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1

Radio channel measurement and modelling for future mobile radio systems  

NASA Astrophysics Data System (ADS)

Digital mobile radio systems will require planning methods that provide accurate predictions of signal strength, distortion, and interference for situations ranging from very small cells in dense urban locations to large rural cells. Topographic and land usage data bases will find increasing use to enhance the accuracy of prediction models. The implications of these issues are discussed and the work in progress at British Telecommunications Research Laboratories on land mobile radio propagation modeling and wide-band channel measurements is presented.

Guerdenli, E.; Huish, P. W.

1989-12-01

2

Modeling of Wide-Band MIMO Radio Channels Based on NLoS Indoor Measurements  

Microsoft Academic Search

In this paper, we first verify a previously proposed Kronecker-structure-based narrow-band model for nonline-of- sight (NLoS) indoor multiple-input-multiple-output (MIMO) radio channels based on 5.2-GHz indoor MIMO channel mea- surements. It is observed that, for the narrow-band case, the measured channel coefficients are complex Gaussian distributed and, consequently, we focus on a statistical description using the first- and second-order moments of

Kai Yu; Mats Bengtsson; Björn Ottersten; Darren McNamara; Peter Karlsson; Mark Beach

2004-01-01

3

Ultra wideband indoor radio channel models: preliminary results  

Microsoft Academic Search

Knowledge of the signal propagation mechanisms in the channel is vital for the radio system design and the system performance analysis. However, currently published wideband or narrowband radio channel models do not offer spatial resolution high enough for the ultra wideband (UWB) applications and real channel measurements are needed. The preliminary UWB radio channel model for a selected radio link-configuration

V. Hovinen; Matti Hamalainen; Tinzo Patsi

2002-01-01

4

A physical mobile radio channel model  

Microsoft Academic Search

A semiempirical model for macrocellular mobile radio channels typically encountered in different outdoor environments is presented. The influence of terrain structure on the time- and frequency-selective channel behavior is analyzed. General functional forms are derived in a parametrized form characterizing the channel impulse response. The relevant parameters are extracted from measured data collected with a narrowband system (resolution 5 ?s,

U. Dersch; W. R. Braun

1991-01-01

5

Car-to-car radio channel measurements at 5 GHz: Pathloss, power-delay profile, and delay-Doppler  

E-print Network

Car-to-car radio channel measurements at 5 GHz: Pathloss, power-delay profile, and delay Contact: apaier@nt.tuwien.ac.at Abstract-- We carried out a car­to­infrastructure (C2I) and car­to­car (C2­Doppler spectra in a C2C highway scenario, where both cars were traveling in opposite directions. A pathloss

Zemen, Thomas

6

Peer-to-peer MIMO radio channel measurements in a rural area  

NASA Astrophysics Data System (ADS)

To demonstrate a real-time, mobile, peer-to-peer, ad-hoc networked MIMO system in a realistic tactical environment, the Defense Advanced Research Projects Agency (DARPA) has instituted a program, called Mobile Network MIMO (MNM). To assess the communication channel quality for ground level MIMO nodes, a comprehensive channel measurement and modeling effort was carried out to determine quantities such as spatial correlations, delay spread as well as propagation loss. It was found that median 8x10 MIMO capacity supported by the channel was about 8 times the corresponding 1x1 capacity, and 3.2 times the corresponding 1x10 capacity. Also conducted were wideband soundings of such channels, where it was found that the median rms delay spreads were 0.6 ?s. Reported are measurements and an empirical model of pathloss, spatial correlation scales, and crosspolarization properties of rural peer-to-peer channels.

Ling, Jonathan; Chizhik, Dmitry; Samardzija, Dragan; Valenzuela, Reinaldo A.

2006-05-01

7

Ultra Wideband Indoor Radio Channel Models: Preliminary Results  

Microsoft Academic Search

ULTRA WIDEBAND RADIO CHAN-NEL MEASUREMENT TECHNIQUES Knowledge of the signal propagation mechanisms in the chan-nel is vital for the radio system design and the system perform-ance analysis. However, currently published wideband or nar-rowband radio channel models do not offer spatial resolution high enough for the ultra wideband (UWB) applications and the real channel measurements are needed. In this paper is

Veikko Hovinen

2002-01-01

8

The indoor radio propagation channel  

Microsoft Academic Search

In this tutorial survey the principles of radio propagation in indoor environments are reviewed. The channel is modeled as a linear time-varying filter at each location in the three-dimensional space, and the properties of the filter's impulse response are described. Theoretical distributions of the sequences of arrival times, amplitudes and phases are presented. Other relevant concepts such as spatial and

HOMAYOUN HASHEMI

1993-01-01

9

Ultra Wideband Indoor Radio Channel Models: Preliminary Results  

Microsoft Academic Search

Knowledge of the signal propagation mechanisms in the chan- nel is vital for the radio system design and the system perform- ance analysis. However, currently published wideband or nar- rowband radio channel models do not offer spatial resolution high enough for the ultra wideband (UWB) applications and the real channel measurements are needed. In this paper is given the preliminary

Veikko Hovinen; Matti Hämäläinen; Timo Pätsi

10

Interference aware throughput measurements for mobile WiMAX over vehicular radio channels  

Microsoft Academic Search

Due to its advantageous properties in multipath propagation scenarios, the Orthogonal Frequency Division Multiple Access (OFDMA) radio transmission scheme is widely spread in current broadband wireless networks. Exemplary emerging systems based on this technology are the UMTS Long Term Evolution (LTE), Mobile WiMAX and some popular WiFi variants (e.g. IEEE 802.11n). Although analytical and simulative investigations have shown that the

Bjoern Dusza; Christoph Ide; Christian Wietfeld

2012-01-01

11

CHANNELIZATION TECHNIQUES FOR SOFTWARE DEFINED RADIO  

Microsoft Academic Search

ABSTRACT The ability to support,multiple communications,channels per RF band is a fundamental,process for many,software defined radio platforms. These platforms typically employ achannelizer,to extract channels from the received RF band for follow-on baseband processing, or to insert channels into the RF band for transmission. This paper will compare ,and ,contrast three of the ,more ,popular channelization techniques: Digital Down Conversion, Frequency

Lee Pucker

12

Impulse Response Modeling of Indoor Radio Propagation Channels  

Microsoft Academic Search

If indoor radio propagation channels are modeled as linear filters, they can be characterized by reporting the parameters of their equivalent impulse response functions. The measurement and modeling of estimates for such functions in two different office buildings are reported. The resulting data base consists of 12000 impulse response estimates of the channel that were obtained by inverse Fourier transforming

Homayoun Hashemi

1993-01-01

13

Achievable rates in cognitive radio channels  

Microsoft Academic Search

Cognitive radio promises a low cost, highly ?exible alternative to the classic single fre- quency band, single protocol wireless device. By sens- ing and adapting to its environment, such a device is able to flll voids in the wireless spectrum and dramat- ically increase spectral e-ciency. In this paper, the cognitive radio channel is deflned as an n-transmitter, m-receiver interference

Natasha Devroye; Patrick Mitran; Vahid Tarokh

2006-01-01

14

Limits on communications in a cognitive radio channel  

Microsoft Academic Search

In this article we review FCC secondary markets initiatives and how smart wireless devices could be used to increase spectral efficiency. We survey the current proposals for cognitive radio deployment, and present a new, potentially more spectrally efficient model for a wireless channel employing cognitive radios; the cognitive radio channel. This channel models the simplest scenario in which a cognitive

Natasha Devroye; Patrick Mitran; Vahid Tarokh

2006-01-01

15

47 CFR 22.757 - Channels for basic exchange telephone radio systems.  

Code of Federal Regulations, 2014 CFR

... Channels for basic exchange telephone radio systems. 22.757 Section 22.757...Radiotelephone Service Basic Exchange Telephone Radio Systems § 22.757 Channels for basic exchange telephone radio systems. The channels listed...

2014-10-01

16

47 CFR 22.757 - Channels for basic exchange telephone radio systems.  

Code of Federal Regulations, 2012 CFR

... Channels for basic exchange telephone radio systems. 22.757 Section 22.757...Radiotelephone Service Basic Exchange Telephone Radio Systems § 22.757 Channels for basic exchange telephone radio systems. The channels listed...

2012-10-01

17

47 CFR 22.757 - Channels for basic exchange telephone radio systems.  

Code of Federal Regulations, 2011 CFR

... Channels for basic exchange telephone radio systems. 22.757 Section 22.757...Radiotelephone Service Basic Exchange Telephone Radio Systems § 22.757 Channels for basic exchange telephone radio systems. The channels listed...

2011-10-01

18

47 CFR 22.757 - Channels for basic exchange telephone radio systems.  

Code of Federal Regulations, 2013 CFR

... Channels for basic exchange telephone radio systems. 22.757 Section 22.757...Radiotelephone Service Basic Exchange Telephone Radio Systems § 22.757 Channels for basic exchange telephone radio systems. The channels listed...

2013-10-01

19

47 CFR 22.757 - Channels for basic exchange telephone radio systems.  

Code of Federal Regulations, 2010 CFR

... Channels for basic exchange telephone radio systems. 22.757 Section 22.757...Radiotelephone Service Basic Exchange Telephone Radio Systems § 22.757 Channels for basic exchange telephone radio systems. The channels listed...

2010-10-01

20

Capacity of a Class of Cognitive Radio Channels: Interference Channels With Degraded Message Sets  

Microsoft Academic Search

This correspondence is motivated by two different scenarios. The first is a cognitive radio system where a cognitive radio knows a ldquodumbrdquo radio's message and the second is a sensor network in a correlated field where sensors possessing a nested message structure assist one another's information transmission. Both scenarios are modeled using the framework of discrete memoryless interference channels with

Wei Wu; Sriram Vishwanath; Ari Arapostathis

2007-01-01

21

Analysis of Cognitive Radio Spectrum Access with Optimal Channel Reservation  

Microsoft Academic Search

A Markov chain analysis for spectrum access in licensed bands for cognitive radios is presented and forced termination probability, blocking probability and traffic throughput are derived. In addition, a channel reservation scheme for cognitive radio spectrum handoff is proposed. This scheme allows the tradeoff between forced termination and blocking according to QoS requirements. Numerical results show that the proposed scheme

Xiaorong Zhu; Lianfeng Shen; Tak-shing Yum

2007-01-01

22

Fading Channel Prediction for Mobile Radio Adaptive Transmission Systems  

Microsoft Academic Search

Adaptive transmission methods can potentially aid the achievement of high data rates required for mobile radio multimedia services. To realize this potential, the transmitter needs accurate channel state information (CSI) for the upcoming transmission frame. In most mobile radio systems, the CSI is estimated at the receiver and fed back to the transmitter. However, unless the mobile speed is very

Alexandra Duel-Hallen

2007-01-01

23

Adaptive channel allocation spectrum etiquette for cognitive radio networks  

Microsoft Academic Search

In this work, we propose a game theoretic framework to analyze the behavior of cognitive radios for distributed adaptive channel allocation. We define two different objective functions for the spectrum sharing games, which capture the utility of selfish users and cooperative users, respectively. Based on the utility definition for cooperative users, we show that the channel allocation problem can be

Nie Nie; Cristina Comaniciu

2005-01-01

24

Adaptive Channel Allocation Spectrum Etiquette for Cognitive Radio Networks  

Microsoft Academic Search

In this work, we propose a game theoretic frame- work to analyze the behavior of cognitive radios for distributed adaptive channel allocation. We define two different objective functions for the spectrum sharing games, which capture the utility of selfish users and cooperative users, respectively. Based on the utility definition for cooperative users, we show that the channel allocation problem can

Nie Nie; Cristina Comaniciu

2006-01-01

25

A simplified stochastic model for the aeronautical mobile radio channel  

Microsoft Academic Search

The aeronautical mobile radio channel is analyzed. A stochastic model for the channel is proposed in terms of the transmission coefficient. The power spectrum and the correlation functions are derived for cases of practical interest. The model is useful for predicting the error rate performance of digital modulation techniques. The results from a flight test showed the validity of the

Said M. Elnoubi

1992-01-01

26

Reliable Distributed Computing on Unreliable Radio Channels  

E-print Network

of the radio spectrum. These bands are increasingly crowded and vulnerable. Designers of proto- cols questions about what can be solved reliably (and efficiently) in this increasingly relevant yet dif- ficult on the increasingly crowded unli- censed bands of the radio spectrum? They setup an 802.11 access point and connected

Lynch, Nancy

27

The Assimilation of Radio Occultation Measurements  

E-print Network

The Assimilation of Radio Occultation Measurements Sean Healy, Adrian Jupp, Dave Offiler and John radio occultation (RO) measurements are a potentially important new source of profile information for the observation error estimates is discussed. Key words: CHAMP, GPS radio occultation, numerical weather

28

Distributed computation on unreliable radio channels  

E-print Network

An important topic in wireless networking is the development of reliable algorithms for environments suffering from adversarial interference. This term captures any type of channel disruption outside the control of the ...

Newport, Calvin (Calvin Charles)

2009-01-01

29

A stochastic MIMO radio channel model with experimental validation  

Microsoft Academic Search

Theoretical and experimental studies of multiple-input\\/multiple-output (MIMO) radio channels are presented. A simple stochastic MIMO model channel has been developed. This model uses the correlation matrices at the mobile station (MS) and base station (BS) so that results of the numerous single-input\\/multiple-output studies that have been published in the literature can be used as input parameters. The model is simplified

Jean Philippe Kermoal; Laurent Schumacher; Klaus Ingemann Pedersen; Preben Elgaard Mogensen; Frank Frederiksen

2002-01-01

30

Channel Bonding in Cognitive Radio Wireless Sensor Networks  

E-print Network

Channel Bonding in Cognitive Radio Wireless Sensor Networks Mubashir Husain Rehmani, St-mail: rehmani@univ-mlv.fr, lohier@univ-mlv.fr, rachedi@univ-mlv.fr Abstract--Recently, wireless sensor networks, Wireless Multimedia Sensor Networks (WMSNs) have lot of new potential applications in different domains

Paris-Sud XI, Université de

31

SPATIAL STABILITY IN INDOOR RADIO PROPAGATION CHANNELS Dana Porrat, Eli Kaminsky and Moshe Uziel  

E-print Network

SPATIAL STABILITY IN INDOOR RADIO PROPAGATION CHANNELS Dana Porrat, Eli Kaminsky and Moshe Uziel.porrat@huji.ac.il, eli.kaminsky@mail.huji.ac.il, uzikiko@gmail.com ABSTRACT Indoor radio channel responses are composed

Porrat, Dana

32

Combined Channel Aggregation and Fragmentation Strategy in Cognitive Radio Networks  

E-print Network

In cognitive radio networks, channel aggregation (CA) and channel fragmentation (CF) techniques have been proposed to enhance the spectrum utilization. While previous literatures study them almost independently, in this paper, we combine CA and CF innovatively and present a new spectrum sharing strategy named CAF (Channel Aggregation and Fragmentation). The performance under our strategy is analyzed using a continuous time Markov chain model in terms of blocking probability, dropping probability, spectrum utilization and throughput of secondary users. Both analytical and simulation results show that our strategy lowers the blocking and dropping probabilities and enhances the spectrum utilization and throughput significantly.

Li, Lei; Wang, Kaiwei; Zhou, Wuyang

2012-01-01

33

Distributed Strategies for Channel Allocation and Scheduling in Software-Defined Radio Networks  

Microsoft Academic Search

Equipping wireless nodes with multiple radios can significantly increase the capacity of wireless networks, b y making these radios simultaneously transmit over multiple non- overlapping channels. However, due to the limited number of radios and available orthogonal channels, designing effici ent channel assignment and scheduling algorithms in such networks is a major challenge. In this paper, we present provably- good

Bo Han; V. S. Anil Kumar; Madhav V. Marathe; Srinivasan Parthasarathy; Anand Srinivasan

2009-01-01

34

Neutron Star Mass Measurements. I. Radio Pulsars  

Microsoft Academic Search

There are now about 50 known radio pulsars in binary systems, including at least five in double neutron star binaries. In some cases, the stellar masses can be directly determined from measurements of relativistic orbital effects. In others, only an indirect or statistical estimate of the masses is possible. We review the general problem of mass measurement in radio pulsar

S. E. Thorsett; Deepto Chakrabarty

1999-01-01

35

Montblanc: GPU accelerated Radio Interferometer Measurement Equations in support of Bayesian Inference for Radio Observations  

NASA Astrophysics Data System (ADS)

Montblanc, written in Python, is a GPU implementation of the Radio interferometer measurement equation (RIME) in support of the Bayesian inference for radio observations (BIRO) technique. The parameter space that BIRO explores results in tens of thousands of computationally expensive RIME evaluations before reduction to a single X2 value. The RIME is calculated over four dimensions, time, baseline, channel and source and the values in this 4D space can be independently calculated; therefore, the RIME is particularly amenable to a parallel implementation accelerated by Graphics Programming Units (GPUs). Montblanc is implemented for NVIDIA's CUDA architecture and outperforms MeqTrees (ascl:1209.010) and OSKAR.

Perkins, Simon; Marais, Patrick; Zwart, Jonathan; Natarajan, Iniyan; Smirnov, Oleg

2015-02-01

36

Channel Assignment Scheme in Multi-Channel Multi-Radio Wireless Mesh Networks  

NASA Astrophysics Data System (ADS)

An important issue of multi-channel multi-radio wireless mesh network is how to assign multiple available channels to the radios in order to minimize the wireless communication interference and maximize the network throughput. In this work, we study the problem of channel assignment in MRMC-WMN, and the optimization problem is known to be NP-complete. We propose a novel dynamic channel assignment scheme, which is based on network coding (NC) and data flow. Our scheme can be performed in distributed manner and is suitable for both unicast and multicast communication. Compared with the basic dynamic CA scheme, the analysis and comparison demonstrates that our proposed scheme has less communication cost and less interference.

Xia, Yan; Zeng, Yingzhi; Xin, Qin; Gong, Zhenghu

2010-09-01

37

Characterization and Modeling of the Indoor Radio Channel at 868 MHz for a Mobile Bodyworn Wireless Personal Area Network  

Microsoft Academic Search

This letter reports the statistical characterization and modeling of the indoor radio channel for a mobile wireless personal area network operating at 868 MHz. Line of sight (LOS) and non-LOS conditions were considered for three environments: anechoic chamber, open office area, and hallway. Overall, the Nakagami-m cdf beast described fading for bodyworn operation in 60% of all measured channels in

Simon L. Cotton; William G. Scanlon

2007-01-01

38

Outage analysis of the hybrid free-space optical and radio-frequency channel  

Microsoft Academic Search

We study the hybrid free-space optical (FSO) and radio-frequency (RF) channel from an information theoretic perspective. Since both links operate at vastly different carrier frequencies, we model the hybrid channel as a pair of parallel channels. Moreover, since the FSO channel signals at a higher rate than the RF channel, we incorporate this key feature in the parallel channel model.

Nick Letzepis; Khoa D. Nguyen; Albert Guillen i Fabregas; William G. Cowley

2009-01-01

39

47 CFR 22.725 - Channels for conventional rural radiotelephone stations and basic exchange telephone radio systems.  

Code of Federal Regulations, 2011 CFR

...radiotelephone stations and basic exchange telephone radio systems. 22.725 Section 22.725...radiotelephone stations and basic exchange telephone radio systems. The following channels are...transmitters in basic exchange telephone radio systems. These channels may be...

2011-10-01

40

47 CFR 22.725 - Channels for conventional rural radiotelephone stations and basic exchange telephone radio systems.  

Code of Federal Regulations, 2012 CFR

...radiotelephone stations and basic exchange telephone radio systems. 22.725 Section 22.725...radiotelephone stations and basic exchange telephone radio systems. The following channels are...transmitters in basic exchange telephone radio systems. These channels may be...

2012-10-01

41

47 CFR 22.725 - Channels for conventional rural radiotelephone stations and basic exchange telephone radio systems.  

Code of Federal Regulations, 2010 CFR

...radiotelephone stations and basic exchange telephone radio systems. 22.725 Section 22.725...radiotelephone stations and basic exchange telephone radio systems. The following channels are...transmitters in basic exchange telephone radio systems. These channels may be...

2010-10-01

42

47 CFR 22.725 - Channels for conventional rural radiotelephone stations and basic exchange telephone radio systems.  

Code of Federal Regulations, 2013 CFR

...radiotelephone stations and basic exchange telephone radio systems. 22.725 Section 22.725...radiotelephone stations and basic exchange telephone radio systems. The following channels are...transmitters in basic exchange telephone radio systems. These channels may be...

2013-10-01

43

47 CFR 22.725 - Channels for conventional rural radiotelephone stations and basic exchange telephone radio systems.  

Code of Federal Regulations, 2014 CFR

...radiotelephone stations and basic exchange telephone radio systems. 22.725 Section 22.725...radiotelephone stations and basic exchange telephone radio systems. The following channels are...transmitters in basic exchange telephone radio systems. These channels may be...

2014-10-01

44

Channel State Prediction in Cognitive Radio, Part I: Response Delays in Practical Hardware Platforms  

E-print Network

Channel State Prediction in Cognitive Radio, Part I: Response Delays in Practical Hardware is the cornerstone of cognitive radio. As a part of the effort toward building a cognitive radio network testbed, we. This work is a part of the effort toward building a cognitive radio network testbed. I. INTRODUCTION

Qiu, Robert Caiming

45

Adaptive and occupancy-based channel selection for unreliable cognitive radio  

E-print Network

Adaptive and occupancy-based channel selection for unreliable cognitive radio networks M. H's wireless networks, radio spectrum is used inefficiently. To counter this issue, Cognitive Radio Networks (CRNs) are designed to allow cognitive radio (CR) nodes (i) utilizing free parts of unlicensed spectrum

Paris-Sud XI, Université de

46

Joint channel assignment and routing for throughput optimization in multi-radio wireless mesh networks  

Microsoft Academic Search

Multi-hop infrastructure wireless mesh networks offer increased reliability, coverage and reduced equipment costs over their single-hop counterpart, wireless LANs. Equipping wireless routers with multiple radios further improves the capacity by transmitting over multiple radios simultaneously using orthogonal channels. Efficient channel assignment and routing is essential for throughput optimization of mesh clients. Efficient channel assignment schemes can greatly relieve the interference

Mansoor Alicherry; Randeep Bhatia; Erran L. Li

2005-01-01

47

Spectrum agile radio: radio resource measurements for opportunistic spectrum usage  

Microsoft Academic Search

Radio spectrum allocation is undergoing radical rethinking. Regulators, government agencies, industry, and the research community have recently established many initiatives for new spectrum policies and seek approaches to more efficiently manage the radio spectrum. In this paper, we examine new approaches, namely, spectrum agile radios, for opportunistic spectrum usage. Spectrum agile radios use parts of the radio spectrum that were

Stefan Mangold; Zhun Zhong; Kiran Challapali; Chun-Ting Chou

2004-01-01

48

Towards Cognitive Radio Networks: Spectrum Utilization Measurements in Suburb Environment  

E-print Network

Towards Cognitive Radio Networks: Spectrum Utilization Measurements in Suburb Environment Václav or more utilized licensed frequency bands that could be possibly used by cognitive radios in an opportunistic way. Cognitive radio concept for better spectrum utilization is introduced here along

Paris-Sud XI, Université de

49

Photonic Technique for Radio Frequency Measurement  

Microsoft Academic Search

A novel photonic technique for radio frequency (RF) measurement utilising dispersion in a multichannel chirped fibre Bragg grating (MCFBG) is developed. The underlying principle for fast photonic RF measurement is based on amplitude comparison of the RF power fading functions of double sideband (DSB) modulated optical carriers propagating through a dispersive medium. In this paper, a demonstration of the photonic

L. V. T. Nguyen; D. B. Hunter; D. J. Borg

2005-01-01

50

Radio occultation measurements of the lunar ionosphere.  

NASA Astrophysics Data System (ADS)

Radio occultation measurements by using interplanetary probes is a well known technique to obtain information on planetary atmospheres. To further understand the morphology of the lunar ionosphere we performed radio occultation experiments by using the radio sounding technique. This method mainly consists in the analisys of the effects produced on the radio wave transmitted from the spacecraft to the Earth when it crosses the atmosphere. The wave amplitude and phase undergo modifications that are correlated to the physical parameters - i.e. electron density - of the crossed medium. The first data set was obtained during the lunar occultations of the European probe SMART-1 shortly before impacting the lunar soil on September 3rd, 2006. During this experiment several radio occultation measurements of the signal transmitted by the spacecraft were performed in S and X band by using the 32 meters radiotelescopes (at Medicina and Noto) of the Istituto di Radioastronomia - Istituto Nazionale di Astrofisica. Further experiments were performed during lunar occultations of Saturn and Venus. On May 22nd and June 18th 2007 the Cassini spacecraft, orbiting Saturn, and the Venus Express spacecraft, orbiting Venus, respectively were occulted by the Moon. The variation of the Total Electron Content (TEC) measured by our instruments (˜ 1013 el/m2) on this occasion is in agreement with values of the electron number density acquired by in situ measuments of the US Apollo missions and the USSR Luna 19 and 22 probes.

Pluchino, S.; Schillirò, F.; Salerno, E.; Pupillo, G.; Maccaferri, G.; Cassaro, P.

51

Cosmological measurements with forthcoming radio continuum surveys  

NASA Astrophysics Data System (ADS)

We present forecasts for constraints on cosmological models that can be obtained using the forthcoming radio continuum surveys: the wide surveys with the Low Frequency Array (LOFAR) for radio astronomy, the Australian Square Kilometre Array Pathfinder (ASKAP) and the Westerbork Observations of the Deep Apertif Northern Sky (WODAN). We use simulated catalogues that are appropriate to the planned surveys in order to predict measurements obtained with the source autocorrelation, the cross-correlation between radio sources and cosmic microwave background (CMB) maps (the integrated Sachs-Wolfe effect), the cross-correlation of radio sources with foreground objects resulting from cosmic magnification, and a joint analysis together with the CMB power spectrum and supernovae (SNe). We show that near-future radio surveys will bring complementary measurements to other experiments, probing different cosmological volumes and having different systematics. Our results show that the unprecedented sky coverage of these surveys combined should provide the most significant measurement yet of the integrated Sachs-Wolfe effect. In addition, we show that the use of the integrated Sachs-Wolfe effect will significantly tighten the constraints on modified gravity parameters, while the best measurements of dark energy models will come from galaxy autocorrelation function analyses. Using a combination of the Evolutionary Map of the Universe (EMU) and WODAN to provide a full-sky survey, it will be possible to measure the dark energy parameters with an uncertainty of {?(w0) = 0.05, ?(wa) = 0.12} and the modified gravity parameters {?(?0) = 0.10, ?(?0) = 0.05}, assuming Planck CMB+SN (current data) priors. Finally, we show that radio surveys would detect a primordial non-Gaussianity of fNL= 8 at 1?, and we briefly discuss other promising probes.

Raccanelli, Alvise; Zhao, Gong-Bo; Bacon, David J.; Jarvis, Matt J.; Percival, Will J.; Norris, Ray P.; Röttgering, Huub; Abdalla, Filipe B.; Cress, Catherine M.; Kubwimana, Jean-Claude; Lindsay, Sam; Nichol, Robert C.; Santos, Mario G.; Schwarz, Dominik J.

2012-08-01

52

Distributed Strategies for Channel Allocation and Scheduling in Software-Defined Radio Networks  

E-print Network

Distributed Strategies for Channel Allocation and Scheduling in Software-Defined Radio Networks Bo allocation of individual links and packet-scheduling, in Software-Defined Radio (SDR) wireless networks. Our technology have led to the design of Software- Defined Radios (SDR) [18], in which packet transmissions

Srinivasan, Aravind

53

Energy coupling channels and effecting mechanism of continuous wave irradiation to radio fuze  

Microsoft Academic Search

Based on introducing experiment equipment and method the irradiation effects experiments of continuous wave to radio fuze are studied Analyzing the experiment results indicate that the coupling channels of continuous wave to radio fuze are the antenna and shell body. The effecting mechanism is that the energy of continuous wave couples into radio fuze via the antenna and shell body,

Zhiqiang Fei; Guanghui Wei; Lifei Geng; Fu Li

2009-01-01

54

Transmission Techniques and Channel Calibration for Spatial Interweave TDD Cognitive Radio  

E-print Network

1 Transmission Techniques and Channel Calibration for Spatial Interweave TDD Cognitive Radio the problem of beamforming design for a Cognitive Radio (CR) system in which a multiple-input multiple- output Long Term Evolution (LTE). I. INTRODUCTION AND STATE OF THE ART Cognitive Radio [1] (CR) has been

Paris-Sud XI, Université de

55

Dynamic Control Channel Assignment in Cognitive Radio Networks Using Swarm Intelligence  

Microsoft Academic Search

In recent years, a variety of algorithms for cognitive radio networks have been proposed. Many of these algorithms rely on the exchange of control information among the cognitive radio nodes and often require the presence of a globally available control channel. This requirement however poses a problem in a practical deployment: First, due to spectrum fluctuations such common control channel

Christian Doerr; Douglas C. Sicker; Dirk Grunwald

2008-01-01

56

Channel Selection Based on Trust and Multiarmed Bandit in Multiuser, Multichannel Cognitive Radio Networks  

PubMed Central

This paper proposes a channel selection scheme for the multiuser, multichannel cognitive radio networks. This scheme formulates the channel selection as the multiarmed bandit problem, where cognitive radio users are compared to the players and channels to the arms. By simulation negotiation we can achieve the potential reward on each channel after it is selected for transmission; then the channel with the maximum accumulated rewards is formally chosen. To further improve the performance, the trust model is proposed and combined with multi-armed bandit to address the channel selection problem. Simulation results validate the proposed scheme. PMID:24711741

Zeng, Fanzi; Shen, Xinwang

2014-01-01

57

Channel selection based on trust and multiarmed bandit in multiuser, multichannel cognitive radio networks.  

PubMed

This paper proposes a channel selection scheme for the multiuser, multichannel cognitive radio networks. This scheme formulates the channel selection as the multiarmed bandit problem, where cognitive radio users are compared to the players and channels to the arms. By simulation negotiation we can achieve the potential reward on each channel after it is selected for transmission; then the channel with the maximum accumulated rewards is formally chosen. To further improve the performance, the trust model is proposed and combined with multi-armed bandit to address the channel selection problem. Simulation results validate the proposed scheme. PMID:24711741

Zeng, Fanzi; Shen, Xinwang

2014-01-01

58

Error analysis of bent ray radio occultation measurments  

NASA Technical Reports Server (NTRS)

There are two types of experimental measurement errors of the Doppler data associated with the radio occultation, random and systematic. Random errors are due to thermal noise in the transmission channel, and the phase lock loop, and quantization error in the digital circuitry. These are called noise type errors. The systematic errors are due to geometric uncertainty and equipment phase instability. Considered is the amount of uncertainty, due to random measurement errors, in the refractivity profiles reconstructed by this type of indirect sensing experiment. A class of refractivity profiles is defined which approximately fit the set of measured data. Bounds are placed on the extent of this class of solution profiles. To accomplish this, the sensivity of the reconstructed refractivity profiles to errors in the measured quantity and the statistics of the errors in the measurement are examined.

Saintgermain, R. L.

1972-01-01

59

An Architecture For Integrating Low Complexity and Reconfigurability for Channel filters in Software Defined Radio Receivers  

Microsoft Academic Search

The most computationally demanding block in the digital front end of a software defined radio (SDR) receiver is the channelizer which operates at the highest sampling rate. Reconfigurability and low complexity are the two key requirements of the SDR channelizers. An architecture for implementing low complexity and reconfigurable finite impulse response (FIR) filters for channelizers is proposed in this paper.

R. Mahesh; A. Prasad Vinod

2007-01-01

60

Control channel based MAC-layer configuration, routing and situation awareness for cognitive radio networks  

Microsoft Academic Search

In a cognitive radio (CR) network, MAC-layer configuration involves determining a common set of channels to facilitate communication among participating nodes. Further, the availability of multiple channels and frequent channel switches add to the complexity of route selection. Knowledge of the global network topology can be used to solve the above-described problems. In this paper, we propose a distributed algorithm

Srinivasan Krishnamurthy; Mansi Thoppian; S. Venkatesan; Ravi Prakash

2005-01-01

61

Land mobile satellite channel measurements and modeling  

Microsoft Academic Search

This paper, tutorial in nature, describes the effort of many investigators who have and still are conducting channel measurements and modeling for land mobile satellite communications. Various channel measurement results, ranging from ultrahigh frequency to Ka-band, are given. Many statistical channel models and simplified models that have been developed are referred to. Some of the models are applicable to geostationary

Chun Loo; JOHN S. BUTTERWORTH

1998-01-01

62

Measurements of radio pulsar braking indices  

NASA Astrophysics Data System (ADS)

A quantitative analysis of radio pulsar timing noise is presented. Our analysis employs the recently reported strong correlation (with correlation coefficient r = 0.95) between the observed second time derivative of the pulse rotation frequency (ddot?obs), obtained from fully phase-coherent timing analyses, and a timing noise statistic (?R23), used to quantify the amount of pulsar rotational fluctuations absorbed by the coefficient of the cubic term, to isolate the presumed deterministic braking index from the effects attributable to pulsar timing activity. Application of this method to a sample of 27 radio pulsars, whose timing data span 9-13 years, reveals that (i) for 22 pulsars, a sensible braking index measurement was impossible: with numerical values of the braking index either appreciably less than the corresponding uncertainty or anomalously large; (ii) save for the relatively large uncertainties, the braking index appears to be significantly measured in five pulsars. Current results are discussed in the context of the prevailing standard model for radio pulsar spin-down.

Chukwude, A. E.; Baiden, A. A.; Onuchukwu, C. C.

2010-06-01

63

Radio Interferometry & The Measurement Equation -1 School of Physics  

E-print Network

Radio Interferometry & The Measurement Equation - 1 School of Physics and Astronomy An Introduction to Radio Interferometry and The Measurement Equation Formalism Pedagogical Seminar Louise M. Ker March 2010 Abstract The next generation of radio telescopes, such as LOFAR, e-Merlin, ASKAP, MeerKat and even- tually

Tittley, Eric

64

A Channel Access Scheme for Large Dense Packet Radio Networks  

Microsoft Academic Search

Prior work in the field of packet radio networks has often assumed a simple success-if-exclusive model of successful reception. This simple model is insufficient to model interference in large dense packet radio networks accurately. In this paper we present a model that more closely approximates communication theory and the underlying physics of radio communication. Using this model we present a

Timothy J. Shepard

1996-01-01

65

Adaptive Game-Based Radio Spectrum Allocation in Doubly Selective Fading Channels  

Microsoft Academic Search

For cognitive radio networks, a popular approach to dynamic spectrum allocation (DSA) is game theoretic, which improves spectrum efficiency in a distributed manner. In a doubly selective fading channel, a conventional game-based DSA can be cumbersome to implement due to channel variation, which requires to re-train the channel estimator and re-calculate DSA decisions for every transmission burst within the channel

Duo Zhang; Zhi Tian

2007-01-01

66

Design and Implementation of an Underlay Control Channel for Cognitive Radios  

SciTech Connect

Implementation of any cognitive radio network requires an effective control channel that can operate under various modes of activity from the primary users. This paper reports the design and implementation of a filter bank multicarrier spread spectrum (FBMC-SS) system for use as the control channel in cognitive radio networks. The proposed design is based on a filtered multitone (FMT) implementation. Carrier and timing acquisition and tracking methods as well as a blind channel estimation method are developed for the proposed control channel. We also report an implementation of the proposed FBMC-SS system on a hardware platform; a FlexRIO FPGA module from National Instruments.

Daryl Wasden; Hussein Moradi; Behrouz Farhang-Boroujeny

2012-11-01

67

Radio frequency sensing measurements and methods for location classification in wireless networks  

NASA Astrophysics Data System (ADS)

The wireless radio channel is typically thought of as a means to move information from transmitter to receiver, but the radio channel can also be used to detect changes in the environment of the radio link. This dissertation is focused on the measurements we can make at the physical layer of wireless networks, and how we can use those measurements to obtain information about the locations of transceivers and people. The first contribution of this work is the development and testing of an open source, 802.11b sounder and receiver, which is capable of decoding packets and using them to estimate the channel impulse response (CIR) of a radio link at a fraction of the cost of traditional channel sounders. This receiver improves on previous implementations by performing optimized matched filtering on the field-programmable gate array (FPGA) of the Universal Software Radio Peripheral (USRP), allowing it to operate at full bandwidth. The second contribution of this work is an extensive experimental evaluation of a technology called location distinction, i.e., the ability to identify changes in radio transceiver position, via CIR measurements. Previous location distinction work has focused on single-input single-output (SISO) radio links. We extend this work to the context of multiple-input multiple-output (MIMO) radio links, and study system design trade-offs which affect the performance of MIMO location distinction. The third contribution of this work introduces the "exploiting radio windows" (ERW) attack, in which an attacker outside of a building surreptitiously uses the transmissions of an otherwise secure wireless network inside of the building to infer location information about people inside the building. This is possible because of the relative transparency of external walls to radio transmissions. The final contribution of this dissertation is a feasibility study for building a rapidly deployable radio tomographic (RTI) imaging system for special operations forces (SOF). We show that it is possible to obtain valuable tracking information using as few as 10 radios over a single floor of a typical suburban home, even without precise radio location measurements.

Maas, Dustin C.

68

Radio frequency channel modeling for proximity networks on the Martian surface  

E-print Network

Radio frequency channel modeling for proximity networks on the Martian surface Vishwanath Chukkala- ronment at selected sites on the surface of Mars with a focus on the link budget and RF coverage patterns networks. The performance of any such wireless network depends fundamentally on the radio frequency (RF

De Leon, Phillip

69

A Framework for Radio Frequency Spectrum Measurement and Analysis  

E-print Network

regarding the use of a low cost, mobile software- defined radio platform as a spectrum data collection including software-defined radios, embedded systems, reconfigurable hardware, communications systemsA Framework for Radio Frequency Spectrum Measurement and Analysis V. Rory Petty ITTC-FY2008-TR

Kansas, University of

70

A Randomized Saturation Degree Heuristic for Channel Assignment in Cellular Radio Networks  

E-print Network

constraints: j f ik \\Gamma f jl j â?? c ij 8 i; k; j; l (k 6= l) : We consider the following frequency the channel assignment problem, that is the problem of assigning channels (codes) to the cells of a cellu­ lar successfully used for code assignment in Packet Radio Networks. We give a new version of this heuristic

Battiti, Roberto

71

Topology-Incurred Delay for Information Dissemination in Large MultiChannel Cognitive Radio Networks  

Microsoft Academic Search

Cognitive Radio (CR) networks have become an important component of the modern communication infrastructure due to their capability of improving spectrum usage efficiency by exploiting channels opportunistically. In CR networks, the network topology changes very frequently because of the temporarily available channels and dynamic transmitting parameters (e.g. transmission power and transmitting frequency), which may even result in network disconnectivity from

Lei Sun; Wenye Wang

2010-01-01

72

Tracking of Time-varying Mobile Radio Channels Part II: A Case Study  

E-print Network

Tracking of Time-varying Mobile Radio Channels Part II: A Case Study Lars Lindbom, Anders Ahl#19;en are encountered, so well designed channel esti- mators are crucial for obtaining adequate performance. Estimates; Lars Lindbom and Magnus Falkenstrom are with Ericsson In- fotech, PO Box 1038, SE-65115 Karlstad

73

Radio Channel Quality in Industrial Wireless Sensor Networks  

Microsoft Academic Search

Wireless mesh sensor networks are being deployed today in various monitoring and control applications. Some radio network designs, such as ZigBee, presume that radio connectivity is reasonably consistent over time. Others take the opposite approach of presuming that links are entirely unreliable, and build large degrees of physical redundancy into the network in the hope that a collection of redundant

Daniel Sexton; Michael Mahony; Michael Lapinski; Jay Werb

2005-01-01

74

A review of radio channel models for body centric communications  

NASA Astrophysics Data System (ADS)

The human body is an extremely challenging environment for the operation of wireless communications systems, not least because of the complex antenna-body electromagnetic interaction effects which can occur. This is further compounded by the impact of movement and the propagation characteristics of the local environment which all have an effect upon body centric communications channels. As the successful design of body area networks (BANs) and other types of body centric system is inextricably linked to a thorough understanding of these factors, the aim of this paper is to conduct a survey of the current state of the art in relation to propagation and channel models primarily for BANs but also considering other types of body centric communications. We initially discuss some of the standardization efforts performed by the Institute of Electrical and Electronics Engineers 802.15.6 task group before focusing on the two most popular types of technologies currently being considered for BANs, namely narrowband and Ultrawideband (UWB) communications. For narrowband communications the applicability of a generic path loss model is contended, before presenting some of the scenario specific models which have proven successful. The impacts of human body shadowing and small-scale fading are also presented alongside some of the most recent research into the Doppler and time dependencies of BANs. For UWB BAN communications, we again consider the path loss as well as empirical tap delay line models developed from a number of extensive channel measurement campaigns conducted by research institutions around the world. Ongoing efforts within collaborative projects such as Committee on Science and Technology Action IC1004 are also described. Finally, recent years have also seen significant developments in other areas of body centric communications such as off-body and body-to-body communications. We highlight some of the newest relevant research in these areas as well as discussing some of the advanced topics which are currently being addressed in the field of body centric communications.

Cotton, Simon L.; D'Errico, Raffaele; Oestges, Claude

2014-06-01

75

Performance of UWB Impulse Radio With Planar Monopoles Over On-Human-Body Propagation Channel for Wireless Body Area Networks  

Microsoft Academic Search

Ultrawideband (UWB) is a promising technology for wireless body area networks (WBANs). This paper studied the impacts of 3.1-10.6 GHz on-human-body UWB channel on the impulse radio WBAN system. A performance evaluation method is presented for the realistic UWB WBAN systems, which observes the waveform distortion along the signal path. The measurement and characterization of the 3.1-10.6 GHz on-human-body UWB

Yue Ping Zhang; Qiang Li

2007-01-01

76

A history of radio astronomy polarisation measurements  

NASA Astrophysics Data System (ADS)

While intensity of electromagnetic radiation (radio, infrared, light, or X-ray) gives us primary information about the distribution of the baryonic matter in the Universe, polarisation is a parameter that enables us to investigate many additional details. Polarisation at radio frequencies gives us details of emission processes since the non-thermal synchrotron process dominates at low radio frequencies in emission regions. In addition, polarised radio sources can be used as probes of the intervening interstellar medium through which the radio waves are propagated. Faraday rotation effects are observed and in conjunction with known thermal emission can be used to determine magnetic fields. The Zeeman effect, a direct method of determining magnetic fields, depends on the observation of the circularpolarisation components of a spectral line. In this paper I describe the early polarisation observations of radio sources, but in addition I follow the developments through to the present day.

Wielebinski, Richard

2012-07-01

77

Analysis of Gravity Waves from Radio Occultation Measurements  

E-print Network

Analysis of Gravity Waves from Radio Occultation Measurements Martin Lange and Christoph Jacobi occultation mea- surements. Due to the spherical symmetry assumption in the retrieval algorithm and the low that with radio occultation measurements more than 90% of the simulated wave spectrum can be resolved

78

Entanglement in channel discrimination with restricted measurements  

SciTech Connect

We study the power of measurements implementable with local quantum operations and classical communication (LOCC) measurements in the setting of quantum channel discrimination. More precisely, we consider discrimination procedures that attempt to identify an unknown channel, chosen uniformly from two known alternatives, that take the following form: (i) the input to the unknown channel is prepared in a possibly entangled state with an ancillary system, (ii) the unknown channel is applied to the input system, and (iii) an LOCC measurement is performed on the output and ancillary systems, resulting in a guess for which of the two channels was given. The restriction of the measurement in such a procedure to be an LOCC measurement is of interest because it isolates the entanglement in the initial input-ancillary systems as a resource in the setting of channel discrimination. We prove that there exist channel discrimination problems for which restricted procedures of this sort can be at either of the two extremes: they may be optimal within the set of all discrimination procedures (and simultaneously outperform all strategies that make no use of entanglement), or they may be no better than unentangled strategies (and simultaneously suboptimal within the set of all discrimination procedures).

Matthews, William; Piani, Marco; Watrous, John [Institute for Quantum Computing and Department of Combinatorics and Optimization, University of Waterloo, Waterloo, Ontario (Canada); Institute for Quantum Computing and Department of Physics and Astronomy, University of Waterloo, Waterloo, Ontario (Canada); Institute for Quantum Computing and School of Computer Science, University of Waterloo, Waterloo, Ontario (Canada)

2010-09-15

79

Entanglement in channel discrimination with restricted measurements  

E-print Network

Entanglement in channel discrimination with restricted measurements William Matthews Institute, Ontario, Canada Marco Piani Institute for Quantum Computing and Department of Physics and Astronomy, University of Waterloo, Waterloo, Ontario, Canada John Watrous Institute for Quantum Computing and School

Watrous, John

80

Multichannel Broadcast Based on Home Channel for Cognitive Radio Sensor Networks  

PubMed Central

Considering the limited resources and the dynamic spectrum distribution in the cognitive radio sensor networks (CRSN), a half-duplex Multichannel broadcast protocol for CRSN is presented based on the home channel. This protocol maintains the networks topology only through the home channel, so there is no need for the public channel to transmit the control information and no need for the synchronization. After network initialization, node broadcasts data via home channel in half-duplex transmission way. The simulation results show that, compared with complete broadcast, the proposed protocol effectively reduces broadcast delay and overhead. PMID:25161397

Zeng, Fanzi; Tang, Yuting; Pu, Jianjie

2014-01-01

81

Multichannel broadcast based on home channel for cognitive radio sensor networks.  

PubMed

Considering the limited resources and the dynamic spectrum distribution in the cognitive radio sensor networks (CRSN), a half-duplex Multichannel broadcast protocol for CRSN is presented based on the home channel. This protocol maintains the networks topology only through the home channel, so there is no need for the public channel to transmit the control information and no need for the synchronization. After network initialization, node broadcasts data via home channel in half-duplex transmission way. The simulation results show that, compared with complete broadcast, the proposed protocol effectively reduces broadcast delay and overhead. PMID:25161397

Zeng, Fanzi; Tang, Yuting; Pu, Jianjie

2014-01-01

82

Radio polarisation measurements of meteor trail echoes with BRAMS  

NASA Astrophysics Data System (ADS)

BRAMS, the Belgian RAdio Meteor Stations, is a network of radio receiving stations using forward scattering techniques to detect and characterize meteoroids. One of the receiving stations located in Uccle is sensitive to all kind of polarisation. We present the preliminary radio polarisation measurements of meteor trail echoes and discuss how these data can be used to retrieve physical information about the meteor trail (e.g. ionisation).

Lamy, H.; Ranvier, S.; Anciaux, M.

2012-09-01

83

BER performance of continuous phase digital angle modulation in aeronautical mobile radio channels  

Microsoft Academic Search

The bit error rate (BER) performance of continuous phase digital angle modulation is theoretically analyzed in the aeronautical mobile radio channel by applying the Pawula theorem to the channel stochastic model that was developed by the author (42nd IEEE Veh. Technol. Conf., 1992). These digital angle modulation techniques include M-ary frequency shift keying (FSK), M-ary differential phase shift keying (DPSK),

S. M. Elnoubi

1992-01-01

84

Performance evaluation of wireless multi-hop networks with directional antennas in an indoor radio propagation channel  

Microsoft Academic Search

Wireless backhaul systems have been considered as a promising candidate of beyond 3G wireless broadband system for mobile communications. The achievable transmission performance over radio relay channel depends on antenna directivity and radiation patterns of each antenna element. To improve the transmission performance and keep radio relay channel in an acceptable condition, it is effective to control the antenna directivity

Ximing Huang; Osamu Muta; Hiroshi Furukawa

2012-01-01

85

A Quantitative Analysis of Spectral Occupancy Measurements for Cognitive Radio  

Microsoft Academic Search

Cognitive radio (CR) is viewed as a possible solution to the problem of radio spectrum congestion. The CR technique utilizes a temporarily unoccupied licensed band. Before investigating the technical and political implications of CR, it is necessary to know to what extent the licensed bands are temporally unoccupied. This paper describes a spectral occupancy measurement campaign conducted in the frequency

Robin I. C. Chiang; Gerard B. Rowe; Kevin W. Sowerby

2007-01-01

86

Measurements of the Continuous Radio Background and Comparison with Simulated  

E-print Network

. . . . . . . . . . . . . . . . . . . . . . . . 31 4.1.1. The logarithmic-periodic dipole Antenna . . . . . . . . 34 4.1.2. Signal ProcessingMeasurements of the Continuous Radio Background and Comparison with Simulated Radio Signals from . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.2. Propagation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.3. Energy Spectrum

Erdmann, Martin

87

Ergodic Capacity of Cognitive Radio under Imperfect Channel State Information  

E-print Network

A spectrum-sharing communication system where the secondary user is aware of the instantaneous channel state information (CSI) of the secondary link, but knows only the statistics and an estimated version of the secondary transmitter-primary receiver (ST-PR) link, is investigated. The optimum power profile and the ergodic capacity of the secondary link are derived for general fading channels (with continuous probability density function) under average and peak transmit-power constraints and with respect to two different interference constraints: an interference outage constraint and a signal-to-interference outage constraint. When applied to Rayleigh fading channels, our results show, for instance, that the interference constraint is harmful at high-power regime in the sense that the capacity does not increase with the power, whereas at low-power regime, it has a marginal impact and no-interference performance corresponding to the ergodic capacity under average or peak transmit power constraint in absence of ...

Rezk, Zouheir

2012-01-01

88

Spectrum Opportunity-Based Control Channel Assignment in Cognitive Radio Networks  

E-print Network

) is proposed to solve this problem. SOC provides a desirable balance between two competing factors: the set radios (PRs). Reliable spectrum sensing can be achieved through cooperation of neighboring CRs, whose functions such as multi-channel access, and multi-hop routing. Collaborative CRN functions

Lazos, Loukas

89

Subwavelength Radio Repeater System Utilizing Miniaturized Antennas and Metamaterial Channel Isolator  

Microsoft Academic Search

Implementation of a novel high gain miniaturized radio repeater for improving wireless network connectivity in complex environment is presented in this paper. Unlike existing repeater systems, this system utilizes two closely spaced low profile miniaturized planar antennas capable of producing om- nidirectional and vertical radiation pattern as well as a channel isolator layer that serves to decouple the adjacent antennas.

Kamal Sarabandi; Young Jun Song

2011-01-01

90

On cognitive radio networks with opportunistic power control strategies in fading channels  

Microsoft Academic Search

In this paper, we consider a cognitive radio system in fading wireless channels and propose an opportunistic power control strategy for the cognitive users, which serves as an alternative way to protect the primary user's transmission and to realize spectrum sharing between the primary user and the cognitive users. The key feature of the proposed strategy is that, via opportunistically

Yan Chen; Guanding Yu; Zhaoyang Zhang; Hsiao-hwa Chen; Peiliang Qiu

2008-01-01

91

Residual White Space Distribution-Based Opportunistic Channel Access for Cognitive Radio Enabled Devices  

E-print Network

(usually referred as white spaces or holes) in various spectrum bands by allow- ing secondary devices, the secondary nodes should be able to identify the white spaces in the spectrum and utilize them. HoweverResidual White Space Distribution-Based Opportunistic Channel Access for Cognitive Radio Enabled

Sahoo, Anirudha

92

AUTOMATIC RADIO TRACKING OF FISH IN EXPERIMENTAL CHANNELS  

EPA Science Inventory

An automatic tracking system controlled by an RCA 1802 microprocessor was developed to locate fish in a 400 m outdoor experimental channel at the U.S. EPA Monticello Ecological Research Station. The monitoring network consisted of 12 horizontally polarized antennas spaced at 30 m...

93

MIMO capacities for different antenna array structures based on double directional wide-band channel measurements  

Microsoft Academic Search

We present an approach for investigating the performance of generic multiple-input multiple-output (MIMO) wireless systems in a realistic way using wideband real-time propagation measurements of the double-directional radio channel. Applying a multidimensional high-resolution channel parameter estimation procedure the descriptive parameters for any relevant propagation path including the path weights, time-delay, Doppler shift and the propagation directions at both ends of

Dirk Hampicke; M. Landmann; C. Schneider; G. Sommerkorn; T. Thoma; T. Fugen; J. Maurer; W. Wiesbeck

2002-01-01

94

A concurrent access MAC protocol for cognitive radio ad hoc networks without common control channel  

NASA Astrophysics Data System (ADS)

Cognitive radio ad hoc networks (CRAHNs) consist of autonomous nodes that operate in ad hoc mode and aim at efficient utilization of spectrum resources. Usually, the cognitive nodes in a CRAHN exploit a number of available channels, but these channels are not necessarily common to all nodes. Such a network environment poses the problem of establishing a common control channel (CCC) as there might be no channel common to all the network members at all. In designing protocols, therefore, it is highly desirable to consider the network environment with no CCC. In this article, we propose a MAC protocol called concurrent access MAC (CA-MAC) that operates in the network environment with no CCC. The two devices in a communication pair can communicate with each other even if they have only one common channel available. Therefore, the problems with CCC (such as channel saturation and denial of service attacks) can also be resolved. In CA-MAC, channel accesses are distributed over communication pairs, resulting in increased network connectivity. In addition, CA-MAC allows different communication pairs to access multiple channels concurrently. According to our performance study, CA-MAC provides higher network connectivity with shorter channel access delay compared to SYN-MAC, which is the conventional key MAC protocol for the network environment with no CCC, resulting in better network throughput.

Timalsina, Sunil K.; Moh, Sangman; Chung, Ilyong; Kang, Moonsoo

2013-12-01

95

A distributed scheme for integrated predictive dynamic channel and power allocation in cellular radio networks  

Microsoft Academic Search

We propose a distributed dynamic channel and power allocation (DCPA) scheme based on a novel predictive power control algorithm. The minimum interference dynamic channel assignment algorithm is employed, while simple Kalman filters are designed to provide the predicted measurements of both the channel gains and the interference levels, which are then used to update the power levels. Extensive computer simulations

Kambiz Shoarinejad; Jason L. Speyer; Gregory J. Pottie

2001-01-01

96

Radio polarisation measurements of meteor trail echoes with BRAMS  

NASA Astrophysics Data System (ADS)

BRAMS, the Belgian RAdio Meteor Stations, is a network of radio receiving stations using forward scatter techniques to detect and characterize meteors. The transmitter is a dedicated beacon located in Dourbes in the south-west of Belgium. It emits towards the zenith a purely sinusoidal wave circularly polarised, at a frequency of 49.97 MHz and with a power of 150 watts. The main goals of the project are to compute meteoroid flux rates and trajectories. Most receiving stations are using a 3 element Yagi antenna and are therefore only sensitive to one polarisation. The station located in Uccle has also a crossed 3 element Yagi antenna and therefore allows measurements of horizontal and vertical polarisations. We present the preliminary radio polarisation measurements of meteor trail echoes and compare them with the theoretical predictions of Jones & Jones (1991) for oblique scattering of radio waves from meteor trails.

Lamy, H.; Ranvier, S.; Anciaux, M.; Calders, S.; De Keyser, J.; Gamby, E.

2012-04-01

97

Pilot symbol assisted channel estimation for OFDM-based cognitive radio systems  

NASA Astrophysics Data System (ADS)

In this article, challenges regarding the provision of channel state information (CSI) in non-contiguous orthogonal frequency division multiplexing (NC-OFDM) cognitive radio (CR) systems are addressed. We propose a novel scheme that utilizes cross entropy (CE) optimization together with an analytical pilot power distribution technique to design pilot symbols that minimizes the channel estimate mean squared error (MSE) of frequency-selective channels. The optimal selection of pilot subcarriers is a combinatorial problem that requires heavy computations. To reduce the computational complexity, the CE optimization is utilized to determine the position of pilot subcarriers. Then, for a given pilot placement obtained by the CE algorithm, a closed form expression to obtain optimal pilot power distribution is employed. Simulation results indicate that, the proposed pilot symbol design provides better channel estimate MSE as well as the bit error rate (BER) performance when compared with the conventional equal powered pilot design.

Manasseh, Emmanuel; Ohno, Shuichi; Nakamoto, Masayoshi

2013-12-01

98

Secured Distributed Cognitive MAC and Complexity Reduction in Channel Estimation for the Cross Layer based Cognitive Radio Networks  

E-print Network

Secured opportunistic Medium Access Control (MAC) and complexity reduction in channel estimation are proposed in the Cross layer design Cognitive Radio Networks deploying the secured dynamic channel allocation from the endorsed channel reservation. Channel Endorsement and Transmission policy is deployed to optimize the free channel selection as well as channel utilization to cognitive radio users. This strategy provide the secured and reliable link to secondary users as well as the collision free link to primary users between the physical and MAC layers which yields the better network performance. On the other hand, Complexity Reduction in Minimum Mean Square Errror (CR-MMSE) and Maximum Likelihood (CR-ML) algorithm on Decision Directed Channel Estimation (DDCE) is deployed significantly to achieve computational complexity as Least Square (LS) method. Rigorously, CR-MMSE in sample spaced channel impulse response (SS-CIR) is implemented by allowing the computationally inspired matrix inversion. Regarding CR-ML...

Shakhakarmi, Niraj

2012-01-01

99

Locally Coherent Ultra-Wideband Radio Channel Model for Sensor Networks in Industrial Environment  

Microsoft Academic Search

We describe a new transfer function model for the static ultra-wideband (UWB) radio channel in industrial indoor environments for SPIN (sensor, positioning, and identification network) applications. The model addresses propagation between one or more transmitter and one or more receiver positions. It is locally coherent, i.e., it accounts for small scale displacements of transmitter and receiver. It is a geometry-based

J. Kunisch; J. Pamp

2006-01-01

100

High resolution of electromagnetic waves in time-varying radio channels  

Microsoft Academic Search

The applicability of the SAGE (space-alternating generalized expectation-maximization) algorithm to the estimation of time variant radio channels is demonstrated. This algorithm allows one to separate the complex multi-dimensional optimization problem required to compute the estimate of the parameters characterizing the impinging waves, i.e. their delay, incidence azimuth, Doppler frequency, and complex amplitude, into separate one dimensional optimization processes that can

Klaus I. Pedersen; Bernard H. Fleury; Preben E. Mogensen

1997-01-01

101

Measurement technique of the Giotto radio science experiment  

NASA Technical Reports Server (NTRS)

The paper describes the technique used to record time delay and waveform measurements for the Giotto radio science experiment of ESA's mission to comet Halley. The data were taken by using either two-way measurements (during pre- and post-encounter) or one-way measurements (during encounter with comet Halley), the downlink of the radio signal of the Giotto spacecraft being received at 8.4 GHz by the 64 m tracking stations of NASA's Deep Space Network (DSN). The waveform measurements were obtained at a sampling frequency of 50 kHz with an open-loop receiver assembly at DSN station Canberra as recently used for the Voyager/Uranus fly-by. Performance and calibration data are given as relevant to the radio subsystems on the ground and aboard Giotto.

Edenhofer, P.; Buschert, H.; Bird, M. K.; Esposito, P. B.; Porsche, H.

1987-01-01

102

Smart antennas for combined DOA and joint channel estimation in time-slotted CDMA mobile radio systems with joint detection  

Microsoft Academic Search

In cellular mobile radio systems, the directional inhomogeneity of the mobile radio channel can be exploited by smart antennas to increase the spectral efficiency. In this paper, a novel smart antenna concept applying receiver antenna diversity at the uplink receiver is investigated for a time-slotted code-division multiple-access (CDMA) mobile radio air interface termed time-division CDMA (TD-CDMA), which has been selected

Josef Johannes Blanz; Apostolos Papathanassiou; Martin Haardt; Ignasi Furió; Paul Walter Baier

2000-01-01

103

Channel Exploration and Exploitation with Imperfect Spectrum Sensing in Cognitive Radio Networks  

E-print Network

In this paper, the problem of opportunistic channel sensing and access in cognitive radio networks when the sensing is imperfect and a secondary user has limited traffic to send at a time is investigated. Primary users' statistical information is assumed to be unknown, and therefore, a secondary user needs to learn the information online during channel sensing and access process, which means learning loss, also referred to as regret, is inevitable. In this research, the case when all potential channels can be sensed simultaneously is investigated first. The channel access process is modeled as a multi-armed bandit problem with side observation. And channel access rules are derived and theoretically proved to have asymptotically finite regret. Then the case when the secondary user can sense only a limited number of channels at a time is investigated. The channel sensing and access process is modeled as a bi-level multi-armed bandit problem. It is shown that any adaptive rule has at least logarithmic regret. Th...

Zhang, Zhou; Tan, Peng; Slevinsky, Jim

2012-01-01

104

GPRS radio network capacity and quality of service using fixed and on-demand channel allocation techniques  

Microsoft Academic Search

The radio network capacity needed for the General Packet Radio Service (GPRS) in coexistence with circuit switched services and the admissible quality of service for mobile Internet users is presented. Since the GPRS is to be integrated into the GSM infrastructure, a number of physical channels has to be made available to GPRS used as fixed and on-demand packet data

Peter Stuckmann; Frank Muller

2000-01-01

105

Packet Switching in Radio Channels: Part I--Carrier Sense Multiple-Access Modes and Their Throughput-Delay Characteristics  

Microsoft Academic Search

Radio communication is considered as a method for providing remote terminal access to computers. Digital byte streams from each terminal are partitioned into packets (blocks) and transmitted in a burst mode over a shared radio channel. When many terminals operate in this fashion, transmissions may conflict with and destroy each other. A means for controlling this is for the terminal

LEONARD KLEINROCK; FOUAD A. TOBAGI

1975-01-01

106

Pilot-Aided Channel Estimation in WCDMA on a Radio-over-Fibre Channel Gholamreza Baghersalimi, Timothy O'Farrell, Vas Postoyalko  

E-print Network

@ee.leeds.ac.uk, v.postoyalko@leeds.ac.uk Abstract In this paper the impact of a Radio-over-Fibre optical sub-aided channel estimation to compensate for the optical sub-system non-linearities in the presence of AWGN. The results show that pilot-aided (optical) channel estimation is an effective method of compensating

Haddadi, Hamed

107

Simulation studies of GPS radio occultation measurements  

NASA Astrophysics Data System (ADS)

The atmospheric propagation of GPS signals under multipath conditions and their detection are simulated. Using the multiple phase screen method, C/A-code modulated L1 signals are propagated through a spherically symmetric refractivity field derived from a high-resolution radio sonde observation. The propagated signals are tracked by a GPS receiver implemented in software and converted to refractivity profiles by the canonical transform technique and the Abel inversion. Ignoring noise and assuming an ideal receiver tracking behavior, the true refractivity profile is reproduced to better than 0.1% at altitudes above 2 km. The nonideal case is simulated by adding between 14 and 24 dB of Gaussian white noise to the signal and tracking the signal with a receiver operating at 50 and 200 Hz sampling frequency using two different carrier phase detectors. In the upper troposphere and stratosphere the fractional refractivity retrieval error is below 0.3% for 50 Hz sampling and below 0.15% for 200 Hz sampling. In the midtroposphere down to altitudes of about 2 km, phase-locked loop tracking induces negative fractional refractivity biases on the order of -1 to -2% at 50 Hz sampling frequency. Modifications to the receiver tracking algorithm significantly improve the retrieval results. In particular, replacing the carrier loop's two-quadrant phase extractor with a four-quadrant discriminator reduces the refractivity biases by a factor of 5; increasing the sampling frequency from 50 to 200 Hz gains another factor of 2.

Beyerle, G.; Gorbunov, M. E.; Ao, C. O.

2003-10-01

108

INDOOR RADIO CHANNEL CHARACTERIZATION OF SPREAD SPECTRUM D. Dres, D. Vouyioukas, Prof. P. Constantinou  

E-print Network

with windows placed in aluminum frame separated by concrete posts. The other outer side of the building to the design of such systems is the knowledge of radio propagation characteristics. This paper focuses is located on a specially designed movable measuring unit (cart) suitable for indoor measurements

Vouyioukas, Demosthenes

109

Measurements of gravity driven granular channel flows  

NASA Astrophysics Data System (ADS)

This dissertation presents experiments that studied two gravity driven granular channel flows. The first experiment used magnetic resonance imaging to measure the density and displacement distributions of poppy seeds flowing in a rough walled channel. Time-averaged measurements of normalized velocity and density showed little flow speed dependence. Instantaneous measurements, however, showed marked velocity dependence in the displacement distributions. There was evidence of aperiodic starting and stopping at lower flow speeds and the onset of density waves on a continuous flow at higher speeds. The second experiment measured forces in all three spatial directions at the boundary of a flow of steel balls. The relationship between the normal and the tangential forces were examined statistically and compared to the Coulomb friction model. For both large and small forces, the tangential and normal forces are unrelated, as there appears to be a strong tendency for the tangential force to maintain a value that will bear the weight the weight of the particles in flow.

Facto, Kevin

110

802.11s based multi-radio multi-channel mesh networking for fractionated spacecraft  

NASA Astrophysics Data System (ADS)

802.11s is a new IEEE standard for mesh networking. It defines the protocols needed to build mobile ad hoc networks that operate over 802.11a, b, g and n waveforms running on inexpensive, and high performance commercial WiFi stations. We have developed a new capability to add to the 802.11s that uses multiple directional radio links that can operate simultaneously within a single mesh node. This is the basis of our multi-channel multi-radio mesh network used in the DARPA F6 program called F6Net. We have developed an analysis and emulation facility that lets us model the F6Net and evaluate the performance in a real world experimentation setup. This paper presents an “ Over-the-Air” experimentation testbed that uses standard Commercial Off-The-Shelf (COTS) 2.4GHz WiFi dongles in an indoor environment, and a shared-code simulation testbed that uses hardware simulated drivers within NS3's channel simulation facility to test 80211s network. To the best of our knowledge, this is the first work that provides a comprehensive evaluation platform with a full-fledged COTS hardware/software prototype to evaluate 802.11s network. Furthermore, we explain the design and development of multi-radio mesh extension for 802.11s that yields a robust and scalable mesh network suitable for clusters of LEO satellites.

Michel, Tony; Thapa, Bishal; Taylor, Steve

111

Weak Lensing Measurements in Simulations of Radio Images  

E-print Network

We present a study of weak lensing shear measurements for simulated galaxy images at radio wavelengths. We construct a simulation pipeline into which we can input galaxy images of known ellipticity, and with which we then simulate observations with eMERLIN and the international LOFAR array. The simulations include the effects of the CLEAN algorithm, uv sampling, observing angle, and visibility noise, and produce realistic restored images of the galaxies. We apply a shapelet-based shear measurement method to these images and test our ability to recover the true source ellipticities. We model and deconvolve the effective PSF, and find suitable parameters for CLEAN and shapelet decomposition of galaxies. We demonstrate that ellipticities can be measured faithfully in these radio simulations, with no evidence of an additive bias and a modest (10%) multiplicative bias on the ellipticity measurements. Our simulation pipeline can be used to test shear measurement procedures and systematics for the next generation of...

Patel, Prina; Bacon, David J; Rowe, Barnaby; Smirnov, Oleg; Beswick, Rob J

2013-01-01

112

Indoor radio measurement and planning for UMTS/HSDPA with antennas  

NASA Astrophysics Data System (ADS)

Over the last decade, mobile communication networks have evolved tremendously with a key focus on providing high speed data services in addition to voice. The third generation of mobile networks in the form of Universal Mobile Telecommunications System (UMTS) is already offering revolutionary mobile broadband experience to its users by deploying High Speed Downlink Packet Access (HSDPA) as its packet-data technology. With data speeds up to 14.4 Mbps and ubiquitous mobility, HSDPA is anticipated to become a preferred broadband access medium for end-users via mobile phones, laptops etc. While majority of these end-users are located indoors most of the time, approximately 70-80% of the HSDPA traffic is estimated to originate from inside buildings. Thus for network operators, indoor coverage has become a necessity for technical and business reasons. Macro-cellular (outdoor) to indoor coverage is a natural inexpensive way of providing network coverage inside the buildings. However, it does not guarantee sufficient link quality required for optimal HSDPA operation. On the contrary, deploying a dedicated indoor system may be far too expensive from an operator's point of view. In this thesis, the concept is laid for the understanding of indoor radio wave propagation in a campus building environment which could be used to plan and improve outdoor-to-indoor UMTS/HSDPA radio propagation performance. It will be shown that indoor range performance depends not only on the transmit power of an indoor antenna, but also on the product's response to multipath and obstructions in the environment along the radio propagation path. An extensive measurement campaign will be executed in different indoor environments analogous to easy, medium and hard radio conditions. The effects of walls, ceilings, doors and other obstacles on measurement results would be observed. Chapter one gives a brief introduction to the evolution of UMTS and HSDPA. It goes on to talk about radio wave propagation and some important properties of antennas which must be considered when choosing an antenna for indoor radio propagation. The challenges of in-building network coverage and also the objectives of this thesis are also mentioned in this chapter. The evolution and standardization, network architecture, radio features and most importantly, the radio resource management features of UMTS/HSDPA are given in chapter two. In this chapter, the reason why Wideband Code Division Multiple Access (WCDMA) was specified and selected for 3G (UMTS) systems would be seen. The architecture of the radio access network, interfaces with the radio access network between base stations and radio network controllers (RNC), and the interface between the radio access network and the core network are also described in this chapter. The main features of HSDPA are mentioned at the end of the chapter. In chapter three the principles of the WCDMA air interface, including spreading, Rake reception, signal fading, power control and handovers are introduced. The different types and characteristics of the propagation environments and how they influence radio wave propagation are mentioned. UMTS transport, logical and physical channels are also mentioned, highlighting their significance and relationship in and with the network. Radio network planning for UMTS is discussed in chapter four. The outdoor planning process which includes dimensioning, detailed planning, optimization and monitoring is outlined. Indoor radio planning with distributed antenna systems (DAS), which is the idea and motivation behind this thesis work, is also discussed. The various antennas considered and the antenna that was selected for this thesis experiment was discussed in chapter five. The antenna radiation pattern, directivity, gain and input impedance were the properties of the antenna that were taken into consideration. The importance of the choice of the antenna for any particular type of indoor environment is also mentioned. In chapter six, the design and fabrication of the monopole antennas used for the experimental m

Eheduru, Marcellinus

113

Physiological measurements during radio-frequency irradiation.  

PubMed

Conventional techniques for monitoring physiological parameters are not suitable for use during RFR exposure. This research note describes transduction methods involving the use of fluorocarbon leads and a pneumatic pressure transducer for reliable measurement of the ECG and respiratory rate in anesthetized or restrained rats during radiofrequency irradiation. PMID:3193340

Frei, M; Jauchem, J; Heinmets, F

1988-01-01

114

Measurement of stream channel habitat using sonar  

USGS Publications Warehouse

An efficient and low cost technique using a sonar system was evaluated for describing channel geometry and quantifying inundated area in a large river. The boat-mounted portable sonar equipment was used to record water depths and river width measurements for direct storage on a laptop computer. The field data collected from repeated traverses at a cross-section were evaluated to determine the precision of the system and field technique. Results from validation at two different sites showed average sample standard deviations (S.D.s) of 0.12 m for these complete cross-sections, with coefficient of variations of 10%. Validation using only the mid-channel river cross-section data yields an average sample S.D. of 0.05 m, with a coefficient of variation below 5%, at a stable and gauged river site using only measurements of water depths greater than 0.6 m. Accuracy of the sonar system was evaluated by comparison to traditionally surveyed transect data from a regularly gauged site. We observed an average mean squared deviation of 46.0 cm2, considering only that portion of the cross-section inundated by more than 0.6 m of water. Our procedure proved to be a reliable, accurate, safe, quick, and economic method to record river depths, discharges, bed conditions, and substratum composition necessary for stream habitat studies. ?? 1998 John Wiley & Sons, Ltd.

Flug, M.; Seitz, H.; Scott, J.

1998-01-01

115

Application of the Hardman methodology to the Single Channel Ground-Airborne Radio System (SINCGARS)  

NASA Technical Reports Server (NTRS)

The HARDMAN methodology was applied to the various configurations of employment for an emerging Army multipurpose communications system. The methodology was used to analyze the manpower, personnel and training (MPT) requirements and associated costs, of the system concepts responsive to the Army's requirement for the Single Channel Ground-Airborne Radio System (SINCGARS). The scope of the application includes the analysis of two conceptual designs Cincinnati Electronics and ITT Aerospace/Optical Division for operating and maintenance support addressed through the general support maintenance echelon.

1984-01-01

116

Optimum Radio Channel Estimation with Periodic Spread Spectrum Signals Adjusted to Amplifier  

Microsoft Academic Search

A system for measuring a multipath channel Impulse response is proposed whlch offers a significantly larger dynamic range as conventlonal systems by using optimized spread spectrum test signals and optimum unbiased estimation in the receiver.

T. Felhauer; P. W. Baier

1992-01-01

117

Distributed Multiuser Sequential Channel Sensing Schemes in Multichannel Cognitive Radio Networks  

E-print Network

Effective spectrum sensing strategies enable cognitive radios (CRs) to identify and opportunistically transmit on under-utilized spectral resources. In this paper, sequential channel sensing problems for single and multiple secondary users (SUs) cases are effectively modeled through finite state Markovian processes. More specifically, a model for single user case is introduced and validated through analytical analysis. In order to address multiple SUs, this model is extended to modified p-persistent access (MPPA) and its generalized version. While the introduced analytical framework facilitates the process of performance evaluation, these algorithms experience a high level of collision among the SUs. To mitigate this problem appropriately, p-persistent random access (PPRA) scheme is proposed, which offers higher average throughput for SUs by statistically distributing their loads among all channels. The structure and performance of the proposed schemes are discussed in detail, and a set of illustrative numeri...

Shokri-Ghadikolaei, Hossein; Nasiri-Kenari, Masoumeh

2012-01-01

118

ATS6-satellite radio beacon measurements at Ootacamund, India  

NASA Technical Reports Server (NTRS)

In August 1975 the ATS6 was repositioned at 35 deg E. Radio beacon measurements of time delay, Faraday rotation and signal amplitude, made at Ootacamund, India in October 1975, are discussed with emphasis on the problem of determining the Faraday content under essentially transverse propagation conditions. It is shown that at the low geomagnetic latitude of Ootacamund the use of a fixed conversion coefficient gives an unreliable Faraday content. It is shown also that corrections to the measured Faraday rotation are important because of pitch and yaw of the satellite, particularly at night when the rotation on 140 MHz can be of the order of 10 to 20 deg. The shape factor shows a low predawn minimum indicating the nearly complete erosion of the F2 layer peak. Amplitude scintillation usually decreases with increase of radio frequency but exceptions are discussed.

Davies, K.; Donnelly, R. F.; Grubb, R. N.; Rama Rao, P. V. S.; Rastogi, R. G.; Deshpande, M. R.; Chandra, H.; Vats, H. O.; Sethia, G.

1978-01-01

119

Rocket radio measurement of electron density in the nighttime ionosphere  

NASA Technical Reports Server (NTRS)

One experimental technique based on the Faraday rotation effect of radio waves is presented for measuring electron density in the nighttime ionosphere at midlatitudes. High frequency linearly-polarized radio signals were transmitted to a linearly-polarized receiving system located in a spinning rocket moving through the ionosphere. Faraday rotation was observed in the reference plane of the rocket as a change in frequency of the detected receiver output. The frequency change was measured and the information was used to obtain electron density data. System performance was evaluated and some sources of error were identified. The data obtained was useful in calibrating a Langmuir probe experiment for electron density values of 100/cu cm and greater. Data from two rocket flights are presented to illustrate the experiment.

Gilchrist, B. E.; Smith, L. G.

1979-01-01

120

Precise Radio-Telescope Measurements Advance Frontier Gravitational Physics  

NASA Astrophysics Data System (ADS)

Scientists using a continent-wide array of radio telescopes have made an extremely precise measurement of the curvature of space caused by the Sun's gravity, and their technique promises a major contribution to a frontier area of basic physics. "Measuring the curvature of space caused by gravity is one of the most sensitive ways to learn how Einstein's theory of General Relativity relates to quantum physics. Uniting gravity theory with quantum theory is a major goal of 21st-Century physics, and these astronomical measurements are a key to understanding the relationship between the two," said Sergei Kopeikin of the University of Missouri. Kopeikin and his colleagues used the National Science Foundation's Very Long Baseline Array (VLBA) radio-telescope system to measure the bending of light caused by the Sun's gravity to an accuracy of 0.03 percent. With further observations, the scientists say their precision technique can make the most accurate measure ever of this phenomenon. Bending of starlight by gravity was predicted by Albert Einstein when he published his theory of General Relativity in 1916. According to relativity theory, the strong gravity of a massive object such as the Sun produces curvature in the nearby space, which alters the path of light or radio waves passing near the object. The phenomenon was first observed during a solar eclipse in 1919. Though numerous measurements of the effect have been made over the intervening 90 years, the problem of merging General Relativity and quantum theory has required ever more accurate observations. Physicists describe the space curvature and gravitational light-bending as a parameter called "gamma." Einstein's theory holds that gamma should equal exactly 1.0. "Even a value that differs by one part in a million from 1.0 would have major ramifications for the goal of uniting gravity theory and quantum theory, and thus in predicting the phenomena in high-gravity regions near black holes," Kopeikin said. To make extremely precise measurements, the scientists turned to the VLBA, a continent-wide system of radio telescopes ranging from Hawaii to the Virgin Islands. The VLBA offers the power to make the most accurate position measurements in the sky and the most detailed images of any astronomical instrument available. The researchers made their observations as the Sun passed nearly in front of four distant quasars -- faraway galaxies with supermassive black holes at their cores -- in October of 2005. The Sun's gravity caused slight changes in the apparent positions of the quasars because it deflected the radio waves coming from the more-distant objects. The result was a measured value of gamma of 0.9998 +/- 0.0003, in excellent agreement with Einstein's prediction of 1.0. "With more observations like ours, in addition to complementary measurements such as those made with NASA's Cassini spacecraft, we can improve the accuracy of this measurement by at least a factor of four, to provide the best measurement ever of gamma," said Edward Fomalont of the National Radio Astronomy Observatory (NRAO). "Since gamma is a fundamental parameter of gravitational theories, its measurement using different observational methods is crucial to obtain a value that is supported by the physics community," Fomalont added. Kopeikin and Fomalont worked with John Benson of the NRAO and Gabor Lanyi of NASA's Jet Propulsion Laboratory. They reported their findings in the July 10 issue of the Astrophysical Journal.

2009-09-01

121

Magnetic fields around radio galaxies from Faraday rotation measure analysis  

NASA Astrophysics Data System (ADS)

The purpose of this thesis is to investigate the strength and structure of the magnetized medium surrounding radio galaxies via observations of the Faraday effect. This study is based on an analysis of the polarization properties of radio galaxies selected to have a range of morphologies (elongated tails, or lobes with small axial ratios) and to be located in a variety of environments (from rich cluster core to small group). The targets include famous objects like M84 and M87. A key aspect of this work is the combination of accurate radio imaging with high-quality X-ray data for the gas surrounding the sources. Although the focus of this thesis is primarily observational, I developed analytical models and performed two- and three-dimensional numerical simulations of magnetic fields. The steps of the thesis are: (a) to analyze new and archival observations of Faraday rotation measure (RM) across radio galaxies and (b) to interpret these and existing RM images using sophisticated two and three-dimensional Monte Carlo simulations. The approach has been to select a few bright, very extended and highly polarized radio galaxies. This is essential to have high signal-to-noise in polarization over large enough areas to allow computation of spatial statistics such as the structure function (and hence the power spectrum) of rotation measure, which requires a large number of independent measurements. New and archival Very Large Array observations of the target sources have been analyzed in combination with high-quality X-ray data from the Chandra, XMM-Newton and ROSAT satellites. The work has been carried out by making use of: 1) Analytical predictions of the RM structure functions to quantify the RM statistics and to constrain the power spectra of the RM and magnetic field. 2) Two-dimensional Monte Carlo simulations to address the effect of an incomplete sampling of RM distribution and so to determine errors for the power spectra. 3) Methods to combine measurements of RM and depolarization in order to constrain the magnetic-field power spectrum on small scales. 4) Three-dimensional models of the group/cluster environments, including different magnetic field power spectra and gas density distributions. This thesis has shown that the magnetized medium surrounding radio galaxies appears more complicated than was apparent from earlier work. Three distinct types of magnetic-field structure are identified: an isotropic component with large-scale fluctuations, plausibly associated with the intergalactic medium not affected by the presence of a radio source; a well-ordered field draped around the front ends of the radio lobes and a field with small-scale fluctuations in rims of compressed gas surrounding the inner lobes, perhaps associated with a mixing layer.

Guidetti, Daria

2011-04-01

122

Saras Measurement of the Radio Background At Long Wavelengths  

NASA Astrophysics Data System (ADS)

SARAS is a correlation spectrometer connected to a frequency independent antenna that is purpose-designed for precision measurements of the radio background at long wavelengths. The design, calibration, and observing strategies admit solutions for the internal additive contributions to the radiometer response, and hence a separation of these contaminants from the antenna temperature. We present here a wideband measurement of the radio sky spectrum by SARAS that provides an accurate measurement of the absolute brightness and spectral index between 110 and 175 MHz. Accuracy in the measurement of absolute sky brightness is limited by systematic errors of magnitude 1.2%; errors in calibration and in the joint estimation of sky and system model parameters are relatively smaller. We use this wide-angle measurement of the sky brightness using the precision wide-band dipole antenna to provide an improved absolute calibration for the 150 MHz all-sky map of Landecker and Wielebinski: subtracting an offset of 21.4 K and scaling by a factor of 1.05 will reduce the overall offset error to 8 K (from 50 K) and scale error to 0.8% (from 5%). The SARAS measurement of the temperature spectral index is in the range ?2.3 to ?2.45 in the 110–175 MHz band and indicates that the region toward the Galactic bulge has a relatively flatter index.

Patra, Nipanjana; Subrahmanyan, Ravi; Sethi, Shiv; Udaya Shankar, N.; Raghunathan, A.

2015-03-01

123

Radio Astronomers Set New Standard for Accurate Cosmic Distance Measurement  

NASA Astrophysics Data System (ADS)

A team of radio astronomers has used the National Science Foundation's Very Long Baseline Array (VLBA) to make the most accurate measurement ever made of the distance to a faraway galaxy. Their direct measurement calls into question the precision of distance determinations made by other techniques, including those announced last week by a team using the Hubble Space Telescope. The radio astronomers measured a distance of 23.5 million light-years to a galaxy called NGC 4258 in Ursa Major. "Ours is a direct measurement, using geometry, and is independent of all other methods of determining cosmic distances," said Jim Herrnstein, of the National Radio Astronomy Observatory (NRAO) in Socorro, NM. The team says their measurement is accurate to within less than a million light-years, or four percent. The galaxy is also known as Messier 106 and is visible with amateur telescopes. Herrnstein, along with James Moran and Lincoln Greenhill of the Harvard- Smithsonian Center for Astrophysics; Phillip Diamond, of the Merlin radio telescope facility at Jodrell Bank and the University of Manchester in England; Makato Inoue and Naomasa Nakai of Japan's Nobeyama Radio Observatory; Mikato Miyoshi of Japan's National Astronomical Observatory; Christian Henkel of Germany's Max Planck Institute for Radio Astronomy; and Adam Riess of the University of California at Berkeley, announced their findings at the American Astronomical Society's meeting in Chicago. "This is an incredible achievement to measure the distance to another galaxy with this precision," said Miller Goss, NRAO's Director of VLA/VLBA Operations. "This is the first time such a great distance has been measured this accurately. It took painstaking work on the part of the observing team, and it took a radio telescope the size of the Earth -- the VLBA -- to make it possible," Goss said. "Astronomers have sought to determine the Hubble Constant, the rate of expansion of the universe, for decades. This will in turn lead to an estimate of the age of the universe. In order to do this, you need an unambiguous, absolute distance to another galaxy. We are pleased that the NSF's VLBA has for the first time determined such a distance, and thus provided the calibration standard astronomers have always sought in their quest for accurate distances beyond the Milky Way," said Morris Aizenman, Executive Officer of the National Science Foundation's (NSF) Division of Astronomical Sciences. "For astronomers, this measurement is the golden meter stick in the glass case," Aizenman added. The international team of astronomers used the VLBA to measure directly the motion of gas orbiting what is generally agreed to be a supermassive black hole at the heart of NGC 4258. The orbiting gas forms a warped disk, nearly two light-years in diameter, surrounding the black hole. The gas in the disk includes water vapor, which, in parts of the disk, acts as a natural amplifier of microwave radio emission. The regions that amplify radio emission are called masers, and work in a manner similar to the way a laser amplifies light emission. Determining the distance to NGC 4258 required measuring motions of extremely small shifts in position of these masers as they rotate around the black hole. This is equivalent to measuring an angle one ten-thousandth the width of a human hair held at arm's length. "The VLBA is the only instrument in the world that could do this," said Moran. "This work is the culmination of a 20-year effort at the Harvard Smithsonian Center for Astrophysics to measure distances to cosmic masers," said Irwin Shapiro, Director of that institution. Collection of the data for the NGC 4258 project was begun in 1994 and was part of Herrnstein's Ph.D dissertation at Harvard University. Previous observations with the VLBA allowed the scientists to measure the speed at which the gas is orbiting the black hole, some 39 million times more massive than the Sun. They did this by observing the amount of change in the wavelength of the radio wave

1999-06-01

124

Radio polarization measurement of meteor trail echoes during the 2012 Perseids  

NASA Astrophysics Data System (ADS)

We present radio polarization measurements of meteor trail echoes with a cross-polarized antenna of BRAMS, a network of radio receiving stations using forward scatter techniques to detect and characterize meteors.

Ranvier, Sylvain; Anciaux, Michel; Lamy, Herve; De Keyser, Johan; Calders, Stijn; Gamby, Emmanuel

2013-01-01

125

WIDEBAND MIMO MEASUREMENTS OF OUTDOOR NLOS CHANNELS  

E-print Network

communication; wideband channel sounder; mul- tipath delay profile; multiple-input-multiple-output channel capacity INTRODUCTION Multiple-input multiple-output (MIMO) communication systems with multiple antennas to simultaneously transmit multiple pseudo-random signals. Multiple receivers then receive the transmitted signals

Yang, Yaoqing "Lamar"

126

Indoor radio channel modeling and mitigation of fading effects using linear and circular polarized antennas in combination for smart home system at 868 MHz  

NASA Astrophysics Data System (ADS)

The markets for smart home products and services are expected to grow over the next years, driven by the increasing demands of homeowners considering energy monitoring, management, environmental controls and security. Many of these new systems will be installed in existing homes and offices and therefore using radio based systems for cost reduction. A drawback of radio based systems in indoor environments are fading effects which lead to a high variance of the received signal strength and thereby to a difficult predictability of the encountered path loss of the various communication links. For that reason it is necessary to derive a statistical path loss model which can be used to plan a reliable and cost effective radio network. This paper presents the results of a measurement campaign, which was performed in six buildings to deduce realistic radio channel models for a high variety of indoor radio propagation scenarios in the short range devices (SRD) band at 868 MHz. Furthermore, a potential concept to reduce the variance of the received signal strength using a circular polarized (CP) patch antenna in combination with a linear polarized antenna in an one-to-one communication link is presented.

Wunderlich, S.; Welpot, M.; Gaspard, I.

2014-11-01

127

Monitoring voltage-dependent charge displacement of Shaker B-IR K+ ion channels using radio frequency interrogation.  

PubMed

Here we introduce a new technique that probes voltage-dependent charge displacements of excitable membrane-bound proteins using extracellularly applied radio frequency (RF, 500 kHz) electric fields. Xenopus oocytes were used as a model cell for these experiments, and were injected with cRNA encoding Shaker B-IR (ShB-IR) K(+) ion channels to express large densities of this protein in the oocyte membranes. Two-electrode voltage clamp (TEVC) was applied to command whole-cell membrane potential and to measure channel-dependent membrane currents. Simultaneously, RF electric fields were applied to perturb the membrane potential about the TEVC level and to measure voltage-dependent RF displacement currents. ShB-IR expressing oocytes showed significantly larger changes in RF displacement currents upon membrane depolarization than control oocytes. Voltage-dependent changes in RF displacement currents further increased in ShB-IR expressing oocytes after ?120 µM Cu(2+) addition to the external bath. Cu(2+) is known to bind to the ShB-IR ion channel and inhibit Shaker K(+) conductance, indicating that changes in the RF displacement current reported here were associated with RF vibration of the Cu(2+)-linked mobile domain of the ShB-IR protein. Results demonstrate the use of extracellular RF electrodes to interrogate voltage-dependent movement of charged mobile protein domains--capabilities that might enable detection of small changes in charge distribution associated with integral membrane protein conformation and/or drug-protein interactions. PMID:21387000

Dharia, Sameera; Rabbitt, Richard D

2011-01-01

128

Monitoring Voltage-Dependent Charge Displacement of Shaker B-IR K+ Ion Channels Using Radio Frequency Interrogation  

PubMed Central

Here we introduce a new technique that probes voltage-dependent charge displacements of excitable membrane-bound proteins using extracellularly applied radio frequency (RF, 500 kHz) electric fields. Xenopus oocytes were used as a model cell for these experiments, and were injected with cRNA encoding Shaker B-IR (ShB-IR) K+ ion channels to express large densities of this protein in the oocyte membranes. Two-electrode voltage clamp (TEVC) was applied to command whole-cell membrane potential and to measure channel-dependent membrane currents. Simultaneously, RF electric fields were applied to perturb the membrane potential about the TEVC level and to measure voltage-dependent RF displacement currents. ShB-IR expressing oocytes showed significantly larger changes in RF displacement currents upon membrane depolarization than control oocytes. Voltage-dependent changes in RF displacement currents further increased in ShB-IR expressing oocytes after ?120 µM Cu2+ addition to the external bath. Cu2+ is known to bind to the ShB-IR ion channel and inhibit Shaker K+ conductance, indicating that changes in the RF displacement current reported here were associated with RF vibration of the Cu2+-linked mobile domain of the ShB-IR protein. Results demonstrate the use of extracellular RF electrodes to interrogate voltage-dependent movement of charged mobile protein domains — capabilities that might enable detection of small changes in charge distribution associated with integral membrane protein conformation and/or drug–protein interactions. PMID:21387000

Dharia, Sameera; Rabbitt, Richard D.

2011-01-01

129

ATS-6 satellite radio beacon measurements at Ootacamund, India  

NASA Technical Reports Server (NTRS)

ATS-6 radio beacon measurements of modulation phase and Faraday rotation made at Ootacamund, India in 1975-1976 are discussed with emphasis on the measurement and analysis errors. The modulation-phase errors are insensitive to the geomagnetic field and provide an accurate determination of the total columnar electron content. Comparison of modulation-phase measurements at different frequencies shows a minor sensitivity to the ATS-6 pitch angle. For the low geomagnetic latitude and nearly transverse propagation conditions of Ootacamund, the use of a fixed conversion coefficient gives an unreliable Faraday content. However, the Faraday rotation measurements may be used to determine the shape factor F, which provides information about the electron density height profile.

Davies, K.; Donnelly, R. F.; Grubb, R. N.; Rao, P. V. S. R.; Rastogi, R. G.; Deshpande, M. R.; Chandra, H.; Vats, H. O.; Sethia, G.

1979-01-01

130

PAD-MAC: Primary User Activity-Aware Distributed MAC for Multi-Channel Cognitive Radio Networks.  

PubMed

Cognitive radio (CR) has emerged as a promising technology to solve problems related to spectrum scarcity and provides a ubiquitous wireless access environment. CR-enabled secondary users (SUs) exploit spectrum white spaces opportunistically and immediately vacate the acquired licensed channels as primary users (PUs) arrive. Accessing the licensed channels without the prior knowledge of PU traffic patterns causes severe throughput degradation due to excessive channel switching and PU-to-SU collisions. Therefore, it is significantly important to design a PU activity-aware medium access control (MAC) protocol for cognitive radio networks (CRNs). In this paper, we first propose a licensed channel usage pattern identification scheme, based on a two-state Markov model, and then estimate the future idle slots using previous observations of the channels. Furthermore, based on these past observations, we compute the rank of each available licensed channel that gives SU transmission success assessment during the estimated idle slot. Secondly, we propose a PU activity-aware distributed MAC (PAD-MAC) protocol for heterogeneous multi-channel CRNs that selects the best channel for each SU to enhance its throughput. PAD-MAC controls SU activities by allowing them to exploit the licensed channels only for the duration of estimated idle slots and enables predictive and fast channel switching. To evaluate the performance of the proposed PAD-MAC, we compare it with the distributed QoS-aware MAC (QC-MAC) and listen-before-talk MAC schemes. Extensive numerical results show the significant improvements of the PAD-MAC in terms of the SU throughput, SU channel switching rate and PU-to-SU collision rate. PMID:25831084

Ali, Amjad; Piran, Md Jalil; Kim, Hansoo; Yun, Jihyeok; Suh, Doug Young

2015-01-01

131

Radio Telescopes' Precise Measurements Yield Rich Scientific Payoffs  

NASA Astrophysics Data System (ADS)

Having the sharpest pictures always is a big advantage, and a sophisticated radio-astronomy technique using continent-wide and even intercontinental arrays of telescopes is yielding extremely valuable scientific results in a wide range of specialties. That's the message delivered to the American Astronomical Society's meeting in Austin, Texas, by Mark Reid of the Harvard-Smithsonian Center for Astrophysics, a leading researcher in the field of ultra-precise astronomical position measurements. Very Long Baseline Interferometry provides extremely high precision that can extend use of the parallax technique to many more celestial objects. Parallax is a direct means of measuring cosmic distances by detecting the slight shift in an object’s apparent position in the sky caused by Earth’s orbital motion. Credit: Bill Saxton, NRAO/AUI/NSF "Using radio telescopes, we are measuring distances and motions of celestial bodies with unprecedented accuracy. That's helping us better understand many processes ranging from star formation to the scale of the entire Universe," Reid said. The observing technique, called Very Long Baseline Interferometry (VLBI), was pioneered in 1967, but has come into continuous use only in the past 10-15 years. The National Science Foundation's Very Long Baseline Array (VLBA), a system of 10 radio-telescope antennas ranging from Hawaii to the Caribbean, was dedicated in 1993. There are other VLBI systems in Europe and Asia, and large radio telescopes around the world cooperate regularly to increase sensitivity. VLBI observations routinely produce images hundreds of times more detailed than those made at visible-light wavelengths by the Hubble Space Telescope. Several groups of researchers from across the globe use the VLBA to study stellar nurseries in our own Milky Way Galaxy and measure distances to regions where new stars are forming. The key has been to improve measurement accuracy to a factor of a hundred times better than that produced by the highly successful Hipparcos satellite. Using small clouds of gas in star-forming regions that strongly amplify radio waves, called cosmic masers, the astronomers measured the tiny shift in the object's position in the sky caused by the Earth's orbit around the sun. This, in turn, yielded highly-accurate distances by the simple surveying technique of triangulation, the "gold standard" of distance measuring techniques available to astronomers. Dr. Mark Reid Dr. Mark Reid Credit: CfA Click image for high-resolution file (1.02 MB) "Knowing the distance accurately means we also know the luminosities, masses and ages of the young stars much more accurately, and that is vital to understanding how star formation works," Reid said. In addition, he pointed out, the VLBA observations have shown the motions of the young stars in the Milky Way are much more complicated than simple circular motion. Massive young stars appear to be born orbiting the Milky Way considerably slower than older stars. "This might be explained by the interaction of giant molecular clouds, the ultimate sites of massive star formation, as they "surf" spiral density waves in the Milky Way." An international team of scientists led by Reid has used VLBI to detect the slight change in apparent position of the object at the Milky Way's center caused by our Solar System's orbit around that center. "It takes our Solar System more than 200 million years to circle the center of our Galaxy, and yet we can detect that motion in only a couple weeks with the VLBA -- truly astounding!" Reid said. The VLBA studies of the Galactic Center have shown that an object called Sagittarius A* is at the exact gravitational center of our Galaxy. That means, the scientists say, that the object must be incredibly massive. "The VLBA measurements, combined with infrared observations of stellar orbits around this object, provide overwhelming evidence that it's a supermassive black hole," Reid explained. "These observations are also going to make it possibl

2008-01-01

132

The finescale structure of the global tropopause derived from COSMIC GPS radio occultation measurements  

E-print Network

The finescale structure of the global tropopause derived from COSMIC GPS radio occultation of the lapserate tropopause is examined by using stateoftheart Global Positioning System radio occultation structure of the global tropopause derived from COSMIC GPS radio occultation measurements, J. Geophys. Res

Son, Seok-Woo

133

Generalized formalisms of the radio interferometer measurement equation  

NASA Astrophysics Data System (ADS)

The radio interferometer measurement equation (RIME) is a matrix-based mathematical model that describes the response of a radio interferometer. The Jones calculus it employs is not suitable for describing the analogue components of a telescope. This is because it does not consider the effect of impedance mismatches between components. This paper aims to highlight the limitations of Jones calculus, and suggests some alternative methods that are more applicable. We reformulate the RIME with a different basis that includes magnetic and mixed coherency statistics. We present a microwave network inspired 2N-port version of the RIME, and a tensor formalism based upon the electromagnetic tensor from special relativity. We elucidate the limitations of the Jones-matrix-based RIME for describing analogue components. We show how measured scattering parameters of analogue components can be used in a 2N-port version of the RIME. In addition, we show how motion at relativistic speed affects the observed flux. We present reformulations of the RIME that correctly account for magnetic field coherency. These reformulations extend the standard formulation, highlight its limitations, and may have applications in space-based interferometry and precise absolute calibration experiments.

Price, D. C.; Smirnov, O. M.

2015-05-01

134

Propagation measurements for the aeronautical satellite channel  

Microsoft Academic Search

Although there is a variety of system design proposals for aeronautical satellite communications, only a few field trials have been accomplished to investigate the behaviour of the aeronautical satellite transmission channel. The German Aerospace Research Establishment (DFVLR) finished in May 86 an extensive test program to provide necessary information for a system design. Over one thousand minutes of useable test

Andreas Neul; Joachim Hagenauer; Wolfgang Papke; Frank Dolainsky; Franz Edbauer

1987-01-01

135

Radio-Frequency Rectification on Membrane Bound Pores  

E-print Network

We present measurements on direct radio-frequency pumping of ion channels and pores bound in bilipid membranes. We make use of newly developed microcoaxes, which allow delivering the high frequency signal in close proximity to the membrane bound proteins and ion channels. We find rectification of the radio-frequency signal, which is used to pump ions through the channels and pores.

Sujatha Ramachandran; Robert H. Blick; Daniel W. van der Weide

2007-09-12

136

Experimental comparison between centimeter- and millimeter-wave ultrawideband radio channels  

NASA Astrophysics Data System (ADS)

This paper analyzes radio wave propagation phenomena at two very different frequency bands: 2-10 GHz (centimeter wave) and 57-66 GHz (millimeter wave (mm-W)). The two frequency bands have been measured using the same equipment and under similar propagation conditions, such as path loss, root-mean-square delay spread, maximum excess delay, and Rician K factor, and their respective correlations compared. Obstructed line of sight situations have also been considered by using metal and cardboard obstructions. The statistical distributions, main specular reflections, and decay factors have been found similar for the two bands. However, the measured path loss, correlation in terms of electrical distances, and the K factor are higher for the millimeter-wave frequency band. Indeed, the importance of propagation mechanism changes from one band to the other, which must be considered in the design of future mm-W systems.

Martinez-Ingles, Maria-Teresa; Molina-Garcia-Pardo, Jose-Maria; Rodríguez, José-Víctor; Pascual-García, Juan; Juan-Llácer, Leandro

2014-06-01

137

Maximizing the utility of radio spectrum: Broadband spectrum measurements and occupancy model for use by cognitive radio  

NASA Astrophysics Data System (ADS)

Radio spectrum is a vital national asset; proper management of this finite resource is essential to the operation and development of telecommunications, radio-navigation, radio astronomy, and passive remote sensing services. To maximize the utility of the radio spectrum, knowledge of its current usage is beneficial. As a result, several spectrum studies have been conducted in urban Atlanta, suburban Atlanta, and rural North Carolina. These studies improve upon past spectrum studies by resolving spectrum usage by nearly all its possible parameters: frequency, time, polarization, azimuth, and location type. The continuous frequency range from 400MHz to 7.2 GHz was measured with a custom-designed system. More than 8 billion spectrum measurements were taken over several months of observation. A multi-parameter spectrum usage detection method was developed and analyzed with data from the spectrum studies. This method was designed to exploit all the characteristics of spectral information that was available from the spectrum studies. Analysis of the spectrum studies showed significant levels of underuse. The level of spectrum usage in time and azimuthal space was determined to be only 6.5 % for the urban Atlanta, 5.3 % for suburban Atlanta, and 0.8 % for the rural North Carolina spectrum studies. Most of the frequencies measured never experienced usage. Interference was detected in several protected radio astronomy and sensitive radio navigation bands. A cognitive radio network architecture to share spectrum with fixed microwave systems was developed. The architecture uses a broker-based sharing method to control spectrum access and investigate interference issues.

Petrin, Allen J.

138

Performance of narrowband CPM systems with limiter-discriminator-integrator detection and decision feedback equalization in mobile radio channels  

Microsoft Academic Search

A completely analytical approach is presented to achieve error probability analysis of limiter-discriminator-integrator (LDI) detection of binary continuous-phase modulation in a land mobile radio channel characterized by Rayleigh fading and Doppler effects. Optimum choice of the postdetection integration time is carried out when varying both system parameters and propagation characteristics, namely the Doppler shift. The improvements obtainable by means of

Oreste Andrisano; Marco Chiani; Roberto Verdone

1993-01-01

139

Radio-frequency measurement of an asymmetric single electron transistor  

NASA Astrophysics Data System (ADS)

Since the invention of the radio-frequency single-electron transistor (RF-SET) by Schoelkopf et al.,[1] most measurements have focused on the symmetric single electron transistor. It has been shown, however, that the symmetric SET has a rather low measurement efficiency in its normal working regime.[2][3] Recently, it has been pointed out that an asymmetric SET can be considerably more efficient than a symmetric SET as a quantum amplifier. In this case the measurement efficiency of the asymmetric SET becomes similar to that of the quantum point contact (QPC) detector which can approach the quantum limit. We investigate the asymmetric SET by fabricating Al/AlOx SETs with junction areas 40x40 nm^2 and 40x80nm^2 and total resistance of about 25k?. The results of RF and DC characterization of such asymmetric SETs will be discussed. [1] R. J. Schoelkopf, P. Wahlgren, A. A. Kozhevnikov, P. Delsing, D. E. Prober, Science, 280, 1242 (1998). [2] A. N. Korotkov, Phys. Rev. B, 63, 085312 (2001); 63, 115403 (2001). [3] D. Mozyrsky, I. Martin, and M. B. Hastings, Phys. Rev. Lett., 92, 018303 (2004). [4] S. A. Gurvitz and G. P. Berman, Phys. Rev. B, 72 , 073303(2005).

Ji, Zhongqing; Xue, Weiwei; Rimberg, A. J.

2007-03-01

140

Potential radio frequency interference with the GPS L5 band for radio occultation measurements  

NASA Astrophysics Data System (ADS)

Future radio occultation (RO) receivers are planned to utilize the newly implemented Global Positioning System (GPS) L5 band centered at 1176.45 MHz. Since there are currently no operational GPS L5 receivers used for space-based RO applications, the interference environment is unclear. Distance measuring equipment (DME) and tactical air navigation (TACAN) stations share the same frequency band as GPS L5. The signals from these stations have been identified as possible sources of interference for any GPS L5 receiver, including those used in RO applications. This study utilizes Systems Tools Kit (STK) simulations to gain insight into the power received by a RO satellite in low Earth orbit (LEO) from a DME-TACAN transmission as well as the amount of interfering stations. In order to confirm the validity of utilizing STK for communication purposes, a theoretical scenario was recreated as a simulation and the results were confirmed. Once the method was validated, STK was used to output a received power level aboard a RO satellite from a DME-TACAN station as well as a tool to detail the number of interfering DME-TACAN stations witnessed by a space-based RO receiver over time. The results indicated a large number of DME-TACAN stations transmitting at similar orientations as a receiving RO satellite, thereby leading to the possibility of signal degradation in an unclear interference environment.

Wolff, A. M.; Akos, D. M.; Lo, S.

2014-11-01

141

Prediction of uncertainties in atmospheric properties measured by radio occultation experiments  

E-print Network

Prediction of uncertainties in atmospheric properties measured by radio occultation experiments occultation experiments measure time series of these frequency shifts, from which Ne and nn can be determined with the uncertainties of the radio occultation experiment on Mars Global Sur- veyor. These expressions can be used

Withers, Paul

142

Walkie-Talkie Measurements for the Speed of Radio Waves in Air  

ERIC Educational Resources Information Center

A handheld emitter-receiver device suitable for the direct estimation of the velocity of radio waves in air is presented. The velocity of radio waves is measured using the direct time-of-flight method, without the need for any tedious and precise settings. The results for two measurement series are reported. Both sets of results give an estimate…

Dombi, Andra; Tunyagi, Arthur; Neda, Zoltan

2013-01-01

143

An in situ measurement of the radio-frequency attenuation in ice at Summit Station, Greenland  

E-print Network

We report an in situ measurement of the electric field attenuation length at radio frequencies for the bulk ice at Summit Station, Greenland, made by broadcasting radio-frequency signals vertically through the ice and measuring the relative power in the return ground bounce signal. We find the depth-averaged field attenuation length to be 947 +92/-85 meters at 75 MHz. While this measurement has clear radioglaciological applications, the radio clarity of the ice also has implications for the detection of ultra-high energy (UHE) astrophysical particles via their radio emission in dielectric media such as ice. The measured attenuation length at Summit Station is comparable to previously measured radio-frequency attenuation lengths at candidate particle detector sites around the world, and strengthens the case for Summit Station as the most promising northern site for UHE neutrino detection.

J. Avva; J. M. Kovac; C. Miki; D. Saltzberg; A. G. Vieregg

2014-09-30

144

Measurement of multipath delay profile in land mobile satellite channels  

NASA Technical Reports Server (NTRS)

Mobile satellite communication channel has been evaluated mainly with fading statistics of signal. When bandwidth of transmitting signal becomes wider, frequency selectivity of fading becomes a significant factor of the channel. Channel characteristics, not only signal variation but multipath delay spread should be evaluated. A multipath measurement system is proposed and developed for mobile satellite applications. With this system and ETS-V satellite, multipath delay profiles are measured in various environments including Tokyo metropolis and Sapporo city at 1.5 GHz. Results show that the maximum excess delay is within 1 microsec and the maximum delay spread is 0.2 microsecs at elevation angles of 40 to 47 degrees. In wideband signal transmission of about 1 MHz and more, designers should consider the effect of selective fading due to the multipath of land mobile satellite channel.

Ikegami, Tetsushi; Arakaki, Yoshiya; Wakana, Hiromitsu; Suzuki, Ryutaro

1993-01-01

145

A wireless multi-channel bioimpedance measurement system for personalized healthcare and lifestyle.  

PubMed

Miniaturized, noninvasive, wearable sensors constitute a fundamental prerequisite for pervasive, predictive, and preventive healthcare systems. In this sense, this paper presents the design, realization, and evaluation of a wireless multi-channel measurement system based on a cost-effective high-performance integrated circuit for electrical bioimpedance (EBI) measurements in the frequency range from 1 kHz to 1 MHz. The resulting on-chip spectrometer provides high measuring EBI capabilities and together with a low-cost, commercially available radio frequency transceiver device. It provides reliable wireless communication, constitutes the basic node to build EBI wireless sensor networks (EBI-WSNs). The proposed EBI-WSN behaves as a high-performance wireless multi-channel EBI spectrometer, where the number of channels is completely scalable and independently configurable to satisfy specific measurement requirements of each individual. A prototype of the EBI node leads to a very small printed circuit board of approximately 8 cm2 including chip-antenna, which can operate several years on one 3-V coin cell battery and make it suitable for long-term preventive healthcare monitoring. PMID:23739358

Ramos, Javier; Ausín, José Luis; Lorido, Antonio Manuel; Redondo, Francisco; Duque-Carrillo, Juan Francisco

2013-01-01

146

Simultaneous Multiplexing and Demultiplexing of Wavelength-Interleaved Channels in DWDM Millimeter-Wave Fiber-Radio Networks  

NASA Astrophysics Data System (ADS)

A simultaneous multiplexing and demultiplexing (MUX/DEMUX) scheme for wavelength-interleaved millimeter-wave 37.5-GHz-band fiber-radio channels spaced at 25 GHz has been proposed. The proposed MUX/DEMUX technique potentially realizes simple, compact, and low-cost central office and remote nodes by avoiding the use of wavelength-selective pre-and postprocessing hardware. The novel scheme incorporates an arrayed-waveguide grating with multiple loop-backs between the input and the output ports, in addition to multiple optical circulators and optical isolators. The multiplexing functionality of the proposed technology enables a carrier subtraction technique and consequently reduces the carrier-to-sideband ratios of the multiplexed channels. Multiplexing of the uplink channels generated via several methods is demonstrated experimentally. These techniques include generation of the channels by using the optical carriers that correspond to wavelengths spaced at the free spectral range (FSR) or multiples of the FSR from the downlink (DL) optical carriers and reuse of the DL optical carriers that are recovered by applying a wavelength reuse technique (?UL = ?DL pm n × FSR, where n = 0, 1, 2, 3, ldots). The demultiplexing functionality of the proposed scheme that separates the 37.5-GHz-band wavelength-interleaved DL channels spaced at 25 GHz is also demonstrated. In addition, the effect of optical crosstalk on the transmission performance of the demultiplexed channels is also characterized experimentally.

Bakaul, Masuduzzaman; Nirmalathas, Ampalavanapillai Thas; Lim, Christina; Novak, Dalma; Waterhouse, Rod B.

2006-09-01

147

Residence times and diel passage distributions of radio-tagged juvenile spring chinook salmon and steelhead in a gatewell and fish collection channel of a Columbia River Dam  

USGS Publications Warehouse

The amount of time radio-tagged juvenile spring chinook salmon Oncorhynchus tshawytscha and juvenile steelhead O. mykiss spent within a gatewell and the juvenile collection channel at McNary Dam, Columbia River, USA, was measured to determine the diel passage behavior and residence times within these portions of the juvenile bypass system. The median gatewell residence times were 8.9 h for juvenile chinook salmon and 3.2 h for steelhead. Juvenile spring chinook salmon spent 83% of their time in the 18-m-deep gatewell at depths of 9 m or less, and juvenile steelhead spent 96% of their time in the upper 11 m. Fish released during midday and those released in the evening generally exited the gatewell in the evening, indicating that fish entering the gatewell during daylight will have prolonged residence times. Median collection-channel residence times of juvenile chinook salmon were much shorter (2.3 min) than those of steelhead (28.0 min), most likely because of the greater size of the steelhead and the high water velocities within the channel (2.1 m/s). This and other studies indicate most juvenile salmonids enter gatewells of several Columbia and Snake river dams in the evening and pass into the collection channels quickly. However, this is not consistent with the natural in-river migration patterns of these species and represents a delay in dam passage.

Beeman, J.W.; Maule, A.G.

2001-01-01

148

A measurement based Markov model for the indoor propagation channel  

Microsoft Academic Search

The assessment of a first order Markov model for data transmission on an indoor fading channel is investigated, on the basis of experimental data. The data have been obtained during the processing of a frequency profile database, stored during a broadband indoor measurement campaign in the 1.7-2.2 GHz band. The measurement has been carried on in a way, such that

F. Babich; G. Lornbardi

1997-01-01

149

Spectroscopic Measurements of Radio Frequency Plasmas in Supercritical Fluids  

SciTech Connect

Spectroscopic measurements of radio frequency (rf) plasma were performed under high pressure CO{sub 2} conditions (5 and 7 MPa) and supercritical (sc)CO{sub 2} conditions (8-20 MPa). The temperatures evaluated from C{sub 2} Swan bands increased from 3600 K to 4600 K with increasing pressure. The broadening and shifting of the O I line profile ({approx}777 nm) of rf plasma was observed under scCO{sub 2} conditions. The width of the line profile increased with increasing pressure. The reason for the broadening and shifting is still unclear because the present theory used to explain them is not valid for such high pressure conditions. Further, the broadening of the Ar I line profile ({approx}811.5 nm) in rf plasmas was observed under atmospheric Ar (0.1 MPa), high pressure Ar conditions (1-4 MPa), and scAr condition (5 MPa); the observation of the O I line profile in CO{sub 2} plasmas is difficult in this pressure range owing to its weak intensity therein. Similar to the case of the O I line in CO{sub 2} plasmas, the reason for the broadening of the Ar I line profile at 5 MPa is unclear.

Maehara, Tsunehiro [Graduate School of Science and Engineering, Ehime University, Matsuyama 790-8577 (Japan); Iwamae, Atsushi [Graduate School of Engineering, Kyoto University, Kyoto 606-8501 (Japan); Kawashima, Ayato [Faculty of Agriculture, Ehime University, Matsuyama 790-8566 (Japan)

2010-10-29

150

Packet Switching in Radio Channels: Part II--The Hidden Terminal Problem in Carrier Sense Multiple-Access and the Busy-Tone Solution  

Microsoft Academic Search

We consider a population of terminals communicating with a central station over a packet-switched multiple-access radio channel. The performance of carrier sense multiple access (CSMA) [1] used as a method for multiplexing these terminals is highly dependent on the ability of each terminal to sense the carrier of any other transmission on the channel. Many situations exist in which some

F. A. Tobagi; L. Kleinrock

1975-01-01

151

Cooperative Sensing in Cognitive Radio Networks-Avoid Non-Perfect Reporting Channel  

Microsoft Academic Search

Problem statement: Cognitive radio is a candidate technology for more efficient spectrum utilization systems based on opportunistic spectrum sharing. However, a common assumption regarding cognitive radios is that they are unlicen sed spectrum users that should defer to (avoid interfering with) existing primary sources. Therefo re effective sensing of primary users was a major focus of current research. Cooperative spectrum

Rania A. Mokhtar; Sabira Khatun; B. M. Ali; A. Ramli

2009-01-01

152

Decentralized Channel Management in Scalable Multihop Spread-Spectrum Packet Radio Networks  

Microsoft Academic Search

This thesis addresses the problems of managing the transmissions of stations in aspread-spectrum packet radio network so that the system can remain effective whenscaled to millions of nodes concentrated in a metropolitan area. The principal difficultyin scaling a system of packet radio stations is interference from other stations inthe system. Interference comes both from nearby stations and from distant stations.Each

Timothy Jason Shepard

1995-01-01

153

A Channel Access Scheme for Large Dense Packet Radio Networks Timothy J. Shepard \\Lambda  

E-print Network

. In this paper we present a model that more closely approximates communication theory and the underlying physics packet radio networks that is free of packet loss due to collisions and that at each hop requires no per? Can a large number (millions) of packet radio sta­ tions concentrated in a metropolitan­sized area

154

MEASURING THE JET POWER OF FLAT-SPECTRUM RADIO QUASARS  

SciTech Connect

We use frequency-dependent position shifts of flat-spectrum radio cores to estimate the kinetic power of active galactic nucleus (AGN) jets. We find a correlation between the derived jet powers and AGN narrow-line luminosity, consistent with the well-known relation for radio galaxies and steep spectrum quasars. This technique can be applied to intrinsically weak jets even at high redshift.

Shabala, S. S.; Santoso, J. S. [School of Mathematics and Physics, University of Tasmania, Private Bag 37, Hobart, TAS 7001 (Australia); Godfrey, L. E. H. [International Centre for Radio Astronomy Research, Curtin University, GPO Box U1987, Perth, Western Australia 6845 (Australia)

2012-09-10

155

Measurement of the radius of Mercury by radio occultation during the MESSENGER flybys  

E-print Network

Measurement of the radius of Mercury by radio occultation during the MESSENGER flybys Mark E. Perry: Mercury MESSENGER Occultation RF Radius a b s t r a c t The MErcury Surface, Space ENvironment, occulting the radio-frequency (RF) transmis- sions. The occultation start and end times, recovered with 0

Zuber, Maria

156

At-sea distribution of radio-marked Ashy Storm-Petrels Oceanodroma homochroa captured on the California Channel Islands  

USGS Publications Warehouse

Small, rare and wide-ranging pelagic birds are difficult to locate and observe at sea; little is therefore known regarding individual movements and habitat affinities among many of the world's storm-petrels (Family Hydrobatidae). We re-located 57 of 70 radio-marked Ashy Storm-Petrels Oceanodroma homochroa captured at three colonies in the California Channel Islands: Scorpion Rocks (2004, 2005), Santa Barbara Island (2004) and Prince Island (2005). Between 23 July and 22 September 2004, and 5 July and 4 August 2005, we flew 29 telemetry surveys, covered more than 65 000 km2 (2004) and 43 000 km2 (2005) of open ocean from San Nicolas Island north to the Farallon Islands and obtained 215 locations from 57 storm-petrels at sea. In both years, radio-marked storm-petrels were aggregated over the continental slope from Point Conception to Point Buchon, within the western Santa Barbara Channel, and over the Santa Cruz Basin between Santa Cruz, San Nicolas and Santa Barbara islands. Individuals captured in the Channel Islands ranged more than 600 km and were located as far north as Gulf of the Farallones National Marine Sanctuary. This is the first study to use radiotelemetry to determine the at-sea distribution and movements for any storm-petrel species.

Adams, J.; Takekawa, J.Y.

2008-01-01

157

A fully implantable multi-channel biotelemetry system for measurement of blood flow and temperature: a first evaluation in the green sturgeon  

Microsoft Academic Search

The objective of this study was to evaluate a novel fully implantable radio-based blood flow biotelemetry system which allows\\u000a simultaneously measurement of blood flow on two channels and temperature on one channel, in fish. These are the first recordings\\u000a of blood flow from free-swimming fish, showing that the system is capable of recording blood flow in the ventral aorta (cardiac

A. Gräns; M. Axelsson; K. Pitsillides; C. Olsson; J. Höjesjö; R. C. Kaufman; J. J. Cech

2009-01-01

158

Distributed channel assignment strategies using coexistence etiquettes for land based radio environment  

Microsoft Academic Search

The performance of two distributed channel assignment algorithms which use coexistenceetiquettes for point to point links have been considered. It has been found that selectingchannels prior to transmission at the transmitter as opposed to the receiver supportsgreater offered traffic with the additional advantage of a less complex protocol.1 IntroductionMany distributed channel assignment schemes select channels based on the signal strength

D. Grace; A. G. Burr; T. C. Tozer

1996-01-01

159

Integrated predictive power control and dynamic channel assignment in mobile radio systems  

Microsoft Academic Search

It is known that dynamic allocation of channels and power in a frequency\\/time-division multiple access system can improve performance and achieve higher capacity. Various algorithms have been separately proposed for dynamic channel assignment (DCA) and power control. Moreover, integrated dynamic channel and power allocation (DCPA) algorithms have already been proposed based on simple power control algorithms. In this paper, we

Kambiz Shoarinejad; Jason L. Speyer; Gregory J. Pottie

2003-01-01

160

Radio Occultation Measurements with the Mars Reconnaissance Orbiter  

NASA Astrophysics Data System (ADS)

The Mars Reconnaissance Orbiter (MRO) circles Mars in a low-altitude, sun-synchronous, polar orbit, crossing the equator at local times of about 3 and 15 h. There are frequent opportunities for radio occultation (RO) sounding of the martian atmosphere, which has been conducted routinely since January 2008. Observations are limited to one orbit per day, so as to minimize the impact on transmission of data collected by the primary scientific instruments. We are retrieving atmospheric profiles from the MRO RO data, and we are delivering the results to the NASA Planetary Data System (PDS) for archiving and public distribution. The value of these RO profiles derives from their combination of accurate absolute calibration, excellent vertical resolution (about 500 m), and accurate registration in radius. The first attribute qualifies the RO profiles as a reliable standard for cross-instrument calibration, and comparisons are underway with atmospheric observations by the MRO Mars Climate Sounder (MCS). The second attribute yields unique insight into the structure and dynamics of the lower atmosphere (0-10 km) and its interaction with surface reservoirs of dust and volatiles. The third attribute allows precise measurements of geopotential height and surface pressure, which constrain the mass distribution of the atmosphere and its seasonal variations. These attributes also enable long-term monitoring of interannual variability and climatic trends. We will characterize the spatial and seasonal coverage of the observations to date, and we will illustrate the atmospheric phenomena captured by the MRO RO profiles. This research is funded in part by Grant NNX12AL48G of the Mars Data Analysis Program.

Hinson, David P.; Asmar, S.; Kahan, D.; Akopian, V.; Maalouf, S.

2012-10-01

161

Radio telescopes  

Microsoft Academic Search

A radio telescope is used in radio astronomy to measure the intensity of the radiation received from various parts of the sky. Such a telescope must be able both to detect and to locate faint radio sources of small angular size, and also to measure the brightness distribution across extended radio sources or over large sky areas. Ideally the telescope

J. Findlay

1964-01-01

162

Experimental Validation of Channel State Prediction Considering Delays in Practical Cognitive Radio  

E-print Network

Radio Zhe Chen, Nan Guo, Senior Member, IEEE, Zhen Hu, and Robert C. Qiu, Senior Member, IEEE Abstract-permissions@ieee.org. Zhe Chen, Zhen Hu, and Robert C. Qiu are with the Department of Electrical and Computer Engineering

Qiu, Robert Caiming

163

Designing a Hardware in the Loop Wireless Digital Channel Emulator for Software Defined Radio  

E-print Network

), and increasing resilience against multipath, Doppler shift, and fading. Software defined radios (SDR) use agile. They can operate over different frequency band and have been proposed for next generation military

Kastner, Ryan

164

Analysis of satellite measurements of terrestrial radio noise  

NASA Technical Reports Server (NTRS)

Worldwide distributions of terrestrial radio noise as monitored by Radio Astronomy Explorer 1 (RAE 1) generated and compared with CCIR predictions. These contour maps show the global morphology of radio noise at 6.55 and 9.18 MHz for fall, winter, spring and summer during the local time blocks of 00-08 LT and 16-24 LT. These computer produced maps show general agreement with CCIR predictions over large land masses. The RAE and CCIR maps diverge at high latitudes over Asia and frequently over ocean regions. Higher noise levels observed by RAE at high latitudes are attributed to magnetospheric emission while higher noise levels observed by RAE over Asia are attributable to high power transmitters. Analysis of RAE noise observations in conjunction with various geophysical phenomena showed no obvious correlation.

Bakalyar, G.; Caruso, J. A.; Vargas-Vila, R.; Ziemba, E.

1974-01-01

165

Analysis of wireless sensor network topology and estimation of optimal network deployment by deterministic radio channel characterization.  

PubMed

One of the main challenges in the implementation and design of context-aware scenarios is the adequate deployment strategy for Wireless Sensor Networks (WSNs), mainly due to the strong dependence of the radiofrequency physical layer with the surrounding media, which can lead to non-optimal network designs. In this work, radioplanning analysis for WSN deployment is proposed by employing a deterministic 3D ray launching technique in order to provide insight into complex wireless channel behavior in context-aware indoor scenarios. The proposed radioplanning procedure is validated with a testbed implemented with a Mobile Ad Hoc Network WSN following a chain configuration, enabling the analysis and assessment of a rich variety of parameters, such as received signal level, signal quality and estimation of power consumption. The adoption of deterministic radio channel techniques allows the design and further deployment of WSNs in heterogeneous wireless scenarios with optimized behavior in terms of coverage, capacity, quality of service and energy consumption. PMID:25664434

Aguirre, Erik; Lopez-Iturri, Peio; Azpilicueta, Leire; Astrain, José Javier; Villadangos, Jesús; Falcone, Francisco

2015-01-01

166

Optimal throughput for cognitive radio with energy harvesting in fading wireless channel.  

PubMed

Energy resource management is a crucial problem of a device with a finite capacity battery. In this paper, cognitive radio is considered to be a device with an energy harvester that can harvest energy from a non-RF energy resource while performing other actions of cognitive radio. Harvested energy will be stored in a finite capacity battery. At the start of the time slot of cognitive radio, the radio needs to determine if it should remain silent or carry out spectrum sensing based on the idle probability of the primary user and the remaining energy in order to maximize the throughput of the cognitive radio system. In addition, optimal sensing energy and adaptive transmission power control are also investigated in this paper to effectively utilize the limited energy of cognitive radio. Finding an optimal approach is formulated as a partially observable Markov decision process. The simulation results show that the proposed optimal decision scheme outperforms the myopic scheme in which current throughput is only considered when making a decision. PMID:24574885

Vu-Van, Hiep; Koo, Insoo

2014-01-01

167

Tracking of Time-varying Mobile Radio Channels with WLMS Algorithms: A Case Study on D-AMPS 1900 Channels  

E-print Network

Channels Mikael Sternad #3; , Lars Lindbom 1 and Anders Ahl#19;en #3; #3; Signals and Systems, Uppsala@signal.uu.se, Lars.Lindbom@ein.ericsson.se, aa@signal.uu.se Abstract - Low-complexity WLMS adaptation algo- rithms. Furthermore, large variations in fading rates and frequency selectivity are encoun- tered, so well designed

168

Wideband channel measurement and characterisation for wireless local loops  

Microsoft Academic Search

The multipath characteristics of the wireless local loop (WLL) channel were studied over both short and long time periods in urban and sub-urban high-rise and small-house environments. Wideband measurements were performed at a centre frequency of 1.3 GHz with a sliding correlation measurement system using a chip rate of 15 MHz. The receiver was situated at regular cellular base stations,

Jaakko Talvitie; Veikko Hovinen; Matti Hamaliiinen; Ian Oppermann

1996-01-01

169

Statistical modeling of the ultra wide band propagation channel through the analysis of experimental measurements  

NASA Astrophysics Data System (ADS)

For the development of future Ultra Wide Band (UWB) communication systems, realistic modeling of the propagation channel is necessary. This article presents an experimental study of the UWB radio channel, based on an extensive sounding campaign covering the indoor office environment. We consider the main characteristics of the UWB channel by studying the propagation loss and wide band parameters, such as the delay spread and the power delay profile decay. From this analysis, we propose a statistical channel model reproducing the UWB channel effects over the frequency bandwidth 3.1-10.6 GHz. To cite this article: P. Pagani, P. Pajusco, C. R. Physique 7 (2006).

Pagani, Pascal; Pajusco, Patrice

2006-09-01

170

Combining Radio Occultation Measurements with Other Instruments to Map the Ionospheric Electron  

E-print Network

tomography. Images showing travelling ionospheric disturbances (TIDs) (Pryse et al. [1995]) have beenCombining Radio Occultation Measurements with Other Instruments to Map the Ionospheric Electron imaging program for the atmosphere and ionosphere. This analysis algorithm can routinely use dual

171

Measuring bankfull channel features, bed sediment, and bed load  

NSDL National Science Digital Library

This class exercise is an opportunity for students to gain valuable field experiences and develop fieldwork skills. The goal is to have students compare their measurements of a bankfull channel and its bed sediments with theoretical values that might imply whether the channel is 'adjusted' or is out of equilibrium with its setting. This is accomplished by having the students calculate a bankfull Shields stress value and then compare that value with both: (1) a theoretical range of values that might comprise an 'adjusted' condition, and (2) experimental values for the minimal Shields stress required to entrain bed grains of different sizes. They are then to evaluate whether the channel is stable or not. Designed for a geomorphology course

Jordan Clayton

172

Multi-channel multi-radio using 802.11 based media access for sink nodes in wireless sensor networks.  

PubMed

The next generation surveillance and multimedia systems will become increasingly deployed as wireless sensor networks in order to monitor parks, public places and for business usage. The convergence of data and telecommunication over IP-based networks has paved the way for wireless networks. Functions are becoming more intertwined by the compelling force of innovation and technology. For example, many closed-circuit TV premises surveillance systems now rely on transmitting their images and data over IP networks instead of standalone video circuits. These systems will increase their reliability in the future on wireless networks and on IEEE 802.11 networks. However, due to limited non-overlapping channels, delay, and congestion there will be problems at sink nodes. In this paper we provide necessary conditions to verify the feasibility of round robin technique in these networks at the sink nodes by using a technique to regulate multi-radio multichannel assignment. We demonstrate through simulations that dynamic channel assignment scheme using multi-radio, and multichannel configuration at a single sink node can perform close to optimal on the average while multiple sink node assignment also performs well. The methods proposed in this paper can be a valuable tool for network designers in planning network deployment and for optimizing different performance objectives. PMID:22163883

Campbell, Carlene E-A; Khan, Shafiullah; Singh, Dhananjay; Loo, Kok-Keong

2011-01-01

173

Energy estimation for cosmic rays measured with the Auger Engineering Radio Array  

NASA Astrophysics Data System (ADS)

The Auger Engineering Radio Array (AERA) is located within the Pierre Auger Observatory and currently consists of 24 self-triggered radio stations. Observation of radio signals from cosmic rays is confirmed by the surface detector (SD) stations of the Observatory which provide well-calibrated information on the cosmic-ray energies and arrival directions. The response of the radio stations has been thoroughly calibrated to enable the reconstruction of the incoming electric field. For estimating the cosmic-ray energy we use the maximum absolute value of the measured electric field vector corrected for the incoming direction and the distance to the shower core. Performing a preliminary energy calibration using the SD information, we observe that the defined radio energy estimator provides an approximately linear dependency on the cosmic-ray energy.

Glaser, Christian; Pierre Auger Collaboration

2013-05-01

174

Radio-telepathy: extracting a secret key from an unauthenticated wireless channel  

Microsoft Academic Search

Securing communications requires the establishment of cryptographic keys, which is challenging in mobile scenarios where a key management infrastructure is not always present. In this paper, we present a protocol that allows two users to establish a common cryptographic key by exploiting special properties of the wireless channel: the underlying channel response between any two parties is unique and decorrelates

Suhas Mathur; Wade Trappe; Narayan B. Mandayam; Chunxuan Ye; Alex Reznik

2008-01-01

175

Technique to determine location of radio sources from measurements taken on spinning spacecraft  

NASA Technical Reports Server (NTRS)

The procedure developed to extract average source direction and average source size from spin-modulated radio astronomy data measured on the IMP-6 spacecraft is described. Because all measurements are used, rather than just finding maxima or minima in the data, the method is very sensitive, even in the presence of large amounts of noise. The technique is applicable to all experiments with directivity characteristics. It is suitable for onboard processing on satellites to reduce the data flow to Earth. The application to spin-modulated nonpolarized radio astronomy data is made and includes the effects of noise, background, and second source interference. The analysis was tested with computer simulated data and the results agree with analytic predictions. Applications of this method with IMP-6 radio data have led to: (1) determination of source positions of traveling solar radio bursts at large distances from the Sun; (2) mapping of magnetospheric radio emissions by radio triangulation; and (3) detection of low frequency radio emissions from Jupiter and Saturn.

Fainberg, J.

1979-01-01

176

A practical approach for channel problem detection and adaptation in tactical radio systems  

Microsoft Academic Search

Soldier-based tactical radio systems in the battlefield have tendencies to be severely affected by various phenomenon such as signal jamming and environment deterioration. This is because many types of wireless handheld and manpack devices carried by soldiers may not have efficient algorithms or the hardware for adapting the device to these conditions. Taking on the advantage that most of these

Woo-Sung Jung; Keun-Woo Lim; Young-Bae Ko; Yooseung Song; Sangjoon Park

2011-01-01

177

Optimal power allocation for fading channels in cognitive radio networks: Ergodic capacity and outage capacity  

Microsoft Academic Search

A cognitive radio network (CRN) is formed by either allowing the secondary users (SUs) in a secondary communication network (SCN) to opportunistically operate in the frequency bands originally allocated to a primary communication network (PCN) or by allowing SCN to coexist with the primary users (PUs) in PCN as long as the interference caused by SCN to each PU is

Xin Kang; Ying-chang Liang; Arumugam Nallanathan; Hari Krishna Garg; Rui Zhang

2009-01-01

178

Multistage block-spreading for impulse radio multiple access through ISI channels  

Microsoft Academic Search

Transmitting digital information using ultra-short pulses, impulse radio (IR) has received increasing interest for multiple access (MA). When IRMA systems have to operate in dense multipath environments, the multiple user interference (MUI) and intersymbol interference (ISI) induced, adversely affect system capacity and performance. Analog IRMA utilizes pulse position modulation (PPM) and random time-hopping codes to mitigate ISI and suppress MUI

Liuqing Yang; Georgios B. Giannakis

2002-01-01

179

Measurement of the top quark mass in the dilepton channel  

Microsoft Academic Search

We present a measurement of the top quark mass in the dilepton channel based\\u000aon approximately 370\\/pb of data collected by the D0 experiment during Run II of\\u000athe Fermilab Tevatron collider. We employ two different methods to extract the\\u000atop quark mass. We show that both methods yield consistent results using\\u000aensemble tests of events generated with the D0

V. M. Abazov; B. Abbott; M. Abolins; B. S. Acharya; M. Adams; T. Adams; M. Agelou; E. Aguilo; S. H. Ahn; M. Ahsan; G. D. Alexeev; G. Alkhazov; A. Alton; G. Alverson; G. Alverson; M. Anastasoaie; C. Barnes; J. Barreto; J. F. Bartlett; D. Bauer; S. Beale; A. Bean; M. Begalli; M. Begel; C. Belanger-Champagne; L. Bellantoni; A. Bellavance; J. A. Benitez; S. B. Beri; G. Bernardi; R. Bernhard; L. Berntzon; I. Bertram; M. Besancon; V. A. Bezzubov; P. Banerjee; V. Bhatnagar; M. Binder; C. Biscarat; I. Blackler; G. Blazey; F. Blekman; S. Blessing; D. Bloch; K. Bloom; A. Boehnlein; D. Boline; T. A. Bolton; G. Borissov; K. Bos; T. Bose; A. Bellavance; R. Brock; G. Brooijmans; A. Bross; D. Brown; N. J. Buchanan; D. Buchholz; M. Besançon; V.A. Bezzubov; S. Burdin; S. Burke; T. H. Burnett; E. Busato; C. P. Buszello; J. M. Butler; S. Calvet; J. Cammin; S. Caron; W. Carvalho; B. C. K. Casey; N. M. Cason; H. Castilla-Valdez; S. Chakrabarti; D. Chakraborty; K. M. Chan; A. Chandra; F. Charles; E. Cheu; F. Chevallier; D. K. Cho; S. Choi; B. Choudhary; L. Christofek; D. Claes; B. Clement; C. Clement; Y. Coadou; M. Cooke; W. E. Cooper; D. Coppage; M. Corcoran; S. Feher; D. Fein; T. Ferbel; G. Finocchiaro; H. E. Fisk; Y. Fisyak; E. Flattum; G. E. Forden; M. Fortner; K. C. Frame; S. Fuess; E. Gallas; A. N. Galyaev; P. Gartung; V. Gavrilov; T. L. Geld; R. J. Genik; K. Genser; C. E. Gerber; Y. Gershtein; B. Gibbard; B. Gobbi; B. Gomez; G. Gomez; P. I. Goncharov; J. L. Gonzalez Solis; H. Gordon; L. T. Goss; K. Gounder; A. Goussiou; N. Graf; P. D. Grannis; H. Greenlee; S. Grinstein; P. Grudberg; G. Guglielmo; J. A. Guida; J. M. Guida; S. N. Gurzhiev; G. Gutierrez; P. Gutierrez; N. J. Hadley; H. Haggerty; S. Hagopian; V. Hagopian; K. S. Hahn; P. Hanlet; S. Hansen; J. M. Hauptman; D. Hedin; A. P. Heinson; R. Hernandez-Montoya; T. Heuring; R. Hirosky; J. D. Hobbs; B. Hoeneisen; J. S. Hoftun; F. Hsieh; T. Huehn; A. S. Ito; E. James; J. Jaques; S. A. Jerger; R. Jesik; T. Joffe-Minor; K. Johns; M. Johnson; A. Jonckheere; M. Jones; H. Jostlein; S. Y. Jun; C. K. Jung; S. Kahn; G. Kalbfleisch; D. Karmanov; D. Karmgard; R. Kehoe; M. L. Kelly; S. K. Kim; B. Klima; C. Klopfenstein; W. Ko; J. M. Kohli; D. Koltick; A. V. Kostritskiy; J. Kotcher; A. V. Kotwal; A. V. Kozelov; E. A. Kozlovsky; J. Krane; M. R. Krishnaswamy; S. Krzywdzinski; S. Kuleshov; S. Kunori; F. Landry; G. Landsberg; A. Leflat; J. Li; Q. Z. Li-Demarteau; J. G. R. Lima; D. Lincoln; S. L. Linn; J. Linnemann; R. Lipton; F. Lobkowicz; S. C. Loken; A. Lucotte; L. Lueking; A. L. Lyon; A. K. A. Maciel; R. J. Madaras; L. Magana-Mendoza; V. Manankov; S. Mani; H. S. Mao; R. Markeloff; T. Marshall; M. I. Martin; A. A. Mayorov; R. McCarthy; J. McDonald; T. McKibben; J. McKinley; T. McMahon; H. L. Melanson; M. Merkin; K. W. Merritt; C. Miao; H. Miettinen; A. Mincer; C. S. Mishra; N. Mokhov; N. K. Mondal; H. E. Montgomery; P. Mooney; M. Mostafa; H. da Motta; C. Murphy; F. Nang; M. Narain; V. S. Narasimham; A. Narayanan; H. A. Neal; J. P. Negret; P. Nemethy; D. Norman; L. Oesch; V. Oguri; E. Oliveira; E. Oltman; N. Oshima; D. Owen; P. Padley; R. Partridge; N. Parua; Anoop Gupta; Y. Hu; Z. Hubacek; V. Hynek; I. Iashvili; R. Illingworth; A. S. Ito; S. Jabeen; M. Jaffré; S. Jain; K. Jakobs; C. Jarvis; A. Jenkins; C. Johnson; P. Jonsson; A. Juste; D. Käfer; E. Kajfasz; A. M. Kalinin; J. M. Kalk; J. R. Kalk; S. Kappler; J. Kasper; P. Kasper; I. Katsanos; D. Kau; R. Kaur; R. Kehoe; S. Kermiche; N. Khalatyan; A. Khanov; A. Kharchilava; Y. M. Kharzheev; D. Khatidze; H. Kim; T. J. Kim; M. H. Kirby; J.-P. Konrath; M. Kopal; V. M. Korablev; B. Kothari; A. Koubarovsky; D. Krop; A. Kryemadhi; T. Kuhl; A. Kumar; A. Kupco; T. Kur?a; J. Kvita; S. Lammers; J. Lazoflores; A.-C. Le Bihan; P. Lebrun; W. M. Lee; A. Leflat; F. Lehner; V. Lesne; J. Leveque; P. Lewis; Q. Z. Li; D. Lincoln; V. V. Lipaev; Z. Liu; L. Lobo; A. Lobodenko; M. Lokajicek; A. Lounis; P. Love; H. J. Lubatti; M. Lynker; P. Mättig; C. Magass; A. Magerkurth; N. Makovec; P. K. Mal; H. B. Malbouisson; S. Malik; V. L. Malyshev; Y. Maravin; M. Martens; R. McCarthy; D. Meder; A. Melnitchouk; L. Mendoza; M. Merkin; A. Meyer; J. Meyer; M. Michaut; T. Millet; J. Mitrevski; J. Monk; R. W. Moore; T. Moulik; G. S. Muanza; M. Mulders; M. Mulhearn; O. Mundal; L. Mundim; Y. D. Mutaf; E. Nagy; M. Naimuddin; N. A. Naumann; H. A. Neal; P. Neustroev; C. Noeding; A. Nomerotski; S. F. Novaes; T. Nunnemann; V. O'Dell; D. C. O'Neil; G. Obrant; N. Oliveira; D. Onoprienko; R. Otec; G. J. Otero y Garzón; M. Owen; N. Parashar; S.-J. Park; J. Parsons; A. Patwa; G. Pawloski; P. M. Perea; E. Perez; K. Peters; P. Pétroff; M. Petteni; R. Piegaia; J. Piper; M.-A. Pleier; P. L. M. Podesta-Lerma; V. M. Podstavkov; Y. Pogorelov; M.-E. Pol; A. Pompoš; B. G. Pope; A. V. Popov; C. Potter; W. L. Prado da Silva; H. B. Prosper; S. Protopopescu; J. Qian

2007-01-01

180

Characterizing radio channels : the science and technology of propagation and interference, 1900-1935  

E-print Network

Guglielmo Marconi's trans-Atlantic wireless experiment in 1900 marked the beginning of a communication revolution that transformed the open space above the earth into channels of information flow. This dissertation grapples ...

Yeang, Chen-Pang.

2004-01-01

181

FOREGROUND PREDICTIONS FOR THE COSMIC MICROWAVE BACKGROUND POWER SPECTRUM FROM MEASUREMENTS OF FAINT INVERTED RADIO SOURCES AT 5 GHz  

SciTech Connect

We present measurements of a population of matched radio sources at 1.4 and 5 GHz down to a flux limit of 1.5 mJy in 7 deg{sup 2} of the NOAO Deep Field South. We find a significant fraction of sources with inverted spectral indices that all have 1.4 GHz fluxes less than 10 mJy and are therefore too faint to have been detected and included in previous radio source count models that are matched at multiple frequencies. Combined with the matched source population at 1.4 and 5 GHz in 1 deg{sup -2} in the ATESP survey, we update models for the 5 GHz differential number counts and distributions of spectral indices in 5 GHz flux bins that can be used to estimate the unresolved point source contribution to the cosmic microwave background temperature anisotropies. We find a shallower logarithmic slope in the 5 GHz differential counts than in previously published models for fluxes {approx}< 100 mJy as well as larger fractions of inverted spectral indices at these fluxes. Because the Planck flux limit for resolved sources is larger than 100 mJy in all channels, our modified number counts yield at most a 10% change in the predicted Poisson contribution to the Planck temperature power spectrum. For a flux cut of 5 mJy with the South Pole Telescope and a flux cut of 20 mJy with the Atacama Cosmology Telescope, we predict a {approx}30% and {approx}10% increase, respectively, in the radio source Poisson power in the lowest frequency channels of each experiment relative to that predicted by previous models.

Schneider, Michael D. [Lawrence Livermore National Laboratory, P.O. Box 808 L-210, Livermore, CA 94551 (United States); Becker, Robert H. [Department of Physics, University of California, One Shields Avenue, Davis, CA 08991 (United States); De Vries, Willem [Lawrence Livermore National Laboratory, P.O. Box 808 L-211, Livermore, CA 94551 (United States); White, Richard L., E-mail: schneider42@llnl.gov [Space Telescope Science Institute, Baltimore, MD 21218 (United States)

2012-05-10

182

Outdoor radiolinks for 2.4 GHz-frequencies: measurement results and experiences within the radio communication network "Intermobil Region Dresden"  

NASA Astrophysics Data System (ADS)

The radio communication network "Intermobil Region Dresden" was developed and built up for data transmission of traffic videos and other traffic data. It uses Pointto- Point (PtP) and Point-to-Multipoint (PtM) bridges, forming the backbone structure. The traffic camera radio clients link up with Accesspoints, installed at the nodal points of the backbone. This paper analyses the physical and technical conditions, building up such radio communication networks. The radio channel properties (e.g. total path loss, multipath propagation) and the technical parameters (e.g. transmission power, sensitivity, antenna gain) belong to this conditions. Based on calculation and spreading measurements it is shown, that reserves have to be considered during the planning already. As well special problems, like Fresnel-zone clearance and shadowing are discussed. The choice of the antenna plays a key role for planning and building of wireless networks. It determines decisively the range and gives an important contribution to elimination of wireless disturbances (interferences). Dependent on topological facts, installation environment and wireless distance omnidirectional-, yagi-, patch- and parabol-antennas are used. Based on antenna measurements the paper discusses the use and property of decoupling. WLANs are working in the license free 2.4 GHz-band. The number of radio systems in this band increases permanently, which leads to a lot of interferences among each other. The paper makes a classification of possible interference sources and discusses their influence on transmission quality. Technical solutions are shown for increase interference robustness.

Michler, O.

2003-05-01

183

Joint Beamforming and Power Allocation for Multiple Access Channels in Cognitive Radio Networks  

Microsoft Academic Search

A cognitive radio (CR) network refers to a secondary network operating in a frequency band originally licensed\\/allocated to a primary network consisting of one or multiple primary users (PUs). A fundamental challenge for realizing such a system is to ensure the quality of service (QoS) of the PUs as well as to maximize the throughput or ensure the QoS, such

Lan Zhang; Ying-chang Liang; Yan Xin

2008-01-01

184

Global Cosmological Parameters Measured Using Classical Double Radio Sources  

E-print Network

Fourteen classical double radio galaxies with redshifts between zero and two were used to determine the cosmological parameters $\\Omega_m$, $\\Omega_{\\Lambda}$, and $\\Omega_k$, where these are the normalized values of the mean mass density, cosmological constant, and space curvature at the present epoch. A low value of $\\Omega_m$ is obtained, and $\\Omega_m = 1$ is ruled out with 97.5% confidence. The low value of $\\Omega_m$ determined using the radio source method described here is also indicated by several independent tests. Thus, it appears that either a cosmological constant, or space curvature, is significant at the present epoch. This means that the universe is undergoing, or has recently undergone, a transition away from a state of matter domination and into a state where either a cosmological constant or space curvature is determining the expansion rate of the universe. The low value of $\\Omega_m$ presented here and by Guerra & Daly (1998) means that we can state with 97.5 % confidence that the universe will continue to expand forever.

Ruth A. Daly; E. J. Guerra; Lin Wan

1998-03-23

185

Application of the Rasch model to measuring the performance of cognitive radios.  

PubMed

Cognitive radios (CRs) are recent technological developments that rely on artificial intelligence to adapt a radio's performance to suit environmental demands, such as sharing radio frequencies with other radios. Measuring the performance of the cognitive engines (CEs) that underlie a CR's performance is a challenge for those developing CR technology. This simulation study illustrates how the Rasch model can be applied to the evaluation of CRs. We simulated the responses of 50 CEs to 35 performance tasks and applied the Random Coefficients Multidimensional Multinomial Logit Model (MRCMLM) to those data. Our results indicate that CEs based on different algorithms may exhibit differential performance across manipulated performance task parameters. We found that a multidimensional mixture model may provide the best fit to the simulated data and that the two algorithms simulated may respond to tasks that emphasize achieving high levels of data throughput coupled with lower emphasis on power conservation differently than they do to other combinations of performance task characteristics. PMID:24064575

Wolfe, Edward W; Dietrich, Carl B; Vanhoy, Garrett

2013-01-01

186

CB Radios  

ERIC Educational Resources Information Center

Citizen band radios keep trucking across the American scene, and no doubt your students are caught in the folk craze. Provides some suggestions for channeling students' interests with a unit on CBs. (Author/RK)

Martin, Dick

1977-01-01

187

Ultrawideband propagation channels-theory, measurement, and modeling  

Microsoft Academic Search

This paper presents an overview of ultrawideband (UWB) propagation channels. It first demonstrates how the frequency selectivity of propagation processes causes fundamental differences between UWB channels and \\

Andreas F. Molisch

2005-01-01

188

SPACE DIVERSITY FOR OFDM-CDMA SYSTEMS OVER FADING RADIO CHANNELS  

Microsoft Academic Search

The application of adaptive space diversity combining algorithms in a Multicarrier Code Division Multiple Access (CDMA) system is presented in this paper. This novel approach enables space and time diversity combining of the signals, and is evaluated over multipath fading channels. Third generation mobile communication systems are expected to provide high quality voice, data and image transmission. Such high quality

R. Uribeetxeberria; R. A. Carrasco

189

A topology control approach for utilizing multiple channels in multi-radio wireless mesh networks   

E-print Network

guided by a novel topology control perspective, and show that the resulting optimization problem is NP-complete. We also present an ILP formulation that is used for obtaining a lower bound for the optimum. We then develop a new greedy heuristic channel...

Marina, Mahesh; Das, Samir R.; Subramanian, Anand Prabhu

190

Radio-Gas Chromatographic Measurement of Separation Factors in Laser Isotope Separation of Tritium  

Microsoft Academic Search

A new method is proposed for the evaluation of the separation factors in laser isotope separation of tritium using radio-gas chromatograph technique, when the radioactivity detection is severely affected by the quenching effect. It is shown mathematically that the overall efficiency of radioactivity measurement with a proportional counter (internal gas flow type) can be described as functions of the intrinsic

Kazuo Takeuchi; Sakae Satooka; Yoshihiro Makide; Ichiro Inoue

1985-01-01

191

Measuring Neutrino Masses Using Radio-Frequency Techniques  

E-print Network

We describe a new technique by which the energy spectrum of low energy electrons can be extracted. The technique relies on the detection and measurement of coherent radiation created from the cyclotron motion of charged ...

Formaggio, Joseph A.

192

An analysis of source structure effects in radio interferometry measurements  

NASA Technical Reports Server (NTRS)

To begin a study of structure effects, this report presents a theoretical framework, proposes an effective position approach to structure corrections based on brightness distribution measurements, and analyzes examples of analytical and measured brightness distributions. Other topics include the effect of the frequency dependence of a brightness distribution on bandwidth synthesis (BWS) delay, the determination of the absolute location of a measured brightness distribution, and structure effects in dual frequency calibration of charged particle delays. For the 10 measured distributions analyzed, it was found that the structure effect in BWS delay at X-band (3.6 cm) can reach 30 cm, but typically falls in the range of 0 to 5 cm. A trial limit equation that is dependent on visibility was successfully tested against the 10 measured brightness distributions (seven sources). If the validity of this particular equation for an upper limit can be established for nearly all sources, the structure effect in BWS delay could be greatly reduced without supplementary measurements of brightness distributions.

Thomas, J. B.

1980-01-01

193

CCD measurements in optical domain and astrometric positions of ICRF2 radio sources  

NASA Astrophysics Data System (ADS)

At the IAU XXIIIth GA in 1997, the International Celestial Reference Frame (ICRF) was adopted; hereafter referred to as ICRF1. After the original list of radio objects there were two extensions, ICRF-ext1 and ICRF-ext2. All together, there were 717 sources: 212 defining ones, 109 new ones, 294 candidate ones, and 102 additional ones. At the IAU XXVIIth GA in 2009, the second realization of the ICRF (the ICRF2) was adopted with the list of precise positions for 3414 compact radio astronomical sources. At that moment there were nearly 30 years of VLBI observations. The ICRF2 has a noise floor of about 0.04 mas (near six times better than ICRF1) and an axis stability of about 0.01 mas (nearly twice as stable as ICRF1). Also, it is of importance to make the observations of some ICRF2 extragalactic radio sources (ERS) which are visible in the optical domain, and to compare their optical (calculated via the reference stars) and radio positions (VLBI ones). We started to do it by using the CCD camera VersArray 1300B and the RCC telescope1 (D/F = 2m/16m) of Rozhen National Astronomical Observatory (Bulgarian Academy of Sciences). About 30 frames were observed at the end of March 2011. The main steps of our calculations and some preliminary results (comparison between the measured optical positions and the radio ones) for a few ERS from ICRF2 list were presented here.

Damljanovic, G.; Milic, I. S.

2012-12-01

194

Measurement of the top quark mass in the dilepton channel  

SciTech Connect

We present a measurement of the top quark mass in the dilepton channel based on approximately 370 pb{sup -1} of data collected by the D0 experiment during Run II of the Fermilab Tevatron collider. We employ two different methods to extract the top quark mass. We show that both methods yield consistent results using ensemble tests of events generated with the D0 Monte Carlo simulation. We combine the results from the two methods to obtain a top quark mass m{sub t} = 178.1 {+-} 8.2 GeV. The statistical uncertainty is 6.7 GeV and the systematic uncertainty is 4.8 GeV.

Abazov, V.M.; Abbott, B.; Abolins, M.; Acharya, B.S.; Adams, M.; Adams, T.; Agelou, M.; Aguilo, E.; Ahn, S.H.; Ahsan, M.; Alexeev, G.D.; /Buenos Aires U. /Rio de Janeiro, CBPF /Rio de Janeiro State U. /Sao Paulo, IFT /Alberta U. /Simon Fraser U. /York U., Canada /McGill U. /Hefei, CUST /Andes U., Bogota /Charles U.

2006-09-01

195

The polar atmosphere of Venus: Radio occultation measurements with Venus Express and Magellan  

NASA Astrophysics Data System (ADS)

The ESA Venus Express (VEx) spacecraft has been conducting radio occultation experiments since 2006. The results reported to date are based on data recorded by 35-m antennas of the ESA Tracking Station Network (e.g., Tellmann et al., J. Geophys. Res., 114, E00B36, 2009). We have recently begun to derive complementary new results through analysis of high-quality "open-loop" data recorded by a 70-m antenna of the NASA Deep Space Network. This experiment sounded the polar atmosphere in both hemispheres at latitudes greater than 75 degrees. As in previous occultation measurements in this region, there is a deep convective layer at altitudes below about 60 km. The convective layer is capped by an abrupt transition to stable stratification, and the overlying free air is modulated by vertically propagating gravity waves. These new results will be compared with Magellan radio occultation measurements acquired at comparable latitudes in the early 1990s and with the VEx results reported by Tellmann et al. (2009). Our analysis also illustrates some of the challenges that can arise in radio occultation measurements at Venus. For example, the sharp temperature minimum at the tropopause creates a thin layer that eludes radio occultation sounding owing to its peculiar refractive properties. This research is funded in part by NASA Grant NNX10AE22G of the Venus Express Participating Scientist Program.

Hinson, D. P.; Tellmann, S.; Paetzold, M.; Haeusler, B.; Bird, M. K.; Tyler, G. L.

2012-12-01

196

Reliable intraocular pressure measurement using automated radio-wave telemetry  

PubMed Central

Purpose To present an autonomous intraocular pressure (IOP) measurement technique using a wireless implantable transducer (WIT) and a motion sensor. Methods The WIT optical aid was implanted within the ciliary sulcus of a normotensive rabbit eye after extracapsular clear lens extraction. An autonomous wireless data system (AWDS) comprising of a WIT and an external antenna aided by a motion sensor provided continuous IOP readings. The sensitivity of the technique was determined by the ability to detect IOP changes resulting from the administration of latanoprost 0.005% or dorzolamide 2%, while the reliability was determined by the agreement between baseline and vehicle (saline) IOP. Results On average, 12 diurnal and 205 nocturnal IOP measurements were performed with latanoprost, and 26 diurnal and 205 nocturnal measurements with dorzolamide. No difference was found between mean baseline IOP (13.08±2.2 mmHg) and mean vehicle IOP (13.27±2.1 mmHg) (P=0.45), suggesting good measurement reliability. Both antiglaucoma medications caused significant IOP reduction compared to baseline; latanoprost reduced mean IOP by 10% (1.3±3.54 mmHg; P<0.001), and dorzolamide by 5% (0.62±2.22 mmHg; P<0.001). Use of latanoprost resulted in an overall twofold higher IOP reduction compared to dorzolamide (P<0.001). Repeatability was ±1.8 mmHg, assessed by the variability of consecutive IOP measurements performed in a short period of time (?1 minute), during which the IOP is not expected to change. Conclusion IOP measurements in conscious rabbits obtained without the need for human interactions using the AWDS are feasible and provide reproducible results. PMID:24531415

Paschalis, Eleftherios I; Cade, Fabiano; Melki, Samir; Pasquale, Louis R; Dohlman, Claes H; Ciolino, Joseph B

2014-01-01

197

Surface figure measurements of radio telescopes with a shearing interferometer  

Microsoft Academic Search

A new technique for determining the surface figure of large submillimeter wavelength telescopes is presented, which is based on measuring the telescope's focal plane diffraction pattern with a shearing interferometer. In addition to the instrumental theory, results obtained using such an interferometer on the 10.4-m diam telescope of the Caltech Submillimeter Observatory are discussed. Using wavelengths near 1 mm, a

E. Serabyn; T. G. Phillips; C. R. Masson

1991-01-01

198

GPS radio occultation measurements of the ionosphere from CHAMP: Early results  

Microsoft Academic Search

The paper deals with initial analyzes of radio occultation measurements of the ionosphere carried out on board the CHAMP satellite since 11 April 2001. The accuracy of the operationally retrieved electron density profiles has been estimated by comparing with independent measurements. The derived ionospheric key parameters such as f0F2 and hmF2 agree with a standard deviation of 18 and 13%,

N. Jakowski; A. Wehrenpfennig; S. Heise; Ch. Reigber; H. Lühr; L. Grunwaldt; T. K. Meehan

2002-01-01

199

Simultaneous radio and satellite optical measurements of high-altitude sprite current and lightning continuing current  

Microsoft Academic Search

We report coordinated measurements of lightning and resulting sprites using ground-level magnetic field sensors (<0.1 Hz to 30 kHz bandwidth) and the ISUAL instrument on the FORMOSAT-2 satellite. These measurements demonstrate two distinct elements of the connection between the radio and optical emissions. First, the quasi-static magnetic field signature is tightly correlated with the low-altitude optical emissions from the lightning

Steven A. Cummer; Harald U. Frey; Stephen B. Mende; Rue-Ron Hsu; Han-Tzong Su; Alfred B. Chen; Hiroshi Fukunishi; Yukihiro Takahashi

2006-01-01

200

Midlatitude D region variations measured from broadband radio atmospherics  

NASA Astrophysics Data System (ADS)

The high power, broadband very low frequency (VLF, 3--30 kHz) and extremely low frequency (ELF, 3--3000 Hz) electromagnetic waves generated by lightning discharges and propagating in the Earth-ionosphere waveguide can be used to measure the average electron density profile of the lower ionosphere (D region) across the wave propagation path due to several reflections by the upper boundary (lower ionosphere) of the waveguide. This capability makes it possible to frequently and even continuously monitor the D region electron density profile variations over geographically large regions, which are measurements that are essentially impossible by other means. These guided waves, usually called atmospherics (or sferics for short), are recorded by our sensors located near Duke University. The purpose of this work is to develop and implement algorithms to derive the variations of D region electron density profile which is modeled by two parameters (one is height and another is sharpness), by comparing the recorded sferic spectra to a series of model simulated sferic spectra from using a finite difference time domain (FDTD) code. In order to understand the time scales, magnitudes and sources for the midlatitude nighttime D region variations, we analyzed the sferic data of July and August 2005, and extracted both the height and sharpness of the D region electron density profile. The heights show large temporal variations of several kilometers on some nights and the relatively stable behavior on others. Statistical calculations indicate that the hourly average heights during the two months range between 82.0 km and 87.2 km with a mean value of 84.9 km and a standard deviation of 1.1 km. We also observed spatial variations of height as large as 2.0 km over 5 degrees latitudes on some nights, and no spatial variation on others. In addition, the measured height variations exhibited close correlations with local lightning occurrence rate on some nights but no correlation with local lightning or displaced lightning on others. The nighttime profile sharpness during 2.5 hours in two different nights was calculated, and the results were compared to the equivalent sharpness derived from International Reference Ionosphere (IRI) models. Both the absolute values and variation trends in IRI models are different from those in broadband measurements. Based on sferic data similar to those for nighttime, we also measured the day-time D region electron density profile variations in July and August 2005 near Duke University. As expected, the solar radiation is the dominant but not the only determinant source for the daytime D region profile height temporal variations. The observed quiet time heights showed close correlations with solar zenith angle changes but unexpected spatial variations not linked to the solar zenith angle were also observed on some days, with 15% of days exhibiting regional differences larger than 0.5 km. During the solar flare, the induced height change was approximately proportional to the logarithm of the X-ray fluxes. During the rising and decaying phases of the solar flare, the height changes correlated more consistently with the short (wavelength 0.5--4 A), rather than the long (wavelength 1--8 A) X-ray flux changes. The daytime profile sharpness during morning, noontime and afternoon periods in three different days and for the solar zenith angle range 20 to 75 degrees was calculated. These broadband measured results were compared to narrowband VLF measurements, IRI models and Faraday rotation base IRI models (called FIRI). The estimated sharpness from all these sources was more consistent when the solar zenith angle was small than when it was large. By applying the nighttime and daytime measurement techniques, we also derived the D region variations during sunrise and sunset periods. The measurements showed that both the electron density profile height and sharpness decrease during the sunrise period while increase during the sunset period.

Han, Feng

201

Weighted sum-rate maximization for multi-user SIMO multiple access channels in cognitive radio networks  

NASA Astrophysics Data System (ADS)

In this article, an efficient distributed and parallel algorithm is proposed to maximize the sum-rate and optimize the input distribution policy for the multi-user single input multiple output multiple access channel (MU-SIMO MAC) system with concurrent access within a cognitive radio (CR) network. The single input means that every user has a single antenna and multiple output means that base station(s) has multiple antennas. The main features are: (i) the power distribution for the users is updated by using variable scale factors which effectively and efficiently maximize the objective function at each iteration; (ii) distributed and parallel computation is employed to expedite convergence of the proposed distributed algorithm; and (iii) a novel water-filling with mixed constraints is investigated, and used as a fundamental block of the proposed algorithm. Due to sufficiently exploiting the structure of the proposed model, the proposed algorithm owns fast convergence. Numerical results verify that the proposed algorithm is effective and fast convergent. Using the proposed approach, for the simulated range, the required number of iterations for convergence is two and this number is not sensitive to the increase of the number of users. This feature is quite desirable for large scale systems with dense active users. In addition, it is also worth noting that the proposed algorithm is a monotonic feasible operator to the iteration. Thus, the stop criterion for computation could be easily set up.

He, Peter; Zhao, Lian; Lu, Jianhua

2013-12-01

202

Magnetization of the ionospheres of Venus and Mars: Results from radio occultation measurements  

SciTech Connect

In situ measurements by the Pioneer Venus orbiting spacecraft, conducted during solar maximum only, have shown that magnetization (permeation of large-scale magnetic fields) of the ionosphere of Venus occurs under high solar wind dynamic pressure and that this takes place most frequently near the subsolar region. In this paper, the authors use remote sensing radio occultation measurements to study magnetization of the ionospheres of Venus and Mars based on these characteristics. For Venus they take advantage of the unique data set consisting of 148 electron density profiles deduced from Pioneer Venus radio occultation measurements. They demonstrate that radio occultation measurements yield results on frequency of occurrence of magnetization during solar maximum that are similar to those obtained from the Pioneer Venus in situ magnetic field measurements. During solar minimum, for which direct ionospheric measurements have never been made, they find that magnetization of the Venus ionosphere is more pervasive than at solar maximum. Magnetization extends to higher solar zenith angles (SZA) and appears stronger than at solar maximum. These results confirm that during solar minimum, the high solar wind dynamic pressure state is more prevalent at Venus because the ionospheric plasma pressure is weaker than at solar maximum. Comparison of a large number of electron density profiles of Mars (deduced from radio occultation measurements by the Viking 1 and 2 and Mariner 9 spacecraft for SZA > 46{degrees}) with those of Venus shows an absence of the ledge and disturbed topside plasma observed in the Venus profiles. These results, however, do not constitute evidence against magnetization of the ionosphere of Mars, as Shinagawa and Cravens (1989) have shown on their one-dimensional MHD models that, even when the ionosphere of Mars is highly magnetized, the magnetic structure differs from that at Venus, and a ledge does not form in its electron density profiles.

Woo, R.; Kliore, A.J. (California Inst. of Tech., Pasadena (USA))

1991-07-01

203

Wireless strain and temperature measurement with radio telemetry  

Microsoft Academic Search

A line of miniature strain and temperature telemetry transmitters have been developed for measurements in areas where direct-wire\\u000a connections are not possible. The units described are 8–16 cu cm in volume (0.5–1.0 cu in.) and operate over a 0C to 150C\\u000a ambient-temperature range with up to 30,000g?s acceleration.\\u000a \\u000a Battery life with a battery about the same size as the transmitter

Alan J. Adler

1971-01-01

204

Measurement and prediction of pressure drop in two-phase micro-channel heat sinks  

E-print Network

Measurement and prediction of pressure drop in two-phase micro-channel heat sinks Weilin Qu, Issam This study explores hydrodynamic instability and pressure drop in a water-cooled two-phase micro-channel heat instability were identified: severe pressure drop oscillation and mild parallel channel instability

Qu, Weilin

205

Investigating MC-CDMA system performance using measurement-based channel models  

Microsoft Academic Search

This paper investigates the performance of the downlink in Multi Carrier CDMA (MC-CDMA) systems using a channel model from in-the-field propagation measurements. Results are presented also for channel models having non-exponentially decaying profiles. Channel coherence bandwidth (Bc) is incorporated within the analysis in order to demonstrate the effect of channel frequency selectivity on system performance. The effect of transmission bandwidth,

Çetin Kurnaz; Hülya Gökalp

2008-01-01

206

Estimating water vapour along the radio path between two LEO satellites through multifrequency differential power measurements  

NASA Astrophysics Data System (ADS)

The Normalized Differential Spectral Attenuation (NDSA) concept was proposed in 2002 by the authors for tropospheric water vapour sounding by means of a couple of LEO (Low Earth Orbit) satellites (one carrying a transmitter, the other a receiver and operating in the Ku/K bands) in limb geometry. In those years, in the course of the ACE+ mission studies (second call for proposal of the ESA Earth Explorer Opportunity Mission), the problem arose of the severe impact of scintillation due to tropospheric turbulence on the water vapour estimates provided by radio occultation measurements made in limb mode between two LEO satellites. In following ESA studies (AlmetLeo - 2004, ACTLIMB -2009) it was demonstrated that NDSA, thanks to its normalised differential approach, is effective for limiting scintillation and for estimating the Integrated Water Vapor (IWV) along the propagation path between the two LEO satellites. NDSA relies on the conversion of a spectral parameter (the spectral sensitivity S), into the IWV through IWV-S relationships. S is a finite-difference approximation of the derivative of the spectral attenuation at a given frequency fo, normalized to the spectral attenuation itself. To measure Sat fo,it is required that two tone signals with equal power at relatively close frequencies f1 and f2 (f1 > f2) symmetrically placed around fo are simultaneously transmitted. The two pertinent received powers P1 and P2 are simultaneously measured and S is provided by: S = -P2--P1- (f1 - f2 )P2 From the very beginning of the NDSA studies, it was evident that in ideal measurement conditions (no disturbance at the receiver nor propagation impairments) S is tightly correlated to the IWV. To verify this, we accounted for natural variations of the atmospheric conditions by generating simulated spherically symmetric atmospheres using real radiosonde profiles. We computed IWV along the radio path and simulated S separately obtaining IWV-S relationships at various altitudes through regression methods. In particular, the ESA-AlMetLEO study yielded a significant insight into such relationships up to 12 km using the K-Ku bands, while the ESA-ACTLIMB study offered the opportunity to investigate the potential of 179 to 182 GHz (M band) for estimates from 10 km upwards, exhibiting a significant robustness to scintillation fluctuations. However, two problems affected the reliability of the empirical IWV-S relations found and have been faced by us during the on-going ESA-ANISAP study: 1) the accuracy of the radiosonde data used to derive them was not uniform in the northern and southern hemisphere, and so their positions; 2) the number of radiosonde samples above 10 km was limited, and their reliability scarce, which affected the analysis of the IWV-S relations in the M band. To overcome both problems, instead of radiosonde data, we utilized atmospheric pro?les equally distributed on a global Earth scale as derived from ECMWF atmospheric analysis data. Such database includes pressure, temperature, humidity, liquid water, ice water and wind components in 8 global datasets in 4 days amid of each of the four seasons and at two time layers (12:00 UTC and 24:00 UTC). In this work, we show the main results of the global scale analysis of the IWV-S relations up to 20 altitude. We point out that NDSA requires a multi-frequency approach to provide reliable IWV estimates up to 20 km, and that S estimates at 17, 19 and 21 GHz are essential to provide IWV profiles in the lower troposphere through linear relationships, while the M band channels (179 and 182 GHz) can be reliably exploited still through linear relationships above 10 km where the water vapour content is smaller. We also demonstrate that an additional spectral sensitivity channel at 32 GHz is very effective both to detect the presence of liquid water along the link and to correct the IWV overestimates caused by such presence when using S measurements in the K/Ku band (17, 19 and 21 GHz).

Facheris, Luca; Cuccoli, Fabrizio

2013-04-01

207

A Fast Time-Domain Wireless Channel Simulation Tool for Radio-Wave Propagation Courses  

E-print Network

and a completely intuitive CAD-style interface. These qualities enable students to design their own 2D environments]. Classical fields and microwave design courses already benefit from a number of time and frequency domain are dynamically animated and measured with precision. We have developed an educational software package

208

Coronal magnetic field strength from Type II radio emission: complementarity with Faraday rotation measurements  

NASA Astrophysics Data System (ADS)

We analyzed the band splitting of a Type II radio burst observed on 1997 May 12 by ground- and space-based radio spectrometers. Type II radio emission is the most evident signature of coronal shock waves and the observed band splitting is generally interpreted as due to plasma emission from both upstream and downstream shock regions. From the inferred compression ratio we estimated, using the magnetohydrodynamic (MHD) Rankine-Hugoniot relations, the ambient Alfvén Mach number. By means of the electron density obtained by inverting white-light polarized brightness (pB) coronagraph data and the shock speed inferred from the Type II frequency drift, we finally derived a radial profile for the magnetic field strength in the middle corona. The result was compared with the field profile obtained in May 1997 (but above ~5 R?) with Faraday rotation measurements of extragalactic radio sources occulted by the corona. The power law of the form B(r) = 3.76 r-2.29 G inferred in that work nicely describes the combined set of data in a wide range of heliocentric distances (r ? 1.8-14 R?).

Mancuso, S.; Garzelli, M. V.

2013-12-01

209

Radio continuum measurements of compact H II regions and other sources  

NASA Technical Reports Server (NTRS)

Results are reported for measurements of the flux densities of 33 sources at wavelengths of 13, 4, and 2 cm, which were conducted using the NASA/JPL Deep Space Network 64-m antenna at Goldstone, Calif. Besides compact H II regions, the sources included five Uhuru X-ray sources, several IR sources, an extragalactic radio source, and a H2O maser. The Lyman continuum flux is derived from the measured radio flux and the assumed distance and temperature for 10 possible H II regions; the spectra of previously known sources are extended to higher frequencies, and upper limits are placed on the flux densities for the five X-ray sources. New compact H II regions are found in the bright nebula M78, the nebula K5, and the Ophiuchus dark cloud/IR region.

Matsakis, D. N.; Evans, N. J., II; Sato, T.; Zuckerman, B.

1976-01-01

210

THE HUYGENS DOPPLER WIND EXPERIMENT Titan Winds Derived from Probe Radio Frequency Measurements  

E-print Network

.K. BIRD1, R. DUTTA-ROY1, M. HEYL1, M. ALLISON2, S.W. ASMAR3, W.M. FOLKNER3, R.A. PRESTON3, D.H. ATKINSON4THE HUYGENS DOPPLER WIND EXPERIMENT Titan Winds Derived from Probe Radio Frequency Measurements M) will be performed during the Titan atmospheric des- cent of the ESA Huygens Probe. The direction and strength

211

A novel approach to high voltage substation surveillance using radio frequency interference measurement  

Microsoft Academic Search

The deployment of radio frequency interference (RFI) measurement has gained increasing acceptance as a front line, non-invasive technique to assess the condition of individual high-voltage (HV) electrical equipment items as part of a substation surveillance program. However, successful detection and discrimination of low-repetition rate discharges that typically accompany electrical deterioration is constrained by the capabilities and limitations of the field

A. Nesbitt; B. G. Stewart; S. G. McMeekin; S. Conner; J. C. Gamio; K. Liebech-Lien; H. O. Kristiansen; S. Krakenes

2009-01-01

212

Lunar occultation of the diffuse radio sky: LOFAR measurements between 35 and 80 MHz  

E-print Network

We present radio observations of the Moon between $35$ and $80$ MHz to demonstrate a novel technique of interferometrically measuring large-scale diffuse emission extending far beyond the primary beam (global signal) for the first time. In particular, we show that (i) the Moon appears as a negative-flux source at frequencies $35z>12$) and the Epoch of Reionization ($12>z>5$).

Vedantham, H K; de Bruyn, A G; Wijnholds, S J; Brentjens, M; Abdalla, F B; Asad, K M B; Bernardi, G; Bus, S; Chapman, E; Ciardi, B; Daiboo, S; Fernandez, E R; Ghosh, A; Harker, G; Jelic, V; Jensen, H; Kazemi, S; Lambropoulos, P; Martinez-Rubi, O; Mellema, G; Mevius, M; Offringa, A R; Pandey, V N; Patil, A H; Thomas, R M; Veligatla, V; Yatawatta, S; Zaroubi, S; Anderson, J; Asgekar, A; Bell, M E; Bentum, M J; Best, P; Bonafede, A; Breitling, F; Broderick, J; Brüggen, M; Butcher, H R; Corstanje, A; de Gasperin, F; de Geus, E; Deller, A; Duscha, S; Eislöffel, J; Engels, D; Falcke, H; Fallows, R A; Fender, R; Ferrari, C; Frieswijk, W; Garrett, M A; Grießmeier, J; Gunst, A W; Hassall, T E; Heald, G; Hoeft, M; Hörandel, J; Iacobelli, M; Juette, E; Kondratiev, V I; Kuniyoshi, M; Kuper, G; Mann, G; Markoff, S; McFadden, R; McKay-Bukowski, D; Mulcahy, D D; Munk, H; Nelles, A; Norden, M J; Orru, E; Pandey-Pommier, M; Pizzo, R; Polatidis, A G; Reich, W; Renting, A; Röttgering, H; Schwarz, D; Shulevski, A; Smirnov, O; Stappers, B W; Steinmetz, M; Swinbank, J; Tagger, M; Tang, Y; Tasse, C; ter Veen, S; Thoudam, S; Toribio, C; vocks, C; Wise, M W; Wucknitz, O; Zarka, P

2014-01-01

213

Assessment of the Impacts of Radio Frequency Interference on SMAP Radar and Radiometer Measurements  

NASA Technical Reports Server (NTRS)

The NASA Soil Moisture Active and Passive (SMAP) mission will measure soil moisture with a combination of Lband radar and radiometer measurements. We present an assessment of the expected impact of radio frequency interference (RFI) on SMAP performance, incorporating projections based on recent data collected by the Aquarius and SMOS missions. We discuss the impacts of RFI on the radar and radiometer separately given the differences in (1) RFI environment between the shared radar band and the protected radiometer band, (2) mitigation techniques available for the different measurements, and (3) existing data sources available that can inform predictions for SMAP.

Chen, Curtis W.; Piepmeier, Jeffrey R.; Johnson, Joel T.; Hirad Ghaemi

2012-01-01

214

Laser measurement of H- ions in a field-effect-transistor based radio frequency ion sourcea)  

NASA Astrophysics Data System (ADS)

Hydrogen negative ion density measurements are required to clarify the characteristics of negative ion production and ion source performance. Both of laser photodetachment and cavity ring down (CRD) measurements have been implemented to a field-effect-transistor based radio-frequency ion source. The density ratio of negative hydrogen ions to electrons was successfully measured by laser photodetachment and effect of magnetic filter field on negative ion density was confirmed. The calculated CRD signal showed that CRD mirrors with >99.990% reflectivity are required and loss of reflectivity due to cesium contamination should be minimized.

Tanaka, N.; Matsuno, T.; Funaoi, T.; Ando, A.; Tauchi, Y.; Nakano, H.; Tsumori, K.; Takeiri, Y.

2012-02-01

215

Historic Rio Grande Channel Change: Relating Channel Adjustments Measured from Aerial Photography to Human and Climate Induced Changes in Hydrology  

NASA Astrophysics Data System (ADS)

Over the last century, flow regulation, changes in land and water use, and climate change, including severe droughts, have altered geomorphic processes along the Middle Rio Grande. In association with the USACE Urban Flood Demonstration Program, we investigated changes in channel and island widths and areas as measured on 1972-2006 aerial photographs in relation to average and peak flows in the Rio Grande through Bernalillo County, NM (Albuquerque). We employed all recent (1992-2006) photographs, which were often taken annually or biannually. Digitized and georeferenced photographs were analyzed using a GIS, with particular attention paid to quantifying potential measurement error and its propagation through estimates of channel areas and bank erosion rates. Average total channel widths decreased from 169 m in 1972 to 130 m in 2006. Narrowing was concentrated in the upper and lower sections of the study reach where tributary sediment inputs and degradation related to dam operations constrict the active channel. Decreases in channel width and area coincide with periods of low flows, although the area changes are associated with large errors. Vegetated island areas have greatly increased since 1972, although islands per se were also lost during the later study period by bank attachment. Bank erosion estimates also have large associated errors. Nonetheless, erosion rates appear to be generally decreasing over time, but accelerated during the 2005 high flows. Additional research will compare geomorphic change along the Rio Grande study reach to channel adjustments along the Rio Chama, both below and above El Vado Dam, to better understand regional channel responses to dam operations and drought cycles. Initial investigations reveal that channel responses to these perturbations along the Rio Chama, a major Rio Grande tributary, are similar to the adjustments observed along the Rio Grande through Albuquerque, but the magnitude of the change is not as dramatic.

Meyer, G. A.; Swanson, B. J.; Coonrod, J.

2008-12-01

216

Venus - Mass, gravity field, atmosphere, and ionosphere as measured by the Mariner 10 dual-frequency radio system  

NASA Technical Reports Server (NTRS)

The unique properties of the Mariner 10 radio system, and the preliminary scientific results obtained from the analysis of the radio signals are described. In the normal two-way communication mode, a command- and range-modulated 2115-MHz signal is transmitted to the spacecraft for reception on its omnidirectional antenna. As implemented for Mariner 10, the dual-frequency system has proven fully capable of performing interplanetary columnar electron content measurements while achieving the prime goals of the celestial mechanics and radio science team. The determination of the mass and gravitational potential of Venus is one of the major objectives of the radio science experiments. Information on Venus's atmosphere was deduced from analysis of the radio signals during occultation. Open-loop receiver differential Doppler data were used to measure the nightside and dayside ionospheres of Venus.

Howard, H. T.; Tyler, G. L.; Fjeldbo, G.; Kliore, A. J.; Levy, G. S.; Brunn, D. L.; Dickinson, R.; Edelson, R. E.; Martin, W. L.; Postal, R. B.

1974-01-01

217

Cirrus Cloud Optical Thickness from Reflectance Measurements in the MODIS 1.38-mum Channel  

Microsoft Academic Search

Cirrus cloud radiative properties are derived using reflectance measurements in the ``cirrus detection'' channel, centered at 1.38-mum, of the Moderate-resolution Imaging Spectroradiometer (MODIS). The 1.38-mum channel is located within a spectral region of strong water vapor absorption; thus, under many circumstances, measured reflectance within this channel is solely attributable to ice clouds (e.g., cirrus). Following a look-up table approach, a

Kerry Meyer; Steven Platnick; Ping Yang; Bo-Cai Gao

2009-01-01

218

Propagation of 2 GHz Radio Waves Over the English Channel: Analysis of Cases of SubRefraction  

Microsoft Academic Search

This paper presents details about the transhorizon propagation of 2 GHz radio waves over the sea during sub- refractive atmospheric conditions. Sub-refraction is perhaps the most rare of the four refractive conditions (ducting, super-refraction, normal refraction and sub-refraction), but nevertheless cannot be ignored when assessing the performance of a radio link. Specifically, for a 50 km, low-altitude, over-sea radio path

E. M. Warrington; D. R. Siddle

219

Method of measuring nitric oxide release by vascular endothelial cells grown in microfluidic channels  

NASA Astrophysics Data System (ADS)

In this paper, a simple and versatile method is presented which enables detection of nitric oxide (NO) released from vascular endothelial cells (ECs) cultured in microfluidic structures. The culturing system and NO measurement method allow cell shape to be controlled in a non-invasive manner using microfluidic structures while NO release is monitored for cell shape versus function studies. The culturing system consists of arrays of polydimethylsiloxane (PDMS) fluidic channels 120 micrometers in depth and ranging from 100 micrometers to 3 mm in width. The number of channels in each array is varied to yield a constant cell culture surface area (75 mm2) independent of channel width. The channel surfaces are collagen-coated and ECs are cultured to confluence within the channels. A cell scraper is then used to scrape extraneous cells cultured between channels, and NO measurements are made 18 to 24 hours later. A chemiluminescence-based sensor system (NOA 280i, Sievers NO Analyzer) is utilized to measure sample NO. Initial results indicate that NO concentrations can be measured from different microfluidic channel-containing samples using this method. It is shown that there is no significant difference in NO concentration derived from channels of different widths even though the degree of cell elongation varies due to physical constraint by microfluidic channel walls. However, cells treated with TNF? release more NO than untreated cells in fluidic channels, which is comparable to the function of ECs cultured in conventional culturing systems such as culturing dishes.

Hosseinpour, S.; Liu, A. C.; Barakat, A. I.; Choy, J. C.; Gray, B. L.

2014-03-01

220

Dynamic channel, rate selection and scheduling for white spaces  

Microsoft Academic Search

We investigate dynamic channel, rate selection and scheduling for wireless systems which exploit the large number of channels available in the White-space spectrum. We first present measurements of radio channel characteristics from an indoor testbed operating in the 500 to 600MHz band and comprising 11 channels. We observe significant and unpredictable (non-stationary) variations in the quality of these channels, and

Bozidar Radunovic; Alexandre Proutiere; Dinan Gunawardena; Peter Key

2011-01-01

221

A comparison of indoor channel measurements and ray tracing simulations at 300 GHz  

Microsoft Academic Search

This paper presents ultra broadband channel measurements in a typical office room. The measured channel impulse response and transfer function is compared to a ray tracing simulation performed with a 3D model of the scenario. Additionally, we show reflection losses of the building materials in the room which are required as input data for the ray tracing algorithm.

S. Priebe; M. Jacob; C. Jastrow; T. Kleine-Ostmann; T. Schrader; T. Ku?rner

2010-01-01

222

Measurement setup for differential-mode and common-mode channels  

E-print Network

1 Measurement setup for differential-mode and common-mode channels Vincent Le Nir, Marc Moonen Abstract Since there is no model available for mixed differential-mode and common-mode transmission, this report gives a measurement setup to determine the channel transfert function of the differential-mode

223

VLF Radio Field Strength Measurement of power line carrier system in San Diego, California  

NASA Technical Reports Server (NTRS)

The radio frequency interference (RFI) potential was evaluated for a Powerline Carriet (PLC) installed in San Diego which monitors the performance of an electrical power system. The PLC system generated 30 amperes at 5.79 kHz. The RF radiations were measured to be (typically) 120 dBuV/m at the beginning of the 12 kV powerline and 60 dBuV/m at the end of the powerline. The RF fields varied inversely as the distance squared. Measurements were also performed with a 45 kHz PLC system. The RF fields were of similar amplitude.

Mertel, H. K.

1981-01-01

224

Rapid estimation of recharge potential in ephemeral-stream channels using electromagnetic methods, and measurements of channel and vegetation characteristics  

USGS Publications Warehouse

To classify recharge potential (RCP) in ephemeral-stream channels, a method was developed that incorporates information about channel geometry, vegetation characteristics, and bed-sediment apparent electrical conductivity (??a). Recharge potential is not independently measurable, but is instead formulated as a site-specific, qualitative parameter. We used data from 259 transects across two ephemeral-stream channels near Sierra Vista, Arizona, a location with a semiarid climate. Seven data types were collected: ??a averaged over two depth intervals (0-3 m, and 0-6 m), channel incision depth and width, diameter-at-breast-height of the largest tree, woody-plant and grass density. A two-tiered system was used to classify a transect's RCP. In the first tier, transects were categorized by estimates of near-surface-sediment hydraulic permeability as low, moderate, or high using measurements of 0-3 m-depth ??a. Each of these categories was subdivided into low, medium, or high RCP classes using the remaining six data types, thus yielding a total of nine RCP designations. Six sites in the study area were used to compare RCP and ??a with previously measured surrogates for hydraulic permeability. Borehole-averaged percent fines showed a moderate correlation with both shallow and deep ??a measurements, however, correlation of point measurements of saturated hydraulic conductivity, percent fines, and cylinder infiltrometer measurements with ??a and RCP was generally poor. The poor correlation was probably caused by the relatively large measurement volume and spatial averaging of ??a compared with the spatially-limited point measurements. Because of the comparatively large spatial extent of measurement transects and variety of data types collected, RCP estimates can give a more complete picture of the major factors affecting recharge at a site than is possible through point or borehole-averaged estimates of hydraulic permeability alone. ?? 2007 Elsevier B.V. All rights reserved.

Callegary, J.B.; Leenhouts, J.M.; Paretti, N.V.; Jones, C.A.

2007-01-01

225

Radio propagation measurements at microwave frequencies for microcellular mobile and personal communications  

Microsoft Academic Search

The design and results of a propagation experiment at 900 MHz and 11 GHz to characterize microcell channels at two distinct frequencies in various environments, from rural to dense urban, are presented. The measurements were made by transmitting a continuous-wave (CW) signal from a mobile source to a fixed base and recording the signal envelope variations as a function of

N. Amitay; R. S. Owens; R. S. Roman

1989-01-01

226

AN INTERLABORATORY COMPARISON PROGRAMME ON RADIO FREQUENCY ELECTROMAGNETIC FIELD MEASUREMENTS: THE SECOND ROUND OF THE SCHEME.  

PubMed

The second round of an interlaboratory comparison scheme on radio frequency electromagnetic field measurements has been conducted in order to evaluate the overall performance of laboratories that perform measurements in the vicinity of mobile phone base stations and broadcast antenna facilities. The participants recorded the electric field strength produced by two high frequency signal generators inside an anechoic chamber in three measurement scenarios with the antennas transmitting each time different signals at the FM, VHF, UHF and GSM frequency bands. In each measurement scenario, the participants also used their measurements in order to calculate the relative exposure ratios. The results were evaluated in each test level calculating performance statistics (z-scores and En numbers). Subsequently, possible sources of errors for each participating laboratory were discussed, and the overall evaluation of their performances was determined by using an aggregated performance statistic. A comparison between the two rounds proves the necessity of the scheme. PMID:25205832

Nicolopoulou, E P; Ztoupis, I N; Karabetsos, E; Gonos, I F; Stathopulos, I A

2014-09-01

227

Gravitational Microlensing by Neutron Stars and Radio Pulsars: Event Rates, Timescale Distributions, and Mass Measurements  

NASA Astrophysics Data System (ADS)

We investigate properties of Galactic microlensing events in which a stellar object is lensed by a neutron star. For an all-sky photometric microlensing survey, we determine the number of lensing events caused by ? {{10}5} potentially observable radio pulsars to be ? 0.2 y{{r}-1} for 1010 background stellar sources. We expect a few detectable events per year for the same number of background sources from an astrometric microlensing survey. We show that such a study could lead to precise measurements of radio pulsar masses. For instance, if a pulsar distance could be constrained through radio observations, then its mass would be determined with a precision of ? 10%. We also investigate the timescale distributions for neutron star events, finding that they are much shorter than had been previously thought. For photometric events toward the Galactic center that last ?15 days, around 7% will have a neutron star lens. This fraction drops rapidly for longer timescales. Away from the bulge region we find that neutron stars will contribute ? 40% of the events that last less than ?10 days. These results are in contrast to earlier work which found that the maximum fraction of neutron star events would occur on timescales of hundreds of days.

Dai, S.; Smith, M. C.; Lin, M. X.; Yue, Y. L.; Hobbs, G.; Xu, R. X.

2015-04-01

228

Plan View and Profile Relations: Measuring Correlation Between Channel Profile and Network Morphology  

NASA Astrophysics Data System (ADS)

In this research, we explore the relationships between channel network attributes and the corresponding channel profile geometries using high-resolution digital topography and model-generated synthetic topographies. This combined analysis addresses one of the long-standing questions in geomorphology relating to the mechanistic significance of various plan-view channel network geometry measures. Statistically based numerical studies suggest that Hortonian measures of channel network architecture (e.g. bifurcation ratio, area ratio, and length ratio) describe virtually all possible network geometries, and so are not diagnostic when evaluating the origins of the geometry of a particular network. We further explore this hypothesis by examining the correlation between Hack exponent, the channel profile characteristics, and process changes (i.e debris flow vs. fluvial flows) within the landscape. Analysis of high resolution DEMs as well as modeled landscapes, suggests that the Hack exponent is likewise insensitive to changes in the channel profile concavity. In contrast, we find that changes in the concavity of channel profiles apparently impacts the spatial distribution of plan-view junction angles of joining stream segments throughout a catchment. In the context of previous work, this angle might be expected to be a function of the ratio between the slopes of the adjoined channels. Channel concavity determines downstream change in this ratio for channel segments throughout the basin, and so such a metric might be used to explicitly link profile channel geometries to plan-view network geometries. Because profile geometries may change with different advective mass transport processes, such a metric may provide a link between the processes that transport material across a landscape, the profile geometry of channels through which these flows traverse, and the overall drainage network geometry. Additional numerical and field data based analysis are required to further explore the sensitivity of the junction angle, as well as other measures, to process changes along the channel network.

Shelef, E.; Hilley, G. E.

2010-12-01

229

Atmospheric channel performance measurements at 10 to 100 GHz  

NASA Astrophysics Data System (ADS)

A diagnostic probe designed to investigate propagation at millimeter wavelengths was operated on 11.8 and 27.2-km line-of-sight paths near Boulder, CO. Fully coherent carrier wave channels at 11.4, 28.8, and 96.1 GHz provide data to analyze fade mechanisms and evaluate frequency dependent performance characteristics of the link. Data during fog, snow, rain, and clear-air fade events are included with statistical analyses of event occurrence, signal levels, and bit error rates. Time delay distortion and amplitude dispersion on the channel are also examined during fading events by the wide-band digital channel operated as an impulse probe. Rain attenuation, path absorption due to water vapor content, and seasonal variations as a function of frequency are presented and described.

Espeland, R. H.; Violette, E. J.; Allen, K. C.

1984-04-01

230

Design of multi-channel radio-frequency front-end for 200mhz parallel magnetic resonance imaging  

E-print Network

The increasing demands for improving magnetic resonance imaging (MRI) quality, especially reducing the imaging time have been driving the channel number of parallel magnetic resonance imaging (Parallel MRI) to increase. When the channel number...

Liu, Xiaoqun

2009-05-15

231

The software radio architecture  

Microsoft Academic Search

As communications technology continues its rapid transition from analog to digital, more functions of contemporary radio systems are implemented in software, leading toward the software radio. This article provides a tutorial review of software radio architectures and technology, highlighting benefits, pitfalls, and lessons learned. This includes a closer look at the canonical functional partitioning of channel coding into antenna, RF,

J. Mitola

1995-01-01

232

Natural convection in an inclined rectangular channel at various aspect ratios and angles - Experimental measurements  

Microsoft Academic Search

Rates of heat transfer were measured for laminar natural convection in silicone oil and air in a long rectangular channel. The aspect ratio (width\\/height) of the cross-section of the channel was varied over 1, 2, 3, 4.2, 8.4 and 15.5, and the Rayleigh number from 3,000 to 300,000. The channel was heated from below and cooled from above while the

H. Ozoe; H. Sayama; S. W. Churchill

1975-01-01

233

A UWB WBAN channel model based on a pseudo-dynamic measurement  

Microsoft Academic Search

In this paper, we expand the knowledge of the ultra-wideband (UWB) channel in the frequency range of 3.1–10 GHz in close proximity\\u000a of a human body. The channels under dynamic conditions due to the effect of body motions are studied through the pseudo-dynamic\\u000a measurement method. Firstly, the first-order statistics of the channels, namely, amplitude distributions are investigated.\\u000a Secondly, the dynamic features

Attaphongse Taparugssanagorn; Bin Zhen; Raffaello Tesi; Matti Hämäläinen; Jari H. Iinatti; Ryuji Kohno

2011-01-01

234

Solar wind interaction with the ionosphere of Venus inferred from radio scintillation measurements  

SciTech Connect

This paper presents the first S-band (2.3 GHz) radio scintillations observed in the ionosphere of Venus and discovered when the Pioneer Venus Orbiter spacecraft traversed the ionosphere of Venus. In situ plasma measurements as well as propagation calculations confirm that the scintillations are caused by electron density irregularities in the topside ionosphere of Venus below the ionopause. While these topside plasma irregularities have not been studied before, simultaneous magnetic field measurements presented here reveal that they are associated with the penetration of large-scale magnetic fields in the ionosphere. Previous studies based on extensive magnetic field measurements have shown that the presence of large-scale magnetic fields occurs in the subsolar region when the solar wind dynamic pressure exceeds the ionospheric plasma pressure. As with the large-scale magnetic fields, the disturbed plasma and resulting scintillations are therefore a manifestation of high-dynamic solar wind interaction with the ionosphere. Since the scintillations only occur in the subsolar region of Venus, the global morphology of ionospheric scintillations at Venus is different from that of the terrestrial ionosphere, where scintillations are observed in both polar and equatorial regions, with peaks occurring during nighttime. This difference apparently stems from the fact that Venus is not a magnetic planet. The authors also demonstrate that the disturbed plasma produced by the high-dynamic solar wind interaction can be remotely sensed by scintillations during radio occultation measurements, that is, when the spacecraft is outside the ionosphere.

Woo, R.; Sjogren, W.L.; Kliore, A.J. (California Institute of Technology, Pasadena (USA)); Luhmann, J.G. (Univ. of California, Los Angeles (USA)); Brace, L.H. (NASA Goddard Space Flight Center, Greenbelt, MD (USA))

1989-02-01

235

Output power distributions of mobile radio base stations based on network measurements  

NASA Astrophysics Data System (ADS)

In this work output power distributions of mobile radio base stations have been analyzed for 2G and 3G telecommunication systems. The approach is based on measurements in selected networks using performance surveillance tools part of the network Operational Support System (OSS). For the 3G network considered, direct measurements of output power levels were possible, while for the 2G networks, output power levels were estimated from measurements of traffic volumes. Both voice and data services were included in the investigation. Measurements were conducted for large geographical areas, to ensure good overall statistics, as well as for smaller areas to investigate the impact of different environments. For high traffic hours, the 90th percentile of the averaged output power was found to be below 65% and 45% of the available output power for the 2G and 3G systems, respectively.

Colombi, D.; Thors, B.; Persson, T.; Wirén, N.; Larsson, L.-E.; Törnevik, C.

2013-04-01

236

First simultaneous measurements of thermospheric winds and zonal ion drifts from the Jicamarca Radio Observatory  

NASA Astrophysics Data System (ADS)

The first simultaneous observations of thermospheric winds and zonal ion drifts have been ob-tained at the Jicamarca Radio Observatory using a new Fabry-Perot interferometer observatory installed on a mountain ridge overlooking the valley where the JRO radar is located. The re-sults show that the neutral winds and ion drifts generally have the same speed and temporal variation characteristics. These results illustrate the simultaneous detection of the midnight temperature maximum as well. The paper will also describe efforts to obtain common volume measurements of thermospheric winds and temperatures utilizing the FPI Arequipa observatory which is located 4 degrees south of the geomagnetic equator.

Meriwether, John; Baker, Brooke; Twork, Greg; Chau, Jorge; Veliz, Oskar; Woodman, Ronald; Hedden, Russell; Hysell, David

237

The performance of the ATS-6 radio beacon as a measurement system  

NASA Technical Reports Server (NTRS)

The overall system performance of the ATS-6 Radio Beacon transmitter in orbit and the Boulder ground receiver will be considered. In particular, the calibration accuracy and stability of the system will be described in terms of the observed difference in total content measured by the 360 to 140 MHz differential group delay and the 360 to 40 MHz differential group delay during the first year of operation. A summary of the transmitter housekeeping data and of the ground data collected on the EIRP and satellite antenna polar diagrams will also be presented.

Grubb, R. N.; Fritz, R. B.; Jones, J. E.

1976-01-01

238

Rayleigh beacon for measuring the surface profile of a radio telescope.  

PubMed

Millimeter-wavelength Rayleigh scattering from water droplets in a cloud is proposed as a means of generating a bright beacon for measuring the surface profile of a radio telescope. A ?=3??mm transmitter, with an output power of a few watts, illuminating a stratiform cloud, can generate a beacon with the same flux as Mars in 10 GHz bandwidth, but the beacon has a narrow line width, so it is extremely bright. The key advantage of the beacon is that it can be used at any time, and positioned anywhere in the sky, as long as there are clouds. PMID:25607971

Padin, S

2014-12-01

239

Radio frequency coupling apparatus and method for measuring minority carrier lifetimes in semiconductor materials  

DOEpatents

An apparatus for measuring the minority carrier lifetime of a semiconductor sample using radio-frequency coupling. The measuring apparatus includes an antenna that is positioned a coupling distance from a semiconductor sample which is exposed to light pulses from a laser during sampling operations. A signal generator is included to generate high frequency, such as 900 MHz or higher, sinusoidal waveform signals that are split into a reference signal and a sample signal. The sample signal is transmitted into a sample branch circuit where it passes through a tuning capacitor and a coaxial cable prior to reaching the antenna. The antenna is radio-frequency coupled with the adjacent sample and transmits the sample signal, or electromagnetic radiation corresponding to the sample signal, to the sample and receives reflected power or a sample-coupled-photoconductivity signal back. To lower impedance and speed system response, the impedance is controlled by limiting impedance in the coaxial cable and the antenna reactance. In one embodiment, the antenna is a waveguide/aperture hybrid antenna having a central transmission line and an adjacent ground flange. The sample-coupled-photoconductivity signal is then transmitted to a mixer which also receives the reference signal. To enhance the sensitivity of the measuring apparatus, the mixer is operated to phase match the reference signal and the sample-coupled-photoconductivity signal.

Johnston, Steven W. (Golden, CO); Ahrenkiel, Richard K. (Lakewood, CO)

2002-01-01

240

The Q/U Imaging Experiment: Polarization Measurements of Radio Sources at 43 and 95 GHz  

E-print Network

We present polarization measurements of extragalactic radio sources observed during the Cosmic Microwave Background polarization survey of the Q/U Imaging Experiment (QUIET), operating at 43 GHz (Q-band) and 95 GHz (W-band). We examine sources selected at 20 GHz from the public, $>$40 mJy catalog of the Australia Telescope (AT20G) survey. There are $\\sim$480 such sources within QUIET's four low-foreground survey patches, including the nearby radio galaxies Centaurus A and Pictor A. The median error on our polarized flux density measurements is 30--40 mJy per Stokes parameter. At S/N $> 3$ significance, we detect linear polarization for seven sources in Q-band and six in W-band; only $1.3 \\pm 1.1$ detections per frequency band are expected by chance. For sources without a detection of polarized emission, we find that half of the sources have polarization amplitudes below 90 mJy (Q-band) and 106 mJy (W-band), at 95% confidence. Finally, we compare our polarization measurements to intensity and polarization meas...

Huffenberger, K M; Bischoff, C; Buder, I; Chinone, Y; Cleary, K; Kusaka, A; Monsalve, R; Næss, S K; Newburgh, L B; Reeves, R; Ruud, T M; Wehus, I K; Zwart, J T L; Dickinson, C; Eriksen, H K; Gaier, T; Gundersen, J O; Hasegawa, M; Hazumi, M; Miller, A D; Radford, S J E; Readhead, A C S; Staggs, S T; Tajima, O; Thompson, K L

2014-01-01

241

DOWNSTREAM CHANNEL CHANGES AFTER A SMALL DAM REMOVAL: USING AERIAL PHOTOS AND MEASUREMENT ERROR FOR CONTEXT;  

E-print Network

DOWNSTREAM CHANNEL CHANGES AFTER A SMALL DAM REMOVAL: USING AERIAL PHOTOS AND MEASUREMENT ERROR and Ecological Engineering, Oregon State University, Corvallis, OR, USA ABSTRACT Dam removal is often implemented to assess downstream channel changes associated with a small dam removal. The Brownsville Dam, a 2.1 m tall

Tullos, Desiree

242

Cognitive intelligence in UAC channel parameter identification, measurement, estimation, and environment mapping  

Microsoft Academic Search

The recent growing interest in underwater acoustic communication (UAC) requires an in depth understanding of a vast and diverse water medium. The UAC channel presents many difficulties such as high frequency, time, and space selectivity, frequency dependent noise, and significant range and band limitation on transmission. The traditional channel parameter measurement and estimation methods may not be sufficient and sometimes

Sadia Ahmed; Huseyin Arslan

2009-01-01

243

A comparative study of charge trapping effects in LDD surface-channel and buried-channel pMOS transistors using charge profiling and threshold voltage shift measurements  

Microsoft Academic Search

Extracted charge profiles of lightly-doped drain (LDD) surface-channel and buried-channel pMOS devices stressed under hot-carrier injection conditions reveal predominant electron trapping near the gate edge at the drain region in both cases. From threshold voltage measurements, there is some evidence of hole trapping after long stress times in surface-channel pMOSFETs, but not in buried-channel devices

C. K. Kok; W. C. Chew; W. K. Chim; D. S. H. Chan; S. E. Leang

1999-01-01

244

Multiple Radios for Effective Rendezvous in Cognitive Radio Networks  

E-print Network

Multiple Radios for Effective Rendezvous in Cognitive Radio Networks Lu Yu1 , Hai Liu1 , Yiu in cognitive radio networks (CRNs) for establishing a communication link on a commonly-available channel, we investigate the rendezvous problem in CRNs where cognitive users are equipped with multiple radios

Chu, Xiaowen

245

Measurement of Channel Temperature in GaN High-Electron Mobility Transistors  

E-print Network

In this paper, a simple and reliable method to estimate the channel temperature of GaN high-electron mobility transistors (HEMTs) is proposed. The technique is based on electrical measurements of performance-related figures ...

Joh, Jungwoo

246

Reconstruction of the energy and depth of maximum of cosmic-ray air showers from LOPES radio measurements  

NASA Astrophysics Data System (ADS)

LOPES is a digital radio interferometer located at Karlsruhe Institute of Technology (KIT), Germany, that measures radio emission from extensive air showers at MHz frequencies in coincidence with KASCADE-Grande. In this article, we explore a method (slope method) that leverages the slope of the measured radio lateral distribution to reconstruct crucial attributes of primary cosmic rays. First, we present an investigation of the method on the basis of pure simulations. Second, we directly apply the slope method to LOPES measurements. Applying the slope method to simulations, we obtain uncertainties on the reconstruction of energy and depth of shower maximum (Xmax) of 13% and 50 g /cm2, respectively. Applying it to LOPES measurements, we are able to reconstruct energy and Xmax of individual events with upper limits on the precision of 20%-25% for the primary energy and 95 g /cm2 for Xmax, despite strong human-made noise at the LOPES site.

Apel, W. D.; Arteaga-Velazquez, J. C.; Bähren, L.; Bekk, K.; Bertaina, M.; Biermann, P. L.; Blümer, J.; Bozdog, H.; Brancus, I. M.; Cantoni, E.; Chiavassa, A.; Daumiller, K.; de Souza, V.; di Pierro, F.; Doll, P.; Engel, R.; Falcke, H.; Fuchs, B.; Fuhrmann, D.; Gemmeke, H.; Grupen, C.; Haungs, A.; Heck, D.; Hörandel, J. R.; Horneffer, A.; Huber, D.; Huege, T.; Isar, P. G.; Kampert, K.-H.; Kang, D.; Krömer, O.; Kuijpers, J.; Link, K.; ?uczak, P.; Ludwig, M.; Mathes, H. J.; Melissas, M.; Morello, C.; Oehlschläger, J.; Palmieri, N.; Pierog, T.; Rautenberg, J.; Rebel, H.; Roth, M.; Rühle, C.; Saftoiu, A.; Schieler, H.; Schmidt, A.; Schröder, F. G.; Sima, O.; Toma, G.; Trinchero, G. C.; Weindl, A.; Wochele, J.; Zabierowski, J.; Zensus, J. A.; Lopes Collaboration

2014-09-01

247

Reconstruction of the energy and depth of maximum of cosmic-ray air-showers from LOPES radio measurements  

E-print Network

LOPES is a digital radio interferometer located at Karlsruhe Institute of Technology (KIT), Germany, which measures radio emission from extensive air showers at MHz frequencies in coincidence with KASCADE-Grande. In this article, we explore a method (slope method) which leverages the slope of the measured radio lateral distribution to reconstruct crucial attributes of primary cosmic rays. First, we present an investigation of the method on the basis of pure simulations. Second, we directly apply the slope method to LOPES measurements. Applying the slope method to simulations, we obtain uncertainties on the reconstruction of energy and depth of shower maximum Xmax of 13% and 50 g/cm^2, respectively. Applying it to LOPES measurements, we are able to reconstruct energy and Xmax of individual events with upper limits on the precision of 20-25% for the primary energy and 95 g/cm^2 for Xmax, despite strong human-made noise at the LOPES site.

W. D. Apel; J. C. Arteaga-Velazquez; L. Bähren; K. Bekk; M. Bertaina; P. L. Biermann; J. Blümer; H. Bozdog; I. M. Brancus; E. Cantoni; A. Chiavassa; K. Daumiller; V. de Souza; F. Di Pierro; P. Doll; R. Engel; H. Falcke; B. Fuchs; D. Fuhrmann; H. Gemmeke; C. Grupen; A. Haungs; D. Heck; J. R. Hörandel; A. Horneffer; D. Huber; T. Huege; P. G. Isar; K. -H. Kampert; D. Kang; O. Krömer; J. Kuijpers; K. Link; P. ?uczak; M. Ludwig; H. J. Mathes; M. Melissas; C. Morello; J. Oehlschläger; N. Palmieri; T. Pierog; J. Rautenberg; H. Rebel; M. Roth; C. Rühle; A. Saftoiu; H. Schieler; A. Schmidt; F. G. Schröder; O. Sima; G. Toma; G. C. Trinchero; A. Weindl; J. Wochele; J. Zabierowski; J. A. Zensus

2014-08-11

248

Implementation of Elliptic Curve Cryptography with Built-In Counter Measures against Side Channel Attacks  

Microsoft Academic Search

Many software implementations of public key cryptosystems have been concerned with efficiency. The advent of side channel\\u000a attacks, such as timing and power analysis attacks, force us to reconsider the strategy of implementation of group arithmetic.\\u000a This paper presents a study of software counter measures against side channel attacks for elliptic curve cryptosystems.\\u000a \\u000a We introduce two new counter measures. The

Elena Trichina; Antonio Bellezza

2002-01-01

249

Laser measurements for experiments on the TROLL accelerator. Beam propagation experiments using laser induced channels  

SciTech Connect

Propagation of an electron beam over long distances can be accomplished by using a laser produced plasma channel. In experiments at the EPOCH Laboratory, a Krypton/Fluoride laser, lasing at 248 nm, is used to ionize trimethylamine gas to create a 91 m long channel. The laser radius was measured as 2.4 cm. Laser energy was measured and ranged from 0.5 to 6 J.

Hogeland, S. [K-Tech Corp., Albuquerque, NM (United States)

1992-06-01

250

Portable Wireless LAN Device and Two-way Radio Threat Assessment for Aircraft Navigation Radios  

NASA Technical Reports Server (NTRS)

Measurement processes, data and analysis are provided to address the concern for Wireless Local Area Network devices and two-way radios to cause electromagnetic interference to aircraft navigation radio systems. A radiated emission measurement process is developed and spurious radiated emissions from various devices are characterized using reverberation chambers. Spurious radiated emissions in aircraft radio frequency bands from several wireless network devices are compared with baseline emissions from standard computer laptops and personal digital assistants. In addition, spurious radiated emission data in aircraft radio frequency bands from seven pairs of two-way radios are provided, A description of the measurement process, device modes of operation and the measurement results are reported. Aircraft interference path loss measurements were conducted on four Boeing 747 and Boeing 737 aircraft for several aircraft radio systems. The measurement approach is described and the path loss results are compared with existing data from reference documents, standards, and NASA partnerships. In-band on-channel interference thresholds are compiled from an existing reference document. Using these data, a risk assessment is provided for interference from wireless network devices and two-way radios to aircraft systems, including Localizer, Glideslope, Very High Frequency Omnidirectional Range, Microwave Landing System and Global Positioning System. The report compares the interference risks associated with emissions from wireless network devices and two-way radios against standard laptops and personal digital assistants. Existing receiver interference threshold references are identified as to require more data for better interference risk assessments.

Nguyen, Truong X.; Koppen, Sandra V.; Ely, Jay J.; Williams, Reuben A.; Smith, Laura J.; Salud, Maria Theresa P.

2003-01-01

251

ATS-6 radio beacon electron content measurements at Ootacamund, India, October 1975-July 1976  

SciTech Connect

An atlas of total slant-path columnar electron content data measured between the ATS-6 satellite and Ootacamund, India, a site near the magnetic Equator is presented. Although these measurements were taken during a solar minimum, the general level of flare and geomagnetic activity that occurred during the observation period is summarized. These total content (N(T)) data were derived from the modulation phase (group delay) of a carrier signal transmitted from the geostationary satellite's Radio Beacon Experiment. This atlas contains two data sets: (1) N(T) as 2-min subsamples digitally recorded between 2 October 1975 and 28 January 1976 corrected for ATS-6 pitch maneuvers and (2) N(T) as 15-min subsamples chart recorded between 21 October 1975 and 22 July 1976 but uncorrected for changes in satellite orientation.

Bouwer, S.D.; Davies, K.; Donnelly, R.F.; Grubb, R.N.; Jones, J.E.

1980-03-01

252

Spectral Index of the Diffuse Radio Background Measured from 100 to 200 MHz  

NASA Astrophysics Data System (ADS)

The mean absolute brightness temperature of the diffuse radio background was measured as a function of frequency in a continuous band between 100 and 200 MHz over an effective solid angle of ~? sr at high Galactic latitude. A spectral brightness temperature index of ? = 2.5 ± 0.1 (? S = 0.5) was derived from the observations, where the error limits are 3? and include estimates of the instrumental systematics. Zenith drift scans with central declination ? = -26.5° and spanning right ascensions 0 < ? < 10 h yielded little variation in the mean spectral index. The mean absolute brightness temperature at ? = 150 MHz was found to reach a minimum of T = 237 ± 10 K at ? = 2.5 h. Combining these measurements with those of Haslam et al. yields a spectral index of ? = 2.52 ± 0.04 between 150 < ? < 408 MHz.

Rogers, Alan E. E.; Bowman, Judd D.

2008-08-01

253

Comparisons Between In-Situ Plasma Fluctuation and Radio Occultation Based Measures of Ionospheric Scintillation  

NASA Astrophysics Data System (ADS)

Ionospheric radio occultation (RO) and in-situ measurements of plasma density fluctuations provide two different approaches for inferring the presence or absence of ionospheric scintillation. The RO technique involves a direct measure of scintillation at L-band frequencies, but in a limb-viewing geometry that entails some uncertainty regarding the precise geolocation of the associated irregularity region or regions. Scintillation over a range of frequencies from UHF to L-band can be inferred from observation of the in-situ irregularity spectrum together with a set of modeling assumptions. The CORISS (C/NOFS Occultation Receiver for Ionospheric Sensing and Specification) and PLP (Planar Langmuir Probe) instruments on board the C/NOFS satellite provide a means to compare and contrast the two approaches in a rigorous manner. This presentation with report initial comparison results based on data collected during the 2008-2010 time frame.

Straus, P. R.; Roddy, P. A.; Bonito, N.

2010-12-01

254

Proton Beam Verification using RF Power Measurement Data for a cw Radio Frequency Quadrupole LINAC  

SciTech Connect

A cw radio frequency quadrupole (RFQ) LINAC section and klystrode based rf system was obtained from the Chalk River Laboratories and was recommissioned at LANL to conduct demonstration proton beam experiments in support of a spallation neutron source driver for tritium production. A variation of the Low Energy Demonstration Accelerator (LEDA) proton injector, modified to operate at 50 keV, was mated to the RFQ and was operated to support the high current (up to 100 mA), proton beam advance studies for the Accelerator Production of Tritium (APT) program. Detailed measurements and calibrations of the RFQ at both low and high power provided the corroborating data to other available beam measurements for verification of the accelerator design.

Bolme, G.O.; Hardek, T.W.; Hansborough, L.D.; Hodgkins, D.J.; Keffeler, D.R.; Sherman, J.D.; Smith, H.V.; Stevens, R.R.; Young, L.M.; Zaugg, T.J.; Arvin, A.H.; Bolt, A.S.; Richards, M.C.; Balleyguier, P.P.; Kamperschroer, J.H.

1999-03-29

255

A New Link-Level Simulation Procedure of Wideband MIMO Radio Channel for Performance Evaluation of Indoor WLANs  

Microsoft Academic Search

Inspired by the requirement of proper link simulation methods in performance analysis of communication systems, we present in this paper a recipe for channel implementation in simulation environments. Our focus here is the indoor applications of wireless local-area networks (WLANs). Specifically, we describe a procedure that beginning with statistical description of the channel impulse response leads to an efficient multi-input

M. Golparvar Roozbahani; E. Jedari; A. R. Enayati

2007-01-01

256

Network performance of mixed traffic on high speed downlink packet access and dedicated channels in WCDMA [cellular radio  

Microsoft Academic Search

Downlink throughput results are presented for cases where the available cell transmission resources are shared between high speed downlink packet access (HSDPA) and dedicated channel users. It is shown that the total cell throughput can be increased by 69% by allocating only 5 high speed downlink shared channel codes and 7 W for HSDPA transmission, compared to a scenario without

Klaus I. Pedersen; Tako F. Lootsma; M. Stottrup; Frank Frederiksen; Troels E. Kolding; Preben E. Mogensen

2004-01-01

257

CAPACITY-MAXIMIZING RESOURCE ALLOCATION FOR DATA-AIDED TIMING AND CHANNEL ESTIMATION IN ULTRA-WIDEBAND RADIOS  

E-print Network

CAPACITY-MAXIMIZING RESOURCE ALLOCATION FOR DATA-AIDED TIMING AND CHANNEL ESTIMATION IN ULTRA) communications relies critically on the accuracy of synchronization and channel estimation during the training phase. The total transmission resources should be properly allocated between training and information

Tian, Zhi "Gerry"

258

Radio Propagation Measurements Before, During, and After the Collapse of Three Large Building Structures  

Microsoft Academic Search

NIST is investigating various schemes for detecting emergency responders and civilians with portable radios or cell phones who may be trapped in voids in a collapsed or partially collapsed building. The first part of this effort is to understand radio propagation in collapsed structures. Buildings scheduled for implosion provide the ideal research environment for investigating radio-wave propagation issues in fully

Christopher L. Holloway; Galen Koepke; Dennis Camell; Kate A. Remley

259

Two-dimensional argon metastable density measurements in a radio frequency plasma reactor by planar laser-induced Jluorescence imaging  

E-print Network

Two-dimensional argon metastable density measurements in a radio frequency plasma reactor by planar-of-sight absorption, or single-point laser-induced fluorescence.iv6 To our knowledge, the only complete two, the measurements cover a wide range of conditions and were performed in a well- characterized reactor (the Gaseous

Zachariah, Michael R.

260

A Campaign Study of Ionospheric Scintillations Using Simultaneous Formosat-3\\/COSMIC Radio Occultation Observations and AFRL SCINDA Ground Scintillation Measurements  

Microsoft Academic Search

We report preliminary results from a campaign study of ionospheric scintillations using ionospheric radio occultation measurements by Formosat-3\\/COSMIC satellites and ground scintillation measurements by the Scintillation Network Decision Aid (SCINDA) network. Under the SCINDA project, scientists at the Air Force Research Laboratory (AFRL) have developed a sensor network for the purpose of monitoring low-latitude ionospheric total electron content (TEC) and

C. S. Lin; M. J. Starks; Y. Chu; S. Syndergarrd; K. M. Groves; S. Basu

2006-01-01

261

Centralized Power Control in Cellular Radio Systems  

Microsoft Academic Search

This paper describes a centralized power control scheme for cellular mobile radio systems. The power for the mobiles in the scheme proposed here is computed based on signal strength measurements. All the mobiles using the same channel in this scheme will attain a common carrier-to-interference ratio. The proposed scheme is analyzed and shown to have an optimal solution. I. INTRODUCTION

Sudheer A. Grandhi; Rajiv Vijayan; David J. Goodman; Jens Zander

1993-01-01

262

Stability measurements of the radio science system at the 34-m high-efficiency antennas  

NASA Technical Reports Server (NTRS)

From 1991 to 1993 the fractional frequency stability of the operational Radio Science System was measured at DSS's 15, 45, and 65. These stations are designed to have the most stable uplink and downlink equipment in the Deep Space Network (DSN). Some measurements were performed when the antenna was moving and the frequency was ramped. The stability, including contributions of all elements in the station except for the antenna and the hydrogen maser, was measured to be 0.3 to 1.3 x 10(exp -15) when the frequency was fixed, and 0.6 to 6.0 x 10(exp -15) when the frequency was ramped (sample interval, 1000 sec). Only one measurement out of fifteen exceeded specification. In all other cases, when previous measurements on the antenna and the hydrogen maser were added, a total system stability requirement of 5.0 x 10(exp -15) as met. In addition, ambient temperature was found to cause phase variation in the measurements at a rate of 5.5 deg of phase per deg C.

Pham, T. T.; Breidenthal, J. C.; Peng, T. K.; Abbate, S. F.; Rockwell, S. T.

1993-01-01

263

Measurement of the t-channel single top quark production cross section  

SciTech Connect

The D0 collaboration reports direct evidence for electroweak production of single top quarks through the t-channel exchange of a virtual W boson. This is the first analysis to isolate an individual single top quark production channel. We select events containing an isolated electron or muon, missing transverse energy, and two, three or four jets from 2.3 fb{sup -1} of p{bar p} collisions at the Fermilab Tevatron Collider. One or two of the jets are identified as containing a b hadron. We combine three multivariate techniques optimized for the t-channel process to measure the t- and s-channel cross sections simultaneously. We measure cross sections of 3.14{sub -0.80}{sup +0.94} pb for the t-channel and 1.05 {+-} 0.81 pb for the s-channel. The measured t-channel result is found to have a significance of 4.8 standard deviations and is consistent with the standard model prediction.

Abazov, Victor Mukhamedovich; /Dubna, JINR; Abbott, Braden Keim; /Oklahoma U.; Abolins, Maris A.; /Michigan State U.; Acharya, Bannanje Sripath; /Tata Inst.; Adams, Mark Raymond; /Illinois U., Chicago; Adams, Todd; /Florida State U.; Aguilo, Ernest; /Alberta U. /Simon Fraser U. /York U., Canada /McGill U.; Ahsan, Mahsana; /Kansas State U.; Alexeev, Guennadi D.; /Dubna, JINR; Alkhazov, Georgiy D.; /St. Petersburg, INP; Alton, Andrew K.; /Michigan U. /Augustana Coll., Sioux Falls /Northeastern U.

2009-07-01

264

Cognitive Radio with Single Carrier TDCS and Multicarrier OFDM Approach with V-BLAST Receiver in Rayleigh Fading Channel  

Microsoft Academic Search

This paper presents the performance comparison of Cognitive Radio TDCS and OFDM based for MIMO system using VBLAST receiver architecture to reconstruct the transmitted data. The interference avoidance performance in terms of BER and bitrate are improved by adding multiple antennas to the system and the use of V-BLAST technique at the receiver. The results show the most promising interference

I. Budiarjo; H. Nikookar; L. P. Ligthart

2007-01-01

265

Quantum correlation evolution of GHZ and states under noisy channels using ameliorated measurement-induced disturbance  

NASA Astrophysics Data System (ADS)

We study quantum correlation of Greenberger-Horne-Zeilinger (GHZ) and W states under various noisy channels using measurement-induced disturbance approach and its optimized version. Although these inequivalent maximal entangled states represent the same quantum correlation in the absence of noise, it is shown that the W state is more robust than the GHZ state through most noisy channels. Also, using measurement-induced disturbance measure, we obtain the analytical relations for the time evolution of quantum correlations in terms of the noisy parameter and remove its overestimating quantum correlations upon implementing the ameliorated measurement-induced disturbance.

Espoukeh, Pakhshan; Pedram, Pouria

2015-01-01

266

Quantitative prediction of radio frequency induced local heating derived from measured magnetic field maps in magnetic resonance imaging: A phantom validation at 7 T  

NASA Astrophysics Data System (ADS)

Electrical Properties Tomography (EPT) technique utilizes measurable radio frequency (RF) coil induced magnetic fields (B1 fields) in a Magnetic Resonance Imaging (MRI) system to quantitatively reconstruct the local electrical properties (EP) of biological tissues. Information derived from the same data set, e.g., complex numbers of B1 distribution towards electric field calculation, can be used to estimate, on a subject-specific basis, local Specific Absorption Rate (SAR). SAR plays a significant role in RF pulse design for high-field MRI applications, where maximum local tissue heating remains one of the most constraining limits. The purpose of the present work is to investigate the feasibility of such B1-based local SAR estimation, expanding on previously proposed EPT approaches. To this end, B1 calibration was obtained in a gelatin phantom at 7 T with a multi-channel transmit coil, under a particular multi-channel B1-shim setting (B1-shim I). Using this unique set of B1 calibration, local SAR distribution was subsequently predicted for B1-shim I, as well as for another B1-shim setting (B1-shim II), considering a specific set of parameter for a heating MRI protocol consisting of RF pulses plaid at 1% duty cycle. Local SAR results, which could not be directly measured with MRI, were subsequently converted into temperature change which in turn were validated against temperature changes measured by MRI Thermometry based on the proton chemical shift.

Zhang, Xiaotong; Van de Moortele, Pierre-Francois; Liu, Jiaen; Schmitter, Sebastian; He, Bin

2014-12-01

267

High-resolution Radio Continuum Measurements of the Nuclear Disks of Arp 220  

NASA Astrophysics Data System (ADS)

We present new Karl G. Jansky Very Large Array radio continuum images of the nuclei of Arp 220, the nearest ultra-luminous infrared galaxy. These new images have both the angular resolution to study the detailed morphologies of the two nuclei that power the galaxy merger and sensitivity to a wide range of spatial scales. At 33 GHz, we achieve a resolution of 0.''081 × 0.''063 (29.9 × 23.3 pc) and resolve the radio emission surrounding both nuclei. We conclude from the decomposition of the radio spectral energy distribution that a majority of the 33 GHz emission is synchrotron radiation. The spatial distributions of radio emission in both nuclei are well described by exponential profiles. These have deconvolved half-light radii (R 50d ) of 51 and 35 pc for the eastern and western nuclei, respectively, and they match the number density profile of radio supernovae observed with very long baseline interferometry. This similarity might be due to the fast cooling of cosmic rays electrons caused by the presence of a strong (~mG) magnetic field in this system. We estimate extremely high molecular gas surface densities of 2.2+2.1-1.0 × 10^5 (east) and 4.5+4.5-1.9 × 10^5 (west) M ? pc-2, corresponding to total hydrogen column densities of N H = 2.7+2.7-1.2 × 1025 (east) and 5.6+5.5-2.4 × 1025 cm-2 (west). The implied gas volume densities are similarly high, {nH_{_2} ˜ 3.8+3.8-1.6 × 10^4} (east) and {˜ } 11+12-4.5 × 10^4 cm-3 (west). We also estimate very high luminosity surface densities of ? _IR ˜ 4.2+1.6-0.7 × 1013 (east) and ? _IR ˜ 9.7+3.7-2.4 × 1013 (west) L? kpc-2, and star formation rate surface densities of ?SFR ~ 103.7 ± 0.1 (east) and ?SFR ~ 104.1 ± 0.1(west) M ? yr-1kpc-2. These values, especially for the western nucleus are, to our knowledge, the highest luminosity surface densities and star formation rate surface densities measured for any star-forming system. Despite these high values, the nuclei appear to lie below the dusty Eddington limit in which radiation pressure is balanced only by self-gravity. The small measured sizes also imply that at wavelengths shorter than ? = 1 mm, dust absorption effects must play an important role in the observed light distribution while below 5 GHz free-free absorption contributes substantial opacity. According to these calculations, the nuclei of Arp 220 are only transparent in the frequency range ~5-350 GHz. Our results offer no clear evidence that an active galactic nucleus dominates the emission from either nucleus at 33 GHz.

Barcos-Muñoz, L.; Leroy, A. K.; Evans, A. S.; Privon, G. C.; Armus, L.; Condon, J.; Mazzarella, J. M.; Meier, D. S.; Momjian, E.; Murphy, E. J.; Ott, J.; Reichardt, A.; Sakamoto, K.; Sanders, D. B.; Schinnerer, E.; Stierwalt, S.; Surace, J. A.; Thompson, T. A.; Walter, F.

2015-01-01

268

The Role of Helium Metastable States in Radio-Frequency Helium-Oxygen Atmospheric Pressure Plasma Jets: Measurement and Numerical Simulation  

NASA Astrophysics Data System (ADS)

Absolute densities of metastable He atoms were measured line-of sight integrated along the plasma channel of a capacitively-coupled radio-frequency driven atmospheric pressure plasma jet operated in helium oxygen mixtures by tunable diode-laser absorption spectroscopy. Dependencies of the He metastable density with oxygen admixtures up to 1 percent were investigated. Results are compared to a 1-d numerical simulation, which includes a semi-kinetical treatment of the electron dynamics and the complex plasma chemistry (20 species, 184 reactions), and very good agreement is found. The main formation mechanisms for the helium metastables are identified and analyzed, including their pronounced spatio-temporal dynamics. Penning ionization through helium metastables is found to be significant for plasma sustainment, while it is revealed that helium metastables are not an important energy carrying species into the jet effluent and therefore will not play a direct role in remote surface treatments.

Niemi, Kari; Waskoenig, Jochen; Sadeghi, Nader; Gans, Timo; O'Connell, Deborah

2011-11-01

269

Measurements of peroxy radicals using dual-channel chemical amplification-cavity ringdown spectroscopy  

NASA Astrophysics Data System (ADS)

Peroxy radicals (hydroperoxy HO2 and organic peroxy RO2) play important roles in the photochemistry of troposphere. They are involved in the production and removal of ozone in the photochemical cycles and are closely related to atmospheric hydroxyl (OH) radical budget. In this work, a dual-channel peroxy radical chemical amplification (PERCA) instrument using diode laser cavity ring down spectroscopy (CRDS) is developed for measurements of the peroxy radicals. The ambient air is sampled into an amplification channel and a reference channel. In the amplification channel, HO2 and RO2 are first converted to NO2 via reactions with an excess amount of NO, and the OH and RO coproducts are recycled back to HO2 in subsequent reactions with an excess amount of CO and O2; the chain reactions of HO2 are repeated and amplify the level of NO2. The reference channel is for the background NO2 and O3. The NO2 concentrations from both channels are monitored simultaneously by two CRDS systems. The concentration of the amplified NO2 from HO2 and RO2 is determined as the difference between the amplification and the reference channel. The optimized amplification factor of the dual-channel PERCA-CRDS system is 180, calibrated using laboratory generated HO2 and CH3O2 radical sources. The detection sensitivity is shown to be ~4 ppt/10s (3?). The results from ambient studies and environmental chamber studies will be discussed.

Zhang, J.; Liu, Y.

2012-12-01

270

Measurement of the Top Quark Mass Simultaneously in Dilepton and Lepton + Jets Decay Channels  

SciTech Connect

The authors present the first measurement of the top quark mass using simultaneously data from two decay channels. They use a data sample of {radical}s = 1.96 TeV collisions with integrated luminosity of 1.9 fb{sup -1} collected by the CDF II detector. They select dilepton and lepton + jets channel decays of t{bar t} pairs and reconstruct two observables in each topology. They use non-parametric techniques to derive probability density functions from simulated signal and background samples. The observables are the reconstructed top quark mass and the scalar sum of transverse energy of the event in the dilepton topology and the reconstructed top quark mass and the invariant mass of jets from the W boson decay in lepton + jets channel. They perform a simultaneous fit for the top quark mass and the jet energy scale which is constrained in situ by the hadronic W boson resonance from the lepton + jets channel. Using 144 dilepton candidate events and 332 lepton + jets candidate events they measure: M{sub top} = 171.9 {+-} 1.7 (stat. + JES) {+-} 1.1 (other sys.) GeV/c{sup 2} = 171.9 {+-} 2.0 GeV/c{sup 2}. The measurement features a robust treatment of the systematic uncertainties, correlated between the two channels and develops techniques for a future top quark mass measurement simultaneously in all decay channels. Measurements of the W boson mass and the top quark mass provide a constraint on the mass of the yet unobserved Higgs boson. The Higgs boson mass implied by measurement presented here is higher than Higgs boson mass implied by previously published, most precise CDF measurements of the top quark mass in lepton + jets and dilepton channels separately.

Fedorko, Wojciech T.; /Chicago U.

2008-09-01

271

A NEW LINK-LEVEL SIMULATION PROCEDURE OF WIDEBAND MIMO RADIO CHANNEL FOR PERFORMANCE EVALUATION OF INDOOR WLANS  

Microsoft Academic Search

Abstract—Inspired by the requirement of proper link simulation methods in performance analysis of communication systems, we present in this paper a recipe for channel implementation in simulation environments. Our focus here is the indoor applications of wireless local-area networks (WLANs). Specifically, we describe a procedure that beginning with statistical description of the channel impulse response leads to an,efficient multi-input multi-output

Mahdi Golparvar Roozbahani; Esrafil Jedari; Amir Ahmad Shishegar

2008-01-01

272

Atmospheric peroxy radical measurements using dual-channel chemical amplification cavity ringdown spectroscopy.  

PubMed

Peroxy (HO2 and RO2) radicals are important intermediates in tropospheric oxidation of hydrocarbons, and their accurate atmospheric measurements remain challenging. In this work, the peroxy radical chemical amplification (PERCA) method was combined with cavity ringdown spectroscopy (CRDS) to develop a dual-channel instrument for measurements of atmospheric peroxy radicals. In the amplification channel, the peroxy radicals were converted in an excess amount of NO and CO into a higher level of NO2 and measured along with the background NO2, while in the reference channel, only the background NO2 (ambient NO2 and NO2 converted from O3 reaction with NO) was monitored. The NO2 levels from both channels were measured simultaneously at a high time resolution (~1 s) using two identical CRDS systems with one 408.5-nm diode laser, and their difference gave the amplified NO2 from PERCA. The peroxy radical concentration was obtained from the amplified NO2 and the calibrated amplification factor or chain length (CL). The optimized CL was 190 ± 20 (1?) using laboratory-generated HO2 and CH3O2 radical sources. The detection sensitivity was 4 ppt/10 s (3?). Ambient measurements in Riverside, CA were carried out. This dual-channel diode-laser PERCA-CRDS instrument was compact and capable of providing real-time, in situ, and sensitive measurements of atmospheric peroxy radicals with fast time response. PMID:24798952

Liu, Yingdi; Zhang, Jingsong

2014-06-01

273

Analysis of the tropopause parameters over the Iranian region using GPS radio occultation measurements  

NASA Astrophysics Data System (ADS)

Near-tropopause phenomena like upper level fronts and cyclones, penetrative cumulus convection and mesoscale mechanisms of exchange make important contributions to the mixing processes in the atmosphere. The dynamic atmospheric processes in the upper troposphere and the lower stratosphere are of significant interest due to their important role and impact on cirrus cloud formation and top of atmosphere radiative balance. Spatio-temporal monitoring of the tropopause height and its evolution over time provides important constraints on the atmospheric processes contributing to stratosphere-troposphere exchange. In this study, GPS radio occultation measurements are used to investigate the fluctuations of the tropopause heights and temperatures over the Iranian region. By applying the least-squares harmonic estimation (LS-HE) to the unevenly spaced time series of the tropopause parameters, annual and diurnal components are detected together with their higher harmonics. Multivariate LS-HE is shown to estimate the main periodic signals, particularly diurnal and semidiurnal cycles, more clearly than the univariate LS-HE. A bimodal pattern is observed in the frequency histograms of the tropopause parameters, in which the primary modes for the southern and northern parts of Iran correspond to subtropical and extra-tropical tropopause heights. Mixing in the values of the tropopause height and temperature is seen to occur in winter at lower latitudes (around 30°) as a result of subtropical jet, and in summer at higher latitudes (above 36°) as an effect of subtropical high. Consistency of the mixing region from the radio occultation data and the total ozone measurements from the Total Ozone Mapping Spectrometer (TOMS) is also observed.

Masoumi, S.; Sharifi, M. A.; Sam-Khaniani, A.; Joghataei, M.; Schmidt, T.; Wickert, J.; McClusky, S.

2013-12-01

274

Atomic nitrogen measurements in a radio-frequency atmospheric-pressure plasma jet  

NASA Astrophysics Data System (ADS)

Atmospheric-pressure plasma jets (APPJs) driven with radio-frequency voltages have the potential to be used in a range of new healthcare applications. To guarantee the safety and effectiveness of these new devices, a thorough understanding of the physics and chemistry of these plasmas is needed. The exact mechanisms through which APPJs affect biological materials like cells, bacteria and DNA are largely unknown, however, recent studies suggest the importance of reactive oxygen and nitrogen species (RONS). The starting point for the creation of many of the different RONS is the production of atomic oxygen and nitrogen in APPJs by breaking up oxygen and nitrogen gas molecules. In order to fully understand and control the production and effects of different RONS it is therforte important to measure atomic oxygen and nitrogen species in APPJs. This contribution presents the first direct measurements of atomic nitrogen species in APPJs. The measurements were performed with a two-photon absorption laser-induced fluorescence diagnostic, using 206.65 nm laser photons for the excitation of ground-state N atoms and observing fluorescence light around 744 nm. The APPJ was run with a helium gas flow of 1 slm and varying small admixtures of molecular nitrogen of 0 -- 0.7 vol%. A maximum in the measured N concentration was observed for an admixture of 0.25 vol% nitrogen gas.

Wagenaars, Erik; Gans, Timo; O'Connell, Deborah; Niemi, Kari

2012-10-01

275

Second order statistics of NLOS indoor MIMO channels based on 5.2 GHz measurements  

Microsoft Academic Search

Herein, results from measurements conducted by the University of Bristol are presented. The channel characteristics of multiple input multiple output (MIMO) indoor systems at 5.2 GHz are studied. Our investigation shows that the envelope of the channel for non-line-of-sight (NLOS) indoor situations are approximately Rayleigh distributed and consequently we focus on a statistical description of the first and second order

Kai Yu; Mats Bengtsson; Björn Ottersten; Darren McNamara; Peter Karlsson; Mark Beach

2001-01-01

276

Measurements and models of radio frequency impulsive noise for indoor wireless communications  

NASA Astrophysics Data System (ADS)

This paper presents the results of average and impulsive noise measurements inside several office buildings and retail stores. The noise measurement system operated at 918 MHz, 2.44 GHz, and 4 GHz with a nominal 40 MHz 3 dB RF bandwidth. Omnidirectional and directional antennas were used to investigate the characteristics and sources of RF noise in indoor channels. Statistical analyses of the measurements are presented in the form of peak amplitude probability distributions, pulse duration distributions, and interarrival time distributions. Simple first-order mathematical models for these statistical characterizations are also presented. These analyses indicate that photocopiers, printers (both line printers and cash register receipt printers), elevators, and microwave ovens are significant sources of impulsive noise in office and retail environments.

Blackard, Kenneth L.; Rappaport, Theodore S.; Bostian, Charles W.

1993-09-01

277

Shallow water radio-magnetotelluric (RMT) measurements in urban environment: A case study from Stockholm city  

NASA Astrophysics Data System (ADS)

The Radio-MagnetoTelluric (RMT) method uses the electromagnetic signal from distant radio transmitters in the frequency range 15 to 250 kHz. RMT applications in near-surface studies have already been well established. Two components of electric field and three components of magnetic field are measured. These measured components are related to each other via transfer functions which contain detailed information about the variation of electrical resistivity of the subsurface. The present study is carried out in the frame of TRUST (TRansparent Underground STructure) project supported by several research and public organizations as well as industry. The study area is located close to central Stockholm in Sweden where the Swedish traffic authority has planned to construct a 21-km long motorway to bypass the city. In order to reduce the impact on natural and cultural environments, 18 km of the motorway will be located in tunnels. The main objective of this study is thus to identify potential fracture zones and faults as well as the general geological settings. The proposed path of the tunnel partly passes under the Lake Mälaren at a depth of about 60 m. Thus a challenge was posed on the applicability of RMT method in shallow water environments. Successful applications of RMT measurements using the Uppsala University's EnviroMT system on land encouraged us to modify the system to acquire data over lake water especially in urban areas. Pioneered by the Geological Survey of Sweden (SGU), RMT data were collected over the Lake Mälaren in spring 2012. The prototype acquisition system did not only turn out to be appropriate for such a challenging environment, but it was also much more efficient as compared with land surveys. Fifty two lines including 1160 stations with an average spacing of 15 m were covered in three days. Cultural noise associated with the city-related environment had to be identified and filtered out before inversion could be carried out. Reliable estimates of the impedance tensor were obtained by the parametric representation combined with a Truncated Singular Value Decomposition (TSVD) regularization of Bastani and Pedersen (2001). The processed data were then inverted to obtain 2D resistivity models. The resulting models along 23 lines correlate well and image variation of water depth, thickness of subaqueous sediments as well as the depth to crystalline bedrock. Low resistivity zones observed in the bedrock coincide well with the low velocity zones identified in refraction seismic surveys available along the RMT lines, indicating the presence of possible fracture zones in the bedrock. The experiment illustrates that the RMT methods can be well adapted to this type of environment; it is fast and cost-effective in shallow water especially in urban settings. Acknowledgments: Formas, SGU, BeFo, SBUF, Skanska, Boliden, FQM and NGI References: Bastani, M., 2001, EnviroMT - a new Controlled Source/Radio Magnetotelluric System: Ph.D. thesis, ISBN 91-554-5051-2, Uppsala University. Bastani, M. and Pedersen, L. B., 2001, Estimation of magnetotelluric transfer functions from radio transmitters. GEOPHYSICS, 66, 1038-1051.

Mehta, Suman; Bastani, Mehrdad; Malehmir, Alireza; Wang, Shunguo; Pedersen, Laust

2014-05-01

278

All-digital impulse radio for MUI\\/ISI-resilient multiuser communications over frequency-selective multipath channels  

Microsoft Academic Search

Impulse radio (IR) is an ultra-wideband system with attractive features for baseband asynchronous multiple access (MA), multimedia services, and tactical wireless communications. Implemented with analog components, the continuous-time IRMA model utilizes pulse-position modulation (PPM) and random time-hopping codes to alleviate multipath effects and suppress multiuser interference (MUI). We introduce a novel continuous-time multiple input multiple output (MIMO) PPM-IRMA scheme, and

Christophe J. Le Martret; Georgios B. Giannakis

2000-01-01

279

Temperature and Pressure Measurements and Visualization of He II Cavitation Flow through Venturi Channel  

SciTech Connect

He II cavitation flow through a Venturi channel was experimentally investigated through temperature and pressure measurements and optical visualization. So far some distinctive features of cavitation between He II and He I flows were clarified. Then, detailed measurements were added for further investigation, such as the measurements of the temperature drop distribution throughout the flow channel and the void fraction. Further considerations were given on the cavitation inception with emphasis on the superheating of liquid helium, and the effect of the flow separation on cavitation.

Ishii, T.; Murakami, M.; Harada, K. [Institute of Engineering Mechanics and Systems, University of Tsukuba, Tennodai 1-1-1, Tsukuba 305-8573 (Japan)

2004-06-23

280

Channel Selection Based on Phase Measurement in P300-Based Brain-Computer Interface  

PubMed Central

Most EEG-based brain-computer interface (BCI) paradigms include specific electrode positions. As the structures and activities of the brain vary with each individual, contributing channels should be chosen based on original records of BCIs. Phase measurement is an important approach in EEG analyses, but seldom used for channel selections. In this paper, the phase locking and concentrating value-based recursive feature elimination approach (PLCV-RFE) is proposed to produce robust-EEG channel selections in a P300 speller. The PLCV-RFE, deriving from the phase resetting mechanism, measures the phase relation between EEGs and ranks channels by the recursive strategy. Data recorded from 32 electrodes on 9 subjects are used to evaluate the proposed method. The results show that the PLCV-RFE substantially reduces channel sets and improves recognition accuracies significantly. Moreover, compared with other state-of-the-art feature selection methods (SSNRSF and SVM-RFE), the PLCV-RFE achieves better performance. Thus the phase measurement is available in the channel selection of BCI and it may be an evidence to indirectly support that phase resetting is at least one reason for ERP generations. PMID:23593261

Xu, Minpeng; Qi, Hongzhi; Ma, Lan; Sun, Changcheng; Zhang, Lixin; Wan, Baikun; Yin, Tao; Ming, Dong

2013-01-01

281

Prediction and measurement of incipient boiling heat flux in micro-channel heat sinks  

E-print Network

-phase heat sink can result in an unusually large stream-wise temper- ature rise in both the cooling liquidPrediction and measurement of incipient boiling heat flux in micro-channel heat sinks Weilin Qu Abstract Experiments were performed to measure the incipient boiling heat flux in a heat sink containing 21

Qu, Weilin

282

Revisiting the radio interferometer measurement equation. I. A full-sky Jones formalism  

NASA Astrophysics Data System (ADS)

Context. Since its formulation by Hamaker et al., the radio interferometer measurement equation (RIME) has provided a rigorous mathematical basis for the development of novel calibration methods and techniques, including various approaches to the problem of direction-dependent effects (DDEs). However, acceptance of the RIME in the radio astronomical community at large has been slow, which is partially due to the limited availability of software to exploit its power, and the sparsity of practical results. This needs to change urgently. Aims: This series of papers aims to place recent developments in the treatment of DDEs into one RIME-based mathematical framework, and to demonstrate the ease with which the various effects can be described and understood. It also aims to show the benefits of a RIME-based approach to calibration. Methods: Paper I re-derives the RIME from first principles, extends the formalism to the full-sky case, and incorporates DDEs. Paper II then uses the formalism to describe self-calibration, both with a full RIME, and with the approximate equations of older software packages, and shows how this is affected by DDEs. It also gives an overview of real-life DDEs and proposed methods of dealing with them. Finally, in Paper III some of these methods are exercised to achieve an extremely high-dynamic range calibration of WSRT observations of 3C 147 at 21 cm, with full treatment of DDEs. Results: The RIME formalism is extended to the full-sky case (Paper I), and is shown to be an elegant way of describing calibration and DDEs (Paper II). Applying this to WSRT data (Paper III) results in a noise-limited image of the field around 3C 147 with a very high dynamic range (1.6 million), and none of the off-axis artifacts that plague regular selfcal. The resulting differential gain solutions contain significant information on DDEs and errors in the sky model. Conclusions: The RIME is a powerful formalism for describing radio interferometry, and underpins the development of novel calibration methods, in particular those dealing with DDEs. One of these is the differential gains approach used for the 3C 147 reduction. Differential gains can eliminate DDE-related artifacts, and provide information for iterative improvements of sky models. Perhaps most importantly, sources as faint as 2 mJy have been shown to yield meaningful differential gain solutions, and thus can be used as potential calibration beacons in other DDE-related schemes.

Smirnov, O. M.

2011-03-01

283

Computer model for selective flow measuring structures in open channels  

NASA Astrophysics Data System (ADS)

Quantifying various pollutants in natural waterways has received increased emphasis with more stringent regulations issued by the Environmental Protection Agency (E.P.A.). Measuring natural stream flows presents a magnitude of problems, the most significant is the type of structure needed to measure the flows at the desired level of accuracy. A computer model designed to select a structure to best fit the engineer's needs is under development. This model, given the pertinent boundary conditions, will pinpoint the structure most suitable, if one exists. This selection process greatly facilitates the old selection process of trial and error.

Hickey, M. J.

1980-02-01

284

Intrinsic noise measurement of an ultra-sensitive radio-frequency single electron transistor  

NASA Astrophysics Data System (ADS)

The radio-frequency single electron transistor (rf-SET) has been the focus of intense interest since its invention in 1998[1]. Using cryogenic ultra-thin film evaporation techniques [2] and an improved on-chip superconducting matching network [3], we have consistently fabricated rf-SETs with charge sensitivity of 1.7--5?e/?Hz and uncoupled energy sensitivity 1.1--5. Using our 1GHz resonant circuit, intrinsic noise in the SET arising from a dc voltage bias was measured in the white noise limit. We measured the offset charge dependence of the intrinsic noise in the vicinity of the Josephson-quasiparticle and double Josephson-quasiparticle transport cycles. In regions for which the offset charge and resistance noise are strongly suppressed, we can determine the SET shot noise in the sup-gap regime. We discuss the effects of correlations between charge carriers on the measured Fano factor. [1] R.J.Schoelkopf et al., Science 280,1238 (1998); [2] N.A.Court et al., Cond-mat 0706.4150 (2007); [3] W.W.Xue et al., Appl.Phys.Lett. 91, 093511 (2007).

Xue, W. W.; Ji, Z.; Pan, Feng; Rimberg, A. J.

2008-03-01

285

Probe measurements of the space potential in a radio frequency discharge  

NASA Astrophysics Data System (ADS)

The dc and radio frequency (rf) components (and harmonics) of the probe potential have been measured in the midplane of a 13.56-MHz parallel-plane rf discharge in argon over a wide range of discharge voltages and at gas pressures between 10 mTorr and 1.0 Torr. rf potential measurements were made with different input capacitances to determine the true magnitude of the rf plasma potential and the probe capacitance. For a symmetrically driven rf discharge, the rf plasma potential Vrf is mainly composed of the second harmonic of the driving voltage Vdr over a wide range of gas pressures. For high values of Vdr, Vrf ?0.1 Vdr while the dc probe potential Vdc is about 0.4 Vdr. These results are in good agreement with corresponding theoretical predictions found in the literature. For an asymmetrically driven rf discharge with equal electrode area, the rf plasma potential has an additional fundamental harmonic component equal to half the rf driving voltage. Values of rf plasma potential and probe capacitance given here allow us to specify the requirements on probe circuitry for different kinds of probe measurements in rf discharges.

Godyak, V. A.; Piejak, R. B.

1990-10-01

286

Measurements of atomic nitrogen distributions in a radio-frequency atmospheric-pressure plasma jet  

NASA Astrophysics Data System (ADS)

Radio-frequency (RF) driven atmospheric-pressure plasma jets (APPJs) are expected to have a range of new healthcare applications. To guarantee the effectiveness and safety of these devices, a thorough understanding of the physics and chemistry of these plasmas is needed. We studied an RF-APPJ in helium with small admixtures of nitrogen and/or oxygen. The low-temperature APPJ effluent contains high concentrations of reactive species such as atomic nitrogen and oxygen. The N and O radicals play a crucial role in the plasma chemistry and discharge dynamics, but are unfortunately difficult to measure experimentally. We present a two-photon absorption laser-induced fluorescence (TALIF) technique for measuring atomic nitrogen species, which uses 207 nm photons for excitation of ground-state N atoms and observes time-resolved fluorescence at 745 nm. With this diagnostic we directly measure the spatial and temporal evolution of atomic nitrogen species, and compare these to the results of a numerical model based on hydrodynamic equations with a semi-kinetic treatment of the electrons.

Wagenaars, Erik; Niemi, Kari; O'Connell, Deborah; Gans, Timo

2011-11-01

287

Radio Frequency Phototube, Optical Clock and Precise Measurements in Nuclear Physics  

E-print Network

Recently a new experimental program of novel systematic studies of light hypernuclei using pionic decay was established at JLab (Study of Light Hypernuclei by Pionic Decay at JLab, JLab Experiment PR-08-012). The highlights of the proposed program include high precision measurements of binding energies of hypernuclei by using a high resolution pion spectrometer, HpiS. The average values of binding energies will be determined within an accuracy of ~10 keV or better. Therefore, the crucial point of this program is an absolute calibration of the HpiS with accuracy 10E-4 or better. The merging of continuous wave laser-based precision optical-frequency metrology with mode-locked ultrafast lasers has led to precision control of the visible frequency spectrum produced by mode-locked lasers. Such a phase-controlled mode-locked laser forms the foundation of an optical clock or femtosecond optical frequency comb (OFC) generator, with a regular comb of sharp lines with well defined frequencies. Combination of this technique with a recently developed radio frequency (RF) phototube results in a new tool for precision time measurement. We are proposing a new time-of-flight (TOF) system based on an RF phototube and OFC technique. The proposed TOF system achieves 10 fs instability level and opens new possibilities for precise measurements in nuclear physics such as an absolute calibration of magnetic spectrometers within accuracy 10E-4 - 10E-5.

Amur Margaryan

2009-10-24

288

Conductive Sphere in a Radio Frequency Field: Theory and Applications to Positioners, Heating, and Noncontact Measurements  

NASA Technical Reports Server (NTRS)

An electrically conductive spherical sample located in an electromagnetic field excited by rf (radio frequency) current in a system of coaxial coils is treated theoretically. Maxwell's equations are solved exactly and all integrals in the formulas for the fields are evaluated analytically for the case where the sphere is on the axis and the coil system is modeled by a stack of filamentary circular loops. Formulas are also derived for electromagnetic force exerted on the sphere, excess impedance in the coil system due to the presence of the sphere, and power absorbed by the sphere. All integrals in those formulas have been evaluated analytically. Force measurements are presented and they are in excellent agreement with the new theory. A low-power electromagnetic levitator that is accurately described by the theory has been demonstrated and is discussed. Experimental measurements of excess impedance are presented and compared with theory, and those results are used to demonstrate an accurate noncontact method for determining electrical conductivity. Theoretical formulas for power absorption are evaluated numerically and their usefulness in both rf heating and in making noncontact measurements of a number of thermophysical properties of materials is discussed.

Jackson, H. W.; Watkins, J. L.; Chung, S.; Wagner, P.

1996-01-01

289

Measurement of heat transfer and pressure drop in rectangular channels with turbulence promoters  

NASA Technical Reports Server (NTRS)

Periodic rib turbulators were used in advanced turbine cooling designs to enhance the internal heat transfer. The objective of the present project was to investigate the combined effects of the rib angle of attack and the channel aspect ratio on the local heat transfer and pressure drop in rectangular channels with two opposite ribbed walls for Reynolds number varied from 10,000 to 60,000. The channel aspect ratio (W/H) was varied from 1 to 2 to 4. The rib angle of attack (alpha) was varied from 90 to 60 to 45 to 30 degree. The highly detailed heat transfer coefficient distribution on both the smooth side and the ribbed side walls from the channel sharp entrance to the downstream region were measured. The results showed that, in the square channel, the heat transfer for the slant ribs (alpha = 30 -45 deg) was about 30% higher that of the transverse ribs (alpha = 90 deg) for a constant pumping power. However, in the rectangular channels (W/H = 2 and 4, ribs on W side), the heat transfer at alpha = 30 -45 deg was only about 5% higher than 90 deg. The average heat transfer and friction correlations were developed to account for rib spacing, rib angle, and channel aspect ratio over the range of roughness Reynolds number.

Han, J. C.; Park, J. S.; Ibrahim, M. Y.

1986-01-01

290

Initial results from radio occultation measurements with the Mars Reconnaissance Orbiter: A nocturnal mixed layer in the tropics  

E-print Network

, Pasadena, CA 91109, USA d Space Science and Astrobiology Division, NASA Ames Research Center, Moffett Field, dynamics Meteorology a b s t r a c t The Mars Reconnaissance Orbiter (MRO) performs radio occultation (RO the measurements with numerical simulations by the NASA Ames Mars General Circulation Model, which demonstrate

Spiga, Aymeric

291

Nighttime D region electron density measurements from ELF-VLF tweek radio atmospherics recorded at low latitudes  

E-print Network

. It plays an important role in the propagation of extremely low frequency (ELF: 30­3000Hz) and very lowNighttime D region electron density measurements from ELF- VLF tweek radio atmospherics recorded at low latitudes Ajeet K. Maurya,1 B. Veenadhari,2 Rajesh Singh,1 Sushil Kumar,3 M. B. Cohen,4 R

292

Measurements of a 150 to 1700 MHz low loss Eleven feed for the 42 m radio telescope at Green Bank  

Microsoft Academic Search

We present measured results for a dual polarized 150 to 1700 MHz Eleven feed for use in the 42 m radio telescope in Green Bank. The feed is manufactured from a 3 mm thick aluminium plate and located inside a steel container with a soft radome over its opening. The feed provides dual polarization and more than a decade bandwidth.

Rikard Olsson; Per-Simon Kildal; Mike Shields

2006-01-01

293

Quantitative measurement of gas pressure drop along T-shaped micro channels by interferometry  

NASA Astrophysics Data System (ADS)

The study of gas flows in microchannels has received considerably more attention in the literature from a simulation perspective than an experimental. The majority of the experimental work has emphasis on the global measurements at the inlet or exit of the microchannel instead locally along it. In this paper some efforts were made to measure the pressure drop along T-shaped micro channel by using interferometry. The two side channels were served as gas entrances and they were both open to air and the channel outlet was being vacuumed during experiments. A Mach-Zehnder interference microscopy was built for the measurement of gas pressure drop along the mixing channel. Some points along the mixing channel were selected for interferometric measurements. Simulations were first developed in unsteady condition by using Ansys Fluent to verify the nonexistence of transient phenomena of gas flow in the defined condition and then run again in steady condition to get the theoretical pressure drop that was would be used for comparison with experimental results.

Li, Y.; Joseph, S.; Colin, S.; Baldas, L.; Barrot, C.; Orieux, S.; Newport, D.; Brandner, J. J.

2012-05-01

294

Streaming potentials in gramicidin channels measured with ion-selective microelectrodes.  

PubMed Central

Streaming potentials have been measured for gramicidin channels with a new method employing ion-selective microelectrodes. It is shown that ideally ion-selective electrodes placed at the membrane surface record the true streaming potential. Using this method for ion concentrations below 100 mM, approximately seven water molecules are transported whenever a sodium, potassium, or cesium ion, passes through the channel. This new method confirms earlier measurements (Rosenberg, P.A., and A. Finkelstein. 1978. Interaction of ions and water in gramicidin A channels. J. Gen. Physiol. 72:327-340) in which the streaming potentials were calculated as the difference between electrical potentials measured in the presence of gramicidin and in the presence of the ion carriers valinomycin and nonactin. PMID:9635745

Tripathi, S; Hladky, S B

1998-01-01

295

A New Top Mass Measurement in The Dilepton Channel  

SciTech Connect

The top quark discovery completed the present picture of the fundamental constituents of the nature. Since then, the Collider Detector at Fermilab and D0 Collaborations have been spending great efforts to measure its properties better. About 30 times larger than the second heaviest quark, the mass of the top has been measured with increased statistic and more and more sophisticated techniques in order to reduce as much as possible its uncertainty. This is because the top is expected to play a fundamental role in the Standard Model. The value of its mass sets boundaries on the mass of the unobserved Higgs boson, and perhaps more appealing, studies of its properties might lead to the discovery of new physics.

Trovato, Marco; /INFN, Pisa /Pisa U.

2008-01-01

296

RADIO WAVE PROPAGATION IN PERPENDICULAR STREETS OF URBAN STREET GRID FOR MICROCELLULAR COMMUNICATIONS. PART I: CHANNEL MODELING - ABSTRACT  

Microsoft Academic Search

This paper proposes a spatial variant wideband propaga- tion model for perpendicular street of urban street grid. Analytical expression of the spatial variant multi-ray channel transfer function is derived. The model provides characteristics of each ray in explicit expressions. The ray characteristics are given in terms of complex amplitude for both vertical and horizontal polarizations, path length, angle of arrival

H. M. El-Sallabi; P. Vainikainen

2003-01-01

297

Acceleration Technique of Radio Propagation Simulator Based on the Ray Tracing for the Prediction of MIMO Channels in Dynamical Railway  

E-print Network

of MIMO Channels in Dynamical Railway Environment Siham HAIROUD, Pierre COMBEAU, Jean-Franc¸ois CAILBAULT the computation time of a railway tunnel simulation. It consists in modifying the modeling envi- ronment some years wireless communications systems found their place in the railway transport. Various

Boyer, Edmond

298

Radio Astronomy Radio astronomy  

E-print Network

Effelsberg 100m telescope (Germany) Green Bank 100m telescope (National Radio Astronomy ObservatoryExperiment -10m (Chile, Europe) #12;Submillimeter radio astronomy #12;Size of telescope Snow sweep at Nobeyama 45;#12;Arecibo 300m telescope #12;Radio interferometer #12;Radio interferometer Very Large Array (VLA) (New

Metchev, Stanimir

299

Voltage-dependent gating and gating charge measurements in the Kv1.2 potassium channel.  

PubMed

Much has been learned about the voltage sensors of ion channels since the x-ray structure of the mammalian voltage-gated potassium channel Kv1.2 was published in 2005. High resolution structural data of a Kv channel enabled the structural interpretation of numerous electrophysiological findings collected in various ion channels, most notably Shaker, and permitted the development of meticulous computational simulations of the activation mechanism. The fundamental premise for the structural interpretation of functional measurements from Shaker is that this channel and Kv1.2 have the same characteristics, such that correlation of data from both channels would be a trivial task. We tested these assumptions by measuring Kv1.2 voltage-dependent gating and charge per channel. We found that the Kv1.2 gating charge is near 10 elementary charges (eo), ?25% less than the well-established 13-14 eo in Shaker. Next, we neutralized positive residues in the Kv1.2 S4 transmembrane segment to investigate the cause of the reduction of the gating charge and found that, whereas replacing R1 with glutamine decreased voltage sensitivity to ?50% of the wild-type channel value, mutation of the subsequent arginines had a much smaller effect. These data are in marked contrast to the effects of charge neutralization in Shaker, where removal of the first four basic residues reduces the gating charge by roughly the same amount. In light of these differences, we propose that the voltage-sensing domains (VSDs) of Kv1.2 and Shaker might undergo the same physical movement, but the septum that separates the aqueous crevices in the VSD of Kv1.2 might be thicker than Shaker's, accounting for the smaller Kv1.2 gating charge. PMID:25779871

Ishida, Itzel G; Rangel-Yescas, Gisela E; Carrasco-Zanini, Julia; Islas, León D

2015-04-01

300

Differential space-frequency coding for a multipath fading channel  

Microsoft Academic Search

This paper will investigate differential space frequency coding and its applicability to multipath fading High Frequency (HF) radio channels. Orthogonal Frequency Division Multiplexing (OFDM) will be combined with differential Alamouti space frequency codes to measure performance on the Watterson HF channel model. Differential coding facilitates non-coherent reception and can thus also reduce receiver complexity. Numerical results will be shown for

Fred C. Kellerman

2004-01-01

301

Channel model for tyre pressure monitoring systems (TPMS)  

Microsoft Academic Search

Tyre pressure monitoring systems rely on radio transmissions to transfer measurement data from the sensors to the vehicle body. These systems operate on a propagation channel which is time variant and introduces Doppler shifts due to vehicle movements. In the following paper we investigate these effects. First we propose, develop and characterise a channel model for TPMS, which is comprised

Gregor Lasser; Christoph F. Mecklenbrauker

2010-01-01

302

Radio Telescopes  

NASA Astrophysics Data System (ADS)

``Radio Telescopes" starts with a brief historical introduction from Jansky's1931 discovery of radio emission from the Milky Way through the development ofradio telescope dishes and arrays to aperture synthesis imaging. It includessufficient basics of electromagnetic radiation to provide some understanding of thedesign and operation of radio telescopes. The criteria such as frequencyrange, sensitivity, survey speed, angular resolution, and field of view thatdetermine the design of radio telescopes are introduced. Because it is soeasy to manipulate the electromagnetic waves at radio frequencies, radiotelescopes have evolved into many different forms, sometimes with "wire"structures tuned to specific wavelengths, which look very different from anykind of classical telescope. To assist astronomers more familiar with otherwavelength domains, the appendix A.1. includes a comparison of radioand optical terminology. Some of the different types of radio telescopesincluding the filled aperture dishes, electronically steered phased arrays, andaperture synthesis radio telescopes are discussed, and there is a sectioncomparing the differences between dishes and arrays. Some of the morerecent developments including hierarchical beam forming, phased arrayfeeds, mosaicing, rotation measure synthesis, digital receivers, and longbaseline interferometers are included. The problem of increasing radiofrequency interference is discussed, and some possible mitigation strategies areoutlined.

Ekers, Ron; Wilson, Thomas L.

303

Simultaneous radio and satellite optical measurements of high-altitude sprite current and lightning continuing current  

E-print Network

postreturn stroke extremely low frequency (ELF) magnetic pulses, the optical emissions demonstrate. On the basis of unusual extremely low frequency (ELF) radio pulses sometimes seen in asso- ciation with sprite] Lightning remote sensing by low-frequency radio emissions is an effective technique for detecting and quan

California at Berkeley, University of

304

Design parameters and measured performance of the IRAM 30-m Millimeter Radio Telescope  

Microsoft Academic Search

The “Millimeter Radio Telescope” (MRT) is operated by the Institute for Radio Astronomy in the millimeter range (IRAM) and is located at 2850-m altitude in the Sierra Nevada, near Granada, Spain. It is a reflector antenna of 30-m diameter with a surface accuracy of 0.08 mm and a pointing accuracy of better than 2 arcsec. The telescope is equipped with

JACOB W. M. BAARS; ALBERT GREVE; HAUKE HEIN; DAVE MORRIS; JUAN PENALVER; CLEMENS THUM

1994-01-01

305

Dispersion measure contributed by a relativistic neutron star wind and implication for fast radio bursts  

E-print Network

The possible contribution to dispersion measure (DM) by neutron star winds is investigated by introducing a relativistic definition of the DM. On one hand, I propose that the observed fast radio bursts (FRBs) could be produced by activities on some peculiar young Galactic neutron stars, where the large DMs of the FRBs can be ascribed to the neutron star winds rather than the intergalactic medium. On the other hand, in the sight of cosmological origin of FRBs, I also investigate the possible association of the FRBs with the collapses of millisecond magnetars harbored in gamma-ray bursts (GRBs). In particular, as required by the observed bright internal X-ray afterglows, a high intrinsic DM could be contributed by the emitting neutron star winds, which could even exceed the contribution from the intergalactic medium. In any case, such a result is strongly dependent on the uncertain dissipation mechanisms of the winds and more DM measurements of FRBs could provide stringent constraints on the wind physics.

Yu, Yun-Wei

2014-01-01

306

Morphology of solar wind fluctuations and structure in the vicinity of the Sun from radio propagation measurements  

NASA Technical Reports Server (NTRS)

Radio propagation measurements represent a powerful means for remote probing of electron density and solar wind speed in the acceleration region of the solar wind not yet explored by in situ measurements. Recent investigations based on radio propagation measurements have led to considerable progress in our knowledge of the general morphology of solar wind fluctuations and structure, especially in terms of their relationship to solar wind properties that have been observed directly by fields and particles measurements, and to coronal features observed in white-light measurements. The purpose of this paper is to present an overview of the latest results on quasi-stationary structure covering the large scale variation of solar wind speed over the streamer belt and coronal hole regions, coronal streamers (source of slow solar wind) and their associated small-scale electron density structure, plumes, density and fractional or relative density fluctuations, and the spectral characteristics of the electron density fluctuations. The radio propagation measurements not only reveal new information on the structure near the Sun, but also show that the structure appears to undergo substantial evolution on its way to 0.3 AU, the closest radial distance for which direct in situ spacecraft measurements are available.

Woo, R.

1995-01-01

307

A Measurement of the Millimeter Emission and the Sunyaev-zel'dovich Effect Associated with Low-frequency Radio Sources  

NASA Technical Reports Server (NTRS)

We present a statistical analysis of the millimeter-wavelength properties of 1.4 GHz-selected sources and a detection of the Sunyaev-Zel'dovich Effect associated with the halos that host them. The Atacama Cosmology Telescope (ACT) has conducted a survey at 148 GHz, 218 GHz and 277 GHz along the celestial equator. Using samples of radio sources selected at 1.4 GHz from the Faint Images of the Radio Sky at Twenty-Centimeters (FIRST) Survey and the National Radio Astronomy Observatory Very Large Array Sky Survey (NVSS), we measure the stacked 148, 218 and 277 GHz flux densities for sources with 1.4 GHz flux densities ranging from 5 to 200 mJy. At these flux densities, the radio source population is dominated by active galactic nuclei (AGN), with both steep and at spectrum populations, which have combined radio-to-millimeter spectral indices ranging from 0.5 to 0.95, reecting the prevalence of steep spectrum sources at high flux densities and the presence of at spectrum sources at lower flux densities. The thermal Sunyaev-Zelapos;dovich (SZ) eect associated with the halos that host the AGN is detected at the 5 level through its spectral signature. When we compare the SZ eect with weak lensing measurements of radio galaxies, we find that the relation between the two is consistent with that measured by Planck for local bright galaxies. We present a detection of the SZ eect in some of the lowest mass halos (average M(sub 200) approx. equals 10(exp 13) solar M h(sup-1) (sub 70) ) studied to date. This detection is particularly important in the context of galaxy evolution models, as it confirms that galaxies with radio AGN also typically support hot gaseous halos. With Herschel* observations, we show that the SZ detection is not significantly contaminated by dusty galaxies or by dust associated with the AGN or galaxies hosting the AGN. We show that 5 mJy < S(sub 1:4) < 200 mJy radio sources contribute l(l +1)C(sub l)/(2 pi ) = 0:37+/- 0:03 micro K(exp 2) to the angular power spectrum at l = 3000 at 148 GHz, after accounting for the SZ effect associated with their host halos.

Gralla, Megan B.; Crichton, Devin; Marriage, Tobias A.; Mo, Wenli; Aguirre, Paula; Addison, Graeme E.; Asboth, V.; Battaglia, Nick; Bock, James; Bond, J. Richard; Devlin, Mark J.; Duenner, Rolando; Hajian, Amir; Halpern, Mark; Hilton, Matt; Hincks, Adam D.; Hlozek Renee A.; Huffenberger, Kevin M.; Hughes, John P.; Ivison, R. J.; Kosowsky, Arthur; Lin, Yen-Ting; Switzer, Eric R.; Wollack, Edward J.; Zemcov, Michael B.

2013-01-01

308

A noise-aware combination of dual-frequency measurements from GPS radio occultation  

NASA Astrophysics Data System (ADS)

of the fundamental difficulties that arise when using GPS Radio Occultation (RO) data in exploiting the stratosphere is that the air becomes rarefied with increasing height and accentuates the ionospheric effect and noise contained in the measurement. Customarily, the conventional linear combination (CLC) is used to extract neutral atmospheric components from dual-frequency (L1 and L2) RO data. The CLC combines and magnifies measurement noises, and thus works well only for those measurements of low noise. Although the L1 data are of considerably higher quality than the L2 data, the CLC does not take this into account and treats both equally; this makes the CLC-produced data less attractive. The authors propose a new approach, named Noise-Aware Combination (NAC), which is a generalized combination that factors in the presence of measurement noise. In this NAC method, the L1 and L2 data are each regarded independently, with each contributing to the combination according to its dynamically assessed accuracy. The performance of both the CLC and NAC are tested with two sets of data: one of synthetic data and the other of real data. The tests confirm that the NAC yields significant error reductions when compared to the CLC. While the noise in the CLC-produced data stands out in high altitudes and compels the data to be blended with the a priori, the NAC relies far less on this blending. The clear advantage of the NAC over the CLC would greatly enhance the value of RO for climate research.

Wee, Tae-Kwon; Kuo, Ying-Hwa

2013-12-01

309

Calibrating high-precision Faraday rotation measurements for LOFAR and the next generation of low-frequency radio telescopes  

NASA Astrophysics Data System (ADS)

Faraday rotation measurements using the current and next generation of low-frequency radio telescopes will provide a powerful probe of astronomical magnetic fields. However, achieving the full potential of these measurements requires accurate removal of the time-variable ionospheric Faraday rotation contribution. We present ionFR, a code that calculates the amount of ionospheric Faraday rotation for a specific epoch, geographic location, and line-of-sight. ionFR uses a number of publicly available, GPS-derived total electron content maps and the most recent release of the International Geomagnetic Reference Field. We describe applications of this code for the calibration of radio polarimetric observations, and demonstrate the high accuracy of its modeled ionospheric Faraday rotations using LOFAR pulsar observations. These show that we can accurately determine some of the highest-precision pulsar rotation measures ever achieved. Precision rotation measures can be used to monitor rotation measure variations - either intrinsic or due to the changing line-of-sight through the interstellar medium. This calibration is particularly important for nearby sources, where the ionosphere can contribute a significant fraction of the observed rotation measure. We also discuss planned improvements to ionFR, as well as the importance of ionospheric Faraday rotation calibration for the emerging generation of low-frequency radio telescopes, such as the SKA and its pathfinders.

Sotomayor-Beltran, C.; Sobey, C.; Hessels, J. W. T.; de Bruyn, G.; Noutsos, A.; Alexov, A.; Anderson, J.; Asgekar, A.; Avruch, I. M.; Beck, R.; Bell, M. E.; Bell, M. R.; Bentum, M. J.; Bernardi, G.; Best, P.; Birzan, L.; Bonafede, A.; Breitling, F.; Broderick, J.; Brouw, W. N.; Brüggen, M.; Ciardi, B.; de Gasperin, F.; Dettmar, R.-J.; van Duin, A.; Duscha, S.; Eislöffel, J.; Falcke, H.; Fallows, R. A.; Fender, R.; Ferrari, C.; Frieswijk, W.; Garrett, M. A.; Grießmeier, J.; Grit, T.; Gunst, A. W.; Hassall, T. E.; Heald, G.; Hoeft, M.; Horneffer, A.; Iacobelli, M.; Juette, E.; Karastergiou, A.; Keane, E.; Kohler, J.; Kramer, M.; Kondratiev, V. I.; Koopmans, L. V. E.; Kuniyoshi, M.; Kuper, G.; van Leeuwen, J.; Maat, P.; Macario, G.; Markoff, S.; McKean, J. P.; Mulcahy, D. D.; Munk, H.; Orru, E.; Paas, H.; Pandey-Pommier, M.; Pilia, M.; Pizzo, R.; Polatidis, A. G.; Reich, W.; Röttgering, H.; Serylak, M.; Sluman, J.; Stappers, B. W.; Tagger, M.; Tang, Y.; Tasse, C.; ter Veen, S.; Vermeulen, R.; van Weeren, R. J.; Wijers, R. A. M. J.; Wijnholds, S. J.; Wise, M. W.; Wucknitz, O.; Yatawatta, S.; Zarka, P.

2013-04-01

310

Instantaneous measure of EEG channel importance for improved patient-adaptive neonatal seizure detection.  

PubMed

A measure of bipolar channel importance is proposed for EEG-based detection of neonatal seizures. The channel weights are computed based on the integrated synchrony of classifier probabilistic outputs for the channels which share a common electrode. These estimated time-varying weights are introduced within a Bayesian probabilistic framework to provide a channel specific and, thus, adaptive seizure classification scheme. Validation results on a clinical dataset of neonatal seizures confirm the utility of the proposed channel weighting for the two patient-independent seizure detectors recently developed by this research group: one based on support vector machines (SVMs) and the other on Gaussian mixture models (GMMs). By exploiting the channel weighting, the receiver operating characteristic (ROC) area can be significantly increased for the most difficult patients, with the average ROC area across 17 patients increased by 22% (relative) for the SVM and by 15% (relative) for the GMM-based detector, respectively. It is shown that the system developed here outperforms the recent published studies in this area. PMID:22156948

Temko, Andriy; Lightbody, Gordon; Thomas, Eoin M; Boylan, Geraldine B; Marnane, William

2012-03-01

311

A measurement of the millimetre emission and the Sunyaev-Zel'dovich effect associated with low-frequency radio sources  

NASA Astrophysics Data System (ADS)

We present a statistical analysis of the millimetre-wavelength properties of 1.4 GHz-selected sources and a detection of the Sunyaev-Zel'dovich (SZ) effect associated with the haloes that host them. We stack data at 148, 218 and 277 GHz from the Atacama Cosmology Telescope at the positions of a large sample of radio AGN selected at 1.4 GHz. The thermal SZ effect associated with the haloes that host the AGN is detected at the 5? level through its spectral signature, representing a statistical detection of the SZ effect in some of the lowest mass haloes (average M200 ? 1013 M_{{?}} h_{70}^{-1}) studied to date. The relation between the SZ effect and mass (based on weak lensing measurements of radio galaxies) is consistent with that measured by Planck for local bright galaxies. In the context of galaxy evolution models, this study confirms that galaxies with radio AGN also typically support hot gaseous haloes. Adding Herschel observations allows us to show that the SZ signal is not significantly contaminated by dust emission. Finally, we analyse the contribution of radio sources to the angular power spectrum of the cosmic microwave background.

Gralla, Megan B.; Crichton, Devin; Marriage, Tobias A.; Mo, Wenli; Aguirre, Paula; Addison, Graeme E.; Asboth, V.; Battaglia, Nick; Bock, James; Bond, J. Richard; Devlin, Mark J.; Dünner, Rolando; Hajian, Amir; Halpern, Mark; Hilton, Matt; Hincks, Adam D.; Hlozek, Renée A.; Huffenberger, Kevin M.; Hughes, John P.; Ivison, R. J.; Kosowsky, Arthur; Lin, Yen-Ting; Marsden, Danica; Menanteau, Felipe; Moodley, Kavilan; Morales, Gustavo; Niemack, Michael D.; Oliver, Seb; Page, Lyman A.; Partridge, Bruce; Reese, Erik D.; Rojas, Felipe; Sehgal, Neelima; Sievers, Jon; Sifón, Cristóbal; Spergel, David N.; Staggs, Suzanne T.; Switzer, Eric R.; Viero, Marco P.; Wollack, Edward J.; Zemcov, Michael B.

2014-11-01

312

A Measurement of the Millimeter Emission and the Sunyaev-Zel'dovich Effect Associated with Low-Frequency Radio Sources  

NASA Technical Reports Server (NTRS)

We present a statistical analysis of the millimeter-wavelength properties of 1.4 GHz-selected sources and a detection of the Sunyaev-Zel'dovich effect associated with the halos that host them. We stack data at 148, 218 and 277 GHz from the Atacama Cosmology Telescope at the positions of a large sample of radio AGN selected at 1.4 GHz. The thermal Sunyaev-Zel'dovich (SZ) effect associated with the halos that host the AGN is detected at the 5 sigma level through its spectral signature, representing a statistical detection of the SZ effect in some of the lowest mass halos (average M(sub 200) approximately equals 10(sup 13) solar mass h(sub 70)(exp -1) ) studied to date. The relation between the SZ effect and mass (based on weak lensing measurements of radio galaxies) is consistent with that measured by Planck for local bright galaxies. In the context of galaxy evolution models, this study confirms that galaxies with radio AGN also typically support hot gaseous halos. Adding Herschel observations allows us to show that the SZ signal is not significantly contaminated by dust emission. Finally, we analyze the contribution of radio sources to the angular power spectrum of the cosmic microwave background.

Gralla, Megan B.; Crichton, Devin; Marriage, Tobias; Mo, Wenli; Aguirre, Paula; Addison, Graeme E.; Asboth, V.; Battaglia, Nick; Bock, James; Bond, J. Richard; Devlin, Mark; Dunner, Rolando; Hajian, Amir; Halpern, Mark; Hilton, Matt; Hincks, Adam D.; Hlozek, Renee A.; Huffenberger, Kevin M.; Hughes, John P.; Ivison, R.J.; Kosowsky, Arthur; Lin, Yen-Ting; Marsden, Danica; Menanteau, Felipe; Wollack, Edward J.

2014-01-01

313

Radio Galaxies.  

ERIC Educational Resources Information Center

Provides background information on radio galaxies. Topic areas addressed include: what produces the radio emission; radio telescopes; locating radio galaxies; how distances to radio galaxies are found; physics of radio galaxies; computer simulations of radio galaxies; and the evolution of radio galaxies with cosmic time. (JN)

Downes, Ann

1986-01-01

314

Quantitative Measurement of Vocal Fold Vibration in Male Radio Performers and Healthy Controls Using High-Speed Videoendoscopy  

PubMed Central

Purpose Acoustic and perceptual studies show a number of differences between the voices of radio performers and controls. Despite this, the vocal fold kinematics underlying these differences are largely unknown. Using high-speed videoendoscopy, this study sought to determine whether the vocal vibration features of radio performers differed from those of non-performing controls. Method Using high-speed videoendoscopy, recordings of a mid-phonatory/i/ in 16 male radio performers (aged 25–52 years) and 16 age-matched controls (aged 25–52 years) were collected. Videos were extracted and analysed semi-automatically using High-Speed Video Program, obtaining measures of fundamental frequency (f0), open quotient and speed quotient. Post-hoc analyses of sound pressure level (SPL) were also performed (n?=?19). Pearson's correlations were calculated between SPL and both speed and open quotients. Results Male radio performers had a significantly higher speed quotient than their matched controls (t?=?3.308, p?=?0.005). No significant differences were found for f0 or open quotient. No significant correlation was found between either open or speed quotient with SPL. Discussion A higher speed quotient in male radio performers suggests that their vocal fold vibration was characterised by a higher ratio of glottal opening to closing times than controls. This result may explain findings of better voice quality, higher equivalent sound level and greater spectral tilt seen in previous research. Open quotient was not significantly different between groups, indicating that the durations of complete vocal fold closure were not different between the radio performers and controls. Further validation of these results is required to determine the aetiology of the higher speed quotient result and its implications for voice training and clinical management in performers. PMID:24971625

Warhurst, Samantha; McCabe, Patricia; Heard, Rob; Yiu, Edwin; Wang, Gaowu; Madill, Catherine

2014-01-01

315

Measurements of Antenna Surface for a Millimeter-Wave Space Radio Telescope II; Metal Mesh Surface for Large Deployable Reflector  

E-print Network

Large deployable antennas with a mesh surface woven by fine metal wires are an important technology for communications satellites and space radio telescopes. However, it is difficult to make metal mesh surfaces with sufficient radio-frequency (RF) performance for frequencies higher than millimeter waves. In this paper, we present the RF performance of metal mesh surfaces at 43 GHz. For this purpose, we developed an apparatus to measure the reflection coefficient, transmission coefficient, and radiative coefficient of the mesh surface. The reflection coefficient increases as a function of metal mesh surface tension, whereas the radiative coefficient decreases. The anisotropic aspects of the reflection coefficient and the radiative coefficient are also clearly seen. They depend on the front and back sides of the metal mesh surface and the rotation angle. The transmission coefficient was measured to be almost constant. The measured radiative coefficients and transmission coefficients would cause significant degr...

Kamegai, Kazuhisa

2012-01-01

316

Modelling and measuring the wind forced inflow to the Irish Sea through the North Channel  

NASA Astrophysics Data System (ADS)

The wind-induced flow though the North Channel of the Irish Sea during the period 13 March-26 March 1994 has been investigated using a range of three-dimensional models, and current observations were made using an acoustic Doppler current profiler (ADCP). Computed surface elevations are compared with shore based and one off shore tide gauge measurements. A shelf wide coarse grid (of order 12 km resolution) model forced by hourly varying wind stresses and pressure gradients, is used to provide boundary conditions for a finer grid (of order 5 km) west coast model. A high-resolution model (of order 1 km) is used to resolve the North Channel region. Calculations with the large area models show the importance of shelf wide wind events particularly those along the west coast of Britain in influencing the flow through the North Channel. Two different meteorological situations producing a flow to the south in the North Channel (an inflow to the Irish Sea) are identified during the simulations. The first is a region of strong winds from the west, off the west coast of Scotland, with only light winds off Ireland and over the Irish Sea. These winds force a flow to the south along the west coast of Scotland, through the North Channel and into the Irish Sea. The second meteorological situation is a region of uniform winds from the southwest over the whole west coast of Britain, which then changes to a wind field from the west. This drives a flow to the north along the west coast of Ireland, part of which continues to the north, although some of the flow passes round northern Ireland, and then flows to the south within the North Channel. The response of the various models to these changing wind events are studied in detail and computed currents are compared with those measured using the ADCP. This shows that computed along-channel currents are underpredicted at all depths, although there is no bias in the computed across-channel currents away from the near-bed layer. However, close to the bed the model has a bias to overpredict the across channel flow. These biases are probably due to inaccuracies in resolving the topography of the deep water region in the central North Channel. On average the model reproduces the current to within±4 cm s -1 for the majority of the period. Similarly, sea surface elevations are accurately (to within 12 cm RMS error) reproduced.

Davies, Alan M.; Hall, Philip; Howarth, M. John; Knight, Philip

2002-03-01

317

Measurement of the top quark pair production cross section in the all-jets decay channel  

E-print Network

of 7.1 +/- 2.8(stat) +/- 1.5(syst) pb at a top quark mass (m(t)) of 172.1 GeV/c(2). Using previous D0 measurements from dilepton and single lepton channels, the combined D0 result for the production cross section is 5.9 +/- 1.2(stat...

Baringer, Philip S.; Coppage, Don; Hebert, C.

1999-09-01

318

THE CORRELATION BETWEEN DISPERSION MEASURE AND X-RAY COLUMN DENSITY FROM RADIO PULSARS  

SciTech Connect

Pulsars are remarkable objects that emit across the entire electromagnetic spectrum, providing a powerful probe of the interstellar medium. In this study, we investigate the relation between dispersion measure (DM) and X-ray absorption column density N{sub H} using 68 radio pulsars detected at X-ray energies with the Chandra X-Ray Observatory or XMM-Newton. We find a best-fit empirical linear relation of N{sub H} (10{sup 20} cm{sup -2})= 0.30{sup +0.13}{sub -0.09} DM (pc cm{sup -3}), which corresponds to an average ionization of 10{sup +4}{sub -3}%, confirming the ratio of one free electron per 10 neutral hydrogen atoms commonly assumed in the literature. We also compare different N{sub H} estimates and note that some N{sub H} values obtained from X-ray observations are higher than the total Galactic H I column density along the same line of sight, while the optical extinction generally gives the best N{sub H} predictions.

He, C.; Ng, C.-Y.; Kaspi, V. M., E-mail: ncy@bohr.physics.hku.hk [Department of Physics, McGill University, Montreal, QC H3A 2T8 (Canada)

2013-05-01

319

A radio-polarisation and rotation measure study of the Gum Nebula and its environment  

E-print Network

The Gum Nebula is 36 degree wide shell-like emission nebula at a distance of only 450 pc. It has been hypothesised to be an old supernova remnant, fossil HII region, wind-blown bubble, or combination of multiple objects. Here we investigate the magneto-ionic properties of the nebula using data from recent surveys: radio-continuum data from the NRAO VLA and S-band Parkes All Sky Surveys, and H-alpha data from the Southern H-Alpha Sky Survey Atlas. We model the upper part of the nebula as a spherical shell of ionised gas expanding into the ambient medium. We perform a maximum-likelihood Markov chain Monte-Carlo fit to the NVSS rotation measure data, using the H-halpha data to constrain average electron density in the shell $n_e$. Assuming a latitudinal background gradient in RM we find $n_e=1.3^{+0.4}_{-0.4} {\\rm cm}^{-3}$, angular radius $\\phi_{\\rm outer}=22.7^{+0.1}_{-0.1} {\\rm deg}$, shell thickness $dr=18.5^{+1.5}_{-1.4} {\\rm pc}$, ambient magnetic field strength $B_0=3.9^{+4.9}_{-2.2} \\mu{\\rm G}$ and warm ...

Purcell, C R; Sun, X H; Carretti, E; Bernardi, G; Haverkorn, M; Kesteven, M J; Poppi, S; Schnitzeler, D H F M; Staveley-Smith, L

2015-01-01

320

Reconciling Models of Luminous Blazars with Magnetic Fluxes Determined by Radio Core-shift Measurements  

NASA Astrophysics Data System (ADS)

Estimates of magnetic field strength in relativistic jets of active galactic nuclei, obtained by measuring the frequency-dependent radio core location, imply that the total magnetic fluxes in those jets are consistent with the predictions of the magnetically arrested disk (MAD) scenario of jet formation. On the other hand, the magnetic field strength determines the luminosity of the synchrotron radiation, which forms the low-energy bump of the observed blazar spectral energy distribution (SED). The SEDs of the most powerful blazars are strongly dominated by the high-energy bump, which is most likely due to the external radiation Compton mechanism. This high Compton dominance may be difficult to reconcile with the MAD scenario, unless (1) the geometry of external radiation sources (broad-line region, hot-dust torus) is quasi-spherical rather than flat, or (2) most gamma-ray radiation is produced in jet regions of low magnetization, e.g., in magnetic reconnection layers or in fast jet spines.

Nalewajko, Krzysztof; Sikora, Marek; Begelman, Mitchell C.

2014-11-01

321

Observation of temporal variations in global sporadic E occurrence rates derived from GPS radio occultation measurements  

NASA Astrophysics Data System (ADS)

The GPS radio occultation (RO) technique has been established as a powerful tool for ionospheric research. With approximately one million of globally distributed profiles per year provided by the FORMOSAT-3/COSMIC satellites, our data base allows for sporadic E (Es) layer observation with a high spatial resolution and global coverage. Sporadic E layers are thin regions of enhanced electron density in the lower ionospheric E region. They cause strong amplitude scintillations in GPS occultation signals. We use Signal-to-Noise Ratio (SNR) profiles of the GPS L1 signal in order to obtain information on the sporadic E occurrence. Sudden changes in the vertical electron density gradients, which indicate the presence of a sporadic E layer, appear as strong fluctuations in the SNR above 85 km altitude. The FORMOSAT-3/COSMIC data, together with measurements collected by the satellites CHAMP and GRACE which provided continuously RO data since 2001 and 2006, respectively, enables initial trend analysis of Es occurrence. In this study we focus on the variations of sporadic E occurrence rates on different time scales. We will present the diurnal, annual and interannual variability of sporadic E layers and show their connection to other geophysical parameters like solar tides.

Arras, Christina; Wickert, Jens; Jacobi, Christoph; Heise, Stefan

2014-05-01

322

Error analysis for intrinsic quality factor measurement in superconducting radio frequency resonators.  

PubMed

In this paper, we discuss error analysis for intrinsic quality factor (Q0) and accelerating gradient (Eacc) measurements in superconducting radio frequency (SRF) resonators. The analysis is applicable for cavity performance tests that are routinely performed at SRF facilities worldwide. We review the sources of uncertainties along with the assumptions on their correlations and present uncertainty calculations with a more complete procedure for treatment of correlations than in previous publications [T. Powers, in Proceedings of the 12th Workshop on RF Superconductivity, SuP02 (Elsevier, 2005), pp. 24-27]. Applying this approach to cavity data collected at Vertical Test Stand facility at Fermilab, we estimated total uncertainty for both Q0 and Eacc to be at the level of approximately 4% for input coupler coupling parameter ?1 in the [0.5, 2.5] range. Above 2.5 (below 0.5) Q0 uncertainty increases (decreases) with ?1 whereas Eacc uncertainty, in contrast with results in Powers [in Proceedings of the 12th Workshop on RF Superconductivity, SuP02 (Elsevier, 2005), pp. 24-27], is independent of ?1. Overall, our estimated Q0 uncertainty is approximately half as large as that in Powers [in Proceedings of the 12th Workshop on RF Superconductivity, SuP02 (Elsevier, 2005), pp. 24-27]. PMID:25554312

Melnychuk, O; Grassellino, A; Romanenko, A

2014-12-01

323

Multi-channel transimpedance measurement of a planar electromagnetic sensor array  

NASA Astrophysics Data System (ADS)

Planar electromagnetic sensor arrays have advantages such as nice coherence, fast response speed and high sensitivity, which can be used for micro damage inspection of crucial parts in equipment, and the key point in improving the inspection performance is to achieve a precise measurement of multi-channel transimpedances (the inductive voltages divided by the exciting current of the sensor). The principle and characteristics of planar electromagnetic sensor arrays are introduced in this paper, and a digital lock-in impedance measurement algorithm was investigated, with which the interference and noise in inductive voltage signals can be restrained effectively and the amplitude and phase of the transimpedance can be obtained with good repeatability. An eight channel impedance measurement system was established based on a field programmable gate array and utilized to inspect the micro damage in metal materials, and the experimental data were analyzed. The experimental results show that the impedance measurement has excellent repeatability when the sensor array is placed in air, and the maximum measurement error of the complete transimpedance measurement system is lower than 10%. A micro crack with a size of 1?mm (length) × 0.1?mm (width) × 1?mm (depth) can be detected through the measurement of multi-channel transimpedance in the planar electromagnetic sensor array.

Chen, Dixiang; Xie, Ruifang; Zhou, Weihong; Hu, Hengjiang; Pan, Mengchun

2015-02-01

324

Three-Channel Imaging Fabry Perot Interferometer for Measurement of MidLatitude Airglow  

Microsoft Academic Search

We have developed a three-channel imaging Fabry -Perot interferometer with which to measure atmospheric wind and temperature in the mesosphere and thermosphere through nocturnal airglow emissions. The interferometer measures two-dimensional wind and temperature for wavelengths of 630.0 nm (OI, altitude, 200 -300 km), 557.7 nm (OI, 96 km), and 839.9 nm (OH, 86 km) simultaneously with a time resolution of

Kazuo Shiokawa; Takurou Kadota; Mitsumu K. Ejiri; Yuichi Otsuka; Yasuo Katoh; Mitsugi Satoh; Tadahiko Ogawa

2001-01-01

325

Revisiting the Dispersion Measure of Fast Radio Bursts Associated with Gamma-Ray Burst Afterglows  

NASA Astrophysics Data System (ADS)

Some fast radio bursts (FRBs) are expected to be associated with the afterglow emission of gamma-ray bursts (GRBs), while a short-lived, supermassive neutron star (NS) forms during the GRBs. I investigate the possible contributions to the dispersion measure (DM) of the FRBs from the GRB ejecta and the wind blown from the precollapsing NS. On the one hand, sometimes an internal X-ray plateau afterglow could be produced by the NS wind, which indicates that a great number of electron-positron pairs are carried by the wind. If the pair-generation radius satisfies a somewhat rigorous condition, the relativistic and dense wind would contribute a high DM to the associated FRB, which can be comparable to and even exceed the DM contributed by the intergalactic medium. On the other hand, if the wind only carries a Goldreich-Julian particle flux, its DM contribution would become negligible; meanwhile, the internal plateau afterglow would not appear. Alternatively, the FRB should be associated with a GRB afterglow produced by the GRB external shock, i.e., an energy-injection-caused shallow-decay afterglow or a normal single-power-law afterglow if the impulsive energy release of the GRB is high enough. In the latter case, the DM contributed by the high-mass GRB ejecta could be substantially important, in particular, for an environment of main-sequence stellar wind. In summary, a careful assessment on the various DM contributors could be required for the cosmological application of the expected FRB-GRB association. The future DM measurements of GRB-associated FRBs could provide a constraint on the physics of NS winds.

Yu, Yun-Wei

2014-12-01

326

Coupled Radon and Water Temperature Measurements to Characterize the Effects of Altered Stream Channel Planform  

NASA Astrophysics Data System (ADS)

In summer 2011, a 2.6 km reach of Meacham Creek, Oregon, USA, was altered from a straight, steep wall-based channel to more a sinuous, low-gradient channel. Key objectives of this restoration project were to increase the rate and magnitude of hyporheic exchange. The overarching goal was to initiate increased buffering and lagging of water temperature in the subsurface to mitigate warm surface water temperature in Meacham Creek, an important spawning and rearing stream for depressed populations of Chinook salmon and summer steelhead. To evaluate progress toward project goals and objectives, stream temperature and groundwater temperature in 22 wells have been measured hourly at the restoration site since March 2011. In addition, the radioactive isotope 222Rn was measured in each well and in the surface water on two occasions. The relative residence time of down welling stream water measured in the wells can be determined by ranked amplitude depression and lagged phase of annual temperature signals in the wells relative to that of the open channel flow. Residence times predicted by annual temperature signal dynamics are corroborated by 222Rn concentrations in each well. The data collected to date provide a foundation for developing a groundwater thermal model to predict the effects of channel reconfiguration on ground-surface water exchange and associated temperature effects at the reach scale.

Amerson, B. E.; Poole, G. C.; O'Daniel, S. J.

2013-12-01

327

Effects of horizontal velocity variations on ultrasonic velocity measurements in open channels  

USGS Publications Warehouse

Use of an ultrasonic velocity meter to determine discharge in open channels involves measuring the velocity in a line between transducers in the stream and relating that velocity to the average velocity in the stream. The standard method of calculating average velocity in the channel assumes that the velocity profile in the channel can be represented by the one-dimensional von Karman universal velocity profile. However, the velocity profile can be described by a two-dimensional equation that accounts for the horizontal velocity variations induced by the channel sides. An equation to calculate average velocity accounts for the two-dimensional variations in velocity within a stream. The use of this new equation to calculate average velocity was compared to the standard method in theoretical trapezoidal cross sections and in the L-31N and Snapper Creek Extension Canals near Miami, Florida. These comparisons indicate that the two-dimensional variations have the most significant effect in narrow, deep channels. Also, the two-dimensional effects may be significant in some field situations and need to be considered when determining average velocity and discharge with an ultrasonic velocity meter.

Swain, E.D.

1992-01-01

328

Pressure Drop Measurements in Rectangular Micro-Channel Using Gas Flow  

E-print Network

Abstract: Due to the need for practical cooling technologies which could dissipate high heat fluxes, an experimental study of pressure drop in micro-channel was performed. In this work, laminar flow friction factors were determined using gas (air) as flow medium. Pressure drop vs flow rate data were used to evaluate friction factors in two parallel microchannels, namely MCP1 and MCP2 (1.0 mm deep x 0.240 mm width and 0.9 mm deep x 0.2 mm width, respectively). Each channel of length 192 mm fabricated on a 304 Stainless Steel substrate by chemical milling Reynolds number was covered between 24 – 5398 for MCP1 and 26 – 6233 for MCP2. Transient pressure drops measured within the channel itself to exclude entrance and exit losses. Friction factor – Reynolds number analyses show that the friction constant are identical as normal channels for gas flow in the laminar region. Transition region lies in Re> 500 and transition set off at lower Re ~ 500 in comparison to normal channel. The discontinuity in f – Re data identified as transition. Further, it may be possible to identify transition (from laminar region) as the deviation of non-dimensional pressure drop (NDPD) values.

329

Fluorescent labeling for patch-clamp fluorometry (PCF) measurements of real-time protein motion in ion channels.  

PubMed

Understanding the function of ion channels is a major goal of molecular neurophysiology. While standard electrophysiological methods are invaluable tools to investigate the gating of ion channels, the structural rearrangements that mediate the way a channel senses physiological signals and opens and closes its gates cannot be measured electrically in a direct way. Here, we describe a method, based on site-specific labeling of a channel of interest with an environmentally sensitive fluorophore, which makes it possible to monitor conformational changes of ion channels in biological membranes in real time. PMID:25560069

Berger, Thomas K; Isacoff, Ehud Y

2015-01-01

330

High Throughput Channel Tracking for JTRS Wireless Channel Emulation  

E-print Network

Tactical Radio System (JTRS) is a standard for software defined radio (SDR) systems. It has an advantage frequency hopping. To meet these requirements we developed a software defined radio channel emulator using is a challenging but an important problem. This is particular true for the Joint Tactical Radio System (JTRS) where

Hasty, Jeff

331

Millimeter-wave urban and suburban propagation measurements using narrow and wide bandwidth channel probes  

NASA Astrophysics Data System (ADS)

Measurements reported are part of a study of propagation characteristics for millimeter-wave communication links operating in an urban-suburban environment. Absorption data were collected for signals propagated through some common building materials. At these same channel frequencies, paths at street level obstructed by office buildings and residential properties were examined in terms of received signal levels resulting from direct penetration and/or propagation by diffraction modes with terminal separation of from 0.1 to 1.2 km. Signal fading was measured for line-of-sight paths traveled down an urban street. Narrow- and wide-beam antenna patterns and both modes of linear antenna polarization were used to compare multipath fading characteristics. A unique 30.3 GHz wide bandwith channel impulse probe was used to record multipath signal amplitudes and delay times. Impulse response measurements were recorded as the transmitter traveled along the urban street.

Violette, E. J.; Espeland, R. H.; Hand, G. R.

1985-11-01

332

Hydration status measurement by radio frequency absorptiometry in young athletes---a new method and preliminary results  

Microsoft Academic Search

A new method for non-invasive measurement of the human state of hydration is presented. This method is based on frequency-dependent absorptiometry of radio-waves passing through tissues. A device utilizing this method was constructed and applied to 12 young (24 ± 1) male volunteers, who were dehydrated for 1-2.5% of their weight by performance of a physical effort (two 30 min

Daniel S. Moran; Yuval Heled; Menachem Margaliot; Yoav Shani; Arie Laor; Shulamit Margaliot; Elazar Eyal Bickels; Yair Shapiro

2004-01-01

333

Method and apparatus for measuring temperature of an earth formation in the presence of a radio frequency electromagnetic field  

SciTech Connect

A method and apparatus for measuring the temperature in a subsurface earth formation that is being heated in situ by subjection to a radio frequency electromagnetic field. It includes lowering a maximum registering thermometer into the formation on a non-conductive flexible line, and holding it there long enough to reach the ambient temperature at that location. Then, the thermometer is raised to the surface fast enough to avoid any significant change on the way up to read that registered maximum.

Kunetka, R.E.; Dowling, D.J.

1984-09-04

334

Characterization of Ionospheric Scintillation Using Simultaneous Formosat-3\\/COSMIC Radio Occultation Observations and AFRL SCINDA Ground Scintillation Measurements  

Microsoft Academic Search

Ionospheric scintillation at low latitudes has been studied using ionospheric radio occultation (RO) measurements by the FORMOSAT-3\\/COSMIC micro-satellites in conjunction with ground-based data from the Scintillation Network Decision Aid (SCINDA) station at Kwajalein Atoll. The Air Force Research Laboratory has developed the SCINDA network for monitoring low-latitude ionospheric total electron content (TEC) and scintillation associated with equatorial spread F. The

M. J. Starks; C. S. Lin; K. M. Groves; T. R. Pedersen; S. Basu; S. Syndergaard; C. Rocken

2007-01-01

335

Simultaneous Transmission of Wireless and Wireline Services Using a Single 60GHz Radio-Over-Fiber Channel by Coherent Subcarrier Modulation  

Microsoft Academic Search

We proposed and experimentally demonstrated a novel hybrid subcarrier modulation (H-SCM) technique to generate a spectral-efficient 60-GHz optical millimeter-wave (mm-wave) that carries independent 2.5-Gb\\/s wireless and 10-Gb\\/s wireline signals using intensity and phase modulation, respectively. The frequency beating components of the 60-GHz channel due to interleaved and imbalanced optical path in H-SCM are numerically analyzed and experimentally measured in terms

Shu-Hao Fan; Hung-Chang Chien; Yu-Ting Hsueh; Arshad Chowdhury; Jianjun Yu; Gee-Kung Chang

2009-01-01

336

Hydration status measurement by radio frequency absorptiometry in young athletes--a new method and preliminary results.  

PubMed

A new method for non-invasive measurement of the human state of hydration is presented. This method is based on frequency-dependent absorptiometry of radio-waves passing through tissues. A device utilizing this method was constructed and applied to 12 young (24 +/- 1) male volunteers, who were dehydrated for 1-2.5% of their weight by performance of a physical effort (two 30 min bouts of treadmill walking/running at 2, 3, 4, 5, 6 and 7 mph, 5 min at each speed, separated by 10 min rest), under moderate heat stress (40 degrees C, 40% RH). Hypohydration level was determined by body weight measurements taken before each session, after 30 min and at the end of each session. Concomitantly, measurements of radio frequency (RF) absorption were taken. Each volunteer underwent the heat stress exercise twice: one in which no drinking was permitted, and another with free drinking. A correlation (R2 = 0.734) between weight loss and a change in the radio-waves absorption pattern was observed in most of the volunteers, in both hypo and euhydration sessions. Further work to establish the reproducibility and validity of the RF methodology in larger and different populations, i.e., females, other age groups and different health conditions, is already being researched. PMID:15005304

Moran, Daniel S; Heled, Yuval; Margaliot, Menachem; Shani, Yoav; Laor, Arie; Margaliot, Shulamit; Bickels, Elazar Eyal; Shapiro, Yair

2004-02-01

337

Venus: ionosphere and atmosphere as measured by dual-frequency radio occultation of mariner v.  

PubMed

Venus has daytime and nighttime ionospheres at the positions probed by radio occulation. The main layers are thin by terrestrial standards, with the nighttime peak concentration of electrons being about two orders of magnitude below that of the daytime peak. Above the nighttime peak were several scale-height regimes extending to a radius of at least 7500, and probably to 9700, kilometers from the center of Venus. Helium and hydrogen at plasma temperatures of 600 degrees to 1100 degrees K seem indicated in the regimes from 6300 to 7500 kilometers, with cooler molecular ions in lower regions. Above the daytime peak a sharp plasmapause was discovered, marking a sudden transition from appreciable ionization concentrations near Venus to the tenuous conditions of the solar wind. This may be indicative of a kind of interaction of the magnetized solar wind with a planetary body that differs from the two different kinds of interaction characterized by Earth and by Moon. For Venus and probably for Mars, the magnetic field of the solar wind may pile up in front of the conducting ionosphere, form an induced magnetosphere that ends at the plasmapause, above which any ionosphere that tends to form is swept away by the shocked solar wind that flows between the stand-off bow-shock and the magnetopause. The neutral atmosphere was also probed and a surface reflection may have been detected, but the data have not yet been studied in detail. Results are consistent with a super-refractive atmosphere, as expected from Soviet measurements near the surface. Thus, two unusual features of Venus can be described in terms of a light trap in the lower atmosphere, and a magnetic trap in the conducting ionosphere. PMID:17749790

1967-12-29

338

Heat transfer and pressure drop measurement in wavy channels with flow disturbers  

SciTech Connect

In the current work, the transient method was employed to obtain the local heat transfer coefficient for a 6 in. x 3/8 in. x 12 in. (15.24cm x .9525cm x 30.48cm) Plexiglas {reg_sign} wavy channel with and without flow disturbers. A short duration transient test was performed to measure the heat transfer coefficient by introducing heated air over test specimen that had been sprayed with calibrated thermochromic liquid crystals. This technique allowed the experimenter to observe the temperature changes using a video camera. because a Plexiglas surface has a low thermal diffusivity, a one-dimensional assumption is a reasonable approximation because the surface temperature response is limited to a thin layer near the surface and lateral conduction is small. The heat transfer coefficient using the transient technique is then determined from the response of the surface temperature to a step change in the local temperature. Using this method, the axial variation in the heat transfer coefficient for Reynolds numbers in the laminar (1100) and turbulent region (2900) were obtained. These Reynolds numbers were based on the hydraulic diameter at the inlet of the wavy channel. Also, in this investigation, the region of greatest heat transfer and the pressure drop were both experimentally and analytically determined and the friction factor across an in-phase corrugated wall channel (wavy channel) at Reynolds numbers of 1100 and 2900 were obtained. A manometer and a pressure transducer were employed to measure pressure drop across the channel. The effect of flow disturbers mounted on each peak, alternate peaks and the first six peaks of a twelve-peak channel were also investigated. For all cases, the pressure drop and friction factor were shown to moderately increase with rib placement in the test section when compared to the results obtained from a similar smooth wavy channel without ribs. Additionally, for all cases, the friction factor also decreased with an increase in the Reynolds number. If the ratio of pumping power to heat transfer rate was selected as the primary criteria, the channel with a flow disturber placed on alternate peaks was determined to be the best configuration. The following figure illustrates the color changes of the liquid crystals.

Dini, S.; Veronesi, R.; Hryniewicz, E.V.

1999-07-01

339

Ultra-wideband channel model for communication around the human body  

Microsoft Academic Search

Using ultra-wideband (UWB) wireless sensors placed on a person to continuously monitor health information is a promising new application. However, there are currently no detailed models describing the UWB radio channel around the human body making it difficult to design a suitable communication system. To address this problem, we have measured radio propagation around the body in a typical indoor

Andrew Fort; Julien Ryckaert; Claude Desset; Philippe De Doncker; Piet Wambacq; Leo Van Biesen

2006-01-01

340

Photogrammetric survey to measure the bed topography of a laboratory large amplitude meandering channel  

NASA Astrophysics Data System (ADS)

One of the main characteristics of the rivers that exhibit a meandering planform is the continuous evolution of the planimetric shape. In order to limit flooding risks and to control the ecological equilibrium of the areas neighboring the channel, it is important to define a forecast methodology of the channel evolution. The pattern of the channel evolution strongly depends on the configuration of the "stable" bed topography along the channel in every stage of the evolution itself. Previous works [Schumm, 1963; Schumm, 1972; Jackson, 1975; Hooke, 1976; Ren and Jun, 1989; Whiting and Dietrich, 1993] show that the localization of the erosion and deposition zones along the channel is not standard but it depends on the planimetric shape of the channel itself. For example, it was shown that at the early stage of a meander wave evolution (small value of deflection angle J0) the deepest erosion of the bed is localized at the inner bank between the sections corresponding respectively to the inflection point and to the apex of the bend. In channels with "large" sinuosity (large value of deflection angle J0) the deepest erosion is localized in the outer bank near the apex of the bend [Yalin, 1992]. Recently, da Silva et al. [2006] verified that every different sinuosity (every J0) has its own convective flow pattern and, as previously observed in a large amplitude meandering channel by Termini (1996), the knowledge of the convective structure of the depth-averaged "initial" (determined at t=0 with flat bed) flow, which is associated only to changing channel curvature, can be used to predict the general features of bed topography. Thus, the knowledge of the stable bed topography is important to predict the channel planimetric evolution. In this paper the equilibrium bed topography determined in a large meandering laboratory channel has been first measured by a using a profile indicator PV09 by Delft Hydraulics (precision of 0.1 mm). The PV09 is designed to maintain a constant distance between the probe and the bed (or between the probe and the free surface) in order to maintain a constant electric capacity. Thus, the instrument is able to monitor the temporal or the spatial variation of the bed (or the free surface) sampling a value per second. Then, the analogical output is converted into digital, filtered and recorded by the help of a PC card NI-DAQ (National Instruments) and of a data acquisition algorithm expressly scheduled in Labview (ver. 7.0) environment. Then a photogrammetric survey has been carried out to produce in a fully automatic way a very dense Digital Surface Model (DSM) of the bed topography of the laboratory channel. The image acquisition has been performed using a Nikon D80 digital camera with a focal length of 28 mm and a resolution of 3872 pixel x 2592 pixel; the pixel size was 6.1 mm. The camera-to-object distance was 0.65 m and the photo scale was 1:23. The photos were taken providing the stereo coverage necessary for automatic DSM generation. The photos orientation was executed by bundle adjustment without control points using only several calibrated scale bar to scale the photogrammetric model. The very dense DSM has been produced with a step of 2 mm for the whole channel using image matching techniques without editing.

Lo Brutto, Mauro

2010-05-01

341

Galileo radio science investigations  

Microsoft Academic Search

The radio science investigations planned for Galileo's 6-year flight to and 2-year orbit of Jupiter use as their instrument the dual-frequency radio system on the spacecraft operating in conjunction with various US and German tracking stations on Earth. The planned radio propagation experiments are based on measurements of absolute and differential propagation time delay, differential phase delay, Doppler shift, signal

H. T. Howard; V. R. Eshleman; D. P. Hinson; A. J. Kliore; G. F. Lindal; R. Woo; M. K. Bird; H. Volland; P. Edenhoffer; M. Paetzold; H. Porsche

1992-01-01

342

Analysis of the Capability and Limitations of Relativistic Gravity Measurements Using Radio Astronomy Methods  

NASA Technical Reports Server (NTRS)

The uses of radar observations of planets and very-long-baseline radio interferometric observations of extragalactic objects to test theories of gravitation are described in detail with special emphasis on sources of error. The accuracy achievable in these tests with data already obtained, can be summarized in terms of: retardation of signal propagation (radar), deflection of radio waves (interferometry), advance of planetary perihelia (radar), gravitational quadrupole moment of sun (radar), and time variation of gravitational constant (radar). The analyses completed to date have yielded no significant disagreement with the predictions of general relativity.

Shapiro, I. I.; Counselman, C. C., III

1975-01-01

343

The role of helium metastable states in radio-frequency driven helium-oxygen atmospheric pressure plasma jets: measurement and numerical simulation  

NASA Astrophysics Data System (ADS)

Absolute densities of metastable He(23S1) atoms were measured line-of-sight integrated along the discharge channel of a capacitively coupled radio-frequency driven atmospheric pressure plasma jet operated in technologically relevant helium-oxygen mixtures by tunable diode-laser absorption spectroscopy. The dependences of the He(23S1) density in the homogeneous-glow-like ?-mode plasma with oxygen admixtures up to 1% were investigated. The results are compared with a one-dimensional numerical simulation, which includes a semi-kinetical treatment of the pronounced electron dynamics and the complex plasma chemistry (in total 20 species and 184 reactions). Very good agreement between measurement and simulation is found. The main formation mechanisms for metastable helium atoms are identified and analyzed, including their pronounced spatio-temporal dynamics. Penning ionization through helium metastables is found to be significant for plasma sustainment, while it is revealed that helium metastables are not an important energy carrying species into the jet effluent and therefore will not play a direct role in remote surface treatments.

Niemi, K.; Waskoenig, J.; Sadeghi, N.; Gans, T.; O'Connell, D.

2011-10-01

344

Measurements of mixed convective heat transfer to low temperature helium in a horizontal channel  

NASA Technical Reports Server (NTRS)

A horizontal 2.85 m long, 19 mm i.d. stainless steel heated circular channel was employed to measure coefficients of heat transfer to low temperature helium flow. Experimental parameters range from 6.5 to 15 K, from 0.12 to 0.3 MPa at heat fluxes up to 1000 W/m square and Reynolds numbers from 9,000 to 20,000. A significantly nonuniform distribution of heat transfer coefficients over the tube periphery is observed. Difference between temperatures on the upper and lower surfaces of the stainless steel channel wall was found to reach 9 K. It was noted that the highest temperature on the wall outer surface is displaced from its uppermost point. Measurements of local flow temperatures revealed vortical structure of the flow. The displacement of the point with the highest temperature is attributable to the effect of vortices. The relationships for calculating local and averaged coefficients of heat transfer are proposed.

Yeroshenko, V. M.; Kuznetsov, Y. V.; Shevchenko, O. A.; Hendricks, R. C.; Daney, D. E.

1979-01-01

345

Measurement of the Top Quark Pair Production Cross Section in the All-Jets Decay Channel  

SciTech Connect

We present a measurement of t{ovr t} production in p{ovr p} collisions at {radical} (s) =1.8 TeV from 110 pb{sup {minus}1} of data collected in the all-jets decay channel with the D0 detector at Fermilab. A neural network analysis yields a cross section of 7.1{plus_minus}2.8(stat){plus_minus}1.5( syst) pb at a top quark mass (m{sub t}) of 172.1 GeV/c{sup 2} . Using previous D0 measurements from dilepton and single lepton channels, the combined D0 result for the t{ovr t} production cross section is 5.9{plus_minus}1.2(stat){plus_minus}1.1( syst) pb for m{sub t}=172.1 GeV /c{sup 2} . {copyright} {ital 1999} {ital The American Physical Society}

Grinstein, S.; Mostafa, M.; Piegaia, R. [Universidad de Buenos Aires, Buenos Aires (Argentina); Alves, G.A.; Carvalho, W.; Maciel, A.K.; da Motta, H.; Santoro, A. [LAFEX, Centro Brasileiro de Pesquisas Fisicas, Rio de Janeiro (Brazil); Lima, J.G.; Oguri, V. [Universidade do Estado do Rio de Janeiro, Rio de Janeiro (Brazil); Gomez, B.; Hoeneisen, B.; Mooney, P.; Negret, J.P. [Universidad de los Andes, Bogota (Colombia); Ducros, Y. [DAPNIA/Service de Physique des Particules, CEA, Saclay (France); Beri, S.B.; Bhatnagar, V.; Kohli, J.M.; Singh, J.B. [Panjab University, Chandigarh (India); Shivpuri, R.K. [Delhi University, Delhi (India); Acharya, B.S.; Banerjee, S.; Dugad, S.R.; Gupta, A.; Krishnaswamy, M.R.; Mondal, N.K.; Narasimham, V.S.; Parua, N.; Shankar, H.C. [Tata Institute of Fundamental Research, Mumbai (India); Park, Y.M. [Kyungsung University, Pusan (Korea); Choi, S.; Kim, S.K. [Seoul National University, Seoul (Korea); Castilla-Valdez, H.; Gonzalez Solis, J.L.; Hernandez-Montoya, R.; Magana-Mendoza, L.; Sanchez-Hernandez, A. [CINVESTAV, Mexico City (Mexico); Pawlik, B. [Institute of Nuclear Physics, Krakow (Poland); Gavrilov, V.; Gershtein, Y.; Kuleshov, S. [Institute for Theoretical and Experimental Physics, Moscow (Russia); Belyaev, A.; Dudko, L.V.; Ermolov, P.; Karmanov, D.; Leflat, A.; Manankov, V.; Merkin, M.; Shabalina, E. [Moscow State University, Moscow (Russia); Abramov, V.; Babintsev, V.V.; Bezzubov, V.A.; Bojko, N.I.; Burtovoi, V.S.; Chekulaev, S.V.; Denisov, S.P.; Dyshkant, A.; Eroshin, O.V.; Evdokimov, V.N.; Galyaev, A.N.; Goncharov, P.I.; Gurzhiev, S.N.; Kostritskiy, A.V.; Kozelov, A.V.; Kozlovsky, E.A.; Mayorov, A.A. [Institute for High Energy Physics, Protvino (Russia); Babukhadia, L.; Davis, K.; Fein, D.; Forden, G.E.; Guida, J.A.; Johns, K.; Nang, F.; Narayanan, A.; Rutherfoord, J.; Shupe, M. [University of Arizona, Tucson, Arizona 85721 (United States); Barberis, E.; Clark, A.R.; Dahl, O.I.; Grudberg, P.; and others

1999-09-01

346

A multi-band IR-UWB HDR transceiver: architecture and indoor channel measurements  

Microsoft Academic Search

This paper presents an architecture of an IR-UWB MB-OOK non-coherent transceiver realized at Mitsubishi Electric. Channel measurements in real indoor environment based on this realized prototype are provided. The different components of this transceiver are described. A comparison between the use of directional and omnidirectional antennas at both emission and reception is presented. Then, a data rate estimation of the

Mohamad Mroué; Stéphane Mallégol; Sylvain Haese; Ghaïs El-Zein; Alexis Bisiaux; Stéphane Paquelet

2009-01-01

347

Plasma Potential Measurements in the Discharge Channel of a 6kW Hall Thruster  

Microsoft Academic Search

In an effort to understand the role of neutral flow dynamics in the operation of Hall thrusters, a floating emissive probe was used to measure the plasma potential, electric field, and electron temperature in the discharge channel of a 6-kW Hall thruster operating at 300 V and anode flow rates of 10, 20, and 30 mg\\/s. To isolate the effect

Bryan M. Reid; Alec D. Gallimore

348

A Dual-Channel Microwave Radiometer for Measurement of Precipitable Water Vapor and Liquid  

Microsoft Academic Search

The design and performance of a two-channel ground-based microwave radiometer (20.6 and 31.6 GHz) for measurement of total integrated water vapor and cloud liquid in a vertical column are discussed. Unique features of this instrument are a single antenna producing equal beamwidth for the two frequencies, and incorporation of two stable reference loads in a three-way Dicke switching sequence. The

Fred Guiraud; Joe Howard; David Hogg

1979-01-01

349

Lightning Return-Stroke Current Waveforms Aloft, from Measured Field Change, Current, and Channel Geometry  

NASA Technical Reports Server (NTRS)

Three-dimensional reconstructions of six rocket-triggered lightning channels are derived from stereo photographs. These reconstructed channels are used to infer the behavior of the current in return strokes above the ground from current waveforms measured at the channel base and electric-field-change waveforms measured at a range of 5.2 kilometers for 24 return strokes in these channels. Streak photographs of 14 of the same strokes are analyzed to determine the rise times, propagation speeds, and amplitudes of relative light intensity for comparison with the electrical inferences. Results include the following: 1) The fine structure of the field-change waveforms that were radiated by these subsequent return strokes can be explained, in large part, by channel geometry. 2) The average 10 - 90% rise time of the stroke current increased by about a factor of seven in our sample, from an observed 0.31 plus or minus 0.17 microseconds at the surface to an inferred 2.2 plus or minus 0.5 microcseconds at 1 kilometer path length above the surface. 3) The three-dimensional propagation speed of the current front averaged 1.80 plus or minus 0.24 X 10(exp 8) meters per second over channel lengths typically greater than 1 kilometer. 4) Assuming that the measured current was entirely due to the return stroke forced an unreasonably large and abrupt reduction in inferred current amplitude over the first few tens of meters above the surface, especially in cases when the leader was bright relative to its stroke. Therefore, a significant fraction of the current at the surface was probably due to the leader, at least in such cases. 5) Peak return-stroke currents decreased by approximately 37 plus or minus 12% from 100 meters to 1 kilometer of path length above the surface. Because of uncertainty about how to partition the measured current between leader and return stroke, we are unable to infer the variation of current amplitude near the ground.

Willett, J. C.; LeVine, D. M.; Idone, V. P.

2006-01-01

350

Thermal measurements and flow visualization of heat convection in a tilted channel  

NASA Astrophysics Data System (ADS)

Convection is the most important heat transport mechanism. We can find it not only in many natural situations such as stars, planet's atmosphere but also in half-natural situations such as industrial plants. Furthermore, the Rayleigh-Benard system, in which a fluid is cooled from above and heated from below, is one of the most studied systems in thermal convection. Nevertheless, in this configuration, the neighborhood of the plates controls the heat transfer. Therefore, we have to make a system in which the flow forgets the cold and the hot plate. We have built a vertical long channel which links two chambers : the hot one at the lower end and the cold one at the upper end. Moreover, this channel, which is hanged to a structure, can be tilted from an angle of 0 degree to 90 degrees. The experimental facility used for this purpose is a square channel with an inner area of 5*5 cm² m and with a height of 20 cm. The cell is filled with water and is heated at the bottom by Joule effect. At the top, the temperature is regulated by a thermal bath and the mean temperature of the bulk is 25°C . It is worth noticing that this configuration could correspond to heat pipes (without phase transformation) used in thermalisation systems or could model a vertical access pit of an underground carry. In this paper, we want to highlight how the thermal convection in the bulk of the channel is. In the first part, the paper will be focused on the visualization of the flow into the channel thanks to particle image velocimetry (PIV) technique. We look at the mean velocity field (transverse and axial components) , the fluctuations of the mean velocity field and the shear Reynolds stress. Besides, we analyze how the influence of the power supply and the dependance of the tilt angle are. At last, we will interpret the PIV measurements in terms of turbulent viscosity and effective heat conduction and we will deduce from the PIV measurements the axial mean profile of temperature. Then, in a second part, we present new thermal measurements. Thanks to a new sensor inserted into the channel and which is not too intrusive, we have measured the axial mean profile of temperature for several tilt angle and several different power supplies. At last, in a third part, a model which allows to account for the competition between stratification and turbulence will be developed.

Tisserand, Jean-Christophe; Creyssels, Mathieu; Riedinger, Xavier; Castaing, Bernard; Chillà, Francesca

2010-05-01

351

Comparison of total electron content measurements made with the ATS-6 radio beacon over the U.S. and Europe  

NASA Technical Reports Server (NTRS)

The ATS-6 radio beacon measurements made at three stations in the U.S.A. are compared and contrasted with similar measurements made in Europe the following year at two locations. It is shown that over the U.S.A. the winter plasmaspheric content reaches its maximum near 0300 LT whereas in Europe the maximum occurs near noon. The plasmaspheric content decreases with increase of magnetic activity in both continents. Winter night maxima are observed in ionospheric content in both hemispheres. Marked differences occurred in magnetic storm effects and in the day-to-night ratio of ionospheric electron content.

Davies, K.; Degenhardt, W.; Hartmann, G. K.; Leitinger, R.

1980-01-01

352

Measuring flood discharge in unstable stream channels using ground-penetrating radar  

USGS Publications Warehouse

Field experiments were conducted to test the ability of ground-penetrating radar (GPR) to measure stream-channel cross sections at high flows without the necessity of placing instruments in the water. Experiments were conducted at four U.S. Geological Survey gaging stations in southwest Washington State. With the GPR antenna suspended above the water surface from a bridge or cableway, traverses were made across stream channels to collect radar profile plots of the streambed. Subsequent measurements of water depth were made using conventional depth-measuring equipment (weight and tape) and were used to calculate radar signal velocities. Other streamflow-parameter data were collected to examine their relation to radar signal velocity and to claritv of streambed definition. These initial tests indicate that GPR is capable of producing a reasonably accurate (??20%) stream-channel profile and discharge far more quickly than conventional stream-gaging procedures, while avoiding the problems and hazards associated with placing instruments in the water.

Spicer, K.R.; Costa, J.E.; Placzek, G.

1997-01-01

353

The 400-channel commutator for measurement of energy distribution in laser beam  

NASA Astrophysics Data System (ADS)

An experimental study of a 400 channel commutator for measurement and analysis of the energy distribution over the beam cross section of pulse lasers was made for the purpose of evaluating its performance characteristics. This commutator transfers electric signals sequentially from 400 channels to the input of a digital high precision voltmeter, signals of a magnitude ranging from a few microvolts to tens of volts and remaining constant during the switching period. Each commutator element is a step-by-step switch and the effect of its performance on the accuracy of voltmeter readings depends on the switching cycle as well as the commutation characteristics. These were tracked through a set of three relays and a digital voltmeter continuously selecting one of two strobe signals. The voltmeter readings were analyzed by equipment including a start-stop cycle setter, a shaper of control pulses for a control module, with two amplifiers and two commutator control windings, and were also printed out after passage through a matching circuit. Calculations based on the voltmeter output data and on the equivalent electrical circuit of the commutator elements, with a high ratio of open resistance to closed resistance, yield an error of 5 x .0001 to 5 x .001 at temperatures of 20 to 65 C or one channel operating alone with crosstalk from the other 399 channels.

Chereugin, V. L.; Kuznetsov, A. A.

1984-11-01

354

Measurement of gating forces of mechanosensitive channels of large conductance in Escherichia coli  

NASA Astrophysics Data System (ADS)

In order to sense and respond to external mechanical stimuli, cells have evolved schemes to incorporate mechanosensors within their plasma membranes. Mechanosensitive channels of large conductance (MscL) are used by bacterial cells to respond quickly and effectively to hypo-osmotic shock: the opening of this channel permits cells to quickly release large amounts of osmolytes in order to quickly equalize unbalanced osmotic pressure across a membrane. In this study, we are investigating the physical mechanism of the MscL gating within the native environment of the Escherichia coli cells. We are using the green fluorescent protein (GFP) and derivative proteins (CFP, BFP) to label the C-termini of MscL subunits in order to observe the channels in live bacteria by fluorescence microscopy. Moreover, we label the opposite termini with a different chromophore system that constitutes an excellent fluorescence resonance energy transfer (FRET) pair with CFP. Channels are activated within the bacterial membrane by osmotic stress and interactions between differently labeled subunits are measured by fluorescence microscopy.

Pandzic, Elvis; Wiseman, Paul; Kilfoil, Maria

2006-03-01

355

Observing Earth's atmosphere with radio occultation measurements using the Global Positioning System  

Microsoft Academic Search

The implementation of the Global Positioning System (GPS) network of satellites and the development of small, high-performance instrumentation to receive GPS signals have cre- ated an opportunity for active remote sounding of the Earth's atmosphere by radio occultation at comparatively low cost. A prototype demonstration of this capability has now been provided by the GPS\\/MET investigation. Despite using relatively immature

E. R. Kursinski; G. A. Hajj; J. T. Schofield; R. P. Linfield; K. R. Hardy

1997-01-01

356

Direct measurement of charged particles associated with auroral zone radio absorption  

Microsoft Academic Search

A rocket experiment to study the charged particles associated with ; auroral radio absorption is described. A primary electron flux, probably in the ; form of beams or colunms, with a maximum intensity of 2 x 10⁶ particles cm-\\/; sup -2\\/ could be represented by exp (-E\\/22 kev) at energies above 30 kev. The ; angular distribution of the incident

I. B. McDiarmid; D. C. Rose; E. Budzinski

1961-01-01

357

Measurement of Field Aligned Electron and Ion Densities and Ducts from the Whistler and Z Mode Radio Sounding from IMAGE  

NASA Astrophysics Data System (ADS)

We present recent results from the application of whistler mode (WM) and Z mode (ZM) radio sounding experiments from the IMAGE satellite to the magnetospheric plasma diagnostics. A recently developed WM radio sounding method [Sonwalkar et al., JGR, 116, A11210, doi:10.1029/2011JA016759, 2011] was applied to 200 cases of WM echoes observed within the plasmasphere to measure field aligned electron density (Ne) and ion densities (NH+, NHe+, NO+) for L~1.6 -4, altitude <5000 km, Kp ~1-7, and F10.7 ~ 72-110 (low solar activity). The measured plasma parameters are in general consistent with the past space borne (e.g. CHAMP, DMSP, Alouette, ISIS, AE) and ground (e.g. ionosonde) measurements, but show significant differences from those predicted by IRI-2012 and GCPM models. We believe our measurements will lead to an improved model of electron and ion densities at <5000 km within the plasmasphere. The WM radio sounding method was applied to a case study of the variation of plasma parameters at L~2 during the development of a major storm, from quiet conditions and subsequent recovery, followed by a moderate and minor storm. Our study showed that relative to the preceding quiet time: (1) There was depletion in electron density, H+, He+ and enhancement in O+ ions leading to increase in O+-H+ transition height; (2) The recovery period of electrons and individual ions was different; (3) A similar trend in the variation of electron density, H+, O+ was observed after the moderate storm and the minor storm but He+ was not affected. Following a ray tracing technique originally developed for whistler mode sounding, we analyzed the fast nonducted and ducted Z mode echoes to obtain field aligned electron density and duct parameters (duct width and enhancement) from the measured dispersion of Z mode echoes. With the help of two case studies, we illustrate that fast Z mode echoes provide measurement of electron density at altitudes <10,000 km and duct width and enhancement within an uncertainty of ~0.05 L and a few percent, respectively. Application of ZM radio sounding method presented here to a large number (~2000) case observed at low- to mid-latitudes should provide distribution of electron density and duct parameters in this latitude range for altitude <10,000 km. Our measurements will contribute towards a better understanding of the ionosphere-magnetosphere coupling.

Sonwalkar, V. S.; Hazra, S.; Mayank, K.; Reddy, A.; Liu, Y.; Carpenter, D. L.

2013-12-01

358

Orthogonal frequency division multiple access with an aggregated sub-channel structure and statistical channel quality measurement  

Microsoft Academic Search

In this paper, an orthogonal frequency division multiple access (OFDMA) is considered for the mobile air interface. To reduce the reverse link overheads for CQI feedback, we consider an aggregated sub-channel structure, where a set of adjacent sub-carriers are tied up to a sub-channel to be used as a unit of user-multiplexing and the corresponding power\\/rate allocation. Modeling the SNR

Seokhyun Yoon; Changho Suh; Youngkwon Cho; D. S. Park

2004-01-01

359

Fading channel simulator  

SciTech Connect

This invention relates to high frequency (HF) radio signal propagation through fading channels and, more particularly, to simulation of fading channels in order to characterize HF radio system performance in transmitting and receiving signals through such fading channels. Fading channel effects on a transmitted communication signal are simulated with both frequency and time variations using a channel scattering function to affect the transmitted signal. A conventional channel scattering function is converted to a series of channel realizations by multiplying the square root of the channel scattering function by a complex number of which the real and imaginary parts are each independent variables. The two-dimensional inverse-FFT of this complex-valued channel realization yields a matrix of channel coefficients that provide a complete frequency-time description of the channel. The transmitted radio signal is segmented to provide a series of transmitted signal and each segment is subject to FFT to generate a series of signal coefficient matrices. The channel coefficient matrices and signal coefficient matrices are then multiplied and subjected to inverse-FFT to output a signal representing the received affected radio signal. A variety of channel scattering functions can be used to characterize the response of a transmitter-receiver system to such atmospheric effects.

Argo, P.E.; Fitzgerald, T.J.

1991-12-31

360

Measurements of the average properties of a suspension of bubbles rising in a vertical channel  

NASA Astrophysics Data System (ADS)

Experiments were performed in a vertical channel to study the behaviour of a monodisperse bubble suspension for which the dual limit of large Reynolds number and small Weber number was satisfied. Measurements of the liquid-phase velocity fluctuations were obtained with a hot-wire anemometer. The gas volume fraction, bubble velocity, bubble velocity fluctuations and bubble collision rate were measured using a dual impedance probe. Digital image analysis was performed to quantify the small polydispersity of the bubbles as well as the bubble shape.

Zenit, Roberto; Koch, Donald L.; Sangani, Ashok S.

2001-02-01

361

Four-channel ZnS scintillator measurements of escaping tritons in TFTR  

SciTech Connect

A four-channel scintillation detector capable of measuring tritons, protons, and alphas escaping from a tokamak plasma was operated during the 1986 run period of the Tokamak Fusion Test Reactor (TFTR). Signals consistent with the expected 1 MeV triton behavior have been observed during deuterium operation. Backgrounds associated with neutrons, gammas, and soft x-rays have been evaluated in situ. Such a detector should be capable of measuring escaping alphas during the D/T phase of TFTR. 16 refs., 10 figs.

Zweben, S.J.

1988-10-01

362

Gravitational microlensing of neutron stars and radio pulsars: event rates, time-scale distributions and mass measurements  

E-print Network

We investigate properties of Galactic microlensing events in which a stellar object is lensed by a neutron star. For an all-sky photometric microlensing survey, we determine the number of lensing events caused by $\\sim10^{5}$ potentially-observable radio pulsars to be $\\sim0.2\\ \\rm{yr^{-1}}$ for $10^{10}$ background stellar sources. We expect a few detectable events per year for the same number of background sources from an astrometric microlensing survey. We show that such a study could lead to precise measurements of radio pulsar masses. For instance, if a pulsar distance could be constrained through radio observations, then its mass would be determined with a precision of $\\sim10\\%$. We also investigate the time-scale distributions for neutron star events, finding that they are much shorter than had been previously thought. For photometric events towards the Galactic centre that last $\\sim15$ days, around $7\\%$ will have a neutron star lens. This fraction drops rapidly for longer time-scales. Away from the...

Dai, Shi; Lin, Mengxiang; Yue, Youling; Hobbs, George; Xu, Renxin

2015-01-01

363

Phase distribution measurements in narrow rectangular channels using image-processing techniques  

SciTech Connect

Phase distribution of air-water flow in a narrow rectangular channel is examined using image-processing techniques. Ink is added to the water, and clear channel walls were used to allow high-speed, still photographs and video tape to be taken of the air-water flow field. Flow field images are digitized and stored in a Macintosh IIci computer using a frame grabber board. Local grey levels are related to liquid thickness in the flow channel using a calibration fixture. Image-processing shareware is used to calculate the spatially averaged liquid thickness from the image of the flow field. Time-averaged spatial liquid distributions are calculated using image calculation algorithms. The spatially averaged liquid distribution is calculated from the time-averaged spatial liquid distribution to formulate the combined temporally and spatially averaged liquid fraction values. The temporally and spatially averaged liquid fractions measured using this technique compare well to those predicted from pressure gradient measurements at zero superficial liquid velocity. 11 refs.

Bentley, C.L.; Ruggles, A.E.

1992-06-01

364

Channeled-proton-induced x-ray measurements of radiation damage in sapphire  

SciTech Connect

Channeled-proton-induced x rays (CPIX) were used to measure displacement damage produced in sapphire (..cap alpha..-Al/sub 2/O/sub 3/) by ion bombardment at room temperature. A method based on dechanneling theory was developed for the interpretation of CPIX results in terms of numbers of displaced atoms. The results agreed with those obtained with the Rutherford-backscattering-channeling (RBC) technique. The dependence of displacement damage on energy partition was evaluated by selection of ion species and incident energy (20 keV, H/sup +//sub 2/; 20 keV, He/sup +/; 70 keV, N/sup +/ and 500 keV, Xe/sup + +/). Except for H/sup +//sub 2/ implantation, the net number of displaced atoms at damage levels below saturation was found to depend almost entirely upon the energy deposited into atomic collision processes. For the hydrogen implantations the damage was approximately a factor of 4 higher for equal energy into atomic collisions. Comparison of channeling along the <0001> and <1120> directions revealed that aluminum atoms are displaced preferentially into sites along c-axis rows. Ionization-stimulated annealing was investigated with the CPIX technique. Exposure of ion-bombardment-damaged samples to ionizing radiation did not produce annealing measureable by CPIX.

Luera, T.F.

1980-11-01

365

Dielectric spectroscopy of thin films by dual-channel impedance measurements on differential interdigitated electrode arrays  

NASA Astrophysics Data System (ADS)

We report a new approach to measuring the dielectric behavior of thin films by means of differential interdigitated electrode (IDE) cells coupled with a dual-channel impedance measurement setup. The differential IDE cell consists of two identical IDE's on a common substrate. With one IDE loaded with sample and the other one empty, the complex permittivities of both capacitors are measured simultaneously by means of a dual-channel impedance measurement setup. The net dielectric response of the material under study is then obtained by the difference of the two permittivities, which corrects for the substrate contribution. The applicability of this approach is examined with bulk glycerol and a 600 nm indomethacin film and is evidenced by the results being consistent with those measured by conventional methods. The main advantages of this new approach include a simplified preparation technique for thin film samples and a straightforward correction for the substrate contribution by subtracting the empty IDE signal obtained at the same temperature and thermal history.

Chen, Z.; Sepúlveda, A.; Ediger, M. D.; Richert, R.

2012-08-01

366

Nondestructive measurement of mode couplings along a multi-core fiber using a synchronous multi-channel OTDR.  

PubMed

We propose and demonstrate a new technique for measuring mode couplings along a multi-core fiber (MCF) that employs a multi-channel optical time domain reflectometer (OTDR). The mode couplings along seven core fibers are successfully obtained using a synchronous seven-channel OTDR. PMID:22714241

Nakazawa, Masataka; Yoshida, Masato; Hirooka, Toshihiko

2012-05-21

367

Measurements of Shear Lift Force on a Bubble in Channel Flow in Microgravity  

NASA Technical Reports Server (NTRS)

Under microgravity conditions, the shear lift force acting on bubbles, droplets or solid particles in multiphase flows becomes important because under normal gravity, this hydrodynamic force is masked by buoyancy. This force plays an important role in furnishing the detachment process of bubbles in a setting where a bubble suspension is needed in microgravity. In this work, measurements of the shear lift force acting on a bubble in channel flow are performed. The shear lift force is deduced from the bubble kinematics using scaling and then compared with predictions from models in literature that address different asymptotic and numerical solutions. Basic trajectory calculations are then performed and the results are compared with experimental data of position of the bubble in the channel. A direct comparison of the lateral velocity of the bubbles is also made with the lateral velocity prediction from investigators, whose work addressed the shear lift on a sphere in different two-dimensional shear flows including Poiseuille flow.

Nahra, Henry K.; Motil, Brian J.; Skor, Mark

2003-01-01

368

Measurements and Analysis of System Noise Temperature of the Low-frequency Bands for the TM65 m Radio Telescope  

NASA Astrophysics Data System (ADS)

We first present the noise characteristics of the receiving systems including L, S, C, and X bands for the TM65 m radio telescope. The measurement methods for the system temperature have been discussed. The important influences, including the non-linearity error, feed network insertion loss, mismatch errors, and so on for measuring the system noise temperature are analyzed. We have measured the system noise temperatures in four bands with both of the calibrations of noise sources and black body in room temperature. We have estimated the temperatures of the noise sources and compared them with the laboratory values. The difference is around 0.2 K. Finally, the system temperatures of the four bands are measured and analyzed.

Wang, J. Q.; Yu, L. F.; Zhao, R. B.; Jiang, D. R.; Lou, F. X.; Lao, B. Q.; Li, B.; Dong, J.; Fan, Q. Y.; Qian, Z. H.; Liu, Q. H.; Jiang, Y. B.

2015-01-01

369

Radio-frequency measurements of UNiX compounds (X= Al, Ga, Ge) in high magnetic fields  

SciTech Connect

We performed radio-frequency (RF) skin-depth measurements of antiferromagnetic UNiX compounds (X=Al, Ga, Ge) in magnetic fields up to 60 T and at temperatures between 1.4 to {approx}60 K. Magnetic fields are applied along different crystallographic directions and RF penetration-depth was measured using a tunnel-diode oscillator (TDO) circuit. The sample is coupled to the inductive element of a TDO resonant tank circuit, and the shift in the resonant frequency {Delta}f of the circuit is measured. The UNiX compounds exhibit field-induced magnetic transitions at low temperatures, and those transitions are accompanied by a drastic change in {Delta}f. The results of our skin-depth measurements were compared with previously published B-T phase diagrams for these three compounds.

Mielke, Charles H [Los Alamos National Laboratory; Mcdonald, David R [Los Alamos National Laboratory; Zapf, Vivien [Los Alamos National Laboratory; Altarawneh, Moaz M [Los Alamos National Laboratory; Lacerda, Alex H [Los Alamos National Laboratory; Adak, Sourav [Los Alamos National Laboratory; Karunakar, Kothapalli [Los Alamos National Laboratory; Nakotte, Heinrich [Los Alamos National Laboratory; Chang, S [NIST; Alsmadi, A M [HASHEMITE UNIV; Alyones, S [HASHEMIT UNIV

2009-01-01

370

High fidelity wireless network evaluation for heterogeneous cognitive radio networks  

NASA Astrophysics Data System (ADS)

We present a high fidelity cognitive radio (CR) network emulation platform for wireless system tests, measure- ments, and validation. This versatile platform provides the configurable functionalities to control and repeat realistic physical channel effects in integrated space, air, and ground networks. We combine the advantages of scalable simulation environment with reliable hardware performance for high fidelity and repeatable evaluation of heterogeneous CR networks. This approach extends CR design only at device (software-defined-radio) or lower-level protocol (dynamic spectrum access) level to end-to-end cognitive networking, and facilitates low-cost deployment, development, and experimentation of new wireless network protocols and applications on frequency- agile programmable radios. Going beyond the channel emulator paradigm for point-to-point communications, we can support simultaneous transmissions by network-level emulation that allows realistic physical-layer inter- actions between diverse user classes, including secondary users, primary users, and adversarial jammers in CR networks. In particular, we can replay field tests in a lab environment with real radios perceiving and learning the dynamic environment thereby adapting for end-to-end goals over distributed spectrum coordination channels that replace the common control channel as a single point of failure. CR networks offer several dimensions of tunable actions including channel, power, rate, and route selection. The proposed network evaluation platform is fully programmable and can reliably evaluate the necessary cross-layer design solutions with configurable op- timization space by leveraging the hardware experiments to represent the realistic effects of physical channel, topology, mobility, and jamming on spectrum agility, situational awareness, and network resiliency. We also provide the flexibility to scale up the test environment by introducing virtual radios and establishing seamless signal-level interactions with real radios. This holistic wireless evaluation approach supports a large-scale, het- erogeneous, and dynamic CR network architecture and allows developing cross-layer network protocols under high fidelity, repeatable, and scalable wireless test scenarios suitable for heterogeneous space, air, and ground networks.

Ding, Lei; Sagduyu, Yalin; Yackoski, Justin; Azimi-Sadjadi, Babak; Li, Jason; Levy, Renato; Melodia, Tammaso

2012-06-01

371

Measurement of the top quark mass in the dilepton channel thinsp  

SciTech Connect

We report a measurement of the top quark mass using six candidate events for the process p{bar p}{r_arrow}t{bar t}+X{r_arrow}l{sup +}{nu}bl{sup {minus}}{bar {nu}}{bar b}+X, observed in the D0 experiment at the Fermilab p{bar p} collider. Using maximum likelihood fits to the dynamics of the decays, we measure a mass for the top quark of m{sub t}=168.4{plus_minus}12.3(stat){plus_minus}3.6(syst) Gev. We combine this result with our previous measurement in the t{bar t}{r_arrow}l+jets channel to obtain m{sub t}=172.1{plus_minus}7.1 GeV as the best value of the mass of the top quark measured by D0. {copyright} {ital 1999} {ital The American Physical Society}

Grinstein, S.; Mostafa, M.; Piegaia, R. [Universidad de Buenos Aires, Buenos Aires (Argentina); Alves, G.A.; Carvalho, W.; Maciel, A.K.; da Motta, H.; Oliveira, E.; Santoro, A. [LAFEX, Centro Brasileiro de Pesquisas Fisicas, Rio de Janeiro (Brazil); Lima, J.G.; Oguri, V. [Universidade do Estado do Rio de Janeiro, Rio de Janeiro (Brazil); Gomez, B.; Hoeneisen, B.; Mooney, P.; Negret, J.P. [Universidad de los Andes, Bogota (Colombia); Ducros, Y. [DAPNIA/Service de Physique des Particules, CEA, Saclay (France); Beri, S.B.; Bhatnagar, V.; Kohli, J.M.; Singh, J.B. [Panjab University, Chandigarh (India); Shivpuri, R.K. [Delhi University, Delhi (India); Acharya, B.S.; Banerjee, S.; Dugad, S.R.; Gupta, A.; Krishnaswamy, M.R.; Mondal, N.K.; Narasimham, V.S.; Parua, N.; Shankar, H.C. [Tata Institute of Fundamental Research, Mumbai (India); Park, Y.M. [Kyungsung University, Pusan (Korea); Choi, S.; Kim, S.K. [Seoul National University, Seoul (Korea); Castilla-Valdez, H.; Gonzalez Solis, J.L.; Hernandez-Montoya, R.; Magana-Mendoza, L.; Sanchez-Hernandez, A. [CINVESTAV, Mexico City (Mexico); Pawlik, B. [Institute of Nuclear Physics, Krakow (Poland); Gavrilov, V.; Gershtein, Y.; Kuleshov, S. [Institute for Theoretical and Experimental Physics, Moscow (Russia); Belyaev, A.; Dudko, L.V.; Ermolov, P.; Karmanov, D.; Leflat, A.; Manankov, V.; Merkin, M.; Shabalina, E. [Moscow State University, Moscow (Russia); Abramov, V.; Babintsev, V.V.; Bezzubov, V.A.; Bojko, N.I.; Burtovoi, V.S.; Chekulaev, S.V.; Denisov, S.P.; Dyshkant, A.; Eroshin, O.V.; Evdokimov, V.N.; Galyaev, A.N.; Goncharov, P.I.; Gurzhiev, S.N.; Kostritskiy, A.V.; Kozelov, A.V.; Kozlovsky, E.A.; Mayorov, A.A. [Institute for High Energy Physics, Protvino (Russia); Babukhadia, L.; Davis, K.; Fein, D.; Forden, G.E.; Guida, J.A.; James, E.; Johns, K.; Nang, F.; Narayanan, A.; Rutherfoord, J.; Shupe, M. [University of Arizona, Tucson, Arizona 85721 (United States); Aihara, H.; Barberis, E.; Chen, L.; and others

1999-09-01

372

Test of the Pioneer anomaly with the Voyager 2 radio-ranging distance measurements to Uranus and Neptune  

E-print Network

In this paper we test the hypothesis that the Pioneer anomaly can be of gravitational origin by comparing the predicted model-independent shifts Delta a/a for the semimajor axis of Uranus and Neptune with the Voyager 2 radio-technical distance measurements performed at JPL-NASA. As in the case of other tests based on different methods and data sets (secular perihelion advance, right ascension/declination residuals over about one century), the orbits of the investigated planets are not affected by any anomalous acceleration like that experienced by the Pioneer 10/11 spacecraft.

Lorenzo Iorio

2006-08-29

373

Optimal Linear Cooperation for Spectrum Sensing in Cognitive Radio Networks  

Microsoft Academic Search

Cognitive radio technology has been proposed to improve spectrum efficiency by having the cognitive radios act as secondary users to opportunistically access under-utilized frequency bands. Spectrum sensing, as a key enabling functionality in cognitive radio networks, needs to reliably detect signals from licensed primary radios to avoid harmful interference. However, due to the effects of channel fading\\/shadowing, individual cognitive radios

Zhi Quan; Shuguang Cui; Ali H. Sayed

2008-01-01

374

Rolling Stone Radio  

NSDL National Science Digital Library

Rolling Stone Radio is a fun and interesting site that may represent the future of Internet radio. The site provides a number of streaming audio channels that can be listened to via RealNetworks' RealPlayer G2 combined with a customized, radio-like interface to the site. Each channel features a particular genre of music, and the interface displays the artist and song title during play. The sound quality ranges from acceptable to excellent, and the sound controls and channel selectors are easy-to-use. While the site borders on the exploitative in its advertising and ability to purchase music by clicking through the interface, it does combine some of the best ideas on the Internet into a seamless entertainment package. All downloadable components of this site are free but run only on Win95/98/NT.

375

Using a novel flood prediction model and GIS automation to measure the valley and channel morphology of large river networks  

EPA Science Inventory

Traditional methods for measuring river valley and channel morphology require intensive ground-based surveys which are often expensive, time consuming, and logistically difficult to implement. The number of surveys required to assess the hydrogeomorphic structure of large river n...

376

Agesotrophic and quasi-geostrophic circulation in the Gulf of Tehuantepec, México. HF-Radio measurements  

NASA Astrophysics Data System (ADS)

Using High Frequency Radios the ocean's surface currents in the inner Gulf of Tehuantepec GT, were mapped every half hour. The GT is characterized by wind outbursts that blow through a gap in the Mexican mountain chain. In this work we show evidence of the relationship between the wind-stress magnitude and the size of eddies excited by the wind-stress. While for wind-stress less than 0.25 N/m2 the mean flow was not modified, for wind stress between 0.25 and 0.5 N/m2 a dipole-like structure was observed with diameter between 10 and 80 km. The anticyclonic gyre was located in the western side of the GT, and apparently was advected towards the southwest. The cyclonic gyre was in the eastern side and disappear after a few hours of its formation. The vertical structure of these gyres was measured using a thermistor chain moored on the wind axis. During wind events of ?0.5 N/m2 the thermocline was pump up from ?60 m depth in a few hours. The relative vorticity maps showed that the cyclonic gyre disappear in a matter of hours, possibly due to the northern limit of the GT, that blocks motion towards the north to conserve vorticity, and to the shallow thermocline. Cyclonic gyres may thus be short-lived in the inner GT. On the other hand the anticyclonic gyres gains negative vorticity by moving towards the south and by thermocline deeping. Wind outburst with wind-stress > 0.6 N/m2 reflected no eddies within the radar's foot print, instead the flow was toward the south. These could be evidence for bigger scale gyres that the HFR were unable to map. Using a transfer function between the wind-stress and the surface currents, we extracted the wind-stress component from the surface currents. In this fashion we separated the ageostrophic and the quasi-geostrophic currents. The ageostrophic current moved most of the time towards the west, in agreement with the expected Ekman transport, while the quasi-geostrophic component was southward, apparently defined by the offshore pressure gradient imposed by the wind-stress. The sum of the two components gives a mean flow towards the south-west, coincident with the path that the anticyclonic gyres tend to follow. On the other hand, under periods of calm winds, both the ageostrophic and quasi-geostrophic components were westward, penetrating the inner GT, intensifying during autumn and decreasing during summer. The importance of these westward currents is found in the relationship with the Costa Rica Current and the Costa Rica Dome, and may be evidence of the interaction between the Eastern Tropical Pacific Ocean and the coastal dynamic in the GT.

Flores-Vidal, X.; Chavanne, C. P.; Durazo, R.; Flament, P. J.

2010-12-01

377

Satellite-to-indoor broadband channel measurements at 1.51 GHz and 5.2 GHz  

Microsoft Academic Search

To investigate the satellite-to-indoor wave propagation channel for navigation applications the German Aerospace Center conducted broadband channel sounder measurements using a mobile crane as transmitter platform with the receiver being placed indoors. Using this setup, measurements were performed for L-band at 1.51 GHz and C-band at 5.2 GHz with a broadband signal of 100 MHz bandwidth. Results are given in

Thomas Jost; Wei Wang; Armin Dammann; Uwe-Carsten Fiebig; Michael Walter; Frank Schubert

2009-01-01

378

Lightning Return-Stroke Current Waveforms Aloft, From Measured Field Change, Current, and Channel Geometry  

NASA Technical Reports Server (NTRS)

Direct current measurements are available near the attachment point from both natural cloud-to-ground lightning and rocket-triggered lightning, but little is known about the rise time and peak amplitude of return-stroke currents aloft. We present, as functions of height, current amplitudes, rise times, and effective propagation velocities that have been estimated with a novel remote-sensing technique from data on 24 subsequent return strokes in six different lightning flashes that were triggering at the NASA Kennedy Space Center, FL, during 1987. The unique feature of this data set is the stereo pairs of still photographs, from which three-dimensional channel geometries were determined previously. This has permitted us to calculate the fine structure of the electric-field-change (E) waveforms produced by these strokes, using the current waveforms measured at the channel base together with physically reasonable assumptions about the current distributions aloft. The computed waveforms have been compared with observed E waveforms from the same strokes, and our assumptions have been adjusted to maximize agreement. In spite of the non-uniqueness of solutions derived by this technique, several conclusions seem inescapable: 1) The effective propagation speed of the current up the channel is usually significantly (but not unreasonably) faster than the two-dimensional velocity measured by a streak camera for 14 of these strokes. 2) Given the deduced propagation speed, the peak amplitude of the current waveform often must decrease dramatically with height to prevent the electric field from being over-predicted. 3) The rise time of the current wave front must always increase rapidly with height in order to keep the fine structure of the calculated field consistent with the observations.

Willett, J. C.; LeVine, D. M.

2002-01-01

379

Factors affecting measurement of channel thickness in asymmetrical flow field-flow fractionation.  

PubMed

Asymmetrical flow field-flow fractionation (AF4) has been considered to be a useful tool for simultaneous separation and characterization of polydisperse macromolecules or colloidal nanoparticles. AF4 analysis requires the knowledge of the channel thickness (w), which is usually measured by injecting a standard with known diffusion coefficient (D) or hydrodynamic diameter (dh). An accurate w determination is a challenge due to its uncertainties arising from the membrane's compressibility, which may vary with experimental condition. In the present study, influence of factors including the size and type of the standard on the measurement of w was systematically investigated. The results revealed that steric effect and the particles-membrane interaction by van der Waals or electrostatic force may result in an error in w measurement. PMID:25817708

Dou, Haiyang; Jung, Euo Chang; Lee, Seungho

2015-05-01

380

Three dimensional profile measurement using multi-channel detector MVM-SEM  

NASA Astrophysics Data System (ADS)

In next generation lithography (NGL) for the 1x nm node and beyond, the three dimensional (3D) shape measurements such as side wall angle (SWA) and height of feature on photomask become more critical for the process control. Until today, AFM (Atomic Force Microscope), X-SEM (cross-section Scanning Electron Microscope) and TEM (Transmission Electron Microscope) tools are normally used for 3D measurements, however, these techniques require time-consuming preparation and observation. And both X-SEM and TEM are destructive measurement techniques. This paper presents a technology for quick and non-destructive 3D shape analysis using multi-channel detector MVM-SEM (Multi Vision Metrology SEM), and also reports its accuracy and precision.

Yoshikawa, Makoto; Harada, Sumito; Ito, Keisuke; Murakawa, Tsutomu; Shida, Soichi; Matsumoto, Jun; Nakamura, Takayuki

2014-07-01

381

Measurements on diproton emission from the break-up channels of 23Al and 22Mg  

NASA Astrophysics Data System (ADS)

Two-proton relative momentum distributions from the break-up channels 23Al?p+p+21Na and 22Mg?p+p+20Ne at an energy of 60-70 A MeV have been measured together with two-proton opening angles at the projectile fragment separator beamline (RIPS) in the RIKEN Ring Cyclotron Facility. The results demonstrate the existence of diproton emission component from single-step 2He for highly excited 23Al and 22Mg.

Ma, YuGang; Fang, DeQing; Sun, XiaoYan; Zhou, Pei; Cai, XiangZhou; Chen, JinGen; Guo, Wei; Tian, WenDong; Wang, HongWei; Zhang, GuoQiang; Cao, XiGuang; Fu, Yao; Hu, ZhengGuo; Wang, JianSong; Wang, Meng; Togano, Y.; Aoi, N.; Baba, H.; Honda, T.; Okada, K.; Hara, Y.; Ieki, K.; Ishibashi, Y.; Itou, Y.; Iwasa, N.; Kanno, S.; Kawabata, T.; Kimura, H.; Kondo, Y.; Kurita, K.; Kurokawa, M.; Moriguchi, T.; Murakami, H.; Oishi, H.; Ota, S.; Ozawa, A.; Sakurai, H.; Shimoura, S.; Shioda, R.; Takeshita, E.; Takeuchi, S.; Yamada, K.; Yamada, Y.; Yasuda, Y.; Yoneda, K.; Motobayashi, T.

2011-08-01

382

Multi-channel optical pyrometer for sub-nanosecond temperature measurements at NDCX-I/II  

SciTech Connect

We present a detailed technical description of a fast multi-channel pyrometer designed for warm-dense-matter (WDM) experiments with intense heavy ion beams at the neutralized-drift-compression-experiment linear accelerator (NDCX-I/II) at Lawrence Berkeley National Laboratory (LBNL). The unique features of the described instrument are its sub-nanosecond temporal resolution (100 ps rise-time) and a broad range, 1,500 K - 12,000 K of measurable brightness temperatures in the visible and near-infrared regions of the spectrum. The working scheme, calibration procedure, experimental data obtained with the pyrometer and future applications are presented.

Ni, P.A.; Bieniosek, F.M.; Waldron, W.L.

2011-04-13

383

Measurements on diproton emission from the break-up channels of 23 Al and 22 Mg  

Microsoft Academic Search

Two-proton relative momentum distributions from the break-up channels 23Al?p+p+21Na and 22Mg?p+p+20Ne at an energy of 60–70 A MeV have been measured together with two-proton opening angles at the projectile fragment separator\\u000a beamline (RIPS) in the RIKEN Ring Cyclotron Facility. The results demonstrate the existence of diproton emission component\\u000a from single-step 2He for highly excited 23Al and 22Mg.

Yugang Ma; Deqing Fang; Xiaoyan Sun; Pei Zhou; Xiangzhou Cai; Jingen Chen; Wei Guo; Wendong Tian; Hongwei Wang; Guoqiang Zhang; Xiguang Cao; Yao Fu; Zhengguo Hu; Jiansong Wang; Meng Wang; Y. Togano; N. Aoi; H. Baba; T. Honda; K. Okada; Y. Hara; K. Ieki; Y. Ishibashi; Y. Itou; N. Iwasa; S. Kanno; T. Kawabata; H. Kimura; Y. Kondo; K. Kurita; M. Kurokawa; T. Moriguchi; H. Murakami; H. Oishi; S. Ota; A. Ozawa; H. Sakurai; S. Shimoura; R. Shioda; E. Takeshita; S. Takeuchi; K. Yamada; Y. Yamada; Y. Yasuda; K. Yoneda; T. Motobayashi

2011-01-01

384

SARAS: a precision system for measurement of the cosmic radio background and signatures from the epoch of reionization  

NASA Astrophysics Data System (ADS)

SARAS is a correlation spectrometer purpose designed for precision measurements of the cosmic radio background and faint features in the sky spectrum at long wavelengths that arise from redshifted 21-cm from gas in the reionization epoch. SARAS operates in the octave band 87.5-175 MHz. We present herein the system design arguing for a complex correlation spectrometer concept. The SARAS design concept provides a differential measurement between the antenna temperature and that of an internal reference termination, with measurements in switched system states allowing for cancellation of additive contaminants from a large part of the signal flow path including the digital spectrometer. A switched noise injection scheme provides absolute spectral calibration. Additionally, we argue for an electrically small frequency-independent antenna over an absorber ground. Various critical design features that aid in avoidance of systematics and in providing calibration products for the parametrization of other unavoidable systematics are described and the rationale discussed. The signal flow and processing is analyzed and the response to noise temperatures of the antenna, reference termination and amplifiers is computed. Multi-path propagation arising from internal reflections are considered in the analysis, which includes a harmonic series of internal reflections. We opine that the SARAS design concept is advantageous for precision measurement of the absolute cosmic radio background spectrum; therefore, the design features and analysis methods presented here are expected to serve as a basis for implementations tailored to measurements of a multiplicity of features in the background sky at long wavelengths, which may arise from events in the dark ages and subsequent reionization era.

Patra, Nipanjana; Subrahmanyan, Ravi; Raghunathan, A.; Udaya Shankar, N.

2013-08-01

385

A determination of the mass of Sagittarius A* from its radio spectral and source size measurements  

NASA Technical Reports Server (NTRS)

There is growing evidence that Sgr A* may be a million solar mass black hole accreting from the Galactic center wind. A consideration of the spectral and source size characteristics associated with this process can offer at least two distinct means of inferring the mass M, complementing the more traditional dynamical arguments. We show that M is unmistakably correlated with both the radio spectral index and the critical wavelength below which the intrinsic source size dominates over the angular broadening due to scattering in the interstellar medium. Current observations can already rule out a mass much in excess of 2 x 10 exp 6 solar masses and suggest a likely value close to 1 x 10 exp 6 solar masses, in agreement with an earlier study matching the radio and high-energy spectral components. We anticipate that such a mass may be confirmed with the next generation of source-size observations using milliarcsecond angular resolution at 0.5 - 1 cm wavelengths.

Melia, Fulvio; Jokipii, J. R.; Narayanan, Ajay

1992-01-01

386

Matrix volume measurements challenge the existence of diazoxide/glibencamide-sensitive KATP channels in rat mitochondria  

PubMed Central

A mitochondrial sulphonylurea-sensitive, ATP-sensitive K+ channel (mitoKATP) that is selectively inhibited by 5-hydroxydecanoate (5-HD) and activated by diazoxide has been implicated in ischaemic preconditioning. Here we re-evaluate the evidence for the existence of this mitoKATP by measuring changes in light scattering (A520) in parallel with direct determination of mitochondrial matrix volumes using 3H2O and [14C]sucrose. Incubation of rat liver and heart mitochondria in KCl medium containing Mg2+ and inorganic phosphate caused a decrease in light scattering over 5 min, which was accompanied by a small (15–30 %) increase in matrix volume. The presence of ATP or ADP in the buffer from the start greatly inhibited the decline in A520, whilst addition after a period of incubation (1–5 min) induced a rapid increase in A520, especially in heart mitochondria. Neither response was accompanied by a change in matrix volume, as measured isotopically. However, the effects of ATP and ADP on A520 were abolished by carboxyatractyloside and bongkrekic acid, inhibitors of the adenine nucleotide translocase (ANT) that lock the transporter in two discrete conformations and cause distinct changes in A520 in their own right. These data suggest that rather than matrix volume changes, the effects of ATP and ADP on A520 reflect changes in mitochondrial shape induced by conformational changes in the ANT. Furthermore, we were unable to demonstrate either a decrease in A520 or increase in matrix volume with a range of ATP-sensitive K+ channel openers such as diazoxide. Nor did glibencamide or 5-HD cause any reduction of matrix volume, whereas the K+ ionophore valinomycin (0.2 nm), produced a 10–20 % increase in matrix volume that was readily detectable by both techniques. Our data argue against the existence of a sulphonylurea-inhibitable mitoKATP channel. PMID:12562892

Das, Manika; Parker, Joanne E; Halestrap, Andrew P

2003-01-01

387

Properties of the plasma channel in liquid discharges inferred from cathode local temperature measurements  

SciTech Connect

The properties of the plasma channel at the cathode surface in a liquid discharge have been studied by means of temperature measurements and heat transfer numerical analysis. The studied discharge (current: 5 A; duration: 100 {mu}s; gap: 10 {mu}m) is typical of electrical discharge machining (EDM) in the semifinishing operation. The temperature information is obtained from two independent experiments: (1) microthermocouples patterned on the cathode, close to the discharge have been used to record the temperature variation caused by a single discharge with a high local resolution and large bandwidth; (2) the geometry of the resolidified layer, which gives the maximum extension of the melting point temperature isotherm, has been measured. These temperature data have then been compared to numerical simulation using inverse calculations allowing the experimental determination of two fundamental quantities of the discharge cathode interaction: (1) the power fraction transferred from the discharge to the sample, which was found to be close to 10% and (2) the exponent n of the power law expansion of the plasma channel r{sub plasma}{proportional_to}t{sup n}, which is n=0.2. The validity of the present analysis relies on the fact that the experimental temperature information is obtained for different values of the parameter r{sub plasma}/t{sub 0}{sup 2}, where t{sub 0}{sup 2} is the characteristic time of the experiment.

Revaz, B.; Witz, G.; Fluekiger, R. [University of Geneva, Department of Condensed Matter Physics, 24 Quai E.-Ansermet, CH-1211 Geneva 4 (Switzerland)

2005-12-01

388

Radio frequency cavity analysis, measurement, and calibration of absolute Dee voltage for K-500 superconducting cyclotron at VECC, Kolkata  

NASA Astrophysics Data System (ADS)

Variable Energy Cyclotron Centre has commissioned a K-500 superconducting cyclotron for various types of nuclear physics experiments. The 3-phase radio-frequency system of superconducting cyclotron has been developed in the frequency range 9-27 MHz with amplitude and phase stability of 100 ppm and ±0.20, respectively. The analysis of the RF cavity has been carried out using 3D Computer Simulation Technology (CST) Microwave Studio code and various RF parameters and accelerating voltages ("Dee" voltage) are calculated from simulation. During the RF system commissioning, measurement of different RF parameters has been done and absolute Dee voltage has been calibrated using a CdTe X-ray detector along with its accessories and known X-ray source. The present paper discusses about the measured data and the simulation result.

Som, Sumit; Seth, Sudeshna; Mandal, Aditya; Paul, Saikat; Duttagupta, Anjan

2013-02-01

389

Radio frequency cavity analysis, measurement, and calibration of absolute Dee voltage for K-500 superconducting cyclotron at VECC, Kolkata.  

PubMed

Variable Energy Cyclotron Centre has commissioned a K-500 superconducting cyclotron for various types of nuclear physics experiments. The 3-phase radio-frequency system of superconducting cyclotron has been developed in the frequency range 9-27 MHz with amplitude and phase stability of 100 ppm and ±0.2(0), respectively. The analysis of the RF cavity has been carried out using 3D Computer Simulation Technology (CST) Microwave Studio code and various RF parameters and accelerating voltages ("Dee" voltage) are calculated from simulation. During the RF system commissioning, measurement of different RF parameters has been done and absolute Dee voltage has been calibrated using a CdTe X-ray detector along with its accessories and known X-ray source. The present paper discusses about the measured data and the simulation result. PMID:23464200

Som, Sumit; Seth, Sudeshna; Mandal, Aditya; Paul, Saikat; Duttagupta, Anjan

2013-02-01

390

Radio frequency cavity analysis, measurement, and calibration of absolute Dee voltage for K-500 superconducting cyclotron at VECC, Kolkata  

SciTech Connect

Variable Energy Cyclotron Centre has commissioned a K-500 superconducting cyclotron for various types of nuclear physics experiments. The 3-phase radio-frequency system of superconducting cyclotron has been developed in the frequency range 9-27 MHz with amplitude and phase stability of 100 ppm and {+-}0.2{sup 0}, respectively. The analysis of the RF cavity has been carried out using 3D Computer Simulation Technology (CST) Microwave Studio code and various RF parameters and accelerating voltages ('Dee' voltage) are calculated from simulation. During the RF system commissioning, measurement of different RF parameters has been done and absolute Dee voltage has been calibrated using a CdTe X-ray detector along with its accessories and known X-ray source. The present paper discusses about the measured data and the simulation result.

Som, Sumit; Seth, Sudeshna; Mandal, Aditya; Paul, Saikat; Duttagupta, Anjan [Variable Energy Cyclotron Centre, Kolkata (India)

2013-02-15

391

Precise measurement of the top quark mass in the dilepton channel at D0.  

PubMed

We measure the top quark mass (m(t)) in p ?p collisions at a center of mass energy ?s = 1.96 TeV using dilepton t ?t?W(+)bW(-) ?b??(+)?(?)b?(-) ??(?) ?b events, where ? denotes an electron, a muon, or a tau that decays leptonically. The data correspond to an integrated luminosity of 5.4 fb(-1) collected with the D0 detector at the Fermilab Tevatron Collider. We obtain m(t)=174.0±1.8(stat)±2.4(syst) GeV, which is in agreement with the current world average m(t)=173.3±1.1 GeV. This is currently the most precise measurement of m(t) in the dilepton channel. PMID:21929164

Abazov, V M; Abbott, B; Acharya, B S; Adams, M; Adams, T; Alexeev, G D; Alkhazov, G; Alton, A; Alverson, G; Alves, G A; Ancu, L S; Aoki, M; Arov, M; Askew, A; Åsman, B; Atramentov, O; Avila, C; BackusMayes, J; Badaud, F; Bagby, L; Baldin, B; Bandurin, D V; Banerjee, S; Barberis, E; Baringer, P; Barreto, J; Bartlett, J F; Bassler, U; Bazterra, V; Beale, S; Bean, A; Begalli, M; Begel, M; Belanger-Champagne, C; Bellantoni, L; Beri, S B; Bernardi, G; Bernhard, R; Bertram, I; Besançon, M; Beuselinck, R; Bezzubov, V A; Bhat, P C; Bhatnagar, V; Blazey, G; Blessing, S; Bloom, K; Boehnlein, A; Boline, D; Boos, E E; Borissov, G; Bose, T; Brandt, A; Brandt, O; Brock, R; Brooijmans, G; Bross, A; Brown, D; Brown, J; Bu, X B; Buehler, M; Buescher, V; Bunichev, V; Burdin, S; Burnett, T H; Buszello, C P; Calpas, B; Camacho-Pérez, E; Carrasco-Lizarraga, M A; Casey, B C K; Castilla-Valdez, H; Chakrabarti, S; Chakraborty, D; Chan, K M; Chandra, A; Chen, G; Chevalier-Théry, S; Cho, D K; Cho, S W; Choi, S; Choudhary, B; Cihangir, S; Claes, D; Clutter, J; Cooke, M; Cooper, W E; Corcoran, M; Couderc, F; Cousinou, M-C; Croc, A; Cutts, D; Das, A; Davies, G; De, K; de Jong, S J; De la Cruz-Burelo, E; Déliot, F; Demarteau, M; Demina, R; Denisov, D; Denisov, S P; Desai, S; Deterre, C; DeVaughan, K; Diehl, H T; Diesburg, M; Dominguez, A; Dorland, T; Dubey, A; Dudko, L V; Duggan, D; Duperrin, A; Dutt, S; Dyshkant, A; Eads, M; Edmunds, D; Ellison, J; Elvira, V D; Enari, Y; Evans, H; Evdokimov, A; Evdokimov, V N; Facini, G; Ferbel, T; Fiedler, F; Filthaut, F; Fisher, W; Fisk, H E; Fortner, M; Fox, H; Fuess, S; Garcia-Bellido, A; Gavrilov, V; Gay, P; Geng, W; Gerbaudo, D; Gerber, C E; Gershtein, Y; Ginther, G; Golovanov, G; Goussiou, A; Grannis, P D; Greder, S; Greenlee, H; Greenwood, Z D; Gregores, E M; Grenier, G; Gris, Ph; Grivaz, J-F; Grohsjean, A; Grünendahl, S; Grünewald, M W; Guillemin, T; Guo, F; Gutierrez, G; Gutierrez, P; Haas, A; Hagopian, S; Haley, J; Han, L; Harder, K; Harel, A; Hauptman, J M; Hays, J; Head, T; Hebbeker, T; Hedin, D; Hegab, H; Heinson, A P; Heintz, U; Hensel, C; Heredia-De la Cruz, I; Herner, K; Hesketh, G; Hildreth, M D; Hirosky, R; Hoang, T; Hobbs, J D; Hoeneisen, B; Hohlfeld, M; Hubacek, Z; Huske, N; Hynek, V; Iashvili, I; Illingworth, R; Ito, A S; Jabeen, S; Jaffré, M; Jamin, D; Jayasinghe, A; Jesik, R; Johns, K; Johnson, M; Johnston, D; Jonckheere, A; Jonsson, P; Joshi, J; Jung, A W; Juste, A; Kaadze, K; Kajfasz, E; Karmanov, D; Kasper, P A; Katsanos, I; Kehoe, R; Kermiche, S; Khalatyan, N; Khanov, A; Kharchilava, A; Kharzheev, Y N; Khatidze, D; Kirby, M H; Kohli, J M; Kozelov, A V; Kraus, J; Kulikov, S; Kumar, A; Kupco, A; Kur?a, T; Kuzmin, V A; Kvita, J; Lammers, S; Landsberg, G; Lebrun, P; Lee, H S; Lee, S W; Lee, W M; Lellouch, J; Li, L; Li, Q Z; Lietti, S M; Lim, J K; Lincoln, D; Linnemann, J; Lipaev, V V; Lipton, R; Liu, Y; Liu, Z; Lobodenko, A; Lokajicek, M; Lopes de Sa, R; Lubatti, H J; Luna-Garcia, R; Lyon, A L; Maciel, A K A; Mackin, D; Madar, R; Magaña-Villalba, R; Malik, S; Malyshev, V L; Maravin, Y; Martínez-Ortega, J; McCarthy, R; McGivern, C L; Meijer, M M; Melnitchouk, A; Menezes, D; Mercadante, P G; Merkin, M; Meyer, A; Meyer, J; Miconi, F; Mondal, N K; Muanza, G S; Mulhearn, M; Nagy, E; Naimuddin, M; Narain, M; Nayyar, R; Neal, H A; Negret, J P; Neustroev, P; Novaes, S F; Nunnemann, T; Obrant, G; Orduna, J; Osman, N; Osta, J; Otero y Garzón, G J; Padilla, M; Pal, A; Parashar, N; Parihar, V; Park, S K; Parsons, J; Partridge, R; Parua, N; Patwa, A; Penning, B; Perfilov, M; Peters, K; Peters, Y; Petridis, K; Petrillo, G; Pétroff, P; Piegaia, R; Piper, J; Pleier, M-A; Podesta-Lerma, P L M; Podstavkov, V M; Polozov, P; Popov, A V; Prewitt, M; Price, D; Prokopenko, N; Protopopescu, S; Qian, J; Quadt, A; Quinn, B; Rangel, M S; Ranjan, K; Ratoff, P N; Razumov, I; Renkel, P; Rijssenbeek, M; Ripp-Baudot, I; Rizatdinova, F; Rominsky, M; Ross, A; Royon, C; Rubinov, P; Ruchti, R; Safronov, G; Sajot, G; Salcido, P; Sánchez-Hernández, A; Sanders, M P; Sanghi, B; Santos, A S; Savage, G; Sawyer, L; Scanlon, T; Schamberger, R D; Scheglov, Y; Schellman, H; Schliephake, T; Schlobohm, S; Schwanenberger, C; Schwienhorst, R; Sekaric, J; Severini, H; Shabalina, E; Shary, V; Shchukin, A A; Shivpuri, R K; Simak, V; Sirotenko, V; Skubic, P; Slattery, P; Smirnov, D; Smith, K J; Snow, G R; Snow, J; Snyder, S; Söldner-Rembold, S; Sonnenschein, L; Soustruznik, K; Stark, J; Stolin, V; Stoyanova, D A; Strauss, M; Strom, D; Stutte, L; Suter, L; Svoisky, P; Takahashi, M; Tanasijczuk, A; Taylor, W; Titov, M; Tokmenin, V V; Tsai, Y-T; Tsybychev, D; Tuchming, B; Tully, C; Uvarov, L; Uvarov, S; Uzunyan, S; Van Kooten, R; van Leeuwen, W M; Varelas, N; Varnes, E W; Vasilyev, I A; Verdier, P; Vertogradov, L S; Verzocchi, M; Vesterinen, M; Vilanova, D; Vokac, P; Wahl, H D; Wang, M H L S

2011-08-19

392

Purity of Gaussian states: Measurement schemes and time evolution in noisy channels  

SciTech Connect

We present a systematic study of the purity for Gaussian states of single-mode continuous variable systems. We prove the connection of purity to observable quantities for these states, and show that the joint measurement of two conjugate quadratures is necessary and sufficient to determine the purity at any time. The statistical reliability and the range of applicability of the proposed measurement scheme are tested by means of Monte Carlo simulated experiments. We then consider the dynamics of purity in noisy channels. We derive an evolution equation for the purity of general Gaussian states both in thermal and in squeezed thermal baths. We show that purity is maximized at any given time for an initial coherent state evolving in a thermal bath, or for an initial squeezed state evolving in a squeezed thermal bath whose asymptotic squeezing is orthogonal to that of the input state.

Paris, Matteo G.A. [Quantum Optics and Information Group, INFM UdR di Pavia, I-27100 Pavia (Italy); Illuminati, Fabrizio; Serafini, Alessio; De Siena, Silvio [Dipartimento di Fisica 'E. R. Caianiello', Universita di Salerno, INFM UdR Salerno, INFN Sez. Napoli, Grupo Collegato Salerno, Via S. Allende, 84081 Baronissi, SA (Italy)

2003-07-01

393

Simultaneously measured lightning return stroke channel-base current and luminosity  

NASA Astrophysics Data System (ADS)

The time delay between lightning return stroke current and the resultant luminosity was measured for 22 return strokes in eight lightning flashes triggered by the rocket-and-wire technique during the summer of 2014 in Florida. The current-to-luminosity delay measured at the channel base at the 20% amplitude level ranged from 30 to 200 ns with an average of 90 ns and at the 50% amplitude level ranged from 30 to 180 ns with an average of 94 ns. The delays are significantly shorter than that predicted by Liang et al. (2014) from theory. The current-to-luminosity delays increase with increasing current risetime, current risetime varying from 190 ns to 570 ns, but the delay appears not to depend on the peak current value.

Carvalho, F. L.; Jordan, D. M.; Uman, M. A.; Ngin, T.; Gamerota, W. R.; Pilkey, J. T.

2014-11-01

394

Frequency Allocation; The Radio Spectrum.  

ERIC Educational Resources Information Center

The Federal Communications Commission (FCC) assigns segments of the radio spectrum to categories of users, and specific frequencies within each segment to individual users. Since demand for channel space exceeds supply, the process is complex. The radio spectrum can be compared to a long ruler: the portion from 10-540 kiloHertz has been set aside…

Federal Communications Commission, Washington, DC.

395

Characterization of Ionospheric Scintillation Using Simultaneous Formosat-3/COSMIC Radio Occultation Observations and AFRL SCINDA Ground Scintillation Measurements  

NASA Astrophysics Data System (ADS)

Ionospheric scintillation at low latitudes has been studied using ionospheric radio occultation (RO) measurements by the FORMOSAT-3/COSMIC micro-satellites in conjunction with ground-based data from the Scintillation Network Decision Aid (SCINDA) station at Kwajalein Atoll. The Air Force Research Laboratory has developed the SCINDA network for monitoring low-latitude ionospheric total electron content (TEC) and scintillation associated with equatorial spread F. The network currently consists of sixteen stations distributed around the globe and the data have been used to conduct numerous studies on the characteristics and climatology of equatorial scintillation. The present study focuses on COSMIC RO and SCINDA data during the three COSMIC campaigns in 2006. Radio occultation events are selected by requiring that ionospheric scintillation was detected by the SCINDA VHF scintillation monitor at Kwajalein, and that the occultation ray path intersected the Kwajalein longitude below the satellite altitude, which varied from 500 to 800 km for the six FORMOSAT-3 satellites. In order to exclude tropospheric effects, only GPS signal amplitudes from FORMOSAT-3 with ray path tangent altitudes above 100 km are considered. Locations of ionospheric scintillation are estimated by triangulation using the satellites and the SCINDA ground station. Airglow images at Kwajalein are also used to confirm occurrence of equatorial ionospheric scintillations. For the selected events, large amplitude L1 and L2 scintillations tend to occur at altitudes below 200 km at frequencies around 0.5 Hz. The results are discussed as a potential path toward better specifying the occurrence of equatorial scintillations.

Starks, M. J.; Lin, C. S.; Groves, K. M.; Pedersen, T. R.; Basu, S.; Syndergaard, S.; Rocken, C.

2007-05-01

396

Aircraft Engine On-Line Diagnostics Through Dual-Channel Sensor Measurements: Development of a Baseline System  

NASA Technical Reports Server (NTRS)

In this paper, a baseline system which utilizes dual-channel sensor measurements for aircraft engine on-line diagnostics is developed. This system is composed of a linear on-board engine model (LOBEM) and fault detection and isolation (FDI) logic. The LOBEM provides the analytical third channel against which the dual-channel measurements are compared. When the discrepancy among the triplex channels exceeds a tolerance level, the FDI logic determines the cause of the discrepancy. Through this approach, the baseline system achieves the following objectives: (1) anomaly detection, (2) component fault detection, and (3) sensor fault detection and isolation. The performance of the baseline system is evaluated in a simulation environment using faults in sensors and components.

Kobayashi, Takahisa; Simon, Donald L.

2008-01-01

397

Channel Strain in Advanced Complementary MetalOxideSemiconductor Field Effect Transistors Measured Using Nano-Beam Electron Diffraction  

Microsoft Academic Search

Using high-precision nano-beam electron diffraction (NBD), we clarified the influences of stress liner and the stress of shallow trench isolation on channel strain in advanced metal-oxide-semiconductor field effect transistors (MOSFETs). For systematic strain measurements, we improved the precision of NBD by observing large reciprocal lattice vectors under appropriate diffraction conditions. The absolute value of the channel strain increases by stress

Akio Toda; Hidetatsu Nakamura; Toshinori Fukai; Nobuyuki Ikarashi

2008-01-01

398

Study of the use of particle channeling in time-of-flight fission-fragment mass-yield measurements  

Microsoft Academic Search

A direct physical measurement of the mass distribution in the thermal-; neutron fission of ²³⁵U was made using the single timeof-fiight method and ; particle channeling in the energy detector. Particle channeling was employed in ; an attempt to achieve good energy resolution to give a mass resolution of better ; than 1 amu. A totally depleted silicon surface-barrier detector

W. J. Sullivan; B. W. Wehring

1974-01-01

399

Novel method to classify hemodynamic response obtained using multi-channel fNIRS measurements into two groups: exploring the combinations of channels  

PubMed Central

Near-infrared spectroscopy (NIRS) in psychiatric studies has widely demonstrated that cerebral hemodynamics differs among psychiatric patients. Recently we found that children with attention-deficit/hyperactivity disorder (ADHD) and children with autism spectrum disorders (ASD) showed different hemodynamic responses to their own mother’s face. Based on this finding, we may be able to classify the hemodynamic data into two those groups and predict to which diagnostic group an unknown participant belongs. In the present study, we proposed a novel statistical method for classifying the hemodynamic data of these two groups. By applying a support vector machine (SVM), we searched the combination of measurement channels at which the hemodynamic response differed between the ADHD and the ASD children. The SVM found the optimal subset of channels in each data set and successfully classified the ADHD data from the ASD data. For the 24-dimensional hemodynamic data, two optimal subsets classified the hemodynamic data with 84% classification accuracy, while the subset contained all 24 channels classified with 62% classification accuracy. These results indicate the potential application of our novel method for classifying the hemodynamic data into two groups and revealing the combinations of channels that efficiently differentiate the two groups. PMID:25071510

Ichikawa, Hiroko; Kitazono, Jun; Nagata, Kenji; Manda, Akira; Shimamura, Keiichi; Sakuta, Ryoichi; Okada, Masato; Yamaguchi, Masami K.; Kanazawa, So; Kakigi, Ryusuke

2014-01-01

400

The principle of a virtual multi-channel lock-in amplifier and its application to magnetoelectric measurement system  

E-print Network

This letter presents principles and applications of a virtual multi-channel lock-in amplifier that is a simple but effective method to recover small ac signal from noise with high presison. The fundamentals of this method are based on calculation of cross-correlation function. Via this method, we successfully built up a magnetoelectric measurement system which can perform precise and versatile measurements without any analog lock-in amplifier. Using the virtual multi-channel lock-in amplifier, the output of the magnetoelectric measurement system is extensively rich in magnetoelectric coupling behaviors, including coupling strength and phase lag, under various dc bias magnetic field and ac magnetic field.

Lu, Jun; Qiao, Lijie

2007-01-01

401

Label-free viscosity measurement of complex fluids using reversal flow switching manipulation in a microfluidic channel.  

PubMed

The accurate viscosity measurement of complex fluids is essential for characterizing fluidic behaviors in blood vessels and in microfluidic channels of lab-on-a-chip devices. A microfluidic platform that accurately identifies biophysical properties of blood can be used as a promising tool for the early detections of cardiovascular and microcirculation diseases. In this study, a flow-switching phenomenon depending on hydrodynamic balancing in a microfluidic channel was adopted to conduct viscosity measurement of complex fluids with label-free operation. A microfluidic device for demonstrating this proposed method was designed to have two inlets for supplying the test and reference fluids, two side channels in parallel, and a junction channel connected to the midpoint of the two side channels. According to this proposed method, viscosities of various fluids with different phases (aqueous, oil, and blood) in relation to that of reference fluid were accurately determined by measuring the switching flow-rate ratio between the test and reference fluids, when a reverse flow of the test or reference fluid occurs in the junction channel. An analytical viscosity formula was derived to measure the viscosity of a test fluid in relation to that of the corresponding reference fluid using a discrete circuit model for the microfluidic device. The experimental analysis for evaluating the effects of various parameters on the performance of the proposed method revealed that the fluidic resistance ratio ( R J L / R L , fluidic resistance in the junction channel ( R J L ) to fluidic resistance in the side channel ( R L )) strongly affects the measurement accuracy. The microfluidic device with smaller R J L / R L values is helpful to measure accurately the viscosity of the test fluid. The proposed method accurately measured the viscosities of various fluids, including single-phase (Glycerin and plasma) and oil-water phase (oil vs. deionized water) fluids, compared with conventional methods. The proposed method was also successfully applied to measure viscosities of blood with varying hematocrits, chemically fixed RBCS, and channel sizes. Based on these experimental results, the proposed method can be effectively used to measure the viscosities of various fluids easily, without any fluorescent labeling and tedious calibration procedures. PMID:24404040

Jun Kang, Yang; Ryu, Jeongeun; Lee, Sang-Joon

2013-01-01

402

Multiband propagation experiment for narrowband characterisation of high elevation angle land mobile-satellite channels  

NASA Astrophysics Data System (ADS)

Results of a recent multiband propagation measurement campaign for the high elevation angle land mobile satellite channel are reported. Simultaneous narrowband sounding of the channel has been carried out in suburban, wooded and open areas of the UK using a helicopter-mounted platform to simulate the satellite signal at various elevation angles. Propagation related link degradations in the land mobile-satellite channel have been observed to be less severe when the path elevation angle is increased or radio frequency decreases.

Butt, G.; Evans, B. G.; Richharia, M.

1992-07-01

403

#EdChat Radio  

NSDL National Science Digital Library

This iTunes radio channel is available for free download by discussion or the entire database by subscription. Each podcast reflects on the Twitter #EdChat conversation of the week on a range of educational topics. Some topics of particular interest to math coaches are Mentoring New Teachers and Reinventing the Classroom.

BAM Radio Network

2013-01-01

404

PIV flow measurements for heat transfer characterization in two-pass square channels with smooth and 90 ribbed walls  

E-print Network

PIV flow measurements for heat transfer characterization in two-pass square channels with smooth the correlation between the high- Reynolds number turbulent flow and wall heat transfer characteristics in a two number (Re) of 30,000. The PIV measurement results were compared with the heat transfer experimental data

Kihm, IconKenneth David

405

CDF note 9841 t t production cross section measurement in the allhadronic channel (2.9 fb -1 )  

E-print Network

classes. Given the signal yields coming from the mass fit, the value of the cross section dependsCDF note 9841 t � t production cross section measurement in the all­hadronic channel (2.9 fb -1 of the t � t production cross section obtained from the results of the Template Method analysis (TMT2D) used to measure

Quigg, Chris

406

in the lipid bilayer Distance measurements reveal a common topology of prokaryotic voltage-gated ion channels  

E-print Network

in the lipid bilayer Distance measurements reveal a common topology of prokaryotic voltage.pnas.org/misc/reprints.shtml To order reprints, see: Notes: #12;Distance measurements reveal a common topology of prokaryotic voltage conformations in a mem- brane environment. The validity of the crystal structure for the prokaryotic K channel

Bezanilla, Francisco

407

Application of left- and right-looking SAR stereo to depth measurements of the Ammavaru outflow channel, Lada Terra, Venus  

NASA Technical Reports Server (NTRS)

Venusian channels are too narrow to be resolved by Magellan's radar altimeter, so they are not visible in the standard topographic data products. Stereo image data, in addition to their benefit to geologic mapping of Venus structures as a whole, are indispensible in measuring the topography across the channels. These measurements can then be used in conjunction with the regional topographic maps based on the altimeter data to produce cross-sectional areas for the channels and estimate the fluid discharge through them. As an example of the application of the stereo image data to venusian channels, a number of test depth and profile measurements were made of the large outflow channel system in Lada Terra, centered at 50 deg S latitude, 21 deg E longitude (F-MIDR 50S021). These measurements were made by viewing the cycle 1 and 2 digital FMIDRs in stereo on a display monitor, so as to minimize the errors in measuring parallax displacement as much as possible. The MIDRs are produced at a scale of 75 m/pixel. This corresponds to a vertical scale of about 17 m/pixel, when calculating the height of a feature from its parallax displacement. An error in placement determination of 1 pixel was assumed to characterize the vertical accuracy as plus or minus 17 m. When this technique was applied to the outflow channel, it was noted that the walls of the collapsed terrain source and 'trough reach' of the channel are laid over in both the cycle 1 and 2 images. This is evident when examining the distance between features on the plateau and the cliff walls in the two images. The layover 'shifts' the features closer to the apparent edge of the wall relative to the oppositely illuminated image.

Parker, T. J.

1992-01-01

408

Experimental measurements in a radio frequency discharge heated supersonic flow: Evaluation of a potential electric propulsion thruster  

SciTech Connect

An operational radio frequency discharge-driven supersonic flow system, which utilizes an inductively and capacitively coupled plasma (ICCP) tube to produce high enthalpy source gas, is described. The ICCP coupled to a properly designed nozzle represents a potential electric propulsion device. The high gas temperatures achieved in the plasma discharge (> 5000 K) and the electrodeless nature of the tube's operation offers potentially high thruster performance coupled and long operational lifetime. A preliminary characterization of the current system was established using emission and probe-based measurements. A nominal peak specific impulse of 155 s was estimated for operation with argon. The calculated thrust based upon the peak velocity and mass flow through the device is 1.1 N. 14 refs., 10 figs.

Wantuck, P.J.; Hull, D.E.

1991-01-01

409

Data assimilation retrieval of electron density profiles from radio occultation measurements  

NASA Astrophysics Data System (ADS)

In this paper, the Kalman filter is used to retrieve the electron density profile along the tangent points by assimilating the slant total electron content data observed during a radio occultation (RO) event into an empirical background model. The RO data observed by COSMIC satellites on day of year 266 in 2009 are selected to do both the simulation work and the real data retrieval test. The results show that the data assimilation technique can improve the electron density retrieval in comparison with the Abel inversion. It is less influenced by the ionospheric inhomogeneity than the Abel method. Some pseudo-large-scale features made by the Abel retrieval, such as the plasma cave underneath the equatorial ionization anomaly region and the three peaks along the latitude direction in the E layer, disappear in the data assimilation retrieval results. Independent validation by ground-based ionosonde observations confirms the improvement of data assimilation retrieval below the F2 peak. In addition, some potential research on RO data assimilation is also discussed.

Yue, Xinan; Schreiner, William S.; Lin, Yu-Cheng; Rocken, Christian; Kuo, Ying-Hwa; Zhao, Biqiang

2011-03-01

410

Field measurements of pressure fluctuations on an instrumented wall: implications for channel-bed erosion  

NASA Astrophysics Data System (ADS)

Debris flows typically increase their volume and flow depth through entrainment of sediment. This produces hazardous flows which are also capable of eroding bedrock and changing the morphology of steep torrent channels. Few observations of entrainment are available to shed light on the mechanisms occurring in the field. Herein we describe pressure observations from a vertical array of six force plates, each 0.3 m x 0.3 m in size, installed in a 14 m long wall, oriented parallel to the mean flow direction, at the Illgraben debris flow observation station, Switzerland. The force plates, sampled at 2 kHz, allow determination of the mean and fluctuating component of the pressure at the lateral edge of a debris flow. The median pressure measurements are consistent with data from a large (8 m2) force plate located near the wall. The fluctuating component of the pressure is typically an order of magnitude larger than the mean pressure at the front of the flow, and probably corresponds to the impact of large boulders (and possibly force chains produced by several boulders) with the force plates as they flow past the sensors. The fluctuating component of the pressure is largest at the head of the debris flow were the flow is not yet fully saturated with the liquid phase of the flow. After the passage of the front of the flow, the pressure fluctuations decrease in amplitude and are of similar magnitude to the median pressure value. Previously published measurements of debris flow erosion at the Illgraben torrent channel (Berger et al., 2011, J. Geophys. Res. Earth Surface) show that sediment erosion takes place at the front of the flow, coinciding with our observations of large pressure fluctuations at the front of the flow. We propose that the pressure fluctuations generated within the debris flow drive both sediment entrainment and bedrock erosion.

McArdell, B. W.; Fritschi, B.

2012-04-01

411

MTF and PSF measurements of the CCD273-84 detector for the Euclid visible channel  

NASA Astrophysics Data System (ADS)

The European Space Agency (ESA) and e2v, together with the Euclid Imaging Consortium, have designed and manufactured pre-development models of a novel imaging detector for the visible channel of the Euclid space telescope. The new detector is an e2v back-illuminated, 4k x 4k, 12 micron square pixel CCD designated CCD273-84. The backilluminated detectors have been characterised for many critical performance parameters such as read noise, charge transfer efficiency, quantum efficiency, Modulation Transfer Function and Point Spread Function. Initial analysis of the MTF and PSF performance of the detectors has been performed by e2v and at MSSL and the results have enabled the Euclid VIS CCD project to move in to the C/D or flight phase delivery contract. This paper describes the CCD273-84 detector, the test method used for MTF measurements at e2v and the test method used for PSF measurements at MSSL. Results are presented for MTF measurements at e2v over all pre development devices. Also presented is a cross comparison of the data from the MTF and PSF measurement techniques on the same device. Good agreement between the measured PSF Full Width Half Maximum and the equivalent Full Width Half Maximum derived from the MTF images and test results is shown, with results that indicate diffusion FWHM values at or below 10 micron for the CCD273-84 detectors over the spectral range measured. At longer wavelengths the diffusion FWHM is shown to be in the 6-8 micron range.

Swindells, I.; Wheeler, R.; Darby, S.; Bowring, S.; Burt, D.; Bell, R.; Duvet, L.; Walton, D.; Cole, R.

2014-08-01

412

On the stability of fiber-optic quantum cryptography at arbitrary losses in a communication channel: Exclusion of unambiguous measurements  

NASA Astrophysics Data System (ADS)

Since a source of quantum states is not strictly single-photon and losses exist in a communication channel, an attack with unambiguous measurements is possible, leading to loss of security. The problem of the stability of quantum key distribution protocols in a channel with large losses is still unsolved. A radical solution of this problem has been proposed by completely excluding unambiguous measurements by an eavesdropper. The problem is solved by means of counting of classical reference pulses. The conservation of the number of classical sync pulses results in the impossibility of unambiguous measurements. In this case, losses in the communication channel are considered as a priori unknown and can vary during a series of messages.

Molotkov, S. N.

2014-11-01

413

Microplate-compatible biamperometry array for parallel 48-channel amperometric or coulometric measurements.  

PubMed

We report a new reusable electrochemical array for parallel biamperometric measurements that has been designed for use with standard microplates. The 48-channel array uses half of the available 96 wells and has 48 pairs of Pt wire electrodes. Applications to the quantitation of a variety of oxidizable species, including acetaminophen, ascorbic acid, hydroquinone, trolox, and uric acid, are demonstrated in assays that use potassium ferricyanide as an oxidant to produce a mixture of ferri- and ferrocyanide. Hydrogen peroxide quantitation is also demonstrated, based on an assay in which ferrocyanide is oxidized, again to produce a mixture of ferri- and ferrocyanide. Detection limits (signal-to-noise ratio (S/N) = 3) in these assays range from 1 (acetaminophen, R2 = 0.994) to 8 microM (ascorbic acid, R2 = 0.967), and linearity was observed to analyte concentrations of at least 100 microM. We also demonstrate the application of the biamperometric array to enzymatic assays, using the glucose oxidase reaction as an example; following a 20 min enzyme reaction time, a detection limit of 0.1 mM glucose was obtained. These results indicate that applications to other oxidase-based assays are feasible in this high-throughput format. The new electrochemical array employs standard, inexpensive microplates, and the biamperometric measurements are simple, precise, and rapid, requiring only 2 min for 48 parallel measurements. PMID:18341302

Mann, Thomas S; O'Hagan, Liam; Ertl, Peter; Sparkes, Douglas I; Mikkelsen, Susan R

2008-04-15

414

Measurement setup and protocol for characterizing and testing radio frequency personal exposure meters.  

PubMed

Body-worn radiofrequency electromagnetic field (RF-EMF) personal exposure meters (PEMs) have been increasingly used for exposure assessment in epidemiological research. However, little research on the measurement accuracy of these devices is available. In this article a novel measurement setup and a measurement protocol are presented for characterizing and testing PEMs. The whole setup and procedure is tested using two EME SPY 120 devices. The performance of the PEM was analyzed for absolute measurements in an anechoic chamber. Modulated signals representing the different services as real signals generated by appropriate testers were used. Measurement results were evaluated with respect to a root mean square detector. We found that measurement accuracy depends strongly on the carrier frequency and also on the number of occupied time slots for Time Division Multiple Access (TDMA)-based services. Thus, correction factors can only be derived if the distribution of the network configuration over the measurement time for all measurement points is available. As a result of the simplicity of the measurement setup and the straightforward measurement protocol, the possibility of fast validation leads to a higher accuracy in the characterization and testing of PEMs. PMID:21755521

Lauer, Oliver; Neubauer, Georg; Röösli, Martin; Riederer, Markus; Frei, Patrizia; Mohler, Evelyn; Fröhlich, Jürg

2012-01-01

415

Film, Radio, and Television.  

ERIC Educational Resources Information Center

This journal issue covers the history of film, radio, and television in Iowa. The first article, "When Pictures and Sound Came to Iowa," summarizes the origin of movies and radio and their early beginnings in Iowa. Using old photographs and measurement charts, the viewing, reading, and listening habits of young people in 1950 and 1958 are…

Hardesty, Carolyn, Ed.

1990-01-01

416

Direct measurements by submersible of surge-type turbidity currents in a fjord channel, southeast Alaska  

SciTech Connect

High density, high-speed turbidity currents were observed and their properties measured in submarine channels in Queen Inlet, southeast Alaska during June, 1990 and 1991. A ROV submersible fitted with two video cameras, a CTD, an optical backscatter turbidity monitor (OBS), and electromagnetic current meter, and sidescan sonar was used to collect data from within and above the flows. Multiple flows were recorded during a ROV dive at 2.3 km from the delta front in a channel at 104 m depth. Flows were marked by sudden increases in turbidity and current velocity. In one flow, turbidity increased from 300 to 1,600 OBS units (instrument maximum) in 10 sec, and within 9.4 min, salinity (S) steadily decreased by 12.1 ppt, with only a 0.2 C temperature (T) increase. Density differences between the flow and ambient water require a minimum sediment concentration of 97 g/l. Maximum flow velocity exceeded 3.3 m/s. A vertical ROV profile indicated a flow thickness of 10 m. The upper surface was visually identified by billowing suspended sediment and by fluctuating OBS and T as ambient and flow water mixed in turbulent eddies. A faster S decrease and slower T increase with distance into and away from the flow indicate that thermal diffusive processes were less efficient than convective mass transfer. The S change indicates that flow water and ambient water mixed well beyond the flow defined by high turbidity. Warm water temperatures within the flow and low meltwater stream discharge suggest that these flows originated from the delta front and are not continuous underflows.

Cowan, E.A. (Appalachian State Univ., Boone, NC (United States). Dept. of Geology); Powell, R.D. (Illinois Univ., DeKalb, IL (United States). Geology Dept.); Lawson, D.E. (USA Cold Regions Research and Engineering Lab., Hanover, NH (United States)); Carlson, P.R. (Geological Survey, Menlo Park, CA (United States))

1992-01-01

417

Measurement of a phase of a radio wave reflected from rock salt and ice irradiated by an electron beam for detection of ultra-high-energy neutrinos  

NASA Astrophysics Data System (ADS)

We have found a radio-wave-reflection effect in rock salt for the detection of ultra-high energy neutrinos (UHE?'s) which are expected to be generated in Greisen, Zatsepin, and Kuzmin (GZK) processes in the universe. When an UHE? interacts with rock salt or ice as a detection medium, a shower is generated. That shower is formed by hadronic and electromagnetic avalanche processes. The energy of the UHE? shower converts to thermal energy through ionization processes. Consequently, the temperature rises along the shower produced by the UHE?. The refractive index of the medium rises with temperature. The irregularity of the refractive index in the medium leads to a reflection of radio waves. This reflection effect combined with the long attenuation length of radio waves in rock salt and ice would yield a new method to detect UHE?'s. We measured the phase of the reflected radio wave under irradiation with an electron beam on ice and rock salt powder. The measured phase showed excellent consistence with the power reflection fraction which was measured directly. A model taking into account the temperature change explained the phase and the amplitude of the reflected wave. Therefore the reflection mechanism was confirmed. The power reflection fraction was compared with that calculated with the Fresnel equations, the ratio between the measured result and that obtained with the Fresnel equations in ice was larger than that of rock salt.

Chiba, Masami; Kamijo, Toshio; Tanikawa, Takahiro; Yano, Hiroyuki; Yabuki, Fumiaki; Yasuda, Osamu; Chikashige, Yuichi; Kon, Tadashi; Shimizu, Yutaka; Watanabe, Souichirou; Utsumi, Michiaki; Fujii, Masatoshi

2013-05-01

418

Measurements and simulation of Faraday rotation across the Coma radio relic  

NASA Astrophysics Data System (ADS)

The aim of this work is to probe the magnetic field properties in relics and infall regions of galaxy clusters using Faraday rotation measures. We present Very Large Array multifrequency observations of seven sources in the region south-west of the Coma cluster, where the infalling group NGC 4839 and the relic 1253+275 are located. The Faraday rotation measure maps for the observed sources are derived and analysed to study the magnetic field in the south-west region of Coma. We discuss how to interpret the data by comparing observed and mock rotation measure maps that are produced simulating different three-dimensional magnetic field models. The magnetic field model that gives the best fit to the Coma central region underestimates the rotation measure in the south-west region by a factor of ˜6, and no significant jump in the rotation measure data is found at the position of the relic. We explore different possibilities to reconcile observed and mock rotation measure trends, and conclude that an amplification of the magnetic field along the south-west sector is the most plausible solution. Our data together with recent X-ray estimates of the gas density obtained with Suzaku suggest that a magnetic field amplification by a factor of ˜3 is required throughout the entire south-west region in order to reconcile real and mock rotation measure trends. The magnetic field in the relic region is inferred to be ˜ 2 ?G, consistent with inverse Compton limits.

Bonafede, A.; Vazza, F.; Brüggen, M.; Murgia, M.; Govoni, F.; Feretti, L.; Giovannini, G.; Ogrean, G.

2013-08-01

419

Low temperature radio-frequency transverse susceptibility measurements using a CMOS oscillator circuit  

NASA Astrophysics Data System (ADS)

A transverse susceptibility (TS) measurement system based on a simple inverter CMOS cell oscillator cross-coupled to a LC tank is presented. The system has been implemented to operate at a Quantum Design Physical Properties Measurement System (PPMS). We introduce several improvements with respect to similar currently operating TS measurement equipments. The electronics have been redesigned to use CMOS transistors as active devices, which simplifies the circuit design and enlarge the tuning range, thus making the proposed electronic block more feasible, predictable, and precise. Additionally, we propose a newly designed sample holder, which facilitates the procedure to change a sample and improves reproducibility of the circuit. Our design minimizes the thermal leak of the measuring probe by one order of magnitude, allowing to measure from 1.8 K in standard PPMS systems, thanks to the use of a low temperature beryllium-copper coaxial cable instead of the conventional RG402 Cu coaxial cable employed in the insert for the PPMS in similar systems. The data acquisition method is also simplified, so that the measuring sequences are implemented directly in the PPMS controller computer by programming them in the Quantum Design MultiVu software that controls the PPMS. We present the test measurements performed on the system without sample to study the background signal and stability of the circuit. Measurements on a Gd2O3 calibrating sample yield to the estimation of the system sensitivity, which is found to be on the order of 10-6 emu. Finally, measurements on a TmCo2 Laves phase sample with a ferrimagnetic transition temperature around 4 K are described, demonstrating that the developed system is well suited to explore interesting magnetic phenomena at this temperature scale.

Figueroa, A. I.; Bartolomé, J.; García del Pozo, J. M.; Arauzo, A.; Guerrero, E.; Téllez, P.; Bartolomé, F.; García, L. M.

2012-08-01

420

Measurement of erythrocyte deformability by the flow-channel diffraction method  

NASA Astrophysics Data System (ADS)

Erythrocyte deformability, known as ability of red blood cell (RBC) to change shape during flow in the microcirculation, is the basic rheological property of erythrocyte. Many techniques have been proposed to measure RBC"s deformability (e.g. micropipette aspiration, micropore filtration, high shear viscometer and rheoscope techniques). Perhaps one of the most elegant technique for measurements of RBC deformability is ektacytometry, technique based on laser diffraction, worked out by Bessis and Mohandas1 and recently developed by others2,3. The laser light scattered by erythrocytes subjected to a well-defined shear stress (z) can be analyzed with the ektacytometer to obtain information regarding the changes in cell shape due to fluid shear. Usually, in order to deform RBC with shear stress the rotating Couette chamber is used 1-5. From the diffraction images the elongation index (E), as a quotient of minor and major axes of the elliptically transformed diffraction patterns, is calculated. However, one has to face a series of methodological problems 5: 1. Occurrence of turbulences and heat shear, 2. Control of gap width within the Couette viscometer and the intensity of transmitted light, 3. The determination of RBC elongation coefficients E from the diffraction patterns. Therefore, in order to get accurate results, we have used unconventional technique which consists of a simple laminar flow system made from two parallel Plexiglas plates (flow-channel diffractometer) and the computer analysis of the diffraction pattern.

Górnicki, A.; Kempczy?ski, A.

2005-08-01

421

Three-Dimensional Holographic Refractive-Index Measurement of Continuously Flowing Cells in a Microfluidic Channel  

NASA Astrophysics Data System (ADS)

The refractive index of biological specimens is a source of intrinsic contrast that can be explored without any concerns of photobleaching or harmful effects caused by extra contrast agents. In addition, the refractive index contains rich information related to the metabolism of cells at the cellular and subcellular levels. Here, we report a no-moving-parts approach that provides three-dimensional refractive-index maps of biological samples continuously flowing in a microfluidic channel. Specifically, we use line illumination and off-axis digital holography to record the angular spectra of light scattered from flowing samples at high speed. Applying the scalar diffraction theory, we obtain accurate refractive-index maps of the samples from the measured spectra. Using this method, we demonstrate label-free three-dimensional imaging of live RKO human colon cancer cells and RPMI8226 multiple myeloma cells, and obtain the volume, dry mass, and density of these cells from the measured three-dimensional refractive-index maps. Our results show that the reported method, alone or in combination with the existing flow cytometry techniques, shows promise as a quantitative tool for stain-free characterization of a large number of cells.

Sung, Yongjin; Lue, Niyom; Hamza, Bashar; Martel, Joseph; Irimia, Daniel; Dasari, Ramachandra R.; Choi, Wonshik; Yaqoob, Zahid; So, Peter

2014-02-01

422

Vector channels for smart antennas. Measurements, statistical modeling, and directional properties in outdoor environments  

Microsoft Academic Search

In wireless communications, smart antenna systems that employ antenna arrays coupled with adaptive signal-processing techniques at the basestation improve capacity, coverage, and trunking efficiency. However, design and performance analysis of smart antenna systems strongly depend on channel propagation characteristics of signals present at the antenna array, the so-called vector channels. Here, variation of narrow-band vector channels (spatial signatures) due to

Adnan Kavak; Murat Torlak; Wolfhard J. Vogel; Guanghan Xu

2000-01-01

423

Measurement and prediction of pressure drop in two-phase micro-channel heat sinks  

Microsoft Academic Search

This study explores hydrodynamic instability and pressure drop in a water-cooled two-phase micro-channel heat sink containing 21 parallel 231×713 ?m micro-channels. Two types of two-phase hydrodynamic instability were identified: severe pressure drop oscillation and mild parallel channel instability. It is shown the severe pressure drop oscillation, which can trigger pre-mature critical heat flux, can be eliminated simply by throttling the

Weilin Qu; Issam Mudawar

2003-01-01

424

Measurement of radio wave reflection due to temperature rising from rock salt and ice irradiated by an electron beam for an ultra-high-energy neutrino detector  

NASA Astrophysics Data System (ADS)

An ultra-high-energy neutrino (UHE?) gives temperature rise along the hadronic and electromagnetic shower when it enters into rock salt or ice. Permittivities of them arise with respect the temperatures at ionization processes of the UHE? shower. It is expected by Fresnel's formula that radio wave reflects at the irregularity of the permittivity in the medium. We had found the radio wave reflection effect in rock salt. The reflection effect and long attenuation length of radio wave in rock salt and ice would yield a new UHE? detection method. An experiment for ice was performed to study the reflection effect. A coaxial tube was filled with rock salt powder or ice. Open end of the coaxial tube was irradiated by a 2 MeV electron beam. Radio wave of 435 MHz was introduced to the coaxial tube. We measured the reflection wave from the open end. We found the radio wave reflection effect due to electron beam irradiation in ice as well as in rock salt.

Tanikawa, Takahiro; Chiba, Masami; Kamijo, Toshio; Yabuki, Fumiaki; Yasuda, Osamu; Akiyama, Hidetoshi; Chikashige, Yuichi; Kon, Tadashi; Shimizu, Yutaka; Utsumi, Michiaki; Fujii, Masatoshi

2012-11-01

425

Measurement of radio wave reflection due to temperature rising from rock salt and ice irradiated by an electron beam for an ultra-high-energy neutrino detector  

SciTech Connect

An ultra-high-energy neutrino (UHE{nu}) gives temperature rise along the hadronic and electromagnetic shower when it enters into rock salt or ice. Permittivities of them arise with respect the temperatures at ionization processes of the UHE{nu} shower. It is expected by Fresnel's formula that radio wave reflects at the irregularity of the permittivity in the medium. We had found the radio wave reflection effect in rock salt. The reflection effect and long attenuation length of radio wave in rock salt and ice would yield a new UHE{nu} detection method. An experiment for ice was performed to study the reflection effect. A coaxial tube was filled with rock salt powder or ice. Open end of the coaxial tube was irradiated by a 2 MeV electron beam. Radio wave of 435 MHz was introduced to the coaxial tube. We measured the reflection wave from the open end. We found the radio wave reflection effect due to electron beam irradiation in ice as well as in rock salt.

Tanikawa, Takahiro; Chiba, Masami; Kamijo, Toshio; Yabuki, Fumiaki; Yasuda, Osamu; Akiyama, Hidetoshi; Chikashige, Yuichi; Kon, Tadashi; Shimizu, Yutaka; Utsumi, Michiaki; Fujii, Masatoshi [Graduate School of Science and Engineering, Tokyo Metropolitan University, 1-1 Minami-Ohsawa, Hachioji-shi, Tokyo 192-0397 (Japan); Faculty of Science and Technology, Seikei University, Musashino-shi, Tokyo 180-8633 (Japan); Department of Applied Science and Energy Engineering, School of Engineering, Tokai University, Hiratsuka-shi, Kanagawa 259-1292 (Japan); School of Medicine, Shimane University, Izumo-shi, Shimane 693-8501 (Japan)

2012-11-12

426

IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 54, NO. 4, APRIL 2006 1827 UWB On-Body Radio Channel Modeling Using  

E-print Network

are essen- tial. The idea of a number of nodes scattered around the human body and communicating wirelessly wearable entertainment systems and high performance mobile PCs. For low-power, reliable, and robust on-body of the on-body radio propagation and its behavior with regards to different environments and system

Hao, Yang

427

The 'Brick Wall' radio loss approximation and the performance of strong channel codes for deep space applications at high data rates  

NASA Technical Reports Server (NTRS)

In order to evaluate performance of strong channel codes in presence of imperfect carrier phase tracking for residual carrier BPSK modulation in this paper an approximate 'brick wall' model is developed which is independent of the channel code type for high data rates. It is shown that this approximation is reasonably accurate (less than 0.7dB for low FERs for (1784,1/6) code and less than 0.35dB for low FERs for (5920,1/6) code). Based on the approximation's accuracy, it is concluded that the effects of imperfect carrier tracking are more or less independent of the channel code type for strong channel codes. Therefore, the advantage that one strong channel code has over another with perfect carrier tracking translates to nearly the same advantage under imperfect carrier tracking conditions. This will allow the link designers to incorporate projected channel code performance of strong channel codes into their design tables without worrying about their behavior in the face of imperfect carrier phase tracking.

Shambayati, Shervin

2001-01-01

428

Measurement of plasma potential fluctuations by emissive probes in CF4 radio-frequency plasma  

NASA Astrophysics Data System (ADS)

Plasma potential fluctuations are measured with an emissive probe in low-pressure CF4 plasma produced by a 13.56 MHz rf source. The inflection point method in the limit of zero emission is employed to determine the plasma potential. The maximum and minimum values of the plasma potential are observed. The values of the potential fluctuations depend on the rf source power, the amplitude of the applied voltage and the plasma density. The variations in the plasma potential fluctuations with the source power show the plasma mode changes from a capacitively coupled to an inductively coupled and then to a helicon mode. Electron density, temperature and ion saturation currents measured with a double probe also exhibit the transition. A Langmuir probe is employed to measure the floating potential and its fluctuation and the result verifies the same transition.

Lee, Dongsoo; Ting, Yuk-Hong; Oksuz, Lutfi; Hershkowitz, Noah

2006-11-01

429

Direct thrust measurements and modelling of a radio-frequency expanding plasma thruster  

SciTech Connect

It is shown analytically that the thrust from a simple plasma thruster (in the absence of a magnetic field) is given by the maximum upstream electron pressure, even if the plasma diverges downstream. Direct thrust measurements of a thruster are then performed using a pendulum thrust balance and a laser displacement sensor. A maximum thrust of about 2 mN is obtained at 700 W for a thruster length of 17.5 cm and a flow rate of 0.9 mg s{sup -1}, while a larger thrust of 4 mN is obtained at a similar power for a length of 9.5 cm and a flow rate of 1.65 mg s{sup -1}. The measured thrusts are in good agreement with the maximum upstream electron pressure found from measurements of the plasma parameters and in fair agreement with a simple global approach used to model the thruster.

Lafleur, T.; Charles, C.; Boswell, R. W. [Space Plasma, Power and Propulsion Group, Research School of Physics and Engineering, The Australian National University, Canberra ACT 0200 (Australia); Takahashi, K. [Space Plasma, Power and Propulsion Group, Research School of Physics and Engineering, The Australian National University, Canberra ACT 0200 (Australia); Department of Electrical Engineering and Computer Science, Iwate University, Morioka 020-8551 (Japan)

2011-08-15

430

Measurement of the ttbar production cross section in the MET+jets channel at CDF  

SciTech Connect

This thesis is focused on an inclusive search of the t{bar t} {yields} E{sub T} + jets decay channel by means of neural network tools in proton antiproton collisions at {radical}s = 1.96 TeV recorded by the Collider Detector at Fermilab (CDF). At the Tevatron p{bar p} collider top quarks are mainly produced in pairs through quark-antiquark annihilation and gluon-gluon fusion processes; in the Standard Model description, the top quark then decays to a W boson and a b quark almost 100% of the times, so that its decay signatures are classified according to the W decay modes. When only one W decays leptonically, the t{bar t} event typically contains a charged lepton, missing transverse energy due to the presence of a neutrino escaping from the detector, and four high transverse momentum jets, two of which originate from b quarks. In this thesis we describe a t{bar t} production cross section measurement which uses data collected by a 'multijet' trigger, and selects this kind of top decays by requiring a high-P{sub T} neutrino signature and by using an optimized neural network to discriminate top quark pair production from backgrounds. In Chapter 1, a brief review of the Standard Model of particle physics will be discussed, focusing on top quark properties and experimental signatures. In Chapter 2 will be presented an overview of the Tevatron accelerator chain that provides p{bar p} collisions at the center-of-mass energy of {radical}s = 1.96 TeV, and proton and antiproton beams production procedure will be discussed. The CDF detector and its components and subsystems used for the study of p{bar p} collisions provided by the Tevatron will be described in Chapter 3. Chapter 4 will detail the reconstruction procedures used in CDF to detect physical objects exploiting the features of the different detector subsystems. Chapter 5 will provide an overview of the main concepts regarding Artificial Neural Networks, one of the most important tools we will use in the analysis. Chapter 6 will be devoted to the description of the main characteristics of the t{bar t} {yields} E{sub T} + jets decay channel used to train our neural network to discriminate the top pair production from background processes. We will discuss the event selection method and the technique used for background prediction, that will rely on b-jets identification rate parameterization. Finally, Chapter 7 will provide a description of the final data sample and a detailed discussion of the systematic uncertainties before determining the cross section measurement by means of a likelihood maximization.

Compostella, Gabriele; /INFN, Trento

2008-03-01

431

Propagation and amplification of short radio-frequency pulses in a plasma channel created in gaseous media by the intense laser radiation  

NASA Astrophysics Data System (ADS)

The evolution of the electron energy distribution function (EEDF) in nonequilibrium plasma channel created in xenon by powerful KrF – femtosecond laser pulse is studied. It is demonstrated that such a plasma channel can be used as a waveguide for both transportation and amplification of the microwave radiation. The specific features of such a plasma waveguide are studied on the basis of the self-consistent solution of the kinetic Boltzmann equation for the EEDF in different spatial points of the gas media and the wave equation in slow-varying amplitude approximation for the microwave radiation guided and amplified in the channel.

Bogatskaya, A. V.; Popov, A. M.; Smetanin, I. V.; Volkova, E. A.

2015-03-01

432

Design and Testing of A Closed Stirring-respirometer for Measuring Oxygen Consumption of Channel Catfish Eggs  

Technology Transfer Automated Retrieval System (TEKTRAN)

A closed stirring-respirometer was designed to allow for agitation of small samples of channel catfish egg masses while measuring oxygen consumption. Egg mass samples ranging in size from 15-46 g were placed on a platform above a magnetic spin bar; the degree of agitation was controlled with a magne...

433

Abel transform inversion of radio occultation measurements made with a receiver inside the Earth's atmosphere.  

E-print Network

to problems encountered when inverting seismic time­travel data and solar occultation measurements, where with a single frequency GPS receiver because the ionospheric bending is removed when the partial bending angle data. Furthermore, the problem is analogous to that of inverting seismic travel­time data for velocity

Haase, Jennifer

434

Determining electrical properties based on B1 fields measured in an MR scanner using a multi-channel transmit/receive coil: a general approach  

NASA Astrophysics Data System (ADS)

Electrical properties tomography (EPT) is a recently developed noninvasive technology to image the electrical conductivity and permittivity of biological tissues at Larmor frequency in magnetic resonance scanners. The absolute phase of the complex radio-frequency magnetic field (B1) is necessary for electrical property calculation. However, due to the lack of practical methods to directly measure the absolute B1 phases, current EPT techniques have been achieved with B1 phase estimation based on certain assumptions on object anatomy, coil structure and/or electromagnetic wave behavior associated with the main magnetic field, limiting EPT from a larger variety of applications. In this study, using a multi-channel transmit/receive coil, the framework of a new general approach for EPT has been introduced, which is independent on the assumptions utilized in previous studies. Using a human head model with realistic geometry, a series of computer simulations at 7 T were conducted to evaluate the proposed method under different noise levels. Results showed that the proposed method can be used to reconstruct the conductivity and permittivity images with noticeable accuracy and stability. The feasibility of this approach was further evaluated in a phantom experiment at 7 T.

Liu, Jiaen; Zhang, Xiaotong; Van de Moortele, Pierre-Francois; Schmitter, Sebastian; He, Bin

2013-07-01

435

1. VIEW TO NORTHWEST WITH RADIO CONTROL HOUSE (RIGHT), TRANSMITTER ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

1. VIEW TO NORTHWEST WITH RADIO CONTROL HOUSE (RIGHT), TRANSMITTER TOWER (CENTER), AND NORTH BREAKWATER LIGHT IN DISTANCE AT LEFT - Frankfort Coast Guard Station, Radio Control House, Second Street at ship channel, Frankfort, Benzie County, MI

436

Automatic Measurement of Water Levels by Using Image Identification Method in Open Channel  

NASA Astrophysics Data System (ADS)

Water level data is indispensable to hydrology research, and it is important information for hydraulic engineering and overall utilization of water resources. The information of water level can be transmitted to management office by the network so that the management office may well understand whether the river level is exceeding the warning line. The existing water level measurement method can only present water levels in a form of data without any of images, the methods which make data just be a data and lack the sense of reality. Those images such as the rising or overflow of river level that the existing measurement method cannot obtain simultaneously. Therefore, this research employs a newly, improved method for water level measurement. Through the Video Surveillance System to record the images on site, an image of water surface will be snapped, and then the snapped image will be pre-processed and be compared with its altitude reference value to obtain a water level altitude value. With the ever-growing technology, the application scope of image identification is widely in increase. This research attempts to use image identification technology to analyze water level automatically. The image observation method used in this research is one of non-contact water level gage but it is quite different from other ones; the image observation method is cheap and the facilities can be set up beside an embankment of river or near the houses, thus the impact coming from external factors will be significantly reduced, and a real scene picture will be transmitted through wireless transmission. According to the dynamic water flow test held in an indoor experimental channel, the results of the research indicated that all of error levels of water level identification were less than 2% which meant the image identification could achieve identification result at different water levels. This new measurement method can offer instant river level figures and on-site video so that a disaster prevention measures can be made accordingly. Keywords: Image identification; Water Level; Video surveillance system.

Chung Yang, Han; Xue Yang, Jia

2014-05-01

437

Localized temperature measurements while using a radio frequency total occlusion ablation system in a porcine model  

NASA Astrophysics Data System (ADS)

A RF ablation guide wire with an optical coherence reflectometry guidance system has been developed to percutaneously open total occlusions in arteries. The ablation energy does generate heat as does any electrosurgical application of RF energy. Prior histology studies using this device had shown that the heat generated in the total occlusion was not a clinical concern. In this study, a novel fiber-optic based temperature measurement sensor was used to actually measure the temperature rise in an artery in vivo in a porcine model. The optical temperature measurement system is immune to RF emissions and interference and could be delivered in the same catheter as the guide wire. Temperature rises in the occluded arteries in a worst-case scenario were shown to be less than 10°C, localized to the volume adjacent to the ablation tip, and the temperature returned to ambient within a few seconds after the energy was no longer applied. The temperature data is in agreement with the prior histology studies.

Neet, John M.; Siglinger, Marlin R.; Palmer, Gail

2003-06-01

438

Determination of the manning coefficient from measured bed roughness in natural channels  

USGS Publications Warehouse

This report presents the results of a study to test the hypothesis that basic values of the Manning roughness coefficient of stream channels may be related to (1) some characteristic size of the streambed particles and to (2) the distribution of particle size. These two elements involving particle size can be combined into a single element by weighting characteristic particle sizes. The investigation was confined to channels with coarse bed material to avoid the complication of bed-form roughness that is associated with alluvial channels composed of fine bed material. Fifty current-meter measurements of discharge and appropriate field surveys were made at 11 sites on California streams for the purpose of computing the roughness coefficient, n, by the Manning formula. The test sites were selected to give a wide range in average size of bed material, and the discharge measurements and surveys were made at such times as to provide data covering a suitable range in stream depth. The sites selected were relatively free of the extraneous flow-retarding effects associated with irregular channel conformation and streambank vegetation. The characteristic bed-particle sizes used in the analyses were the 16,- 50,- and 84-percentile sizes as obtained from a cumulative frequency distribution of the diameters of randomly sampled surficial bed material. Separate distributions were computed for the minimum and intermediate values of the three diameters of a particle. The minimum diameters of the streambed particles were used in the study because a particle at rest on the bed invariably has its minimum diameter in the vertical position; this diameter is, therefore, the most representative measure of roughness height. The intermediate diameter was also studied because this is the diameter most easily measurable-either by sieve analysis or by photographic techniques--and--because it is the diameter that had been used in previous studies by other investigators. No significant difference in reliability was found between the results obtained using minimum diameters and those obtained using intermediate diameters. In analyzing the field data, the roughness parameter, n/R1/6 (where R is hydraulic radius), was related to relative smoothness, R/d (where d is a characteristic, or weighted characteristic, particle size). The parameter n/R1/6, rather than n, was used because it is directly proportional to the square root of the Darcy-Weisbach friction factor, f, which is more widely used in theoretical studies of hydraulic friction. If the transformation of n/R1/6 to vf is made, the relations obtained in this study are of a form that is identical with that of the theoretical friction equation obtained by several investigators and that derived from field data by Leopold and Wolman (1957). The constants in the equation vary, of course, with the characteristic particle size used. The relations best fitting the field data for this study were obtained by using either a characteristic particle diameter equal to the 84-percentile size (d84, the size equal to, or exceeding, that of 84 percent of the streambed particles), or a diameter obtained by weighting three characteristic particle sizes (dw, the size obtained by assigning a weight of 0.1 to d16 , a weight of 0.3 to d50 , and a weight of 0.6 to d84). The use of d84 alone gave slightly better results than the use of dw, and, in addition, the use of d84 alone is attractive from a standpoint of simplicity. It is difficult, however, to rationalize the use of d84 alone because of the implication that the distribution of sizes is irrelevant, and it matters not at all whether 84 percent of the bed material is sand or whether it is large cobbles, as long as 16 percent of the material is of greater size. Consequently, the author recommends the use of dw rather than d84 , although there was no unanimity of opinion on this recommendation among his colleagues who reviewed this paper. The reader is free to

Limerinos, John Thomas

1970-01-01

439

Radio Ghosts  

E-print Network

We investigate the possibility that patches of old radio plasma (`radio ghosts') of former radio galaxies form a second distinct phase of the inter-galactic medium (IGM), not mixed with the thermal gas. The separation of this phase from the ambient gas and its resistance against eroding turbulent forces is given by magnetic fields, which are expected to be roughly in pressure equilibrium with the surrounding medium. Since patches of this plasma are largely invisible in the radio we use the term `radio ghost' to characterize their nature. Possibilities and difficulties of different detection strategies of ghosts are discussed. These involve radio emission, cosmic microwave background (CMB) and starlight Comptonization, and Faraday rotation. Re-activation of the electron population in shock waves of cosmological structure formation, which seems to lead to the cluster radio relic phenomena. We discuss the role radio ghosts can have: They are able to store relativistic particles for cosmological times, but are al...

Ensslin, T A

1999-01-01

440

Different experimental WBAN channel models and IEEE802.15.6 models: Comparison and effects  

Microsoft Academic Search

In this paper, a summary of the IEEE802.15.6 wireless body area network (WBAN) radio channel models is given and the models are compared to the corresponding results obtained from the measurements carried out at the Oulu University hospital, Oulu, Finland. CWC has done a set of experimental UWB on-body channel modeling independently of the measurements that are behind the IEEE

Harri Viittala; Matti Hämäläinen; Jari Iinatti; Attaphongse Taparugssanagorn

2009-01-01

441

Radio Astronomy  

NSDL National Science Digital Library

This article is a Why Files short piece on how astronomers use information from radio astronomy. Contrary to popular belief, large radio telescopes are not looking for signs of life outside our solar system, but are making images of black holes, centers of galaxies, and gamma ray bursts. These phenomena cannot be seen in visible light, but emit radio waves which can be translated into images. The article discusses how this process works, and the information gathered from radio waves.

Tenenbaum, David

442

Cognitive radio: Making software radios more personal  

Microsoft Academic Search

Software radios are emerging as platforms for multiband multimode personal communications systems. Radio etiquette is the set of RF bands, air interfaces, protocols, and spatial and temporal patterns that moderate the use of the radio spectrum. Cognitive radio extends the software radio with radio-domain model-based reasoning about such etiquettes. Cognitive radio enhances the flexibility of personal services through a Radio

Joseph Mitola; Gerald Quentin Maguire Jr.

1999-01-01

443

Application of Digital Industrial Photogrammetric Technology to Measure the Surface Accuracy of 13.7 m Millimeter-wave Radio Telescope Antenna  

NASA Astrophysics Data System (ADS)

In this paper, the surface accuracy of 13.7 m millimeter-wave radio telescope antenna is measured by digital industrial photogrammetric technology. In order to overcome the inconvenience introduced by local conditions, the circular orbits are used to transport the camera and wireless transmission is used to take on-line photos. Measuring targets are made of retro-reflective material. All camera stations are orientated and the homologous image points are matched automatically by the coded targets. The 3D point coordinates are calculated by the bundle adjustment method. Using the methods of CAD surface conversion algorithm and best fitting to calculate the deviation value of the surface, the RMS of the 480 points gotten from CAD best fitting algorithm is adjusted to 0.083 mm. The feasibility and superiority of photogrammetric technology, which is used to measure the radio astronomy antenna's surface, is demonstrated.

Fan, Q. H.; Fang, S. H.; Zuo, Y. X.; Li, Y.; Sun, J. X.; Yang, J.; Li, J. J.; Xu, Y.; He, D. Y.