An analytic continuation method for obtaining rigorous bounds on the effective complex permittivity * of polycrystalline composite materials is developed. It is assumed that the composite consists of many identical anisotropic crystals, each with a unique orientation. The key step in obtaining the bounds involves deriving an integral representation for * , which separates parameter information from geometrical information. Forward bounds are then found using knowledge of the single crystal permittivity tensor and mean crystal orientation. Inverse bounds are also developed, which recover information about the mean crystal orientation from * . We apply the polycrystalline bounds to sea ice, a
Thermal metamaterials are of great importance in advanced energy control and management. Previous studies mainly focused on interfaces with perfect bonding conditions. In principle, imperfectness always exists across interface and the effect is intriguingly important with small-length scales. This work reports the imperfect interface effect in thermal metamaterials thoroughly. Low conductivity- and high conductivity-type interfaces are considered. We show that an object can always be made thermally invisible, with the effect of imperfect interface, as that of a homogeneous background material. This unprecedented condition is derived in an exact and analytic form, systematically structured, with much versatile and physical implications. Conditions for thermal shielding and enhancements are analytically found and numerically exemplified, highlighting the specific role of material and geometric parameters. We find that both types of interfaces are complementing with each other which, all together, will constitute a full spectrum to achieve the thermal invisibility. The analytic finding offers a general perception that adds to the understanding of heat transport mechanism across interfaces in thermal metamaterials, in ways that drastically distinct from that of ideal interfaces. This finding opens up new possibilities for the control and management of thermal metamaterials with imperfect bonding interfaces.
Abstract. Along with the rapid progress and widely used of mobile application, security protection to software application has become an important issue. The lack of binary protections makes it important to implement packing services. By analyzing traditional features of software reinforcement technology, the paper describes the basic functions for security reinforcement, illustrates the principle of protection method and put forward corresponding preventive measures and technical solutions. New strategies including elliptic curve encryption and dynamic loading mechanism, agile reinforcement process as well as two-step self-modified obfuscation are proposed to satisfy the effectiveness and efficiency requirements for application reinforcement.
We present new exact results for the design of spherical thermal cloaks with the effect of imperfect interfaces. Thermal metamaterials are of great importance in advanced energy control and management. However, nearly all relevant studies considered that interfaces are ideally perfect. In principle, bonding imperfectness always exists at interfaces, and this effect is particularly important in small-length scales. Here, we will examine in detail the effect of bonding imperfectness on the performance of thermal functionality. The thermal metamaterial is made of a homogeneous spherically anisotropic material with a constant conductivity tensor. Low conductivity- and high conductivity-type interfaces are considered. We show how the anisotropic layer, together with the effect of imperfect bonding interfaces, can be made thermally invisible. An exact condition for thermal invisibility is derived in a simple algebraic form. Conditions for thermal shielding or enhancement are theoretically analyzed and numerically exemplified, in which relevant material and geometric parameters can be tuned to achieve the functionality. In addition, numerical simulations based on finite element calculations are carried out to validate our analytic solutions. The present findings offer a general guideline in the design of spherical thermal metamaterials with imperfect interfaces.
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