Microscopic Nuclear Level Densities from Fe to Ge by the Shell Model Monte Carlo Method

We calculate microscopically total and parity-projected level densities for $\beta$-stable even-even nuclei between Fe and Ge, using the shell model Monte Carlo methods in the complete $(pf+0g_{9/2})$-shell. A single-particle level density parameter $a$ and backshift parameter $\Delta$ are extracted by fitting the calculated densities to a backshifted Bethe formula, and their systematics are studied across the region. Shell effects are observed in $\Delta$ for nuclei with Z=28 or N=28 and in the behavior of $A/a$ as a function of the number of neutrons. We find a significant parity-dependence of the level densities for nuclei with A \alt 60, which diminishes as $A$ increases.Comment: to be published in Phys. Lett. B; includes 5 eps figure

Age differences in intertemporal choice among children, adolescents, and adults

When choosing between sooner–smaller and later–larger rewards (i.e., intertemporal choices), adults typically prefer later–larger rewards more often than children. Intertemporal choice preferences have been implicated in various impulsivity-related psychopathologies, making it important to understand the underlying mechanisms not only in terms of how reward magnitude and delay affect choice but also in terms of how these mechanisms develop across age. We administered an intertemporal choice paradigm to 60 children (8–11 years), 79 adolescents (14–16 years), and 60 young adults (18–23 years). The paradigm systematically varied amounts and delays of the available rewards, allowing us to identify mechanisms underlying age-related differences in patience. Compared with young adults, both children and adolescents made fewer later–larger choices. In terms of underlying mechanisms, variation in delays, absolute reward magnitudes, and relative amount differences affected choice in each age group, indicating that children showed sensitivity to the same choice-relevant factors as young adults. Sensitivity to both absolute reward magnitude and relative amount differences showed a further monotonic age-related increase, whereas no change in delay sensitivity occurred. Lastly, adolescents and young adults weakly displayed a present bias (i.e., overvaluing immediate vs. future rewards; nonsignificant and trend, respectively), whereas children showed a nonsignificant but opposite pattern, possibly indicating that specifically dealing with future rewards changed with age. These findings shed light on the underlying mechanisms that contribute to the development of patience. By decomposing overt choices, our results suggest that the age-related increase in patience may be driven specifically by stronger sensitivity to amount differences with age.</p

Binomial level densities

It is shown that nuclear level densities in a finite space are described by a continuous binomial function, determined by the first three moments of the Hamiltonian, and the dimensionality of the underlying vector space. Experimental values for $^{55}$Mn, $^{56}$Fe, and $^{60}$Ni are very well reproduced by the binomial form, which turns out to be almost perfectly approximated by Bethe's formula with backshift. A proof is given that binomial densities reproduce the low moments of Hamiltonians of any rank: A strong form of the famous central limit result of Mon and French. Conditions under which the proof may be extended to the full spectrum are examined.Comment: 4 pages 2 figures Second version (previous not totally superseeded

Parity Dependence of Nuclear Level Densities

A simple formula for the ratio of the number of odd- and even-parity states as a function of temperature is derived. This formula is used to calculate the ratio of level densities of opposite parities as a function of excitation energy. We test the formula with quantum Monte Carlo shell model calculations in the $(pf+g_{9/2})$-shell. The formula describes well the transition from low excitation energies where a single parity dominates to high excitations where the two densities are equal.Comment: 14 pages, 4 eps figures included, RevTe

Determination of Porphyrins in Bile Using High Performance Liquid Chromatography and Some Clinical Applications

Peer Reviewe

Formal Models of Differential Framing Effects in Decision Making Under Risk

An intriguing finding in the decision-making literature is that, when people have to choose between sure and risky options of equal expected value, they typically take more risks when decisions are framed as losses instead of gains (Tversky &amp; Kahneman, 1981). This framing effect is robust and has important implications for health, finance, and politics. However, theoretical debate exists on the origins of this effect. Moreover, pronounced task-related, individual, and developmental differences exist in the magnitude of the effect. These two issues—theoretical debate and differential framing effects— can be solved together, as an adequate theory of the framing effect should both describe the effect itself and describe differences therein. Therefore, we compare four theories on their capacity to describe differential framing effects: cumulative prospect theory (CPT), fuzzy trace theory (FTT), dual process theory, and a hybrid theory (HT) incorporating elements from lexicographic theory and fuzzy trace theory. First, in a theoretical analysis and empirical review, we build on recent advances in the fields of decision making, brain– behavior relationships, and cognitive development. Second, in an empirical study, we directly compare these theories by using a new experimental task and new analytic approach in which we use hierarchical Bayesian model-based mixture analysis of theories. Taken together, results indicate that differential framing effects are best described by the notion that the majority of decision makers decide according to the hybrid theory, and a sizable minority according to cumulative prospect theory and fuzzy trace theory. We discuss implications of these results for our understanding of the framing effect, and for decision making in general.</p