[Comparative study of two novel nickel-titanium instruments for root canal preparation in curved canals on shaping ability and microcrack formation].

PURPOSE: To evaluate the shaping ability and microcrack formation of ProTaper Next (PTN) and XP-endo Shaper (XPS) systems in the mesial curved root canals of mandibular molars by using micro-CT scans. METHODS: Sixteen mandibular molars with two independent mesial root canals and curvature ranging from 25° to 35° were randomly divided into two groups. The preparation time was recorded. Pre-and-postoperative images were scanned by micro-CT. The following parameters were evaluated: canal transportation, centering ratio, changes in canal volume, canal/root width ratio and microcrack formation. SPSS 22.0 software package was used to analyze the data. RESULTS: Significant difference (P＜0.05) was found for canal transportation at the section of 1, 3, 5, 7 mm from the apical foramen and centering ratio at the section of 1, 3, 7 mm from the apical foramen, where XPS files were superior. There was no significant difference for centering ratio at the section of 5 mm from the apical foramen(P＞0.05). XPS groups significantly consumed less time during the preparation(P＜0.05). There was no significant difference between the two groups for the increase amount of volume, and canal/root width ratio(P＞0.05). Both instruments did not induce new microcrack after preparation. CONCLUSIONS: PTN and XPS can both shape curved canals effectively and safely. XPS showed better centering ability and reduced preparation time during preparation.

A New Distance Stereotest by Autostereoscopic Display Using an Eye-Tracking Method.

Objectives: This research aimed to present a novel glasses-free distance random-dot stereotest system (GFDRDSS) using an eye-tracking method. Methods: A single-view autostereoscopic display applying a backlight control system combined with an eye-tracking method and the corresponding random-dot stereotest software were developed to create a GFDRDSS with a viewing distance of 5 m. The stereoacuity of 12 subjects with normal eye position was evaluated using the Randot Stereotest, Stereoscopic Test Charts vol. 3 (Yan's Charts), Distance Randot® Stereotest, and GFDRDSS. Results: The GFDRDSS could provide distinct and stable glasses-free stereoscopic perception even while the subject was moving their head. It could evaluate binocular disparities of 40-2,400 arcsec. Eleven subjects with normal near visual acuity had fine near stereovision (20-60 arcsec) using the Randot stereotest and Yan's Charts. Under refractive correction, 10 subjects had fine stereovision (≤60 arcsec) using the GFDRDSS at a distance of 5 m, and 9 had fine stereovision using the Distance Randot® Stereotest at 3 m. Other subjects described the 100 arcsec-level stereograms correctly. The results exhibited a concordance of stereoacuity within one degrade between the two distance stereotests. Conclusion: The proposed GFDRDSS can alternately project a couple of random-dot stereograms to the subjects' eyes and provide a glasses-free distance stereotest, which showed good concordance with the Distance Randot® Stereotest. More data are needed for statistical studies.

Ab initio neural network MD simulation of thermal decomposition of a high energy material CL-20/TNT.

CL-20 (2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane, also known as HNIW) is one of the most powerful energetic materials. However, its high sensitivity to environmental stimuli greatly reduces its safety and severely limits its application. In this work, ab initio based neural network potential (NNP) energy surfaces for both ß-CL-20 and CL-20/TNT co-crystals were constructed. To accurately simulate the thermal decomposition processes of these two crystal systems, reactive molecular dynamics simulations based on the NNPs were performed. Many important intermediate species and their associated reaction paths during the decomposition had been identified in the simulations and the direct results on detonation temperatures of both systems were provided. The simulations also showed clearly that 2,4,6-trinitrotoluene (TNT) molecules in the co-crystal act as a buffer to slow down the chain reactions triggered by nitrogen dioxide and this effect is more significant at lower temperatures. Specifically, the addition of TNT molecules in the CL-20/TNT co-crystal introduces intermolecular hydrogen bonds between CL-20 and TNT molecules in the system, thereby increasing the thermal stability of the co-crystal. The current reactive molecular dynamics simulation is performed based on the NNP which helps in accelerating the speed of ab initio molecular dynamics (AIMD) simulation by more than 3 orders of magnitude while preserving the accuracy of density functional theory (DFT) calculations. This enabled us to perform longer-time simulations at more realistic temperatures that traditional AIMD methods cannot achieve. With the advantage of the NNP in its powerful fitting ability and transferability, the NNP-based MD simulation can be widely applied to energetic material systems.

Fragment-Based Ab Initio Molecular Dynamics Simulation for Combustion.

We develop a fragment-based ab initio molecular dynamics (FB-AIMD) method for efficient dynamics simulation of the combustion process. In this method, the intermolecular interactions are treated by a fragment-based many-body expansion in which three- or higher body interactions are neglected, while two-body interactions are computed if the distance between the two fragments is smaller than a cutoff value. The accuracy of the method was verified by comparing FB-AIMD calculated energies and atomic forces of several different systems with those obtained by standard full system quantum calculations. The computational cost of the FB-AIMD method scales linearly with the size of the system, and the calculation is easily parallelizable. The method is applied to methane combustion as a benchmark. Detailed reaction network of methane reaction is analyzed, and important reaction species are tracked in real time. The current result of methane simulation is in excellent agreement with known experimental findings and with prior theoretical studies.

Complex reaction processes in combustion unraveled by neural network-based molecular dynamics simulation.

Combustion is a complex chemical system which involves thousands of chemical reactions and generates hundreds of molecular species and radicals during the process. In this work, a neural network-based molecular dynamics (MD) simulation is carried out to simulate the benchmark combustion of methane. During MD simulation, detailed reaction processes leading to the creation of specific molecular species including various intermediate radicals and the products are intimately revealed and characterized. Overall, a total of 798 different chemical reactions were recorded and some new chemical reaction pathways were discovered. We believe that the present work heralds the dawn of a new era in which neural network-based reactive MD simulation can be practically applied to simulating important complex reaction systems at ab initio level, which provides atomic-level understanding of chemical reaction processes as well as discovery of new reaction pathways at an unprecedented level of detail beyond what laboratory experiments could accomplish.

Correlates of stalking victimization in Canada: A model of social support and comorbidity.

Research into stalking victimization has proliferated over the last three decades, but little research has been done with Canadian data and several theoretical questions related to stalking victimization risk remain largely unanswered. To address the gaps in the literature, this study advances an integrated approach of neighborhood social support from criminology and comorbidity model from health science to examine the correlates of stalking victimization. Relying on data from Canadian General Social Survey, results confirm that the correlation model is better justifiable than the causal model in exploring the relationships between risk factors and being stalked and that variables broadly derived from social support theory, such as community order and trust, are statistically significant correlates of stalking victimization. In addition, most variables in the comorbidity model are significant correlates of stalking victimization. We conclude that social contexts and individual life habits are both important for the risk of stalking victimization.

Young patients with divergence insufficiency related to excessive near work.

The purpose of this study is to explore the relationships between excessive near work and divergence insufficiency esotropia in young adults. A prospective study described a series of young patients with divergence insufficiency esotropia related to excessive near work between 2012 and 2017. The medical records of twelve young patients with divergence insufficiency esotropia and a history of excessive near work were reviewed, and the duration of near work, angle of primary position deviations at distance and at near, and angle of primary position deviations after refraining from near work for 3 months were analyzed. All patients with divergence insufficiency esotropia (age range: 21-35 years) showed an initial esodeviation ranging from 18 to 35 prism diopters for distance fixation and ranging from 8 to 20 prism diopters for near. Neurological evaluation in all cases was normal. Myopic refractive errors were detected in twelve patients. Every patient persisted near work for more than 6 h a day over a period of several months (minimum 4 months). Reductions in esodeviation were noted in twelve patients after refraining from near work for more than 3 months. Only one patient was diplopia free in all positions of gaze. The remaining eleven patients were treated successfully, six with prisms and five with surgery. They were all orthophoric and demonstrated restored binocularity at the post-treatment examinations. Our findings suggested that excessive near work might influence the development of divergence insufficiency esotropia in young adults. Refraining from excessive near work could decrease the degree of esodeviation in these patients.

Social Integration and Indigenous Suicidality.

Aspects of social integration including religion and residential stability have often been found to serve as protective factors against suicide in sociological analyses. However, empirical research on Canadian indigenous suicidality has neglected these dimensions of integration. The present study fills this gap, while controlling for other major predictors of suicide ideation (SI). Methods: Data are from a national representative sample (N = 15,294) from the 2012 Aboriginal Peoples Survey. The dependent variable is a dichotomy: lifetime prevalence of SI. Measures of social integration include religious affiliation, marital status, family ties, and residential stability. Controls are incorporated for alternative predictors of SI including psychiatric symptoms (e.g., mood disorder), economic strain, ethnicity, and demographics. Results: Findings from a multivariate logistic regression analysis confirmed an association between SI and most measures of social integration (e.g., married persons were 14% less apt to report SI than non married persons), but not with religious affiliation. Further, each unit increase in income reduced the risk of SI by 3.8%. Psychiatric symptoms increased risk of SI (e.g., mood disorder, OR = 3.16, substance abuse, OR = 2.38), and Inuit ethnicity increased SI risk by 57% (OR = 1.57). The model explained 26.1% of the variance in SI. Conclusions: Generally, measures of social integration, psychiatric symptoms, and economic strain predicted SI. However, there was no evidence that religion acted as a protective factor against SI. Future research is needed on other dimensions of religion such as self-reported religiousness, which may protect against suicidality.

ReacNetGenerator: an automatic reaction network generator for reactive molecular dynamics simulations.

Reactive molecular dynamics (MD) simulation makes it possible to study the reaction mechanism of complex reaction systems at the atomic level. However, the analysis of MD trajectories which contain thousands of species and reaction pathways has become a major obstacle to the application of reactive MD simulation in large-scale systems. Here, we report the development and application of the Reaction Network Generator (ReacNetGenerator) method. It can automatically extract the reaction network from the reaction trajectory without any predefined reaction coordinates and elementary reaction steps. Molecular species can be automatically identified from the cartesian coordinates of atoms and the hidden Markov model is used to filter the trajectory noises which makes the analysis process easier and more accurate. The ReacNetGenerator has been successfully used to analyze the reactive MD trajectories of the combustion of methane and 4-component surrogate fuel for rocket propellant 3 (RP-3), and it has great advantages in terms of efficiency and accuracy compared to traditional manual analysis.

Nanoporous Ni3P Evolutionarily Structured onto a Ni Foam for Highly Selective Hydrogenation of Dimethyl Oxalate to Methyl Glycolate.

Methyl glycolate (MG) is a versatile platform molecule to produce numerous important chemicals and materials, especially new-generation biocompatible and biodegradable poly(glycolic acid). In principle, it can be massively produced from syngas (CO + H2) via gas-phase hydrogenation of CO-derived dimethyl oxalate (DMO), but the groundbreaking catalyst represents a grand challenge. Here, we report the discovery of a Ni-foam-structured nanoporous Ni3P catalyst, evolutionarily transformed from a Ni2P/Ni-foam engineered from nano- to macro-scale, being capable of nearly fully converting DMO into MG at >95% selectivity and stable for at least 1000 h without any sign of deactivation. As revealed by kinetic experiments and theoretical calculations, in comparison with Ni2P, Ni3P achieves a higher surface electron density that is favorable for MG adsorption in a molecular manner rather than in a dissociative manner and has much higher activation energy for MG hydrogenation to ethylene glycol (EG), thereby markedly suppressing its overhydrogenation to EG.

Correlates of Illicit Drug Use Among Indigenous Peoples in Canada: A Test of Social Support Theory.

Relying on a national stratified random sample of Indigenous peoples aged 19 years old and above in Canada, this study investigates the correlates of illicit drug use among Indigenous peoples, paying special attention to the association between social support measures and illegal drug use. Results from multivariate logistical regression show that measures of social support, such as residential mobility, strength of ties within communities, and lack of timely counseling, are statistically significant correlates of illicit drug use. Those identifying as Christian are significantly less likely to use illegal drugs. This is the first nationwide analysis of the illicit drug usage of Indigenous peoples in Canada. The results are robust because we have controlled for a range of comorbidity variables as well as a series of sociodemographic variables. Policy implications from these findings are discussed.

Governance and Regional Variation of Homicide Rates: Evidence From Cross-National Data.

Criminological theories of cross-national studies of homicide have underestimated the effects of quality governance of liberal democracy and region. Data sets from several sources are combined and a comprehensive model of homicide is proposed. Results of the spatial regression model, which controls for the effect of spatial autocorrelation, show that quality governance, human development, economic inequality, and ethnic heterogeneity are statistically significant in predicting homicide. In addition, regions of Latin America and non-Muslim Sub-Saharan Africa have significantly higher rates of homicides ceteris paribus while the effects of East Asian countries and Islamic societies are not statistically significant. These findings are consistent with the expectation of the new modernization and regional theories.

Acceptance of Prostitution and Its Social Determinants in Canada.

The nature of collective perception of prostitution is understudied in Canada. Except some rudimentary reports on the percentages of the key legal options, multivariate analysis has never been used to analyze the details of public opinion on prostitution. The current study explores the trend of public attitude toward prostitution acceptability in Canada over a 25-year span and examines the social determinants of the acceptability of prostitution, using structural equation modeling (SEM), which allows researchers to elaborate both direct and indirect effects (through mediating variables) on the outcome variable. Results show that the public has become more acceptant of prostitution over time. In addition, the less religious, less authoritarian, and more educated are more acceptant of prostitution than the more religious, more authoritarian, and less well educated. The effects of religiosity and authoritarianism mediate out the direct effects of age, gender, gender equality, marriage, marriage as an outdated institution, Quebec, race, and tolerance. The findings may serve as a reference point for the law reform regarding the regulation of prostitution in Canada.

Effects of cold light bleaching on the color stability of composite resins.

To evaluate the effects of cold light bleaching on the color stability of four restorations using a thermocycling stain challenge. 160 specimens (10 mm in diameter and 2 mm thick) were fabricated from 4 composite resins (Gradia Direct-A, Z350XT, Premisa, and Précis) and divided into 4 subgroups. Color was assessed according to the CIEL*a*b* color scale at baseline, after the first cycle of bleaching, after thermocycling stain challenges, and after the second cycle of bleaching. Mean values were compared using three-way analysis of variance, and multiple comparisons of the mean values were performed using the Tukey-Kramer test. All groups showed significant color changes after stain challenge, the color change was more significant in Gradia Direct and Z350XT than in Premisa and Précis. After the second cycle of bleaching, color mostly recovered to its original values. The color stability of Gradia Direct and Z350XT was inferior to that of Premisa and Précis. The discoloration of composite resin materials can be partly removed after cold light bleaching.

An in vitro investigation of wear resistance and hardness of composite resins.

PURPOSE: The aim of the present study was to investigate the wear resistance and hardness of five kinds of composite resins. MATERIALS AND METHODS: Sixty-five specimens were fabricated with one nano-hybrid (Charisma Diamond), two micro-hybrid (3MZ250, Clearfil AP-X) and two packable (3MP60, Surefil) composite resins, according to a randomized complete block design (n=13, 8 for wear test; 5 for hardness test). The composites were filled in a rectangular mold, and light polymerization. After storage in 37°C deionized water for 24h, all specimens were tested with a custom-made toothbrush machine with a stainless-steel ball as antagonist (3N loads, 1Hz, 6×10(5) cycles) immersed in calcium fluoride slurry. Wear volume, hardness and surface structure of each tested material was examined by a three-dimensional non-contact optical profilometer, Vickers indentation technique and scanning electron microscope. RESULTS: The volume loss ranked from least to most as follows: Charisma Diamond, P60, Z250, Clearfil AP-X and Surefil. Regarding hardness, the rank from highest to lowest as follows: Clearfil AP-X, P60, Surefil, Z250, Charisma Diamond. The interactions between wear resistance and microhardness were not significant. CONCLUSIONS: The custom-made machine is considered suitable to simulate sliding of an antagonist cusp on an opposing occlusal composite restoration. Nanofilled composite may have superior wear compared to other composite resins.

In vivo implantation of hydrophobic acrylic intraocular lenses with surface modification.

PURPOSE: To assess the surface properties of modified hydrophobic acrylic intraocular lenses (IOL) implanted in rabbits. METHODS: The hydrophobic acrylic IOLs were modified with monomer vinyl pyrrolidone by surface modification technique. Phacoemulsification combined with IOL implantation was conducted in 9 rabbits (18 eyes). Postoperative responses were observed by slit-lamp microscope at 3, 7, 15, 30, 90 days after surgery. RESULTS: During the early stage after IOL implantation, corneal edema and anterior chamber fibrin exudation were observed. The exudate fluid was almost absorbed at the 15th day postoperatively. At 7th day, the anterior chamber exudation in the modification group was significantly less severe than that in non-modification group (P < 0.05). Posterior capsular opacification occurred at 30th day after surgery and was aggravated 90 days later. IOL dislocation was seen in 5 eyes and occlusion of pupil in 3 eyes. CONCLUSION: The hydrophobic acrylic IOLs with surface modification have improved surface properties and higher uveal biocompatibility.

Returning to normality: anomie and crime in China.

The current study explored the value change as manifested in the sense of anomie during the 1990s and sources of anomie in contemporary China. The multiple regression analysis found that employment, having children, and satisfaction in life were significantly related to anomie; however, the effect of education was related to anomie in the direction that was inconsistent with what was known in the Western literature. Age had no significant effect on anomie. It is concluded that the crime rates remain relatively low even after many years of dramatic increase, and that China may not be able to maintain its tight control over politics forever.