Dynamical evolution of an effective two-level system with PT symmetry

We investigate the dynamics of parity- and time-reversal (PT ) symmetric two-energy-level atoms in the presence of two optical and a radio-frequency (rf) fields. The strength and relative phase of fields can drive the system from unbroken to broken PT symmetric regions. Compared with the Hermitian model, Rabi-type oscillation is still observed, and the oscillation characteristics are also adjusted by the strength and relative phase in the region of unbroken PT symmetry. At exception point (EP), the oscillation breaks down. To better understand the underlying properties we study the effective Bloch dynamics and find the emergence of the z components of the fixed points is the feature of the PT symmetry breaking and the projections in x-y plane can be controlled with high flexibility compared with the standard two-level system with PT symmetry. It helps to study the dynamic behavior of the complex PT symmetric model.Comment: 10 pages, 6 figures,to appear in CP

When expectations meet reality : exploring Chinese tertiary graduates’ post-study transitional experience and migratory outcomes in New Zealand : a thesis presented in fulfilment of the requirements for the degree of Doctor of Philosophy, Massey University, Wellington, New Zealand

International students’ post-academic mobility in the host country is an under-researched area. The purpose of this study is to explore Chinese tertiary graduates’ pre-arrival expectations and their transitional experience from students to permanent residents in New Zealand. The study assesses the challenges and barriers facing Chinese graduates during the transitional stage and their associated strategies and tactics to tackle those problems. Drawing on the data from 25 semi-structured interviews, the study finds that Chinese graduates’ expectations shifted and evolved during the process of seeking employment and adapting to the workplace culture in the host country. Participants securing employment through different effective strategies and tactics had successfully adapted to the workplace culture. However, there was a discrepancy between their expectations and experience manifested in insufficient pre-arrival information about the host country, visa constraints, recruiters’ bias and stereotypes, and exploitation by co-national employers. Meanwhile, despite experiencing more difficulties during the post-study transition, female Chinese graduates demonstrated high adaptability to local workplaces which allowed them to integrate into New Zealand’s workplace culture swiftly. The unmet expectations pushed some graduates to either return to their home country or migrate to a different country. These results provide valuable insights into the study of international students’ post-study mobility by analysing their migrants’ perspectives, expectations and personal experience in the host country. In addition, the study makes recommendations for stakeholders in the education industry on how to collaborate on improving international graduates’ post-academic experience

RSA: Byzantine-Robust Stochastic Aggregation Methods for Distributed Learning from Heterogeneous Datasets

In this paper, we propose a class of robust stochastic subgradient methods for distributed learning from heterogeneous datasets at presence of an unknown number of Byzantine workers. The Byzantine workers, during the learning process, may send arbitrary incorrect messages to the master due to data corruptions, communication failures or malicious attacks, and consequently bias the learned model. The key to the proposed methods is a regularization term incorporated with the objective function so as to robustify the learning task and mitigate the negative effects of Byzantine attacks. The resultant subgradient-based algorithms are termed Byzantine-Robust Stochastic Aggregation methods, justifying our acronym RSA used henceforth. In contrast to most of the existing algorithms, RSA does not rely on the assumption that the data are independent and identically distributed (i.i.d.) on the workers, and hence fits for a wider class of applications. Theoretically, we show that: i) RSA converges to a near-optimal solution with the learning error dependent on the number of Byzantine workers; ii) the convergence rate of RSA under Byzantine attacks is the same as that of the stochastic gradient descent method, which is free of Byzantine attacks. Numerically, experiments on real dataset corroborate the competitive performance of RSA and a complexity reduction compared to the state-of-the-art alternatives.Comment: To appear in AAAI 201

Existence of positive ground state solutions of critical nonlinear Klein-Gordon-Maxwell systems

In this paper we study the following nonlinear Klein–Gordon–Maxwell system −∆u + [m2 0 − (ω + φ) 2 ]u = f(u) in R3 ∆φ = (ω + φ)u in R3 where 0 < ω < m0. Based on an abstract critical point theorem established by Jeanjean, the existence of positive ground state solutions is proved, when the nonlinear term f(u) exhibits linear near zero and a general critical growth near infinity. Compared with other recent literature, some different arguments have been introduced and some results are extended

Evidence for short-range magnetic order in the nematic phase of FeSe from anisotropic in-plane magnetostriction and susceptibility measurements

The nature of the nematic state in FeSe remains one of the major unsolved mysteries in Fe- based superconductors. Both spin and orbital physics have been invoked to explain the origin of this phase. Here we present experimental evidence for frustrated, short-range magnetic order, as suggested by several recent theoretical works, in the nematic state of FeSe. We use a combination of magnetostriction, susceptibility and resistivity measurements to probe the in-plane anisotropies of the nematic state and its associated fluctuations. Despite the absence of long-range magnetic order in FeSe, we observe a sizable in-plane magnetic susceptibility anisotropy, which is responsible for the field-induced in-plane distortion inferred from magnetostriction measurements. Further we demonstrate that all three anisotropies in FeSe are very similar to those of BaFe2As2, which strongly suggests that the nematic phase in FeSe is also of magnetic origin.Comment: 5 pages, 4 figure