Algebra of chiral currents on the physical surface

Using a particular structure for the Lagrangian action in a one-dimensional Thirring model and performing the Dirac's procedure, we are able to obtain the algebra for chiral currents which is entirely defied on the constraint surface in the corresponding hamiltonian description of the theory.Comment: 10 page

An early warning indicator for atmospheric blocking events using transfer operators

The existence of persistent midlatitude atmospheric flow regimes with time-scales larger than 5-10 days and indications of preferred transitions between them motivates to develop early warning indicators for such regime transitions. In this paper, we use a hemispheric barotropic model together with estimates of transfer operators on a reduced phase space to develop an early warning indicator of the zonal to blocked flow transition in this model. It is shown that, the spectrum of the transfer operators can be used to study the slow dynamics of the flow as well as the non-Markovian character of the reduction. The slowest motions are thereby found to have time scales of three to six weeks and to be associated with meta-stable regimes (and their transitions) which can be detected as almost-invariant sets of the transfer operator. From the energy budget of the model, we are able to explain the meta-stability of the regimes and the existence of preferred transition paths. Even though the model is highly simplified, the skill of the early warning indicator is promising, suggesting that the transfer operator approach can be used in parallel to an operational deterministic model for stochastic prediction or to assess forecast uncertainty

Discovery of close companions to the nearby young stars HD 199143 and HD 358623

Young stellar systems in the solar neighborhood provide valuable laboratories for detailed studies of star and planet formation. The bright F8V star HD 199143 and the Li-rich late-type emission line star HD 358623 are among the nearest young stars identified to date, and may be members of a young association in Capricornus. We present high-resolution near-infrared images of these two sources, obtained using the adaptive optics system on the 3.6-meter telescope at the European Southern Observatory in La Silla, Chile. Our observations reveal that both are in fact close binary systems. The newly discovered companion at a separation of $\sim$1'' may account for the unusual characteristics of HD 199143 --rapid rotation, emission lines, ultraviolet variability, and excess infrared emission-- recently discussed by van den Ancker and co-workers. HD 199143 may be a rare example of a close binary with only a circum{\it secondary} disk. With the detection of a $\sim$2'' companion, HD 358623 is now possibly one of the closest known T Tauri binaries. Both binary systems are prime targets for follow-up spectroscopic and astrometric observations.Comment: 9 pages, 1 PostScript figure, to appear in The Astrophysical Journal Letter

Effects of Surface Roughness on the Electrochemical Reduction of CO₂ over Cu

We have investigated the role of surface roughening on the CO₂ reduction reaction (CO₂RR) over Cu. The activity and product selectivity of Cu surfaces roughened by plasma pretreatment in Ar, O₂, or N₂ were compared with that of electrochemically polished Cu samples. Differences in total and product current densities, the ratio of current densities for HER (the hydrogen evolution reaction) to CO₂RR, and the ratio of current densities for C₂₊ to C₁ products depend on the electrochemically active surface and are nearly independent of plasma composition. Theoretical analysis of an electropolished and roughened Cu surface reveals a higher fraction of undercoordinated Cu sites on the roughened surface, sites that bind CO preferentially. Roughened surfaces also contain square sites similar to those on a Cu(100) surface but with neighboring step sites, which adsorb OC–COH, a precursor to C₂₊ products. These findings explain the increases in the formation of oxygenates and hydrocarbons relative to CO and the ratio of oxygenates to hydrocarbons observed with increasing surface roughness

Braking the Gas in the beta Pictoris Disk

(Abridged) The main sequence star beta Pictoris hosts the best studied circumstellar disk to date. Nonetheless, a long-standing puzzle has been around since the detection of metallic gas in the disk: radiation pressure from the star should blow the gas away, yet the observed motion is consistent with Keplerian rotation. In this work we search for braking mechanisms that can resolve this discrepancy. We find that all species affected by radiation force are heavily ionized and dynamically coupled into a single fluid by Coulomb collisions, reducing the radiation force on species feeling the strongest acceleration. For a gas of solar composition, the resulting total radiation force still exceeds gravity, while a gas of enhanced carbon abundance could be self-braking. We also explore two other braking agents: collisions with dust grains and neutral gas. Grains surrounding beta Pic are photoelectrically charged to a positive electrostatic potential. If a significant fraction of the grains are carbonaceous (10% in the midplane and larger at higher altitudes), ions can be slowed down to satisfy the observed velocity constraints. For neutral gas to brake the coupled ion fluid, we find the minimum required mass to be $\approx$ 0.03 M_\earth, consistent with observed upper limits of the hydrogen column density, and substantially reduced relative to previous estimates. Our results favor a scenario in which metallic gas is generated by grain evaporation in the disk, perhaps during grain-grain collisions. We exclude a primordial origin for the gas, but cannot rule out the possibility of its production by falling evaporating bodies near the star. We discuss the implications of this work for observations of gas in other debris disks.Comment: 19 pages, 12 figures, emulateapj. Accepted for publication in Ap

Stepwise drying of Lake Turkana at the end of the African Humid Period: a forced regression modulated by solar activity variations?

Although the timing of the termination of the African Humid Period (AHP) is now relatively well estab- lished, the modes and controlling factors of this drying are still debated. Here, through a geomorphological approach, we characterize the regression of Lake Turkana at the end of the AHP. We show that lake level fall during this period was not continuous but rather stepwise and consisted of five episodes of rapid lake level fall separated by episodes marked by slower rates of lake level fall. Whereas the overall regres- sive trend reflects a decrease in regional precipitations linked to the gradual reduction in Northern Hemisphere summer in- solation, itself controlled by orbital precession, we focus dis- cussion on the origin of the five periods of accelerated lake level fall. We propose that these periods are due to temporary reductions in rainfall across the Lake Turkana area associ- ated with repeated westward displacement of the Congo Air Boundary (CAB) during solar activity minima

Chemical composition and biological stability of pyrogenic C from a natural fire

2 pages, 1 figure, 3 references.-- Comunicación oral presentada en la Session 1. Pyrogenic C: Dstribution and Stability, en European Science Foundation-Exploratory Workshop, celebrado del 5-7 de noviembre 2013, en Sevilla, España.The work presented here is a synthesis of an article series conducted on natural charcoal in the environment (Alexis et al., 2007, Alexis et al. 2010, Alexis et al., 2012). The objective was to characterize the alteration of OM resulting from thermal alteration and to follow the fate of the produced pyrogenic C in soil.Peer reviewe

Police Crime Arrests Across the United States, 2005‐2016

Presentation at the Annual Meeting of the Academy of Criminal Justice Sciences, Las Vegas, NV, on March 18, 2022

Safety of titanium dioxide nanoparticles in cosmetics

Titanium dioxide (TiO2) is widely used in a variety of products including cosmetics. TiO2 in its nanoparticle form (nano-TiO2) is now the only form used as an ultraviolet (UV) filter in sunscreens, but also in some day creams, foundations and lip balms. While its efficacy as a UV filter is proven in the prevention of skin cancers and sunburns, some concerns have been raised about its safety. Indeed, considering its small size, nano-TiO2 is suspected to penetrate dermal, respiratory or gastrointestinal barriers, disseminate in the body and therefore constitute a potential risk to the consumer. At the skin level, most studies performed in humans or animals showed that nano-TiO2 did not penetrate beyond the outer layers of stratum corneum to viable cells and did not reach the general circulation, either in healthy or in compromised skin. The Scientific Committee on Consumer Safety (SCCS) considers nano-TiO2 as a non-sensitizer and as mild- or non-irritant to skin and concludes in no evidence of carcinogenicity (supported by the European Chemicals Agency), mutagenicity or reproductive toxicity after dermal exposure to nano-TiO2. According to the SCCS, nano-TiO2 from sunscreens does not present any health risk when applied on the skin at a concentration up to 25%. However, the SCCS does not recommend the use of nano-TiO2 in formulations that may lead to exposure of the consumer's lungs by inhalation (sprayable products and powders). Indeed, even if human data are sparse and inconsistent, lung inflammation was reported in animals. In 2016, the EU Cosmetic Regulation made nano-TiO2 as an authorized UV filter, except in products that could lead to exposure of the lungs. After oral exposure, nano-TiO2 absorption and toxicity are limited. The incidental oral exposure to nano-TiO2 contained in lip balms is thus not expected to induce adverse health effects