Microwave Signature of Topological Andreev level Crossings in a Bismuth-based Josephson Junction.

Demonstrating the topological protection of Andreev states in Josephson junctions is an experimental challenge. In particular the telltale 4π periodicity expected for the current phase relation has remained elusive, because of fast parity breaking processes. It was predicted that low temperature ac susceptibility measurements could reveal the topological protection of quantum spin Hall edge states by probing their low energy Andreev spectrum at finite frequency. We have performed such a microwave probing of a phase-biased Josephson junction built around a bismuth nanowire, a predicted second order topological insulator, and which was previously shown to host one-dimensional ballistic edge states. We find absorption peaks at the Andreev level crossings, whose temperature and frequency dependencies point to protected topological crossings with an accuracy limited by the electronic temperature of our experiment.

Measuring the Degeneracy of Discrete Energy Levels Using a GaAs/AlGaAs Quantum Dot.

We demonstrate an experimental method for measuring quantum state degeneracies in bound state energy spectra. The technique is based on the general principle of detailed balance and the ability to perform precise and efficient measurements of energy-dependent tunneling-in and -out rates from a reservoir. The method is realized using a GaAs/AlGaAs quantum dot allowing for the detection of time-resolved single-electron tunneling with a precision enhanced by a feedback control. It is thoroughly tested by tuning orbital and spin degeneracies with electric and magnetic fields. The technique also lends itself to studying the connection between the ground-state degeneracy and the lifetime of the excited states.

Transmission and fluorescence X-ray absorption spectroscopy cell/flow reactor for powder samples under vacuum or in reactive atmospheres.

X-ray absorption spectroscopy is an element-specific technique for probing the local atomic-scale environment around an absorber atom. It is widely used to investigate the structures of liquids and solids, being especially valuable for characterization of solid-supported catalysts. Reported cell designs are limited in capabilities-to fluorescence or transmission and to static or flowing atmospheres, or to vacuum. Our goal was to design a robust and widely applicable cell for catalyst characterizations under all these conditions-to allow tracking of changes during genesis and during operation, both under vacuum and in reactive atmospheres. Herein, we report the design of such a cell and a demonstration of its operation both with a sample under dynamic vacuum and in the presence of gases flowing at temperatures up to 300 °C, showing data obtained with both fluorescence and transmission detection. The cell allows more flexibility in catalyst characterization than any reported.

Spin-Orbit Coupling at the Level of a Single Electron.

We utilize electron counting techniques to distinguish a spin-conserving fast tunneling process and a slower process involving spin flips in AlGaAs/GaAs-based double quantum dots. By studying the dependence of the rates on the interdot tunnel coupling of the two dots, we find that as many as 4% of the tunneling events occur with a spin flip related to spin-orbit coupling in GaAs. Our measurement has a fidelity of 99% in terms of resolving whether a tunneling event occurred with a spin flip or not.

Microwave Emission from Hybridized States in a Semiconductor Charge Qubit.

We explore the microwave radiation emitted from a biased double quantum dot due to the inelastic tunneling of single charges. Radiation is detected over a broad range of detuning configurations between the dot energy levels, with pronounced maxima occurring in resonance with a capacitively coupled transmission line resonator. The power emitted for forward and reverse resonant detuning is found to be in good agreement with a rate equation model, which considers the hybridization of the individual dot charge states.

Structured Ni catalysts on porous anodic alumina membranes for methane dry reforming: NiAl2O4 formation and characterization.

This communication presents the successful design of a structured catalyst based on porous anodic alumina membranes for methane dry reforming. The catalyst with a strong Ni-NiAl2O4 interaction shows both excellent activity and stability.

Direct observation of supported W bis-methylidene from supported W-methyl/methylidyne species.

Extensive solid-state NMR analyses unambiguously determine the formation of silica supported W bis-methylidene methyl species by reaction of the corresponding methyl carbyne with trimethylphosphine or a cyclic olefin.

Measurement of quantum noise in a carbon nanotube quantum dot in the Kondo regime.

The current emission noise of a carbon nanotube quantum dot in the Kondo regime is measured at frequencies ν of the order or higher than the frequency associated with the Kondo effect k(B)T (K)/h, with TK the Kondo temperature. The carbon nanotube is coupled via an on-chip resonant circuit to a quantum noise detector, a superconductor-insulator-superconductor junction. We find for hν ≈ k(B)T(K) a Kondo effect related singularity at a voltage bias eV ≈ hν, and a strong reduction of this singularity for hν ≈ 3k(B)T(K), in good agreement with theory. Our experiment constitutes a new original tool for the investigation of the nonequilibrium dynamics of many-body phenomena in nanoscale devices.

Non-oxidative coupling of methane catalysed by supported tungsten hydride onto alumina and silica-alumina in classical and H2 permeable membrane fixed-bed reactors.

Non-oxidative coupling of methane with high selectivity into ethane (>99% among hydrocarbon) in a classical fixed-bed reactor catalysed by SiO(2)-Al(2)O(3) or gamma-Al(2)O(3) supported tungsten hydride is presented. Continuous hydrogen separation, using a Pd-Ag membrane in a fixed-bed reactor, led to methane coupling far beyond the thermodynamic equilibrium conversion.

Emission and absorption quantum noise measurement with an on-chip resonant circuit.

Using a quantum detector, a superconductor-insulator-superconductor junction, we probe separately the emission and absorption noise in the quantum regime of a superconducting resonant circuit at equilibrium. At low temperature the resonant circuit exhibits only absorption noise related to zero point fluctuations, whereas at higher temperature emission noise is also present. By coupling a Josephson junction, biased above the superconducting gap, to the same resonant circuit, we directly measure the noise power of quasiparticles tunneling through the junction at two resonance frequencies. It exhibits a strong frequency dependence, consistent with theoretical predictions.

Dinitrogen dissociation on an isolated surface tantalum atom.

Both industrial and biochemical ammonia syntheses are thought to rely on the cooperation of multiple metals in breaking the strong triple bond of dinitrogen. Such multimetallic cooperation for dinitrogen cleavage is also the general rule for dinitrogen reductive cleavage with molecular systems and surfaces. We have observed cleavage of dinitrogen at 250 degrees C and atmospheric pressure by dihydrogen on isolated silica surface-supported tantalum(III) and tantalum(V) hydride centers [(identical with Si-O)2Ta(III)-H] and [(identical with Si-O)2Ta(V)H3], leading to the Ta(V) amido imido product [(identical with SiO)2Ta(=NH)(NH2)]: We assigned the product structure based on extensive characterization by infrared and solid-state nuclear magnetic resonance spectroscopy, isotopic labeling studies, and supporting data from x-ray absorption and theoretical simulations. Reaction intermediates revealed by in situ monitoring of the reaction with infrared spectroscopy support a mechanism highly distinct from those previously observed in enzymatic, organometallic, and heterogeneous N2 activating systems.

Hydrogenolysis of cyclohexane over Ir/SiO(2) catalyst: a mechanistic study of carbon--carbon bond cleavage on metallic surfaces.

The hydrogenolysis of cyclohexane catalyzed by supported Ir/SiO(2) has been studied to get mechanistic information on the elementary steps of C--C bond cleavage for cyclic saturated hydrocarbons. The reaction was studied under conditions in which no dehydrogenation to benzene occurs. When a mixture of cyclohexane and H(2) flows over a Ir/SiO(2) catalyst at 200 degrees C and for a H(2)/cyclohexane ratio superior to 40, methane, ethane, propane, n-butane, n-pentane, and n-hexane are identified to be primary products. The hydrogenolysis of ethane and n-hexane has also been studied to clarify several mechanistic questions. To account for the primary products in the above reactions, a mechanism is proposed in which the key step of the carbon--carbon bond cleavage occurs via concerted electronic transfer in dimetallacyclopentane intermediate. The comparison of product distributions in the hydrogenolysis of cyclohexane and that observed for n-hexane led to conclusions about the relative ease of carbon--carbon bond cleavage with respect to surface alkyl isomerization.

Supported metallocene catalysts by surface organometallic chemistry. Synthesis, characterization, and reactivity in ethylene polymerization of oxide-supported mono- and biscyclopentadienyl zirconium alkyl complexes: establishment of structure/reactivity relationships.

The reactions of CpZr(CH(3))(3), 1, and Cp(2)Zr(CH(3))(2), 2, with partially dehydroxylated silica, silica-alumina, and alumina surfaces have been carried out with careful identification of the resulting surface organometallic complexes in order to probe the relationship between catalyst structure and polymerization activity. The characterization of the supported complexes has been achieved in most cases by in situ infrared spectroscopy, surface microanalysis, qualitative and quantitative analysis of evolved gases during surface reactions with labeled surface, solid state (1)H and (13)C NMR using (13)C-enriched compounds, and EXAFS. 1 and 2 react with silica(500) and silica-alumina(500) by simple protonolysis of one Zr-Me bond by surface silanols with formation of a single well-defined neutral compound. In the case of silica-alumina, a fraction of the supported complexes exhibits some interactions with electronically unsaturated surface aluminum sites. 1 and 2 also react with the hydroxyl groups of gamma-alumina(500), leading to several surface structures. Correlation between EXAFS and (13)C NMR data suggests, in short, two main surface structures having different environments for the methyl group: [Al](3)-OZrCp(CH(3))(2) and [Al](2)-OZrCp(CH(3))(mu-CH(3))-[Al] for the monoCp series and [Al](2)-OZrCp(2)(CH(3)) and [Al]-OZrCp(2)(mu-CH(3))-[Al] for the bisCp series. Ethylene polymerization has been carried out with all the supported complexes under various reaction conditions. Silica-supported catalysts in the absence of any cocatalyst exhibited no activity whatsoever for ethylene polymerization. When the oxide contained Lewis acidic sites, the resulting surface species were active. The activity, although improved by the presence of additional cocatalysts, remained very low by comparison with that of the homogeneous metallocene systems. This trend has been interpreted on the basis of various possible parameters, including the (p-pi)-(d-pi) back-donation of surface oxygen atoms to the zirconium center.

Cinegammography and 3-D emission tomoscintigraphy for evaluation of revascularized mandibular bone grafts: a preliminary report.

The following reports a study conducted to investigate a scintigraphic monitoring procedure for bone free flap in mandibular reconstruction. This procedure is based on the one hand, on vascular and bone cinegammography, and on the other hand, on vascular and bone 3-D tomoscintigraphy. We used a prospective cohort study design. All patients who underwent free flap mandibular reconstruction from April 1993 to April 1998 in the Salpêtrière University Hospital, France (20 cases) have been evaluated in relation to this scintigraphic procedure. Vascular and bone scintigraphy were performed within the second week after surgery during 2 consecutive days. All images were read by one author (J.- Y. B.), who did not know the skin status of the flap. The results were compared with the viability of revascularized bone grafts as evaluated by the skin status and Greenberg classification based on bone radiographs three months after reconstruction. Vascular cinegammography seems to be closely related to anastomosis patency. Bone cinegammography gives appreciable information on bone viability. 3-D vascular tomoscintigraphy remains difficult to interpret. 3-D bone tomoscintigraphy gives precise information on the viability of the different segments of the bone flap. These results suggest that vascular and bone 3-D tomoscintigraphy coupled with cinegammography have an excellent prognostic value. In the event of partial failure it can give information on the location of the impaired patency and on the osseous fragment which has lost any viability.

Indium-111 antimyosin scintigraphy before and after coronary bypass surgery: unexpected preoperative myocardial uptakes.

The present study was designed to evaluate 111In-antimyosin scintigraphy in detecting pre- and post-operative myocardial infarction in patients undergoing coronary artery bypass surgery. Fab antimyosin scintigraphy has been shown to be sensitive and specific in detecting myocardial necrosis and to be potentially valuable in situations where other criteria are not reliable. In a previous study, postoperative antimyosin uptakes occurred in 82% of the studied patients. Sixteen consecutive patients with an indication of coronary artery surgery were assessed by preoperative coronary angiography, serial electrocardiograms, and myocardial scanning with 111Indium-labeled antimyosin antibodies performed before and after operation. In four patients, a recent myocardial infarction (1 to 3 months) was detected with an accurate localization when compared to the classic criteria of myocardial infarction. One more patient with a 21-year old myocardial infarction showed an intense uptake whereas there was no recent acute coronary event. Four other patients had an unexpected preoperative uptake, since there were no acute coronary events in their medical history. All preoperative scintigraphic uptakes were still present on the second scan performed postoperatively in these nine patients. Only one patient showed a new postoperative uptake when compared to the preoperative scan which was normal; this postoperative septal infarct was confirmed by a postoperative coronary angiography. Extracardiac uptakes (sternum and ribs) were frequently observed after operation and might hamper the interpretation of postoperative scintigrams. Unexpected preoperative uptakes may be related to non diagnosed small necrosis. A preoperative reference scan is required for an accurate interpretation of a postoperative 111In-antimyosin uptake. Moreover, extracardiac uptakes may limit the interpretation of perioperative cardiac damage.

[Indium III monoclonal antimyosin antibody scintigraphy for the detection of chronic myocardial infarction apart from the acute phase]. / Scintigraphie aux anticorps monoclonaux antimyosine marqués à l'indium 111 pour la détection de l'infarctus du myocarde en dehors de la phase aiguë.

Fab antimyosin scintigraphy has been shown to be sensitive and specific in detecting acute myocardial necrosis. This study was designed to evaluate the preoperative frequency of Indium-111 (In-111) antimyosin myocardial uptake in patients scheduled for coronary artery bypass surgery. The scintigraphic results were compared with other criteria of myocardial infarction (MI). Sixteen consecutive patients were included. Recent MI (1 to 3 months) were detected in four patients, with an accurate localization in three cases when compared to the classic criteria for MI. Two more patients had old Q wave MI: one did not show any uptake in the territory of MI whereas the second patient with a 21 year old infarct without recent acute coronary events showed an intense uptake consistent with the ECG and angiographic localization. Four other patients with stable angina showed limited uptakes that were unexpected, since there were no acute coronary events in their medical history, and ECG. Their left ventricle angiography were considered as normal. In these four cases, the scintigraphic location corresponded to a territory supplied by an occluded coronary artery (n = 2) or by a coronary artery with a tight stenosis requiring a bypass graft (n = 2). These antimyosin uptakes are probably related to small necroses which did not modify the ECG and did not alter the ventricular segmental wall motion. We conclude: 1) recent MI are detected by In-111 antimyosin scintigraphy; 2) In-111 antimyosin uptake may occur in patients without a diagnosis of recent myocardial infarction and correspond to older MI or limited necroses without detectable changes of the ECG and left ventricle angiography.