Temporal linear instability analysis of an electrified coaxial jet with inner driving liquid inside a coaxial electrode

In this paper, a temporal linear stability analysis is performed of a coaxial jet composed of two immiscible liquids inside a coaxial electrode. This analysis is carried out to investigate the case of an inner driving coaxial electrospray system. The assumption is made that the inner liquid has high electric conductivity, and the outer liquid is an insulating dielectric. The dimensionless dispersion equation for both the axisymmetric and non-axisymmetric modes is derived and solved numerically for the axisymmetric case. The effects of the relevant dimensionless parameters on the instability of the jet are discussed in detail. These parameters include the dimensionless electrostatic force E, the dielectric constant ratio ε, the diameter ratios a and b, the velocity ratio Λ, the density ratio S, the Weber number, and the interface tension ratio ζ. Two independent unstable modes, modes 1 and 2, are found and analyzed. Among the various parameters, the dimensionless electrostatic force and the dielectric constant have a similar and remarkable influence on modes 1 and 2, altering drastically the regime of the jet as they vary. The interface tension on the outer interface promotes the instability of both modes 1 and 2 in the region of long wavelengths while suppressing the growth rate in the region characterized by short wavelengths. The interface tension on the inner interface, however, promotes instability of only mode 2 in the same way. The diameter ratio a has a great effect on mode 2 while a negligible influence on mode 1. And the diameter ratio b has a slight effect on both the unstable modes.     

Das ESR-Signalg=1,957 von Zinkoxid

The ESR-lineg=1,957 of self-activated ZnO-powder is investigated. It can be shown that the well-known ZnO-line consists of two parts (g _h=1,9555 andg _a=1,9580). The two paramagnetic centers can be identified by considering corresponding luminescence properties. The part ?h” with the lowerg-valueg _h is given by the filled hole traps, i.e. by oxygen-ions on interstitual places. The second part of the ESR-signal results from activators, which are not ionized, i.e. oxygen defects filled by one electron.     

High-frequency PIN–PMN–PT single crystal ultrasonic transducer for imaging applications

A high-frequency (～60 MHz) ultrasonic transducer with a [001]-oriented 0.27Pb(In_1/2Nb_1/2)O₃–0.45Pb(Mg_1/3Nb_2/3)O₃–0.28PbTiO₃ (PIN–PMN–PT) piezoelectric single crystal as an active element has been fabricated and characterized. The poled PIN–PMN–PT single crystal has thickness mode electromechanical coefficient k _t of 0.56 and piezoelectric constant d ₃₃ of 1550 pC/N. The ?6 dB bandwidth of the transducer is 73 % and the insertion loss at its centre frequency is ?20 dB. With the study as a function of temperature, the PIN–PMN–PT transducer shows better thermal stability than the binary single crystal transducer. Furthermore, the transducer was evaluated using a 30-μm aluminum wire phantom image, in which the ?6 dB axial and lateral resolutions are found to be 26 μm and 127 μm, respectively. Ultrasonic images of fish eyes were obtained with the 60-MHz transducer. It is shown that the high-sensitivity transducer can produce the images with high signal-to-noise ratio and good contrast.     

Initial operation at liquid-helium temperature of the M =2270 kg Al 5056 gravitational-wave antenna of the Rome group

Summary We report on the cooling at liquid-helium temperature of our 2270 kg 5056 Al bar at CERN. The liquid-helium container had been filled up to 1500 liters ensuring to keep the antenna cold for more than one month. The antenna is equipped with a resonant capacitive transducer operating at constant electrical charge with a FET low-noise amplifier. The transducer is tuned to the antenna within less than I Hz and the two normal-mode frequencies are ν₋=908.160 Hz and ν₊=924.234 Hz with an applied electrical field in the transducer of 10⁶ V/m. The corresponding overall merit factors areQ ₋=5.20·10⁶ andQ ₊=7.25·10⁶. The transducer has been tested up to an electrical field of 6·10⁶ V/m: in this condition we have βQ≈10⁴. The antenna has been in operation for several weeks giving, for the Brownian noise, values in agreement with the calculated values. We report also on the results of tests performed on a DC SQUID, whose input was connected to a commercial capacitor via a transformer with turn ratio of 1000. Supported in part by Japan Society for the Promotion of Science.     

Numerical and experimental investigation of kerf depth effect on high-frequency phased array transducer

Background

High-frequency ultrasonic transducer arrays are essential for high resolution imaging in clinical analysis and Non-Destructive Evaluation (NDE). However, the structure design and fabrication of the kerfed ultrasonic array is quite challenging when very high frequency (?100 MHz) is required.

Objective and method

Here we investigate the effect of kerf depth on the performances of array transducers. A finite element tool, COMSOL, is employed to simulate the properties of acoustic field and to calculate the electrical properties of the arrays, including crosstalk effect and electrical impedance. Furthermore, Inductively Coupled Plasma (ICP) deep etching process is used to etch 36°/Y-cut lithium niobate (LiNbO₃) crystals and the limitation of etching aspect ratio is studied. Several arrays with different profiles are realized under optimized processes. At last, arrays with a pitch of 25 μm and 40 μm are fabricated and characterized by a network analyzer.

Results

Kerf depth plays an important role in the performance of the transducer array. The crosstalk is proportional to kerf depth. When kerf depth is more than 13 μm, the array with crosstalk less than −20 dB, which is acceptable for the real application, could provide a desired resolution. Compared to beam focusing, kerf depth exhibits more effect on the beam steering/focusing. The lateral pressure distribution is quantitatively summarized for four types of arrays with different kerf depth. The results of half-cut array are similar to those of the full-cut one in both cases of focusing and steering/focusing. The Full-Width-at-Half-Maximum (FWHM) is 55 μm for the half-cut array, and is 42 μm for the full-cut one. The 5-μm-cut array, suffering from severe undesired lobes, demonstrates similar behaviors with the no-cut one. ICP process is used to etch the 36°/Y-cut LiNbO₃ film. The aspect ratio of etching profile increases with the kerf width decreasing till it stops by forming a V-shaped groove, and the positive tapered profile angle ranges between 62° and 80°. If the mask selectivity does not limit the process in terms of achievable depth, the aspect ratio is limited to values around 1.3. The measurement shows the electrical impedance and crosstalk are consistent with the numerical calculation.

Conclusion

The numerical results indicate that half-cut array is a promising alternative for the fabrication of high-frequency ultrasonic linear arrays. In fact, the minimum pitch that could be obtained is around 25 μm, equivalent to a pitch of 1.6λ, with a kerf depth of 16 μm under the optimized ICP parameters.     

Electronic and optical properties of LiMgN, LiMgP and LiMgAs under hydrostatic pressure

First principles calculations, by means of the full-potential linearized augmented plane wave method within the local density approximation, were carried out for the effect of pressure on the electronic and optical properties of the filled tetrahedral compounds LiMgN, LiMgP and LiMgAs. The bandgap pressure coefficient trend in the ternaries is found to be similar to the one encountered in the zinc-blende-like AlX. The first order bandgap pressure coefficient a^Γ-Γ in LiMgN is larger than the corresponding one in AlN, while it is smaller in LiMgP and LiMgAs compared to the one in AlP and AlAs. The predicted values of the dielectric constants for LiMgN, LiMgP and LiMgAs are close to those of the binary compounds AlN, AlP and AlAs.     

Final state band gap effects in UV photoemission from Cu(111)

The crystal momentum dependence of the final states involved in bulk photoemission from the sp-bands through a (111) surface of copper was investigated with a photon energy hν = 11.7 eV. Plane wave hybridization was observed and is described in terms of a 2-OPW model Hamiltonian with parameters determined to be V₀=7.1±0.1 eV for the inner potential and E_g = 1.6 ± 0.2 eV for the energy gap. The model is also shown to account for a rapid intensity variation with crystal momentum of the form |a_G(k)|², where a_G(k) is a plane wave amplitude of the final state wave function.     

Ordering in FeII–III Hydroxysalt green rusts from XRD and Mössbauer analysis (chloride, carbonate, sulphate, oxalate...); about the structure of hydrotalcite-like compounds

The domain of existence of Fe^II–III hydroxysalt green rusts (GR) is characterised by the ratio x = [Fe^III]/[Fe_total] lying in [1/4, 1/3] as it is for any layered double hydroxide (LDH). Since Fe^III cations balance the charges of intercalated anions, cation and anion distributions are correlated. However, the distribution of anions depends on their charge, shape and size. For Cl^? and CO₃ ^2?, x belongs to the complete range whereas for C₂O₄ ^2? and SO₄ ^2? it is limited to x = 1/4 and 1/3, respectively. Mössbauer spectra present in all cases two ferrous and one ferric doublets, which characterise each GR by their relative abundance. Intermediate values of x are in fact obtained by intrincate domains of two types, one where the cation periodicity is 2×a ₀ and the other one √3×a ₀ if a ₀ is the lattice parameter.     

Analyse von Hyperfeinstrukturen des Eu151, Am241 und einiger 3 d-Elemente mittels „Exchange Polarization“

It is shown how several discrepancies in the optical hfs of the Eu can be understood as consequences of the exchange polarization of the inner and outers-electrons by the spin of the half filled (4f ⁷)-subshell, an effect which should produce additional magnetic fields at the nucleus. Thus from the two different values of the electronic splitting constanta _6s in the two Eu-II ground states the polarization field from the 6s-shell (Δ H _6s ) is determined to be ca. +260 KG, and the formal splitting constantσ (??3 mK) of the (4f ⁷)-subshell yields ca. ?350 KG for the fieldΔ H _(1?5) from the five innern s-shells (n=1?5) in good agreement with the strength of the inner field obtained from recent Mössbauer effect studies.Δ H _(1?5) is deduced to be approximately equal in all sufficiently analysed ground and excited configurations of the neutral and ionised Eu atom ((4f ⁷) 6s, 6p, 5d, 6s ² and 6s 6p). Other elements with half filled subshells (Am, Mn) show similar features in their optical hfs. For Am⁺ ((5f ⁷) 7s) ca. ?2200 KG are found for the inner field (Δ H _(1?6)). For several 3d-elements it was found that the agreement between the calculated polarization fields and those following from experimental results is better than assumed so far.     

The input mobility of an infinite circular cylindrical elastic shell filled with fluid

The force input mobility of an infinite elastic circular cylindrical shell filled with fluid is derived by using the spectral equations of motion. Mobilities are evaluated and their physical interpretations are discussed for a steel shell of thickness $\text{h}\text{a}\text{= 0·05}$ filled with water and vibrating in the n = 0, 1 and 2 circumferential modes. The results are subsequently used to analyze the related situations of wave transmission through a radial ring constraint and the far field vibrational energy distributions between the contained fluid and the shell wall for line and point driving forces.     

Existence of ground states and KMS states for approximately inner dynamics

A strongly continuous one parameter group of *-automorphisms of aC*-algebra with unit is said to be approximately inner if it can be approximated strongly by inner one parameter groups of *-automorphisms. It is shown that an approximately inner one parameter group of *-automorphisms has a ground state and, if there exists a trace state, a KMS state for all inverse temperatures. It follows that quantum lattice systems have ground states and KMS states. Conditions that a strongly continuous one parameter group of *-automorphisms of a UHF algebra be approximately inner are given in terms of the unbounded derivation which generates the automorphism group.     

Computer optimization of retarding lens systems for ESCA spectrometers

The performance of four-element electrostatic lenses as retarding systems between source and analyzer in ESCA spectrometers is calculated. The potential distribution in the lens is defined by an axial potential of the type (?(z) = V_o + Σ(V_i - V_{i- 1})/2 · tanh (ω/a_i (z - z_i)). For a given general shape of the lens and a given retardation ratio, the potentials of the two middle electrodes are fitted to give a paraxial image with a prescribed magnification at the exit slit of the lens system. The equipotential surfaces forming the electrodes are found by calculating the potential in an off-axis point, using the series expansion. All third-order geometrical and first-order chromatic aberrations of the lenses are calculated and used together with the second-order aberrations of the analyzer to calculate optimum dimensions of the lens elements and of the emittance-defining slits. A computer program, of which one part calculates the lens properties and one the properties of the entire system lens-analyzer, is described.Two lens systems are presented in some detail. The first one is intended for use with a hemispherical electrostatic analyzer. The angular acceptance is here defined by an aperture stop inside the lens. In this system, the image position and magnification can be kept constant for retardation ratios at least between 1:2 and 60:1, with moderate potentials on the middle electrodes. The second lens system is designed for a magnetic spectrometer of the π √2-type. Here, the central trajectory in the lens is slightly curved by the magnetic field, and the angular acceptance is defined by a baffle after the lens. This system is optimized for a constant retardation ratio of 5:1.     

Neutron flux distribution on the wall of toroidal controlled thermonuclear reactor devices with elongated cross section

The neutron flux distribution on the wall of a toroidal CTR device with strongly elongated cross section is calculated. On the inner and outer cylindrical walls (belt-pinch device) the flux distribution has a plateau region with a half-width equal to about the height of the plasma. The maximum flux is found on the outer cylinder and in the symmetry plane (z ₀=0). The neutron flux asymmetry and reductionη of the mean wall loading are determined. For standard data anη of 57% is computed. This is mainly due to the flux profiles on the cylindrical walls and does not depend sensitively on the toroidal curvature. For standard parameters the inner cylinder absorbs 22.6%, the outer cylinder 68.6% and the end plates together 8.8% of the total neutron emission. The corresponding values for a straight device with the same coil and plasma cross section are 44%, 44% and 12%. A reduction of toroidal curvature diminishes flux asymmetry between the inner and outer cylinders. The maximum flux and minimumη-value are obtained at a large torus radius equal to two times the coil width. For small aspect ratios (R _t W0.5) the neutron flux through the inner cylinder becomes so small that its interior may be filled with a material other than a blanket material, e.g. with an iron core.     

Quasiclassical analysis of the spectra of two groups of central potentials

A method is suggested for analyzing the spectra of central attractive potentials either with Coulomb singularity (intra-atomic potentials) or finite at zero point (potentials in spherical clusters and nuclei). It is shown that, if the orbital degeneracy is removed, then $\varepsilon _{nl} - \varepsilon _{n0} \cong a_{\varepsilon _{n0} } (l + 1/2)^2 $ for small l in the shell n. In atoms and ions, the coefficient a _ε is nonnegative, so that the energy in the n shell increases with l. The validity of this formula for the inner electrons is illustrated by calculating the spectrum of the mercury atom. In cluster potentials, the opposite situation, as a rule, occurs: the larger l, the lower the corresponding level (a _ε<0). However, in the soft potentials of small clusters, spectral regions with different signs of a _ε coexist and the orbitally degenerate level exists in the spectral region where a _ε=0. Aluminum clusters Al_N are taken as an example to find out how the position of the region with the degenerate level varies with varying cluster size N, and it is found that this region is “pushed out” to higher energies with an increase in N. In this connection, the presence of multiply ionized Al_N clusters of the corresponding size in a low-temperature aluminum plasma is discussed.     

Mechanochemical synthesis in the Ni-Al-C system

Specific features of the phase formation during mechanochemical synthesis of mixtures of elementary components, Ni, Al, and graphite, in an atomic ratio of 2:1:1 and a mixture of the intermetallic compound Ni₃Al and graphite (1:1) have been considered. It is shown that nanocrystalline (D = 4–6 nm) three-component solid solutions Ni(Al, C) with identical lattice constants (a = 0.366 nm) are formed during mechanosynthesis, independent of the initial components. Annealing at a temperature of 800°C for 2 h leads to decomposition of solid solutions into three phases: double carbide Ni₃AlC_0.46 (a = 0.3592 nm), solid solution Ni(Al, C) with the lattice constant 0.3546 nm, and graphite with the lattice constants a = 0.2461 nm and c = 0.660 nm.     

A method for the determination of lattice parameters on single crystals

The ratio method, designed originally for powder materials, is modified for single crystals. A relatively simple goniometer with photographic registration is used. Discussion of random and systematic errors shows that an accuracyΔa/a = 10^?4, or better, can be achieved. An application for single crystals of Fe and Fe-Si alloys is demonstrated. For pure iron the valuea= = (2·8664±00001)×10^?10 m is found.     

Stochastic resonance in multi-stable system driven by Lévy noise

In this paper, the stochastic resonance (SR) of a multi-stable system driven by Lévy noise is investigated by the mean signal-to-noise ratio gain (SNR-GM). The characteristics for resonant output of multi-stable system, governed by the system parameters (a and c), the noise amplification factor D of Lévy noise are investigated under different values of stability index α and asymmetry parameter β of Lévy noise. The results reveal that the parameter α is closer to 1, the amplitude of SNR-GM versus system parameter a (or c) is larger. The interval of SR presents a trend that the curve of SNR-GM shifts to the right with the increase of α especially when α > 1. In addition, the SNR-GM for different values of system parameter a (or c) exhibits a tendency to move to the left with the increase of system parameter c (or a). Finally, the simulation results prove that the proposed multi-stable model has better advantage than bistable system and monostable system in signal enhancement and SNR-GM performance.     

Finite element analysis of micropipette aspiration considering finite size and compressibility of cells

Micropipette aspiration (MA) is widely applied in cell mechanics, however, at small deformations a common model corresponding to the MA is the half-space model wherein the finite cell size and cell compressibility are neglected. This study extends the half-space model by accounting for the influence of cell geometry and compressibility (sphere model). Using a finite element analysis of cell aspiration into a micropipette, an elastic approximation formula of the aspirated length was derived for the sphere model. The approximation formula includes the geometry parameter ξ of the sphere model (ξ= R/a, R is the radius of the cell, and a is the inner radius of the micropipette) and the Poisson’s ratio v of the cell. The results indicate that the parameter ξ and Poisson’s ratio v markedly affect the aspirated length, particularly for smallξ and v. Whenξ→∞ and v→0.5, the approximation formula tends to the analytical solution for the half-space model. In the incompressible case (v = 0.5), within the general experimental range (ξ varying from 2 to 4), the difference between the analytical solution and the approximate one is significant, and is up to 29% of the approximation solution whenξ = 2. Additionally, parametere was introduced to evaluate the error of elastic moduli between the half-space model and sphere model. Based on the approximation formula, theξ thresholds, beyond which e becomes larger than 10% and 20%, were derived.     

Instability of layered quantum liquids: 6. Strongly correlated bosons

We calculate the local-field corrections G(q, q _z) for charged bosons at zero temperature in a superlattice with interlayer distance d. An analytical expression for the local-field correction is described. The sum-rule version of the self-consistent approach for the local-field correction is used to discuss the effects of correlation. The RPAparameter r _s and the ratio d/a* determine correlation effects. a* is the effective Bohr radius. The stability region for the Bose condensate r _s < r _sc as a function of d/a* is determined: r _sc ≈ (d/a*)^3/4. The ground-state energy of the layered Bose condensate is calculated and optical and acoustical plasmons are discussed. We predict a roton structure for optical plasmons for r _s > r _sr with r _sr ≈ 0.5 (d/a*)^3/4.     

Free vibrations of laminated composite cylindrical shells with an interior rectangular plate

The free vibration analysis of a laminated composite cylindrical shell with an interior rectangular plate is performed by the analytical and experimental methods. The frequency equations of vibration of the shell including the plate are formulated by using the receptance method. To obtain the free vibration characteristics before the combination of two structures, the energy principle based on the classical plate theory and Love's thin shell theory is adopted. The numerical results are compared with the results from an experiment, as well as a finite element analysis, to validate the current formulation. The influences of the length-to-radius ratio (L_S/a) and radius-to-thickness ratio (a/h_S) of the shell and fiber orientation angles (Θ) of symmetric cross- and angle-ply composite materials on the natural frequencies of a cylindrical laminated combined shell are also discussed in details.