First-principle density-functional calculation of the Raman spectra of BEDT-TTF

We present a first-principles density-functional calculation for the Raman spectra of a neutral BEDT-TTF molecule. Our results are in excellent agreement with experimental results. We show that a planar structure is not a stable state of a neutral BEDT-TTF molecule. We consider three possible conformations and discuss their relation to disorder in these systems.Comment: 3 pages, 2 figures, submitted to the proceedings of ISCOM 200

Active noise compensation for multichannel magnetocardiography in an unshielded environment

A multichannel high-T/sub c/-SQUID-based heart scanner for unshielded environments is under development, Outside a magnetically shielded room, sensitive SQUID measurements are possible using gradiometers. However, it is difficult to realize large-baseline gradiometers in high-T/sub c/ materials, Therefore, the authors developed two active noise compensation techniques. In the Total Field Compensation technique, a Helmholtz type coil set is placed around the sensors. One magnetometer is used as a zero detector controlling the compensation current through the coil set. For Individual Flux Compensation, the reference signal is sent to the separate SQUIDs (or their flux transformer circuits) to compensate the local environmental noise fluxes, The latter technique was tested on low-T/sub c/ rf-SQUID magnetometers, each sensor set to a field resolution SQUID magnetometers, i.e. 0.1 pT/sub RMS///spl radic/Hz. The authors were able to suppress the environmental disturbances to such an extent that magnetocardiograms could be recorded in an ordinary environment. Here the two suppression techniques are described and experimental results are presente

Non-random dispersal in the butterfly Maniola jurtina: implications for metapopulation models

The dispersal patterns of animals are important in metapopulation ecology because they affect the dynamics and survival of populations. Theoretical models assume random dispersal but little is known in practice about the dispersal behaviour of individual animals or the strategy by which dispersers locate distant habitat patches. In the present study, we released individual meadow brown butterflies (Maniola jurtina) in a non-habitat and investigated their ability to return to a suitable habitat. The results provided three reasons for supposing that meadow brown butterflies do not seek habitat by means of random flight. First, when released within the range of their normal dispersal distances, the butterflies orientated towards suitable habitat at a higher rate than expected at random. Second, when released at larger distances from their habitat, they used a non-random, systematic, search strategy in which they flew in loops around the release point and returned periodically to it. Third, butterflies returned to a familiar habitat patch rather than a non-familiar one when given a choice. If dispersers actively orientate towards or search systematically for distant habitat, this may be problematic for existing metapopulation models, including models of the evolution of dispersal rates in metapopulations

Development of a novel method for the exploration of the thermal response of superfluid helium cooled superconducting cables to pulse heat loads

Management of transient heat deposition in superconducting magnets and its extraction from the aforementioned is becoming increasingly important to bring high energy particle accelerator performance to higher beam energies and intensities. Precise knowledge of transient heat deposition phenomena in the magnet cables will permit to push the operation of these magnets as close as possible to their current sharing limit, without unduly provoking magnet quenches. With the prospect of operating the Large Hadron Collider at CERN at higher beam energies and intensities an investigation into the response to transient heat loads of LHC magnets, operating in pressurized superfluid helium, is being performed. The more frequently used approach mimics the cable geometry by resistive wires and uses Joule-heating to deposit energy. Instead, to approximate as closely as possible the real magnet conditions, a novel method for depositing heat in cable stacks made out of superconducting magnet-cables has been developed. The goal is to measure the temperature difference as a function of time between the cable stack and the superfluid helium bath depending on heat load and heat pulse length. The heat generation in the superconducting cable and precise measurement of small temperature differences are major challenges. The functional principle and experimental set-up are presented together with proof of principle measurements

A European Turn in Early American History? A Discussion of Evan Haefeli's Accidental Pluralism: America and the Religious Politics of English Expansion, 1497-1662

From the nineteenth century onwards, Americans have naturalized their colonial origins into a consensual nationalist history, emphasizing America’s perceived role as a refuge for the persecuted, while smoothing out a myriad of complexities in the process. Evan Haefeli attempts to overturn the assumptions underpinning this narrative and is convinced that many important aspects of early America need to be understood within a broader European context. In Accidental Pluralism, he argues that the collapse of religious unity in England lies at the root of the emergence of pluralism in colonial America, in which he includes Canada and the Caribbean. Relationships among states, churches, and publics were contested from the earliest decades of colonization and created a pluralistic religious landscape that no one had anticipated. The four reviewers are fulsome in their praise, calling it an impressive, important, powerful, and sweeping book that few scholars could have written. The reviewers also raise questions, for instance by problematizing the incorporation of the colonial American dimension into early British history, criticizing the validity of the chosen end date, and questioning his definitions of diversity, pluralism, and religious toleration. In his response Evan Haefeli takes the opportunity to reflect on what drove him to write the book and to organize it in this way. He acknowledges that connecting early American history with its broader European context was more difficult than it should have been, as the dominant questions in the two historiographies are an ocean apart. While the argument of the book is aimed at early Americanists, Haefeli is grateful that the reviewers situate the story he tells within the broader early modern European history of toleration

Vibration-free Cooler for the METIS Instrument Using Sorption Compressors

METIS is the “Mid-infrared ELT Imager and Spectrograph” for the European Extremely Large Telescope (E-ELT) that will cover the thermal/mid-infrared wavelength range from 3-14 micron. Starting from a pumped nitrogen line at 70K, it requires cryogenic cooling of detectors and optics at 40 K (1.4 W), 25 K (1.1 W), and 8 K (0.4 W). A vibration-free cooling technology for this instrument based on sorption coolers is under development at the University of Twente in collaboration with Dutch Space. We propose a sorption-based cooler with three cascaded Joule-Thomson coolers of which the sorption compressors are all heat sunk at the 70K platform. A helium-operated cooler is used to obtain the 8K level with a cooling power of 0.4 W. Here, three pre-cooling stages are used at 40K, 25K and 15K. The latter two levels are provided by a hydrogen-based cooler, whereas the 40K level is realized by a neon-based sorption cooler. Based on our space-cooler heritage, our preliminary design used sorption compressors equipped with gas-gap heat switches. These have maximum efficiency, but the gas-gap switches add significantly to the complexity of the system. Since in METIS relatively high cooling powers are required, and thus a high number of compressor cells, manufacturability is an important issue. We, therefore, developed an alternative cylindrical compressor design that uses short-pulse heating establishing a thermal wave in radial direction. This allows to omit the gas-gap heat switch. The paper discusses the adapted cell design and two METIS cooler demonstrator setups that are currently under construction

A Passive, Adaptive and Autonomous Gas Gap Heat Switch

We report on the development of a heat switch for autonomous temperature control of electronic components in a satellite. A heat switch can modulate when needed between roles of a good thermal conductor and a good thermal insulator. Electronic boxes on a satellite should be maintained within a typical optimum temperature range of 260 to 310 K. The heat sinking is usually by means of a radiator. When the operating temperature of the electronic box increases beyond 310 K, a good contact to the radiator is desired for maximum cooling. On the other hand, when the satellite is in a cold dormant state, the electronics box should be heated by the onboard batteries. In this state a weak thermal contact is desired between the electronic box and the heat sink. In the present study, we are developing a gas gap heat switch in which the sorber material is thermally anchored to the electronic box. A temperature change of the electronic box triggers the (de-)sorption of gas from the sorber material and subsequently the gas pressure in the gas gap. This paper describes the physical principles and the current status of this technology. This approach can be extended to cryogenic temperature rang

Heat transfer at dielectric-metallic interfaces in the ultra-low temperature range

In the framework of the AEgIS project a series of steady state and dynamic heat transfer measurements at ultra-low temperatures was conducted in the Central Cryogenic Laboratory at CERN. Two sandwich setups, simulating the behaviour of ultra-cold AEgIS electrodes, were investigated and compared, namely: a sapphire − indium − copper and a sapphire − titanium − gold − indium − copper sandwich. The total thermal resistivity of both sandwich setups was evaluated as a function of the influence of normal and superconducting thin layers and multiple dielectric − metallic interfaces in terms of Kapitza resistance. The resulting limitations of the electrode’s design are presented