Intrinsic interface exchange coupling of ferromagnetic nanodomains in a charge ordered manganite

We present a detailed magnetic study of the Pr1/3Ca2/3MnO3 manganite, where we observe the presence of small ferromagnetic (FM) domains (diameter ~ 10A) immersed within the charge-ordered antiferromagnetic (AFM) host. Due to the interaction of the FM nanodroplets with a disordered AFM shell, the low-temperature magnetization loops present exchange bias (EB) under cooling in an applied magnetic field. Our analysis of the cooling field dependence of the EB yields an antiferromagnetic interface exchange coupling comparable to the bulk exchange constant of the AFM phase. We also observe training effect of the EB, which is successfully described in terms of a preexisting relaxation model developed for other classical EB systems. This work provides the first evidence of intrinsic interface exchange coupling in phase separated manganites.Comment: 7 pages, 6 figure

A Unified and Complete Construction of All Finite Dimensional Irreducible Representations of gl(2|2)

Representations of the non-semisimple superalgebra $gl(2|2)$ in the standard basis are investigated by means of the vector coherent state method and boson-fermion realization. All finite-dimensional irreducible typical and atypical representations and lowest weight (indecomposable) Kac modules of $gl(2|2)$ are constructed explicitly through the explicit construction of all $gl(2)\oplus gl(2)$ particle states (multiplets) in terms of boson and fermion creation operators in the super-Fock space. This gives a unified and complete treatment of finite-dimensional representations of $gl(2|2)$ in explicit form, essential for the construction of primary fields of the corresponding current superalgebra at arbitrary level.Comment: LaTex file, 23 pages, two references and a comment added, to appear in J. Math. Phy

Two novel nonlinear companding schemes with iterative receiver to reduce PAPR in multi-carrier modulation systems

Companding transform is an efficient and simple method to reduce the Peak-to-Average Power Ratio (PAPR) for Multi-Carrier Modulation (MCM) systems. But if the MCM signal is only simply operated by inverse companding transform at the receiver, the resultant spectrum may exhibit severe in-band and out-of-band radiation of the distortion components, and considerable peak regrowth by excessive channel noises etc. In order to prevent these problems from occurring, in this paper, two novel nonlinear companding schemes with a iterative receiver are proposed to reduce the PAPR. By transforming the amplitude or power of the original MCM signals into uniform distributed signals, the novel schemes can effectively reduce PAPR for different modulation formats and sub-carrier sizes. Despite moderate complexity increasing at the receiver, but it is especially suitable to be combined with iterative channel estimation. Computer simulation results show that the proposed schemes can offer good system performances without any bandwidth expansion

A model of rotating hotspots for 3:2 frequency ratio of HFQPOs in black hole X-ray binaries

We propose a model to explain a puzzling 3:2 frequency ratio of high frequency quasi-periodic oscillations (HFQPOs) in black hole (BH) X-ray binaries, GRO J1655-40, GRS 1915+105 and XTE J1550-564. In our model a non-axisymmetric magnetic coupling (MC) of a rotating black hole (BH) with its surrounding accretion disc coexists with the Blandford-Znajek (BZ) process. The upper frequency is fitted by a rotating hotspot near the inner edge of the disc, which is produced by the energy transferred from the BH to the disc, and the lower frequency is fitted by another rotating hotspot somewhere away from the inner edge of the disc, which arises from the screw instability of the magnetic field on the disc. It turns out that the 3:2 frequency ratio of HFQPOs in these X-ray binaries could be well fitted to the observational data with a much narrower range of the BH spin. In addition, the spectral properties of HFQPOs are discussed. The correlation of HFQPOs with jets from microquasars is contained naturally in our model.Comment: 8 pages, 4 figures. accepted by MNRA

Long-range quantum gates using dipolar crystals

We propose the use of dipolar spin chains to enable long-range quantum logic between distant qubits. In our approach, an effective interaction between remote qubits is achieved by adiabatically following the ground state of the dipolar chain across the paramagnet to crystal phase transition. We demonstrate that the proposed quantum gate is particularly robust against disorder and derive scaling relations, showing that high-fidelity qubit coupling is possible in the presence of realistic imperfections. Possible experimental implementations in systems ranging from ultracold Rydberg atoms to arrays of Nitrogen-Vacancy defect centers in diamond are discussed.Comment: 5 pages, 3 figure

GraphSE2^2: An Encrypted Graph Database for Privacy-Preserving Social Search

In this paper, we propose GraphSE$^2$, an encrypted graph database for online social network services to address massive data breaches. GraphSE$^2$ preserves the functionality of social search, a key enabler for quality social network services, where social search queries are conducted on a large-scale social graph and meanwhile perform set and computational operations on user-generated contents. To enable efficient privacy-preserving social search, GraphSE$^2$ provides an encrypted structural data model to facilitate parallel and encrypted graph data access. It is also designed to decompose complex social search queries into atomic operations and realise them via interchangeable protocols in a fast and scalable manner. We build GraphSE$^2$ with various queries supported in the Facebook graph search engine and implement a full-fledged prototype. Extensive evaluations on Azure Cloud demonstrate that GraphSE$^2$ is practical for querying a social graph with a million of users.Comment: This is the full version of our AsiaCCS paper "GraphSE$^2$: An Encrypted Graph Database for Privacy-Preserving Social Search". It includes the security proof of the proposed scheme. If you want to cite our work, please cite the conference version of i