Kinetic Theory of Jet Dynamics in the Stochastic Barotropic and 2D Navier-Stokes Equations

We discuss the dynamics of zonal (or unidirectional) jets for barotropic flows forced by Gaussian stochastic fields with white in time correlation functions. This problem contains the stochastic dynamics of 2D Navier-Stokes equation as a special case. We consider the limit of weak forces and dissipation, when there is a time scale separation between the inertial time scale (fast) and the spin-up or spin-down time (large) needed to reach an average energy balance. In this limit, we show that an adiabatic reduction (or stochastic averaging) of the dynamics can be performed. We then obtain a kinetic equation that describes the slow evolution of zonal jets over a very long time scale, where the effect of non-zonal turbulence has been integrated out. The main theoretical difficulty, achieved in this work, is to analyze the stationary distribution of a Lyapunov equation that describes quasi-Gaussian fluctuations around each zonal jet, in the inertial limit. This is necessary to prove that there is no ultraviolet divergence at leading order, in such a way that the asymptotic expansion is self-consistent. We obtain at leading order a Fokker–Planck equation, associated to a stochastic kinetic equation, that describes the slow jet dynamics. Its deterministic part is related to well known phenomenological theories (for instance Stochastic Structural Stability Theory) and to quasi-linear approximations, whereas the stochastic part allows to go beyond the computation of the most probable zonal jet. We argue that the effect of the stochastic part may be of huge importance when, as for instance in the proximity of phase transitions, more than one attractor of the dynamics is present.     

Process interpretation of current entropic bounds

We show for Markov diffusion processes that the quadratic entropic bound, recently derived for the rate functions of nonequilibrium currents, can be seen as being produced by an effective process that creates current fluctuations in a sub-optimal way by modifying only the non-reversible part of the drift or force of the process considered while keeping its reversible part constant. This provides a clear interpretation of the bound in terms of a physical process, which explains, among other things, its relation to the fluctuation relation, linear response, and reversible limits. The existence of more general quadratic bounds, and related uncertainty relations, for physical quantities other than currents is also discussed.     

A new approach to free vibration analysis using boundary elements

A boundary element method for the analysis of free vibrations in solid mechanics is developed using a non-standard boundary integral approach. It is shown that, utilizing the statical fundamental solution and employing a special class of coordinate functions, the algebraic eigenvalue problem results. The method has been realized numerically for the two-dimensional elastodynamics, and a number of examples demonstrating its accuracy have been included.     

Analytical methods for the characterization of surface finishing in bricks

The recent restoration works of Santo Stefano Church Façade (XV century) in Venice have shown traces variously saved of different kind of surface finishes. These finishes were found on the brick's surface both in the masonry and in the decorative elements.Different brick's surface and decorative tile samples were investigated using several techniques: optical microscopy, scanning electron-microscopy, thermal analysis, infrared spectroscopy and reflectance Fourier transform infrared microspectroscopy.The evaluation of the reached results was used to understand the decorative techniques and to recognize the material employed.     

Su un caso particolare di stabilità in media della magnetoidrodinamica

Sunto Si considera un particolare fenomeno magnetoidrodinamico, che è una generalizzazione del problema di Couette per un liquido elettricamente conduttore in presenza di un opportuno campo magnetico e si dimostra che qualunque soluzione del problema dotata di una certa regolarità e stabile in media, ossia la somma delle energie cinetica e magnetica di una generica perturbazione è una funzione decrescente del tempo. A Bruno Finzi nel suo 70^mo compleanno. Lavoro eseguito nell'ambito dell'attività dei Raggruppamenti di ricerea matematica del C.N.R. Entrata in Redazione il 9 dicembre 1969.     

Directed evolution of an enantioselective lipase

BACKGROUND: The biocatalytic production of enantiopure compounds is of steadily increasing importance to the chemical and biotechnological industry. In most cases, however, it is impossible to identify an enzyme that possesses the desired enantioselectivity. Therefore, there is a strong need to create by molecular biological methods novel enzymes which display high enantioselectivity. RESULTS: A bacterial lipase from Pseudomonas aeruginosa (PAL) was evolved to catalyze with high enantioselectivity the hydrolysis of the chiral model substrate 2-methyldecanoic acid p-nitrophenyl ester. Successive rounds of random mutagenesis by ep-PCR and saturation mutagenesis resulted in an increase in enantioselectivity from E=1.1 for the wild-type enzyme to E=25.8 for the best variant which carried five amino acid substitutions. The recently solved three-dimensional structure of PAL allowed us to analyze the structural consequences of these substitutions. CONCLUSIONS: A highly enantioselective lipase was created by increasing the flexibility of distinct loops of the enzyme. Our results demonstrate that enantioselective enzymes can be created by directed evolution, thereby opening up a large area of novel applications in biotechnology.     

Experimental Investigation of Opposing Mixed Convection in a Channel with an open Cavity Below

Abstract

In this article, mixed convection in an open cavity with a heated wall bounded by a horizontal unheated plate is investigated experimentally. The heated wall is on the opposite side of the forced inflow. The results are reported in terms of wall temperature profiles of the heated wall and flow visualization. The range of pertinent parameters used in this experiment are Reynolds numbers (Re) from 100 to 2,000 and Richardson numbers (Ri) from 4.3 to 6,400. Also, the ratio between the length and the height of cavity (L/D) ranges from 0.5–2.0, and the ratio between the channel and cavity height (H/D) is equal to 1.0. The lack of experimental results on mixed convection in a channel with an open cavity below was an impetus for investigating this configuration when one cavity vertical wall is heated at uniform heat flux. The present results show that at the lowest investigated Reynolds number, the surface temperatures are lower than the corresponding surface temperatures for Re = 2,000 at the same ohmic heat flux. The flow visualization shows that for Re = 1,000, there are two nearly distinct fluid motions: a parallel forced flow in the channel and a recirculation flow inside the cavity. For Re = 100, the effect of a stronger buoyancy determines a penetration of thermal plumes from the heated plate wall into the upper channel. Moreover, the flow visualization shows that for lower Reynolds numbers, the forced motion penetrates inside the cavity, and a vortex structure is adjacent to the unheated vertical plate. At higher Reynolds numbers, the vortex structure has a larger extension while L/D is held constant.     

Experimental Investigation of Mixed Convection in a Channel With an Open Cavity

Mixed convection in an open cavity with a heated wall bounded by a horizontally unheated plate is investigated experimentally. The cavity has the heated wall on the inflow side. Mixed convection fluid flow and heat transfer within the cavity is governed by the buoyancy parameter, Richardson number (Ri), and Reynolds number (Re). The results are reported in terms of wall temperature profiles of the heated wall and flow visualization for Re = 100 and 1000, Ri in the range 30–110 (for Re = 1000) and 2800–8700 (for Re = 100), the ratio of the length to the height of cavity (L/D) is in the range 0.5–1.5, and the ratio of the channel height to cavity height (H/D) is in the range of 0.5 and 1.0. The present results show that the maximum dimensional temperature rise values decrease as the Reynolds and the Richardson numbers decrease. The flow visualization points out that for Re = 1000 there are two nearly distinct fluid motions: a parallel forced flow in the channel and a recirculation flow inside the cavity. For Re = 100 the effect of a stronger buoyancy determines a penetration of thermal plume from the heated plate wall into the upper channel. Nusselt numbers increase when L/D increase in the considered range of Richardson numbers.     

The use of commercially available personal UV-meters does cause less safe tanning habits: a randomized-controlled trial

UV Index information is currently recommended as a vehicle to raise public awareness about the risk of sun-exposure. It remains unknown to what extent this information can change personal sun-protective behavior. The aim of the study was to analyze the effects of UV-Index (UV-I) information provided by low cost, commercially available UV-I sensors on major indicators of sun-tanning behavior. A randomized-controlled trial was carried out on 94 healthy volunteers aged 21-23 years. After the exclusion of subjects with photosensitive disorders (n=3), 91 subjects were randomized in two arms after stratification based on phototype and sex. Both arms received a diary to be filled every day with a log of intentional sun-exposure during summer. Subjects in the intervention group also received a commercially available UV-I sensor. The UV-I sensors were switched on and the UV-value was recorded in 77% of days with sun-exposure. During days of sun-exposure, subjects randomized to the intervention group had longer average time of sun-exposure (227.7 vs 208.7 min per day, P=0.003), also between noon and 4 pm (P<0.001), and less frequently adopted sun protective measures than controls (hat [6.4%vs 10.2%, P=0.007], sunglasses [23.9%vs 30.8%, P=0.003], sunscreen [41.4%vs 47.2%, P=0.02]) and they experienced more frequent sunburns (27.8%vs 21.5%, P=0.004). The odd ratio of sunburns was 1.60 for subjects in the intervention group compared with controls (after adjustment for sex, sunscreen use and skin type). The mean UV-I value recorded by volunteers was lower (5.6 [SD+/-0.9]) than that (7.3 [SD+/-0.46]) recorded by a professional instrument in the same period at the same latitude. Poststudy laboratory tests showed that the sensor was able to detect only about 60% of the solar diffuse radiation. The use of UV-I sensors changed the sun protective behavior of sunbathers in the direction of less use of sun protective measures. One possible explanation is that the low cost UV-meters may have functioned incorrectly and under-reported UV exposure. This may have led to an underestimation of UV-I values, erroneously reassuring subjects and causing a less protective sunbathing behavior. Another hypothesis relies on a cognitive pitfall in the subjects' dealing with intermediate UV-I values, as they may have been discouraged in the use of sunscreen as they did not feel that they had yet been exposed to very harmful UV radiation.