Coarse-grained interaction potentials for poly(ethylene terephthalate) (PET) have been developed using the concept of potential of mean force and employing results of atomistic molecular dynamics simulations of ethylene terephthalate dimer. The end bridging Monte Carlo method has been adopted to handle coarse-grained PET chains. The resulting method permits for thorough, multiscale equilibration of a 100-mer PET melt, and is applicable to a wide range of industrially important polymers. The coarse-grained melt density, characteristic ratio and other conformational properties agree with experiment. Topological analyses of the melt using the CReTA and Z algorithms reveal that the melt is also well equilibrated with respect to entanglement density.

The effect of higher α-olefin comonomer on physical properties of short chain branched (SCB) polyethylene (PE) melts at 450 K has been studied using connectivity altering Monte Carlo simulations. The calculated chain dimensions per molecular mass scale with backbone weight fraction, ϕ, as ⟨S 2⟩/M ∼ ϕ1.27±0.03 for the radius of gyration S and ⟨R 2⟩/M ∼ ϕ1.27±0.03 for the end-to-end distance R, in very good agreement with the experiment-based result ⟨R 2⟩/M ∼ ϕ1.30. The observed dependence is consistent with the decrease in the fraction of trans states along the backbone. The entanglement tube diameter, a pp, computed for SCB melts scales as ⟨a pp⟩ ∼ ϕ–0.46±0.01, which is close to the result for model concentrated (⟨R 2⟩ = const) PE solutions created by deleting randomly chosen chains from equilibrated melt configurations of linear PE (⟨a pp⟩ ∼ ϕ–0.41±0.01). The latter result agrees very well with the scaling based on rheological experiments on concentrated hydrogenated polybutadiene (HPB)/C24H50 solutions at 413 K (⟨a pp⟩ ∼ ϕ–0.45). The tube diameter in model athermal PE solutions scales as ⟨a pp⟩ ∼ ϕ–0.6±0.03, in excellent agreement with the scaling based on the neutron spin-echo experiments on athermal HPB/C19D40 solutions at 509 K (⟨a pp⟩ ∼ ϕ–0.6). The computed scaling relationships for both SCB melts and model PE solutions are close to the binary contact model (a pp ∼ ϕ–0.5) and disagree with the packing model (a pp ∼ ϕ–1.27). The solubility parameters calculated for poly(ethylene-co-1-butene) (PEB) melts are in excellent agreement with relative solubility parameters based on SANS analysis of appropriate SCB blends, which scale as δ ∼ ϕ0.18. The SANS-derived relative solubility parameters for poly(ethylene-co-1-hexene) (PEH) and poly(ethylene-1-octene) (PEO) systems scale more weakly (δ ∼ ϕ0.1) and suggest breakdown of a universal correlation. This pattern is followed by simulated relative solubility parameters.

Abstract. Clutter rejection is among the most important issues in radar signal processing, for which the adaptive antenna technique can be a powerful means. Compared to other applications of the adaptive antenna, however, atmospheric radars require strict conditions, which have prevented application of this technique; the main antenna beam pattern should not be altered since the target region is defined by its shape. In particular, the loss of the antenna gain should be kept to no more than about 0.5 dB, in order to maintain the high sensitivity of the system. Also, clutter from surrounding mountains is often stronger than the desired weak scattering from atmospheric turbulence. We introduce a new algorithm which satisfies the above conditions, and confirms its capability by applying it to actual data taken by the MU radar. This paper presents the first report that demonstrates the effectiveness of the adaptive antenna technique in atmospheric radar applications. Despite the fact that no information is given on the spectral features of the desired and undesired signals, only the clutter echoes from surrounding mountains were effectively cancelled without affecting the desired echoes from atmospheric turbulence.

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