Control over phase separation and nucleation using a laser-tweezing potential

Control over the nucleation of new phases is highly desirable but elusive. Even though there is a long history of crystallization engineering by varying physicochemical parameters, controlling which polymorph crystallizes or whether a molecule crystallizes or forms an amorphous precipitate is still a poorly understood practice. Although there are now numerous examples of control using laser-induced nucleation, the absence of physical understanding is preventing progress. Here we show that the proximity of a liquid–liquid critical point or the corresponding binodal line can be used by a laser-tweezing potential to induce concentration gradients. A simple theoretical model shows that the stored electromagnetic energy of the laser beam produces a free-energy potential that forces phase separation or triggers the nucleation of a new phase. Experiments in a liquid mixture using a low-power laser diode confirm the effect. Phase separation and nucleation using a laser-tweezing potential explains the physics behind non-photochemical laser-induced nucleation and suggests new ways of manipulating matter

Sleep-Disordered Breathing in Michigan: A Practice Pattern Survey

Objectives: This survey sought to determine whether self-professed sleep specialists in the State of Michigan show practice variations in the diagnosis and management of sleep-disordered breathing (SDB), and whether such variations occur between pulmonologists and neurologists. Methods: Questionnaires on practice volume and patterns during the prior 12 months were mailed to physician members of the Michigan Sleep Disorders Association ( n = 119); 67 were completed and returned. Results: Respondents reported that they personally saw a median of 8 new patients each week for suspected SDB; estimates were that 86% of these patients were eventually confirmed to have SDB. Most patients (82%) had laboratory-based polysomnography after an initial clinic evaluation, and most (69%) of those treated for SDB received continuous positive airway pressure. However, practice patterns differed substantially among respondents, even when the analysis was limited to the 42 who reported board certification by the American Board of Sleep Medicine. For example, among all surveyed practices the likelihood that suspected SDB would be evaluated with a split-night diagnostic and treatment polysomnogram varied from 0 to 90%. The likelihood of SDB treatment with bilevel positive airway pressure varied from 0 to 50%, with automatically titrating devices from 0 to 100%, with surgery from 0 to 100% (0 to 50% among certified practitioners), and with oral appliances from 0 to 20%. The practice patterns of pulmonologists and neurologists did not differ significantly. Conclusion: Approaches to SDB vary widely in Michigan, though not according to clinician background in pulmonary medicine or neurology. A patient’s experience, in both assessment and treatment, could differ substantially based on which clinician is consulted.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47959/1/11325_2003_Article_95.pd

Kinematic effects in rotationally inelastic A + BC collisions

Three-dimensional quasiclassical trajectory results obtained using an ab initio potential energy surface for rigid rotor HF---Li collisions exhibit an interesting kinematic effect: with increase in mass of the projectile atom the amount of rotational energy transferred decreases in contrast to the reverse trend known in homonuclear diatom-atom collisions. The differing kinematics effects are explained on the basis of differing effective anisotropies that become evident in plots of potential energy contours in mass-weighted coordinates (R, δ) proposed recently by Loesch. We also work out the conditions for multiple collisions using different ellipse models