382 research outputs found

    Reversible Exchange of L‑Type and Bound-Ion-Pair X‑Type Ligation on Cadmium Selenide Quantum Belts

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    CdSe quantum belts of composition {CdSe­[<i>n</i>-octylamine]<sub>0.53</sub>} and protic acids HX (X = Cl, Br, NO<sub>3</sub>, acetate (OAc), and benzoate (OBz)) react to exchange the L-type amine ligation to bound-ion-pair X-type ligation. The latter ligation has X<sup>–</sup> anions bound to the nanocrystal surfaces and closely associated LH<sup>+</sup> counter-cations (protonated <i>n</i>-octylamine or tri-<i>n</i>-octylphosphine (TOP) to balance the surface charges. The compositions of the exchanged QBs are {CdSe­[Br]<sub>0.44</sub>[<i>n</i>-octylammonium]<sub>0.41</sub>}, {CdSe­[NO<sub>3</sub>]<sub>0.10</sub>[TOPH]<sub>0.12</sub>}, {CdSe­[OBz]<sub>0.08</sub>[<i>n</i>-octylammonium]<sub>0.02</sub>[TOPH]<sub>0.06</sub>}, and {CdSe­[OAc]<sub>0.16</sub>[<i>n</i>-octylammonium]<sub>0.02</sub>[TOPH]<sub>0.14</sub>}. (The HCl-exchanged QBs are insufficiently stable for elemental analysis.) The bound-ion-pair X-type ligation is fully reversed to L-type <i>n</i>-octylamine ligation in the cases of X = NO<sub>3</sub>, acetate, and benzoate. The ligand exchanges are monitored by absorption spectroscopy, and the exchanged, bound-ion-pair X-type ligated nanocrystals are characterized by a range of methods

    Data file for "Economic Freedom, Capital and Growth: Evidence from the States"

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    Data file from: Sarah Ihlenfeld, Joshua Hall, and Yang Zhou, “Economic Freedom, Capital, and Growth: Evidence from the States,” American Business Review 25(1) 2022: 25-35. </p

    Data File for "Measuring A Contract's Breadth: A Textual Analysis"

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    Data file for "Measuring a Contract's Breadth: A Text Analysis"</p

    The Harmonic and Gaussian Approximations in the Potential Energy Landscape Formalism for Quantum Liquids

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    The potential energy landscape (PEL) formalism has been used in the past to describe the behavior of classical low-temperature liquids and glasses. Here, we extend the PEL formalism to describe the behavior of liquids and glasses that obey quantum mechanics. In particular, we focus on the (i) harmonic and (ii) Gaussian approximations of the PEL, which have been commonly used to describe classical systems, and show how these approximations can be applied to quantum liquids/glasses. Contrary to the case of classical liquids/glasses, the PEL of quantum liquids is temperature-dependent, and hence, the main expressions resulting from approximations (i) and (ii) depend on the nature (classical vs quantum) of the system. The resulting theoretical expressions from the PEL formalism are compared with results from path-integral Monte Carlo (PIMC) simulations of a monatomic model liquid. In the PIMC simulations, every atom of the quantum liquid is represented by a ring-polymer. Our PIMC simulations show that at the local minima of the PEL (inherent structures, or IS), sampled over a wide range of temperatures and volumes, the ring-polymers are collapsed. This considerably facilitates the description of quantum liquids using the PEL formalism. Specifically, the normal modes of the ring-polymer system/quantum liquid at an IS can be calculated analytically if the normal modes of the classical liquid counterpart are known (as obtained, e.g., from classical MC or molecular dynamics simulations of the corresponding atomic liquid)

    Green Preparation of Epoxy/Graphene Oxide Nanocomposites Using a Glycidylamine Epoxy Resin as the Surface Modifier and Phase Transfer Agent of Graphene Oxide

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    In studies of epoxy/graphene oxide (GO) nanocomposites, organic solvents are commonly used to disperse GO, and vigorous mechanical processes and complicated modification of GO are usually required, increasing the cost and hindering the development and application of epoxy nanocomposites. Here, we report a green, facile, and efficient method of preparing epoxy/GO nanocomposites. When triglycidyl <i>para</i>-aminophenol (TGPAP), a commercially available glycidyl amine epoxy resin with one tertiary amine group per molecule, is used as both the surface modifier and phase transfer agent of GO, GO can be directly and rapidly transferred from water to diglycidyl ether of bisphenol A and other types of epoxy resins by manual stirring under ambient conditions, whereas GO cannot be transferred to these epoxy resins in the absence of TGPAP. The interaction between TGPAP and GO and the effect of the TGPAP content on the dispersion of GO in the epoxy matrix were investigated systematically. Superior dispersion and exfoliation of GO nanosheets and remarkably improved mechanical properties, including tensile and flexural properties, toughness, storage modulus, and microhardness, of the epoxy/GO nanocomposites with a suitable amount of TGPAP were demonstrated. This method is organic-solvent-free and technically feasible for large-scale preparation of high-performance nanocomposites; it opens up new opportunities for exploiting the unique properties of graphene or even other nanofillers for a wide range of applications

    Table_1_Care burden on family caregivers of patients with dementia and affecting factors in China: A systematic review.DOCX

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    BackgroundDementia is a chronic and progressive illness characterized by severe impairment and high dependencies. Under the influence of Chinese traditional culture, 80% of patients with dementia are watched over at home by family caregivers as primary caregivers. However, long-term care brings formidable burdens to them and reduces the quality of their life. It is necessary to find out the influencing factors of caregivers’ burden.MethodsA scoping search was conducted on eight electronic databases from 1 January 2010 to 14 June 2022: PubMed, Embase, the Cochrane Library, Web of Science, China National Knowledge Infrastructure, China VIP Database, China Biomedical Literature Database, and Wanfang Data Knowledge Service Platform. Research articles included in this review discussed the factors affecting Chinese dementia family caregivers’ care burden or stress, and the level of care burden was evaluated by a standardized care burden scale.ResultsA total of 1,888 related articles were found and 23 cross-sectional studies were eventually included. After quality assessment, 12 were of good quality and 11 were of fair quality. A total of 32 factors were identified that were associated with caregiver burden, and the results were grouped into three categories: patient, caregiver, and society. The severity of disease, poor self-care ability, neuropsychiatric symptoms, care time, number of helpers, poor health status, economic stress, poor psychological status, social support, and age were reported in many previous studies.ConclusionIn this review, the factors that affect the caregiver burden for people with dementia were clarified. By identifying these factors, hospitals, decision-makers, and communities can carry out special projects for these populations, provide appropriate assistance, or design corresponding intervention measures to reduce the caregiver burden and improve the quality of care for patients with dementia.Systematic review registration[https://www.crd.york.ac.uk/PROSPERO/], identifier [CRD42022347816].</p

    Table_2_Care burden on family caregivers of patients with dementia and affecting factors in China: A systematic review.docx

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    BackgroundDementia is a chronic and progressive illness characterized by severe impairment and high dependencies. Under the influence of Chinese traditional culture, 80% of patients with dementia are watched over at home by family caregivers as primary caregivers. However, long-term care brings formidable burdens to them and reduces the quality of their life. It is necessary to find out the influencing factors of caregivers’ burden.MethodsA scoping search was conducted on eight electronic databases from 1 January 2010 to 14 June 2022: PubMed, Embase, the Cochrane Library, Web of Science, China National Knowledge Infrastructure, China VIP Database, China Biomedical Literature Database, and Wanfang Data Knowledge Service Platform. Research articles included in this review discussed the factors affecting Chinese dementia family caregivers’ care burden or stress, and the level of care burden was evaluated by a standardized care burden scale.ResultsA total of 1,888 related articles were found and 23 cross-sectional studies were eventually included. After quality assessment, 12 were of good quality and 11 were of fair quality. A total of 32 factors were identified that were associated with caregiver burden, and the results were grouped into three categories: patient, caregiver, and society. The severity of disease, poor self-care ability, neuropsychiatric symptoms, care time, number of helpers, poor health status, economic stress, poor psychological status, social support, and age were reported in many previous studies.ConclusionIn this review, the factors that affect the caregiver burden for people with dementia were clarified. By identifying these factors, hospitals, decision-makers, and communities can carry out special projects for these populations, provide appropriate assistance, or design corresponding intervention measures to reduce the caregiver burden and improve the quality of care for patients with dementia.Systematic review registration[https://www.crd.york.ac.uk/PROSPERO/], identifier [CRD42022347816].</p

    Hydrogen-Bonding Assembly of Rigid-Rod Poly(<i>p</i>‑sulfophenylene terephthalamide) and Flexible-Chain Poly(vinyl alcohol) for Transparent, Strong, and Tough Molecular Composites

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    Molecular composites comprising poly­(<i>p</i>-sulfophenylene terephthalamide) (sPPTA), a sulfonated polyaramid rigid-rod polyelectrolyte, and flexible-chain poly­(vinyl alcohol) (PVA) were prepared by a green and easy-to-scale-up water casting method. Influence of sPPTA on the microstructure and properties of the molecular composites was systematically investigated. Fourier transform infrared spectroscopy confirms the existence of hydrogen bonding between sPPTA and PVA. Wide-angle X-ray diffraction patterns do not show the characteristic of neat sPPTA crystalline aggregates in the composites even when the sPPTA content is as high as 33 wt %, suggesting that the strong interaction between sPPTA and PVA prevents the self-aggregation of sPPTA and leads to the formation of PVA/sPPTA complexes inside the composites. Transmission electron microscopy shows that sPPTA has good compatibility with PVA, and nanoscale fibril-like supramolecular assemblies dispersing uniformly in the composites become observable with the increase of sPPTA content. Moreover, the PVA/sPPTA complexes have a strong effect on the melt point, crystallinity, mechanical properties, and thermal stability of PVA. The PVA/sPPTA composites exhibit both high strength and high ductility. When the content of sPPTA is 5 wt %, the PVA/sPPTA composite exhibits the best mechanical properties, with a tensile strength of 169 ± 13 MPa, which is 54% higher than that of neat PVA (110 ± 10 MPa). Surprisingly, the reinforcement factor is even superior to that of multiwalled carbon nanotubes, vapor grown carbon fibers, and nanodiamonds previously reported for the reinforcement of PVA nanocomposites. Moreover, the PVA/sPPTA molecular composites have a relatively low modulus but a much larger elongation at break than prefabricated nanocomposites, showing good ductility. The strong and tough PVA/sPPTA molecular composites can be potentially used as high performance membranes or fibers in the future

    In Situ Analysis of Catalytic Effect of Calcium Nitrate on Shenmu Coal Pyrolysis with Pyrolysis Vacuum Ultraviolet Photoionization Mass Spectrometry

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    To investigate the effect of calcium mineral on the product distribution of low-rank coal pyrolysis, a Chinese subbituminous coal (Shenmu coal), and samples with 5% and 10% added calcium content, were selected to study with a homemade pyrolysis vacuum ultraviolet photoionization mass spectrometry (py-VUV-PIMS) system. In this system, secondary reactions of the pyrolysis products were generally inhibited because of in situ sampling, soft ionization, and high vacuum environment, which allowed direct detection of the initial pyrolytic products. Most evolved compounds during temperature-programmed heating from 30 to 650 °C were ionized by a VUV lamp (10.6 eV). The main products include five categories: alkenes, dienes, aromatics, phenols, and dihydroxy aromatics, which were formed via homolytic scission of weak bonds in side chains and bridges between aromatic nuclei in coal structure. The calcium mineral additives can dramatically affect pyrolytic product distribution, especially oxygen-containing compounds. The main reason is that calcium mineral plays a catalytic role in deoxygenation, which prompted incorporation of oxygen-containing compounds into corresponding aromatics, and resulted in the product of BTX levels increase significantly. The decrease in relative average molecular weight indicated the conversion of heavier components into lighter species, in terms of the observed <i>m</i>/<i>z</i> of the evolved gas components

    Magic-Size II–VI Nanoclusters as Synthons for Flat Colloidal Nanocrystals

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    Five new, discretely sized, magic-size II–VI nanoclusters are synthesized in primary-amine bilayer templates and are isolated as the derivatives [(CdS)<sub>34</sub>(<i>n</i>-butylamine)<sub>18</sub>], [(ZnS)<sub>34</sub>(<i>n</i>-butylamine)<sub>34</sub>], [(ZnSe)<sub>13</sub>(<i>n</i>-butylamine)<sub>13</sub>], [(CdTe)<sub>13</sub>(<i>n</i>-propylamine)<sub>13</sub>], and [(ZnTe)<sub>13</sub>(<i>n</i>-butylamine)<sub>13</sub>]. The nanoclusters are characterized by elemental analysis, UV–visible absorption spectroscopy, laser-desorption-ionization mass spectrometry, and transmission electron microscopy. Four of the nanocluster precursors are converted to wurtzitic CdS, ZnS, and ZnSe quantum platelets and CdTe quantum belts, respectively, under mild conditions
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