The evolutionary state of the southern dense core Cha-MMS1

Aims: Our goal is to set constraints on the evolutionary state of the dense core Cha-MMS1 in the Chamaeleon I molecular cloud. Methods: We analyze molecular line observations carried out with the new submillimeter telescope APEX. We look for outflow signatures around the dense core and probe its chemical structure, which we compare to predictions of models of gas-phase chemistry. We also use the public database of the Spitzer Space Telescope (SST) to compare Cha-MMS1 with the two Class 0 protostars IRAM 04191 and L1521F, which are at the same distance. Results: We measure a large deuterium fractionation for N2H+ (11 +/- 3 %), intermediate between the prestellar core L1544 and the very young Class 0 protostar L1521F. It is larger than for HCO+ (2.5 +/- 0.9 %), which is probably the result of depletion removing HCO+ from the high-density inner region. Our CO(3-2) map reveals the presence of a bipolar outflow driven by the Class I protostar Ced 110 IRS 4 but we do not find evidence for an outflow powered by Cha-MMS1. We also report the detection of Cha-MMS1 at 24, 70 and 160 microns by the instrument MIPS of the SST, at a level nearly an order of magnitude lower than IRAM 04191 and L1521F. Conclusions: Cha-MMS1 appears to have already formed a compact object, either the first hydrostatic core at the very end of the prestellar phase, or an extremely young protostar that has not yet powered any outflow, at the very beginning of the Class 0 accretion phase.Comment: Accepted by Astronomy & Astrophysics as a letter, to appear in the special issue on the APEX first result

REXEBIS the Electron Beam Ion Source for the REX-ISOLDE project

The REXEBIS is an Electron Beam Ion Source (EBIS) developed especially to trap and further ionise the sometimes rare and short-lived isotopes that are produced in the ISOLDE separator for the Radioactive beam EXperiment at ISOLDE (REX-ISOLDE). By promoting the single-charged ions to a high charge-state the ions are more efficiently accelerated in the following linear accelerator. The EBIS uses an electron gun capable of producing a 0.5 A electron beam. The electron gun is immersed in a magnetic field of 0.2 T, and the electron beam is compressed to a current density of >200 A/cm2 inside a 2 T superconducting solenoid. The EBIS is situated on a high voltage (HV) platform with an initial electric potential of 60 kV allowing cooled and bunched 60 keV ions extracted from a Penning trap to be captured. After a period of confinement in the electron beam (<20 ms), the single-charged ions have been ionised to a charge-to-mass ratio of approximately ¼. During this confinement period, the platform potential is decreased to about 20 kV, and an axial potential barrier is lowered to allow the now highly charged ions to be extracted from the EBIS at an energy matching the requirement of the Radio Frequency Quadrupole (RFQ). Several different topics are presented in this report, all connected with the design and construction of an EBIS. Old 'truths' have also been scrutinised, for instance alignment tolerances. A large part is devoted to the description of a novel EBIS simulation implementation. A complete injection, breeding and extraction cycle has been simulated to certify high injection and extraction efficiencies. The entire EBIS was modelled in an ion-tracing program called SIMION, and the accepted and emitted phase spaces were determined. Beam optics parameters such as lens positions, voltages, accepted beam-tilt and displacement tolerances at the focal points were also settled using SIMION. An analytically derived acceptance formula was verified with simulations, and general conclusions on acceptance, emittance and energy spread of an EBIS are presented in this report. Any possible correlation between the two transverse phase spaces was shown to be insignificant. Furthermore, continuous injection, and maximal obtainable efficiency for such an injection mode were studied theoretically. The electron reflection and back-scattering in the collector was simulated using a combination of EGUN and SIMION. The result showed that a much lower degree of electron back-scattering may be obtained with this design as compared to previously published estimations. Furthermore, the Penning trapping of electrons at the trap barrier (or the post anode) was addressed, and techniques to avoid it were evaluated. Vacuum considerations for residual gas in the warm-bore magnet chamber, and the back-flow of Ar cooling gas from the Penning trap, have also been addressed since there is a risk of outnumbering the small number of radioactive ions. Simulated extraction spectra for different pressure scenarios are presented. All different REXEBIS elements (magnet, electron gun, inner structure, collector etc) are described from a design and performance perspective, and preliminary investigations of the platform high voltage switching and the beam diagnostics are included as well. A very elegant and simple method to align the solenoid within the iron yoke was developed and used. The high experimental emittance value obtained for electron beam ion source at MSL in Stockholm (4 times larger than the absolute upper theoretical value) was reproduced in simulations and could be justified by aberrations in the small einzel lens following the collector. The result of this simulation also verified the validity of the developed EBIS code

Tapered-amplified AR-coated laser diodes for Potassium and Rubidium atomic-physics experiments

We present a system of room-temperature extended-cavity grating-diode lasers (ECDL) for production of light in the range 760-790nm. The extension of the tuning range towards the blue is permitted by the weak feedback in the cavity: the diodes are anti-reflection coated, and the grating has just 10% reflectance. The light is then amplified using semiconductor tapered amplifiers to give more than 400mW of power. The outputs are shown to be suitable for atomic physics experiments with potassium (767nm), rubidium (780nm) or both, of particular relevance to doubly-degenerate boson-fermion mixtures

Determination of digestible energy values and fermentabilities of dietary fibre supplements: a European interlaboratory study in vivo

The performance of methods to determine energy conversion factors for dietary fibre (DF) supplements and fermentability (D) values of their non-starch polysaccharides (NSP) was investigated. Heats of combustion, digestible energy (DE) and D values were determined on five DF supplements in five European laboratories on five separate occasions. In each instance the DF supplements were fed to juvenile male VVistar rats at two doses, 50 and 100 g/kg basal diet, for 3 weeks with food and faeces collected in the 3rd week. Among-laboratory variations in heats of combustion (DHC<) were <2%. DE values (kJ/g dry weight) at the upper and lower doses respectively were: 10·4 and 9·9 for a high-methoxyl apple pectin, 9·5 and 9·4 for a sugar-beet DF supplement, 12·2 and 12·7 for soyabean DF supplement, 38 and 4·0 for maize bran, and 0·3 and 0·3 for Solka-floc cellulose. Variations among laboratories, among occasions and among animals were <1, <2 and <2·5 kJ/g respectively. The among-occasion: among-laboratory variance ratio for DE was 0·5, suggesting the method performed equally well in all laboratories. There was no evidence of learning or fatigue in the performance of the method. D values were also independent of dose and at the high and lower doses were: pectin 0·92 and 0·95, sugar-beet NSP 0·68 and 0·68, soyabean NSP 0·86 and 0·88, maize bran 0·17 and 0·18, cellulose 0·07 and 0·06. Among-laboratory variance tended to increase with decreasing fermentability and ranged from 0·03 to 0·18. The DE and D data were not significantly different from a previously proposed relationship DE = 0·7 × DHc × D, where DHc is the heat of combustion of the supplement. We conclude that while the among-laboratory variation in the D of difficult-to-ferment NSP is too large for the reliable prediction of energy value the method for the direct determination of DE is both reproducible and repeatable, that DE is independent of dosage of DF supplement up to 100 g/kg diet, and that it is safe to discriminate between energy values with a precision of 3 kJ/g. The conversion of both DE and D to net metabolizable energy for the purpose of food labelling, tables and databases is describe

Results of the ESO-SEST Key Programme on CO in the Magellanic Clouds. IX. The giant LMC HII region complex N11

We present maps and a catalogue containing the J=1-0 12CO parameters of 29 individual molecular clouds in the second-brightest LMC star formation complex, N11. In the southwestern part of N11, molecular clouds occur in a ring or shell surrounding the major OB star association LH9. In the northeastern part, a chain of molecular clouds delineates the rim of one of the so-called supergiant shells in the LMC. The well-defined clouds have dimensions close to those of the survey beam (diameters of 25 pc or less). Some of the clouds were also observed in J=2-1 12CO, and in the lower two transitions of 13CO. Clouds mapped with a twice higher angular resolution in J=2-1 12CO show substructure with dimensions once again comparable to those of the mapping beam. The few clouds for which we could model physical parameters have fairly warm (T(kin) = 60 - 150 K) and moderately dense (n(H2) = 3000 cm-3) gas. The northeastern chain of CO clouds, although lacking in diffuse intercloud emission, is characteristic of the more quiescent regions of the LMC and appears to have been subject to relatively little photo-processing. The clouds forming part of the southwestern shell or ring, however, are almost devoid of diffuse intercloud emission and also exhibit other characteristics of an extreme photon-dominated region (PDR).Comment: 14 pages; accepted for publication in A&

Anatomy of the Soft-Photon Approximation in Hadron-Hadron Bremsstrahlung

A modified Low procedure for constructing soft-photon amplitudes has been used to derive two general soft-photon amplitudes, a two-s-two-t special amplitude $M^{TsTts}_{\mu}$ and a two-u-two-t special amplitude $M^{TuTts}_{\mu}$, where s, t and u are the Mandelstam variables. $M^{TsTts}_{\mu}$ depends only on the elastic T-matrix evaluated at four sets of (s,t) fixed by the requirement that the amplitude be free of derivatives ($\partial$T/$\partial$s and /or $\partial$T/$\partial t$). Likewise $M^{TuTts}_{\mu}$ depends only on the elastic T-matrix evaluated at four sets of (u,t). In deriving these amplitudes, we impose the condition that $M^{TsTts}_{\mu}$ and $M^{TuTts}_{\mu}$ reduce to $\bar{M}^{TsTts}_{\mu}$ and $\bar{M}^{TuTts}_{\mu}$, respectively, their tree level approximations. The amplitude $\bar{M}^{TsTts}_{\mu}$ represents photon emission from a sum of one-particle t-channel exchange diagrams and one-particle s-channel exchange diagrams, while the amplitude $\bar{M}^{TuTts} _{\mu}$ represents photon emission from a sum of one-particle t-channel exchange diagrams and one-particle u-channel exchange diagrams. The precise expressions for $\bar{M}^{TsTts}_{\mu}$ and $\bar{M}^{TuTts}_{\mu}$ are determined by using the radiation decomposition identities of Brodsky and Brown. We point out that it is theoretically impossible to describe all bremsstrahlung processes by using only a single class of soft-photon amplitudes. At least two different classes are required: the amplitudes which depend on s and t or the amplitudes which depend on u and t. When resonance effects are important, the amplitude $M^{TsTts}_{\mu}$, not $M^{Low(st)}_{\mu}$, should be used. For processes with strong u-channel exchange effects, the amplitude $M^{TuTts}_{\mu}$ should be the first choice.Comment: 49 pages report # LA-UR-92-270

Three-body correlations in Borromean halo nuclei

Three-body correlations in the dissociation of two-neutron halo nuclei are explored using a technique based on intensity interferometry and Dalitz plots. This provides for the combined treatment of both the n-n and core-n interactions in the exit channel. As an example, the breakup of 14Be into 12Be+n+n by Pb and C targets has been analysed and the halo n-n separation extracted. A finite delay between the emission of the neutrons in the reaction on the C target was observed and is attributed to 13Be resonances populated in sequential breakup.Comment: 5 pages, 4 figures, submitted to PR

Consistent off-shell πNN\pi N N vertex and nucleon self-energy

We present a consistent calculation of half-off-shell form factors in the pion-nucleon vertex and the nucleon self-energy. Numerical results are presented. Near the on-shell point the pion-nucleon vertex is dominated by the pseudovector coupling, while at large nucleon invariant masses we find a sizable pseudoscalar admixture.Comment: 23 pages, 7 figures, REVTeX, submitted to Phys. Rev. C, replaced with corrected versio