9,538 research outputs found
Absolute flux measurements for swift atoms
While a torsion balance in vacuum can easily measure the momentum transfer from a gas beam impinging on a surface attached to the balance, this measurement depends on the accommodation coefficients of the atoms with the surface and the distribution of the recoil. A torsion balance is described for making absolute flux measurements independent of recoil effects. The torsion balance is a conventional taut suspension wire design and the Young modulus of the wire determines the relationship between the displacement and the applied torque. A compensating magnetic field is applied to maintain zero displacement and provide critical damping. The unique feature is to couple the impinging gas beam to the torsion balance via a Wood's horn, i.e., a thin wall tube with a gradual 90 deg bend. Just as light is trapped in a Wood's horn by specular reflection from the curved surfaces, the gas beam diffuses through the tube. Instead of trapping the beam, the end of the tube is open so that the atoms exit the tube at 90 deg to their original direction. Therefore, all of the forward momentum of the gas beam is transferred to the torsion balance independent of the angle of reflection from the surfaces inside the tube
Cavity QED with separate photon storage and qubit readout modes
We present the realization of a cavity quantum electrodynamics setup in which
photons of strongly different lifetimes are engineered in different harmonic
modes of the same cavity. We achieve this in a superconducting transmission
line resonator with superconducting qubits coupled to the different modes. One
cavity mode is strongly coupled to a detection line for qubit state readout,
while a second long lifetime mode is used for photon storage and coherent
quantum operations. We demonstrate sideband based measurement of photon
coherence, generation of n photon Fock states and the scaling of the sideband
Rabi frequency with the square root of n using a scheme that may be extended to
realize sideband based two-qubit logic gates.Comment: 4 pages, 5 figures, version with high resolution figures available at
http://qudev.ethz.ch/content/science/PubsPapers.htm
Exceptional type-I superconductivity of the layered silver oxide AgPbO
We report zero-resistivity transition and the details of magnetic transition
of a layered silver oxide AgPbO single crystal, which make
definitive evidence of superconductivity in this compound. In the AC
susceptibility of a mono-crystal, we observed large supercooling, as well as
positive peaks in the real part of the susceptibility indicating the
reversibility of magnetic process. These observations reveal that
AgPbO is probably the first oxide that shows type-I
superconductivity. Evaluation of the superconducting parameters not only gives
confirming evidence of type-I superconductivity, but also indicates that it is
a dirty-limit superconductor. We also analyze supercooling to determine the
upper limit of the Ginzburg-Landau parameter.Comment: v2: PACS numbers are adde
Reduction and analysis of photometric data on Comet Halley
The discovery that periodic variations in the brightness of Comet Halley were characterized by two unrelated frequencies implies that the nucleus is in a complex state of rotation. It either nutates as a result of the random addition of small torque perturbations accumulated over many perihelion passages, or the jet activity torques are so strong that it precesses wildly at each perihelion passage. To diagnose the state of nuclear rotation, researchers began a program to acquire photometric time series of the comet as it recedes from the sun. The intention is to observe the decay of the comet's atmosphere and then, when it is unemcumbered by the light of the coma, follow the light variation of the nucleus itself. The latter will be compared with preperihelion time series and the orientation of the nucleus at the time of Vega and Giotto flybys and an accurate rotational ephemeris constructed. Halley was observed on 38 nights during 1987 and approximately 21 nights in 1988. The comet moved from 5 AU to 8.5 AU during this time. The brightness of the coma was found to rapidly decrease in 1988 as the coma and cometary activity collapses. The magnitude in April 1988 was 19 mag (visual) and it is predicted that the nucleus itself will be the major contributor to the brightness in the 1988 and 1989 season
Multi-Modal Human-Machine Communication for Instructing Robot Grasping Tasks
A major challenge for the realization of intelligent robots is to supply them
with cognitive abilities in order to allow ordinary users to program them
easily and intuitively. One way of such programming is teaching work tasks by
interactive demonstration. To make this effective and convenient for the user,
the machine must be capable to establish a common focus of attention and be
able to use and integrate spoken instructions, visual perceptions, and
non-verbal clues like gestural commands. We report progress in building a
hybrid architecture that combines statistical methods, neural networks, and
finite state machines into an integrated system for instructing grasping tasks
by man-machine interaction. The system combines the GRAVIS-robot for visual
attention and gestural instruction with an intelligent interface for speech
recognition and linguistic interpretation, and an modality fusion module to
allow multi-modal task-oriented man-machine communication with respect to
dextrous robot manipulation of objects.Comment: 7 pages, 8 figure
Unpacking the associations between heterogeneous externalising symptom development and academic attainment in middle childhood
This study explores children’s externalising symptom development pathways between 8 and 11 years of age (three time points across 2 years) and examines their sociodemographic correlates and associations with change in academic attainment. Externalising symptoms were assessed for 5485 children across three consecutive years (Mage = 8.7 years, SD = 0.30 at time 1). National standardised test scores served as an index of academic attainment. Using latent class growth analysis, six distinct trajectories of externalising symptom development were identified. Children who showed increasing externalising symptomatology across the three time points were more likely to be male or have special educational needs. These derived trajectories differentially predicted children’s subsequent academic attainment (controlling for earlier attainment). Children with increasing externalising symptomatology were significantly more likely to demonstrate negative change in academic achievement compared with children with consistently low externalising problems. The study helps to clarify the longitudinal association between externalising symptom development and academic attainment, and highlights the importance of early intervention for children with increasing externalising symptoms across middle childhoo
Electron-phonon coupling in 122 Fe pnictides analyzed by femtosecond time-resolved photoemission
Based on results from femtosecond time-resolved photoemission, we compare
three different methods for determination of the electron-phonon coupling
constant {\lambda} in Eu and Ba-based 122 FeAs compounds. We find good
agreement between all three methods, which reveal a small {\lambda} < 0.2. This
makes simple electron-phonon mediated superconductivity unlikely in these
compounds.Comment: 11 pages, 3 figure
Spin Waves in the Ferromagnetic Ground State of the Kagome Staircase System Co3V2O8
Inelastic neutron scattering measurements were performed on single crystal
Co3V2O8 wherein magnetic cobalt ions reside on distinct spine and cross-tie
sites within kagome staircase planes. This system displays a rich magnetic
phase diagram which culminates in a ferromagnetic ground state below Tc~6 K. We
have studied the low-lying magnetic excitations in this phase within the kagome
plane. Despite the complexity of the system at higher temperatures, linear
spin-wave theory describes most of the quantitative detail of the inelastic
neutron measurements. Our results show two spin-wave branches, the higher
energy of which displays finite spin-wave lifetimes well below Tc, and
negligible magnetic exchange coupling between Co moments on the spine sites.Comment: 4 pages and 4 figure
Inhibitor regulation of tissue kallikrein activity in the synovial fluid of patients with rheumatoid athritis
Tissue kallikrein (TK) and 1-antitrypsin (AT)/TK complexes can be detected in SF from patients with RA if components of the fluids which interfere with the detection of TK are removed. 2-Macroglobulin (2-M) in SF was demonstrated to contain trapped proteases which were still active in amidase assays. Removal of 2-M from RA SF reduced their amidase activity. However, at least some of the remaining activity was due to TK because it was soya bean trypsin inhibitor resistant and trasylol sensitive and was partly removed by affinity chromatography on anti-TK sepharose. Removal of RF from the fluids reduced the values obtained for TK levels by ELISA. Addition of SF to human urinary kallikrein (HUK) considerably reduced the levels of TK detected suggesting the presence of a TK ELISA inhibitor in the fluids. Removal of components of >300 kDa from SF markedly reduced the TK ELISA inhibitory activity and increased the values for both the TK and l-AT/TK levels in fluids as measured by ELISA. It is considered this novel inhibitor does not bind to the active site of TK but rather binds to the site reactive with anti-TK antibodies
Mechanical On-Chip Microwave Circulator
Nonreciprocal circuit elements form an integral part of modern measurement
and communication systems. Mathematically they require breaking of
time-reversal symmetry, typically achieved using magnetic materials and more
recently using the quantum Hall effect, parametric permittivity modulation or
Josephson nonlinearities. Here, we demonstrate an on-chip magnetic-free
circulator based on reservoir engineered optomechanical interactions.
Directional circulation is achieved with controlled phase-sensitive
interference of six distinct electro-mechanical signal conversion paths. The
presented circulator is compact, its silicon-on-insulator platform is
compatible with both superconducting qubits and silicon photonics, and its
noise performance is close to the quantum limit. With a high dynamic range, a
tunable bandwidth of up to 30 MHz and an in-situ reconfigurability as beam
splitter or wavelength converter, it could pave the way for superconducting
qubit processors with integrated and multiplexed on-chip signal processing and
readout.Comment: References have been update
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