Aperiodic tumbling of microrods advected in a microchannel flow

We report on an experimental investigation of the tumbling of microrods in the shear flow of a microchannel (40 x 2.5 x 0.4 mm). The rods are 20 to 30 microns long and their diameters are of the order of 1 micron. Images of the centre-of-mass motion and the orientational dynamics of the rods are recorded using a microscope equipped with a CCD camera. A motorised microscope stage is used to track individual rods as they move along the channel. Automated image analysis determines the position and orientation of a tracked rods in each video frame. We find different behaviours, depending on the particle shape, its initial position, and orientation. First, we observe periodic as well as aperiodic tumbling. Second, the data show that different tumbling trajectories exhibit different sensitivities to external perturbations. These observations can be explained by slight asymmetries of the rods. Third we observe that after some time, initially periodic trajectories lose their phase. We attribute this to drift of the centre of mass of the rod from one to another stream line of the channel flow.Comment: 14 pages, 8 figures, as accepted for publicatio

Dimer Expansion Study of the Bilayer Square Lattice Frustrated Quantum Heisenberg Antiferromagnet

The ground state of the square lattice bilayer quantum antiferromagnet with nearest ($J_1$) and next-nearest ($J_2$) neighbour intralayer interaction is studied by means of the dimer expansion method up to the 6-th order in the interlayer exchange coupling $J_3$. The phase boundary between the spin-gap phase and the magnetically ordered phase is determined from the poles of the biased Pad\'e approximants for the susceptibility and the inverse energy gap assuming the universality class of the 3-dimensional classical Heisenberg model. For weak frustration, the critical interlayer coupling decreases linearly with $\alpha (= J_2/J_1)$. The spin-gap phase persists down to $J_3=0$ (single layer limit) for 0.45 \simleq \alpha \simleq 0.65. The crossover of the short range order within the disordered phase is also discussed.Comment: 4 pages, 6 figures, One reference adde

Modified Spin Wave Thoery of the Bilayer Square Lattice Frustrated Quantum Heisenberg Antiferromagnet

The ground state of the square lattice bilayer quantum antiferromagnet with nearest and next-nearest neighbour intralayer interaction is studied by means of the modified spin wave method. For weak interlayer coupling, the ground state is found to be always magnetically ordered while the quantum disordered phase appear for large enough interlayer coupling. The properties of the disordered phase vary according to the strength of the frustration. In the regime of weak frustration, the disordered ground state is an almost uncorrelated assembly of interlayer dimers, while in the strongly frustrated regime the quantum spin liquid phase which has considerable N\'eel type short range order appears. The behavior of the sublattice magnetization and spin-spin correlation length in each phase is discussed.Comment: 15 pages, revtex, figures upon reques

Anthropogenic and natural ground deformation in the Hengill geothermal area, Iceland

We investigate crustal deformation due to the extraction of water and steam from a high-enthalpy geothermal reservoir; a common occurrence, yet not well understood. The cause of this deformation can be a change in pressure or in temperature in the reservoir, both of which can be caused by extraction or injection of geothermal fluids. Our study area, the Hengill mountains in SW Iceland, is an active volcanic center and a plate triple junction that hosts two power plants producing geothermal energy. This combination of natural and anthropogenic processes causes a complex displacement field at the surface. We analyze geodetic data—Global Navigation Satellite System and Interferometric Synthetic Aperture Radar—to obtain the surface velocity field, which we then simulate using an inverse modeling approach. We focus on the deformation around the geothermal power plants but need to model the regional tectonic and volcanic deformation as well, because the signals are overlapping. We find that plate motion and a deep contracting body can explain the broad scale signal in the area. Local deformation near the two power plants, Hellisheidi and Nesjavellir, can be explained by extraction of geothermal fluids. We estimate reservoirs extending from 0.6 to 3.0 km depth at Hellisheidi, and 1.0 to 3.0 km depth at Nesjavellir for observed pressure decrease rates of 0.25 MPa/yr and 0.1 MPa/yr, respectively. We find that the main cause for the subsidence in the geothermal area is the observed pressure drawdown

Linear plasmon dispersion in single-wall carbon nanotubes and the collective excitation spectrum of graphene

We have measured a strictly linear pi-plasmon dispersion along the axis of individualized single wall carbon nanotubes, which is completely different from plasmon dispersions of graphite or bundled single wall carbon nanotubes. Comparative ab initio studies on graphene based systems allow us to reproduce the different dispersions. This suggests that individualized nanotubes provide viable experimental access to collective electronic excitations of graphene, and it validates the use of graphene to understand electronic excitations of carbon nanotubes. In particular, the calculations reveal that local field effects (LFE) cause a mixing of electronic transitions, including the 'Dirac cone', resulting in the observed linear dispersion

Microevolutionary change in wild stickleback: Using integrative time-series data to infer responses to selection

Traits of wild animals can change over contemporary timescales, but concluding that evolution played a role requires demonstrating that trait change is linked to genetic change. This is because while selection acts on organisms? traits, evolution in the strict sense is a process resulting in changes to the genome. But natural selection operating in natural ecosystems rarely acts in a single direction, and many factors that cause selection vary through time. We study wild stickleback in a well-studied lake to characterize how the genetics of correlated traits respond to different types of selection (e.g., directional or fluctuating). Our study clearly demonstrates how evolutionary processes cause trait change in the wild on a contemporary timescale. A central goal in evolutionary biology is to understand how different evolutionary processes cause trait change in wild populations. However, quantifying evolutionary change in the wild requires linking trait change to shifts in allele frequencies at causal loci. Nevertheless, datasets that allow for such tests are extremely rare and existing theoretical approaches poorly account for the evolutionary dynamics that likely occur in ecological settings. Using a decade-long integrative phenome-to-genome time-series dataset on wild threespine stickleback (Gasterosteus aculeatus), we identified how different modes of selection (directional, episodic, and balancing) drive microevolutionary change in correlated traits over time. Most strikingly, we show that feeding traits changed by as much 25% across 10 generations which was driven by changes in the genetic architecture (i.e., in both genomic breeding values and allele frequencies at genetic loci for feeding traits). Importantly, allele frequencies at genetic loci related to feeding traits changed at a rate greater than expected under drift, suggesting that the observed change was a result of directional selection. Allele frequency dynamics of loci related to swimming traits appeared to be under fluctuating selection evident in periodic population crashes in this system. Our results show that microevolutionary change in a wild population is characterized by different modes of selection acting simultaneously on different traits, which likely has important consequences for the evolution of correlated traits. Our study provides one of the most thorough descriptions to date of how microevolutionary processes result in trait change in a natural population

Health-related quality of life of patients before and after treatment

Neðst á síðunni er hægt að nálgast greinina í heild sinni með því að smella á hlekkinn View/OpenObjective: Health-related quality of life (HRQL) is increasingly used to estimate needs for medical treatment, to evaluate its outcome and quality of care. The aim of this study was to compare the HRQL of several diagnostic groups before and after treatment with the HL-test (HL = IQL, Icelandic Quality of Life test) and to study its validity for measuring changes in quality of life. Material and methods: Patients on waiting lists for coronary catheterization, orthopedic or urologic operations, patients in psychiatric out-patient treatment and patients entering treatment for alcohol dependence were asked to fill in the HL-test, a total of 1195 patients. Three months after treatment they were retested. The results of tests were standarized with population norms available to make them directly comparable with those of the general population. Results: The response rate was 75% in each round. The HRQL of all patients was reduced in all aspects compared to that of the general population, that of the heart and urology patients less so than that of the orthopedic and psychiatric patients. Each group had a specific profile, especially marked for the orthopedic and psychiatric patients. Following treatment the HRQL or some aspects of it improved in all groups, especially for those which it had been most impaired. Conclusions: Studies of HRQL provide information useful for planning and delivery of health services. The HL-test is an instrument with good validity and reliability which is easy to use for such studies.Tilgangur: Heilsutengd lífsgæði (HL) hafa í vaxandi mæli verið notuð til að meta þörf fyrir læknismeðferð, árangur hennar og gæði umönnunar. Tilgangur rannsóknarinnar var að bera saman heilsutengd lífsgæði nokkurra sjúklingahópa fyrir og eftir meðferð með HL-prófinu og athuga frekar réttmæti þess og getu til að mæla breytingar á líðan fólks. Efniviður og aðferðir: Sjúklingar sem biðu hjartaþræðingar, aðgerða á bæklunar- eða þvagfæraskurðdeild, voru í meðferð á göngudeild geðdeildar eða voru að byrja í meðferð vegna áfengissýki, samtals 1195 sjúklingar, voru beðnir að svara HL-prófinu. Þremur mánuðum eftir meðferð voru þeir beðnir að svara prófinu aftur. Niðurstöður prófanna voru staðlaðar samkvæmt viðmiðum eftir kyni og aldri svo að hægt væri að sjá beint hvernig þær viku frá því sem almennt gerist. Niðurstöður: Heildarsvörun var 75% í hvorri umferð. Allir sjúklingarnir voru með skert lífsgæði á öllum þáttum prófsins miðað við jafnaldra þeirra, hjarta- og þvagfærasjúklingar minna en bæklunar- og geðsjúklingar. Skerðingin var sérkennandi fyrir hvern hóp, sérstaklega aðgreindust bæklunar- og geðsjúklingarnir greinilega hvor frá öðrum og frá hinum. Eftir meðferð bötnuðu lífsgæðin eða einhverjir þættir þeirra hjá öllum hópunum, mest þeir sem höfðu verið lakastir fyrir. Ályktanir: Með rannsóknum á heilsutengdum lífsgæðum er unnt að afla frekari þekkingar sem nýtist við skipulagningu og framkvæmd heilbrigðisþjónustu. HL-prófið er einfalt tæki til slíkra rannsókna, réttmætt og áreiðanlegt