57,493 research outputs found
Time-Reversal-Violating Schiff Moment of 199Hg
We calculate the Schiff moment of the nucleus 199Hg, created by pi-N-N
vertices that are odd under parity (P) and time-reversal (T). Our approach,
formulated in diagrammatic perturbation theory with important core-polarization
diagrams summed to all orders, gives a close approximation to the expectation
value of the Schiff operator in the odd-A Hartree-Fock-Bogoliubov ground state
generated by a Skyrme interaction and a weak P- and T-odd pion-exchange
potential. To assess the uncertainty in the results, we carry out the
calculation with several Skyrme interactions (the quality of which we test by
checking predictions for the isoscalar-E1 strength distribution in 208Pb) and
estimate most of the important diagrams we omit.Comment: 13 pages, 7 figure
Dye laser remote sensing of marine plankton
Dye laser, emitting four wavelengths sequentially in time, has been incorporated into helicopter-borne lidar flight package, for performing studies of laser-induced fluorescence of chlorophyll A in algae. Data obtained by multicolor lidar technique can provide water-resource management with rapid-access wide-area coverage of the impact of various environmental factors for any body of water
The spectral evolution of impulsive solar X-ray flares. II.Comparison of observations with models
We study the evolution of the spectral index and the normalization (flux) of
the non-thermal component of the electron spectra observed by RHESSI during 24
solar hard X-ray flares. The quantitative evolution is confronted with the
predictions of simple electron acceleration models featuring the soft-hard-soft
behaviour. The comparison is general in scope and can be applied to different
acceleration models, provided that they make predictions for the behavior of
the spectral index as a function of the normalization. A simple stochastic
acceleration model yields plausible best-fit model parameters for about 77% of
the 141 events consisting of rise and decay phases of individual hard X-ray
peaks. However, it implies unphysically high electron acceleration rates and
total energies for the others. Other simple acceleration models such as
constant rate of accelerated electrons or constant input power have a similar
failure rate. The peaks inconsistent with the simple acceleration models have
smaller variations in the spectral index. The cases compatible with a simple
stochastic model require typically a few times 10^36 electrons accelerated per
second at a threshold energy of 18 keV in the rise phases and 24 keV in the
decay phases of the flare peaks.Comment: 9 pages, 4 figures, accepted for publication by A&
Sums and differences of four k-th powers
We prove an upper bound for the number of representations of a positive
integer as the sum of four -th powers of integers of size at most ,
using a new version of the Determinant method developed by Heath-Brown, along
with recent results by Salberger on the density of integral points on affine
surfaces. More generally we consider representations by any integral diagonal
form. The upper bound has the form , whereas earlier
versions of the Determinant method would produce an exponent for of order
in this case. Furthermore, we prove that the number of
representations of a positive integer as a sum of four -th powers of
non-negative integers is at most for
, improving upon bounds by Wisdom.Comment: 18 pages. Mistake corrected in the statement of Theorem 1.2. To
appear in Monatsh. Mat
Local atomic arrangement and martensitic transformation in NiMnIn: An EXAFS Study
Heusler alloys that undergo martensitic transformation in ferromagnetic state
are of increasing scientific and technological interest. These alloys show
large magnetic field induced strains upon martensitic phase change thus making
it a potential candidate for magneto-mechanical actuation. The crystal
structure of martensite is an important factor that affects both the magnetic
anisotropy and mechanical properties of such materials. Moreover, the local
chemical arrangement of constituent atoms is vital in determining the overall
physical properties. NiMnIn is one such ferromagnetic
shape memory alloy that displays exotic properties like large magnetoresistance
at moderate field values. In this work, we present the extended x-ray
absorption fine-structure measurements (EXAFS) on the bulk
NiMnIn which reveal the local structural change that
occurs upon phase transformation. The change in the bond lengths between
different atomic species helps in understanding the type of hybridization which
is an important factor in driving such Ni-Mn based systems towards martensitic
transformation
Using Wii technology to explore real spaces via virtual environments for people who are blind
Purpose - Virtual environments (VEs) that represent real spaces (RSs) give people who are blind the opportunity to build a cognitive map in advance that they will be able to use when arriving at the RS. Design - In this research study Nintendo Wii based technology was used for exploring VEs via the Wiici application. The Wiimote allows the user to interact with VEs by simulating walking and scanning the space. Finding - By getting haptic and auditory feedback the user learned to explore new spaces. We examined the participants' abilities to explore new simple and complex places, construct a cognitive map, and perform orientation tasks in the RS. Originality – To our knowledge, this finding presents the first virtual environment for people who are blind that allow the participants to scan the environment and by this to construct map model spatial representations
Resonance parameters of the first 1/2+ state in 9Be and astrophysical implications
Spectra of the 9Be(e,e') reaction have been measured at the S-DALINAC at an
electron energy E_0 = 73 MeV and scattering angles of 93{\deg} and 141{\deg}
with high energy resolution up to excitation energies E_x = 8 MeV. The
astrophysically relevant resonance parameters of the first excited 1/2+ state
of 9Be have been extracted in a one-level approximation of R-matrix theory
resulting in a resonance energy E_R = 1.748(6) MeV and width Gamma_R = 274(8)
keV in good agreement with the latest 9Be(gamma,n) experiment but with
considerably improved uncertainties. However, the reduced B(E1) transition
strength deduced from an extrapolation of the (e,e') data to the photon point
is a factor of two smaller. Implications of the new results for a possible
production of 12C in neutron-rich astrophysical scenarios are discussed.Comment: 8 pages, 7 figures, accepted for publication in Phys. Rev.
Quantum dynamics of the Neel vector in the antiferromagnetic molecular wheel CsFe8
The inelastic neutron scattering (INS) spectrum is studied for the
antiferromagnetic molecular wheel CsFe8, in the temperature range 2 - 60 K, and
for transfer energies up 3.6 meV. A qualitative analysis shows that the
observed peaks correspond to the transitions between the L-band states, from
the ground state up to the S = 5 multiplet. For a quantitative analysis, the
wheel is described by a microscopic spin Hamiltonian (SH), which includes the
nearest-neighbor Heisenberg exchange interactions and uniaxial easy-axis
single-ion anisotropy, characterized by the constants J and D, respectively.
For a best-fit determination of J and D, the L band is modeled by an effective
SH, and the effective SH concept extended such as to facilitate an accurate
calculation of INS scattering intensities, overcoming difficulties with the
dimension of the Hilbert space. The low-energy magnetism in CsFe8 is
excellently described by the generic SH used. The two lowest states are
characterized by a tunneling of the Neel vector, as found previously, while the
higher-lying states are well described as rotational modes of the Neel vector.Comment: 12 pages, 10 figures, REVTEX4, to appear in PR
Short distance physics with heavy quark potentials
We present lattice studies of heavy quark potentials in the quenched
approximation of QCD at finite temperatures. Both, the color singlet and color
averaged potentials are calculated. While the potentials are well known at
large distances, we give a detailed analysis of their short distance behavior
(from 0.015 fm to 1 fm) near the critical temperature. At these distances we
expect that the T-dependent potentials go over into the zero temperature
potential. Indeed, we find evidences that the temperature influence gets
suppressed and the potentials starts to become a unique function of the
underlying distance scale. We use this feature to normalize the heavy quark
potentials at short distances and extract the free energy of the quark system
in a gluonic heat bath.Comment: Lattice2001(hightemp), 3 pages, 2 figure
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