Supersonic flow past axisymmetric flared cones

Systematic data on the determination of the aerodynamic characteristics of axisymmetric bodies with a break in the generating line (Fig. 1a, b) in supersonic flow at zero angle of attack are presented in [1, 2, and others]. A characteristic feature of the flow past such bodies is the appearance of an extensive separation zone dec in the region of the break in the generator when the break angle exceeds some minimum value _min, which for a turbulent boundary layer depends basically on the Mach number M at the body surface ahead of the separation zone. In this case, compression waves which change into the oblique compression shocks dc and cc, emanate both from the beginning of the separation zone (point c) and from the end of it (point d). These shocks, intersecting at the point c, form the triple shock configuration acd and acc for which we introduce the notationac[c, d]. The maximum value (_max) of the generator break angle is limited by the possibility of the existence of an attached compression shock, dc. According to these data a change in the generator break angle for the range _minmax of the angle does not disrupt the nature of the flow in the separation zone, but only alters the size of this zone.We shall examine the flow past cones with values of the generator break angles (_max) for which the attached shock dc cannot exist.     

An in situ STM/AFM and impedance spectroscopy study of the extremely pure 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl)trifluorophosphate/Au(111) interface: potential dependent solvation layers and the herringbone reconstruction

The structure and dynamics of the interfacial layers between the extremely pure air- and water-stable ionic liquid 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl)trifluorophosphate and Au(111) has been investigated using in situ scanning tunneling microscopy, cyclic voltammetry, electrochemical impedance spectroscopy, and atomic force microscopy measurements. The in situ scanning tunnelling microscopy measurements reveal that the Au(111) surface undergoes a reconstruction, and at -1.2 V versus Pt quasi-reference the famous (22 × √3) herringbone superstructure is probed. Atomic force microscopy measurements show that multiple ion pair layers are present at the ionic liquid/Au interface which are dependent on the electrode potential. Upon applying cathodic electrode potentials, stronger ionic liquid near surface structure is detected: both the number of near surface layers and the force required to rupture these layers increases. The electrochemical impedance spectroscopy results reveal that three distinct processes take place at the interface. The fastest process is capacitive in its low-frequency limit and is identified with electrochemical double layer formation. The differential electrochemical double layer capacitance exhibits a local maximum at -0.2 V versus Pt quasi-reference, which is most likely caused by changes in the orientation of cations in the innermost layer. In the potential range between -0.84 V and -1.04 V, a second capacitive process is observed which is slower than electrochemical double layer formation. This process seems to be related to the herringbone reconstruction. In the frequency range below 1 Hz, the onset of an ultraslow faradaic process is found. This process becomes faster when the electrode potential is shifted to more negative potentials.     

Method for Measurement of Static Parameters of Axially Symmetric Beams in Devices of Millimeter Wave Band

The new method for metering of the static parameters of the axially symmetric electron beams in the devices of the extremely high frequency (EHF) range is proposed in the paper. The method is based on using properties of the transition radiation of the optical range. The transition radiation appears when bombarding a metallic target electrode with electrons. Results of the meterings on distribution of current beam density by way of this method are given. The results are compared with the trajectory analysis when moving the electrons in the field of the investigated electron-optical system.     

Anomalous proximity effect in superconducting oxide structures with an antiferromagnetic layer

The electrophysical parameters of superconductor/antiferromagnetic insulator structures based on the Nb/Au/Ca_1?x Sr _x CuO₂/YBa₂Cu₃O_7?δ hybrid heterostructure have been examined. YBa₂Cu₃O_7?δ and Ca_1?x Sr _x SuO₂ epitaxial films are grown by the laser ablation method on NdGaO₃ single crystal substrates, the thickness of the Ca_1?x Sr _x CuO₂ layer varies from 20 to 50 nm, and x = 0.15 and 0.5. The superconducting pair potential in the interface between the YBa₂Cu₃O_7?δ superconductor and Ca_1?x Sr _x CuO₂ antiferromagnet is found to penetrate into the antiferromagnet at distances much larger than the coherence length calculated for the ferromagnetic layer. The critical current of the superconducting transition manufactured at such an interface is highly sensitive to the magnetic field.     

Ab initio modeling of the electronic and spin properties of the [NV]<Superscript>−</Superscript> centers in diamond nanocrystals

The electronic and spin properties of different nanocrystals of carbon are studied. The properties of these cluster systems are modeled in terms of the ab initio (Hartree-Fock) and semiempirical (PM3, AM1) quantum-chemical methods. The calculations are performed for different carbon nanocluster systems: defect-free and with [NV]^? centers, hydrogen passivated (C₃₈H₄₂, C₇₁H₈₄, C₈₆H₇₈), and with a free (unpassivated) surface (C₃₈, C₇₁, C₈₆). The spin properties of unhydrated nanoclusters were studied for the first time. The structure of all the clusters under study was optimized using the total energy minimization principle. It is shown that, in the case of hydrated carbon nanocrystals passivated by hydrogen atoms, diamond-like clusters are formed. The atomic structure of an unpassivated nanocrystal depends on the number of atoms in the cluster, as well as on its initial geometrical parameters. In some cases, clusters with a fullerene-like surface are formed. In hydrogenpassivated diamond nanocrystals with [NV]^? centers, the spin density is localized at the nuclei of C atoms nearest to the center vacancies. For the unpassivated counterparts, the spin density is localized at the nuclei of C atoms forming the surface of the corresponding nanocrystal.     

A Ground Miniband Width of a Superlattice with Rectangular Quantum Wells versus Constructive Parameters

A convenient formula for the ground miniband width as a function of constructive parameters of the superlattice is derived from the solution of the Kronig–Penney equation using the perturbation theory. The conditions of applicability of this formula are verified for the GaAs/Al_xGa_1–x As superlattices used as infrared photodetectors.     

Scattering of Quasi-Two-Dimentional Electrons of the GaAs/Al x Ga1–x As Superlattice by Polar Optical Phonons in the Dielectric Continuum Model

The longitudinal and transverse mobility of electrons in the ground miniband of the GaAs/AlGaAs superlattice (SL) is calculated for the case of scattering on the long-range potential of polar optical (PO) phonons at T = 300 K. The partial contributions of different oscillation modes of the long-range PO-phonon potential to the mobility and effective relaxation time are analyzed. The dependences of the mobility and pulse effective relaxation time on the SL parameters are investigated. The calculation is made using a linearized Boltzmann equation. The scalar PO-phonon potential is calculated within the dielectric continuum model.