Showing papers in "Science China-physics Mechanics & Astronomy in 2020"

Overview to the Hard X-ray Modulation Telescope ( Insight -HXMT) Satellite

Abstract: As China’s first X-ray astronomical satellite, the Hard X-ray Modulation Telescope (HXMT), which was dubbed as Insight -HXMT after the launch on June 15, 2017, is a wide-band (1- 250 keV) slat-collimator-based X-ray astronomy satellite with the capability of all-sky monitoring in 0.2-3 MeV. It was designed to perform pointing, scanning and gamma-ray burst (GRB) observations and, based on the Direct Demodulation Method (DDM), the image of the scanned sky region can be reconstructed. Here we give an overview of the mission and its progresses, including payload, core sciences, ground calibration/facility, ground segment, data archive, software, in-orbit performance, calibration, background model, observations and some preliminary results.

The Giant Radio Array for Neutrino Detection (GRAND): Science and design

Abstract: The Giant Radio Array for Neutrino Detection (GRAND) is a planned large-scale observatory of ultra-high-energy (UHE) cosmic particles, with energies exceeding 108 GeV. Its goal is to solve the long-standing mystery of the origin of UHE cosmic rays. To do this, GRAND will detect an unprecedented number of UHE cosmic rays and search for the undiscovered UHE neutrinos and gamma rays associated to them with unmatched sensitivity. GRAND will use large arrays of antennas to detect the radio emission coming from extensive air showers initiated by UHE particles in the atmosphere. Its design is modular: 20 separate, independent sub-arrays, each of 10000 radio antennas deployed over 10000 km2. A staged construction plan will validate key detection techniques while achieving important science goals early. Here we present the science goals, detection strategy, preliminary design, performance goals, and construction plans for GRAND.

Measurement-device-independent quantum secure direct communication

Abstract: Quantum secure direct communication (QSDC) is a unique technique, which supports the secure transmission of confidential information directly through a quantum channel without the need for a secret key and for ciphertext. Hence this secure communication protocol fundamentally differs from its conventional counterparts. In this article, we report the first measurement-device-independent (MDI) QSDC protocol relying on sequences of entangled photon pairs and single photons. Explicitly, it eliminates the security loopholes associated with the measurement device. Additionally, this MDI technique is capable of doubling the communication distance of its conventional counterpart operating without using our MDI technique. We also conceive a protocol associated with linear optical Bell-basis measurements, where only two of the four Bell-basis states could be measured. When the number of qubits in a sequence reduces to 1, the MDI-QSDC protocol degenerates to a deterministic MDI quantum key distribution protocol.

The recent progress of functionally graded CNT reinforced composites and structures

Abstract: In the last decade, the functionally graded carbon nanotube reinforced composites (FG-CNTRCs) have attracted considerable interest due to their excellent mechanical properties, and the structures made of FG-CNTRCs have found broad potential applications in aerospace, civil and ocean engineering, automotive industry, and smart structures. Here we review the literature regarding the mechanical analysis of bulk CNTR nanocomposites and FG-CNTRC structures, aiming to provide a clear picture of the mechanical modeling and properties of FG-CNTRCs as well as their composite structures. The review is organized as follows: (1) a brief introduction to the functionally graded materials (FGM), CNTRCs and FG-CNTRCs; (2) a literature review of the mechanical modeling methodologies and properties of bulk CNTRCs; (3) a detailed discussion on the mechanical behaviors of FG-CNTRCs; and (4) conclusions together with a suggestion of future research trends.

The Low Energy X-ray telescope (LE) onboard the Insight-HXMT astronomy satellite

Abstract: The Insight -Hard X-ray Modulation Telescope ( Insight -HXMT) is a broadband X-ray and γ-ray (1-3000 keV) astronomy satellite. One of its three main telescopes is the High Energy X-ray telescope (HE). The main detector plane of HE comprises 18 NaI(Tl)/CsI(Na) phoswich detectors, where NaI(Tl) is used as the primary detector to measure ~ 20-250 keV photons incident from the field of view (FOV) defined by collimators, and CsI(Na) is used as the active shielding detector to NaI(Tl) by pulse shape discrimination. Additionally, CsI(Na) is used as an omnidirectional γ-ray monitor. The HE collimators have a diverse FOV, i.e. 1.1°×5.7° (15 units), 5.7°×5.7° (2 units), and blocked (1 unit). Therefore, the combined FOV of HE is approximately 5.7°×5.7°. Each HE detector has a diameter of 190 mm resulting in a total geometrical area of approximately 5100 cm2, and the energy resolution is ~15% at 60 keV. For each recorded X-ray event by HE, the timing accuracy is less than 10 μs and the dead-time is less than 10 μs. HE is used for observing spectra and temporal variability of X-ray sources in the 20-250 keV band either by pointing observations for known sources or scanning observations to unveil new sources. Additionally, HE is used for monitoring the γ-ray burst in 0.2-3 MeV band. This paper not only presents the design and performance of HE instruments but also reports results of the on-ground calibration experiments.

Non-Hermitian topological Anderson insulators

Abstract: Non-Hermitian systems can exhibit exotic topological and localization properties. Here we elucidate the non-Hermitian effects on disordered topological systems using a nonreciprocal disordered Su-Schrieffer-Heeger model. We show that the non-Hermiticity can enhance the topological phase against disorders by increasing bulk gaps. Moreover, we uncovera topological phase which emerges under both moderate non-Hermiticity and disorders, and is characterized by localized insulating bulk states with a disorder-averaged winding number and zero-energy edge modes. Such topological phases induced by the combination of non-Hermiticity and disorders are dubbed non-Hermitian topological Anderson insulators . We reveal that the system has unique non-monotonous localization behavior and the topological transition is accompanied by an Anderson transition. These properties are general in other non-Hermitian models.

The mass of our Milky Way

Abstract: We perform an extensive review of the numerous studies and methods used to determine the total mass of the Milky Way. We group the various studies into seven broad classes according to their modeling approaches. The classes include: i) estimating Galactic escape velocity using high velocity objects; ii) measuring the rotation curve through terminal and circular velocities; iii) modeling halo stars, globular clusters and satellite galaxies with the spherical Jeans equation and iv) with phase-space distribution functions; v) simulating and modeling the dynamics of stellar streams and their progenitors; vi) modeling the motion of the Milky Way, M31 and other distant satellites under the framework of Local Group timing argument; and vii) measurements made by linking the brightest Galactic satellites to their counterparts in simulations. For each class of methods, we introduce their theoretical and observational background, the method itself, the sample of available tracer objects, model assumptions, uncertainties, limits and the corresponding measurements that have been achieved in the past. Both the measured total masses within the radial range probed by tracer objects and the extrapolated virial masses are discussed and quoted. We also discuss the role of modern numerical simulations in terms of helping to validate model assumptions, understanding systematic uncertainties and calibrating the measurements. While measurements in the last two decades show a factor of two scatters, recent measurements using Gaia DR2 data are approaching a higher precision. We end with a detailed discussion of future developments in the field, especially as the size and quality of the observational data will increase tremendously with current and future surveys. In such cases, the systematic uncertainties will be dominant and thus will necessitate a much more rigorous testing and characterization of the various mass determination methods.

Excellent thermoelectric performance in weak-coupling molecular junctions with electrode doping and electrochemical gating

Abstract: Excellent thermoelectric performance in molecular junctions requires a high power factor, a low thermal conductance, and a maximum figure of merit ( ZT ) near the Fermi level. In the present work, we used density functional theory in combination with a nonequilibrium Green’s function to investigate the thermoelectric performance of carbon chain-graphene junctions with both strong-coupling and weak-coupling contact between the electrodes and the molecules. The results revealed that a room temperature ZT of 4 could be obtained for the weak-coupling molecular junction, approximately one order of magnitude higher than that reached by the strong-coupling junction. The reason for this is that strong interfacial scattering suppresses most of the phonon modes in weak-coupling systems, resulting in ultralow phonon thermal conductance. The influence of electrode width, electrode doping, and electrochemical gating on the thermoelectric performance of the weak-coupling system was also investigated, and the results revealed that an excellent thermoelectric performance can be obtained near the Fermi level.

Efficient quantum arithmetic operation circuits for quantum image processing

Abstract: Efficient quantum circuits for arithmetic operations are vital for quantum algorithms. A fault-tolerant circuit is required for a robust quantum computing in the presence of noise. Quantum circuits based on Clifford+T gates are easily rendered fault-tolerant. Therefore, reducing the T-depth and T-Count without increasing the qubit number represents vital optimization goals for quantum circuits. In this study, we propose the fault-tolerant implementations for TR and Peres gates with optimized T-depth and T-Count. Next, we design fault-tolerant circuits for quantum arithmetic operations using the TR and Peres gates. Then, we implement cyclic and complete translations of quantum images using quantum arithmetic operations, and the scalar matrix multiplication. Comparative analysis and simulation results reveal that the proposed arithmetic and image operations are efficient. For instance, cyclic translations of a quantum image produce 50% T-depth reduction relative to the previous best-known cyclic translation.

A data-efficient self-supervised deep learning model for design and characterization of nanophotonic structures

Abstract: With its tremendous success in many machine learning and pattern recognition tasks, deep learning, as one type of data-driven models, has also led to many breakthroughs in other disciplines including physics, chemistry and material science. Nevertheless, the supremacy of deep learning over conventional optimization approaches heavily depends on the huge amount of data collected in advance to train the model, which is a common bottleneck of such a data-driven technique. In this work, we present a comprehensive deep learning model for the design and characterization of nanophotonic structures, where a self-supervised learning mechanism is introduced to alleviate the burden of data acquisition. Taking reflective metasurfaces as an example, we demonstrate that the self-supervised deep learning model can effectively utilize randomly generated unlabeled data during training, with the total test loss and prediction accuracy improved by about 15% compared with the fully supervised counterpart. The proposed self-supervised learning scheme provides an efficient solution for deep learning models in some physics-related tasks where labeled data are limited or expensive to collect.

Can non-standard recombination resolve the Hubble tension?

Abstract: The inconsistent Hubble constant values derived from cosmic microwave background (CMB) observations and from local distance-ladder measurements may suggest new physics beyond the standard $\\Lambda$CDM paradigm. It has been found in earlier studies that, at least phenomenologically, non-standard recombination histories can reduce the $\\gtrsim~4\\sigma$ Hubble tension to $\\sim~2\\sigma$. Following this path, we vary physical and phenomenological parameters in RECFAST, the standard code to compute ionization history of the universe, to explore possible physics beyond standard recombination. We find that the CMB constraint on the Hubble constant is sensitive to the hydrogen ionization energy and $2s~\\rightarrow~1s$ two-photon decay rate, both of which are atomic constants, and is insensitive to other details of recombination. Thus, the Hubble tension is very robust against perturbations of recombination history, unless exotic physics modifies the atomic constants during the recombination epoch.

Quantum coherence of multiqubit states in correlated noisy channels

Abstract: The long-time maintenance of quantum coherence is crucial for its practical applications. We explore decoherence process of a multiqubit system passing through a correlated channel (phase flip, bit flip, bit-phase flip, and depolarizing). The results show that the decay of coherence was evidently delayed when the consecutive actions of the channel on the sequence of qubits has some classical correlations. In particular, the relative entropy of coherence for a system with large number of qubits is more robust than that with small number of qubits. We also provide an explanation for the delayed decoherence by exploring the interplay between the change of the unlocalized quantum coherence and the total correlation gain of the multiqubit system.

Weak-force sensing with squeezed optomechanics

Abstract: We investigate quantum-squeezing-enhanced weak-force sensing via a nonlinear optomechanical resonator containing a movable mechanical mirror and an optical parametric amplifier (OPA). Herein, we determined that tuning the OPA parameters can considerably suppress quantum noise and substantially enhance force sensitivity, enabling the device to extensively surpass the standard quantum limit. This indicates that under realistic experimental conditions, we can achieve ultrahigh-precision quantum force sensing by harnessing nonlinear optomechanical devices.

Deterministic measurement-device-independent quantum secret sharing

Abstract: Multiparty quantum communication ensures information-theoretic security for transmitting private information among multiuser networks. In principle, measurement-device-independent (MDI) techniques can close all detection loopholes while usually utilizing large amounts of quantum resources in basis reconciliation. We propose a three-party MDI quantum secret sharing (QSS) protocol that is secure against all detection attacks and does not require any basis reconciliation, avoiding the corresponding waste arising from it. The proposed protocol allows a sender to divide a private message into two parts and send those parts to different receivers in a deterministic way. The message can only be read through cooperation between the two receivers. Finally, we discuss the generalized extension of a multiparty QSS protocol.

Quantum secure direct communication with entanglement source and single-photon measurement

Abstract: Quantum secure direct communication (QSDC) transmits information directly over a quantum channel. In addition to security in transmission, it avoids loopholes of key loss and prevents the eavesdropper from getting ciphertext. In this article, we propose a QSDC protocol using entangled photon pairs. This protocol differs from existing entanglement-based QSDC protocols because it does not perform Bell-state measurement, and one photon of the entangled pair is measured after the entanglement distribution. It has the advantage of high signal-to-noise ratio due to the heralding function of entanglement pairs, and it also has the relative ease in performing single-photon measurement. The protocol can use a practical entanglement source from spontaneous parametric down-conversion (SPDC); Gottesman-Lo-Lutkenhaus-Preskill theory and the decoy state method give a better estimate of the error rate. Security analysis is completed with Wyner’s wiretap channel theory, and the lower bound of the secrecy capacity is estimated. Numerical simulations were carried out to study the performance of the protocol. These simulations demonstrated that the protocol with a practical SPDC entanglement source performed well and was close to the case with an ideal entanglement source.

Quasi-topological electromagnetism: Dark energy, dyonic black holes, stable photon spheres and hidden electromagnetic duality

Abstract: We introduce the quasi-topological electromagnetism which is defined to be the squared norm of the topological 4-form F ∧ F. A salient property is that its energy-momentum tensor is of the isotropic perfect fluid with the pressure being precisely the opposite to its energy density. It can thus provide a model for dark energy. We study its application in both black hole physics and cosmology. The quasi-topological term has no effect on the purely electric or magnetic Reissner-Nordstrom black holes, the dyonic solution is however completely modified. We find that the dyonic black holes can have four real horizons. For suitable parameters, the black hole can admit as many as three photon spheres, with one being stable. Another intriguing property is that although the quasi-topological term breaks the electromagnetic duality, the symmetry emerges in the on-shell action in the Wheeler-DeWitt patch. In cosmology, we demonstrate that the quasi-topological term alone is equivalent to a cosmological constant, but the model provides a mechanism for the dark energy to couple with other types of matter. We present a concrete example of the quasi-topological electromagnetism coupled to a scalar field that admits the standard FLRW cosmological solutions.

Strain effect on the orientation-dependent harmonic spectrum of monolayer aluminum nitride

Abstract: In this study, we theoretically investigate the strain effect on the orientation-dependent high-order harmonic generation (HHG) of monolayer aluminum nitride (AlN) by solving the multiband semiconductor Bloch equations in strong laser fields. Our simulations denote that the efficiency of the orientation-dependent HHG is considerably enhanced when a 15% biaxial tensile strain is applied to AlN, which is attributed to the downshifting energy level of the conduction band. Furthermore, the odd-even feature in the orientation-dependent high harmonic spectra owing to the strain is considerably different when compared with that in the case without strain. The enhanced quantum interference between different energy bands in strained AlN around the Γ-M direction is responsible for the observed odd-even distributions of the orientation-dependent HHG. This study helps to better understand the HHG in solids by tuning their electronic structures.

Large transverse thermoelectric figure of merit in a topological Dirac semimetal

Abstract: The Seebeck effect encounters a few fundamental constraints hindering its thermoelectric (TE) conversion efficiency. Most notably, there are the charge compensation of electrons and holes that diminishes this effect, and the Wiedemann-Franz (WF) law that makes independent optimization of the corresponding electrical and thermal conductivities impossible. Here, we demonstrate that in the topological Dirac semimetal Cd3As2 the Nernst effect, i.e., the transverse counterpart of the Seebeck effect, can generate a large TE figure of merit z N T . At room temperature, z N T ≈ 0.5 in a small field of 2 T and it significantly surmounts its longitudinal counterpart for any field. A large Nernst effect is generically expected in topological semimetals, benefiting from both the bipolar transport of compensated electrons and holes and their high mobilities. In this case, heat and charge transport are orthogonal, i.e., not intertwined by the WF law anymore. More importantly, further optimization of z N T by tuning the Fermi level to the Dirac node can be anticipated due to not only the enhanced bipolar transport, but also the anomalous Nernst effect arising from a pronounced Berry curvature. A combination of the topologically trivial and nontrivial advantages promises to open a new avenue towards high-efficient transverse thermoelectricity.

Exploring neutrino mass and mass hierarchy in interacting dark energy models

Abstract: We investigate how the dark energy properties impact the constraints on the total neutrino mass in interacting dark energy (IDE) models. In this study, we focus on two typical interacting dynamical dark energy models, i.e., the interacting w cold dark matter (IwCDM) model and the interacting holographic dark energy (IHDE) model. To avoid the large-scale instability problem in IDE models, we apply the parameterized post-Friedmann approach to calculate the perturbation of dark energy. We employ the Planck 2015 cosmic microwave background temperature and polarization data, combined with low-redshift measurements on baryon acoustic oscillation distance scales, type Ia supernovae, and the Hubble constant, to constrain the cosmological parameters. We find that the dark energy properties could influence the constraint limits on the total neutrino mass. Once dynamical dark energy is considered in the IDE models, the upper bounds of ∑ mv will be changed. By considering the values of χ2min, we find that in these IDE models the normal hierarchy case is slightly preferred over the inverted hierarchy case; for example, Δχ2 = 2.720 is given in the IHDE+∑ mv model. In addition, we also find that in the IwCDM+∑ mv model β = 0 is consistent with current observational data inside the 1σ range, and in the IHDE+∑ mv model β > 0 is favored at more than 2σ level.

Search for the doubly charmed baryon $\Xi_{cc}^{+}$

Abstract: A search for the doubly charmed baryon Ξcc+ is performed through its decay to the Λc+K−π+ final state, using proton-proton collision data collected with the LHCb detector at centre-of-mass energies of 7, 8 and 13 TeV. The data correspond to a total integrated luminosity of 9 fb−1. No significant signal is observed in the mass range from 3.4 to 3.8 GeV/c2. Upper limits are set at 95% credibility level on the ratio of the Ξcc+ production cross-section times the branching fraction to that of Λc+ and Ξcc++ baryons. The limits are determined as functions of the Ξcc+ mass for different lifetime hypotheses, in the rapidity range from 2.0 to 4.5 and the transverse momentum range from 4 to 15 GeV/c.

Spin excitations in nickelate superconductors

Abstract: Applying a three-band model and the random phase approximation, we theoretically study the spin excitations in nickelate superconductors, which have been newly discovered. The spin excitations were found to be incommensurate in the low energy region. The spin resonance phenomenon emerged as the excitation energy increased. The intensity can be maximized at the incommensurate or commensurate momentum, depending on the out-of-plane momentum. The spin excitations reverted to incommensurate at higher energies. We also discuss the similarities and differences in the spin excitations of nickelate and cuprate superconductors. Our predicted results can be later validated in inelastic neutron scattering experiments.

Holographic Topological Semimetals

Abstract: The holographic duality allows to construct and study models of strongly coupled quantum matter via dual gravitational theories. In general such models are characterized by the absence of quasiparticles, hydrodynamic behavior and Planckian dissipation times. One particular interesting class of quantum materials are ungapped topological semimetals which have many interesting properties from Hall transport to topologically protected edge states. We review the application of the holographic duality to this type of quantum matter including the construction of holographic Weyl semimetals, nodal line semimetals, quantum phase transition to trivial states (ungapped and gapped), the holographic dual of Fermi arcs and how new unexpected transport properties, such as Hall viscosities arise. The holographic models promise to lead to new insights into the properties of this type of quantum matter.

Forecast for weighing neutrinos in cosmology with SKA

Abstract: We investigate what role the SKA neutral hydrogen (HI) intensity mapping (IM) and galaxy sky surveys will play in weighing neutrinos in cosmology. We use the simulated data of the baryon acoustic oscillation (BAO) measurements from the HI surveys based on SKA1 (IM) and SKA2 (galaxy) to do the analysis. For the current observations, we use the Planck 2015 cosmic microwave background (CMB) anisotropies observation, the optical BAO measurements, the type Ia supernovae (SN) observation (Pantheon compilation), and the latest H0 measurement. We consider three mass ordering cases for massive neutrinos, i.e., the normal hierarchy (NH), inverted hierarchy (IH), and degenerate hierarchy (DH) cases. It is found that the SKA observation can significantly improve the constraints on Ωm and H0. Compared to the current observation, the SKA1 data can improve the constraints on Ωm by about 33%, and on H0 by about 36%; the SKA2 data can improve the constraints on Ωm by about 58%, and on H0 by about 66%. It is also found that the SKA observation can only slightly improve the constraints on ∑mv. Compared to the current observation, the SKA1 data can improve the constraints on ∑mv by about 4%, 3%, and 10%, for the NH, IH, and DH cases, respectively; the SKA2 data can improve the constraints on ∑mv by about 7%, 7%, and 16%, for the NH, IH, and DH cases, respectively.

β-Ga 2 O 3 MOSFETs on the Si substrate fabricated by the ion-cutting process

Abstract: β-Ga2O3 MOSFETs are demonstrated on heterogeneous Ga2O3-Al2O3-Si (GaOISi) substrate fabricated by ion-cutting process. Enhancement (E)- and depletion (D)-mode β-Ga2O3 transistors are realized on by varying the channel thickness ( T ch). E-mode GaOISi transistor with a T ch of 15 nm achieves a high threshold voltage V TH of ~ 8 V. With the same T increase, GaOISi transistors demonstrate more stable ON-current I ON and OFF-current I OFF performance compared to the reported devices on bulk Ga2O3 wafer. Transistors on GaOISi achieve the breakdown voltage of 522 and 391 V at 25°C and 200°C, respectively.

Anharmonic multi-phonon nonradiative transition: An ab initio calculation approach

Abstract: Nonradiative carrier recombinations at deep centers in semiconductors are of great importance for both fundamental physics and device engineering. In this article, we provide a revised analysis of Huang’s original nonradiative multi-phonon (NMP) theory with ab initio calculations. First, we confirmed at the first-principles level that Huang’s concise formula gives the same results as the matrix-based formula, and that Huang’s high-temperature formula provides an analytical expression for the coupling constant in Marcus theory. Secondly, we correct for anharmonic effects by taking into account local phonon-mode variations for different charge states of a defect. The corrected capture rates for defects in GaN and SiC agree well with experiments.

Strong Pauli paramagnetic effect in the upper critical field of KCa 2 Fe 4 As 4 F 2

Abstract: Recently, 12442 system of Fe-based superconductors has attracted considerable attention owing to its unique double-FeAs-layer structure. A steep increase in the in-plane upper critical field with cooling has been observed near the superconducting transition temperature, $T_{\rm~c}$, in KCa$_2$Fe$_4$As$_4$F$_2$ single crystals.Herein, we report a high-field investigation on upper critical field of this material over a wide temperature range, and both out-of-plane ($H\|c$, $H_{c2}^{c}$) and in-plane ($H\|ab$, $H_{c2}^{ab}$) directions have been measured.A sublinear temperature-dependent behavior is observed for the out-of-plane $H_{c2}^{c}$, whereas strong convex curvature with cooling is observed for the in-plane $H_{c2}^{ab}$.Such behaviors could not be described by the conventional Werthamer-Helfand-Hohenberg (WHH) model. The data analysis based on the WHH model by considering the spin aspects reveals a largeMaki parameter $\alpha=9$, indicating thatthe in-plane upper critical field is affected by a very strong Pauli paramagnetic effect.

On-shell methods for form factors in N =4 SYM and their applications

Abstract: Form factors are quantities that involve both asymptotic on-shell states and gauge invariant operators. They provide a natural bridge between on-shell amplitudes and off-shell correlation functions of operators, thus allowing us to use modern on-shell amplitude techniques to probe into the off-shell side of quantum field theory. In particular, form factors have been successfully used in computing the cusp (soft) anomalous dimensions and anomalous dimensions of general local operators. This review is intended to provide a pedagogical introduction to some of these developments. We will first review some amplitudes background using four-point amplitudes as main examples. Then we generalize these techniques to form factors, including (1) tree-level form factors, (2) Sudakov form factor and infrared singularities, and (3) form factors of general operators and their anomalous dimensions. Although most examples we consider are in $$\mathcal{N}=4$$ super-Yang-Mill theory, the on-shell methods are universal and are expected to be applicable to general gauge theories.

Ground state properties and potential energy surfaces of 270 Hs from multidimensionally-constrained relativistic mean field model

Abstract: We study the ground state properties, potential energy curves and potential energy surfaces of the superheavy nucleus 270Hs by using the multidimensionally-constrained relativistic mean-field model with the effective interaction PC-PK1. The binding energy, size and shape as well as single particle shell structure corresponding to the ground state of this nucleus are obtained. 270Hs is well deformed and exhibits deformed doubly magic feature in the single neutron and proton level schemes. One-dimensional potential energy curves and two-dimensional potential energy surfaces are calculated for 270Hs with various spatial symmetries imposed. We investigate in detail the effects of the reflection asymmetric and triaxial distortions on the fission barrier and fission path of 270Hs. When the axial symmetry is imposed, the reflection symmetric and reflection asymmetric fission barriers both show a double-hump structure and the former is higher. However, when triaxial shapes are allowed the reflection symmetric barrier is lowered very much and then the reflection symmetric fission path becomes favorable.

Ga 2 O 3 solar-blind position-sensitive detectors

Abstract: Monoclinic Ga2O3 (β-Ga2O3) is a promising material for achieving solar-blind photodetection because of its unique characteristics, including its high breakdown electric field, radiation hardness, thermal and chemical stabilities, and intrinsic visible/solar-blind properties. Until now, several studies have investigated the development of high-performance β-Ga2O3 solar-blind photodetectors. However, these photodetectors can only detect the light intensity but not the light position. In this work, four-quadrant position-sensitive detectors (4Q-PSDs) were developed and demonstrated based on β-Ga2O3. 4Q-PSDs, comprising four identical metal-semiconductor-metal-structured photodetector components, demonstrate high uniformity, large signal-to-noise ratio, good ultraviolet/visible rejection ratio, and fast response/recovery time. Subsequently, the position of the illumination beam can be determined by analyzing the output signals of the four photodetector components. This work may indicate the promising application potential of the Ga2O3-based photodetectors in the fields of positioning, aligning, and monitoring the solar-blind beams.

A gigaparsec-scale local void and the Hubble tension

Abstract: We explore the possibility of using a gigaparsec-scale local void to reconcile the Hubble tension. Such a gigaparsec-scale void can be produced by multi-stream inflation where different parts of the observable universe follow different inflationary trajectories. These trajectories become different parts of the observable universe after inflation, when these scales return to the horizon. If these trajectories have different e-folding numbers, these parts of the universe have different energy densities, possibly creating a local large void. The impacts of such a void for cosmological observations are studied, especially those involving supernovae, Baryon Acoustic Oscillations (BAO) and the kinetic Sunyaev-Zel’dovich (kSZ) effect. We show that with the presence of the void, supernovae observations may be more consistent with the CMB. We also estimate the impacts of a local large void on BAO observations. In addition, we show that a local large void and hence its capabilities to ease the Hubble tension is limited by the kSZ effect. As a benchmark model, a 1.7 Gpc scale void with boundary width 0.7 Gpc and density contrast −0.14 may ease the Hubble tension, evading the kSZ limit.