219 research outputs found
Dissipation in Mesoscopic Superconductors with Ac Magnetic Fields
The response of mesoscopic superconductors to an ac magnetic field is
investigated both experimentally and with numerical simulations. We study small
square samples with dimensions of the order of the penetration depth. We obtain
the ac susceptibitity at microwave frequencies as a
function of the dc magnetic field . We find that the dissipation, given
by , has a non monotonous behavior in mesoscopic samples. In the
numerical simulations we obtain that the dissipation increases before the
penetration of vortices and then it decreases abruptly after vortices have
entered the sample. This is verified experimentally, where we find that
has strong oscillations as a function of in small squares of
Pb.Comment: 4 pages, 2 figure
Investigating the Origin of Mycobacterium chimaera Contamination in Heater-Cooler Units: Integrated Analysis with Fourier Transform Infrared Spectroscopy and Whole-Genome Sequencing
Mycobacterium chimaera is ubiquitously spread in the environment, including factory and hospital water systems. Invasive cases of M. chimaera infection have been associated with aerosols produced by the use of heater-cooler units (HCU) during cardiac surgery. The aim of this study was to evaluate for the first time the performance of IR-Biotyper system on a large number of M. chimaera isolates collected from longitudinal environmental HCUs samples and water sources from hospitals located in three Italian provinces. In addition, IR-Biotyper results were compared with whole-genome sequencing (WGS) analysis, the reference method for molecular epidemiology, to investigate the origin of M. chimaera contamination of HCUs. From November 2018 to May 2021, 417 water samples from 52 HCUs (Stockert 3T, nâ=â41 and HCU40, nâ=â11) and 23 hospital taps (used to fill the HCU tanks) were concentrated, decontaminated, and cultured for M. chimaera. Positive cultures (nâ=â53) were purified by agar plate subcultures and analyzed by IR-Biotyper platform and Ion Torrent sequencing system. IR-Biotyper spectra results were analyzed using a statistical approach of dimensionality reduction by linear discriminant analysis (LDA), generating three separate clusters of M. chimaera, ascribable to each hospital. Furthermore, the only M. chimaera-positive sample from tap water clustered with the isolates from the HCUs of the same hospital, confirming that the plumbing system could represent the source of HCU contamination and, potentially, of patient infection. According to the genome-based phylogenies and following the classification proposed by van Ingen and collaborators in 2017, three distinct M. chimaera groups appear to have contaminated the HCU water systems: subgroups 1.1, 2.1, and branch 2. Most of the strains isolated from HCUs at the same hospital share a highly similar genetic profile. The nonrandom distribution obtained with WGS and IR-Biotyper leads to the hypothesis that M. chimaera subtypes circulating in the local plumbing colonize HCUs through the absolute filter, in addition with the current hypothesis that contamination occurs at the HCU production site. This opens the possibility that other medical equipment, such as endoscope reprocessing device or hemodialysis systems, could be contaminated by M. chimaera. IMPORTANCE Our manuscript focuses on interventions to reduce waterborne disease transmission, improve sanitation, and control infection. Sanitary water can be contaminated by nontuberculous Mycobacteria, including M. chimaera, a causative agent of invasive infections in immunocompromised patients. We found highly similar genetic and phenotypic profiles of M. chimaera isolated from heater-cooler units (HCU) used during surgery to thermo-regulate patients' body temperature, and from the same hospital tap water. These results lead to the hypothesis that M. chimaera subtypes circulating in the local plumbing colonize HCUs through the absolute filter, adding to the current hypothesis that contamination occurs at the HCU production site. In addition, this opens the possibility that other medical equipment using sanitized water, such as endoscope reprocessing devices or hemodialysis systems, could be contaminated by nontuberculous Mycobacteria, suggesting the need for environmental surveillance and associated control measures
Examining the early distribution of the artemisinin-resistant Plasmodium falciparum kelch13 R561H mutation in areas of higher transmission in Rwanda
BACKGROUND: Artemisinin resistance mutations in Plasmodium falciparum kelch13 (Pfk13) have begun to emerge in Africa, with Pfk13-R561H being the first reported in Rwanda in 2014, but limited sampling left questions about its early distribution and origin. METHODS: We genotyped P. falciparum positive dried blood spot (DBS) samples from a nationally representative 2014-2015 Rwanda Demographic Health Surveys (DHS) HIV study. DBS were subsampled from DHS sampling clusters with >15% P. falciparum prevalence, as determined by rapid testing or microscopy done during the DHS study (n clusters = 67, n samples = 1873). RESULTS: We detected 476 parasitemias among 1873 residual blood spots from a 2014-2015 Rwanda Demographic Health Survey. We sequenced 351 samples: 341/351 were wild-type (97.03% weighted), and 4 samples (1.34% weighted) harbored R561H that were significantly spatially clustered. Other nonsynonymous mutations found were V555A (3), C532W (1), and G533A (1). CONCLUSIONS: Our study better defines the early distribution of R561H in Rwanda. Previous studies only observed the mutation in Masaka as of 2014, but our study indicates its presence in higher-transmission regions in the southeast of the country at that time
Magnetic and elastic anisotropy in magnetorheological elastomers using nickel-based nanoparticles and nanochains
Nickel (Ni) based nanoparticles and nanochains were incorporated as fillers in polydimethylsiloxane (PDMS) elastomers and then these mixtures were thermally cured in the presence of a uniform magnetic field. In this way, macroscopically structured-anisotropic PDMS-Ni based magnetorheological composites were obtained with the formation of pseudo-chains-like structures (referred as needles) oriented in the direction of the applied magnetic field when curing. Nanoparticles were synthesized at room temperature, under air ambient atmosphere (open air, atmospheric pressure) and then calcined at 400 °C (in air atmosphere also). The size distribution was obtained by fitting SAXS experiments with a polydisperse hard spheres model and a Schulz-Zimm distribution, obtaining a size distribution centered at (10.0 - 0.6) nm with polydispersivity given by sigma= (8.0 ± 0.2) nm. The SAXS, XRD and TEM experiments are consistent with single crystal nanoparticles of spherical shape (average particle diameter obtained by TEM: (12 ± 1) nm). Nickel-based nanochains (average diameter: 360 nm; average length: 3 mm, obtained by SEM; aspect ratio=length/diameter ~10) were obtained at 85 ÂșC and ambient atmosphere (open air, atmospheric pressure). The magnetic properties of Ni-based nanoparticles and nanochains at room temperature are compared and discussed in terms of surface and size effects. Both Ni-based nanoparticles and nanochains were used as fillers for obtaining the PDMS structured magnetorheological composites, observing the presence of oriented needles. Magnetization curves, ferromagnetic resonance spectra (FMR) and strain-stress curves of low fillerÂŽs loading composites (2% w/w of fillers) were determined as functions of the relative orientation respect to the needles. The results indicate that even at low loadings it is possible to obtain magnetorheological composites with anisotropic properties, with larger anisotropy when using nanochains. For instance, the magnetic remanence, the FMR-resonance field and the elastic response to compression are higher when measured parallel to the needles (about 30% with nanochains as fillers). Analogously, the elastic response is also anisotropic, with larger anisotropy when using nanochains as fillers. Therefore, all experiments performed confirm the high potential of nickel nanochains to induce anisotropic effects in magnetorheological materials.Fil: Landa, Romina AilĂn. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Instituto de QuĂmica FĂsica de los Materiales del Medioambiente y EnergĂa; Argentina;Fil: P Soledad Antonel. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Instituto de QuĂmica FĂsica de los Materiales del Medioambiente y EnergĂa; Argentina;Fil: Mariano M. Ruiz. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Instituto de QuĂmica FĂsica de los Materiales del Medioambiente y EnergĂa; Argentina;Fil: Oscar E PĂ©rez. Universidad de Buenos Aires. Facultad de Cs.exactas y Naturales. Departamento de Industrias;Fil: Alejandro Butera. ComisiĂłn Nacional de EnergĂa AtĂłmica;Fil: Guillermo Jorge. Universidad Nacional de General Sarmiento;Fil: Cristiano L. P. Oliveira. Instituto de FĂsica, Universidade De SĂŁo Paulo; Brasil;Fil: MartĂn Negri. Universidad de Buenos Aires. Facultad de Cs.exactas y Naturales. Departamento de Industrias
Synthesis effects on the magnetic and superconducting properties of RuSr2GdCu2O8
A systematic study on the synthesis of the Ru-1212 compound by preparing a
series of samples that were annealed at increasing temperatures and then
quenched has been performed. It results that the optimal temperature for the
annealing lies around 1060-1065 C; a further temperature increase worsens the
phase formation. Structural order is very important and the subsequent grinding
and annealing improves it. Even if from the structural point of view the
samples appear substantially similar, the physical characterization highlight
great differences both in the electrical and magnetic properties related to
intrinsic properties of the phase as well as to the connection between the
grains as inferred from the resistive and the Curie Weiss behaviour at high
temperature as well as in the visibility of ZFC anf FC magnetic signals.Comment: 17 pages, 12 figures. Proc. Int. Workshop " Ruthenate and
rutheno-cuprate materials: theory and experiments", Vietri, October 2001. To
be published on LNP Series, Springer Verlag, Berlin, C. Noce, A. Vecchione,
M. Cuoco, A. Romano Eds, 200
Spin Glass Behavior in RuSr2Gd1.5Ce0.5Cu2O10
The dynamics of the magnetic properties of polycrystalline
RuSr2Gd1.5Ce0.5Cu2O10 (Ru-1222) have been studied by ac susceptibility and dc
magnetization measurements, including relaxation and ageing studies. Ru-1222 is
a reported magneto-superconductor with Ru spins magnetic ordering at
temperatures near 100 K and superconductivity in Cu-O2 planes below Tc ~ 40 K.
The exact nature of Ru spins magnetic ordering is still debated and no
conclusion has been reached yet. In this work, a frequency-dependent cusp was
observed in ac susceptibility vs. T measurements, which is interpreted as a
spin glass transition. The change in the cusp position with frequency follows
the Vogel-Fulcher law, which is commonly accepted to describe a spin glass with
magnetically interacting clusters. Such interpretation is supported by
themoremanaent magnetization (TRM) measurements at T = 60 K. TRM relaxations
are well described by a stretched exponential relation, and present significant
ageing effects.Comment: 4 pages, 6 figures, submitted to Phys. Rev.
Critical exponents and equation of state of the three-dimensional Heisenberg universality class
We improve the theoretical estimates of the critical exponents for the
three-dimensional Heisenberg universality class. We find gamma=1.3960(9),
nu=0.7112(5), eta=0.0375(5), alpha=-0.1336(15), beta=0.3689(3), and
delta=4.783(3). We consider an improved lattice phi^4 Hamiltonian with
suppressed leading scaling corrections. Our results are obtained by combining
Monte Carlo simulations based on finite-size scaling methods and
high-temperature expansions. The critical exponents are computed from
high-temperature expansions specialized to the phi^4 improved model. By the
same technique we determine the coefficients of the small-magnetization
expansion of the equation of state. This expansion is extended analytically by
means of approximate parametric representations, obtaining the equation of
state in the whole critical region. We also determine a number of universal
amplitude ratios.Comment: 40 pages, final version. In publication in Phys. Rev.
Magneto-Transport Properties of Doped RuSrGdCuO
RuSrGdCuO, in which magnetic order and superconductivity coexist
with , is a complex material which poses new and
important questions to our understanding of the interplay between magnetic and
superconducting (SC) order. Resistivity, Hall effect and thermopower
measurements on sintered ceramic RuSrGdCuO are presented, together
with results on a broad range of substituted analogues. The Hall effect and
thermopower both show anomalous decreases below which may be
explained within a simple two-band model by a transition from localized to more
itinerant behavior in the RuO layer at .Comment: 10 pages, 7 figures, submitted to Phys. Rev. B., correspondence to
[email protected]
Multicenter analysis of sputum microbiota in tuberculosis patients.
The impact of tuberculosis and of anti-tuberculosis therapy on composition and modification of human lung microbiota has been the object of several investigations. However, no clear outcome has been presented so far and the relationship between M. tuberculosis pulmonary infection and the resident lung microbiota remains vague. In this work we describe the results obtained from a multicenter study of the microbiota of sputum samples from patients with tuberculosis or unrelated lung diseases and healthy donors recruited in Switzerland, Italy and Bangladesh, with the ultimate goal of discovering a microbiota-based biomarker associated with tuberculosis. Bacterial 16S rDNA amplification, high-throughput sequencing and extensive bioinformatic analyses revealed patient-specific flora and high variability in taxon abundance. No common signature could be identified among the individuals enrolled except for minor differences which were not consistent among the different geographical settings. Moreover, anti-tuberculosis therapy did not cause any important variation in microbiota diversity, thus precluding its exploitation as a biomarker for the follow up of tuberculosis patients undergoing treatment
Pathologies of the large-N limit for RP^{N-1}, CP^{N-1}, QP^{N-1} and mixed isovector/isotensor sigma-models
We compute the phase diagram in the N\to\infty limit for lattice RP^{N-1},
CP^{N-1} and QP^{N-1} sigma-models with the quartic action, and more generally
for mixed isovector/isotensor models. We show that the N=\infty limit exhibits
phase transitions that are forbidden for any finite N. We clarify the origin of
these pathologies by examining the exact solution of the one-dimensional model:
we find that there are complex zeros of the partition function that tend to the
real axis as N\to\infty. We conjecture the correct phase diagram for finite N
as a function of the spatial dimension d. Along the way, we prove some new
correlation inequalities for a class of N-component sigma-models, and we obtain
some new results concerning the complex zeros of confluent hypergeometric
functions.Comment: LaTeX, 88 pages, 33 figure
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