Potenziamento delle stazioni di monitoraggio video esistenti e istallazione di nuove telecamere all’Osservatorio Astrofisico di “Serra la Nave”, a “La Montagnola” e a “Monte Vetore

Directed evolution is a method to tune the properties of enzymes for use in organic chemistry and biotechnology, to study enzyme mechanisms, and to shed light on Darwinian evolution in nature. In order to enhance its efficacy, iterative saturation mutagenesis (ISM) was implemented. This involves: 1) randomized mutation of appropriate sites of one or more residues; 2) screening of the initial mutant libraries for properties such as enzymatic rate, stereoselectivity, or thermal robustness; 3) use of the best hit in a given library as a template for saturation mutagenesis at the other sites; and 4) continuation of the process until the desired degree of enzyme improvement has been reached. Despite the success of a number of ISM-based studies, the question of the optimal choice of the many different possible pathways remains unanswered. Here we considered a complete 4-site ISM scheme. All 24 pathways were systematically explored, with the epoxide hydrolase from Aspergillus niger as the catalyst in the stereoselective hydrolytic kinetic resolution of a chiral epoxide. All 24 pathways were found to provide improved mutants with notably enhanced stereoselectivity. When a library failed to contain any hits, non-improved or even inferior mutants were used as templates in the continuation of the evolutionary pathway, thereby escaping from the local minimum. These observations have ramifications for directed evolution in general and for evolutionary biological studies in which protein engineering techniques are applied

Measuring stellar oscillations using equivalent widths of absorption lines

Kjeldsen et al. (1995, AJ 109, 1313; astro-ph/9411016) have developed a new technique for measuring stellar oscillations and claimed a detection in the G subgiant eta Boo. The technique involves monitoring temperature fluctuations in a star via their effect on the equivalent width of Balmer lines. In this paper we use synthetic stellar spectra to investigate the temperature dependence of the Balmer lines, Ca II, Fe I, the Mg b feature and the G~band. We present a list of target stars likely to show solar-like oscillations and estimate their expected amplitudes. We also show that centre-to-limb variations in Balmer-line profiles allow one to detect oscillation modes with l<=4, which accounts for the detection by Kjeldsen et al. of modes with degree l=3 in integrated sunlight.Comment: MNRAS (accepted); 7 pages, LaTeX with necessary style file and PostScript figures in a single uuencoded Z-compressed .tar fil

Invariant Solution underlying Oblique Stripe Patterns in Plane Couette Flow

When subcritical shear flows transition to turbulence, laminar and turbulent flow often coexists in space, giving rise to turbulent-laminar patterns. Most prominent are regular stripe patterns with large-scale periodicity and oblique orientation. Oblique stripes are a robust phenomenon, observed in experiments and flow simulations, yet their origin remains unclear. We demonstrate the existence of an invariant equilibrium solution of the fully nonlinear 3D Navier-Stokes equations that resembles the oblique pattern of turbulent-laminar stripes in plane Couette flow. We uncover the origin of the stripe equilibrium and show how it emerges from the well-studied Nagata equilibrium via two successive symmetry-breaking bifurcations

Modeling many-particle mechanical effects of an interacting Rydberg gas

In a recent work [Phys. Rev. Lett. 98, 023004 (2007)] we have investigated the influence of attractive van der Waals interaction on the pair distribution and Penning ionization dynamics of ultracold Rydberg gases. Here we extend this description to atoms initially prepared in Rydberg states exhibiting repulsive interaction. We present calculations based on a Monte Carlo algorithm to simulate the dynamics of many atoms under the influence of both repulsive and attractive longrange interatomic forces. Redistribution to nearby states induced by black body radiation is taken into account, changing the effective interaction potentials. The model agrees with experimental observations, where the ionization rate is found to increase when the excitation laser is blue-detuned from the atomic resonance

Finding the First Stars: The Hamburg/ESO Objective Prism Survey

We report on a search for extremely metal-poor ([Fe/H]<-3.0) turnoff stars in the Hamburg/ESO objective prism survey (HES). Metal-poor stars are selected by automatic spectral classification. Extensive simulations show that the selection efficiency for turnoff stars of [Fe/H]25% at B<16.5. Since the HES is more than 1 mag deeper than the HK survey of Beers et al. (1992), the HES offers the possibility to efficiently increase the total number of metal-poor stars by at least a factor of 4.Comment: To appear in: Proceedings of ESO/MPA conference "The First Stars". 2 pages, 1 figur

Mechanical effect of van der Waals interactions observed in real time in an ultracold Rydberg gas

We present time-resolved spectroscopic measurements of Rydberg-Rydberg interactions in an ultracold gas, revealing the pair dynamics induced by long-range van der Waals interactions between the atoms. By detuning the excitation laser, a specific pair distribution is prepared. Penning ionization on a microsecond timescale serves as a probe for the pair dynamics under the influence of the attractive long-range forces. Comparison with a Monte Carlo model not only explains all spectroscopic features but also gives quantitative information about the interaction potentials. The results imply that the interaction-induced ionization rate can be influenced by the excitation laser. Surprisingly, interaction-induced ionization is also observed for Rydberg states with purely repulsive interactions