Guiding properties of a non-isothermal atmosphere for acoustic-gravity waves

The propagation of pressure waves in a stratified, non-isothermal atmosphere is studied in the linear approximation. It is found that acoustic and acoustic-gravity waves can be horizontally guided by the effect of the Earth’s thermocline alone, under very mild conditions on the temperature gradient steepness. The effect of the Earth’s surface is also studied. Lamb’s modes associated with the rigid surface are, then, identified and their behaviour, as a function of the Earth’s position, is discussed. Finally, dissipation is included, and its effect is derived using a perturbation technique

Work statistics and Entanglement across the fermionic superfluid-insulator transition

Entanglement in many-body systems may display interesting signatures of quantum phase transitions and similar properties are starting to be encountered in the analysis of work fluctuations. Here, we consider the fermionic superfluid-to-insulator transition (SIT) and relate its entanglement properties with its work distribution statistics. The SIT is modeled by the attractive fermionic Hubbard model in the presence of randomly distributed impurities. The work distribution is calculated across two quench protocols, both triggering the SIT. In the first, the concentration of impurities is increased; in the second, the impurities' disorder strength is varied. Our results indicate that, the critical state that induces minimization of the entanglement also maximizes the average work. We demonstrate that, for this state, density fluctuations vanish at all orders, hence all central moments of the work probability distribution are exactly zero at criticality. For systems undergoing a precursor to the transition (short chains with finite impurity potential) numerical results confirm these predictions, with higher moments further from the ideal result. For both protocols, at criticality, the system absorbs the most energy with almost no penalty in terms of fluctuations: ultimately this feature could be used to implement a quantum critical battery. The effects of temperature on these signatures of critical behaviour are also investigated and shown to favor work extraction for high enough temperatures

Linear entropy fails to predict entanglement behavior in low-density fermionic systems

Entanglement is considered a fundamental ingredient for quantum technologies and condensed matter systems are among the good candidates for quantum devices. For bipartite pure states the von Neumann entropy is a proper measure of entanglement, while the linear entropy, associated to the mixedness of the reduced density matrices, is a simpler quantity to be obtained and is considered to be qualitatively equivalent to the von Neumann. Here we investigate both linear and von Neumann entropies for quantifying entanglement in homogeneous, superlattice and disordered Hubbard chains. We find regimes of parameters for which the linear entropy fails in reproducing the qualitative behavior of the von Neumann entropy. This then may lead to incorrect predictions i) of maximum and minimum entanglement states and ii) of quantum phase transitions

High-resolution mid-infrared spectroscopy based on ultrafast Cr:ZnSe laser

High-resolution broadband direct frequency comb spectroscopy in the mid-infrared spectral region is an extremely powerful and versatile experimental technique that allows study of the molecular structure of gaseous compounds with multiple applicative and scientific implications. Here we present the first implementation of an ultrafast Cr:ZnSe mode-locked laser covering more than 7 THz at around the emission wavelength of 2.4 um, for direct frequency comb molecular spectroscopy with a frequency sampling of 220 MHz and a frequency resolution of 100 kHz. This technique is based on a scanning micro-cavity resonator with a Finesse of 12,000 and a diffraction reflecting grating. We demonstrate its application in high-precision spectroscopy of the acetylene molecule by retrieving line center frequencies of more than 68 roto-vibrational lines. Our technique paves the way for real time spectroscopic studies as well as for hyperspectral imaging techniques

Incorporating changes in albedo in estimating the climate mitigation benefits of land use change projects

International audienceSome climate scientists are questioning whether the practice of converting of non-forest lands to forest land (afforestation or reforestation) is an effective climate change mitigation option. The discussion focuses particularly on areas where the new forest is primarily coniferous and there is significant amount of snow since the increased climate forcing due to the change in albedo may counteract the decreased climate forcing due to carbon dioxide removal. In this paper, we develop a stand-based model that combines changes in surface albedo, solar radiation, latitude, cloud cover and carbon sequestration. As well, we develop a procedure to convert carbon stock changes to equivalent climatic forcing or climatic forcing to equivalent carbon stock changes. Using the model, we investigate the sensitivity of combined affects of changes in surface albedo and carbon stock changes to model parameters. The model is sensitive to amount of cloud, atmospheric absorption, timing of canopy closure, carbon sequestration rate among other factors. The sensitivity of the model is investigated at one Canadian site, and then the model is tested at numerous sites across Canada. In general, we find that the change in albedo reduces the carbon sequestration benefits by approximately 30% over 100 years, but this is not drastic enough to suggest that one should not use afforestation or reforestation as a climate change mitigation option. This occurs because the forests grow in places where there is significant amount of cloud in winter. As well, variations in sequestration rate seem to be counterbalanced by the amount and timing of canopy closure. We close by speculating that the effects of albedo may also be significant in locations at lower latitudes, where there are less clouds, and where there are extended dry seasons. These conditions make grasses light coloured and when irrigated crops, dark forests or other vegetation such as biofuels replace the grasses, the change in carbon stocks may not compensate for the darkening of the surface

Neurohormonas y citocinas en la insuficiencia cardíaca. Correlación con la reserva de flujo coronario

Introduction and objectives. In heart failure, the coronary flow reserve (CFR) measured by positron-emission tomography (PET) is reduced. As neurohormone and cytokine levels are also altered in patients with the condition, our aim was to determine whether there is a correlation between CFR and neurohormone and cytokine levels. Patients and method. The study included 40 patients with heart failure but without ischemic heart disease. Myocardial blood flow was measured by PET using nitrogen- 13 ammonia at baseline and during ATP infusion. The CFR was calculated for each patient. In addition, levels of the following were determined: norepinephrine, endothelin- 1, angiotensin-II, atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), tumor necrosis factor-alpha, interleukin (IL)-1β, soluble IL-2 receptor, and IL-6. Results. All neurohormone levels were elevated above reference values. The levels of all cytokines, except IL-1β, were also elevated. There was a significant negative correlation between CFR and the levels of several neurohormones: ANP (r=–0.476), BNP (r=–0.442), and IL-6 (r=–0.509). Conclusions. In heart failure, the decrease in CFR is correlated with increases in the levels of certain neurohormones (i.e., ANP and BNP) and cytokines (i.e., IL-6), with vasodilatory effect. These increases are probably are related to compensatory mechanisms that are unable to correct for the endothelial dysfunction present in these patients