A variety of monolayer crystals have been proposed to be two-dimensional topological insulators exhibiting the quantum spin Hall effect (QSHE), possibly even at high temperatures. Here we report the ...observation of the QSHE in monolayer tungsten ditelluride (WTe
) at temperatures up to 100 kelvin. In the short-edge limit, the monolayer exhibits the hallmark transport conductance, ~
/
per edge, where
is the electron charge and
is Planck's constant. Moreover, a magnetic field suppresses the conductance, and the observed Zeeman-type gap indicates the existence of a Kramers degenerate point and the importance of time-reversal symmetry for protection from elastic backscattering. Our results establish the QSHE at temperatures much higher than in semiconductor heterostructures and allow for exploring topological phases in atomically thin crystals.
Abstract Objectives To review the history, theory and current applications of Weibull analyses sufficient to make informed decisions regarding practical use of the analysis in dental material ...strength testing. Data References are made to examples in the engineering and dental literature, but this paper also includes illustrative analyses of Weibull plots, fractographic interpretations, and Weibull distribution parameters obtained for a dense alumina, two feldspathic porcelains, and a zirconia. Sources Informational sources include Weibull's original articles, later articles specific to applications and theoretical foundations of Weibull analysis, texts on statistics and fracture mechanics and the international standards literature. Study selection The chosen Weibull analyses are used to illustrate technique, the importance of flaw size distributions, physical meaning of Weibull parameters and concepts of “equivalent volumes” to compare measured strengths obtained from different test configurations. Conclusions Weibull analysis has a strong theoretical basis and can be of particular value in dental applications, primarily because of test specimen size limitations and the use of different test configurations. Also endemic to dental materials, however, is increased difficulty in satisfying application requirements, such as confirming fracture origin type and diligence in obtaining quality strength data.
Novel second-line treatments are needed for patients with advanced urothelial cancer (UC). Interim analysis of the phase III KEYNOTE-045 study showed a superior overall survival (OS) benefit of ...pembrolizumab, a programmed death 1 inhibitor, versus chemotherapy in patients with advanced UC that progressed on platinum-based chemotherapy. Here we report the long-term safety and efficacy outcomes of KEYNOTE-045.
Adult patients with histologically/cytologically confirmed UC whose disease progressed after first-line, platinum-containing chemotherapy were enrolled. Patients were randomly assigned 1 : 1 to receive pembrolizumab 200mg every 3weeks (Q3W) or investigator’s choice of paclitaxel (175mg/m2 Q3W), docetaxel (75mg/m2 Q3W), or vinflunine (320mg/m2 Q3W). Primary end points were OS and progression-free survival (PFS) per Response Evaluation Criteria in Solid Tumors, version 1.1 (RECIST v1.1) by blinded independent central radiology review (BICR). A key secondary end point was objective response rate per RECIST v1.1 by BICR.
A total of 542 patients were enrolled (pembrolizumab, n=270; chemotherapy, n=272). Median follow-up as of 26 October 2017 was 27.7months. Median 1- and 2-year OS rates were higher with pembrolizumab (44.2% and 26.9%, respectively) than chemotherapy (29.8% and 14.3%, respectively). PFS rates did not differ between treatment arms; however, 1- and 2-year PFS rates were higher with pembrolizumab. The objective response rate was also higher with pembrolizumab (21.1% versus 11.0%). Median duration of response to pembrolizumab was not reached (range 1.6+ to 30.0+ months) versus chemotherapy (4.4months; range 1.4+ to 29.9+ months). Pembrolizumab had lower rates of any grade (62.0% versus 90.6%) and grade ≥3 (16.5% versus 50.2%) treatment-related adverse events than chemotherapy.
Long-term results (>2 years’ follow-up) were consistent with those of previously reported analyses, demonstrating continued clinical benefit of pembrolizumab over chemotherapy for efficacy and safety for treatment of locally advanced/metastatic, platinum-refractory UC.
ClinicalTrials.gov: NCT02256436.
Turning on superconductivity in a topologically nontrivial insulator may provide a route to search for non-Abelian topological states. However, existing demonstrations of superconductor-insulator ...switches have involved only topologically trivial systems. Here we report reversible, in situ electrostatic on-off switching of superconductivity in the recently established quantum spin Hall insulator monolayer tungsten ditelluride (WTe
). Fabricated into a van der Waals field-effect transistor, the monolayer's ground state can be continuously gate-tuned from the topological insulating to the superconducting state, with critical temperatures
up to ~1 kelvin. Our results establish monolayer WTe
as a material platform for engineering nanodevices that combine superconducting and topological phases of matter.
Pristine graphene, its derivatives, and composites have been widely reported to possess antibacterial properties. Most of the studies simulating the interaction between bacterial cell membranes and ...the surface of graphene have proposed that the graphene-induced bacterial cell death is caused either by (1) the insertion of blade-like graphene-based nanosheets or (2) the destructive extraction of lipid molecules by the presence of the lipophilic graphene. These simulation studies have, however, only take into account graphene–cell membrane interactions where the graphene is in a dispersed form. In this paper, we report the antimicrobial behavior of graphene sheet surfaces in an attempt to further advance the current knowledge pertaining to graphene cytotoxicity using both experimental and computer simulation approaches. Graphene nanofilms were fabricated to exhibit different edge lengths and different angles of orientation in the graphene sheets. These substrates were placed in contact with Pseudomonas aeruginosa and Staphylococcus aureus bacteria, where it was seen that these substrates exhibited variable bactericidal efficiency toward these two pathogenic bacteria. It was demonstrated that the density of the edges of the graphene was one of the principal parameters that contributed to the antibacterial behavior of the graphene nanosheet films. The study provides both experimental and theoretical evidence that the antibacterial behavior of graphene nanosheets arises from the formation of pores in the bacterial cell wall, causing a subsequent osmotic imbalance and cell death.
The electrical Hall effect is the production, upon the application of an electric field, of a transverse voltage under an out-of-plane magnetic field. Studies of the Hall effect have led to important ...breakthroughs, including the discoveries of Berry curvature and topological Chern invariants
. The internal magnetization of magnets means that the electrical Hall effect can occur in the absence of an external magnetic field
; this 'anomalous' Hall effect is important for the study of quantum magnets
. The electrical Hall effect has rarely been studied in non-magnetic materials without external magnetic fields, owing to the constraint of time-reversal symmetry. However, only in the linear response regime-when the Hall voltage is linearly proportional to the external electric field-does the Hall effect identically vanish as a result of time-reversal symmetry; the Hall effect in the nonlinear response regime is not subject to such symmetry constraints
. Here we report observations of the nonlinear Hall effect
in electrical transport in bilayers of the non-magnetic quantum material WTe
under time-reversal-symmetric conditions. We show that an electric current in bilayer WTe
leads to a nonlinear Hall voltage in the absence of a magnetic field. The properties of this nonlinear Hall effect are distinct from those of the anomalous Hall effect in metals: the nonlinear Hall effect results in a quadratic, rather than linear, current-voltage characteristic and, in contrast to the anomalous Hall effect, the nonlinear Hall effect results in a much larger transverse than longitudinal voltage response, leading to a nonlinear Hall angle (the angle between the total voltage response and the applied electric field) of nearly 90 degrees. We further show that the nonlinear Hall effect provides a direct measure of the dipole moment
of the Berry curvature, which arises from layer-polarized Dirac fermions in bilayer WTe
. Our results demonstrate a new type of Hall effect and provide a way of detecting Berry curvature in non-magnetic quantum materials.
The Vickers indentation fracture toughness test, or VIF, is addressed by considering its origins and the numerous equations that have been applied along with the technique to estimate the fracture ...resistance, or the KIc of ceramics. Initiation and propagation of cracks during the VIF test are described and contrasted with the pre‐cracking and crack growth for internationally standardized fracture toughness tests. It is concluded that the VIF test technique is fundamentally different than standard fracture toughness tests. The VIF test has a complex three‐dimensional crack system with substantial deformation residual stresses and damage around the cracks. The VIF test relates to an ill‐defined crack arrest condition as opposed to the rapid crack propagation of the standardized fracture toughness tests.
Previously published fracture toughness results employing the VIF technique are reviewed. These reveal serious discrepancies in reported VIF fracture toughness values. Finally, recent fracture resistance measurements by the VIF technique for the Standard Reference Material SRM 2100 are presented. These are compared with standardized test results for the same material. It is concluded that the VIF technique is not reliable as a fracture toughness test for ceramics or for other brittle materials. What the VIF actually measures in terms of fracture resistance cannot be readily defined. It is recommended that the VIF technique no longer be acceptable for the fracture toughness testing of ceramic materials.
In a randomized trial involving 542 patients with relapsed urothelial cancer, treatment with pembrolizumab resulted in overall survival of more than 10 months, as compared with 7 months with ...chemotherapy.
Urothelial cancer is highly lethal in the metastatic state.
1
Platinum-based combination chemotherapy remains the standard first-line treatment for metastatic disease. Carboplatin-based combinations are associated with a median overall survival of 9 months,
2
and cisplatin-based combinations with a median overall survival of 12 to 15 months.
3
However, after platinum-based chemotherapy, there is no internationally accepted standard of care. Single-agent paclitaxel and docetaxel are commonly used worldwide,
4
,
5
and in Europe, vinflunine has been approved on the basis of an overall survival advantage of 2 months over best supportive care.
6
,
7
Because the median overall survival with second-line therapy is only 6 . . .
Recent experimental evidence for the quantum spin Hall (QSH) state in monolayer WTe2 has linked the fields of two-dimensional materials and topological physics1–7. This two-dimensional topological ...crystal also displays unconventional spin–torque8 and gate-tunable superconductivity7. Whereas the realization of the QSH has demonstrated the nontrivial topology of the electron wavefunctions of monolayer WTe2, the geometrical properties of the wavefunction, such as the Berry curvature9, remain unstudied. Here we utilize mid-infrared optoelectronic microscopy to investigate the Berry curvature in monolayer WTe2. By optically exciting electrons across the inverted QSH gap, we observe an in-plane circular photogalvanic current even under normal incidence. The application of an out-of-plane displacement field allows further control of the direction and magnitude of the photocurrent. The observed photocurrent reveals a Berry curvature dipole that arises from the nontrivial wavefunctions near the inverted gap edge. The Berry curvature dipole and strong electric field effect are enabled by the inverted band structure and tilted crystal lattice of monolayer WTe2. Such an electrically switchable Berry curvature dipole may facilitate the observation of a wide range of quantum geometrical phenomena such as the quantum nonlinear Hall10,11, orbital-Edelstein12 and chiral polaritonic effects13,14.
Abstract
Background
Quantitative PCR (qPCR) aims to measure the DNA or RNA concentration in diagnostic and biological samples based on the quantification cycle (Cq) value observed in the ...amplification curves. Results of qPCR experiments are regularly calculated as if all assays are 100% efficient or reported as just Cq, ΔCq, or ΔΔCq values.
Contents
When the reaction shows specific amplification, it should be deemed to be positive, regardless of the observed Cq. Because the Cq is highly dependent on amplification efficiency that can vary among targets and samples, accurate calculation of the target quantity and relative gene expression requires that the actual amplification efficiency be taken into account in the analysis and reports. PCR efficiency is frequently derived from standard curves, but this approach is affected by dilution errors and hampered by properties of the standard and the diluent. These factors affect accurate quantification of clinical and biological samples used in diagnostic applications and collected in challenging conditions. PCR efficiencies determined from individual amplification curves avoid these confounders. To obtain unbiased efficiency-corrected results, we recommend absolute quantification with a single undiluted calibrator with a known target concentration and efficiency values derived from the amplification curves of the calibrator and the unknown samples.
Summary
For meaningful diagnostics or biological interpretation, the reported results of qPCR experiments should be efficiency corrected. To avoid ambiguity, the Minimal Information for Publications on Quantitative Real-Time PCR Experiments (MIQE) guidelines checklist should be extended to require the methods that were used (1) to determine the PCR efficiency and (2) to calculate the reported target quantity and relative gene expression value.
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