An update on the middle levels problem

The middle levels problem is to find a Hamilton cycle in the middle levels, M_{2k+1}, of the Hasse diagram of B_{2k+1} (the partially ordered set of subsets of a 2k+1-element set ordered by inclusion). Previously, the best result was that M_{2k+1} is Hamiltonian for all positive k through k=15. In this note we announce that M_{33} and M_{35} have Hamilton cycles. The result was achieved by an algorithmic improvement that made it possible to find a Hamilton path in a reduced graph of complementary necklace pairs having 129,644,790 vertices, using a 64-bit personal computer.Comment: 11 pages, 5 figure

Effects of Early-Adolescent, Mid-Adolescent, or Adult Stress on Morphine Conditioned Place Preference

In light of previous work demonstrating that stress can increase subjective drug reward in adult rats, the present study investigated the influence of stress on morphine conditioned place preference (CPP) in early-adolescent, mid-adolescent, and adult male Sprague-Dawley rats. Subjects in each age group were assigned to either a no stress condition or a stress condition in which they were exposed to an unpredictable eight-day schedule of elevated platform and synthetic fox odor stressors. Place conditioning then evaluated subjective morphine reward in all animals. Using a biased procedure, subjects were assigned to receive morphine on the initially non-preferred side of the apparatus and saline on the initially preferred side as identified at pretest. After eight days of conditioning in which drug presentation alternated by day (i.e., morphine one day and saline the next), a post-test was conducted identical to pre-test. Results comparing pre- and post-test time on the non-preferred side indicated no difference between stress conditions or age groups, though place preference was observed in all animals. Activity, scored as midline crosses during conditioning trials, revealed expected habituation to the motor suppressing effects of morphine. Although no effects of stress or age were observed on measures of drug conditioning, the findings suggest that duration between the end of stress exposure and the start of conditioning may have weakened any effect of age-dependent stress on morphine CPP

A normalised seawater strontium isotope curve: possible implications for Neoproterozoic-Cambrian weathering rates and the further oxygenation of the Earth

The strontium isotope composition of seawater is strongly influenced on geological time scales by changes in the rates of continental weathering relative to ocean crust alteration. However, the potential of the seawater 87Sr/86Sr curve to trace globally integrated chemical weathering rates has not been fully realised because ocean 87Sr/86Sr is also influenced by the isotopic evolution of Sr sources to the ocean. A preliminary attempt is made here to normalise the seawater 87Sr/86Sr curve to plausible trends in the 87Sr/86Sr ratios of the three major Sr sources: carbonate dissolution, silicate weathering and submarine hydrothermal exchange. The normalised curve highlights the Neoproterozoic-Phanerozoic transition as a period of exceptionally high continental influence, indicating that this interval was characterised by a transient increase in global weathering rates and/or by the weathering of unusually radiogenic crustal rocks. Close correlation between the normalised 87Sr/86Sr curve, a published seawater δ34S curve and atmospheric pCO2 models is used here to argue that elevated chemical weathering rates were a major contributing factor to the steep rise in seawater 87Sr/86Sr from 650 Ma to 500 Ma. Elevated weathering rates during the Neoproterozoic-Cambrian interval led to increased nutrient availability, organic burial and to the further oxygenation of Earth's surface environment. Use of normalised seawater 87Sr/86Sr curves will, it is hoped, help to improve future geochemical models of Earth System dynamics

‘My work is bleeding’: exploring students’ emotional responses to first-year assignment feedback

This paper explores the emotional responses that assignment feedback can provoke in first-year undergraduates. The literature on the link between emotions and learning is well established, but surprisingly research on the relationship between emotions and feedback is still relatively scarce. This article aims to make an additional contribution to this emerging field. Semi-structured interviews with 24 first-year undergraduate students from the Humanities and Social Sciences department in a post-1992 institution were conducted. The interview narratives identified how the emotional impact of feedback was related to: prior experiences of education, the significance participants attached to the feedback received on their first assignment and how their interpretations of feedback comments were linked to beliefs about themselves as learners. The implications of these experiences on student ‘belonging’ and learning are discussed. The underlying themes that emerged from the findings are the polarised emotions of anxiety and confidence. Based on the findings, the paper concludes by making recommendations for reconceptualising feedback on first-year assignments. It suggests that a holistic assessment approach, which incorporates timely feedback indicating if students are ‘on the right lines’ with low-stakes assignments, is a practice that may both reduce anxiety and increase confidence to support students

Refracting the Male Gaze: Mary Cassatt’s Ocularcentric Message of Female Agency

Through analysis of ocularcentric (vision-privileged) messages in Mary Cassatt’s Reading Le Figaro (1878), I argue the portrait represents a strong early-career interest in countering gender hegemony that is largely unmatched in the artist’s later work. Reading the painting as a reaction to decreased autonomy following a consolidation of family living spaces, the present paper satisfies a dearth in Cassatt scholarship by addressing a yet-undiscussed motif of vision in Cassatt’s painting: the mirror. In a complete subversion of classic vanitas paintings, Cassatt alters the woman-and-mirror trope to emphasize her subject’s desire for an identity of female mind over female body. Defying European culture’s hyperspecularization (concentration on display value), which converted women into objects of male desire, Reading Le Figaro challenges preconceived schemas of gender and offers autonomy, self-definition, and active female sight as alternatives to the gaze-controlling subjugation of women

Farm Safety Net Programs: Background and Issues

The U.S. Department of Agriculture (USDA) operates several programs that supplement the income of farmers and ranchers in times of low farm prices and natural disasters. Federal crop insurance, farm programs, and disaster assistance are collectively called the farm safety net. Federal crop insurance is often referred to as the centerpiece of the farm safety net because of its cost and broad scope for addressing natural disasters. The program is permanently authorized and makes available subsidized insurance for more than 130 commodities (ranging from apples to wheat) to help farmers manage risks associated with a loss in yield or revenue. Program cost is projected by the Congressional Budget Office to total $8.8 billion per year over the next decade. Producers pay a portion of the premium which increases as the level of coverage rises. The federal government pays the rest of the premium—62Farm commodity programs historically represented the heart of U.S. farm policy by virtue of their long history (dating back to the 1930s). Price and income support is based primarily on statutorily fixed prices and not market prices (as in crop insurance), which can be quite low in some years. For crop years 2014-2018, the Agricultural Act of 2014 (2014 farm bill, P.L. 113-79) established minimum prices via the marketing loan program for approximately two dozen commodities, including corn, soybeans, wheat, rice, and peanuts. In addition, producers with production histories for covered crops have a one-time choice between Price Loss Coverage (PLC) payments and Agriculture Risk Coverage (ARC) payments. Costs were projected in March 2015 at about$4 billion per year over the next decade. Programs are free for producers. Agricultural disaster assistance is permanently authorized for livestock and orchards. Under the 2014 farm bill, nearly all parts of the U.S. farm sector are now covered by either a disaster program or federal crop insurance, which is expected to reduce calls for ad hoc assistance. As of May 2015, producer payments had totaled more than $5 billion for losses in FY2012-FY2015. Compared with the previous farm bill, the 2014 farm bill was enacted with more crop insurance options and higher reference prices designed to trigger payments more often than under previous law. Funding was accomplished by eliminating direct payments that had been made annually since 1996 but played no role in managing farm risk because they did not vary with farm prices. Several facets of the current farm safety net might be of interest to the 114th Congress. An initial focus could be on USDA’s implementation of the farm safety net provisions. Issues could include the delayed payment schedule, which could expose cashflow problems, and the pending “actively engaged” rule that could affect program eligibility for some producers. With ongoing concern for budget deficits and federal spending, Congress also might be interested in reviewing the effectiveness of the revised safety net and actual costs, which are expected to be higher than earlier projections due to lower farm prices. Farm safety net proponents say the current suite of programs has been designed for such situations and is needed to adequately protect producers and the overall agriculture sector. Critics believe that a simplified approach might be more effective and less expensive, with funds used instead for broad societal gains, such as investment in agricultural research or transportation infrastructure. The Administration has proposed trimming crop insurance subsidies, arguing that the safety net could remain effective

Agricultural Disaster Assistance

[Excerpt] The U.S. Department of Agriculture (USDA) has at its disposal several programs designed to help farmers and ranchers recover from the financial effects of natural disasters. These are (1) federal crop insurance, (2) the Noninsured Crop Disaster Assistance Program (NAP), (3) livestock and fruit tree disaster programs, and (4) emergency disaster loans for both crop and livestock producers. All have permanent authorization, and the emergency loan program is the only one requiring a federal disaster designation. Most programs receive funding amounts of “such sums as necessary” and are not subject to annual discretionary appropriations

X-ray source uses interchangeable target anodes to vary X-ray wavelength

Compact laboratory X ray tube generates X rays of various wavelengths by using interchangeable target anodes. The wavelength of the X rays depends on the metal from which the anode is made