323,499 research outputs found

    A Cosmopolitan response to the 'war on terror'

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    This article explores the relevance and the significance of cosmopolitanism as an approach to understanding the ‘war on terror’. The article details how cosmopolitanism affords a perspective through which it is possible to critique and deconstruct the ‘war on terror’ and create narratives which include the impact of harmful state practices. The facets of cosmopolitanism which make it relevant to the ‘war on terror’ include its emphasis on justice and human rights. It also accounts for interactions between the global level and the local level, which are necessary to understanding the contemporary discourses of securitization and deviancy which are prominent in the ‘war on terror’. Through discussing the value of cosmopolitanism, and its concepts of human rights, equality, humanity, ethics, responsibility and justice, the article demonstrates how although the ‘war on terror’ has been constructed to defend and uphold such values, it has eroded these very values and in doing so, it facilitates the radicalization process

    Eigenvalue problems for the complex PT-symmetric potential V(x)= igx

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    The spectrum of complex PT-symmetric potential, V(x)=igxV(x)=igx, is known to be null. We enclose this potential in a hard-box: V(∣x∣≥1)=∞V(|x| \ge 1) =\infty and in a soft-box: V(∣x∣≥1)=0V(|x|\ge 1)=0. In the former case, we find real discrete spectrum and the exceptional points of the potential. The asymptotic eigenvalues behave as En∼n2.E_n \sim n^2. The solvable purely imaginary PT-symmetric potentials vanishing asymptotically known so far do not have real discrete spectrum. Our solvable soft-box potential possesses two real negative discrete eigenvalues if ∣g∣<(1.22330447)|g|<(1.22330447). The soft-box potential turns out to be a scattering potential not possessing reflectionless states.Comment: no figures, 9 page

    Optimal Selection of Spectrum Sensing Duration for an Energy Harvesting Cognitive Radio

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    In this paper, we consider a time-slotted cognitive radio (CR) setting with buffered and energy harvesting primary and CR users. At the beginning of each time slot, the CR user probabilistically chooses the spectrum sensing duration from a predefined set. If the primary user (PU) is sensed to be inactive, the CR user accesses the channel immediately. The CR user optimizes the sensing duration probabilities in order to maximize its mean data service rate with constraints on the stability of the primary and cognitive queues. The optimization problem is split into two subproblems. The first is a linear-fractional program, and the other is a linear program. Both subproblems can be solved efficiently.Comment: Accepted in GLOBECOM 201

    All-Digital Self-interference Cancellation Technique for Full-duplex Systems

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    Full-duplex systems are expected to double the spectral efficiency compared to conventional half-duplex systems if the self-interference signal can be significantly mitigated. Digital cancellation is one of the lowest complexity self-interference cancellation techniques in full-duplex systems. However, its mitigation capability is very limited, mainly due to transmitter and receiver circuit's impairments. In this paper, we propose a novel digital self-interference cancellation technique for full-duplex systems. The proposed technique is shown to significantly mitigate the self-interference signal as well as the associated transmitter and receiver impairments. In the proposed technique, an auxiliary receiver chain is used to obtain a digital-domain copy of the transmitted Radio Frequency (RF) self-interference signal. The self-interference copy is then used in the digital-domain to cancel out both the self-interference signal and the associated impairments. Furthermore, to alleviate the receiver phase noise effect, a common oscillator is shared between the auxiliary and ordinary receiver chains. A thorough analytical and numerical analysis for the effect of the transmitter and receiver impairments on the cancellation capability of the proposed technique is presented. Finally, the overall performance is numerically investigated showing that using the proposed technique, the self-interference signal could be mitigated to ~3dB higher than the receiver noise floor, which results in up to 76% rate improvement compared to conventional half-duplex systems at 20dBm transmit power values.Comment: Submitted to IEEE Transactions on Wireless Communication

    On Phase Noise Suppression in Full-Duplex Systems

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    Oscillator phase noise has been shown to be one of the main performance limiting factors in full-duplex systems. In this paper, we consider the problem of self-interference cancellation with phase noise suppression in full-duplex systems. The feasibility of performing phase noise suppression in full-duplex systems in terms of both complexity and achieved gain is analytically and experimentally investigated. First, the effect of phase noise on full-duplex systems and the possibility of performing phase noise suppression are studied. Two different phase noise suppression techniques with a detailed complexity analysis are then proposed. For each suppression technique, both free-running and phase locked loop based oscillators are considered. Due to the fact that full-duplex system performance highly depends on hardware impairments, experimental analysis is essential for reliable results. In this paper, the performance of the proposed techniques is experimentally investigated in a typical indoor environment. The experimental results are shown to confirm the results obtained from numerical simulations on two different experimental research platforms. At the end, the tradeoff between the required complexity and the gain achieved using phase noise suppression is discussed.Comment: Published in IEEE transactions on wireless communications on October-2014. Please refer to the IEEE version for the most updated documen

    Access to Education in Bangladesh: Country Analytic Review of Primary and Secondary Education

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    This country analytical review examines the key issues in access to and participation in primary and secondary education in Bangladesh, with a special focus on areas and dimensions of exclusion. Against a background of overall progress, particularly in closing the gender gap in primary and secondary enrollment, the research applies a conceptual framework outlining different forms of exclusion and presents two significant findings which compromise access and diminish gains made: high dropout rates at primary and secondary levels and nominal access but virtual exclusion from quality learning. Other areas surveyed in the review include interventions by public sector and non-governmental providers in primary and secondary education as well as the financing of basic education. This review of the literature concludes with suggestions for future research directions that might lead to new understanding and insights on equitable access and participation

    Optimal Random Access and Random Spectrum Sensing for an Energy Harvesting Cognitive Radio

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    We consider a secondary user with energy harvesting capability. We design access schemes for the secondary user which incorporate random spectrum sensing and random access, and which make use of the primary automatic repeat request (ARQ) feedback. The sensing and access probabilities are obtained such that the secondary throughput is maximized under the constraints that both the primary and secondary queues are stable and that the primary queueing delay is kept lower than a specified value needed to guarantee a certain quality of service (QoS) for the primary user. We consider spectrum sensing errors and assume multipacket reception (MPR) capabilities. Numerical results are presented to show the enhanced performance of our proposed system over a random access system, and to demonstrate the benefit of leveraging the primary feedback.Comment: in WiMob 201

    Handedness of complex PT-symmetric potential barriers

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    Generally, when imaginary part of an optical potential is non-symmetric the reflectivity, R(E)R(E), shows left/right handedness, further if it is not negative-definite the reflection and transmission, T(E)T(E), coefficients become anomalous in some energy intervals and absorption is indefinite (±\pm). We find that the complex PT-symmetric potentials could be exceptional in this regard. They may act effectively like an absorptive potential for any incident energy provided the particle enters from the preferred (absorptive) side.Comment: 9 pages and 4 figure
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