Signatures of Type III Solar Radio Bursts from Nanoflares: Modeling

There is a wide consensus that the ubiquitous presence of magnetic reconnection events and the associated impulsive heating (nanoflares) are strong candidates for solving the solar coronal heating problem. Whether nanoflares accelerate particles to high energies like full-sized flares is unknown. We investigate this question by studying the type III radio bursts that the nanoflares may produce on closed loops. The characteristic frequency drifts that type III bursts exhibit can be detected using a novel application of the time-lag technique developed by Viall & Klimchuk (2012) even when there are multiple overlapping events. We present a simple numerical model that simulates the expected radio emission from nanoflares in an active region, which we use to test and calibrate the technique. We find that in the case of closed loops the frequency spectrum of type III bursts is expected to be extremely steep such that significant emission is produced at a given frequency only for a rather narrow range of loop lengths. We also find that the signature of bursts in the time-lag signal diminishes as: (1) the variety of participating loops within that range increases; (2) the occurrence rate of bursts increases; (3) the duration of bursts increases; and (4) the brightness of bursts decreases relative to noise. In addition, our model suggests a possible origin of type I bursts as a natural consequence of type III emission in a closed-loop geometry.

Limitations of the Double-Bounce Power Estimation in Model-Based Polarimetric Decompositions of Vegetated Terrain

In this research, we discuss the possibility of incorrect prediction of the double-bounce scattering (DBS) power in model-based decomposition (MBD) algorithms applied to polarimetric synthetic aperture radar (SAR) images of vegetated terrain. In most of the MBD schemes, the estimation of the DBS component is based on the assumption that the co-polarized phase difference (CPD) of the DBS is similar to those of backscattering from a pair of orthogonal planer conducting surfaces. However, for dielectric surfaces such as soil or vegetation trunks, this assumption is only valid within a certain range of radar incidence angle, which is dictated by the Brewster angles of the dielectric surfaces. If the incidence angle is out of this range, the DBS contribution is incorrectly estimated as the surface scattering. Moreover, because the Brewster angle is a function of surface permittivity, the angular range depends on moisture contents of the surfaces; therefore, correctness of the MBD results also depend on the surface moisture contents. To demonstrate this problem, we provide a simple numerical model of vegetated terrain, and we validate theoretical results by a series of controlled experiments carried out in an anechoic chamber with a simplified vegetation model.

On the Self-Shielding in the Unresolved Resonance Range

Resonance behavior is a feature of nuclear reaction cross sections. Resonance density increases with increasing incident particle energy and they begin to overlap, until they can no longer be resolved experimentally, but they still contribute to self-shielding and must be accounted for. This is usually done by representing them with statistical average parameters according to methods and approximations described in standard text-books. Self-shielding factors are commonly used in deterministic transport codes, while statistical Monte Carlo codes use probability tables or multi-band parameters. An exercise was conducted at the International Atomic Energy Agency (IAEA) to validate codes and methods for generating data that account for self-shielding in deterministic and Monte Carlo codes. A simple numerical model problem was defined, considering a sphere of 1 m radius with a 20 MeV isotropic neutron source at the center. The chosen material for testing was 139La from the ENDF/B-VIII.0 library, which clearly showed anomalous behavior.

OPTIMISATION OF MONTE CARLO BURNUP SIMULATIONS

We show here that computing efficiency of Monte Carlo burnup simulations depends on chosen values of certain free parameters, such as the length of the time steps and the number of neutron histories simulated at each Monte Carlo criticality run. The efficiency can thus be improved by optimising these parameters. We have set up a simple numerical model that made it possible for us to test a large number of combinations of the free parameters, and suggest a way to optimise their selection.

Games Theory and Real Options: A model to asses strategies, agreements and penalties

In competitive environments, the design and election of strategies demand to consider three potential sources of uncertainty: risks derived from self-actions, risks emerged from states of nature and risks derived from competitors´ decisions. For that, a numerical model that considers the competitors´ actions is required, for value strategies, join venture design and penalty quantification. The paper proposes a simple numerical model of Game Theory and Real Options with multiples source of risk. The first part exposes the mathematical basis of the model. Its functioning is illustrated with the cases valuation related to strategies without collaborative agreement. Next, the cooperation strategy and default monetary penalties are valued. Finally, the main conclusions are exposed.

SALINITY RESPONSE TO ENVIRONMENTAL FLOW RELEASE IN ESTUARIES

The Snowy River in southern Australia has been impacted by flow diversion since the construction of a dam in the upper catchment, constructed between 1955 and 1967. As part of a monitoring program the effects of two flow releases were studied in 2010 and 2011. The estuarine component of the monitoring and the estuarine modelling phase of the Snowy River Increased Flows Program has been presented. The impact on the estuarine salinity distribution for the selected flow releases is reported and a subsequent modelling exercise outlined. A simple numerical model has been used to simulate about 100 events in a mature barrier estuary, from which a sequence of response types has been identified. The occurrence of each response type has been related to the duration, inflow volume and peak flow rate of the inflow event and to relevant parameters of the estuary. It has been found that the salinity changes may be classified in terms of a dimensionless "estuary flushing parameter" E, which represents the ratio of the direct flushing by the river inflow to the tidal exchange.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/76fefltUCro

A Simple Numerical Model for Studying Cloud Formation Process Inthe Tropics : Heated and Cooled Surface Experiments

A simple numerical model for demonstrating local cloud formation processes in the tropics is beingdeveloped. The model equations are derived from the fundamental system of partial differential equations ofcomputational fluid dynamics and the deep convection approximation is used to eliminate sound waves. Themodel domain is two-dimensional with length100 kilometers and height 17.5 kilometers. A non-uniform grid isused with the thinnest layer (100 meters) at the earth's surface and thickest layer (1,300 meters) at the top of thetroposphere. The horizontal cell's width one kilometer. The Arakawa-C grid is used for the leapfrog method andforward Euler method. Experiments to study the effects of heating and cooling at the surface and the deepconvection approximation in moist air are discussed. The deep convection approximation was found to beunsuitable for a model. The model without the deep convection approximation gives processes expected in thereal atmosphere.

Chaos in a simple model of a delta network

The flux partitioning in delta networks controls how deltas build land and generate stratigraphy. Here, we study flux-partitioning dynamics in a delta network using a simple numerical model consisting of two orders of bifurcations. Previous work on single bifurcations has shown periodic behavior arising due to the interplay between channel deepening and downstream deposition. We find that coupling between upstream and downstream bifurcations can lead to chaos; despite its simplicity, our model generates surprisingly complex aperiodic yet bounded dynamics. Our model exhibits sensitive dependence on initial conditions, the hallmark signature of chaos, implying long-term unpredictability of delta networks. However, estimates of the predictability horizon suggest substantial room for improvement in delta-network modeling before fundamental limits on predictability are encountered. We also observe periodic windows, implying that a change in forcing (e.g., due to climate change) could cause a delta to switch from predictable to unpredictable or vice versa. We test our model by using it to generate stratigraphy; converting the temporal Lyapunov exponent to vertical distance using the mean sedimentation rate, we observe qualitatively realistic patterns such as upwards fining and scale-dependent compensation statistics, consistent with ancient and experimental systems. We suggest that chaotic behavior may be common in geomorphic systems and that it implies fundamental bounds on their predictability. We conclude that while delta “weather” (precise configuration) is unpredictable in the long-term, delta “climate” (statistical behavior) is predictable.

Estimation of Coal and Rock Mechanical Properties for Numerical Modelling of Longwall Extraction

Reliable estimation of coal and rock mechanical properties at field scale is a prerequisite for numerical modelling of rock behaviours associated with longwall extraction. This paper describes a systematic approach from data collection, laboratory testing to rock mass properties derivation for simulation of longwall extraction, taking two longwall panels at Quang Ninh coalfield in Vietnam for example. The mechanical properties are verified through comparison with published data of the field, indicating close agreements. A simple numerical model is further developed to demonstrate the proper use of the obtained data. The simulation suggests that the ratio of model length to excavation length should be in the range of 2.5–5; uniaxial compressive strength, deformation modulus and tensile strength can be reduced by a factor of 5.0, 2.13 and 2.0, respectively; and a calibration and validation process must be performed to match in-situ longwall’s behaviours. The approach can be applied for derivation of reliable rock mass properties for numerical simulation of underground excavations.