910 research outputs found
Variation in wood properties among five full-sib families of Norway spruce (Picea abies)
Genetic- and environmental variation and correlation patterns were
characterized for modulus of elasticity (MOE), modulus of rupture (MOR) and
related wood traits: latewood proportion, wood density, spiral grain,
microfibril angle and lignin content in five full-sib families of Norway
spruce. The families were evaluated on the basis of clearwood specimens from
the juvenile -mature wood transition zone of 93 sampled trees at age 30 year
from seed. Family-means varied significantly ( < 0.05) for all wood traits
studied except lignin content. MOE varied between 7.9–14.1 GPa among trees
and 9.4–11.0 GPa among families. MOR varied between 47–87 MPa among trees
and 61–71 MPa among families. Families remained significantly different in
an analysis of specific MOE (MOE/density) and MOR (MOR/density). Hence,
solely relying on wood density as a wood quality trait in tree breeding
would not fully yield the potential genetic gain for MOE and MOR.
Correlations between wood structural traits and specific MOE and MOR are
presented and discussed.Variabilité des propriétés du bois pour
cinq familles de pleins-frères d'épicéa commun
(Picea abies). La variabilité
génétique et environnementale pour le module d'élasticité
(MOE), le module de rupture (MOR) et certaines autres propriétés de
base du bois (proportion de bois final, densité du bois, angle du fil,
angle des microfibrilles et teneur en lignine) ont été
étudiées au sein de cinq familles de pleins-frères
d'épicéa commun ainsi que la liaison entre caractères. L'analyse
a été réalisée à partir d'échantillons sans
défaut issus de la zone de transition entre bois juvenile et bois mature
de 93 arbres âgés de 30 ans (depuis la graine). Des différences
significatives ( < 0.05) entre familles ont été observées pour
tous les caractères sauf pour la teneur en lignine. Les valeurs de MOE
variaient entre 7.9–14.1 GPa entre arbres et entre 9.4–11.0 GPa entre
familles. Pour MOR, ces valeurs s'échelonnaient entre 47–87 MPa entre
arbres et entre 61–71 MPa entre familles. Les différences entre familles
pour MOE et MOR sont restées significatives après normalisation pour
la densité du bois. Il est noté que l'utilisation seule de la
densité du bois comme critère de sélection ne permettrait pas
d'obtenir les gains génétiques potentiels escomptés d'une
sélection directe pour MOE et MOR. Les corrélations entre
propriétés de base du bois et les valeurs normalisées de MOE et
MOR sont présentées et discutées
Vertically coupled double quantum rings at zero magnetic field
Within local-spin-density functional theory, we have investigated the
`dissociation' of few-electron circular vertical semiconductor double quantum
ring artificial molecules at zero magnetic field as a function of inter-ring
distance. In a first step, the molecules are constituted by two identical
quantum rings. When the rings are quantum mechanically strongly coupled, the
electronic states are substantially delocalized, and the addition energy
spectra of the artificial molecule resemble those of a single quantum ring in
the few-electron limit. When the rings are quantum mechanically weakly coupled,
the electronic states in the molecule are substantially localized in one ring
or the other, although the rings can be electrostatically coupled. The effect
of a slight mismatch introduced in the molecules from nominally identical
quantum wells, or from changes in the inner radius of the constituent rings,
induces localization by offsetting the energy levels in the quantum rings. This
plays a crucial role in the appearance of the addition spectra as a function of
coupling strength particularly in the weak coupling limit.Comment: 18 pages, 8 figures, submitted to Physical Review
The on-top pair-correlation density in the homogeneous electron liquid
The ladder theory, in which the Bethe-Goldstone equation for the effective
potential between two scattering particles plays a central role, is well known
for its satisfactory description of the short-range correlations in the
homogeneous electron liquid. By solving exactly the Bethe-Goldstone equation in
the limit of large transfer momentum between two scattering particles, we
obtain accurate results for the on-top pair-correlation density , in both
three dimensions and two dimensions. Furthermore, we prove, in general, the
ladder theory satisfies the cusp condition for the pair-correlation density
at zero distance .Comment: 8 pages, 4 figure
Virtualization for cost-effective teaching of assembly language
A virtual system that emulates an ARM-based processor machine has been created to replace a traditional hardware-based system for teaching assembly language. The proposed virtual system integrates, in a single environment, all the development tools necessary to deliver introductory or advanced courses on modern assembly language programming. The virtual system runs a Linux operating system in either a graphical or console mode on a Windows or Linux host machine. No software licenses or extra hardware are required to use the virtual system, thus students are free to carry their own ARM emulator with them on a USB memory stick. Institutions adopting this, or a similar virtual system, can also benefit by reducing capital investment in hardware-based development kits and enable distance learning courses
Tractable non-local correlation density functionals for flat surfaces and slabs
A systematic approach for the construction of a density functional for van
der Waals interactions that also accounts for saturation effects is described,
i.e. one that is applicable at short distances. A very efficient method to
calculate the resulting expressions in the case of flat surfaces, a method
leading to an order reduction in computational complexity, is presented.
Results for the interaction of two parallel jellium slabs are shown to agree
with those of a recent RPA calculation (J.F. Dobson and J. Wang, Phys. Rev.
Lett. 82, 2123 1999). The method is easy to use; its input consists of the
electron density of the system, and we show that it can be successfully
approximated by the electron densities of the interacting fragments. Results
for the surface correlation energy of jellium compare very well with those of
other studies. The correlation-interaction energy between two parallel jellia
is calculated for all separations d, and substantial saturation effects are
predicted.Comment: 10 pages, 6 figure
Hydrodynamic theory of an electron gas
The generalised hydrodynamic theory of an electron gas, which does not rely
on an assumption of a local equilibrium, is derived as the long-wave limit of a
kinetic equation. Apart from the common hydrodynamics variables the theory
includes the tensor fields of the higher moments of the distribution function.
In contrast to the Bloch hydrodynamics, the theory leads to the correct plasmon
dispersion and in the low frequency limit recovers the Navies-Stocks
hydrodynamics. The linear approximation to the generalised hydrodynamics is
closely related to the theory of highly viscous fluids.Comment: 4 pages, revte
A Spitzer Space Telescope study of SN 2002hh: an infrared echo from a Type IIP supernova
We present late-time (590-994 d) mid-IR photometry of the normal, but
highly-reddened Type IIP supernova SN 2002hh. Bright, cool, slowly-fading
emission is detected from the direction of the supernova. Most of this flux
appears not to be driven by the supernova event but instead probably originates
in a cool, obscured star-formation region or molecular cloud along the
line-of-sight. We also show, however, that the declining component of the flux
is consistent with an SN-powered IR echo from a dusty progenitor CSM. Mid-IR
emission could also be coming from newly-condensed dust and/or an ejecta/CSM
impact but their contributions are likely to be small. For the case of a CSM-IR
echo, we infer a dust mass of as little as 0.036 M(solar) with a corresponding
CSM mass of 3.6(0.01/r(dg))M(solar) where r(dg) is the dust-to-gas mass ratio.
Such a CSM would have resulted from episodic mass loss whose rate declined
significantly about 28,000 years ago. Alternatively, an IR echo from a
surrounding, dense, dusty molecular cloud might also have been responsible for
the fading component. Either way, this is the first time that an IR echo has
been clearly identified in a Type IIP supernova. We find no evidence for or
against the proposal that Type IIP supernovae produce large amounts of dust via
grain condensation in the ejecta. However, within the CSM-IR echo scenario, the
mass of dust derived implies that the progenitors of the most common of
core-collapse supernovae may make an important contribution to the universal
dust content.Comment: 41 pages, 11 figures, 4 tables, accepted for publication in
Astrophysical Journal (References corrected
Associations between Vitamin D Status and Type 2 Diabetes Measures among Inuit in Greenland May Be Affected by Other Factors
OBJECTIVE:Epidemiological studies have provided evidence of an association between vitamin D insufficiency and type 2 diabetes. Vitamin D levels have decreased among Inuit in Greenland, and type 2 diabetes is increasing. We hypothesized that the decline in vitamin D could have contributed to the increase in type 2 diabetes, and therefore investigated associations between serum 25(OH)D3 as a measure of vitamin D status and glucose homeostasis and glucose intolerance in an adult Inuit population. METHODS:2877 Inuit (≥18 years) randomly selected for participation in the Inuit Health in Transition study were included. Fasting- and 2hour plasma glucose and insulin, C-peptide and HbA1c were measured, and associations with serum 25(OH)D3 were analysed using linear and logistic regression. A subsample of 330 individuals who also donated a blood sample in 1987, were furthermore included. RESULTS:After adjustment, increasing serum 25(OH)D3 (per 10 nmol/L) was associated with higher fasting plasma glucose (0.02 mmol/L, p = 0.004), 2hour plasma glucose (0.05 nmol/L, p = 0.002) and HbA1c (0.39%, p<0.001), and with lower beta-cell function (-1.00 mmol/L, p<0.001). Serum 25(OH)D3 was positively associated with impaired fasting glycaemia (OR: 1.08, p = 0.001), but not with IGT or type 2 diabetes. CONCLUSIONS:Our results did not support an association between low vitamin D levels and risk of type 2 diabetes. Instead, we found weak positive associations between vitamin D levels and fasting- and 2hour plasma glucose levels, HbA1c and impaired fasting glycaemia, and a negative association with beta-cell function, underlining the need for determination of the causal relationship
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