Triple vortex ring structure in superfluid helium II

Superfluids such as helium II consist of two interpenetrating fluids: the normal fluid and the superfluid. The helium II vortex ring has generally been considered merely as a superfluid object, neglecting any associated motion of the normal fluid. We report a three-dimensional calculation of the coupled motion of the normal-fluid and superfluid components, which shows that the helium II vortex ring consists of a superfluid vortex ring accompanied by two coaxial normal-fluid vortex rings of opposite polarity. The three vortex rings form a coherent, dissipative structure.     

A high phase-space-density gas of polar molecules

A quantum gas of ultracold polar molecules, with long-range and anisotropic interactions, not only would enable explorations of a large class of many-body physics phenomena but also could be used for quantum information processing. We report on the creation of an ultracold dense gas of potassium-rubidium (40K87Rb) polar molecules. Using a single step of STIRAP (stimulated Raman adiabatic passage) with two-frequency laser irradiation, we coherently transfer extremely weakly bound KRb molecules to the rovibrational ground state of either the triplet or the singlet electronic ground molecular potential. The polar molecular gas has a peak density of 10(12) per cubic centimeter and an expansion-determined translational temperature of 350 nanokelvin. The polar molecules have a permanent electric dipole moment, which we measure with Stark spectroscopy to be 0.052(2) Debye (1 Debye = 3.336 x 10(-30) coulomb-meters) for the triplet rovibrational ground state and 0.566(17) Debye for the singlet rovibrational ground state.     

Collagen molecules: distribution of alpha chains

To ascertain the distribution of alpha chains within the collagen molecule, intramolecular cross-links were introduced into tropocollagen by reacting formaldehyde with dilute homogeneous molecular dispersions of collagen extracted from lathyritic guinea pig skin. Denaturation, chromatography on carboxymethyl cellulose, measurement of molecular weight, and analyses of the amino acids of the cross-linked product indicate that most, if not all, of the collagen molecules consist of two alpha1 chains and one alpha2 chain [(alpha1)(2)(alpha2)(1)].     

Antibody molecules: discontinuous heterogeneity of heavy chains

The heavy polypeptide chains of antibody ( and of gammaG-immnunoglobulin) molecules show discrete bands on disc electrophoresis. The same bands are present for chains from antibodies of the same or diverse specificities. Individual bands are of different intensities for chains from the different rabbits tested even if the antibodies are directed against the same hapten. The bands appear to represent classes of heterogeneous H-chains of the same size having discrete differences in mizobilities with respect to a single charge difference.     

Separation of long DNA molecules in a microfabricated entropic trap array

A nanofluidic channel device, consisting of many entropic traps, was designed and fabricated for the separation of long DNA molecules. The channel comprises narrow constrictions and wider regions that cause size-dependent trapping of DNA at the onset of a constriction. This process creates electrophoretic mobility differences, thus enabling efficient separation without the use of a gel matrix or pulsed electric fields. Samples of long DNA molecules (5000 to approximately 160,000 base pairs) were efficiently separated into bands in 15-millimeter-long channels. Multiple-channel devices operating in parallel were demonstrated. The efficiency, compactness, and ease of fabrication of the device suggest the possibility of more practical integrated DNA analysis systems.     

The resilience of long and short food chains: a case study of flooding in Queensland,Australia

This paper provides new insights into the food security performance of long and short food chains, through an analysis of the resilience of such chains during the severe weather events that occurred in the Australian State of Queensland in early 2011. Widespread flooding cut roads and highways, isolated towns, and resulted in the deaths of people and animals. Farmlands were inundated and there were food shortages in many towns. We found clear evidence that the supermarket-based (long) food chain delivery system experienced significant difficulties in supplying food to flood-affected towns. In contrast, more localized (short) food supply chains—which relied upon supply from growers in peri-urban areas and community-based food initiatives—remained largely intact, and provided food at a time when the supermarkets were limited in their ability to respond to consumer demand. However, on closer examination of food distribution during flooding in the regional city of Rockhampton and in the State capital, Brisbane, the demarcation of success between “long” and “short” food chains became blurred. Both types of food supply chains shared some key resilience characteristics in responding to crisis but diverged in other important ways. We argue that conceptualizing food chains in terms of key elements of resilience—scale, diversity, flexibility and cohesion—may be more fruitful than the short-long dichotomy alone. This approach is particularly useful when prioritizing food security as the basis for evaluating food system sustainability in a context of predicted increases in extreme weather events and future climate change.     

Observation of superflow in solid helium

We report on the observation of nonclassical rotational inertia in solid helium-4 confined to an annular channel in a sample cell under torsional motion, demonstrating superfluid behavior. The effect shows up as a drop in the resonant oscillation period as the sample cell is cooled below 230 millikelvin. Measurement of 17 solid samples allows us to map out the boundary of this superfluid-like solid or supersolid phase from the melting line up to 66 bars. This experiment indicates that superfluid behavior is found in all three phases of matter.     

Evidence of supersolidity in rotating solid helium

Supersolidity, the appearance of zero-viscosity flow in solids, was first indicated in helium-4 torsional oscillator (TO) experiments. In this apparatus, the irrotationality of the superfluid component causes it to decouple from the underlying normal solid, leading to a reduction in the resonant period of the TO. However, the resonant period may be altered for reasons other than supersolidity, such as the temperature dependence of the elastic modulus of solid helium. Superimposing rotation onto oscillatory measurements may distinguish between supersolidity and classical effects. We performed such simultaneous measurements of the TO and the shear modulus, and observed substantial change in the resonant period with rotational speed where the modulus remained unchanged. This contrasting behavior suggests that the decrease in the TO period is a result of supersolidity.     

Photoejection of electrons from flavins in polar media

Riboflavin and 12 of its derivatives have been shown to form solvated electrons under ultraviolet irradiation (253.7 nanometers) in various water-methanol solvent mixtures. The highest quantum yield of solvated electrons (about 0.03) was obtained for flavins containing tyrosine on a side chain in the isoalloxazine N-3 or N-10 position. The splitting of hydrogen atoms from excited flavin molecules was also observed. From the results presented here, it can be determined that the semiquinone transients are formed not only by way of the flavin triplet, as usually suggested, but also by the attack of the electrons and hydrogen atoms on flavin molecules in the ground state. This is important, because the flavin radicals remaining after the electron-ejection or hydrogen-splitting processes must also be considered in the subsequent reaction mechanisms. The electron-ejection process from electronically excited flavins has important implications in the photobiology of these compounds.     

Role of the stratospheric polar freezing belt in denitrification

Homogeneous freezing of nitric acid hydrate particles can produce a polar freezing belt in either hemisphere that can cause denitrification. Computed denitrification profiles for one Antarctic and two Arctic cold winters are presented. The vertical range over which denitrification occurs is normally quite deep in the Antarctic but limited in the Arctic. A 4 kelvin decrease in the temperature of the Arctic stratosphere due to anthropogenic and/or natural effects can trigger the occurrence of widespread severe denitrification. Ozone loss is amplified in a denitrified stratosphere, so the effects of falling temperatures in promoting denitrification must be considered in assessment studies of ozone recovery trends.     

The isotopic composition of methane in polar ice cores

Air bubbles in polar ice cores indicate that about 300 years ago the atmospheric mixing ratio of methane began to increase rapidly. Today the mixing ratio is about 1.7 parts per million by volume, and, having doubled once in the past several hundred years, it will double again in the next 60 years if current rates continue. Carbon isotope ratios in methane up to 350 years in age have been measured with as little as 25 kilograms of polar ice recovered in 4-meter-long ice-core segments. The data show that (i) in situ microbiology or chemistry has not altered the ice-core methane concentrations, and (ii) that the carbon-13 to carbon-12 ratio of atmospheric CH(4) in ice from 100 years and 300 years ago was about 2 per mil lower than at present. Atmospheric methane has a rich spectrum of isotopic sources: the ice-core data indicate that anthropogenic burning of the earth's biomass is the principal cause of the recent (13)CH(4) enrichment, although other factors may also contribute.     

Revealing the superfluid lambda transition in the universal thermodynamics of a unitary Fermi gas

Fermi gases, collections of fermions such as neutrons and electrons, are found throughout nature, from solids to neutron stars. Interacting Fermi gases can form a superfluid or, for charged fermions, a superconductor. We have observed the superfluid phase transition in a strongly interacting Fermi gas by high-precision measurements of the local compressibility, density, and pressure. Our data completely determine the universal thermodynamics of these gases without any fit or external thermometer. The onset of superfluidity is observed in the compressibility, the chemical potential, the entropy, and the heat capacity, which displays a characteristic lambda-like feature at the critical temperature T(c)/T(F) = 0.167(13). The ground-state energy is 3/5ξN E(F) with ξ = 0.376(4). Our measurements provide a benchmark for many-body theories of strongly interacting fermions.     

Possible mechanism for the antiarrhythmic effect of helium in anesthetized dogs

Breathing a mixture of 75 percent helium and 25 percent oxygen instead of 75 percent nitrogen and 25 percent oxygen reduced the occurrence of dangerous cardiac arrhythmias after ligation of the circumflex coronary artery in open-chest dogs anesthetized with pentobarbital. In dogs not subjected to circumflex ligation, the sensitivity of blood pressure, heart rate, and extrasystoles to epinephrine injected intravenously was not altered by the substitution of helium for nitrogen; however, helium did reduce the baseline heart rate and the concentration of endogenous plasma catecholamines. The antiarrhythmic effect of helium may thus be mediated by changes in sympathetic activity.     

Gravitational separation of gases and isotopes in polar ice caps

Atmospheric gases trapped in polar ice at the firn to ice transition layer are enriched in heavy isotopes (nitrogen-15 and oxygen-18) and in heavy gases (O(2)/N(2) and Ar/N(2) ratios) relative to the free atmosphere. The maximum enrichments observed follow patterns predicted for gravitational equilibrium at the base of the firn layer, as calculated from the depth to the transition layer and the temperature in the firn. Gas ratios exhibit both positive and negative enrichments relative to air: the negative enrichments of heavy gases are consistent with observed artifacts of vacuum stripping of gases from fractured ice and with the relative values of molecular diameters that govern capillary transport. These two models for isotopic and elemental fractionation provide a basis for understanding the initial enrichments of carbon-13 and oxygen-18 in trapped CO(2), CH(4), and O(2) in ice cores, which must be known in order to decipher ancient atmospheric isotopic ratios.     

生长素极性运输PIN基因在拟南芥和荠菜不同组织的表达定量分析

为了解拟南芥和荠菜形态差异与其生长素极性分布的关系,采用荧光定量PCR,以–actin为内参基因,对拟南芥和荠菜的根、茎、叶、花等组织中与生长素极性运输相关的PIN1、PIN3、PIN7基因的表达进行定量分析。结果表明：拟南芥各组织中PIN1的表达量都高于荠菜各组织中PIN1的表达量,拟南芥的茎和花中PIN1的表达量分别比荠菜茎和花中PIN1表达量高3倍和10倍;拟南芥各组织中PIN7的表达量也高于荠菜各组织的PIN7表达量,其叶片中PIN7的表达量比荠菜叶片中PIN7的表达量高10倍以上;荠菜各组织中PIN3的表达都高于拟南芥相应组织中PIN3的表达量,在茎、叶中的表达分别高3倍和10倍以上,这些生长素极性运输蛋白相关基因表达的差异可能是导致2种植物形态差异的直接原因。