visiting fellowship Professor Adamenko 2007

强相互作用的声子系统通常是各向同性的，直到最近才被认真研究。我们继续发现和测量由于各向异性而产生的新的和有趣的效应，这些效应包括：1.产生高能声子束，其角宽度比产生它们的低能声子窄，2.发现声子脉冲形成具有均匀能量密度的薄片，该能量密度随着加热器尺寸的减小而变宽，3.表明两个声子片之间的碰撞导致在液氦中产生热线，强烈地依赖于两个声子片之间的夹角，以及4.测量声子脉冲的角依赖作为压力的函数的丰富行为。这些效应都源于注入的激发在动量空间中只占据一个小的立体角。再加上强烈的各向异性相互作用，使得该系统在性质上不同于通常的各向同性系统。我们从理论上发现，脉冲的漂移速度与声子的温度一样，都是一个重要的基本参数。这项申请是为了让资金继续与阿达门科教授和他的团队一起发展这一理论，解释我们的一些实验结果。我们将分析各向异性旋子系统中的第二旋子声，以测量旋子密度，计算高能声子之间的散射率，并开始建立高能声子和旋子之间的散射理论，开始发展低能声子在与加热器法线的所有角度和压力0-24巴的传播理论，以及通过加热器和凝聚产生旋子的理论。

Strongly interacting phonon systems are usually isotropic and only recently have anisotropic systems been seriously investigated. We continue to discover and measure new and interesting effects which are due to the anisotropy, these include: 1. the creation of a beam of high energy phonons which have a narrower angular width than the low energy phonons which create them, 2. discovering that a phonon pulse forms a sheet with a uniform energy density which get wider as the heater dimensions are reduced, 3.showing that collisions between two phonon sheets, which leads to the creation of a hot line in the liquid helium, depends strongly on the angle between the sheets, and 4. measuring the rich behacviour of the angular dependence of phonon pulses as a function of pressure. These effects all stem from the fact that the injected excitations only occupy a small solid angle in momentum space. This coupled with strongly anisotropic interactions, makes the system qualitatively different to the usual isotropic system. The low energy phonons strongly interact and come into a dynamic equilibrium and we find theoretically that the drift velocity of the pulse is as an important and fundamental parameter as the temperature of the phonons. This application is for funds to continue to develop the theory with Professor Adamenko and his group, to explain some of our experimental results. We shall analyse roton second sound in anisotropic roton systems with a view to measuring the roton density, calculate the rate of scattering between high energy phonons and start formulating a theory for the scattering between high- energy phonon and rotons, start developing a theory for low-energy phonon propagation at all angles to the heater normal and at pressures 0-24 bar, and for the creation of rotons by a heater and by condensation.