B meson decays to baryons in the diquark model

We study B meson decays to two charmless baryons in the diquark model, including strong and electroweak penguins as well as the tree operators. It is shown that penguin operators can enhance \bar{B} \to \Bb_s \bar{\Bb} considerably, but affect \bar{B} \to \Bb_1 \bar{\Bb}_2 only slightly, where \Bb_{(1,2)} and \Bb_s are non-strange and strange baryons, respectively. The $\gamma$ dependence of the decay rates due to tree-penguin interference is illustrated. In principle, some of the \Bb_s \bar{\Bb} modes could dominate over \Bb_1 \bar{\Bb}_2 for $\gamma > 90^\circ$, but in general the effect is milder than their mesonic counterparts. This is because the $O_6$ operator can only produce vector but not scalar diquarks, while the opposite is true for $O_1$ and $O_4$. Predictions from diquark model are compared to those from the sum rule calculation. The decays \bar{B} \to \Bb_s \bar{\Bb}_s and inclusive baryonic decays are also discussed.Comment: 9 pages, 6 figures, Revte

Molecular biomechanics of collagen molecules

Collagenous tissues, made of collagen molecules, such as tendon and bone, are intriguing materials that have the ability to respond to mechanical forces by altering their structures from the molecular level up, and convert them into biochemical signals that control many biological and pathological processes such as wound healing and tissue remodeling. It is clear that collagen synthesis and degradation are influenced by mechanical loading, and collagenous tissues have a remarkable built-in ability to alter the equilibrium between material formation and breakdown. However, how the mechanical force alters structures of collagen molecules and how the structural changes affect collagen degradation at molecular level is not well understood. The purpose of this article is to review the biomechanics of collagen, using a bottom-up approach that begins with the mechanics of collagen molecules. The current understanding of collagen degradation mechanisms is presented, followed by a discussion of recent studies on how mechanical force mediates collagen breakdown. Understanding the biomechanics of collagen molecules will provide the basis for understanding the mechanobiology of collagenous tissues. Addressing challenges in this field provides an opportunity for developing treatments, designing synthetic collagen materials for a variety of biomedical applications, and creating a new class of ‘smart’ structural materials that autonomously grow when needed, and break down when no longer required, with applications in nanotechnology, devices and civil engineering.National Science Foundation (U.S.)United States. Office of Naval Research. Presidential Early Career Award for Scientists and EngineersNational Institutes of Health (U.S.) (U01EB014976