Dirac Fermions in Antiferromagnetic FeSn Kagome Lattices with Combined Space Inversion and Time Reversal Symmetry

Symmetry principles play a critical role in formulating the fundamental laws of nature, with a large number of symmetry-protected topological states identified in recent studies of quantum materials. As compelling examples, massless Dirac fermions are jointly protected by the space inversion symmetry $P$ and time reversal symmetry $T$ supplemented by additional crystalline symmetry, while evolving into Weyl fermions when either $P$ or $T$ is broken. Here, based on first-principles calculations, we reveal that massless Dirac fermions are present in a layered FeSn crystal containing antiferromagnetically coupled ferromagnetic Fe kagome layers, where each of the $P$ and $T$ symmetries is individually broken but the combined $PT$ symmetry is preserved. These stable Dirac fermions protected by the combined $PT$ symmetry with additional non-symmorphic $S_{\rm{2z}}$ symmetry can be transformed to either massless/massive Weyl or massive Dirac fermions by breaking the $PT$ or $S_{\rm{2z}}$ symmetry. Our angle-resolved photoemission spectroscopy experiments indeed observed the Dirac states in the bulk and two-dimensional Weyl-like states at the surface. The present study substantially enriches our fundamental understanding of the intricate connections between symmetries and topologies of matter, especially with the spin degree of freedom playing a vital role.Comment: 6 pages, 4 figure

Ultrasonography Monitoring of Trauma-Induced Heterotopic Ossification: Guidance for Rehabilitation Procedures

Traumatic injury is one of varying causes of heterotopic ossification (HO). After HO occurrence, rehabilitation training need alterations to avoid the aggravation of HO. Therefore, monitoring of HO development plays an important role in the rehabilitation procedure. The aims of this study are to evaluate the post-traumatic HO occurring at various joints, to describe the features of HO development in ultrasound images, and to provide a guidance for the orthopedist to make individualized rehabilitation therapy. Eight subjects with the post-traumatic HO were recruited in this study. The joints on the injured side was examined by plain radiography. The joints on the injured side and the corresponding sites on the uninjured sides were scanned by ultrsonography. The HO tissues were segmented automatically using a semi-supervised segmentation algorithm. Then the HO tissues were evaluated in comparison with the corresponding region of the uninjured side. During the development stage of immature HO, ultrasonography was sensitive to observe the involved soft tissue and the calcification of HO. The characteristics of HO tissues in ultrasound image included the hyperechoic mass occasionally accompanied with acoustic shadow and the irregular muscular architecture. It was found that the mean grayscale value of HO was significantly higher (p < 0.001) than that of the uninjured side at the middle and late stages. During the development period of HO, the HO grayscale value gradually increased and the mean grayscale of value of mature HO was significantly higher (p < 0.05) than that of immature HO. According to the information of HO provided by ultrasound, the orthopedist properly adjusted the rehabilitation treatment. The results demonstrated that the visualization of HO using ultrasonography revealed the development of HO in the muscle tissues around the injured joints and thus provide a guidance for the orthopedist to make individualized rehabilitation therapy. Ultrasound could be a useful imaging modality for quantitative evaluation of HO during the rehabilitation of traumatic injury

Direct transformation of-alkane into all-conjugated polyene via cascade dehydrogenation

Selective C(sp$^{3}$) −H activation is of fundamental importance in processing alkane feedstocks to produce high-value-added chemical products. By virtue of an on-surface synthesis strategy, we report selective cascade dehydrogenation of n-alkane molecules under surface constraints, which yields monodispersed all-trans conjugated polyenes with unprecedented length controllability. We are also able to demonstrate the generality of this concept for alkyl-substituted molecules with programmable lengths and diverse functionalities, and more importantly its promising potential in molecular wiring

Metabolic engineering of oleaginous yeast Yarrowia lipolytica for the production of fatty alcohols

Fatty alcohols are long-chain aliphatic hydrocarbons with one hydroxyl group usually attached to their terminal carbon. These important oleaginous chemicals are widely used in detergent, lubricant, personal care, and pharmaceutical industries. The use of oleaginous yeasts as a cell factory to produce fatty alcohols from renewable resources is a sustainable and promising alternative to traditional approaches relying on plant oils or petrochemicals. In this thesis project, the expression levels of multi-copy insertion of tafar1 gene in a model oleaginous yeast Yarrowia lipolytica was quantitatively measured first. Then the possibility of knocking out negative regulators of INO1 in this yeast to increase its fatty alcohol productivity was explored. Through NCBI protein BLAST, gene deletion targets, mot1, pah1, rpd3, and isw2, were selected, and each gene was then deleted separately from yeast genome by homologous recombination. Engineered strains were cultivated in shake flasks for 5 days using the YPD medium with 40g/L glucose (YPD4). Every 24 hours, the OD600 value of each strain was measured with a UVspectrophotometer, and concentrations of fatty alcohols produced by engineered strains were detected using GC-FID. The growth curve showed that the deletion of RPD3 gene significantly inhibited cell growth while no obvious change was observed for other gene deletions. Among the knockout strains, the RPD3 knockout strain produced the highest titer of hexadecanol 278.5 mg/L. However, no single gene knockout was found to enhance fatty alcohol production in comparison to the control strain. The results highlight the complexity and uncertainty of manipulating both structural and regulatory genes. Finally, based on these findings, future metabolic engineering strategies to increase fatty alcohol production in Y. lipolytica were proposed