On positivity and roots in operator algebras

In earlier papers the second author and Charles Read have introduced and studied a new notion of positivity for operator algebras, with an eye to extending certain C*-algebraic results and theories to more general algebras. The present paper consists of complements to some facts in the just mentioned papers, concerning this notion of positivity. For example we prove a result on the numerical range of products of the roots of commuting operators with numerical range in a sector.Comment: 11 pages, to appear Integral Equations Operator Theor

Chemical approaches to carbon dioxide utilization for manned Mars missions

Use of resources available in situ is a critical enabling technology for a permanent human presence in space. A permanent presence on Mars, e.g., requires a large infrastructure to sustain life under hostile conditions. As a resource on Mars, atmospheric CO2 is as follows: abundant; available at all points on the surface; of known presence; chemically simple; and can be obtained by simple compression. Many studies focus on obtaining O2 and the various uses for O2 including life support and fuel; discussion of CO, the coproduct from CO2 fixation revolves around its uses as a fuel, being oxidized back to CO2. Several new proposals are studied for CO2 fixation through chemical, photochemical, and photoelectrochemical means. For example, the reduction of CO2 to hydrocarbons such as acetylene (C2H2) can be accomplished with H2. C2H2 has a theoretical vacuum specific impulse of approx. 375 secs. Potential uses were also studied of CO2, as obtained or further reduced to carbon, as a reducing agent in metal oxide processing to form metals or metal carbides for use as structural or power materials; the CO2 can be recycled to generate O2 and CO

Orbit decidability, applications and variations

We present the notion of orbit decidability into a more general framework, exploring interesting generalizations and variations of this algorithmic problem. A recent theorem by Bogopolski-Martino-Ventura gave a renovated protagonism to this notion and motivated several interesting algebraic applications

Addressing the Mars ISRU Challenge: Production of Oxygen and Fuel from CO_2 using Sunlight

Advanced exploration of Mars, particularly human missions, will require vast amounts of fuel and oxygen for extended campaigns and the return of samples or humans back to Earth. If fuel and oxygen can be prepared on Mars from in-situ resources, this would greatly reduce the launch mass of the mission from Earth. In this Keck Institute for Space Sciences (KISS) study, the viability of Mars near-ambient temperature photoelectrochemical (PEC) or electrochemical (EC) production of fuel and oxygen from atmospheric carbon dioxide—with or without available water—was examined. With PEC devices incorporated into lightweight, large-area structures operating near 25°C and collecting solar energy to directly convert carbon dioxide into oxygen, it may be possible to reduce the launch mass (compared with bringing oxygen directly from Earth) by a factor of three or more. There are other numerous benefits of such a system relative to other in-situ resource utilization (ISRU) schemes, notably reduced thermal management (e.g., lower heating demand and decreased amplitude of thermal cycling) and the elimination of a need for a fission power source. However, there are considerable technical hurdles that must be surmounted before a PEC or EC ISRU system could be competitive with other more mature ISRU approaches, such as solid oxide electrolysis (SOXE) technology. Noteworthy challenges include: the identification of highly stable homogeneous or heterogeneous catalysts for oxygen evolution and carbon monoxide or methane evolution; quantification of long-term operation under the harsh Martian conditions; and appropriate coupled catalyst–light absorber systems that can be reliably stowed then deployed over large areas, among other challenges described herein. This report includes recommendations for future work to assess the viability of and advance the state-of-the-art for EC and PEC technologies for future ISRU applications. Importantly, the challenges of mining, transporting, purifying, and delivering water from Mars resources to a PEC or EC reactor system, development and demonstration of a low-temperature-capable, non-aqueous-based CO2 reduction scheme as described below is perhaps the first logical step toward implementing an efficient near-surface Mars temperature oxygen generation system on Mars

Post-Newtonian gravitational radiation and equations of motion via direct integration of the relaxed Einstein equations. III. Radiation reaction for binary systems with spinning bodies

Using post-Newtonian equations of motion for fluid bodies that include radiation-reaction terms at 2.5 and 3.5 post-Newtonian (PN) order (O[(v/c)^5] and O[(v/c)^7] beyond Newtonian order), we derive the equations of motion for binary systems with spinning bodies. In particular we determine the effects of radiation-reaction coupled to spin-orbit effects on the two-body equations of motion, and on the evolution of the spins. For a suitable definition of spin, we reproduce the standard equations of motion and spin-precession at the first post-Newtonian order. At 3.5PN order, we determine the spin-orbit induced reaction effects on the orbital motion, but we find that radiation damping has no effect on either the magnitude or the direction of the spins. Using the equations of motion, we find that the loss of total energy and total angular momentum induced by spin-orbit effects precisely balances the radiative flux of those quantities calculated by Kidder et al. The equations of motion may be useful for evolving inspiraling orbits of compact spinning binaries.Comment: 19 pages, small corrections, equivalent to published versio

Hedge Fund Boards and the Market for Independent Directors

We provide the first examination of hedge fund boards and their directors. The majority of directorships are held by extremely busy independent directors. These directors are sought after by funds because they have more reputational capital at stake, making them independent and credible monitors whose presence can certify fund quality to investors. Busy independent directors are more likely to be hired by high quality funds, and their departure from the board is associated with investor withdrawals. Moreover, funds with busy independent directors are less likely to commit fraud, abuse discretionary liquidity restrictions, or engage in performance-based risk shifting

Feasibility and acceptability of regular weighing, setting weight gain limits and providing feedback by community midwives to prevent excess weight gain during pregnancy:randomised controlled trial and qualitative study

BACKGROUND: Regular weighing in pregnant women is not currently recommended in many countries but has been suggested to prevent excessive gestational weight gain. This study aimed to establish the feasibility and acceptability of incorporating regular weighing, setting maximum weight gain targets and feedback by community midwives. METHODS: Low risk pregnant women cared for by eight community midwives were randomised to usual care or usual care plus the intervention at 10–14 weeks of pregnancy. The intervention involved community midwives weighing and plotting weight on a weight gain chart, setting weight gain limit targets, giving brief feedback at each antenatal appointment and encouraging women to weigh themselves weekly between antenatal appointments. Women and midwives were interviewed about their views of the intervention. The focus of the study was on process evaluation. RESULTS: Community midwives referred 123 women and 115 were scheduled for their dating scan within the study period. Of these, 84/115 were approached at their dating scan and 76/84 (90.5 %) randomised. Data showed a modest difference favouring the intervention group in the percentage of women gaining excessive gestational weight (23.5 % versus 29.4 %). The intervention group consistently reported smaller increases in depression and anxiety scores throughout pregnancy compared with usual care. Most women commented the intervention was useful in encouraging them to think about their weight and believed it should be part of routine antenatal care. Community midwives felt the intervention could be implemented within routine care without adding substantially to consultation length, thus not perceived as adding substantially to their workload. CONCLUSIONS: The intervention was feasible and acceptable to pregnant women and community midwives and was readily implemented in routine care. TRIAL REGISTRATION: ISRCTN8160516

Non-equilibrium microtubule fluctuations in a model cytoskeleton

Biological activity gives rise to non-equilibrium fluctuations in the cytoplasm of cells; however, there are few methods to directly measure these fluctuations. Using a reconstituted actin cytoskeleton, we show that the bending dynamics of embedded microtubules can be used to probe local stress fluctuations. We add myosin motors that drive the network out of equilibrium, resulting in an increased amplitude and modified time-dependence of microtubule bending fluctuations. We show that this behavior results from step-like forces on the order of 10 pN driven by collective motor dynamics