An Asymmetrical Model for High Energy Radiation of Cassiopeia A

Cassiopeia A (Cas A) supernova remnant shows strong radiation from radio to gamma-ray bands. The mechanism of gamma-ray radiation in Cas A and its possible contribution to PeV cosmic rays are still under debate. The X-ray imaging reveals an asymmetric profile of Cas A, suggesting the existence of a jet-like structure. In this work, we propose an asymmetrical model for Cas A, consisting of a fast moving jet-like structure and a slowly expanding isotropic shell. This model can account for the multi-wavelength spectra of Cas A, especially for the power-law hard X-ray spectrum from $\sim$ 60 to 220 keV. The GeV to TeV emission from Cas A should be contributed by both hadronic and leptonic processes. Moreover, the jet-like structure may produce a gamma-ray flux of $\sim 10^{-13}\rm erg\ cm^{-2}\ s^{-1}$ at $\sim 100$ TeV, to be examined by LHAASO and CTA.Comment: 7 pages, 7 figures. MNRAS in pres

Floquet Engineering of Nonequilibrium Valley-Polarized Quantum Anomalous Hall Effect with Tunable Chern Number

Numerous attempts have been made so far to explore the quantum anomalous Hall effect (QAHE), but the ultralow observed temperature strongly hinders its practical applications. Hence, it is of great interest to go beyond the existing paradigm of QAHE. Here, we propose that Floquet engineering offers a strategy to realize the QAHE via hybridization of Floquet-Bloch bands. Based on first-principles calculations and Floquet theorem, we unveil that nonequilibrium valley-polarized QAHE (VP-QAHE), independent of magnetic orders, is widely present in ferromagnetic and nonmagnetic members of two-dimensional family materials $M$Si$_2$$Z_4$ ($M$ = Mo, W, V; $Z$ = N, P, As) by irradiating circularly polarized light (CPL). Remarkably, by tuning the frequency, intensity, and handedness of incident CPL, the Chern number of VP-QAHE is highly tunable and up to $\mathcal{C}=\pm 4$. We reveal that such Chern number tunable VP-QAHE attributes to light-induced trigonal warping and multiple band inversion at different valleys. The valley-resolved chiral edge states and quantized plateau of Hall conductance, which facilitates the experimental measurement, are visible inside the global band gap. Our work not only establishes Floquet Engineering of nonequilibrium VP-QAHE with tunable Chern number in realistic materials, but also provides a promising avenue to explore emergent topological phases under light irradiation.Comment: 6 pages, 4 figure

Influence of ground-Rydberg coherence in two-qubit gate based on Rydberg blockade

For neutral atom qubits, the two-qubit gate is typically realized via the Rydberg blockade effect, which hints about the special status of the Rydberg level besides the regular qubit register states. Here, we carry out experimental and theoretical studies to reveal how the ground-Rydberg coherence of the control qubit atom affects the process of two-qubit Controlled-Z ($C_Z$) gate, such as the commonly used ground-Rydberg $\pi$-gap-$\pi$ pulse sequence originally proposed in Phys. Rev. Lett. \textbf{85}, 2208 (2000). We measure the decoherence of the control qubit atom after the $\pi$-gap-$\pi$ pulses and make a direct comparison with the typical decoherence time $\tau_{gr}$ extracted from Ramsey fringes of the ground-Rydberg transition. In particular, we observe that the control qubit atom subject to such pulse sequences experiences a process which is essentially similar to the ground-Rydberg Ramsey interference. Furthermore, we build a straightforward theoretical model to link the decoherence process of control qubit subject to $C_Z$ gate $\pi$-gap-$\pi$ pulse sequence and the $\tau_{gr}$, and also analyze the typical origins of decoherence effects. Finally, we discuss the $C_Z$ gate fidelity loss due to the limits imposed by the ground-Rydberg coherence properties and prospective for improving fidelity with new gate protocols.Comment: 8 figure

Non-linear micro-mechanical behavior of heterogeneous cement-stabilized macadam

Ovim istraživanjem nastoji se ispitati unutarnje mehaničko ponašanje makadama stabiliziranog cementom koje je oštećeno opterećenjem uslijed uranjanja u vodu. Izradom modela numeričke analize ispitani su mehanizam slabljenja makadamskog materijala stabiliziranog cementom i unutarnje mikromehaničko ponašanje uzoraka. Rezultati dobiveni numeričkom simulacijom uspoređeni su s laboratorijskim podacima. Pogreška uslijed vršnog naprezanja iznosila je 2,414 %, a najveća je pogreška u naprezanju odgovarala vršnom naprezanju uzoraka pri različitom trajanju uranjanja te je iznosila 3,05 %. Usporedbom razdiobe smjera normalnih i tangentnih kontaktnih sila u svakoj fazi ustanovilo se da su tangentne sile pri približno 0º, 90º, 180º i 270º puno manje nego one pri drugim kutovima. U fazi vršnog naprezanja, normalni kontaktni kutovi između 45-135º i 225-285º znatno su viši od onih pod drugim kutovima. Kad je model M (srednji faktor) manji od 20, vršno naprezanje značajno se promijenilo i povećalo kao funkcija M. Kad je M bio veći od 20, vršno naprezanje variralo je unutar malog raspona kao funkcija M. Prikazano istraživanje nudi novu metodu ispitivanja u svrhu analize strukturnih mehaničkih učinaka koje imaju kolničke konstrukcije temeljene na makadamima stabiliziranim cementom i oštećenim uslijed uranjanja u vodu.This study aims to examine the internal meso-mechanical behaviour of cement-stabilised macadams subjected to loading damage following water immersion. By constructing a numerical analysis model, the mechanism of water-immersion weakening of the cement-stabilised macadam material and the internal micro-mechanical behaviour of the specimen were analysed. The numerical simulation results were compared with laboratory test data. The peak stress error was 2.414%, whereas the maximum error in the strain corresponding to the peak stress of the specimens with different immersion durations was 3.05%. By comparing the direction distributions of the normal and tangential contact forces in each stage, it was found that the tangential forces at approximately 0º, 90º, 180º, and 270º were much smaller than those at other angles. In the peak stress stage, the normal contact angles between 45–135º and 225–285º were higher than those at other angles. For model M (mean factor) less than 20, the peak stress was significantly affected and increased as a function of M. When M was greater than 20, the peak stress fluctuated within a small range as a function of M. This study provides a new research method for the study of the structural mechanical effect of pavement structures based on cement-stabilised macadam materials damaged following water immersion

Validation of an algorithm to evaluate the appropriateness of outpatient antibiotic prescribing using big data of Chinese diagnosis text

OBJECTIVE: We aimed to evaluate the validity of an algorithm to classify diagnoses according to the appropriateness of outpatient antibiotic use in the context of Chinese free text. SETTING AND PARTICIPANTS: A random sample of 10 000 outpatient visits was selected between January and April 2018 from a national database for monitoring rational use of drugs, which included data from 194 secondary and tertiary hospitals in China. RESEARCH DESIGN: Diagnoses for outpatient visits were classified as tier 1 if associated with at least one condition that 'always' justified antibiotic use; as tier 2 if associated with at least one condition that only 'sometimes' justified antibiotic use but no conditions that 'always' justified antibiotic use; or as tier 3 if associated with only conditions that never justified antibiotic use, using a tier-fashion method and regular expression (RE)-based algorithm. MEASURES: Sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of the classification algorithm, using classification made by chart review as the standard reference, were calculated. RESULTS: The sensitivities of the algorithm for classifying tier 1, tier 2 and tier 3 diagnoses were 98.2% (95% CI 96.4% to 99.3%), 98.4% (95% CI 97.6% to 99.1%) and 100.0% (95% CI 100.0% to 100.0%), respectively. The specificities were 100.0% (95% CI 100.0% to 100.0%), 100.0% (95% CI 99.9% to 100.0%) and 98.6% (95% CI 97.9% to 99.1%), respectively. The PPVs for classifying tier 1, tier 2 and tier 3 diagnoses were 100.0% (95% CI 99.1% to 100.0%), 99.7% (95% CI 99.2% to 99.9%) and 99.7% (95% CI 99.6% to 99.8%), respectively. The NPVs were 99.9% (95% CI 99.8% to 100.0%), 99.8% (95% CI 99.7% to 99.9%) and 100.0% (95% CI 99.8% to 100.0%), respectively. CONCLUSIONS: The RE-based classification algorithm in the context of Chinese free text had sufficiently high validity for further evaluating the appropriateness of outpatient antibiotic prescribing

Cyclic deformation leads to defect healing and strengthening of small-volume metal crystals

When microscopic and macroscopic specimens of metals are subjected to cyclic loading, the creation, interaction, and accumulation of defects lead to damage, cracking, and failure. Here we demonstrate that when aluminum single crystals of submicrometer dimensions are subjected to low-amplitude cyclic deformation at room temperature, the density of preexisting dislocation lines and loops can be dramatically reduced with virtually no change of the overall sample geometry and essentially no permanent plastic strain. This “cyclic healing” of the metal crystal leads to significant strengthening through dramatic reductions in dislocation density, in distinct contrast to conventional cyclic strain hardening mechanisms arising from increases in dislocation density and interactions among defects in microcrystalline and macrocrystalline metals and alloys. Our real-time, in situ transmission electron microscopy observations of tensile tests reveal that pinned dislocation lines undergo shakedown during cyclic straining, with the extent of dislocation unpinning dependent on the amplitude, sequence, and number of strain cycles. Those unpinned mobile dislocations moving close enough to the free surface of the thin specimens as a result of such repeated straining are then further attracted to the surface by image forces that facilitate their egress from the crystal. These results point to a versatile pathway for controlled mechanical annealing and defect engineering in submicrometer-sized metal crystals, thereby obviating the need for thermal annealing or significant plastic deformation that could cause change in shape and/or dimensions of the specimen.National Science Foundation (U.S.) (Grant DMR-1120901)National Science Foundation (U.S.) (DMR-1410636)Singapore-MIT Allianc