The diffraction of elastic waves by an imperfect fusion bond

We consider diffraction by a semi-infinite crack located alonga fusion interface between two differing elastic media. Twotypes of crack, namely open and partially closed cracks, areinvestigated. An open crack is modelled by a stress-free contactboundary condition and a partially closed crack is modelledby a spring contact boundary condition. For the latter, thejump in the stress across the crack is assumed to be proportionalto the jump in the displacement across the crack. This situationarises in, for example, a K-weld where the fine grain of theparent material (for example, ferritic or forged austeniticsteel) is in stark contrast with the coarse-grained weld metal(for example, austenitic weld metal). In the metal weld thedirection of the grain axis varies through the metal. However,diffraction is a local phenomenon and so the austenitic steelis assumed to have a zonal axis so that it may be modelled bya transversely isotropic composite. The ferritic or forged austeniticsteel will be modelled as an isotropic material.     

Single DNA molecule stretching in sudden mixed shear and elongational microflows

High-throughput stretching and monitoring of single DNA molecules in continuous elongational flow offers compelling advantages for biotechnology applications such as DNA mapping. However, the polymer dynamics in common microfluidic implementations are typically complicated by shear interactions. These effects were investigated by observation of fluorescently labeled 185 kb bacterial artificial chromosomes in sudden mixed shear and elongational microflows generated in funneled microfluidic channels. The extension of individual free DNA molecules was studied as a function of accumulated fluid strain and strain rate. Under constant or gradually changing strain rate conditions, stretching by the sudden elongational component proceeded as previously described for an ideal elongational flow (T. T. Perkins, D. E. Smith and S. Chu, Science, 1997, 276, 2016): first, increased accumulated fluid strain and increased strain rate produced higher stretching efficiencies, despite the complications of shear interactions; and second, the results were consistent with unstretched molecules predominantly in hairpin conformations. More abrupt strain rate profiles did not deliver a uniform population of highly extended molecules, highlighting the importance of balance between shear and elongational components in the microfluidic environment for DNA stretching applications. DNA sizing with up to 10% resolution was demonstrated. Overall, the device delivered 1000 stretched DNA molecules per minute in a method compatible with diffraction-limited optical sequence motif mapping and without requiring laborious chemical modifications of the DNA or the chip surface. Thus, the method is especially well suited for genetic characterization of DNA mixtures such as in pathogen fingerprinting amidst high levels of background DNA.     

ON AVOIDANCE ACTIVITIES IN FISHERY ENFORCEMENT MODELS

Compliance and enforcement in fisheries are important issues from an economic point of view since management measures are useless without a certain level of enforcement. These conclusions come from the well‐established theoretical literature on compliance and enforcement problems within fisheries and a common result is that, it is efficient to set fines as high as possible and monitoring as low as possible, when fines are costless and offenders are risk neutral. However, this result is sensitive to the assumption that fishermen cannot engage in avoidance activities, e.g., activities to reduce the likelihood of being detected when noncomplying. The paper presents a model of fisheries that allows the fishermen to engage in avoidance activities. The conclusions from the model are that, under certain circumstances, fines are costly transfers to society since they not only have a direct positive effect on the level of deterrence, but also an indirect negative effect in the form of increased avoidance activities to reduce the probability of detection. The paper contributes to the literature on avoidance activities by introducing the externality from the illegal behavior as an endogenous effect on other offenders. For an externality, that has an exogenous effect on other actors, Malik shows that fines are only costly transfers for conditional deterrence (when one actor is deterred while another actor is not). For fisheries, we show that fines are also costly transfers under no deterrence (when no agents are deterred).     

Orthogonal Polynomials and Second-order Differential Equations

We show that a sequence of polynomials can be eigenfunctionsof a second-order differential operator only under severe restrictions.     

焙烧硼钠钙石在高固液比氯化铵溶液中的溶解动力学

Boron is available in the form of metal borates, especially of sodium and calcium, in nature[1]. The production of boron compounds has substantially increased recently due to increasing uses of these compounds in nuclear technology, in rocket engines as f…     

Lattice dynamics of InAs under hydrostatic pressures

The lattice dynamics of InAs under variable hydrostatic pressures is investigated on the basis of an ‘11-parameter’ rigid-ion model (RIM). The calculated phonon dispersion curves are in satisfactory agreement with the neutron scattering data (available for the TA modes only) measured at room temperature and atmospheric pressure. The one- and two-phonon densities of states functions and mode Gruneisen parameters have been computed at two arbitrary hydrostatic pressures. The effect of high pressure on the phonon dispersion curves is shown to lead to a typical ‘softening’ in the transverse acoustic modes and eventually to a phase trnasformation of the compound.     

Fast-neutron-flux measurements in the underground facilities at Baksan

The fast-neutron flux in one of the deep underground facilities situated at a depth of 4900 mwe in the Baksan Neutrino Observatory are measured. The relative neutron-shielding properties of several commonly available natural materials are also investigated. Preliminary results obtained with a highly sensitive fast-neutron spectrometer at a sensitivity level of about 10^?7 neutron cm^?2 s^?1 are presented and discussed.