Browsing by Author "Zhang, Jing"

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  • Enhancement of Vertical Shear Resistance in a Slim Floor Composite Section
    (2008) Zhang, Jing
     Helsinki University of Technology | Master's thesis
    Deltabeam is a typical slim floor beam developed and produced by Finnish producers. This type of composite beam can be analyzed by strut-and-tie model. The vertical shear resistance of this composite beam becomes critical in some design cases; the strut force in the concrete content enclosed in the steel sections exceeds the resistance of the bottom plate. When headed studs embedded in concrete are under tension load, they transfer tension loads into based concrete by bearing surface, exploit the local tensile capacity of concrete to carry tensile stresses with a concrete cone failure mode. According to STM, the headed studs can be applied into Deltabeam and behave as tension chords to enhance the vertical shear resistance. Because of the special cross-section properties of Deltabeam, simplifications were made in the analyzing procedure. Preliminary tests were arranged to find out the real behaviours and failure loads of the single headed stud in Deltabeam-shaped concrete block. The results of this group tests fulfilled the theoretical assumptions. Based on the preliminary tests, studs were arranged into Deltabeam for beam tests. The objectives of beam tests include: 1) to investigate if the application of studs could improve the vertical shear resistance of beam; 2) to verify the extent of improved shear resistance; 3) to observe other phenomena during the tests procedure, such as bottom plate behaviour, steel web behaviour and concrete push-out. From the data got from tests, the application of studs increased the vertical shear resistance of Deltabeam. The bottom steel strips were bent due to concrete push-out, it indicates the bottoms flanges may not lost stiffness absolutely and still contribute to preventing concrete push out. As a conclusion, applying studs into Deltabeam is a reliable and economic to enhance the vertical shear resistance.
  • Enhancing and controlling valley magnetic response in MoS2/WS2 heterostructures by all-optical route
    (2019-09-17) Zhang, Jing; Du, Luojun; Feng, Shun; Zhang, Run Wu; Cao, Bingchen; Zou, Chenji; Chen, Yu; Liao, Mengzhou; Zhang, Baile; Yang, Shengyuan A.; Zhang, Guangyu; Yu, Ting
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Van der Waals heterostructures of transition metal dichalcogenides with interlayer coupling offer an exotic platform to realize fascinating phenomena. Due to the type II band alignment of these heterostructures, electrons and holes are separated into different layers. The localized electrons induced doping in one layer, in principle, would lift the Fermi level to cross the spin-polarized upper conduction band and lead to strong manipulation of valley magnetic response. Here, we report the significantly enhanced valley Zeeman splitting and magnetic tuning of polarization for the direct optical transition of MoS2 in MoS2/WS2 heterostructures. Such strong enhancement of valley magnetic response in MoS2 stems from the change of the spin-valley degeneracy from 2 to 4 and strong many-body Coulomb interactions induced by ultrafast charge transfer. Moreover, the magnetic splitting can be tuned monotonically by laser power, providing an effective all-optical route towards engineering and manipulating of valleytronic devices and quantum-computation.
  • Fates of hemicellulose, lignin and cellulose in concentrated phosphoric acid with hydrogen peroxide (PHP) pretreatment
    (2018) Wang, Qing; Tian, Dong; Hu, Jinguang; Shen, Fei; Yang, Gang; Zhang, Yanzong; Deng, Shihuai; Zhang, Jing; Zeng, Yongmei; Hu, Yaodong
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Xylan, de-alkaline lignin and microcrystalline cellulose were employed as representative models of hemicellulose, lignin and cellulose in lignocellulosic biomass. These three model compounds, together with the real-world biomass, wheat straw were pretreated using the newly developed PHP pretreatment (concentrated phosphoric acid plus hydrogen peroxide) to better understand the structural changes of the recovered solid and chemical fractions in the liquid. Results showed that almost all xylan and higher than 70% lignin were removed from wheat straw, and more than 90% cellulose was recovered in the solid fraction. The pretreated model xylan recovered via ethanol-precipitation still maintained its original structural features. The degree of polymerization of soluble xylooligosaccharides in liquid was reduced, resulting in the increase of monomeric xylose release. Further xylose oxidization via the path of 2-furancarboxylic acid → 2(5H)-furanone → acrylic acid → formic acid was mainly responsible for xylan degradation. The chemical structure of de-alkaline lignin was altered significantly by PHP pretreatment. Basic guaiacyl units of lignin were depolymerized, and aromatic rings and side aliphatic chains were partially decomposed. Ring-opening reactions of the aromatics and cleavage of C-O-C linkages were two crucial paths to lignin oxidative degradation. In contrast to lignin, no apparent changes occurred on microcrystalline cellulose. The reason was likely that acid-depolymerization and oxidative degradation of cellulose were greatly prevented by the formed cellulose phosphate.