Suspensions: fluids with fading memories

A sheared liquid suspension whose flow is reversed remembers with various degrees of perfection all earlier configurations of the particles. The memory effects, studied primarily because of their importance in suspension rheology, may be of wider significance.     

Empathy and pro-social behavior in rats

Whereas human pro-social behavior is often driven by empathic concern for another, it is unclear whether nonprimate mammals experience a similar motivational state. To test for empathically motivated pro-social behavior in rodents, we placed a free rat in an arena with a cagemate trapped in a restrainer. After several sessions, the free rat learned to intentionally and quickly open the restrainer and free the cagemate. Rats did not open empty or object-containing restrainers. They freed cagemates even when social contact was prevented. When liberating a cagemate was pitted against chocolate contained within a second restrainer, rats opened both restrainers and typically shared the chocolate. Thus, rats behave pro-socially in response to a conspecific's distress, providing strong evidence for biological roots of empathically motivated helping behavior.     

Xenon Difluoride and the Nature of the Xenon-Fluorine Bond

Xenon reacts with fluorine to form XeF(2) which can be isolated before it reacts with fluorine to form XeF(4). The linear configuration of XeF(2) with the 2.00-A bond length and the vibrational force constants support the assignment of 10 electrons to the valence shell of xenon. Similar arguments support the assignment of 12 and 14 valence electrons respectively to xenon in XeF(4) and XeF(6).     

Imprecision when using measuring cups to weigh out extruded dry kibbled food

Many pet cats and dogs are fed dry extruded kibbled food by measuring cup, yet the precision and accuracy of this feeding strategy is not known. Over 12 studies, we assessed precision and accuracy of weighing out food portions, of various dry kibbled foods, by measuring cup. Poor precision was noted in all studies, with intra- and inter-subject coefficients of variation ranging from 2 to 13% and 2 to 28% respectively. Variable accuracy was also noted, which ranged from an 18% under-estimate to an 80% over-estimate in portion size. No specific factors were associated with imprecision, but the degree of inaccuracy was negatively associated with portion size (R = -0.67, p = 0.022), and positively associated with the number of subjects participating in the study (R = 0.60, p = 0.048). This is the first study to document imprecision and inaccuracy of using measuring cups to estimate portions of extruded dry kibbled food. Over time, such errors could contribute to insidious weight gain in companion animals, potentially contributing to the development of obesity. Imprecision in measuring food portions could also contribute to failure of weight management programmes for obese animals.