438 research outputs found
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
Intracavity intensity noise suppression in the inverse Compton scattering source BriXSinO exploiting carrier-envelope offset manipulation
We report on a technique that exploits the control of the carrier -envelope offset to suppress the frequency-to-intensity noise conversion in the locking of a mode-locking laser against a high-finesse optical enhancement resonator. A proper combination of the laser carrier-envelope offset and the resonator finesse allows the improvement of the signal-to-noise ratio of the optical intensity trapped into the optical resonator. In this paper, we show the application of this technique in the laser system of the inverse Compton scattering source BriXSinO, currently under development in Milan, Italy, demonstrating the possibility of achieving an intracavity intensity noise reduction of a factor of 20
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
Architettura e Realismo. Programma
Il convegno "«Uno spazio reale adeguato»: architettura e realismo", la giornata di studi e mostra "«Il sempre teorizzar nulla rileva...»: nuovo realismo e architettura della città ", il convegno "Per una nozione operativa di realismo: espressione critica e impegno civile e la mostra Il realismo nella didattica del progetto: Torino Napoli Milano", uniti sotto il titolo comune di Architettura e realismo sono promossi da un gruppo di lavoro costituito da giovani ricercatori e docenti delle facoltà di Architettura di Torino, Milano e Napoli, a partire dalla avvertita esigenza di aggiornare la riflessione sulla architettura come pratica costruttiva e sulla città come luogo per eccellenza della vita dell'uomo a partire da una analisi critica di quanto si è prodotto negli ultimi decenni. Da un lato grandi architetture spettacolari che rispondono alle logiche del mercato e della comunicazione e, dall'altro - in una sorta di inspiegabile paradosso - la de- regolazione della città diffusa priva di struttura, elementi riconoscibili e spazio pubblico. In entrambi i casi, pur nella loro diversità , si è prodotto un pericoloso distacco della architettura dal suo obiettivo ultimo: conformare lo spazio fisico dei manufatti e della città , del territorio e del paesaggio, per determinare in maniera consistente lo scenario della vita dell'uomo, nella sua dimensione, innanzitutto, collettiv
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
Carrier-envelope offset frequency measurement by means of an external optical resonator
A general-purpose method based on the implementation of the asymmetric Pound-Drever-Hall (PDH) technique is proposed to measure the carrier-envelope offset (CEO) frequency of a mode-locked laser using an external optical cavity. By analyzing the synchronously demodulated signal of the spectrally filtered cavity reflection when the optical resonator is locked to the mode-locked laser, a discriminating signal depending on the relative frequency offset between the mode-locked and optical cavity comb-like spectra is obtained. For a given geometry and group delay dispersion (GDD) of the cavity parameters (i.e., a known cavity mode offset), this signal can be used to retrieve the laser CEO. This approach turns out to be advantageous in terms of setup complexity with respect to other well-known techniques that rely on non-linear frequency generation, such as f-2f interferometers. In addition, this method can be used to precisely determine the laser-cavity spectral coupling, which is an important topic in cavity-enhanced spectroscopy and non-linear optics applications. After the theoretical description of the generalized asymmetric PDH signal, an experimental validation of the proposed method is reported using an Er-doped fiber frequency comb source centered at 1,550 nm, with a repetition rate of 250 MHz, locked to a linear optical cavity with a 1 GHz free spectral range. The theoretical effect of the GDD is confirmed experimentally using different cavity configurations. Moreover, the comparison with the CEO frequency values measured using an f-2f interferometer demonstrates the feasibility of the proposed method
Design and Optimization of a Pneumatic Clamping System for Direct-Driven Rotary Tables
Modern direct-driven and high-speed rotary tables with torque motor are optimally suited for all handling and assembly applications that require the shortest indexing times and flexible positioning. The following paper is devoted to the study, the design, and the optimization of an innovative table clamping system (brake for accurate positioning) actuated by pneumatic energy, working at a maximum clamping pressure of 6 bar. The challenge for the aforementioned application is related to developing a solution able to provide a maximum tangential torque (with clamping actuated) in the range of thousands of Nm without leveraging the use of high-pressure hydraulic energy. The optimization of the proposed solution is based on the precise calculation of the stresses in order to perform a fatigue assessment and on the elastic deformation of the clamps in order to set the correct tolerances between the mating parts. Eventually, an experimental campaign is carried out in order to tune the numerical model, which is then used to validate the proposed design solution
Platelet rich plasma from different preparations: effect on chondrocytes and synoviocytes of osteoarthritis patients
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