Universal probes of two-dimensional topological insulators: Dislocation and pi-flux

We show that the pi-flux and the dislocation represent topological observables that probe two-dimensional topological order through binding of the zero-energy modes. We analytically demonstrate that pi-flux hosts a Kramers pair of zero modes in the topological Gamma (Berry phase skyrmion at the zero momentum) and M (Berry phase skyrmion at a finite momentum) phases of the M-B model introduced for the HgTe quantum spin Hall insulator. Furthermore, we analytically show that the dislocation acts as a pi-flux, but only so in the M phase. Our numerical analysis confirms this through a Kramers pair of zero modes bound to a dislocation appearing in the M phase only, and further demonstrates the robustness of the modes to disorder and the Rashba coupling. Finally, we conjecture that by studying the zero modes bound to dislocations all translationally distinguishable two-dimensional topological band insulators can be classified.Comment: 5 pages, 2 figures; version accepted in Physical Review Letter

Disclosures of funding sources and conflicts of interest in published HIV/AIDS research conducted in developing countries

Objectives: Disclosures of funding sources and conflicts of interests (COI) in published peer-reviewed journal articles have recently begun to receive some attention, but many critical questions remain, for example, how often such reporting occurs concerning research conducted in the developing world and what factors may be involved. Design: Of all articles indexed in Medline reporting on human subject HIV research in 2007 conducted in four countries (India, Thailand, Nigeria and Uganda), this study explored how many disclosed a funding source and COI, and what factors are involved. Results: Of 221 articles that met the criteria, 67.9% (150) disclosed the presence or absence of a funding source, but only 20% (44) disclosed COI. Studies from Uganda were more likely, and those from Nigeria were less likely to mention a funding source (p<0.001). Of articles in journals that had adopted International Committee of Medical Journal Editors (ICMJE) guidelines, 56% did not disclose COI. Disclosure of funding was more likely when: ≥50% of the authors and the corresponding author were from the sponsoring country, the sponsor country was the USA, and the articles were published in journals in which more of the editors were from the sponsoring countries. Conclusions: Of the published studies examined, over a third did not disclose funding source (ie, whether or not there was a funding source) and 80% did not disclose whether COI existed. Most articles in ICMJE-affiliated journals did not disclose COI. These data suggest the need to consider alteration of policies to require that published articles include funding and COI information, to allow readers to assess articles as fully as possible

On piecewise linear approximations of bilinear terms: structural comparison of univariate and bivariate mixed-integer programming formulations

Bilinear terms naturally appear in many optimization problems. Their inherent non-convexity typically makes them challenging to solve. One approach to tackle this difficulty is to use bivariate piecewise linear approximations for each variable product, which can be represented via mixed-integer linear programming (MIP) formulations. Alternatively, one can reformulate the variable products as a sum of univariate functions. Each univariate function can again be approximated by a piecewise linear function and modelled via an MIP formulation. In the literature, heterogeneous results are reported concerning which approach works better in practice, but little theoretical analysis is provided. We fill this gap by structurally comparing bivariate and univariate approximations with respect to two criteria. First, we compare the number of simplices sufficient for an ε-approximation. We derive upper bounds for univariate approximations and compare them to a lower bound for bivariate approximations. We prove that for a small prescribed approximation error  ε, univariate ε-approximations require fewer simplices than bivariate ε-approximations. The second criterion is the tightness of the continuous relaxations (CR) of corresponding sharp MIP formulations. Here, we prove that the CR of a bivariate MIP formulation describes the convex hull of a variable product, the so-called McCormick relaxation. In contrast, we show by a volume argument that the CRs corresponding to univariate approximations are strictly looser. This allows us to explain many of the computational effects observed in the literature and to give theoretical evidence on when to use which kind of approximation.Bayerisches Staatsministerium für Wirtschaft, Infrastruktur, Verkehr und Technologie http://dx.doi.org/10.13039/501100005017Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659Bayerische Staatsregierun

HIV/AIDS Research Conducted in the Developing World and Sponsored by the Developed World: Reporting of Research Ethics Committee Review in Two Countries

We explored how often journal articles reporting HIV research sponsored by a developed country, but conducted in a developing country, mention research ethics committee (REC) approval from both countries, and what factors are involved. Of all such 2007 articles on Medline conducted in one of four developing countries (N = 154), only 52% mentioned such dual approval. Mention of dual vs. single approval was more likely among articles with ≥ 50% sponsor country authors, and the United States as the sponsor country. Also, dual approval was more likely among articles that mentioned informed consent and funding, had ≥ 50% sponsor country authors, were biomedical (vs. psychosocial), and appeared in journals adopting International Committee Medical Journal Editors (ICMJE) guidelines. Dual approval was thus obtained in only half of the articles and was associated with ethical and logistic issues, indicating the need for clearer and more universally accepted guidelines

Applications of density matrix in the fractional quantum mechanics

The many-body space fractional quantum system is studied using the density matrix method. We give the new results of the Thomas-Fermi model, and obtain the quantum pressure of the free electron gas. We also show the validity of the Hohenberg-Kohn theory in the space fractional quantum mechanics and generalize the density functional theory to the fractional quantum mechanics.Comment: 1 figur

Time-bin entanglement at telecom wavelengths from a hybrid photonic integrated circuit

Mass-deployable implementations for quantum communication require compact, reliable, and low-cost hardware solutions for photon generation, control and analysis. We present a fiber-pigtailed hybrid photonic circuit comprising nonlinear waveguides for photon-pair generation and a polymer interposer reaching 68dB of pump suppression and photon separation with >25dB polarization extinction ratio. The optical stability of the hybrid assembly enhances the quality of the entanglement, and the efficient background suppression and photon routing further reduce accidental coincidences. We thus achieve a 96(-8,+3)% concurrence and a 96(-5,+2)% fidelity to a Bell state. The generated telecom-wavelength, time-bin entangled photon pairs are ideally suited for distributing Bell pairs over fiber networks with low dispersion

Role of spinon and spinon singlet pair excitations on phase transitions in d−waved-wave superconductors

We examine the roles of massless Dirac spinon and spin singlet pair excitations on the phase transition in $d-wave$ superconductors. Although the massless spinon excitations in the presence of the spin singlet pair excitations do not alter the nature of the phase transition at $T = 0$, that is, the XY universality class, they are seen to induce an additional attractive interaction potential between vortices, further stabilizing vortex-antivortex pairs at low temperature for lightly doped high $T_c$ samples.Comment: 5 pages, 1 figur

The Information Content of Mandatory Disclosures

The information quality of mandatory financial reporting depends on two factors: (1) Are standards appropriate to produce financial statements that provide investors with sufficient information? (2) Is compliance to standards enforced by appropriate institutions? This paper addresses the question if firms should be able to create hidden reserves as an example for the effect of standards on information quality. The analysis shows that rational investors are able to correctly decipher financial statements independent of the standards in use. The question of sufficient enforcement proves to have a deeper impact on the quality of information