Bohmian quantum gravity and cosmology

Quantum gravity aims to describe gravity in quantum mechanical terms. How exactly this needs to be done remains an open question. Various proposals have been put on the table, such as canonical quantum gravity, loop quantum gravity, string theory, etc. These proposals often encounter technical and conceptual problems. In this chapter, we focus on canonical quantum gravity and discuss how many conceptual problems, such as the measurement problem and the problem of time, can be overcome by adopting a Bohmian point of view. In a Bohmian theory (also called pilot-wave theory or de Broglie-Bohm theory, after its originators de Broglie and Bohm), a system is described by certain variables in space-time such as particles or fields or something else, whose dynamics depends on the wave function. In the context of quantum gravity, these variables are a space-time metric and suitable variable for the matter fields (e.g., particles or fields). In addition to solving the conceptual problems, the Bohmian approach yields new applications and predictions in quantum cosmology. These include space-time singularity resolution, new types of semi-classical approximations to quantum gravity, and approximations for quantum perturbations moving in a quantum background.Comment: 45 pages, 6 figures, PDFLaTeX; written for "Applied Bohmian Mechanics: From Nanoscale Systems to Cosmology", edited by Xavier Oriols Pladevall and Jordi Mompart; v2 typos correcte

On the evolution of eccentric and inclined protoplanets embedded in protoplanetary disks

Young planets embedded in their protoplanetary disk interact gravitationally with it leading to energy and angular momentum exchange. This interaction determines the evolution of the planet through changes to the orbital parameters. We investigate changes in the orbital elements of a 20 Earth--mass planet due to the torques from the disk. We focus on the non-linear evolution of initially non-vanishing eccentricity $e$ and/or inclination $i$. We treat the disk as a two- or three-dimensional viscous fluid and perform hydrodynamical simulations with an embedded planet. We find rapid exponential decay of the planet orbital eccentricity and inclination for small initial values of $e$ and $i$, in agreement with linear theory. For larger values of $e > 0.1$ the decay time increases and the decay rate scales as $\dot{e} \propto e^{-2}$, consistent with existing theoretical models. For large inclinations ($i$ > 6 deg) the inclination decay rate shows an identical scaling $di/dt \propto i^{-2}$. We find an interesting dependence of the migration on the eccentricity. In a disk with aspect ratio $H/r=0.05$ the migration rate is enhanced for small non-zero eccentricities ($e < 0.1$), while for larger values we see a significant reduction by a factor of $\sim 4$. We find no indication for a reversal of the migration for large $e$, although the torque experienced by the planet becomes positive when $e \simeq 0.3$. This inward migration is caused by the persisting energy loss of the planet. For non gap forming planets, eccentricity and inclination damping occurs on a time scale that is very much shorter than the migration time scale. The results of non linear hydrodynamic simulations are in very good agreement with linear theory for small $e$ and $i$.Comment: accepted for Astronomy & Astrophysics, 16 pages, 16 figures, animations under: http://www.tat.physik.uni-tuebingen.de/~kley/publ/paper/eccp.htm

Broiler Vitamin Nutrition Guidelines

In a time of record feed prices, nutritionists and production managers continue to look for opportunities to lower growout costs. Even though their contribution seldom exceeds 1-2% of feed costs, vitamins are not immune to this cost-crunching scrutiny. Furthermore, in late 2017, an unparalleled drop in global vitamin supply resulted in sharply increased prices, and in some cases, outright shortages. Such events have placed pressure on vitamin fortification levels in broiler feeds. Nutritionists decide on the fortification rates based on a variety of criteria – bird age, production phase, field experience, research trials, and so forth. The rapid change in broiler genetics is probably the biggest factor that affects long-term fortification levels

How does disk gravity really influence type-I migration ?

We report an analytical expression for the locations of Lindblad resonances induced by a perturbing protoplanet, including the effect of disk gravity. Inner, outer and differential torques are found to be enhanced compared to situations where a keplerian velocity field for the dynamics of both the disk and the planet is assumed. Inward migration is strongly accelerated when the disk gravity is only accounted for in the planet orbital motion. The addition of disk self-gravity slows down the planet drift but not enough to stop it.Comment: 4 pages, accepted for publication in A&A Letter

A Fast Potential and Self-Gravity Solver for Non-Axisymmetric Disks

Disk self-gravity could play an important role in the dynamic evolution of interaction between disks and embedded protoplanets. We have developed a fast and accurate solver to calculate the disk potential and disk self-gravity forces for disk systems on a uniform polar grid. Our method follows closely the method given by Chan et al. (2006), in which an FFT in the azimuthal direction is performed and a direct integral approach in the frequency domain in the radial direction is implemented on a uniform polar grid. This method can be very effective for disks with vertical structures that depend only on the disk radius, achieving the same computational efficiency as for zero-thickness disks. We describe how to parallelize the solver efficiently on distributed parallel computers. We propose a mode-cutoff procedure to reduce the parallel communication cost and achieve nearly linear scalability for a large number of processors. For comparison, we have also developed a particle-based fast tree-code to calculate the self-gravity of the disk system with vertical structure. The numerical results show that our direct integral method is at least two order of magnitudes faster than our optimized tree-code approach.Comment: 8 figures, accepted to ApJ

Mid- and long-term effects of stock type on the growth and yield of spruce seedlings in a non-herbicide scenario

Stock types used in reforestation projects can influence plantation success, as they determine the morphological attributes of the planted seedlings. They can also interact with silviculture treatments to influence early seedling survival and growth. As nurseries develop and produce new stock types in response to –and in interaction with– manager needs, research efforts must be pursued to validate early seedling performance and long-term growth and yields. In this context, we aimed to evaluate the main and interactive effects of mechanical site preparation and stock type on planted black (Picea mariana [Mill.] BSP) and white spruce (P. glauca [Moench.] Voss) seedling dimensions at 16-y, and estimate the long-term impact of stock type on the merchantable volume at rotation age for white spruce. We hence compared medium (200 cm3 root plug) and large (350 cm3 root plug) containerized seedlings, as well as large bare-root seedlings of both species, in a field experiment established in Quebec (Canada), where there is a ban on the use of chemical herbicides for vegetation management treatments. Our results confirm that there is a significant, although limited impact of stock type on the size of black and white spruce at the juvenile stage, when medium and large stock types are compared, but that these small differences have a negligible effect on the estimated merchantable volume produced at rotation age (60 years). Mechanical site preparation does not promote seedling growth on these rich sites with thin humus. Therefore, selection of a medium or larger stock type for reforestation projects and application of mechanical site preparation in ecosystems similar to the one studied here should be based on other considerations than growth and yield, such as seedling availability, production and planting costs, or operational constraints

Texas-Oklahoma Producer Cotton Market Summary: 2000/2001

The size of the Texas-Oklahoma spot market analyzed by the Daily Price Estimation System (DPES) for the 2000/2001 marketing year decreased considerably from the previous year. The average price received by producers during the 2000/2001 marketing year was about 50.9 cents/lb. The 2000 crop was generally of good quality, but the averages for the first digit of the color grade and leaf grade detoriated as compared with the 1999 crop. The percentage of bales having level 1 and 2 bark, and level 1 and 2 other extraneous matter decreased in comparison to the 1999 crop. With the exception of the second digit of the color grade price discounts for the 2000 crop decreased for all quality attributes. The premiums for the first digit of the color grade and strength both decreased, while the premium for leaf increased and that of staple remained about the same.Crop Production/Industries,