491 research outputs found
Status of the standard vector—axial-vector model for nuclear beta decay
The complete set of experimental results on correlations in nuclear beta decay is analyzed in terms of the general Hamiltonian including scalar, vector, axial vector, and tensor interactions with an arbitrary degree of parity violation. It is concluded that the standard vector minus axial-vector model with maximal parity violation (left-handed lepton current) is compatible with the data and rigorous limits are obtained for the values of possible additional coupling constants. In the scalar and tensor case the new constraints are considerably tighter than those published before: |CS / CV| and |CS′ / CV|≤0.2, |(CS+CS′) / CV|≤0.06; |CT / CA| and |CT′ / CA|≤0.09, |(CT+CT′) / CA|≤0.01, all at the 95% confidence level. On the other hand, rather large admixtures of the right-handed lepton currents (CV′ / CV≠1 or CA′ / CA≠1) are allowed by the data. An analysis of the correlations between various coupling constants implied by the data is also performed
GHIGLS: HI mapping at intermediate Galactic latitude using the Green Bank Telescope
This paper introduces the data cubes from GHIGLS, deep Green Bank Telescope
surveys of the 21-cm line emission of HI in 37 targeted fields at intermediate
Galactic latitude. The GHIGLS fields together cover over 1000 square degrees at
9.55' spatial resolution. The HI spectra have an effective velocity resolution
about 1.0 km/s and cover at least -450 < v < +250 km/s. GHIGLS highlights that
even at intermediate Galactic latitude the interstellar medium is very complex.
Spatial structure of the HI is quantified through power spectra of maps of the
column density, NHI. For our featured representative field, centered on the
North Ecliptic Pole, the scaling exponents in power-law representations of the
power spectra of NHI maps for low, intermediate, and high velocity gas
components (LVC, IVC, and HVC) are -2.86 +/- 0.04, -2.69 +/- 0.04, and -2.59
+/- 0.07, respectively. After Gaussian decomposition of the line profiles, NHI
maps were also made corresponding to the narrow-line and broad-line components
in the LVC range; for the narrow-line map the exponent is -1.9 +/- 0.1,
reflecting more small scale structure in the cold neutral medium (CNM). There
is evidence that filamentary structure in the HI CNM is oriented parallel to
the Galactic magnetic field. The power spectrum analysis also offers insight
into the various contributions to uncertainty in the data. The effect of 21-cm
line opacity on the GHIGLS NHI maps is estimated.Comment: Accepted for publication in The Astrophysical Journal, 2015 July 16.
32 pages, 21 figures (Fig. 10 new). Minor revisions from review, particularly
Section 8 and Appendix C; results unchanged. Additional surveys added and
made available; new Appendix B. Added descriptions of available FITS files
and links to four illustrative movies on enhanced GHIGLS archive
(www.cita.utoronto.ca/GHIGLS/
Influence of static Jahn-Teller distortion on the magnetic excitation spectrum of PrO2: A synchrotron x-ray and neutron inelastic scattering study
A synchrotron x-ray diffraction study of the crystallographic structure of
PrO2 in the Jahn-Teller distorted phase is reported. The distortion of the
oxygen sublattice, which was previously ambiguous, is shown to be a chiral
structure in which neighbouring oxygen chains have opposite chiralities. A
temperature dependent study of the magnetic excitation spectrum, probed by
neutron inelastic scattering, is also reported. Changes in the energies and
relative intensities of the crystal field transitions provide an insight into
the interplay between the static and dynamic Jahn-Teller effects.Comment: 7 pages, 6 figure
Active involved community partnerships: co-creating implementation infrastructure for getting to and sustaining social impact
Active involved community partnerships (AICPs) are essential to co-create implementation infrastructure and translate evidence into real-world practice. Across varied forms, AICPs cultivate community and tribal members as agents of change, blending research and organizational knowledge with relationships, context, culture, and local wisdom. Unlike selective engagement, AICPs enable active involvement of partners in the ongoing process of implementation and sustainability. This includes defining the problem, developing solutions, detecting practice changes, aligning organizational supports, and nurturing shared responsibility, accountability, and ownership for implementation. This paper builds on previously established active implementation and scaling functions by outlining key AICP functions to close the research-practice gap. Part of a federal initiative, California Partners for Permanency (CAPP) integrated AICP functions for implementation and system change to reduce disproportionality and disparities in long-term foster care. This paper outlines their experience defining and embedding five AICP functions: (1) relationship-building; (2) addressing system barriers; (3) establishing culturally relevant supports and services; (4) meaningful involvement in implementation; and (5) ongoing communication and feedback for continuous improvement. Planning for social impact requires the integration of AICP with other active implementation and scaling functions. Through concrete examples, authors bring multilevel AICP roles to life and discuss implications for implementation research and practice
Synthesis, Characterization, and Magnetic Properties of gamma-NaxCoO2 (0.70 < x <0.84)
Powder NaCoO () samples were synthesized and
characterized carefully by X-ray diffraction analysis, inductive-coupled plasma
atomic emission spectroscopy, and redox titration. It was proved that
-NaCoO is formed only in the narrow range of . Nevertheless, the magnetic properties depend strongly on . We
found, for the first time, two characteristic features in the magnetic
susceptibility of NaCoO, a sharp peak at K and an
anomaly at K, as well as the transition at K and the broad
maximum at K which had already been reported. A type of weak
ferromagnetic transition seems to occur at . The transition at ,
which is believed to be caused by spin density wave formation, was observed
clearly for with constant and independent of .
On the other hand, ferromagnetic moment varies systematically depending on .
These facts suggest the occurrence of a phase separation at the microscopic
level, such as the separation into Na-rich and Na-poor domains due to the
segregation of Na ions. The magnetic phase diagram and transition mechanism
proposed previously should be reconsidered.Comment: 4 pages (2 figures included) and 2 extra figures (gif), to be
published in J. Phys. Soc. Jpn. 73 (8) with possible minor revision
Coupling of magnetic order to planar Bi electrons in the anisotropic Dirac metals AMnBi2 (A = Sr, Ca)
We report powder and single crystal neutron diffraction measurements of the
magnetic order in AMnBi2 (A = Sr and Ca), two layered manganese pnictides with
anisotropic Dirac fermions on a Bi square net. Both materials are found to
order at TN approx 300 K in k = 0 antiferromagnetic structures, with ordered Mn
moments at T = 10 K of approximately 3.8 muB aligned along the c axis. The
magnetic structures are Neel-type within the Mn--Bi layers but the inter-layer
ordering is different, being antiferromagnetic in SrMnBi2 and ferromagnetic in
CaMnBi2. This allows a mean-field coupling of the magnetic order to Bi
electrons in CaMnBi2 but not in SrMnBi2. We find clear evidence that magnetic
order influences electrical transport. First principles calculations explain
the experimental observations and suggest that the mechanism for different
inter-layer ordering in the two compounds is the competition between the
anteiferromagnetic superexchange and ferromagnetic double exchange carried by
itinerant Bi electrons.Comment: Accepted for publication in Physical Review B. Version 2 includes
additional sample characterisation and bulk measurements, and ab initio
electronic structure calculation
Phase segregation in NaxCoO2 for large Na contents
We have investigated a set of sodium cobaltates (NaxCoO2) samples with
various sodium content (0.67 \le x \le 0.75) using Nuclear Quadrupole Resonance
(NQR). The four different stable phases and an intermediate one have been
recognized. The NQR spectra of 59Co allowed us to clearly differentiate the
pure phase samples which could be easily distinguished from multi-phase
samples. Moreover, we have found that keeping samples at room temperature in
contact with humid air leads to destruction of the phase purity and loss of
sodium content. The high sodium content sample evolves progressively into a
mixture of the detected stable phases until it reaches the x=2/3 composition
which appears to be the most stable phase in this part of phase diagram.Comment: 5 pages, 4 figure
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