Ultrasound conditioning of suspensions--studies of streaming influence on particle aggregation on a lab- and pilot-plant scale

Suspension conditioning by ultrasound induced particle aggregation in a 3.3 MHz standing wave field was investigated in lab- and pilot scale sedimentation reactors (sonicated volume approx. 375 ml and 10 l). These were equipped with a variable number of acoustically transparent film (ATF) elements, inserted perpendicular to the sound propagation direction. ATFs control the development of undesired large-range Eckart-type acoustic streaming and thermal convection. ATF insertion led to increased separation efficiency especially for particles smaller than 10 microns. Results with a varied geometric set-up indicate the existence of an optimum for the number of ATFs inserted. Optical investigation of particle behaviour in different pilot plant configurations showed reduced streaming within the divided 24 mm pathlength sonic chamber, whereas at 100 mm pathlength, turbulent streaming dominated.     

Carrier relaxation in InGaAs

A modelocked Nd: YAG pumped optical parametric amplifier providing 35 ps pulses in the wavelength range λ = 1.45−2.1 μm has been used to study photoexcited carrier recombination in InGaAs. At carrier densities in excess of 10¹⁸ cm^-3 Auger processes are found to dominate the carrier recombination. An Auger rate of 2.5±0.5×10^-28 cm⁶ s^-1 is determined.     

Structural properties of diamond fine particles and clusters prepared by detonation and decomposition of TNT

The thermal parameter B for three different particle sizes of diamond samples (bulk powder 1–4 μm, fine particle 144–195 Å and cluster 55–61 Å) was determined by the grazing incidence X-ray diffraction method. The values of B were found to be in the range 0.50–0.70 Å² for particles in the size range 195–55 Å and 0.27 Å² for 1–4 μm. All of them are larger than that of diamond bulk. A clear size dependence of B, increasing with decreasing particle size, was found. By analysing X-ray diffraction data at several temperatures the magnitude of B was found to be due to B_S (static part) instead of B_T (dynamic part). The average B_S values obtained were 0.04 Å², 0.19 Å² and 0.27 Å² for bulk powder, fine particle and cluster samples respectively. Ultrahigh resolution transmission electron microscope (TEM) observation confirmed the presence of strain, distortion, roughness and dislocation lines in many particles. TEM images of particles indicate that the clusters were not spherical in shape; they were mostly cubiform and some were truncated prism-like polyhedral. The present study reveals that the B_S component is responsible for the large B value in diamond fine particles and clusters. No clear surface local atomic distortion was found in the particles.     

Electron-muon permutation symmetry and multiplicatively conserved lepton number in gauge theories

The similarity between the weak interactions of electron and muon is extended to the principle that all e and μ interactions in gauge models are invariant under e ↔ μ exchange. This necessitates the existence of two Higgs doublets φ_e and φ_μ, and an extended e ↔ μ permutation invariance. After symmetry-breaking, a multiplicatively conserved “permutation parity” π = ± 1 for all particles naturally emerges, with π_μ = −π_e = 1. The model forbids μ → eγ but predicts e⁻e⁻ → μ⁻μ⁻ mediated by π = −1 Higgs bosons at 10⁻¹¹ times the rate of typical weak cross sections.     

The geometry of the SU(2) Kepler problem

The SU(2) Kepler problem is defined and analyzed, which is a Hamiltonian system reduced from the conformal Kepler problem on T^*( ⁸ − {0}) by the use of the symplectic SU(2) action lifted from the SU(2) left action on the SU(2) bundle ⁸ − {0} → ⁵ − {0}. This reduced system has a parameter μ ε su(2) coming from the value of the moment map associated with the symplectic SU(2) action. If μ ≠ 0, the phase space of this system have a bundle structure with base space T^*( ⁵ − {0}) and fibre S². The fibre, a (co)adjoint orbit through μ for SU(2), represents the internal degrees of freedom, called the isospin, of the particle of this system. The SU(2) Kepler problem with μ ≠ 0 is then interpreted as describing the motion of a classical particle with isospin in the Newtonian potential plus a specific repulsive potential together with a Yang-Mills field. This Yang-Mills field is to be referred to as BPST Yang's monopole field in ⁵ − {0};, since it becomes the Belavin-Polyakov-Schwartz-Tyupkin instanton, restricted on S⁴. If μ = 0, the SU(2) Kepler problem reduces to the ordinary Kepler problem. Like the ordinary Kepler problem, the Hamiltonian flows of the SU(2) Kepler problem of negative energy are all closed. It is shown in an explicit manner that the energy manifolds and isoenergetic orbit spaces for the SU(2) Kepler problem of negative energy are both homogeneous manifolds on which SU(4) acts transitively to the right; those homogeneous manifold are classified into two, according as the parameter μ is zero or not. For a certain value of μ, however, they contracts to the manifold which represents the set of all the equilibrium states. The isoenergetic orbit spaces are finally shown to be symplectomorphic to certain Kirillov-Konstant-Souriau coadjoint orbits for U(4), if μ is not the exceptional value mentioned above.     

Secondary particle contribution to LET spectra on LDEF

Four experiments utilizing passive detectors (P0006, P0004, A0015, M0004) were flown on LDEF to study the radiation environment. These experiments have been summarized in a companion paper (Benton et al., 1996). One of the experimental goals was to measure LET spectra at different locations and shielding depths with plastic nuclear track detectors (PNTD). It was found that the LET spectra extended well above the LET cutoff imposed by the geomagnetic field on GCR particle penetration into LEO. The high LET particles detected were mostly short-range (range < 2000 μm), indicating that they were secondaries produced locally within the PNTD. The presence of these high LET particle fluences is important for the determination of dose equivalent because of the high Quality Factors (Q) involved. A relatively small fraction of particle fluence can contribute a large fraction of dose equivalent.

Short-range, inelastic secondary particles produced by trapped protons in the South Atlantic Anomaly (SAA) were found to be a major contributor to the LET spectra above 100 keV/μm. The LET spectra were found to extend beyond the 137 keV/μm relativistic GCR Fe peak to over 1000 keV/μm. The high LET tail of the LET spectra was measured in CR-39 and polycarbonate PNTDs using different techniques. GCR made a relatively modest contribution to the LET spectra as compared to the contributions from short-range secondary particles and stopping protons.

LET spectra intercomparisons were made between LDEF measurements and exposures to 154 MeV accelerated proton beams. The similarities support the role of nuclear interactions by trapped protons as the major source of secondary particles in the PNTDs. Also techniques were employed to reduce the range cutoff for detection of the short-range secondaries to 1 μm, so that essentially all secondary particles were included in the LET spectra. This has allowed a more realistic assessment of secondary contribution to dose equivalent.

Comparisons of measured and calculated LET spectra have been made that demonstrate the need for more accurate modeling of secondary particles in radiation transport codes. Comparisons include preliminary calculations in which attempts have been made to include secondary particles.     

基于跨平台红外高光谱观测的对流层三维风场测量

精确的风场数据对提高数值天气预报准确性具有重要意义,对流层风是改进天气预报的要素之一。虽然利用气象卫星成像仪对连续云图追踪特征目标进行导风是一种有效的风场观测方法,且在区域和全球尺度上改善了数值天气预报,但仍存在风场高度分配模糊问题而产生误差。星基红外高光谱探测仪具备大气温湿度廓线垂直探测能力,通过分析各个垂直分层内的大气参数运动得到三维风场,能够提升风场垂直高度的准确性,改进风场高度分配模糊问题。提出了利用跨平台极轨气象卫星FY-3D星红外高光谱大气探测仪HIRAS和NOAA-20星跨轨红外探测仪CrIS交叉观测对流层三维风场的创新方法,根据两仪器近重叠轨道星下点交叉观测辐射数据匹配水汽通道图像,通过稠密光流法分析目标运动变化并计算风场,对风矢量进行质量控制后同ERA-Interim再分析资料作定量化比较,分析风速均值绝对偏差、均方根误差和风向均值绝对偏差。分别对2019年2月20日UTC世界时00:00,06:00,12:00的HIRAS和CrIS交叉数据计算200,300,400,600,650和1 000 hPa六组垂直高度风场,结果表明,风速范围的变化趋势与再分析资料表现一致,风速范围随高度降低而减小,高层对20 m·s-1以上风速更敏感,地表附近测得风速集中在10 m·s-1以内。风速均值绝对偏差多数小于3 m·s-1,最大不超过4 m·s-1,风速均方根误差多数小于3.5 m·s-1,最大不超过4.5 m·s-1,风向均值绝对偏差多数小于30°,最大不超过40°。风场误差主要来自仪器自身设计参数不同引入辐射数据的观测偏差,以及因数据空间分辨率不同导致在图像重投影处理过程中引入的定位偏差。     

Particle transport by standing waves on an electric curtain

Discrete-element simulations are performed to study particle transport by standing waves on an electric curtain. An electric curtain consists of a series of parallel electrodes with oscillating potential field embedded in a dielectric surface. The study shows that particles can be transported in two different modes under excitation by standing waves. In the first mode, particles roll along the surface in a constant direction with average velocity equal to the wave speed. In the second mode, particles hop along the surface in a manner akin to a Brownian motion. Effect of particle collisions on these transport modes is evaluated.     

Magnetic domain walls and pulsed magnetization reversal in amorphous Fe40Ni40P14B6 ribbon under tension

Magnetization reversal has been studied in long ribbons of Metglas 2826 under tension. At low fields propagating head-on domain boundaries of the Sixtus-Tonks type were observed. Measurements of their lengths, of order 20 to 50 cm, together with a simple magnetostatic model of their structure, yield values of the specific domain wall surface energy γ = 3.8 × 10^-8 σ^1/2 J m^-2 for tensile stress σ Pa. A value A= 5.6 × 10^-12 J m^-1 for the exchange constant follows. The low-fi eld mobility of these domain walls shows no evidence of relaxation damping at speeds below 1.2 m s^-1. The threshold field at which reverse domains nucleate is found to be proportional to the square root of the tension. At high fields (>200 A m^-1) the rough surface of the ribbon (the surface that came in contact with the quenching wheel during manufacture) reverses first and saturates at about the same time as the smooth surface begins to reverse and the volume reversal rate peaks. A simple quantitative model of the high field reversal process satisfactorily predicts both the surface and volume reversal rates. It yields a consistent value β_R = 14 kg m^-2s^-1 for the relaxation damping constant at wall speeds in excess of 13 m s^-1 and estimates the number of reversal nuclei in accord with Yagi and Anayama.     

Influence of the Sb dopant distribution on far infrared photoconductivity in Ge:Sb blocked impurity band detectors

Extended long wavelength response to 200 μm (50 cm⁻¹) has been observed in Ge:Sb blocked impurity band (BIB) detectors with N_D1×10¹⁶ cm⁻³. The cut-off wavelength increases from 150 μm (65 cm⁻¹) to 200 μm (50 cm⁻¹) with increasing bias. The responsivity at long wavelengths was lower than expected. This can be explained by considering the observed Sb diffusion profile in a transition region between the blocking layer and active layer. BIB modeling is presented which indicates that this Sb concentration profile increases the electric field in the transition region and reduces the field in the blocking layer. The depletion region consists partially of the transition region between the active and blocking layer, which could contribute to the reduced long wavelength response. The field spike at the interface is the likely cause of breakdown at a lower bias than expected.     

Domain wall pinning in polycrystalline perovskite La0.7Sr0.3MnO3

Reversible and irreversible domain wall (DW) motions have been investigated in La_0.7Sr_0.3MnO₃ ceramic samples using frequency-response complex permeability with various amplitudes of AC field. We also examine the effects of temperature in the range from 293 to 368 K and transverse DC magnetic field with a maximum of 4.40×10⁵ A/m on the real part of permeability (μ′). Two relaxations corresponding to reversible wall motions and domain rotations occur in low and high frequency regions, respectively. The irreversible DW displacements can be activated as the amplitude larger than the pinning field of 3 A/m, leading to an increase in μ′. The μ′ obeys a Rayleigh law at the temperature below 343 K or under DC field of less than 4.22×10⁴ A/m. The Rayleigh constant η increases from 5.45×10⁻² to 1.54×10⁻¹ (A/m)⁻¹ as the temperature rises from 293 to 343 K, and η decreases from 5.58×10⁻² to 3.67×10⁻² (A/m)⁻¹ with increasing DC field from 1.99×10³ to 4.22×10⁴ A/m.     

Field emission properties and surface structure of nickel containing amorphous carbon

Nickel containing amorphous carbon (a-C:Ni) films have been deposited by filtered cathodic vacuum arc (FCVA) technique by introducing pure nickel into the graphite target. The field electron emission property of a-C:Ni was improved when compared to that of pure tetrahedral amorphous carbon (ta-C) by FCVA. The emission threshold field of a-C:Ni film is about 5 V μm⁻¹, whilst the threshold field of the ta-C film is about 13 V μm⁻¹. Raman spectroscopy suggests that the sp² clusters in the carbon film increase both in size and number when Ni is introduced. However, the emission was found to degrade to threshold fields beyond 20 V μm⁻¹ after the a-C:Ni film was left in ambient for a week. This observation is attributed to surface absorption of oxygen on the a-C:Ni film, as determined by X-ray Photoelectron Spectroscopy.     

Near-infrared absorptions of monomethylhydrazine

The peak absorption coefficients for two near-infrared absorptions of monomethylhydrazine, CH₃-N₂H₃, (MMH) were measured. Absorption bands located at 1.524 μm (6560 cm^-1), 1.557 μm (6423 cm^-1), and 1.583 μm (6316 cm^-1) are assigned to the υ = 2 overtones of the infrared N-H stretching fundamentals at 3317, 3245 and 3177 cm^-1. An absorption band located at 1.04 μm (9620±100 cm^-1) is assigned to the υ = 3 overtone of one of these fundamentals. The peak absorption coefficients (₁₀) at 1.524 μm (6560±20 cm^-1) and 1.04 μm (9620±100 cm^-1) are 31 × 10^-3 and 0.97 × 10^-3 (cm atm)^-1, respectively. Uncertainties in these coefficients were estimated to be less than ±20% due primarily to uncertainties in the partial vapor pressure of MMH.     

The application of high speed photography and white light speckle to the study of dynamic fracture

A white light speckle technique is combined with high speed photography to study the dynamic fracture of a sample of PMMA. A series of single exposure speckle patterns are photographically recorded at the rate of 2 × 10⁵ frames s^-1 during fracture of the sample. The displacement field around the tip of the propagating crack may then be determined by superimposing pairs of individual frames to form a ‘double-exposure’ speckle pattern. It is shown that the method gives values for the stress intensity factor K which are consistent with those obtained from other techniques.     

Detection, dosimetry and microdosimetry using high energy C beams

Samples of polyallyldiglycolcarbonate (PADC) track etch detectors (TED) were exposed to high energy ¹²C nuclei at the particle beam of the Dubna synchrophasotron. The energy of ¹²C nuclei varied between 0.1 and 1.5 GeV per amu.

At the low studied energies the linear energy transfer (LET) of these nuclei is higher than the detector threshold value. Then, the primary particle tracks are directly etched in the detector surface. The detection efficiency approaches to 100% at perpendicular incidence. Their LET has been established by means of standard authomatized procedure recently developed. The LET values found here are in good agreement with theoretical ones.

At 1.5 GeV per amu (LET 8.4 KeV μm⁻¹) the secondary particle tracks were evaluated in all the exposed detectors. The energy deposited by these particles was compared to the energy deposited through primary ionization losses. It was found out that its contribution to the total dose is relatively lower than for protons of comparable energies. In some of these samples even the tracks of the primary nuclei were observed. It follows that the detection threshold of the developed LET spectrometer should be below 10 keV μm⁻¹.     

Observation of enhanced dielectric permittivity in Bi doped BaFe12O19 ferrite

The dielectric properties of a 2.5 mol% Bi₂O₃ doped Ba-ferrite (BaFe₁₂O₁₉) have been investigated. The specimen shows a drastically enhanced (≈ 10⁵ times) permittivity (ε) through local polarization of Fe³⁺ electronic charges activated with nearby Bi³⁺ sites. The ε value also depends reasonably on thermal annealing (causes grain growth) of the samples. The specimens comprising large particle sizes (1–20 μ m) usually exhibit smaller ε values and low dielectric losses.     

Constraints on PSC particle microphysics derived from lidar observations

Based on extensive T-matrix computations of light scattering by polydispersions of randomly oriented, rotationally symmetric nonspherical particles, we analyze existing lidar observations of polar stratospheric clouds (PSCs) and derive several constraints on PSC particle microphysical properties. We show that sharp-edged nonspherical particles (finite circular cylinders) exhibit less variability of lidar backscattering characteristics with particle size and aspect ratio than particles with smooth surfaces (spheroids). For PSC particles significantly smaller than the wavelength, the backscatter color index and the depolarization color index β are essentially shape independent. Observations for type Ia PSCs can be reproduced by spheroids with aspect ratios larger than 1.2, oblate cylinders with diameter-to-length ratios greater than 1.6, and prolate cylinders with length-to-diameter ratios greater than 1.4. The effective equal-volume-sphere radius for type Ia PSCs is about 0.8 μm or larger. Type Ib PSCs are likely to be composed of spheres or nearly spherical particles with effective radii smaller than 0.8 μm. Observations for type II PSCs are consistent with large ice crystals (effective radius greater than 1 μm) modeled as cylinders or prolate spheroids.     

On- and off-resonance spin-lock MR imaging of normal human brain at 0.1 T: possibilities to modify image contrast

The aim of the present investigation was to determine spin lock (SL) relaxation parameters for the normal brain tissues and thus, to provide basis for optimizing the imaging contrast at 0.1 T. 68 healthy volunteers were included. On-resonance spin lock relaxation time (T_1ρ) and off-resonance spin lock relaxation parameters (T_1ρ^off, M_e/M_o), MT parameters (T_1sat, M_s/M_o), and T₁, T₂ were determined for the cortical gray matter, and for the frontal and parietal white matters. The T_1ρ for the frontal and parietal white matters ranged from 110 to 133 ms and from 122 to 155 ms with locking field strengths from 50 μT to 250 μT, respectively. Accordingly, the values for the gray matter ranged from 127 to 155 ms. With a locking field strength of 50 μT, T_1ρ^off for the frontal and parietal white matters were from 114 to 217 ms and from 126 to 219 ms, and for the gray matter from 136 to 267 ms with the angle between the effective magnetic field (B_eff) and the z-axis (θ) ranging from 60° to 15°, respectively. The T_1ρ of the white and gray matters increased significantly with increasing locking field amplitude (p < 0.001). The T_1ρ^off decreased significantly with increasing θ (p < 0.001). T_1ρ and T_1ρ^off with θ ≥ 30° were statistically significantly shorter in the frontal than in the parietal white matters (p < 0.05). The duration, amplitude and θ of the locking pulse provide additional parameters to optimize contrast in brain SL imaging.     

Microwave studies of the superconducting state in Rb3C60

Methods of electron-spin resonance (ESR) and direct, non-linear field-modulated microwave absorption (FMMA) were applied for the measurements in low- and high-purity samples of rubidium-doped fullerene, Rb₃C₆₀. The coexistence of the normal strong ESR signals and regular series of weak absorption lines similar to those seen in systems of Josephson junctions was observed in the high-purity sample. The possible influence of the vortex lattice on the ESR signals was also studied. We determined from FMMA investigations using the Portis model the critical field μ₀H^* = 40 μT, the depinning current density J_c^*(μ₀H₀ = 1 mT) 4 × 10⁸ A/m² in low magnetic field and J_c^*(μ₀H₀ > 100 mT) 1.6 × 10⁸ A/m² in higher fields. These values were generally one order of magnitude higher than the highest corresponding values previously observed in high-temperature superconductors (HTS's).     

Outer curvature and conformal geometry of an imbedding

The differential geometry of an imbedded (e.g. string or membrane world sheet) surface in a higher-dimensional background is shown to be conveniently describable (except in the null limit case) in terms of what are designated as its first, second, and third fundamental tensors, which will have the respective symmetry properties η_μν = η_(μν) as a trivial algebraic identity, K_μν^ρ = K_(μν)^ρ as the “generalised Weingarten identity”, which is the (Frobenius type) integrability condition for the imbedding, and Ξ_λμν^ρ = Ξ_(λμν)^ρ as a “generalised Codazzi equation”, which depends on the background geometry being flat or of constant curvature, needing replacement by a more complicated expression for a generic value of the background curvature B_κλ^μ_ν. The “generalised Gauss equation” expressing the dependence on this background curvature of the internal curvature tensor R_κλ^μ_ν of the imbedded surface is converted into terms of the first and second fundamental tensors, and it is thereby demonstrated that the vanishing of the (conformally invariant) “conformation tensor”, i.e. the trace free part C_μν^ρ of the second fundamental tensor K_μv^ρ, is a sufficient condition for conformal flatness of the imbedded surface (and thus in particular for the vanishing of its (Weyl type) conformal curvature tensor C_κλ^μ_ν) provided the background is itself conformally flat. In a trio of which the first two members are the generalised Gauss and Codazzi equations, the “third” member is shown to give an expression in terms of C_μν^ρ for the (trace free, conformally invariant) “outer curvature” tensor Ω_κλ^μ_ν whose vanishing is the condition for feasibility of the natural generalisation of the Walker frame transportation ansatz. The vanishing of C_μν^ρ is shown to be sufficient in a conformally flat background for the vanishing also of Ω_κλ^μ_ν.