Varying constants, Gravitation and Cosmology

Fundamental constants are a cornerstone of our physical laws. Any constant varying in space and/or time would reflect the existence of an almost massless field that couples to matter. This will induce a violation of the universality of free fall. It is thus of utmost importance for our understanding of gravity and of the domain of validity of general relativity to test for their constancy. We thus detail the relations between the constants, the tests of the local position invariance and of the universality of free fall. We then review the main experimental and observational constraints that have been obtained from atomic clocks, the Oklo phenomenon, Solar system observations, meteorites dating, quasar absorption spectra, stellar physics, pulsar timing, the cosmic microwave background and big bang nucleosynthesis. At each step we describe the basics of each system, its dependence with respect to the constants, the known systematic effects and the most recent constraints that have been obtained. We then describe the main theoretical frameworks in which the low-energy constants may actually be varying and we focus on the unification mechanisms and the relations between the variation of different constants. To finish, we discuss the more speculative possibility of understanding their numerical values and the apparent fine-tuning that they confront us with.Comment: 145 pages, 10 figures, Review for Living Reviews in Relativit

AI and Administrative Decisions under Uncertainty

How should artificial intelligence guide administrative decisions under risk and uncertainty? I argue that artificial intelligence, specifically machine learning, lifts the veil covering many of the biases and cognitive errors engrained in administrative decisions. Machine learning has the potential to make administrative agencies smarter, fairer and more effective. However, this potential can only be exploited if administrative law addresses the implicit normative choices made in the design of machine learning algorithms. These choices pertain to the generalizability of machine-based outcomes, counterfactual reasoning, error weighting, the proportionality principle, the risk of gaming and decisions under complex constraints

Spatiotemporal modelling of correlated small-area outcomes: Analyzing the shared and typespecific patterns of crime and disorder

This research applies a Bayesian spatio-temporal modeling approach to jointly analyze physical disorder, social disorder, property crime, and violent crime over five years at the small-area scale. Despite crime and disorder outcomes exhibiting similar spatio-temporal patterns, as hypothesized by broken windows and collective efficacy theories, past research often analyzes one outcome and overlooks correlations between related crimes as well as underlying spatial and/or temporal patterns common to multiple crime and disorder types. In this article, the best fitting model partitions the area-specific risk of each type of crime and disorder into one spatial shared component and four type-specific spatial, temporal, and space-time components. The shared component captures the spatial pattern common to physical disorder, social disorder, property crime, and violent crime. Results show that the spatial shared component explains the largest amounts of variability for all types of crime and disorder and that temporal components explained the least. Space-time interaction hotspots are identified via posterior probabilities and are examined to contextualize the broken windows theory. The applications of joint spatio-temporal modeling to ecological crime theories, policing, and urban policy are discussed

Effects of posture on gastric emptying, transpyloric flow, and hunger after a glucose drink in healthy humans

The original publication can be found at www.springerlink.comPrevious studies suggest that posture has relatively little effect on gastric emptying of high-nutrient liquids; these studies have, however, only assessed overall rates of gastric emptying, whereas gastric emptying is known to be predominantly a pulsatile phenomenon. In healthy subjects perceptions of appetite, such as hunger, are inversely related to antral area and content; hence, changes in intragastric meal distribution induced by posture may affect appetite. Gastric emptying is a major determinant of postprandial glycemia. The aims of this study were to evaluate the effects of posture on patterns of transpyloric flow (TF), gastric emptying (GE), antral area (AA), hunger, and the glycemic response to oral glucose. Eight healthy young subjects (five males, three females; mean age, 24.0 ± 2.4 years; BMI, 21.2 ± 0.6 kg/m2) were studied twice in random order, once in the sitting position and once in the lying (supine) position. After consuming 600 ml water with 75 g glucose, labeled with 20 MBq 99mTc-sulfur colloid, subjects had simultaneous measurements of (i) TF during consumption of the drink by Doppler ultrasonography, (ii) GE with scintigraphy, (iii) AA at t = −5 and t = 30 min by ultrasonography, and (iv) perceptions of appetite with a visual analogue scale. During drink ingestion TF was greater in the sitting, compared with the lying, position (586 ± 170 vs. 177 ± 65 [cm/sec]×sec; P < 0.05). Posture affected intragastric distribution; more of the drink was retained in the distal stomach in the sitting position (e.g., at 30 min: sitting, 29 ± 3%, vs. lying, 12 ± 3%; P < 0.0001) but had no effect on the overall rate of GE or the blood glucose response. AA at t = 30 min (P<0.005) was greater in the sitting position; there was an inverse relationship between hunger and AA at 30 min (r = −0.53, P < 0.05). We conclude that posture influences initial TF and intragastric distribution, but not the overall rate of GE of, or the glycemic response to, a large-volume nutrient liquid. The increases in AA and content in the sitting position are associated with a reduction in hunger.Karen L. Jones, Deirdre O’Donovan, Michael Horowitz, Antonietta Russo, Yong Lei, Trygve Hauske