6,350 research outputs found
Full-gap superconductivity robust against disorder in heavy-fermion CeCu2Si2
A key aspect of unconventional pairing by the antiferromagnetic
spin-fluctuation mechanism is that the superconducting energy gap must have
opposite sign on different parts of the Fermi surface. Recent observations of
non-nodal gap structure in the heavy-fermion superconductor CeCuSi were
then very surprising, given that this material has long been considered a
prototypical example of a superconductor where the Cooper pairing is
magnetically mediated. Here we present a study of the effect of controlled
point defects, introduced by electron irradiation, on the temperature-dependent
magnetic penetration depth in CeCuSi. We find that the
fully-gapped state is robust against disorder, demonstrating that low-energy
bound states, expected for sign-changing gap structures, are not induced by
nonmagnetic impurities. This provides bulk evidence for -wave
superconductivity without sign reversal.Comment: 5 pages, 4 figures + Supplemental Material (1 page, 1 figure). Will
appear in Phys. Rev. Let
Are Participants Good Evaluators?
Managers of workforce training programs are often unable to afford costly, full-fledged experimental or nonexperimental evaluations to determine their programs’ impacts. Therefore, many rely on the survey responses of program participants to gauge program impacts.
Smith, Whalley, and Wilcox present the first attempt to assess such measures despite their already widespread use in program evaluations. They develop a multidisciplinary framework for addressing the issue and apply it to three case studies: the National Job Training Partnership Act Study, the U.S. National Supported Work Demonstration, and the Connecticut Jobs First Program.
Each of these studies were subjected to experimental evaluations that included a survey-based participant evaluation measure. The authors apply econometric methods specifically developed to obtain estimates of program impacts among individuals in the studies and then compare these estimates with survey-based participant evaluation measures to obtain an assessment of the surveys’ efficacy.
The authors also discuss how their findings fit into the broader literatures in economics, psychology, and survey research.https://research.upjohn.org/up_press/1285/thumbnail.jp
Optimization of element length for imaging small volumetric reflectors with linear ultrasonic arrays
Neutron Electric Dipole Moment with Domain Wall Quarks
We present preliminary results for nucleon dipole moments computed with
domain wall fermions. Our main target is the electric dipole moment of the
neutron arising from the theta term in the gauge part of the QCD lagrangian.
The calculated magnetic dipole moments of the proton and neutron are in rough
accord with experimental values.Comment: 3 pages. Contribution to the proceedings of Lattice 2004 (Fermilab
A Paleoecological Test of a Classical Hydrosere in the Lake Michigan Dunes
Aquatic vegetation varies along a chronosequence of dune ponds at Miller Woods, Indiana Dunes National Lakeshore. Submersed and floating-leaved macrophytes dominate the vegetation of the youngest ponds. Older ponds contain mixed assemblages of submersed, floating-leaved, and emergent plant taxa. The oldest ponds are dominated by emergent plants, especially Typha angustifolia. We conducted paleoecological studies at one of the oldest ponds to test the hypothesis that the modern vegetational array along the pond chronosequence represents a hydrarch successional sequence. Macrofossil stratigraphy of the 3000-yr-old pond indicates no significant changes in pond vegetation following early colonization until \u3c 150 BP. Pond vegetation before 150 BP consisted of a diverse assemblage of submersed, floating-leaved, and emergent macrophyte taxa. Pollen and macrofossil data indicate a major, rapid vegetational change at \u3c150 BP, evidently in response to local human disturbance. Pollen data reveal that the extensive Typha stands in the older ponds have developed recently, following postsettlement disturbance. Modern vegetational differences along the chronosequence reflect differential effects of disturbance rather than autogenic hydrarch succession. This study illustrates a major pitfall in inferring successional trends from spatial sequences of vegetation
Decuplet Baryon Structure from Lattice QCD
The electromagnetic properties of the SU(3)-flavor baryon decuplet are
examined within a lattice simulation of quenched QCD. Electric charge radii,
magnetic moments, and magnetic radii are extracted from the E0 and M1 form
factors. Preliminary results for the E2 and M3 moments are presented giving the
first model independent insight to the shape of the quark distribution in the
baryon ground state. As in our octet baryon analysis, the lattice results give
evidence of spin-dependent forces and mass effects in the electromagnetic
properties. The quark charge distribution radii indicate these effects act in
opposing directions. Some baryon dependence of the effective quark magnetic
moments is seen. However, this dependence in decuplet baryons is more subtle
than that for octet baryons. Of particular interest are the lattice predictions
for the magnetic moments of and for which new recent
experimental measurements are available. The lattice prediction of the
ratio appears larger than the experimental ratio, while the
lattice prediction for the magnetic moment ratio is in good
agreement with the experimental ratio.Comment: RevTeX manuscript, 34 pages plus 21 figures (available upon request
Muscular Activity and Physical Interaction Forces during Lower Limb Exoskeleton Use
Spinal cord injury (SCI) typically manifests with a loss of sensorimotor control of the lower limbs. In order to overcome som
e of the
disadvantages of chronic wheelchair use by such patients, robotic exoskeletons are an emerging technology that has the pot
ential to transform the
lives of patients. However, there are a number of points of contact between the robot and the user, which lead to interaction
forces. In a recent
study, we have shown that peak interaction forces are particularly prominent at the an
terior aspect of the right leg. This study uses a similar
experimental protocol with additional EMG (electromyography) analysis to examine whether such interaction forces are due to t
he muscular
activity of the participant or the movement of the exoskeleto
n itself. Interestingly, we found that that peak forces preceded peak EMG activity. This
study did not find a significant correlation between EMG activity and force data, which would indicate that the interaction f
orces can largely be
attributed to the mov
ement of the exoskeleton itself. However, we also report significantly higher correlation coefficients in muscle/force pairs
located at the anterior aspect of the right leg. In our previous research, we have shown peak interaction forces at the same
locati
ons, which suggests
that muscular activity of the participant makes a more significant contribution to the interaction forces at these locations.
The findings of this study
are of significance for incomplete SCI patients, for whom EMG activity may provide
an important input to an intuitive control schema
Application of Tracking and Data Relay Satellite (TDRS) Differenced One-Way Doppler (DOWD) Tracking Data for Orbit Determination and Station Acquisition Support of User Spacecraft Without TDRS Compatible Transponders
Many spacecraft are launched today with only an omni-directional (omni) antenna and do not have an onboard Tracking and Data Relay Satellite (TDRS) transponder that is capable of coherently returning a carrier signal through TDRS. Therefore, other means of tracking need to be explored and used to adequately acquire the spacecraft. Differenced One-Way Doppler (DOWD) tracking data are very useful in eliminating the problems associated with the instability of the onboard oscillators when using strictly one-way Doppler data. This paper investigates the TDRS DOWD tracking data received by the Goddard Space Flight Center (GSFC) Flight Dynamics Facility (FDF) during the launch and early orbit phases for the the Interplanetary Physics Laboratory (WIND) and the National Oceanographic and Atmospheric Administration (NOAA)-J missions. In particular FDF personnel performed an investigation of the data residuals and made an assessment of the acquisition capabilities of DOWD-based solutions. Comparisons of DOWD solutions with existing data types were performed and analyzed in this study. The evaluation also includes atmospheric editing of the DOWD data and a study of the feasibility of solving for Doppler biases in an attempt to minimize error. Furthermore, by comparing the results from WIND and NOAA-J, an attempt is made to show the limitations involved in using DOWD data for the two different mission profiles. The techniques discussed in this paper benefit the launches of spacecraft that do not have TDRS transponders on board, particularly those launched into a low Earth orbit. The use of DOWD data is a valuable asset to missions which do not have a stable local oscillator to enable high-quality solutions from the one-way/return-link Doppler tracking data
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