A "fast growth" method of computing free energy differences

Let Delta F be the free energy difference between two equilibrium states of a system. An established method of numerically computing Delta F involves a single, long ``switching simulation'', during which the system is driven reversibly from one state to the other (slow growth, or adiabatic switching). Here we study a method of obtaining the same result from numerous independent, irreversible simulations of much shorter duration (fast growth). We illustrate the fast growth method, computing the excess chemical potential of a Lennard-Jones fluid as a test case, and we examine the performance of fast growth as a practical computational tool.Comment: 17 pages + 4 figures, accepted for publication in J.Chem.Phy

Book Review: The Tallgrass Restoration Handbook: For Prairies, Savannas, and Woodlands

The Tallgrass Restoration Handbook: For Prairies, Savannas, and Woodlands. Stephen Packard and Cornelia F. Mutel, eds. 1997. Society for Ecological Restoration. 463 pages. ISBN 1-55963-319-0 hdbd. The publication of the Tallgrass Restoration Handbook is an enormous step in the right direction for people who have already learned to appreciate and admire the beauty and utility of prairies and who now want to roll up their sleeves and begin the restoration of their own bit of tallgrass prairie. All of this volume excluding the first two introductory chapters (Part I) is dedicated to the practical aspects of prairie restoration

Model-Based Control Using Model and Mechanization Fusion Techniques for Image-Aided Navigation

Unmanned aerial vehicles are no longer used for just reconnaissance. Current requirements call for smaller autonomous vehicles that replace the human in high-risk activities. Many times these activities are performed in GPS-degraded environments. Without GPS providing today\u27s most accurate navigation solution, autonomous navigation in tight areas is more difficult. Today, image-aided navigation is used and other methods are explored to more accurately navigate in such areas (e.g., indoors). This thesis explores the use of inertial measurements and navigation solution updates using cameras with a model-based Linear Quadratic Gaussian controller. To demonstrate the methods behind this research, the controller will provide inputs to a micro-sized helicopter that allows the vehicle to maintain hover. A new method for obtaining a more accurate navigation solution was devised, originating from the following basic setup. To begin, a nonlinear system model was identified for a micro-sized, commercial, off-the-shelf helicopter. This model was verified, then linearized about the hover condition to construct a Linear Quadratic Regulator (LQR). The state error estimates, provided by an Unscented Kalman Filter using simulated image measurement updates, are used to update the navigation solution provided by inertial measurement sensors using strapdown mechanization equations. The navigation solution is used with a reference signal to determine the position and heading error. This error, along with other states, is fed to the LQR, which controls the helicopter. Research revealed that by combining the navigation solution from the INS mechanization block with a model-based navigation solution, and combining the INS error model and system model during the time propagation in the UKF, the navigation solution error decreases by 20%. The equations used for this modification stem from state and covariance combination methods utilized in the Federated Kalman Filter

Directional solidification of flake and nodular cast iron during KC-135 low-g maneuvers

Alloys solidified in a low-gravity environment can, due to the elimination of sedimentation and convection, form unique and often desirable microstructures. One method of studying the effects of low-gravity (low-g) on alloy solidification was the use of the NASA KC-135 aircraft flying repetitive low-g maneuvers. Each maneuver gives from 20 to 30 seconds of low-g which is between about 0.1 and 0.001 gravity. A directional solidification furnace was used to study the behavior of off eutectic composition case irons in a low-g environment. The solidification interface of hypereutectic flake and spheroidal graphite case irons was slowly advanced through a rod sample, 5 mm in diameter. Controlled solidification was continued through a number of aircraft parabolas. The known solidification rate of the sample was then correlated with accelerometer data to determine the gravity level during solidification for any location of the sample. The thermal gradient and solidification rate were controlled independently. Samples run on the KC-135 aircraft exhibited bands of coarser graphite or of larger nodules usually corresponding to the regions solidified under low-g. Samples containing high phosphorous (used in order to determine the eutectic cell) exhibited larger eutectic cells in the low-g zone, followed by a band of coarser graphite

Preliminary science report on the directional solidification of hypereutectic cast iron during KC-135 low-G maneuvers

An ADSS-P directional solidification furnace was reconfigured for operation on the KC-135 low-g aircraft. The system offers many advantages over quench ingot methods for study of the effects of sedimentation and convection on alloy formation. The directional sodification furnace system was first flown during the September 1982 series of flights. The microstructure of the hypereutectic cast iron sample solidified on one of these flights suggests a low-g effect on graphite morphology. Further experiments are needed to ascertain that this effect is due to low-gravity and to deduce which of the possible mechanisms is responsible for it

Energy spectrum of turbulent fluctuations in boundary driven reduced magnetohydrodynamics

The nonlinear dynamics of a bundle of magnetic flux ropes driven by stationary fluid motions at their endpoints is studied, by performing numerical simulations of the magnetohydrodynamic (MHD) equations. The development of MHD turbulence is shown, where the system reaches a state that is characterized by the ratio between the Alfven time (the time for incompressible MHD waves to travel along the field lines) and the convective time scale of the driving motions. This ratio of time scales determines the energy spectra and the relaxation toward different regimes ranging from weak to strong turbulence. A connection is made with phenomenological theories for the energy spectra in MHD turbulence.Comment: Published in Physics of Plasma

Application of Fall Nitrogen Increased Spring Tall Fescue Yield

Late season nitrogen fertilization is a practice that has long been implemented in turfgrass production. This practice involves applying nitrogen from September through December and results in an extended green period in the fall without stimulating excessive shoot growth. The longer green period results in higher levels of carbohydrate reserves and enhanced root growth compared with a spring-summer fertilization program. In addition to these benefits, sods fertilized in late fall have been shown to green up two to six weeks earlier in the spring. Limited research has considered the impact of late fall nitrogen applications on grass growth in hayfields and pastures. The objective of this study was to evaluate the impact of late fall nitrogen fertilization on dry matter production of an established tall fescue stand. In 2020 and 2021, the study was conducted at the UK Research and Extension Center located in Princeton, KY. The experimental design was a random complete block with four replications. In early December 2020 and 2021, 0, 34, 67, and 101 kg ha-1 was applied as ammonium nitrate, ammonium sulfate, and Anuvia SYMTRX 20S. An additional 90 kg ha-1 was applied as urea to all plots the following spring. Plots were harvested on 13-May-2021 and 24-May-2022 using a self-propelled sickle bar type forage harvester equipped with load cells. Averaged across sources, first harvest yields ranged from 3428 to 5675 and 3929 to 5831 kg ha-1 in 2021 and 2022, respectively. Fall applied nitrogen resulted in a linear increase in dry matter yield of 25.0 and 21.2 kg ha-1 in 2021 and 2022, respectively. Nitrogen sources had no impact on dry matter yield (P \u3e 0.05). Plots receiving fall applied nitrogen also initiated growth earlier in the spring

EUREGIO MRSA-net Twente/Munsterland - a Dutch-German cross-border network for the prevention and control of infections caused by methicillin-resistant Staphylococcus aureus

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Magnetospheric considerations for solar system ice state

The current lattice configuration of the water ice on the surfaces of the inner satellites of Jupiter and Saturn is likely shaped by many factors. But laboratory experiments have found that energetic proton irradiation can cause a transition in the structure of pure water ice from crystalline to amorphous. It is not known to what extent this process is competitive with other processes in solar system contexts. For example, surface regions that are rich in water ice may be too warm for this effect to be important, even if the energetic proton bombardment rate is very high. In this paper, we make predictions, based on particle flux levels and other considerations, about where in the magnetospheres of Jupiter and Saturn the ∼MeV proton irradiation mechanism should be most relevant. Our results support the conclusions of Hansen and McCord (2004), who related relative level of radiation on the three outer Galilean satellites to the amorphous ice content within the top 1 mm of surface. We argue here that if magnetospheric effects are considered more carefully, the correlation is even more compelling. Crystalline ice is by far the dominant ice state detected on the inner Saturnian satellites and, as we show here, the flux of bombarding energetic protons onto these bodies is much smaller than at the inner Jovian satellites. Therefore, the ice on the Saturnian satellites also corroborates the correlation