DLSR: a solution to the parallax artefact in X-ray diffraction computed tomography data

A new tomographic reconstruction algorithm is presented, termed direct least-squares reconstruction (DLSR), which solves the well known parallax problem in X-ray-scattering-based experiments. The parallax artefact arises from relatively large samples where X-rays, scattered from a scattering angle 2θ, arrive at multiple detector elements. This phenomenon leads to loss of physico-chemical information associated with diffraction peak shape and position (i.e. altering the calculated crystallite size and lattice parameter values, respectively) and is currently the major barrier to investigating samples and devices at the centimetre level (scale-up problem). The accuracy of the DLSR algorithm has been tested against simulated and experimental X-ray diffraction computed tomography data using the TOPAS software.

Photon-Momentum-Induced Molecular Dynamics in Photoionization of N_{2} at hν=40 keV

We investigate K-shell ionization of N_{2} at 40 keV photon energy. Using a cold target recoil ion momentum spectroscopy reaction microscope, we determine the vector momenta of the photoelectron, the Auger electron, and both N^{+} fragments. These fully differential data show that the dissociation process of the N_{2}^{2+} ion is significantly modified not only by the recoil momentum of the photoelectron but also by the photon momentum and the momentum of the emitted Auger electron. We find that the recoil energy introduced by the photon and the photoelectron momentum is partitioned with a ratio of approximately 30∶70 between the Auger electron and fragment ion kinetic energies, respectively. We also observe that the photon momentum induces an additional rotation of the molecular ion.

Controlling Near-Surface Ni Composition in Octahedral PtNi(Mo) Nanoparticles by Mo Doping for a Highly Active Oxygen Reduction Reaction Catalyst

We report and study the translation of exceptionally high catalytic oxygen electroreduction activities of molybdenum-doped octahedrally shaped PtNi(Mo) nanoparticles from conventional thin-film rotating disk electrode screenings (3.43 ± 0.35 A mg_Pt^-1 at 0.9 V_RHE) to membrane electrode assembly (MEA)-based single fuel cell tests with sustained Pt mass activities of 0.45 A mg_Pt^-1 at 0.9 V_cell, one of the highest ever reported performances for advanced shaped Pt alloys in real devices. Scanning transmission electron microscopy with energy dispersive X-ray analysis (STEM-EDX) reveals that Mo preferentially occupies the Pt-rich edges and vertices of the element-anisotropic octahedral PtNi particles. Furthermore, by combining in situ wide-angle X-ray spectroscopy, X-ray fluorescence, and STEM-EDX elemental mapping with electrochemical measurements, we finally succeeded to realize high Ni retention in activated PtNiMo nanoparticles even after prolonged potential-cycling stability tests. Stability losses at the anodic potential limits were mainly attributed to the loss of the octahedral particle shape. Extending the anodic potential limits of the tests to the Pt oxidation region induced detectable Ni losses and structural changes. Our study shows on an atomic level how Mo adatoms on the surface impact the Ni surface composition, which, in turn, gives rise to the exceptionally high experimental catalytic ORR reactivity and calls for strategies on how to preserve this particular surface composition to arrive at performance stabilities comparable with state-of-the-art spherical dealloyed Pt core-shell catalysts.

5D operando tomographic diffraction imaging of a catalyst bed

We report the results from the first 5D tomographic diffraction imaging experiment of a complex Ni–Pd/CeO₂–ZrO₂/Al₂O₃ catalyst used for methane reforming. This five-dimensional (three spatial, one scattering and one dimension to denote time/imposed state) approach enabled us to track the chemical evolution of many particles across the catalyst bed and relate these changes to the gas environment that the particles experience. Rietveld analysis of some 2 × 10⁶ diffraction patterns allowed us to extract heterogeneities in the catalyst from the Å to the nm and to the μm scale (3D maps corresponding to unit cell lattice parameters, crystallite sizes and phase distribution maps respectively) under different chemical environments. We are able to capture the evolution of the Ni-containing species and gain a more complete insight into the multiple roles of the CeO₂-ZrO₂ promoters and the reasons behind the partial deactivation of the catalyst during partial oxidation of methane.

Multi-scale chemical imaging holds the potential to revolutionize our understanding of the relationships between structure and functionality in complex catalytic materials. Here the authors report the results from the first 5D tomographic diffraction imaging experiment of a complex Ni – Pd/ CeO₂ – ZrO₂/ Al₂O₃ catalyst used for methane reforming.

Transport and storage of Helicobacter pylori from gastric mucosal biopsies and clinical isolates

Various transport and storage conditions for the recovery of Helicobacter pylori from gastric biopsies were evaluated. Gastric mucosal biopsies from 16 Helicobacter pylori-infected patients were stored in cysteine-Albimi medium containing 20% glycerol in a refrigerator (4 degrees C) for 1 and 2 weeks and in a -20 degrees C laboratory freezer for 4 and 12 weeks. Two clinical isolates were stored in saline, Stuart's transport media, cysteine-Albimi broth with 20% glycerol, brucella broth with 20% glycerol and skim milk with 17% glycerol at room temperature, 4 degrees C, -20 degrees C and -70 degrees C. Storage at 4 degrees C for 1 and 2 weeks resulted in Helicobacter pylori recovery from 81% and 19% of biopsies, respectively. Storage at -20 degrees C yielded Helicobacter pylori recovery in 100% and 57% after 4 and 12 weeks, respectively. At room temperature after 6 h, the Helicobacter pylori titer was reduced. The best storage media for frozen isolates were skim milk/glycerol, brucella broth/glycerol and cysteine-Albimi/glycerol (in descending order). Recovery was better at -70 degrees C than -20 degrees C.

Clarithromycin as monotherapy for eradication of Helicobacter pylori: a randomized, double-blind trial

Current regimens to eradicate Helicobacter pylori usually consist of metronidazole plus a bismuth compound, as well as a third agent such as tetracycline. Such regimens are not ideal because organisms may be metronidazole-resistant, side-effects occur, and compliance is often poor. This randomized, double-blind study was designed to assess the ability of clarithromycin, a new macrolide antimicrobial, as monotherapy to eradicate H. pylori. Thirty-seven healthy volunteers who were H. pylori positive by 13C-urea breath test plus histology and/or culture completed 14 days of oral therapy with clarithromycin in one of three dosages. Eradication, defined as all three tests negative at 4-6 wk after the end of therapy, was achieved in 2/13 (15%) with clarithromycin 500 mg bid, 4/11 (36%) with 1000 mg bid, and 7/13 (54%) with 500 mg qid. Isolates of H. pylori were resistant to clarithromycin prior to therapy in 12% of subjects, and became resistant during therapy in 21% of subjects. Taste perversion, the most common side effect, resulted in one subject terminating therapy.

CONCLUSIONS

Whereas clarithromycin is a promising antimicrobial in the eradication of H. pylori, it is not sufficient to be used as monotherapy.

Efficacy of clarithromycin against Mycoplasma pneumoniae

The in-vitro susceptibility of Mycoplasma pneumoniae to clarithromycin, a new macrolide, was compared with that to erythromycin. A broth microdilution assay was used to evaluate 30 clinical isolates collected over a 15 year period from four countries (United States, Australia, Denmark and Japan). Clarithromycin inhibited the growth of all M. pneumoniae strains at low concentrations (less than or equal to 0.008 mg/l) similarly to erythromycin (less than or equal to 0.008 mg/l). In 120 outpatients with radiographically confirmed community acquired pneumonia (mean age 46.2 years), M. pneumoniae was detected culturally and/or serologically by ELISA and immunoblotting in 13% of patients, thus confirming the continued importance of this organism as a respiratory pathogen. M. pneumoniae isolates from these patients were shown to be equally susceptible to clarithromycin (less than or equal to 0.008 mg/l) and erythromycin (less than or equal to 0.008 mg/l). Both clarithromycin and erythromycin were effective in the treatment of community-acquired pneumonia. There were no statistically significant or clinically important differences between the two treatment groups with respect to clinical or radiographic resolution of disease or improvement in signs and symptoms. While the number of clinically evaluable patients with M. pneumoniae infections was small, both macrolides seemed equally effective.

Radioimmunoassay for detection of hepatitis B e antigen and its antibody. Results of clinical evaluation

The performance of a solid phase radioimmunoassay (ABBOTT-HBe) for the detection of hepatitis B e antigen (HBeAg) and its antibody anti-HBe was evaluated in clinical studies. The reagents and procedure were found to be reproducible by seven investigators, and lab-to-lab variations were minimal. In HBsAg positive sera, ABBOTT-HBe detected HBeAg or anti-HBe in 90% of the specimens compared to 50% tested by immunodiffusion. During the early acute stage of viral infection, serum HBeAg coincided with the rise and decline of HBsAg and seroconversion to anti-HBe occurred most often prior to loss of HBsAg. Patients with clinical evidence of chronic liver disease showed persistence of HBsAg and HBeAg. Vertical transmission studies of hepatitis B virus infection from mother to newborns, showed that mothers whose sera were positive for both HBsAg and HBeAg resulted in a greater incidence of transmission of hepatitis B virus to their offspring than mothers whose sera were HBsAg positive but HBeAg negative.