Prebreakdown phenomena at high voltage in liquid nitrogen and comparison with mineral oil

This paper presents a study of prebreakdown phenomena (usually called streamers) occurring at high voltage in liquid nitrogen. A special cryostat has been constructed to allow dielectric measurements in liquid nitrogen up to 200 kV, and 0.5 MPa hydrostatic pressure. Streamers are detected and studied with various techniques: high speed visualization, streak camera, and recording of transient currents and emitted light. The propagation of positive and negative streamers is investigated at gap distances up to 80 mm. Streamers are then compared to similar phenomena observed in mineral oil. In liquid nitrogen, streamers are different compared to mineral oil. A transition from slow to fast positive streamers (velocity about 10 km/s) is observed at a threshold voltage below the breakdown voltage. The hydrostatic pressure has almost no influence on this phenomenon. Some experiments carried out with a solid barrier perpendicular to the gap axis are also presented. The practical consequences for the design of HV insulation in superconducting systems are then discussed.     

MA‐NOTMP: A Triazacyclononane Trimethylphosphinate Based Bifunctional Chelator for Gallium Radiolabelling of Biomolecules

In the past few years, gallium‐68 has demonstrated significant potential as a radioisotope for positron emission tomography (PET), and the optimization of chelators for gallium coordination is a major goal in the development of radiopharmaceuticals. Methylaminotriazacyclononane trimethylphosphinate (MA‐NOTMP), a new C‐functionalized triazacyclononane derivative with phosphinate pendant arms, presents excellent coordination properties for ⁶⁸Ga (low ligand concentration, labelling at low pH even at room temperature). A “ready‐to‐be‐grafted” bifunctional chelating agent (p‐NCS‐Bz‐MA‐NOTMP) was prepared to allow ⁶⁸Ga labelling of sensitive biological vectors. Conjugation to a bombesin_(7–14) derivative was performed, and preliminary in vitro experiments demonstrated the potential of MA‐NOTMP in the development of radiopharmaceuticals. This new chelator is therefore of major interest for labelling sensitive biomolecules, and further in vivo experiments will soon be performed.     

Bubble formation in synthetic insulating liquids in a pulseddivergent electric field

This is a study of high field conduction phenomena in two aromatic insulating liquids (monobenzyltoluene and dibenzyltoluene) in a point-plane electrode geometry. These liquids behave qualitatively like saturated hydrocarbons; current instability (electron avalanche) for high enough fields near the negative point giving rise to a current pulse regime, which causes the formation of bubbles by local heating. The generation and dynamics of these bubbles as a function of various parameters (injected energy, hydrostatic pressure and the nature of the liquid) are presented and discussed     

Novel Heterobimetallic Radiotheranostic: Preparation,Activity, and Biodistribution

A novel Ru^II(arene) theranostic complex is presented. It is based on a 1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetraacetic acid macrocycle bearing a triarylphosphine and can be tracked in vivo by using the γ emission of ¹⁵³Sm atoms. Notably, the heteroditopic ligand can be selectively metalated with ruthenium at the phosphorus atom despite the presence of other functionalities that are prone to metal coordination. Subsequent labeling with radionuclides such as ¹⁵³Sm can then be performed easily. The resulting heterobimetallic complex exhibits favorable solubility and stability properties in biologically relevant media. It also shows in vitro cytotoxicity in line with that expected for this type of metallodrug, and is nontoxic to the organism as a whole. As a proof of concept, initial studies in healthy mice were performed to obtain information about the uptake, biodistribution, and excretion of the radiolabeled complex.     

High field conduction and prebreakdown phenomena in dielectric liquids

The present paper is mainly devoted to phenomena occurring in point-plane electrode geometry, where breakdown is the result of the initiation and propagation of prebreakdown phenomena called "streamers". In this configuration, an investigative study of the streamer initiation processes, requiring very high electric field strengths (/spl sim/ MV/cm), and of propagation (requiring low electric field, /spl sim/ kV/cm) can easily be carried out for negative streamer development as well as for the positive case. From analysis of experimental results in pure liquids the physical processes connected with streamer initiation and propagation, particularly the electronic ones, are presented and discussed. Estimations of the main parameters of slower subsonic streamers and of the faster filamentary ones (such as field strength at the streamer tip, field inside the channel, charge density, etc.) have been obtained from qualitative considerations and compared to experimental data.     

Development of Anti-LRRC15 Small Fragments for Imaging Purposes Using a Phage-Display ScFv Approach

The human leucine-rich repeat-containing protein 15 (LRRC15) is a membrane protein identified as a marker of CAF (cancer-associated fibroblast) cells whose overexpression is positively correlated with cancer grade and outcome. Nuclear molecular imaging (i.e., SPECT and PET) to track LRRC15 expression could be very useful in guiding further therapeutic strategies. In this study, we developed an ScFv mouse phage-display library to obtain small fragment antibodies against human LRRC15 for molecular imaging purposes. Mice were immunized with recombinant human LRRC15 (hLRRC15), and lymph node cells were harvested for ScFv (single-chain variable fragment) phage-display analysis. The built library was used for panning on cell lines with constitutive or induced expression after transfection. The choice of best candidates was performed by screening various other cell lines, using flow cytometry. The selected candidates were reformatted into Cys-ScFv or Cys-diabody by addition of cysteine, and cloned in mammalian expression vectors to obtain batches of small fragments that were further used in site-specific radiolabeling tests. The obtained library was 1.2 × 10⁷ cfu/µg with an insertion rate >95%. The two panning rounds performed on cells permittedenrichment of 2 × 10⁻³. Screening with flow cytometry allowed us to identify 28 specific hLRRC15 candidates. Among these, two also recognized murine LRCC15 and were reformatted into Cys-ScFv and Cys-diabody. They were expressed transiently in a mammalian system to obtain 1.0 to 4.5 mg of Cys fragments ready for bioconjugation and radiolabeling. Thus, in this paper, we demonstrate the relevance of the phage-display ScFv library approach for the fast-track development of small antibodies for imaging and/or immunotherapy purposes.     

Insulating properties of some liquids after an electrical arc

The insulating properties of a liquid are commonly studied before a breakdown occurs. In HV industrial apparatus such as high energy plastic metallized and liquid impregnated films capacitors, some local breakdowns, named self-healing, occur and the ability of the liquid to remain insulating after electrical degradation is of interest. To understand the influence of the liquid on the behavior of such capacitors, the post-arc behavior of the liquid alone has to be studied in a range of energy (~mJ) close to the self-healing process. The present work deals with the study of the ability of different liquids to restore in the millisecond range their insulating property after an electrical arc. Using an experimental apparatus based on the repetitive charging with a dc HV generator and discharging through an arc of a resistor-capacity system, different kind of liquids were tested. The liquids we used were alcane, esters, alkyl benzene and polyaromatic. We showed as expected that liquids with the smallest ratio of carbon versus hydrogen in their molecular formula present the best restoration property after an electrical arc, property that is crucial for liquids impregnating metallized capacitors     

A Macroscopic Approach to Determine Electron Mobilities in Low-Density Helium

We have developed a macroscopic approach to predict electron mobilities and cavity sizes in liquid and supercritical helium using the free-volume concept. We demonstrate very good agreement with experimental electron mobility data and significant improvement with respect to the commonly used ??bubble?? model, especially for low hydrostatic pressures. The reason for this advancement is the use of heuristically developed thermodynamic state laws that account for the variations with density, temperature, and the isothermal compressibility of dense helium. The state equation uses the scattering length as input and parameters that are adjusted to experimental data. The conventional ??bubble?? method is based on the surface tension which is not defined for all accessible thermodynamic states. We investigate the limit of very low densities, with Knudsen numbers larger than 1.5. Here, the mobilities predicted by our method coincide well with experimental data until the mobility diverges abruptly. This behaviour is interpreted as a cross-over from Stokes-flow to gas kinetics behaviour.     

Thermally and electrically induced bubbles in liquid argon andnitrogen

An experimental study of high field conduction phenomena in liquid argon and liquid nitrogen in a point-plane electrode geometry is reported. These liquids behave qualitatively like saturated hydrocarbons except when they are studied close to their normal boiling point. The generation and dynamics of microscopic bubbles (thermally and electrically induced) as a function of various parameters (nature of the liquid, injected energy, hydrostatic pressure) are presented and discussed. Possible influences of these phenomena on the electrical insulation at cryogenic temperatures is also discussed     

Stability of airborne microbes in the Louvre Museum over time

The microbial content of air has as yet been little described, despite its public health implications, and there remains a lack of environmental microbial data on airborne microflora in enclosed spaces. In this context, the aim of this study was to characterize the diversity and dynamics of airborne microorganisms in the Louvre Museum using high‐throughput molecular tools and to underline the microbial signature of indoor air in this human‐occupied environment. This microbial community was monitored for 6 month during occupied time. The quantitative results revealed variations in the concentrations of less than one logarithm, with average values of 10³ and 10⁴ Escherichia coli/Aspergillus fumigatus genome equivalent per m³ for bacteria and fungi, respectively. Our observations highlight the stability of the indoor airborne bacterial diversity over time, while the corresponding eukaryote community was less stable. Bacterial diversity characterized by pyrosequencing 454 showed high diversity dominated by the Proteobacteria which represented 51.1%, 46.9%, and 38.4% of sequences, for each of the three air samples sequenced. A common bacterial diversity was underlined, corresponding to 58.4% of the sequences. The core species were belonging mostly to the Proteobacteria and Actinobacteria, and to the genus Paracoccus spp., Acinetobacter sp., Pseudomonas sp., Enhydrobacter sp., Sphingomonas sp., Staphylococcus sp., and Streptococcus sp.