Local Simulation Algorithms for Coulomb Gases with Dynamical Dielectric Effects

We discuss the application of the local lattice technique of Maggs and Rossetto to problems that involve the motion of objects with different dielectric constants than the background. In these systems the simulation method produces a spurious interaction force which causes the particles to move in an unphysical manner. We show that this term can be removed using a variant of a method known from high-energy physics simulations, the multiboson method, and demonstrate the effectiveness of this corrective method on a system of neutral particles. We then apply our method to a one-component plasma to show the effect of the spurious interaction term on a charged system.Comment: 13 pages, 4 figure

Automorphisms of Partially Commutative Groups II: Combinatorial Subgroups

We define several "standard" subgroups of the automorphism group Aut(G) of a partially commutative (right-angled Artin) group and use these standard subgroups to describe decompositions of Aut(G). If C is the commutation graph of G, we show how Aut(G) decomposes in terms of the connected components of C: obtaining a particularly clear decomposition theorem in the special case where C has no isolated vertices. If C has no vertices of a type we call dominated then we give a semi-direct decompostion of Aut(G) into a subgroup of locally conjugating automorphisms by the subgroup stabilising a certain lattice of "admissible subsets" of the vertices of C. We then characterise those graphs for which Aut(G) is a product (not necessarily semi-direct) of two such subgroups.Comment: 7 figures, 63 pages. Notation and definitions clarified and typos corrected. 2 new figures added. Appendix containing details of presentation and proof of a theorem adde

A Southern Hemisphere radar meteor orbit survey

A meteor radar system has been operated on a routine basis near Christchurch, New Zealand, to determine the orbits of Earth-impacting interplanetary dust and meteoroids. The system sensitivity is +13 visual magnitude, corresponding to approximately 100 micron sized meteoroids. With an orbital precision of 2 degrees in angular elements and 10 percent in orbital energy (1/a), the operation yields an average of 1500 orbits daily with a total to date in excess of 10(exp 5). The use of pc's and automated data reduction permit the large orbital data sets we collect to be routinely reduced. Some illustrative examples are presented of the signal formats/processing and the results of data reduction, giving the individual orbital elements and hence the overall distributions. Current studies include the distribution of dust in the inner solar system; the influx of meteoroids associated with near-Earth asteroids; and the orbital structure existing in comet-produced streams

Regional differences in store-operated Ca2+ entry in the epithelium of the intact human lens

An elevated level of Ca2+ is an important factor in cataract, yet precisely how Ca2+ enters the lens is unknown. Lens epithelial cells contain a range of G-protein–coupled receptors and receptor tyrosine kinases that induce increases in intracellular Ca2+. Receptor-associated Ca2+ influx is, therefore, likely to be an important route for Ca2+ influx to the lens. The authors investigated stimulated and passive Ca2+ influx in in situ human lens epithelium. Ca2+ changes in equatorial (E) and central anterior (CA) epithelial cells were monitored with the use of a Ca2+ indicator (Fluo4) and confocal microscopy. Gene expression was monitored by RT-PCR and immunoblotting. Adenosine triphosphate (ATP) induced Ca2+ responses that were smaller in CA than E. Ca2+ store depletion, using ATP (100 µM) or thapsigargin (1 µM), revealed greater relative store capacity and Ca2+ influx in E. Ca2+ influx was blocked by La3+ (0.5 µM) in both regions. Unstimulated Ca2+ influx was greater in E than CA. Greater expression of Orai1 and STIM1 was detected in E than in CA. Greater Ca2+ store capacity and Ca2+ influx in E compared with CA reflects underlying differences in proliferation and differentiation between the regions. The relatively small resting Ca2+ influx in CA epithelium suggests that store-operated Ca2+ entry (SOCE) is the main route of Ca2+ influx in these cells. Greater resting influx and SOCE in E cells suggests that these are a major route for Ca2+ influx into the lens. Increased expression of Orai1 and STIM1 in E could account for the differences in Ca2+ entry. Receptor activation will modulate Ca2+ influx, and inappropriate activity may contribute to cortical cataract

Risk factors and mortality associated with multimorbidity in people with stroke or transient ischaemic attack: a study of 8,751 UK Biobank participants

Background: Multimorbidity is common in stroke, but the risk factors and effects on mortality remain poorly understood. Objective: To examine multimorbidity and its associations with sociodemographic/lifestyle risk factors and all-cause mortality in UK Biobank participants with stroke or transient ischaemic attack (TIA). Design: Data were obtained from an anonymized community cohort aged 40–72 years. Overall, 42 comorbidities were self-reported by those with stroke or TIA. Relative risk ratios demonstrated associations between participant characteristics and number of comorbidities. Hazard ratios demonstrated associations between the number and type of comorbidities and all-cause mortality. Results were adjusted for age, sex, socioeconomic status, smoking, and alcohol intake. Data were linked to national mortality data. Median follow-up was 7 years. Results: Of 8,751 participants (mean age 60.9±6.7 years) with stroke or TIA, the all-cause mortality rate over 7 years was 8.4%. Over 85% reported ≥1 comorbidities. Age, socioeconomic deprivation, smoking and less frequent alcohol intake were associated with higher levels of multimorbidity. Increasing multimorbidity was associated with higher all-cause mortality. Mortality risk was double for those with ≥5 comorbidities compared to those with none. Having cancer, coronary heart disease, diabetes, or chronic obstructive pulmonary disease significantly increased mortality risk. Presence of any cardiometabolic comorbidity significantly increased mortality risk, as did any non-cardiometabolic comorbidity. Conclusions: In stroke survivors, the number of comorbidities may be a more helpful predictor of mortality than type of condition. Stroke guidelines should take greater account of comorbidities, and interventions are needed that improve outcomes for people with multimorbidity and stroke

Channel Closing in Multiphoton Ionization of Mg

Experimental data are presented showing the channel closing of four-photon ionization of Mg. It is shown that, for circularly polarized light, the ionization versus intensity spectra exhibit sharp breaks from the normal I4 intensity dependence at the critical intensity where the channel closing occurs. Above the critical intensity, the population of Rydberg states which survives the laser pulse is observed. The residual Rydberg population is found to be greatly reduced for linearly polarized light due to the relatively large probability of ionization of the low-angular-momentum Rydberg states. The data are in good agreement with a model which includes averaging over the spatial profile of the laser

Floquet Description of Multiphoton Processes in Li

We have made several different types of measurements of the three-photon ionization of Li produced by 3-ps laser pulses and describe the results using a Floquet picture. Over the photon frequency range 15 000 to 15 800 cm-1, Li represents a strongly coupled three-state system with the 2s ground state coupled to the 2p and 3d states by one and two photons, respectively. Energy analysis of the photoelectrons allows the measurement of the intensity dependent shift of the 2s Floquet state during the laser pulse. The shift shows a strong frequency dependence that is not predicted by first-order perturbation theory. We have also measured the total ionization spectrum over several ranges of frequency, as well as the angular distribution of the ionization and the first above-threshold ionization peak for frequencies where the ground state is near resonance with the 4s and 4d excited states. Calculations based on the Floquet Hamiltonian indicate that all of these processes may be understood in terms of a Floquet description

Spatially Resolved Transitions to Autoionizing States

We have observed transitions to autoionizing states in Mg using two short optical pulses. Mg atoms are initially prepared in a high lying Rydberg wave packet with the first ps laser. A second ps laser is then used to excite the inner electron, producing an autoionizing state. The dependence of the transition probability on the delay between the two lasers shows that when the second laser is tuned away from the ionic resonance, the inner electron can make a transition only when the Rydberg wave packet is near the core

Social Stress and Welfare Problems in Agricultural Animals

Disruptions of an animal\u27s social behaviour can, in some respects at least, mimic the effects of such classical stressors as infection and exposure to low temperatures. For example, Barnett (1958) found enlarged adrenals among wild rats which were subjected to attack by other rats in the laboratory. However, the experience of being attacked was not necessary for this physiological response, as the aggressors showed much the same changes as the victims. In fact Archer (1969) reported heightened adrenocortical activity among individually caged mice simply as a result of their being housed next to other mice, without actual physical contact. If adrenocortical activity is increased by social interaction, it seems reasonable that it should be reduced by solitary confinement. Up to a point this appears to be true for male mice (Brain & Nowell, 1970), but prolonged social isolation, lasting a month or more, may have the opposite effect (Sigg et al., 1966)

Landau-Zener Treatment of Intensity-Tuned Multiphoton Resonances of Potassium

When exposed to intense light of ~580 nm, the ground state of K shifts up in energy, passing through two photon resonances with Rydberg states, and finally crossing the two-photon ionization limit. We have used laser pulses of varying duration to study the nature of the population transfer from the ground state to the excited state due to the intensity-tuned resonances encountered during the rising edge of the pulse. A dynamic Floquet approach in which the resonances are treated as avoided crossings of the Floquet energy levels is used to model the population transfer and gives excellent agreement with the data. The model is extended into the strong-coupling regime where the ground state interacts with many excited states simultaneously, and we show that this model can be used to describe multiphoton ionization as a series of avoided crossings with the continuum