Reversible H_2 Addition across a Nickel−Borane Unit as a Promising Strategy for Catalysis

We report the synthesis and characterization of a series of nickel complexes of the chelating diphosphine-borane ligands ArB(o-Ph_2PC_6H_4)_2 ([^(Ar)DPB^(Ph)]; Ar = Ph, Mes). The [^(Ar)DPB^(Ph)] framework supports pseudo-tetrahedral nickel complexes featuring η^2-B,C coordination from the ligand backbone. For the B-phenyl derivative, the THF adduct [^(Ph)DPB^(Ph)]Ni(THF) has been characterized by X-ray diffraction and features a very short interaction between nickel and the η^2-B,C ligand. For the B-mesityl derivative, the reduced nickel complex [^(Mes)DPB^(Ph)]Ni is isolated as a pseudo-three-coordinate “naked” species that undergoes reversible, nearly thermoneutral oxidative addition of dihydrogen to give a borohydrido-hydride complex of nickel(II) which has been characterized in solution by multinuclear NMR. Furthermore, [^(Mes)DPB^(Ph)]Ni is an efficient catalyst for the hydrogenation of olefin substrates under mild conditions

Black Hole Thermodynamics in MOdified Gravity (MOG)

We analyze the thermodynamical properties of black holes in a modified theory of gravity, which was initially proposed to obtain correct dynamics of galaxies and galaxy clusters without dark matter. The thermodynamics of non-rotating and rotating black hole solutions resembles similar solutions in Einstein-Maxwell theory with the electric charge being replaced by a new mass dependent gravitational charge $Q = \sqrt{\alpha G_N}M$. This new mass dependent charge modifies the effective Newtonian constant from $G_N$ to $G = G_N(1+\alpha)$, and this in turn critically affects the thermodynamics of the black holes. We also investigate the thermodynamics of regular solutions, and explore the limiting case when no horizons forms. So, it is possible that the modified gravity can lead to the absence of black hole horizons in our universe. Finally, we analyze corrections to the thermodynamics of a non-rotating black hole and obtain the usual logarithmic correction term.Comment: Title changed slightly; new section on BH entropy corrections added; matches version published in PL

The assessment of long-term orbital debris models

Existing long-term orbital debris models are assessed as a first step in the Air Force's effort to develop an Air Force long-term orbital debris model which can perform the following functions: (1) operate with the necessary accuracy at the relevant altitudes and orbital parameters; (2) benefit from new Air Force and non-Air Force debris measurements; and (3) accommodate current and future Air Force space scenarios. Model assessment results are shown for the NASA engineering model. The status of the NASA EVOLVE model assessment is discussed

The association of agricultural information services and technical efficiency among maize producers in Kakamega, western Kenya

Maize is the staple food for most Kenyan households, and grown in almost all the farming systems. Due to diminishing farm sizes in Kakamega District, crop productivity and the efficiency of farming systems are of great concern. This paper aims to provide empirical evidence on the links between efficiency in maize production and access to soil-related agricultural information services. Using cluster sampling, a total of 154 farmers in Kakamega District were interviewed. A 2–step estimation technique (Data Envelopment Analysis (DEA) and Tobit model) were used to evaluate the technical efficiencies among the farmers and the factors explaining the estimated efficiency scores. Data was disaggregated into farmers with and those without access to soil-related agricultural information services. The results shows that farmers with access to soil-related agricultural information services were more technically efficient (average technical efficiency of 90%) in maize production compared to those without access to information (technical efficiency at 70%). Given the significant role that access to soil-related agricultural information services play on technical efficiency in maize production in the study area, the paper recommends improvements in farmers access to this important resources through: (i) the strengthening of the formal and informal agricultural extension services, (ii) a stronger linkage among agricultural research, agricultural extension, and farm level activities; and (iii) policy support for increased distribution of soil management inputs.Maize, Soil information, Technical efficiency, Tobit analysis, DEA, Teaching/Communication/Extension/Profession,

Trajectory Optimization Through Contacts and Automatic Gait Discovery for Quadrupeds

In this work we present a trajectory Optimization framework for whole-body motion planning through contacts. We demonstrate how the proposed approach can be applied to automatically discover different gaits and dynamic motions on a quadruped robot. In contrast to most previous methods, we do not pre-specify contact switches, timings, points or gait patterns, but they are a direct outcome of the optimization. Furthermore, we optimize over the entire dynamics of the robot, which enables the optimizer to fully leverage the capabilities of the robot. To illustrate the spectrum of achievable motions, here we show eight different tasks, which would require very different control structures when solved with state-of-the-art methods. Using our trajectory Optimization approach, we are solving each task with a simple, high level cost function and without any changes in the control structure. Furthermore, we fully integrated our approach with the robot's control and estimation framework such that optimization can be run online. By demonstrating a rough manipulation task with multiple dynamic contact switches, we exemplarily show how optimized trajectories and control inputs can be directly applied to hardware.Comment: Video: https://youtu.be/sILuqJBsyK

Robust Whole-Body Motion Control of Legged Robots

We introduce a robust control architecture for the whole-body motion control of torque controlled robots with arms and legs. The method is based on the robust control of contact forces in order to track a planned Center of Mass trajectory. Its appeal lies in the ability to guarantee robust stability and performance despite rigid body model mismatch, actuator dynamics, delays, contact surface stiffness, and unobserved ground profiles. Furthermore, we introduce a task space decomposition approach which removes the coupling effects between contact force controller and the other non-contact controllers. Finally, we verify our control performance on a quadruped robot and compare its performance to a standard inverse dynamics approach on hardware.Comment: 8 Page

Inferring muscle functional roles of the ostrich pelvic limb during walking and running using computer optimization

Owing to their cursorial background, ostriches (Struthio camelus) walk and run with high metabolic economy, can reach very fast running speeds and quickly execute cutting manoeuvres. These capabilities are believed to be a result of their ability to coordinate muscles to take advantage of specialized passive limb structures. This study aimed to infer the functional roles of ostrich pelvic limb muscles during gait. Existing gait data were combined with a newly developed musculoskeletal model to generate simulations of ostrich walking and running that predict muscle excitations, force and mechanical work. Consistent with previous avian electromyography studies, predicted excitation patterns showed that individual muscles tended to be excited primarily during only stance or swing. Work and force estimates show that ostrich gaits are partially hip-driven with the bi-articular hip–knee muscles driving stance mechanics. Conversely, the knee extensors acted as brakes, absorbing energy. The digital extensors generated large amounts of both negative and positive mechanical work, with increased magnitudes during running, providing further evidence that ostriches make extensive use of tendinous elastic energy storage to improve economy. The simulations also highlight the need to carefully consider non-muscular soft tissues that may play a role in ostrich gait