Critical behavior of ion mobilities near the superfluid transition

Measurements are reported of the mobilities of helium ions in superfluid helium very close to the λ transition. The mobilities of both positive and negative ions appear to be singular in the sense of having infinite slope at the transition. The measurements are made by a new differential technique, based on the space-charge-limited method, which makes possible a sensitivity to changes in mobility of the order of parts in 104. This allows mobility measurements into the range |ε|<10-4, where ε=(T/Tλ)-1. Most of the reported measurements are taken along isotherms which cross the λ line at elevated pressures, although a series at saturated vapor pressure is also reported. Means of transforming the data between various thermodynamic paths are discussed. Uncertainty as to which thermodynamic path should be considered fundamental together with experimental problems in the technique at this stage in its development make quantitative assessment of the singularity difficult. However, if we assume a limiting form (μ-μλ)/μλ∼(-ε)ρ′, where μ is the mobility and μλ its value at the transition, we find for the exponent ρ′=0.94±0.02

Experiments on Quantum and Thermal Desorption from ^4He Films

Desorption of He atoms from thin films may be resolved experimentally into quantum and thermal components. We show that quantum desorption becomes the dominant part of the signal in submonolayer films. We also show that, when all effects of collisions between desorbed atoms are eliminated, quantum desorption is not focused normal to the surface of optically polished sapphire crystals

Why early collective action pays off: evidence from setting Protected Geographical Indications

AbstractThe registration of Geographical Indications (GIs) under the European Union (EU) legislation requires collective action and considerable efforts borne by multiple actors such as producers, processors, public authorities and research centers. We analyze their efforts, risks and benefits by comparing two EU GI registration processes in Italy and Austria, namely the Sorana bean Protected Geographical Indication (PGI) and the Perry from Mostviertel PGI. Results from the institutional and transaction costs analysis suggest that intensive interaction for solving conflicting interests, negotiating quality standards and defining common rules might pay off in indirect benefits and reduced risks. In particular, an inclusion of diverse and heterogeneous interest groups and a high degree of direct enterprise participation along the GI application process (as observed in the Italian case) generate benefits such as trust and social cohesion, which then support the actual use of the GI label and a better implementation of associated quality standards. A supportive legal framework with assistance from public authorities can back up the community of producers not only in technical aspects, but also as mediators when conflicts seem to be difficult to solve. As there seems to be a positive relationship between the intensity and effectiveness of collective action and the likelihood of achieving broadly accepted standards and social cohesion needed for successful GI implementation, the question for future research would not be how to avoid collective efforts but how to effectively organize the interaction among heterogeneous producer groups

Viscosity and positive-ion mobility near the melting transition in liquid ^4He

New measurements are presented of the shear viscosity η and the positive-ion mobility μ near the melting transition in liquid 4He. Interpreted in terms of the Stokes law for the drag on a sphere in a viscous medium, it is found, contrary to expectation, that the effective radius of the ion remains constant or decreases slightly as the melting transition is approached at constant temperature. Attempts to explain this observation have not been successful. On the other hand, an older mystery concerning the effective radius of the ion is cleared up: Ahlers and Gamota, comparing data for η and μ at the vapor pressure curve found that the effective radius has a maximum 40 mK below the λ transition (i.e., the lower triple point). We have observed a similar maximum on the melting curve, 40 mK below the upper triple point. It is shown that these maxima may be accounted for by an electrostrictively induced λ transition around the ion. In this interpretation, the maximum along the melting curve serves as the first empirical evidence that the λ line extends into the region of supercooled liquid at pressures above the melting curve

Foregrounds in the BOOMERANG-LDB data: a preliminary rms analysis

We present a preliminary analysis of the BOOMERanG LDB maps, focused on foregrounds. BOOMERanG detects dust emission at moderately low galactic latitudes ($b > -20^o$) in bands centered at 90, 150, 240, 410 GHz. At higher Galactic latitudes, we use the BOOMERanG data to set conservative upper limits on the level of contamination at 90 and 150 GHz. We find that the mean square signal correlated with the IRAS/DIRBE dust template is less than 3% of the mean square signal due to CMB anisotropy

Mapping the CMB Sky: The BOOMERANG experiment

We describe the BOOMERanG experiment, a stratospheric balloon telescope intended to measure the Cosmic Microwave Background anisotropy at angular scales between a few degrees and ten arcminutes. The experiment has been optimized for a long duration (7 to 14 days) flight circumnavigating Antarctica at the end of 1998. A test flight was performed on Aug.30, 1997 in Texas. The level of performance achieved in the test flight was satisfactory and compatible with the requirements for the long duration flight.Comment: 11 pages, 6 figure

Extinction of the Kapitza Anomaly for Phonons along the Surface Normal Direction

We have succeeded in extinguishing the anomalous Kapitza transmission of phonons whose wave vector is normal to a surface treated by conventional means and handled in air. In the same experiments, phonons approaching the surface with oblique wave vectors are anomalously transmitted. We argue that these results demonstrate that the Kapitza anomaly is due to surface defects which couple to the phonon strain field

The BOOMERANG North America Instrument: a balloon-borne bolometric radiometer optimized for measurements of cosmic background radiation anisotropies from 0.3 to 4 degrees

We describe the BOOMERANG North America (BNA) instrument, a balloon-borne bolometric radiometer designed to map the Cosmic Microwave Background (CMB) radiation with 0.3 deg resolution over a significant portion of the sky. This receiver employs new technologies in bolometers, readout electronics, millimeter-wave optics and filters, cryogenics, scan and attitude reconstruction. All these subsystems are described in detail in this paper. The system has been fully calibrated in flight using a variety of techniques which are described and compared. It has been able to obtain a measurement of the first peak in the CMB angular power spectrum in a single balloon flight, few hours long, and was a prototype of the BOOMERANG Long Duration Balloon (BLDB) experiment.Comment: 40 pages, 22 figures, submitted to Ap

Noise Properties of the BOOMERANG Instrument

In this paper we report a short description of the BOOMERANG experiment explaining his scientific goal and the technologies implied. We concentrate then on the analysis of the noise properties discussing in particular the scan synchronous noise. Finally we present the calibration technique and the sensitivity of all the channels