614 research outputs found
Morphometric study of Acipenser nuccurii (Bonaparte, 1836) in fish farm individuals
The main objective of this study was to analyse differences and
similarities in morphometric characteristics among specimens of
the same year class of Acipenser naccarii (Bonaparte, 1836),
comparing fish raised either in Italy or Spain. All specimens were
F1 of captive broodstock in Italy.
Fifteen biometric variables were measured, and three derived
indices were calculated, on 30 individuals of 3+ year class from
Lombardy (Italy) and 90 individuals of I+, 2+ and 3+ year class
from Riofrio (Granada, Spain). A stepwise discriminate analysis
(SDA) was carried out, and the results were contrasted using a
non-hierarchical cluster analysis. The two groups proved to be
similar, so a principal component analysis and a simple
regression analysis were performed on all individuals, taking total
length (TI) as the independent variable and all the biometric
variables as dependent.
The study revealed that although the Soljan index (i.e. ratio of
mouth width to snout length) is related to TI, and is a valid
taxonomic characteristic, the CA index (i.e. relative position of
the barbels) and FB index (i.e. ratio of snout length to width) are also valid characteristics for individuals longer than 57 cm, being independent of TI
On quantitative analysis of interband recombination dynamics: Theory and application to bulk ZnO
The issue of the quantitative analysis of time-resolved photoluminescence
experiments is addressed by developing and describing two approaches for
determination of unimolecular lifetime, bimolecular recombination coefficient,
and equilibrium free-carrier concentration, based on a quite general
second-order expression of the electron-hole recombination rate. Application to
the case of band-edge emission of ZnO single crystals is reported, evidencing
the signature of sub-nanosecond second-order recombination dynamics for optical
transitions close to the interband excitation edge. The resulting findings are
in good agreement with the model prediction and further confirm the presence,
formerly evidenced in literature by non-optical methods, of near-surface
conductive layers in ZnO crystals with sheet charge densities of about
3{\div}5*10^13 cm^-2Comment: 4 pages, 5 figure
Saldatura e trattamento termico laser di acciai inossidabili bifasici
Nonostante la loro continua diffusione, la saldatura laser degli acciai inossidabili bifasici rimane un processo molto critico, a causa del decadimento delle proprietà meccaniche e di resistenza alla corrosione che si verifica nel giunto. Presentiamo qui un procedimento innovativo di trattamento laser localizzato in grado di ripristinare le proprietà meccaniche e la resistenza alla corrosione del giunto inossidabile bifasico saldato laser del tipo SAF 2205
Transfer of passive immunity in dairy calves: The effectiveness of providing a supplementary colostrum meal in addition to nursing from the dam
Effect of Doublon-Holon Binding on Mott transition---Variational Monte Carlo Study of Two-Dimensional Bose Hubbard Models
To understand the mechanism of Mott transitions in case of no magnetic
influence, superfluid-insulator (Mott) transitions in the S=0 Bose Hubbard
model at unit filling are studied on the square and triangular lattices, using
a variational Monte Carlo method. In trial many-body wave functions, we
introduce various types of attractive correlation factors between a
doubly-occupied site (doublon, D) and an empty site (holon, H), which play a
central role for Mott transitions, in addition to the onsite repulsive
(Gutzwiller) factor. By optimizing distance-dependent parameters, we study
various properties of this type of wave functions. With a hint from the Mott
transition arising in a completely D-H bound state, we propose an improved
picture of Mott transitions, by introducing two characteristic length scales,
the D-H binding length and the minimum D-D exclusion length
. Generally, a Mott transition occurs when becomes
comparable to . In the conductive (superfluid) state, domains of
D-H pairs overlap with each other (); thereby D and
H can propagate independently as density carriers by successively exchanging
the partners. In contrast, intersite repulsive Jastrow (D-D and H-H) factors
have little importance for the Mott transition.Comment: 16 pages, 22 figures, submitted to J. Phys. Soc. Jp
Long-term re-evaluation of primary aldosteronism after medical treatment reveals high proportion of normal mineralocorticoid secretion.
Effects of Long-Range Correlations on Nonmagnetic Mott Transitions in Hubbard model on Square Lattice
The mechanism of Mott transition in the Hubbard model on the square lattice
is studied without explicit introduction of magnetic and superconducting
correlations, using a variational Monte Carlo method. In the trial wave
functions, we consider various types of binding factors between a
doubly-occupied site (doublon, D) and an empty site (holon, H), like a
long-range type as well as a conventional nearest-neighbor type, and add
independent long-range D-D (H-H) factors. It is found that a wide choice of D-H
binding factor leads to Mott transitions at critical values near the band
width. We renew the D-H binding picture of Mott transitions by introducing two
characteristic length scales, the D-H binding length l_{DH} and the minimum D-D
distance l_{DD}, which we appropriately estimate. A Mott transition takes place
at l_{DH}=l_{DD}. In the metallic regime (l_{DH}>l_{DD}), the domains of D-H
pairs overlap with one another, thereby doublons and holons can move
independently by exchanging the partners one after another. In contrast, the
D-D factors give only a minor contribution to the Mott transition.Comment: 13 pages, 18 figures, submitted to J. Phys. Soc. Jp
Mott Transitions and d-wave Superconductivity in Half-Filled-Band Hubbard Model on Square Lattice with Geometric Frustration
Mechanisms of Mott transitions and dx2-y2-wave superconductivity (SC) are
studied in the half-filled-band Hubbard model on square lattices with a
diagonal hopping term (t'), using an optimization (or correlated) variational
Monte Carlo method. In the trial wave functions, a doublon-holon binding effect
is introduced in addition to the onsite Gutzwiller projection. We mainly treat
a d-wave singlet state and a projected Fermi sea. In both wave functions,
first-order Mott transitions without direct relevance to magnetic orders take
place at U=Uc approximately of the bandwidth for arbitrary t'/t. These
transitions originate in the binding or unbinding of a doublon to a holon.
d-wave SC appears in a narrow range immediately below Uc. The robust d-wave
superconducting correlation are necessarily accompanied by enhanced
antiferromagnetic correlation; the strength of SC becomes weak, as t'/t
increases.Comment: 18 pages, 30 figure
Current Response in Extended Systems as a Geometric Phase: Application to Variational Wavefunctions
The linear response theory for current is investigated in a variational
context. Expressions are derived for the Drude and superfluid weights for
general variational wavefunctions. The expression for the Drude weight
highlights the difficulty in its calculation since it depends on the exact
energy eigenvalues which are usually not available in practice. While the Drude
weight is not available in a simple form, the linear current response is shown
to be expressible in terms of a geometric phase, or alternatively in terms of
the expectation value of the total position shift operator. The contribution of
the geometric phase to the current response is then analyzed for some commonly
used projected variational wavefunctions (Baeriswyl, Gutzwiller, and combined).
It is demonstrated that this contribution is independent of the projectors
themselves and is determined by the wavefunctions onto which the projectors are
applied.Comment: 13 pages, 1 tabl
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