Effect of metal catalyst on the mechanism of hydrogen spillover in three-dimensional covalent-organic frameworks

Hydrogen spillover mechanism of metal-supported covalent-organic frameworks COF-105 is investigated by means of the density functional theory, and the effects of metal catalysts M_4（Pt_4, Pd_4, and Ni_4） on the whole spillover process are systematically analyzed. These three metal catalysts exhibit several similar phenomena：（i） they prefer to deposit on the tetra（_4-dihydroxyborylphenyl） silane（TBPS） cluster with surface-contacted configuration;（ii） only the H atoms at the bridge site can migrate to 2,3,6,7,10,11-hexahydroxy triphenylene（HHTP） and TBPS surfaces, and the migration process is an endothermic reaction and not stable;（iii） the introduction of M_4 catalyst can greatly reduce the diffusion energy barrier of H atoms, which makes it easier for the H atoms to diffuse on the substrate surface. Differently, all of the H2 molecules spontaneously dissociate into H atoms onto Pt_4 and Pd_4clusters. However, the adsorbed H2 molecules on Ni_4 cluster show two types of adsorption states： one activated state with stretched H–H bond length of 0.88 ？A via the Kubas interaction and five dissociated states with separated hydrogen atoms. Among all the M_4 catalysts, the orders of the binding energy of M_4 deposited on the substrate and average chemisorption energy per H2 molecule are Pt_4〉Ni_4〉Pd_4. On the contrary, the orders of the migration and diffusion barriers of H atoms are Pt_4

Understanding Health Worker Perspectives on Risk Screening for HIV Testing—A Qualitative Study from Zimbabwe

Background: Zimbabwe recorded a 55% increase in HIV testing from 2011 to 2018 but with decreasing HIV-testing yields from 20% to 6% respectively as we aim to identify the narrowing gap of undiagnosed people living with HIV. As such adoption of screening tools during targeted HIV testing services improves efficiency by identifying individuals who are likely to test positive. Effective utilization of screening tools requires an understanding of health care worker perception and willingness to use the tools. Methods: We conducted a qualitative study among healthcare workers at 8 selected primary healthcare facilities in Zimbabwe. Interviewer-guided, in-depth interviews were conducted with healthcare workers and their immediate supervisors. Thematic analysis was performed following a framework built around the grounded theory model to describe perspectives that influence the utilization of HIV screening tools and suggestions for improved eligibility screening. Results: Behavioural factors facilitating the utilisation of the screening tool included motivation to adhere to standard practice, awareness of screening in targeting testing, and its ability to manage workload through screening out ineligible clients. This was evident across service delivery levels. Barriers included limited healthcare capacity, confidentiality space, multiple screening tools and opaque screening in/out criteria and the potential of clients not responding to screening questions truthfully. Conclusions: Across geographical and service delivery levels, placing screening tools at HIV testing entry points, healthcare worker knowledge on screening in/out criteria emerged as enablers for correct and consistent utilization. Further, standardizing the tools and adopting a decision aid algorithm would improve the accurate utilisation of screening tools.

Review on theory and applications of wavefront recording plane framework in generation and processing of digital holograms

The wavefront recording plane （WRP）, subsequently generalized to be known as the virtual diffraction plane （VDP）, is a recent concept that has been successfully deployed in fast generation and processing of digital holograms. In brief, the WRP and its extension, the VDP, is a hypothetical plane that is located between the hologram and the object scene, and which is at close proximity to the latter. As such, the fringe patterns on the hypothetical plane are carrying the holistic information of the hologram, as well as the local optical properties of the object scene. This important property enables a hologram to be processed with classical image processing techniques that are normally unsuitable for handling holographic information. In this paper we shall review a number of works, that have been developed based on the framework of the WRP and the VDP.

Metal-organic framework-derived porous shuttle-like vanadium oxides for sodium-ion battery application

Vanadium oxides with a layered structure are promising candidates for both lithium-ion batteries and sodium-ion batteries （SIBs）. The self-template approach, which involves a transformation from metal-organic frameworks （MOFs） into porous metal oxides, is a novel and effective way to achieve desirable electrochemical performance. In this stud~ porous shuttle-like vanadium oxides （i.e., V205, V203/C） were successfully prepared by using MIL-88B （V） as precursors with a specific calcination process. As a proof-of-concept application, the as- prepared porous shuttle-like VaOdC was used as an anode material for SIBs. The porous shuttle-like V203/C, which had an inherent layered structure with metallic behavior, exhibited excellent electrochemical properties. Remarkable rate capacities of 417, 247, 202, 176, 164, and 149 mAh.g-1 were achieved at current densities of 50, 100, 200, 500, 1,000, and 2,000 mA.g-1, respectively. Under cycling at 2 A.g-1, the specific discharge capacity reached 181 mAh.g-1, with a low capacity fading rate of 0.032% per cycle after 1,000 cycles. Density functional theory calculation results indicated that Na ions preferred to occupy the interlamination rather than the inside of each layer in the V203. Interestingly, the special layered structure with a skeleton of dumbbell-like V-V bonds and metallic behavior was maintained after the insertion of Na ions, which was beneficial for the cycle performance. We consider that the MOF precursor of MIL-88B （V） can be used to synthesize other porous V-based materials for various applications.