Momentum contrastive learning for few-shot COVID-19 diagnosis from chest CT images.

The current pandemic, caused by the outbreak of a novel coronavirus (COVID-19) in December 2019, has led to a global emergency that has significantly impacted economies, healthcare systems and personal wellbeing all around the world. Controlling the rapidly evolving disease requires highly sensitive and specific diagnostics. While RT-PCR is the most commonly used, it can take up to eight hours, and requires significant effort from healthcare professionals. As such, there is a critical need for a quick and automatic diagnostic system. Diagnosis from chest CT images is a promising direction. However, current studies are limited by the lack of sufficient training samples, as acquiring annotated CT images is time-consuming. To this end, we propose a new deep learning algorithm for the automated diagnosis of COVID-19, which only requires a few samples for training. Specifically, we use contrastive learning to train an encoder which can capture expressive feature representations on large and publicly available lung datasets and adopt the prototypical network for classification. We validate the efficacy of the proposed model in comparison with other competing methods on two publicly available and annotated COVID-19 CT datasets. Our results demonstrate the superior performance of our model for the accurate diagnosis of COVID-19 based on chest CT images.

Strain induced new phase and indirect-direct band gap transition of monolayer InSe.

The effect of in-plane strain on monolayer InSe has been systematically investigated by using first-principles calculations. It is found that monolayer InSe exhibits superior mechanical flexibility, which can sustain a tensile strain up to 27% in the armchair direction. More importantly, a new phase with inversion symmetry denoted as phase-II is obtained when the tensile strain increases over 25% along the zigzag direction, which is predicted to be metallic and thermodynamically stable at room temperature. And the phase-II InSe could show an out-of-plane negative Poisson's ratio after the uniaxial tensile strain is larger than 5%. Moreover, both uniaxial and biaxial compressive strains can trigger the indirect-to-direct band gap transition in the pristine monolayer InSe and its band gap decreases monotonously with the applied tensile strain, which offers an effective method to tune the electronic properties of monolayer InSe for its promising application in electronics and optoelectronics.

Predicted Quantum Topological Hall Effect and Noncoplanar Antiferromagnetism in K_{0.5}RhO_{2}.

The quantum anomalous Hall (QAH) phase is a two-dimensional bulk ferromagnetic insulator with a nonzero Chern number in the presence of spin-orbit coupling (SOC) but in the absence of applied magnetic fields. Associated metallic chiral edge states host dissipationless current transport in electronic devices. This intriguing QAH phase has recently been observed in magnetic impurity-doped topological insulators, albeit, at extremely low temperatures. Based on first-principles density functional calculations, here we predict that layered rhodium oxide K_{0.5}RhO_{2} in the noncoplanar chiral antiferromagnetic state is an unconventional three-dimensional QAH insulator with a large band gap and a Néel temperature of a few tens of Kelvins. Furthermore, this unconventional QAH phase is revealed to be the exotic quantum topological Hall effect caused by nonzero scalar spin chirality due to the topological spin structure in the system and without the need of net magnetization and SOC.

Two new phases of monolayer group-IV monochalcogenides and their piezoelectric properties.

Two stable structural phases of the monolayer group-IV monochalcogenides GeS, GeSe, SnS and SnSe have been found using first-principles calculations, and will be called as A-MX and H-MX. It is found that these two new phases are energetically nearly degenerate with the pristine phase Z-MX and are semiconductors for all four group-IV monochalcogenides. The band gaps of A-MX range from 1.62 eV to 1.86 eV, while H-MX exhibits wider band gaps in the range from 2.21 eV to 2.47 eV. Moreover, both of them exhibit significant piezoelectric properties. The piezoelectric coefficient of A-MX is about 1-2 orders of magnitude higher than those of other frequently used piezoelectric materials, showing obvious anisotropic characters, while that of H-MX is isotropic and comparable with those of other piezoelectric materials.

Geometric and electronic structures of mono- and di-vacancies in phosphorene.

The geometric structures, stabilities and diffusions of the monovacancy (MV) and divacancy (DV) in two-dimensional phosphorene, as well as their influences on their vibrational and electronic properties have been studied by first-principles calculations. Two possible MVs and 14 possible DVs have been found in phosphorene, in which the MV-(5|9) with a pair of pentagon-nonagon is the ground state of MVs, and the DV-(5|8|5) with a pentagon-octagon-pentagon structure is the most stable DV. All 14 DVs could be divided into four basic types based upon their topological structures and transform between different configurations via bond rotations. The diffusion of MV-(5|9) is found to exhibit an anisotropic character, preferring to migrate along the zigzag direction in the same half-layer. The introduction of MV and DV in phosphorene influences its vibrational properties, inducing the localized defect modes, which could be used to distinguish different vacancy structures. The MVs and DVs also have a significant influence on the electronic properties of phosphorene. It is found that the phosphorene with MV-(5|9) is a ferromagnetic semiconductor with the magnetic moment of 1.0 µB and a band gap of about 0.211 eV, while the DV induces a direct-indirect band gap transition. Our calculation results on the MV and DV in phosphorene are important for the promising application of the phosphorene in the nanoelectronics.

Substrate effects on the monovacancies of silicene: studied from first principle methods.

The geometrical structures and electronic properties of defective silicene with monovacancies (MVs), placed on two different substrates, a h-BN sheet and an Ag(111) surface, have been investigated using the first-principles method. It is found that due to the weak van der Waals interaction from the h-BN sheet, there exists two kinds of MVs in the Si|h-BN composite, i.e., the self-healing MV-1 and MV-2 with a closed five- and nine-membered (5-9) pair of rings, with the former as the ground state MV, which is the same as in the case of the free-standing silicene with MVs. The electronic bands around the Fermi level of the Si|h-BN composite with the Si MVs are all induced by the Si atoms, leading to a nonmagnetically metallic ground state. But the Ag(111) substrate has a stronger coupling with the Si adlayer, leading to the existence of three kinds of inequivalent Si atoms, greatly changing the MV structures and the stability of the defective silicene adlayer, as well as its corresponding electronic structures. For example, the symmetric-like MVs are found to always be the stable MV structures in the Si|Ag(111) composite, no matter which type of inequivalent Si atom is removed from it. The Ag substrate has a dominant contribution to the electronic bands of the defective Si|Ag(111) composite with the Si MVs. Even so, some characteristic bands induced by the Si MV defects could still be found.

Stabilities and electronic properties of monolayer MoS2 with one or two sulfur line vacancy defects.

Stimulated by the recent experimental observation that single sulfur vacancies in monolayer MoS2 are mobile under the electron beam and easily agglomerate into the sulfur line vacancy defects [Phys. Rev. B: Condens. Matter Mater. Phys., 2013, 88, 035301], the stabilities and electronic properties of monolayer MoS2 with one or two staggered sulfur line vacancy defects (SV or DV), along the armchair or zigzag direction (AC-SV, AC-DV or ZZ-SV, ZZ-DV), have been investigated systematically by first-principles calculations. It is found that: (1) The ZZ-types (ZZ-SV and ZZ-DV) are more stable at different line vacancy densities than the AC-types (AC-SV and AC-DV), which is in good agreement with previous experimental findings. (2) More interestingly, it is predicted from our numerical calculations that, in the same ZZ-types, the ZZ-DV is more stable than the ZZ-SV, indicating that two separate ZZ-SV line vacancy defects tend to move closely to each other for coalescing into a ZZ-DV, which is in contrast to the AC-type with AC-SV being a little more stable than the AC-DV. (3) The monolayer MoS2 with the AC-SV or AC-DV are both semiconductors with a direct or an indirect band gap, respectively, both of which are significantly smaller than that of the perfect monolayer. (4) Furthermore, the out-of-plane distortion induced by strain release in the monolayer MoS2 with ZZ-SV or ZZ-DV is more severe than that with the AC-type, which can further considerably decrease the system's gap value or even make the gap nearly closed. Our calculation results will be helpful in future nanoelectronics and nanoelectromechanics based on MoS2 materials.

Mechanical and electronic properties of monolayer and bilayer phosphorene under uniaxial and isotropic strains.

The mechanical and electronic properties of both the monolayer and bilayer phosphorenes under either isotropic or uniaxial strain have been systematically investigated using first-principles calculations. It is interesting to find that: 1) Under a large enough isotropic tensile strain, the monolayer phosphorene would lose its pucker structure and transform into a flat hexagonal plane, while two inner sublayers of the bilayer phosphorene could be bonded due to its interlayer distance contraction. 2) Under the uniaxial tensile strain along a zigzag direction, the pucker distance of each layer in the bilayer phosphorene can exhibit a specific negative Poisson's ratio. 3) The electronic properties of both the monolayer and bilayer phosphorenes are sensitive to the magnitude and direction of the applied strains. Their band gaps decrease more rapidly under isotropic compressive strain than under uniaxial strain. Also, their direct-indirect band gap transitions happen at the larger isotropic tensile strains compared with that under uniaxial strain. 4) Under the isotropic compressive strain, the bilayer phosphorene exhibits a transition from a direct-gap semiconductor to a metal. In contrast, the monolayer phosphorene initially has the direct-indirect transition and then transitions to a metal. However, under isotropic tensile strain, both the bilayer and monolayer phosphorene show the direct-indirect transition and, finally, the transition to a metal. Our numerical results may open new potential applications of phosphorene in nanoelectronics and nanomechanical devices by external isotropic strain or uniaxial strain along different directions.

Electronic and magnetic properties of boron nitride nanoribbons with square-octagon (4 | 8) line defects.

The electronic and magnetic properties of boron nitride nanoribbons (BNNRs) with square-octagon (4 | 8) line defects (LD-(4 | 8)), parallel to their edges, have been investigated by first-principles calculations. It is found that the zigzag type LD-(4 | 8) BNNR with boron terminated edges is an antiferromagnetic (AFM' + - + -') insulator with an indirect bandgap, but that with nitrogen terminated edges has two degenerate ground states with the same energy, among which one is ferromagnetic (FM ' + + + +') half-metallic and the other is AFM ' + + - -' metallic. In contrast, it is more interesting to find that the bare and fully-hydrogen terminated armchair edge BNNRs with unsymmetric (4 | 8) line defects have an indirect and direct gap, respectively, both of which show a characteristic three family oscillation behavior, depending only on the ribbon width in its narrower part, but not the whole BNNR's width. Finally, the stabilities of a two-dimensional h-BN sheet with a zigzag or armchair type LD-(4 | 8) in it are further confirmed, among which the one with the armchair type LD-(4 | 8) is much more stable than that with the zigzag type counterpart.

The oral administration of Lacticaseibacillus casei Shirota alleviates acetaminophen-induced liver injury through accelerated acetaminophen metabolism via the liver-gut axis in mice.

Acetaminophen is a widely used antipyretic and analgesic drug, and its overdose is the leading cause of drug-induced acute liver failure. This study aimed to investigate the effect and mechanism of Lacticaseibacillus casei Shirota (LcS), an extensively used and highly studied probiotic, on acetaminophen-induced acute liver injury. C57BL/6 mice were gavaged with LcS suspension or saline once daily for 7 days before acute liver injury was induced via intraperitoneal injection of 300 mg/kg acetaminophen. The results showed that LcS significantly decreased acetaminophen-induced liver and ileum injury, as demonstrated by reductions in the increases in aspartate aminotransferase, total bile acids, total bilirubin, indirect bilirubin, and hepatic cell necrosis. Moreover, LcS alleviated acetaminophen-induced intestinal mucosal permeability, decreased serum IL-1α and lipopolysaccharide levels, and elevated serum eosinophil chemokine (eotaxin) and hepatic glutathione levels. Furthermore, analysis of the gut microbiota and metabolome showed that LcS reduced the acetaminophen-enriched levels of Cyanobacteria, Oxyphotobacteria, long-chain fatty acids, cholesterol, and sugars in the gut. Additionally, the transcriptomic and proteomic results showed that LcS mitigated the decrease in metabolic and immune pathways as well as glutathione formation during acetaminophen-induced acute liver injury. This is the first study showing that pretreatment with LcS alleviates acetaminophen-enriched acute liver injury, and it provides a reference for the application of LcS.IMPORTANCEAcetaminophen is the most frequently used antipyretic analgesic worldwide. As a result, overdoses easily occur and lead to drug-induced acute liver injury, which quickly progresses to liver failure with a mortality of 60%-80% if not corrected in time. The current emergency treatment for overused acetaminophen needs to be administered within 8 hours to avoid liver injury or even liver failure. Therefore, developing preventive strategies for liver injury during planned acetaminophen medication is particularly important, preferably nonpharmacological methods. Lacticaseibacillus casei Shirota (LcS) is a famous probiotic that has been used for many years. Our study found that LcS significantly alleviated acetaminophen-induced acute liver injury, especially acetaminophen-induced liver injury toward fulminant hepatic failure. Here, we elucidated the function and potential mechanisms of LcS in alleviating acetaminophen-induced acute liver injury, hoping it will provide preventive strategies to people during acetaminophen treatment.

First-principles simulations on suspended coinage-metal nanotubes composed of different atomic species.

Substitutional doping of gold and copper atoms in a (4, 4) silver single-wall nanotube has been investigated using first-principles simulations. It is found that the Au- and Cu-substitutional doping of the tip-suspended (4, 4) Ag tube can maintain the hollow tubular structure at different alloy compositions due to the existence of a local minimum in the string tension variation with their unit cell lengths. The bonding energy differences between the mono-elements and hetero-elements and string tension may play important roles in suppressing the "self-purification" effects so that the nanoalloy tubes can be formed. Analysis of the band structure suggests that the number of conduction channels of the Ag-Au alloy tubes may lie between the pure (4, 4) Ag and Au tubes.

Formation of single-walled bimetallic coinage alloy nanotubes in confined carbon nanotubes: molecular dynamics simulations.

The growth of single-walled bimetallic Au-Ag, Au-Cu and Ag-Cu alloy nanotubes (NTs) and nanowires (NWs) in confined carbon nanotubes (CNTs) has been investigated by using the classical molecular dynamics (MD) method. It is found that three kinds of single-walled gold-silver, gold-copper and silver-copper alloy NTs could indeed be formed in confined CNTs at any alloy concentration, whose geometric structures are less sensitive to the alloy concentration. And an extra nearly pure Au (Cu) chain will exist at the center of Au-Ag (Au-Cu and Ag-Cu) NTs when the diameters of the outside CNTs are big enough, thus producing a new type of tube-like alloy NWs. The bonding energy differences between the mono- and hetero-elements of the coinage metal atoms and the quasi-one-dimensional confinement from the CNT play important roles in suppressing effectively the "self-purification" effects, leading to formation of these coinage alloy NTs. In addition, the fluid-solid phase transition temperatures of the bimetallic alloy NTs are found to locate between those of the corresponding pure metal tubes. Finally, the dependences of the radial breathing mode (RBM) frequencies and the tube diameters of the alloy NTs on the alloying concentration were obtained, which will be very helpful for identifying both the alloying concentration and the alloy tube diameters in future experiments.

A new (2 × 1) dimerized structure of monolayer 1T-molybdenum disulfide, studied from first principles calculations.

The geometric, electronic, and vibrational properties of monolayer 1T-molybdenum disulfide (MoS2) have been studied by using the first-principles calculations. A new (2 × 1) dimerized structure of monolayer 1T-MoS2, called as 1T'-MoS2, has been found, which is semi-conducting and more stable than the previously found ones. Interestingly, a semiconductor-metal transition is found under an applied tensile strain at about 4% or a compressive strain at about 5%, while the dimerization structure has been retained under both the tensile and compressive strains. Moreover, the vibrational properties of three kinds of monolayer MoS2, i.e., the 1T-MoS2, 1T'-MoS2, as well as the 1H-MoS2, have been studied, based upon which the different isomer structures of monolayer MoS2 can be easily distinguishable in experiments by analyzing their characteristic Raman spectra.

A new (2 × 1) reconstructed edge structure of zigzag Si nanoribbon: first principles study.

Based upon the first principles calculations, a new (2 × 1) reconstructed edge structure (edge-4) with a triangle-pentagon pair topological defect at its edges is found for the zigzag Si nanoribbon, which is different from the previously found ones (edge-2 and edge-3) and more stable in energy than them. More interestingly, it is found that the edge-2 and edge-3 can transform into the new edge-4 under a little bit compression force along the ribbon edge, and the edge-4 could also be transformed into the edge-3 by a tensile strain larger than 9%. The calculated vibrational modes of the edge-4 show that two new characteristic vibrational edge defect modes appear at 434 cm(-1) and 515 cm(-1), which could be used in experiment to distinguish easily the new edge-4 from the edge-2 and edge-3. Finally, a sharp peak near the Fermi level is found to exist in the projected density of states from the edge's pz orbital of edge-4, making its energy bands spin-split and the antiferromagnetic state to be its ground state.

Identification and Functional Characterization of Two Chitin Synthases in the Black Cutworm, Agrotis ipsilon (Hufnagel) (Lepidoptera: Noctuidae).

The black cutworm, Agrotis ipsilon (Hufnagel), a seasonal migrant and a prolific generalist, can feed on nearly all vegetables and grain crops, causing considerable economic impacts on a global scale. Given its cryptic nature, A. ipsilon management has been extremely challenging. Chitin synthase (CHS), a key enzyme involved in chitin biosynthetic pathway and crucially important for the growth and development of insects, is the molecular target of chitin synthesis inhibitors, a group of broad-spectrum insecticides that is compatible with Integrated Pest Management practices. In this study, we investigated the potential of targeting chitin synthases to control A. ipsilon. As a result, two chitin synthases, AiCHS1 and AiCHS2, were identified and cloned from A. ipsilon. The temporal-spatial distribution study showed that AiCHS1 was predominantly expressed at the pupal stage and most abundant among tissues of head capsule and integument, while AiCHS2 was mainly expressed at the sixth instar larval stage and tissues of foregut and midgut. RNAi-based functional study confirmed gene silencing caused significant reduction in the expression levels of the corresponding mRNA, as well as resulted in abnormal pupation and mortality, respectively. Furthermore, under the treatment of lufenuron, a chitin synthesis inhibitor, A. ipsilon responded with an elevated expression in AiCHS1 and AiCHS2, while larvae showed difficulty in shedding old cuticle, and a cumulative mortality of 69.24% at 48 h. In summary, chitin synthases are crucial for chitin biosynthesis in A. ipsilon and can be targeted for the control (e.g., RNAi-based biopesticides) of this devastating insect pest.

Zitterbewegung in the honeycomb photonic lattice.

The propagation of a wave packet in a honeycomb photonic lattice has been studied using the time-dependent wave packet dynamics. It is found that the wave packet, superposed from the positive and negative energy modes at the vicinity of the two inequivalent Dirac points, can transform into a double-ring structure, which is caused by the interference between the two positive and negative energy modes around the Dirac points and is closely related to the Zitterbewegung (ZB). Also, a possible way to detect the ZB effect is proposed in the honeycomb photonic lattice.

Coinage metal (4, 4) nanotubes, simulated by first-principles calculations.

The structural stability of coinage metal nanotubes with a square cross-section has been investigated by the first-principles numerical simulations. In addition to the reported (4, 4) silver tube, it is found that the hollow (4, 4) copper and gold nanotubes can also be formed by applying an appropriate stress to an 8(A)/8(B) fcc wire. The stability of these coinage metal (4, 4) nanotubes, formed by tip-stretching the wires, has been explained by a local minimum in the string tension variation with their tube lengths. Interestingly, we have explained why a low-stress stretching is needed to obtain the (4, 4) Cu tube in contrast to a higher one for both the (4, 4) Ag and Au tubes due to the larger stiffness coefficient of copper than those of silver and gold, which could be proved by future experiments.

Infrared and Raman spectra of AA-stacking bilayer graphene.

The infrared (IR) absorption and resonant Raman spectra of the undoped AA-stacking bilayer graphene have been calculated using density-functional theory in the local density approximation. It is found that the undoped AA-stacking bilayer graphene exhibits a different characteristic jump and peak structure in its IR spectra, and a different G-band peak structure in its resonant Raman spectra, compared with those of the AB-stacking one, which are caused by the different interlayer coupling effects, due to different stacking types in both of them. Based upon the different IR and Raman spectra, a powerful experimental method can be proposed to identify accurately the stacking type and the layer number in future experiments.

Magnetic properties of transition-metal-doped tubular gold clusters: M@Au(24) (M = V, Cr, Mn, Fe, Co, and Ni).

The energetic and magnetic properties of the tubular cluster Au(24), doped endohedrally by a 3d transition-metal atom M (M = V, Cr, Mn, Fe, Co, and Ni) have been investigated by the scalar relativistic density functional simulations. It is found that (1) these 3d transition-metal atoms can be encapsulated stably into the tubular Au(24) and do not significantly perturb the atomic and electronic structures of the parent tubular Au(24), (2) the infrared (IR) spectra of the tubular Au(24) cluster are significantly changed by the dopant atoms, inducing a characteristic absorption peak in the IR spectra of all the M@Au(24), and (3) protected by the tubular Au(24), the 3d states of the dopant atoms are largely localized, and the atom-like magnetism is retained for all the doped gold clusters, exhibiting 3, 6, 5, 4, 3, and 2 mu(B) for V-Ni, respectively.

Higher energy optical transitions in semiconducting carbon nanotubes.

We have studied the high energy optical transitions of semiconducting single-walled carbon nanotubes using the nonorthogonal tight-binding model, which takes into account the exciton effect. It is found from our calculations that the exciton's binding energies for the high energy E(33) and E(44) transitions are large enough, indicating clearly they are also excitonic in nature. More importantly, the logarithmic Kane-Mele correction, successful for the low energy E(11) and E(22) transitions, is now found to fail for describing the many-body effects in the higher energy transitions, which is consistent with the experimental result of Araujo et al (2007 Phys. Rev. Lett. 98 067401). Finally, it is interesting to find the possibility of a crossover effect between the E(33) and E(44) energies for certain mod 1 chiralities and the family behavior of the many-body corrections in the E(33) and E(44) transitions, both of which are well supported by the recent experiment of Haroz et al (2008 Phys. Rev. B 77 125405).