A Neo-Institutional Assessment of Cooperative Evolution: Comparing the Australian Wheat Board and the Fonterra Dairy Group

Agribusiness,

Density Matrix Renormalization Group in the Heisenberg Picture

In some cases the state of a quantum system with a large number of subsystems can be approximated efficiently by the density matrix renormalization group, which makes use of redundancies in the description of the state. Here we show that the achievable efficiency can be much better when performing density matrix renormalization group calculations in the Heisenberg picture, as only the observable of interest but not the entire state is considered. In some non-trivial cases, this approach can even be exact for finite bond dimensions.Comment: version to appear in PRL, acronyms in title and abstract expanded, new improved numerical example

Combining Biophysical and Price Simulations to Assess the Economics of Long-Term Crop Rotations

Biophysical simulation models (e.g. APSIM) using historical rainfall data are increasingly being used to provide yield and other data on crop rotations in various regions of Australia. However, to analyse the economics of these rotations it is desirable to incorporate the other main driver of profitability, price variation. Because the context was that APSIM was being used to simulate an existing trial site being monitored by a farmer group Gross Margin output was considered most appropriate. Long-run rotational gross margins were calculated for the various rotations with yields (and other physical outputs) derived from APSIM simulations over a period of 100+ years and prices simulated in @Risk based on subjective triangular price distributions elicited from farmers in the group. Rotations included chickpeas, cotton, lucerne, sorghum, wheat and different lengths of fallow. Output presented to the farmers included mean annual gross margins and distributions of gross margins presented as probability distributions, cumulative probability distributions and box and whisker plots. Cotton rotations were the most profitable but had greater declines in soil fertility and greater drainage out of the root zone.Crop Production/Industries,

Combining biophysical and price simulations to assess the economics of long-term crop rotations

Long-run rotational gross margins were calculated with yields derived from biophysical simulations in APSIM over a period of 100+ years and prices simulated in @Risk based on subjective triangular price distributions elicited from the Jimbour Plains farmer group. Rotations included chickpeas, cotton, lucerne, sorghum, wheat and different lengths of fallow. Output presented to the farmers included mean annual GMs and distributions of GMs with box and whisker plots found to be suitable. Mean-standard deviation and first and second-degree stochastic dominance efficiency measures were also calculated. Including lucerne in the rotations improved some sustainability indicators but reduced profitability.Crop Production/Industries, Farm Management,

Transport enhancement from incoherent coupling between one-dimensional quantum conductors

We study the non-equilibrium transport properties of a highly anisotropic two-dimensional lattice of spin-1/2 particles governed by a Heisenberg XXZ Hamiltonian. The anisotropy of the lattice allows us to approximate the system at finite temperature as an array of incoherently coupled one-dimensional chains. We show that in the regime of strong intrachain interactions, the weak interchain coupling considerably boosts spin transport in the driven system. Interestingly, we show that this enhancement increases with the length of the chains, which is related to superdiffusive spin transport. We describe the mechanism behind this effect, compare it to a similar phenomenon in single chains induced by dephasing, and explain why the former is much stronger

A comparison of value-added models for school accountability

School accountability systems increasingly hold schools to account for their performances using value-added models purporting to measure the effects of schools on student learning. The most common approach is to fit a linear regression of student current achievement on student prior achievement, where the school effects are the school means of the predicted residuals. In the literature, further adjustments are usually made for student sociodemographics and sometimes school composition and 'non-malleable' characteristics. However, accountability systems typically make fewer adjustments: for transparency to end users, because data is unavailable or of insufficient quality, or for ideological reasons. There is therefore considerable interest in understanding the extent to which simpler models give similar school effects to more theoretically justified but complex models. We explore these issues via a case study and empirical analysis of England's 'Progress 8' secondary school accountability system

Phase-dependent exciton transport and energy harvesting from thermal environments

Non-Markovian effects in the evolution of open quantum systems have recently attracted widespread interest, particularly in the context of assessing the efficiency of energy and charge transfer in nanoscale biomolecular networks and quantum technologies. With the aid of many-body simulation methods, we uncover and analyse an ultrafast environmental process that causes energy relaxation in the reduced system to depend explicitly on the phase relation of the initial state preparation. Remarkably, for particular phases and system parameters, the net energy flow is uphill, transiently violating the principle of detailed balance, and implying that energy is spontaneously taken up from the environment. A theoretical analysis reveals that non-secular contributions, significant only within the environmental correlation time, underlie this effect. This suggests that environmental energy harvesting will be observable across a wide range of coupled quantum systems.Comment: 5 + 4 pages, 3 + 2 figures. Comments welcom