Refinement of primary Si in hypereutectic Al-Si alloys by intensive melt shearing

Hypereutectic Al-Si based alloys are gaining popularity for applications where a combination of light weight and high wear resistance is required. The high wear resistance arising from the hard primary Si particles comes at the price of extremely poor machine tool life. To minimize machining problems while exploiting outstanding wear resistance, the primary Si particles must be controlled to a uniform small size and uniform spatial distribution. The current industrial means of refining primary Si chemically by the addition of phosphorous suffers from a number of problems. In the present paper an alternative, physical means of refining primary Si by intensive shearing of the melt prior to casting is investigated. Al-15wt%Si alloy has been solidified under varying casting conditions (cooling rate) and the resulting microstructures have been studied using microscopy and quantitative image analysis. Primary Si particles were finer, more compact in shape and more numerous with increasing cooling rate. Intensive melt shearing led to greater refinement and more enhanced nucleation of primary Si than was achieved by adding phosphorous. The mechanism of enhanced nucleation is discussed.EPSRC (grant EP/H026177/1)

Correlates of Mental Health After COVID-19 Bereavement in Mainland China

Context: Pioneering empirical studies show that people bereaved due to COVID-19 experience elevated acute grief, posttraumatic stress, anxiety, and depressive symptom levels, which relate to functional impairment. However, studies focused on Western samples and multivariate analyses of relations between potential risk factors and mental health in this population are lacking. Objectives: To assess the mental health of Chinese adults bereaved due to COVID-19. To elucidate the associations of demographic and loss-related characteristics with mental health after COVID-19 bereavement. Methods: Four hundred twenty-two Chinese adults (56% male; Mean age: 32.73 years) recently bereaved due to COVID-19 completed an online survey. Demographic and loss-related characteristics and prolonged grief, posttraumatic stress, anxiety, and depressive symptoms were assessed. Results: Clinically relevant prolonged grief (49%, n = 207), posttraumatic stress (22%, n = 92), depressive (70%; n = 294), and anxiety symptoms (65%; n = 272) were reported by a substantial group of participants. In four multiple regressions predicting each mental health indicator, Fs(15,406) = 5.08–7.74, Ps < 0.001, loss-characteristics (i.e., a shorter time since loss, βs = -.12–.11, loss of a first-degree relative, βs = .18-.37) and subjective loss experiences (i.e., feeling traumatized by the loss, βs = .13-.18, or a close and/or conflictual relation with the deceased, βs = .12-.23) related most consistently to mental health problems. Conclusion: Many Chinese adults bereaved due to COVID-19 experience severe mental health problems. The recent loss of first-degree relatives, feeling traumatized by the loss, and having a close and/or conflictual relationship with the deceased may elevate risk for these mental health problems, which could require indicated psychological treatment

A right-handed isotropic medium with a negative refractive index

The sign of the refractive index of any medium is soley determined by the requirement that the propagation of an electromagnetic wave obeys Einstein causality. Our analysis shows that this requirement predicts that the real part of the refractive index may be negative in an isotropic medium even if the electric permittivity and the magnetic permeability are both positive. Such a system may be a route to negative index media at optical frequencies. We also demonstrate that the refractive index may be positive in left-handed media that contain two molecular species where one is in its excited state.Comment: 4.1 pages, 4 figures, submitted to Physical Review Letter

Optical Monitoring of 3C 390.3 from 1995 to 2004 and Possible Periodicities in the Historical Light Curve

We report V, R, and I band CCD photometry of the radio galaxy 3C 390.3 obtained with the 1.56-m telescope of the Shanghai Astronomical Observatory from March 1995 to August 2004. Combining these data with data from the literature, we have constructed a historical light curve from 1894 to 2004 and searched for periodicities using the CLEANest program. We find possible periods of 8.30+-1.17, 5.37+-0.49, 3.51+-0.21, and 2.13+-0.08 years.Comment: Accepted by AJ, 34 pages, 11 figure

General Quantum Key Distribution in Higher Dimension

We study a general quantum key distribution protocol in higher dimension. In this protocol, quantum states in arbitrary $g+1$ ($1\le g\le d$) out of all $d+1$ mutually unbiased bases in a d-dimensional system can be used for the key encoding. This provides a natural generalization of the quantum key distribution in higher dimension and recovers the previously known results for $g=1$ and $d$. In our investigation, we study Eve's attack by two slightly different approaches. One is considering the optimal cloner for Eve, and the other, defined as the optimal attack, is maximizing Eve's information. We derive results for both approaches and show the deviation of the optimal cloner from the optimal attack. With our systematic investigation of the quantum key distribution protocols in higher dimension, one may balance the security gain and the implementation cost by changing the number of bases in the key encoding. As a side product, we also prove the equivalency between the optimal phase covariant quantum cloning machine and the optimal cloner for the $g=d-1$ quantum key distribution

An ultra-luminous quasar at z=5.363 with a ten billion solar mass black hole and a Metal-Rich DLA at z~5

We report the discovery of an ultra-luminous quasar J030642.51+185315.8 (hereafter J0306+1853) at redshift 5.363, which hosts a super-massive black hole (SMBH) with $M_{BH} = (1.07 \pm 0.27) \times10^{10}~M_\odot$. With an absolute magnitude $M_{1450}=-28.92$ and bolometric luminosity $L_{bol}\sim3.4\times10^{14} L_{\odot}$, J0306+1853 is one of the most luminous objects in the early Universe. It is not likely to be a beamed source based on its small flux variability, low radio loudness and normal broad emission lines. In addition, a $z=4.986$ Damped Ly$\alpha$ system (DLA) with $\rm [M/H]=-1.3\pm0.1$, among the most metal rich DLAs at $z \gtrsim 5$, is detected in the absorption spectrum of this quasar. This ultra-luminous quasar puts strong constraint on the bright-end of quasar luminosity function and massive-end of black hole mass function. It will provide a unique laboratory to the study of BH growth and the co-evolution between BH and host galaxy with multi-wavelength follow-up observations. The future high resolution spectra will give more insights to the DLA and other absorption systems along the line-of-sight of J0306+1853.Comment: 5 pages, 3 figures, accepted for publication in ApJ

State diagram for packed granular particles under shear: two types of /quaking/ and "shear unjamming"

Understanding intermittency, an ubiquitous behavior in flows of packed grains, is pivotal for establishing the rheology of granular material. A straightforward explanation has been missing despite the long development of theories at different levels of abstraction. In this work, we propose the use of a Stribeck-Hertz model that starts with the classic Coulomb friction but also takes into account the tribology between particles, i.e. the reduction of friction coefficient with speed as is commonly observed. Our numerical studies reveal a state diagram covering a wide range of packing fractions, and produce the quaking intermittency in the mid-range of a dimensionless shear rate defined accordingly, in consistence with our recent experimental observation [Phys. Rev. Lett. 126.128001 (2021)]. Monitoring the change of mean contact number allows us to distinguish two types of quaking. Above the random-close-packing density, the quakes are exclusively of the first type, occurred with a sudden increase of the contact number. At lower packing fractions, the dominant quaking depends in part on the dimensionless shear rate. The second type of quaking is identified as the prelude for a granular packing to "unjam" upon increase of the dimensionless shear rate -- a phenomenon that occurs only when the essential tribology is taken into accoun

Neurobiological Changes of Schizotypy: Evidence From Both Volume-Based Morphometric Analysis and Resting-State Functional Connectivity

The current study sought to examine the underlying brain changes in individuals with high schizotypy by integrating networks derived from brain structural and functional imaging. Individuals with high schizotypy (n = 35) and low schizotypy (n = 34) controls were screened using the Schizotypal Personality Questionnaire and underwent brain structural and resting-state functional magnetic resonance imaging on a 3T scanner. Voxel-based morphometric analysis and graph theory-based functional network analysis were conducted. Individuals with high schizotypy showed reduced gray matter (GM) density in the insula and the dorsolateral prefrontal gyrus. The graph theoretical analysis showed that individuals with high schizotypy showed similar global properties in their functional networks as low schizotypy individuals. Several hubs of the functional network were identified in both groups, including the insula, the lingual gyrus, the postcentral gyrus, and the rolandic operculum. More hubs in the frontal lobe and fewer hubs in the occipital lobe were identified in individuals with high schizotypy. By comparing the functional connectivity between clusters with abnormal GM density and the whole brain, individuals with high schizotypy showed weaker functional connectivity between the left insula and the putamen, but stronger connectivity between the cerebellum and the medial frontal gyrus. Taken together, our findings suggest that individuals with high schizotypy present changes in terms of GM and resting-state functional connectivity, especially in the frontal lobe

Criteria for the experimental observation of multi-dimensional optical solitons in saturable media

Criteria for experimental observation of multi-dimensional optical solitons in media with saturable refractive nonlinearities are developed. The criteria are applied to actual material parameters (characterizing the cubic self-focusing and quintic self-defocusing nonlinearities, two-photon loss, and optical-damage threshold) for various glasses. This way, we identify operation windows for soliton formation in these glasses. It is found that two-photon absorption sets stringent limits on the windows. We conclude that, while a well-defined window of parameters exists for two-dimensional solitons (spatial or spatiotemporal), for their three-dimensional spatiotemporal counterparts such a window \emph{does not} exist, due to the nonlinear loss in glasses.Comment: 8 pages, to appear in Phys. Rev.