15 research outputs found
Symmetry-protected higher-order exceptional points in staggered flatband rhombic lattices
Higher-order exceptional points (EPs), which appear as multifold degeneracies
in the spectra of non-Hermitian systems, are garnering extensive attention in
various multidisciplinary fields. However, constructing higher-order EPs still
remains as a challenge due to the strict requirement of the system symmetries.
Here we demonstrate that higher-order EPs can be judiciously fabricated in PT
-symmetric staggered rhombic lattices by introducing not only on-site gain/loss
but also nonHermitian couplings. Zero-energy flatbands persist and
symmetry-protected third-order EPs (EP3) arise in these systems owing to the
non-Hermitian chiral/sublattice symmetry, but distinct phase transitions and
propagation dynamics occur. Specifically, the EP3 arises at the Brillouin zone
(BZ) boundary in the presence of on-site gain/loss. The single-site excitations
display an exponential power increase in the PT -broken phase. Meanwhile, a
nearly flatband sustains when a small lattice perturbation is applied. For the
lattices with non-Hermitian couplings, however, the EP3 appears at the BZ
center. Quite remarkably, our analysis unveils a dynamical
delocalization-localization transition for the excitation of the dispersive
bands and a quartic power increase beyond the EP3. Our scheme provides a new
platform towards the investigation of the higher-order EPs, and can be further
extended to the study of topological phase transitions or nonlinear processes
associated with higher-order EPs.Comment: 10 pages, 10 figure
Regenerable Subnanometer Pd Clusters on Zirconia for Highly Selective Hydrogenation of Biomass-Derived Succinic Acid in Water
The size of metal particles is an important factor to determine the performance of the supported metal catalysts. In this work, we report subnanometer Pd clusters supported on zirconia by the microwave-assisted hydrothermal method. The presence of subnanometer Pd clusters on the zirconia surface was confirmed by two-dimensional Gaussian-function fits of the aberration-corrected high-angle annual dark-field images. These subnanometer Pd catalysts exhibit high catalytic performance for the hydrogenation of biomass-derived succinic acid to γ-butyrolactone in water and avoid the formation of overhydrogenated products, such as 1,4-butanediol and tetrahydrofuran. The catalyst with an ultra-low Pd loading of 0.2 wt. % demonstrated high selectivity (95%) for γ-butyrolactone using water as a solvent at 473 K and 10 MPa. Moreover, it can be reused at least six times without the loss of catalytic activity, illustrating high performance of the small Pd clusters
Efficient Aerobic Oxidation of 5-Hydroxymethylfurfural in Aqueous Media with Au-Pd Supported on Zinc Hydroxycarbonate
MnOx/P25 with tuned surface structures of anatase-rutile phase for aerobic oxidation of 5-hydroxymethylfurfural into 2,5-diformylfuran
Highly Selective Aerobic Oxidation of 5-Hydroxymethyl Furfural into 2,5-Diformylfuran over Mn-Co Binary Oxides
Comparative Transcriptomic Analysis Provides Insight into the Key Regulatory Pathways and Differentially Expressed Genes in Blueberry Flower Bud Endo- and Ecodormancy Release
Endodormancy is the stage that perennial plants must go through to prepare for the next seasonal cycle, and it is also an adaptation that allows plants to survive harsh winters. Blueberries (Vaccinium spp.) are known to have high nutritional and commercial value. To better understand the molecular mechanisms of bud dormancy release, the transcriptomes of flower buds from the southern highbush blueberry variety “O’Neal” were analyzed at seven time points of the endo- and ecodormancy release processes. Pairwise comparisons were conducted between adjacent time points; five kinds of phytohormone were identified via these processes. A total of 12,350 differentially expressed genes (DEGs) were obtained from six comparisons. Gene Ontology analysis indicated that these DEGs were significantly involved in metabolic processes and catalytic activity. KEGG pathway analysis showed that these DEGs were predominantly mapped to metabolic pathways and the biosynthesis of secondary metabolites in endodormancy release, but these DEGs were significantly enriched in RNA transport, plant hormone signal transduction, and circadian rhythm pathways in the process of ecodormancy release. The contents of abscisic acid (ABA), salicylic acid (SA), and 1-aminocyclopropane-1-carboxylate (ACC) decreased in endo- and ecodormancy release, and the jasmonic acid (JA) level first decreased in endodormancy release and then increased in ecodormancy release. Weighted correlation network analysis (WGCNA) of transcriptomic data associated with hormone contents generated 25 modules, 9 of which were significantly related to the change in hormone content. The results of this study have important reference value for elucidating the molecular mechanism of flower bud dormancy release