Searching for protostars

Summary We present molecular-line observations of young stellar objects (YSOs) suspected to be protostars in the main accretion phase. The aim of this work is to define a list of the best protostellar candidates to be observed in the near future with the ISO spectrometers with the precise scope of searching for the final proof of the infall, theHoly Grail of astrophysics. The sources were mapped in the CS 3?2 and CO 3?2 lines; our data were used to investigate the presence of clumps of materials around these objects and the amount of this material, as well as to detect outflows associated with these objects that would enormously complicate the interpretation of further dynamics studies. Only one of our sources suspected to be protostars resulted to have a good chance of being in the accretion phase and to deserve further spectroscopic measurements. Paper presented at the 6th Cosmic Physics National Conference, Palermo, 3–7 November 1992.     

Continuous variable encoding by ponderomotive interaction

Recently it has been proposed to construct quantum error-correcting codes that embed a finite-dimensional Hilbert space in the infinite-dimensional Hilbert space of a system described by continuous quantum variables [D. Gottesman et al., Phys. Rev. A 64, 012310 (2001)]. The main difficulty of this continuous variable encoding relies on the physical generation of the quantum codewords. We show that ponderomotive interaction suffices to this end. As a matter of fact, this kind of interaction between a system and a meter causes a frequency change on the meter proportional to the position quadrature of the system. Then, a phase measurement of the meter leaves the system in an eigenstate of the stabilizer generators, provided that system and meter's initial states are suitably prepared. Here we show how to implement this interaction using trapped ions, and how the encoding can be performed on their motional degrees of freedom. The robustness of the codewords with respect to the various experimental imperfections is then analyzed.     

Ultrasonic velocity,isothermal compressibility,free volume andP i/T f values in molten stearic,palmitic and lauric acids. Reflections on fusion

Ultrasonic measurements on molten stearic, palmitic and lauric acids enable us to calculate the internal pressure (P _i), free volume, isoentropic compressibility, isothermal compressibility and heat capacity at constant volume as functions of the temperature. TheP _i/T _f values are compared withS _f /b — v_intr) values previously published and a general discussion on the fusion phenomenon is given. An equation connecting internal pressure, molar volume and temperature (P _i V=RT + (at/V)) is proposed and thea values are given.

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Zusammenfassung Die an geschmolzener Stearin-, Palmitin und Laurinsäure durchge-führten Ultraschallmessungen ermöglichen die Berechnung des inneren Druckes, des freien Volumens, der isoenthropischen Kompressibilität, der isothermen Kompressibilität und der Wärmekapazität bei konstantem Volumen als Funktion der Temperatur. DieP _i T _f Werte werden mit den früher veröffentlichten Werten von S_f (b —V _intl) verglichen und eine allgemeine Beschreibung des Schmelzvorgangs wird gegeben. Eine Gleichung zur Verbindung des inneren Druckes, des Molarvolumens und der Temperatur (P_i,V=RT + (a/V)) wird vorgeschlagen und diea Werte angegeben.

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Résumé Le calcul de la variation de la pression interne, du volume libre, de la compressibilité isoentropique, de la compressibilité isotherme et de la chaleur spécifique à volume constant des acides stéarique, palmitique et laurique, en fonction de la température, a été effectué à partir de mesures aux ultrasons. Les valeurs P_i/T_i sont comparées à celles de S_f(b- V_intl déjà publiées. Une discussion générale porte sur le phénomène de fusion. Une équation reliant la pression interne, le volume molaire et la température (P V=RT + (a/V)) est proposée et les valeurs de a' sont données.

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, , , , , , . PiTs. gD_fS/(b — V_tr) . , , : P_iV=RT + (a/V) a.

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We thank the CNR (Rome) for financial support.     

Size-dependent pressure-induced amorphization in nanoscale TiO2

We investigated the size-dependent high-pressure phase transition behavior of nanocrystalline anatase TiO2 with synchrotron x-ray diffraction and Raman spectroscopy to 45 GPa at ambient temperature. Pressure-induced amorphization results in a high-density amorphous (HDA) form when the starting crystallite size is < 10 mm. The HDA-TiO2 transforms to a low-density amorphous form at lower pressures. Harnessing the nanometer length scale thus provides a new window for experimental investigation of amorphization in poor glass formers and a synthesis route for new amorphous materials.     

Local pressure-induced metallization of a semiconducting carbon nanotube in a crossed junction

The electronic and vibrational density of states of a semiconducting carbon nanotube in a crossed junction was investigated by elastic and inelastic scanning tunneling spectroscopy. The strong radial compression of the nanotube at the junction induces local metallization spatially confined to a few nanometers. The local electronic modifications are correlated with the observed changes in the radial breathing and G band phonon modes, which react very sensitively to local mechanical deformation. In addition, the experiments reveal the crucial contribution of the image charges to the contact potential at nanotube-metal interfaces.