4,759 research outputs found
Intrinsic Anharmonicities In The Bx4 2- Orthorhombic Sublattice
We have measured the room-temperature polarized Raman spectra of the internal modes of K2SO4 and K2SeO4 under hydrostatic pressure up to 10 GPa in a backscattering configuration. It was found that phonons involving the motion of selenium atoms have distinctive pseudoanharmonicities that can be traced to isotopic natural abundances. Accordingly, a reinterpretation is given to the origin of the fourth-order anharmonicity (g4 coupling constant) within the quartic potential formalism as representing dynamical isotopic effects in the cluster picture. We found that this analysis may be extended to other molecular systems with either phonon instabilities or order-disorder commensurate- incommensurate phase transitions. © 1986 The American Physical Society.3353379338
Symmetry Plays a Key Role in the Erasing of Patterned Surface Features
We report on how the relaxation of patterns prepared on a thin film can be
controlled by manipu- lating the symmetry of the initial shape. The validity of
a lubrication theory for the capillary-driven relaxation of surface profiles is
verified by atomic force microscopy measurements, performed on films that were
patterned using focused laser spike annealing. In particular, we observe that
the shape of the surface profile at late times is entirely determined by the
initial symmetry of the perturba- tion, in agreement with the theory. Moreover,
in this regime the perturbation amplitude relaxes as a power-law in time, with
an exponent that is also related to the initial symmetry. The results have
relevance in the dynamical control of topographic perturbations for
nanolithography and high density memory storage
Determination of Wave Function Functionals: The Constrained-Search--Variational Method
In a recent paper [Phys. Rev. Lett. \textbf{93}, 130401 (2004)], we proposed
the idea of expanding the space of variations in variational calculations of
the energy by considering the approximate wave function to be a
functional of functions rather than a function. The
space of variations is expanded because a search over the functions can
in principle lead to the true wave function. As the space of such variations is
large, we proposed the constrained-search-- variational method whereby a
constrained search is first performed over all functions such that the
wave function functional satisfies a physical constraint such as
normalization or the Fermi-Coulomb hole sum rule, or leads to the known value
of an observable such as the diamagnetic susceptibility, nuclear magnetic
constant or Fermi contact term. A rigorous upper bound to the energy is then
obtained by application of the variational principle. A key attribute of the
method is that the wave function functional is accurate throughout space, in
contrast to the standard variational method for which the wave function is
accurate only in those regions of space contributing principally to the energy.
In this paper we generalize the equations of the method to the determination of
arbitrary Hermitian single-particle operators as applied to two-electron atomic
and ionic systems. The description is general and applicable to both ground and
excited states. A discussion on excited states in conjunction with the theorem
of Theophilou is provided.Comment: 26 pages, 4 figures, 5 table
La Biogeografia della Sicilia: considerazioni conclusive sul XXXVII Congresso della Societ\ue0 Italiana di Biogeografia.
A taxonomic revision of western Eupholidoptera bush crickets (Orthoptera: Tettigoniidae): testing the discrimination power of DNA barcode.
The genus Eupholidoptera includes 46 Mediterranean species distributed
from Turkey to Greece, Italy and southern France. In the eastern part of its range,
Eupholidoptera has been considered to consist of several distinct species, while in the
Balkans and Italian peninsula only E. chabrieri has been recognized. However, the
status of some Italian populations, confined to particular geographic areas, remains
uncertain. To investigate the delimitation of the Italian taxa of Eupholidoptera, we
performed both morphological and molecular analyses. Morphological analysis was
carried out by considering diagnostic characters usually used to distinguish different
taxa, such as the shape of titillators in males and the subgenital plate in females.
Molecular analysis was performed by sequencing three mitochondrial genes: 12S
rRNA, 16S rRNA, partially sequenced and the entire gene of cox1 . Molecular markers
were used to infer phylogenetic relationships among the Italian Eupholidoptera
species and to reconstruct the historical processes that shaped their current geographic
distribution. Results from both morphological and molecular analyses were used to
revise the taxonomic arrangement of species. On the whole we were able to distinguish
nine lineages of Italian Eupholidoptera, of which E. tyrrhenica sp.n. from Corsica is
described as a new species
Determination of a Wave Function Functional
In this paper we propose the idea of expanding the space of variations in
standard variational calculations for the energy by considering the wave
function to be a functional of a set of functions , rather than a function. In this manner a greater flexibility to
the structure of the wave function is achieved. A constrained search in a
subspace over all functions such that the wave function functional
satisfies a constraint such as normalization or the Fermi-Coulomb
hole charge sum rule, or the requirement that it lead to a physical observable
such as the density, diamagnetic susceptibility, etc. is then performed. A
rigorous upper bound to the energy is subsequently obtained by variational
minimization with respect to the parameters in the approximate wave function
functional. Hence, the terminology, the constrained-search variational method.
The \emph{rigorous} construction of such a constrained-search--variational wave
function functional is demonstrated by example of the ground state of the
Helium atom.Comment: 10 pages, 2 figures, changes made, references adde
Genetic interaction of Pax3 mutation and canonical Wnt signaling modulates neural tube defects and neural crest abnormalities
Mouse models provide opportunities to investigate genetic interactions that cause or modify the frequency of neural tube defects (NTDs). Mutation of the PAX3 transcription factor prevents neural tube closure, leading to cranial and spinal NTDs whose frequency is responsive to folate status. Canonical Wnt signalling is implicated both in regulation of Pax3 expression and as a target of PAX3. This study investigated potential interactions of Pax3 mutation and canonical Wnt signalling using conditional gain- and loss-of-function models of β-catenin. We found an additive effect of β-catenin gain of function and Pax3 loss of function on NTDs and neural crest defects. β-catenin gain of function in the Pax3 expression domain led to significantly increased frequency of cranial but not spinal NTDs in embryos that are heterozygous for Pax3 mutation, while both cranial and spinal neural tube closure were exacerbated in Pax3 homozygotes. Similarly, deficits of migrating neural crest cells were exacerbated by β-catenin gain of function, with almost complete ablation of spinal neural crest cells and derivatives in Pax3 homozygous mutants. Pax3 expression was not affected by β-catenin gain of function, while we confirmed that loss of function led to reduced Pax3 transcription. In contrast to gain of function, β-catenin knockout in the Pax3 expression domain lowered the frequency of cranial NTDs in Pax3 null embryos. However, loss of function of β-catenin and Pax3 resulted in spinal NTDs, suggesting differential regulation of cranial and spinal neural tube closure. In summary, β-catenin function modulates the frequency of PAX3-related NTDs in the mouse
[The role of endoscopy in gastroenteropancreatic neuroendocrine tumors].
[The role of endoscopy in gastroenteropancreatic
neuroendocrine tumors].
[Article in Italian]
Magno L, Sivero L, Napolitano V, Ruggiero S, Fontanarosa G, Massa S.
Source
Dipartmento di Chirurgia Generale, Geriatrica ed Endoscopia Diagnostica ed Geriatrica, Universitá
degli Studi, Federico II di Napoli.
Abstract
Versione italiana Riassunto: Il ruolo dell'endoscopia nei tumori neuroendocrini
gastroenteropancreatici. L. Magno, L. Sivero, V. Napolitano, S. Ruggiero, G.
Fontanarosa, S. Massa I tumori neuroendocrini (NET) gastro-entero-pancreatici (GEP)
sono neoplasie rare che originano dalle cellule neuroendocrine del tubo digerente e
del pancreas. L'endoscopia digestiva e l'ecoendoscopia rivestono un ruolo importante
nella diagnosi, stadiazione e sorveglianza dei pazienti con NET. Inoltre, in casi
selezionati, le tecniche endoscopiche operative consentono il trattamento di queste
neoplasie in fase precoce. English version Summary: The role of endoscopy in
gastroenteropancreatic neuroendocrine tumors. L. Magno, L. Sivero, V. Napolitano, S.
Ruggiero, G. Fontanarosa, S. Massa Gastroenteropancreatic (GEP) neuroendocrine
tumors (NET) are rare neoplasia arisen from neuroendocrine cells present in the gut
mucosa and pancreas. Digestive endoscopy and endoscopic ultrasonography play a
relevant role in NET diagnosis, stadiation and surveillance. Moreover, in selected
patients, surgical endoscopy allows the tratment of these cancers at an early stage
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