Quantum transport experiments in strain-engineered graphene

In this thesis, we have successfully developed routes to engineer the electronic properties of graphene, either by controllable strain or by double moiré superlattices. A new platform that combines in situ strain tuning and transport experiments was developed. With this platform, various strain effects were studied in different transport measurements at low temperatures. In addition, we discovered a new generation of moiré superlattices in doubly aligned hBN/graphene/hBN heterostructures

In-situ strain tuning in hBN-encapsulated graphene electronic devices

Using a simple setup to bend a flexible substrate, we demonstrate deterministic and reproducible in-situ strain tuning of graphene electronic devices. Central to this method is the full hBN encapsulation of graphene, which preserves the exceptional quality of pristine graphene for transport experiments. In addition, the on-substrate approach allows one to exploit strain effects in the full range of possible sample geometries and at the same time guarantees that changes in the gate capacitance remain negligible during the deformation process. We use Raman spectroscopy to spatially map the strain magnitude in devices with two different geometries and demonstrate the possibility to engineer a strain gradient, which is relevant for accessing the valley degree of freedom with pseudo-magnetic fields. Comparing the transport characteristics of a suspended device with those of an on-substrate device, we demonstrate that our new approach does not suffer from the ambiguities encountered in suspended devices

Phylogenetic analysis, structural evolution and functional divergence of the 12-oxo-phytodienoate acid reductase gene family in plants

BACKGROUND: The 12-oxo-phytodienoic acid reductases (OPRs) are enzymes that catalyze the reduction of double-bonds in α, β-unsaturated aldehydes or ketones and are part of the octadecanoid pathway that converts linolenic acid to jasmonic acid. In plants, OPRs belong to the old yellow enzyme family and form multigene families. Although discoveries about this family in Arabidopsis and other species have been reported in some studies, the evolution and function of multiple OPRs in plants are not clearly understood. RESULTS: A comparative genomic analysis was performed to investigate the phylogenetic relationship, structural evolution and functional divergence among OPR paralogues in plants. In total, 74 OPR genes were identified from 11 species representing the 6 major green plant lineages: green algae, mosses, lycophytes, gymnosperms, monocots and dicots. Phylogenetic analysis showed that seven well-conserved subfamilies exist in plants. All OPR genes from green algae were clustered into a single subfamily, while those from land plants fell into six other subfamilies, suggesting that the events leading to the expansion of the OPR family occurred in land plants. Further analysis revealed that lineage-specific expansion, especially by tandem duplication, contributed to the current OPR subfamilies in land plants after divergence from aquatic plants. Interestingly, exon/intron structure analysis showed that the gene structures of OPR paralogues exhibits diversity in intron number and length, while the intron positions and phase were highly conserved across different lineage species. These observations together with the phylogenetic tree revealed that successive single intron loss, as well as indels within introns, occurred during the process of structural evolution of OPR paralogues. Functional divergence analysis revealed that altered functional constraints have occurred at specific amino acid positions after diversification of the paralogues. Most notably, significant functional divergence was also found in all pairs, except for the II/IV, II/V and V/VI pairs. Strikingly, analysis of the site-specific profiles established by posterior probability revealed that the positive-selection sites and/or critical amino acid residues for functional divergence are mainly distributed in α-helices and substrate binding loop (SBL), indicating the functional importance of these regions for this protein family. CONCLUSION: This study highlights the molecular evolution of the OPR gene family in all plant lineages and indicates critical amino acid residues likely relevant for the distinct functional properties of the paralogues. Further experimental verification of these findings may provide valuable information on the OPRs' biochemical and physiological functions

Energy transfer from tunneling electrons to excitons

Excitons in optoelectronic devices have been generated through optical excitation, external carrier injection, or employing pre-existing charges. Here, we reveal a new way to electrically generate excitons in transition metal dichalcogenides (TMDs). The TMD is placed on top of a gold-hBN-graphene tunnel junction, outside of the tunneling pathway. This electrically driven device features a photoemission spectrum with a distinct peak at the exciton energy of the TMD. We interpret this observation as exciton generation by energy transfer from tunneling electrons, which is further supported by a theoretical model based on inelastic electron tunneling. Our findings introduce a new paradigm for exciton creation in van der Waals heterostructures and provide inspiration for a new class of optoelectronic devices in which the optically active material is separated from the electrical pathway

The Role of Postoperative Radiotherapy on Stage N2 Non-small Cell Lung Cancer

Background and objective The clinical value of postoperative radiotherapy (PORT) in stage N2 nonsmall-cell lung cancer (NSCLC) is controversy. The aim of this study is to analyze the efficacy of PORT in subgroup of stage N2 NSCLC, which can help clinicians to choose proper patients for PORT. Methods Clinical data of 359 patients with stage N2 NSCLC treated with radical surgery between Mar. 2000 and Jul. 2005 were retrospectively reviewed. Two hundred and seven patients received adjuvant chemotherapy and one hundred and four patients received adjuvant radiotherapy. First, the group of patients were analyzed to evaluate the factors affecting the overall survival. The all patients were divided based on tumor size and the number of lymph node metastasis station (single station or multiple station) so as to evaluate the role of PORT. The endpoint was overall survival (OS) and local recurrence-free survival (LRFS). Kaplan-Meier method was used to calculate the OS, LRFS and Log-rank was used to compare the difference in OS and LRFS between different groups. Results The median duration of follow-up was 2.3 years. 224 patients died. The median survival was 1.5 years and 1, 3, 5-year survival were 78%, 38% and 26%. Univariate analysis showed tumor size, the number of lymph node metastasis station and PORT were correlated with OS. Among patients, 5-year survival rates in PORT and non-PORT were 29% and 24% (P=0.047) respectively. In subgroups, PORT was related with high survival in patients with multiple station N2 compared to non-PORT: 36% vs 20% (P=0.013) and 33% vs 15% (P=0.002) in patients in patients with tumor size > 3 cm. Also, it was related with low local recurrence compared to non-PORT: 65% vs 48% (P=0.006) and 62% vs 48% (P=0.033). Conclusion PORT can improve overall survival for N2 NSCLC, especially the patients with the factors as follows: tumor size > 3 cm and multiple station N2 can benefit from PORT more or less