Strong second-harmonic generation by sublattice polarization in non-uniformly strained monolayer graphene.

Despite the potential of graphene for building a variety of quantum photonic devices, its centrosymmetric nature forbids the observation of second harmonic generation (SHG) for developing second-order nonlinear devices. To activate SHG in graphene, extensive research efforts have been directed towards disrupting graphene's inversion symmetry using external stimuli like electric fields. However, these methods fail to engineer graphene's lattice symmetry, which is the root cause of the forbidden SHG. Here, we harness strain engineering to directly manipulate graphene's lattice arrangement and induce sublattice polarization to activate SHG. Surprisingly, the SHG signal is boosted 50-fold at low temperatures, which can be explained by resonant transitions between strain-induced pseudo-Landau levels. The second-order susceptibility of strained graphene is found to be larger than that of hexagonal boron nitride with intrinsic broken inversion symmetry. Our demonstration of strong SHG in strained graphene offers promising possibilities for developing high-efficiency nonlinear devices for integrated quantum circuits.

Helmet-Wearing Tracking Detection Based on StrongSORT.

Object detection based on deep learning is one of the most important and fundamental tasks of computer vision. High-performance detection algorithms have been widely used in many practical fields. For the management of workers wearing helmets in construction scenarios, this paper proposes a framework model based on the YOLOv5 detection algorithm, combined with multi-object tracking algorithms, to monitor and track whether workers wear safety helmets in real-time video. The improved StrongSORT tracking algorithm of DeepSORT is selected to reduce the loss of the tracked object caused by the occlusion, trajectory blur, and motion scale of the object. The safety helmet dataset is trained with YOLOv5s, and the best result of training is used as the weight model in the StrongSORT tracking algorithm. The experimental results show that the mAP@0.5 of all classes in the YOLOv5s model can reach 95.1% in the validation dataset, mAP@0.5:0.95 is 62.1%, and the precision of wearing helmet is 95.7%. After the box regression loss function was changed from CIOU to Focal-EIOU, the mAP@0.5 increased to 95.4%, mAP@0.5:0.95 increased to 62.9%, and the precision of wearing helmet increased to 96.5%, which were increased by 0.3%, 0.8% and 0.8%, respectively. StrongSORT can update object trajectories in video frames at a speed of 0.05 s per frame. Based on the improved YOLOv5s combined with the StrongSORT tracking algorithm, the helmet-wearing tracking detection can achieve better performance.

Molecular Characteristics and Pathogenicity of a Novel Recombinant Porcine Reproductive and Respiratory Syndrome Virus Strain from NADC30-, NADC34-, and JXA1-Like Strains That Emerged in China.

Recently, the emergence of a NADC34-like porcine reproductive and respiratory syndrome virus (PRRSV), which causes a large number of abortions in swine herds, has raised great concern in China. In this study, a PRRSV variant strain, PRRSV/CN/FJGD01/2021, evolved from recombination between NADC30-like, NADC34-like, and JXA1-like viruses was isolated in Fujian province in 2021, and its pathogenicity in piglets was examined. Animal experiments demonstrated that PRRSV/CN/FJGD01/2021 infection could induce 100% morbidity and cause higher viremia, a persistently higher fever (>40°C for 14 consecutive days), significant weight loss, and severe histopathological lung lesions compared to the NADC30-like FJZ03 strain and NADC34-like FJ0908 strain in piglets. The PRRSV/CN/FJGD01/2021 strain displayed higher pathogenicity than the FJZ03 and FJ0908 strains, but lower pathogenicity than the Chinese highly pathogenic (HP)-PRRSVs in piglets. Moreover, the Ingelvac PRRS modified live vaccine (MLV) provides incomplete cross-protection against heterologous PRRSV/CN/FJGD01/2021 in piglets. Our findings contribute to the understanding of the current epidemic situation of NADC34-like PRRSV in China. IMPORTANCE The pathogenicity of NADC34-like PRRSV has broad variations in virulence. Importantly, NADC34-like PRRSV has undergone complex recombination with local strains since it first emerged in 2017 in China. However, the pathogenicity of the recombinant NADC34-like virus was rarely experimentally evaluated in pigs. In this study, a novel PRRSV strain, PRRSV/CN/FJGD01/2021, was isolated from sows enduring a high-abortion-rate (20%) period in China in 2021. Notably, phylogenetic and recombination analyses revealed that PRRSV/CN/FJGD01/2021 is a recombinant virus from NADC30-, NADC34-, and JXA1-like isolates. PRRSV/CN/FJGD01/2021 was shown to cause higher virus load, persistent fever, significant weight loss, moderate respiratory clinical signs, and severe histopathological lung lesions in piglets. PRRSV/CN/FJGD01/2021 exhibited higher pathogenicity than NADC30-like FJZ03 and NADC34-like FJ0908, but lower than Chinese HP-PRRSVs for piglets. These data indicated that PRRSV/CN/FJGD01/2021 has intermediate virulence for piglets. Furthermore, the Ingelvac PRRS MLV could partly provide protective efficacy against PRRSV/CN/FJGD01/2021 challenge in piglets.

Efficient Avalanche Photodiodes with a WSe2/MoS2 Heterostructure via Two-Photon Absorption.

Two-dimensional (2D) materials-based photodetectors in the infrared range hold the key to enabling a wide range of optoelectronics applications including infrared imaging and optical communications. While there exist 2D materials with a narrow bandgap sensitive to infrared photons, a two-photon absorption (TPA) process can also enable infrared photodetection in well-established 2D materials with large bandgaps such as WSe2 and MoS2. However, most of the TPA photodetectors suffer from low responsivity, preventing this method from being widely adopted for infrared photodetection. Herein, we experimentally demonstrate 2D materials-based TPA avalanche photodiodes achieving an ultrahigh responsivity. The WSe2/MoS2 heterostructure absorbs infrared photons with an energy smaller than the material bandgaps via a low-efficiency TPA process. The significant avalanche effect with a gain of ∼1300 improves the responsivity, resulting in the record-high responsivity of 88 µA/W. We believe that this work paves the way toward building practical and high-efficiency 2D materials-based infrared photodetectors.

Ultrafast light emission at telecom wavelengths from a wafer-scale monolayer graphene enabled by Fabry-Perot interferences.

Ultrafast light emission from monolayer graphene shows attractive potential for developing integrated light sources for next-generation graphene-based electronic-photonic integrated circuits. In particular, graphene light sources operating at the telecom wavelengths are highly desired for the implementation of graphene-based ultrahigh-speed optical communication. Currently, most of the studies on ultrafast light emission from graphene have been performed in the visible spectrum, while studies on ultrafast emission at the telecom wavelengths remain scarce. Here, we present experimental observations of strong ultrafast thermal emission at telecom wavelengths from wafer-scale monolayer graphene. Our results show that the emission spectra can be strongly modified by the presence of the cavity effect to produce an enhanced emission at telecom wavelengths. We corroborate our experimental results with simulations and show that by designing a suitable cavity thickness, one can easily tune the emission profile from visible to telecom wavelength regardless of the pump power. In addition, we demonstrate that the insertion of a monolayer of hexagonal boron nitride between graphene and the substrate helps improve the thermal stability of graphene, thereby providing more than five times enhancement of the ultrafast thermal emission. Our results provide a potential solution for stable on-chip nanoscale light sources with ultrahigh speed modulation.

Triaxially strained suspended graphene for large-area pseudo-magnetic fields.

Strain-engineered graphene has garnered much attention recently owing to the possibilities of creating substantial energy gaps enabled by pseudo-magnetic fields (PMFs). While theoretical works proposed the possibility of creating large-area PMFs by straining monolayer graphene along three crystallographic directions, clear experimental demonstration of such promising devices remains elusive. Herein, we experimentally demonstrate a triaxially strained suspended graphene structure that has the potential to possess large-scale and quasi-uniform PMFs. Our structure employs uniquely designed metal electrodes that function both as stressors and metal contacts for current injection. Raman characterization and tight-binding simulations suggest the possibility of achieving PMFs over a micrometer-scale area. Current-voltage measurements confirm an efficient current injection into graphene, showing the potential of our devices for a new class of optoelectronic applications. We also theoretically propose a photonic crystal-based laser structure that obtains strongly localized optical fields overlapping with the spatial area under uniform PMFs, thus presenting a practical route toward the realization of graphene lasers.

Pseudo-magnetic field-induced slow carrier dynamics in periodically strained graphene.

The creation of pseudo-magnetic fields in strained graphene has emerged as a promising route to investigate intriguing physical phenomena that would be unattainable with laboratory superconducting magnets. The giant pseudo-magnetic fields observed in highly deformed graphene can substantially alter the optical properties of graphene beyond a level that can be feasible with an external magnetic field, but the experimental signatures of the influence of such pseudo-magnetic fields have yet to be unveiled. Here, using time-resolved infrared pump-probe spectroscopy, we provide unambiguous evidence for slow carrier dynamics enabled by the pseudo-magnetic fields in periodically strained graphene. Strong pseudo-magnetic fields of ~100 T created by non-uniform strain in  graphene on nanopillars are found to significantly decelerate the relaxation processes of hot carriers by more than an order of magnitude. Our findings offer alternative opportunities to harness the properties of graphene enabled by pseudo-magnetic fields for optoelectronics and condensed matter physics.

Development of a Real-Time Quantitative RT-PCR Assay for Detection of Bovine Rhinitis B Virus.

Bovine rhinitis B virus (BRBV) has been frequently identified in cattle diagnosed with bovine respiratory disease complex (BRDC) in recent years, suggesting its potential contribution to BRDC. The goal of this study was to develop a TaqMan-based real-time quantitative RT-PCR assay for efficient BRBV detection. A pair of primers and a probe were designed based on the 3D gene of the BRBV genome. The assay was specific for BRBV and able to exclude bovine rhinitis A virus, foot-and-mouth disease virus and Senecavirus A. The limit of detection of the assay was 4.46 copies per reaction. A standard curve was plotted, with a coefficient of determination of 0.999 in the concentration range of 100-108 copies/µl. The reproducibility of the assay was acceptable, with the standard deviations of cycle threshold values lower than 1.00 in both intra- and inter-assay. Of 200 samples collected from 150 head of cattle in recent years in China, 11% (22/200) of the samples tested positive in the assay, i.e., 4.6% (7/150) of the cattle were BRBV positive. This study provides an efficient diagnostic tool for the epidemiological investigations of BRBV.

Rapid fabrication of complex nanostructures using room-temperature ultrasonic nanoimprinting.

Despite its advantages of scalable process and cost-effectiveness, nanoimprinting faces challenges with imprinting hard materials (e.g., crystalline metals) at low/room temperatures, and with fabricating complex nanostructures rapidly (e.g., heterojunctions of metal and oxide). Herein, we report a room temperature ultrasonic nanoimprinting technique (named nanojackhammer) to address these challenges. Nanojackhammer capitalizes on the concentration of ultrasonic energy flow at nanoscale to shape bulk materials into nanostructures. Working at room temperature, nanojackhammer allows rapid fabrication of complex multi-compositional nanostructures made of virtually all solid materials regardless of their ductility, hardness, reactivity and melting points. Atomistic simulations reveal a unique alternating dislocation generation and recovery mechanism that significantly reduces the imprinting force under ultrasonic cyclic loading. As a proof-of-concept, a metal-oxide-metal plasmonic nanostructure with built-in nanogap is rapidly fabricated and employed for biosensing. As a fast, scalable, and cost-effective nanotechnology, nanojackhammer will enable various unique applications of complex nanostructures in optoelectronics, biosensing, catalysis and beyond.

Biaxially strained germanium crossbeam with a high-quality optical cavity for on-chip laser applications.

The creation of CMOS compatible light sources is an important step for the realization of electronic-photonic integrated circuits. An efficient CMOS-compatible light source is considered the final missing component towards achieving this goal. In this work, we present a novel crossbeam structure with an embedded optical cavity that allows both a relatively high and fairly uniform biaxial strain of ∼0.9% in addition to a high-quality factor of >4,000 simultaneously. The induced biaxial strain in the crossbeam structure can be conveniently tuned by varying geometrical factors that can be defined by conventional lithography. Comprehensive photoluminescence measurements and analyses confirmed that optical gain can be significantly improved via the combined effect of low temperature and high strain, which is supported by a three-fold reduction of the full width at half maximum of a cavity resonance at ∼1,940 nm. Our demonstration opens up the possibility of further improving the performance of germanium lasers by harnessing geometrically amplified biaxial strain.

Frequency-tunable terahertz graphene laser enabled by pseudomagnetic fields in strain-engineered graphene.

Graphene-based optoelectronic devices have recently attracted much attention for the next-generation electronic-photonic integrated circuits. However, it remains elusive whether it is feasible to create graphene-based lasers at the chip scale, hindering the realization of such a disruptive technology. In this work, we theoretically propose that Landau-quantized graphene enabled by strain-induced pseudomagnetic field can become an excellent gain medium that supports lasing action without requiring an external magnetic field. Tight-binding theory is employed for calculating electronic states in highly strained graphene while analytical and numerical analyses based on many-particle Hamiltonian allow studying detailed microscopic mechanisms of zero-field graphene Landau level laser dynamics. Our proposed laser presents unique features including a convenient, wide-range tuning of output laser frequency enabled by changing the level of strain in graphene gain media. The chip-scale graphene laser may open new possibilities for graphene-based electronic-photonic integrated circuits.

A Novel Technique for Constructing Infectious Cloning of Type 3 Porcine Circovirus.

Porcine circovirus type 3 (PCV3), which currently lacks effective preventive measures, has caused tremendous economic losses to the pig husbandry. Obtaining the strain of PCV3 is the key to preparing related vaccines and developing corresponding antiviral drugs. In this study, according to the linear sequence of PCV3 DNA published on GenBank, the sequence was rearranged with SnapGene gene-editing software, and after rearrangement, the HindIII restriction endonuclease site was added to the end of the linear DNA, so that both ends have the same restriction endonuclease site. On this basis, the rearranged linear DNA is obtained by gene synthesis, PCR amplification, DNA purification, etc., and is digested and connected in vitro to obtain cyclized DNA. PCV3 infectious clones were obtained by transfecting 3D4/21 cell lines. The obtained PCV3 was identified by PCR, Western blotting, and indirect immunofluorescence tests. The results showed that this study successfully obtained the strain of PCV3 in vitro. To further evaluate the pathogenicity of the obtained PCV3 infectious clones, this study established an animal model of Kunming mice infected with PCV3. The results of RT-PCR, Western blotting and immunohistochemistry showed that PCV3 can infect myocardium and alveoli of Kunming mice, but no PCV3 was detected in other tissues. The above studies indicate that PCV3 circular DNA can be used to construct PCV3 infectious clones. This research will provide a new method for the construction of circular DNA viruses and lay the foundation for the research and pathogenesis of PCV3 vaccine.

Development of a real-time loop-mediated isothermal amplification assay for detection of porcine circovirus 3.

BACKGROUND: Porcine circovirus type 3 (PCV3) is an emerging circovirus species, that has been reported in major pig-raising countries including the United States, China, South Korea, Brazil, Spain, and Poland. RESULTS: A real-time loop-mediated isothermal amplification (LAMP) assay was developed for rapid detection of porcine circovirus 3 (PCV3). The method had a detection limit of 1 × 101 copies/µL with no cross-reactions with classical swine fever virus (CSFV) C strain, foot-and-mouth disease virus (FMDV), porcine circovirus 2 (PCV2) LG vaccine strain, porcine epidemic diarrhoea virus (PEDV), porcine respiratory and reproductive syndrome virus (PRRSV), or pseudorabies virus (PRV). The PCV3 positive detection rate of 203 clinical samples for the real-time LAMP assay was 89.66% (182/203). CONCLUSIONS: The real-time LAMP assay is highly sensitive, and specific for use in epidemiological investigations of PCV3.

Emergence of a novel recombinant porcine circovirus type 2 in China: PCV2c and PCV2d recombinant.

Porcine circovirus type 2 (PCV2) has been causing huge economic losses in Chinese swine herds since it was first identified in China in 1999. Genotypes of PCV2 except for PCV2c coexist in swine herds in China, which may facilitate virus recombination. In the current study, six novel PCV2 strains were detected in China, and these strains shared high nucleotide similarity of the Rep gene with the PCV2c strain DK1987PMWSfree and high homology of the Cap gene with PCV2d. Genome sequence analysis revealed that the complete genomes of these strains were 1767 nucleotides (nt) in length and shared 99.8%-99.9% nucleotide identity with each other and 91.7%-98.7% with representative strains. Phylogenetic analysis, sequencing analysis, base-by-base comparisons and comprehensive recombination analysis demonstrated that these six strains originated from recombination within the Rep gene between PCV2c and PCV2d strains. Surprisingly, further investigation through theoretical recombination analysis of Chinese PCV2 GenBank sequences showed that these novel patterns of recombinant PCV2 strains have been generated since 2010. Collectively, our findings provide additional evidence of inter-genotypic recombination of PCV2.

Efficacy of Type 2 PRRSV vaccine against challenge with the Chinese lineage 1 (NADC30-like) PRRSVs in pigs.

The objective of the present study was to determine the cross-protection of Ingelvac PRRS MLV against challenge with the new lineage 1 PRRSV emerged in China in pigs. Two lineage 1 PRRSV strains (FJZ03 and FJWQ16 originated from recombination event between NADC30 and JXA1-like strain). We found that pigs vaccinated with the vaccine were protected against challenge with the FJZ03 as shown by fewer days of clinical fever, reduced lung pathology scores, lower PRRS virus load in the blood and developed broadly neutralizing antibodies with high titers to FJZ03. In contrast, vaccine provided limited protection against challenge with FJWQ16 with higher fever, lower antibody titers, lower neutralizing antibodies and higher viral loads in blood. These results demonstrate PRRSV-MLV provides incomplete protection against new lineage 1 PRRSVs.

Expression and characterization of albumin fusion protein canine IFNγ-CSA in baculovirus-insect cell expression system.

In this study, canine IFNγ was fused by a flexible linker with canine serum albumin to construct the fusion protein IFNγ-CSA for the purpose to design a long-acting canine IFNγ. The fusion protein was successfully expressed in baculovirus-infected Sf9 insect cells and was purified by salting-out and ion exchange chromatography. The IFNγ-CSA fusion possessed potent anti-viral assay against vesicular stomatitis virus in cultured cells. IFNγ-CSA was also stable at 37 °C up to 72 h compared with 8 h for IFNγ alone. In vivo pharmacokinetics demonstrated a significantly longer half-life for IFNγ-CSA (15.42 h) than for canine reIFNγ (1.51 h) in KM mice. These results indicate that IFNγ-CSA expression in the baculovirus system was successful and provide a promising long-acting cytokine for veterinary clinical applications.

Albumin fusion improves the pharmacokinetics and in vivo antitumor efficacy of canine interferon gamma.

Interferon (IFN)-γ plays an important role in antiviral, anti-proliferative, immunomodulatory and pro-inflammatory activities. However, the short therapeutic half-life of IFN-γ lessens its efficacy. Albumin fusion strategy is one of the most effective ways to improve the pharmacokinetic properties of cytokines. In this study, N- and C-terminal canine albumin fusions with canine IFN-γ were expressed in the baculovirus expression system. The fusion proteins stimulated Stat1 phosphorylation at levels similar to that of the recombinant IFN. The antiviral, anti-proliferative and promote apoptosis activity of CSA-IFN-γ was lower than IFN-γ-CSA and both were less than that of recombinant IFN-γ. In vivo pharmacokinetics demonstrated a significantly longer half-life for CSA-IFN-γ (21.73 h) than for IFN-γ-CSA (6.51 h) and canine reIFN-γ (2.22 h) in Wistar rats. CSA-IFN-γ was also more effective than IFN-γ-CSA and canine reIFN-γ at inhibiting growth of canine renal malignant histiocytosis in nude mice. Our results indicated that a canine serum albumin fusion at the N-terminus of IFN-γ prolongs its half-life and improves its in vivo antitumor activity.

Development of a real time loop-mediated isothermal amplification method for detection of Senecavirus A.

Senecavirus A (SVA), formerly known as Seneca Valley Virus (SVV), is one of causative agents of vesicular diseases in swine. Recently, the outbreaks associated with vesicular disease caused by SVA infection in pig herds have been reported in Brazil, USA, China, Thailand and Canada. Several molecular detection methods have been established to determine the infection of SVA, including real time reverse transcription PCR assay, nested PCR, a TaqMan-based qRT-PCR assay and RNA-based in situ hybridization method. In our study, an assay for the identification of SVA in pig herds using real time reverse transcription loop-mediated isothermal amplification (real time RT-LAMP) was developed. The limit of detection for the assay was 1 TCID50/ml. One hundred and eighteen field samples from pigs were used to validate the assay for clinical application. Our result demonstrated that real time RT-LAMP assay is a cost-effective and highly specific and sensitive alternative for the rapid detection of SVA in clinical samples.

Strained germanium nanowire optoelectronic devices for photonic-integrated circuits.

Strained germanium nanowires have recently become an important material of choice for silicon-compatible optoelectronic devices. While the indirect bandgap nature of germanium had long been problematic both in light absorption and emission, recent successful demonstrations of bandstructure engineering by elastic strain have opened up the possibility of achieving direct bandgap in germanium, paving the way towards the realization of various high-performance optical devices integrated on a silicon platform. In particular, the latest demonstration of a low-threshold optically pumped laser in a highly strained germanium nanowire is expected to vitalize the field of silicon photonics further. Here, we review recent advances and challenges in strained germanium nanowires for optoelectronic applications such as photodetectors and lasers. We firstly introduce the theoretical foundation behind strained germanium nanowire optoelectronics. And several practical approaches that have been proposed to apply tensile strain in germanium nanowires are further discussed. Then we address the latest progress in the developments of strained germanium nanowire optoelectronic devices. Finally, we discuss the implications of these experimental achievements and the future outlook in this promising research field.

Development of a real time reverse transcription loop-mediated isothermal amplification method (RT-LAMP) for detection of a novel swine acute diarrhea syndrome coronavirus (SADS-CoV).

A novel swine acute diarrhea syndrome Coronavirus (SADS-CoV) that causes severe diarrhea in suckling piglets was identified in southern China in 2017. A simple and rapid detection test was developed for this virus using real-time RT-LAMP based on the conserved N gene of the virus. The method had a detection limit of 1.0 × 101 copies/µL with no cross-reactions with classical swine fever virus, porcine and respiratory syndrome virus NA, porcine and respiratory syndrome virus EU, transmissible gastroenteritis coronavirus, foot and mouth disease virus, porcine epidemic diarrhea virus (S-INDEL and non-S-INDEL), swine influenza virus subtype H1N1, porcine circovirus type 2, seneca valley virus, porcine parvovirus, porcine deltacoronavirus and rotavirus. This method was also reproducible. Twenty of 24 clinical samples were identified as SADS-CoV RNA-positive by the real-time RT-LAMP and the results were consistent with that of the real time RT-PCR method. This new method for detecting SADS-CoV is specific and sensitive for the detection of SADS-CoV.