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  1. Abstract

    The distribution of gas in the circumgalactic medium (CGM) of galaxies of all types is poorly constrained. Foreground CGMs contribute an extra amount to the dispersion measure (DM) of fast radio bursts (FRBs). We measure this DM excess for the CGMs of 1011–1013Mhalos using the CHIME/FRB first data release, a halo mass range that is challenging to probe in any other way. Because of the uncertainty in the FRBs’ angular coordinates, only for nearby galaxies is the localization sufficient to confidently associate them with intersecting any foreground halo. Thus we stack on galaxies within 80 Mpc, optimizing the stacking scheme to approximately minimize the stack’s variance and marginalize over uncertainties in FRB locations. The sample has 20–30 FRBs intersecting halos with masses of 1011–1012Mand also of 1012–1013M, and these intersections allow a marginal 1σ–2σdetection of the DM excess in both mass bins. The bin of 1011–1012Mhalos also shows a DM excess at 1–2 virial radii. By comparing data with different models for the CGM gas profile, we find that all models are favored by the data up to 2σlevel compared to the null hypothesis of no DM excess. With 3000 more bursts from a future CHIME data release, wemore »project a 4σdetection of the CGM. Distinguishing between viable CGM models by stacking FRBs with CHIME-like localization would require tens of thousands of bursts.

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  2. Abstract

    Monolayer molybdenum disulfide has been previously discovered to exhibit non-volatile resistive switching behavior in a vertical metal-insulator-metal structure, featuring ultra-thin sub-nanometer active layer thickness. However, the reliability of these nascent 2D-based memory devices was not previously investigated for practical applications. Here, we employ an electron irradiation treatment on monolayer MoS2film to modify the defect properties. Raman, photoluminescence, and X-ray photoelectron spectroscopy measurements have been performed to confirm the increasing amount of sulfur vacancies introduced by the e-beam irradiation process. The statistical electrical studies reveal the reliability can be improved by up to 1.5× for yield and 11× for average DC cycling endurance in the devices with a moderate radiation dose compared to unirradiated devices. Based on our previously proposed virtual conductive-point model with the metal ion substitution into sulfur vacancy, Monte Carlo simulations have been performed to illustrate the irradiation effect on device reliability, elucidating a clustering failure mechanism. This work provides an approach by electron irradiation to enhance the reliability of 2D memory devices and inspires further research in defect engineering to precisely control the switching properties for a wide range of applications from memory computing to radio-frequency switches.

  3. How and when do opportunities for political participation through courts change under authoritarianism? Although China is better known for tight political control than for political expression, the 2008 Open Government Information (OGI) regulation ushered in a surge of political-legal activism. We draw on an original dataset of 57,095 OGI lawsuits, supplemented by interview data and government documents, to show how a feedback loop between judges and court users shaped possibilities for political activism and complaint between 2008 and 2019. Existing work suggests that authoritarian leaders crack down on legal action when they feel politically threatened. In contrast, we find that courts minted, defined, and popularized new legal labels to cut off access to justice for the super-active litigants whose lawsuits had come to dominate the OGI docket. This study underscores the power of procedural rules and frontline judges in shaping possibilities for political participation under authoritarianism.
  4. MoS 2 has been reported to exhibit a resistive switching phenomenon in a vertical metal–insulator–metal (MIM) structure and has attracted much attention due to its ultra-thin active layer thickness. Here, the resistance evolutions in the high resistance state (HRS) and low resistance state (LRS) are investigated under constant voltage stress (CVS) or constant current stress (CCS) on MoS 2 resistive switching devices. Interestingly, compared with bulk transition metal oxides (TMO), MoS 2 exhibits an opposite characteristic in the fresh or pre-RESET device in the “HRS” wherein the resistance will increase to an even higher resistance after applying CVS, a unique phenomenon only accessible in 2D-based resistive switching devices. It is inferred that instead of in the highest resistance state, the fresh or pre-RESET devices are in an intermediate state with a small amount of Au embedded in the MoS 2 film. Inspired by the capability of both bipolar and unipolar operation, positive and negative CVS measurements are performed and show similar characteristics. In addition, it is observed that the resistance state transition is faster when using higher electric stress. Numerical simulations have been performed to study the temperature effect with small-area integration capability. These results can be explained by amore »modified conductive-bridge-like model based on Au migration, uncovering the switching mechanisms in the ultrathin 2D materials and inspiring future studies in this area.« less
  5. Abstract We present self-consistent radiation hydrodynamic simulations of hydrogen reionization performed with arepo-rt complemented by a state-of-the-art galaxy formation model. We examine how photoheating feedback, due to reionization, shapes the galaxies properties. Our fiducial model completes reionization by z ≈ 6 and matches observations of the Ly α forest, the cosmic microwave background electron scattering optical depth, the high-redshift ultraviolet (UV) luminosity function, and stellar mass function. Contrary to previous works, photoheating suppresses star formation rates by more than $50{{\ \rm per\ cent}}$ only in haloes less massive than ∼108.4 M⊙ (∼108.8 M⊙) at z = 6 (z = 5), suggesting inefficient photoheating feedback from photons within galaxies. The use of a uniform UV background that heats up the gas at z ≈ 10.7 generates an earlier onset of suppression of star formation compared to our fiducial model. This discrepancy can be mitigated by adopting a UV background model with a more realistic reionization history. In the absence of stellar feedback, photoheating alone is only able to quench haloes less massive than ∼109 M⊙ at z ≳ 5, implying that photoheating feedback is sub-dominant in regulating star formation. In addition, stellar feedback, implemented as a non-local galactic wind scheme in the simulations, weakens the strength of photoheating feedback by reducing the amountmore »of stellar sources. Most importantly, photoheating does not leave observable imprints in the UV luminosity function, stellar mass function, or the cosmic star formation rate density. The feasibility of using these observables to detect imprints of reionization therefore requires further investigation.« less