1,516 research outputs found
Boundary between the thermal and statistical polarization regimes in a nuclear spin ensemble
As the number of spins in an ensemble is reduced, the statistical uctuations
in its polarization eventually exceed the mean thermal polarization. This
transition has now been surpassed in a number of recent nuclear magnetic
resonance experiments, which achieve nanometer-scale detection volumes. Here,
we measure nanometer- scale ensembles of nuclear spins in a KPF6 sample using
magnetic resonance force microscopy. In particular, we investigate the
transition between regimes dominated by thermal and statistical nuclear
polarization. The ratio between the two types of polarization provides a
measure of the number of spins in the detected ensemble
Quantum dot opto-mechanics in a fully self-assembled nanowire
We show that fully self-assembled optically-active quantum dots (QDs)
embedded in MBE-grown GaAs/AlGaAs core-shell nanowires (NWs) are coupled to the
NW mechanical motion. Oscillations of the NW modulate the QD emission energy in
a broad range exceeding 14 meV. Furthermore, this opto-mechanical interaction
enables the dynamical tuning of two neighboring QDs into resonance, possibly
allowing for emitter-emitter coupling. Both the QDs and the coupling mechanism
-- material strain -- are intrinsic to the NW structure and do not depend on
any functionalization or external field. Such systems open up the prospect of
using QDs to probe and control the mechanical state of a NW, or conversely of
making a quantum non-demolition readout of a QD state through a position
measurement.Comment: 20 pages, 6 figure
Utilization of morphological and AFLP molecular markers in the identification of native and cultivated germplasm of Elymus scabrifolius (Poaceae)
Elymus scabrifolius es una gramínea
perenne nativa de Sudamérica con gran
potencial como recurso forrajero para ambientes
con limitantes edáficas. En el presente trabajo se
analizó la utilización de caracteres morfológicos
y marcadores moleculares AFLP para la
identificación genotípica de seis accesiones,
un cultivar comercial y siete híbridos artificiales
de esta especie. Ambos tipos de marcadores
permitieron diferenciar a los materiales
analizados en los respectivos dendrogramas,
aunque las relaciones entre materiales variaron
según el tipo de marcador. El Análisis de
Componentes Principales permitió identificar las
variables más relevantes para la diferenciación
morfológica. Los híbridos se diferenciaron
morfológicamente de ambos parentales, excepto
un híbrido que se agrupó con su material
paterno. Aunque en el análisis de los marcadores
AFLP los híbridos se agruparon con uno de sus
parentales, se pudo corroborar su origen híbrido
mediante el registro de bandas paternas y
polimórficas entre parentales. Se concluye que
las metodologías empleadas para caracterizar
los materiales analizados de E. scabrifolius
serían de gran utilidad para el manejo eficiente
de colecciones de germoplasma como así
también para su utilización en programas de
mejoramiento genético.Elymus scabrifolius is a South American
perennial grass exhibiting great potential as a
forage resource, especially for environments
with edaphic limitations. In the present
work we use morphological traits and AFLP
molecular markers to genotypically identify six
E. scabrifolius accessions, one commercial
cultivar and seven artificial hybrids of this
species. Both types of marker systems resulted
in an accurate differentiation of the interrogated
E. scabrifolius germplasm in the dendrograms.
Moreover, relationships between the tested
germplasm tend to vary according to the type
of marker system used. Principal Component
Analysis was used to identify the traits that
best described the morphological variation.
The morphological study revealed that almost
all hybrids were different from their parents,
with exception of one hybrid that was clustered
with their own male parent. In the AFLP marker
analysis, all the hybrids were clustered with one
of their own parents. However, hybrid origin of
those individuals was verified by the presence
of paternal bands and polymorphic bands. In
conclusion, the use of different methodologies
to characterize and analyze E. scabrifolius
materials has the potential to become of
great benefit for the efficient management
of germplasm collections and also for their
utilization in breeding programs.Fil: Tomas, Pablo A..
Universidad Nacional del Litoral. Facultad de Ciencias Agrarias. Cátedra de Mejoramiento Vegetal y Animal.Fil: Gottlieb, Alexandra M..
Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ecología, Genética y Evolución.Fil: Schrauf, Gustavo E..
Universidad de Buenos Aires. Facultad de AgronomíaFil: Poggio, Lidia.
Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ecología, Genética y Evolución
Gluon Condensate and Beyond
We review briefly and in retrospect the development which brought about the
QCD sum rules based on introduction of the gluon condensate (M.A. Shifman, A.I.
Vainshtein, and V.I. Zakharov (1978)).Comment: 15 pages, 5 figures, uses sprocl.sty (included). The 1999 Sakurai
Prize Lectur
Centric relation—A biological perspective of a technical concept
Background: Few terms and concepts have been so extensively debated in dentistry as the words 'centric relation' (CR). Debates involve its biological, diagnostic and therapeutic usefulness. Methods: A review of the literature on the current concepts on CR as a diagnostic or therapeutic aid in dentistry was provided. Clinical trials assessing the superiority of one CR recording method over the others to identify patients with temporomandibular disorders (diagnostic use) or to manage patients with prosthodontic or orthodontic needs (therapeutic use) were tentatively included. Results: Due to the absence of literature addressing either of the above targets, a comprehensive overview was provided. The diagnostic use of CR as a reference position to identify the correct position of the temporomandibular joint condyle within the glenoid fossa is not supported and lacks anatomical support. From a therapeutic standpoint, the use of CR can be pragmatically useful in prosthodontics as a maxillo-mandibular reference position when occlusal re-organization is warranted and/or when the position of maximum intercuspation is no longer available. Conclusions: The derived occlusal goals from a diagnostic misuse of CR are generally the result of circular reasoning, that is a technique is based on the recording of a certain condylar position that is believed to be 'ideal' and the treatment is considered successful when such position is shown by the specific instrument that was manufactured for that purpose. The term 'Centric Relation' might be replaced with the term 'Maxillo-Mandibular Utility Position'
Magnetic anisotropy of individual maghemite mesocrystals
Interest in creating magnetic metamaterials has led to methods for growing superstructures of magnetic nanoparticles. Mesoscopic crystals of maghemite (gamma-Fe2O3) nanoparticles can be arranged into highly ordered body-centered tetragonal lattices of up to a few micrometers. Although measurements on disordered ensembles have been carried out, determining the magnetic properties of individual mesoscopic crystals is challenging due to their small total magnetic moment. Here, we overcome these challenges by utilizing sensitive dynamic cantilever magnetometry to study individual micrometer-sized gamma-Fe2O3 mesocrystals. These measurements reveal an unambiguous cubic anisotropy, resulting from the crystalline anisotropy of the constituent maghemite nanoparticles and their alignment within the mesoscopic lattice. The signatures of anisotropy and its origins come to light because we combine the self-assembly of highly ordered mesocrystals with the ability to resolve their individual magnetism. This combination is promising for future studies of the magnetic anisotropy of other nanoparticles, which are too small to investigate individually
Relationships among genome size, environmental conditions and geographical distribution in natural populations of NW Patagonian species of Berberis L. (Berberidaceae)
Variation in genome size of 24 populations belonging to 11 NW Patagonian species of Berberis was analysed as a function of the environment and geographical location. The variation showed three levels of discontinuity, two of which corresponded to diploid species (2n = 28) while the third corresponded to polyploid species (2n = 56). Diploids with DNA content ranging from 1.463 pg to 1.857 pg included Berberis cabrerae, B. chillanensis, B. montana, B. serrato-dentata and B. bidentata. Diploids with DNA content ranging from 2.875 pg to 3.806 pg included B. linearifolia, B. darwinii, B. parodii and B. empetrifolia. The genome size of the polyploid species B. buxifolia and B. heterophylla ranged from 5.809 pg to 6.844 pg. Principal component analysis (PCA) was applied to represent the variability of environmental conditions. The eigenvectors of the principal component axes showed that PCl discriminates the populations according to rainfall, types of vegetation and geomorphology; altitude and latitude, on the other hand, contribute to PC2 and PC3, respectively. From these results it is concluded: (1) that diploids with lower DNA content grow in high-elevation sites having greater rainfall but lower water availability; (2) diploids with higher DNA content are associated with half-elevation forests where the vegetative period is longer, the water availability is greater and the temperatures are higher; and (3) the distribution pattern of polyploids is considerably wider than that of diploids, which are geographically and ecologically restricted to forest areas. These results suggest that the C-value plays an important role in the ability of the species to adapt to different growing conditions.Facultad de Ciencias Agrarias y Forestale
K -> pi pi Electroweak Penguins in the Chiral Limit
We report on dispersive and finite energy sum rule analyses of the
electroweak penguin matrix elements in the chiral
limit. We accomplish the correct perturbative matching (scale and scheme
dependence) at NLO in alpha_s, and we describe two different strategies for
numerical evaluation.Comment: 4 pages, 2 figures. Contribution to QCD02, International Conference
on Quantum Chromo-Dynamics, Montpellier (France), July 2-9 200
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