the help of analytic spin-polaron approaches
directly in two dimensions. Our main result is that the presence of robust
antiferromagnetic correlations between spins located at both sides of a hole
either along the x or y axis, observed before numerically on square clusters,
is also found using ladders, as well as applying techniques based on a
string-basis expansion. This so-called "across-the-hole" nontrivial structure
exists even in the two-leg spin-gapped ladder system, and leads to an effective
reduction in dimensionality and spin-charge separation at short-distances, with
a concomitant drastic reduction in the quasiparticle (QP) weight Z. In general,
it appears that holes tend to induce one-dimensional-like spin arrangements to
improve their mobility. Using ladders it is also shown that the very small
J/t0.1 regime of the standard t-J model may be more realistic than
anticipated in previous investigations, since such regime shares several
properties with those found in the extended model at realistic couplings.
Another goal of the present article is to provide additional information on the
recently discussed tendencies to stripe formation and spin incommensurability
reported for the extended t-J model.Comment: 14 pages, 21 figures, LateX, submited to Phys. Rev.
The biocompatibility of titanium in a buffer solution: compared effects of a thin film of TiO2 deposited by MOCVD and of collagen deposited from a gel
This study aims at evaluating the biocompatibility of titanium surfaces modified according two different ways: (i) deposition of a bio-inert, thin film of rutile TiO2 by chemical vapour deposition (MOCVD), and (ii) biochemical treatment with collagen gel, in order to obtain a bio-interactive coating. Behind the comparison is the idea that either the bio-inert or the bio-active coating has specific advantages when applied to implant treatment, such as the low price of the collagen treatment for instance. The stability in buffer solution was evaluated by open circuit potential (OCP) for medium time and cyclic voltametry. The OCP stabilized after 5104 min for all the specimens except the collagen treated sample which presented a stable OCP from the first minutes. MOCVD treated samples stabilized to more electropositive values. Numeric results were statistically analysed to obtain the regression equations for long time predictable evolution. The corrosion parameters determined from cyclic curves revealed that the MOCVD treatment is an efficient way to improve corrosion resistance. Human dermal fibroblasts were selected for cell culture tests, taking into account that these cells are present in all bio-interfaces, being the main cellular type of connective tissue. The cells grew on either type of surface without phenotype modification. From the reduction of yellow, water-soluble 3-(4,5-dimethyldiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT cytotoxicity test), MOCVD treated samples offer better viability than mechanically polished Ti and collagen treated samples as well. Cell spreading, as evaluated from microscope images processed by the program Sigma Scan, showed also enhancement upon surface modification. Depending on the experimental conditions, MOCVD deposited TiO2 exhibits different nanostructures that may influence biological behaviour. The results demonstrate the capacity of integration in simulated physiologic liquids for an implant pretreated by either method
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