11,413 research outputs found
Chiral pion-nucleon dynamics in finite nuclei: spin-isospin excitations
The nuclear density functional framework, based on chiral dynamics and the
symmetry breaking pattern of low-energy QCD, is extended to the description of
collective nuclear excitations. Starting from the relativistic point-coupling
Lagrangian previously introduced [Nucl. Phys. A770 (2006) 1], the
proton-neutron (quasiparticle) random phase approximation is formulated and
applied to investigate the role of chiral pion-nucleon dynamics in excitation
modes involving spin and isospin degrees of freedom, e.g. isobaric analog
states and Gamow-Teller resonances.Comment: 17 pages, 6 figures, elsart class. Minor revisions, Nuclear Physics A
in prin
Symmetrization and enhancement of the continuous Morlet transform
The forward and inverse wavelet transform using the continuous Morlet basis
may be symmetrized by using an appropriate normalization factor. The loss of
response due to wavelet truncation is addressed through a renormalization of
the wavelet based on power. The spectral density has physical units which may
be related to the squared amplitude of the signal, as do its margins the mean
wavelet power and the integrated instant power, giving a quantitative estimate
of the power density with temporal resolution. Deconvolution with the wavelet
response matrix reduces the spectral leakage and produces an enhanced wavelet
spectrum providing maximum resolution of the harmonic content of a signal.
Applications to data analysis are discussed.Comment: 12 pages, 8 figures, 2 tables, minor revision, final versio
A fluorescent lectin-agarose bead immunoassay for pancreatic autoantigen involved in Crohn´s disease
Nuclear Many-Body Dynamics constrained by QCD and Chiral Symmetry
We present a novel description of nuclear many-body systems, both for nuclear
matter and finite nuclei, emphasizing the connection with the condensate
structure of the QCD ground state and spontaneous chiral symmetry breaking.
Lorentz scalar and vector mean-fields are introduced in accordance with QCD sum
rules. Nuclear binding arises from pionic fluctuations, using in-medium chiral
perturbation theory up to three-loop order. Ground state properties of O
and Ca are calculated. The built-in QCD constraints reduce the number of
input parameters significantly in comparison with purely phenomenological
relativistic mean-field approaches.Comment: 6 pages, 3 figures, to be published in European Physical Journal
"Oxide-free" tip for scanning tunneling microscopy
We report a new tip for scanning tunneling microscopy and a tip repair procedure that allows one to reproducibly obtain atomic images of highly oriented pyrolytic graphite with previously inoperable tips. The tips are shown to be relatively oxide-free and highly resistant to oxidation. The tips are fabricated with graphite by two distinct methods
Scanning tunneling microscopy investigation of 2H-MoS_2: A layered semiconducting transition‐metal dichalcogenide
Scanning tunneling microscopy (STM) has been enormously
successful in solving several important problems in the geometric and electronic structure of homogeneous metallic and semiconducting surfaces. A central question which remains to be answered with respect to the study of
compound surfaces, however, is the extent to which the
chemical identity of constituent atoms may be established.
Recently, progress in this area was made by Feenstra et al.
who succeeded in selectively imaging either Ga or As atoms
on the GaAs (110) surface. So far this is the only case where such selectivity has been achieved. In an effort to add to our understanding of compound surface imaging we have undertaken a vacuum STM study of 2H-MoS_2, a material which has two structurally and electronically different atomic species at its surface
Evidence of O2 consumption in underway seawater lines: Implications for air-sea O2 and CO2 fluxes
We observed O2 deficits of 0.5 to 2.0% (1 to 4 mol/kg) in the underway seawater lines of three different ships. Deficits in O2/Ar and isotopic enrichments in dissolved O2 observed in underway seawater lines indicate a respiratory removal process. A 1% respiratory bias in underway lines would lead to a 2.5-5 atm (2.5-5pbar) enhancement in surface water pCO2. If an underway pCO2 bias of this magnitude affectedall measurements, the global oceanic carbon uptake based on pCO 2 climatologies would be 0.5-0.8 Pg/yr higher than the present estimate of 1.6 Pg/yr. Treatment of underway lines with bleach for several hours and thorough flushing appeared to minimize O2 loss. Given the increasing interest in underway seawater measurements for the determination of surface CO2 and O2 fluxes, respiration in underway seawater lines must be identified and eliminated on all observing ships to ensure unbiased data
In-medium chiral SU(3) dynamics and hypernuclear structure
A previously introduced relativistic energy density functional, successfully
applied to ordinary nuclei, is extended to hypernuclei. The density-dependent
mean field and the spin-orbit potential are consistently calculated for a
hyperon in the nucleus using the SU(3) extension of in-medium chiral
perturbation theory. The leading long range interaction arises from
kaon-exchange and -exchange with hyperon in the intermediate
state. Scalar and vector mean fields reflecting in-medium changes of the quark
condensates are constrained by QCD sum rules. The model, applied to oxygen as a
test case, describes spectroscopic data in good agreement with experiment. In
particular, the smallness of the spin-orbit interaction finds a
natural explanation in terms of an almost complete cancellation between
scalar-vector background contributions and long-range terms generated by
two-pion exchange.Comment: 10 pages, 2 figures, elsart class. Minor revision
Lower critical field measurements in YBa2Cu3O(6+x) single crystals
The temperature dependence of the lower critical field in YBa2Cu3O(6+x) single crystals was determined by magnetization measurements with the applied field parallel and perpendicular to the c-axis. Results are compared with data from the literature and fitted to Ginzberg-Landau equations by assuming a linear dependence of the parameter kappa on temperature. A value of 7 plus or minus 2 kOe was estimated for the thermodynamic critical field at T = O by comparison of calculated H (sub c2) values with experimental data from the literature
Measurement of H(sub c1) in a single crystal of YBa2Cu3O7 with low pinning
The measurement of H(sub c1) in barium yttrium copper oxide (BYCO) is often ambiguous because the presence of large pinning forces makes it difficult to discern exactly where the first deviation from linearity occurs. In addition there are complications because demagnetizing factors are often not well known. By utilizing a single crystal of YBCO with a nearly cubic shape, the uncertainty in the demagnetizing factor was minimized. In addition, the crystal used exhibited a very small amount of pinning with H applied perpendicular to the c axis, and a sharp break in the initial magnetization vs. field curve could be observed over a wide range of temperature. This allowed a precise determination of H(sub c1). The measured values of H(sub c1) could be well described by the Abrikosov relation with a Ginzburg-Landau parameter which varied linearly with temperature
- …