14,800 research outputs found

    Quantum oscillations in insulators with neutral Fermi surfaces

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    We develop a theory of quantum oscillations in insulators with an emergent fermi sea of neutral fermions minimally coupled to an emergent U(1)U(1) gauge field. As pointed out by Motrunich (Phys. Rev. B 73, 155115 (2006)), in the presence of a physical magnetic field the emergent magnetic field develops a non-zero value leading to Landau quantization for the neutral fermions. We focus on the magnetic field and temperature dependence of the analogue of the de Haas-van Alphen effect in two- and three-dimensions. At temperatures above the effective cyclotron energy, the magnetization oscillations behave similarly to those of an ordinary metal, albeit in a field of a strength that differs from the physical magnetic field. At low temperatures the oscillations evolve into a series of phase transitions. We provide analytical expressions for the amplitude and period of the oscillations in both of these regimes and simple extrapolations that capture well their crossover. We also describe oscillations in the electrical resistivity of these systems that are expected to be superimposed with the activated temperature behavior characteristic of their insulating nature and discuss suitable experimental conditions for the observation of these effects in mixed-valence insulators and triangular lattice organic materials.Comment: 20 pages, 9 figures, 1 tabl

    Mixed-valence insulators with neutral Fermi surfaces

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    Samarium hexaboride is a classic three-dimensional mixed valence system with a high-temperature metallic phase that evolves into a paramagnetic charge insulator below 40 kelvin. A number of recent experiments have suggested the possibility that the low-temperature insulating bulk hosts electrically neutral gapless fermionic excitations. Here we show that a possible ground state of strongly correlated mixed valence insulators - composite exciton Fermi liquid - hosts a three dimensional Fermi surface of a neutral fermion, that we name the "composite exciton". We describe the mechanism responsible for the formation of such excitons, discuss the phenomenology of the composite exciton Fermi liquids and make comparison to experiments in SmB6_6.Comment: Final published versio

    Overlapped-MIMO Radar Waveform Design for Coexistence With Communication Systems

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    This paper explores an overlapped-multiple-input multiple-output (MIMO) antenna architecture and a spectrum sharing algorithm via null space projection (NSP) for radar-communications coexistence. In the overlapped-MIMO architecture, the transmit array of a collocated MIMO radar is partitioned into a number of subarrays that are allowed to overlap. Each of the antenna elements in these subarrays have signals orthogonal to each other and to the elements of the other subarrays. The proposed architecture not only improves sidelobe suppression to reduce interference to communications system, but also enjoys the advantages of MIMO radar without sacrificing the main desirable characteristics. The radar-centric spectrum sharing algorithm then projects the radar signal onto the null space of the communications system's interference channel, which helps to avoid interference from the radar. Numerical results are presented which show the performance of the proposed waveform design algorithm in terms of overall beampattern and sidelobe levels of the radar waveform and finally shows a comparison of the proposed system with existing collocated MIMO radar architectures.Comment: accepted at IEEE WCN

    Ministry of Defence impunity: the Overseas Operations (Service Personnel and Veterans) Act 2021

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    This article critically interrogates the policy objectives of the Overseas Operations (Service Personnel and Veterans) Act 2021 and its means to achieve them. While the Ministry of Defence claimed the legislation aimed to protect service personnel and veterans from the “problem of ‘lawfare’” following “repeated investigations … in connection with historical operations”, the Act, despite amendments, continues to strengthen impunity of the British Government for human rights violations, and international and domestic crimes committed in overseas military operations. It does so through three flawed modus operandi: introducing an unwarranted presumption against prosecutions, the superfluous curtailing of judicial discretion over time limitations to bring tort and human rights claims, and the securing of finality of claims despite less-than-adequate investigations. As such, the Act remains deeply problematic as it intentionally curtails the bringing of the types of claims that led to the International Criminal Court’s probe into British war crimes in Iraq. It is argued that the consequences of the Act’s policy aims are symptomatic of the British state’s refusal to confront the crimes, liability, and human rights violations of proximate military conflicts such as Iraq and Afghanistan and limit claims arising from abuse committed during future overseas operations. More generally, the Act is part of a wider attempt by this government to put the executive beyond legal or parliamentary reproach

    Grand Challenges of Traceability: The Next Ten Years

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    In 2007, the software and systems traceability community met at the first Natural Bridge symposium on the Grand Challenges of Traceability to establish and address research goals for achieving effective, trustworthy, and ubiquitous traceability. Ten years later, in 2017, the community came together to evaluate a decade of progress towards achieving these goals. These proceedings document some of that progress. They include a series of short position papers, representing current work in the community organized across four process axes of traceability practice. The sessions covered topics from Trace Strategizing, Trace Link Creation and Evolution, Trace Link Usage, real-world applications of Traceability, and Traceability Datasets and benchmarks. Two breakout groups focused on the importance of creating and sharing traceability datasets within the research community, and discussed challenges related to the adoption of tracing techniques in industrial practice. Members of the research community are engaged in many active, ongoing, and impactful research projects. Our hope is that ten years from now we will be able to look back at a productive decade of research and claim that we have achieved the overarching Grand Challenge of Traceability, which seeks for traceability to be always present, built into the engineering process, and for it to have "effectively disappeared without a trace". We hope that others will see the potential that traceability has for empowering software and systems engineers to develop higher-quality products at increasing levels of complexity and scale, and that they will join the active community of Software and Systems traceability researchers as we move forward into the next decade of research

    Optimizing Traffic Lights in a Cellular Automaton Model for City Traffic

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    We study the impact of global traffic light control strategies in a recently proposed cellular automaton model for vehicular traffic in city networks. The model combines basic ideas of the Biham-Middleton-Levine model for city traffic and the Nagel-Schreckenberg model for highway traffic. The city network has a simple square lattice geometry. All streets and intersections are treated equally, i.e., there are no dominant streets. Starting from a simple synchronized strategy we show that the capacity of the network strongly depends on the cycle times of the traffic lights. Moreover we point out that the optimal time periods are determined by the geometric characteristics of the network, i.e., the distance between the intersections. In the case of synchronized traffic lights the derivation of the optimal cycle times in the network can be reduced to a simpler problem, the flow optimization of a single street with one traffic light operating as a bottleneck. In order to obtain an enhanced throughput in the model improved global strategies are tested, e.g., green wave and random switching strategies, which lead to surprising results.Comment: 13 pages, 10 figure

    Subtleties in the quasi-classical calculation of Hawking radiation

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    he quasi-classical method of deriving Hawking radiation is investigated. In order to recover the original Hawking temperature one must take into account a previously ignored contribution coming from the temporal part of the action. This contribution plus a contribution coming from the spatial part of the action gives the correct temperature.Comment: 6 pages revtex. Honorable Mention in 2008 GRF essay contest, typos fixed, sign errors corrected. To be published in Special Issue of IJMP

    Pregnancy with chronic myeloid leukemia: case report and literature review

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    Chronic myeloid leukemia (CML) is a rare condition during reproductive age. Still, women may present with pre-existing or newly diagnosed CML during pregnancy. The management of chronic myeloid leukemia during pregnancy requires balancing the well-being of the mother with that of fetus. Tyrosine Kinase inhibitors are considered the most effective drug against CML but they are still not considered safe during pregnancy and breast feeding. So, there is a need for management of CML with alternate drugs during pregnancy. Here we report a case of a 26-year-old lady who was diagnosed with chronic myelogenous leukemia (CML) at 20 weeks of gestation and had an atypical chromosome translocation t (9:22). She was managed jointly by obstetrician and haemato-oncologist for the remainder of her pregnancy and eventually she delivered a healthy baby at term
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