A novel plasma jet with RF and HF coupled electrodes

In order to achieve low processing temperature and efficient coatings deposition for manufacturing applications, a novel torch has been developed that couples in a double DBD design high frequency (HF ~17 kHz) and radio frequency (RF ~27 MHz) excitations. The design allows to obtain a stable RF plasma also in reactive processes and with the possibility to control on the treated substrates ions flux and surface charging, avoiding the micro-discharges. The plasma has been electrically and optically characterized by emission spectroscopy

Chlamydia pneumoniae and Mycoplasma pneumoniae in children with cystic fibrosis: impact on bacterial respiratory microbiota diversity.

The contribution of intracellular and fastidious bacteria in Cystic fibrosis (CF) pulmonary exacerbations, and progressive lung function decline remains unknown. This project aimed to explore their impact on bacterial microbiota diversity over time in CF children. Sixty-one children enrolled in the MUCOVIB multicentre prospective cohort provided 746 samples, mostly nasopharyngeal swabs, throat swabs and sputa which were analysed using culture, specific real-time qPCRs and 16S rRNA amplicon metagenomics. Chlamydia pneumoniae (n = 3) and Mycoplasma pneumoniae (n = 1) were prospectively documented in 6.6% of CF children. Microbiota alpha-diversity in children with a documented C. pneumoniae was highly variable, similarly to children infected with Staphylococcus aureus or Pseudomonas aeruginosa. The transition from routine follow-up visits to pulmonary exacerbation (n = 17) yielded variable changes in diversity indexes with some extreme loss of diversity. The high rate of C. pneumoniae detection supports the need for regular screenings in CF patients. A minor impact of C. pneumoniae on the microbial community structure was documented. Although detected in a single patient, M. pneumoniae should also be considered as a possible aetiology of lung infection in CF subjects

Evolution of field-induced metastable phases in the Shastry-Sutherland lattice magnet TmB4

The appearance of a plateau in the magnetization of a quantum spin system subject to continuously varying magnetic field invites the identification of a topological quantization. Indeed, the magnetization plateaus at 1/8 and 1/2 of saturation in TmB4 have been suggested to be intrinsic, resulting from such a topological quantization, or, alternatively, to be metastable phases. By means of neutron- and x-ray-scattering experiments and magnetization measurements, we show that the 1/8 plateau is metastable, arising because the spin dynamics are frozen below T ≈ 4.5 K. Our experiments show that in this part of the phase diagram of TmB4, many long-ranged orders with different propagation vectors may appear and coexist, particularly as the applied field drives the system from one plateau to another. The magnetic structures accommodating a magnetization of ≈1/8 seem to be particularly favorable, but still only appear if the system has sufficient dynamics to reorganize into a superstructure as it is driven toward the expected plateau. This work demonstrates that TmB4 represents a model material for the study of slow dynamics, in and out of equilibrium

Pressure tuning of bond-directional exchange interactions and magnetic frustration in the hyperhoneycomb iridate β−Li₂IrO₃

We explore the response of Ir 5 d orbitals to pressure in β − Li 2 IrO 3 , a hyperhoneycomb iridate in proximity to a Kitaev quantum spin-liquid (QSL) ground state. X-ray absorption spectroscopy reveals a reconstruction of the electronic ground state below 2 GPa, the same pressure range where x-ray magnetic circular dichroism shows an apparent collapse of magnetic order. The electronic reconstruction, which manifests a reduction in the effective spin-orbit interaction in 5 d orbitals, pushes β − Li 2 IrO 3 further away from the pure J eff = 1 / 2 limit. Although lattice symmetry is preserved across the electronic transition, x-ray diffraction shows a highly anisotropic compression of the hyperhoneycomb lattice which affects the balance of bond-directional Ir-Ir exchange interactions driven by spin-orbit coupling at Ir sites. An enhancement of symmetric anisotropic exchange over Kitaev and Heisenberg exchange interactions seen in theoretical calculations that use precisely this anisotropic Ir-Ir bond compression provides one possible route to the realization of a QSL state in this hyperhoneycomb iridate at high pressures

Different routes to pressure-induced volume collapse transitions in gadolinium and terbium metals

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)The sudden decrease in molar volume exhibited by most lanthanides under high pressure is often attributed to changes in the degree of localization of their 4f electrons. We give evidence, based on electrical resistivity measurements of dilute Y(Gd) and Y(Tb) alloys to 120 GPa, that the volume collapse transitions in Gd and Tb metals have different origins, despite their being neighbors in the periodic table. Remarkably, the change under pressure in the magnetic state of isolated Pr or Tb impurity ions in the nonmagnetic Y host appears to closely mirror corresponding changes in pure Pr or Tb metals. The collapse in Tb appears to be driven by an enhanced negative exchange interaction between 4f and conduction electrons under pressure (Kondo resonance) which, in the case of Y(Tb), dramatically alters the superconducting properties of the Y host, much like previously found for Y(Pr). In Gd, our resistivity measurements suggest that a Kondo resonance is not the main driver for its volume collapse. X-ray absorption and emission spectroscopies clearly show that 4f local moments remain largely intact across both volume collapse transitions ruling out 4f band formation (delocalization) and valence transition models as possible drivers. The results highlight the richness of behavior behind the volume collapse transition in lanthanides and demonstrate the stability of the 4f level against band formation to extreme pressure.8824National Science Foundation [DMR-1104742]Carnegie/DOE Alliance Center (CDAC) through NNSA/DOE [DE-FC52-08NA28554]US Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences [DE-AC-02-06CH11357]Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)National Science Foundation [DMR-1104742]Carnegie/DOE Alliance Center (CDAC) through NNSA/DOE [DE-FC52-08NA28554]US Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences [DE-AC-02-06CH11357]FAPESP [2011/24166-0

Large negative thermal expansion in the cubic phase of CaMn7O12\mathrm{CaMn_{7}O_{12}}

Observations of multiferroicity and giant improper ferroelectricity in CaMn$_7$O$_{12}$ invigorated the research on this material. Delicate structural changes have been reported to cause ferroelectricity in the magnetically ordered state of CaMn$_7$O$_{12}$ as well as high-temperature crystallographic transformations. Through high-resolution synchrotron x-ray diffraction experiments we show for the first time the large negative thermal expansion (NTE) behavior of the cubic phase of CaMn$_7$O$_{12}$. A large NTE coefficient αL for a temperature window of around 60 K is inferred for the cubic phase in the phase coexistence region during the high-temperature structural transition. It is explained using quasirigid unit modes. We also observe a large phase coexistence region of about 100 K across the high-temperature first-order structural transition, which is different from previous reports