Second harmonic magnetoacoustic responses of magnetic nanoparticles in magnetoacoustic tomography with magnetic induction

Due to the unique magnetic, mechanical and thermal properties, magnetic nanoparticles(MNPs) have comprehensive applications as the contrast and therapeutic agents in biomedical imaging and magnetic hyperthermia. The linear and nonlinear magnetoacoustic responses determined by the magnetic properties of MNPs have attracted more and more attention in biomedical engineering. By considering the relaxation time of MNPs, we derive the formulae of second harmonic magnetoacoustic responses(2H-MARs) for a cylindrical MNP solution model based on the mechanical oscillations of MNPs in magnetoacoustic tomography with magnetic induction(MAT-MI). It is proved that only the second harmonic magnetoacoustic oscillations can be generated by MNPs under an alternating magnetic excitation. The acoustic pressure of the 2H-MAR is proportional to the square of the magnetic field intensity and exhibits a linear increase with the concentration of MNPs. Numerical simulations of the 2H-MAR are confirmed by the experimental measurements for various magnetic field intensities and solution concentrations using a laser vibrometer. The favorable results demonstrate the feasibility of the harmonic measurements without the fundamental interference of the electromagnetic excitation, and suggest a new harmonic imaging strategy of MAT-MI for MNPs with enhanced spatial resolution and improved signal-to-noise ratio in biomedical applications.     

Measurement of the G asymmetry for the γp↦Nπ channels in the Δ(1232) resonance region

The G asymmetry of the γp↦Nπ reaction has been measured for the first time for E_γ = 340±14 MeV. This observable, for which very scarce published data exist, plays an important role to disentangle the contributions of the various nucleon resonances. The experiment, performed at the Mainz microtron MAMI, used a 4π-detector system, a linearly polarized, tagged photon beam, and a longitudinally polarized proton target.     

Investigation of scattering of elastic waves by cylinders in 1-3 piezocomposites

The scattering behavior of P-waves in piezoelectric composites with 1–3 connectivity is studied. The method of wave function expansion is adopted for the theoretical derivations. Analytical expressions are obtained for the distributions of mechanical displacement in z-direction along the circumferences of piezoelectric cylinders. These solutions are used to study the influence of each element of the stiffness matrix and the piezoelectric matrix on the various resonant modes of vibration. Numerical results obtained indicate that perturbations of the elements c₄₄ and e₁₅ significantly affect resonant frequencies and amplitudes, perturbations of c₁₁ and c₁₂ have pronounced effects on resonant modes of high frequencies also. However, the resonant modes are not so sensitive to the perturbations of c₁₃, e₃₁ and e₃₃. The dynamic characteristics of 1–3 connectivity piezoelectric composites exposed here are meaningful for the design and manufacture of sensor/actuator elements by this kind of composites as well as the on-line health monitoring of the mechanical properties variations of the composites itself.     

The second Born approximation in electron-helium scattering in a Nd-YAG laser field

The dynamics of laser-assisted elastic collisions in helium is studied using the second-order Born approximation. Detailed calculations of the scattering amplitudes are performed by using the Sturmian basis expansion. Differential cross sections for elastic scattering with the net absorption/emission of up to two photons are calculated for collision energies of 5 eV, 10 eV, and 20 eV. We discuss the influence of the low-energy electrons on the differential cross section (DCS) as a function of the scattering angle for selected choices of the laser frequency and the number of photons exchanged between the external field and electron-helium system.     

Isospin symmetry breaking in ρ→πγ decay

In terms of effective field theory and mixed-propagator approach, we show that there is a larger hidden effect of isospin breaking in ρ→πγ decay due to a ω exchange, ρ→ω→πγ. The branching ratio is predicted as B(ρ→πγ) = (11.67±2.0)×10^-4, which is much larger than Particle Data Group's datum (6.8±1.7)×10^-4 and one of charged mode, B(ρ^±→π^±γ) = (4.5±0.5)×10^-4. Received: 7 January 2002 / Accepted: 2 April 2002     

Some basic principles in dynamic theory of viscoelastic materials with voids

According to the basic idea of classical yin-yang complementarity and modern dual-complementarity, in a simple and unified way proposed by Luo, some basic principles in the dynamic theory of viscoelastic materials with voids can be estab- lished systematically. In this paper, an important integral relation in terms of con- volutions is given, which can be considered as the generalized principle of virtual work in mechanics. Based on this relation, it is possible not only to obtain the principle of virtual work and the reciprocal theorem, but also to derive systemati- cally the complementary functionals for the eight-field, six-field, four-field simpli- fied Gurtin-type variational principles and the potential energy-functional for the two-field one in the dynamic theory of viscoelastic materials with voids by the generalized Legendre transformations given in this paper. Furthermore, with this approach, the intrinsic relationship among various principles can be explained clearly.     

Beam-helicity asymmetry in photon and pion electroproduction in the Δ(1232)-resonance region at Q2 = 0.35(GeV/c)2

The beam-helicity asymmetry has been measured simultaneously for the reactions p→epγ and p→epπ ⁰ in the Δ(1232)-resonance region at Q ² = 0.35(GeV/c)². The experiment was performed at MAMI with a longitudinally polarized beam and an out-of-plane detection of the proton. The results are compared with calculations based on dispersion relations for virtual Compton scattering and with the MAID model for pion electroproduction. There is an overall good agreement between experiment and theoretical calculations. The remaining discrepancies may be ascribed to an imperfect parametrization of some γ ^(*) N→πN multipoles, mainly contributing to the non-resonant background. The beam-helicity asymmetry in both channels (γ and π ⁰) shows a good sensitivity to these multipoles and should allow future improvement in their parametrization.     

Higgs and Bottom Quarks Associated Production at High Energy Colliders in the Littlest Higgs Model with T-Parity

In the littlest Higgs Model with T-parity,we discuss the Higgs production in association with bottom quarks at the LHC and future electron-positron collider.We calculate the cross sections of production channels pp→bb H,bb→H and bg→b H at 14 Te V LHC and the cross sections of production channel e~+e~-→bb H in(un)polarized beams at the lowest order.In order to investigate the observability,we display some typical final state distributions in the Higgs to diphoton channel.     

光学元件双转子抛光技术中类高斯型去除函数建模与逼近

在Preston假设基础上,研究并推导了光学元件抛光过程中"花瓣"型截面磨头在双转子运动形式下的去除函数.提出了"花瓣"型截面磨头的离散点弧长表达方法,并讨论了该方法的适用范围;基于离散点弧长法,推导了"花瓣"型截面磨头在双转子运动形式下的去除函数表达式;根据可调步长式曲线逼近原理研究了类高斯型目标去除函数的逼近算法;并得到了类余弦型去除函数的双转子抛光模参量.从而证明了双转子抛光技术可以得到类高斯型去除函数.     

On the problematic rising ratio of cosmic-ray positrons at ultra-high energies

Summary The rising ratio of cosmic-ray positrons at ultra-high energies of interactions seems to have puzzled the theorists to a great extent. We have made here a somewhat successful attempt to interpret the behaviour of this ratio,R=e⁺/(e⁺+e⁻), by putting into use the main physical ideas from our two previous works. The importance and the implications of this observation have also been highlighted and emphasized in the proper background.

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Riassunto Il crescente rapporto dei positroni dei raggi cosmici ad energie ultra-alte di interazioni sembra aver non poco confuso i teorici. Qui si tenta con un certo successo di interpretare il comportamento di questo rapportoR=e⁺/(e⁺+e⁻) usando i principali concetti fisici dei nostri due precedenti lavori. L'importanza e le implicazioni di questa osservazione sono state sottolineate ed enfatizzate nell'appropriato contesto.

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Резюме Увеличивающиеся отношение позитронов космических лучей при ультравыс оких энергиях, по-видимому, представляет загадку для теоретиков. В этой статье мы предпринимает отчасти успешную попытку интерпретировать поведение этого отношенияR=e⁺/(e⁺+e⁻), используя основные физические идеи из наших двух предыдущих публикаций. Отмчаются важностя и приложения полученных результатов.