Direct and Inverse Magnetocaloric effects in A-site ordered PrBaMn2O6 manganite in low magnetic fields

The magnetocaloric effect (MCE) of A-site ordered PrBaMn2O6 manganite has been studied by direct methods and by the specific heat measurements. Direct measurements of the MCE in low magnetic fields were performed using recently proposed modulation technique and by classic direct method in high fields. Direct and inverse MCE are observed at Curie and Neel points correspondingly. A value of the inverse MCE in the heating run is less than in the cooling regime. This effect can be attributing to competition between ferromagnetic and antiferromagnetic interactions. Indirectly estimated and direct MCE values considerably differ in around first order AF transition.Comment: 8 pages, 5 figure

Spontaneous magnetization above TC in polycrystalline La0.7 Ca0.3 MnO3 and La0.7 Ba0.3 MnO3

In the present work, spontaneous magnetization is observed in the inverse magnetic susceptibility of La0.7Ca0.3MnO3 and La0.7Ba0.3MnO3 compounds above TC up to a temperature T*. From information gathered from neutron diffraction, dilatometry, and high-field magnetization data, we suggest that T* is related to the transition temperature of the low-temperature (high magnetic field) magnetic phase. In the temperature region between T* and TC, the application of a magnetic field drives the system from the high-temperature to low-temperature magnetic phases, the latter possessing a higher magnetization. © 2014 American Physical Society

Polyhydroxyalkanoate granules quantification in mixed microbial cultures using image analysis: Sudan Black B versus Nile Blue A staining

Polyhydroxyalkanoates (PHA) can be produced and intracellularly accumulated as inclusions by mixed microbial cultures (MMC) for bioplastic production and in enhanced biological phosphorus removal (EBPR) systems. Classical methods for PHA quantification use a digestion step prior to chromatography analysis, rendering them labor intensive and time-consuming. The present work investigates the use of two quantitative image analysis (QIA) procedures specifically developed for PHA inclusions identification and quantification. MMC obtained from an EBPR system were visualized by bright-field and fluorescence microscopy for PHA inclusions detection, upon Sudan Black B (SBB) and Nile Blue A (NBA) staining, respectively. The captured color images were processed by QIA techniques and the image analysis data were further treated using multivariate statistical analysis. Partial least squares (PLS) regression coefficients of 0.90 and 0.86 were obtained between QIA parameters and PHA concentrations using SBB and NBA, respectively. It was found that both staining procedures might be seen as alternative methodologies to classical PHA determination.The authors thank the Fundacao para a Ciencia e a Tecnologia (FCT) Strategic Project PEst-OE/EQB/LA0023/2013 and the Project "BioEnv - Biotechnology and Bioengineering for a sustainable world", REF. NORTE-07-0124-FEDER-000048, co-funded by the Programa Operacional Regional do Norte (ON.2 - O Novo Norte), QREN, FEDER. The authors also acknowledge the financial support to Daniela P. Mesquita through the postdoctoral grant (SFRH/BPD/82558/2011) and the project PTDC/EBB-EBI/103147/2008 provided by FCT

Universality in Bacterial Colonies

The emergent spatial patterns generated by growing bacterial colonies have been the focus of intense study in physics during the last twenty years. Both experimental and theoretical investigations have made possible a clear qualitative picture of the different structures that such colonies can exhibit, depending on the medium on which they are growing. However, there are relatively few quantitative descriptions of these patterns. In this paper, we use a mechanistically detailed simulation framework to measure the scaling exponents associated with the advancing fronts of bacterial colonies on hard agar substrata, aiming to discern the universality class to which the system belongs. We show that the universal behavior exhibited by the colonies can be much richer than previously reported, and we propose the possibility of up to four different sub-phases within the medium-to-high nutrient concentration regime. We hypothesize that the quenched disorder that characterizes one of these sub-phases is an emergent property of the growth and division of bacteria competing for limited space and nutrients.Comment: 12 pages, 5 figure

DIS and the effects of fluctuations: a momentum space analysis

Among the dipole models of deep inelastic scattering at small values of the Bjorken variable $x$, one has been recently proposed which relates the virtual photon-proton cross section to the dipole-proton forward scattering amplitude in momentum space. The latter is parametrized by an expression which interpolates between its behavior at saturation and the travelling wave, ultraviolet, amplitudes predicted by perturbative QCD from the Balitsky-Kovchegov equation. Inspired by recent developments in coordinate space, we use this model to parametrize the proton structure function and confront it to HERA data on $ep$ deep inelastic scattering. Both event-by-event and the physical amplitudes are considered, the latter used to investigate the effect of gluon number fluctuations, beyond the mean-field approximation. We conclude that fluctuations are not present in DIS at HERA energies.Comment: 9 pages, 2 figure

Measurement of the partial widths of the Z into up- and down-type quarks

Using the entire OPAL LEP1 on-peak Z hadronic decay sample, Z -> qbarq gamma decays were selected by tagging hadronic final states with isolated photon candidates in the electromagnetic calorimeter. Combining the measured rates of Z -> qbarq gamma decays with the total rate of hadronic Z decays permits the simultaneous determination of the widths of the Z into up- and down-type quarks. The values obtained, with total errors, were Gamma u = 300 ^{+19}_{-18} MeV and Gamma d = 381 ^{+12}_{-12} MeV. The results are in good agreement with the Standard Model expectation.Comment: 22 pages, 5 figures, Submitted to Phys. Letts.

Search for R-Parity Violating Decays of Scalar Fermions at LEP

A search for pair-produced scalar fermions under the assumption that R-parity is not conserved has been performed using data collected with the OPAL detector at LEP. The data samples analysed correspond to an integrated luminosity of about 610 pb-1 collected at centre-of-mass energies of sqrt(s) 189-209 GeV. An important consequence of R-parity violation is that the lightest supersymmetric particle is expected to be unstable. Searches of R-parity violating decays of charged sleptons, sneutrinos and squarks have been performed under the assumptions that the lightest supersymmetric particle decays promptly and that only one of the R-parity violating couplings is dominant for each of the decay modes considered. Such processes would yield final states consisting of leptons, jets, or both with or without missing energy. No significant single-like excess of events has been observed with respect to the Standard Model expectations. Limits on the production cross- section of scalar fermions in R-parity violating scenarios are obtained. Constraints on the supersymmetric particle masses are also presented in an R-parity violating framework analogous to the Constrained Minimal Supersymmetric Standard Model.Comment: 51 pages, 24 figures, Submitted to Eur. Phys. J.