Big Band Jazz的现场扩声及录制

在现场扩声、录制爵士音乐会前,首先要准确掌握乐队的基本配制,同时还要熟悉演出曲目的详细情况,之后才能确定拾音方案及设备的选择,并确定现场扩声、调音、录音的方案。     

Big Band Jozz的现场扩声及录制

在现场扩声、录制爵士音乐会前,首先要准确掌握乐队的基本配制,同时还要熟悉演出曲目的详细情况,之后才能确定拾音方案及设备的选择,并确定现场扩声、调音、录音的方案.     

Superconductivity in MgB2: A Case Study of the “Flat Band–Steep Band” Scenario

The electronic structure of MgB₂ is analyzed in terms of the flat band–steep band scenario for superconductivity. Good agreement between the Fermi surfaces obtained from de Haas–van Alphen measurements and from TB-LMTO and FP-LMTO calculations was achieved. The decomposed electron–phonon coupling (q) reveals a pronounced peak-like structure along the –A and –M directions.     

A “Flat/Steep Band” Scenario in Momentum Space

Based on chemical bonding considerations in a crystalline solid, a Hamiltonian was proposed for the flat/steep band scenario. This model has been studied with the first-principles method. With Hg and MgB₂ as examples, we have explained the characteristics of this model and observed peak-like structure of the electron–phonon coupling constant (q) in q space. The strong coupling of the flat band electrons with phonons has been corroborated by developing a new functional Psib(), through which we can quantitatively compare different electronic states in coupling to a specific phonon. In the case of MgB₂ a multigap structure of the superconducting state results from our model.     

Broadening of Photonic Band Gap in a One—Dimensional Superconductor Star Waveguide Structure

The present paper describes the theoretical investigation of enlarged reflection bands (photonic band gaps) in a 1D star waveguide (SWG) structure consists of superconductor and dielectric as its constituent materials. For the present study, we take the different combinations of superconductor and dielectric materials as a backbone and side branches of the SWG structure. In order to obtain the dispersion relation, Interface Response Theory (IRT) has been employed. Photonic band gaps of SWG structure having superconductor?Csuperconductor, superconductor?Cdielectric, and dielectric?Csuperconductor materials are compared with the band gaps of the conventional photonic crystal (PC) structure having superconductor?Csuperconductor and dielectric?Csuperconductor materials. Analysis of the dispersion characteristics shows that there exists no band gaps for conventional PC when both layers are made of the same superconducting materials (as the usual case) while the SWG structure shows forbidden bands of finite width even the backbone and side branches are made of same materials. Also, the SWG structure having superconductor?Cdielectric shows the wider reflection bands in comparison with the structure having dielectric?Csuperconductor as its constituent materials, while for the conventional PC structure it is same in both the cases. Further, the effect of temperature and the effect of variation of number of grafted branches on the photonic bands of SWG structure have been studied.     

Origion of Band-like and Atom-like Features of the Valence Band Auger Emission from Thansition Metals

TheideaofcorrelatingAuger-lineshapesfromel-ementalmetalswiththeirelectronicstructuregoesbacktoLander[1]wh0pointedoutthatthespectralformofacore-valence-valence(CVV)Augertransi-tionresultsfromaselfconvolutionofthelocaldensityof(valence)states(LDOS),ifthetransitionmatrixel-emelltsmaytoagoodapproximationberegardedasaconstalltacrossthevalenceband.Formanycases,discrepanciesbetweenexperimentallineshapesandLander'sformulacanbereducedbytakingintoac-countoftheactualvariationofthematrixelementsandthe…     

Properties of high-T C Copper Oxides from Band Models of Spin–Phonon Coupling

The mechanism of spin–phonon coupling (SPC) and possible consequences for the properties of high-T _C copper oxides are presented. The results are based on ab initio LMTO band calculations and a nearly free-electron (NFE) model of the band near E _F . Many observed properties are compatible with SPC, as for the relation between doping and for spin excitations and their energy dependence. The main pseudogap is caused by SPC and waves along [1,0,0], but it is suggested that secondary waves, generated along [1,1,0], contribute to a ‘waterfall’ structure. Conditions for optimal T _C , and the possibilities for spin enhancement at the surface are discussed.      

Anomalous Resistivity and the Electron–Polaron Effect in the Two-Band Hubbard Model with One Narrow Band

We search for anomalous normal and superconductive behavior in the two-band Hubbard model with one narrow band. We analyze the influence of the electron?Cpolaron effect and the Altshuler?CAronov effect on effective mass enhancement and scattering times of heavy and light components in the clean case. We find anomalous behavior of resistivity at high temperatures $T > W_{h}^{*}$ both in 3D and 2D situations. The SC instability in the model is governed by an enhanced Kohn?CLuttinger effect for p-wave pairing of heavy electrons via polarization of light electrons.     

Design of an Ultra Broad Band YIG-Tuned FET Oscillator Operating within -45～＋65℃

In this paper, the design of an ultra broad band YIG-Tuned FET oscillator is briefly presented. These performances of the superior linearity, the pure spectrum and the ultra broad band tuned oscillation have been realized by a common source circuit topology and a dual coupling YIG resonator. Using a BeO substrate and a buffering amplification stage made up of monolithic MIC traveling wave amplifier, the RF output power has been obtained above 13 dBm in the range from 4 to 16.5 GHz; By means of YIG heater and the temperature compensation of the magnetic circuit, the broad temperature operation performance of YTO has been realized within -45～+65℃.     

Investigation of Portevin–Le Chatelier Band Strain and Elastic Shrinkage in Al-Based Alloys Associated with Mg Contents

The Portevin–Le Chatelier(PLC) effect in Al–2.30wt%Mg, Al–4.57wt%Mg and Al–6.91wt%Mg alloys has been investigated at various applied strain rates at room temperature in this study. Three-dimensional digital image correlation(3D-DIC) technique was applied to obtaining the further insight into the spatiotemporal characteristics, in particular the influence of Mg content on deformation behaviors. Mg content has a pronounced effect on serration characteristics, including the serration type and amplitude; Mg content tends to weaken the spatial correlation of the propagative bands. Additionally, the serration amplitude linearly increases with the maximum PLC band strain; high Mg content generates a higher PLC band strain at a given serration amplitude compared with low Mg content. Mg content is found to be effective to enhance the serration amplitude, the maximum PLC band strain and also the amount of elastic shrinkage outside PLC bands.     

Omnidirectional Photonic Band Gap in One-Dimensional Ternary Superconductor-Dielectric Photonic Crystals Based on a New Thue–Morse Aperiodic Structure

In this paper, an omnidirectional photonic band gap (OBG) of one-dimensional (1D) ternary superconductor-dielectric photonic crystals (SDPCs) based on a new Thue–Mores aperiodic structure is theoretically studied by the transfer matrix method (TMM) in detail. Compared to zero- $\bar{n}$ gap or single negative (negative permittivity or negative permeability) gap, such OBG originates from Bragg gap. From the numerical results, the bandwidth and central frequency of OBG can be notably enlarged by manipulating the thicknesses of superconductor and dielectric layers but cease to change with increasing the Thue–Mores order. The OBG also can be tuned by the ambient temperature of the system especially close to the critical temperature. However, the damping coefficient of the superconductor layer has no effects on the OBG. The relative bandwidth of OBG also is investigated by the parameters as mentioned above. It is clear that such 1D ternary SDPCs have a superior feature in the enhancement of the bandwidth of OBG compared to the conventional ternary SDPCs and conventional ternary Thue–Mores aperiodic SDPCs. These results may provide theoretical instructions to design the future SDPCs devices.     

Band Engineering and Morphology Control of Oxygen‑Incorporated Graphitic Carbon Nitride Porous Nanosheets for Highly Efficient Photocatalytic Hydrogen Evolution

Graphitic carbon nitride(g-C3N4)-based photocatalysts have shown great potential in the splitting of water.However,the intrinsic drawbacks of g-C3N4,such as low surface area,poor diffusion,and charge separation efficiency,remain as the bottleneck to achieve highly efficient hydrogen evolution.Here,a hollow oxygen-incorporated g-C3N4 nanosheet(OCN)with an improved surface area of 148.5 m2 g^−1 is fabricated by the multiple thermal treatments under the N2/O2 atmosphere,wherein the C–O bonds are formed through two ways of physical adsorption and doping.The physical characterization and theoretical calculation indicate that the O-adsorption can promote the generation of defects,leading to the formation of hollow morphology,while the O-doping results in reduced band gap of g-C3N4.The optimized OCN shows an excellent photocatalytic hydrogen evolution activity of 3519.6μmol g^−1 h^−1 for~20 h,which is over four times higher than that of g-C3N4(850.1μmol g^−1 h^−1)and outperforms most of the reported g-C3N4 catalysts.     

Study of Band Structure Properties of Pnictide LaO1−xF x FeAs (x = 0, 0.2) Superconducting Compound

This paper reports on the band structure properties and changes in band structure of fluorine-doped LaO_1?x F _x FeAs (x = 0, 0.2) compound, measured using X-ray photoemission spectroscopy (XPS). The band structure of the superconducting compound is compared with nonsuperconducting parent compound LaOFeAs. With fluorine doping, a shift of the shallow core level is observed in XPS spectra, which may be a response of the band structure due to fluorine doping in the system. The balance of the chemical potential shift with the screening effect of conduction electrons near the Fe and As ions is discussed using nearly unchanged Fe 2p and As 3d core-level spectra. The La 3d core-level spectra shift towards the high energy, ～0.36 eV, may be due to the chemical potential shift caused by fluorine doping. In our valence band spectra, a small peak at around 0.2 eV is observed, which disappeared with the fluorine doping in the system, indicating a change of Fe 3d state from low spin to high spin states and also confirming the nature of Fe 3d electrons as itinerant, which is responsible for superconductivity in these compounds.     

Band edge motion in quantizing magnetic field and nonequilibrium states in Pb1−x Sn x Te alloys doped with In

Galvanomagnetic and oscillation effects in Pb_1–x Sn _x Te single crystals doped with 0.5 at % In have been studied in magnetic fields up to 60 kOe at temperatures from 4.2 to 30 K under hydrostatic pressure up to 18 kbar. Beyond the ultraquantum magnetic field limit (H _uql) for the metallic state of Pb_1–x Sn _x Te(In) alloys, Fermi level pinning by high-density quasilocal states takes place. In a strong fieldH>H _uql the equationE _F = const is valid instead of the equationn = const which is usual for degenerate semiconductors (E _F is the electron or hole Fermi energy, andn is their concentration). This makes it possible to determine the direction of the band edge motion in the Pb_1–x Sn _x Te energy spectrum in a quantizing magnetic field in the direct and inverse spectral regions. It is found that the charge carrier transitions between quasilocal and band states are of anomalously long duration (10⁵ sec atT=4.2 K). By the application of a quantizing magnetic field we obtained a nonequilibrium metallic state of the system with a frozen or slowly diminishing Fermi surface. The characteristic time of the transition was found as a function of temperature and pressure. The relaxation kinetics of the nonequilibrium states induced by a quantizing magnetic field and infrared irradiation is discussed.     

Manipulating the Interfacial Band Bending For Enhancing the Thermoelectric Properties of 1T′-MoTe2/Bi2Te3 Superlattice Films

Interfacial charge effects, such as band bending, modulation doping, and energy filtering, are critical for improving electronic transport properties of superlattice films. However, effectively manipulating interfacial band bending has proven challenging in previous studies. In this study, (1T′-MoTe₂)_x(Bi₂Te₃)_y superlattice films with symmetry-mismatch were successfully fabricated via the molecular beam epitaxy. This enables to manipulate the interfacial band bending, thereby optimizing the corresponding thermoelectric performance. These results demonstrate that the increase of Te/Bi flux ratio (R) effectively tailored interfacial band bending, resulting in a reduction of the interfacial electric potential from ≈127 meV at R = 16 to ≈73 meV at R = 8. It is further verified that a smaller interfacial electric potential is more beneficial for optimizing the electronic transport properties of (1T′-MoTe₂)_x(Bi₂Te₃)_y. Especially, the (1T′-MoTe₂)₁(Bi₂Te₃)₁₂ superlattice film displays the highest thermoelectric power factor of 2.72 mW m⁻¹ K⁻² among all films, due to the synergy of modulation doping, energy filtering, and the manipulation of band bending. Moreover, the lattice thermal conductivity of the superlattice films is significantly reduced. This work provides valuable guidance to manipulate the interfacial band bending and further enhance the thermoelectric performances of superlattice films.     

Porous Host–Guest MOF-Semiconductor Hybrid with Multisites Heterojunctions and Modulable Electronic Band for Selective Photocatalytic CO2 Conversion and H2 Evolution

Optimizing catalysts for competitive photocatalytic reactions demand individually tailored band structure as well as intertwined interactions of light absorption, reaction activity, mass, and charge transport.  Here, a nanoparticulate host–guest structure is rationally designed that can exclusively fulfil and ideally control the aforestated uncompromising requisites for catalytic reactions. The all-inclusive model catalyst consists of porous Co₃O₄ host and Zn_xCd_1-xS guest with controllable physicochemical properties enabled by self-assembled hybrid structure and continuously amenable band gap. The effective porous topology nanoassembly, both at the exterior and the interior pores of a porous metal–organic framework (MOF), maximizes spatially immobilized semiconductor nanoparticles toward high utilization of particulate heterojunctions for vital charge and reactant transfer. In conjunction, the zinc constituent band engineering is found to regulate the light/molecules absorption, band structure, and specific reaction intermediates energy to attain high photocatalytic CO₂ reduction selectivity. The optimal catalyst exhibits a H₂-generation rate up to 6720 µmol g⁻¹ h⁻¹ and a CO production rate of 19.3 µmol g⁻¹ h⁻¹. These findings provide insight into the design of discrete host–guest MOF-semiconductor hybrid system with readily modulated band structures and well-constructed heterojunctions for selective solar-to-chemical conversion.     

Excitation of Narrow‐Band Pulsations in a Short Portion of Transition from the Smaller Diameter of a Pipe to a Larger Diameter and Possibilities of Preventing Them

By using models of the portions of the circuit of main gascompressor stations, data on the frequencies of narrowband pressure pulsations have been obtained; these data demonstrate the jet character of flow in divergent channels with angles of opening on one side of 12°47 and 23°50. It has been shown that narrowband acoustic disturbances are generated in the internal flow with largescale hydrodynamic structures. Intense narrowband pulsations are prevented by a grid of internal divergent channels in the transition portion with small angles of opening in canals and in excitation of certain disturbances upstream of a short divergent channel.     

Band gap tailoring, structural and morphological properties of Zn0.98−xMn0.02CuxO (0 ≤ x ≤ 0.05) nanopowders by sol–gel method

Zn_0.98?xMn_0.02Cu_xO (0 ≤ x ≤ 0.05) nanopowders have been synthesized by sol–gel method. The synthesized nanopowders were characterized by powder X-ray diffraction, energy dispersive X-ray spectra, UV–visible spectrophotometer and Fourier transform infrared spectroscopy. The XRD measurement revealed that the prepared nanopowders have different microstructure without changing a hexagonal wurtzite structure. The calculated average crystallite size was decreased from 22.4 to 16.7 nm for Cu = 0–0.02 then gradually increased to 21.5 nm for Cu = 0.05 which were confirmed by SEM. The change in lattice parameters, shift in X-ray diffraction peaks and the change in energy gap revealed the substitution of Cu²⁺ ions into Zn–Mn–O lattice. The observed red shift of optical energy gap (E_g ≈ 0.27 eV) at lower concentrations (Cu ≤ 2 %) is explained by increasing charge carriers and Moss–Burstein effect meanwhile blue shift (E_g ≈ 0.56 eV) at higher Cu concentrations (Cu > 2 %) is explained in terms of the distortion of host lattice and generation of defects. The variation of crystallite size was discussed in terms of micro-strain.     

Band gap tailoring,structural and morphological behavior of Zn0.96−x Co0.04Cu x O (0 ≤ x ≤ 0.10) alloys by sol–gel method

Zn_0.96?x Co_0.04Cu _x O (0 ≤ x ≤ 0.1) nanopowders were successfully synthesized by sol–gel method. Hexagonal structure was confirmed by X-ray diffraction spectra. A new phase around 38.4° corresponding to CuO was noticed after Cu = 4 %. The reduced crystal size up to Cu = 4 % is due to the substitution of Cu²⁺ and the increasing crystal size after Cu = 4 % is due to the interference between Co and Cu metal ions. The higher absorption of Cu doped Zn_0.96Co_0.04O than undoped was due to the created charge carries. The tuning of energy gap from 3.18 to 3.69 eV by Cu-doping was discussed in terms of crystal size, the created charge carriers and the interstitial zinc atoms and oxygen deficiencies. Presence of chemical bonding and purity of the nanopowders were confirmed by Fourier transform infrared spectra.     

Band gap modified Al-doped Zn1?xMgxO and Zn1?yCdyO transparent conducting thin films

Al-doped Zn_1−x Mg _x O and Zn_1−y Cd _y O thin films were prepared on glass substrates by sol–gel method. The codoping thin films showed preferential c-axis orientation, and the lattice constant c evaluated from the shift of the position of (002) peak displayed an increasing evolution from x = 8 at.% to y = 8 at.%, indicating a roughly statistical substitution of Mg²⁺ and Cd²⁺ for Zn²⁺ in their solid solution. The effects of narrowing and widening band gap (E _g) on conductivity of (Cd, Al) and (Mg, Al) codoped ZnO thin films were simultaneously investigated using transmission spectra and electrical measurements. The transmittances of these films are obviously decreased by vacuum annealing to 50–60%. However, the carrier concentration and Hall mobility both increase, and resistivity decreases with narrowing band gap in 1 at.% Al-doped Zn_1−x Mg _x O and Zn_1−y Cd _y O thin films from x = 8 at.% to y = 8 at.%. It is revealed that the conductivity of Al-doped ZnO thin films could be enhanced by this simple band gap modification.