Symmetry, incommensurate magnetism and ferroelectricity: the case of the rare-earth manganites RMnO3

The complete irreducible co-representations of the paramagnetic space group provide a simple and direct path to explore the symmetry restrictions of magnetically driven ferroelectricity. The method consists of a straightforward generalization of the method commonly used in the case of displacive modulated systems and allows us to determine, in a simple manner, the full magnetic symmetry of a given phase originated from a given magnetic order parameter. The potential ferroic and magneto-electric properties of that phase can then be established and the exact Landau free energy expansions can be derived from general symmetry considerations. In this work, this method is applied to the case of the orthorhombic rare-earth manganites RMnO3. This example will allow us to stress some specific points, such as the differences between commensurate or incommensurate magnetic phases regarding the ferroic and magnetoelectric properties, the possible stabilization of ferroelectricity by a single irreducible order parameter or the possible onset of a polarization oriented parallel to the magnetic modulation. The specific example of TbMnO3 will be considered in more detail, in order to characterize the role played by the magneto-electric effect in the mechanism for the polarization rotation induced by an external magnetic field.Comment: Conference: Aperiodic`0

Shakespearean allusion and the detective fiction of Georgette Heyer

This essay argues that Shakespearean allusion is a recurrent and important factor in the detective novels of Georgette Heyer. Though the master text for Heyer is Hamlet, a variety of Shakespeare plays are referred to, and mention of them functions in multiple ways. Quotations from Shakespeare reveal truths about the characters and comment on their situations and personalities. They also afford points of entry for people previously unacquainted to talk to each other, and finally they have effects in terms of genre, since their presence can, with equal facility, tend towards comic relief (in line with a tradition in Golden Age crime fiction of using Macbeth in particular to comic effect) or work to add gravitas and resonance. The use of Shakespearean allusion is thus central to Heyer’s technique. This article is published as part of a collection to commemorate the 400th anniversary of William Shakespeare’s death

Striations in the Taurus molecular cloud: Kelvin-Helmholtz instability or MHD waves?

The origin of striations aligned along the local magnetic field direction in the translucent envelope of the Taurus molecular cloud is examined with new observations of 12CO and 13CO J=2-1 emission obtained with the 10~m submillimeter telescope of the Arizona Radio Observatory. These data identify a periodic pattern of excess blue and redshifted emission that is responsible for the striations. For both 12CO and 13CO, spatial variations of the J=2-1 to J=1-0 line ratio are small and are not spatially correlated with the striation locations. A medium comprised of unresolved CO emitting substructures (cells) with a beam area filling factor less than unity at any velocity is required to explain the average line ratios and brightness temperatures. We propose that the striations result from the modulation of velocities and the beam filling factor of the cells as a result of either the Kelvin-Helmholtz instability or magnetosonic waves propagating through the envelope of the Taurus molecular cloud. Both processes are likely common features in molecular clouds that are sub-Alfvenic and may explain low column density, cirrus-like features similarly aligned with the magnetic field observed throughout the interstellar medium in far-infrared surveys of dust emission.Comment: 11 pages, 4 figures. Accepted for publication in MNRA

Molecular hydrogen beyond the optical edge of an isolated spiral galaxy

We know little about the outermost portions of galaxies because there is little light coming from them. We do know that in many cases atomic hydrogen (HI) extends well beyond the optical radius \cite{Casertano91}. In the centers of galaxies, however, molecular hydrogen (H2) usually dominates by a large factor, raising the question of whether H2 is abundant also in the outer regions but hitherto unseen.Here we report the detection of emission from carbon monoxide (CO), the most abundant tracer of H2, beyond the optical radius of the nearby galaxy NGC 4414. The molecular clouds probably formed in the regions of relatively high HI column density and in the absence of spiral density waves. The relative strength of the lines from the two lowest rotational levels indicates that both the temperature and density of the H2 are quite low compared to conditions closer to the center. The inferred surface density of the molecular material continues the monotonic decrease from the inner regions. We conclude that while molecular clouds can form in the outer region of this galaxy, there is little mass associated with them.Comment: 3 Nature page

Barbiturate reduction of calcium-dependent action potentials: Correlation with anesthetic action

Calcium-dependent action potentials were recorded from mouse spinal cord neurons in primary dissociated cell culture following addition of the potassium channel blockers tetraethylammonium ion and 3-aminopyridine. The pharmacologically active barbiturates, pentobarbital and phenobarbital, but not the pharmacologically inactive barbiturate, barbituric acid, produced reversible, dose-dependent reduction of action potential duration at sedative-hypnotic and anesthetic concentrations. Pentobarbital reduced action potential duration at concentrations from 25 to 600 [mu]M (50% reduction at 170 [mu]M) while phenobarbital reduced action potential duration at concentrations from 100 to 5000 [mu]M (50% reduction at 900 [mu]M). The barbiturate concentrations which reduced calcium-dependent action potential duration in this study correlate with reduction of neurotransmitter release from other neuronal preparations and with reduction of calcium uptake by synaptosomes. The results suggest that barbiturates may produce anesthesia in part by reduction of presynaptic calcium entry and consequent reduction of neurotransmitter release in addition to postsynaptic increase of membrane chloride ion conductance. Barbiturate anticonvulsant actions are probably due to postsynaptic augmentation of GABA-mediated inhibition and depression of excitatory synaptic transmission. The major difference between anticonvulsant (phenobarbital) and anesthetic (pentobarbital) barbiturates was the dose-dependency of these actions. Phenobarbital produced postsynaptic modulation of neurotransmitter responses at low concentrations and decreased calcium-dependent action potential duration and increased chloride ion conductance at high concentrations. In contrast, pentobarbital produced all actions at low concentrations. Thus for phenobarbital there would be a large therapeutic index for anticonvulsant activity compared to anesthetic activity but for pentobarbital there would be a small therapeutic index.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/24032/1/0000281.pd

Sow body condition at weaning and reproduction performance in organic piglet production

The objective was to investigate the variation in backfat at weaning and its relations to reproduction results in organic sow herds in Denmark. The study included eight herds and 573 sows. The average backfat at weaning mean�13 mm; SD�4.2 mm) ranging from 10.5 to 17.3 mm among herds shows that it is possible to avoid poor body condition at weaning even with a lactation length of seven weeks or more. No main effect of backfat at weaning on reproduction performance was found, but the probability of a successful reproduction after weaning tended to decrease with decreasing backfat for first parity sows, whereas the opposite was the case for multiparous sows

A new young stellar cluster embedded in a molecular cloud in the far outer Galaxy

We report the discovery of a new young stellar cluster and molecular cloud located in the far outer Galaxy, seen towards IRAS 06361-0142, and we characterise their properties. Near-infrared images were obtained with VLT/ISAAC through JHKs filters, millimetre line observations of CO(1-0) were obtained with SEST, and VLA 6 cm continuum maps obtained from archive data. The cloud and cluster are located at a distance of 7 kpc and a Galactocentric distance of 15 kpc, well in the far outer Galaxy. Morphologically, IRAS 06361-0142 appears as a cluster of several tens of stars surrounded by a nearly spherical nebular cavity centred at the position of the IRAS source. The cluster appears composed of low and intermediate-mass, young reddened stars with a large fraction having cleared the inner regions of their circumstellar discs responsible for (H - Ks) colour excess. The observations are compatible with a 4 Myr cluster with variable spatial extinction between Av = 6 and Av = 13.Comment: 6 pages, 6 figure

Cross-ecosystem effects of terrestrial predators link treefrogs, zooplankton, and aquatic primary production

Predators can directly or indirectly shape food webs through a combination of consumptive and non-consumptive effects. Yet, how these effects vary across natural populations and their consequences for adjacent ecosystems remains poorly resolved. We examined links between terrestrial predators and aquatic ecosystems through their effects on a locally abundant amphibian, the red-eyed treefrog (Agalychnis callidryas), which has arboreal eggs (heavily predated by snakes and wasps) and aquatic larvae; embryos can escape terrestrial threats by hatching at an earlier age and smaller size. Our multi-site field survey indicates that in natural populations, the relative contributions of these consumptive and non-consumptive effects of predators can be substantial and remarkably similar. However, in mesocosms where we experimentally mimicked these predator effects, changes in the density and initial hatching age of tadpoles carried distinct consequences for aquatic food webs. Density-dependent growth resulted in peak tadpole biomass at intermediate densities (reflecting intermediate predation), and early-hatched tadpoles grew 16% faster and produced 26% more biomass than their late-hatched counterparts. These changes in tadpole growth and size differentially affected zooplankton communities, and the production and stability of phytoplankton. Together, these results illustrate multiple pathways through which predators in one ecosystem can modulate the structure of adjacent food webs

Comparison of Coulomb Blockade Thermometers with the International Temperature Scale PLTS-2000

The operation of the primary Coulomb blockade thermometer (CBT) is based on a measurement of bias voltage dependent conductance of arrays of tunnel junctions between normal metal electrodes. Here we report on a comparison of a CBT with a high accuracy realization of the PLTS-2000 temperature scale in the range from 0.008 K to 0.65 K. An overall agreement of about 1% was found for temperatures above 0.25 K. For lower temperatures increasing differences are caused by thermalization problems which are accounted for by numerical calculations based on electron-phonon decoupling.Comment: 6 pages, 5 figure