Non-linear response of single-molecule magnets: field-tuned quantum-to-classical crossovers

Quantum nanomagnets can show a field dependence of the relaxation time very different from their classical counterparts, due to resonant tunneling via excited states (near the anisotropy barrier top). The relaxation time then shows minima at the resonant fields H_{n}=n D at which the levels at both sides of the barrier become degenerate (D is the anisotropy constant). We showed that in Mn12, near zero field, this yields a contribution to the nonlinear susceptibility that makes it qualitatively different from the classical curves [Phys. Rev. B 72, 224433 (2005)]. Here we extend the experimental study to finite dc fields showing how the bias can trigger the system to display those quantum nonlinear responses, near the resonant fields, while recovering an classical-like behaviour for fields between them. The analysis of the experiments is done with heuristic expressions derived from simple balance equations and calculations with a Pauli-type quantum master equation.Comment: 4 pages, 3 figures. Submitted to Phys. Rev. B, brief report

The Role of Stellar Feedback in the Dynamics of HII Regions

Stellar feedback is often cited as the biggest uncertainty in galaxy formation models today. This uncertainty stems from a dearth of observational constraints as well as the great dynamic range between the small scales (<1 pc) where the feedback occurs and the large scales of galaxies (>1 kpc) that are shaped by this feedback. To bridge this divide, in this paper we aim to assess observationally the role of stellar feedback at the intermediate scales of HII regions. In particular, we employ multiwavelength data to examine several stellar feedback mechanisms in a sample of 32 HII regions in the Large and Small Magellanic Clouds (LMC and SMC, respectively). Using optical, infrared, radio, and X-ray images, we measure the pressures exerted on the shells from the direct stellar radiation, the dust-processed radiation, the warm ionized gas, and the hot X-ray emitting gas. We find that the warm ionized gas dominates over the other terms in all of the sources, although two have comparable dust-processed radiation pressures to their warm gas pressures. The hot gas pressures are comparatively weak, while the direct radiation pressures are 1-2 orders of magnitude below the other terms. We discuss the implications of these results, particularly highlighting evidence for hot gas leakage from the HII shells and regarding the momentum deposition from the dust-processed radiation to the warm gas. Furthermore, we emphasize that similar observational work should be done on very young HII regions to test whether direct radiation pressure and hot gas can drive the dynamics at early times.Comment: 19 pages, 8 figures; accepted by Ap

Razvoj sustava proizvodnje iberijskih svinja u Španjolskoj

Total number of Iberian swine sows in Spain is close to 230.000, giving rise to around 2 mill finished Iberian pigs in 2003. The Iberian swine constitutes a singular breed, strongly adapted to the ecological conditions of the "Dehesa" ecosystem. This breed includes a number of strains, all of them showing low prolific and growth rates, very early maturing fat deposition, and an excellent meat quality, which is valuated in the market according to the fatty acid Drofile (palmitic, stearic, oleic and linoleic acids) of subcutaneous fat. This paper mainly deals with available feeding sources of the "Dehesa" for Iberian pigs, the productive features of this breed and the evolution that feeding and production systems have experienced last years.Ukupan broj krmača iberijske svinje u Španjolskoj iznosi blizu 230 000 pa je prema tome u 2003. god. bilo oko 2 milijuna gotovih iberijskih svinja. Iberijska svinja je rijetka pasmina, dobro prilagođena ekološkim uvjetima ekosustava "Dehesa". Ova pasmina ima brojne značajke koje sve pokazuju nisku stopu plodnosti i rasta, vrlo rano dozrijevanje naslaga masti te izvrsnu kakvoću mesa koje se vrednuje na tržištu prema profilu masne kiseline (palmitinske, stearinske, oleinske i linolne kiseline) potkožne masti. Ovaj se članak uglavnom bavi dostupnim izvorima hranidbe "Dehesa" za iberijske svinje, proiz¬vodnim značajkama ove pasmine i razvojem sustava hranidbe i proizvodnje prošle godine

Bidimensional chronoabsorptometric study of electropolymerisation of 4,4 '-bis(2-methylbutylthio)-2,2 '-bithiophene

Bidimensional chronoabsorptometry is a novel spectroelectrochemical technique that monitors simultaneously three different signals: current and absorbance both normal to the electrode plane and parallel to this plane during a time in which a fixed potential is imposed. This technique is applied in the visible range to the study of the electropolymerisation of 4,4'-bis(2-methylbutylthio)2,2'-bithiophene (MBTBT). Experiments are performed in a spectroelectrochemical cell under finite diffusion conditions (thin layer cell) with the aim of interpreting the processes taking place both at the electrode surface and in the adjacent solution during the potentiostatic electrogeneration and deposition of the polymer. Correlations are drawn out among the trends of the oligomers concentration in solution, the polymer electrodeposition and charging, and the current flow, on the time scales of the different steps of the process. (C) 2002 Elsevier Science B.V. All rights reserved