149 research outputs found
Photovoltaic properties and size-pH phase stability of iron disulfide from density-functional theory
No full textThesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2013.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (pages 105-114).Despite its exceptional optical absorptivity, suitable band gap, and earth abundance, the low open-circuit voltage of pyrite FeS₂ has remained the biggest challenge preventing its use in photovoltaic devices. Two widely-accepted causes are: (i) Fermi level pinning caused by intrinsic surface states that appear as gap states; (ii) presence of the polymorph marcasite. Based on density-functional theory (DFT) calculations, (i) the intrinsic (100) surface states are not gap states but located at the conduction band edge; (ii) epitaxial growth of marcasite on pyrite is thermodynamically favorable, but its band gap (from Kohn-Sham [delta]-sol method) is not less than pyrite. It is unlikely that the photovoltaic performance of pyrite is undermined by intrinsic surface states or marcasite. The stoichiometry and the ubiquitous observation of unintentional p-type conductivity of pyrite thin films are investigated via DFT defect computations. Native defects occur in low concentrations due to high formation energies, implying that pyrite is intrinsically stoichiometric. The p-type conductivity can be caused by OS defects under oxidizing conditions. Band gap engineering of pyrite is studied by alloying with non-rare-earth isovalent elements via DFT computations. We identify six MS₂ candidates that have larger band gaps than pyrite. Band gap enhancement of pyrite is observed only in the Ru and Os alloyed systems, but their incorporation into pyrite may be severely limited. All other candidate alloys exhibit large gap bowing effects due to size and/or electronegativity mismatch. The effects of particle size and pH on the relative phase stability of pyrite and marcasite polymorphs are explored. The size effect is incorporated through volume scaling of Wulff shapes. The pH effect is modeled by generalized, charged surface energies as a result of ion adsorption from the aqueous environment. Based on joint density-functional theory calculations, pyrite is unstable in highly acidic conditions due to a negative H+-adsorbed (110) surface energy, but stabilized for pH >/~ 2. Directions for future work are briefly discussed.by Ruoshi Sun.Ph. D
Analyzing Nation Branding Through Public Relations Lenses-- the Case of the 2008 Olympics Opening Ceremony
No full textAbstract
Studies across several disciplines, including marketing, political science and culture studies, have already touched on the concept of nation branding. Different experts with distinct academic backgrounds look at nation branding from different angles. This paper first takes a critical review of the conceptualizations of nation branding and then revisits the public relations theories, followed by a synthesis of public relations concepts with nation branding in a case study of the Beijing 2008 Opening Ceremony. It also seeks to open a conversation within the field of communication and public relations on the trend of nation branding. With an aim of contributing to the theoretical development of nation branding, the author attempts to review classic public relations theories and seeks for possibilities to integrate public relations theories into this fast-growing field.
Because nation branding is an umbrella term, the author narrows the research field to the case study of the Beijing Olympics Opening Ceremony. By comparatively analyzing the commentaries of the Opening Ceremony from CCTV and Australia Seven, this study attempts to to bring the Chinese nation branding events into the lenses of image management and communication
Poverty and exclusion in urban China
No full textThis paper discusses how widespread poverty and exclusion are in urban China during the period of transition from central planning to a market economy. Two poverty lines have been employed to measure poverty rates in urban areas: a diagnostic poverty line calculated by the Asian Development Bank (ADB) experts and a benefit poverty line used in the Minimum Living Allowance Program of the Chinese government. Both sets of estimates show marked variations by province. According to the former standard, the poverty headcount of China in 1998 was estimated as 14.8 million, with a poverty rate of 4.7 percent. According to the later standard, the poverty headcount for 2007 is estimated as 22.7 million, amounting to a poverty rate of 3.9 percent. Poor people are generally not living in absolute poverty, as their basic needs in food, clothing and shelter can largely be met. However, they have low incomes and restricted consumption potential. Economic constraints also entail adverse consequences like poor health, poor education and limited social contacts. Two groups of people are here considered as the new poor: unemployed or laid-off workers and labor migrants. This means that China now has two new forms of urban poverty which are caused by different factors and are combined with different forms of deprivation. Therefore, policy programs designed to eradicate poverty in urban areas have to be tailored carefully to the poor people's special needs. Job creation and a comprehensive social protection system are here proposed as two effective instruments in the fight against urban poverty. --
Ring Expansion and Oxidative Transformations of Octaethyl-2-oxochlorin
No full textThis thesis demonstrates in many ways how the extraordinary structural stability of the porphyrin macrocycle redirects the reactivity of classic ring expansion reactions, delineating the limits of the “breaking and mending of porphyrins” approach toward pyrrole-modified porphyrins on the activity of octaethyl-2-oxochlorin and its derivatives.
The Baeyer-Villiger oxidations are potentially suited to generate such pyrrole-expanded porphyrinoids from known octaethyloxochlorin. However, the application of a number of Baeyer- Villiger oxidation conditions to this ketone merely led to the formation of novel or known porphyrinic meso-OH or N-oxide derivatives. Applied to octaethyloxochlorin oxime, a Beckmann rearrangement is potentially suited to generate a nitrogen-expanded porphyrinoid. Unexpectedly, this reaction led to a ring-expansion by an oxygen atom. The Schmidt reaction is an alternative to the Beckmann rearrangement to expand a cyclic ketone to a lactam. However, when applied toward the conversion of a synthetic porphyrin to a derivative containing a non-pyrrolic building block this approach failed to generate the expected lactam. Instead, a novel heptaethyl-2-hydroxy-chlorin-3-one and a somewhat regioselective chlorination of themeso-positions of the oxochlorin were observed. The work demonstrates how the extraordinary structural stability of the porphyrin macrocycle redirects the reactivity of classic ring expansion reactions, delineating some limits of the methodology to convert a pyrrole into a non- pyrrolic building block
We describe the oxidative ring-opening of octaethyl-2-oxochlorin using two different oxidation methods, providing a mixture of all possible regioisomeric products. The three major products were spectroscopically characterized (IR, MS, 1D- and 2D NMR spectroscopy) and their configurations were deduce
Ultrasonic Degradation of Xanthan and Locust Bean Gums in Aqueous Solutions: Rheological and Kinetic Studies
No full textAbstract B32: Fidelity of genomic and proteomic features of patient-derived xenografts of lung cancers
No full textAbstract
The establishment of valid lung carcinoma preclinical models for testing new cancer therapies is necessary, as existing cell lines and mouse models may not recapitulate the full spectrum of heterogeneity of patient tumors. Studies suggest lung cancer patient-derived xenograft (PDX) models recapitulate well gene copy number variation, gene expression profiles, and metabolic states of corresponding patient tumors. However, an understanding of mechanisms linking cancer-associated genome, transcriptome, and proteome alterations with driver mutations and dysregulated signal transduction networks in primary and PDX models is lacking. We report a large (>150) resource of lung cancer PDX models, derived from surgically resected tumors, and endobronchial ultrasound-guided (EBUS) and CT-guided biopsies. Tumor specimens were grown and serially passaged in the subcutaneous pocket at the flanks of NSG mice (NOD SCID gamma) at initial implant, and following passages in NOD SCID (non-obese diabetic severe combined immunodeficiency) mice. Among 127 established PDX models from 441 surgically derived tumor specimens, all major histological subtypes were included: 52 adenocarcinomas, 62 squamous cell carcinomas, 1 adeno-squamous cell carcinomas, 5 sarcomatoid carcinomas, 5 large cell neuroendocrine carcinomas, and 2 small cell lung cancers. Over 100 PDX models have been profiled by next-generation exome sequencing (SureSelect Human 50Mbp kit), and array-based assays for copy number variant (HumanOmni 2.5-Quad BeadChip), DNA methylation (Infinium HumanMethylation450 BeadChip) and mRNA (DASL HumanHT-12 v4 BeadChip) profiles. Smaller subsets of PDXs have been characterized by mass spectrometry (MS)-based comprehensive proteome and protein-phosphotyrosine characterization.
Genome/transcriptome/proteome profiles of 36 non-small cell lung carcinoma (NSCLC) PDX models correlated with patient primary tumors but to a much lesser extent with established NSCLC cell lines. A number of PDX models have genetic abnormalities linked to targeted therapies including mutations in EGFR (6), PIK3CA (13), and KRAS (21), and amplifications in FGFR1 (7) and CDK4 (6). This study provides the most solid evidence as yet that PDXs established from lung cancers mimic closely the genomic and proteomic characteristics of patient primary tumors and retain driver genetic abnormalities.
Citation Format: Nhu-An Pham, Dennis Wang, Jiefei Tong, Chang-Qi Zhu, Lei Li, Wen Zhang, Ruoshi Shi, Shingo Sakashita, Melania Pintilie, Michael F. Moran, Geoffrey Liu, Ming-Sound Tsao. Fidelity of genomic and proteomic features of patient-derived xenografts of lung cancers. [abstract]. In: Proceedings of the AACR Special Conference: Patient-Derived Cancer Models: Present and Future Applications from Basic Science to the Clinic; Feb 11-14, 2016; New Orleans, LA. Philadelphia (PA): AACR; Clin Cancer Res 2016;22(16_Suppl):Abstract nr B32.</jats:p
Nitrogen-Free Tetrafunctional Epoxy and Its DDS-Cured High-Performance Matrix for Aerospace Applications
No full textTetrafunctional epoxy is an indispensable matrix for the aerospace industry, high-temperature adhesives, and encapsulation materials, where high service temperatures (>220 C-omicron) are required. N,N,N',N'-Tetraglycidyl-4,4'-diaminodiphenylmethane (TGDDM) has long been the dominant candidate in those applications; however, fully cured TGDDM epoxy materials suffer from poor. toughness, unwanted side reactions, and inadequate moisture resistance. A novel tetrafunctional epoxy, TFTE, is synthesized to address those issues, which have not been resolved for decades. TFTE can be prepared through a simple three-step procedure using readily available raw materials. Each step shows a high yield (>90%) and involves only mild reaction conditions. When TFTE is mixed with diglycidyl ether of bisphenol A (DGEBA) and cured with 4,4'-diaminodiphenylsulfone (DDS), the cured epoxy shows a T-g value of 252 C-omicron, a tensile strength of 80.0 MPa, and, more importantly, a higher toughness (29.8 kJ/m(2)) and better moisture resistance than the TGDDM/DDS system. In addition, the interfacial strength, thermal stability, and processability of TFTE/DGEBA are comparable to those of TGDDM. These excellent properties and processability make TFTE a potential replacement for TGDDM.National Natural Science Foundation of China [51173012]; Equipment Preresearch Foundation [6141A02022207]; Ministry of Education [6141A02022207]SCI(E)ARTICLE277708-77195
Intermolecular Cross‐Coupling of Simple Arenes via C—H Activation by Tuning Concentrations of Arenes and TFA.
No full textOxidative ring-openings of octaethyl-2-oxochlorin: Regioisomeric β-oxobiliverdins
No full text We describe the oxidative ring opening of octaethyl-2-oxochlorin using two different oxidation methods, both providing a mixture of all possible regioisomeric products (8-[Formula: see text] through 8-[Formula: see text]. While isomers 8-[Formula: see text], 8-[Formula: see text], and 8-[Formula: see text] formed in isolable yields and relative ratios that varied with the oxidation method used, isomer 8-[Formula: see text] was invariably formed in trace amounts only. The three major products were spectroscopically characterized (IR, MS, 1D- and 2D NMR spectroscopy) and their configurations were deduced by NMR spectroscopy. The spectroscopic findings correlated well with the single crystal X-ray structure of the novel cleavage product 8-[Formula: see text] and the known compound of 8-[Formula: see text]. The work broadens the number of octaethylporphyrin-derived biliverdin derivatives available and presents a methodology of controlling the biliverdin backbone configuration by introduction of a [Formula: see text]-ketone functionality into select positions. </jats:p
Surprising Outcomes of Classic Ring‐Expansion Conditions Applied to Octaethyloxochlorin, 1. Baeyer–Villiger‐Oxidation Conditions
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