3,439 research outputs found
Collective charge density wave motion through an ensemble of Aharonov-Bohm rings
We investigate theoretically the collective charge density wave motion
through an ensemble of small disordered Aharonov-Bohm rings. It is shown that
the magnetic flux modulates the threshold field and the magnetoresistance with
a half flux quantum periodicity , resulting from ensemble
averaging over random scattering phases of multiple rings. The magnitude of the
magnetoresistance oscillations decreases rapidly with increasing bias. This is
consistent with recent experiments on in presence of columnar defects
[Phys. Rev. Lett. 78, 919 (1997)].Comment: 4 pages Revtex, 2 figures. Submitted to Phys. Rev. Let
Comment on "Peierls Gap in Mesoscopic Ring Threated by a Magnetic Flux"
In a recent letter, Yi et al. PRL 78, 3523 (1997), have considered the
stability of a Charge Density Wave in a one-dimensional ring, in the presence
of an Aharonov-Bohm flux. This comment shows that, in one dimension, the
stability of the Charge Density Wave depends on the parity of the number of
electrons in the ring. This effect is similar to the parity effect known for
the persistent current in one-dimensional rings.Comment: Latex, 1 page, 2 figure
On the derivation of the t-J model: electron spectrum and exchange interactions in narrow energy bands
A derivation of the t-J model of a highly-correlated solid is given starting
from the general many-electron Hamiltonian with account of the
non-orthogonality of atomic wave functions. Asymmetry of the Hubbard subbands
(i.e. of ``electron'' and ``hole''cases) for a nearly half-filled bare band is
demonstrated. The non-orthogonality corrections are shown to lead to occurrence
of indirect antiferromagnetic exchange interaction even in the limit of the
infinite on-site Coulomb repulsion. Consequences of this treatment for the
magnetism formation in narrow energy bands are discussed. Peculiarities of the
case of ``frustrated'' lattices, which contain triangles of nearest neighbors,
are considered.Comment: 4 pages, RevTe
Screening and interlayer coupling in multilayer graphene field-effect transistors
With the motivation of improving the performance and reliability of
aggressively scaled nano-patterned graphene field-effect transistors, we
present the first systematic experimental study on charge and current
distribution in multilayer graphene field-effect transistors. We find a very
particular thickness dependence for Ion, Ioff, and the Ion/Ioff ratio, and
propose a resistor network model including screening and interlayer coupling to
explain the experimental findings. In particular, our model does not invoke
modification of the linear energy-band structure of graphene for the multilayer
case. Noise reduction in nano-scale few-layer graphene transistors is
experimentally demonstrated and can be understood within this model as well.Comment: 13 pages, 4 figures, 20 reference
Editorial
‘A new spring, and a new sound’, so begins a famous Dutch poem. Will the birds sing differently, as the poet wishes in the next line? BKI, now 178 years old—surely one of the longest-running journals of Southeast Asian studies in the world, and known around its original home, the KITLV (Royal Institute), as ‘the Old Dame’—starts 2022 with a remarkable new development. For this reason, the first issue of the year opens with an Editorial. After generations of sound and steady editing under the direction of two scholars, one in the role of Chief Editor and one as Managing Editor, from now on, BKI will be run by an expanded editorial team of seven scholars drawn both from the geographical region, Southeast Asia, and the disciplines in the humanities and social sciences that BKI is dedicated to examining..
Interobserver and intraobserver variability in the radiological assessment of sialolithiasis using cone beam computed tomography
BACKGROUND: Data regarding the inter- and intraobserver variability in the radiological assessment of sialolithiasis using cone beam computed tomography are missing in the current literature. This study assessed the inter- and intraobserver variability in the radiological assessment of sialolithiasis using cone beam computed tomography (CBCT). MATERIAL AND METHODS: In 107 patients, 130 salivary glands (65 parotid and 65 submandibular) with clinical signs of obstruction were assessed by four independent observers; 2 residents OMFS and 2 experienced OMFS. The observers analyzed the CBCT images and determined the absence or presence of one or more salivary stones in the affected gland. This procedure was repeated after three months. RESULTS: Interobserver agreements showed kappa values of 0.84 for the parotid gland, and 0.93 for the submandibular gland. Intraobserver agreements for the whole group reported kappa values between 0.83 - 0.95. There was no significant difference between residents and experienced OMFS. CONCLUSIONS: Due to the good inter- and intraobserver agreement, CBCT appears to be a reproducible imaging modality for detecting salivary stones in patients with signs and symptoms of obstructed parotid and submandibular glands. Key words:Salivary gland calculi, cone-beam computed tomography, observer variation
Disequilibrium Carbon, Oxygen, and Nitrogen Chemistry in the Atmospheres of HD 189733b and HD 209458b
We have developed 1-D photochemical and thermochemical kinetics and diffusion
models for the transiting exoplanets HD 189733b and HD 209458b to study the
effects of disequilibrium chemistry on the atmospheric composition of "hot
Jupiters." Here we investigate the coupled chemistry of neutral carbon,
hydrogen, oxygen, and nitrogen species, and we compare the model results with
existing transit and eclipse observations. We find that the vertical profiles
of molecular constituents are significantly affected by transport-induced
quenching and photochemistry, particularly on cooler HD 189733b; however, the
warmer stratospheric temperatures on HD 209458b can help maintain
thermochemical equilibrium and reduce the effects of disequilibrium chemistry.
For both planets, the methane and ammonia mole fractions are found to be
enhanced over their equilibrium values at pressures of a few bar to less than a
mbar due to transport-induced quenching, but CH4 and NH3 are photochemically
removed at higher altitudes. Atomic species, unsaturated hydrocarbons
(particularly C2H2), some nitriles (particularly HCN), and radicals like OH,
CH3, and NH2 are enhanced overequilibrium predictions because of quenching and
photochemistry. In contrast, CO, H2O, N2, and CO2 more closely follow their
equilibrium profiles, except at pressures < 1 microbar, where CO, H2O, and N2
are photochemically destroyed and CO2 is produced before its eventual
high-altitude destruction. The enhanced abundances of HCN, CH4, and NH3 in
particular are expected to affect the spectral signatures and thermal profiles
HD 189733b and other, relatively cool, close-in transiting exoplanets. We
examine the sensitivity of our results to the assumed temperature structure and
eddy diffusion coefficientss and discuss further observational consequences of
these models.Comment: 40 pages, 16 figures, accepted for publication in Astrophysical
Journa
Contrasting models for lactation curve analysis
Several statistical models have been proposed for the genetic evaluation of production traits in dairy cattle based on test-day records. Three main approaches have been put forward in the literature: random regression, orthogonal polynomials, and, more recently, character process models. The aim of this paper is to show how these different approaches are related, to compare their performance for the genetic analysis of lactation curves, and to assess equivalence between sire and animal models for repeated measures analyses. It was found that, with an animal model, a character process model with 11 parameters performed better, regarding the likelihood criterion, than a quartic random regression model (with 31 parameters). However, although the likelihood was higher, the genetic variance was very different with the character process model from the unstructured model, which raises important issues concerning model selection criteria. There are advantages in combining methodologies. A quadratic random regression model for the environmental part, combined with a character process model for the residual, performed better than the quartic random regression model and had fewer parameters. A character process structure allowing for a correlation pattern modeled the residual better than a simple quadratic variance, and had only one extra parameter
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