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1.
Phys Rev Lett ; 122(6): 067001, 2019 Feb 15.
Artigo em Inglês | MEDLINE | ID: mdl-30822059

RESUMO

To unravel the nature of the superconducting symmetry of the enigmatic 5f heavy-fermion UBe_{13}, the pressure dependence of the upper critical field and of the normal state are studied up to 10 GPa. Remarkably, the pressure evolution of the anomalous H_{c2}(T,P) over the entire pressure range up to 5.9 GPa can be successfully explained by the gradual admixture of a field-pressure-induced E_{u} component in an A_{1u} spin-triplet ground state. This result provides strong evidence for parallel-spin pairing in UBe_{13}, which is also supported by the recently observed fully gapped excitation spectrum at ambient pressure. Moreover, we have also found a novel non-Fermi-liquid behavior of the resistivity, ρ(T)∼T^{n} (n≲1), which disappears with the collapse of the negative magnetoresistance behavior and the existence of a superconducting ground state around P=6 GPa, suggesting a close interplay between Kondo scattering and superconductivity.

2.
Phys Rev Lett ; 120(3): 037001, 2018 Jan 19.
Artigo em Inglês | MEDLINE | ID: mdl-29400517

RESUMO

In most unconventional superconductors, like the high-T_{c} cuprates, iron pnictides, or heavy-fermion systems, superconductivity emerges in the proximity of an electronic instability. Identifying unambiguously the pairing mechanism remains nevertheless an enormous challenge. Among these systems, the orthorhombic uranium ferromagnetic superconductors have a unique position, notably because magnetic fields couple directly to ferromagnetic order, leading to the fascinating discovery of the reemergence of superconductivity in URhGe at a high field. Here we show that uniaxial stress is a remarkable tool allowing the fine-tuning of the pairing strength. With a relatively small stress, the superconducting phase diagram is spectacularly modified, with a merging of the low- and high-field superconducting states and a significant enhancement of the superconductivity. The superconducting critical temperature increases both at zero field and under a field, reaching 1 K, more than twice higher than at ambient pressure. This enhancement of superconductivity is shown to be directly related to a change of the magnetic dimensionality detected from an increase of the transverse magnetic susceptibility: In addition to the Ising-type longitudinal ferromagnetic fluctuations, transverse magnetic fluctuations also play an important role in the superconducting pairing.

3.
Rev Sci Instrum ; 87(2): 023907, 2016 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-26931866

RESUMO

We present a new specially designed pressure cell and technique adapted for resistivity measurements in pulsed magnetic fields up to 60 T at pressures up to at least 4 GPa, and temperatures down to 1.5 K. We show that heating effects during the pulse are acceptable (less than 1 K) and can be corrected allowing reliable temperature dependences of the magnetoresistance to be obtained. We illustrate the performance with a study of the phase diagram of the heavy fermion antiferromagnet CeRh2Si2.

4.
PLoS One ; 9(9): e107460, 2014.
Artigo em Inglês | MEDLINE | ID: mdl-25202990

RESUMO

Understanding the microbial community structure and genetic potential of anode biofilms is key to improve extracellular electron transfers in microbial fuel cells. We investigated effect of substrate and temporal dynamics of anodic biofilm communities using phylogenetic and metagenomic approaches in parallel with electrochemical characterizations. The startup non-steady state anodic bacterial structures were compared for a simple substrate, acetate, and for a complex substrate, landfill leachate, using a single-chamber air-cathode microbial fuel cell. Principal coordinate analysis showed that distinct community structures were formed with each substrate type. The bacterial diversity measured as Shannon index decreased with time in acetate cycles, and was restored with the introduction of leachate. The change of diversity was accompanied by an opposite trend in the relative abundance of Geobacter-affiliated phylotypes, which were acclimated to over 40% of total Bacteria at the end of acetate-fed conditions then declined in the leachate cycles. The transition from acetate to leachate caused a decrease in output power density from 243±13 mW/m2 to 140±11 mW/m2, accompanied by a decrease in Coulombic electron recovery from 18±3% to 9±3%. The leachate cycles selected protein-degrading phylotypes within phylum Synergistetes. Metagenomic shotgun sequencing showed that leachate-fed communities had higher cell motility genes including bacterial chemotaxis and flagellar assembly, and increased gene abundance related to metal resistance, antibiotic resistance, and quorum sensing. These differentially represented genes suggested an altered anodic biofilm community in response to additional substrates and stress from the complex landfill leachate.


Assuntos
Fontes de Energia Bioelétrica/microbiologia , Geobacter/genética , Biofilmes , Eletrodos/microbiologia , Transporte de Elétrons/genética , Elétrons , Metagenômica/métodos , Filogenia , Poluentes Químicos da Água/metabolismo
5.
J Healthc Eng ; 5(1): 23-53, 2014.
Artigo em Inglês | MEDLINE | ID: mdl-24691385

RESUMO

For hospitalized patients requiring intravenous insulin therapy, an objective is to quantify the intravenous insulin infusion rate (IR) across the domain of blood glucose (BG) values at a single timepoint. The algorithm parameters include low BG (70 mg/dL), critical high BG, target range BG limits, and maintenance rate (MR) of insulin infusion, which, after initialization, depends on rate of change of blood glucose, previous IR, and other inputs. The restraining rate (RR) is a function of fractional completeness of ascent of BG (FCABG) from BG 70 mg/dL to target. The correction rate (CR) is a function of fractional elevation of BG (FEBG), in comparison to elevation of a critical high BG, above target. IR = RR + CR. The proposed mathematical model describing a sigmoidal relationship between IR and BG may offer a safety advantage over the linear relationship currently employed in some intravenous glucose management systems.


Assuntos
Glicemia/análise , Hiperglicemia/tratamento farmacológico , Hipoglicemia/prevenção & controle , Sistemas de Infusão de Insulina , Insulina/administração & dosagem , Algoritmos , Glicemia/metabolismo , Cetoacidose Diabética/prevenção & controle , Hospitalização , Humanos , Hiperglicemia/prevenção & controle , Hipoglicemia/induzido quimicamente , Hipoglicemia/tratamento farmacológico , Infusões Intravenosas , Modelos Teóricos
6.
Methods Enzymol ; 531: 487-523, 2013.
Artigo em Inglês | MEDLINE | ID: mdl-24060134

RESUMO

The democratized world of sequencing is leading to numerous data analysis challenges; MG-RAST addresses many of these challenges for diverse datasets, including amplicon datasets, shotgun metagenomes, and metatranscriptomes. The changes from version 2 to version 3 include the addition of a dedicated gene calling stage using FragGenescan, clustering of predicted proteins at 90% identity, and the use of BLAT for the computation of similarities. Together with changes in the underlying software infrastructure, this has enabled the dramatic scaling up of pipeline throughput while remaining on a limited hardware budget. The Web-based service allows upload, fully automated analysis, and visualization of results. As a result of the plummeting cost of sequencing and the readily available analytical power of MG-RAST, over 78,000 metagenomic datasets have been analyzed, with over 12,000 of them publicly available in MG-RAST.


Assuntos
Biologia Computacional/métodos , Metagenômica , Software , Bactérias/classificação , Bactérias/genética , Genoma Bacteriano , Sequenciamento de Nucleotídeos em Larga Escala , Internet
7.
Adv Mater ; 20(14): 2760-5, 2008 Jul 17.
Artigo em Inglês | MEDLINE | ID: mdl-25213903

RESUMO

Experimental evidence of a nonvolatile electric-pulse-induced insulator-to-metal transition and possible superconductivity in the Mott insulator GaTa4 Se8 is reported. Scanning tunneling microscopy experiments show that this unconventional response of the system to short electric pulses arises from a nanometer-scale electronic phase separation generated in the bulk material.

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