Complementary Approximations to the Solution of a Problem in Water Waves

A surface wave is incident upon two vertical parallel barriersimmersed to a given depth beneath the surface of water of infinitedepth. The problem has an exact but complicated solution. Simplercomplementary approximations to the reflection coefficient arederived which may be computed easily. These approximations arefound to be very good for all wavelengths provided the ratioof separation to depth of the barrier is not too small. It isshown that there exist certain wavelengths for each barrierconfiguration for which total reflection of the incident waveoccurs.     

The Effect of a Fixed Vertical Barrier on Obliquely Incident Surface Waves in Deep Water

A plane wave in deep water is obliquely incident on an infinitelylong fixed vertical barrier immersed to a given depth. Partof the wave energy is reflected by the barrier and part is transmittedunder the barrier. Expressions for the reflection and transmissioncoefficients are derived in terms of an integral equation foreither the potential across the barrier or the horizontal velocityunder the barrier. The known exact solution for normally incidentwaves is then used as a one term Galerkin approximation to givevery accurate upper and lower bounds for the reflection andtransmission coefficients for all wavelengths and angles ofincidence.     

Suppression of plasma turbulence during optimized shear configurations in JET

Correlation of density turbulence suppression and reduced plasma transport is observed in the internal transport barrier (ITB) region of JET tokamak discharges with optimized magnetic shear. The suppression occurs in two stages. First, low frequency turbulence and ion transport are reduced across the plasma core by a toroidal velocity shear generated by intense auxiliary heating. Then with the ITB formation, high frequency turbulence and electron transport are reduced locally within the steep pressure gradient region of the ITB.     

超声浸渍法制备Pd/Al2O3催化剂及其催化蒽醌加氢性能

 以球形 γ-Al2O3 和 θ-Al2O3 为载体,分别采用超声浸渍和普通浸渍方法制备了Pd含量为0.3%的负载型催化剂,并将其用于蒽醌加氢反应. 采用X射线衍射、 N2吸附和透射电镜等手段对催化剂的理化性质和孔结构进行了分析,考察了浸渍方法对催化剂活性金属分散度的影响. 结果表明,与普通浸渍法相比,超声浸渍法制备的负载型Pd催化剂金属分散度明显提高,因而对蒽醌加氢反应表现出较高的催化活性. 以960 ℃焙烧的球θ-Al2O3 为载体,通过超声浸渍制备的负载型Pd催化剂具有较高的Pd分散度和较大的孔径,在蒽醌加氢反应中对反应物的扩散阻力较小,因而表现出更高的催化活性,而且反应中催化剂的稳定性良好.     

Ti-MCM-41催化剂的表面性质及介质极性对

用不同的铝源改性Ti MCM 41催化剂 ,得到了具有长程有序结构、n(Si) /n(Ti) =2 5的不同Si/Al比的改性Ti MCM 41.通过研究芳烃羟化反应随催化剂表面性质的变化规律发现 ,调变催化剂的表面性质 ,可控制反应物苯及目的产物苯酚与Al Ti MCM 41催化活性中心接近的程度 ,从而可实现对芳烃羟化反应化学选择性的控制 .介质极性对芳烃的化学亲和选择性也有影响 ,只有富含供电子氧原子且其极性大于苯的介质才有利于芳烃的羟化反应     

Configurational temperature thermostat for fluids undergoing shear flow: application to liquid chlorine

Non-equilibrium molecular dynamics (NEMD) simulations play a major role in characterizing the rheological properties of fluids undergoing shear flow. However, all previous studies of flows in molecular fluids either use an ‘atomic’ thermostat which makes incorrect assumptions concerning the streaming velocity of atoms within their constituent molecules, or they employ a centre of mass kinetic (COM) thermostat which only controls the temperature of relatively few degrees of freedom (3) in complex high molecular weight compounds. In the present paper we show how recently developed configurational expressions for the thermodynamic temperature can be used to develop thermostatting mechanisms which avoid both of these problems. In this work, we propose a thermostat based on a configurational expression for the temperature and apply it to NEMD simulations of chlorine undergoing Couette flow. The results so obtained are compared with those obtained using a COM kinetic thermostat. At equilibrium the properties of systems thermostatted in the two different ways are of course equivalent. We show that the two responses only differ far from equilibrium. In particular, we show that the formation of a string phase for extremely high shear rates is an artefact of the COM thermostat. At the largest shear rates studied with the configurational thermostat, no string phase is observed.     

A Note on the Transparency of a Submerged Circular Cylinder to the Waves Radiated by a Pulsating Line Source

A remarkable result from linear water-wave theory states thatthe direction of the energy flux in a progressive two-dimensionalplane surface wave in deep water is unaffected by the presenceof a fixed submerged circular cylinder. This result is heregeneralized to the energy flux radiated from a pulsating two-dimensionalwave source. Thus it is shown that the energy flux radiatesequally to either infinity regardless of the relative positionsof the cylinder and the source, the result being true for arbitrarycylinder radius and depth of submergence, and for any frequencyof pulsation of the source.