Formation of Fermi surfaces and the appearance of liquid phases in holographic theories with hyperscaling violation

We consider a holographic fermionic system in which the fermions are interacting with a U(1) gauge field in the presence of a dilaton field in a gravity bulk of a charged black hole with hyperscaling violation. Using both analytical and numerical methods, we investigate the properties of the infrared and ultaviolet Green's functions of the holographic fermionic system. Studying the spectral functions of the system, we find that as the hyperscaling violation exponent is varied, the fermionic system possesses Fermi, non-Fermi, marginal-Fermi and log-oscillating liquid phases. Various liquid phases of the fermionic system with hyperscaling violation are also generated with the variation of the fermionic mass. We also explore the properties of the flat band and the Fermi surface of the non-relativistic fermionic fixed point dual to the hyperscaling violation gravity.Comment: 19 pages, 8 figures; v2: minor clarifications, section VI added, references added; accepted for publication in JHE

Fermionic phase transition induced by the effective impurity in holography

We investigate the holographic fermionic phase transition induced by the effective impurity in holography, which is introduced by massless scalar fields in Einstein-Maxwell-massless scalar gravity. We obtain a phase diagram in $(\alpha, T)$ plane separating the Fermi liquid phase and the non-Fermi liquid phase.Comment: 17 pages, 9 figure

Phonon and Raman scattering of two-dimensional transition metal dichalcogenides from monolayer, multilayer to bulk material

Two-dimensional (2D) transition metal dichalcogenide (TMD) nanosheets exhibit remarkable electronic and optical properties. The 2D features, sizable bandgaps, and recent advances in the synthesis, characterization, and device fabrication of the representative MoS$_2$, WS$_2$, WSe$_2$, and MoSe$_2$ TMDs make TMDs very attractive in nanoelectronics and optoelectronics. Similar to graphite and graphene, the atoms within each layer in 2D TMDs are joined together by covalent bonds, while van der Waals interactions keep the layers together. This makes the physical and chemical properties of 2D TMDs layer dependent. In this review, we discuss the basic lattice vibrations of monolayer, multilayer, and bulk TMDs, including high-frequency optical phonons, interlayer shear and layer breathing phonons, the Raman selection rule, layer-number evolution of phonons, multiple phonon replica, and phonons at the edge of the Brillouin zone. The extensive capabilities of Raman spectroscopy in investigating the properties of TMDs are discussed, such as interlayer coupling, spin--orbit splitting, and external perturbations. The interlayer vibrational modes are used in rapid and substrate-free characterization of the layer number of multilayer TMDs and in probing interface coupling in TMD heterostructures. The success of Raman spectroscopy in investigating TMD nanosheets paves the way for experiments on other 2D crystals and related van der Waals heterostructures.Comment: 30 pages, 23 figure

Research on the Running Speed Prediction Model of Interchange Ramp

AbstractRamp is an important part of the interchange. The ramp design concept based on the running speed is a new design idea of the highway and interchange. By analysis of the influence factors of the interchange ramp running speed, this paper formulates the orthogonal experiment, and collects 14 ramps, in total of 147 groups of the running speed as the samples, and then analyzes the characteristics of the running speed of the vehicles on interchange ramp. According to the change trend of the running speed, the ramp is divided into three sections: deceleration section, uniform section, acceleration section. This paper mainly analyzes the relationship between the interchange ramp running speed of the three sections and the influence factors; and then this paper builds the interchange ramp running speed prediction model of the three sections. At last, correlation test will be validated, and verify the applicability of the model

Digital distance control system research and implementation

AbstractThe paper introduced a mathematical model of three segment speed reference in main shaft hoist system, and an application of equivalent area method to control shaft hoist shut-down precisely using three segment speed reference curve. In order to verify the correctness of the theory, we established a MATLAB model. From mathematical analysis and computer simulation, we can see that this control approach is feasible