1,889 research outputs found
First steps of a nucleation theory in disordered systems
We devise a field theoretical formalism for a microscopic theory of
nucleation processes and phase coexistence in finite dimensional glassy
systems. We study disordered -spin models with large but finite range of
interaction. We work in the framework of glassy effective potential theory
which in mean-field is a non-convex, two minima function of the overlap. We
will associate metastability and phase coexistence with the existence of space
inhomogeneous solution of suitable field equations and we will study the
simplest of such solutions.Comment: 31 pages, 4 figures. Content revised, typos correcte
Revisiting the definition of field capacity as a functional parameter in a layered agronomic soil profile beneath irrigated maize
The soil water content at the condition of field capacity (θFC) is a key parameter in irrigation scheduling and has been suggested to be determined by running a synthetic drainage experiment until the flux rate (q) at the bottom of the soil profile achieves a predefined negligible value (qFC). We question the impact of qFC on the assessment of field capacity. Moreover, calculating θFC as the integral mean of the water content profile when q is equal to qFC is strictly valid only for uniform soil profiles. By contrast, this practice is ambiguous and biased for stratified soil profiles due to the soil water content discontinuity at the layer interfaces. In this study, the concept of field capacity was revisited and adapted to practical agronomic heuristics. By resorting to the assessment of root-zone water storage capacity (W), we envision field capacity as a functional hydraulic parameter derived from synthetic irrigation scheduling scenarios to minimize drought stress, drainage, and nitrate leachate below the root zone. A functional analysis was carried out on a 135-cm-thick layered soil profile beneath maize in eastern Nebraska. Onfarm irrigation scheduling applications and agricultural practices were recorded for 20 years (2001–2020) at a daily time step. Hydrus-1D was calibrated and validated with direct measurements of the soil water retention curve and soil water content data, respectively, in each soil layer. A set of functional field capacity values was derived from 24 irrigation scheduling scenarios, and the optimal water storage capacity at field capacity (WFC) was approximately 50 cm (corresponding to about 80% saturation in the soil profile). An average irrigation amount of 217.5 mm distributed over 21 events was obtained by using optimal irrigation scheduling, which was initiated when the matric pressure head took on a value of - 700 cm and the irrigation rate was set at 1.0 cm d-1. This irrigation practice ensured water storage at approximately the same level (ideally at WFC) by sustaining only evapotranspiration fluxes in the uppermost portion of the root zone and by limiting excessive drainage. This protocol can be transferred to other agricultural fields
Design and Performance of Odyssey IV: A Deep Ocean Hover-Capable AUV
The Odyssey IV class AUV was designed to fill the evolving needs of research and industry for a deep rated (6000 meter) vehicle, which is capable of both efficient cruising and precise hovering. This AUV is powerful enough to reject currents typical in the open ocean environment and yet small enough to be deployed from a small fishing boat. The thruster layout, two vectored side thrusters and two fixed cross-body thrusters, allow for 4-DOF control, which gives this vehicle precision and flexibility not possible in previous Odyssey class AUVs. An adaptable payload area allows the mounting of sensors, actuators, or other hardware suitable to a particular mission. The dynamic control layer of our behavior-based MOOS software was completely redesigned to take advantage of the capabilities of this vehicle. This is also the first platform to utilize new graphical controls and database-driven logging which increase operator efficiency and make the vehicle safer to operate. Odyssey IV's intended uses include survey and inspection of cold water corals, fisheries, archaeological sites, and subsea infrastructure. It will also serve as a research platform for computer vision-based servoing and acoustic supervisory control. This paper will document the design considerations and implementation of the Odyssey IV, as well as report on a series of field tests culminating in its first scientific deployment at Georges Bank, observing and mapping the invasive tunicate Didemnum.United States. National Oceanic and Atmospheric Administration (Grant NA16RG2255); United States. National Oceanic and Atmospheric Administration (Grant NA06AOR4170019
Real space Renormalization Group analysis of a non-mean field spin-glass
A real space Renormalization Group approach is presented for a non-mean field
spin-glass. This approach has been conceived in the effort to develop an
alternative method to the Renormalization Group approaches based on the replica
method. Indeed, non-perturbative effects in the latter are quite generally out
of control, in such a way that these approaches are non-predictive. On the
contrary, we show that the real space method developed in this work yields
precise predictions for the critical behavior and exponents of the model
Measuring equilibrium properties in aging systems
We corroborate the idea of a close connection between replica symmetry
breaking and aging in the linear response function for a large class of
finite-dimensional systems with short-range interactions. In these system,
characterized by a continuity condition with respect to weak random
perturbations of the Hamiltonian, the ``fluctuation dissipation ratio'' in
off-equilibrium dynamics should be equal to the static cumulative distribution
function of the overlaps. This allows for an experimental measurement of the
equilibrium order parameter function.Comment: 5 pages, LaTeX. The paper has been completely rewritten and shortene
Langevin dynamics of the Lebowitz-Percus model
We revisit the hard-spheres lattice gas model in the spherical approximation
proposed by Lebowitz and Percus (J. L. Lebowitz, J. K. Percus, Phys. Rev.{\
144} (1966) 251). Although no disorder is present in the model, we find that
the short-range dynamical restrictions in the model induce glassy behavior. We
examine the off-equilibrium Langevin dynamics of this model and study the
relaxation of the density as well as the correlation, response and overlap
two-time functions. We find that the relaxation proceeds in two steps as well
as absence of anomaly in the response function. By studying the violation of
the fluctuation-dissipation ratio we conclude that the glassy scenario of this
model corresponds to the dynamics of domain growth in phase ordering kinetics.Comment: 21 pages, RevTeX, 14 PS figure
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