How strong is a covalent bond?

The rupture force of single covalent bonds under an external load was measured with an atomic force microscope (AFM). Single polysaccharide molecules were covalently anchored between a surface and an AFM tip and then stretched until they became detached. By using different surface chemistries for the attachment, it was found that the silicon-carbon bond ruptured at 2.0 +/- 0.3 nanonewtons, whereas the sulfur-gold anchor ruptured at 1.4 +/- 0.3 nanonewtons at force-loading rates of 10 nanonewtons per second. Bond rupture probability calculations that were based on density functional theory corroborate the measured values.     

How low can you go? Physical production mechanism of elephant infrasonic vocalizations

Elephants can communicate using sounds below the range of human hearing ("infrasounds" below 20 hertz). It is commonly speculated that these vocalizations are produced in the larynx, either by neurally controlled muscle twitching (as in cat purring) or by flow-induced self-sustained vibrations of the vocal folds (as in human speech and song). We used direct high-speed video observations of an excised elephant larynx to demonstrate flow-induced self-sustained vocal fold vibration in the absence of any neural signals, thus excluding the need for any "purring" mechanism. The observed physical principles of voice production apply to a wide variety of mammals, extending across a remarkably large range of fundamental frequencies and body sizes, spanning more than five orders of magnitude.     

How is a food bank managed? Different profiles in Spain

Within the current economic situation, poverty indexes in developed countries are becoming more and more alarming. This makes the role of food banks very relevant, and in addition contributes towards reducing the problem of food waste. Motivated by the social importance of these non-profit organizations, this paper analyzes the impact of food banks on the supply chains to which they belong. Differences in the functioning of these supply chains are highlighted attending to the relations induced by the food banks. First, the international research background for this topic is summarized; then, the results of an empirical study in Spain are presented. Data were collected through surveys and analyzed using cluster methodology. Two different types of food bank were identified. These are described, characterized, and compared in terms of efficacy and efficiency.