10,643 research outputs found
Covariant Helicity-Coupling Amplitudes: A New Formulation
We have worked out covariant amplitudes for any two-body decay of a resonance
with an arbitrary non-zero mass, which involves arbitrary integer spins in the
initial and the final states. One key new ingredient for this work is the
application of the total intrinsic spin operator which is given
directly in terms of the generators of the Poincar\'e group.
Using the results of this study, we show how to explore the Lorentz factors
which appear naturally, if the momentum-space wave functions are used to form
the covariant decay amplitudes. We have devised a method of constructing our
covariant decay amplitudes, such that they lead to the Zemach amplitudes when
the Lorentz factors are set one
Inhomogeneous Low Frequency Spin Dynamics in La_{1.65}Eu_{0.2}Sr_{0.15}CuO_4
We report Cu and La nuclear magnetic resonance (NMR) measurements in the
title compound that reveal an inhomogeneous glassy behavior of the spin
dynamics. A low temperature peak in the La spin lattice relaxation rate and the
``wipeout'' of Cu intensity both arise from these slow electronic spin
fluctuations that reveal a distribution of activation energies. Inhomogeneous
slowing of spin fluctuations appears to be a general feature of doped lanthanum
cuprate.Comment: 4 pages, 2 figures. Very slight modifications to figure
Learning Mathematics with Technology: The Influence of Virtual Manipulatives on Different Achievement Groups
This study examined the influence of virtual manipulatives on different achievement groups during a teaching experiment in four fifth-grade classrooms. During a two-week unit focusing on two rational number concepts (fraction equivalence and fraction addition with unlike denominators) one low achieving, two average achieving, and one high achieving group participated in two instructional treatments (three groups used virtual manipulatives and one group used physical manipulatives). Data sources included pre- and post-tests of students’ mathematical content knowledge and videotapes of classroom sessions. Results of paired samples t-tests examining the three groups using virtual manipulatives indicated a statistically significant overall gain following the treatment. Follow-up paired samples individual t-tests on the low, average, and high achieving groups indicated a statistically significant gain for students in the low achieving group, but only numerical gains for students in the average and high achieving groups. There were no significant differences between the average achieving student groups in the virtual manipulatives and physical manipulatives treatments. Qualitative data gathered during the study indicated that the different achievement groups experienced the virtual manipulatives in different ways, with the high achieving group recognizing patterns quickly and transitioning to the use of symbols, while the average and low achieving groups relied heavily on pictorial representations as they methodically worked stepby- step through processes and procedures with mathematical symbols
Electronic structures of ZnCoO using photoemission and x-ray absorption spectroscopy
Electronic structures of ZnCoO have been investigated using
photoemission spectroscopy (PES) and x-ray absorption spectroscopy (XAS). The
Co 3d states are found to lie near the top of the O valence band, with a
peak around eV binding energy. The Co XAS spectrum provides
evidence that the Co ions in ZnCoO are in the divalent Co
() states under the tetrahedral symmetry. Our finding indicates that the
properly substituted Co ions for Zn sites will not produce the diluted
ferromagnetic semiconductor property.Comment: 3 pages, 2 figure
Putative spin liquid in the triangle-based iridate BaIrTiO
We report on thermodynamic, magnetization, and muon spin relaxation
measurements of the strong spin-orbit coupled iridate BaIrTiO,
which constitutes a new frustration motif made up a mixture of edge- and
corner-sharing triangles. In spite of strong antiferromagnetic exchange
interaction of the order of 100~K, we find no hint for long-range magnetic
order down to 23 mK. The magnetic specific heat data unveil the -linear and
-squared dependences at low temperatures below 1~K. At the respective
temperatures, the zero-field muon spin relaxation features a persistent spin
dynamics, indicative of unconventional low-energy excitations. A comparison to
the isostructural compound BaRuTiO suggests that a concerted
interplay of compass-like magnetic interactions and frustrated geometry
promotes a dynamically fluctuating state in a triangle-based iridate.Comment: Physical Review B accepte
Stripe structure, spectral feature and soliton gap in high Tc cuprates
We show that the lightly doped La_{2-x}Sr_{x}CuO_{4} can be described in
terms of a stripe magnetic structure or soliton picture. The internal
relationship between the recent neutron observation of the diagonal (x=0.05) to
vertical (x >= 0.06) stripe transition, which was predicted, and the
concomitant metal-insulator transition is clarified by this solitonic physics.
The phase diagram with the unidentified transition lines between
antiferromagnetic to stripe phases, the doping dependence of the modulation
period, the origin of the mid-infrared optical absorption are investigated
comparatively with other single layer systems: La_{2-x}Sr_{x}NiO_{4} and
(La,Nd)_{2-x}Sr_{x}CuO_{4}. The novel type of quasi-particles and holes is
fully responsible for metallic conduction and ultimately superconductivity.Comment: 4 pages RevTex, 5 figure
Mechanically Detecting and Avoiding the Quantum Fluctuations of a Microwave Field
During the theoretical investigation of the ultimate sensitivity of
gravitational wave detectors through the 1970's and '80's, it was debated
whether quantum fluctuations of the light field used for detection, also known
as photon shot noise, would ultimately produce a force noise which would
disturb the detector and limit the sensitivity. Carlton Caves famously answered
this question with "They do." With this understanding came ideas how to avoid
this limitation by giving up complete knowledge of the detector's motion. In
these back-action evading (BAE) or quantum non-demolition (QND) schemes, one
manipulates the required quantum measurement back-action by placing it into a
component of the motion which is unobserved and dynamically isolated. Using a
superconducting, electro-mechanical device, we realize a sensitive measurement
of a single motional quadrature with imprecision below the zero-point
fluctuations of motion, detect both the classical and quantum measurement
back-action, and demonstrate BAE avoiding the quantum back-action from the
microwave photons by 9 dB. Further improvements of these techniques are
expected to provide a practical route to manipulate and prepare a squeezed
state of motion with mechanical fluctuations below the quantum zero-point
level, which is of interest both fundamentally and for the detection of very
weak forces
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