Effects of mixed rare earth occupancy on the low temperature properties of (R, R',R''...)Ni2Ge2 single crystals

Temperature and applied magnetic field dependent magnetization measurements on 34 single crystalline samples of (R, R',R''...)Ni2Ge2 compounds (R, R', R'', etc. being primarily Gd-Lu, Y), were made. These measurements reveal that, despite extremes in local moment anisotropy, the average de Gennes parameter is a remarkably good predictor of the paramagnetic to antiferromagnetic ordering temperature. In addition, the pronounced metamagnetic phase transitions seen in the low temperature phase of TbNi2Ge2 are found to be remarkably robust to high substitution levels of Gd and 25% substitutions of other heavy rare earths

Liquid bridging of cylindrical colloids in near-critical solvents

Within mean field theory, we investigate the bridging transition between a pair of parallel cylindrical colloids immersed in a binary liquid mixture as a solvent which is close to its critical consolute point $T_c$. We determine the universal scaling functions of the effective potential and of the force between the colloids. For a solvent which is at the critical concentration and close to $T_c$, we find that the critical Casimir force is the dominant interaction at close separations. This agrees very well with the corresponding Derjaguin approximation for the effective interaction between the two cylinders, while capillary forces originating from the extension of the liquid bridge turn out to be more important at large separations. In addition, we are able to infer from the wetting characteristics of the individual colloids the first-order transition of the liquid bridge connecting two colloidal particles to the ruptured state. While specific to cylindrical colloids, the results presented here provide also an outline for identifying critical Casimir forces acting on bridged colloidal particles as such, and for analyzing the bridging transition between them.Comment: 23 pages, 12 figure

Broken Symmetry as a Stabilizing Remnant

The Goldberger-Wise mechanism enables one to stabilize the length of the warped extra dimension employed in Randall-Sundrum models. In this work we generalize this mechanism to models with multiple warped throats sharing a common ultraviolet brane. For independent throats this generalization is straight forward. If the throats possess a discrete interchange symmetry like Z_n the stabilizing dynamics may respect the symmetry, resulting in equal throat lengths, or they may break it. In the latter case the ground state of an initially symmetric configuration is a stabilized asymmetric configuration in which the throat lengths differ. We focus on two- (three-) throat setups with a Z_2 (Z_3) interchange symmetry and present stabilization dynamics suitable for either breaking or maintaining the symmetry. Though admitting more general application, our results are relevant for existing models in the literature, including the two throat model with Kaluza-Klein parity and the three throat model of flavor based on a broken Z_3 symmetry.Comment: 23 pages; v2 minor cosmetic chang

Do early-life exposures explain why more advantaged children get eczema? Findings from the U.K. Millennium Cohort Study

Background: Atopic dermatitis (eczema) in childhood is socially patterned, with higher incidence in more advantaged populations. However, it is unclear what factors explain the social differences. Objectives: To identify early-life risk factors for eczema, and to explore how early-life risk factors explain any differences in eczema. Methods: We estimated odds ratios (ORs) for ever having had eczema by age 5 years in 14 499 children from the U.K. Millennium Cohort Study (MCS), with a focus on maternal, antenatal and early-life risk factors and socioeconomic circumstances (SECs). Risk factors were explored to assess whether they attenuated associations between SECs and eczema. Results: Overall 35·1% of children had ever had eczema by age 5 years. Children of mothers with degree-level qualifications vs. no educational qualifications were more likely to have eczema (OR 1·52, 95% confidence interval 1·31–1·76), and there was a gradient across the socioeconomic spectrum. Maternal atopy, breastfeeding (1–6 weeks and ≥ 6 months), introduction of solids under 4 months or cow's milk under 9 months, antibiotic exposure in the first year of life and grime exposure were associated with an increased odds of having eczema. Female sex, Pakistani and Bangladeshi ethnicity, smoking during pregnancy, exposure to environmental tobacco smoke and having more siblings were associated with reduced odds for eczema. Controlling for maternal, antenatal and early-life characteristics (particularly maternal smoking during pregnancy, breastfeeding and number of siblings) reduced the OR for eczema to 1·26 (95% confidence interval 1·03–1·50) in the group with the highest educational qualifications compared with the least. Conclusions: In a representative U.K. child cohort, eczema was more common in more advantaged children. This was explained partially by early-life factors including not smoking during pregnancy, breastfeeding and having fewer siblings

An exploratory study to identify risk factors for the development of capecitabine-induced palmar plantar erythrodysesthesia (PPE)

Aims: to identify pre-treatment risk factors for the development of Palmar Plantar Erythrodysesthesia in participants receiving capecitabine monotherapy. Specifically the hypothesis that avoidance of activities that cause friction and pressure cause Palmar Plantar Erythrodysesthesia was tested. Background. Previous literature showed contradictory evidence on the subject of predictors of chemotherapy-induced Palmar Plantar Erythrodysesthesia. There is a lack of empirical evidence to support the theory that Palmar Plantar Erythrodysesthesia is caused by damage to the microcapillaries due to everyday activities that cause friction or pressure to the hands or feet. Design. Prospective epidemiological study of risk factors. Methods. Prospective data collection. All patients prior to commencing capecitabine monotherapy between 11 June 2009–31 December 2010, were offered recruitment into the study and followed up for six cycles of treatment (n = 174). Data were collected during semi-structured interviews, from participants’ diaries, physical examination of the hands and feet and review of notes. Data relating to activities that cause friction, pressure or heat were collected. Data were analysed using bivariate (chi-square and independent groups Student’s t) tests where each independent variable was analysed against Palmar Plantar Erythrodysesthesia. Results. The only variables that were associated with an increased risk of Palmar Plantar Erythrodysesthesia were a tendency to have warm hands and pre-existing inflammatory disease. Conclusions. This study gives no support for the hypothesis that avoidance of activities that cause friction and pressure cause Palmar Plantar Erythrodysesthesia

The effect of glucose absorption from peritoneal dialysates on changes in lipid profiles in prevalent peritoneal dialysis patients

The majority of peritoneal dialysates contain glucose, which can potentially be absorbed from the peritoneal cavity. Previous studies have reported an observation between dialysate glucose exposure and increases in total cholesterol (TC), low-density lipoproteins (LDLs) and triglycerides (TGs). As most of these studies reported glucose exposure in peritoneal dialysis (PD) patients treated by continuous ambulatory peritoneal dialysis (CAPD), we wished to determine whether measured peritoneal glucose absorption resulted in an increase in lipid profile with CAPD and automated PD (APD) cycler treatments. Glucose absorption was measured in 143 patients; 89 (62.2%) males, 53 (37.1%) diabetics, mean age 61.3 ± 14.9 years, with 90 (62.1%) using a daytime icodextrin exchange; 37 (25.9%) CAPD, attending for their first assessment of peritoneal membrane function, when PD prescriptions were then individualised for peritoneal transporter status and repeated after 12 months. Median glucose absorption was 172.5 (75.5-265.5) mmol/day. Although glycated haemoglobin increased (42 ± 16 to 45.4 ± 17.7 mmol/mol, p = 0.006), there was no change in TC (4.8 ± 1.3 to 4.7 ± 1.3 mmol/L), high-density lipoproteins (1.39 ± 0.45 to 1.33 ± 0.51 mmol/L), LDL (2.48 ± 1.12 to 2.21 ± 0.87 mmol/L) or TGs (2.0 (1.3-2.6) to 2.0 (1.3-2.8) mmol/L, adjusted p > 0.05). We found no association between glucose absorption and either lipid profiles or changes in serum lipids. In the current era of APD cyclers and icodextrin, PD prescriptions can be individualised to accommodate patients with a different peritoneal transport status, so that despite daily glucose absorption from dialysates, and a minor increase in glycated haemoglobin, we were unable to demonstrate any significant increase in standard lipid profiles

Glucose absorption from peritoneal dialysate is associated with a gain in fat mass and a reduction in lean body mass in prevalent peritoneal dialysis patients

The majority of peritoneal dialysates use glucose to generate an osmotic gradient for the convective removal of water and sodium. Although glucose can potentially be absorbed, previous studies have failed to establish whether this leads to increased fat weight gain. We measured body composition using bioimpedance in peritoneal dialysis (PD) patients, electively starting PD, attending for their first assessment of peritoneal membrane function after 2-3 months, and then after 12 months. We studied 143 patients; 89 (62.2%) males, 53 (37.1%) diabetics, mean age 61.3±14.9 years, with 90 (62.1%) of patients treated by automated PD cyclers (APD) with a daytime icodextrin exchange and 37 (25.9%) by continuous ambulatory PD (CAPD). Median fat mass increased by 1.8 (-0.5 to 4.1) kg, whereas fat free mass fell -1.3 (-2.9 to 1.0) kg, and the increase in fat mass was negatively associated with the fall in soft lean mass (r-0.41, p<0.001). Increased fat mass was associated with measured peritoneal glucose absorption (r=0.69, p<0.001), and glucose absorption was associated with the amount of 22.7 g/L glucose dialysate (odds ratio (OR) 2.0, 95% confidence limits (CL) 1.5-2.5, p<0.001), peritoneal urea clearance (OR 9.5 (CL 2.4-37.1) p=0.001), and male gender (OR 4.8 (CL 1.5-14.9) p=0.008). We report an observational study in prevalent PD patients following body composition from their first assessment of peritoneal dialysis membrane function for approximately 12 months, and despite the majority of patients prescribed icodextrin, we have demonstrated an association between intra-peritoneal glucose absorption and fat weight gain, but also loss of fat-free mass

Laser-only adaptive optics achieves significant image quality gains compared to seeing-limited observations over the entire sky

Adaptive optics laser guide star systems perform atmospheric correction of stellar wavefronts in two parts: stellar tip-tilt and high-spatial-order laser-correction. The requirement of a sufficiently bright guide star in the field-of-view to correct tip-tilt limits sky coverage. Here we show an improvement to effective seeing without the need for nearby bright stars, enabling full sky coverage by performing only laser-assisted wavefront correction. We used Robo-AO, the first robotic AO system, to comprehensively demonstrate this laser-only correction. We analyze observations from four years of efficient robotic operation covering 15,000 targets and 42,000 observations, each realizing different seeing conditions. Using an autoguider (or a post-processing software equivalent) and the laser to improve effective seeing independent of the brightness of a target, Robo-AO observations show a 39+/-19% improvement to effective FWHM, without any tip-tilt correction. We also demonstrate that 50% encircled-energy performance without tip-tilt correction remains comparable to diffraction-limited, standard Robo-AO performance. Faint-target science programs primarily limited by 50% encircled-energy (e.g. those employing integral field spectrographs placed behind the AO system) may see significant benefits to sky coverage from employing laser-only AO.Comment: Accepted for publication in The Astronomical Journal. 7 pages, 6 figure

Statistical mechanics of ecosystem assembly

We introduce a toy model of ecosystem assembly for which we are able to map out all assembly pathways generated by external invasions. The model allows to display the whole phase space in the form of an assembly graph whose nodes are communities of species and whose directed links are transitions between them induced by invasions. We characterize the process as a finite Markov chain and prove that it exhibits a unique set of recurrent states (the endstate of the process), which is therefore resistant to invasions. This also shows that the endstate is independent on the assembly history. The model shares all features with standard assembly models reported in the literature, with the advantage that all observables can be computed in an exact manner.Comment: Accepted for publication in Physical Review Letter

Counter-Intuitive Vacuum-Stimulated Raman Scattering

Vacuum-stimulated Raman scattering in strongly coupled atom-cavity systems allows one to generate free-running single photon pulses on demand. Most properties of the emitted photons are well defined, provided spontaneous emission processes do not contribute. Therefore, electronic excitation of the atom must not occur, which is assured for a system adiabatically following a dark state during the photon-generation process. We experimentally investigate the conditions that must be met for adiabatic following in a time-of-flight driven system, with atoms passing through a cavity and a pump beam oriented transverse to the cavity axis. From our results, we infer the optimal intensity and relative pump-beam position with respect to the cavity axis.Comment: 4 pages, 4 figure