We investigate polarization-dependent ultrafast photocurrents in the Weyl semimetal TaAs using terahertz (THz) emission spectroscopy. Our results reveal that highly directional, transient ...photocurrents are generated along the noncentrosymmetric c axis regardless of incident light polarization, while helicity-dependent photocurrents are excited within the ab plane. This is consistent with earlier static photocurrent experiments, and demonstrates on the basis of both the physical constraints imposed by symmetry and the temporal dynamics intrinsic to current generation and decay that optically induced photocurrents in TaAs are inherent to the underlying crystal symmetry of the transition metal monopnictide family of Weyl semimetals.
A highly pathogenic pig disease emerged in China in 2006, which was characterized by prolonged high fever, red discoloration of the body, and blue ears associated with high mortality. Porcine ...reproductive and respiratory syndrome virus (PRRSV) was isolated as the single most prominent virus in the samples collected from affected pigs. The full-length genomic sequence of the virus revealed two distinct deletions in the non-structural protein 2 (NSP2) in comparison to all previously reported North American genotype PRRSV. Through extensive surveys in 14 different provinces, 56 additional PRRSV isolates were obtained from affected farms. All of the isolates were found to contain identical deletions in NSP2. To confirm the etiology, eight 60-day-old PRRSV-free pigs were divided into two groups and the test group was intranasally infected at a titer of 2 x 10⁵.⁰ tissue culture infectious dose 50 per pig. The inoculated pigs all died at 7, 8, 12, 16, or 21 days post-inoculation with their clinical and pathological findings similar to those in the field. The viruses recovered from dead pigs were identical to the inoculated virus in NSP2 and GP5 genes. Our study shows that the recently emerged PRRSV in China is characterized by two discontiguous deletions in NSP2 and is the cause for the current epizootics in China.
Strong coupling between discrete phonon and continuous electron-hole pair excitations can induce a pronounced asymmetry in the phonon line shape, known as the Fano resonance. This effect has been ...observed in various systems. Here we reveal explicit evidence for strong coupling between an infrared-active phonon and electronic transitions near the Weyl points through the observation of a Fano resonance in the Weyl semimetal TaAs. The resulting asymmetry in the phonon line shape, conspicuous at low temperatures, diminishes continuously with increasing temperature. This behaviour originates from the suppression of electronic transitions near the Weyl points due to the decreasing occupation of electronic states below the Fermi level (E
) with increasing temperature, as well as Pauli blocking caused by thermally excited electrons above E
. Our findings not only elucidate the mechanism governing the tunable Fano resonance but also open a route for exploring exotic physical phenomena through phonon properties in Weyl semimetals.
Using femtosecond time-resolved x-ray diffraction, we investigated optically excited coherent acoustic phonons in the Weyl semimetal TaAs. The low symmetry of the (112) surface probed in our ...experiment enables the simultaneous excitation of longitudinal and shear acoustic modes, whose dispersion closely matches our simulations. We observed an asymmetry in the spectral line shape of the longitudinal mode that is notably absent from the shear mode, suggesting a time-dependent frequency chirp that is likely driven by photoinduced carrier diffusion. We argue on the basis of symmetry that these acoustic deformations can transiently alter the electronic structure near the Weyl points and support this with model calculations. Our study underscores the benefit of using off-axis crystal orientations when optically exciting acoustic deformations in topological semimetals, allowing one to transiently change their crystal and electronic structures.
We present an infrared spectroscopy study of ZrTe5, which confirms a recent theoretical proposal that this material exhibits a temperature-driven topological quantum phase transition from a weak to a ...strong topological insulating state with an intermediate Dirac semimetal state around Tp≃138 K. Our study details the temperature evolution of the energy gap in the bulk electronic structure. We found that the energy gap closes around Tp, where the optical response exhibits characteristic signatures of a Dirac semimetal state, i.e., a linear frequency-dependent optical conductivity extrapolating to the origin (after subtracting a weak Drude response). This finding allows us to reconcile previous diverging reports about the topological nature of ZrTe5 in terms of a variation of Tp that depends on the crystal growth condition.
As silicon is the basis of conventional electronics, so strontium titanate (SrTiO3) is the foundation of the emerging field of oxide electronics1,2.SrTiO3 is the preferred template for the creation ...of exotic, two-dimensional (2D) phases of electronmatter at oxide interfaces3-5 that have metal-insulator transitions6,7, superconductivity8,9 or large negative magnetoresistance10. However, the physical nature of the electronic structure underlying these 2D electron gases (2DEGs), which is crucial to understanding their remarkable properties11,12, remains elusive. Here we show, using angle-resolved photoemission spectroscopy, that there is a highly metallic universal 2DEG at the vacuum-cleaved surface of SrTiO3 (including the non-doped insulating material) independently of bulk carrier densities over more than seven decades. This 2DEG is confined within a region of about five unit cells and has a sheet carrier density of 0.33 electrons per square lattice parameter. The electronic structure consists of multiple subbands of heavy and light electrons. The similarity of this 2DEG to those reported in SrTiO3-based heterostructures6,8,13 and field-effect transistors9,14 suggests that different forms of electron confinement at the surface of SrTiO3 lead to essentially the same 2DEG. Our discovery provides a model system for the study of the electronic structure of 2DEGs in SrTiO3-based devices and a novel means of generating 2DEGs at the surfaces of transition-metal oxides.
Because of the half-filled t_{2g}-electron configuration, the BO_{6} octahedral distortion in a 3d^{3} perovskite system is usually very limited. In this Letter, a perovskitelike oxide ...Hg_{0.75}Pb_{0.25}MnO_{3} (HPMO) with a 3d^{3} Mn^{4+} state was synthesized by using high pressure and high temperature methods. This compound exhibits an unusually large octahedral distortion enhanced by approximately 2 orders of magnitude compared with that observed in other 3d^{3} perovskite systems like RCr^{3+}O_{3} (R=rare earth). Essentially different from centrosymmetric HgMnO_{3} and PbMnO_{3}, the A-site doped HPMO presents a polar crystal structure with the space group Ama2 and a substantial spontaneous electric polarization (26.5 μC/cm^{2} in theory) arising from the off-center displacements of A- and B-site ions. More interestingly, a prominent net photocurrent and switchable photovoltaic effect with a sustainable photoresponse were observed in the current polycrystalline HPMO. This Letter provides an exceptional d^{3} material system which shows unusually large octahedral distortion and displacement-type ferroelectricity violating the "d^{0}-ness" rule.
Polyamines play an important role in stress response. In the pathway of polyamines synthesis, S-adenosylmethionine decarboxylase (SAMDC) is one of the key enzymes. In this study, a full length cDNA ...of SAMDC (AhSAMDC) was isolated from peanut (Arachis hypogaea L.). Phylogenetic analysis revealed high sequence similarity between AhSAMDC and SAMDC from other plants.
In peanut seedlings exposed to sodium chloride (NaCl), the transcript level of AhSAMDC in roots was the highest at 24 h that decreased sharply at 72 and 96 h after 150 mM NaCl treatment. However, the expression of AhSAMDC in peanut leaves was significantly inhibited, and the transcript levels in leaves were not different compared with control
These results implied the tissue‐specific and time-specific expression of AhSAMDC. The physiological effects and functional mechanism of AhSAMDC were further evaluated by overexpressing AhSAMDC in tobaccos. The transgenic tobacco lines exhibited higher germination rate and longer root length under salt stress. Reduced membrane damage, higher antioxidant enzyme activity, and higher proline content were also observed in the transgenic tobacco seedlings. What's more, AhSAMDC also led to higher contents of spermidine and spermine, which can help to scavenge reactive oxygen species.
Together, this study suggests that AhSAMDC enhances plant resistance to salt stress by improving polyamine content and alleviating membrane damage
AhSAMDC subcloned into tobacco plants may play an important role in alleviating oxidative stress and membrane damages by improving antioxidant enzymes under salt stress.
A retrospective study on the correlation between preoperative pulmonary function tests, preoperative pulmonary symptoms, and postoperative pulmonary complications.
To evaluate the incidence of ...immediate postoperative pulmonary complications and their correlation to pulmonary function tests, preoperative pulmonary symptoms, and surgical approaches.
The pulmonary function of patients with scoliosis is likely to be abnormal, whereas surgical procedures may lead to further deterioration and postoperative pulmonary complications. Evaluation of the pulmonary symptoms and pulmonary function before surgery is helpful to predict and avoid postoperative pulmonary complications by selecting the appropriate surgical approach.
This study reviewed 298 scoliosis patients (107 male, 191 female) who underwent anterior and/or posterior operation. The mean age of the patients was 16.4 years (range 6-62 years). The average coronal Cobb angle was 73.26 degrees (range 45-141 degrees). Preoperative pulmonary function tests of 115 cases were normal, whereas the other 183 cases were abnormal. Seventeen cases had preoperative pulmonary symptoms and 3 of them had normal preoperative pulmonary function tests. Seventy-nine cases received transthoracic surgery, and 19 cases had postoperative pulmonary complications, including postoperative ventilation support in 6 cases, atelectasis in 4 cases, hydrothorax in 2 cases, pneumothorax in 3 cases, pneumonia in 3 cases, and hypoxemia in 1 case. Of these 19 patients, 12 patients received anterior transthoracic procedure. When the patients with abnormal pulmonary function tests were divided into 3 groups: 1) 60% < or = forced vital capacity ratio < 80%; 2) 40% < or = forced vital capacity ratio < 60%; and 3) forced vital capacity ratio < 40%, the incidence of postoperative pulmonary complications were 2.72% (3 out of 110), 7.40% (4 out of 54) and 31.60% (6 out of 19), respectively.
There was significant correlation between abnormal preoperative pulmonary function tests and preoperative pulmonary symptoms (P = 0.0086). No significant correlation was found between preoperative pulmonary symptoms and postoperative pulmonary complications (P = 0.5164). There was a trend that the postoperative complications increased with the deterioration of pulmonary function. The correlation between postoperative pulmonary complications and the surgical approach was statistically significant (P = 0.0000); the incidence of postoperative pulmonary complication of transthoracic procedure was 18 times as that of posterior approach. No significant difference was noted regarding ages, preoperative coronal Cobb angles, and preoperative pulmonary function between these 2 groups. There was no significant correlation between preoperative pulmonary symptoms and postoperative complications.
The incidence of postoperative pulmonary complications increased with the deterioration of pulmonary function tests. The posterior procedure had a very low incidence of postoperative pulmonary complications, but a transthoracic procedure increased the complications significantly. Preoperative pulmonary symptoms usually predicted abnormal results of pulmonary function tests but had no correlation with postoperative pulmonary complication.
We report our photometric and spectroscopic follow-up observations of the superoutbursts of three dwarf novae (DNe; GWAC 180415A, GWAC 181017A, and GWAC 181211A) identified independently by the ...Ground Wide-angle Cameras system, one of the ground-based instruments of the China-France SVOM mission. Based on a combination of our photometry and that taken from the American Association of Variable Star Observers, our period analysis of the superhumps enables us to determine the mass ratios to be 0.0967-0.1163, 0.1879-0.1883, and 0.0981-0.1173 for GWAC 180415A, GWAC 181017A, and GWAC 181211A, respectively. GWAC 180415A can be firmly identified as a WZ sge-type DNe due to its long duration (∼2 weeks) multiple rebrightenings with amplitudes of 3-4 mag, the early superhump associated with a double-wave modulation and the low-mass ratio. The inferred low-mass ratio and location in the diagram suggest that GWAC 181211A is a WZ sge-type DNe candidate. The measured Balmer decrements suggest the Balmer line emission is produced from an optical thick region in GWAC 180415A and GWAC 181017A, and from an optically thin region in GWAC 181211A.
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