We have invented a novel technique to measure the radio image of a pulsar scattered by the interstellar plasma with 0.1 mas resolution. We extend the "secondary spectrum" analysis of parabolic arcs by Stinebring et al. (2001) to very long baseline interferometry and, when the scattering is anisotropic, we are able to map the scattered brightness astrometrically with much higher resolution than the diffractive limit of the interferometer. We employ this technique to measure an extremely anisotropic scattered image of the pulsar B0834+06 at 327 MHz. We find that the scattering occurs in a compact region about 420 pc from the Earth. This image has two components, both essentially linear and nearly parallel. The primary feature, which is about 16 AU long and less than 0.5 AU in width, is highly inhomogeneous on spatial scales as small as 0.05 AU. The second feature is much fainter and is displaced from the axis of the primary feature by about 9 AU. We find that the velocity of the scattering plasma is 16±10 km s −1 approximately parallel to the axis of the linear feature. The origin of the observed anisotropy is unclear and we discuss two very different models. It could be, as has been assumed in earlier work, that the turbulence on spatial scales of (∼ 1000 km) is homogeneous but anisotropic. However it may be that the turbulence on these scales is homogeneous and isotropic but the anisotropy is produced by highly elongated (filamentary) inhomogeneities of scale 0.05-16 AU.

Along with the technology evolution for dense integration of high-power, high-frequency devices in electronics, the accompanying interfacial heat transfer problem leads to urgent demands for advanced thermal interface materials (TIMs) with both high through-plane thermal conductivity and good compressibility. Most metals have satisfactory thermal conductivity but relatively high compressive modulus, and soft silicones are typically thermal insulators (0.3 W m–1 K–1). Currently, it is a great challenge to develop a soft material with the thermal conductivity up to metal level for TIM application. This study solves this problem by constructing a graphene-based microstructure composed of mainly vertical graphene and a thin cap of horizontal graphene layers on both the top and bottom sides through a mechanical machining process to manipulate the stacked architecture of conventional graphene paper. The resultant graphene monolith has an ultrahigh through-plane thermal conductivity of 143 W m–1 K–1, exceeding that of many metals, and a low compressive modulus of 0.87 MPa, comparable to that of silicones. In the actual TIM performance measurement, the system cooling efficiency with our graphene monolith as TIM is 3 times as high as that of the state-of-the-art commercial TIM, demonstrating the superior ability to solve the interfacial heat transfer issues in electronic systems.

The rapid development of integrated circuits and electronic devices creates a strong demand for highly thermally conductive yet electrically insulating composites to efficiently solve “hot spot” problems during device operation. On the basis of these considerations, hexagonal boron nitride nanosheets (BNNS) have been regarded as promising fillers to fabricate polymer matrix composites. However, so far an efficient approach to prepare ultrahigh-aspect-ratio BNNS with large lateral size while maintaining an atomically thin nature is still lacking, seriously restricting further improvement of the thermal conductivity for BNNS/polymer composites. Here, a rapid and high-yield method based on a microfluidization technique is developed to obtain exfoliated BNNS with a record high aspect ratio of ≈1500 and a low degree of defects. A foldable and electrically insulating film made of such a BNNS and poly­(vinyl alcohol) (PVA) matrix through filtration exhibits an in-plane thermal conductivity of 67.6 W m–1 K–1 at a BNNS loading of 83 wt %, leading to a record high value of thermal conductivity enhancement (≈35 500). The composite film then acts as a heat spreader for heat dissipation of high-power LED modules and shows superior cooling efficiency compared to commercial flexible copper clad laminate. Our findings provide a practical route to produce electrically insulating polymer composites with high thermal conductivity for thermal management applications in modern electronic devices.