565 research outputs found
Fisheries Management under Irreversible Investment: Does Stochasticity Matter?
We present a continuous, nonlinear, stochastic and dynamic model for capital investment in the exploitation of a renewable resource. Both the resource stock and capital stock are treated as state variables. The resource owner controls fishing effort and the investment rate in an optimal way. Biological stock growth and capital depreciation rate are stochastic in the model. We find that the stochastic resource should be managed conservatively. The capital utilization rate is found to be a non-increasing function of stochasticity. Investment could be either higher or lower depending on the interaction between the capital and the resource stocks. In general a stochastic capital depreciation rate has only weak influence on optimal management. In the long run, the steady state harvest for a stochastic resource becomes lower than the deterministic level.Physical capital; irreversible investment; stochastic growth; long-term sustainable optimal
Low chilling trait of Vitis ficifolia var. Ganebu and its introduction into Vitis vinifera by cross breeding
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Magnetization-driven Lifshitz transition and charge-spin coupling in the kagome metal YMn6Sn6
The Fermi surface (FS) is essential for understanding the properties of metals. It can change under both conventional symmetry-breaking phase transitions and Lifshitz transitions (LTs), where the FS, but not the crystal symmetry, changes abruptly. Magnetic phase transitions involving uniformly rotating spin textures are conventional in nature, requiring strong spin-orbit coupling (SOC) to influence the FS topology and generate measurable properties. LTs driven by a continuously varying magnetization are rarely discussed. Here we present two such manifestations in the magnetotransport of the kagome magnet YMn6Sn6: one caused by changes in the magnetic structure and another by a magnetization-driven LT. The former yields a 10% magnetoresistance enhancement without a strong SOC, while the latter a 45% reduction in the resistivity. These phenomena offer a unique view into the interplay of magnetism and electronic topology, and for understanding the rare-earth counterparts, such as TbMn6Sn6, recently shown to harbor correlated topological physics
Microscopic mechanism of low thermal conductivity in lead-telluride
The microscopic physics behind low lattice thermal conductivity of single
crystal rocksalt lead telluride (PbTe) is investigated. Mode-dependent phonon
(normal and umklapp) scattering rates and their impact on thermal conductivity
were quantified by the first-principles-based anharmonic lattice dynamics
calculations that accurately reproduce thermal conductivity in a wide
temperature range. The low thermal conductivity of PbTe is attributed to the
scattering of longitudinal acoustic phonons by transverse optical phonons with
large anharmonicity, and small group velocity of the soft transverse acoustic
phonons. This results in enhancing the relative contribution of optical
phonons, which are usually minor heat carrier in bulk materials.Comment: 18 pages, 4 figures, accepted for publication in Phys. Rev.
Optical conductivity and vibrational spectra of the narrow-gap semiconductor FeGa
Intermetallic narrow-gap semiconductors have been intensively explored due to
their large thermoelectric power at low temperatures and a possible role of
strong electronic correlations in their unusual thermodynamic and transport
properties. Here we study the optical spectra and vibrational properties of
single crystal. The optical conductivity indicates that
has a direct band gap of \,eV, consistent with
density functional theory (DFT) calculations. Most importantly, we find a
substantial spectral weight also below 0.4~eV, which is the energy of the
indirect (charge) gap found in resistivity measurements and ab initio
calculations. We find that the spectral weight below the gap decreases with
increasing temperature, which indicates that it originates from the impurity
states and not from the electronic correlations. Interestingly, we did not find
any signatures of the impurity states in vibrational spectra. The infrared and
Raman vibrational lines are narrow and weakly temperature dependent. The
vibrational frequencies are in excellent agreement with our DFT calculations,
implying a modest role of electronic correlations. Narrow M\" ossbauer spectral
lines also indicate high crystallinity of the sample
Nonlinear thermoelectric response of quantum dots: renormalized dual fermions out of equilibrium
The thermoelectric transport properties of nanostructured devices continue to
attract attention from theorists and experimentalist alike as the spatial
confinement allows for a controlled approach to transport properties of
correlated matter. Most of the existing work, however, focuses on
thermoelectric transport in the linear regime despite the fact that the
nonlinear conductance of correlated quantum dots has been studied in some
detail throughout the last decade. Here, we review our recent work on the
effect of particle-hole asymmetry on the nonlinear transport properties in the
vicinity of the strong coupling limit of Kondo-correlated quantum dots and
extend the underlying method, a renormalized superperturbation theory on the
Keldysh contour, to the thermal conductance in the nonlinear regime. We
determine the charge, energy, and heat current through the nanostructure and
study the nonlinear transport coefficients, the entropy production, and the
fate of the Wiedemann-Franz law in the non-thermal steady-state. Our approach
is based on a renormalized perturbation theory in terms of dual fermions around
the particle-hole symmetric strong-coupling limit.Comment: chapter contributed to 'New Materials for Thermoelectric
Applications: Theory and Experiment' Springer Series: NATO Science for Peace
and Security Series - B: Physics and Biophysics, Veljko Zlatic (Editor), Alex
Hewson (Editor). ISBN: 978-9400749863 (2012
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