Chiral molecules that are non-superimposable mirror images of each other, known as enantiomers, have identical chemical and physical properties unless they interact with another chiral entity, such ...as chiral light. Chiroptical1 eects arising from such interactions are used to detect enantiomers in mixtures and to induce enantioselective synthesis and catalysis. Chiroptical eects often arise from the interplay between light-induced electric- and magnetic-dipole transitions in a molecule and evolve on ultrafast electronic timescales. Here we use high-harmonic generation2,3 from a randomly oriented gas of molecules subjected to an intense laser eld, to probe chiral interactions on these sub-femtosecond timescales. We show that a slight disparity in the laser-driven electron dynamics in the two enantiomers is recorded and amplied by several orders of magnitude in the harmonic spectra. Our work shows that chiroptical detection can go beyond detecting chiral structure47 to resolving and controlling chiral dynamics on electronic timescales.
Circular dichroism in the extreme ultraviolet range is broadly used as a sensitive structural probe of matter, from the molecular photoionization of chiral species to the magnetic properties of ...solids. Extending such techniques to the dynamical regime has been a long-standing quest of solid-state physics and physical chemistry, and was only achieved very recently thanks to the development of femtosecond circular extreme ultraviolet sources. Only a few large facilities, such as femtosliced synchrotrons or free-electron lasers, are currently able to produce such pulses. Here, we propose a new compact and accessible alternative solution: resonant high-order harmonic generation of an elliptical laser pulse. We show that this process, based on a simple optical set-up, delivers bright, coherent, ultrashort, quasi-circular pulses in the extreme ultraviolet. We use this source to measure photoelectron circular dichroism on chiral molecules, opening the route to table-top time-resolved femtosecond and attosecond chiroptical experiments.
This study combines major ion and isotope chemistry, age tracers, fracture density characterizations, and physical hydrology measurements to understand how the structure of the critical zone (CZ) ...influences its function, including water routing, storage, mean water residence times, and hydrologic response. In a high elevation rhyolitic tuff catchment in the Jemez River Basin Critical Zone Observatory (JRB-CZO) within the Valles Caldera National Preserve (VCNP) of northern New Mexico, a periodic precipitation pattern creates different hydrologic flow regimes during spring snowmelt, summer monsoon rain, and fall storms. Hydrometric, geochemical, and isotopic analyses of surface water and groundwater from distinct stores, most notably shallow groundwater that is likely a perched aquifer in consolidated collapse breccia and deeper groundwater in a fractured tuff aquifer system, enabled us to untangle the interactions of these groundwater stores and their contribution to streamflow across 1 complete water year (WY).
Fast neutrons are generated naturally at the land surface by energetic cosmic rays. These “background” neutrons respond strongly to the presence of water at or near the land surface and represent a ...hitherto elusive intermediate spatial scale of observation that is ideal for land surface studies and modeling. Soil moisture, snow, and biomass each have a distinct influence on the spectrum, height profile, and directional intensity of neutron fluxes above the ground, suggesting that different sources of water at the land surface can be distinguished with neutron data alone. Measurements can be taken at fixed sites for long‐term monitoring or in a moving vehicle for mapping over large areas. We anticipate applications in many previously problematic contexts, including saline environments, wetlands and peat bogs, rocky soils, the active layer of permafrost, and water and snow intercepted by vegetation, as well as calibration and validation of data from spaceborne sensors.
Photoionization of chiral molecules by circularly polarized radiation gives rise to a strong forward/backward asymmetry in the photoelectron angular distribution, referred to as photoelectron ...circular dichroism (PECD). Here we show that PECD is a universal effect that reveals the inherent chirality of the target in all ionization regimes: single photon, multiphoton, above-threshold and tunnel ionization. These different regimes provide complementary spectroscopic information at electronic and vibrational levels. The universality of the PECD can be understood in terms of a classical picture of the ionizing process, in which electron scattering on the chiral potential under the influence of a circularly polarized electric field results in a strong forward/backward asymmetry.
Although there are solid findings regarding the detrimental effect of alcohol consumption, the existing evidence on the effect of other dietary factors on breast cancer (BC) risk is inconclusive. ...This study aimed to evaluate the association between dietary patterns and risk of BC in Spanish women, stratifying by menopausal status and tumour subtype, and to compare the results with those of Alternate Healthy Index (AHEI) and Alternate Mediterranean Diet Score (aMED).
We recruited 1017 incident BC cases and 1017 matched healthy controls of similar age (±5 years) without a history of BC. The association between 'a priori' and 'a posteriori' developed dietary patterns and BC in general and according to menopausal status and intrinsic tumour subtypes (ER+/PR+ and HER2-; HER2+; and ER-/PR- and HER2-) was evaluated using logistic and multinomial regression models.
Adherence to the Western dietary pattern was related to higher risk of BC (OR for the top vs the bottom quartile 1.46 (95% CI 1.06-2.01)), especially in premenopausal women (OR=1.75; 95% CI 1.14-2.67). In contrast, the Mediterranean pattern was related to a lower risk (OR for the top quartile vs the bottom quartile 0.56 (95% CI 0.40-0.79)). Although the deleterious effect of the Western pattern was similarly observed in all tumour subtypes, the protective effect of our Mediterranean pattern was stronger for triple-negative tumours (OR=0.32; 95% CI 0.15-0.66 and Pheterogeneity=0.04). No association was found between adherence to the Prudent pattern and BC risk. The associations between 'a priori' indices and BC risk were less marked (OR for the top vs the bottom quartile of AHEI=0.69; 95% CI 0.51-0.94 and aMED=0.74; 95% CI 0.46-1.18)).
Our results confirm the harmful effect of a Western diet on BC risk, and add new evidence on the benefits of a diet rich in fruits, vegetables, legumes, oily fish and vegetable oils for preventing all BC subtypes, and particularly triple-negative tumours.
ABSTRACT
Low-mass compact galaxies (ultracompact dwarfs, UCDs, and compact ellipticals, cEs) populate the stellar size–mass plane between globular clusters and early-type galaxies. Known to be formed ...either in situ with an intrinsically low mass or resulting from the stripping of a more massive galaxy, the presence of a supermassive or an intermediate-mass black hole (BH) could help discriminate between these possible scenarios. With this aim, we have performed a multiwavelength search of active BH activity, i.e. active galactic nuclei (AGN), in a sample of 937 low-mass compact galaxies (580 UCDs and 357 cEs). This constitutes the largest study of AGN activity in these types of galaxies. Based on their X-ray luminosity, radio luminosity, and morphology, and/or optical emission line diagnostic diagrams, we find a total of 11 cEs that host an AGN. We also study for the first time the location of both low-mass compact galaxies (UCDs and cEs) and dwarf galaxies hosting AGN on the BH–galaxy scaling relations, finding that low-mass compact galaxies tend to be overmassive in the BH mass–stellar mass plane but not as much in the BH mass–stellar velocity dispersion correlation. This, together with available BH mass measurements for some of the low-mass compact galaxies, supports a stripping origin for the majority of these objects that would contribute to the scatter seen at the low-mass end of the BH–galaxy scaling relations. However, the differences are too large to be explained solely by this scatter, and thus our results suggest that a flattening at such low masses is also plausible, happening at a velocity dispersion of ∼20–40 km s−1.
The size of a hard K
x-ray source (Formula: see text = 17.48 keV) produced by a high intensity femtosecond laser interacting with a solid molybdenum target is experimentally investigated for a wide ...range of laser intensity (I ~ 10
-2.8 × 10
W/cm
) and for four values of the temporal contrast ratio (6.7 × 10
< CR < 3.3 × 10
). Results point out the size enlargement of the x-ray source with the increase of laser intensity and with the deterioration of temporal contrast. It amounts up to sixteen times the laser spot size at the highest laser intensity and for the lowest temporal contrast ratio. Using hydrodynamic simulations, we evaluate the density scale length of the pre-plasma L/λ just before the main pulse peak. This allows us to show that a direct correlation with the laser absorption mechanisms is not relevant to explain the large size broadening. By varying the thickness of the molybdenum target down to 4 µm, the impact of hot electron scattering inside the solid is also proved irrelevant to explain the evolution of both the x-ray source size and the K
photon number. We deduce that the most probable mechanism yielding to the broadening of the source size is linked to the creation of surface electromagnetic fields which confine the hot electrons at the solid surface. This assumption is supported by dedicated experiments where the evolution of the size enlargement of the x-ray source is carefully studied as a function of the laser focal spot size for the highest contrast ratio.
This study explores the ability of a hard K
x-ray source (17.48 keV) produced by a 10 TW class laser system operated at high temporal contrast ratio and high repetition rate for phase contrast ...imaging. For demonstration, a parametric study based on a known object (PET films) shows clear evidence of feasibility of phase contrast imaging over a large range of laser intensity on target (from ~10
W/cm
to 7.0 × 10
W/cm
). To highlight this result, a comparison of raw phase contrast and retrieved phase images of a biological object (a wasp) is done at different laser intensities below the relativistic intensity regime and up to 1.3 × 10
W/cm
. This brings out attractive imaging strategies by selecting suitable laser intensity for optimizing either high spatial resolution and high quality of image or short acquisition time.
Resumen Introducción El síndrome de fatiga crónica (SFC) se caracteriza por la presencia de fatiga intratable y sueño no reparador, síntomas con una alta prevalencia en múltiples enfermedades y/o ...como efecto secundario de diferentes fármacos. Diferentes trabajos demostraron una alta prevalencia de los trastornos del sueño asociados al SFC. Además, los síntomas de sueño no reparador y fatiga son síntomas frecuentes en los trastornos del sueño, lo que hace que en muchos pacientes con SFC haya que descartar un trastorno de sueño primario. Desarrollo Este trabajo se ha realizado a través de una búsqueda sistematizada con términos MeSH (Sleep + Chronic fatigue syndrome) en la base de datos PubMed. Conclusión La identificación de los diferentes trastornos primarios del sueño en los pacientes con criterios diagnósticos de SFC, nos permitiría realizar un abordaje del paciente más completo, con nuevas estrategias diagnósticas y terapéuticas que podrían mejorar la calidad de vida de estos pacientes.
PDF
