Effective identification of terrain positions from gridded DEM data using multimodal classification integration

Terrain positions are widely used to describe the Earth’s topographic features and play an important role in the studies of landform evolution, soil erosion and hydrological modeling. This work develops a new multimodal classification system with enhanced classification performance by integrating different approaches for terrain position identification. The adopted classification approaches include local terrain attribute (LA)-based and regional terrain attribute (RA)-based, rule-based and supervised, and pixel-based and object-oriented methods. Firstly, a double-level definition scheme is presented for terrain positions. Then, utilizing a hierarchical framework, a multimodal approach is developed by integrating different classification techniques. Finally, an assessment method is established to evaluate the new classification system from different aspects. The experimental results, obtained at a Loess Plateau region in northern China on a 5 m digital elevation model (DEM), show reasonably positional relationship, and larger inter-class and smaller intra-class variances. This indicates that identified terrain positions are consistent with the actual topography from both overall and local perspectives, and have relatively good integrity and rationality. This study demonstrates that the current multimodal classification system, developed by taking advantage of various classification methods, can reflect the geographic meanings and topographic features of terrain positions from different levels

Matrix Infrared Spectroscopic and Theoretical Studies on the Reactions of Late Lanthanoid Atoms with Nitrous Oxide in Excess Argon

Reactions of laser-ablated late lanthanoid atoms (Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) with N2O molecules in excess argon have been investigated using matrix-isolation infrared spectroscopy. Lanthanoid monoxide−dinitrogen complexes, OLn(N2) and OLnNN, are observed for Gd, Tb, Ho, and Er, and the OLnNN+ cations are observed for Gd to Lu except for Yb. The new products are characterized on the basis of isotopic shifts, mixed isotopic splitting patterns, and CCl4-doping experiments. Density functional theory calculations have been performed on the new species, which support identification of the OLn(N2), OLnNN, and OLnNN+ complexes from the matrix infrared spectra. Together with our earlier work involving early lanthanoid atoms, several trends are identified for the reactions of lanthanoid atoms with N2O molecules

Experimental and Theoretical Evidence for the Formation of Zinc Tricarbonyl in Solid Argon

Zinc carbonyls are extremely rare. Here we report experimental and theoretical evidence of unprecedented zinc tricarbonyl, Zn(CO)3, the next member of the series of 18-electron metal carbonyls Cr(CO)6 → Fe(CO)5 → Ni(CO)4, whereas there is no evidence for the formation of the zinc mono- and dicarbonyls Zn(CO)n (n = 1, 2). DFT calculations predict that the Zn(CO)3 molecule has a singlet ground state with D3h symmetry. The formation of Zn(CO)3 involves 4s → 4p promotion of the Zn atom, which increases the Zn−CO bonding by decreasing the σ repulsion and significantly increasing the Zn 4sp hybrid orbitals → CO π* back-donation

Observation of Anomalous C−O Bond Weakening on Discandium and Activation Process to CO Dissociation

Sc2[η2(μ2-C,O)], the first homoleptic dinuclear metal carbonyl with an unprecedented bridging and side-on-bonded CO, generated from the reaction of laser-ablated Sc atoms with CO in a solid argon matrix, exhibits an unusually low C−O stretching frequency at 1193.4 cm-1, characteristic of an anomalously weakened C−O bond. This CO-activated molecule undergoes ultraviolet−visible photoinduced rearrangement to the CO-dissociated molecule, c-Sc2(μ-C)(μ-O). The infrared absorptions of the new molecules are accurately predicted by quantum chemical calculations, and the activation energy for the isomerization of Sc2[η2(μ2-C, O)] to c-Sc2(μ-C)(μ-O) is calculated to be 15.10 kcal/mol. Our experimental and theoretical results schematically depict an activation process to CO dissociation

Structure–Property Relationships in Amorphous Thieno[3,2‑<i>b</i>]thiophene–Diketopyrrolopyrrole–Thiophene-Containing Polymers

We present calculations of electronic structure properties of disordered conducting polymers containing thieno­[3,2-b]­thiophene, diketopyrrolopyrrole, and thiophene. Atomistic force field parameters for the polymer were optimized to minimize the difference between the ab initio and empirical potential energy surfaces and their corresponding first derivatives. These new force fields are employed to propagate the nuclear dynamics, and the equilibrium trajectories are sampled for subsequent electronic structure calculations. We found that the fluctuations of the bulk density of states are negligibly small and do not vary significantly with the length of the backbone and the side-chains. The localization length near the band gap is between 8 and 12 Å, which is about half of the length of the monomer and significantly less than the length of the extended polymer (∼200–400 Å). This indicates that the orbital localization is not affected by the length of the polymer. The inter-chain excitonic couplings are usually smaller than 5 meV, suggesting that the transport mechanism across chains is described by incoherent hopping, and excitons mainly move along the chain. Furthermore, thermal fluctuations cause the evolution of the excitons along the chain. Characterization of the relationships between the geometric disorder of the polymers and the distributions of the lowest excited states reveals that the low-energy excitons tend to localize in regions that are more planar and less folded. However, some excitons are also spread over defects. Thus, our theoretical calculations and the new force fields provide a direct route for characterizing the structure–property relationships and helpful information for constructing more realistic models for the exciton dynamics study of this class of polymeric materials

Structure–Property Relationships in Amorphous Thieno[3,2‑<i>b</i>]thiophene–Diketopyrrolopyrrole–Thiophene-Containing Polymers

We present calculations of electronic structure properties of disordered conducting polymers containing thieno­[3,2-b]­thiophene, diketopyrrolopyrrole, and thiophene. Atomistic force field parameters for the polymer were optimized to minimize the difference between the ab initio and empirical potential energy surfaces and their corresponding first derivatives. These new force fields are employed to propagate the nuclear dynamics, and the equilibrium trajectories are sampled for subsequent electronic structure calculations. We found that the fluctuations of the bulk density of states are negligibly small and do not vary significantly with the length of the backbone and the side-chains. The localization length near the band gap is between 8 and 12 Å, which is about half of the length of the monomer and significantly less than the length of the extended polymer (∼200–400 Å). This indicates that the orbital localization is not affected by the length of the polymer. The inter-chain excitonic couplings are usually smaller than 5 meV, suggesting that the transport mechanism across chains is described by incoherent hopping, and excitons mainly move along the chain. Furthermore, thermal fluctuations cause the evolution of the excitons along the chain. Characterization of the relationships between the geometric disorder of the polymers and the distributions of the lowest excited states reveals that the low-energy excitons tend to localize in regions that are more planar and less folded. However, some excitons are also spread over defects. Thus, our theoretical calculations and the new force fields provide a direct route for characterizing the structure–property relationships and helpful information for constructing more realistic models for the exciton dynamics study of this class of polymeric materials

Terahertz spectroscopy of amino acid crystals based on dispersion-correction functional theory

The terahertz spectra of solid-state amino acids with different polarities were measured by terahertz time-domain spectroscopy and Fourier transform infrared spectroscopy. The measured absorption spectra were in good agreement with the results simulated by density functional theory using hybrid functional Becke–3–Lee–Yang–Parr and generalized-gradient approximation Perdew–Burke–Ernzerhof functional with the same basis set of 6-311 G (d, p), respectively. In order to construct a precise crystal structure, dispersion-corrected density functionals were included in the simulation. It was found that Becke–3–Lee–Yang–Parr functional combined with dispersion-correction could produce accurate simulation results that corresponded to the experimental terahertz spectra of solid-state amino acids. However, it greatly increased the time for calculation. The method of Perdew–Burke–Ernzerhof functional with dispersion-correction provided comparable accuracy to Becke–3–Lee–Yang–Parr with dispersion-correction, and much higher simulation speed. The spectral features are assigned as primarily external lattice translations and rotations with lesser contributions to intramolecular torsions.</p

Binding-Induced 3D-Bipedal DNA Walker for Cascade Signal Amplification Detection of Thrombin Combined with Catalytic Hairpin Assembly Strategy

As an important biomarker, thrombin (TB) is a major player in thrombosis and hemostasis and has attracted increasing attention involving its determination. Herein a universal and ultrasensitive fluorescence biosensor based on a binding-induced 3D-bipedal DNA walker and catalytic hairpin assembly (CHA) strategy has been proposed for cascade signal amplification detection of thrombin. In this study, we designed two proximity probes (foot 1 and foot 2) which include a specific affinity ligand for TB binding and a Pb2+-dependent DNAzyme tail sequence. In the presence of TB, the simultaneous binding of TB to foot 1 (F1) and foot 2 (F2) via TB aptamer (TBA) brings the tail sequences into close proximity and the melting temperature for tail sequences and track DNA is increased, allowing the Pb2+-dependent DNAzyme to cleave the track DNA into two short fragments which have lower affinities for the DNAzyme and, finally, leading to the release of trigger DNA (T-DNA) for subsequent CHA reaction. In the meantime, the dissociated DNA walkers (F1 and F2) explore adjacent unwound track DNA, and the walking procedure is conducted. Unlike the conventional unipedal DNA walkers that anchor foot DNA and track DNA on the same sensing surface, the proposed 3D-bipedal DNA walking machine can not only increase the local concentration of track DNA but can also improve the walking efficiency and expand the range of the walkers to some extent due to the two free feet. Moreover, with the advantages of superior sensitivity and excellent specificity, this biosensing platform exhibits a huge potential in practical application in biomedical research and clinical diagnosis

CO Activation on the Late Lanthanide Dimers: Matrix Infrared Spectra of the Ln₂[η²(μ₂-C, O)]<i>_x</i> (Ln = Tb, Dy, Ho, Er, Lu; <i>x</i> = 1, 2) Molecules

Reactions of laser-ablated late lanthanide atoms (Tb, Dy, Ho, Er, Tm, Yb, and Lu) with dilute carbon monoxide molecules in solid argon have been investigated using matrix-isolation infrared spectroscopy. The Ln2[η2(μ2-C, O)]x (Ln = Tb, Dy, Ho, Er, Lu; x = 1, 2) molecules are observed upon sample annealing, whereas no product is observed for Tm and Yb. The C−O stretching frequencies in these dilanthanide carbonyls range from 1100 to 1300 cm-1, far below the value of free CO in the gas phase (2143.5 cm-1), implying that the C−O bonds are highly activated. Density functional theory calculations have been performed on these products. These Ln2[η2(μ2-C, O)]x molecules are predicted to have planar structures, which carry asymmetrically bridging CO moieties that are tilted to the side

Unique Structural Trends in the Lanthanoid Oxocarbonyl Complexes

Reactions of laser-ablated lanthanoid atoms (except for radioactive Pm) with carbon dioxide molecules in solid argon have been investigated using matrix-isolation infrared spectroscopy. On the basis of isotopic shifts, mixed isotopic splitting patterns, and CCl4-doping experiments, the lanthanoid oxocarbonyl complexes have been identified. Density functional theory calculations have been performed on these products, which support the experimental assignments of the infrared spectra. Infrared spectroscopic studies of these lanthanoid complexes combined with theoretical calculations reveal that the early lanthanoid (La−Sm) oxocarbonyl complexes adopt trans configurations, the europium and ytterbium ones adopt side-on-bonded modes (Eu-(η2-OC)O and Yb-(η2-OC)O), and the late lanthanoid (Gd−Lu) ones adopt cis configurations. Natural bond orbital analysis indicates that the formation of the lanthanoid oxocarbonyl complexes involves the promotion of 6s and 4f electrons into the metal valence shell