6,998 research outputs found
Four-element ultrawideband textile cross array for dual-spatial and dual-polarization diversity
The emergence of miniaturized flexible electronics enables on-duty first responders to collect biometrical and environmental data through multiple on-body sensors, integrated into their clothing. However, gathering these life-saving data would be useless if they cannot set up reliable, preferable high-data-rate, wireless communication links between the sensors and a remote base station. Therefore, we have developed a four-element ultrawideband textile cross array that combines dual-spatial and dual-polarization diversity and is easily deployable in a first responder's garment. The impedance bandwidth of the array equals 1.43 GHz, while mutual coupling between its elements remains below -25 dB. For a maximal bit error rate of 1e-4, the array realizes a diversity gain of 24.81 dB. When applying adaptive subcarrier modulation, the mean throughput per orthogonal frequency division multiplexing (OFDM) subcarrier increases by an extra bit/symbol when comparing fourth- to second-order diversity
Searching for Gamma-Ray counterparts to Gravitational Waves from merging binary neutron stars with the Cherenkov Telescope Array
The merger of binary neutron star (BNS) systems are predicted to be
progenitors of short gamma-ray bursts (GRBs); the definitive probe of this
association came with the recent detection of gravitational waves (GWs) from a
BNS merger by Advanced LIGO and Advanced Virgo (GW170817), in coincidence with
the short GRB 170817A observed by Fermi-GBM and INTEGRAL. Short GRBs are also
expected to emit very-high energy (VHE, > 100 GeV) photons and VHE
electromagnetic (EM) upper limits have been set with observations performed by
ground-based gamma-ray detectors and during the intense EM follow-up campaign
associated with GW170817/GRB 170817A. In the next years, the searches for VHE
EM counterparts will become more effective thanks to the Cherenkov Telescope
Array (CTA): this instrument will be fundamental for the EM follow-up of
transient GW events at VHE, owing to its unprecedented sensitivity, rapid
response (few tens of seconds) and capability to monitor large sky areas via
survey-mode operation. We present a comprehensive study on the prospects for
joint GW and VHE EM observations of merging BNSs with Advanced LIGO, Advanced
Virgo and CTA, based on detailed simulations of the multi-messenger emission
and detection. We propose a new observational strategy optimized on the prior
assumptions about the EM emission. The method can be further generalized to
include other electromagnetic emission models. According to this study CTA will
cover most of the region of the GW skymap for the intermediate and most
energetic on-axis GRBs associated to the GW event. We estimate the expected
joint GW and VHE EM detection rates and we found this rate goes from 0.08 up to
0.5 events per year for the most energetic EM sources.Comment: 26 pages, 8 figures. Submitted to JCA
Let the Tree Bloom: Scalable Opportunistic Routing with ORPL
Routing in battery-operated wireless networks is challenging, posing a tradeoff between energy and latency. Previous work has shown that opportunistic routing can achieve low-latency data collection in duty-cycled networks. However, applications are now considered where nodes are not only periodic data sources, but rather addressable end points generating traffic with arbitrary patterns.
We present ORPL, an opportunistic routing protocol that supports any-to-any, on-demand traffic. ORPL builds upon RPL, the standard protocol for low-power IPv6 networks. By combining RPL's tree-like topology with opportunistic routing, ORPL forwards data to any destination based on the mere knowledge of the nodes' sub-tree. We use bitmaps and Bloom filters to represent and propagate this information in a space-efficient way, making ORPL scale to large networks of addressable nodes. Our results in a 135-node testbed show that ORPL outperforms a number of state-of-the-art solutions including RPL and CTP, conciliating a sub-second latency and a sub-percent duty cycle. ORPL also increases robustness and scalability, addressing the whole network reliably through a 64-byte Bloom filter, where RPL needs kilobytes of routing tables for the same task
Scientific Objectives of Einstein Telescope
The advanced interferometer network will herald a new era in observational
astronomy. There is a very strong science case to go beyond the advanced
detector network and build detectors that operate in a frequency range from 1
Hz-10 kHz, with sensitivity a factor ten better in amplitude. Such detectors
will be able to probe a range of topics in nuclear physics, astronomy,
cosmology and fundamental physics, providing insights into many unsolved
problems in these areas.Comment: 18 pages, 4 figures, Plenary talk given at Amaldi Meeting, July 201
The Formation of the First Massive Black Holes
Supermassive black holes (SMBHs) are common in local galactic nuclei, and
SMBHs as massive as several billion solar masses already exist at redshift z=6.
These earliest SMBHs may grow by the combination of radiation-pressure-limited
accretion and mergers of stellar-mass seed BHs, left behind by the first
generation of metal-free stars, or may be formed by more rapid direct collapse
of gas in rare special environments where dense gas can accumulate without
first fragmenting into stars. This chapter offers a review of these two
competing scenarios, as well as some more exotic alternative ideas. It also
briefly discusses how the different models may be distinguished in the future
by observations with JWST, (e)LISA and other instruments.Comment: 47 pages with 306 references; this review is a chapter in "The First
Galaxies - Theoretical Predictions and Observational Clues", Springer
Astrophysics and Space Science Library, Eds. T. Wiklind, V. Bromm & B.
Mobasher, in pres
SPARTAN: a global network to evaluate and enhance satellite-based estimates of ground-level particulate matter for global health applications
Ground-based observations have insufficient spatial coverage to assess long-term human exposure to fine particulate matter (PM2.5) at the global scale. Satellite remote sensing offers a promising approach to provide information on both short-and long-term exposure to PM2.5 at local-to-global scales, but there are limitations and outstanding questions about the accuracy and precision with which ground-level aerosol mass concentrations can be inferred from satellite remote sensing alone. A key source of uncertainty is the global distribution of the relationship between annual average PM2.5 and discontinuous satellite observations of columnar aerosol optical depth (AOD). We have initiated a global network of ground-level monitoring stations designed to evaluate and enhance satellite remote sensing estimates for application in health-effects research and risk assessment. This Surface PARTiculate mAtter Network (SPARTAN) includes a global federation of ground-level monitors of hourly PM2.5 situated primarily in highly populated regions and collocated with existing ground-based sun photometers that measure AOD. The instruments, a three-wavelength nephelometer and impaction filter sampler for both PM2.5 and PM10, are highly autonomous. Hourly PM2.5 concentrations are inferred from the combination of weighed filters and nephelometer data. Data from existing networks were used to develop and evaluate network sampling characteristics. SPARTAN filters are analyzed for mass, black carbon, water-soluble ions, and metals. These measurements provide, in a variety of regions around the world, the key data required to evaluate and enhance satellite-based PM2.5 estimates used for assessing the health effects of aerosols. Mean PM2.5 concentrations across sites vary by more than 1 order of magnitude. Our initial measurements indicate that the ratio of AOD to ground-level PM2.5 is driven temporally and spatially by the vertical profile in aerosol scattering. Spatially this ratio is also strongly influenced by the mass scattering efficiency.Fil: Snider, G.. Dalhousie University Halifax; CanadáFil: Weagle, C. L.. Dalhousie University Halifax; CanadáFil: Martin, R. V.. Dalhousie University Halifax; Canadá. University of Cambridge; Reino UnidoFil: van Donkelaar, A.. Dalhousie University Halifax; CanadáFil: Conrad, K.. Dalhousie University Halifax; CanadáFil: Cunningham, D.. Dalhousie University Halifax; CanadáFil: Gordon, C.. Dalhousie University Halifax; CanadáFil: Zwicker, M.. Dalhousie University Halifax; CanadáFil: Akoshile, C.. University of Ilorin; NigeriaFil: Artaxo, P.. Governo Do Estado de Sao Paulo; BrasilFil: Anh, N. X.. Vietnam Academy of Science and Technology. Institute of Geophysics; VietnamFil: Brook, J.. University of Toronto; CanadáFil: Dong, J.. Tsinghua University; ChinaFil: Garland, R. M.. North-West University; SudáfricaFil: Greenwald, R.. Rollins School of Public Health; Estados UnidosFil: Griffith, D.. Council for Scientific and Industrial Research; SudáfricaFil: He, K.. Tsinghua University; ChinaFil: Holben, B. N.. NASA Goddard Space Flight Center; Estados UnidosFil: Kahn, R.. NASA Goddard Space Flight Center; Estados UnidosFil: Koren, I.. Weizmann Institute Of Science Israel; IsraelFil: Lagrosas, N.. Manila Observatory, Ateneo de Manila University campus; FilipinasFil: Lestari, P.. Institut Teknologi Bandung; IndonesiaFil: Ma, Z.. Rollins School of Public Health; Estados UnidosFil: Vanderlei Martins, J.. University of Maryland; Estados UnidosFil: Quel, Eduardo Jaime. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; ArgentinaFil: Rudich, Y.. Weizmann Institute Of Science Israel; IsraelFil: Salam, A.. University Of Dhaka; BangladeshFil: Tripathi, S. N.. Indian Institute Of Technology, Kanpur; IndiaFil: Yu, C.. Rollins School of Public Health; Estados UnidosFil: Zhang, Q.. Tsinghua University; ChinaFil: Zhang, Y.. Tsinghua University; ChinaFil: Brauer, M.. University of British Columbia; CanadáFil: Cohen, A.. Health Effects Institute; Estados UnidosFil: Gibson, M. D.. Dalhousie University Halifax; CanadáFil: Liu, Y.. Rollins School of Public Health; Estados Unido
The BLIXER, a Wideband Balun-LNA-I/Q-Mixer Topology
This paper proposes to merge an I/Q current-commutating mixer with a noise-canceling balun-LNA. To realize a high bandwidth, the real part of the impedance of all RF nodes is kept low, and the voltage gain is not created at RF but in baseband where capacitive loading is no problem. Thus a high RF bandwidth is achieved without using inductors for bandwidth extension. By using an I/Q mixer with 25% duty-cycle LO waveform the output IF currents have also 25% duty-cycle, causing 2 times smaller DC-voltage drop after IF filtering. This allows for a 2 times increase in the impedance level of the IF filter, rendering more voltage gain for the same supply headroom. The implemented balun-LNA-I/Q-mixer topology achieves > 18 dB conversion gain, a flat noise figure < 5.5 dB from 500 MHz to 7 GHz, IIP2 = +20 dBm and IIP3 = -3 dBm. The core circuit consumes only 16 mW from a 1.2 V supply voltage and occupies less than 0.01 mm2 in 65 nm CMOS
Broadband infrastructure: The regulatory framework, market transparency and risk-sharing partnerships are the key factors
Around the globe countries are attempting to forge ahead with the expansion and upgrading of advanced communications networks. In most cases they are setting very ambitious goals with regard to technology and coverage. However, the specific cost structure for broadband projects results in the private-sector-driven, competitive market for network upgrading being primarily focused on densely populated urban areas. By contrast, major progress in rolling out broadband to unserved rural areas will not be made in the foreseeable future without state subsidies. Without having to steer a course towards the return of a monopoly in the telecommunications sector, which would have a detrimental long-term impact, the public sector can in this situation promote sustainable progress in telecommunication by merging projects, entering into risk-sharing partnerships, setting realistic broadband targets, providing essential market information to market participants, offering e-government digital services itself and, on top of that, further enhancing investment incentives with a regulatory framework in a competitive environment.broadband; telecommunications; Infrastructure; investment; financing
Diseños de capa cruzada para redes inalámbricas de área corporal energéticamente eficientes: una revisión
RESUMEN: El diseño de capa cruzada se considera una poderosa alternativa para dar soluciĂłn a las complejidades introducidas por las comunicaciones inalámbricas en redes de área corporal (WBAN), donde el modelo clásico de comunicaciones no ha exhibido un desempeño adecuado. Respecto al problema puntual de consumo de energĂa, hemos preparado la presente revisiĂłn de las publicaciones más relevantes que tratan la eficiencia energĂ©tica para WBAN usando diseño de capa cruzada. En este artĂculo se proporciona una revisiĂłn exhaustiva de los avances en aproximaciones, protocolos y optimizaciones de capa cruzada cuyo objetivo es incrementar el tiempo de vida de las redes WBAN mediante el ahorro de energĂa. Luego, se discute los aspectos relevantes y deficiencias de las tĂ©cnicas de capa cruzada energĂ©ticamente eficientes. Además, se introducen aspectos de investigaciĂłn abiertos y retos en el diseño de capa cruzada para WBAN. En esta revisiĂłn proponemos una taxonomĂa de las aproximaciones de capa cruzada, de modo que las tĂ©cnicas revisadas se ajustan en categorĂas de acuerdo a los protocolos involucrados en el diseño. Una clasificaciĂłn novedosa se incluye para hacer claridad en los conceptos teĂłricos involucrados en cada esquema de capa cruzada y para luego agrupar aproximaciones similares evidenciando las diferencias con otras tĂ©cnicas entre sĂ. Nuestras conclusiones consideran los aspectos de movilidad y modelamiento del canal en escenarios de WBAN como las direcciones para futura investigaciĂłn en WBAN y en aplicaciones de telemedicina.ABSTRACT: Cross-layer design is considered a powerful alternative to solve the complexities of wireless communication in wireless body area networks (WBAN), where the classical communication model has been shown to be inaccurate. Regarding the energy consumption problem, we have prepared a current survey of the most relevant scientific publications on energy-efficient cross-layer design for WBAN. In this paper, we provide a comprehensive review of the advances in cross-layer approaches, protocols and optimizations aimed at increasing the network lifetime by saving energy in WBANs. Subsequently, we discuss the relevant aspects and shortcomings of these energy-efficient cross-layer techniques and point out the open research issues and challenges in WBAN cross-layer design. In this survey, we propose a taxonomy for cross-layer approaches to fit them into categories based on the protocols involved in the cross-layer scheme. A novel classification is included to clarify the theoretical concepts behind each cross-layer scheme; and to group similar approaches by establishing their differences from the other strategies reviewed. Our conclusion considers the aspects of mobility and channel modeling in WBAN scenarios as the directions of future cross-layer research for WBAN and telemedicine applications
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