Mount makes liquid nitrogen-cooled gamma ray detector portable

Liquid nitrogen-cooled gamma ray detector system is made portable by attaching the detector to a fixture which provides a good thermal conductive path between the detector and the liquid nitrogen in a dewar flask and a low heat leak path between the detector and the external environment

Adaptive Restart of the Optimized Gradient Method for Convex Optimization

First-order methods with momentum such as Nesterov's fast gradient method are very useful for convex optimization problems, but can exhibit undesirable oscillations yielding slow convergence rates for some applications. An adaptive restarting scheme can improve the convergence rate of the fast gradient method, when the parameter of a strongly convex cost function is unknown or when the iterates of the algorithm enter a locally strongly convex region. Recently, we introduced the optimized gradient method, a first-order algorithm that has an inexpensive per-iteration computational cost similar to that of the fast gradient method, yet has a worst-case cost function rate that is twice faster than that of the fast gradient method and that is optimal for large-dimensional smooth convex problems. Building upon the success of accelerating the fast gradient method using adaptive restart, this paper investigates similar heuristic acceleration of the optimized gradient method. We first derive a new first-order method that resembles the optimized gradient method for strongly convex quadratic problems with known function parameters, yielding a linear convergence rate that is faster than that of the analogous version of the fast gradient method. We then provide a heuristic analysis and numerical experiments that illustrate that adaptive restart can accelerate the convergence of the optimized gradient method. Numerical results also illustrate that adaptive restart is helpful for a proximal version of the optimized gradient method for nonsmooth composite convex functions

Radiofrequency system analysis of the Lewis cyclotron modification

Computer code for analyzing radio frequency system of modified cyclotro

Relaxed Linearized Algorithms for Faster X-Ray CT Image Reconstruction

Statistical image reconstruction (SIR) methods are studied extensively for X-ray computed tomography (CT) due to the potential of acquiring CT scans with reduced X-ray dose while maintaining image quality. However, the longer reconstruction time of SIR methods hinders their use in X-ray CT in practice. To accelerate statistical methods, many optimization techniques have been investigated. Over-relaxation is a common technique to speed up convergence of iterative algorithms. For instance, using a relaxation parameter that is close to two in alternating direction method of multipliers (ADMM) has been shown to speed up convergence significantly. This paper proposes a relaxed linearized augmented Lagrangian (AL) method that shows theoretical faster convergence rate with over-relaxation and applies the proposed relaxed linearized AL method to X-ray CT image reconstruction problems. Experimental results with both simulated and real CT scan data show that the proposed relaxed algorithm (with ordered-subsets [OS] acceleration) is about twice as fast as the existing unrelaxed fast algorithms, with negligible computation and memory overhead.Comment: Submitted to IEEE Transactions on Medical Imagin

Harm, authority and generalizability: further experiments on the moral/conventional distinction

Certain researchers in the field of moral psychology, following Turiel (1983), argue that children and adults in different cultures make a distinction between moral and conventional transgressions. One interpretation of the theory holds that moral transgressions elicit a signature moral response pattern while conventional transgressions elicit a signature conventional response pattern (e.g., Kelly et al. 2007). Four dimensions distinguish the moral response pattern from the conventional response pattern (e.g., Nichols 2004). 1. HARM/JUSTICE/RIGHTS – Subjects justify the wrongness of moral transgressions by stating that they involve a victim that is harmed, whose rights have been violated or who has been subject to an injustice. Conventional transgressions do not involve a victim that is harmed, whose rights have been violated or who has been subject to an injustice. 2. AUTHORITY – Subjects judge moral transgressions as wrong independent of structures of authority while the wrongness of conventional transgressions can be changed by an authority. 3. GENERALIZABILITY – Subjects judge moral transgressions as generalizably wrong, i.e., independent of time and place, while conventional transgressions’ wrongness depends on time and place. 4. SERIOUSNESS – Subjects judge moral transgressions as more seriously wrong than conventional transgressions. Others have criticized this view for a diversity of reasons. Relevant for our purposes is that, first, there appear to be cultural differences in what constitutes a moral transgression (e.g., Haidt et al. 1993) and second, it is unclear what the exact hypotheses are, surrounding this supposed moral/conventional distinction (e.g., Stich et al. 2009). I will present planned and ongoing experimental research that investigates two specific problems we encountered in the moral-conventional literature. First of all, we cannot draw reliable conclusions from previous work about the generalizability of the wrongness of different kinds of transgressions. In previous experiments, differences in time and place are often but not always confounded with a variety of other differences. For example, Huebner et al. (2010) ask participants if the depicted act would be OK for someone who lived elsewhere where everyone else did this. Moreover, when varying time and/or place, participants are likely to assume that other things differ as well. In our study, we vary time and/or place in a variety of scenarios in order to investigate what assumptions participants make when confronted with the generalizability question. Second, it is an open question as to what extent any transgression will universally elicit one of the two signature response patterns. In our study, we make use of existing differences in participants’ value hierarchy to test this. For one and the same scenario, we compare the response of participants for whom authority is an important value with the results of participants for whom authority is not an important value, in order to see if there are differences in the two groups’ response patterns. References: Haidt J., Koller S. & Dias M. 1993. Affect, culture and morality, or is it wrong to eat your dog? Journal of Personality and Social Psychology 65:613-628. Huebner B., Lee, J.L. & Hauser, M.D. 2010. The Moral-Conventional Distinction in Mature Moral Competence. Journal of Cognition and Culture 10: 1-26. Kelly D., Stich S., Haley K.J., Eng S.J. & Fessler D.M.T. 2007. Harm, Affect, and the Moral/Conventional Distinction. Mind & Language 22:117-131. Nichols S. 2004. Sentimental Rules: on the Natural Foundations of Moral Judgment. Oxford University Press. Stich S., Fessler, D.M.T. & Kelly D. 2009. On the Morality of Harm: A response to Sousa, Holbrook and Piazza. Cognition 113:93-97. Turiel E. 1983. The Development of Social Knowledge. Morality & Convention. Cambridge University Press