A first-principles study on the promising thermoelectric properties of SnX (X = S, Se, Te) compounds.

SnSe has emerged as an outstanding thermoelectric material due to its exceptional performance. In this study, first-principles calculations are employed to investigate the thermoelectric properties of materials within the SnX family, where X can be either S, Se, or Te. Initially, we assessed the stability of SnX (X = S, Se, Te). We found that SnS exhibits better mechanical and thermal stability than SnSe and SnTe. We then conduct phonon and electronic transport analysis. Following the general rule that heavier atoms have lower thermal conductivity, SnTe demonstrates lower thermal conductivity due to its low group velocity compared with SnS and SnSe. Regarding electrical transport properties, the band gaps for SnS, SnSe, and SnTe are 0.56, 0.54, and 0.35 eV, respectively. Notably, the small band gap and higher degeneracy in its band valleys for SnTe make it more effective for achieving a high power factor. The maximum ZT values are determined to be 1.41, 1.41, and 1.87 for SnS, SnSe, and SnTe, respectively. Remarkably, ZTmax of SnTe exceeds that of SnSe by 32.6%. Overall, the results clearly demonstrate that SnTe exhibits superior thermoelectric properties compared to SnSe and SnS. This study provides valuable insights into the electronic structure, thermal conductivity, and mechanical and thermal stability of materials within the SnSe family, such as SnS or SnTe, without the need for extensive and costly experimental work.

Synergistic modulation of electrical and thermal transport toward promising n-type MgOCuSbSe2 thermoelectric performance by MO-intercalated CuSbSe2.

The layered ternary CuSbSe2 semiconductor with ultralow thermal conductivity is particularly suitable for thermoelectric applications. Nevertheless, its poor electrical conductivity greatly lowers the dimensionless figure of merit ZT and accordingly limits its thermoelectric applications. Here, we use first-principles calculations combined with semi-classical Boltzmann transport theory to evaluate the thermoelectric properties of MO-intercalated (M = Mg, Ca, Sr, and Ba) CuSbSe2. Compared with CuSbSe2, MO-intercalated CuSbSe2 semiconductors, as a new class of semiconductors, host distorted lattices with low symmetry monoclinic structures. Such a structure feature provides desired channels for electron transport between adjacent layers and accordingly enhances electrical transport properties. Meanwhile, the MO intercalation effectively softens phonons and gives rise to an ultralow lattice thermal conductivity in MOCuSbSe2. These synergistically yield a high figure of merit ZT of ∼4.17 for MgO-intercalated CuSbSe2 at 200 K with electron doping being n = 1018 cm-3. Our study provides an effective route to improve the thermoelectric performance of layered CuSbSe2 by designing new multicomponent thermoelectric compounds with alternatively stacked [CuSbSe2] (electronic conduction units) and [MO] (electronic insulation units) layers. The approach can be extended to similar chalcostibite compounds for screening and designing thermoelectric materials.

Fabrication and application of carbohydrate microarray for analyzing human serum antibody-carbohydrate interaction.

We introduced a strategy for preparing a carbohydrate microarray and demonstrated its utility for characterizing carbohydrate binding and activities. We isolated the lipopolysaccharide (LPS) components from different bacteria and explored the possibility of immobilizing these glycoconjugates on a high-binding polystyrene plate. Carbohydrate-specific combination was examined by observing the binding of the blood group B analogic LPS O-polysaccharide from Escherichia coli on the high-binding polystyrene plate and anti-B from a broad spectra antibody of human blood serum. Strong binding of antibodies was screened, as it was evident that relative response value is two times higher than control. The hybridization results indicated that this method is a reliable technique for the detection of human intestinal bacteria and is expected to be applied in diagnostics and seroepidemiology.

Ultralow Melting Temperature of High-Pressure Face-Centered Cubic Superionic Ice.

Superionic ice with oxygen in a face-centered cubic (fcc) sublattice is ascribed to the origin of magnetic fields of Uranus and Neptune, since the melting temperature (Tm) of fcc-superionic ice is believed to be higher than the isentropes of ice giants. However, precisely measuring the fcc-superionic phase experimentally remains a difficult task. The majority of the systematic investigations of its Tm were performed using perfect oxygen fcc-sublattice computations, which could result in superheating and overestimation of Tm. On the basis of the ab initio molecular dynamics method and the model with H2O vacancy, we avoid superheating and obtain a much lower Tm than previous reports, indicating that fcc-superionic ice cannot exist in the interiors of Uranus and Neptune. Further simulations with the two-phase method justify the conclusion. The results suggest that superheating should be seriously treated when simulating the phase diagram of other hydrogen-related superionic states, which are widely used to understand the properties of ice giants, Earth, and Venus.

Investigations of Structural, Electronic and Magnetic Properties of MnSe under High Pressure.

Properties of pressurized MnSe were investigated based on the first-principles methods using exchange-correlation functionals of the local density approximation (generalized gradient approximation) with and without the Hubbard U correction. Our results show that the Hubbard U (U = 4 eV) correction is necessary to correctly describe the phase transition behaviors of MnSe. We found that at the static condition, phase transitions from the low-temperature phase with a NiAs-type structure (P63/mmc) to the P4/nmm phase at 50.5 GPa and further to the Pnma phase at 81 GPa are observed. However, if the transition starts from the room-temperature phase with a NaCl-type structure (Fm-3m), the transition-sequences and -pressures will be different, indicating that temperature can strongly affect the phase transition behaviors of MnSe. Furthermore, we found that pressure-induced negative charge transfer will promote spin crossover. The calculated superconducting properties of the Pnma phase indicate that it may be an unconventional superconductor.

Structural, electronic and magnetic properties of TlFeSe2under high pressure.

The high-pressure (HP) properties of TlFeSe2are investigated based on the first-principles calculations combined with structure-searching method. The low-pressureC2/mphase will transform into the orthorhombicPnmaphase at 2 GPa, with 8% volume collapse, the insulator-metal transition and the bicollinear antiferromagnetic-to-nonmagnetic spin-crossover. At pressure higher than 8 GPa, the HPC2/mphase will become the ground state. BothPnmaphase and HPC2/mphase are constituted by one-dimensional chains of edge-sharing FeSe5tetragonal pyramids. Pressuring decrease the Se-Se bond length giving rise to the transition from [Se2]3-to [Se2]2-. Negative charge transfer causes the Fe2+with ∼2 µBmagnetic moment at ambient pressure and the nonmagnetic Fe1.5+at higher pressure. The Fermi surfaces of HP phases are also discussed.

Polymerization of Nitrogen in Nitrogen-Fluorine Compounds under Pressure.

A wide range of polynitrogen species have attracted much attention because of their potential applications as high-energy-density materials. Until now, predicted polynitrogen was found to be negatively charged, with charge transfer from introduced atoms to nitrogen in nitrogen-bearing compounds. Using an evolutionary algorithm combined with first-principles calculations, stoichiometries and structures in nitrogen-fluorine compounds at pressures ranging from 0 to 200 GPa are investigated. In addition to two fluorine-rich compounds NF3 and NF5, two other compounds, NF and N6F, emerge with increasing pressure. N6F, as a nitrogen-rich compound, will become stable at pressures greater than 180 GPa with a positively charged nitrogen network. Above 120 GPa, the NF compound with polymeric zigzag nitrogen chains is discovered, and it is quenchable to the ambient conditions, acquiring the highest energy density of 5.38 kJ/g among reported binary covalent nitrogen compounds. These newly predicted N-F compounds are useful in understanding the chemistry of polynitrogen.

Spin-crossover induced ferromagnetism and layer stacking-order change in pressurized 2D antiferromagnet MnPS3.

Spin-crossover combined with metal-insulator transition and superconductivity has been found in 2D transition-metal phosphorous trichalcogenides when tuning them by high pressure. Simulation of such intriguing spin-crossover behaviors is crucial to understanding the mechanism. The Hubbard U correction is widely used to describe the strong on-site Coulomb interaction in the d electrons of transition-metal compounds, while the U values are sensitive to the crystal field and spin state varying greatly with pressure. In this work, we show that taking MnPS3 as an example and based on a uniform parameter set, the hybrid functional calculations give a spin-crossover pressure of 35 GPa consistent with experimental observation (30 GPa), which is less than half of the existing reported value (63 GPa) using the Hubbard U correction. Notably, we find a spin-crossover induced transition from an antiferromagnetic semiconductor with monoclinic stacking-order to a ferromagnetic semiconductor with rhombohedral stacking-order, and the ferromagnetism originates from the partially occupied t2g orbitals. Different from previous understanding, the Mott metal-insulator transition of MnPS3 does not occur simultaneously with the spin-crossover but in a pressurized low-spin phase.

Fungal Zn(II)2Cys6 Transcription Factor ADS-1 Regulates Drug Efflux and Ergosterol Metabolism under Antifungal Azole Stress.

Antifungal azoles are the most widely used antifungal drugs in clinical and agricultural practice. Fungi can mount adaptive responses to azole stress by modifying the transcript levels of many genes, and the responsive mechanisms to azoles are the basis for fungi to develop azole resistance. In this study, we identified a new Zn(II)2Cys6 transcription factor, ADS-1, with a positive regulatory function in transcriptional responses to azole stress in the model filamentous fungal species Neurospora crassa Under ketoconazole (KTC) stress, the ads-1 transcript level was significantly increased in N. crassa Deletion of ads-1 increased susceptibility to different azoles, while its overexpression increased resistance to these azoles. The cdr4 gene, which encodes the key azole efflux pump, was positively regulated by ADS-1. Deletion of ads-1 reduced the transcriptional response by cdr4 to KTC stress and increased cellular KTC accumulation under KTC stress, while ads-1 overexpression had the opposite effect. ADS-1 also positively regulated the transcriptional response by erg11, which encodes the azole target lanosterol 14α-demethylase for ergosterol biosynthesis, to KTC stress. After KTC treatment, the ads-1 deletion mutant had less ergosterol but accumulated more lanosterol than the wild type, while ads-1 overexpression had the opposite effect. Homologs of ADS-1 are widely present in filamentous fungal species of Ascomycota but not in yeasts. Deletion of the gene encoding an ADS-1 homolog in Aspergillus flavus also increased susceptibility to KTC and itraconazole (ITZ). Besides, deletion of A. flavusads-1 (Afads-1) significantly reduced the transcriptional responses by genes encoding homologs of CDR4 and ERG11 in A. flavus to KTC stress, and the deletion mutant accumulated more KTC but less ergosterol. Taken together, these findings demonstrate that the function and regulatory mechanism of ADS-1 homologs among different fungal species in azole responses and the basal resistance of azoles are highly conserved.

Boron-dopant enhanced stability of diamane with tunable band gap.

The structural, electronic, and superconducting properties of B-doped cubic and hexagonal diamane (single layer diamond) were investigated based on the first-principles methods. B atom tends to stay in the substitutional site, and the most stable configuration is the structure with vertical B-B dimer. The formation energy of B-doped diamane is lower than the counterpart of pristine diamane indicating that B dopant can facilitate the synthesis of diamane. The configurations with vertical B-B dimers are semiconductors with tunable band gaps, which decrease with the B concentration increasing due to the interaction between B-B dimers. For example, the band gap of 3.125 mol% and 6.25 mol% B-doped cubic diamane is 1.82 eV and 1.44 eV, respectively. Moreover, configurations with meta-stable B distributions are metals, which have comparable superconducting transition temperatures with B-doped diamond (~4 K).

Mode splitting in high-index-contrast grating with mini-scale finite size.

The mode-splitting phenomenon within finite-size, mini-scale high-index-contrast gratings (HCGs) has been investigated theoretically and experimentally. The high-Q resonance splits into a series of in-plane modes due to the confinement of boundaries but can still survive even on a mini-scale footprint. Q factors up to ∼3300 and ∼2200 have been observed for the HCGs with footprints that are only 55 µm×300 µm and 27.5 µm×300 µm, which would be promising for realizing optical communication and sensing applications with compact footprint.

Fruiting Body Formation in Volvariella volvacea Can Occur Independently of Its MAT-A-Controlled Bipolar Mating System, Enabling Homothallic and Heterothallic Life Cycles.

Volvariella volvacea is an important crop in Southeast Asia, but erratic fruiting presents a serious challenge for its production and breeding. Efforts to explain inconsistent fruiting have been complicated by the multinucleate nature, typical lack of clamp connections, and an incompletely identified sexual reproductive system. In this study, we addressed the life cycle of V. volvacea using whole genome sequencing, cloning of MAT loci, karyotyping of spores, and fruiting assays. Microscopy analysis of spores had previously indicated the possible coexistence of heterothallic and homothallic life cycles. Our analysis of the MAT loci showed that only MAT-A, and not MAT-B, controlled heterokaryotization. Thus, the heterothallic life cycle was bipolar. Karyotyping of single spore isolates (SSIs) using molecular markers supported the existence of heterokaryotic spores. However, most SSIs were clearly not heterokaryotic, yet contained structural variation (SV) markers relating to both alleles of both parents. Heterokaryons from crossed, self-sterile homokaryons could produce fruiting bodies, agreeing with bipolar heterothallism. Meanwhile, some SSIs with two different MAT-A loci also produced fruiting bodies, which supported secondary homothallism. Next, SSIs that clearly contained only one MAT-A locus (homothallism) were also able to fruit, demonstrating that self-fertile SSIs were not, per definition, secondary homothallic, and that a third life cycle or genetic mechanism must exist. Finally, recombination between SV markers was normal, yet 10 out of 24 SV markers showed 1:2 or 1:3 distributions in the spores, and large numbers of SSIs contained doubled SV markers. This indicated selfish genes, and possibly partial aneuploidy.

Coordinated and distinct functions of velvet proteins in Fusarium verticillioides.

Velvet-domain-containing proteins are broadly distributed within the fungal kingdom. In the corn pathogen Fusarium verticillioides, previous studies showed that the velvet protein F. verticillioides VE1 (FvVE1) is critical for morphological development, colony hydrophobicity, toxin production, and pathogenicity. In this study, tandem affinity purification of FvVE1 revealed that FvVE1 can form a complex with the velvet proteins F. verticillioides VelB (FvVelB) and FvVelC. Phenotypic characterization of gene knockout mutants showed that, as in the case of FvVE1, FvVelB regulated conidial size, hyphal hydrophobicity, fumonisin production, and oxidant resistance, while FvVelC was dispensable for these biological processes. Comparative transcriptional analysis of eight genes involved in the ROS (reactive oxygen species) removal system revealed that both FvVE1 and FvVelB positively regulated the transcription of a catalase-encoding gene, F. verticillioides CAT2 (FvCAT2). Deletion of FvCAT2 resulted in reduced oxidant resistance, providing further explanation of the regulation of oxidant resistance by velvet proteins in the fungal kingdom.

Heat stress impairs the nutritional metabolism and reduces the productivity of egg-laying ducks.

This research was conducted to determine the effect of heat stress on the nutritional metabolism and productivity of egg-laying shelducks. Healthy shelducks (n=120) in the early laying stage (uniform body weights and normal feed intakes) were randomly assigned to two identical climate chambers and exposed to constant high temperature (34°C) or control temperature (23°C) for 28d. The heat-exposed ducks had reduced feed intakes and laying rates (P<0.05), increased frequency of panting and spreading wings and dull featheration; egg weight, eggshell thickness and strength, and Haugh unit also decreased and malondialdehyde (MDA) content of egg yolk increased (P<0.05). Compared with the control ducks, the plasma concentrations of HCO3(-), phosphorus, glucose, thyroxine and activities of glutamic-pyruvic transaminase and glutamic oxaloacetic transaminase were decreased, while there were increased concentrations of corticosterone (P<0.05). The content of MDA and lactate in plasma and liver was greater in heat-exposed than in control ducks, but superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), total antioxidant enzymes (T-AOC) activities and glutathione (GSH) contents were less. The expression of HSP70 gene expression in the liver was increased in heat-stressed ducks. The relative weight of oviduct, number of large ovarian follicles, length of the oviduct all decreased (P<0.05) in heat-treated ducks, as did expression of carbonic anhydrase and calcium binding protein genes in the shell gland as a result of heat stress. In summary, heat stress decreased the productivity of ducks, which related to reduced feed intake, protein synthesis, endocrine dysfunction, less antioxidant capacity, and derangement of calcium and phosphorous balance.

Transcription factor CCG-8 as a new regulator in the adaptation to antifungal azole stress.

Antifungal azoles are widely used for controlling fungal infections. Fungi are able to change the expression of many genes when they adapt to azole stress, and increased expression of some of these genes can elevate resistance to azoles. However, the regulatory mechanisms behind transcriptional adaption to azoles in filamentous fungi are poorly understood. In this study, we found that deletion of the transcription factor gene ccg-8, which is known to be a clock-controlled gene, made Neurospora crassa hypersensitive to azoles. A comparative genome-wide analysis of the responses to ketoconazole of the wild type and the ccg-8 mutant revealed that the transcriptional responses to ketoconazole of 78 of the 488 transcriptionally ketoconazole-upregulated genes and the 427 transcriptionally ketoconazole-downregulated genes in the wild type were regulated by CCG-8. Ketoconazole sensitivity testing of all available knockout mutants for CCG-8-regulated genes revealed that CCG-8 contributed to azole adaption by regulating the ketoconazole responses of many genes, including the target gene (erg11), an azole transporter gene (cdr4), a hexose transporter gene (hxt13), a stress response gene (locus number NCU06317, named kts-1), two transcription factor genes (NCU01386 [named kts-2] and fsd-1/ndt80), four enzyme-encoding genes, and six unknown-function genes. CCG-8 also regulated phospholipid synthesis in N. crassa in a manner similar to that of its homolog in Saccharomyces cerevisiae, Opi1p. However, there was no cross talk between phospholipid synthesis and azole resistance in N. crassa. CCG-8 homologs are conserved and are common in filamentous fungi. Deletion of the CCG-8 homolog-encoding gene in Fusarium verticillioides (Fvccg-8) also made this fungus hypersensitive to antifungal azoles.

Homologous recombination as a mechanism to recognize repetitive DNA sequences in an RNAi pathway.

Quelling is an RNAi-related phenomenon that post-transcriptionally silences repetitive DNA and transposons in Neurospora. We previously identified a type of DNA damage-induced small RNA called qiRNA that originates from ribosomal DNA. To understand how small RNAs are generated from repetitive DNA, we carried out a genetic screen to identify genes required for qiRNA biogenesis. Factors directly involved in homologous recombination (HR) and chromatin remodeling factors required for HR are essential for qiRNA production. HR is also required for quelling, and quelling is also the result of DNA damage, indicating that quelling and qiRNA production share a common mechanism. Together, our results suggest that DNA damage-triggered HR-based recombination allows the RNAi pathway to recognize repetitive DNA to produce small RNA.

CDR4 is the major contributor to azole resistance among four Pdr5p-like ABC transporters in Neurospora crassa.

Pdr5p-like ABC transporters play a significant role in azole resistance in Saccharomyces cerevisiae and Candida spp. Most of filamentous fungal species have multiple Pdr5p homologues. In this study, phylogenic analysis identified that filamentous fungi have at least two phylogenically distant groups of Pdr5p homologues. One contains PMR1-like Pdr5p homologues while the other contains both AtrF-like and AtrB-like Pdr5p homologues. Neurospora crassa has a total of four genes encoding Pdr5p homologues including CDR4 (PMR1-like), ATRB (AtrB-like), and ATRF (AtrF-like) and ATRF-2 (AtrF-like). By analyzing the susceptibilities of their knockout mutants to azole drugs including ketoconazole, fluconazole, and itraconazole, we found that deletion of cdr4 increased the susceptibility to antifungal azoles. In contrast, neither single-gene nor triple-gene deletion of atrb, atrf, and atrf-2 could not alter the susceptibility to azoles. In addition, cdr4, but not other Pdr5p homologue-coding genes, responded transcriptionally to ketoconazole stress. Together with the previous findings in other fungal species, these results suggest that the PMR1-like but not the AtrF-like or AtrB-like Pdr5p homologues play a key role in antifungal azole resistance in filamentous fungi.

Analysis of the role of transcription factor VAD-5 in conidiation of Neurospora crassa.

Conidiation is the major mode of reproduction in many filamentous fungi. The Neurospora crassa gene vad-5, which encodes a GAL4-like Zn2Cys6 transcription factor, was suggested to contribute to conidiation in a previous study using a knockout mutant. In this study, we confirmed the positive contribution of vad-5 to conidiation by gene complementation. To understand the role of vad-5 in conidiation, transcriptomic profiles generated by digital gene expression profiling from the vad-5 deletion mutant and the wild-type strain were compared. Among 7559 detected genes, 176 genes were found to be transcriptionally down-regulated and 277 genes transcriptionally upregulated in the vad-5 deletion mutant, using ≥1-fold change as a cutoff threshold. Among the down-regulated genes, four which were already known to be involved in conidiation -fluffy, ada-6, rca-1, and eas - were examined further in a time course experiment. Transcription of each of the four genes in the vad-5 deletion mutant was lower than in the wild-type strain during conidial development. Phenotypic observation of deletion mutants for 132 genes down-regulated by vad-5 deletion revealed that deletion mutants for 17 genes, including fluffy, ada-6, and eas, produced fewer conidia than the wild type. By phenotypic observation of deletion mutants for 211 genes upregulated in the vad-5 deletion mutant, two types of deletion mutants were found. One type, which produced more conidia than the wild-type strain, includes deletion mutants for previously characterized genes cat-2, cat-3, and sah-1 and for a non-characterized gene NCU07221. Deletion mutants of NCU06302 and NCU11090, representing the second type, produced conidia earlier than the wild-type strain. Based on these conidiation phenotypes, we designated NCU07221 as high conidial production-1 (hcp-1) and named NCU06302 and NCU11090 as early conidial development-1 (ecd-1) and ecd-2, respectively. Given the collective results from this study, we propose that vad-5 exerts an effect on conidiation by activating genes that positively contribute to conidiation as well as by repressing genes that negatively influence conidial development.

Involvement of a helix-loop-helix transcription factor CHC-1 in CO(2)-mediated conidiation suppression in Neurospora crassa.

The morphological switch from vegetative growth to conidiation in filamentous fungi is highly regulated, but the understanding of the regulatory mechanisms is limited. In this study, by screening a set of knock-out mutants corresponding to 103 transcription factor encoding genes in Neurospora crassa, a mutant was found to produce abundant conidia in race tubes in which conidiation in the wild-type strain was suppressed. The corresponding gene NCU00749 encodes a protein containing a helix-loop-helix DNA binding region. Unlike enhanced conidiation in ras-1 and sod-1 mutants, which was completely suppressed by antioxidant N-acetyl cysteine, enhanced conidiation in the NCU00749 mutant was only slightly affected by N-acetyl cysteine. When grown on slants, the NCU00749 deletion mutant exhibited earlier conidial formation than the wild-type strain, and this was more evident at a higher (5%) CO(2) concentration. Therefore, we named NCU00749 as conidiation at high carbon dioxide-1 (chc-1). Genes that are highly expressed during conidial development, eas, con-6, con-8 and con-10, were transcribed at a higher rate in the chc-1 deletion mutant than the wild-type strain in response to conidiation induction. To determine the mechanisms by which CHC-1 regulates conidiation, we conducted a RNA sequencing analysis and found that 404 genes exhibited ≥ 2 fold changes in transcription in response to chc-1 deletion. Among them, fluffy and ada-6, two transcription factor genes that positively regulate conidiation in N. crassa, and rca-1, whose homolog flbD in Aspergillus nidulans is essential for conidiation, were upregulated in the chc-1 deletion mutant. Results of RNA sequencing also suggest that signal transduction via the cAMP and the MAK-2 mediated signal pathways, and ROS generation and removal, mechanisms known to regulate conidiation, are not involved in chc-1 mediated control of conidiation. In addition, chc-1 also influences expression of genes involved in other important biological processes besides conidiation such as carbon metabolism, sphingolipid synthesis, cell wall synthesis, and calcium signaling.