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The century-long development of surface sciences has witnessed the discoveries of a variety of quantum states. In the recently proposed "obstructed atomic insulators", insulators with symmetric charges pinned at virtual sites where no real atoms reside, the cleavage through these sites could lead to a set of obstructed surface states with partial occupation. Here, utilizing scanning tunneling microscopy, angle-resolved photoemission spectroscopy and first-principles calculations, we observe spectroscopic signature of obstructed surface states in SrIn$_2$P$_2$. We find a pair of surface states originated from the pristine obstructed surface states split by a unique surface reconstruction. The upper branch is marked with a striking differential conductance peak followed by negative differential conductance, signaling its localized nature, while the lower branch is found to be highly dispersive. This pair of surface states is in consistency with our calculational results. Our finding not only demonstrates a surface quantum state induced by a new type of bulk-boundary correspondence, but also provides a platform for exploring efficient catalysts and related surface engineering., 20 Pages, 4 Figures

On the basis of the spectral analysis of the $$4\times 4$$ Lax pair associated with the spin-1 Gross–Pitaevskii equation and the scattering matrix, the solution to the Cauchy problem of the spin-1 Gross–Pitaevskii equation is transformed into the solution to the corresponding Riemann–Hilbert problem. The Deift–Zhou nonlinear steepest descent method is extended to the Riemann–Hilbert problem, from which a model Riemann–Hilbert problem is established with the help of distinct factorizations of the jump matrix for the Riemann–Hilbert problem and a decomposition of the matrix-valued spectral function. Finally, the long-time asymptotics of the solution to the Cauchy problem of the spin-1 Gross–Pitaevskii equation is obtained.

Proteoglycans are proteins that are modified with glycosaminoglycan chains. Chondroitin sulfate proteoglycans (CSPGs) are currently being exploited as targets for drug-delivery in various cancer indications, however basic knowledge on how CSPGs are internalized in tumor cells is lacking. In this study we took advantage of a recombinant CSPG-binding lectin VAR2CSA (rVAR2) to track internalization and cell fate of CSPGs in tumor cells. We found that rVAR2 is internalized into cancer cells via multiple internalization mechanisms after initial docking on cell surface CSPGs. Regardless of the internalization pathway used, CSPG-bound rVAR2 was trafficked to the early endosomes in an energy-dependent manner but not further transported to the lysosomal compartment. Instead, internalized CSPG-bound rVAR2 proteins were secreted with exosomes to the extracellular environment in a strictly chondroitin sulfate-dependent manner. In summary, our work describes the cell fate of rVAR2 proteins in tumor cells after initial binding to CSPGs, which can be further used to inform development of rVAR2-drug conjugates and other therapeutics targeting CSPGs.

Recently, the layered transition metal dichalcogenide 1T′-MoTe2 has generated considerable interest due to their superconducting and non-trivial topological properties. Here, we present a systematic study on 1T′-MoTe2 single-crystal and exfoliated thin-flakes by means of electrical transport, scanning tunnelling microscope (STM) measurements and band structure calculations. For a bulk sample, it exhibits large magneto-resistance (MR) and Shubnikov–de Hass oscillations in ρxx and a series of Hall plateaus in ρxy at low temperatures. Meanwhile, the MoTe2 thin films were intensively investigated with thickness dependence. For samples, without encapsulation, an apparent transition from the intrinsic metallic to insulating state is observed by reducing thickness. In such thin films, we also observed a suppression of the MR and weak anti-localization (WAL) effects. We attributed these effects to disorders originated from the extrinsic surface chemical reaction, which is consistent with the density functional theory (DFT) calculations and in-situ STM results. In contrast to samples without encapsulated protection, we discovered an interesting superconducting transition for those samples with hexagonal Boron Nitride (h-BN) film protection. Our results indicate that the metallic or superconducting behavior is its intrinsic state, and the insulating behavior is likely caused by surface oxidation in few layer 1T’-MoTe2 flakes.

The frequency-assisted phase tracking (FAPT) is investigated extensively in comparison with the phase tracking (PT) in a Kalman filter (KF) frame to explore the role the augmented frequency measurement plays in FAPT. It is found that the FLL-assisted PLL is suboptimal in structure, while the FAPT is optimal in the minimum variance sense. Hence, the KF frame provides not only a rational method to compare the FAPT with the PT but also an insight into the effects of frequency and phase measurements on PT. The impact of the two typical discriminators, ATAN and ATAN2, on the phase tracking performance in the FAPT and the PT is studied by Monte Carlo simulations and covariance analysis. The results show that the pull-in range affects the lock-in threshold, and the linear region determines the performance under high dynamic environments. In addition, the measurement variance dominates the tracking accuracy under weak signal conditions. The phase discriminator governs the performance of the FAPT. In terms of both the tracking accuracy and the lock-in threshold, the augmented frequency measurement in the FAPT filters is very helpful in tracking the high dynamic signal, but it contributes little to the weak signal tracking.

We present elastic integral cross sections for electron collisions with ethylene oxide and thiirane. The calculations were performed with R-matrix method in the static-exchange and static exchange polarization approximations for electron energies ranging from 0.01 to 15 eV. We found two shape resonances in the 2B1 and 2B2 symmetry in each molecule. We also detected one shape resonance in the 2A1 symmetry for thiirane. The positions of the resonances agree well with available results. We shed some light on the nature of the resonances of these two compounds together with molecular orbital calculations. The similarities and differences among the resonances are discussed.

Design of a GPS signal acquisition algorithm is a trade-off between improvement of the acquisition frequency resolution and reduction in the acquisition time. A new algorithm is proposed to acquire the carrier frequency accurately by correlation of the GPS signal after completion of the coarse acquisition of the signals. The CA code in a period of 1 ms is stripped off first. Then, several local replica carriers are generated and mixed with the CA-code-stripped data. Finally, the mixed data are integrated to detect the carrier frequency accurately. By analyzing the correlated integration result, the algorithm performance is evaluated on the aspects of the computational load, the effects of the carrier-to-noise ratio, and the navigation data transition. Performance of the proposed method is verified by simulations and experiments.

We present a comprehensive study of electron collisions with germylene (GeH2 using the UK molecular R-matrix codes for electron energies ranging from 0.01 to 10 eV. The calculations are performed within the static-exchange, static-exchange-polarization, and 17-state close-coupling approximations. The elastic integral, differential, momentum transfer cross sections and the excitation cross sections from the ground state to the six low-lying electron excited states are presented. We found three Feshbach resonances and one Core-excited resonance. These resonances reveal the probability of anion formation by an electron attachment process and further decay to neutral and negative ion fragments. The electronic and rotational excitation cross sections for e-GeH2 scattering are reported for the first time. The cross-section dataset obtained from the present calculations are expected to be sufficiently accurate and comprehensive for most current modeling applications involving neutral GeH2.

The photodetachment of the negative ion of boron, B−(2s 22p 2)3P, is investigated by employing the B-spline R-matrixmethod for photon energies ranging from threshold to 12 eV. A multi-configuration Hartree-Fock method with nonorthogonal, term-dependent orbitals is employed to generate accurate initial bound-state and final continuum-state wavefunctions. The close-coupling expansion includes all principal scattering channels for photodetachment from both the 2p and 2s orbitals. The calculated photodetachment cross sections are in good agreement with the available experimental data. Several prominent resonance features are predicted, thereby providing new challenges in the study of this highly correlated process. To classify the resonance structure, both the partial cross sections and the main contributions of the individual scattering channels are discussed. The presented cross sections, along with the asymmetry parameter β for the angular distribution, are believed to be the most comprehensive and accurate dataset currently available for the B− photodetachment process at low energies.

Scanning tunneling microscopy (STM) is not only an excellent tool for the study of static geometric structures and electronic structures of surfaces due to its high spatial and energy resolution, but also a powerful tool for the study of surface dynamic behaviors, including surface diffusion, molecular rotation, and surface chemical reactions. Because of the limitation of the scanning speed, the video-STM technique cannot study the fast dynamic processes. Alternatively, a time-dependent tunneling current, I-t curve, method is employed in the research of fast dynamic processes. Usually, this method can detect about 1000 times faster dynamic processes than the traditional video-STM method. When placing the STM tip over a certain interesting position on the sample surface, the changing of tunneling current induced by the surface dynamic phenomena can be recorded as a function of time. In this article, we review the applications of the time-dependent tunneling current method to the studies of surface dynamic phenomena in recent years, especially on surface diffusion, molecular rotation, molecular switching, and chemical reaction.

The R-matrix approach is used to calculate the elastic differential, integral, and momentum transfer cross sections for electron impact on H2CNH within static-exchange-polarization (SEP) and close-coupling (CC) approximations. The electron-impact excitation cross sections from the ground state to the first three low-lying electronic excited states of H2CNH molecule have been also studied for the first time. A shape resonance of 2 A′′ symmetry located at 1.95 eV with a width of 0.56 eV is detected within CC model. The effective collision frequencies over a wide electron temperature range (200−30 000 K) are calculated using the data of the momentum-transfer cross section.

Self-assembled monolayers of novel C60 derivative, N-3-γ-pyridyl Aza[60]fulleroid (C60Py), on Au(111) were studied by a scanning tunneling microscope under ultrahigh vacuum (UHV). C60Py molecules were assembled on Au (111) via pyridyl nitrogen-Au interaction. The sole assembly of C60Py molecules on Au (111) only exhibited randoml aggregation of C60Py even the films were annealed at 50 and 105°C. By co-assembling with benzyl mercaptan (BM), the C60PyBM films showed highly dense aggregation, but C60Py assemblies still had disordered structure. After the co-assembled C60Py-BM films were annealed at 50°C, BM molecules were partially desorbed, but the assembly of C60Py remained without obvious change. After the co-assembled C60Py-BM films were further annealed at 105°C, the C60Py monolayers with ordered structure were obtained, while the BM molecules were nearly thoroughly desorbed from the surface. Here, the BM molecules play a key role as a surfactant in the formation of the ordered C60Py monolayer.

The performance of ten density functionals and four force field methods in describing non-covalent interactions have been assessed by studying the interaction energies and structures of the four anion–π complexes involving tetraoxacalix[2]arene[2]triazine and various anions. Their structures are optimized at MP2/6-311++G(d,p) level, and interaction energies are obtained at DF-MP2-F12/aug-cc-pVDZ level. The result shows that the functional M06-2X predicts the most reliable interaction energy, followed by wB97XD and BHandH. B97D slightly overestimates the interaction energy. Other functionals and force field methods seriously overestimate the interaction energy. For the structures, three functionals M06-2X, wB97XD and BH and H predict the most reliable results, followed by B97D. The force field methods predict the largest deviations. The present work suggests that the functional M06-2X is a reliable method to describe energies and structural properties of the large molecules involving the anion–π interactions.