Ground-State Electronic Structure of Quasi-One-Dimensional Wires in Semiconductor Heterostructures

We apply density-functional theory, in the local-density approximation, to a quasi-one-dimensional electron gas in order to quantify the effect of Coulomb and correlation effects in modulating and, therefore, patterning, the charge-density distribution. Our calculations are presented specifically for surface-gate-defined quasi-one-dimensional quantum wires in a GaAs-(AlGa)As heterostructure, but we expect our results to apply more generally for other low-dimensional semiconductor systems. We show that at high densities with strong confinement, screening of electrons in the direction transverse to the wire is efficient and density modulations are not visible. In the low-density, weak-confinement regime, the exchange-correlation potential induces small density modulations as the electrons are depleted from the wire. At the weakest confinements and lowest densities, the electron density splits into two rows, thereby forming a pair of quantum wires that lies beneath the surface gates. An additional double-well external potential forms at very low density which enhances this row-splitting phenomenon. We produce phase diagrams that show a transition between the presence of a single quantum wire in a split-gate structure and two quantum wires. We suggest that this phenomenon can be used to pattern and modulate the electron density in low-dimensional structures with particular application to systems where a proximity effect from a surface gate is valuable

How Should Justice Policy Treat Young Offenders?

The justice system in the United States has long recognized that juvenile offenders are not the same as adults, and has tried to incorporate those differences into law and policy. But only in recent decades have behavioral scientists and neuroscientists, along with policymakers, looked rigorously at developmental differences, seeking answers to two overarching questions: Are young offenders, purely by virtue of their immaturity, different from older individuals who commit crimes? And, if they are, how should justice policy take this into account? A growing body of research on adolescent development now confirms that teenagers are indeed inherently different from adults, not only in their behaviors, but also (and of course relatedly) in the ways their brains function. These findings have influenced a series of Supreme Court decisions relating to the treatment of adolescents, and have led legislators and other policymakers across the country to adopt a range of developmentally informed justice policies. New research is showing distinct changes in the brains of young adults, ages 18 to 21, suggesting that they too may be immature in ways that are relevant to justice policy. This knowledge brief from the MacArthur Foundation Research Network on Law and Neuroscience considers the implications of this new research

Predicting the Knowledge: Recklessness Distinction in the Human Brain

Criminal convictions require proof that a prohibited act was performed in a statutorily specified mental state. Different legal consequences, including greater punishments, are mandated for those who act in a state of knowledge, compared with a state of recklessness. Existing research, however, suggests people have trouble classifying defendants as knowing, rather than reckless, even when instructed on the relevant legal criteria. We used a machine-learning technique on brain imaging data to predict, with high accuracy, which mental state our participants were in. This predictive ability depended on both the magnitude of the risks and the amount of information about those risks possessed by the participants. Our results provide neural evidence of a detectable difference in the mental state of knowledge in contrast to recklessness and suggest, as a proof of principle, the possibility of inferring from brain data in which legally relevant category a person belongs. Some potential legal implications of this result are discussed

Search for the rare hadronic decay Bs0ppBs0pp

A search for the rare hadronic decay B0s→p¯p is performed using proton-proton collision data recorded by the LHCb experiment at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 6  fb−1. No evidence of the decay is found and an upper limit on its branching fraction is set at B(B0s→p¯p)<4.4(5.1)×10−9 at 90% (95%) confidence level; this is currently the world’s best upper limit. The decay mode B0→p¯p is measured with very large significance, confirming the first observation by the LHCb experiment in 2017. The branching fraction is determined to be B(B0→p¯p)=(1.27±0.15±0.05±0.04)×10−8, where the first uncertainty is statistical, the second is systematic and the third is due to the external branching fraction of the normalization channel B0→K+π−. The combination of the two LHCb measurements of the B0→p¯p branching fraction yields B(B0→p¯p)=(1.27±0.13±0.05±0.03)×10−8

The Upgrade of LHCb VELO

LHCb physics achievements to date include some of the world’s most precise flavour physics measurements, including the CKM phase and the discovery of CP violation in the charm sector. These achievements have been possible thanks to the enormous data samples collected and the performance of the subdetectors, with the efficiency and precision of the silicon vertex detector (VELO) being a major contributor to this success. The experiment has been upgraded to run at higher luminosity, requiring 40 MHz readout. The VELO Upgrade modules are composed of hybrid pixel detectors and electronics circuits glued onto a cooling substrate, made of thin silicon plates with embedded micro-channels, allowing for the circulation of evaporative CO2. The detectors are located in vacuum, separated from the beam by a thin aluminium box. The upgraded VELO is composed of 52 modules placed along the beam axis divided into two retractable halves. The design, production, installation and commissioning of the VELO Upgrade system is presented together with test results