Browsing by Author "Zhang, Ning"
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Item Adherence to treatment guidelines and survival for older patients with stage II or III colon cancer in Texas from 2001 through 2011(Wiley, 2018) Zhao, Hui; Zhang, Ning; Ho, Vivian; Ding, Minming; He, Weiguo; Niu, Jiangong; Yang, Ming; Du, Xianglin; Zorzi, Daria; Chavez-MacGregor, Mariana; Giordano, Sharon H.BACKGROUND: Treatment guidelines for colon cancer recommend colectomy with lymphadenectomy of at least 12 lymph nodes for patients with stage I to stage III disease as surgery adherence (SA) and adjuvant chemotherapy for individuals with stage III disease. Herein, the authors evaluated adherence to these guidelines among older patients in Texas with colon cancer and the associated survival outcomes. METHODS: Using Texas Cancer Registry data linked with Medicare data, the authors included patients with AJCC stage II and III colon cancer who were aged ?66 years and diagnosed between 2001 and 2011. SA and adjuvant chemotherapy adherence rates to treatment guidelines were estimated. The chi-square test, general linear regression, survival probability, and Cox regression were used to identify factors associated with adherence and survival. RESULTS: The rate of SA increased from 47.2% to 84% among 6029 patients with stage II or stage III disease from 2001 to 2011, and the rate of adjuvant chemotherapy increased from 48.9% to 53.1% for patients with stage III disease during the same time period. SA was associated with marital status, tumor size, surgeon specialty, and year of diagnosis. Patient age, sex, marital status, Medicare state buy-in status, comorbidity status, and year of diagnosis were found to be associated with adjuvant chemotherapy. The 5-year survival probability for patients receiving guideline-concordant treatment was the highest at 87% for patients with stage II disease and was 73% for those with stage III disease. After adjusting for demographic and tumor characteristics, improved cancer cause-specific survival was associated with the receipt of stage-specific, guideline-concordant treatment for patients with stage II or stage III disease. CONCLUSIONS: The adherence to guideline-concordant treatment among older patients with colon cancer residing in Texas improved over time, and was associated with better survival outcomes. Future studies should be focused on identifying interventions to improve guideline-concordant treatment adherence.Item Balancing strength and toughness of calcium-silicate-hydrate via random nanovoids and particle inclusions: Atomistic modeling and statistical analysis(Elsevier, 2016) Zhang, Ning; Shahsavari, RouzbehAs the most widely used manufactured material on Earth, concrete poses serious societal and environmental concerns which call for innovative strategies to develop greener concrete with improved strength and toughness, properties that are exclusive in man-made materials. Herein, we focus on calcium silicate hydrate (C-S-H), the major binding phase of all Portland cement concretes, and study how engineering its nanovoids and portlandite particle inclusions can impart a balance of strength, toughness and stiffness. By performing an extensive +600 molecular dynamics simulations coupled with statistical analysis tools, our results provide new evidence of ductile fracture mechanisms in C-S-H – reminiscent of crystalline alloys and ductile metals – decoding the interplay between the crack growth, nanovoid/particle inclusions, and stoichiometry, which dictates the crystalline versus amorphous nature of the underlying matrix. We found that introduction of voids and portlandite particles can significantly increase toughness and ductility, specially in C-S-H with more amorphous matrices, mainly owing to competing mechanisms of crack deflection, voids coalescence, internal necking, accommodation, and geometry alteration of individual voids/particles, which together regulate toughness versus strength. Furthermore, utilizing a comprehensive global sensitivity analysis on random configuration-property relations, we show that the mean diameter of voids/particles is the most critical statistical parameter influencing the mechanical properties of C-S-H, irrespective of stoichiometry or crystalline or amorphous nature of the matrix. This study provides new fundamental insights, design guidelines, and de novo strategies to turn the brittle C-S-H into a ductile material, impacting modern engineering of strong and tough concrete infrastructures and potentially other complex brittle materials.Item Screw-Dislocation-Induced Strengthening–Toughening Mechanisms in Complex Layered Materials: The Case Study of Tobermorite(American Chemical Society, 2017) Zhang, Ning; Carrez, Philippe; Shahsavari, Rouzbeh; The Richard E. Smalley Institute for Nanoscale Science and TechnologyNanoscale defects such as dislocations have a profound impact on the physics of crystalline materials. Understanding and characterizing the motion of screw dislocation and its corresponding effects on the mechanical properties of complex low-symmetry materials has long been a challenge. Herein, we focus on triclinic tobermorite, as a model system and a crystalline analogue of layered hydrated cement, and report for the first time how the motion of screw dislocation can influence the strengthening–toughening relationship, imparting brittle-to-ductile transitions. By applying shear loading in tobermorite systems with single and dipole screw dislocations, we observe dislocation jogs around the dislocation core, which increases the yield shear stress and the work-of-fracture when the dislocation lines are along the [100] and [010] directions. Our results demonstrate that the dislocation core acts as a bottleneck for the initial straight gliding to induce intralaminar gliding, which consequently leads to a significant improvement in the mechanical properties. Together, the fundamental knowledge gained in this work on the role of the motion of the dislocation core on the mechanical properties provides an improved understanding of deformation mechanisms in cementitious materials and other complex layered systems, providing new hypotheses and design guidelines for the development of strong, ductile, and tough materials.