The aims of this study were to: (1) synthesize an anti-biofilm and protein-repellent dental composite by combining 2-methacryloyloxyethyl phosphorylcholine (MPC) with quaternary ammonium ...dimethylaminohexadecyl methacrylate (DMAHDM); and (2) evaluate the effects of water-aging for 180 days on protein resistance, bacteria-killing ability, and mechanical properties of MPC-DMAHDM composite. MPC and DMAHDM were added into a resin composite. Specimens were stored in distilled water at 37 °C for 1, 30, 90, and 180 days. Mechanical properties were measured in three-point flexure. Protein attachment onto the composite was evaluated by a micro bicinchoninic acid approach. An oral plaque microcosm biofilm model was employed to evaluate oral biofilm viability vs. water-aging time. Mechanical properties of the MPC-DMAHDM composite after 180-day immersion matched those of the commercial control composite. The composite with 3% MPC + 1.5% DMAHDM had much stronger resistance to protein adhesion than control (
< 0.05). MPC + DMAHDM achieved much stronger biofilm-eradicating effects than MPC or DMAHDM alone (
< 0.05). Biofilm colony-forming units on the 3% MPC + 1.5% DMAHDM composite were three orders of magnitude lower than commercial control. The protein-repellent and antibacterial effects were durable and showed no loss in water-aging from 1 to 180 days. The novel MPC-DMAHDM composite possessed strong and durable resistance to protein adhesion and potent bacteria-eradicating function, while matching the load-bearing ability of a commercial dental composite. The novel MPC-DMAHDM composite represents a promising means of suppressing oral plaque growth, acid production, and secondary caries.
Quantitative understanding of reactivity and stability for a chemical species is fundamental to chemistry. The concept has undergone many changes and additions throughout the history of chemistry, ...stemming from the ideas such as Lewis acids and bases. For a given complexing ligand (Lewis base) and a group of isovalent metal cations (Lewis acids), the stability constants of metal–ligand (ML) complexes can simply correlate to the known properties of metal ions ionic radii (r M n+ ), Gibbs free energy of formation (ΔG°f,M n+ ), and solvation energy (ΔG°s,M n+ ) by 2.303RT log K ML = (α*MLΔG°f,M n+ – β*ML r M n+ + γ*MLΔG°s,M n+ – δ*ML), where the coefficients (α*ML, β*ML, γ*ML, and intercept δ*ML) are determined by fitting the equation to the existing experimental data. Coefficients β*ML and γ*ML have the same sign and are in a linear relationship through the origin. Gibbs free energies of formation of cations (ΔG°f,M n+ ) are found to be natural indices for the softness or hardness of metal cations, with positive values corresponding to soft acids and negative values to hard acids. The coefficient α*ML is an index for the softness or hardness of a complexing ligand. Proton (H+) with the softness index of zero is a unique acid that has strong interactions with both soft and hard bases. The stability energy resulting from the acid–base interactions is determined by the term α*MLΔG°f,M n+ ; a positive product of α*ML and ΔG°f,M n+ indicates that the acid–base interaction between the metal cation and the complexing ligand stabilizes the complex. The terms β*ML r M n+ and γ*MLΔG°s,M n+ , which are related to ionic radii of metal cations, represent the steric and solvation effects of the cations. The new softness indices proposed here will help to understand the interactions of ligands (Lewis bases) with metal cations (Lewis acids) and provide guidelines for engineering materials with desired chemical reactivity and selectivity. The new correlation can also enhance our ability for predicting the speciation, mobility, and toxicity of heavy metals in the earth environments and biological systems.
The Geography of Information Acquisition Chen, Honghui; Qu, Yuanyu; Shen, Tao ...
Journal of financial and quantitative analysis,
09/2022, Letnik:
57, Številka:
6
Journal Article
Recenzirano
Odprti dostop
Using detailed data on company visits by Chinese mutual funds, we provide direct evidence of mutual fund information acquisition activities and the consequent informational advantages mutual funds ...establish in local firms. Mutual funds are more likely to visit local and nearby firms both in and outside of their portfolios, but the ease of travel between fund and firm locations can substantially alleviate geographic distance constraints. Company visits by mutual funds are strongly associated with both fund trading activities and fund trading performance. Our results show that geographic constraints and costly information acquisition amplify information asymmetry in financial markets.
The authors aimed to systematically review the literature to clarify the natural history of brain arteriovenous malformations (BAVMs).
The authors searched PubMed for one or more of the following ...terms: natural history, brain arteriovenous malformations, cerebral arteriovenous malformations, and risk of rupture. They included studies that reported annual rates of hemorrhage and that included either 100 patients or 5 years of treatment-free follow-up.
The incidence of BAVMs is 1.12-1.42 cases per 100,000 person-years; 38%-68% of new cases are first-ever hemorrhage. The overall annual rates of hemorrhage for patients with untreated BAVMs range from 2.10% to 4.12%. Consistently implicated in subsequent hemorrhage are initial hemorrhagic presentation, exclusively deep venous drainage, and deep and infrantentorial brain location. The risk for rupture seems to be increased by large nidus size and concurrent arterial aneurysms, although these factors have not been studied as thoroughly. Venous stenosis has not been implicated in increased risk for rupture.
For patients with BAVMs, although the overall risk for hemorrhage seems to be 2.10%-4.12% per year, calculating an accurate risk profile for decision making involves clinical attention and accounting for specific features of the malformation.
Lumbar interbody fusion involves insertion of a structural graft into an intervertebral disc space to promote bony arthrodesis. It is a well-established surgical strategy for multiple spinal ...disorders ranging from degenerative conditions to trauma, neoplastic diseases, and deformities requiring correction. Since the inception of lumbar interbody fusion, the most established techniques have been two posterior approaches, the posterior lumbar interbody fusion (PLIF) and the transforaminal lumbar interbody fusion (TLIF). Within the past 15 years, multiple anterolateral approaches to the spine have become widely adopted. These approaches can be performed minimally invasively and spare disruption of the paraspinal muscles and posterior spinal column while enabling wide exposure of the disc space for insertion of interbody grafts much larger than PLIF and TLIF instrumentation. This review highlights three minimally invasive anterolateral approaches: the anterior lumbar interbody fusion (ALIF), the transpsoas lateral lumbar interbody fusion (LLIF), and prepsoas or anterior to the psoas oblique lumbar interbody fusion (OLIF). Relevant topics for discussion and comparison include patient selection, surgical techniques, outcomes, and complications for the three surgical approaches.
Bhattacherjee and Premkumar (2004) propose a temporal model of belief and attitude change to understand fluctuating patterns of information technology (IT) usage. However, they overlook the role of ...perceived enjoyment in the process of temporal IT usage. Perceived enjoyment has become an increasingly important part of how consumers assess technology. Thus, we build on Bhattacherjee and Premkumar's model (BP model) and propose a new model by investigating the comparative role of perceived usefulness (PU) and perceived enjoyment (PE) for explaining temporal changes in users' beliefs and attitudes toward IT usage. We name our proposed model the integrated temporal model (ITM). Through an empirical study of iPad usage in a classroom setting at three different stages, we found that 1) the effect of PE on PU was stronger at the pre-usage (vs. post-usage) stage and that its effect was stronger at the initial-usage (vs. later-usage) stage; 2) while PE has a stronger effect than PU on attitude at both pre-usage and initial-usage stages, that was not the case at the later-usage stage; instead, the effect of PU on attitude was stronger at the later-usage (vs. initial-usage) stage; 3) the effect of disconfirmation on modified PU and PE was stronger at the initial (vs. later) stage, while the effect of PU and PE expectation on modified PU and PE was weaker at the initial (vs. later) stage. Our study extends the BP model to IT with hedonic elements (i.e., the iPad) and is the first of its kind to empirically examine the combined and relative impact of PU and PE on the temporal usage of IT with hedonic elements in the classroom setting.
Back-to-back converters have been typically used to interconnect microgrids. For a back-to-back current-source converter, the dc-link current ripple is one of the important parameters. A large ripple ...will cause electromagnetic interference, undesirable high-frequency losses, and system instability. Conventionally, with a given switching frequency and rated voltage, the current ripple can be reduced by increasing the dc-link inductor, but it leads to bulky size, high cost, and slow dynamic response. To solve this problem, this paper reveals that the current ripple can be significantly reduced by adjusting the gate patterns of space vector modulation between the rectifier and the inverter in a back-to-back converter. The experimental results verify the effectiveness of the proposed method.
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