High resolution angle-resolved photoemission measurements on an underdoped (La(2-x)Srx)CuO4 system show that, at energies below 70 meV, the quasiparticle peak is well defined around the (pi/2,pi/2) nodal region and disappears rather abruptly when the momentum is changed from the nodal point to the (pi,0) antinodal point along the underlying "Fermi surface." It indicates that there is an extra low energy scattering mechanism acting upon the antinodal quasiparticles. We propose that this mechanism is the scattering of quasiparticles across the nearly parallel segments of the Fermi surface near the antinodes.

Polymeric nanomaterials emerge as key building blocks for engineering materials in a variety of applications. In particular, the high modulus polymeric nanofibers are suitable to prepare flexible yet strong membrane separators to prevent the growth and penetration of lithium dendrites for safe and reliable high energy lithium metal-based batteries. High ionic conductance, scalability, and low cost are other required attributes of the separator important for practical implementations. Available materials so far are difficult to comply with such stringent criteria. Here, we demonstrate a high-yield exfoliation of ultrastrong poly(p-phenylene benzobisoxazole) nanofibers from the Zylon microfibers. A highly scalable blade casting process is used to assemble these nanofibers into nanoporous membranes. These membranes possess ultimate strengths of 525 MPa, Young's moduli of 20 GPa, thermal stability up to 600 °C, and impressively low ionic resistance, enabling their use as dendrite-suppressing membrane separators in electrochemical cells. With such high-performance separators, reliable lithium-metal based batteries operated at 150 °C are also demonstrated. Those polyoxyzole nanofibers would enrich the existing library of strong nanomaterials and serve as a promising material for large-scale and cost-effective safe energy storage.

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With the development of energy science and electronic technology, interfacial thermal transport has become a key issue for nanoelectronics, nanocomposites, energy transmission, and conservation, etc. The application of thermal interfacial materials and other physical methods can reliably improve the contact between joined surfaces and enhance interfacial thermal transport at the macroscale. With the growing importance of thermal management in micro/nanoscale devices, controlling and tuning the interfacial thermal resistance (ITR) at the nanoscale is an urgent task. This Review examines nanoscale interfacial thermal transport mainly from a theoretical perspective. Traditional theoretical models, multiscale models, and atomistic methodologies for predicting ITR are introduced. Based on the analysis and summary of the factors that influence ITR, new methods to control and reduce ITR at the nanoscale are described in detail. Furthermore, the challenges facing interfacial thermal management and the further progress required in this field are discussed.

We report angle-resolved photoemission spectra both above and below T c in the single-plane cuprate superconductor Bi 2 Sr 22x La x CuO 61d . The superconducting state measurements show a highly anisotropic excitation gap with a maximum magnitude smaller than that of the bilayer compound Bi 2 Sr 2 CaCu 2 O 8 by a factor of 3. For a range of doping, the gap persists well above T c , behavior previously associated with underdoped bilayer cuprates. The anisotropy and magnitude of the normalstate gap are very similar to the superconducting state gap, indicating that the two gaps may have a common origin in a pairing interaction.[S0031-9007(97) A central issue in the physics of high-T c superconductivity is the role of coupling between the two-dimensional copper-oxygen planes in producing superconductivity. The T c of these materials tends to increase with the number of layers per unit cell. It is currently an open question whether the superconducting state order parameter symmetry will be the same in one-layer and the more strongly coupled two-layer compounds. Angle-resolved photoemission spectroscopy (ARPES) has the potential to resolve this issue since it is able to measure directly the anisotropy of the superconducting state gap (the magnitude of the order parameter). In the two-plane material Bi 2 Sr 2 -CaCu 2 O 81d (Bi2212), the gap was found by ARPES to be highly anisotropic and consistent with a d x 2 2y 2 order parameter [1,2]. We report measurements of the one-plane material Bi2201 that show a similarly large anisotropy with a smaller overall gap magnitude.In underdoped Bi2212, ARPES measurements have shown that the anisotropic gap persists well above T c [3,4], consistent with many other experiments that have shown a pseudogap or spin gap in the normal state of cuprate superconductors [5]. Current evidence for the normalstate gap in one-plane materials is much weaker than in two-plane materials, and its existence is controversial [6]. Our results show a clear normal-state gap up to high temperatures in optimally doped and underdoped Bi2201, but not in overdoped Bi2201.Single crystal samples of Bi 21x Sr 22͑x1y͒ La y CuO 61d were grown using a floating zone method, and for comparison by a self-flux method. X-ray scattering confirms that the crystals are single-phase Bi2201, and electron-probe microanalysis was used to measure the atomic ratios of the cations. Substitution of trivalent La or Bi for divalent Sr reduces the hole concentration in the CuO 2 planes. The effect of La doping goes beyond changing the carrier density [7], however, and raises the maximum T c from 10 to 30 K.A roughly parabolic dependence of T c on ͑x 1 y͒ has been observed [8]. Our optimally doped crystals (T c 29 K) come from substituting La 0.35 for Sr. With no La substitution, Bi͞Sr ratios of 2.3͞1.7 and 2.1͞1.9 give the underdoped samples with T c , 4 K and the overdoped samples with T c 8 K, respectively. The transition temperatures were taken as the zero resistance values and confirmed by SQUID magnetization measurements. The tr...

An improved phased array using pattern reconfigurable antenna elements in this communication is proposed to realize wide-angle scanning performance with low gain fluctuation. The pattern reconfigurable element is a microstrip Yagi antenna with its parasitic strips loaded with varactors. The reconfigurability of radiation pattern from the element is enabled by tuning the capacitive reactance of the varactors. Five elements were arranged in an equally-spaced linear array, and the effects of several key parameter variations on the radiation characteristics of the array are provided. The proposed array is fabricated and experimentally verified. It is seen from the measured results that the main beam of the array can scan from -70° to 70° in the H-plane with a gain fluctuation less than 2 dB. Meanwhile, the coverage of 3 dB beamwidth of the array is from about -87° to 87°. The agreement between simulated and measured results validates our design exhibiting a good performance of wide-angle scanning.

Abstract-A new circular ultra-wideband fractal monopole antenna based on descartes circle theorem (DCT) with elliptical iterations is presented. The proposed fractal design is optimized for return loss below −15 dB. The basic structure is slightly modified to ensure an overall smooth current distribution limited by the junction point nature of the fractal geometries. The measured return loss of the proposed design is below −15 dB within its impedance bandwidth along with omni-directional radiation pattern. Moreover due to the fractal shape, the proposed design has less weight and wind loading effect.

A compact printed ultrawideband (UWB) multipleinput-multiple-output (MIMO)/diversity antenna system (of two elements) with a size of 35 40 mm 2 operating at a frequency range of 3.1-10.6 GHz is proposed. The wideband isolation can be achieved through a tree-like structure on the ground plane. The effectiveness of the tree-like structure is analyzed. Measured S-parameters show that the isolation is better than 16 dB ( 20 dB in most of the band) across the UWB of 3.1-10.6 GHz. The radiation patterns, gain, and envelope correlation coefficient are also measured. The proposed antenna is suitable for some portable MIMO/ diversity applications.