A Dynamic Packet Recovery Mechanism for Realtime Service in Mobile Computing Environments

This paper analyzes the characteristics of packet losses in mobile computing environments based on the Gilbert model and then describes a mechanism that can recover the lost audio packets using redundant data. Using information periodically reported by a receiver, the sender dynamically adjusts the amount and offset values of redundant data with the constraint of minimizing the bandwidth consumption of wireless links. Since mobile computing environments can be often characterized by frequent and consecutive packet losses, loss recovery mechanisms need to deal efficiently with both random and consecutive packet losses. To achieve this, the suggested mechanism uses relatively large, discontinuous exponential offset values. That gives the same effect as using both the sequential and interleaving redundant information. To verify the effectiveness of the mechanism, we extended and implemented RTP/RTCP and applications. The experimental results show that our mechanism, with an exponential offset, achieves a remarkably low complete packet loss rate and adapts dynamically to the fluctuation of the packet loss pattern in mobile computing environments.     

带有Gilbert阻尼项的Landau-Lifshitz铁磁链方程解的最佳衰减率

主要研究带有Gilbert阻尼项的Landau-Lifshitz铁磁链方程的柯西问题.当初值的一阶导数适当小时,基于加权能量估计,证明了强解的整体存在性并且给出了解的最优的L2和L∞衰减估计.     

Light scattering by a homogeneous sphere near a plane boundary II

ABSTRACT

The problem of light scattering by a homogeneous sphere above a plane boundary is considered in this paper. Hankel transformation and Erdélyi's formula are used to satisfy the boundary conditions on the plane and the determination of the unknown coefficients in the scattered field is achieved by matching the electromagnetic boundary conditions on the surface of the sphere. Existence and uniqueness of the solution involving these unknown coefficients are shown and the extinction efficiency factor is presented.     

Study on the Gilbert damping of polycrystalline YIG films with different capping layers

This paper describes the effect of 5-nm thick platinum (Pt), aluminum (Al) and silicon oxide (SiO_x) capping layers on the static and dynamic magnetic properties of 400-nm thick polycrystalline YIG films deposited on a Pt buffer layer. Both static and dynamic magnetic properties of Pt capped YIG film are totally different among all YIG films. Namely, the squareness of the magnetization curve for Pt capped YIG film increases, indicating that Pt capped YIG film is magnetically softer than other YIG films. Interestingly, the effective Gilbert damping parameter of Pt capped YIG films is about four times as large as those of other YIG films, and its value is approximately 9.52 × 10⁻⁴. However, the value of Gilbert damping is 2.55 × 10⁻⁴, 3.46 × 10⁻⁴ and 3.85 × 10⁻⁴ respectively for no capping, SiOx capping and Al capping samples respectively. This huge change in Gilbert damping parameter is mainly originating from the spin pumping effect, which arises at the interface of a material having strong spin orbit interaction such as Pt. Moreover, the enourmous increase in the value of effective anisotropic field and decrese in effective saturation magnetization indicates interface anisotropy is induced in Pt capped sample. These results suggest that the static and dynamic magnetic properties of YIG film can be controlled by selecting an appropriate capping layer.     

Irreversible thermodynamics of non-uniform insulating ferromagnets

Two types of damping are commonly applied to describe ferromagnets at the phenomenological level: one by Landau and Lifshitz, and the other by Gilbert. This work successively applies the methods of irreversible thermodynamics to insulators, insulating paramagnets, and uniform insulating ferromagnets, in the last case uniquely obtaining Landau–Lifshitz damping. These methods are then applied to non-uniform insulating ferromagnets, for which new, non-current-related, spin fluxes and spin torques appear. These may be relevant to the dynamics of magnets in confined geometries, where boundary conditions impose complex non-trivial textures. Study of systems with very large damping might help distinguish between the two proposed forms of damping.     

Micromagnetic simulation of ferromagnetic resonance of perpendicular granular media: Influence of the intergranular exchange on the Landau-Lifshitz-Gilbert damping constant

A micromagnetic approach was used to simulate ferromagnetic resonance frequency (FMR) profiles of perpendicular granular CoCrPt-oxide thin films. From the obtained FMR line-width we computed the effective damping constant. The influence of the intergranular exchange on the effective damping was investigated, showing an increase in the damping constant with increase in intergranular exchange coupling. Moreover, the effective damping constant increases with decrease in mesh size of the model, and eventually saturates for mesh sizes of about 1 nm. These dependencies are explained in terms of different modes that can be excited in the granular medium due to interactions between the individual spins.     

An explicit derivation of a relation between magnetization M and saturation magnetization Ms

An explicit relationship between a magnetization vector M and its saturation magnetization M_s is derived using the definition of M along with assumptions of the continuum exchange theory. The obtained expression is found to be an extension of the commonly used fixed-length constraint and represents the continuous analog of it for the elementary moment per unit volume. The derivation of this relation is carried out in detail and important potential implications relating to equations for M are also highlighted.     

吉尔伯特·牛顿·路易斯——加州大学伯克利分校化学系的缔造者*

吉尔伯特·牛顿·路易斯是20世纪最伟大的化学家之一。在加州大学伯克利分校,路易斯通过大力引进人才、提倡学术民主和学术合作、改革人才培养模式,逐步建立起了世界上最强大、最具创造力的化学系之一,培养了一批日后在化学领域做出了重大贡献的博士研究生。介绍了路易斯担任加州大学伯克利分校化学学院院长兼化学系主任期间的教育改革措施。     

集成CMOS四象限模拟乘法器

给出了一种CMOS型四象限模拟乘法器，该乘法器采用有源衰减器结合吉尔伯特单元结构.利用基于CSMC的0.6μm n阱2p2m工艺SPICE BSIM3V3 MOS模型(level=49)进行仿真，采用单电源5V电压供电.利用HSPICE仿真并给出了仿真的结果及版图实现.     

高线性度的CMOS下变频混频器的设计

采用正交反馈的跨导级设计了一种基于数字电视调谐芯片中的高线性度的下变频混频器,该混频器在3.3V的工作电压下,采用改进的Gilbert单元,使用基于Chartered0.25μm标准CMOS工艺进行流片测试,结果表明该混频器IIP3可达到15dBm,增益达到9dB。