In quantum field theory, Lorentz invariance leads to three types of fermion-Dirac, Weyl and Majorana. Although the existence of Weyl and Majorana fermions as elementary particles in high-energy ...physics is debated, all three types of fermion have been proposed to exist as low-energy, long-wavelength quasiparticle excitations in condensed-matter systems. The existence of Dirac and Weyl fermions in condensed-matter systems has been confirmed experimentally, and that of Majorana fermions is supported by various experiments. However, in condensed-matter systems, fermions in crystals are constrained by the symmetries of the 230 crystal space groups rather than by Lorentz invariance, giving rise to the possibility of finding other types of fermionic excitation that have no counterparts in high-energy physics. Here we use angle-resolved photoemission spectroscopy to demonstrate the existence of a triply degenerate point in the electronic structure of crystalline molybdenum phosphide. Quasiparticle excitations near a triply degenerate point are three-component fermions, beyond the conventional Dirac-Weyl-Majorana classification, which attributes Dirac and Weyl fermions to four- and two-fold degenerate points, respectively. We also observe pairs of Weyl points in the bulk electronic structure of the crystal that coexist with the three-component fermions. This material thus represents a platform for studying the interplay between different types of fermions. Our experimental discovery opens up a way of exploring the new physics of unconventional fermions in condensed-matter systems.
High-temperature superconductivity emerges on doping holes or electrons into antiferromagnetic copper oxides. The large energy scale of magnetic excitations, for example, compared with phonon ...energies, is thought to drive superconductivity with high transition temperatures (Tc). Comparing high-energy magnetic excitations of hole- and electron-doped superconductors provides an opportunity to test this hypothesis. Here, we use resonant inelastic X-ray scattering at the Cu L3-edge to reveal collective excitations in the electron-doped cuprate Nd2xCexCuO4. Surprisingly, magnetic excitations harden signicantly across the antiferromagnetic high-temperature superconductivity phase boundary despite short-ranged antiferromagnetic correlations, in contrast to the hole-doped cuprates. Furthermore, we nd an unexpected branch of collective modes in superconducting compounds, absent in hole-doped cuprates. These modes emanate from the zone centre and possess a higher temperature scale than Tc, signalling a distinct quantum phase. Despite their dierences, the persistence of magnetic excitations and the existence of a distinct quantum phase are apparently universal in both hole- and electron-doped cuprates.
Topological Dirac and Weyl semimetals not only host quasiparticles analogous to the elementary fermionic particles in high-energy physics, but also have a non-trivial band topology manifested by ...gapless surface states, which induce exotic surface Fermi arcs1,2. Recent advances suggest new types of topological semimetal, in which spatial symmetries protect gapless electronic excitations without high-energy analogues3–11. Here, using angle-resolved photoemission spectroscopy, we observe triply degenerate nodal points near the Fermi level of tungsten carbide with space group \P\bar{6}m2\ (no. 187), in which the low-energy quasiparticles are described as three-component fermions distinct from Dirac and Weyl fermions. We further observe topological surface states, whose constant-energy contours constitute pairs of ‘Fermi arcs’ connecting to the surface projections of the triply degenerate nodal points, proving the non-trivial topology of the newly identified semimetal state.
Life table gives the most comprehensive description on the survival, stage differentiation and reproduction of a population and is thus the most important basis of population ecology and pest ...management. In this study, we constructed life tables for Bactrocera cucurbitae on cucumber (Cucumis sativus L.) in the laboratory and under simulated field conditions. To assess the variability of the life tables, we carried out two experiments under each treatment. Means, variances and standard errors of life table parameters were estimated for each of the two experiments by using the jackknife technique. At 25°C, the intrinsic rates of increase (r) found for the two experiments were 0.1354 and 0.1002 per day, and the net reproductive rates (R0) were 206.3 and 66.0 offspring, respectively. For cucumbers kept in the field and covered with leaves, the r and R0 for the two experiments were 0.0935 and 0.0909 per day, and 17.5 and 11.4 offspring, respectively. However, if cucumbers were kept in the field but were not covered, the r and R0 for the two experiments were 0.1043 and 0.0904 per day, and 27.7 and 10.1 offspring, respectively. Our results revealed significant variability between the experiments under both laboratory and field conditions; this variability should be taken into consideration in the data collection and application of life tables. However, our mathematical analysis shows that the application of the jackknife technique will result in biologically unrealistic R0,i‐pseudo and consequently overestimation of the variance of R0. According to our analysis, we suggest that the jackknife technique should not be used for the estimation of variability of the net reproductive rate.
Topological semimetals are characterized by symmetry-protected band crossings, which can be preserved in different dimensions in momentum space, forming zero-dimensional nodal points, one-dimensional ...nodal lines, or even two-dimensional nodal surfaces. Materials harboring nodal points and nodal lines have been experimentally verified, whereas experimental evidence of nodal surfaces is still lacking. Here, using angle-resolved photoemission spectroscopy (ARPES), we reveal the coexistence of Dirac nodal surfaces and nodal lines in the bulk electronic structures of ZrSiS. As compared with previous ARPES studies on ZrSiS, we obtained pure bulk states, which enable us to extract unambiguously intrinsic information of the bulk nodal surfaces and nodal lines. Our results show that the nodal lines are the only feature near the Fermi level and constitute the whole Fermi surfaces. We not only prove that the low-energy quasiparticles in ZrSiS are contributed entirely by Dirac fermions but also experimentally realize the nodal surface in topological semimetals.
By combining angle-resolved photoemission spectroscopy and quantum oscillation measurements, we performed a comprehensive investigation on the electronic structure of LaSb, which exhibits ...near-quadratic extremely large magnetoresistance (XMR) without any sign of saturation at magnetic fields as high as 40 T. We clearly resolve one spherical and one intersecting-ellipsoidal hole Fermi surfaces (FSs) at the Brillouin zone (BZ) center Γ and one ellipsoidal electron FS at the BZ boundary X. The hole and electron carriers calculated from the enclosed FS volumes are perfectly compensated, and the carrier compensation is unaffected by temperature. We further reveal that LaSb is topologically trivial but shares many similarities with the Weyl semimetal TaAs family in the bulk electronic structure. Based on these results, we have examined the mechanisms that have been proposed so far to explain the near-quadratic XMR in semimetals.
Layered deformation in the Taiwan orogen Huang, T.-Y.; Gung, Y.; Kuo, B.-Y. ...
Science (American Association for the Advancement of Science),
08/2015, Letnik:
349, Številka:
6249
Journal Article
Recenzirano
The underthrusting of continental crust during mountain building is an issue of debate for orogens at convergent continental margins. We report three-dimensional seismic anisotropic tomography of ...Taiwan that shows a nearly 90° rotation of anisotropic fabrics across a 10- to 20-kilometer depth, consistent with the presence of two layers of deformation. The upper crust is dominated by collision-related compressional deformation, whereas the lower crust of Taiwan, mostly the crust of the subducted Eurasian plate, is dominated by convergence-parallel shear deformation. We interpret this lower crustal shearing as driven by the continuous sinking of the Eurasian mantle lithosphere when the surface of the subducted plate is coupled with the orogen. The two-layer deformation clearly defines the role of subduction in the formation of the Taiwan mountain belt.
. Huang C‐N, Huang S‐P, Pao J‐B, Hour T‐C, Chang T‐Y, Lan Y‐H, Lu T‐L, Lee H‐Z, Juang S‐H, Wu P‐P, Huang C‐Y, Hsieh C‐J, Bao B‐Y (Kaohsiung Medical University Hospital, Kaohsiung; Kaohsiung Medical ...University, Kaohsiung; Taipei City Hospital, Taipei; Kaohsiung Medical University, Kaohsiung; China Medical University, Taichung; National Taiwan University Hospital; Oriental Institute of Technology; National Taiwan University, Taipei; China Medical University Hospital, Taichung, Taiwan). Genetic polymorphisms in oestrogen receptor‐binding sites affect clinical outcomes in patients with prostate cancer receiving androgen‐deprivation therapy. J Intern Med 2012; 271: 499–509.
Background. Accumulating evidence indicates that oestrogens have significant direct effects on normal prostate development and carcinogenesis. The majority of the biological activities of oestrogens are mediated through the oestrogen receptor (ER), which functions as a hormone‐inducible transcription factor to regulate target gene expression by binding to oestrogen response elements (EREs) in the regulatory regions of target genes. Sequence variants in EREs might affect the ER–ERE interaction and subsequent physiological activities. Therefore, we tested whether common single‐nucleotide polymorphisms (SNPs) inside EREs are related to the clinical outcomes of androgen‐deprivation therapy (ADT) in men with prostate cancer.
Methods. We systematically evaluated 49 ERE SNPs predicted using a genome‐wide database in a cohort of 601 men with advanced prostate cancer treated with ADT. The prognostic significance of these SNPs on disease progression, prostate cancer‐specific mortality (PCSM) and all‐cause mortality (ACM) after ADT was assessed using Kaplan–Meier analysis and a Cox regression model.
Results. Based on multiple hypothesis testing, BNC2 rs16934641 was found to be associated with disease progression; in addition, TACC2 rs3763763 was associated with PCSM, and ALPK1 rs2051778 and TACC2 rs3763763 were associated with ACM. These SNPs remained significant in multivariate analyses that included known clinicopathological predictors. Moreover, a combined genotype effect on ACM was observed when ALPK1 rs2051778 and TACC2 rs3763763 were analysed in combination. Patients with a greater number of unfavourable genotypes had a shorter time to ACM during ADT (P for trend <0.001).
Conclusion. The incorporation of ERE SNPs into models with known predictors might improve outcome prediction in patients with prostate cancer receiving ADT.
We used resonant inelastic x-ray scattering (RIXS) with and without analysis of the scattered photon polarization, to study dispersive spin excitations in the high temperature superconductor ...YBa_{2}Cu_{3}O_{6+x} over a wide range of doping levels (0.1≤x≤1). The excitation profiles were carefully monitored as the incident photon energy was detuned from the resonant condition, and the spin excitation energy was found to be independent of detuning for all x. These findings demonstrate that the largest fraction of the spin-flip RIXS profiles in doped cuprates arises from magnetic collective modes, rather than from incoherent particle-hole excitations as recently suggested theoretically Benjamin et al. Phys. Rev. Lett. 112, 247002 (2014). Implications for the theoretical description of the electron system in the cuprates are discussed.
The role of autotransplantation in end-stage hepatic alveolar echinococcosis (AE) is unclear. We aimed to present our 15-case experience and propose selection criteria for autotransplantation. All ...patients were considered to have unresectable hepatic AE by conventional resection due to critical invasion to retrohepatic vena cava, hepatocaval region along with three hepatic veins, and the tertiary portal and arterial branches. All patients successfully underwent ex vivo extended right hepatectomy and autotransplantation without intraoperative mortality. The median autograft weight was 706 g (380–1000 g); operative time was 15.5 hours (11.5–20.5 hours); and anhepatic time was 283.8 minutes (180–435 min). Postoperative hospital stay was 32.3 days (12–60 days). Postoperative complication Clavien–Dindo grade IIIa or higher occurred in three patients including one death that occurred 12 days after the surgery due to acute liver failure. One patient was lost to follow-up after the sixth month. Thirteen patients were followed for a median of 21.6 months with no relapse. This is the largest reported series of patients with end-stage hepatic AE treated with liver autotransplantation. The technique requires neither organ donor nor postoperative immunosuppressant. The early postoperative mortality was low with acceptable morbidity. Preoperative precise assessment and strict patient selection are of utmost importance.
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