183 research outputs found
In-situ TEM study of carbon nanomaterials and thermoelectric nanomaterials
No full textThesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2011.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from PDF version of thesis.Includes bibliographical references (p. 103-112).Graphene nanoribbons (GNRs) are quasi one dimensional structures which have unique transport properties, and have a potential to open a bandgap at small ribbon widths. They have been extensively studied in recent years due to their high potential for future electronic and spintronic device applications. The edge structures - including the edge roughness and chirality - dramatically affect the transport, electronic, and magnetic properties of GNRs, and are of the critical importance. We have developed an efficient way of modifying the edges structures, to produce atomically smooth zigzag and armchair edges by using insitu TEM with a controlled bias. This work provides us with many opportunities for both fundamental studies and for future applications. I also report the use of either furnace heating or Joule heating to pacify the exposed graphene edges by loop formation in the graphitic nanoribbons. The edge energy minimization process involves the formation of loops between adjacent graphene layers. An estimation of the temperature during in-situ Joule heating is also reported based on the melting and evaporation of Pt nanoparticles. In this thesis work, I have also investigated the morphological and electronic properties of GNRs grown by chemical vapor deposition. Our results suggest that the GNRs have a surprisingly high crystallinity and a clean surface. Both folded and open edges are observed in GNRs. Atomic resolution scanning tunneling microscopy (STM) images were obtained on the folded layer and the bottom layer of the GNR, which enables clear identification of the chirality for both layers. We have also studied the electronic properties of the GNRs using low temperature scanning tunneling spectroscopy (STS). Our findings suggest that edges states exist at GNR edges which are dependent on the chiral angles of the GNRs.by Xiaoting Jia.Ph.D
Locally Administered Particle-Anchored Cytokines Safely Enhance Cancer Immunotherapy
No full textCancer immunotherapy has long been proposed as a powerful approach to curing tumors, based on the natural function of the immune system in protecting its host with specificity, thus holding the potential for developing long-term memory that prevents tumor recurrence. However, the immunosuppressive feature of the tumor microenvironment prevents the patients' own immune system from functioning normally in the fight against cancer. As one of the most potent cancer immunotherapies, immunostimulatory cytokines have been shown to elicit anti-tumor immune responses in preclinical studies, but their clinical application is limited by severe immune-related adverse events upon systemic administration. None of the current delivery strategies can fully address issues of toxicities and sustainably supply cytokines over the course of a few days without compromising cytokines' structural integrity. Herein, we have developed a novel formulation to anchor potent cytokine molecules to the surface of large-sized particles (1 µm) for local cancer treatment. The cytokines are confined in tumors and have minimal systemic exposure over a few days following intratumoral injection, thereby eliciting anti-tumor immunity while avoiding the systemic toxicities caused by the circulating cytokines. Such particle-anchored cytokines can be synergistic with other immunotherapies, including immune checkpoint blockade antibodies and tumor antigens, to safely promote tumor regressions in various syngeneic tumor models and genetically engineered murine tumor models.Doctor of PhilosophyCancer immunotherapy is a promising method to treat cancer by harnessing the power of the body's immune system, which naturally fights off diseases and can remember and prevent diseases from returning. Unfortunately, cancers create a hostile environment that weakens the immune system's ability to combat the disease effectively. Among the treatments explored, immunostimulatory cytokines (unique proteins that boost the immune system) have shown great promise in laboratory studies for their ability to fight cancer. However, when these proteins are administered to patients, they can cause severe side effects due to their systemic dissemination throughout the body. Herein, by attaching the potent cytokines to large-sized particles (1 µm), and injecting them directly into the tumor, their cancer-fighting abilities are focused precisely where they are most needed. This targeted delivery minimizes the cytokines' presence in the rest of the body, dramatically reducing the risk of side effects associated with their systemic dissemination. This method not only shows promise on its own but also enhances the effectiveness of other cancer treatments. Our findings suggest a new, safer way to encourage the body's defense system to fight cancer more effectively
Analysis of the Spatiotemporal Evolution and Driving Factors of China’s Digital Economy Development Based on ESDA and GM-GWR Model
No full textResearch on the geographical aspects of the digital economy is valuable. We base our study on 10 consecutive years of panel data from 2011–2020 for 31 Chinese provinces. First, we measure the Digital Economy Index using the entropy weight method and analyze its spatiotemporal heterogeneity characteristics using the Exploratory Spatial Data Analysis (ESDA) method. Next, the Grey Model (GM) is utilized to conduct time series predictions of each geographical unit. Finally, we use the GM predicted values and Geographic Weighted Regression (GWR) model to explore the spatial heterogeneity effects of external factors. This study finds that: (1) The overall development shows a trend of vigorous growth, with significant spatial heterogeneity. The gradient difference shows a decreasing trend from the eastern coastal areas to the western inland areas. (2) There is an obvious “digital divide” and a “Matthew effect” in regional development, with agglomeration and spillover effects gradually increasing. (3) Considering the influencing factors, technological progress has a positive impact, and the technology-oriented spatial spillover is obvious, showing a pattern of high in the south and low in the north. The industrial structure is significantly positive, and increases year by year, showing a distribution characteristic of high in the north and low in the south in general, with a clear effect of reducing the “bipolar” distribution. The marginal effects of government support and foreign investment are reduced and there is spatial non-stationarity. This study provides a scientific basis for further research on the spatial development of the digital economy
Constructing Multidimensional and Integrated Experimental Teaching System of Economics and Management
No full textWord of Mouth Propagation in Online Social Networks
No full textAbstract—Online social networks (OSNs) are becoming an important propagation platform for Word of mouth (WOM). Therefore, it is of great significance to study the propagation of WOM in OSNs. A WOM propagation model named N-P-N is proposed in this paper, and some simulation experiments are carried out to investigate the mechanism of WOM propagation. From the sensitivity analysis of degree of initial information source node, it can be seen that the degree of initial information source node determines the scope and speed of the propagation of WOM in OSNs in some extent. Then the sensitivity analysis of number of initial information source nodes shows that the initial source nodes are crucial for controlling the propagation of negative information in OSNs. Moreover, from the user behavior respect, it is found that different user behavior in OSNs causes different propagation results, the more users who are willing to diffuse WOM, the more scope WOM can propagate and the faster the information diffuses. Findings in this paper are helpful for enterprises to form an effective WOM. Index Terms—word of mouth, online social networks, information propagation/diffusion I
Research on the relationship between enterprise size, ownership structure and R&D Investment
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Recent Advances in Superhydrophobic Surfaces and Applications on Wood
No full textSuperhydrophobic substances were favored in wood protection. Superhydrophobic treatment of wood is of great significance for improving the service life of wood and expanding its application fields, such as improving dimensional stability, durability, UV stability, and reducing wetting. The superhydrophobic phenomenon is attributed to the interaction of micro/nano hierarchical structure and low surface energy substances of the wood surface. This is the common method for obtaining superhydrophobic wood. The article introduces the common preparation methods of superhydrophobic wood material coatings and their mechanisms. These techniques include lithography, sol–gel methods, graft copolymerization, chemical vapor deposition, etc. The latest research progress of superhydrophobic wood material coatings application at domestic and overseas is reviewed, and the current status of superhydrophobic coating application in wood materials and construction is summarized. Finally, superhydrophobic on wood in the field of applied research is presented, and the development trend in the field of functional improvement of wood is foreseen
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