51,951 research outputs found
Decrease in the high energy X-ray flux from Cen XR-2. Search for X-rays from the large and small Magellanic clouds
High energy X ray sky survey data on decreased intensity of Cen XR-2, and X ray energy flux from Magellanic clouds - Mildura, Australia, October 15 and 24, 196
H-NMR spin-echo measurements of the static and dynamic spin properties in -(BETS)FeCl
H-NMR spin-echo measurements of the spin-echo decay with a
decay rate 1/ and the frequency shift under applied
magnetic field = 9 T along the a-axis over a temperature
range 2.0180 K are reported for a single crystal of the organic conductor
-(BETS)FeCl. It provides the spin dynamic and static
properties in the paramagnetic metal (PM) and antiferromagnetic insulator (AFI)
states as well as across the PMAFI phase transition. A large slow beat
structure in the spin-echo decay is observed with a typical beat frequency of
7 kHz and it varies across the spectrum. Its origin is attributed to
the HH dipole interactions rather than to the much larger
dipolar field contribution from the Fe electrons (spin = 5/2). A
simple phenomenological model provides an excellent fit to the data. The
dominant H-NMR frequency shift comes from the dipolar field from the 3d
Fe ions, and the Fe Fe exchange interactions ()
( includes the dd exchange interactions through the electrons)
have a substantial effect to the local field at the proton sites expecially at
low temperatures. A good fit is obtained with = - 1.7 K. The data of
the spin-echo decay rate 1/ indicates that there is a significant change
in the slow fluctuations of the local magnetic field at the H-sites on
traversing the PM to AFI phase. This evidence supports earlier reports that the
PMAFI phase transition in -(BETS)FeCl is driven
magnetically and first order.Comment: 9 pages, 10 figures, resubmitted to Phys. Rev. B in response to
comments of Editor and reviewers on March 23, 200
Suboptimal compensation of gyroscopic coupling for inertia-wheel attitude control
Suboptimal compensation of gyroscopic coupling for inertia-wheel attitude control by mathematical technique
Switching and Extension of a [c2]Daisy-Chain Dimer Polymer
We report the synthesis of a [c2]daisy-chain dimer via ruthenium-catalyzed ring-closing olefin metathesis. Confirmation of the interlocked nature of the structure was achieved through single-crystal X-ray diffraction analysis. The dimer could be readily switched from the bound to the unbound conformation by treatment with 3.0 equiv of KOH and subsequently reprotonated by treatment with 3.0 equiv of HPF_6. Azide functionalization of the dimer enabled incorporation in linear step-growth polymer chains using the alkyne-azide “click” reaction. Gel permeation chromatography coupled with multiangle laser light scattering analysis showed the polymers contained 22 dimers and had a radius of gyration of 14.8 nm. Acylation of the amines of the dimers sterically forced elongation of the interlocked units, and MALLS analysis of the polymer showed a 48% increase in the R_g (21.4 nm)
Polarizabilities of Si^{2+}: a benchmark test of theory and experiment
We have calculated electric-dipole polarizabilities of the 3s^2 ^1S_0, 3s3p
^3P_0, and 3s3p ^1P_1 states of the Si^{2+} ion using recently developed
configuration interaction + all-order method. Detailed evaluation of the
uncertainties of the final results is carried out. Our value for the ground
state electric-dipole polarizability 11.670(13) a.u. is in excellent agreement
with the resonant excitation Stark ionization spectroscopy value 11.669(9) a.u.
[Komara et al., J. Phys. B 38, 87 (2005); Mitroy, Phys. Rev. A 78, 052515
(2008)]. This work represents the most precise benchmark test to date of theory
and experiment in divalent atoms. The near cancellation of the ns^2 ^1S_0
ground state and the lowest nsnp ^3P_0 polarizabilities previously observed in
B+, Al+, In+, Tl+, and Pb^{2+} is also found in Si^{2+} ion.Comment: 6 page
Microscopic Study of Superfluidity in Dilute Neutron Matter
Singlet -wave superfluidity of dilute neutron matter is studied within the
correlated BCS method, which takes into account both pairing and short-range
correlations. First, the equation of state (EOS) of normal neutron matter is
calculated within the Correlated Basis Function (CBF) method in lowest cluster
order using the and components of the Argonne
potential, assuming trial Jastrow-type correlation functions. The
superfluid gap is then calculated with the corresponding component of the
Argonne potential and the optimally determined correlation functions.
The dependence of our results on the chosen forms for the correlation functions
is studied, and the role of the -wave channel is investigated. Where
comparison is meaningful, the values obtained for the gap within
this simplified scheme are consistent with the results of similar and more
elaborate microscopic methods.Comment: 9 pages, 6 figure
Subglacial floods beneath ice sheets.
Subglacial floods (jökulhlaups) are well documented as occurring beneath present day glaciers and ice caps. In addition, it is known that massive floods have occurred from ice-dammed lakes proximal to the Laurentide ice sheet during the last ice age, and it has been suggested that at least one such flood below the waning ice sheet was responsible for a dramatic cooling event some 8000 years ago. We propose that drainage of lakes from beneath ice sheets will generally occur in a time-periodic fashion, and that such floods can be of severe magnitude. Such hydraulic eruptions are likely to have caused severe climatic disturbances in the past, and may well do so in the future
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