High yield production of inorganic graphene-like materials (MoS₂, WS₂, BN) through liquid exfoliation testing key parameters

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2012.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student submitted PDF version of thesis.Includes bibliographical references (p. 41).Inorganic graphene-like materials such as molybdenum disulfide (MoS₂), tungsten sulfide (WS₂), and boron nitride (BN) are known to have electronic properties. When exfoliated into layers and casted onto carbon nanofilms, they can become potentially cheap and efficient electronic materials for magnetic sensing and energy storage devices. The goal of this experiment is to use a general liquid-phase method to exfoliate and optimize a number of parameters that can yield the highest concentration of layered quantities of MoS₂, WS₂, and BN. The key parameters optmized were material concentration, surfactant concentration, sonication method and duration, and centrifuge speed. Therefore, different concentrations of the three materials were mixed with different concentrations of the surfactant, sodium cholate hydrate (C₂₄H₃₉NaO₅ · xH₂O), to make suspensions. These suspensions were then sonicated and centrifuged at different durations and speeds, respectively. Absorption was measured for all of the suspensions using ultraviolet-visible spectrometer to determine what parameters yielded the highest concentration of the three materials since a high UV absorption generally equated to a high yield of the layered materials. The final optimal parameters that yielded the highest concentration of each material were: 3 mg/ml material concentration, 3 mg/ml surfactant concentration, 30-minute continuous tip sonication method, and 1-hr 500 RPM centrifugation. Droplets of these optimal suspensions were then casted onto carbon nanofilms, and transmission electron microscopy (TEM) was performed on the films to confirm the layered, flaked characteristics and the hexagonal structures of MoS₂, WS₂, and BN.by Fei Pu.S.B

Spin squeezing and pairwise entanglement for symmetric multiqubit states

We show that spin squeezing implies pairwise entanglement for arbitrary symmetric multiqubit states. If the squeezing parameter is less than or equal to 1, we demonstrate a quantitative relation between the squeezing parameter and the concurrence for the even and odd states. We prove that the even states generated from the initial state with all qubits being spin down, via the one-axis twisting Hamiltonian, are spin squeezed if and only if they are pairwise entangled. For the states generated via the one-axis twisting Hamiltonian with an external transverse field for any number of qubits greater than 1 or via the two-axis counter-twisting Hamiltonian for any even number of qubits, the numerical results suggest that such states are spin squeezed if and only if they are pairwise entangled.Comment: 6 pages. Version 3: Small corrections were mad

Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries

Background Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres. Methods This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and low–middle-income countries. Results In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of ‘single-use’ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for low–middle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia. Conclusion This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both high– and low–middle–income countries

Clustering effect on the viscosity of nondilute sodium polystyrenesulfonate solutions

10.1021/la026994jLangmuir1994034-4036LANG