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Sample records for frequency selective mimo

  1. Single-Tap Precoders and Decoders for Multiuser MIMO FBMC-OQAM Under Strong Channel Frequency Selectivity

    NASA Astrophysics Data System (ADS)

    Rottenberg, Francois; Mestre, Xavier; Horlin, Francois; Louveaux, Jerome

    2017-02-01

    The design of linear precoders or decoders for multiuser (MU) multiple-input multiple-output (MIMO) filterbank multicarrier (FBMC) modulations in the case of strong channel frequency selectivity is presented. The users and the base station (BS) communicate using space division multiple access (SDMA). The low complexity proposed solution is based on a single tap per-subcarrier precoding/decoding matrix at the base station (BS) in the downlink/uplink. As opposed to classical approaches that assume flat channel frequency selectivity at the subcarrier level, the BS does not make this assumption and takes into account the distortion caused by channel frequency selectivity. The expression of the FBMC asymptotic mean squared error (MSE) in the case of strong channel selectivity derived in earlier works is developed and extended. The linear precoders and decoders are found by optimizing the MSE formula under two design criteria, namely zero forcing (ZF) or minimum mean squared error (MMSE). Finally, simulation results demonstrate the performance of the optimized design. As long as the number of BS antennas is larger than the number of users, it is shown that those extra degrees of freedom can be used to compensate for the channel frequency selectivity.

  2. An iterative detection method of MIMO over spatial correlated frequency selective channel: using list sphere decoding for simplification

    NASA Astrophysics Data System (ADS)

    Shi, Zhiping; Yan, Bing

    2010-08-01

    In multiple-input multiple-output(MIMO) wireless systems, combining good channel codes(e.g., Non-binary Repeat Accumulate codes) with adaptive turbo equalization is a good option to get better performance and lower complexity under Spatial Correlated Frequency Selective(SCFS) Channel. The key of this method is after joint antennas MMSE detection (JAD/MMSE) based on interruption cancelling using soft information, considering the detection result as an output of a Gaussian equivalent flat fading channel, and performing maximum likelihood detection(ML) to get more correct estimated result. But the using of ML brings great complexity increase, which is not allowed. In this paper, a low complexity method called list sphere decoding is introduced and applied to replace the ML in order to simplify the adaptive iterative turbo equalization system.

  3. Double Space Time Transmit Diversity OFDM System with Antenna Shuffling in Spatial Correlated Frequency Selective MIMO Channels

    NASA Astrophysics Data System (ADS)

    Zhou, Liang; Shimizu, Masahiko

    In this paper, we study low complexity transceiver for double space time transmit diversity (DSTTD) and orthogonal frequency division multiplexing (OFDM) system with antenna shuffling. Firstly, we propose a novel antenna shuffling method based on the criterion of minimizing the condition number of channel correlation matrix. The condition number is an indicator about the quality of the channel. By selecting the minimum of condition number which has better channel quality, consequently, a linear detector with respect to this new channel may achieve better performance results. A low complexity variant of the condition number calculation is also proposed, and it is shown that this criterion can be reduced to the minimum mean square error (MMSE) based criterion. Furthermore, the weighted soft decision Viterbi decoding is applied to mitigate noise enhancement inherent to zero forcing (ZF) and MMSE linear receivers and improve error rate performance. Next, we propose an algorithm to reduce the amount of feedback by exploiting the fact that the channel frequency responses across OFDM subcarriers are correlated. In the proposed algorithm, subcarriers are clustered in blocks, which are allocated the same shuffling pattern with the largest number of the shuffling patterns in the cluster. This way, the signaling overhead can be reduced in comparison with each subcarrier based feedback. Extensive simulations show that the proposed techniques for DSTTD-OFDM system outperform other existing techniques under both uncorrelated and highly spatial correlated frequency selective MIMO fading channels.

  4. Analysis on the Diversity and Multiplexing Tradeoff of Antenna Selected MIMO System

    NASA Astrophysics Data System (ADS)

    Feng, Zhenjie; Zhang, Taiyi

    Antenna selection is a practical way to decrease system complexity and the hardware cost of radio frequency (RF) chains in multiple input multiple output (MIMO) system. In this study, we give a simple characterization of the optimal diversity and multiplexing tradeoff (DMT) curve of the MIMO system with antenna subset selection at both the transmitter and the receiver for Rayleigh fading channel.

  5. Studies on an Iterative Frequency Domain Channel Estimation Technique for MIMO-UWB Communications

    NASA Astrophysics Data System (ADS)

    Takanashi, Masaki; Ogawa, Yasutaka; Nishimura, Toshihiko; Ohgane, Takeo

    MIMO (Multiple-Input Multiple-Output) technologies have attracted much interest for high-rate and high-capacity wireless communications. MIMO technologies under frequency-selective fading environments (wideband MIMO technologies) have also been studied. A wideband MIMO system is affected by ISI (Inter Symbol Interference) and CCI (Co-Channel Interference). Hence, we need a MIMO signal detection technique that simultaneously suppresses ISI and CCI. The OFDM system and SC-FDE (Single Carrier-Frequency Domain Equalization) techniques are often used for suppressing ISI. By employing these techniques with the ZF (Zero Forcing) or the MMSE (Minimum Mean Square Error) spatial filtering technique, we can cancel both ISI and CCI. To use ZF or MMSE, we need channel state information for calculating the receive weights. Although an LS (Least Square) channel estimation technique has been proposed for MIMO-OFDM systems, it needs a large estimation matrix at the receiver side to obtain sufficient estimation performance in heavy multipath environments. However, the use of a large matrix increases computational complexity and the circuit size. We use frequency domain channel estimation to solve these problems and propose an iterative method for achieving better estimation performance. In this paper, we assume the use of a MIMO-UWB system that employs a UWB-IR (Ultra-Wideband Impulse Radio) scheme with the FDE technique as the wideband wireless transmission scheme for heavy multipath environments, and we evaluate the iterative frequency domain channel estimation through computer simulations and computational complexity calculations.

  6. A Low-Complexity Antenna Selection Scheme in MIMO Systems

    NASA Astrophysics Data System (ADS)

    Chen, Jung-Chieh

    This paper considers the use of an antenna selection mechanism to reduce the cost of multiple analog transmit/receive chains in multiple-input multiple-output (MIMO) systems. With the optimal antenna selection scheme, radio-frequency chains can optimally connect with the best subset of transmitter and/or receiver antennas. However, the optimal antenna selection algorithm requires an exhaustive search of all possible combinations to find the optimum subset at the transmitter and/or receiver, thus resulting in high complexity. In order to reduce the computational load while still maximizing channel capacity, we introduce the simulated annealing (SA) method, an effective algorithm that solves various combinatorial optimization problems, to search the optimal subset. The simulation results show that the performance of the proposed SA method provides almost the same channel capacity as that of the optimal exhaustive search algorithm while maintaining low complexity.

  7. Time-Frequency Based Channel Estimation for High-Mobility OFDM Systems-Part I: MIMO Case

    NASA Astrophysics Data System (ADS)

    Önen, Erol; Akan, Aydın; Chaparro, LuisF

    2010-12-01

    Multiple-input multiple-output (MIMO) systems hold the potential to drastically improve the spectral efficiency and link reliability in future wireless communications systems. A particularly promising candidate for next-generation fixed and mobile wireless systems is the combination of MIMO technology with Orthogonal Frequency Division Multiplexing (OFDM). OFDM has become the standard method because of its advantages over single carrier modulation schemes on multipath, frequency selective fading channels. Doppler frequency shifts are expected in fast-moving environments, causing the channel to vary in time, that degrades the performance of OFDM systems. In this paper, we present a time-varying channel modeling and estimation method based on the Discrete Evolutionary Transform to obtain a complete characterization of MIMO-OFDM channels. Performance of the proposed method is evaluated and compared on different levels of channel noise and Doppler frequency shifts.

  8. Reduced Complexity in Antenna Selection for Polarized MIMO System with SVD for the Practical MIMO Communication Channel Environment

    NASA Astrophysics Data System (ADS)

    Sann Maw, Maung; Sasase, Iwao

    In the conventional multi-input multi-output (MIMO) communication systems, most of the antenna selection methods considered are suitable only for spatially separated uni-polarized system under Rayleigh fading channel in non-line of sight (NLOS) condition. There have a few antenna selection schemes for the cross-polarized system in LOS condition and Ricean fading channel, and no antenna selection scheme for the MIMO channel with both LOS and NLOS. In the practical MIMO channel case, influence of LOS and NLOS conditions in the channel can vary from time to time according to the channel parameters and user movement in the system. Based on these influences and channel condition, uni-polarized system may outperform a cross-polarized. Thus, we should consider this kind of practical MIMO channel environment when developing the antenna selection scheme. Moreover, no research work has been done on reducing the complexity of antenna selection for this kind of practical MIMO channel environment. In this paper, reduced complexity in antenna selection is proposed to give the higher throughput in the practical MIMO channel environment. In the proposed scheme, suitable polarized antennas are selected based on the calculation of singular value decomposition (SVD) of channel matrix and then adaptive bit loading is applied. Simulation results show that throughput of the system can be improved under the constraint of target BER and total transmit power of the MIMO system.

  9. Optical frequency upconversion technique for transmission of wireless MIMO-type signals over optical fiber.

    PubMed

    Shaddad, R Q; Mohammad, A B; Al-Gailani, S A; Al-Hetar, A M

    2014-01-01

    The optical fiber is well adapted to pass multiple wireless signals having different carrier frequencies by using radio-over-fiber (ROF) technique. However, multiple wireless signals which have the same carrier frequency cannot propagate over a single optical fiber, such as wireless multi-input multi-output (MIMO) signals feeding multiple antennas in the fiber wireless (FiWi) system. A novel optical frequency upconversion (OFU) technique is proposed to solve this problem. In this paper, the novel OFU approach is used to transmit three wireless MIMO signals over a 20 km standard single mode fiber (SMF). The OFU technique exploits one optical source to produce multiple wavelengths by delivering it to a LiNbO3 external optical modulator. The wireless MIMO signals are then modulated by LiNbO3 optical intensity modulators separately using the generated optical carriers from the OFU process. These modulators use the optical single-sideband with carrier (OSSB+C) modulation scheme to optimize the system performance against the fiber dispersion effect. Each wireless MIMO signal is with a 2.4 GHz or 5 GHz carrier frequency, 1 Gb/s data rate, and 16-quadrature amplitude modulation (QAM). The crosstalk between the wireless MIMO signals is highly suppressed, since each wireless MIMO signal is carried on a specific optical wavelength.

  10. Optical Frequency Upconversion Technique for Transmission of Wireless MIMO-Type Signals over Optical Fiber

    PubMed Central

    Shaddad, R. Q.; Mohammad, A. B.; Al-Gailani, S. A.; Al-Hetar, A. M.

    2014-01-01

    The optical fiber is well adapted to pass multiple wireless signals having different carrier frequencies by using radio-over-fiber (ROF) technique. However, multiple wireless signals which have the same carrier frequency cannot propagate over a single optical fiber, such as wireless multi-input multi-output (MIMO) signals feeding multiple antennas in the fiber wireless (FiWi) system. A novel optical frequency upconversion (OFU) technique is proposed to solve this problem. In this paper, the novel OFU approach is used to transmit three wireless MIMO signals over a 20 km standard single mode fiber (SMF). The OFU technique exploits one optical source to produce multiple wavelengths by delivering it to a LiNbO3 external optical modulator. The wireless MIMO signals are then modulated by LiNbO3 optical intensity modulators separately using the generated optical carriers from the OFU process. These modulators use the optical single-sideband with carrier (OSSB+C) modulation scheme to optimize the system performance against the fiber dispersion effect. Each wireless MIMO signal is with a 2.4 GHz or 5 GHz carrier frequency, 1 Gb/s data rate, and 16-quadrature amplitude modulation (QAM). The crosstalk between the wireless MIMO signals is highly suppressed, since each wireless MIMO signal is carried on a specific optical wavelength. PMID:24772009

  11. MIMO Channel Matrix Condition Number Estimation and Threshold Selection for Combined K-Best Sphere Decoders

    NASA Astrophysics Data System (ADS)

    Roger, Sandra; Gonzalez, Alberto; Almenar, Vicenc; Vidal, Antonio M.

    It is known that MIMO channel matrix condition number influences detectors performance. Several authors have proposed combined decoders, mainly suboptimal, to cope with this fact. These combined algorithms require an estimation of the MIMO channel matrix condition number and a selection of a suitable threshold condition number. This letter presents practical algorithms to carry out the referred tasks and shows their performance in practice.

  12. Frequency-Domain Iterative Parallel Interference Cancellation for Multicode Spread-Spectrum MIMO Multiplexing

    NASA Astrophysics Data System (ADS)

    Nakajima, Akinori; Garg, Deepshikha; Adachi, Fumiyuki

    Very high-speed data services are demanded in the next generation wireless systems. However, the available bandwidth is limited. The use of multi-input multi-output (MIMO) multiplexing can increase the transmission rate without bandwidth expansion. For high-speed data transmission, however, the channel becomes severely frequency-selective and the achievable bit error rate (BER) performance degrades. In our previous work, we proposed the joint use of iterative frequency-domain parallel interference cancellation (PIC) and two-dimensional (2D) MMSE-FDE for the non-spread single-carrier (SC) transmission in a frequency-selective fading channel. The joint use of PIC and 2D MMSE-FDE can effectively suppress the inter-path interference (IPI) and the inter-code interference (ICI), resulting from the channel frequency-selectivity, and the interference from other antennas simultaneously. An iterative PIC with 2D MMSE-FDE has a high computational complexity. In this paper, to well suppress the interference from other antennas while reducing the computational complexity, we propose to replace 2D MMSE-FDE by 1D MMSE-FDE except for the initial iteration stage and to use multicode spread-spectrum (SS) transmission instead of the non-spread SC transmission. The BER performance of the proposed scheme in a frequency-selective Rayleigh fading channel is evaluated by computer simulation to show that the proposed scheme can basically match the BER performance of 2D MMSE-FDE with lower complexity.

  13. Unified tensor model for space-frequency spreading-multiplexing (SFSM) MIMO communication systems

    NASA Astrophysics Data System (ADS)

    de Almeida, André LF; Favier, Gérard

    2013-12-01

    This paper presents a unified tensor model for space-frequency spreading-multiplexing (SFSM) multiple-input multiple-output (MIMO) wireless communication systems that combine space- and frequency-domain spreadings, followed by a space-frequency multiplexing. Spreading across space (transmit antennas) and frequency (subcarriers) adds resilience against deep channel fades and provides space and frequency diversities, while orthogonal space-frequency multiplexing enables multi-stream transmission. We adopt a tensor-based formulation for the proposed SFSM MIMO system that incorporates space, frequency, time, and code dimensions by means of the parallel factor model. The developed SFSM tensor model unifies the tensorial formulation of some existing multiple-access/multicarrier MIMO signaling schemes as special cases, while revealing interesting tradeoffs due to combined space, frequency, and time diversities which are of practical relevance for joint symbol-channel-code estimation. The performance of the proposed SFSM MIMO system using either a zero forcing receiver or a semi-blind tensor-based receiver is illustrated by means of computer simulation results under realistic channel and system parameters.

  14. 2 × 2 MIMO radio-over-fiber system at 60 GHz employing frequency domain equalization.

    PubMed

    Lin, Chun-Ting; Ng'oma, Anthony; Lee, Wei-Yuan; Wei, Chia-Chien; Wang, Chih-Yun; Lu, Tsung-Hung; Chen, Jyehong; Jiang, Wen-Jr; Ho, Chun-Hung

    2012-01-02

    This work experimentally demonstrates the efficacy of the 2 × 2 multiple-input multiple-output (MIMO) technique for capacity improvement of a 60-GHz radio-over-fiber (RoF) system employing single-carrier modulation format. We employ frequency domain equalization (FDE) to estimate the channel response, including frequency response of the 60 GHz RoF system and the MIMO wireless channel. Using FDE and MIMO techniques, we experimentally demonstrate the doubling the of wireless data capacity of a 60 GHz RoF system to 27.15 Gb/s using 16-QAM modulation format, with transmission over 25 km of standard single-mode fiber and 3 m wireless distance.

  15. Performance evaluation of space-time-frequency spreading for MIMO OFDM-CDMA systems

    NASA Astrophysics Data System (ADS)

    Dahman, Haysam; Shayan, Yousef

    2011-12-01

    In this article, we propose a multiple-input-multiple-output, orthogonal frequency division multiplexing, code-division multiple-access (MIMO OFDM-CDMA) scheme. The main objective is to provide extra flexibility in user multiplexing and data rate adaptation, that offer higher system throughput and better diversity gains. This is done by spreading on all the signal domains; i.e, space-time frequency spreading is employed to transmit users' signals. The flexibility to spread on all three domains allows us to independently spread users' data, to maintain increased system throughput and to have higher diversity gains. We derive new accurate approximations for the probability of symbol error and signal-to-interference noise ratio (SINR) for zero forcing (ZF) receiver. This study and simulation results show that MIMO OFDM-CDMA is capable of achieving diversity gains significantly larger than that of the conventional 2-D CDMA OFDM and MIMO MC CDMA schemes.

  16. A New User Selection Measure in Block Diagonalization Algorithm for Multiuser MIMO Systems

    NASA Astrophysics Data System (ADS)

    Kudo, Riichi; Takatori, Yasushi; Nishimori, Kentaro; Ohta, Atsushi; Kubota, Shuji; Mizoguchi, Masato

    Multiuser — Multiple Input Multiple Output (MU-MIMO) techniques were proposed to increase spectrum efficiency; a key assumption was that the Mobile Terminals (MTs) were simple with only a few antennas. This paper focuses on the Block Diagonalization algorithm (BD) based on the equal power allocation strategy as a practical MU-MIMO technique. When there are many MTs inside the service area of the access point (AP), the AP must determine, at each time slot, the subset of the MTs to be spatially multiplexed. Since the transmission performance depends on the subsets of MTs, the user selection method needs to use the Channel State Information (CSI) obtained in the physical layer to maximize the Achievable Transmission Rate (ATR). In this paper, we clarify the relationship between ATR with SU-MIMO and that with MU-MIMO in a high eigenvalue channel. Based on the derived relationship, we propose a new measure for user selection. The new measure, the eigenvalue decay factor, represents the degradation of the eigenvalues in null space compared to those in SU-MIMO; it is obtained from the signal space vectors of the MTs. A user selection method based on the proposed measure identifies the combination of MTs that yields the highest ATR; our approach also reduces the computational load of user selection. We evaluate the effectiveness of user selection with the new measure using numerical formulations and computer simulations.

  17. Compressive inverse scattering: I. High-frequency SIMO/MISO and MIMO measurements

    NASA Astrophysics Data System (ADS)

    Fannjiang, Albert C.

    2010-03-01

    Inverse scattering from discrete targets with the single-input-multiple-output (SIMO), multiple-input-single-output (MISO) or multiple-input-multiple-output (MIMO) measurements is analyzed by compressed sensing theory with and without the Born approximation. High-frequency analysis of (probabilistic) recoverability by the L1-based minimization/regularization principles is presented. In the absence of noise, it is shown that the L1-based solution can recover exactly the target of sparsity up to the dimension of the data either with the MIMO measurement for the Born scattering or with the SIMO/MISO measurement for the exact scattering. The stability with respect to noisy data is proved for weak or widely separated scatterers. Reciprocity between the SIMO and MISO measurements is analyzed. Finally a coherence bound (and the resulting recoverability) is proved for diffraction tomography with high-frequency, few-view and limited-angle SIMO/MISO measurements.

  18. A Portable MIMO Testbed and Selected Channel Measurements

    NASA Astrophysics Data System (ADS)

    Goud, Paul, Jr.; Hang, Robert; Truhachev, Dmitri; Schlegel, Christian

    2006-12-01

    A portable[InlineEquation not available: see fulltext.] multiple-input multiple-output (MIMO) testbed that is based on field programmable gate arrays (FPGAs) and which operates in the 902-928 MHz industrial, scientific, and medical (ISM) band has been developed by the High Capacity Digital Communications (HCDC) Laboratory at the University of Alberta. We present a description of the HCDC testbed along with MIMO channel capacities that were derived from measurements taken with the HCDC testbed for three special locations: a narrow corridor, an athletics field that is surrounded by a metal fence, and a parkade. These locations are special because the channel capacities are different from what is expected for a typical indoor or outdoor channel. For two of the cases, a ray-tracing analysis has been performed and the simulated channel capacity values closely match the values calculated from the measured data. A ray-tracing analysis, however, requires accurate geometrical measurements and sophisticated modeling for each specific location. A MIMO testbed is ideal for quickly obtaining accurate channel capacity information.

  19. Frequency selective infrared sensors

    DOEpatents

    Davids, Paul; Peters, David W

    2013-05-28

    A frequency selective infrared (IR) photodetector having a predetermined frequency band. The exemplary frequency selective photodetector includes: a dielectric IR absorber having a first surface and a second surface substantially parallel to the first surface; an electrode electrically coupled to the first surface of the dielectric IR absorber; and a frequency selective surface plasmonic (FSSP) structure formed on the second surface of the dielectric IR absorber. The FSSP structure is designed to selectively transmit radiation in the predetermined frequency band that is incident on the FSSP structure substantially independent of the angle of incidence of the incident radiation on the FSSP structure.

  20. Frequency selective infrared sensors

    DOEpatents

    Davids, Paul; Peters, David W

    2014-11-25

    A frequency selective infrared (IR) photodetector having a predetermined frequency band. The exemplary frequency selective photodetector includes: a dielectric IR absorber having a first surface and a second surface substantially parallel to the first surface; an electrode electrically coupled to the first surface of the dielectric IR absorber; and a frequency selective surface plasmonic (FSSP) structure formed on the second surface of the dielectric IR absorber. The FSSP structure is designed to selectively transmit radiation in the predetermined frequency band that is incident on the FSSP structure substantially independent of the angle of incidence of the incident radiation on the FSSP structure.

  1. Efficient Antenna Selection for Amplify-and-Forward Two-Way MIMO Relay Systems

    NASA Astrophysics Data System (ADS)

    Ding, Ming; Zou, Jun; Yang, Zeng; Luo, Hanwen

    In this letter, we propose an efficient relay antenna selection algorithm for the amplify and forward (AF) two-way multiple-input multiple-output (MIMO) relay systems with analogue network coding (ANC). The proposed algorithm greedily selects the additional receive-transmit antenna pair that provides the maximum sum-rate. An iterative computation method is also designed to evaluate the sum-rate efficiently.

  2. A novel optical single-sideband frequency translation technique for transmission of wireless MIMO signals over fiber-wireless system

    NASA Astrophysics Data System (ADS)

    Shaddad, Redhwan Q.; Mohammad, Abu Bakar; Al-Hetar, Abdulaziz M.; Al-Gailani, Samir A.

    2013-04-01

    The fiber-wireless (FiWi) access network is a powerful hybrid architecture of optical backhaul and wireless front-end to support high data rates and throughput with minimal time delay. By using radio over fiber (ROF) technique, the optical fiber is well adapted to propagate multiple wireless services having different carrier frequencies. However, multiple wireless signals which have the same carrier frequency cannot propagate over a single optical fiber on the same wavelength, such as multi-input multi-output (MIMO) signals. A novel optical single-sideband frequency translation technique is designed and simulated to solve this problem. 240 Mb/s 802.11n MIMO signals are proposed to transport over FiWi system using the proposed approach at 2.4 GHz and 5.0 GHz carrier frequencies. The crosstalk between MIMO signals with the same carrier frequency is excluded, since each MIMO signal is carried on a specific optical wavelength. Error vector magnitude (EVM) values of -29.83 dB (for 2.4 GHz) and -28.41 dB (for 5.0 GHz) have been achieved for bit error rate (BER) 10-5 in the proposed FiWi system.

  3. Space-Frequency Block Code with Matched Rotation for MIMO-OFDM System with Limited Feedback

    NASA Astrophysics Data System (ADS)

    Zhang, Min; Abhayapala, Thushara D.; Jayalath, Dhammika; Smith, David; Athaudage, Chandra

    2009-12-01

    This paper presents a novel matched rotation precoding (MRP) scheme to design a rate one space-frequency block code (SFBC) and a multirate SFBC for MIMO-OFDM systems with limited feedback. The proposed rate one MRP and multirate MRP can always achieve full transmit diversity and optimal system performance for arbitrary number of antennas, subcarrier intervals, and subcarrier groupings, with limited channel knowledge required by the transmit antennas. The optimization process of the rate one MRP is simple and easily visualized so that the optimal rotation angle can be derived explicitly, or even intuitively for some cases. The multirate MRP has a complex optimization process, but it has a better spectral efficiency and provides a relatively smooth balance between system performance and transmission rate. Simulations show that the proposed SFBC with MRP can overcome the diversity loss for specific propagation scenarios, always improve the system performance, and demonstrate flexible performance with large performance gain. Therefore the proposed SFBCs with MRP demonstrate flexibility and feasibility so that it is more suitable for a practical MIMO-OFDM system with dynamic parameters.

  4. Radio frequency electromagnetic field compliance assessment of multi-band and MIMO equipped radio base stations.

    PubMed

    Thors, Björn; Thielens, Arno; Fridén, Jonas; Colombi, Davide; Törnevik, Christer; Vermeeren, Günter; Martens, Luc; Joseph, Wout

    2014-05-01

    In this paper, different methods for practical numerical radio frequency exposure compliance assessments of radio base station products were investigated. Both multi-band base station antennas and antennas designed for multiple input multiple output (MIMO) transmission schemes were considered. For the multi-band case, various standardized assessment methods were evaluated in terms of resulting compliance distance with respect to the reference levels and basic restrictions of the International Commission on Non-Ionizing Radiation Protection. Both single frequency and multiple frequency (cumulative) compliance distances were determined using numerical simulations for a mobile communication base station antenna transmitting in four frequency bands between 800 and 2600 MHz. The assessments were conducted in terms of root-mean-squared electromagnetic fields, whole-body averaged specific absorption rate (SAR) and peak 10 g averaged SAR. In general, assessments based on peak field strengths were found to be less computationally intensive, but lead to larger compliance distances than spatial averaging of electromagnetic fields used in combination with localized SAR assessments. For adult exposure, the results indicated that even shorter compliance distances were obtained by using assessments based on localized and whole-body SAR. Numerical simulations, using base station products employing MIMO transmission schemes, were performed as well and were in agreement with reference measurements. The applicability of various field combination methods for correlated exposure was investigated, and best estimate methods were proposed. Our results showed that field combining methods generally considered as conservative could be used to efficiently assess compliance boundary dimensions of single- and dual-polarized multicolumn base station antennas with only minor increases in compliance distances.

  5. Frequency selective terahertz retroreflectors

    NASA Astrophysics Data System (ADS)

    Williams, Richard James

    The use of novel optical structures operating at terahertz frequencies in industrial and military applications continues to grow. Some of these novel structures include gratings, frequency selective surfaces, metamaterials and metasurfaces, and retroreflectors. A retroreflector is a device that exhibits enhanced backscatter by concentrating the reflected wave in the direction of the source. Retroreflectors have applications in a variety of diverse fields such as aviation, radar systems, antenna technology, communications, navigation, passive identification, and metrology due to their large acceptance angles and frequency bandwidth. This thesis describes the design, fabrication, and characterization of a retroreflector designed for terahertz frequencies and the incorporation of a frequency selective surface in order to endow the retroreflector with narrow-band frequency performance. The radar cross section of several spherical lens reflectors operating at terahertz frequencies was investigated. Spherical lens reflectors with diameters ranging from 2 mm to 8 mm were fabricated from fused silica ball lenses and their radar cross section was measured at 100 GHz, 160 GHz, and 350 GHz. Crossed-dipole frequency selective surfaces exhibiting band-pass characteristics at 350 GHz fabricated from 12 um-thick Nickel screens were applied to the apertures of the spherical lens reflectors. The radar cross section of the frequency selective retroreflectors was measured at 160 GHz and 350 GHz to demonstrate proof-of-concept of narrow-band terahertz performance.

  6. Multiband frequency selective surface

    NASA Astrophysics Data System (ADS)

    Wu, Te-Kao

    1998-10-01

    This paper addresses the similarity of microwave/millimeter wave frequency selective surfaces (FSS) to optical filters. Specifically, the design approaches of the 4-band FSSs developed for NASA's CASSINI high gain antenna are described in detail. Representative RF test results are given to demonstrate the validity of these designs. These design approaches are very general and can be applied to multiband optical filters.

  7. Low-Complexity User Selection for Rate Maximization in MIMO Broadcast Channels with Downlink Beamforming

    PubMed Central

    Silva, Adão; Gameiro, Atílio

    2014-01-01

    We present in this work a low-complexity algorithm to solve the sum rate maximization problem in multiuser MIMO broadcast channels with downlink beamforming. Our approach decouples the user selection problem from the resource allocation problem and its main goal is to create a set of quasiorthogonal users. The proposed algorithm exploits physical metrics of the wireless channels that can be easily computed in such a way that a null space projection power can be approximated efficiently. Based on the derived metrics we present a mathematical model that describes the dynamics of the user selection process which renders the user selection problem into an integer linear program. Numerical results show that our approach is highly efficient to form groups of quasiorthogonal users when compared to previously proposed algorithms in the literature. Our user selection algorithm achieves a large portion of the optimum user selection sum rate (90%) for a moderate number of active users. PMID:24574928

  8. Joint DOD/DOA Estimation in MIMO Radar Exploiting Time-Frequency Signal Representations

    DTIC Science & Technology

    2012-05-08

    direction-of-departure (DOD) and direction-of- arrival (DOA) information of maneuvering targets in a bistatic multiple-input multiple-output (MIMO) radar...CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT Same as Report ( SAR ) 18. NUMBER OF PAGES 21 19a. NAME OF RESPONSIBLE PERSON a. REPORT unclassified b...departure (DOD) and direction-of- arrival (DOA) information of maneuvering targets in a bistatic multiple-input multiple-output (MIMO) radar system

  9. Joint Network Selection and Discrete Power Control in Heterogeneous MIMO Networks: A Game Theoretical Approach

    NASA Astrophysics Data System (ADS)

    Chen, Gang; Tian, Hua; Xie, Wei; Zhong, Wei

    2013-09-01

    Next-generation wireless networks will integrate multiple wireless access technologies and the users will access the network using one of several available radio access technologies. In this paper, we study the spectrum access problem in heterogeneous multipleinput multiple-output (MIMO) networks through a game theoretic approach. The spectrum access problem in the considered system model is defined as joint network selection and discrete power control. We formulate the problem as a noncooperative game where the players are the multi-mode terminals and. The proposed common utility function takes both transmission rate and the power consumption into account. This game is shown to be a potential game which possess at least one pure strategy Nash equilibrium (NE) and the optimal strategy profile which maximizes the total energy efficiency of the heterogeneous MIMO network constitutes a pure strategy NE of our proposed game. Furthermore, we prove that the price of anarchy of the proposed game is equal to 1. In order to achieve the pure strategy NE, we design an iterative spectrum access algorithm. The convergence and the complexity of our designed algorithm is discussed. It is shown that the designed algorithm can achieve optimal performance with low complexity.

  10. On the Performance of Code Acquisition in MIMO CDMA Systems

    NASA Astrophysics Data System (ADS)

    Kim, Sangchoon; An, Jinyoung

    This letter investigates the effects of using multiple transmit antennas on code acquisition for preamble search in the CDMA uplink when MIMO is used for signal transmission and reception. The performance of a ML code acquisition technique in the presence of MIMO channel is analyzed by considering the detection and miss probabilities. The acquisition performance is numerically evaluated on a frequency selective fading channel. It is found that the performance of code acquisition scheme for a SIMO system is better than that for the case of MIMO on the low thresholds in terms of detection performance and MAT.

  11. BER Analysis of Dual-Hop Amplify-and-Forward MIMO Relaying with Best Antenna Selection in Rayleigh Fading Channels

    NASA Astrophysics Data System (ADS)

    Kim, Jung-Bin; Kim, Dongwoo

    Combining relaying and multi-input multi-output (MIMO) transmission is a generic way to overcome the channel-fading impairments. Best antenna selection is a simple but efficient MIMO method that achieves the full diversity and also serves as a lower bound reference of MIMO performance. For a dual-hop MIMO system with an ideal amplify-and-forward (AF) relaying gain and best antenna selection, we provide a probability density function (PDF) of received signal-to-noise ratio (SNR) and an analytic BER equation when using M-ary PSK in Rayleigh fading channels. The analytic result is shown to exactly match with simulated one. Furthermore, the effect of link unbalance between the first hop and the second hop, due to differences in the number of antennas deployed in both hops as well as in the average power of channel coefficients, on the BER performance is numerically investigated and the results show that the links with better balance give better performance.

  12. Statistical Space-Time-Frequency Characterization of MIMO Shallow Water Acoustic Channels

    DTIC Science & Technology

    2010-06-01

    multiple - input multiple - output ( MIMO ) SWA communication systems. By taking into account...20375 USA Abstract—This paper proposes a geometry-based statistical model for multiple - input multiple - output shallow water acous- tic multipath fading...statistical model for multiple - input multiple - output shallow water acoustic multipath fading channels. From the reference model, the corresponding

  13. MIMO Transceiver Systems on AUVs

    DTIC Science & Technology

    2008-09-30

    MIMO Transceiver Systems on AUVs Mohsen Badiey 107 Robinson Hall College of Marine and Earth Studies, University of Delaware phone...acoustic MIMO communication testbed on a small AUV at the frequency band of 8-50 kHz for data communication studies, and 2) Make this system capable...environments. The MIMO transceiver system on the AUV is designed for ease of use and low-cost deployment during at-sea experiments. The system under

  14. Broadband frequency selective surface

    NASA Astrophysics Data System (ADS)

    Palma, D. A.; Wong, W. C.

    A method for designing broadband dichroic surfaces is described. A tripole and a Jerusalem cross are evaluated as candidate resonant elements. The effects of dielectric substrates on resonant frequency and bandwidth are investigated. The theoretical and measured frequency responses of tripoles and Jerusalem crosses are presented. It is observed that the metallic area of the tripole within a given period increases the bandwidth, the maximum theoretical bandwidth of the tripole dichroic sheet being about 50 percent; for a Jerusalem cross, increasing the metallic area of the two perpendicular strips and increasing the end cap capacitative loading increases the bandwidth to a theoretical maximum about 60 percent. Multilayered dichroic panels capable of producing a 4:1 stopband and 1.4:1 band separation have been designed for circular polarization and angles of incidence up to 40 degrees.

  15. Cross-layer Design for MIMO Systems with Transmit Antenna Selection and Imperfect CSI

    NASA Astrophysics Data System (ADS)

    Yu, Xiangbin; Liu, Yan; Rui, Yun; Zhou, Tingting; Yin, Xin

    2013-04-01

    In this paper, by combining adaptive modulation and automatic repeat request (ARQ), a cross-layer design (CLD) scheme for multiple-input and multiple-output (MIMO) system with transmit antenna selection (TAS) and imperfect channel state information (CSI) is presented. Based on the imperfect CSI, the probability density function of the effective signal to noise ratio (SNR) is derived, and the fading gain switching thresholds are also derived subject to a target packet loss rate and fixed power constraint. According to these results, we further derive the average spectrum efficiency (SE) and packet error rate (PER) of the system. As a result, closed-form expressions of the average SE and PER are obtained, respectively. The derived expressions include the expressions under perfect CSI as special cases, and can provide good performance evaluation for the CLD system with imperfect CSI. Simulation results verify the validity of the theoretical analysis. The results show that the CLD system with TAS provides better SE than that with space-time block coding, but the SE and PER performance of the system with imperfect CSI are worse than those with perfect CSI due to the estimation error.

  16. Low PAPR space frequency block coding for multiuser MIMO SC-FDMA systems: specific issues for users with different spectral allocations

    NASA Astrophysics Data System (ADS)

    Ciochina, Cristina; Mottier, David; Castelain, Damien

    2011-12-01

    Single-carrier space frequency block coding (SC-SFBC) is an innovative mapping scheme suitable for implementing transmit diversity in single-carrier frequency division multiple access (SC-FDMA) systems. The main advantage of SC-SFBC is that it preserves the low envelope variations of SC-FDMA, which is particularly interesting for the uplink of wireless communications systems. In this article, we apply the SC-SFBC concept in a multiuser multiple-input multiple-output (MU-MIMO) scenario. We introduce a novel algorithm allowing the optimization of the parameters of SC-SFBC to enable low-complexity decoding at the receiver side and to maximize the overall spectral occupancy in MU-MIMO SC-FDMA systems, and we show the good performance of the proposed MU scheme.

  17. Fast frequency selective MR imaging.

    PubMed

    Medic, Jure; Tomazic, Saso; Demsar, Franci

    2005-09-01

    With the proposed fast frequency selective MR imaging (FFSMRI) method, we focused on the elimination of all off-resonance components from the image of the observed object. To maintain imaging speed and simultaneously achieve good frequency selectivity, MRI was divided into two steps: signal acquisition and postprocessing. After the preliminary phase in which we determine imaging parameters, MRI takes place; the signal from the same object is successively acquired M times. As a result, we obtain M partial signals in k-space, from which we calculate the image of the observed object in postprocessing phase, after signal acquisition has been completed. With proper selection of parameters, it is possible to exclude from the image a majority of off-resonance components present in the observed object. However, we can decide to keep only a chosen off-resonance component in the image and eliminate all other components, including the on-resonance component and thus producing a different image from the same acquisition. The experiments with Fe(OH)(3) and oil showed that signal-to-noise ratio (SNR) can be improved by about a factor of four. The proposed FFSMRI method is suitable for frequency selective MR imaging and quantitative measurements in dynamic MRI where exclusion of off-resonance components can improve the reliability of measurement.

  18. Single-Carrier Layered Space-Frequency Equalization with Time Domain Noise-Prediction for MIMO Systems

    NASA Astrophysics Data System (ADS)

    Feng, Ang; Yin, Qinye; Ding, Le

    Error-propagation is an important issue and should be carefully coped with in the decision-feedback equalizers (DFE). Ignoring the impact of error-propagation often leads to impractical laboratory results. In this paper, we investigate two novel layered space-frequency equalizers (LSFE) for single-carrier multiple-input multiple-output (MIMO) systems, where the recently proposed frequency-domain equalizer with time domain noise-predictor (FDE-NP) is adopted at each stage of the LSFE. We first derive the partially-connected LSFE with noise predictor (PC-LSFE-NP) which has exactly the same mean square error (MSE) as the conventional LSFE under the assumption of perfect feedback. However, if error-propagation is considered, the proposed PC-LSFE-NP can achieve better performance than the conventional LSFE due to the more reliable feedback output by the decoders. To reduce the interference from the not yet detected layers in the feedback section, we then introduce the fully-connected LSFE with noise predictor (FC-LSFE-NP), in which all layers are implicitly equalized within each stage and their decisions fed back internally. The powerful feedback filter of FC-LSFE-NP brings significant performance superiority over the conventional LSFE and PC-LSFE-NP with either perfect or imperfect feedback. Moreover, we propose a simple soft-demapper for the equalizers to avoid information loss during decoding, and thus, further improve the performance. Finally, we compare the performance of (PC/FC)-LSFE-NP with the existing schemes by computer simulations.

  19. 47 CFR 74.503 - Frequency selection.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 47 Telecommunication 4 2011-10-01 2011-10-01 false Frequency selection. 74.503 Section 74.503... § 74.503 Frequency selection. (a) Each application for a new station or change in an existing station shall be specific with regard to frequency. In general, the lowest suitable frequency will be assigned...

  20. 47 CFR 74.503 - Frequency selection.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 47 Telecommunication 4 2014-10-01 2014-10-01 false Frequency selection. 74.503 Section 74.503... § 74.503 Frequency selection. (a) Each application for a new station or change in an existing station shall be specific with regard to frequency. In general, the lowest suitable frequency will be assigned...

  1. 47 CFR 74.503 - Frequency selection.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 47 Telecommunication 4 2013-10-01 2013-10-01 false Frequency selection. 74.503 Section 74.503... § 74.503 Frequency selection. (a) Each application for a new station or change in an existing station shall be specific with regard to frequency. In general, the lowest suitable frequency will be assigned...

  2. 47 CFR 74.503 - Frequency selection.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 47 Telecommunication 4 2012-10-01 2012-10-01 false Frequency selection. 74.503 Section 74.503... § 74.503 Frequency selection. (a) Each application for a new station or change in an existing station shall be specific with regard to frequency. In general, the lowest suitable frequency will be assigned...

  3. 47 CFR 74.503 - Frequency selection.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 4 2010-10-01 2010-10-01 false Frequency selection. 74.503 Section 74.503... § 74.503 Frequency selection. (a) Each application for a new station or change in an existing station shall be specific with regard to frequency. In general, the lowest suitable frequency will be assigned...

  4. Frequency-Domain QR-Decomposed and Equalized MLD for Single-Carrier MIMO Systems over Multipath Fading Channels

    NASA Astrophysics Data System (ADS)

    Miyatani, Tetsuhiko

    This letter describes a new QR-decomposition maximum likelihood detector that is combined with frequency-domain equalization for single-carrier transmission based multiple-input multiple-output systems. By utilizing the equalized substreams to adjust the frequency selectivity in corresponding substreams in subsequent stages, the packet error rate performances of the proposed detector is superior to that of the minimum mean squared error receiver by a factor of the receive antenna diversity gain.

  5. 16 × 16 MIMO Testbed for MU-MIMO Downlink Transmission

    NASA Astrophysics Data System (ADS)

    Nishimori, Kentaro; Kudo, Riichi; Honma, Naoki; Takatori, Yasushi; Mizoguchi, Masato

    Multi-user multiple input multiple output (MU-MIMO) systems have attracted much attention as a technology that enhances the total system capacity by generating a virtual MIMO channel between a base station and multiple terminal stations. Extensive evaluations are still needed because there are many more system parameters in MU-MIMO than in single user (SU)-MIMO and the MU-MIMO performance in actual environments is still not well understood. This paper describes the features and effectiveness of a 16 × 16 MU-MIMO testbed in an actual indoor environment. Moreover, we propose a simple adaptive modulation scheme for MU-MIMO-OFDM transmission that employs a bit interleaver in the frequency and space domains. We evaluate the frequency efficiency by obtaining the bit error rate of this testbed in an actual indoor environment. We show that 16 × 4 × 4-user MU-MIMO transmission using the proposed modulation scheme achieves the frequency utilization of 870Mbps and 1Gbps (respective SNRs: 31 and 36dB) with a 20-MHz bandwidth.

  6. Wideband MIMO channel characterization in TV studios and inside buildings in the 2.2-2.5 GHz frequency band

    NASA Astrophysics Data System (ADS)

    Razavi-Ghods, N.; Salous, S.

    2009-10-01

    Multiple input multiple output (MIMO) measurements were performed with a chirp sounder with a switched antenna array at the transmitter and eight parallel receiver channels with 96-MHz bandwidth at 2.25 GHz in TV studios and 240-MHz bandwidth at 2.38 GHz inside buildings. MIMO capacity was estimated from the data with linear and circular arrays with array sizes 2 by 2, 4 by 4, and 6 by 8. Mean capacity estimates for 30-dB signal-to-noise ratio for both line of sight and obstructed line of sight were on the order of 11-31 b/s/Hz for the 2 by 2 to 4 by 4 antenna configurations and for the 6 by 8 directional antenna measurements a median capacity of 50 b/s/Hz. This is an increase of 20 b/s/Hz from the 4 by 4 omnidirectional antenna array indicating diversity gain as well as an increase due to the number of antennas.

  7. Performance Analysis of Adaptive Interleaving for MIMO-OFDM Systems

    DTIC Science & Technology

    2005-01-01

    multiple - input and multiple - output orthogonal frequency division multiplexing ( MIMO -OFDM) systems is proposed... multiple transmit-and-receive antennas are used to form a multiple - input and multiple - output ( MIMO ) system. The orthogonal frequency division multiple xing...transmit and receive antennas compared with a single - input single- output (SISO) system with flat Rayleigh fading or narrowband channels

  8. Frequency Selective Volumes for Optical Spatial Filters

    SciTech Connect

    E Topsakal; JL Volakis

    2004-04-15

    A new model is proposed for modeling metallic losses at optical frequencies and is used in the analysis of Frequency Selective Surfaces (FSSs) and Volumes (FSVs). Conventional methods for simulating metallic losses are also outlined and a comparison with those models is given for a patch FSS. Measured data for a slot-ring FSS are also given for model validation.

  9. A frequency selective atom interferometer magnetometer

    NASA Astrophysics Data System (ADS)

    Braje, D. A.; DeSavage, S. A.; Adler, C. L.; Davis, J. P.; Narducci, F. A.

    2014-01-01

    In this article, we discuss the magnetic-field frequency selectivity of a time-domain interferometer based on the number and timing of intermediate ? pulses. We theoretically show that by adjusting the number of ? pulses and the ?-pulse timing, we can control the frequency selectivity of the interferometer to time varying and DC magnetic fields. We present experimental data demonstrating increased coherence time due to bandwidth filtering with the inclusion of a ? pulse between the initial and final ? pulses, which mitigates sensitivity to low frequency magnetic fields.

  10. Precise SER Analysis and Performance Results of OSTBC MIMO-OFDM Systems over Uncorrelated Nakagami-m Fading Channels

    NASA Astrophysics Data System (ADS)

    Ahmad Ansari, Ejaz; Rajatheva, Nandana

    Although the topic of multiple-input multiple-output (MIMO) based orthogonal frequency division multiplexing (OFDM) over different fading channels is well investigated, its closed form symbol error rate (SER) expressions and performance results employing orthogonal space time block codes (OSTBCs) over uncorrelated frequency-selective Nakagami-m fading channels are still not available. The closed form expressions are extremely useful for evaluating system's performance without carrying out time consuming simulations. Similarly, the performance results are also quite beneficial for determining the system's performance in the sense that many practical wireless standards extensively employ MIMO-OFDM systems in conjunction with M-ary quadrature amplitude modulation (M-QAM) constellation. This paper thus, derives exact closed form expressions for the SER of M-ary Gray-coded one and two dimensional constellations when an OSTBC is employed and Nt transmit antennas are selected for transmission over frequency-selective Nakagami-m fading channels. For this purpose, first an exact closed-form of average SER expression of OSTBC based MIMO-OFDM system for M-ary phase shift keying (M-PSK) using traditional probability density function (PDF) approach is derived. We then compute exact closed form average SER expressions for M-ary pulse amplitude modulation (M-PAM) and M-QAM schemes by utilizing this generalized result. These expressions are valid over both frequency-flat and frequency-selective Nakagami-m fading MIMO channels and can easily be evaluated without using any numerical integration methods. We also show that average SER of MIMO-OFDM system using OSTBC in case of frequency-selective Rayleigh fading channels remains independent to the number of taps, L of that fading channel and the performance of the same system for two-tap un-correlated Rayleigh and Nakagami-m fading channels is better than that of the correlated one. Moreover, Monte Carlo simulation of MIMO-OFDM system

  11. Performance Analysis of MIMO Schemes in Residential Home Environment via Wideband MIMO Propagation Measurement

    NASA Astrophysics Data System (ADS)

    Tran, Gia Khanh; Dao, Nguyen Dung; Sakaguchi, Kei; Araki, Kiyomichi; Iwai, Hiroshi; Sakata, Tsutomu; Ogawa, Koichi

    This paper illustrates a large-scale MIMO propagation channel measurement in a real life environment and evaluates throughput performance of various MIMO schemes in that environment. For that purpose, 4 × 4 MIMO transceivers and a novel spatial scanner are fabricated for wideband MIMO channel measurements in the 5GHz band. A total of more than 50, 000 spatial samples in an area of 150m2, which includes a bedroom, a Japanese room, a hallway, and the living and dining areas, are taken in a real residential home environment. Statistical properties of the propagation channel and throughput performance of various MIMO schemes are evaluated by using measured data. Propagation measurement results show large dynamic channel variations occurring in a real environment in which statistical properties of the channel, such as frequency correlation and spatial correlation are not stationary any more, and become functions of the SNR. Furthermore, evaluation of throughput shows that although MIMO schemes outperform the SISO system in most areas, open loop systems perform badly in the far areas with low SNR. Paying for the cost of CSI or partial CSI at Tx, closed loop and hybrid systems have superior performance compared to other schemes, especially in reasonable SNR areas ranging from 10dB to 30dB. Spatial correlation, which is common in Japanese wooden residences, is also found to be a dominant factor causing throughput degradation of the open loop MIMO schemes.

  12. Waveform selectivity at the same frequency.

    PubMed

    Wakatsuchi, Hiroki; Anzai, Daisuke; Rushton, Jeremiah J; Gao, Fei; Kim, Sanghoon; Sievenpiper, Daniel F

    2015-04-13

    Electromagnetic properties depend on the composition of materials, i.e. either angstrom scales of molecules or, for metamaterials, subwavelength periodic structures. Each material behaves differently in accordance with the frequency of an incoming electromagnetic wave due to the frequency dispersion or the resonance of the periodic structures. This indicates that if the frequency is fixed, the material always responds in the same manner unless it has nonlinearity. However, such nonlinearity is controlled by the magnitude of the incoming wave or other bias. Therefore, it is difficult to distinguish different incoming waves at the same frequency. Here we present a new concept of circuit-based metasurfaces to selectively absorb or transmit specific types of waveforms even at the same frequency. The metasurfaces, integrated with schottky diodes as well as either capacitors or inductors, selectively absorb short or long pulses, respectively. The two types of circuit elements are then combined to absorb or transmit specific waveforms in between. This waveform selectivity gives us another degree of freedom to control electromagnetic waves in various fields including wireless communications, as our simulation reveals that the metasurfaces are capable of varying bit error rates in response to different waveforms.

  13. Waveform Selectivity at the Same Frequency

    PubMed Central

    Wakatsuchi, Hiroki; Anzai, Daisuke; Rushton, Jeremiah J.; Gao, Fei; Kim, Sanghoon; Sievenpiper, Daniel F.

    2015-01-01

    Electromagnetic properties depend on the composition of materials, i.e. either angstrom scales of molecules or, for metamaterials, subwavelength periodic structures. Each material behaves differently in accordance with the frequency of an incoming electromagnetic wave due to the frequency dispersion or the resonance of the periodic structures. This indicates that if the frequency is fixed, the material always responds in the same manner unless it has nonlinearity. However, such nonlinearity is controlled by the magnitude of the incoming wave or other bias. Therefore, it is difficult to distinguish different incoming waves at the same frequency. Here we present a new concept of circuit-based metasurfaces to selectively absorb or transmit specific types of waveforms even at the same frequency. The metasurfaces, integrated with schottky diodes as well as either capacitors or inductors, selectively absorb short or long pulses, respectively. The two types of circuit elements are then combined to absorb or transmit specific waveforms in between. This waveform selectivity gives us another degree of freedom to control electromagnetic waves in various fields including wireless communications, as our simulation reveals that the metasurfaces are capable of varying bit error rates in response to different waveforms. PMID:25866071

  14. Multiuser MIMO Systems

    DTIC Science & Technology

    2004-03-16

    Multiuser MIMO Systems H. Vincent Poor Princeton University phone: 609-258-1816 email: poor@prnceton.udu Abstract Communication systems with multiple ...This talk will discuss implications of using MIMO systems in multiple -access networks. The main focus of the talk will be on receiver signal processing... MIMO Systm Space-time Coded Systems Space-time Coded Systems - Single-user Channels: " Encoding of symbols across multiple transmit antennas. "* ST

  15. Doppler-Offset Waveforms for MIMO Radar

    DTIC Science & Technology

    2010-01-01

    Division Multiple Access, or FDMA . In the MIMO radar literature, the term FDMA is used, generically, to refer to sets of waveforms occupying different...frequencies at the same time. Mathematically, the lit" FDMA waveform can be written as: S" (I) = s (I) ej 2K I.’ 0 5, 1 5, T . for /I = I, ... ,N...noise) whenever i i’ j . Page 3 of 13 Pages On transmit, FDMA MIMO radars emit all N, frequency offset waveforms simultaneously. Then, each of the N

  16. Saliency computation via whitened frequency band selection.

    PubMed

    Lv, Qi; Wang, Bin; Zhang, Liming

    2016-06-01

    Many saliency computational models have been proposed to simulate bottom-up visual attention mechanism of human visual system. However, most of them only deal with certain kinds of images or aim at specific applications. In fact, human beings have the ability to correctly select attentive focuses of objects with arbitrary sizes within any scenes. This paper proposes a new bottom-up computational model from the perspective of frequency domain based on the biological discovery of non-Classical Receptive Field (nCRF) in the retina. A saliency map can be obtained according to the idea of Extended Classical Receptive Field. The model is composed of three major steps: firstly decompose the input image into several feature maps representing different frequency bands that cover the whole frequency domain by utilizing Gabor wavelet. Secondly, whiten the feature maps to highlight the embedded saliency information. Thirdly, select some optimal maps, simulating the response of receptive field especially nCRF, to generate the saliency map. Experimental results show that the proposed algorithm is able to work with stable effect and outstanding performance in a variety of situations as human beings do and is adaptive to both psychological patterns and natural images. Beyond that, biological plausibility of nCRF and Gabor wavelet transform make this approach reliable.

  17. Variable Is Better Than Invariable: Sparse VSS-NLMS Algorithms with Application to Adaptive MIMO Channel Estimation

    PubMed Central

    Gui, Guan; Chen, Zhang-xin; Xu, Li; Wan, Qun; Huang, Jiyan; Adachi, Fumiyuki

    2014-01-01

    Channel estimation problem is one of the key technical issues in sparse frequency-selective fading multiple-input multiple-output (MIMO) communication systems using orthogonal frequency division multiplexing (OFDM) scheme. To estimate sparse MIMO channels, sparse invariable step-size normalized least mean square (ISS-NLMS) algorithms were applied to adaptive sparse channel estimation (ACSE). It is well known that step-size is a critical parameter which controls three aspects: algorithm stability, estimation performance, and computational cost. However, traditional methods are vulnerable to cause estimation performance loss because ISS cannot balance the three aspects simultaneously. In this paper, we propose two stable sparse variable step-size NLMS (VSS-NLMS) algorithms to improve the accuracy of MIMO channel estimators. First, ASCE is formulated in MIMO-OFDM systems. Second, different sparse penalties are introduced to VSS-NLMS algorithm for ASCE. In addition, difference between sparse ISS-NLMS algorithms and sparse VSS-NLMS ones is explained and their lower bounds are also derived. At last, to verify the effectiveness of the proposed algorithms for ASCE, several selected simulation results are shown to prove that the proposed sparse VSS-NLMS algorithms can achieve better estimation performance than the conventional methods via mean square error (MSE) and bit error rate (BER) metrics. PMID:25089286

  18. Variable is better than invariable: sparse VSS-NLMS algorithms with application to adaptive MIMO channel estimation.

    PubMed

    Gui, Guan; Chen, Zhang-xin; Xu, Li; Wan, Qun; Huang, Jiyan; Adachi, Fumiyuki

    2014-01-01

    Channel estimation problem is one of the key technical issues in sparse frequency-selective fading multiple-input multiple-output (MIMO) communication systems using orthogonal frequency division multiplexing (OFDM) scheme. To estimate sparse MIMO channels, sparse invariable step-size normalized least mean square (ISS-NLMS) algorithms were applied to adaptive sparse channel estimation (ACSE). It is well known that step-size is a critical parameter which controls three aspects: algorithm stability, estimation performance, and computational cost. However, traditional methods are vulnerable to cause estimation performance loss because ISS cannot balance the three aspects simultaneously. In this paper, we propose two stable sparse variable step-size NLMS (VSS-NLMS) algorithms to improve the accuracy of MIMO channel estimators. First, ASCE is formulated in MIMO-OFDM systems. Second, different sparse penalties are introduced to VSS-NLMS algorithm for ASCE. In addition, difference between sparse ISS-NLMS algorithms and sparse VSS-NLMS ones is explained and their lower bounds are also derived. At last, to verify the effectiveness of the proposed algorithms for ASCE, several selected simulation results are shown to prove that the proposed sparse VSS-NLMS algorithms can achieve better estimation performance than the conventional methods via mean square error (MSE) and bit error rate (BER) metrics.

  19. Flexible frequency selective metamaterials for microwave applications.

    PubMed

    Gao, Bo; Yuen, Matthew M F; Ye, Terry Tao

    2017-03-21

    Metamaterials have attracted more and more research attentions recently. Metamaterials for electromagnetic applications consist of sub-wavelength structures designed to exhibit particular responses to an incident EM (electromagnetic) wave. Traditional EM (electromagnetic) metamaterial is constructed from thick and rigid structures, with the form-factor suitable for applications only in higher frequencies (above GHz) in microwave band. In this paper, we developed a thin and flexible metamaterial structure with small-scale unit cell that gives EM metamaterials far greater flexibility in numerous applications. By incorporating ferrite materials, the thickness and size of the unit cell of metamaterials have been effectively scaled down. The design, mechanism and development of flexible ferrite loaded metamaterials for microwave applications is described, with simulation as well as measurements. Experiments show that the ferrite film with permeability of 10 could reduce the resonant frequency. The thickness of the final metamaterials is only 0.3mm. This type of ferrite loaded metamaterials offers opportunities for various sub-GHz microwave applications, such as cloaks, absorbers, and frequency selective surfaces.

  20. Flexible frequency selective metamaterials for microwave applications

    PubMed Central

    Gao, Bo; Yuen, Matthew M. F; Ye, Terry Tao

    2017-01-01

    Metamaterials have attracted more and more research attentions recently. Metamaterials for electromagnetic applications consist of sub-wavelength structures designed to exhibit particular responses to an incident EM (electromagnetic) wave. Traditional EM (electromagnetic) metamaterial is constructed from thick and rigid structures, with the form-factor suitable for applications only in higher frequencies (above GHz) in microwave band. In this paper, we developed a thin and flexible metamaterial structure with small-scale unit cell that gives EM metamaterials far greater flexibility in numerous applications. By incorporating ferrite materials, the thickness and size of the unit cell of metamaterials have been effectively scaled down. The design, mechanism and development of flexible ferrite loaded metamaterials for microwave applications is described, with simulation as well as measurements. Experiments show that the ferrite film with permeability of 10 could reduce the resonant frequency. The thickness of the final metamaterials is only 0.3mm. This type of ferrite loaded metamaterials offers opportunities for various sub-GHz microwave applications, such as cloaks, absorbers, and frequency selective surfaces. PMID:28322338

  1. Flexible frequency selective metamaterials for microwave applications

    NASA Astrophysics Data System (ADS)

    Gao, Bo; Yuen, Matthew M. F.; Ye, Terry Tao

    2017-03-01

    Metamaterials have attracted more and more research attentions recently. Metamaterials for electromagnetic applications consist of sub-wavelength structures designed to exhibit particular responses to an incident EM (electromagnetic) wave. Traditional EM (electromagnetic) metamaterial is constructed from thick and rigid structures, with the form-factor suitable for applications only in higher frequencies (above GHz) in microwave band. In this paper, we developed a thin and flexible metamaterial structure with small-scale unit cell that gives EM metamaterials far greater flexibility in numerous applications. By incorporating ferrite materials, the thickness and size of the unit cell of metamaterials have been effectively scaled down. The design, mechanism and development of flexible ferrite loaded metamaterials for microwave applications is described, with simulation as well as measurements. Experiments show that the ferrite film with permeability of 10 could reduce the resonant frequency. The thickness of the final metamaterials is only 0.3mm. This type of ferrite loaded metamaterials offers opportunities for various sub-GHz microwave applications, such as cloaks, absorbers, and frequency selective surfaces.

  2. Continuous metal plasmonic frequency selective surfaces.

    PubMed

    Zhang, Jianfa; Ou, Jun-Yu; Papasimakis, Nikitas; Chen, Yifang; Macdonald, Kevin F; Zheludev, Nikolay I

    2011-11-07

    In the microwave part of the spectrum, where losses are minimal, metal films regularly patterned (perforated) on the sub-wavelength scale achieve spectral selectivity by balancing the transmission and reflection characteristics of the surface. Here we show for optical frequencies, where joule losses are important, that periodic structuring of a metal film without violation of continuity (i.e. without perforation) is sufficient to achieve substantial modification of reflectivity. By engineering the geometry of the structure imposed on a surface one can dramatically change the perceived color of the metal without employing any form of chemical modification, thin-film coating or diffraction effects. This novel frequency selective effect is underpinned by plasmonic Joule losses in the constituent elements of the patterns (dubbed 'intaglio' and 'bas relief' metamaterials to distinguish indented and raised structures respectively) and is specific to the optical part of the spectrum. It has the advantage of maintaining the integrity of metal surfaces and is well suited to high-throughput fabrication via techniques such as nano-imprint.

  3. Ultrasonic frequency selection for aqueous fine cleaning

    NASA Technical Reports Server (NTRS)

    Becker, Joann F.

    1995-01-01

    A study was conducted to evaluate ultrasonic cleaning systems for precision cleaning effectiveness for oxygen service hardware. This evaluation was specific for Rocketdyne Division of Rockwell Aerospace alloys and machining soils. Machining lubricants and hydraulic fluid were applied as soils to standardized complex test specimens designed to simulate typical hardware. The study consisted of tests which included 20, 25, 30, 40, 50, and 65 kHz ultrasonic cleaning systems. Two size categories of cleaning systems were evaluated, 3- to 10-gal laboratory size tanks and 35- to 320-gal industrial size tanks. The system properties of cavitation, frequency vs. cleaning effectiveness, the two types of transducers, and the power level of the system vs. size of the cleaning tank were investigated. The data obtained from this study was used to select the ultrasonic tanks for the aqueous fine clean facility installed at Rocketdyne.

  4. Ultrasonic frequency selection for aqueous fine cleaning

    NASA Technical Reports Server (NTRS)

    Becker, Joann F.

    1994-01-01

    A study was conducted to evaluate ultrasonic cleaning systems for precision cleaning effectiveness for oxygen service hardware. This evaluation was specific for Rocketdyne Div. of Rockwell Aerospace alloys and machining soils. Machining lubricants and hydraulic fluid were applied as soils to standardized complex test specimens designed to simulate typical hardware. The study consisted of tests which included 20, 25, 30, 40, 50, and 65 kHz ultrasonic cleaning systems. Two size categories of cleaning systems were evaluated, 3- to 10-gal laboratory size tanks and 35- to 320-gal industrial size tanks. The system properties of cavitation; frequency vs. cleaning effectiveness; the two types of transducers; and the power level of the system vs. size of the cleaning tank were investigated. The data obtained from this study was used to select the ultrasonic tanks for the aqueous fine clean facility installed at Rocketdyne.

  5. Ultrasonic frequency selection for aqueous fine cleaning

    NASA Astrophysics Data System (ADS)

    Becker, Joann F.

    1995-03-01

    A study was conducted to evaluate ultrasonic cleaning systems for precision cleaning effectiveness for oxygen service hardware. This evaluation was specific for Rocketdyne Division of Rockwell Aerospace alloys and machining soils. Machining lubricants and hydraulic fluid were applied as soils to standardized complex test specimens designed to simulate typical hardware. The study consisted of tests which included 20, 25, 30, 40, 50, and 65 kHz ultrasonic cleaning systems. Two size categories of cleaning systems were evaluated, 3- to 10-gal laboratory size tanks and 35- to 320-gal industrial size tanks. The system properties of cavitation, frequency vs. cleaning effectiveness, the two types of transducers, and the power level of the system vs. size of the cleaning tank were investigated. The data obtained from this study was used to select the ultrasonic tanks for the aqueous fine clean facility installed at Rocketdyne.

  6. Statistical MIMO Radar

    DTIC Science & Technology

    2004-12-20

    improve the radar’s performance. MIMO radar utilizes multiple antennas at both the transmitter and receiver. It can be applied in monostatic or bistatic...signal at the output of the beamformer equals , , HE t x y x y t t M E y t x y x M r a b s n a b        20y s t n t S- MIMO Radar

  7. 47 CFR 74.403 - Frequency selection to avoid interference.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 4 2010-10-01 2010-10-01 false Frequency selection to avoid interference. 74... Pickup Broadcast Stations § 74.403 Frequency selection to avoid interference. (a) Where two or more... select frequencies or schedule operation in such manner as to avoid mutual interference. If mutual...

  8. Characteristic Analysis on UAV-MIMO Channel Based on Normalized Correlation Matrix

    PubMed Central

    Xi jun, Gao; Zi li, Chen; Yong Jiang, Hu

    2014-01-01

    Based on the three-dimensional GBSBCM (geometrically based double bounce cylinder model) channel model of MIMO for unmanned aerial vehicle (UAV), the simple form of UAV space-time-frequency channel correlation function which includes the LOS, SPE, and DIF components is presented. By the methods of channel matrix decomposition and coefficient normalization, the analytic formula of UAV-MIMO normalized correlation matrix is deduced. This formula can be used directly to analyze the condition number of UAV-MIMO channel matrix, the channel capacity, and other characteristic parameters. The simulation results show that this channel correlation matrix can be applied to describe the changes of UAV-MIMO channel characteristics under different parameter settings comprehensively. This analysis method provides a theoretical basis for improving the transmission performance of UAV-MIMO channel. The development of MIMO technology shows practical application value in the field of UAV communication. PMID:24977185

  9. Characteristic analysis on UAV-MIMO channel based on normalized correlation matrix.

    PubMed

    Gao, Xi jun; Chen, Zi li; Hu, Yong Jiang

    2014-01-01

    Based on the three-dimensional GBSBCM (geometrically based double bounce cylinder model) channel model of MIMO for unmanned aerial vehicle (UAV), the simple form of UAV space-time-frequency channel correlation function which includes the LOS, SPE, and DIF components is presented. By the methods of channel matrix decomposition and coefficient normalization, the analytic formula of UAV-MIMO normalized correlation matrix is deduced. This formula can be used directly to analyze the condition number of UAV-MIMO channel matrix, the channel capacity, and other characteristic parameters. The simulation results show that this channel correlation matrix can be applied to describe the changes of UAV-MIMO channel characteristics under different parameter settings comprehensively. This analysis method provides a theoretical basis for improving the transmission performance of UAV-MIMO channel. The development of MIMO technology shows practical application value in the field of UAV communication.

  10. 47 CFR 90.723 - Selection and assignment of frequencies.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 5 2010-10-01 2010-10-01 false Selection and assignment of frequencies. 90.723... SERVICES PRIVATE LAND MOBILE RADIO SERVICES Regulations Governing Licensing and Use of Frequencies in the 220-222 MHz Band § 90.723 Selection and assignment of frequencies. (a) Phase II applications for...

  11. Performance analysis of low-complexity adaptive frequency-domain equalization and MIMO signal processing for compensation of differential mode group delay in mode-division multiplexing communication systems using few-mode fibers

    NASA Astrophysics Data System (ADS)

    Weng, Yi; He, Xuan; Pan, Zhongqi

    2016-02-01

    Mode-division multiplexing (MDM) transmission systems utilizing few-mode fibers (FMF) have been intensively explored to sustain continuous traffic growth. The key challenges of MDM systems are inter-modal crosstalk due to random mode coupling (RMC), and largely-accumulated differential mode group delay (DMGD), whilst hinders mode-demultiplexer implementation. The adaptive multi-input multi-output (MIMO) frequency-domain equalization (FDE) can dynamically compensate DMGD using digital signal processing (DSP) algorithms. The frequency-domain least-mean squares (FD-LMS) algorithm has been universally adopted for high-speed MDM communications, mainly for its relatively low computational complexity. However, longer training sequence is appended for FD-LMS to achieve faster convergence, which incurs prohibitively higher system overhead and reduces overall throughput. In this paper, we propose a fast-convergent single-stage adaptive frequency-domain recursive least-squares (FD-RLS) algorithm with reduced complexity for DMGD compensation at MDM coherent receivers. The performance and complexity comparison of FD-RLS, with signal-PSD-dependent FD-LMS method and conventional FD-LMS approach, are performed in a 3000 km six-mode transmission system with 65 ps/km DMGD. We explore the convergence speed of three adaptive algorithms, including the normalized mean-square-error (NMSE) per fast Fourier transform (FFT) block at 14-30 dB OSNR. The fast convergence of FD-RLS is exploited at the expense of slightly-increased necessary tap numbers for MIMO equalizers, and it can partially save the overhead of training sequence. Furthermore, we demonstrate adaptive FD-RLS can also be used for chromatic dispersion (CD) compensation without increasing the filter tap length, thus prominently reducing the DSP implementation complexity for MDM systems.

  12. Frequency selective surfaces with multiple periodic elements

    NASA Astrophysics Data System (ADS)

    Reed, Jeffrey Alan

    A thorough computer design study using the method of Chen1,2,3 was undertaken for band-pass filters constructed from frequency selective surfaces (FSSs). The FSSs, modeled as thin, perfectly conducting surfaces with periodically arranged apertures, were designed to produce a transmission profile with a bandpass characteristic centered at 10.6 μm and to have various specified bandwidths. The effects of aperture shape and dimensions, configuration and periodicity of the aperture array, and presence of a dielectric substrate were examined in- depth. For comparison purposes, a complimentary array of metallic patches was also examined. The successful design (a thin, planar sheet of aluminum perforated with narrow rectangular apertures in a triangular array configuration on a thick zinc selenide substrate) provided a preliminary set of basic design rules for creating bandpass filters from FSSs. Dual resonance transmission profiles were generated by considering a FSS with a group of apertures as the periodic element. Chen's method1,2,3 was modified to work with periodic groups of up to four rectangular or circular shaped apertures (or metallic patches). Combinations of different length narrow slot apertures, combinations of square and narrow slot apertures, and variation of periodicity along alternating rows of narrow slot apertures, all produced a dual resonance transmission profile in the computer model. For the combination of different length narrow apertures, the dual resonance resulted from the natural resonance associated with the two different length narrow apertures, while for the combination of squares and narrow slots, an enhancement of the Wood's anomaly at the diffraction edge created the second resonance peak. Variation of the periodicity along alternating rows produced a dual resonance because each of the 'superimposed arrays' had a different periodicity. The presence of Wood's anomalies in the transmission profile was also examined. Finally, 'proof of

  13. Multi-Band Frequency Selective Surfaces: Analysis

    DTIC Science & Technology

    2008-08-01

    should be completely transparent at frequencies of GSM (900 MHz and 1800 MHz) and WiFi LAN (2400 MHz), without degrading the thermal response of the...and slot-based FSSs [13]. The formulation is centred on a single integral equation with a fixed kernel, containing only localised modes (reduced

  14. 47 CFR 74.803 - Frequency selection to avoid interference.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... SERVICES EXPERIMENTAL RADIO, AUXILIARY, SPECIAL BROADCAST AND OTHER PROGRAM DISTRIBUTIONAL SERVICES Low Power Auxiliary Stations § 74.803 Frequency selection to avoid interference. (a) Where two or more low... 47 Telecommunication 4 2011-10-01 2011-10-01 false Frequency selection to avoid interference....

  15. Selection of frequencies for deep-space telecommunications

    NASA Technical Reports Server (NTRS)

    Degroot, N. F.; Sue, M. K.

    1982-01-01

    The procedures used by the Jet Propulsion Laboratory to select and recommend frequencies to be used for deep space telecommunications are explained. The frequency selection process described deals only with the potential for radio frequency interference between deep space telecommunication links. Channel plans based on bandwidth, hardware implementation, and frequency ratio considered are used. The channel selection process is based on calculations and analysis of interference-to-signal power ratios as a function of time for each possible pair of missions. The modes of interference and the interference protection ratio are explained, and the interference analysis procedure described. Equations used in calculating the downlink and uplink interference analyses are presented.

  16. When Does Frequency-Independent Selection Maintain Genetic Variation?

    PubMed

    Novak, Sebastian; Barton, Nicholas H

    2017-10-01

    Frequency-independent selection is generally considered as a force that acts to reduce the genetic variation in evolving populations, yet rigorous arguments for this idea are scarce. When selection fluctuates in time, it is unclear whether frequency-independent selection may maintain genetic polymorphism without invoking additional mechanisms. We show that constant frequency-independent selection with arbitrary epistasis on a well-mixed haploid population eliminates genetic variation if we assume linkage equilibrium between alleles. To this end, we introduce the notion of frequency-independent selection at the level of alleles, which is sufficient to prove our claim and contains the notion of frequency-independent selection on haploids. When selection and recombination are weak but of the same order, there may be strong linkage disequilibrium; numerical calculations show that stable equilibria are highly unlikely. Using the example of a diallelic two-locus model, we then demonstrate that frequency-independent selection that fluctuates in time can maintain stable polymorphism if linkage disequilibrium changes its sign periodically. We put our findings in the context of results from the existing literature and point out those scenarios in which the possible role of frequency-independent selection in maintaining genetic variation remains unclear. Copyright © 2017 by the Genetics Society of America.

  17. Selective Frequency Invariant Uniform Circular Broadband Beamformer

    NASA Astrophysics Data System (ADS)

    Zhang, Xin; Ser, Wee; Zhang, Zhang; Krishna, AnoopKumar

    2010-12-01

    Frequency-Invariant (FI) beamforming is a well known array signal processing technique used in many applications. In this paper, an algorithm that attempts to optimize the frequency invariant beampattern solely for the mainlobe, and relax the FI requirement on the sidelobe is proposed. This sacrifice on performance in the undesired region is traded off for better performance in the desired region as well as reduced number of microphones employed. The objective function is designed to minimize the overall spatial response of the beamformer with a constraint on the gain being smaller than a pre-defined threshold value across a specific frequency range and at a specific angle. This problem is formulated as a convex optimization problem and the solution is obtained by using the Second Order Cone Programming (SOCP) technique. An analysis of the computational complexity of the proposed algorithm is presented as well as its performance. The performance is evaluated via computer simulation for different number of sensors and different threshold values. Simulation results show that, the proposed algorithm is able to achieve a smaller mean square error of the spatial response gain for the specific FI region compared to existing algorithms.

  18. Floodflow frequency model selection in Australia

    NASA Astrophysics Data System (ADS)

    Vogel, Richard M.; McMahon, Thomas A.; Chiew, Francis H. S.

    1993-06-01

    Uniform flood frequency guidelines in Australia and the United States recommend the use of the log Pearson type 3 (LP3) distribution in flood frequency investigations. Many investigators have suggested alternate models such as the Generalized Extreme Value (GEV) distribution as an improvement over the LP3 distribution. Using floodflow data at 61 sites across Australia, we explore the suitability of various flood frequency models using L-moment diagrams. We also repeat the experiment performed in the original US Water Resource Council report (Bulletin 17B) which led to the LP3 mandate in the United States. Our evaluations reveal that among the models tested, the GEV and Wakeby distributions provide the best approximation to floodflow data in the regions of Australia that are dominated by rainfall during the winter months, such as southwest Western Australia and Tasmania. For the remainder of the continent, the Generalized Pareto (GPA) and Wakeby distributions provide the best approximation to floodflow data. The two- and three-parameter log-normal models and the LP3 distribution performed satisfactorily, yet not as well as either the GEV or GPA distributions. Other models such as the Gumbel, log-normal, normal, Pearson, exponential, and uniform distributions are shown to perform poorly. Recent research indicates that regional index-flood type procedures should be more accurate and more robust than the type of at-site procedures evaluated here. Nevertheless, this study reveals that index-flood procedures should not be restricted to a single distribution such as the GEV distribution because other distributions such as the GPA distribution perform significantly better in the most densely populated regions of Australia.

  19. Radio frequency selection and interference prevention

    NASA Technical Reports Server (NTRS)

    Degroot, N. F.

    1982-01-01

    The bands available for deep-space communications, and the choice of particular mission frequencies are discussed. The more general susceptibility of deep-space Earth stations to various kinds of interference is then presented. An associated topic is the development of protection criteria that specify maximum allowable levels of interference. Next, the prediction of interference from near-Earth satellites is described, with particular emphasis on the problems and uncertainties of such predictions. Finally, a brief description of other activities aimed at the prevention or avoidance of interference to deep-space radio communications is given.

  20. Does word frequency affect lexical selection in speech production?

    PubMed

    Navarrete, Eduardo; Basagni, Benedetta; Alario, F-Xavier; Costa, Albert

    2006-10-01

    We evaluated whether lexical selection in speech production is affected by word frequency by means of two experiments. In Experiment 1 participants named pictures using utterances with the structure "pronoun + verb + adjective". In Experiment 2 participants had to perform a gender decision task on the same pictures. Access to the noun's grammatical gender is needed in both tasks, and therefore lexical selection (lemma retrieval) is required. However, retrieval of the phonological properties (lexeme retrieval) of the referent noun is not needed to perform the tasks. In both experiments we observed faster latencies for high-frequency pictures than for low-frequency pictures. This frequency effect was stable over four repetitions of the stimuli. Our results suggest that lexical selection (lemma retrieval) is sensitive to word frequency. This interpretation runs against the hypothesis that a word's frequency exerts its effects only at the level at which the phonological properties of words are retrieved.

  1. Capacity Optimization of MIMO Links with Interference

    DTIC Science & Technology

    2011-06-01

    Multiple - Input Multiple - Output ( MIMO ) systems have shown great promise in providing high spectral efficiency for single user...the case of strong interference. 15. SUBJECT TERMS Multiple - input multiple - output systems, capacity optimization, cochannel interference. 16...wireless link without interference [3], [4]. There has also much work on the MIMO -based cellular networks, which include MIMO multiple access ( MIMO

  2. Advanced Techniques for MIMO Broadband Communications

    DTIC Science & Technology

    2005-12-01

    Multiple input multiple output ( MIMO ) systems can provide high...Approved for Public Release Distribution Unlimited 20060614025 Abstract Multiple input multiple output ( MIMO ) systems can provide high diversity, high... multiple transmit/receive antennas are referred to as multiple input multiple output ( MIMO ) systems. As studies advance, it is shown that MIMO

  3. Frequency selective tunable spin wave channeling in the magnonic network

    SciTech Connect

    Sadovnikov, A. V. Nikitov, S. A.; Beginin, E. N.; Odincov, S. A.; Sheshukova, S. E.; Sharaevskii, Yu. P.; Stognij, A. I.

    2016-04-25

    Using the space-resolved Brillouin light scattering spectroscopy, we study the frequency and wavenumber selective spin-wave channeling. We demonstrate the frequency selective collimation of spin-wave in an array of magnonic waveguides, formed between the adjacent magnonic crystals on the surface of yttrium iron garnet film. We show the control over spin-wave propagation length by the orientation of an in-plane bias magnetic field. Fabricated array of magnonic crystal can be used as a magnonic platform for multidirectional frequency selective signal processing applications in magnonic networks.

  4. Experimental study on the statistic characteristics of a 3x3 RF MIMO channel over a single conventional multimode fiber.

    PubMed

    Lei, Yi; Li, Jianqiang; Wu, Rui; Fan, Yuting; Fu, Songnian; Yin, Feifei; Dai, Yitang; Xu, Kun

    2017-06-01

    Based on the observed random fluctuation phenomenon of speckle pattern across multimode fiber (MMF) facet and received optical power distribution across three output ports, we experimentally investigate the statistic characteristics of a 3×3 radio frequency multiple-input multiple-output (MIMO) channel enabled by mode division multiplexing in a conventional 50 µm MMF using non-mode-selective three-dimensional waveguide photonic lanterns as mode multiplexer and demultiplexer. The impacts of mode coupling on the MIMO channel coefficients, channel matrix, and channel capacity have been analyzed over different fiber lengths. The results indicate that spatial multiplexing benefits from the greater fiber length with stronger mode coupling, despite a higher optical loss.

  5. Frequency-Selective Attention in Auditory Scenes Recruits Frequency Representations Throughout Human Superior Temporal Cortex.

    PubMed

    Riecke, Lars; Peters, Judith C; Valente, Giancarlo; Kemper, Valentin G; Formisano, Elia; Sorger, Bettina

    2017-05-01

    A sound of interest may be tracked amid other salient sounds by focusing attention on its characteristic features including its frequency. Functional magnetic resonance imaging findings have indicated that frequency representations in human primary auditory cortex (AC) contribute to this feat. However, attentional modulations were examined at relatively low spatial and spectral resolutions, and frequency-selective contributions outside the primary AC could not be established. To address these issues, we compared blood oxygenation level-dependent (BOLD) responses in the superior temporal cortex of human listeners while they identified single frequencies versus listened selectively for various frequencies within a multifrequency scene. Using best-frequency mapping, we observed that the detailed spatial layout of attention-induced BOLD response enhancements in primary AC follows the tonotopy of stimulus-driven frequency representations-analogous to the "spotlight" of attention enhancing visuospatial representations in retinotopic visual cortex. Moreover, using an algorithm trained to discriminate stimulus-driven frequency representations, we could successfully decode the focus of frequency-selective attention from listeners' BOLD response patterns in nonprimary AC. Our results indicate that the human brain facilitates selective listening to a frequency of interest in a scene by reinforcing the fine-grained activity pattern throughout the entire superior temporal cortex that would be evoked if that frequency was present alone. © The Author 2016. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.

  6. Airborne MIMO GMTI Radar

    DTIC Science & Technology

    2011-03-31

    applications [1], [2], [3], [4]. [5]. [6]. [7]. [8]. [9]. [10]. [11]. [12]. Conventional phased array radars form a single coherent transmit beam and...intentionally left blank. 1. INTRODUCTION Conventional phased - array radars form a single coherent transmit beam and measure the backscattered response... steering vector for a SI MO array with nr"/? receiver phase centers located at positions xm + y„. This is how the MIMO virtual array arises. The waveforms

  7. Studies of Hybrid MIMO

    DTIC Science & Technology

    2008-08-01

    beamforming approaches to improve radar target detection, tracking and classification. 15. SUBJECT TERMS EOARD, target ...Sammartino, C.J. Baker, H.D. Griffiths – “ Target Model Effects On MIMO Radar Performance” – 2006 IEEE ICASSP, International Confer- ence on Acoustic...2007, St. Thomas, US Virgin Islands, 12th-14th Dec 2007. 11. P.F. Sammartino, C.J. Baker, M. Rangaswamy – “Moving target localization with multistatic

  8. Three-dimensional near-field MIMO array imaging using range migration techniques.

    PubMed

    Zhuge, Xiaodong; Yarovoy, Alexander G

    2012-06-01

    This paper presents a 3-D near-field imaging algorithm that is formulated for 2-D wideband multiple-input-multiple-output (MIMO) imaging array topology. The proposed MIMO range migration technique performs the image reconstruction procedure in the frequency-wavenumber domain. The algorithm is able to completely compensate the curvature of the wavefront in the near-field through a specifically defined interpolation process and provides extremely high computational efficiency by the application of the fast Fourier transform. The implementation aspects of the algorithm and the sampling criteria of a MIMO aperture are discussed. The image reconstruction performance and computational efficiency of the algorithm are demonstrated both with numerical simulations and measurements using 2-D MIMO arrays. Real-time 3-D near-field imaging can be achieved with a real-aperture array by applying the proposed MIMO range migration techniques.

  9. Multi-Band Frequency-Selective Microwave Reflectors

    NASA Technical Reports Server (NTRS)

    Wu, Te-Kao

    1995-01-01

    Double-loop patch and slot elements used in two different frequency-multiplexing designs. Array of double-round-loop conductive patches highly reflective at frequencies around 33 GHz (in Ka band). Array of double-square loop slots in conductive plane highly transmissive in S and Ku bands and highly reflective in X band. These frequency-selective reflectors closely related to several previous articles in NASA Tech Briefs, including "Frequency-Selective Microwave Reflectors" (NPO-18701), "Improved Dichroic Microwave Reflector" (NPO-18664), "Double-Square-Loop Dichroic Microwave Reflector" (NPO-18676), "Triband Circular-Loop Dichroic Microwave Reflector" (NPO-18714), "Making Curved Frequency-Selective Microwave Reflectors" (NPO-18755), "More Circular-Loop Dichroic Microwave Reflectors" (NPO-18940).

  10. MIMO Radar - Diversity Means Superiority

    DTIC Science & Technology

    2007-10-01

    MIMO radar than wit ,11 its plascd- array counterpart. In [9], a MIMO radar technique is suggested to improve the radar tesoilluOll. The idea is to...AB - XSH(SSH)-]H +Iq = QI I+±l 7 - [ AnB -XSH(SSH)-] (SSH)[An-XSH(SSH)-I] 1 Q - IQI I XssHH[ABxsH(ssH)

  11. Circular-Loop-Element Microwave Frequency-Selective Reflectors

    NASA Technical Reports Server (NTRS)

    Huang, John; Wu, Te-Kao; Lee, Shung-Wu

    1995-01-01

    Double or single planar arrays of circular loops laminated with dielectric sheets. Reflectors designed for use in multiplexing signals at several frequencies in microwave antenna system. Well suited to both circularly and linearly polarized radiation. Transmission and reflection characteristics relatively insensitive to angle of incidence. Similar device described in "Triband Circular-Loop Frequency-Selective Microwave Reflector" (NPO-18714).

  12. Frequency-Dependent Selection Predicts Patterns of Radiations and Biodiversity

    PubMed Central

    Melián, Carlos J.; Alonso, David; Vázquez, Diego P.; Regetz, James; Allesina, Stefano

    2010-01-01

    Most empirical studies support a decline in speciation rates through time, although evidence for constant speciation rates also exists. Declining rates have been explained by invoking pre-existing niches, whereas constant rates have been attributed to non-adaptive processes such as sexual selection and mutation. Trends in speciation rate and the processes underlying it remain unclear, representing a critical information gap in understanding patterns of global diversity. Here we show that the temporal trend in the speciation rate can also be explained by frequency-dependent selection. We construct a frequency-dependent and DNA sequence-based model of speciation. We compare our model to empirical diversity patterns observed for cichlid fish and Darwin's finches, two classic systems for which speciation rates and richness data exist. Negative frequency-dependent selection predicts well both the declining speciation rate found in cichlid fish and explains their species richness. For groups like the Darwin's finches, in which speciation rates are constant and diversity is lower, speciation rate is better explained by a model without frequency-dependent selection. Our analysis shows that differences in diversity may be driven by incipient species abundance with frequency-dependent selection. Our results demonstrate that genetic-distance-based speciation and frequency-dependent selection are sufficient to explain the high diversity observed in natural systems and, importantly, predict decay through time in speciation rate in the absence of pre-existing niches. PMID:20865126

  13. Optically transparent frequency selective surfaces on flexible thin plastic substrates

    SciTech Connect

    Dewani, Aliya A. O’Keefe, Steven G.; Thiel, David V.; Galehdar, Amir

    2015-02-15

    A novel 2D simple low cost frequency selective surface was screen printed on thin (0.21 mm), flexible transparent plastic substrate (relative permittivity 3.2). It was designed, fabricated and tested in the frequency range 10-20 GHz. The plane wave transmission and reflection coefficients agreed with numerical modelling. The effective permittivity and thickness of the backing sheet has a significant effect on the frequency characteristics. The stop band frequency reduced from 15GHz (no backing) to 12.5GHz with polycarbonate. The plastic substrate thickness beyond 1.8mm has minimal effect on the resonant frequency. While the inner element spacing controls the stop-band frequency, the substrate thickness controls the bandwidth. The screen printing technique provided a simple, low cost FSS fabrication method to produce flexible, conformal, optically transparent and bio-degradable FSS structures which can find their use in electromagnetic shielding and filtering applications in radomes, reflector antennas, beam splitters and polarizers.

  14. Precoded spatial multiplexing MIMO system with spatial component interleaver.

    PubMed

    Gao, Xiang; Wu, Zhanji

    In this paper, the performance of precoded bit-interleaved coded modulation (BICM) spatial multiplexing multiple-input multiple-output (MIMO) system with spatial component interleaver is investigated. For the ideal precoded spatial multiplexing MIMO system with spatial component interleaver based on singular value decomposition (SVD) of the MIMO channel, the average pairwise error probability (PEP) of coded bits is derived. Based on the PEP analysis, the optimum spatial Q-component interleaver design criterion is provided to achieve the minimum error probability. For the limited feedback precoded proposed scheme with linear zero forcing (ZF) receiver, in order to minimize a bound on the average probability of a symbol vector error, a novel effective signal-to-noise ratio (SNR)-based precoding matrix selection criterion and a simplified criterion are proposed. Based on the average mutual information (AMI)-maximization criterion, the optimal constellation rotation angles are investigated. Simulation results indicate that the optimized spatial multiplexing MIMO system with spatial component interleaver can achieve significant performance advantages compared to the conventional spatial multiplexing MIMO system.

  15. Frequency-domain method based on the singular value decomposition for frequency-selective NMR spectroscopy.

    PubMed

    Stoica, Petre; Sandgren, Niclas; Selén, Yngve; Vanhamme, Leentje; Van Huffel, Sabine

    2003-11-01

    In several applications of NMR spectroscopy the user is interested only in the components lying in a small frequency band of the spectrum. A frequency selective analysis deals precisely with this kind of NMR spectroscopy: parameter estimation of only those spectroscopic components that lie in a preselected frequency band of the NMR data spectrum, with as little interference as possible from the out-of-band components and in a computationally efficient way. In this paper we introduce a frequency-domain singular value decomposition (SVD)-based method for frequency selective spectroscopy that is computationally simple, statistically accurate, and which has a firm theoretical basis. To illustrate the good performance of the proposed method we present a number of numerical examples for both simulated and in vitro NMR data.

  16. A molecular explanation of frequency-dependent selection in Drosophila.

    PubMed

    Haj-Ahmad, Y; Hickey, D A

    1982-09-23

    Frequency-dependent selection provides a means for maintaining genetic variability within populations, without incurring a large genetic load. There is a wealth of experimental evidence for the existence of frequency-dependent changes in genotypic fitness among a wide variety of organisms. Examples of traits which have been shown to be subject to frequency-dependent selection include the self-incompatibility alleles of plants, chromosomal rearrangements in Drosophila, visible mutations, enzyme variants and rare-male mating advantage in Drosophila. These experiments have been interpreted in a number of different ways. Principally, frequency dependence of genotype fitness may result from intergenotype facilitation due to the production of biotic residues, or from the differential use of resources by the competing genotypes. However, it has proved extremely difficult to isolate and identify any biotic residue of importance or, alternatively, to understand the manner in which genotypes partition the environment. Thus, the difficulty in the interpretation of experiments which show frequency-dependent selective effects stems largely from our lack of understanding of the exact physiological mechanisms which produce these frequency-dependent effects. The principal aim of this study was to investigate the mechanisms associated with frequency-dependent selection at the amylase locus in Drosophila melanogaster. The excretion of catalytically active amylase enzyme and its effect on food medium composition were correlated with the outcome of intraspecific competition between amylase-deficient and amylase-producing genotypes. Amylase-producing genotypes were shown to excrete enzymatically active amylase protein into the food medium. The excreted amylase causes the external digestion of dietary starch; this accounts for the frequency-dependent increase in the viability of the amylase-deficient mutants in mixed cultures, maintained on a starch-rich diet.

  17. Techniques for analyzing frequency selective surfaces - A review

    NASA Technical Reports Server (NTRS)

    Mittra, Raj; Chan, Chi H.; Cwik, Tom

    1988-01-01

    A number of representative techniques for analyzing frequency-selective surfaces (FSSs), which comprise periodic arrays of patches or apertures in a conducting screen and find important applications as filters in microwaves and optics, are discussed. The basic properties of the FSSs are reviewed and several different approaches to predicting their frequency-response characteristics are described. Some recent developments in the treatment of truncated, curved, and doubly periodic screens are mentioned and representative experimental results are included.

  18. Responses to selection for postmeiotic segregation frequencies in Ascobolus immersus.

    PubMed

    Lamb, Bernard C; Saleem, Muhammad

    2003-02-01

    A composite cross was made between 12 strains of the fungus Ascobolus immersus, six with wild-type red ascospores (w1+) and six with white ascospore mutation w1-78. A high postmeiotic segregation (PMS) frequency line was set up from colonies from ascospores from dehisced octads showing PMS, 5+ : 3w and 3+ : 5w. A low PMS line was started from ascospores from 4+ : 4w or 6+ : 2w octads, and a 'no selection' line was set up from ascospores from random octads. Colonies were crossed to tester strains to determine PMS frequencies and the selected lines were continued from ascospores of crosses of the red ascospore strain with the most extreme (e.g. high for the high line) PMS frequency with the white-ascospore strain of most extreme PMS frequency and of opposite mating type. Significant responses to selection were obtained for increased (+100%) and decreased (-58%) PMS, giving a 4.8-times difference in generation 4, with little change in the frequencies of conversion classes showing meiotic segregation (6+ : 2w and 2+ : 6w). The continuous, symmetrical, roughly normal distributions for PMS frequencies obtained when generation 5 strains were crossed to unselected tester strains are those expected if PMS frequencies are controlled by a number of polygenes, not major genes. Crosses of selected fifth-generation red-ascospore strains with extreme PMS values to base-substitution mutant w1-78, to frame-shift mutant w1-3C1 and to white-ascospore mutants w-BHj and w-9 at two loci unlinked to w1 showed that the effects of selection were not allele specific, locus specific or mutation-type specific.

  19. Frequency selectivity in canaries with a hereditary hearing loss

    NASA Astrophysics Data System (ADS)

    Lauer, Amanda M.; Dooling, Robert J.

    2002-05-01

    Sensorineural hearing loss is associated with reduced frequency selectivity due to the broadening of the auditory filters in mammals. In European starlings, hearing loss caused by the ototoxic drug kanamycin results in the widening of auditory filters at 5 kHz [Marean et al. (1998)]. In the present study, we examine frequency selectivity in a bird with a permanent hereditary hearing impairment, the Belgian Waterslager (BWS) canary. This strain of canary has long been bred for its loud, low-frequency song, and has been shown to have a hearing loss primarily at higher frequencies (2 kHz and above). Using operant conditioning and the method of constant stimuli, thresholds for detecting pure tones in flat-spectrum broadband noise were measured in BWS and non-BWS canaries. Critical ratios were calculated for comparison with other species of birds. At higher frequencies, critical ratios for BWS canaries were much larger than those of non-BWS canaries and other birds, suggesting reduced frequency selectivity in the region of the birds' hearing loss. [Work supported by NIDCD R01DC001372 to RJD and Brenda M. Ryals.

  20. Remote sensing using MIMO systems

    DOEpatents

    Bikhazi, Nicolas; Young, William F; Nguyen, Hung D

    2015-04-28

    A technique for sensing a moving object within a physical environment using a MIMO communication link includes generating a channel matrix based upon channel state information of the MIMO communication link. The physical environment operates as a communication medium through which communication signals of the MIMO communication link propagate between a transmitter and a receiver. A spatial information variable is generated for the MIMO communication link based on the channel matrix. The spatial information variable includes spatial information about the moving object within the physical environment. A signature for the moving object is generated based on values of the spatial information variable accumulated over time. The moving object is identified based upon the signature.

  1. MIMO to LS-MIMO: A road to realization of 5G

    NASA Astrophysics Data System (ADS)

    Koppati, Naveena; Pavani, K.; Sharma, Dinesh; Sharma, Purnima K.

    2017-07-01

    MIMO means multiple inputs multiple outputs. As it refers MIMO is a RF technology used in many new technologies these days to increase link capacity and spectral efficiency. MIMO is used in Wi-Fi, LTE, 4G, 5G and other wireless technologies. This paper describes the earlier history of MIMO-OFDM and the antenna beam forming development in MIMO and types of MIMO. Also this treatise describes several decoding algorithms. The MIMO combined with OFDM increases the channel capacity. But the main problem is in estimating the transmitted signal from the received signal. So the channel knowledge is to be known in estimating the channel capacity. The advancement in MIMO-OFDM is Massive MIMO which is beneficial in providing additional data capacity in the increased traffic environment is described. In this memoir various application scenarios of LS-MIMO which increases the capacity are discussed.

  2. 47 CFR 74.803 - Frequency selection to avoid interference.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... Power Auxiliary Stations § 74.803 Frequency selection to avoid interference. (a) Where two or more low.... In these bands, low power auxiliary station usage is secondary to TV broadcasting and land mobile... occurs, low power auxiliary station operation must immediately cease and may not be resumed until...

  3. 47 CFR 74.803 - Frequency selection to avoid interference.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... Power Auxiliary Stations § 74.803 Frequency selection to avoid interference. (a) Where two or more low.... In these bands, low power auxiliary station usage is secondary to TV broadcasting and land mobile... occurs, low power auxiliary station operation must immediately cease and may not be resumed until...

  4. 47 CFR 74.803 - Frequency selection to avoid interference.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... Power Auxiliary Stations § 74.803 Frequency selection to avoid interference. (a) Where two or more low.... In these bands, low power auxiliary station usage is secondary to TV broadcasting and land mobile... occurs, low power auxiliary station operation must immediately cease and may not be resumed until...

  5. 47 CFR 74.803 - Frequency selection to avoid interference.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... Power Auxiliary Stations § 74.803 Frequency selection to avoid interference. (a) Where two or more low.... In these bands, low power auxiliary station usage is secondary to TV broadcasting and land mobile... occurs, low power auxiliary station operation must immediately cease and may not be resumed until...

  6. Characteristics of spectro-temporal modulation frequency selectivity in humans.

    PubMed

    Oetjen, Arne; Verhey, Jesko L

    2017-03-01

    There is increasing evidence that the auditory system shows frequency selectivity for spectro-temporal modulations. A recent study of the authors has shown spectro-temporal modulation masking patterns that were in agreement with the hypothesis of spectro-temporal modulation filters in the human auditory system [Oetjen and Verhey (2015). J. Acoust. Soc. Am. 137(2), 714-723]. In the present study, that experimental data and additional data were used to model this spectro-temporal frequency selectivity. The additional data were collected to investigate to what extent the spectro-temporal modulation-frequency selectivity results from a combination of a purely temporal amplitude-modulation filter and a purely spectral amplitude-modulation filter. In contrast to the previous study, thresholds were measured for masker and target modulations with opposite directions, i.e., an upward pointing target modulation and a downward pointing masker modulation. The comparison of this data set with previous corresponding data with the same direction from target and masker modulations indicate that a specific spectro-temporal modulation filter is required to simulate all aspects of spectro-temporal modulation frequency selectivity. A model using a modified Gabor filter with a purely temporal and a purely spectral filter predicts the spectro-temporal modulation masking data.

  7. A time domain frequency-selective multivariate Granger causality approach.

    PubMed

    Leistritz, Lutz; Witte, Herbert

    2016-08-01

    The investigation of effective connectivity is one of the major topics in computational neuroscience to understand the interaction between spatially distributed neuronal units of the brain. Thus, a wide variety of methods has been developed during the last decades to investigate functional and effective connectivity in multivariate systems. Their spectrum ranges from model-based to model-free approaches with a clear separation into time and frequency range methods. We present in this simulation study a novel time domain approach based on Granger's principle of predictability, which allows frequency-selective considerations of directed interactions. It is based on a comparison of prediction errors of multivariate autoregressive models fitted to systematically modified time series. These modifications are based on signal decompositions, which enable a targeted cancellation of specific signal components with specific spectral properties. Depending on the embedded signal decomposition method, a frequency-selective or data-driven signal-adaptive Granger Causality Index may be derived.

  8. Optimal Power Schedule for Distributed MIMO Links

    DTIC Science & Technology

    2006-11-01

    INTRODUCTION A multiple - input multiple - output ( MIMO ) wireless link is well known to provide a much higher capacity than a single- input single- output ...However, for a wireless network of multiple distributed MIMO links, such as a network in the future combat sys- tems, there are new issues of research...The existing MIMO theory is not sufficient for such a wireless network where multiple MIMO links cause mutual interferences to each other. This

  9. Robust High Data Rate MIMO Underwater Acoustic Communications

    DTIC Science & Technology

    2010-12-31

    Figure 2, on the other hand, plots the evolution of the Doppler frequency for each hydrophone. The reverberating Doppler frequency estimates obtained...Figure 3, by feeding 250 source bits into a 1/2 rate convolutional encoder followed by a random interleaver and QPSK modulation. Segment b, as well as...by leveraging the MIMO scheme. The payload sequence was divided into blocks, each of length 250, and each block was encoded using a lA convolutional

  10. Spectro-temporal modulation masking patterns reveal frequency selectivity.

    PubMed

    Oetjen, Arne; Verhey, Jesko L

    2015-02-01

    The present study investigated the possibility that the human auditory system demonstrates frequency selectivity to spectro-temporal amplitude modulations. Threshold modulation depth for detecting sinusoidal spectro-temporal modulations was measured using a generalized masked threshold pattern paradigm with narrowband masker modulations. Four target spectro-temporal modulations were examined, differing in their temporal and spectral modulation frequencies: a temporal modulation of -8, 8, or 16 Hz combined with a spectral modulation of 1 cycle/octave and a temporal modulation of 4 Hz combined with a spectral modulation of 0.5 cycles/octave. The temporal center frequencies of the masker modulation ranged from 0.25 to 4 times the target temporal modulation. The spectral masker-modulation center-frequencies were 0, 0.5, 1, 1.5, and 2 times the target spectral modulation. For all target modulations, the pattern of average thresholds for the eight normal-hearing listeners was consistent with the hypothesis of a spectro-temporal modulation filter. Such a pattern of modulation-frequency sensitivity was predicted on the basis of psychoacoustical data for purely temporal amplitude modulations and purely spectral amplitude modulations. An analysis of separability indicates that, for the present data set, selectivity in the spectro-temporal modulation domain can be described by a combination of a purely spectral and a purely temporal modulation filter function.

  11. Learning natural selection from the site frequency spectrum.

    PubMed

    Ronen, Roy; Udpa, Nitin; Halperin, Eran; Bafna, Vineet

    2013-09-01

    Genetic adaptation to external stimuli occurs through the combined action of mutation and selection. A central problem in genetics is to identify loci responsive to specific selective constraints. Many tests have been proposed to identify the genomic signatures of natural selection by quantifying the skew in the site frequency spectrum (SFS) under selection relative to neutrality. We build upon recent work that connects many of these tests under a common framework, by describing how selective sweeps affect the scaled SFS. We show that the specific skew depends on many attributes of the sweep, including the selection coefficient and the time under selection. Using supervised learning on extensive simulated data, we characterize the features of the scaled SFS that best separate different types of selective sweeps from neutrality. We develop a test, SFselect, that consistently outperforms many existing tests over a wide range of selective sweeps. We apply SFselect to polymorphism data from a laboratory evolution experiment of Drosophila melanogaster adapted to hypoxia and identify loci that strengthen the role of the Notch pathway in hypoxia tolerance, but were missed by previous approaches. We further apply our test to human data and identify regions that are in agreement with earlier studies, as well as many novel regions.

  12. Detecting and Measuring Selection from Gene Frequency Data

    PubMed Central

    Vitalis, Renaud; Gautier, Mathieu; Dawson, Kevin J.; Beaumont, Mark A.

    2014-01-01

    The recent advent of high-throughput sequencing and genotyping technologies makes it possible to produce, easily and cost effectively, large amounts of detailed data on the genotype composition of populations. Detecting locus-specific effects may help identify those genes that have been, or are currently, targeted by natural selection. How best to identify these selected regions, loci, or single nucleotides remains a challenging issue. Here, we introduce a new model-based method, called SelEstim, to distinguish putative selected polymorphisms from the background of neutral (or nearly neutral) ones and to estimate the intensity of selection at the former. The underlying population genetic model is a diffusion approximation for the distribution of allele frequency in a population subdivided into a number of demes that exchange migrants. We use a Markov chain Monte Carlo algorithm for sampling from the joint posterior distribution of the model parameters, in a hierarchical Bayesian framework. We present evidence from stochastic simulations, which demonstrates the good power of SelEstim to identify loci targeted by selection and to estimate the strength of selection acting on these loci, within each deme. We also reanalyze a subset of SNP data from the Stanford HGDP–CEPH Human Genome Diversity Cell Line Panel to illustrate the performance of SelEstim on real data. In agreement with previous studies, our analyses point to a very strong signal of positive selection upstream of the LCT gene, which encodes for the enzyme lactase–phlorizin hydrolase and is associated with adult-type hypolactasia. The geographical distribution of the strength of positive selection across the Old World matches the interpolated map of lactase persistence phenotype frequencies, with the strongest selection coefficients in Europe and in the Indus Valley. PMID:24361938

  13. Infrared transparent frequency selective surface based on metallic meshes

    SciTech Connect

    Yu, Miao; Xu, Nianxi; Liu, Hai; Gao, Jinsong

    2014-02-15

    This paper presents an infrared transparent frequency selective surface (ITFSS) based on metallic meshes. In this ITFSS structure, periodic cross-slot units are integrated on square metallic meshes empowered by coating and UV-lithography. A matching condition is proposed to avoid the distortion of units. Experimental results show that this ITFSS possesses a good transmittance of 80% in the infrared band of 3–5 μm, and also a stable band-pass behavior at the resonance frequency of 36.4 GHz with transmittance of −0.56 dB. Theoretical simulations about the ITFSS diffractive characteristics and frequency responses are also investigated. The novel ITFSS will attract renewed interest and be exploited for applications in various fields.

  14. Mechanical stress-controlled tunable active frequency-selective surface

    NASA Astrophysics Data System (ADS)

    Huang, Bo-Cin; Hong, Jian-Wei; Lo, Cheng-Yao

    2017-01-01

    This study proposes a tunable active frequency-selective surface (AFSS) realized by mechanically expanding or contracting a split-ring resonator (SRR) array. The proposed AFSS transfers mechanical stress from its elastic substrate to the top of the SRR, thereby achieving electromagnetic (EM) modulation without the need for an additional external power supply, meeting the requirements for the target application: the invisibility cloak. The operating mechanism of the proposed AFSS differs from those of other AFSSs, supporting modulations in arbitrary frequencies in the target range. The proposed stress-controlled or strain-induced EM modulation proves the existence of an identical and linear relationship between the strain gradient and the frequency shift, implying its suitability for other EM modulation ranges and applications.

  15. Frequency Selective Surface Based Bandpass Filter for THz Communication System

    NASA Astrophysics Data System (ADS)

    Das, Subrata; Reza, Khan Mamun; Habib, Md. Ahsan

    2012-11-01

    In this work, a band pass filter based on frequency selective surface (FSS) is presented. The resonance of the FSS is achieved by perforating slot type ring structure on an Aluminum layer. To ensure adequate mechanical strength, this structure is again supported by a dielectric layer. The physical dimensions of the FSS, i.e. ring radius, slot width, cell dimension and width of the layers all are responsible for the resonance behavior. In its electrical equivalent circuit, these dimensions act as inductor and capacitor. The center frequency of the designed filter is at 0.16 THz with a -3 dB bandwidth of 18 GHz. This filter can be utilized as a part of any THz communication system to achieve application specific frequency discrimination. The simulation has been carried by using commercial software-CST Microwave Studio. The performance of the fabricated FSS is evaluated by Microwave Vector Network Analyzer.

  16. Frequency selection for magnetization switching in spin torque magnetic memory

    NASA Astrophysics Data System (ADS)

    Sbiaa, Rachid

    2015-03-01

    The change of magnetization states by spin transfer torque brought momentum to research on magnetic random access memory (MRAM), however, there is still a need for improvement of memory performances. The conventional multi-bit per cell (MBPC) scheme has the potential of increasing the storage capacity of MRAM but the overwritability issue remains the major drawback of this scheme. In fact, for systems with more than one free layer, the low anisotropy layer can have its magnetization reversed during the writing on the higher anisotropy one. To access each free layer independently, a spin torque oscillator with an optimal frequency is proposed to assist the magnetization switching. This study reveals that the free layer magnetization can be reversed through a selection of a frequency value which depends on its intrinsic magnetic properties. This resonance phenomenon based on frequency selection and spin transfer torque effect can be used for writing in the MBPC scheme without undesirable overwriting. A spin torque oscillator with an optimal frequency integrated with a conventional magnetic tunnel junction could be the platform of future magnetic memory.

  17. Massive MIMO-OFDM indoor visible light communication system downlink architecture design

    NASA Astrophysics Data System (ADS)

    Lang, Tian; Li, Zening; Chen, Gang

    2014-10-01

    Multiple-input multiple-output (MIMO) technique is now used in most new broadband communication system, and orthogonal frequency division multiplexing (OFDM) is also utilized within current 4th generation (4G) of mobile telecommunication technology. With MIMO and OFDM combined, visible light communication (VLC) system's diversity gain is increase, yet system capacity for dispersive channels is also enhanced. Moreover, with the emerging massive MIMO-OFDM VLC system, there are significant advantages than smaller systems' such as channel hardening, further increasing of energy efficiency (EE) and spectral efficiency (SE) based on law of large number. This paper addresses one of the major technological challenges, system architecture design, which was solved by semispherical beehive structure (SBS) receiver and so that diversity gain can be identified and applied in Massive MIMO VLC system. Simulation results shows that the proposed design clearly presents a spatial diversity over conventional VLC systems.

  18. Analysis of tuning methods in semiconductor frequency-selective surfaces

    NASA Astrophysics Data System (ADS)

    Shemelya, Corey; Palm, Dominic; Fip, Tassilo; Rahm, Marco

    2017-02-01

    Advanced technology, such as sensing and communication equipment, has recently begun to combine optically sensitive nano-scale structures with customizable semiconductor material systems. Included within this broad field of study is the aptly named frequency-selective surface; which is unique in that it can be artificially designed to produce a specific electromagnetic or optical response. With the inherent utility of a frequency-selective surface, there has been an increased interest in the area of dynamic frequency-selective surfaces, which can be altered through optical or electrical tuning. This area has had exciting break throughs as tuning methods have evolved; however, these methods are typically energy intensive (optical tuning) or have met with limited success (electrical tuning). As such, this work investigates multiple structures and processes which implement semiconductor electrical biasing and/or optical tuning. Within this study are surfaces ranging from transmission meta-structures to metamaterial surface-waves and the associated coupling schemes. This work shows the utility of each design, while highlighting potential methods for optimizing dynamic meta-surfaces. As an added constraint, the structures were also designed to operate in unison with a state-of-the-art Ti:Sapphire Spitfire Ace and Spitfire Ace PA dual system (12 Watt) with pulse front matching THz generation and an EOS detection system. Additionally, the Ti:Sapphire laser system would provide the means for optical tunablity, while electrical tuning can be obtained through external power supplies.

  19. Joint Channel and Phase Noise Estimation in MIMO-OFDM Systems

    NASA Astrophysics Data System (ADS)

    Ngebani, I. M.; Chuma, J. M.; Zibani, I.; Matlotse, E.; Tsamaase, K.

    2017-05-01

    The combination of multiple-input multiple-output (MIMO) techniques with orthogonal frequency division multiplexing (OFDM), MIMO-OFDM, is a promising way of achieving high spectral efficiency in wireless communication systems. However, the performance of MIMO-ODFM systems is highly degraded by radio frequency (RF) impairments such as phase noise. Similar to the single-input single-output (SISO) case, phase noise in MIMO-OFDM systems results in a common phase error (CPE) and inter carrier interference (ICI). In this paper the problem of joint channel and phase noise estimation in a system with multiple transmit and receive antennas where each antenna is equipped with its own independent oscillator is tackled. The technique employed makes use of a novel placement of pilot carriers in the preamble and data portion of the MIMO-OFDM frame. Numerical results using a 16 and 64 quadrature amplitude modulation QAM schemes are provided to illustrate the effectiveness of the proposed scheme for MIMO-OFDM systems.

  20. A Differential MIMO SC-FDE Transceiver Design over Multipath Fast Fading Channels

    NASA Astrophysics Data System (ADS)

    Deng, Juinn-Horng; Hwang, Jeng-Kuang

    In this paper, we propose a new differential MIMO single-carrier system with frequency-domain equalization (SC-FDE) aided by the insertion of cyclic prefix. This block transmission system not only inherits all the merits of the SISO SC-FDE system, but is also equipped with a differential space-time block coding (DSTBC) such as to combat the fast-changing frequency selective fading channels without the needs to estimate and then compensate the channel effects. Hence, for practical applications, it has the additional merits of decoding simplicity and robustness against high mobility transmission environments. Computer simulations show that the proposed system can provide diversity benefit as the non-differential system does, while greatly reducing the receiver complexity.

  1. Estimating cochlear frequency selectivity with stimulus-frequency otoacoustic emissions in chinchillas.

    PubMed

    Charaziak, Karolina K; Siegel, Jonathan H

    2014-12-01

    It has been suggested that the tuning of the cochlear filters can be derived from measures of otoacoustic emissions (OAEs). Two approaches have been proposed to estimate cochlear frequency selectivity using OAEs evoked with a single tone (stimulus-frequency (SF)) OAEs: based on SFOAE group delays (SF-GDs) and on SFOAE suppression tuning curves (SF-STCs). The aim of this study was to evaluate whether either SF-GDs or SF-STCs obtained with low probe levels (30 dB SPL) correlate with more direct measures of cochlear tuning (compound action potential suppression tuning curves (CAP-STCs)) in chinchillas. The SFOAE-based estimates of tuning covaried with CAP-STCs tuning for >3 kHz probe frequencies, indicating that these measures are related to cochlear frequency selectivity. However, the relationship may be too weak to predict tuning with either SFOAE method in an individual. The SF-GD prediction of tuning was sharper than CAP-STC tuning. On the other hand, SF-STCs were consistently broader than CAP-STCs implying that SFOAEs may have less restricted region of generation in the cochlea than CAPs. Inclusion of <3 kHz data in a statistical model resulted in no significant or borderline significant covariation among the three methods: neither SFOAE test appears to reliably estimate an individual's CAP-STC tuning at low-frequencies. At the group level, SF-GDs and CAP-STCs showed similar tuning at low frequencies, while SF-STCs were over five times broader than the CAP-STCs indicating that low-frequency SFOAE may originate over a very broad region of the cochlea extending ≥5 mm basal to the tonotopic place of the probe.

  2. All-printed, flexible, reconfigurable frequency selective surfaces

    NASA Astrophysics Data System (ADS)

    Haghzadeh, Mahdi; Akyurtlu, Alkim

    2016-11-01

    We demonstrate a new fully printed, conformal, band-pass frequency selective surface (FSS) utilizing a novel interdigitated capacitor (IDC), in which the space between the fingers can be filled with dielectric materials with different dielectric constants. Every dielectric constant corresponds to a different resonance frequency for the FSS, leading to a bandpass performance that can be tuned in a static manner based on the dielectric choice. The 2-D FSS consists of a periodic array of non-resonant and subwavelength structures (i.e., a metallic square loop and a wire grid) printed on either side of a flexible polyimide film using direct-ink writing methodologies. The miniaturized-element nature of this metamaterial-inspired FSS results in localized frequency-selective properties with very low sensitivity to the angle of incidence. Moreover, its symmetric design makes it polarization independent. A multiphase barium strontium titanate/cyclic olefin copolymer (BST/COC) composite with two different BST loadings, corresponding to two different dielectric constants, is the dielectric ink that is printed on the IDCs to vary the resonance frequency of the FSS. Different models of the FSS involving various IDC designs, with a first-order bandpass response at X-band, were simulated, printed, and measured. The center frequency of the template FSS with the air-filled IDC was tuned by 4.52% and 21.08% from 9.96 GHz by printing BST/COC dielectrics with different BST loadings on the IDCs. Moreover, the operation mode of the FSS was switched from a first order filter to a dual-band filter using printed BST/COC ink in a novel FSS design.

  3. The perceived spatial frequency shift: evidence for frequency-selective neurones in the human brain

    PubMed Central

    Blakemore, Colin; Nachmias, Jacob; Sutton, Peter

    1970-01-01

    1. Prolonged observation of a high-contrast grating pattern causes an apparent shift in the spatial frequency of gratings subsequently viewed with the same retinal region. Gratings of higher and lower frequency than the adapting pattern seem, respectively, higher and lower than in fact they are. 2. There is no significant after-effect at the adapting frequency itself nor at frequencies more than two octaves away. 3. For very low adapting frequencies, the after-effect remains centred at about 3·0 c/deg and declines in strength as the adapting frequency is successively lowered. 4. The magnitude of the after-effect increases with the contrast of the adapting grating and the length of time spent in adaptation. It takes several hours to recover completely from 30 min adaptation. 5. The phenomenon is orientation-specific: a horizontal adapting grating has no effect on vertical test gratings. There is partial interocular transfer of the after-effect. 6. These findings provide further evidence that the visual system of man, like those of the cat and the monkey, contains neurones selectively sensitive to the orientation and dimensions of retinal images, and that these adaptable cells are actually involved in the encoding and perception of the size of simple patterns. PMID:5499822

  4. Frequency selective bolometer development at Argonne National Laboratory.

    SciTech Connect

    Datesman, A.; Pearson, J.; Wang, G.; Yefremenko, V.; Divan, R.; Downes, T.; Chang, C.; McMahon, J.; Meyer, S.; Carlstrom, J.; Logan, D.; Perera, T.; Wilson, G.; Novosad, V.; Univ. of Chicago; Univ. of Massachusetts

    2008-07-01

    We discuss the development, at Argonne National Laboratory, of a four-pixel camera suitable for photometry of distant dusty galaxies located by Spitzer and SCUBA, and for study of other millimeter-wave sources such as ultra-luminous infrared galaxies, the Sunyaev-Zeldovich (SZ) effect in clusters, and galactic dust. Utilizing Frequency Selective Bolometers (FSBs) with superconducting Transition-Edge Sensors (TESs), each of the camera's four pixels is sensitive to four colors, with frequency bands centered approximately at 150, 220, 270, and 360 GHz. The current generation of these devices utilizes proximity effect superconducting bilayers of Mo/Au or Ti/Au for TESs, along with frequency selective circuitry on membranes of silicon nitride 1 cm across and 1 micron thick. The operational properties of these devices are determined by this circuitry, along with thermal control structures etched into the membranes. These etched structures do not perforate the membrane, so that the device is both comparatively robust mechanically and carefully tailored in terms of its thermal transport properties. In this paper, we report on development of the superconducting bilayer TES technology and characterization of the FSB stacks. This includes the use of new materials, the design and testing of thermal control structures, the introduction of desirable thermal properties using buried layers of crystalline silicon underneath the membrane, detector stability control, and optical and thermal test results. The scientific motivation, FSB design, FSB fabrication, and measurement results are discussed.

  5. Frequency selective detection of nuclear quadrupole resonance (NQR) spin echoes

    NASA Astrophysics Data System (ADS)

    Somasundaram, Samuel D.; Jakobsson, Andreas; Smith, John A. S.; Althoefer, Kaspar A.

    2006-05-01

    Nuclear Quadrupole Resonance (NQR) is a radio frequency (RF) technique that can be used to detect the presence of quadrupolar nuclei, such as the 14N nucleus prevalent in many explosives and narcotics. The technique has been hampered by low signal-to-noise ratios and is further aggravated by the presence of RF interference (RFI). To ensure accurate detection, proposed detectors should exploit the rich form of the NQR signal. Furthermore, the detectors should also be robust to any remaining residual interference, left after suitable RFI mitigation has been employed. In this paper, we propose a new NQR data model, particularly for the realistic case where multiple pulse sequences are used to generate trains of spin echoes. Furthermore, we refine two recently proposed approximative maximum likelihood (AML) detectors, enabling the algorithm to optimally exploit the data model of the entire echo train and also incorporate knowledge of the temperature dependent spin-echo decay time. The AML-based detectors ensure accurate detection and robustness against residual RFI, even when the temperature of the sample is not precisely known, by exploiting the dependencies of the NQR resonant lines on temperature. Further robustness against residual interference is gained as the proposed detector is frequency selective; exploiting only those regions of the spectrum where the NQR signal is expected. Extensive numerical evaluations based on both simulated and measured NQR data indicate that the proposed Frequency selective Echo Train AML (FETAML) detector offers a significant improvement as compared to other existing detectors.

  6. Improved Stack Algorithm for MIMO Wireless Communication Systems

    NASA Astrophysics Data System (ADS)

    Liu, Li; Wang, Jinkuan; Yan, Dongmei; Du, Ruiyan; Wang, Bin

    The use of multiple antennas at both transmitter and receiver can increase wireless communication system capacity enormously. The optimal detection algorithm for MIMO system is Maximum likelihood detection (MLD) algorithm, which provides the best bit error rate (BER) performance for MIMO system. However, the computational complexity of MLD algorithm grows exponentially with the number of transmit antennas and the order of modulation. An improved MIMO detection algorithm which combined M-algorithm with stack algorithm was presented in this paper. The proposed algorithm was a multistage detection which was consisted with three parts: MLD, M-algorithm and stack algorithm. In MIMO communication system with m transmit antennas, after performing QR decomposition of the channel matrix, the MLD with length L was done firstly. The partial accumulated metrics were calculated and sorted, which produced an ordered set. Then selecting the first M partial symbol vectors to form a new ordered set. Based on the new ordered set, stack algorithm was performed to search for the symbols with the minimum accumulated metrics. The proposed algorithm combining M algorithm and stack algorithm reduced numbers of ordering with the original stack algorithm, the probability of look back and improving the detection performance.

  7. High Frequency Performance of SiGeC HBTs with Selectively & Non-Selectively Grown Collector

    NASA Astrophysics Data System (ADS)

    Suvar, Erdal; Haralson, Erik; Radamson, Henry H.; Wang, Yong-Bin; Malm, B. Gunnar; Östling, Mikael

    2004-01-01

    Two high-frequency heterojunction bipolar transistor (HBT) architectures based on SiGeC have been fabricated and characterized. Different collector designs were applied either by using selective epitaxial growth doped with phosphorous or by nonselective epitaxial growth doped with arsenic. Both designs have a nonselectively deposited SiGeC base doped with boron and a poly-crystalline emitter doped with phosphorous. Both HBT designs exhibit similar electrical characteristics with a peak DC current gain of around 1600 and a BVCEO of 1.8V. The cut-off frequency (fT) and maximum frequency of oscillation (fmax) vary from 40 80GHz and 15 30GHz, respectively, depending on lateral design relations. Good high frequency performance for a device with a selectively grown collector is demonstrated for the first time.

  8. Broadbeam for Massive MIMO Systems

    NASA Astrophysics Data System (ADS)

    Qiao, Deli; Qian, Haifeng; Li, Geoffrey Ye

    2016-05-01

    Massive MIMO has been identified as one of the promising disruptive air interface techniques to address the huge capacity requirement demanded by 5G wireless communications. For practical deployment of such systems, the control message need to be broadcast to all users reliably in the cell using broadbeam. A broadbeam is expected to have the same radiated power in all directions to cover users in any place in a cell. In this paper, we will show that there is no perfect broadbeam. Therefore, we develop a method for generating broadbeam that can allow tiny fluctuations in radiated power. Overall, this can serve as an ingredient for practical deployment of the massive MIMO systems.

  9. Optical frequency tripling with improved suppression and sideband selection.

    PubMed

    Thakur, Manoj P; Medeiros, Maria C R; Laurêncio, Paula; Mitchell, John E

    2011-12-12

    A novel optical dispersion tolerant millimetre-wave radio-over-fibre system using optical frequency tripling technique with enhanced and selectable sideband suppression is demonstrated. The implementation utilises cascaded optical modulators to achieve either an optical single sideband (OSSB) or double sideband-suppressed carrier (DSB-SC) signal with high sideband suppression. Our analysis and simulation results indicate that the achievable suppression ratio of this configuration is only limited by other system factors such as optical noise and drifting of the operational conditions. The OSSB transmission system performance is assessed experimentally by the transport of 4 WiMax channels modulating a 10 GHz optical upconverted RF carrier as well as for optical frequency doubling and tripling. The 10 GHz and tripled carrier at 30 GHz are dispersion tolerant resulting both in an average relative constellation error (RCE) of -28.7 dB after 40 km of fibre.

  10. A novel broadband bi-mode active frequency selective surface

    NASA Astrophysics Data System (ADS)

    Xu, Yang; Gao, Jinsong; Xu, Nianxi; Shan, Dongzhi; Song, Naitao

    2017-05-01

    A novel broadband bi-mode active frequency selective surface (AFSS) is presented in this paper. The proposed structure is composed of a periodic array of convoluted square patches and Jerusalem Crosses. According to simulation results, the frequency response of AFSS definitely exhibits a mode switch feature between band-pass and band-stop modes when the diodes stay in ON and OFF states. In order to apply a uniform bias to each PIN diode, an ingenious biasing network based on the extension of Wheatstone bridge is adopted in prototype AFSS. The test results are in good agreement with the simulation results. A further physical mechanism of the bi-mode AFSS is shown by contrasting the distribution of electric field on the AFSS patterns for the two working states.

  11. DNP enhanced frequency-selective TEDOR experiments in bacteriorhodopsin

    NASA Astrophysics Data System (ADS)

    Bajaj, Vikram S.; Mak-Jurkauskas, Melody L.; Belenky, Marina; Herzfeld, Judith; Griffin, Robert G.

    2010-01-01

    We describe a new approach to multiple 13C- 15N distance measurements in uniformly labeled solids, frequency-selective (FS) TEDOR. The method shares features with FS-REDOR and ZF- and BASE-TEDOR, which also provide quantitative 15N- 13C spectral assignments and distance measurements in U-[ 13C, 15N] samples. To demonstrate the validity of the FS-TEDOR sequence, we measured distances in [U- 13C, 15N]-asparagine which are in good agreement with other methods. In addition, we integrate high frequency dynamic nuclear polarization (DNP) into the experimental protocol and use FS-TEDOR to record a resolved correlation spectrum of the Arg- 13C γ- 15N ɛ region in [U- 13C, 15N]-bacteriorhodopsin. We resolve six of the seven cross-peaks expected based on the primary sequence of this membrane protein.

  12. A flexible and rapid frequency selective scheme for SRS microscopy

    NASA Astrophysics Data System (ADS)

    Li, Jingting; Yue, Yuankai; Shih, Wei-Chuan

    2017-02-01

    Stimulated Raman scattering (SRS) is a label-free imaging technique suitable for studying biological systems. Due to stimulated nature by ultrafast laser pulses, SRS microscopy has the advantage of significantly higher sensitivity but often reduced spectroscopic information. In this paper, we present a newly constructed femtosecond SRS microscope with a high-speed dynamic micromirror device based pulse shaper to achieve flexible and rapid frequency selection within the C-H stretch region near 2800 to 3100 cm-1 with spectral width of 30 cm-1. This technique is applicable to lipid profiling such as cell activity mapping, lipid distribution mapping and distinction among subclasses.

  13. TFSSRA - THICK FREQUENCY SELECTIVE SURFACE WITH RECTANGULAR APERTURES

    NASA Technical Reports Server (NTRS)

    Chen, J. C.

    1994-01-01

    Thick Frequency Selective Surface with Rectangular Apertures (TFSSRA) was developed to calculate the scattering parameters for a thick frequency selective surface with rectangular apertures on a skew grid at oblique angle of incidence. The method of moments is used to transform the integral equation into a matrix equation suitable for evaluation on a digital computer. TFSSRA predicts the reflection and transmission characteristics of a thick frequency selective surface for both TE and TM orthogonal linearly polarized plane waves. A model of a half-space infinite array is used in the analysis. A complete set of basis functions with unknown coefficients is developed for the waveguide region (waveguide modes) and for the free space region (Floquet modes) in order to represent the electromagnetic fields. To ensure the convergence of the solutions, the number of waveguide modes is adjustable. The method of moments is used to compute the unknown mode coefficients. Then, the scattering matrix of the half-space infinite array is calculated. Next, the reference plane of the scattering matrix is moved half a plate thickness in the negative z-direction, and a frequency selective surface of finite thickness is synthesized by positioning two plates of half-thickness back-to-back. The total scattering matrix is obtained by cascading the scattering matrices of the two half-space infinite arrays. TFSSRA is written in FORTRAN 77 with single precision. It has been successfully implemented on a Sun4 series computer running SunOS, an IBM PC compatible running MS-DOS, and a CRAY series computer running UNICOS, and should run on other systems with slight modifications. Double precision is recommended for running on a PC if many modes are used or if high accuracy is required. This package requires the LINPACK math library, which is included. TFSSRA requires 1Mb of RAM for execution. The standard distribution medium for this program is one 5.25 inch 360K MS-DOS format diskette. It is also

  14. Frequency-dependent selection and the evolution of assortative mating.

    PubMed

    Otto, Sarah P; Servedio, Maria R; Nuismer, Scott L

    2008-08-01

    A long-standing goal in evolutionary biology is to identify the conditions that promote the evolution of reproductive isolation and speciation. The factors promoting sympatric speciation have been of particular interest, both because it is notoriously difficult to prove empirically and because theoretical models have generated conflicting results, depending on the assumptions made. Here, we analyze the conditions under which selection favors the evolution of assortative mating, thereby reducing gene flow between sympatric groups, using a general model of selection, which allows fitness to be frequency dependent. Our analytical results are based on a two-locus diploid model, with one locus altering the trait under selection and the other locus controlling the strength of assortment (a "one-allele" model). Examining both equilibrium and nonequilibrium scenarios, we demonstrate that whenever heterozygotes are less fit, on average, than homozygotes at the trait locus, indirect selection for assortative mating is generated. While costs of assortative mating hinder the evolution of reproductive isolation, they do not prevent it unless they are sufficiently great. Assortative mating that arises because individuals mate within groups (formed in time or space) is most conducive to the evolution of complete assortative mating from random mating. Assortative mating based on female preferences is more restrictive, because the resulting sexual selection can lead to loss of the trait polymorphism and cause the relative fitness of heterozygotes to rise above homozygotes, eliminating the force favoring assortment. When assortative mating is already prevalent, however, sexual selection can itself cause low heterozygous fitness, promoting the evolution of complete reproductive isolation (akin to "reinforcement") regardless of the form of natural selection.

  15. High efficiency in mode-selective frequency conversion.

    PubMed

    Quesada, Nicolás; Sipe, J E

    2016-01-15

    Frequency conversion (FC) is an enabling process in many quantum information protocols. Recently, it has been observed that upconversion efficiencies in single-photon, mode-selective FC are limited to around 80%. In this Letter, we argue that these limits can be understood as time-ordering corrections (TOCs) that modify the joint conversion amplitude of the process. Furthermore, using a simple scaling argument, we show that recently proposed cascaded FC protocols that overcome the aforementioned limitations act as "attenuators" of the TOCs. This observation allows us to argue that very similar cascaded architectures can be used to attenuate TOCs in photon generation via spontaneous parametric downconversion. Finally, by using the Magnus expansion, we argue that the TOCs, which are usually considered detrimental for FC efficiency, can also be used to increase the efficiency of conversion in partially mode-selective FC.

  16. Performance analysis of cooperative virtual MIMO systems for wireless sensor networks.

    PubMed

    Rafique, Zimran; Seet, Boon-Chong; Al-Anbuky, Adnan

    2013-05-28

    Multi-Input Multi-Output (MIMO) techniques can be used to increase the data rate for a given bit error rate (BER) and transmission power. Due to the small form factor, energy and processing constraints of wireless sensor nodes, a cooperative Virtual MIMO as opposed to True MIMO system architecture is considered more feasible for wireless sensor network (WSN) applications. Virtual MIMO with Vertical-Bell Labs Layered Space-Time (V-BLAST) multiplexing architecture has been recently established to enhance WSN performance. In this paper, we further investigate the impact of different modulation techniques, and analyze for the first time, the performance of a cooperative Virtual MIMO system based on V-BLAST architecture with multi-carrier modulation techniques. Through analytical models and simulations using real hardware and environment settings, both communication and processing energy consumptions, BER, spectral efficiency, and total time delay of multiple cooperative nodes each with single antenna are evaluated. The results show that cooperative Virtual-MIMO with Binary Phase Shift Keying-Wavelet based Orthogonal Frequency Division Multiplexing (BPSK-WOFDM) modulation is a promising solution for future high data-rate and energy-efficient WSNs.

  17. Performance Analysis of Cooperative Virtual MIMO Systems for Wireless Sensor Networks

    PubMed Central

    Rafique, Zimran; Seet, Boon-Chong; Al-Anbuky, Adnan

    2013-01-01

    Multi-Input Multi-Output (MIMO) techniques can be used to increase the data rate for a given bit error rate (BER) and transmission power. Due to the small form factor, energy and processing constraints of wireless sensor nodes, a cooperative Virtual MIMO as opposed to True MIMO system architecture is considered more feasible for wireless sensor network (WSN) applications. Virtual MIMO with Vertical-Bell Labs Layered Space-Time (V-BLAST) multiplexing architecture has been recently established to enhance WSN performance. In this paper, we further investigate the impact of different modulation techniques, and analyze for the first time, the performance of a cooperative Virtual MIMO system based on V-BLAST architecture with multi-carrier modulation techniques. Through analytical models and simulations using real hardware and environment settings, both communication and processing energy consumptions, BER, spectral efficiency, and total time delay of multiple cooperative nodes each with single antenna are evaluated. The results show that cooperative Virtual-MIMO with Binary Phase Shift Keying-Wavelet based Orthogonal Frequency Division Multiplexing (BPSK-WOFDM) modulation is a promising solution for future high data-rate and energy-efficient WSNs. PMID:23760087

  18. Spatial tuning of a RF frequency selective surface through origami

    NASA Astrophysics Data System (ADS)

    Fuchi, Kazuko; Buskohl, Philip R.; Bazzan, Giorgio; Durstock, Michael F.; Joo, James J.; Reich, Gregory W.; Vaia, Richard A.

    2016-05-01

    Origami devices have the ability to spatially reconfigure between 2D and 3D states through folding motions. The precise mapping of origami presents a novel method to spatially tune radio frequency (RF) devices, including adaptive antennas, sensors, reflectors, and frequency selective surfaces (FSSs). While conventional RF FSSs are designed based upon a planar distribution of conductive elements, this leaves the large design space of the out of plane dimension underutilized. We investigated this design regime through the computational study of four FSS origami tessellations with conductive dipoles. The dipole patterns showed increased resonance shift with decreased separation distances, with the separation in the direction orthogonal to the dipole orientations having a more significant effect. The coupling mechanisms between dipole neighbours were evaluated by comparing surface charge densities, which revealed the gain and loss of coupling as the dipoles moved in and out of alignment via folding. Collectively, these results provide a basis of origami FSS designs for experimental study and motivates the development of computational tools to systematically predict optimal fold patterns for targeted frequency response and directionality.

  19. TES development for a frequency selective bolometer camera.

    SciTech Connect

    Datesman, A. M.; Downes, T. P.; Perera, T. A.; Wang, G.; Yefremenko, V. G.; Pearson, J. E.; Novosad, V.; Divan, R.; Chang, C. L.; Logan, D. W.; Meyer, S. S.; Wilson , G. W.; Bleem, L. E.; Crites, A. T.; McMahon, J. J.; Carlstrom, J. E.; Materials Science Division; Kavli Inst. Cosmological Phys.; Univ. of Massachusetts

    2009-06-01

    We discuss the development, at Argonne National Laboratory (ANL), of a four-pixel camera with four spectral channels centered at 150, 220, 270, and 360 GHz. The scientific motivation involves photometry of distant dusty galaxies located by Spitzer and SCUBA, as well as the study of other millimeter-wave sources such as ultra-luminous infrared galaxies, the Sunyaev-Zeldovich effect in clusters, and galactic dust. The camera incorporates Frequency Selective Bolometer (FSB) and superconducting Transition-Edge Sensor (TES) technology. The current generation of TES devices we examine utilizes proximity effect superconducting bilayers of Mo/Au, Ti, or Ti/Au as TESs, located along with frequency selective absorbing structures on silicon nitride membranes. The detector incorporates lithographically patterned structures designed to address both TES device stability and detector thermal transport concerns. The membrane is not perforated, resulting in a detector which is comparatively robust mechanically. In this paper, we report on the development of the superconducting bilayer TES technology, the design and testing of the detector thermal transport and device stability control structures, optical and thermal test results, and the use of new materials.

  20. Selecting Test Frequencies for Two-Tone Phase Plane Analysis of ADC's

    SciTech Connect

    Blair, J.J.

    2001-02-01

    The authors show how to select the frequencies for a two-tone sinewave test of an analog to digital converter. The frequencies are selected in a manner to guarantee nearly uniform coverage of a selected ellipse in the phase plane. A proof that the selected frequencies provide the desired coverage is given.

  1. Methods, computer readable media, and graphical user interfaces for analysis of frequency selective surfaces

    DOEpatents

    Kotter, Dale K [Shelley, ID; Rohrbaugh, David T [Idaho Falls, ID

    2010-09-07

    A frequency selective surface (FSS) and associated methods for modeling, analyzing and designing the FSS are disclosed. The FSS includes a pattern of conductive material formed on a substrate to form an array of resonance elements. At least one aspect of the frequency selective surface is determined by defining a frequency range including multiple frequency values, determining a frequency dependent permittivity across the frequency range for the substrate, determining a frequency dependent conductivity across the frequency range for the conductive material, and analyzing the frequency selective surface using a method of moments analysis at each of the multiple frequency values for an incident electromagnetic energy impinging on the frequency selective surface. The frequency dependent permittivity and the frequency dependent conductivity are included in the method of moments analysis.

  2. Double-loop frequency selective surfaces for multi frequency division multiplexing in a dual reflector antenna

    NASA Technical Reports Server (NTRS)

    Wu, Te-Kao (Inventor)

    1994-01-01

    A multireflector antenna utilizes a frequency-selective surface (FSS) in a subreflector to allow signals in two different RF bands to be selectively reflected back into a main reflector and to allow signals in other RF bands to be transmitted through it to the main reflector for primary focus transmission. A first approach requires only one FSS at the subreflector which may be an array of double-square-loop conductive elements. A second approach uses two FSS's at the subreflector which may be an array of either double-square-loop (DSL) or double-ring (DR). In the case of DR elements, they may be advantageously arranged in a triangular array instead of the rectangular array for the DSL elements.

  3. Tunable antenna radome based on graphene frequency selective surface

    NASA Astrophysics Data System (ADS)

    Qu, Meijun; Rao, Menglou; Li, Shufang; Deng, Li

    2017-09-01

    In this paper, a graphene-based frequency selective surface (FSS) is proposed. The proposed FSS exhibits a tunable bandpass filtering characteristic due to the alterable conductivity of the graphene strips which is controlled by chemical potential. Based on the reconfigurable bandpass property of the proposed FSS, a cylindrical antenna radome is designed using the FSS unit cells. A conventional omnidirectional dipole can realize a two-beam directional pattern when it is placed into the proposed antenna radome. Forward and backward endfire radiations of the dipole loaded with the radome is realized by properly adjusting the chemical potential. The proposed antenna radome is extremely promising for beam-scanning in terahertz and mid-infrared plasmonic devices and systems when the gain of a conventional antenna needs to be enhanced.

  4. Optimization of the selective frequency damping parameters using model reduction

    NASA Astrophysics Data System (ADS)

    Cunha, Guilherme; Passaggia, Pierre-Yves; Lazareff, Marc

    2015-09-01

    In the present work, an optimization methodology to compute the best control parameters, χ and Δ, for the selective frequency damping method is presented. The optimization does not suppose any a priori knowledge of the flow physics, neither of the underlying numerical methods, and is especially suited for simulations requiring large quantity of grid elements and processors. It allows for obtaining an optimal convergence rate to a steady state of the damped Navier-Stokes system. This is achieved using the Dynamic Mode Decomposition, which is a snapshot-based method, to estimate the eigenvalues associated with global unstable dynamics. Validations test cases are presented for the numerical configurations of a laminar flow past a 2D cylinder, a separated boundary-layer over a shallow bump, and a 3D turbulent stratified-Poiseuille flow.

  5. Smoothing techniques for decision-directed MIMO OFDM channel estimation

    NASA Astrophysics Data System (ADS)

    Beinschob, P.; Zölzer, U.

    2011-07-01

    With the purpose of supplying the demand of faster and more reliable communication, multiple-input multiple-output (MIMO) systems in conjunction with Orthogonal Frequency Division Multiplexing (OFDM) are subject of extensive research. Successful Decoding requires an accurate channel estimate at the receiver, which is gained either by evaluation of reference symbols which requires designated resources in the transmit signal or decision-directed approaches. The latter offers a convenient way to maximize bandwidth efficiency, but it suffers from error propagation due to the dependency between the decoding of the current data symbol and the calculation of the next channel estimate. In our contribution we consider linear smoothing techniques to mitigate error propagation by the introduction of backward dependencies in the decision-based channel estimation. Designed as a post-processing step, frame repeat requests can be lowered by applying this technique if the data is insensitive to latency. The problem of high memory requirements of FIR smoothing in the context of MIMO-OFDM is addressed with an recursive approach that acquires minimal resources with virtual no performance loss. Channel estimate normalized mean square error and bit error rate (BER) performance evaluations are presented. For reference, a median filtering technique is presented that operates on the MIMO time-frequency grids of channel coefficients to reduce the peak-like outliers produced by wrong decisions due to unsuccessful decoding. Performance in terms of Bit Error Rate is compared to the proposed smoothing techniques.

  6. Mode Selection for a Single-Frequency Fiber Laser

    NASA Technical Reports Server (NTRS)

    Liu, Jian

    2010-01-01

    A superstructured fiber-grating-based mode selection filter for a single-frequency fiber laser eliminates all free-space components, and makes the laser truly all-fiber. A ring cavity provides for stable operations in both frequency and power. There is no alignment or realignment required. After the fibers and components are spliced together and packaged, there is no need for specially trained technicians for operation or maintenance. It can be integrated with other modules, such as telescope systems, without extra optical alignment due to the flexibility of the optical fiber. The filter features a narrow line width of 1 kHz and side mode suppression ratio of 65 dB. It provides a high-quality laser for lidar in terms of coherence length and signal-to-noise ratio, which is 20 dB higher than solid-state or microchip lasers. This concept is useful in material processing, medical equipment, biomedical instrumentation, and optical communications. The pulse-shaping fiber laser can be directly used in space, airborne, and satellite applications including lidar, remote sensing, illuminators, and phase-array antenna systems.

  7. Maintenance of an aminopeptidase allele frequency cline by natural selection.

    PubMed Central

    Koehn, R K; Newell, R I; Immermann, F

    1980-01-01

    The product of the Lap locus in the marine bivalve Mytilus edulis is a neutral, membrane-associated aminopeptidase that is primarily localized on intestinal microvilli and in digestive cell lysosomes. Natural populations are genetically differentiated at the Lap locus between areas of differing salinity. A steep (0.55-0.15) allele frequency cline connects differentiated populations between the Atlantic Ocean and Long Island Sound. We demonstrate an annual gene flow/mortality cycle in cline populations whereby gene frequencies after mortality are correlated with salinity and enzyme activity. The cline is spatially and temporally unstable in immigrants, but stable in residents after mortality. Mortality is nonrandom with regard to the Lap locus; genotype-dependent properties of the aminopeptidase enzyme apparently led to a differential rate of the utilizaiton of nutrient reserves because selected genotypes exhibited an increased rate of tissue weight loss. Aminopeptidase genotypes are differentially adapted to different temperatures and salinities, which provides a mechanism for the relationship among biochemical, physiological, and population phenotypes. PMID:6933563

  8. Efficiency of model selection criteria in flood frequency analysis

    NASA Astrophysics Data System (ADS)

    Calenda, G.; Volpi, E.

    2009-04-01

    The estimation of high flood quantiles requires the extrapolation of the probability distributions far beyond the usual sample length, involving high estimation uncertainties. The choice of the probability law, traditionally based on the hypothesis testing, is critical to this point. In this study the efficiency of different model selection criteria, seldom applied in flood frequency analysis, is investigated. The efficiency of each criterion in identifying the probability distribution of the hydrological extremes is evaluated by numerical simulations for different parent distributions, coefficients of variation and skewness, and sample sizes. The compared model selection procedures are the Akaike Information Criterion (AIC), the Bayesian Information Criterion (BIC), the Anderson Darling Criterion (ADC) recently discussed by Di Baldassarre et al. (2008) and Sample Quantile Criterion (SQC), recently proposed by the authors (Calenda et al., 2009). The SQC is based on the principle of maximising the probability density of the elements of the sample that are considered relevant to the problem, and takes into account both the accuracy and the uncertainty of the estimate. Since the stress is mainly on extreme events, the SQC involves upper-tail probabilities, where the effect of the model assumption is more critical. The proposed index is equal to the sum of logarithms of the inverse of the sample probability density of the observed quantiles. The definition of this index is based on the principle that the more centred is the sample value in respect to its density distribution (accuracy of the estimate) and the less spread is this distribution (uncertainty of the estimate), the greater is the probability density of the sample quantile. Thus, lower values of the index indicate a better performance of the distribution law. This criterion can operate the selection of the optimum distribution among competing probability models that are estimated using different samples. The

  9. A TDMA MIMO SAR radar for automated position-keeping

    NASA Astrophysics Data System (ADS)

    Wang, Zhonghai; Lin, Xingping; Cumber, Steven; Fish, Ensign John; Pham, Khanh; Blasch, Erik; Chen, Genshe; Shen, Dan; Jia, Bin; Wang, Gang

    2015-05-01

    This paper presents a time division multiple access (TDMA) multiple-input and multiple-output (MIMO) synthetic aperture radar (SAR) with a sliding range window for automated position-keeping, which can be applied in vessel tracking/escorting, offshore deepwater drillship equipment servicing, etc. A MIMO SAR sensor predefines a special part of the target (i.e., the drillship, ship, or submarine) as the measurement target and does not need special assistant devices/targets installed on the target vessel/platform, so its application is convenient. In the measurement process, the sensor scans the target with multiple ranging gates, forms images of multiple sections of the target, detects the predefined part/target in these images, and then obtains the range and angle of the predefined target for relative localization. Our MIMO SAR has 13 transmitting antennas and 8 receiving antennas. All transmitting antennas share a transmitter and all receiving antennas share a receiver using switches to reduce cost. The MIMO SAR radar has 44 effective SAR phase centers, and the azimuth angle resolution is θ0.5/44 (finest, θ 0.5 is the antenna element's 3dB beamwidth). The transmitter transmits a chirped linear frequency modulated continuous wave (LFMCW) signal, and the receiver only processes the signal limited in the beat frequency region defined by the distance from the measurement target to the sensor and the interested measurement target extension, which is determined by the receiver bandwidth. With the sliding range window, the sensor covers a large range, and in the covered range window, it provides high accuracy measurements.

  10. Design and analysis of frequency-selective surface enabled microbolometers

    NASA Astrophysics Data System (ADS)

    Liu, Tao; Qu, Chuang; Almasri, Mahmoud; Kinzel, Edward

    2016-05-01

    Frequency Selective Surfaces (FSS) are periodic array of sub-wavelength antenna elements. They allow the absorptance and reflectance of a surface to be engineered with respect to wavelength, polarization and angle-of-incidence. This paper applies this technique to microbolometers for uncooled infrared sensing applications. Both narrowband and broadband near perfect absorbing surfaces are synthesized and applied engineer the response of microbolometers. The paper focuses on simple FSS geometries (hexagonal close packed disk arrays) that can be fabricated using conventional lithographic tools for use at thermal infrared wavelengths (feature sizes > 1 μm). The affects of geometry and material selection for this geometry is described in detail. In the microbolometer application, the FSS controls the absorption rather than a conventional Fabry-Perot cavity and this permits an improved thermal design. A coupled full wave electromagnetic/transient thermal model of the entire microbolometer is presented and analyzed using the finite element method. The absence of the cavity also permits more flexibility in the design of the support arms/contacts. This combined modeling permits prediction of the overall device sensitivity, time-constant and the specific detectivity.

  11. Frequency-dependent selection at rough expanding fronts

    NASA Astrophysics Data System (ADS)

    Kuhr, Jan-Timm; Stark, Holger

    2015-10-01

    Microbial colonies are experimental model systems for studying the colonization of new territory by biological species through range expansion. We study a generalization of the two-species Eden model, which incorporates local frequency-dependent selection, in order to analyze how social interactions between two species influence surface roughness of growing microbial colonies. The model includes several classical scenarios from game theory. We then concentrate on an expanding public goods game, where either cooperators or defectors take over the front depending on the system parameters. We analyze in detail the critical behavior of the nonequilibrium phase transition between global cooperation and defection and thereby identify a new universality class of phase transitions dealing with absorbing states. At the transition, the number of boundaries separating sectors decays with a novel power law in time and their superdiffusive motion crosses over from Eden scaling to a nearly ballistic regime. In parallel, the width of the front initially obeys Eden roughening and, at later times, passes over to selective roughening.

  12. Multiple-Optimizing Dynamic Sensor Networks with MIMO Technology (PREPRINT)

    DTIC Science & Technology

    2010-06-01

    Multiple - Input Multiple - Output ( MIMO ) transceiver...wchen@tnstate.edu, hmiao@tnstate.edu, havokjinx@gmial.com) Abstract: A Multiple - Input Multiple - Output ( MIMO ) transceiver provides extremely high...After comparing the simulation results in SISO (Single Input Single Output ), 2×2 MIMO and 4×4 MIMO WSNs for different filed size,

  13. 47 CFR 90.621 - Selection and assignment of frequencies.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... application the frequencies on which the proposed system will operate pursuant to a recommendation by the... frequencies by including in their applications the frequencies requested. (1) For trunked systems, the... the frequencies listed in §§ 90.615, 90.617, and 90.619. (2) For conventional systems the assignment...

  14. Transmission Subspace Tracing for MIMO Communications Systems

    DTIC Science & Technology

    2001-11-01

    multiple - input multiple - output ( MIMO ...3. DATES COVERED (From - To) 4. TITLE AND SUBTITLE TRANSMISSION SUBSPACE TRACKING FOR MULTIPLE - INPUT MULTIPLE - OUPUT ( MIMO ) COMMUNICATIONS SYSTEMS...publications/pubs/index.html 14. ABSTRACT This paper describes the benefits of transmission subspace tracking for multiple input multiple output

  15. Atmospheric turbulence mitigation in an OAM-based MIMO free-space optical link using spatial diversity combined with MIMO equalization.

    PubMed

    Ren, Yongxiong; Wang, Zhe; Xie, Guodong; Li, Long; Willner, Asher J; Cao, Yinwen; Zhao, Zhe; Yan, Yan; Ahmed, Nisar; Ashrafi, Nima; Ashrafi, Solyman; Bock, Robert; Tur, Moshe; Willner, Alan E

    2016-06-01

    We explore the mitigation of atmospheric turbulence effects for orbital angular momentum (OAM)-based free-space optical (FSO) communications with multiple-input multiple-output (MIMO) architecture. Such a system employs multiple spatially separated aperture elements at the transmitter/receiver, and each transmitter aperture contains multiplexed data-carrying OAM beams. We propose to use spatial diversity combined with MIMO equalization to mitigate both weak and strong turbulence distortions. In a 2×2 FSO link with each transmitter aperture containing two multiplexed OAM modes of ℓ=+1 and ℓ=+3, we experimentally show that at least two OAM data channels could be recovered under both weak and strong turbulence distortions using selection diversity assisted with MIMO equalization.

  16. MIMO based 3D imaging system at 360 GHz

    NASA Astrophysics Data System (ADS)

    Herschel, R.; Nowok, S.; Zimmermann, R.; Lang, S. A.; Pohl, N.

    2016-05-01

    A MIMO radar imaging system at 360 GHz is presented as a part of the comprehensive approach of the European FP7 project TeraSCREEN, using multiple frequency bands for active and passive imaging. The MIMO system consists of 16 transmitter and 16 receiver antennas within one single array. Using a bandwidth of 30 GHz, a range resolution up to 5 mm is obtained. With the 16×16 MIMO system 256 different azimuth bins can be distinguished. Mechanical beam steering is used to measure 130 different elevation angles where the angular resolution is obtained by a focusing elliptical mirror. With this system a high resolution 3D image can be generated with 4 frames per second, each containing 16 million points. The principle of the system is presented starting from the functional structure, covering the hardware design and including the digital image generation. This is supported by simulated data and discussed using experimental results from a preliminary 90 GHz system underlining the feasibility of the approach.

  17. Distributed MIMO-OFDM in imperfectly synchronized cooperative network

    NASA Astrophysics Data System (ADS)

    Zhang, Yimin; Wang, Genyuan; Amin, Moeness G.

    2006-05-01

    Coded space-time cooperation is an efficient approach in delivering information over a relay network. Multiple cooperative terminals (nodes) form a distributed multiple-input-multiple-output (MIMO) systems, thus providing high data rates and high diversity gains. However, unlike conventional co-located MIMO systems, it is impractical for distributed MIMO networks to maintain perfect timing synchronization between different transmit terminals. In particular, the presence of a fractional-symbol delay difference between the signals transmitted from different terminals can cause erroneous sampling positions and yield highly dispersive channels even at a memoryless channel environment. Existing methods solve such problem based on time-domain approaches where adaptive equalization is required at the receivers for combining the information transmitted from distributed sources. In this paper, we propose the use of OFDM-based approaches using distributed space-frequency codes. The proposed schemes are insensitive to fractional-symbol delays and lead to higher data rate transmission and simplified implementation. In addition, the proposed schemes permit the use of relatively simple amplify-and-forward algorithm in multi-hop wireless networks without delay accumulations. The time delay in each relaying hop by reconstructing the cyclic prefix and, as such, improve the spectral efficiency, while keeping a simple relaying structure.

  18. A Minimized MIMO-UWB Antenna with High Isolation and Triple Band-Notched Functions

    NASA Astrophysics Data System (ADS)

    Kong, Yuanyuan; Li, Yingsong; Yu, Kai

    2016-11-01

    A compact high isolation MIMO-UWB antenna with triple frequency rejection bands is proposed for UWB communication applications. The proposed MIMO-UWB antenna consists of two identical UWB antennas and each antenna element has a semicircle ring shaped radiation patch fed by a bend microstrip feeding line for covering the UWB band, which operates from 2.85 GHz to 11.79 GHz with an impedance bandwidth of 122.1 %. By etching a L-shaped slot on the ground plane, and embedding an "anchor" shaped stub into the patch and integrating an open ring under the semicircle shaped radiation patch, three notch bands are realized to suppress WiMAX (3.3-3.6 GHz), WLAN(5.725-5.825 GHz) and uplink of X-band satellite (7.9-8.4 GHz) signals. The high isolation with S21<-20 dB in most UWB band is obtained by adding a protruded decoupling structure. The design procedure of the MIMO-UWB antenna is given in detail. The proposed MIMO-UWB antenna is simulated, fabricated and measured. Experimental results demonstrate that the proposed MIMO-UWB antenna has a stable gain, good impedance match, high isolation, low envelope correlation coefficient and good radiation pattern at the UWB operating band and it can provide three designated notch bands.

  19. Hierarchical Interference Mitigation for Massive MIMO Cellular Networks

    NASA Astrophysics Data System (ADS)

    Liu, An; Lau, Vincent

    2014-09-01

    We propose a hierarchical interference mitigation scheme for massive MIMO cellular networks. The MIMO precoder at each base station (BS) is partitioned into an inner precoder and an outer precoder. The inner precoder controls the intra-cell interference and is adaptive to local channel state information (CSI) at each BS (CSIT). The outer precoder controls the inter-cell interference and is adaptive to channel statistics. Such hierarchical precoding structure reduces the number of pilot symbols required for CSI estimation in massive MIMO downlink and is robust to the backhaul latency. We study joint optimization of the outer precoders, the user selection, and the power allocation to maximize a general concave utility which has no closed-form expression. We first apply random matrix theory to obtain an approximated problem with closed-form objective. We show that the solution of the approximated problem is asymptotically optimal with respect to the original problem as the number of antennas per BS grows large. Then using the hidden convexity of the problem, we propose an iterative algorithm to find the optimal solution for the approximated problem. We also obtain a low complexity algorithm with provable convergence. Simulations show that the proposed design has significant gain over various state-of-the-art baselines.

  20. A Desired PAR-Achieving Precoder Design for Multiuser MIMO OFDM Based on Concentration of Measure

    NASA Astrophysics Data System (ADS)

    Cha, Hyun-Su; Kim, Dong Ku

    2017-03-01

    For multi-user multiple-input and multiple-output (MIMO) wireless communications in orthogonal frequency di- vision multiplexing systems, we propose a MIMO precoding scheme providing a desired peak-to-average power ratio (PAR) at the minimum cost that is defined as received SNR degradation. By taking advantage of the concentration of measure, we formulate a convex problem with constraint on the desired PAR. Consequently, the proposed scheme almost exactly achieves the desired PAR on average, and asymptotically attains the desired PAR at the 0.001 point of its complementary cumulative distribution function, as the number of subcarriers increases.

  1. Channel estimation based on quantized MMP for FDD massive MIMO downlink

    NASA Astrophysics Data System (ADS)

    Guo, Yao-ting; Wang, Bing-he; Qu, Yi; Cai, Hua-jie

    2016-10-01

    In this paper, we consider channel estimation for Massive MIMO systems operating in frequency division duplexing mode. By exploiting the sparsity of propagation paths in Massive MIMO channel, we develop a compressed sensing(CS) based channel estimator which can reduce the pilot overhead. As compared with the conventional least squares (LS) and linear minimum mean square error(LMMSE) estimation, the proposed algorithm is based on the quantized multipath matching pursuit - MMP - reduced the pilot overhead and performs better than other CS algorithms. The simulation results demonstrate the advantage of the proposed algorithm over various existing methods including the LS, LMMSE, CoSaMP and conventional MMP estimators.

  2. Dielectric measurements of selected ceramics at microwave frequencies

    NASA Technical Reports Server (NTRS)

    Dahiya, J. N.; Templeton, C. K.

    1994-01-01

    Dielectric measurements of strontium titanate and lead titanate zirconate ceramics are conducted at microwave frequencies using a cylindrical resonant cavity in the TE(sub 011) mode. The perturbations of the electric field are recorded in terms of the frequency shift and Q-changes of the cavity signal. Slater's perturbation equations are used to calculate e' and e" of the dielectric constant as a function of temperature and frequency.

  3. 47 CFR 74.403 - Frequency selection to avoid interference.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... SERVICES EXPERIMENTAL RADIO, AUXILIARY, SPECIAL BROADCAST AND OTHER PROGRAM DISTRIBUTIONAL SERVICES Remote... remote pickup broadcast station licensees are authorized to operate on the same frequency or group of...

  4. 47 CFR 74.403 - Frequency selection to avoid interference.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... SERVICES EXPERIMENTAL RADIO, AUXILIARY, SPECIAL BROADCAST AND OTHER PROGRAM DISTRIBUTIONAL SERVICES Remote... remote pickup broadcast station licensees are authorized to operate on the same frequency or group of...

  5. 47 CFR 74.403 - Frequency selection to avoid interference.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... SERVICES EXPERIMENTAL RADIO, AUXILIARY, SPECIAL BROADCAST AND OTHER PROGRAM DISTRIBUTIONAL SERVICES Remote... remote pickup broadcast station licensees are authorized to operate on the same frequency or group of...

  6. Polymer (PDMS-Fe3O4) magneto-dielectric substrate for a MIMO antenna array

    NASA Astrophysics Data System (ADS)

    Alqadami, Abdulrahman Shueai Mohsen; Jamlos, Mohd Faizal; Soh, Ping Jack; Kamarudin, Muhammad Ramlee

    2016-01-01

    This paper presents the design of a 2 × 4 multiple-input multiple-output (MIMO) antenna array fabricated on a nanocomposite magneto-dielectric polymer substrate. The 10-nm iron oxide (Fe3O4) nanoparticles and polydimethylsiloxane (PDMS) composite is used as substrate to enhance the performance of a MIMO antenna array. The measured results showed up to 40.8 % enhancement in terms of bandwidth, 9.95 dB gain, and 57 % of radiation efficiency. Furthermore, it is found that the proposed magneto-dielectric (PDMS-Fe3O4) composite substrate provides excellent MIMO parameters such as correlation coefficient, diversity gain, and mutual coupling. The prototype of the proposed antenna is transparent, flexible, lightweight, and resistant against dust and corrosion. Measured results indicate that the proposed antenna is suitable for WLAN and ultra-wideband biomedical applications within frequency range of 5.33-7.70 GHz.

  7. Neural network L1 adaptive control of MIMO systems with nonlinear uncertainty.

    PubMed

    Zhen, Hong-tao; Qi, Xiao-hui; Li, Jie; Tian, Qing-min

    2014-01-01

    An indirect adaptive controller is developed for a class of multiple-input multiple-output (MIMO) nonlinear systems with unknown uncertainties. This control system is comprised of an L 1 adaptive controller and an auxiliary neural network (NN) compensation controller. The L 1 adaptive controller has guaranteed transient response in addition to stable tracking. In this architecture, a low-pass filter is adopted to guarantee fast adaptive rate without generating high-frequency oscillations in control signals. The auxiliary compensation controller is designed to approximate the unknown nonlinear functions by MIMO RBF neural networks to suppress the influence of uncertainties. NN weights are tuned on-line with no prior training and the project operator ensures the weights bounded. The global stability of the closed-system is derived based on the Lyapunov function. Numerical simulations of an MIMO system coupled with nonlinear uncertainties are used to illustrate the practical potential of our theoretical results.

  8. Neural Network L 1 Adaptive Control of MIMO Systems with Nonlinear Uncertainty

    PubMed Central

    Zhen, Hong-tao; Qi, Xiao-hui; Li, Jie; Tian, Qing-min

    2014-01-01

    An indirect adaptive controller is developed for a class of multiple-input multiple-output (MIMO) nonlinear systems with unknown uncertainties. This control system is comprised of an L 1 adaptive controller and an auxiliary neural network (NN) compensation controller. The L 1 adaptive controller has guaranteed transient response in addition to stable tracking. In this architecture, a low-pass filter is adopted to guarantee fast adaptive rate without generating high-frequency oscillations in control signals. The auxiliary compensation controller is designed to approximate the unknown nonlinear functions by MIMO RBF neural networks to suppress the influence of uncertainties. NN weights are tuned on-line with no prior training and the project operator ensures the weights bounded. The global stability of the closed-system is derived based on the Lyapunov function. Numerical simulations of an MIMO system coupled with nonlinear uncertainties are used to illustrate the practical potential of our theoretical results. PMID:25147871

  9. RF Lens-Embedded Massive MIMO Systems: Fabrication Issues and Codebook Design

    NASA Astrophysics Data System (ADS)

    Kwon, Taehoon; Lim, Yeon-Geun; Min, Byung-Wook; Chae, Chan-Byoung

    2016-07-01

    In this paper, we investigate a radio frequency (RF) lens-embedded massive multiple-input multiple-output (MIMO) system and evaluate the system performance of limited feedback by utilizing a technique for generating a suitable codebook for the system. We fabricate an RF lens that operates on a 77 GHz (mmWave) band. Experimental results show a proper value of amplitude gain and an appropriate focusing property. In addition, using a simple numerical technique--beam propagation method (BPM)--we estimate the power profile of the RF lens and verify its accordance with experimental results. We also design a codebook--multi-variance codebook quantization (MVCQ)--for limited feedback by considering the characteristics of the RF lens antenna for massive MIMO systems. Numerical results confirm that the proposed system shows significant performance enhancement over a conventional massive MIMO system without an RF lens.

  10. Measurement Based MIMO Channel Capacity in an Urban Canyon Environment at the 3.7GHz Band

    NASA Astrophysics Data System (ADS)

    Lim, Jae-Woo; Kwon, Se-Woong; Park, Youn-Hyun; Yoon, Hyun-Goo; Yook, Jong-Gwan; Yoon, Yong-Joong

    This paper describes the measurements made in an urban canyon environment of a relay network scenario to determine the capacity of the multiple-input-multiple-output (MIMO) channel. While varying antenna number and spacing, we measure the channel matrices in the 3.7GHz band using a 4×4 switching MIMO channel sounder. The results show that antenna spacing is shown to have less impact than signal-to-noise (SNR) on MIMO channel capacity in a line-of-sight (LOS) environment when physical antenna spacing is selected at four wavelengths. As a result, in an urban MIMO LOS scenario, a base station can provide sufficient data throughput to relay station because most links from base station to relay station have LOS environment and are free from restriction of antenna spacing.

  11. Deep-subwavelength Decoupling for MIMO Antennas in Mobile Handsets with Singular Medium.

    PubMed

    Xu, Su; Zhang, Ming; Wen, Huailin; Wang, Jun

    2017-09-22

    Decreasing the mutual coupling between Multi-input Multi-output (MIMO) antenna elements in a mobile handset and achieving a high data rate is a challenging topic as the 5(th)-generation (5G) communication age is coming. Conventional decoupling components for MIMO antennas have to be re-designed when the geometries or frequencies of antennas have any adjustment. In this paper, we report a novel metamaterial-based decoupling strategy for MIMO antennas in mobile handsets with wide applicability. The decoupling component is made of subwavelength metal/air layers, which can be treated as singular medium over a broad frequency band. The flexible applicable property of the decoupling strategy is verified with different antennas over different frequency bands with the same metamaterial decoupling element. Finally, 1/100-wavelength 10-dB isolation is demonstrated for a 24-element MIMO antenna in mobile handsets over the frequency band from 4.55 to 4.75 GHz.

  12. How Metastrategic Considerations Influence the Selection of Frequency Estimation Strategies

    ERIC Educational Resources Information Center

    Brown, Norman R.

    2008-01-01

    Prior research indicates that enumeration-based frequency estimation strategies become increasingly common as memory for relevant event instances improves and that moderate levels of context memory are associated with moderate rates of enumeration [Brown, N. R. (1995). Estimation strategies and the judgment of event frequency. Journal of…

  13. How Metastrategic Considerations Influence the Selection of Frequency Estimation Strategies

    ERIC Educational Resources Information Center

    Brown, Norman R.

    2008-01-01

    Prior research indicates that enumeration-based frequency estimation strategies become increasingly common as memory for relevant event instances improves and that moderate levels of context memory are associated with moderate rates of enumeration [Brown, N. R. (1995). Estimation strategies and the judgment of event frequency. Journal of…

  14. MimoDB: a new repository for mimotope data derived from phage display technology.

    PubMed

    Ru, Beibei; Huang, Jian; Dai, Ping; Li, Shiyong; Xia, Zhongkui; Ding, Hui; Lin, Hao; Guo, Fengbiao; Wang, Xianlong

    2010-11-15

    Peptides selected from phage-displayed random peptide libraries are valuable in two aspects. On one hand, these peptides are candidates for new diagnostics, therapeutics and vaccines. On the other hand, they can be used to predict the networks or sites of protein-protein interactions. MimoDB, a new repository for these peptides, was developed, in which 10,716 peptides collected from 571 publications were grouped into 1,229 sets. Besides peptide sequences, other important information, such as the target, template, library and complex structure, was also included. MimoDB can be browsed and searched through a user-friendly web interface. For computational biologists, MimoDB can be used to derive customized data sets and benchmarks, which are useful for new algorithm development and tool evaluation. For experimental biologists, their results can be searched against the MimoDB database to exclude possible target-unrelated peptides. The MimoDB database is freely accessible at http://immunet.cn/mimodb/.

  15. [Frequency-domain quantification based on the singular value decomposition and frequency-selection for magnetic resonance spectra].

    PubMed

    Men, Kuo; Quan, Hong; Yang, Peipei; Cao, Ting; Li, Weihao

    2010-04-01

    The frequency-domain magnetic resonance spectroscopy (MRS) is achieved by the Fast Fourier Transform (FFT) of the time-domain signals. Usually we are only interested in the portion lying in a frequency band of the whole spectrum. A method based on the singular value decomposition (SVD) and frequency-selection is presented in this article. The method quantifies the spectrum lying in the interested frequency band and reduces the interference of the parts lying out of the band in a computationally efficient way. Comparative experiments with the standard time-domain SVD method indicate that the method introduced in this article is accurate and timesaving in practical situations.

  16. Performance Evaluation of MIMO-UWB Systems Using Measured Propagation Data and Proposal of Timing Control Scheme in LOS Environments

    NASA Astrophysics Data System (ADS)

    Takanashi, Masaki; Nishimura, Toshihiko; Ogawa, Yasutaka; Ohgane, Takeo

    Ultrawide-band impulse radio (UWB-IR) technology and multiple-input multiple-output (MIMO) systems have attracted interest regarding their use in next-generation high-speed radio communication. We have studied the use of MIMO ultrawide-band (MIMO-UWB) systems to enable higher-speed radio communication. We used frequency-domain equalization based on the minimum mean square error criterion (MMSE-FDE) to reduce intersymbol interference (ISI) and co-channel interference (CCI) in MIMO-UWB systems. Because UWB systems are expected to be used for short-range wireless communication, MIMO-UWB systems will usually operate in line-of-sight (LOS) environments and direct waves will be received at the receiver side. Direct waves have high power and cause high correlations between antennas in such environments. Thus, it is thought that direct waves will adversely affect the performance of spatial filtering and equalization techniques used to enhance signal detection. To examine the feasibility of MIMO-UWB systems, we conducted MIMO-UWB system propagation measurements in LOS environments. From the measurements, we found that the arrival time of direct waves from different transmitting antennas depends on the MIMO configuration. Because we can obtain high power from the direct waves, direct wave reception is critical for maximizing transmission performance. In this paper, we present our measurement results, and propose a way to improve performance using a method of transmit (Tx) and receive (Rx) timing control. We evaluate the bit error rate (BER) performance for this form of timing control using measured channel data.

  17. 47 CFR 90.621 - Selection and assignment of frequencies.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... SERVICES PRIVATE LAND MOBILE RADIO SERVICES Regulations Governing Licensing and Use of Frequencies in the 806-824, 851-869, 896-901, and 935-940 MHz Bands Policies Governing the Processing of Applications...

  18. 47 CFR 90.621 - Selection and assignment of frequencies.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... SERVICES PRIVATE LAND MOBILE RADIO SERVICES Regulations Governing Licensing and Use of Frequencies in the 806-824, 851-869, 896-901, and 935-940 MHz Bands Policies Governing the Processing of Applications...

  19. Selective Heating of Regolith Grains Using Dynamic Phase and Frequency

    NASA Astrophysics Data System (ADS)

    Cash, T. J.; Blair, B. R.

    2016-11-01

    This paper will present concepts for heating lunar granular media using a dynamic strategy that varies phase and frequency to maximize the coupling efficiency of inbound radiation to a hypothetical work zone.

  20. Temperature and frequency dependence of ultrasonic attenuation in selected tissues

    NASA Technical Reports Server (NTRS)

    Gammell, P. M.; Croissette, D. H. L.; Heyser, R. C.

    1979-01-01

    Ultrasonic attenuation over the frequency range of 1.5-10 MHz has been measured as a function of temperature for porcine liver, backfat, kidney and spleen as well as for a single specimen of human liver. The attenuation in these excised specimens increases nearly linearly with frequency. Over the temperature range of approximately 4-37 C the attenuation decreases with increasing temperature for most soft tissue studied.

  1. Tuning Mechanisms in a Corrugated Origami Frequency Selective Surface (Preprint)

    DTIC Science & Technology

    2017-07-09

    spacing at different rates are used to examine the frequency response in relation to special re-arrangements. Folding decreases the in-plane spacing ...leading to smaller Floquet periodicity lengths and higher resonant frequency, while in some fold arrangements folding increases the out-of-plane spacing ...is investigated. Three types of 1D folding patterns that alter the in- plane and out-of-plane dipole spacing at different rates are used to examine

  2. Development of characteristic equations and robust stability analysis for MIMO move suppressed and shifted DMC.

    PubMed

    Dubay, R; Kember, G; Lakshminarayan, C V; Pramujati, B

    2005-10-01

    Discrete-time controller and closed-loop transfer functions were developed for move suppressed lambda and the recently formulated m-shifted multiple-input-multiple-output (MIMO) dynamic matrix control (DMC). Using these transfer functions, robust analyses were conducted for MIMO plants by varying corresponding delay and gain ratios of the system. In all instances, robust plots indicate that the shifted DMC is less sensitive and hence more robust to variations in the plant parameters than move suppressed DMC. It was shown that the design of these MIMO DMC controllers depends on the plant closed-loop performance and overall stability, since the selection of lambda and m directly influences the plant robustness and closed-loop dynamics.

  3. Breast Cancer Nodes Detection Using Ultrasonic Microscale Subarrayed MIMO RADAR

    PubMed Central

    Siwamogsatham, Siwaruk; Pomalaza-Ráez, Carlos

    2014-01-01

    This paper proposes the use of ultrasonic microscale subarrayed MIMO RADARs to estimate the position of breast cancer nodes. The transmit and receive antenna arrays are divided into subarrays. In order to increase the signal diversity each subarray is assigned a different waveform from an orthogonal set. High-frequency ultrasonic transducers are used since a breast is considered to be a superficial structure. Closed form expressions for the optimal Neyman-Pearson detector are derived. The combination of the waveform diversity present in the subarrayed deployment and traditional phased-array RADAR techniques provides promising results. PMID:25309591

  4. Frequency Selectivity Behaviour in the Auditory Midbrain: Implications of Model Study

    NASA Astrophysics Data System (ADS)

    Kuang, Shen-Bing; Wang, Jia-Fu; Zeng, Ting

    2006-12-01

    By numerical simulations on frequency dependence of the spiking threshold, i.e. on the critical amplitude of periodic stimulus, for a neuron to fire, we find that bushy cells in the cochlear nuclear exhibit frequency selectivity behaviour. However, the selective frequency band of a bushy cell is far away from that of the preferred spectral range in human and mammal auditory perception. The mechanism underlying this neural activity is also discussed. Further studies show that the ion channel densities have little impact on the selective frequency band of bushy cells. These findings suggest that the neuronal behaviour of frequency selectivity in bushy cells at both the single cell and population levels may be not functionally relevant to frequency discrimination. Our results may reveal a neural hint to the reconsideration on the bushy cell functional role in auditory information processing of sound frequency.

  5. Application of MIMO technology in ultraviolet communication

    NASA Astrophysics Data System (ADS)

    Huang, Gang; Tang, Yi; Ni, Guoqiang; Huang, Heqing; Zhang, Xuan

    2013-12-01

    Affected by atmospheric turbulence and multipath transmission, inter-symbol interference (ISI) is generated, and communication speed is limited in the channel of non-line-of-sight ultraviolet (NLOS UV) communication. Thus, MIMO space division multiplexing (MIMO-SDM) technology has a significant effect to reduce co-channel interference, fading and improve the transmission rate. Combined with characteristics of UV channel and noise, model of UV communication MIMO channel and channel capacity is developed, and the application of SDM technology based on vertical bell laboratories layered space-time coding (V-BLAST) is investigated. Also bit error rate (BER) performances with zero-forcing (ZF), minimum mean square error (MMSE) detection algorithm are obtained. Simulation results show that the capacity of UV communication MIMO channel is related to the number of transmit and received antennas , and channel SNR. And the BER performance with MMSE detection algorithm is better than ZF detection algorithm.

  6. Model validity and frequency band selection in operational modal analysis

    NASA Astrophysics Data System (ADS)

    Au, Siu-Kui

    2016-12-01

    Experimental modal analysis aims at identifying the modal properties (e.g., natural frequencies, damping ratios, mode shapes) of a structure using vibration measurements. Two basic questions are encountered when operating in the frequency domain: Is there a mode near a particular frequency? If so, how much spectral data near the frequency can be included for modal identification without incurring significant modeling error? For data with high signal-to-noise (s/n) ratios these questions can be addressed using empirical tools such as singular value spectrum. Otherwise they are generally open and can be challenging, e.g., for modes with low s/n ratios or close modes. In this work these questions are addressed using a Bayesian approach. The focus is on operational modal analysis, i.e., with 'output-only' ambient data, where identification uncertainty and modeling error can be significant and their control is most demanding. The approach leads to 'evidence ratios' quantifying the relative plausibility of competing sets of modeling assumptions. The latter involves modeling the 'what-if-not' situation, which is non-trivial but is resolved by systematic consideration of alternative models and using maximum entropy principle. Synthetic and field data are considered to investigate the behavior of evidence ratios and how they should be interpreted in practical applications.

  7. Adaptive reconfigurable V-BLAST type equalizer for cognitive MIMO-OFDM radios

    NASA Astrophysics Data System (ADS)

    Ozden, Mehmet Tahir

    2015-12-01

    An adaptive channel shortening equalizer design for multiple input multiple output-orthogonal frequency division multiplexing (MIMO-OFDM) radio receivers is considered in this presentation. The proposed receiver has desirable features for cognitive and software defined radio implementations. It consists of two sections: MIMO decision feedback equalizer (MIMO-DFE) and adaptive multiple Viterbi detection. In MIMO-DFE section, a complete modified Gram-Schmidt orthogonalization of multichannel input data is accomplished using sequential processing multichannel Givens lattice stages, so that a Vertical Bell Laboratories Layered Space Time (V-BLAST) type MIMO-DFE is realized at the front-end section of the channel shortening equalizer. Matrix operations, a major bottleneck for receiver operations, are accordingly avoided, and only scalar operations are used. A highly modular and regular radio receiver architecture that has a suitable structure for digital signal processing (DSP) chip and field programable gate array (FPGA) implementations, which are important for software defined radio realizations, is achieved. The MIMO-DFE section of the proposed receiver can also be reconfigured for spectrum sensing and positioning functions, which are important tasks for cognitive radio applications. In connection with adaptive multiple Viterbi detection section, a systolic array implementation for each channel is performed so that a receiver architecture with high computational concurrency is attained. The total computational complexity is given in terms of equalizer and desired response filter lengths, alphabet size, and number of antennas. The performance of the proposed receiver is presented for two-channel case by means of mean squared error (MSE) and probability of error evaluations, which are conducted for time-invariant and time-variant channel conditions, orthogonal and nonorthogonal transmissions, and two different modulation schemes.

  8. Ultrahigh capacity 2 × 2 MIMO RoF system at 60  GHz employing single-sideband single-carrier modulation.

    PubMed

    Lin, Chun-Ting; Ho, Chun-Hung; Huang, Hou-Tzu; Cheng, Yu-Hsuan

    2014-03-15

    This article proposes and experimentally demonstrates a radio-over-fiber system employing single-sideband single-carrier (SSB-SC) modulation at 60 GHz. SSB-SC modulation has a lower peak-to-average-power ratio than orthogonal frequency division multiplex (OFDM) modulation; therefore, the SSB-SC signals provide superior nonlinear tolerance, compared to OFDM signals. Moreover, multiple-input multiple-output (MIMO) technology was used extensively to enhance spectral efficiency. A least-mean-square-based equalizer was implemented, including MIMO channel estimation, frequency response equalization, and I/Q imbalance compensation to recover the MIMO signals. Thus, using 2×2 MIMO technology and 64-QAM SSB-SC signals, we achieved the highest data rate of 84 Gbps with 12  bit/s/Hz spectral efficiency using the 7-GHz license-free band at 60 GHz.

  9. Unbalanced synaptic inputs underlying multi-peaked frequency selectivity in rat auditory cortex.

    PubMed

    Zhou, Chang; Tao, Can; Zhang, Guangwei; Yan, Sumei; Wang, Lijuan; Zhou, Yi; Xiong, Ying

    2017-04-01

    By measuring the frequency selectivity at different intensities in the primary auditory cortex of adult rats, we found that a small group of cortical neurons can exhibit relatively weak but robust selectivity at multiple frequencies that are different from the most preferred frequency. Both in vivo multi-unit recordings (26/93 recordings) and single-unit recordings (16/137 neurons) confirmed that the preferred frequencies are periodic and have an averaged bandwidth (BW) of 0.3-0.4 octaves, which leads to multi-peaked frequency selectivity. Interestingly, the averaged bandwidth of the ripple in the frequency response tuning curve was invariant with the sound intensity. An investigation of the synaptic currents in vivo also revealed similar multi-peaked frequency selectivity for both excitation and inhibition. While the excitatory and inhibitory inputs were relatively balanced for most frequencies, the ratio between excitation and inhibition at the peak and valley of each ripple was highly unbalanced. Since this multi-peaked frequency selectivity can be observed at the synaptic, single-cell, and population levels, our results reveal a potential mechanism underlying the multi-peaked pattern of frequency selectivity in the primary auditory cortex. © 2017 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.

  10. Frequency-Domain Block Signal Detection for Single-Carrier Transmission

    NASA Astrophysics Data System (ADS)

    Yamamoto, Tetsuya; Takeda, Kazuki; Adachi, Fumiyuki

    One-tap frequency-domain equalization (FDE) based on the minimum mean square error (MMSE) criterion can significantly improve the bit error rate (BER) performance of single-carrier (SC) transmission in a frequency-selective fading channel. However, a big performance gap from the theoretical lower bound still exists due to the presence of residual inter-symbol interference (ISI) after MMSE-FDE. In this paper, we point out that the frequency-domain received SC signal can be expressed using the matrix representation similar to the multiple-input multiple-output (MIMO) multiplexing and therefore, signal detection schemes developed for MIMO multiplexing, other than simple one-tap MMSE-FDE, can be applied to SC transmission. Then, for the reception of SC signals, we propose a new signal detection scheme, which combines FDE with MIMO signal detection, such as MMSE detection and Vertical-Bell Laboratories layered space-time architecture (V-BLAST) detection (we call this frequency-domain block signal detection). The achievable average BER performance using the proposed frequency-domain block signal detection is evaluated by computer simulation.

  11. Spatial Tuning of a RF Frequency Selective Surface through Origami (Postprint)

    DTIC Science & Technology

    2016-05-12

    experimental study and motivates the development of computational tools to systematically predict optimal fold patterns for targeted frequency response...alignment via folding. Collectively, these results provide a basis of origami FSS designs for experimental study and motivates the development of...computational tools to systematically predict optimal folds. 15. SUBJECT TERMS origami, frequency selective surface, tuning, radio frequency 16

  12. Verification and Validation Report: Frequency Selective Surface Simulation Tool

    DTIC Science & Technology

    2005-06-01

    tration’s (NASA) Cassini mission [9], which was launched in 1997. The spacecraft requires multiple RF frequencies (S-, X-, Ku-, and Ka-bands) for...RF goals. The Cassini spacecraft requires multiple RF functions in the S-, X-, Ku-, and Ka-bands. A single high-gain antenna combined with an FSS...particularly in spacecraft applications. The V&V test cases discussed in this section represent a broad cross-section of FSS structures that are useful

  13. Wireless Communication of Intraoral Devices and Its Optimal Frequency Selection

    PubMed Central

    Park, Hangue; Ghovanloo, Maysam

    2015-01-01

    This paper explores communication methods and frequencies for wireless intraoral electronic devices, by using an intraoral tongue drive system (iTDS) as a practical example. Because intraoral devices do not meet the operating conditions of the body channel communication, we chose radio frequency communication. We evaluated and compared three frequencies in industrial, scientific, and medical bands (27 MHz, 433.9 MHz, and 2.48 GHz) in terms of their data link performance based on path loss and radiation patterns over horizontal and vertical planes. To do so, we dynamically minimize the impedance mismatch caused by the varying oral environment by applying the adaptive impedance matching technique to 433.9 MHz and 2.48 GHz bands. Experimental results showed that 27 MHz has the smallest path loss in the near-field up to 39 cm separation between transmitter and receiver antennas. However, 433.9 MHz shows the best performance beyond 39 cm and offers a maximum operating distance of 123 cm with 0 dBm transmitter output power. These distances were obtained by a bit error rate test and verified by a link budget analysis and full functionality test of the iTDS with computer access. PMID:26236039

  14. Wireless Communication of Intraoral Devices and Its Optimal Frequency Selection.

    PubMed

    Park, Hangue; Ghovanloo, Maysam

    2014-12-01

    This paper explores communication methods and frequencies for wireless intraoral electronic devices, by using an intraoral tongue drive system (iTDS) as a practical example. Because intraoral devices do not meet the operating conditions of the body channel communication, we chose radio frequency communication. We evaluated and compared three frequencies in industrial, scientific, and medical bands (27 MHz, 433.9 MHz, and 2.48 GHz) in terms of their data link performance based on path loss and radiation patterns over horizontal and vertical planes. To do so, we dynamically minimize the impedance mismatch caused by the varying oral environment by applying the adaptive impedance matching technique to 433.9 MHz and 2.48 GHz bands. Experimental results showed that 27 MHz has the smallest path loss in the near-field up to 39 cm separation between transmitter and receiver antennas. However, 433.9 MHz shows the best performance beyond 39 cm and offers a maximum operating distance of 123 cm with 0 dBm transmitter output power. These distances were obtained by a bit error rate test and verified by a link budget analysis and full functionality test of the iTDS with computer access.

  15. Quantification of MDL-induced signal degradation in MIMO-OFDM mode-division multiplexing systems.

    PubMed

    Tian, Yu; Li, Juhao; Zhu, Paikun; Wu, Zhongying; Chen, Yuanxiang; He, Yongqi; Chen, Zhangyuan

    2016-08-22

    Mode-division multiplexing (MDM) transmission over few-mode optical fiber has emerged as a promising technology to enhance transmission capacity, in which multiple-input-multiple-output (MIMO) digital signal processing (DSP) after coherent detection is used to demultiplex the signals. Compared with conventional single-mode systems, MIMO-MDM systems suffer non-recoverable signal degradation induced by mode-dependent loss (MDL). In this paper, the MDL-induced signal degradation in orthogonal-frequency-division-multiplexing (OFDM) MDM systems is theoretically quantified in terms of mode-average error vector magnitude (EVM) through frequency domain norm analysis. A novel scalar MDL metric is proposed considering the probability distribution of the practical MDM input signals, and a closed-form expression for EVM measured after zero-force (ZF) MIMO equalization is derived. Simulation results show that the EVM estimations utilizing the novel MDL metric remain unbiased for unrepeated links. For a 6 × 100 km 20-mode MDM transmission system, the estimation accuracy is improved by more than 90% compared with that utilizing traditional condition number (CN) based MDL metric. The proposed MDL metric can be used to predict the MDL-induced SNR penalty in a theoretical manner, which will be beneficial for the design of practical MIMO-MDM systems.

  16. Selection by parasites may increase host recombination frequency.

    PubMed

    Fischer, O; Schmid-Hempel, P

    2005-06-22

    Meiotic recombination destroys successful genotypes and it is therefore thought to evolve only under a very limited set of conditions. Here, we experimentally show that recombination rates across two linkage groups of the host, the red flour beetle Tribolium castaneum, increase with exposure to the microsporidian parasite, Nosema whitei, particularly when parasites were allowed to coevolve with their hosts. Selection by randomly varied parasites resulted in smaller effects, while directional selection for insecticide resistance initially reduced recombination slightly. These results, at least tentatively, suggest that short-term benefits of recombination--and thus the evolution of sex--may be related to parasitism.

  17. Iterative Block Decision Feedback Equalization for MIMO Underwater Acoustic Communications

    DTIC Science & Technology

    2010-06-01

    multiple - input , multiple - output ( MIMO ) underwa- ter acoustic (UWA...communications are limited to several kilo-bits per second within 40 km range. Multiple - input , multiple - output ( MIMO ) communications which improve the data...has been proposed in [16], both for single- input single- output (SISO) systems. In this paper, we develop an iterative BDFE for MIMO systems and

  18. Waveform Design for MIMO Radar Using an Alternating Projection Approach

    DTIC Science & Technology

    2010-01-23

    multiple - input multiple - output ( MIMO ) radar waveform design problem which optimizes both minimum mean-square error estimation (MMSE) and...Report Title ABSTRACT Revisiting an earlier examined multiple - input multiple - output ( MIMO ) radar waveform design problem which optimizes both minimum...mtu.edu Abstract— Revisiting an earlier examined multiple - input multiple - output ( MIMO ) radar waveform design problem which

  19. Application of MIMO Techniques in sky-surface wave hybrid networking sea-state radar system

    NASA Astrophysics Data System (ADS)

    Zhang, L.; Wu, X.; Yue, X.; Liu, J.; Li, C.

    2016-12-01

    The sky-surface wave hybrid networking sea-state radar system contains of the sky wave transmission stations at different sites and several surface wave radar stations. The subject comes from the national 863 High-tech Project of China. The hybrid sky-surface wave system and the HF surface wave system work simultaneously and the HF surface wave radar (HFSWR) can work in multi-static and surface-wave networking mode. Compared with the single mode radar system, this system has advantages of better detection performance at the far ranges in ocean dynamics parameters inversion. We have applied multiple-input multiple-output(MIMO) techniques in this sea-state radar system. Based on the multiple channel and non-causal transmit beam-forming techniques, the MIMO radar architecture can reduce the size of the receiving antennas and simplify antenna installation. Besides, by efficiently utilizing the system's available degrees of freedom, it can provide a feasible approach for mitigating multipath effect and Doppler-spread clutter in Over-the-horizon Radar. In this radar, slow-time phase-coded MIMO method is used. The transmitting waveforms are phase-coded in slow-time so as to be orthogonal after Doppler processing at the receiver. So the MIMO method can be easily implemented without the need to modify the receiver hardware. After the radar system design, the MIMO experiments of this system have been completed by Wuhan University during 2015 and 2016. The experiment used Wuhan multi-channel ionospheric sounding system(WMISS) as sky-wave transmitting source and three dual-frequency HFSWR developed by the Oceanography Laboratory of Wuhan University. The transmitter system located at Chongyang with five element linear equi-spaced antenna array and Wuhan with one log-periodic antenna. The RF signals are generated by synchronized, but independent digital waveform generators - providing complete flexibility in element phase and amplitude control, and waveform type and parameters

  20. Frequency selectivity of the human cochlea: Suppression tuning of spontaneous otoacoustic emissions.

    PubMed

    Manley, Geoffrey A; van Dijk, Pim

    2016-06-01

    Frequency selectivity is a key functional property of the inner ear and since hearing research began, the frequency resolution of the human ear has been a central question. In contrast to animal studies, which permit invasive recording of neural activity, human studies must rely on indirect methods to determine hearing selectivity. Psychophysical studies, which used masking of a tone by other sounds, indicate a modest frequency selectivity in humans. By contrast, estimates using the phase delays of stimulus-frequency otoacoustic emissions (SFOAE) predict a remarkably high selectivity, unique among mammals. An alternative measure of cochlear frequency selectivity are suppression tuning curves of spontaneous otoacoustic emissions (SOAE). Several animal studies show that these measures are in excellent agreement with neural frequency selectivity. Here we contribute a large data set from normal-hearing young humans on suppression tuning curves (STC) of spontaneous otoacoustic emissions (SOAE). The frequency selectivities of human STC measured near threshold levels agree with the earlier, much lower, psychophysical estimates. They differ, however, from the typical patterns seen in animal auditory nerve data in that the selectivity is remarkably independent of frequency. In addition, SOAE are suppressed by higher-level tones in narrow frequency bands clearly above the main suppression frequencies. These narrow suppression bands suggest interactions between the suppressor tone and a cochlear standing wave corresponding to the SOAE frequency being suppressed. The data show that the relationship between pre-neural mechanical processing in the cochlea and neural coding at the hair-cell/auditory nerve synapse needs to be reconsidered.

  1. A CORDIC based FFT processor for MIMO channel emulator

    NASA Astrophysics Data System (ADS)

    Xiong, Yanwei; Zhang, Jianhua; Zhang, Ping

    2013-03-01

    With the advent of Multi Input Multi Output (MIMO) systems, the system performance is highly dependent on the accurate representation of the channel condition that causes the wireless channel emulation to become increasingly important. The conventional Finite Impulse Response (FIR) based emulator has a high real-time but the complexity rapidly becomes impractical for larger array sizes. However, the frequency domain approach can avoid this problem and reduce the complexity for higher order arrays. The complexity comparison between in time domain and in frequency domain is made in this paper. The Fast Fourier Transform (FFT) as an important component of signal processing in frequency domain is briefly introduced and an FGPA system architecture based on CORDIC algorithm is proposed. The full design is implemented in Xilinx's Virtex-5.

  2. Frequency-selective exocytosis by ribbon synapses of hair cells in the bullfrog's amphibian papilla

    PubMed Central

    Patel, Suchit H.; Salvi, Joshua D.; Maoiléidigh, Dáibhid Ó; Hudspeth, A. J.

    2012-01-01

    The activity of auditory afferent fibers depends strongly on the frequency of stimulation. Although the bullfrog's amphibian papilla lacks the flexible basilar membrane that effects tuning in mammals, its afferents display comparable frequency selectivity. Seeking additional mechanisms of tuning in this organ, we monitored the synaptic output of hair cells by measuring changes in their membrane capacitance during sinusoidal electrical stimulation at various frequencies. Using perforated-patch recordings, we found that individual hair cells displayed frequency selectivity in synaptic exocytosis within the frequency range sensed by the amphibian papilla. Moreover, each cell's tuning varied in accordance with its tonotopic position. Using confocal imaging, we observed a tonotopic gradient in the concentration of proteinaceous Ca2+ buffers. A model for synaptic release suggests that this gradient maintains the sharpness of tuning. We conclude that hair cells of the amphibian papilla use synaptic tuning as an additional mechanism for sharpening their frequency selectivity. PMID:23015434

  3. 47 CFR 80.359 - Frequencies for digital selective calling (DSC).

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 47 Telecommunication 5 2011-10-01 2011-10-01 false Frequencies for digital selective calling (DSC... for digital selective calling (DSC). (a) General purpose calling. The following table describes the...-R Recommendation M.541-9, “Operational Procedures for the Use of Digital Selective-Calling...

  4. 47 CFR 80.359 - Frequencies for digital selective calling (DSC).

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 5 2010-10-01 2010-10-01 false Frequencies for digital selective calling (DSC... for digital selective calling (DSC). (a) General purpose calling. The following table describes the...-R Recommendation M.541-9, “Operational Procedures for the Use of Digital Selective-Calling...

  5. Ecological genetics of the Bromus tectorum (Poaceae) - Ustilago Bullata (Ustilaginaceae): A role for frequency dependent selection?

    Treesearch

    Susan E. Meyer; David L. Nelson; Suzette Clement; Alisa Ramakrishnan

    2010-01-01

    Evolutionary processes that maintain genetic diversity in plants are likely to include selection imposed by pathogens. Negative frequency-dependent selection is a mechanism for maintenance of resistance polymorphism in plant - pathogen interactions. We explored whether such selection operates in the Bromus tectorum - Ustilago bullata pathosystem. Gene-for-gene...

  6. Beyond the Classical Performance Limitations Controlling Uncertain MIMO Systems: UAV Applications

    DTIC Science & Technology

    2008-05-01

    multiple - input - multiple - output , MIMO ) with model...theory (QFT) [8]. 2.0 NON-DIAGONAL MIMO QFT CONTROL DESIGN METHODOLOGY [2-7] Control of multivariable systems ( multiple - input - multiple - output , MIMO ... MIMO QFT, Horowitz proposed to translate the original nxn MIMO problem into n separate quantitative multiple - input -single- output MISO problems,

  7. Selection of optimum frequencies for atmospheric electric path length measurement by satellite-borne microwave radiometers

    NASA Technical Reports Server (NTRS)

    Pandey, P. C.; Kakar, R. K.

    1983-01-01

    Numerical experiments using regressions by leaps and bounds have been performed to determine the optimum frequencies for satellite-borne microwave radiometers to estimate atmospheric electrical path length over the sea. The frequency range 5-40 GHz was searched. The effect of surface wind speed, sea surface temperature, and clouds was considered in the optimum frequency selection. The analysis indicates that approximately 0.6-cm rms accuracy is possible for one-way path length measurement using a proper pair of frequencies. The best two-channel subset selected by the leaps and bounds techniques is (16.0, 21.0) GHz.

  8. On Frequency Offset Estimation Using the iNET Preamble in Frequency Selective Fading Channels

    DTIC Science & Technology

    2014-03-01

    ASM fields; (bottom) the relationship between the indexes of the received samples r(n), the signal samples s(n), the preamble samples p (n) and the short...frequency offset estimators for SOQPSK-TG equipped with the iNET preamble and operating in ISI channels. Four of the five estimators exam - ined here are...sync marker ( ASM ), and data bits (an LDPC codeword). The availability of a preamble introduces the possibility of data-aided synchro- nization in

  9. MIMO equalization with adaptive step size for few-mode fiber transmission systems.

    PubMed

    van Uden, Roy G H; Okonkwo, Chigo M; Sleiffer, Vincent A J M; de Waardt, Hugo; Koonen, Antonius M J

    2014-01-13

    Optical multiple-input multiple-output (MIMO) transmission systems generally employ minimum mean squared error time or frequency domain equalizers. Using an experimental 3-mode dual polarization coherent transmission setup, we show that the convergence time of the MMSE time domain equalizer (TDE) and frequency domain equalizer (FDE) can be reduced by approximately 50% and 30%, respectively. The criterion used to estimate the system convergence time is the time it takes for the MIMO equalizer to reach an average output error which is within a margin of 5% of the average output error after 50,000 symbols. The convergence reduction difference between the TDE and FDE is attributed to the limited maximum step size for stable convergence of the frequency domain equalizer. The adaptive step size requires a small overhead in the form of a lookup table. It is highlighted that the convergence time reduction is achieved without sacrificing optical signal-to-noise ratio performance.

  10. Gravitational lensing frequencies - Galaxy cross-sections and selection effects

    NASA Technical Reports Server (NTRS)

    Fukugita, Masataka; Turner, Edwin L.

    1991-01-01

    Four issues - (1) the best currently available data on the galaxy velocity-dispersion distribution, (2) the effects of finite core radii potential ellipticity on lensing cross sections, (3) the predicted distribution of lens image separations compared to observational angular resolutions, and (4) the preferential inclusion of lens systems in flux limited samples - are considered in order to facilitate more realistic predictions of multiple image galaxy-quasar lensing frequencies. It is found that (1) the SIS lensing parameter F equals 0.047 +/-0.019 with almost 90 percent contributed by E and S0 galaxies, (2) observed E and S0 core radii are remarkably small, yielding a factor of less than about 2 reduction in total lensing cross sections, (3) 50 percent of galaxy-quasar lenses have image separations greater than about 1.3 arcsec, and (4) amplification bias factors are large and must be carefully taken into account. It is concluded that flat universe models excessively dominated by the cosmological constant are not favored by the small observed galaxy-quasar lensing rate.

  11. Low frequency electroacupuncture selectively decreases voluntarily ethanol intake in rats.

    PubMed

    Li, Jing; Zou, Yihuai; Ye, Jiang-Hong

    2011-11-25

    Although there is increasing clinical acceptance of acupuncture and electroacupuncture (EA) as a treatment of substance abuse-related disorders, our understanding of this treatment remains incomplete. Previous clinical and pre-clinical studies have shown that acupuncture and EA are effective in reducing ethanol consumption. Recent studies have shown that Sprague-Dawley (SD) rats under an intermittent-access two-bottle choice drinking procedure (IE procedure) voluntarily drank high amounts of ethanol. However, an effect of EA on ethanol consumption of the SD rats under this drinking procedure has not been demonstrated. In the present study, we demonstrated that SD rats escalated their ethanol intake and subsequently developed ethanol dependence under the IE procedure. A single low (2 Hz), but not high frequency (100 Hz) EA treatment applied at the bilateral acupoint Zusanli (ST36), but not at the tail reduced voluntary intake of, and preference for ethanol, but not sucrose. Furthermore, repeated EA treatments decreased the intake of and preference for ethanol, without resulting in a rebound increase in ethanol intake when the EA treatments were terminated. These observations indicate that EA may be a useful treatment for alcohol abuse.

  12. Energy Saving Glass Lamination via Selective Radio Frequency Heating

    SciTech Connect

    Shawn M. Allan; Patricia M. Strickland; Holly S. Shulman

    2009-11-11

    Ceralink Inc. developed FastFuse™, a rapid, new, energy saving process for lamination of glass and composites using radio frequency (RF) heating technology. The Inventions and Innovations program supported the technical and commercial research and development needed to elevate the innovation from bench scale to a self-supporting technology with significant potential for growth. The attached report provides an overview of the technical and commerical progress achieved for FastFuse™ during the course of the project. FastFuse™ has the potential to revolutionize the laminate manufacturing industries by replacing energy intensive, multi-step processes with an energy efficient, single-step process that allows higher throughput. FastFuse™ transmits RF energy directly into the interlayer to generate heat, eliminating the need to directly heat glass layers and the surrounding enclosures, such as autoclaves or vacuum systems. FastFuse™ offers lower start-up and energy costs (up to 90% or more reduction in energy costs), and faster cycles times (less than 5 minutes). FastFuse™ is compatible with EVA, TPU, and PVB interlayers, and has been demonstrated for glass, plastics, and multi-material structures such as photovoltaics and transparent armor.

  13. A robust and scalable neuromorphic communication system by combining synaptic time multiplexing and MIMO-OFDM.

    PubMed

    Srinivasa, Narayan; Zhang, Deying; Grigorian, Beayna

    2014-03-01

    This paper describes a novel architecture for enabling robust and efficient neuromorphic communication. The architecture combines two concepts: 1) synaptic time multiplexing (STM) that trades space for speed of processing to create an intragroup communication approach that is firing rate independent and offers more flexibility in connectivity than cross-bar architectures and 2) a wired multiple input multiple output (MIMO) communication with orthogonal frequency division multiplexing (OFDM) techniques to enable a robust and efficient intergroup communication for neuromorphic systems. The MIMO-OFDM concept for the proposed architecture was analyzed by simulating large-scale spiking neural network architecture. Analysis shows that the neuromorphic system with MIMO-OFDM exhibits robust and efficient communication while operating in real time with a high bit rate. Through combining STM with MIMO-OFDM techniques, the resulting system offers a flexible and scalable connectivity as well as a power and area efficient solution for the implementation of very large-scale spiking neural architectures in hardware.

  14. Individual brain-frequency responses to self-selected music.

    PubMed

    Höller, Yvonne; Thomschewski, Aljoscha; Schmid, Elisabeth Verena; Höller, Peter; Crone, Julia Sophia; Trinka, Eugen

    2012-12-01

    Music is a stimulus which may give rise to a wide range of emotional and cognitive responses. Therefore, brain reactivity to music has become a focus of interest in cognitive neuroscience. It is possible that individual preference moderates the effectof music on the brain. In the present study we examined whether there are common effects of listening to music even if each subject in a sample chooses their own piece of music. We invited 18 subjects to bring along their favorite relaxing music, and their favourite stimulating music. Additionally, a condition with tactile stimulation on the foot and a baseline condition (rest) without stimulation were used. The tactile stimulation was chosen to provide a simple, non-auditory condition which would be identical for all subjects. The electroencephalogram was recorded for each of the 3 conditions and during rest. We found responses in the alpha range mainly on parietal and occipital sites that were significant compared to baseline in 13 subjects during relaxing music, 15 subjects during activating music, and 16 subjects during tactile stimulation. Most subjects showed an alpha desynchronization in a lower alpha range followed by a synchronization in an upper frequency range. However, some subjects showed an increase in this area, whereas others showed a decrease only. In addition, many subjects showed reactivity in the beta range. Beta activity was especially increased while listening to activating music and during tactile stimulation in most subjects. We found interindividual differences in the response patterns even though the stimuli provoked comparable subjective emotions (relaxation, activation), and even if the stimulus was the same for all subjects (somatosensory stimulation). We suggest that brain responsivity to music should be examined individually by considering individual characteristics. Copyright © 2012 Elsevier B.V. All rights reserved.

  15. Energy Saving Glass Lamination via Selective Radio-Frequency Heating

    SciTech Connect

    Shulman, Holly S.; Allan, Shawn M.

    2009-11-11

    This Inventions and Innovations program supported the technical and commercial research and development needed to elevate Ceralink's energy saving process for flat glass lamination from bench scale to a self-supporting technology with significant potential for growth. Radio-frequency heating was any un-explored option for laminating glass prior to this program. With significant commercial success through time and energy savings in the wood, paper, and plastics industries, RF heating was found to have significant promise for the energy intensive glass lamination industry. A major technical goal of the program was to demonstrate RF lamination across a wide range of laminate sizes and materials. This was successfully accomplished, dispelling many skeptics' concerns about the abilities of the technology. Ceralink laminated panels up to 2 ft x 3 ft, with four sets processed simultaneously, in a 3 minute cycle. All major categories of interlayer materials were found to work with RF lamination. In addition to laminating glass, other materials including photovoltaic silicon solar cells, light emitting diodes, metallized glass, plastics (acrylic and polycarbonate), and ceramics (alumina) were found compatible with the RF process. This opens up a wide range of commercial opportunities beyond the initially targeted automotive industry. The dramatic energy savings reported for RF lamination at the bench scale were found to be maintained through the scale up of the process. Even at 2 ft x 3 ft panel sizes, energy savings are estimated to be at least 90% compared to autoclaving or vacuum lamination. With targeted promotion through conference presentations, press releases and internet presence, RF lamination has gained significant attention, drawing large audiences at American Ceramic Society meetings. The commercialization success of the project includes the establishment of a revenue-generating business model for providing process development and demonstrations for potential RF

  16. Study of the cortical representation of whisker frequency selectivity using voltage-sensitive dye optical imaging

    PubMed Central

    Tsytsarev, Vassiliy; Pumbo, Elena; Tang, Qinggong; Chen, Chao-Wei; Kalchenko, Vyacheslav; Chen, Yu

    2016-01-01

    ABSTRACT The facial whiskers of rodents act as a high-resolution tactile apparatus that allow the animal to detect the finest details of its environment. Previously it was shown that whisker-sensitive neurons in the somatosensory cortex show frequency selectivity to small amplitude stimuli, An intravital voltage-sensitive dye optical imaging (VSDi) method in combination with the different frequency whisker stimulation was used in order to visualize neural activity in the mice somatosensory cortex in response to the stimulation of a single whisker by different frequencies. Using the intravital voltage-sensitive dye optical imaging (VSDi) method in combination with the different frequency whisker stimulation we visualized neural activity in the mice somatosensory cortex in response to the stimulation of a single whisker by different frequencies. We found that whisker stimuli with different frequencies led to different optical signals in the barrel field. Our results provide evidence that different neurons of the barrel cortex have different frequency preferences. This supports prior research that whisker deflections cause responses in cortical neurons within the barrel field according to the frequency of the stimulation. Many studies of the whisker frequency selectivity were performed using unit recording but to map spatial organization, imaging methods are essential. In the work described in the present paper, we take a serious step toward detailed functional mapping of the somatosensory cortex using VSDi. To our knowledge, this is the first demonstration of whisker frequency sensitivity and selectivity of barrel cortex neurons with optical imaging methods. PMID:28243518

  17. The influence of density on frequency-dependent selection by wild birds feeding on artificial prey

    PubMed Central

    Allen, J. A.; Raison, H. E.; Weale, M. E.

    1998-01-01

    Previous work has demonstrated frequency-dependent selection by wild garden birds when feeding on green and brown pastry 'baits'. When the density of baits is low, the common colour is eaten disproportionately more than the rare colour (apostatic selection), and when the density is very high, the rare colour is eaten disproportionately more than the common (anti-apostatic selection). We explored the relationship between frequency-dependent predation and density in an experiment at 16 separate sites, using four levels of density and two frequencies of green and brown. Analysis of estimates of log-relative risk ratios showed little evidence for frequency-independent selection, but frequency-dependent selection changed gradually from apostatic at low density to anti-apostatic at high density. The validity of these conclusions in terms of individual bird behaviour was confirmed by Monte-Carlo simulations. We thus conclude that selection by wild birds feeding on green and brown artificial prey is frequency dependent, and that the strength and direction of this selection changes with prey density in a gradual and predictable manner.

  18. Cooperative MIMO technology in multiple hops wireless sensor networks

    NASA Astrophysics Data System (ADS)

    Yuan, Lina; Chen, Huajun; Gong, Jing

    2017-03-01

    The limited lifetime is one of the important factors restricted wireless sensor networks (WSNs), when possible, wireless nodes often operate with small batteries, while battery replacement is a very difficult and expensive. So the nodes must work long hours in the case of no battery replacement. Therefore, in WSNs, minimizing energy consumption is an important design consideration, at the same time, the transmission strategies of energy efficiency must be used for data forwarding. This paper, using cooperative multiple input multiple output(MIMO) technology combined with multiple hops technology, has put forward a new transmission model, i.e., the MIMO-MISO(multi-input multi-output)/MIMO-MIMO model. Simulation results demonstrate the proposed MIMO-MISO/MIMO-MIMO to minimize energy consumption of each node every node for multi-hop WSNs, to save a great deal of energy for a larger transmission distance, which makes the life of the entire network be extended.

  19. MIMO Precoding for Networked Control Systems with Energy Harvesting Sensors

    NASA Astrophysics Data System (ADS)

    Cai, Songfu; Lau, Vincent K. N.

    2016-09-01

    In this paper, we consider a MIMO networked control system with an energy harvesting sensor, where an unstable MIMO dynamic system is connected to a controller via a MIMO fading channel. We focus on the energy harvesting and MIMO precoding design at the sensor so as to stabilize the unstable MIMO dynamic plant subject to the energy availability constraint at the sensor. Using the Lyapunov optimization approach, we propose a closed-form dynamic energy harvesting and dynamic MIMO precoding solution, which has an event-driven control structure. Furthermore, the MIMO precoding solution is shown to have an eigenvalue water-filling structure, where the water level depends on the state estimation covariance, energy queue and the channel state, and the sea bed level depends on the state estimation covariance. The proposed scheme is also compared with various baselines and we show that significant performance gains can be achieved.

  20. Frequency selective infrared optical filters for micro-bolometers

    NASA Astrophysics Data System (ADS)

    Creazzo, Timothy A.; Zablocki, Mathew J.; Zaman, Lenin; Sharkawy, Ahmed; Mirotznik, Mark S.; Prather, Dennis W.

    2017-05-01

    Current micro-bolometers are broadband detectors and tend to absorb a broad window of the IR spectrum for thermal imaging. Such systems are limited due to their lack of sensitivity to blackbody radiation, as well as the inability to spectrally discern multiple wavelengths in the field of view for hyperspectral imaging (HSI). As a result, many important applications such as low concentration chemical detection cannot be performed. One solution to this problem is to employ a system with thermoelectrically cooled or liquid nitrogen cooled sensors, which can lead to higher sensitivity in detection. However, one major drawback of these systems is the size, weight and power (SWaP) issue as they tend to be rather bulky and cumbersome, which largely challenges their use in unmanned aerial vehicles. Further, spectral filtering is commonly performed with large hardware and moving gratings, greatly increasing the SWaP of the system. To this point, Lumilant's effort is to develop wavelength selective uncooled IR filters that can be integrated onto a microbolometer, to exceed the sensitivity imposed by the blackbody radiation limit. We have demonstrated narrowband absorbers and electrically tunable filters addressing the need for low-SWaP platforms.

  1. Selection of optimal artificial boundary condition (ABC) frequencies for structural damage identification

    NASA Astrophysics Data System (ADS)

    Mao, Lei; Lu, Yong

    2016-07-01

    In this paper, the sensitivities of artificial boundary condition (ABC) frequencies to the damages are investigated, and the optimal sensors are selected to provide the reliable structural damage identification. The sensitivity expressions for one-pin and two-pin ABC frequencies, which are the natural frequencies from structures with one and two additional constraints to its original boundary condition, respectively, are proposed. Based on the expressions, the contributions of the underlying mode shapes in the ABC frequencies can be calculated and used to select more sensitive ABC frequencies. Selection criteria are then defined for different conditions, and their performance in structural damage identification is examined with numerical studies. From the findings, conclusions are given.

  2. Surface plasmon optical antennae in the infrared region with high resonant efficiency and frequency selectivity.

    PubMed

    Ueno, Kosei; Sun, Quan; Mino, Masahiro; Itoh, Takumi; Oshikiri, Tomoya; Misawa, Hiroaki

    2016-08-08

    Infrared light has received attention for sensor applications, including fingerprint spectroscopy, in the bioengineering and security fields. Surface plasmon physics enables the operation of a light harvesting optical antenna. Gold nanochains exhibit localized surface plasmon resonance (LSPR) in the infrared region with high frequency selectivity. However, a feasible design for optical antennae with a higher resonant efficiency and frequency selectivity as a function of structural design and periodicity is still unknown. In the present study, we investigated the relationship between the resonant efficiency and frequency selectivity as a function of the structural design of gold nanochains and explored structural periodicity for obtaining highly frequency-selective optical antennae. An optical antenna design with higher resonant efficiency is proposed on the basis of its efficient interaction with non-polarized light.

  3. Frequency-dependent selection for rare genotypes promotes genetic diversity of a tropical palm.

    PubMed

    Browne, Luke; Karubian, Jordan

    2016-12-01

    Negative frequency-dependent selection among species is a key driver of community diversity in natural systems, but the degree to which negative frequency-dependent selection shapes patterns of survival and genetic diversity within species is poorly understood. In a 5-year field experiment, we show that seedlings of a tropical palm with rare genotypes had a pronounced survival advantage over seedlings with common genotypes, with effect sizes comparable to that of light availability. This 'rare genotype advantage' led to an increase in population-wide genetic diversity among seedlings compared to null expectations, as predicted by negative frequency-dependent selection, and increased reproductive success in adult trees with rare genotypes. These results suggest that within-species negative frequency-dependent selection of genotypes can shape genetic variation on ecologically relevant timescales in natural systems and may be a key, overlooked source of non-random mortality for tropical plants.

  4. Development of a four-frequency selective surface prototype spacecraft antenna

    NASA Astrophysics Data System (ADS)

    Hickey, Gregory S.; Wu, Te-Kao

    NASA-JPL's four-frequency telecommunication system design entails the creation and integration of a frequency-selective surface (FSS) subreflector into the high-gain antenna subsystem. The FSS design, which incorporates a periodic array of conducting elements on a kevlar/polymer composite structure, will be able to multiplex S, X, Ku, and Ka frequency-band wavelengths. Accounts are presented of the FSS's development, mechanical testing, and electrical testing.

  5. Frequency selectivity of chemi-acoustic amplification in a constant volume gas

    SciTech Connect

    Riley, M.E.

    1984-06-01

    The fact that chemical reactions can amplify disturbances suggests that the cellular structure of gaseous detonations is a result of frequency selective amplification of random initial fluctuations. Unfortunately, previous studies have shown a minimal frequency dependence in the chemi-acoustic growth rate. The calculations in this paper demonstrate that the amplification process is strongly frequency dependent in a uniform gas. These results encourage a new exploration of the perturbation-theoretic analysis of detonation waves.

  6. Development of a four-frequency selective surface prototype spacecraft antenna

    NASA Technical Reports Server (NTRS)

    Hickey, Gregory S.; Wu, Te-Kao

    1992-01-01

    NASA-JPL's four-frequency telecommunication system design entails the creation and integration of a frequency-selective surface (FSS) subreflector into the high-gain antenna subsystem. The FSS design, which incorporates a periodic array of conducting elements on a kevlar/polymer composite structure, will be able to multiplex S, X, Ku, and Ka frequency-band wavelengths. Accounts are presented of the FSS's development, mechanical testing, and electrical testing.

  7. MIMO-OFDM signal optimization for SAR imaging radar

    NASA Astrophysics Data System (ADS)

    Baudais, J.-Y.; Méric, S.; Riché, V.; Pottier, É.

    2016-12-01

    This paper investigates the optimization of the coded orthogonal frequency division multiplexing (OFDM) transmitted signal in a synthetic aperture radar (SAR) context. We propose to design OFDM signals to achieve range ambiguity mitigation. Indeed, range ambiguities are well known to be a limitation for SAR systems which operates with pulsed transmitted signal. The ambiguous reflected signal corresponding to one pulse is then detected when the radar has already transmitted the next pulse. In this paper, we demonstrate that the range ambiguity mitigation is possible by using orthogonal transmitted wave as OFDM pulses. The coded OFDM signal is optimized through genetic optimization procedures based on radar image quality parameters. Moreover, we propose to design a multiple-input multiple-output (MIMO) configuration to enhance the noise robustness of a radar system and this configuration is mainly efficient in the case of using orthogonal waves as OFDM pulses. The results we obtain show that OFDM signals outperform conventional radar chirps for range ambiguity suppression and for robustness enhancement in 2 ×2 MIMO configuration.

  8. Selective Impairment in Frequency Discrimination in a Mouse Model of Tinnitus

    PubMed Central

    Mwilambwe-Tshilobo, Laetitia; Davis, Andrew J. O.; Aizenberg, Mark; Geffen, Maria N.

    2015-01-01

    Tinnitus is an auditory disorder, which affects millions of Americans, including active duty service members and veterans. It is manifested by a phantom sound that is commonly restricted to a specific frequency range. Because tinnitus is associated with hearing deficits, understanding how tinnitus affects hearing perception is important for guiding therapies to improve the quality of life in this vast group of patients. In a rodent model of tinnitus, prolonged exposure to a tone leads to a selective decrease in gap detection in specific frequency bands. However, whether and how hearing acuity is affected for sounds within and outside those frequency bands is not well understood. We induced tinnitus in mice by prolonged exposure to a loud mid-range tone, and behaviorally assayed whether mice exhibited a change in frequency discrimination acuity for tones embedded within the mid-frequency range and high-frequency range at 1, 4, and 8 weeks post-exposure. A subset of tone-exposed mice exhibited tinnitus-like symptoms, as demonstrated by selective deficits in gap detection, which were restricted to the high frequency range. These mice exhibited impaired frequency discrimination both for tones in the mid-frequency range and high-frequency range. The remaining tone exposed mice, which did not demonstrate behavioral evidence of tinnitus, showed temporary deficits in frequency discrimination for tones in the mid-frequency range, while control mice remained unimpaired. Our findings reveal that the high frequency-specific deficits in gap detection, indicative of tinnitus, are associated with impairments in frequency discrimination at the frequency of the presumed tinnitus. PMID:26352864

  9. Energy Saving Glass Lamination via Selective Radio Frequency Heating

    SciTech Connect

    Allan, Shawn M.

    2012-02-27

    This project focused on advancing radio-frequency (RF) lamination technology closer to commercial implementation, in order to reduce the energy intensity of glass lamination by up to 90%. Lamination comprises a wide range of products including autoglass, architectural safety and innovative design glass, transparent armor (e.g. bullet proof glass), smart glass, mirrors, and encapsulation of photovoltaics. Lamination is also the fastest growing segment of glass manufacturing, with photovoltaics, architectural needs, and an anticipated transition to laminated side windows in vehicles. The state-of-the-art for glass lamination is to use autoclaves, which apply heat and uniform gas pressure to bond the laminates over the course of 1 to 18 hours. Laminates consist of layers of glass or other materials bonded with vinyl or urethane interlayers. In autoclaving, significant heat energy is lost heating the chamber, pressurized air, glass racks, and the glass. In RF lamination, the heat is generated directly in the vinyl interlayer, causing it to heat and melt quickly, in just 1 to 10 minutes, without significantly heating the glass or the equipment. The main purpose of this project was to provide evidence that low energy, rapid RF lamination quality met the same standards as conventionally autoclaved windows. The development of concepts for laminating curved glass with RF lamination was a major goal. Other primary goals included developing a stronger understanding of the lamination product markets described above, and to refine the potential benefits of commercial implementation. The scope of the project was to complete implementation concept studies in preparation for continuation into advanced development, pilot studies, and commercial implementation. The project consisted of 6 main tasks. The first dealt with lamination with poly-vinyl butyral (PVB) interlayers, which prior work had shown difficulties in achieving good quality laminates, working with Pilkington North

  10. Energy Saving Glass Lamination via Selective Radio Frequency Heating

    SciTech Connect

    Allan, Shawn M; Baranova, Inessa; Poley, Joseph; Reis, Henrique

    2012-02-27

    This project focused on advancing radio-frequency (RF) lamination technology closer to commercial implementation, in order to reduce the energy intensity of glass lamination by up to 90%. Lamination comprises a wide range of products including autoglass, architectural safety and innovative design glass, transparent armor (e.g. bullet proof glass), smart glass, mirrors, and encapsulation of photovoltaics. Lamination is also the fastest growing segment of glass manufacturing, with photovoltaics, architectural needs, and an anticipated transition to laminated side windows in vehicles. The state-of-the-art for glass lamination is to use autoclaves, which apply heat and uniform gas pressure to bond the laminates over the course of 1 to 18 hours. Laminates consist of layers of glass or other materials bonded with vinyl or urethane interlayers. In autoclaving, significant heat energy is lost heating the chamber, pressurized air, glass racks, and the glass. In RF lamination, the heat is generated directly in the vinyl interlayer, causing it to heat and melt quickly, in just 1 to 10 minutes, without significantly heating the glass or the equipment. The main purpose of this project was to provide evidence that low energy, rapid RF lamination quality met the same standards as conventionally autoclaved windows. The development of concepts for laminating curved glass with RF lamination was a major goal. Other primary goals included developing a stronger understanding of the lamination product markets described above, and to refine the potential benefits of commercial implementation. The scope of the project was to complete implementation concept studies in preparation for continuation into advanced development, pilot studies, and commercial implementation. The project consisted of 6 main tasks. The first dealt with lamination with poly-vinyl butyral (PVB) interlayers, which prior work had shown difficulties in achieving good quality laminates, working with Pilkington North

  11. Underwater acoustic channel estimation using multiple sources and receivers in shallow waters at very-high frequencies

    NASA Astrophysics Data System (ADS)

    Kaddouri, Samar

    The underwater channel poses numerous challenges for acoustic communication. Acoustic waves suffer long propagation delay, multipath, fading, and potentially high spatial and temporal variability. In addition, there is no typical underwater acoustic channel; every body of water exhibits quantifiably different properties. Underwater acoustic modems are traditionally operated at low frequencies. However, the use of broadband, high frequency communication is a good alternative because of the lower background noise compared to low-frequencies, considerably larger bandwidth and better source transducer efficiency. One of the biggest problems in the underwater acoustic communications at high frequencies is time-selective fading, resulting in the Doppler spread. While many Doppler detection, estimation and compensation techniques can be found in literature, the applications are limited to systems operating at low frequencies contained within frequencies ranging from a few hundred Hertz to around 30 kHz. This dissertation proposes two robust channel estimation techniques for simultaneous transmissions using multiple sources and multiple receivers (MIMO) that closely follows the rapidly time-varying nature of the underwater channel. The first method is a trended least square (LS) estimation that combines the traditional LS method with an empirical modal decomposition (EMD) based trend extraction algorithm. This method allows separating the slow fading modes in the MIMO channels from the fast-fading ones and thus achieves a close tracking of the channel impulse response time fluctuations. This dissertation also outlines a time-varying underwater channel estimation method based on the channel sparsity characteristic. The sparsity of the underwater communication channel is exploited by using the MIMO P-iterative greedy orthogonal matching pursuit (MIMO-OMP) algorithm for the channel estimation. Both techniques are demonstrated in a fully controlled environment, using simulated

  12. Aircraft Free-Space MIMO Communications

    DTIC Science & Technology

    2011-08-01

    separation of 700 m. The capacity limit for large longitudinal separation is 6.92 bits/sec per Hz, the keyhole[3] single- input - multiple (12)- output (SIMO...DATES COVERED (From - To) JAN 2008 – JAN 2009 4. TITLE AND SUBTITLE AIRCRAFT FREE-SPACE MIMO COMMUNICATIONS 5a. CONTRACT NUMBER IN-HOUSE 5b. GRANT...ABSTRACT We investigate the use of MIMO to increase the data rate of air to air wireless links without scattered propagation. The conditions for

  13. Robust adaptive beamforming for MIMO monopulse radar

    NASA Astrophysics Data System (ADS)

    Rowe, William; Ström, Marie; Li, Jian; Stoica, Petre

    2013-05-01

    Researchers have recently proposed a widely separated multiple-input multiple-output (MIMO) radar using monopulse angle estimation techniques for target tracking. The widely separated antennas provide improved tracking performance by mitigating complex target radar cross-section fades and angle scintillation. An adaptive array is necessary in this paradigm because the direct path from any transmitter could act as a jammer at a receiver. When the target-free covariance matrix is not available, it is critical to include robustness into the adaptive beamformer weights. This work explores methods of robust adaptive monopulse beamforming techniques for MIMO tracking radar.

  14. Bidirectional MIMO Channel Tracking Based on PASTd and Performance Evaluation

    NASA Astrophysics Data System (ADS)

    Ehrenberg, Livnat; Gannot (Eurasipmember), Sharon; Shayevitz, Ofer; Leshem, Amir; Zehavi, Ephraim

    2010-12-01

    We consider a bidirectional time division duplex (TDD) multiple-input multiple-output (MIMO) communication system with time-varying channel and additive white Gaussian noise (AWGN). A blind bidirectional channel tracking algorithm, based on the projection approximation subspace tracking (PAST) algorithm, is applied in both terminals. The resulting singular value decomposition (SVD) of the channel matrix is then used to approximately diagonalize the channel. The proposed method is applied to an orthogonal frequency-division multiplexing-(OFDM-)MIMO setting with a typical indoor time-domain reflection model. The computational cost of the proposed algorithm, compared with other state-of-the-art algorithms, is relatively small. The Kalman filter is utilized for establishing a benchmark for the obtained performance of the proposed tracking algorithm. The performance degradation relative to a full channel state information (CSI) due to the application of the tracking algorithm is evaluated in terms of average effective rate and the outage probability and compared with alternative tracking algorithms. The obtained results are also compared with a benchmark obtained by the Kalman filter with known input signal and channel characteristics. It is shown that the expected degradation in performance of frequency-domain algorithms (which do not exploit the smooth frequency response of the channel) is only minor compared with time-domain algorithms in a range of reasonable signal-to-noise ratio (SNR) levels. The proposed bidirectional frequency-domain tracking algorithm, proposed in this paper, is shown to attain communication rates close to the benchmark and to outperform a competing algorithm. The paper is concluded by evaluating the proposed blind tracking method in terms of the outage probability and the symbol error rate (SER) versus. SNR for binary phase shift keying (BPSK) and 4-Quadrature amplitude modulation (QAM) constellations.

  15. Investigation of Doppler Effects on high mobility OFDM-MIMO systems with the support of High Altitude Platforms (HAPs)

    NASA Astrophysics Data System (ADS)

    Mohammed, H. A.; Sibley, M. J. N.; Mather, P. J.

    2012-05-01

    The merging of Orthogonal Frequency Division Multiplexing (OFDM) with Multiple-input multiple-output (MIMO) is a promising mobile air interface solution for next generation wireless local area networks (WLANs) and 4G mobile cellular wireless systems. This paper details the design of a highly robust and efficient OFDM-MIMO system to support permanent accessibility and higher data rates to users moving at high speeds, such as users travelling on trains. It has high relevance for next generation wireless local area networks (WLANs) and 4G mobile cellular wireless systems. The paper begins with a comprehensive literature review focused on both technologies. This is followed by the modelling of the OFDM-MIMO physical layer based on Simulink/Matlab that takes into consideration high vehicular mobility. Then the entire system is simulated and analysed under different encoding and channel estimation algorithms. The use of High Altitude Platform system (HAPs) technology is considered and analysed.

  16. 60-GHz optical/wireless MIMO system integrated with optical subcarrier multiplexing and 2x2 wireless communication.

    PubMed

    Lin, Chi-Hsiang; Lin, Chun-Ting; Huang, Hou-Tzu; Zeng, Wei-Siang; Chiang, Shou-Chih; Chang, Hsi-Yu

    2015-05-04

    This paper proposes a 2x2 MIMO OFDM Radio-over-Fiber scheme based on optical subcarrier multiplexing and 60-GHz MIMO wireless transmission. We also schematically investigated the principle of optical subcarrier multiplexing, which is based on a dual-parallel Mach-Zehnder modulator (DP-MZM). In our simulation result, combining two MIMO OFDM signals to drive DP-MZM gives rise to the PAPR augmentation of less than 0.4 dB, which mitigates nonlinear distortion. Moreover, we applied a Levin-Campello bit-loading algorithm to compensate for the uneven frequency responses in the V-band. The resulting system achieves OFDM signal rates of 61.5-Gbits/s with BER of 10(-3) over 25-km SMF transmission followed by 3-m wireless transmission.

  17. Frequency-selective multilayer electromagnetic bandgap structure combining carbon nanotubes with polymeric or ceramic substrates

    NASA Astrophysics Data System (ADS)

    Danlée, Y.; Huynen, I.; Bailly, C.

    2014-09-01

    We present an electromagnetic bandgap (EBG) multilayer structure, acting as a frequency-selective surface able to absorb in specified narrow frequency bands within the GHz-range. The structure is a lossy EBG using ultra-thin conductive layers to generate a controlled resonance in homogenous high permittivity slabs. The basic structure is composed of carbon nanotubes depositions sandwiched between polycarbonate films, which are stacked in alternation between dielectric slabs. The physical properties (i.e., relative permittivity and thickness) of the dielectric spacers allow creating narrow high-absorption bands at defined frequencies. This multilayer approach offers a smart and versatile solution for tuning the selectivity of EBG performance.

  18. Frequency-Selective Response of the Tectorial Membrane in the Frog Basilar Papilla

    NASA Astrophysics Data System (ADS)

    Schoffelen, R. L. M.; Segenhout, J. M.; van Dijk, P.

    2009-02-01

    The frog's basilar papilla is a useful study object for cochlear mechanics, because of it's relatively simple anatomy and functionality. We investigated the displacement amplitudes of the basilar papilla's tectorial membrane in response to stimulation of the oval window at various frequencies within the auditory range of the Northern leopard frog. From our measurement data we find that the tectorial membrane exhibits a frequency selective response. The peak response was found to occur at 1500Hz in correspondence with known data for the response of auditory nerve fibers from the organ. From these data we conclude that mechanical tuning contributes significantly to the frequency selectivity of the frog's basilar papilla

  19. Frequency-Domain Eigenbeam-SDM and Equalization for Single-Carrier Transmissions

    NASA Astrophysics Data System (ADS)

    Ozaki, Kazuyuki; Nakajima, Akinori; Adachi, Fumiyuki

    In mobile communications, the channel consists of many resolvable paths with different time delays, resulting in a severely frequency-selective fading channel. The frequency-domain equalization (FDE) can take advantage of the channel selectivity and improve the bit error rate (BER) performance of the single-carrier (SC) transmission. Recently, multi-input multi-output (MIMO) multiplexing is gaining much attention for achieving very high speed data transmissions with the limited bandwidth. Eigenbeam space division multiplexing (E-SDM) is known as one of MIMO multiplexing techniques. In this paper, we propose frequency-domain SC E-SDM for SC transmission. In frequency-domain SC E-SDM, the orthogonal transmission channels to transmit different data in parallel are constructed at each orthogonal frequency. At a receiver, FDE is used to suppress the inter-symbol interference (ISI). In this paper, the transmit power allocation and adaptive modulation based on the equivalent channel gains after performing FDE are applied. The BER performance of the frequency-domain SC E-SDM in a severe frequency-selective Rayleigh fading channel is evaluated by computer simulation.

  20. Layered Soft Interference Cancellation for SC-MIMO Spatial Multiplexing Transmission with High Level Data Modulation

    NASA Astrophysics Data System (ADS)

    Nakajima, Akinori; Fukui, Noriyuki; Kubo, Hiroshi

    For multiple-input multiple-output (MIMO) spatial multiplexing, signal separation/detection is one of the most important signal processing parts, so that signal separation/detection schemes are being vigorously researched. As a promising signal separation/detection scheme, frequency-domain iterative soft interference cancellation (FD-SIC) has been proposed. Although iterative FD-SIC can provide the transmission performance close to lower bound for QPSK, the accuracy of signal separation/detection significantly degrades in case of high level data modulation. Therefore, in this paper, we propose layered soft interference cancellation (LSIC). We consider single-carrier (SC)-MIMO spatial multiplexing with frequency domain equalization (FDE). The achievable frame error rate (FER) performances with LSIC are evaluated by computer simulation to show that LSIC can provide better FER performance than iterative FD-SIC.

  1. 47 CFR 80.359 - Frequencies for digital selective calling (DSC).

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 47 Telecommunication 5 2013-10-01 2013-10-01 false Frequencies for digital selective calling (DSC). 80.359 Section 80.359 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND... for digital selective calling (DSC). (a) General purpose calling. The following table describes...

  2. 47 CFR 80.359 - Frequencies for digital selective calling (DSC).

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 47 Telecommunication 5 2014-10-01 2014-10-01 false Frequencies for digital selective calling (DSC). 80.359 Section 80.359 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND... for digital selective calling (DSC). (a) General purpose calling. The following table describes...

  3. 47 CFR 80.359 - Frequencies for digital selective calling (DSC).

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 47 Telecommunication 5 2012-10-01 2012-10-01 false Frequencies for digital selective calling (DSC). 80.359 Section 80.359 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND... for digital selective calling (DSC). (a) General purpose calling. The following table describes...

  4. The long-term evolution of multilocus traits under frequency-dependent disruptive selection.

    PubMed

    van Doorn, G Sander; Dieckmann, Ulf

    2006-11-01

    Frequency-dependent disruptive selection is widely recognized as an important source of genetic variation. Its evolutionary consequences have been extensively studied using phenotypic evolutionary models, based on quantitative genetics, game theory, or adaptive dynamics. However, the genetic assumptions underlying these approaches are highly idealized and, even worse, predict different consequences of frequency-dependent disruptive selection. Population genetic models, by contrast, enable genotypic evolutionary models, but traditionally assume constant fitness values. Only a minority of these models thus addresses frequency-dependent selection, and only a few of these do so in a multilocus context. An inherent limitation of these remaining studies is that they only investigate the short-term maintenance of genetic variation. Consequently, the long-term evolution of multilocus characters under frequency-dependent disruptive selection remains poorly understood. We aim to bridge this gap between phenotypic and genotypic models by studying a multilocus version of Levene's soft-selection model. Individual-based simulations and deterministic approximations based on adaptive dynamics theory provide insights into the underlying evolutionary dynamics. Our analysis uncovers a general pattern of polymorphism formation and collapse, likely to apply to a wide variety of genetic systems: after convergence to a fitness minimum and the subsequent establishment of genetic polymorphism at multiple loci, genetic variation becomes increasingly concentrated on a few loci, until eventually only a single polymorphic locus remains. This evolutionary process combines features observed in quantitative genetics and adaptive dynamics models, and it can be explained as a consequence of changes in the selection regime that are inherent to frequency-dependent disruptive selection. Our findings demonstrate that the potential of frequency-dependent disruptive selection to maintain polygenic

  5. Broadband Frequency-Selective Spoof Surface Plasmon Polaritons on Ultrathin Metallic Structure

    PubMed Central

    Yin, Jia Yuan; Ren, Jian; Zhang, Hao Chi; Pan, Bai Cao; Cui, Tie Jun

    2015-01-01

    We propose an ultrathin metallic structure to produce frequency-selective spoof surface plasmon polaritons (SPPs) in the microwave and terahertz frequencies. Designed on a thin dielectric substrate, the ultrathin metallic structure is composed of two oppositely oriented single-side corrugated strips, which are coupled to two double-side corrugated strips. The structure is fed by a traditional coplanar waveguide (CPW). To make a smooth conversion between the spatial modes in CPW and SPP modes, two transition sections are also designed. We fabricate and measure the frequency-selective spoof SPP structure in microwave frequencies. The measurement results show that the reflection coefficient is less than -10 dB with the transmission loss around 1.5 dB in the selective frequency band from 7 to 10 GHz, which are in good agreements with numerical simulations. The proposed structure can be used as an SPP filter with good performance of low loss, high transmission, and wide bandwidth in the selective frequency band. PMID:25641730

  6. Tuning in to sound: frequency-selective attentional filter in human primary auditory cortex.

    PubMed

    Da Costa, Sandra; van der Zwaag, Wietske; Miller, Lee M; Clarke, Stephanie; Saenz, Melissa

    2013-01-30

    Cocktail parties, busy streets, and other noisy environments pose a difficult challenge to the auditory system: how to focus attention on selected sounds while ignoring others? Neurons of primary auditory cortex, many of which are sharply tuned to sound frequency, could help solve this problem by filtering selected sound information based on frequency-content. To investigate whether this occurs, we used high-resolution fMRI at 7 tesla to map the fine-scale frequency-tuning (1.5 mm isotropic resolution) of primary auditory areas A1 and R in six human participants. Then, in a selective attention experiment, participants heard low (250 Hz)- and high (4000 Hz)-frequency streams of tones presented at the same time (dual-stream) and were instructed to focus attention onto one stream versus the other, switching back and forth every 30 s. Attention to low-frequency tones enhanced neural responses within low-frequency-tuned voxels relative to high, and when attention switched the pattern quickly reversed. Thus, like a radio, human primary auditory cortex is able to tune into attended frequency channels and can switch channels on demand.

  7. Wide Angle, Single Screen, Gridded Square-Loop Frequency Selective Surface for Diplexing Two Closely Separated Frequency Bands

    NASA Technical Reports Server (NTRS)

    Wu, Te-Kao (Inventor)

    1996-01-01

    The design and performance of a wide angle, single screen, frequency selective surface (FSS) with gridded square-loop path elements are described for diplexing closely separated signal bands, for example, X- and Ku-band signals in an Orbiting Very Long Baseline Interferometer (OVLBI) earth station reflector antenna system, as well as other applications such as military and commercial communications via satellites. Excellent agreement is obtained between the predicted and measured results of this FSS design using the gridded square-loop patch elements sandwiched between 0.0889 cm thick tetrafluoroethylene fluorocarbon polymer (PTFE) slabs. Resonant frequency drift is reduced by 1 GHz with an incidence angle from 0 deg normal to 40 deg from normal.

  8. Eating frequency and energy regulation in free-living adults consuming self-selected diets.

    PubMed

    McCrory, Megan A; Howarth, Nancy C; Roberts, Susan B; Huang, Terry T-K

    2011-01-01

    The relative importance of eating frequency to weight control is poorly understood. This review examines the evidence to date on the role of eating frequency in weight control in free-living adults. The majority of cross-sectional studies in free-living adults show an inverse relationship between eating frequency and adiposity; however, this is likely an artifact produced by the underreporting of eating frequency concurrent with underreporting of energy intake. When implausible energy intake reporting (which is mostly underreporting) is taken into account, the association between eating frequency and adiposity becomes positive. In studies in which eating frequency is prescribed and food intake is mostly self-selected, there is either no effect or a minor positive effect of eating frequency on energy intake. Most of those studies have been short-term and lack the necessary dietary biomarkers to validate reported energy intakes and eating frequencies. In conclusion, there is some suggestion from cross-sectional studies in which energy intake underreporting is taken into account and from experimental studies to date that greater eating frequency may promote positive energy balance. However, experimental studies of longer-term duration that include objective dietary biomarkers are necessary before firm conclusions about the relative importance of eating frequency in weight control can be made.

  9. Mechanisms underlying intensity-dependent changes in cortical selectivity for frequency-modulated sweeps.

    PubMed

    Razak, K A

    2012-04-01

    Frequency-modulated (FM) sweeps are common components of species-specific vocalizations. The intensity of FM sweeps can cover a wide range in the natural environment, but whether intensity affects neural selectivity for FM sweeps is unclear. Bats, such as the pallid bat, which use FM sweeps for echolocation, are suited to address this issue, because the intensity of echoes will vary with target distance. In this study, FM sweep rate selectivity of pallid bat auditory cortex neurons was measured using downward sweeps at different intensities. Neurons became more selective for FM sweep rates present in the bat's echolocation calls as intensity increased. Increased selectivity resulted from stronger inhibition of responses to slower sweep rates. The timing and bandwidth of inhibition generated by frequencies on the high side of the excitatory tuning curve [sideband high-frequency inhibition (HFI)] shape rate selectivity in cortical neurons in the pallid bat. To determine whether intensity-dependent changes in FM rate selectivity were due to altered inhibition, the timing and bandwidth of HFI were quantified at multiple intensities using the two-tone inhibition paradigm. HFI arrived faster relative to excitation as sound intensity increased. The bandwidth of HFI also increased with intensity. The changes in HFI predicted intensity-dependent changes in FM rate selectivity. These data suggest that neural selectivity for a sweep parameter is not static but shifts with intensity due to changes in properties of sideband inhibition.

  10. Spike frequency adaptation mediates looming stimulus selectivity in a collision-detecting neuron

    PubMed Central

    Peron, Simon; Gabbiani, Fabrizio

    2009-01-01

    How active membrane conductance dynamics tunes neurons for specific time-varying stimuli remains poorly understood. We studied the biophysical mechanisms by which spike frequency adaptation shapes visual stimulus selectivity in an identified visual interneuron of the locust. The lobula giant movement detector (LGMD) responds preferentially to objects approaching on a collision course with the locust. Using calcium imaging, pharmacology and modeling, we show that spike frequency adaptation in the LGMD is mediated by a Ca2+-dependent potassium conductance closely resembling those associated with ‘small-conductance’ (SK) channels. Intracellular block of this conductance minimally affected the LGMD’s response to approaching stimuli, but substantially increased its response to translating ones. Thus, spike frequency adaptation contributes to the neuron’s tuning by selectively decreasing its responses to nonpreferred stimuli. Our results identify a new mechanism by which spike frequency adaptation may tune visual neurons to behaviorally relevant stimuli. PMID:19198607

  11. MIMO-UAC for Rate Enhancement and Range Extension

    DTIC Science & Technology

    2008-12-01

    multiple transducers and hydrophones, we plan to develop multiple - input multiple - output ( MIMO -)UAC systems to provide range/rate enhancement...year, our research on multi- input multi- output underwater acoustic communications ( MIMO -UAC) can be categorized into two thrusts: Robust M1MO-UAC with...SUBJECT TERMS Underwater acoustic communications, multi- input multi- output ( MIMO ), transmit beamforming, differential modulation, diversity 16.

  12. Universal MIMO-OFDM SDR for Mobile Autonomous Networks (OPTIONS)

    DTIC Science & Technology

    2005-05-05

    Multiple such systems can be cascaded for larger MIMO configurations. The transmitter RF frontend is a two step up-conversion implementation with an... multiplications per second. This is shown graphically in Figure 3. A SISO-OFDM system (1x1) requires about 0.3 GOPS for all the algorithms. But as the MIMO ...to be MIMO decoded. Therefore multiple such processing units are required. However, depending on the bandwidth multiple subcarriers can be time

  13. A MIMO-Inspired Rapidly Switchable Photonic Interconnect Architecture (Postprint)

    DTIC Science & Technology

    2009-07-01

    Multiple Input Multiple Output ( MIMO ) architecture. 15. SUBJECT TERMS Free-space optical interconnects, Optical Phased Arrays, High-Speed...architecture takes advantage of spatial and wavelength diversity and in this regard may be regarded as a Multiple Input Multiple Output ( MIMO ) architecture...DATES COVERED (From - To) June 2008 – August 2008 4. TITLE AND SUBTITLE A MIMO -INSPIRED RAPIDLY SWITCHABLE PHOTONIC INTERCONNECT ARCHITECTURE

  14. MU-MIMO Pairing Algorithm Using Received Power

    NASA Astrophysics Data System (ADS)

    Kim, Young-Joon; Lee, Jung-Seung; Baik, Doo-Kwon

    In this letter, a new received power pairing scheduling (PPS) algorithm is proposed for Multi User Multiple Input and Multiple Output (MU-MIMO) systems. In contrast to existing algorithms that manage complex orthogonal factors, the PPS algorithm simply utilizes CINR to determine a MU-MIMO pair. Simulation results show that the PPS algorithm achieves up to 77% of MU-MIMO gain of determinant pairing scheduling (DPS) with low complexity.

  15. Evaluating and expressing uncertainty in high-frequency electromagnetic measurements: a selective review

    NASA Astrophysics Data System (ADS)

    Ridler, Nick M.; Salter, Martin J.

    2014-08-01

    This paper provides a selected review of topics relating to evaluating and expressing uncertainty for some measurands that occur in high-frequency electromagnetic metrology. Specific emphasis is given to complex-valued quantities (i.e. vector measurands having both an associated magnitude and phase component), such as scattering parameters (i.e. S-parameters) used at radio, microwave, millimetre-wave and terahertz frequencies.

  16. Development and RF Evaluation of a Four-Frequency Selective Surface Spacecraft Subreflector Antenna

    NASA Technical Reports Server (NTRS)

    Hickey, George S.; Wu, Te-Kao

    1996-01-01

    NASA Jet Propulsion Laboratory has baselined a four frequency telecommunication system for the Cassini spacecraft antenna subsystems. This design required the design and development of a Frequency Selective Surface Subreflector (FSS) that is integrated into the High Gain Antenna Subsystem. This paper will discuss the development, mechanical and RF electrical testing of two alternate designs as flat panel prototypes that were conducted to verify the multifrequency design approach.

  17. Frequency-dependent selection on female morphs driven by premating interactions with males.

    PubMed

    Bots, Jessica; Iserbyt, Arne; Van Gossum, Hans; Hammers, Martijn; Sherratt, Thomas N

    2015-07-01

    Species showing color polymorphisms-the presence of two or more genetically determined color morphs within a single population-are excellent systems for studying the selective forces driving the maintenance of genetic diversity. Despite a shortage of empirical evidence, it is often suggested that negative frequency-dependent mate preference by males (or diet choice by predators) results in fitness benefits for the rare female morph (or prey type). Moreover, most studies have focused on the male (or predator) behavior in these systems and largely overlooked the importance of female (or prey) resistance behavior. Here, we provide the first explicit test of the role of frequency-dependent and frequency-independent intersexual interactions in female polymorphic damselflies. We identify the stage of the mating sequence when frequency-dependent selection is likely to act by comparing indexes of male mate preference when the female has little (females presented on sticks), moderate (females in cages), and high (females free to fly in the field) ability to avoid male mating attempts. Frequency-dependent male preferences were found only in those experiments where females had little ability to resist male harassment, indicating that premating interactions most likely drive negative frequency-dependent selection in this system. In addition, by separating frequency-dependent male mating preference from the baseline frequency-independent component, we reconcile the seemingly contradictory results of previous studies and highlight the roles of both forms of selection in maintaining the polymorphism at a given equilibrium. We conclude that considering interactions among all players-here, males and females-is crucial to fully understanding the mechanisms underlying the maintenance of genetic polymorphisms in the wild.

  18. Channel Estimation and Performance Analysis of One-Bit Massive MIMO Systems

    NASA Astrophysics Data System (ADS)

    Li, Yongzhi; Tao, Cheng; Seco-Granados, Gonzalo; Mezghani, Amine; Swindlehurst, A. Lee; Liu, Liu

    2017-08-01

    This paper considers channel estimation and system performance for the uplink of a single-cell massive multiple-input multiple-output (MIMO) system. Each receive antenna of the base station (BS) is assumed to be equipped with a pair of one-bit analog-to-digital converters (ADCs) to quantize the real and imaginary part of the received signal. We first propose an approach for channel estimation that is applicable for both flat and frequency-selective fading, based on the Bussgang decomposition that reformulates the nonlinear quantizer as a linear functionwith identical first- and second-order statistics. The resulting channel estimator outperforms previously proposed approaches across all SNRs. We then derive closed-form expressions for the achievable rate in flat fading channels assuming low SNR and a large number of users for the maximal ratio and zero forcing receivers that takes channel estimation error due to both noise and one-bit quantization into account. The closed-form expressions in turn allow us to obtain insight into important system design issues such as optimal resource allocation, maximal sum spectral efficiency, overall energy efficiency, and number of antennas. Numerical results are presented to verify our analytical results and demonstrate the benefit of optimizing system performance accordingly.

  19. Parametric methods for frequency-selective MR spectroscopy-a review.

    PubMed

    Sandgren, Niclas; Selén, Yngve; Stoica, Petre; Li, Jian

    2004-06-01

    Accurate quantitation of the spectral components in a pre-selected frequency band for magnetic resonance spectroscopy (MRS) signals is a frequently addressed problem in the MR community. One obvious application for such a frequency-selective technique is to lower the computational burden in situations when the measured data sequence contains too many samples to be processed using a standard full-spectrum method. Among the frequency-selective methods previously proposed in the literature, only a few possess the two features of primary concern: high robustness against interferences from out-of-band components and low computational complexity. In this survey paper we consider five spectral analysis methods which can be used for MRS signal parameter estimation in a selected frequency band. We re-derive the filter diagonalization method (FDM) in a new way that allows an easy comparison to the other methods presented. Then we introduce a frequency-selective version of the method of direction estimation (MODE) which has not been applied to MR-spectroscopy before. In addition, we present a filtering and decimation technique using a maximum phase bandpass FIR-filter and relate it to a similar ARMA-modeling approach known as SB-HOYWSVD (sub-band high-order Yule-Walker singular value decomposition). Finally, we study the numerical performances of these four methods and compare them to that of the recently introduced SELF-SVD (Singular Value Decomposition-based method usable in a SELected Frequency band) in several examples using simulated MR data, and discuss the benefits and disadvantages of each technique.

  20. Distinct fast and slow processes contribute to the selection of preferred step frequency during human walking

    PubMed Central

    Ton, Robert; Kuo, Arthur D.; Donelan, J. Maxwell

    2011-01-01

    Humans spontaneously select a step frequency that minimizes the energy expenditure of walking. This selection might be embedded within the neural circuits that generate gait so that the optimum is pre-programmed for a given walking speed. Or perhaps step frequency is directly optimized, based on sensed feedback of energy expenditure. Direct optimization is expected to be slow due to the compounded effect of delays and iteration, whereas a pre-programmed mechanism presumably allows for faster step frequency selection, albeit dependent on prior experience. To test for both pre-programmed selection and direct optimization, we applied perturbations to treadmill walking to elicit transient changes in step frequency. We found that human step frequency adjustments (n = 7) occurred with two components, the first dominating the response (66 ± 10% of total amplitude change; mean ± SD) and occurring quite quickly (1.44 ± 1.14 s to complete 95% of total change). The other component was of smaller amplitude (35 ± 10% of total change) and took tens of seconds (27.56 ± 16.18 s for 95% completion). The fast process appeared to be too fast for direct optimization and more indicative of a pre-programmed response. It also persisted even with unusual closed-loop perturbations that conflicted with prior experience and rendered the response energetically suboptimal. The slow process was more consistent with the timing expected for direct optimization. Our interpretation of these results is that humans may rely heavily on pre-programmed gaits to rapidly select their preferred step frequency and then gradually fine-tune that selection with direct optimization. PMID:21393467

  1. Parametric methods for frequency-selective MR spectroscopy—a review

    NASA Astrophysics Data System (ADS)

    Sandgren, Niclas; Selén, Yngve; Stoica, Petre; Li, Jian

    2004-06-01

    Accurate quantitation of the spectral components in a pre-selected frequency band for magnetic resonance spectroscopy (MRS) signals is a frequently addressed problem in the MR community. One obvious application for such a frequency-selective technique is to lower the computational burden in situations when the measured data sequence contains too many samples to be processed using a standard full-spectrum method. Among the frequency-selective methods previously proposed in the literature, only a few possess the two features of primary concern: high robustness against interferences from out-of-band components and low computational complexity. In this survey paper we consider five spectral analysis methods which can be used for MRS signal parameter estimation in a selected frequency band. We re-derive the filter diagonalization method (FDM) in a new way that allows an easy comparison to the other methods presented. Then we introduce a frequency-selective version of the method of direction estimation (MODE) which has not been applied to MR-spectroscopy before. In addition, we present a filtering and decimation technique using a maximum phase bandpass FIR-filter and relate it to a similar ARMA-modeling approach known as SB-HOYWSVD (sub-band high-order Yule-Walker singular value decomposition). Finally, we study the numerical performances of these four methods and compare them to that of the recently introduced SELF-SVD (Singular Value Decomposition-based method usable in a SELected Frequency band) in several examples using simulated MR data, and discuss the benefits and disadvantages of each technique.

  2. Selective attention modulates human auditory brainstem responses: relative contributions of frequency and spatial cues.

    PubMed

    Lehmann, Alexandre; Schönwiesner, Marc

    2014-01-01

    Selective attention is the mechanism that allows focusing one's attention on a particular stimulus while filtering out a range of other stimuli, for instance, on a single conversation in a noisy room. Attending to one sound source rather than another changes activity in the human auditory cortex, but it is unclear whether attention to different acoustic features, such as voice pitch and speaker location, modulates subcortical activity. Studies using a dichotic listening paradigm indicated that auditory brainstem processing may be modulated by the direction of attention. We investigated whether endogenous selective attention to one of two speech signals affects amplitude and phase locking in auditory brainstem responses when the signals were either discriminable by frequency content alone, or by frequency content and spatial location. Frequency-following responses to the speech sounds were significantly modulated in both conditions. The modulation was specific to the task-relevant frequency band. The effect was stronger when both frequency and spatial information were available. Patterns of response were variable between participants, and were correlated with psychophysical discriminability of the stimuli, suggesting that the modulation was biologically relevant. Our results demonstrate that auditory brainstem responses are susceptible to efferent modulation related to behavioral goals. Furthermore they suggest that mechanisms of selective attention actively shape activity at early subcortical processing stages according to task relevance and based on frequency and spatial cues.

  3. Top down and bottom up selection drives variations in frequency and form of a visual signal

    PubMed Central

    Yeh, Chien-Wei; Blamires, Sean J.; Liao, Chen-Pan; Tso, I.-Min

    2015-01-01

    The frequency and form of visual signals can be shaped by selection from predators, prey or both. When a signal simultaneously attracts predators and prey, selection may favour a strategy that minimizes risks while attracting prey. Accordingly, varying the frequency and form of the silken decorations added to their web may be a way that Argiope spiders minimize predation while attracting prey. Nonetheless, the role of extraneous factors renders the influences of top down and bottom up selection on decoration frequency and form variation difficult to discern. Here we used dummy spiders and decorations to simulate four possible strategies that the spider Argiope aemula may choose and measured the prey and predator attraction consequences for each in the field. The strategy of decorating at a high frequency with a variable form attracted the most prey, while that of decorating at a high frequency with a fixed form attracted the most predators. These results suggest that mitigating the cost of attracting predators while maintaining prey attraction drives the use of variation in decoration form by many Argiope spp. when decorating frequently. Our study highlights the importance of considering top-down and bottom up selection pressure when devising evolutionary ecology experiments. PMID:25828030

  4. Top down and bottom up selection drives variations in frequency and form of a visual signal.

    PubMed

    Yeh, Chien-Wei; Blamires, Sean J; Liao, Chen-Pan; Tso, I-Min

    2015-03-30

    The frequency and form of visual signals can be shaped by selection from predators, prey or both. When a signal simultaneously attracts predators and prey selection may favour a strategy that minimizes risks while attracting prey. Accordingly, varying the frequency and form of the silken decorations added to their web may be a way that Argiope spiders minimize predation while attracting prey. Nonetheless, the role of extraneous factors renders the influences of top down and bottom up selection on decoration frequency and form variation difficult to discern. Here we used dummy spiders and decorations to simulate four possible strategies that the spider Argiope aemula may choose and measured the prey and predator attraction consequences for each in the field. The strategy of decorating at a high frequency with a variable form attracted the most prey, while that of decorating at a high frequency with a fixed form attracted the most predators. These results suggest that mitigating the cost of attracting predators while maintaining prey attraction drives the use of variation in decoration form by many Argiope spp. when decorating frequently. Our study highlights the importance of considering top-down and bottom up selection pressure when devising evolutionary ecology experiments.

  5. Frequency-selective propagation of localized spoof surface plasmons in a graded plasmonic resonator chain

    PubMed Central

    Gao, Zhen; Gao, Fei; Shastri, Kunal Krishnaraj; Zhang, Baile

    2016-01-01

    Localized spoof surface plasmon polaritons (spoof-SPPs) in a graded spoof-plasmonic resonator chain with linearly increasing spacing are experimentally investigated at microwave frequencies. Transmission measurements and direct near-field mappings on this graded chain show that the propagation of localized spoof-SPPs can be cutoff at different positions along the graded chain under different frequencies due to the graded coupling between adjacent resonators. This mechanism can be used to guide localized spoof-SPPs in the graded chain to specific positions depending on the frequency and thereby implement a device that can work as a selective switch in integrated plasmonic circuits. PMID:27149656

  6. Frequency-selective propagation of localized spoof surface plasmons in a graded plasmonic resonator chain

    NASA Astrophysics Data System (ADS)

    Gao, Zhen; Gao, Fei; Shastri, Kunal Krishnaraj; Zhang, Baile

    2016-05-01

    Localized spoof surface plasmon polaritons (spoof-SPPs) in a graded spoof-plasmonic resonator chain with linearly increasing spacing are experimentally investigated at microwave frequencies. Transmission measurements and direct near-field mappings on this graded chain show that the propagation of localized spoof-SPPs can be cutoff at different positions along the graded chain under different frequencies due to the graded coupling between adjacent resonators. This mechanism can be used to guide localized spoof-SPPs in the graded chain to specific positions depending on the frequency and thereby implement a device that can work as a selective switch in integrated plasmonic circuits.

  7. Distributed MIMO Radar for Imaging and High Resolution Target Localization

    DTIC Science & Technology

    2012-02-02

    28-2012 Final Report 04/15/2009 - 11/30/2011 Distributed MIMO Radar for Imaging and High Resolution Target Localization FA9550-09-1-0303 Alexander M...randomly placed sensors. MIMO radar, High-Resolution radar 19 Distributed MIMO Radar for Imaging and High Resolution Target Localization Air Force Office...configured with its antennas collocated [6] or distributed over an area [7, 8]. We refer to radio elements of a MIMO radar as nodes. Nodes may be equipped

  8. Effect of photonic crystal and frequency selective surface implementation on gain enhancement in the microstrip patch antenna at terahertz frequency

    NASA Astrophysics Data System (ADS)

    Nejati, Ameneh; Sadeghzadeh, Ramezan Ali; Geran, Fatemeh

    2014-09-01

    In this paper, microstrip patch antenna with frequency selective surface (FSS) and photonic band gap (PBG) structures in the frequency range of 0.5-0.7 THz is presented for wireless communications. Proposed patch antenna is designed on a substrate with uniform and non-uniform PBG structures. Here, the effects of substrate thickness, various radii and arrangement of holes on antenna resonance in both PBG forms are studied. Near zero characteristic on uniform and non-uniform PBG substrate is compared and the results show that along with increase in hole radius, antenna operating frequency and bandwidth are increased. Also, the FSS structure is designed as a perfect absorber. Finally, by using FSS and PBG structures simultaneously, gain enhancement, increase in directivity and pattern shaping are studied at THz field. The antenna gain in final structure is increased by 2 dBi (32%) in comparison to simple form and Half-Power beam width is reduced from 100°×80° in simple form to 72°×48° by using FSS and PBG. All simulations and designs are done by Ansoft HFSS and CST Microwave Studio simulation tools with different full wave methods.

  9. Link Correlation Based Transmit Sector Antenna Selection for Alamouti Coded OFDM

    NASA Astrophysics Data System (ADS)

    Ahn, Chang-Jun

    In MIMO systems, the deployment of a multiple antenna technique can enhance the system performance. However, since the cost of RF transmitters is much higher than that of antennas, there is growing interest in techniques that use a larger number of antennas than the number of RF transmitters. These methods rely on selecting the optimal transmitter antennas and connecting them to the respective. In this case, feedback information (FBI) is required to select the optimal transmitter antenna elements. Since FBI is control overhead, the rate of the feedback is limited. This motivates the study of limited feedback techniques where only partial or quantized information from the receiver is conveyed back to the transmitter. However, in MIMO/OFDM systems, it is difficult to develop an effective FBI quantization method for choosing the space-time, space-frequency, or space-time-frequency processing due to the numerous subchannels. Moreover, MIMO/OFDM systems require antenna separation of 5 ∼ 10 wavelengths to keep the correlation coefficient below 0.7 to achieve a diversity gain. In this case, the base station requires a large space to set up multiple antennas. To reduce these problems, in this paper, we propose the link correlation based transmit sector antenna selection for Alamouti coded OFDM without FBI.

  10. Finite time control for MIMO nonlinear system based on higher-order sliding mode.

    PubMed

    Liu, Xiangjie; Han, Yaozhen

    2014-11-01

    Considering a class of MIMO uncertain nonlinear system, a novel finite time stable control algorithm is proposed based on higher-order sliding mode concept. The higher-order sliding mode control problem of MIMO nonlinear system is firstly transformed into finite time stability problem of multivariable system. Then continuous control law, which can guarantee finite time stabilization of nominal integral chain system, is employed. The second-order sliding mode is used to overcome the system uncertainties. High frequency chattering phenomenon of sliding mode is greatly weakened, and the arbitrarily fast convergence is reached. The finite time stability is proved based on the quadratic form Lyapunov function. Examples concerning the triple integral chain system with uncertainty and the hovercraft trajectory tracking are simulated respectively to verify the effectiveness and the robustness of the proposed algorithm.

  11. A new subcarrier allocation strategy for MIMO-OFDMA multicellular networks based on cooperative interference mitigation.

    PubMed

    Gkonis, Panagiotis K; Seimeni, Maria A; Asimakis, Nikolaos P; Kaklamani, Dimitra I; Venieris, Iakovos S

    2014-01-01

    The goal of the study presented in this paper is to investigate the performance of a new subcarrier allocation strategy for Orthogonal Frequency Division Multiple Access (OFDMA) multicellular networks which employ Multiple Input Multiple Output (MIMO) architecture. For this reason, a hybrid system-link level simulator has been developed executing independent Monte Carlo (MC) simulations in parallel. Up to two tiers of cells around the central cell are taken into consideration and increased loading per cell. The derived results indicate that this strategy can provide up to 12% capacity gain for 16-QAM modulation and two tiers of cells around the central cell in a symmetric 2 × 2 MIMO configuration. This gain is derived when comparing the proposed strategy to the traditional approach of allocating subcarriers that maximize only the desired user's signal.

  12. A fast forward/backward semi-blind channel estimation for MIMO STC-OFDM systems

    NASA Astrophysics Data System (ADS)

    Chang, Lena; Cheng, Ching-Min; Tang, Zay-Shing

    2013-09-01

    In the study, we propose an efficient subspace-based semiblind channel estimation for multiple-input-multiple-output (MIMO) space-time code (STC) orthogonal frequency-division multiplexing (OFDM) systems. We first proposed a forward-backward estimation (FBE) method which can improve the channel estimation accuracy by using both the forward and backward receiving data. Then, based on the symmetric property of the forward and backward smoothed correlation matrix, we develop a fast forward-backward (FFB) estimation method which estimates the noise subspace by performing eigen-decomposition of two half dimensionality sub-matrices obtained from the forward and backward smoothed correlation matrix. FFB achieves the same performance as the FBE but only requires one-fourth computation complexity of FBE. Computer simulations demonstrate the effectiveness and accuracy in channel estimation of the proposed FFB for the MIMO STC-OFDM systems.

  13. A New Subcarrier Allocation Strategy for MIMO-OFDMA Multicellular Networks Based on Cooperative Interference Mitigation

    PubMed Central

    Gkonis, Panagiotis K.; Seimeni, Maria A.; Asimakis, Nikolaos P.; Kaklamani, Dimitra I.; Venieris, Iakovos S.

    2014-01-01

    The goal of the study presented in this paper is to investigate the performance of a new subcarrier allocation strategy for Orthogonal Frequency Division Multiple Access (OFDMA) multicellular networks which employ Multiple Input Multiple Output (MIMO) architecture. For this reason, a hybrid system-link level simulator has been developed executing independent Monte Carlo (MC) simulations in parallel. Up to two tiers of cells around the central cell are taken into consideration and increased loading per cell. The derived results indicate that this strategy can provide up to 12% capacity gain for 16-QAM modulation and two tiers of cells around the central cell in a symmetric 2 × 2 MIMO configuration. This gain is derived when comparing the proposed strategy to the traditional approach of allocating subcarriers that maximize only the desired user's signal. PMID:24683351

  14. Resource Allocation Scheme in MIMO-OFDMA System for User's Different Data Throughput Requirements

    NASA Astrophysics Data System (ADS)

    Sann Maw, Maung; Sasase, Iwao

    In the subcarrier and power allocation schemes in Multi-Input Multi-Output and Orthogonal Frequency Division Multiple Access (MIMO-OFDMA) systems, only equal fairness among users has been considered and no scheme for proportional data rate fairness has been considered. In this paper, a subcarrier, bit and power allocation scheme is proposed to maximize the total throughput under the constraints of total power and proportional data rate fairness among users. In the proposed scheme, joint subchannel allocation and adaptive bit loading is firstly performed by using singular value decomposition (SVD) of channel matrix under the constraint of users' data throughput requirements, and then adaptive power loading is applied. Simulation results show that effective performance of the system has been improved as well as each throughput is proportionally distributed among users in MIMO-OFDMA systems.

  15. Channel Acquisition for Massive MIMO-OFDM With Adjustable Phase Shift Pilots

    NASA Astrophysics Data System (ADS)

    You, Li; Gao, Xiqi; Swindlehurst, A. Lee; Zhong, Wen

    2016-03-01

    We propose adjustable phase shift pilots (APSPs) for channel acquisition in wideband massive multiple-input multiple-output (MIMO) systems employing orthogonal frequency division multiplexing (OFDM) to reduce the pilot overhead. Based on a physically motivated channel model, we first establish a relationship between channel space-frequency correlations and the channel power angle-delay spectrum in the massive antenna array regime, which reveals the channel sparsity in massive MIMO-OFDM. With this channel model, we then investigate channel acquisition, including channel estimation and channel prediction, for massive MIMO-OFDM with APSPs. We show that channel acquisition performance in terms of sum mean square error can be minimized if the user terminals' channel power distributions in the angle-delay domain can be made non-overlapping with proper phase shift scheduling. A simplified pilot phase shift scheduling algorithm is developed based on this optimal channel acquisition condition. The performance of APSPs is investigated for both one symbol and multiple symbol data models. Simulations demonstrate that the proposed APSP approach can provide substantial performance gains in terms of achievable spectral efficiency over the conventional phase shift orthogonal pilot approach in typical mobility scenarios.

  16. Selective engineering of cavity resonance for frequency matching in optical parametric processes

    SciTech Connect

    Lu, Xiyuan; Rogers, Steven; Jiang, Wei C.; Lin, Qiang

    2014-10-13

    We propose to selectively engineer a single cavity resonance to achieve frequency matching for optical parametric processes in high-Q microresonators. For this purpose, we demonstrate an approach, selective mode splitting (SMS), to precisely shift a targeted cavity resonance, while leaving other cavity modes intact. We apply SMS to achieve efficient parametric generation via four-wave mixing in high-Q silicon microresonators. The proposed approach is of great potential for broad applications in integrated nonlinear photonics.

  17. Reducing Sweeping Frequencies in Microwave NDT Employing Machine Learning Feature Selection

    PubMed Central

    Moomen, Abdelniser; Ali, Abdulbaset; Ramahi, Omar M.

    2016-01-01

    Nondestructive Testing (NDT) assessment of materials’ health condition is useful for classifying healthy from unhealthy structures or detecting flaws in metallic or dielectric structures. Performing structural health testing for coated/uncoated metallic or dielectric materials with the same testing equipment requires a testing method that can work on metallics and dielectrics such as microwave testing. Reducing complexity and expenses associated with current diagnostic practices of microwave NDT of structural health requires an effective and intelligent approach based on feature selection and classification techniques of machine learning. Current microwave NDT methods in general based on measuring variation in the S-matrix over the entire operating frequency ranges of the sensors. For instance, assessing the health of metallic structures using a microwave sensor depends on the reflection or/and transmission coefficient measurements as a function of the sweeping frequencies of the operating band. The aim of this work is reducing sweeping frequencies using machine learning feature selection techniques. By treating sweeping frequencies as features, the number of top important features can be identified, then only the most influential features (frequencies) are considered when building the microwave NDT equipment. The proposed method of reducing sweeping frequencies was validated experimentally using a waveguide sensor and a metallic plate with different cracks. Among the investigated feature selection techniques are information gain, gain ratio, relief, chi-squared. The effectiveness of the selected features were validated through performance evaluations of various classification models; namely, Nearest Neighbor, Neural Networks, Random Forest, and Support Vector Machine. Results showed good crack classification accuracy rates after employing feature selection algorithms. PMID:27104533

  18. Reducing Sweeping Frequencies in Microwave NDT Employing Machine Learning Feature Selection.

    PubMed

    Moomen, Abdelniser; Ali, Abdulbaset; Ramahi, Omar M

    2016-04-19

    Nondestructive Testing (NDT) assessment of materials' health condition is useful for classifying healthy from unhealthy structures or detecting flaws in metallic or dielectric structures. Performing structural health testing for coated/uncoated metallic or dielectric materials with the same testing equipment requires a testing method that can work on metallics and dielectrics such as microwave testing. Reducing complexity and expenses associated with current diagnostic practices of microwave NDT of structural health requires an effective and intelligent approach based on feature selection and classification techniques of machine learning. Current microwave NDT methods in general based on measuring variation in the S-matrix over the entire operating frequency ranges of the sensors. For instance, assessing the health of metallic structures using a microwave sensor depends on the reflection or/and transmission coefficient measurements as a function of the sweeping frequencies of the operating band. The aim of this work is reducing sweeping frequencies using machine learning feature selection techniques. By treating sweeping frequencies as features, the number of top important features can be identified, then only the most influential features (frequencies) are considered when building the microwave NDT equipment. The proposed method of reducing sweeping frequencies was validated experimentally using a waveguide sensor and a metallic plate with different cracks. Among the investigated feature selection techniques are information gain, gain ratio, relief, chi-squared. The effectiveness of the selected features were validated through performance evaluations of various classification models; namely, Nearest Neighbor, Neural Networks, Random Forest, and Support Vector Machine. Results showed good crack classification accuracy rates after employing feature selection algorithms.

  19. Frequency channel-dependent selectivity for temporal call characteristics in gray treefrogs, Hyla versicolor.

    PubMed

    Reichert, Michael S; Höbel, Gerlinde

    2017-04-01

    Sensory receptors transmit information on multiple stimulus dimensions. Much remains to be understood about how the processing of different signal characteristics is partitioned and integrated in different areas of the nervous system. Amphibian hearing involves two morphologically distinct inner-ear organs that process different components of the frequency spectrum. Many anuran signals contain two frequency peaks, each one matching the sensitivity of one of these two organs. We hypothesized that the processing of temporal characteristics of acoustic signals would differ in these two frequency channels, perhaps because of differences in the response properties of the two inner-ear organs. We tested this hypothesis in the gray treefrog, Hyla versicolor; male advertisement calls of this species contain a bimodal frequency spectrum. We generated synthetic male advertisement calls in which we independently manipulated the pattern of amplitude modulation in the low-frequency peak or the high-frequency peak and measured the attractiveness of these stimuli to females in single-speaker and two-speaker phonotaxis tests. We obtained multiple lines of evidence that females were more selective for fine-temporal characteristics in the high-frequency peak. We discuss the potential implications of frequency channel-dependent temporal processing for signal evolution and suggest that additional neurophysiological investigations of the anuran auditory periphery will give important insights into how the nervous system partitions the encoding of multiple characteristics of complex signals. © 2017. Published by The Company of Biologists Ltd.

  20. Allele frequency changes due to hitch-hiking in genomic selection programs

    PubMed Central

    2014-01-01

    Background Genomic selection makes it possible to reduce pedigree-based inbreeding over best linear unbiased prediction (BLUP) by increasing emphasis on own rather than family information. However, pedigree inbreeding might not accurately reflect loss of genetic variation and the true level of inbreeding due to changes in allele frequencies and hitch-hiking. This study aimed at understanding the impact of using long-term genomic selection on changes in allele frequencies, genetic variation and level of inbreeding. Methods Selection was performed in simulated scenarios with a population of 400 animals for 25 consecutive generations. Six genetic models were considered with different heritabilities and numbers of QTL (quantitative trait loci) affecting the trait. Four selection criteria were used, including selection on own phenotype and on estimated breeding values (EBV) derived using phenotype-BLUP, genomic BLUP and Bayesian Lasso. Changes in allele frequencies at QTL, markers and linked neutral loci were investigated for the different selection criteria and different scenarios, along with the loss of favourable alleles and the rate of inbreeding measured by pedigree and runs of homozygosity. Results For each selection criterion, hitch-hiking in the vicinity of the QTL appeared more extensive when accuracy of selection was higher and the number of QTL was lower. When inbreeding was measured by pedigree information, selection on genomic BLUP EBV resulted in lower levels of inbreeding than selection on phenotype BLUP EBV, but this did not always apply when inbreeding was measured by runs of homozygosity. Compared to genomic BLUP, selection on EBV from Bayesian Lasso led to less genetic drift, reduced loss of favourable alleles and more effectively controlled the rate of both pedigree and genomic inbreeding in all simulated scenarios. In addition, selection on EBV from Bayesian Lasso showed a higher selection differential for mendelian sampling terms than selection on

  1. Numerical analysis of curved frequency selective surface by finite-difference time-domain

    NASA Astrophysics Data System (ADS)

    Chen, Xin-yi; Wang, Jian-bo; Chen, Gui-bo; Sun, Guan-cheng; Lu, Jun

    2011-08-01

    Frequency selective surface is a monolayer or multilayer 2D periodic structure which is composed of multiple resonance units scattering by a two-dimensional periodic array on dielectric layer. FSS can't absorb radio frequency energy, but can filter the frequency which is therefore applied in microwave technique or stealth technology. The relative research on curved FSS is relatively scarce since the curved FSS structure can be obtained only when FSS is attached on the materials surfaces of curved structures in engineering application. However, curved FSS is widely applied in practical engineering; therefore, the research on curved FSS structure has important significance. In this paper, a curved FSS structure model of Y-pore unit is established and numerical simulated by means of FDTD. The influence of curvature on FSS transmission characteristics is studied according to the analysis on the changing of radar cross section (RCS). The results show: the center frequency point of the plane band pass FSS structure drifts after the curve surface deformation of the structure; the center frequency point of the curved band pass FSS structure drifts with the changing of the curvature radius, i. e. with the decreasing of curvature radius, the frequency point drifts towards high points and the transmittance decreases. The design of FSS radome demands of accurate and stable center resonance frequency; therefore, the actual situation of curved surface should be considered in practical engineering application when band pass FSS is made into frequency selection filtering radome. The curvature radius should be long enough to avoid center frequency drifting and transmittance deceasing.

  2. Mechanical frequency selectivity of an artificial basilar membrane using a beam array with narrow supports

    NASA Astrophysics Data System (ADS)

    Kim, Sangwon; Song, Won Joon; Jang, Jongmoon; Jang, Jeong Hun; Choi, Hongsoo

    2013-09-01

    The study presented in this paper assessed the frequency selectivity of an artificial basilar membrane (ABM) constructed using a piezoelectric beam array with narrow supports. Three ABM samples were constructed. Each ABM contained 16 beams with various lengths in a one-dimensional array. To experimentally assess the frequency selectivity of the ABM, mechanical vibration induced either by an electrical or an acoustic stimulus was measured with a scanning laser-Doppler vibrometer. The electro-mechanical and acousto-mechanical transfer functions were defined for the same purpose. The tonotopy of each beam array was visualized by post-processing the experimental results. Finite element analyses were conducted to numerically compute the resonance frequencies, identify the associated vibrational modes, and evaluate the harmonic responses of the beams. The influence of the residual stresses existing in the beams was reflected in the geometric models by introducing three different levels of arc-shaped lateral deformations in the beams. The harmonic analyses revealed that each beam of the ABM samples presented independent band-pass characteristics. The experiments and simulations commonly showed a frequency selectivity of the fabricated ABMs in the range of 2-20 kHz. Therefore, the device is suitable for development of a totally implantable artificial cochlea, implementing a mechanical frequency analyzer. This work is part of research to develop a prototype of a totally implantable artificial cochlea.

  3. Warning signals are under positive frequency-dependent selection in nature.

    PubMed

    Chouteau, Mathieu; Arias, Mónica; Joron, Mathieu

    2016-02-23

    Positive frequency-dependent selection (FDS) is a selection regime where the fitness of a phenotype increases with its frequency, and it is thought to underlie important adaptive strategies resting on signaling and communication. However, whether and how positive FDS truly operates in nature remains unknown, which hampers our understanding of signal diversity. Here, we test for positive FDS operating on the warning color patterns of chemically defended butterflies forming multiple coexisting mimicry assemblages in the Amazon. Using malleable prey models placed in localities showing differences in the relative frequencies of warningly colored prey, we demonstrate that the efficiency of a warning signal increases steadily with its local frequency in the natural community, up to a threshold where protection stabilizes. The shape of this relationship is consistent with the direct effect of the local abundance of each warning signal on the corresponding avoidance knowledge of the local predator community. This relationship, which differs from purifying selection acting on each mimetic pattern, indicates that predator knowledge, integrated over the entire community, is saturated only for the most common warning signals. In contrast, among the well-established warning signals present in local prey assemblages, most are incompletely known to local predators and enjoy incomplete protection. This incomplete predator knowledge should generate strong benefits to life history traits that enhance warning efficiency by increasing the effective frequency of prey visible to predators. Strategies such as gregariousness or niche convergence between comimics may therefore readily evolve through their effects on predator knowledge and warning efficiency.

  4. Warning signals are under positive frequency-dependent selection in nature

    PubMed Central

    Chouteau, Mathieu; Arias, Mónica; Joron, Mathieu

    2016-01-01

    Positive frequency-dependent selection (FDS) is a selection regime where the fitness of a phenotype increases with its frequency, and it is thought to underlie important adaptive strategies resting on signaling and communication. However, whether and how positive FDS truly operates in nature remains unknown, which hampers our understanding of signal diversity. Here, we test for positive FDS operating on the warning color patterns of chemically defended butterflies forming multiple coexisting mimicry assemblages in the Amazon. Using malleable prey models placed in localities showing differences in the relative frequencies of warningly colored prey, we demonstrate that the efficiency of a warning signal increases steadily with its local frequency in the natural community, up to a threshold where protection stabilizes. The shape of this relationship is consistent with the direct effect of the local abundance of each warning signal on the corresponding avoidance knowledge of the local predator community. This relationship, which differs from purifying selection acting on each mimetic pattern, indicates that predator knowledge, integrated over the entire community, is saturated only for the most common warning signals. In contrast, among the well-established warning signals present in local prey assemblages, most are incompletely known to local predators and enjoy incomplete protection. This incomplete predator knowledge should generate strong benefits to life history traits that enhance warning efficiency by increasing the effective frequency of prey visible to predators. Strategies such as gregariousness or niche convergence between comimics may therefore readily evolve through their effects on predator knowledge and warning efficiency. PMID:26858416

  5. Agile Blocker and Clock Jitter Tolerant Low-Power Frequency Selective Receiver with Energy Harvesting Capability.

    PubMed

    Hasan, Abul; Helaoui, Mohamed; Ghannouchi, Fadhel M

    2017-08-29

    In this article, a novel tunable, blocker and clock jitter tolerant, low power, quadrature phase shift frequency selective (QPS-FS) receiver with energy harvesting capability is proposed. The receiver's design embraces and integrates (i) the baseband to radio frequency (RF) impedance translation concept to improve selectivity over that of conventional homodyne receiver topologies and (ii) broadband quadrature phase shift circuitry in the RF path to remove an active multi-phase clock generation circuit in passive mixer (PM) receivers. The use of a single local oscillator clock signal with a passive clock division network improves the receiver's robustness against clock jitter and reduces the source clock frequency by a factor of N, compared to PM receivers using N switches (N≥4). As a consequence, the frequency coverage of the QPS-FS receiver is improved by a factor of N, given a clock source of maximum frequency; and, the power consumption of the whole receiver system can eventually be reduced. The tunable QPS-FS receiver separates the wanted RF band signal from the unwanted blockers/interferers. The desired RF signal is frequency down-converted to baseband, while the undesired blocker/interferer signals are reflected by the receiver, collected and could be energy recycled using an auxiliary energy harvesting device.

  6. Negative frequency-dependent selection between Pasteuria penetrans and its host Meloidogyne arenaria

    USDA-ARS?s Scientific Manuscript database

    In negative frequency-dependant selection (NFDS), parasite genotypes capable of infecting the numerically dominant host genotype are favored, while host genotypes resistant to the dominant parasite genotype are favored, creating a cyclical pattern of resistant genotypes in the host population and, a...

  7. An exponential ESS model and its application to frequency-dependent selection.

    PubMed

    Li, J; Liu, L

    1989-10-01

    A nonlinear ESS model is put forward, that is, a nonnegative exponential ESS model. For a simple case, we discuss the existence, uniqueness, and stability of an ESS. As an application of the model, we give a quantitative analysis of frequency-dependent selection in population genetics when the rare type has an advantage.

  8. Information Theoretic Comparison of MIMO Wireless Communication Receivers in the Presence of Interference

    DTIC Science & Technology

    2004-12-20

    input multiple - output ( MIMO ) wireless communication provides a number of advantages over traditional single- input single- output (SISO) approaches...Performance Comparison 0 0 0 007)))o MIT Lincoln Laboratory mimoNTI-2 bliss MIMO Communication Multiple - Input Multiple - Output Complicated Multipath...difficult environments MIMO Communication - Ignore the possibility of jamming or Multiple - Input Multiple -

  9. Performance Limits and Design of MIMO for Sensor and Ad Hoc Wireless and Networks

    DTIC Science & Technology

    2009-01-05

    Multiple - input multiple output ( MIMO ) systems, MIMO Radar, Sensor networks, Energy... multiple - input multiple - output ( MIMO ) channels, provided at least as many transmit as receive antennas are used, recent research shows that...research. Multiple - input multiple - output ( MIMO ) channels formed by using multiple transmit and receive antennas have lead to a revolution

  10. Impedance-based structural health monitoring using neural networks for autonomous frequency range selection

    NASA Astrophysics Data System (ADS)

    Min, Jiyoung; Park, Seunghee; Yun, Chung-Bang

    2010-12-01

    The impedance-based structural health monitoring (SHM) method has come to the forefront in the SHM community due to its practical potential for real applications. In the impedance-based SHM method, the selection of optimal frequency ranges plays an important role in improving the sensitivity of damage detection, since an improper frequency range can lead to erroneous damage detection results and provide false positive damage alarms. To tackle this issue, this paper proposes an innovative technique for autonomous selection of damage-sensitive frequency ranges using artificial neural networks (ANNs). First, the impedance signals are obtained in a wide frequency band, and the signals are split into multiple sub-ranges of this wide band. Then, the predefined damage index is evaluated for each sub-range by comparing impedance signals between the intact and the concurrent cases. Here, the cross correlation coefficients (CCs) are used as the predefined damage index. The ANN is constructed and trained using all CC values at multiple frequency ranges as multi-inputs and the real damage severity as the single output for various preselected damage scenarios, so that subsequent damage estimations may be carried out by selecting the governing frequency ranges autonomously. The performance of the proposed approach has been examined via a series of experimental studies to detect loose bolts and cracks induced on real steel bridge and building structures. It is found that the proposed approach autonomously determines the damage-sensitive frequency ranges and can be used for effective evaluation of damage severity in a wide variety of damage cases in real structures.

  11. Negative frequency-dependent selection or alternative reproductive tactics: maintenance of female polymorphism in natural populations

    PubMed Central

    2013-01-01

    Background Sex-limited polymorphisms have long intrigued evolutionary biologists and have been the subject of long-standing debates. The coexistence of multiple male and/or female morphs is widely believed to be maintained through negative frequency-dependent selection imposed by social interactions. However, remarkably few empirical studies have evaluated how social interactions, morph frequencies and fitness parameters relate to one another under natural conditions. Here, we test two hypotheses proposed to explain the maintenance of a female polymorphism in a species with extreme geographical variation in morph frequencies. We first elucidate how fecundity traits of the morphs vary in relation to the frequencies and densities of males and female morphs in multiple sites over multiple years. Second, we evaluate whether the two female morphs differ in resource allocation among fecundity traits, indicating alternative tactics to maximize reproductive output. Results We present some of the first empirical evidence collected under natural conditions that egg number and clutch mass was higher in the rarer female morph. This morph-specific fecundity advantage gradually switched with the population morph frequency. Our results further indicate that all investigated fecundity traits are negatively affected by relative male density (i.e. operational sex ratio), which confirms male harassment as selective agent. Finally, we show a clear trade-off between qualitative (egg mass) and quantitative (egg number) fecundity traits. This trade-off, however, is not morph-specific. Conclusion Our reported frequency- and density-dependent fecundity patterns are consistent with the hypothesis that the polymorphism is driven by a conflict between sexes over optimal mating rate, with costly male sexual harassment driving negative frequency-dependent selection on morph fecundity. PMID:23822745

  12. Frequency selective reflection and transmission at a layer composed of a periodic dielectric

    NASA Technical Reports Server (NTRS)

    Bertoni, Henry L.; Cheo, Li-Hsiang S.; Tamir, Theodor

    1987-01-01

    The feasibility of using a periodic dielectric layer, composed of alternating bars having dielectric constants epsilon sub 1 and epsilon sub 2, as a frequency selective subreflector in order to permit feed separation in large aperture reflecting antenna systems was examined. For oblique incidence, it is found that total transmission and total reflection can be obtained at different frequencies for proper choices of epsilon sub 1, epsilon 2, and the geometric parameters. The frequencies of total reflection and transmission can be estimated from wave phenomena occurring in a layer of uniform dielectric constant equal to the average for the periodic layers. About some of the frequencies of total transmission, the bandwidth for 90% transmission is found to be 40%. However, the bandwidth for 90% reflection is always found to be much narrower; the greatest value found being 2.5%.

  13. Detection of Allelic Frequency Differences between the Sexes in Humans: A Signature of Sexually Antagonistic Selection

    PubMed Central

    Lucotte, Elise A.; Laurent, Romain; Heyer, Evelyne; Ségurel, Laure; Toupance, Bruno

    2016-01-01

    Sexually antagonistic (SA) selection, a form of selection that can occur when both sexes have different fitness optima for a trait, is a major force shaping the evolution of organisms. A seminal model developed by Rice (Rice WR. 1984. Sex chromosomes and the evolution of sexual dimorphism. Evolution 38:735–742.) predicts that the X chromosome should be a hotspot for the accumulation of loci under SA selection as compared with the autosomes. Here, we propose a methodological framework designed to detect a specific signature of SA selection on viability, differences in allelic frequencies between the sexes. Applying this method on genome-wide single nucleotide polymorphism (SNP) data in human populations where no sex-specific population stratification could be detected, we show that there are overall significantly more SNPs exhibiting differences in allelic frequencies between the sexes on the X chromosome as compared with autosomes, supporting the predictions of Rice’s model. This pattern is consistent across populations and is robust to correction for potential biases such as differences in linkage disequilibrium, sample size, and genotyping errors between chromosomes. Although SA selection is not the only factor resulting in allelic frequency differences between the sexes, we further show that at least part of the identified X-linked loci is caused by such a sex-specific processes. PMID:27189992

  14. Natural Selection VS. Random Drift: Evidence from Temporal Variation in Allele Frequencies in Nature

    PubMed Central

    Mueller, Laurence D.; Barr, Lorraine G.; Ayala, Francisco J.

    1985-01-01

    We have obtained monthly samples of two species, Drosophila pseudoobscura and Drosophila persimilis, in a natural population from Napa County, California. In each species, about 300 genes have been assayed by electrophoresis for each of seven enzyme loci in each monthly sample from March 1972 to June 1975. Using statistical methods developed for the purpose, we have examined whether the allele frequencies at different loci vary in a correlated fashion. The methods used do not detect natural selection when it is deterministic (e.g., overdominance or directional selection), but only when alleles at different loci vary simultaneously in response to the same environmental variations. Moreover, only relatively large fitness differences (of the order of 15%) are detectable. We have found strong evidence of correlated allele frequency variation in 13–20% of the cases examined. We interpret this as evidence that natural selection plays a major role in the evolution of protein polymorphisms in nature. PMID:4054608

  15. Ferrite Film Loaded Frequency Selective Metamaterials for Sub-GHz Applications

    PubMed Central

    Gao, Bo; Yuen, Matthew M. F.; Ye, Terry

    2016-01-01

    Electromagnetic metamaterials are constructed with sub-wavelength structures that exhibit particular electromagnetic properties under a certain frequency range. Because the form-factor of the substructures has to be comparable to the wavelength of the operating frequency, few papers have discussed the metamaterials under GHz frequency. In this paper, we developed an innovative method to reduce the resonant frequency of metamaterals. By integrating the meta-structures with ferrite materials of higher permeability, the cell size of the meta-structure can be scaled down. This paper describes the methodology, design, and development of low-profile GHz ferrite loaded metamaterials. A ferrite film with a permeability of 20 could reduce the resonant frequency of metamaterials by up to 50%. A prototype has been fabricated and the measurement data align well with the simulation results. Because of the lowered operational frequency, the proposed ferrite loaded metamaterials offer more flexibility for various sub-GHz microwave applications, such as cloaks, absorbers, and frequency selective surfaces. PMID:28774128

  16. Ferrite Film Loaded Frequency Selective Metamaterials for Sub-GHz Applications.

    PubMed

    Gao, Bo; Yuen, Matthew M F; Ye, Terry

    2016-12-13

    Electromagnetic metamaterials are constructed with sub-wavelength structures that exhibit particular electromagnetic properties under a certain frequency range. Because the form-factor of the substructures has to be comparable to the wavelength of the operating frequency, few papers have discussed the metamaterials under GHz frequency. In this paper, we developed an innovative method to reduce the resonant frequency of metamaterals. By integrating the meta-structures with ferrite materials of higher permeability, the cell size of the meta-structure can be scaled down. This paper describes the methodology, design, and development of low-profile GHz ferrite loaded metamaterials. A ferrite film with a permeability of 20 could reduce the resonant frequency of metamaterials by up to 50%. A prototype has been fabricated and the measurement data align well with the simulation results. Because of the lowered operational frequency, the proposed ferrite loaded metamaterials offer more flexibility for various sub-GHz microwave applications, such as cloaks, absorbers, and frequency selective surfaces.

  17. Scalable System Design for Covert MIMO Communications

    DTIC Science & Technology

    2014-06-01

    Vehicles US United States VHDL VHSIC Hardware Description Language VLSI Very Large Scale Integration WARP Wireless open-Access Research Platform WLAN...considering the lessons learned in Chapter III a MIMO receiver is developed in VHSIC Hardware Description Language (VHDL). Resource utilization is...Military Communications Conference, vol. 2, pp. 1113–1117 vol.2, October 2002. [39] J. Milton and J. Arnold, Introduction to Probability and

  18. SIRE: a MIMO radar for landmine/IED detection

    NASA Astrophysics Data System (ADS)

    Ojowu, Ode; Wu, Yue; Li, Jian; Nguyen, Lam

    2013-05-01

    Multiple-input multiple-output (MIMO) radar systems have been shown to have significant performance improvements over their single-input multiple-output (SIMO) counterparts. For transmit and receive elements that are collocated, the waveform diversity afforded by this radar is exploited for performance improvements. These improvements include but are not limited to improved target detection, improved parameter identifiability and better resolvability. In this paper, we present the Synchronous Impulse Reconstruction Radar (SIRE) Ultra-wideband (UWB) radar designed by the Army Research Lab (ARL) for landmine and improvised explosive device (IED) detection as a 2 by 16 MIMO radar (with collocated antennas). Its improvement over its SIMO counterpart in terms of beampattern/cross range resolution are discussed and demonstrated using simulated data herein. The limitations of this radar for Radio Frequency Interference (RFI) suppression are also discussed in this paper. A relaxation method (RELAX) combined with averaging of multiple realizations of the measured data is presented for RFI suppression; results show no noticeable target signature distortion after suppression. In this paper, the back-projection (delay and sum) data independent method is used for generating SAR images. A side-lobe minimization technique called recursive side-lobe minimization (RSM) is also discussed for reducing side-lobes in this data independent approach. We introduce a data-dependent sparsity based spectral estimation technique called Sparse Learning via Iterative Minimization (SLIM) as well as a data-dependent CLEAN approach for generating SAR images for the SIRE radar. These data-adaptive techniques show improvement in side-lobe reduction and resolution for simulated data for the SIRE radar.

  19. Resource Allocation in MIMO-Based Ad Hoc Networks

    DTIC Science & Technology

    2011-03-01

    Multiple - Input Multiple - Output ( MIMO ...Hoc Networks Peng Wang∗, John Matyjas† and Michael Medley† †Air Force Research Lab, Rome, NY Abstract— Multiple - Input Multiple - Output ( MIMO ) commu... input multiple - output systems, capacity optimization, joint routing, scheduling and power control. 16. SECURITY CLASSIFICATION OF: 17. LIMITATION

  20. Vast Volatility Matrix Estimation using High Frequency Data for Portfolio Selection.

    PubMed

    Fan, Jianqing; Li, Yingying; Yu, Ke

    2012-01-01

    Portfolio allocation with gross-exposure constraint is an effective method to increase the efficiency and stability of portfolios selection among a vast pool of assets, as demonstrated in Fan et al. (2011). The required high-dimensional volatility matrix can be estimated by using high frequency financial data. This enables us to better adapt to the local volatilities and local correlations among vast number of assets and to increase significantly the sample size for estimating the volatility matrix. This paper studies the volatility matrix estimation using high-dimensional high-frequency data from the perspective of portfolio selection. Specifically, we propose the use of "pairwise-refresh time" and "all-refresh time" methods based on the concept of "refresh time" proposed by Barndorff-Nielsen et al. (2008) for estimation of vast covariance matrix and compare their merits in the portfolio selection. We establish the concentration inequalities of the estimates, which guarantee desirable properties of the estimated volatility matrix in vast asset allocation with gross exposure constraints. Extensive numerical studies are made via carefully designed simulations. Comparing with the methods based on low frequency daily data, our methods can capture the most recent trend of the time varying volatility and correlation, hence provide more accurate guidance for the portfolio allocation in the next time period. The advantage of using high-frequency data is significant in our simulation and empirical studies, which consist of 50 simulated assets and 30 constituent stocks of Dow Jones Industrial Average index.

  1. Vast Volatility Matrix Estimation using High Frequency Data for Portfolio Selection*

    PubMed Central

    Fan, Jianqing; Li, Yingying; Yu, Ke

    2012-01-01

    Portfolio allocation with gross-exposure constraint is an effective method to increase the efficiency and stability of portfolios selection among a vast pool of assets, as demonstrated in Fan et al. (2011). The required high-dimensional volatility matrix can be estimated by using high frequency financial data. This enables us to better adapt to the local volatilities and local correlations among vast number of assets and to increase significantly the sample size for estimating the volatility matrix. This paper studies the volatility matrix estimation using high-dimensional high-frequency data from the perspective of portfolio selection. Specifically, we propose the use of “pairwise-refresh time” and “all-refresh time” methods based on the concept of “refresh time” proposed by Barndorff-Nielsen et al. (2008) for estimation of vast covariance matrix and compare their merits in the portfolio selection. We establish the concentration inequalities of the estimates, which guarantee desirable properties of the estimated volatility matrix in vast asset allocation with gross exposure constraints. Extensive numerical studies are made via carefully designed simulations. Comparing with the methods based on low frequency daily data, our methods can capture the most recent trend of the time varying volatility and correlation, hence provide more accurate guidance for the portfolio allocation in the next time period. The advantage of using high-frequency data is significant in our simulation and empirical studies, which consist of 50 simulated assets and 30 constituent stocks of Dow Jones Industrial Average index. PMID:23264708

  2. Insonation frequency selection may assist detection and therapeutic delivery of targeted ultrasound contrast agents.

    PubMed

    Payne, Edward; Ooi, Andrew; Manasseh, Richard

    2011-02-01

    Ultrasound-targeted drug delivery relies on the unique nature of ultrasound contrast agents--they are microbubbles that respond strongly to ultrasound. Intravenously injected microbubbles are smaller than a blood cell. By increasing the ultrasound power, the bubbles can be ruptured at the targeted endothelial wall, locally releasing any molecules in the bubble shell. Furthermore, ultrasound-activated microbubbles are known to cause sonoporation--the process by which ultrasound drives molecules through cellular membranes. However, techniques are required to selectively detect and rupture only those microbubbles on target walls. Experiments are presented on the behaviour of microbubbles on walls. For accuracy, imaging measurements are made on model microbubbles larger than contrast agents. Bubble size was varied and the resonant frequency peak determined. Microbubbles on walls have a shifted frequency in good agreement with theory: a 20-25% downshift from the frequency when far from walls. Effects other than the presence of the wall account for less than 5% of the shift. Theory predicts the frequency downshift should be sustained for actual contrast-agent sized bubbles. The effect of real, compliant cell walls requires investigation. An appropriate downshift in the applied ultrasound frequency could selectively tune gene or drug delivery. To make this feasible, it may be necessary to manufacture monodispersed microbubbles.

  3. Responses of Waveform-Selective Absorbing Metasurfaces to Oblique Waves at the Same Frequency

    PubMed Central

    Wakatsuchi, Hiroki; Gao, Fei; Yagitani, Satoshi; Sievenpiper, Daniel F.

    2016-01-01

    Conventional materials vary their electromagnetic properties in response to the frequency of an incoming wave, but these responses generally remain unchanged at the same frequency unless nonlinearity is involved. Waveform-selective metasurfaces, recently developed by integrating several circuit elements with planar subwavelength periodic structures, allowed us to distinguish different waves even at the same frequency depending on how long the waves continued, namely, on their pulse widths. These materials were thus expected to give us an additional degree of freedom to control electromagnetic waves. However, all the past studies were demonstrated with waves at a normal angle only, although in reality electromagnetic waves scatter from various structures or boundaries and therefore illuminate the metasurfaces at oblique angles. Here we study angular dependences of waveform-selective metasurfaces both numerically and experimentally. We demonstrate that, if designed properly, capacitor-based waveform-selective metasurfaces more effectively absorb short pulses than continuous waves (CWs) for a wide range of the incident angle, while inductor-based metasurfaces absorb CWs more strongly. Our study is expected to be usefully exploited for applying the concept of waveform selectivity to a wide range of existing microwave devices to expand their functionalities or performances in response to pulse width as a new capability. PMID:27516346

  4. Responses of Waveform-Selective Absorbing Metasurfaces to Oblique Waves at the Same Frequency.

    PubMed

    Wakatsuchi, Hiroki; Gao, Fei; Yagitani, Satoshi; Sievenpiper, Daniel F

    2016-08-12

    Conventional materials vary their electromagnetic properties in response to the frequency of an incoming wave, but these responses generally remain unchanged at the same frequency unless nonlinearity is involved. Waveform-selective metasurfaces, recently developed by integrating several circuit elements with planar subwavelength periodic structures, allowed us to distinguish different waves even at the same frequency depending on how long the waves continued, namely, on their pulse widths. These materials were thus expected to give us an additional degree of freedom to control electromagnetic waves. However, all the past studies were demonstrated with waves at a normal angle only, although in reality electromagnetic waves scatter from various structures or boundaries and therefore illuminate the metasurfaces at oblique angles. Here we study angular dependences of waveform-selective metasurfaces both numerically and experimentally. We demonstrate that, if designed properly, capacitor-based waveform-selective metasurfaces more effectively absorb short pulses than continuous waves (CWs) for a wide range of the incident angle, while inductor-based metasurfaces absorb CWs more strongly. Our study is expected to be usefully exploited for applying the concept of waveform selectivity to a wide range of existing microwave devices to expand their functionalities or performances in response to pulse width as a new capability.

  5. Responses of Waveform-Selective Absorbing Metasurfaces to Oblique Waves at the Same Frequency

    NASA Astrophysics Data System (ADS)

    Wakatsuchi, Hiroki; Gao, Fei; Yagitani, Satoshi; Sievenpiper, Daniel F.

    2016-08-01

    Conventional materials vary their electromagnetic properties in response to the frequency of an incoming wave, but these responses generally remain unchanged at the same frequency unless nonlinearity is involved. Waveform-selective metasurfaces, recently developed by integrating several circuit elements with planar subwavelength periodic structures, allowed us to distinguish different waves even at the same frequency depending on how long the waves continued, namely, on their pulse widths. These materials were thus expected to give us an additional degree of freedom to control electromagnetic waves. However, all the past studies were demonstrated with waves at a normal angle only, although in reality electromagnetic waves scatter from various structures or boundaries and therefore illuminate the metasurfaces at oblique angles. Here we study angular dependences of waveform-selective metasurfaces both numerically and experimentally. We demonstrate that, if designed properly, capacitor-based waveform-selective metasurfaces more effectively absorb short pulses than continuous waves (CWs) for a wide range of the incident angle, while inductor-based metasurfaces absorb CWs more strongly. Our study is expected to be usefully exploited for applying the concept of waveform selectivity to a wide range of existing microwave devices to expand their functionalities or performances in response to pulse width as a new capability.

  6. Frequency-dependent selection by wild birds promotes polymorphism in model salamanders

    PubMed Central

    Fitzpatrick, Benjamin M; Shook, Kim; Izally, Reuben

    2009-01-01

    Background Co-occurrence of distinct colour forms is a classic paradox in evolutionary ecology because both selection and drift tend to remove variation from populations. Apostatic selection, the primary hypothesis for maintenance of colour polymorphism in cryptic animals, proposes that visual predators focus on common forms of prey, resulting in higher survival of rare forms. Empirical tests of this frequency-dependent foraging hypothesis are rare, and the link between predator behaviour and maintenance of variation in prey has been difficult to confirm. Here, we show that predatory birds can act as agents of frequency-dependent selection on terrestrial salamanders. Polymorphism for presence/absence of a dorsal stripe is widespread in many salamander species and its maintenance is a long-standing mystery. Results We used realistic food-bearing model salamanders to test whether selection by wild birds maintains a stripe/no-stripe polymorphism. In experimental manipulations, whichever form was most common was most likely to be attacked by ground-foraging birds, resulting in a survival advantage for the rare form. Conclusion This experiment demonstrates that frequency-dependent foraging by wild birds can maintain colour polymorphism in cryptic prey. PMID:19426509

  7. An improved MIMO-SAR simulator strategy with ray tracing

    NASA Astrophysics Data System (ADS)

    Xiang, Xingyu; Mo, Zijian; Wang, Zhonghai; Chen, Genshe; Pham, Khanh; Blasch, Erik

    2016-05-01

    High resolution and wide-swath imaging can be obtained by Multiple-Input Multiple-Output (MIMO) synthetic aperture radar (SAR) with the state of the art technologies. The time division multiple access (TDMA) MIMO SAR mimics the motion of the antenna of SAR systems by switching the array channels to transmit the radar signals at different time slots. In this paper, we develop a simulation tool with ray tracing techniques to retrieve high resolution and accurate SAR images for development of MIMO SAR imaging methods. Without loss of generality, in the proposed simulator, we apply a TDMA MIMO SAR system with 13 transmitting antennas and 8 receiving antennas, where all transmitting antennas share a single transmitter and the receiving antennas share a single receiver. By comparing with the normal simulation MIMO SAR strategies, the simulation image using ray tracing results validate that the proposed method provides more accurate and higher resolution SAR images.

  8. Frequency-dependent selection acting on the widely fluctuating sex ratio of the aphid Prociphilus oriens.

    PubMed

    Li, Y; Akimoto, S

    2017-07-01

    Frequency-dependent selection is a fundamental principle of adaptive sex ratio evolution in all sex ratio theories but has rarely been detected in the wild. Through long-term censuses, we confirmed large fluctuations in the population sex ratio of the aphid Prociphilus oriens and detected frequency-dependent selection acting on these fluctuations. Fluctuations in the population sex ratio were partly attributable to climatic factors during the growing season. Climatic factors likely affected the growth conditions of host plants, which in turn led to yearly fluctuations in maternal conditions and sex ratios. In the process of frequency-dependent selection, female proportion higher or lower than ca. 60% was associated with a reduction or increase in female proportion, respectively, the next year. The rearing of aphid clones in the laboratory indicated that mothers of each clone produced an increasing number of females as maternal size increased. However, the mean male number was not related to maternal size, but varied largely among clones. Given genetic variance in the ability to produce males among clones, selection should favour clones that can produce more numerous males in years with a high female proportion. Population-level sex allocation to females was on average 71%-73% for three localities and more female-biased when maternal conditions were better. This tendency was accounted for by the hypothesis of competition among foundresses rather than the hypothesis of local mate competition. We conclude that despite consistent operation of frequency-dependent selection, the sex ratio continues to fluctuate because environmental conditions always push it away from equilibrium. © 2017 European Society For Evolutionary Biology. Journal of Evolutionary Biology © 2017 European Society For Evolutionary Biology.

  9. Dynamic frequency feature selection based approach for classification of motor imageries.

    PubMed

    Luo, Jing; Feng, Zuren; Zhang, Jun; Lu, Na

    2016-08-01

    Electroencephalography (EEG) is one of the most popular techniques to record the brain activities such as motor imagery, which is of low signal-to-noise ratio and could lead to high classification error. Therefore, selection of the most discriminative features could be crucial to improve the classification performance. However, the traditional feature selection methods employed in brain-computer interface (BCI) field (e.g. Mutual Information-based Best Individual Feature (MIBIF), Mutual Information-based Rough Set Reduction (MIRSR) and cross-validation) mainly focus on the overall performance on all the trials in the training set, and thus may have very poor performance on some specific samples, which is not acceptable. To address this problem, a novel sequential forward feature selection approach called Dynamic Frequency Feature Selection (DFFS) is proposed in this paper. The DFFS method emphasized the importance of the samples that got misclassified while only pursuing high overall classification performance. In the DFFS based classification scheme, the EEG data was first transformed to frequency domain using Wavelet Packet Decomposition (WPD), which is then employed as the candidate set for further discriminatory feature selection. The features are selected one by one in a boosting manner. After one feature being selected, the importance of the correctly classified samples based on the feature will be decreased, which is equivalent to increasing the importance of the misclassified samples. Therefore, a complement feature to the current features could be selected in the next run. The selected features are then fed to a classifier trained by random forest algorithm. Finally, a time series voting-based method is utilized to improve the classification performance. Comparisons between the DFFS-based approach and state-of-art methods on BCI competition IV data set 2b have been conducted, which have shown the superiority of the proposed algorithm.

  10. Secrecy and Energy Efficiency in Massive MIMO Aided Heterogeneous C-RAN: A New Look at Interference

    NASA Astrophysics Data System (ADS)

    Wang, Lifeng; Wong, Kai-Kit; Elkashlan, Maged; Nallanathan, Arumugam; Lambotharan, Sangarapillai

    2016-12-01

    In this paper, we investigate the potential benefits of the massive multiple-input multiple-output (MIMO) enabled heterogeneous cloud radio access network (C-RAN) in terms of the secrecy and energy efficiency (EE). In this network, both remote radio heads (RRHs) and massive MIMO macrocell base stations (BSs) are deployed and soft fractional frequency reuse (S-FFR) is adopted to mitigate the inter-tier interference. We first examine the physical layer security by deriving the area ergodic secrecy rate and secrecy outage probability. Our results reveal that the use of massive MIMO and C-RAN can greatly improve the secrecy performance. For C-RAN, a large number of RRHs achieves high area ergodic secrecy rate and low secrecy outage probability, due to its powerful interference management. We find that for massive MIMO aided macrocells, having more antennas and serving more users improves secrecy performance. Then we derive the EE of the heterogeneous C-RAN, illustrating that increasing the number of RRHs significantly enhances the network EE. Furthermore, it is indicated that allocating more radio resources to the RRHs can linearly increase the EE of RRH tier and improve the network EE without affecting the EE of the macrocells.

  11. Polarization multiplexing of two MIMO RoF signals and one baseband signal over a single wavelength

    NASA Astrophysics Data System (ADS)

    Elmagzoub, M. A.; Bakar Mohammad, Abu; Shaddad, Redhwan Q.; Al-Gailani, Samir A.

    2016-01-01

    Next-generation (NG) access networks require simultaneous provision of wired and wireless services and high data rates to meet the large demands of mobility and multiple services. In this paper, we propose a novel spectral efficient radio over fiber (RoF) scheme to simultaneously provide two spatially multiplexed multiple input multiple output (MIMO) wireless signals with a baseband (BB) wired signal in one wavelength using a centralized light source. The proposed scheme can be applicable to wavelength division multiplexed passive optical networks (WDM-PONs). The BB signal is modulated at a low extinction ratio (ER). The modulated light is re-used to modulate two MIMO signals that have the same carrier frequency that is combined optically using polarization-division-multiplexing (PDM). The data rate for each MIMO stream was 1.25 Gb/s, and the data rate was 2.5 Gb/s for the BB signal. Error free performance with a bit error rate (BER) of 10-9 was achieved for all three signals after 20 km and 60 km through single mode fiber (SMF) for 16-QAM and 4-QAM for the MIMO signals, respectively.

  12. New RoF-PON architecture using polarization multiplexed wireless MIMO signals for NG-PON

    NASA Astrophysics Data System (ADS)

    Elmagzoub, M. A.; Mohammad, Abu Bakar; Shaddad, Redhwan Q.; Al-Gailani, Samir A.

    2015-06-01

    Next-generation access networks require provision of wireless services and high data rate to meet the huge demands for mobility and multiple services. Moreover, reusing the currently deployed optical distribution networks (ODNs) is highly beneficial and cost effective for providing the new high data rate wireless demands. In this paper, bidirectional radio over fiber passive optical network (RoF-PON) capable of handling multiple-input-multiple-output (MIMO) streams at low cost, high spectral efficiency and backward compatibility with currently deployed PON, is proposed. To the best of our knowledge, all the existing RoF MIMO solutions have not considered compatibility with currently deployed ODNs. Eight laser diodes (LDs) at the central office (CO) are enough for the whole system, instead of having LD or optical transmitter at each remote antenna unit (RAU), which makes a colorless and cost-effective RAU. Twenty four wavelengths are generated using optical comb technique. Each two 16-QAM MIMO signals that have the same carrier frequency in the downstream (DS) transmission are optically combined using polarization-division-multiplexing (PDM), where each two upstream (US) MIMO signals are time division multiplexed. The PDM configuration doubles spectral efficiency with a power penalty of only 1.5 dB. The proposed architecture is a bidirectional asymmetric RoF-PON with total 40/10 Gb/s for DS/US transmission. Even after transmission over 20 km SMF and splitting ratio of 32, acceptable transmission performance and widely separated constellation diagrams for the 16-QAM signals are achieved, with bit error rate (BER) of 10-6 for DS signals and 10-3 for the US signals which can be reduced down to 10-6 by using forward error correction (FEC).

  13. Selection and amplification of modes of an optical frequency comb using a femtosecond laser injection-locking technique

    SciTech Connect

    Moon, H. S.; Kim, E. B.; Park, S. E.; Park, C. Y.

    2006-10-30

    The authors have demonstrated the selection and the amplification of the components of an optical frequency comb using a femtosecond laser injectionlocking technique. The author used a mode-locked femtosecond Ti:sapphire laser as the master laser and a single-mode diode laser as the slave laser. The femtosecond laser injection-locking technique was applied to a filter for mode selection of the optical frequency comb and an amplifier for amplification of the selected mode. The authors could obtain the laser source selected only the desired mode of the optical frequency comb and amplified the power of the selected modes several thousand times.

  14. A Smartphone Application for Customized Frequency Table Selection in Cochlear Implants.

    PubMed

    Jethanamest, Daniel; Azadpour, Mahan; Zeman, Annette M; Sagi, Elad; Svirsky, Mario A

    2017-09-01

    A novel smartphone-based software application can facilitate self-selection of frequency allocation tables (FAT) in postlingually deaf cochlear implant (CI) users. CIs use FATs to represent the tonotopic organization of a normal cochlea. Current CI fitting methods typically use a standard FAT for all patients regardless of individual differences in cochlear size and electrode location. In postlingually deaf patients, different amounts of mismatch can result between the frequency-place function they experienced when they had normal hearing and the frequency-place function that results from the standard FAT. For some CI users, an alternative FAT may enhance sound quality or speech perception. Currently, no widely available tools exist to aid real-time selection of different FATs. This study aims to develop a new smartphone tool for this purpose and to evaluate speech perception and sound quality measures in a pilot study of CI subjects using this application. A smartphone application for a widely available mobile platform (iOS) was developed to serve as a preprocessor of auditory input to a clinical CI speech processor and enable interactive real-time selection of FATs. The application's output was validated by measuring electrodograms for various inputs. A pilot study was conducted in six CI subjects. Speech perception was evaluated using word recognition tests. All subjects successfully used the portable application with their clinical speech processors to experience different FATs while listening to running speech. The users were all able to select one table that they judged provided the best sound quality. All subjects chose a FAT different from the standard FAT in their everyday clinical processor. Using the smartphone application, the mean consonant-nucleus-consonant score with the default FAT selection was 28.5% (SD 16.8) and 29.5% (SD 16.4) when using a self-selected FAT. A portable smartphone application enables CI users to self-select frequency allocation

  15. Frequency-sweeping: A new technique for energy-selective transport

    SciTech Connect

    Mynick, H.E.; Pomphrey, N.

    1994-02-01

    A new method is described for inducing energy-selective transport by `sweeping` the frequency of applied low-n magnetic perturbations. The mechanism, formally analogous to the `rising buckets` concept in accelerator physics, can move particles with a selected velocity in a nondiffusive fashion from one specified radius to another. The technique is considered principally as a means for removal of Helium ash. Other likely applications are as a method for burn control, profile control, as a diagnostic, and perhaps as a nonstochastic means of effecting the direct coupling of alpha power recently discussed by Fisch and Rax.

  16. Frequency selective heterojunction metal-insulator-metal mirror for surface plasmons

    NASA Astrophysics Data System (ADS)

    Hwang, Yongsop; Shin, Jonghwa; Kim, Jae-Eun; Park, Hae Yong; Kee, Chul-Sik

    2011-06-01

    The authors introduce a mode-gap mirror for surface plasmon polaritons in a metal-insulator-metal (MIM) structure. At the heterojunction of MIMs which consists of two MIMs of different insulators, it is shown that a mode gap exists for a certain frequency range and the junction works as an effective mirror. Transmission and reflection properties of plasmonic modes at the interface of the heterojunction are investigated, and explained by the band theory. By showing that the mirror has high reflection and transmission of nearly zero, it is verified that the frequency range in which no plasmonic modes exist is an actual mode-gap range. It is also shown that by varying both the thickness and the dielectric constant of the insulator layer, one can select the frequency range in which the reflection coefficient is greater than 0.9.

  17. Tandem filters using frequency selective surfaces for enhanced conversion efficiency in a thermophotovoltaic energy conversion system

    DOEpatents

    Dziendziel, Randolph J.; DePoy, David Moore; Baldasaro, Paul Francis

    2007-01-23

    This invention relates to the field of thermophotovoltaic (TPV) direct energy conversion. In particular, TPV systems use filters to minimize parasitic absorption of below bandgap energy. This invention constitutes a novel combination of front surface filters to increase TPV conversion efficiency by reflecting useless below bandgap energy while transmitting a very high percentage of the useful above bandgap energy. In particular, a frequency selective surface is used in combination with an interference filter. The frequency selective surface provides high transmission of above bandgap energy and high reflection of long wavelength below bandgap energy. The interference filter maintains high transmission of above bandgap energy and provides high reflection of short wavelength below bandgap energy and a sharp transition from high transmission to high reflection.

  18. Tandem filters using frequency selective surfaces for enhanced conversion efficiency in a thermophotovoltaic energy conversion system

    DOEpatents

    Dziendziel, Randolph J.; Baldasaro, Paul F.; DePoy, David M.

    2010-09-07

    This invention relates to the field of thermophotovoltaic (TPV) direct energy conversion. In particular, TPV systems use filters to minimize parasitic absorption of below bandgap energy. This invention constitutes a novel combination of front surface filters to increase TPV conversion efficiency by reflecting useless below bandgap energy while transmitting a very high percentage of the useful above bandgap energy. In particular, a frequency selective surface is used in combination with an interference filter. The frequency selective surface provides high transmission of above bandgap energy and high reflection of long wavelength below bandgap energy. The interference filter maintains high transmission of above bandgap energy and provides high reflection of short wavelength below bandgap energy and a sharp transition from high transmission to high reflection.

  19. Noncoherent Maximum Likelihood Detection for Differential Spatial Multiplexing MIMO Systems

    NASA Astrophysics Data System (ADS)

    Jia, Ziyan; Yoshii, Katsunobu; Handa, Shiro; Sasamori, Fumihito; Oshita, Shinjiro

    In this paper, we propose a novel noncoherent maximum likelihood detection (NMLD) method for differential spatial multiplexing (SM) multiple-input multiple-output (MIMO) systems. Unlike the conventional maximum likelihood detection (MLD) method which needs the knowledge of channel state information (CSI) at the receiver, NMLD method has no need of CSI at either the transmitter orreceiver. After repartitioning the observation block of multiple-symbol differential detection (MSDD) and following a decision feedback process, the decision metric of NMLD is derived by reforming that of MSDD. Since the maximum Doppler frequency and noise power are included in the derived decision metric, estimations of both maximum Doppler frequency and noise power are needed at the receiver for NMLD. A fast calculation algorithm (FCA) is applied to reduce the computational complexity of NMLD. The feasibility of the proposed NMLD is demonstrated by computer simulations in both slow and fast fading environments. Simulation results show that the proposed NMLD has good bit error rate (BER) performance, approaching that of the conventional coherent MLD with the extension of reference symbols interval. It is also proved that the BER performance is not sensitive to the estimation errors in maximum Doppler frequency and noise power.

  20. Application of Wave Guide Propagation to Selection of Transmitter Power and Frequency

    DTIC Science & Technology

    1992-03-01

    the night. However. when an ionospheric 119611 and was first described by Pappert el al. disturbance occurs, such as those caused by solar g1967]. In...in a complicated way on latitude. solar zenith angle, and season. The ionospheric conductivity parameter co, is a snapshot can change from hour to...R.A, id 1.). 0i Mo rtiu. I hoeizladepnina The selection of frequency and powert for it trans- ainriwe trode consersion reults at VII. Rd i 11

  1. Optimization of meander line radiators for frequency selective surfaces by using genetic algorithm

    NASA Astrophysics Data System (ADS)

    Bucuci, Stefania C.; Dumitrascu, Ana; Danisor, Alin; Berescu, Serban; Tamas, Razvan D.

    2015-02-01

    In this paper we propose the use of frequency selective surfaces based on meander line radiators, as targets for monitoring slow displacements with synthetic aperture radars. The optimization of the radiators is performed by using genetic algorithms on only two parameters i.e., gain and size. As an example, we have optimized a single meander antenna, resonating in the X-band, at 9.65 GHz.

  2. Frequency Selective Properties of Coaxial Transmission Lines Loaded with Combined Artificial Inclusions

    PubMed Central

    2014-01-01

    The properties of a modified coaxial transmission line by periodic inclusions will be discussed. The introduction of split ring resonators, conductor stubs, air gaps, and combination of these gives rise to new frequency selective properties, such as stopband or passband behavior, observable in planar as well as volumetric metamaterial structures. These results envisage new potential applications and implementation of devices in coaxial transmission line technology. PMID:24587748

  3. Time-frequency based feature selection for discrimination of non-stationary biosignals

    NASA Astrophysics Data System (ADS)

    D Martínez-Vargas, Juan; I Godino-Llorente, Juan; Castellanos-Dominguez, Germán

    2012-12-01

    This research proposes a generic methodology for dimensionality reduction upon time-frequency representations applied to the classification of different types of biosignals. The methodology directly deals with the highly redundant and irrelevant data contained in these representations, combining a first stage of irrelevant data removal by variable selection, with a second stage of redundancy reduction using methods based on linear transformations. The study addresses two techniques that provided a similar performance: the first one is based on the selection of a set of the most relevant time-frequency points, whereas the second one selects the most relevant frequency bands. The first methodology needs a lower quantity of components, leading to a lower feature space; but the second improves the capture of the time-varying dynamics of the signal, and therefore provides a more stable performance. In order to evaluate the generalization capabilities of the methodology proposed it has been applied to two types of biosignals with different kinds of non-stationary behaviors: electroencephalographic and phonocardiographic biosignals. Even when these two databases contain samples with different degrees of complexity and a wide variety of characterizing patterns, the results demonstrate a good accuracy for the detection of pathologies, over 98 %.The results open the possibility to extrapolate the methodology to the study of other biosignals.

  4. Improved frequency selective fat suppression in the posterior neck with tissue susceptibility matched pyrolytic graphite foam.

    PubMed

    Lee, Gary; Jordan, Caroline; Tiet, Pamela; Ruiz, Carlos; McCormick, Jeff; Phuong, Kevin; Hargreaves, Brian; Conolly, Steven

    2015-03-01

    To demonstrate improved frequency selective fat suppression in MRI using a magnetic susceptibility matching foam by reducing B0 inhomogeneities induced within the body by air-tissue interfaces. Flexible pyrolytic graphite (PG) composite foam was tailored to match the magnetic susceptibility of human tissue and was shaped to surround the cervical spine region. Field maps and frequency selective fat suppressed T1 -weighted FLASH images were acquired at 3 Tesla in both phantoms and six healthy necks. B0 field uniformity was shimmed to a target critical threshold of 1 ppm for fat suppression. The percentage of voxels in the phantom that did not achieve the critical threshold was reduced from 64% without the PG foam to only 1% with the foam. A similar decrease from 16% to 2% was observed in the in vivo region of interest. PG foam improved B0 field uniformity by moving air-tissue field gradients outside of the neck where they cannot cause MRI artifacts. The PG foams consistently mitigated signal dropout, improved overall SNR, and enabled more robust frequency selective fat suppression. © 2014 Wiley Periodicals, Inc.

  5. Selective visual scaling of time-scale processes facilitates broadband learning of isometric force frequency tracking.

    PubMed

    King, Adam C; Newell, Karl M

    2015-10-01

    The experiment investigated the effect of selectively augmenting faster time scales of visual feedback information on the learning and transfer of continuous isometric force tracking tasks to test the generality of the self-organization of 1/f properties of force output. Three experimental groups tracked an irregular target pattern either under a standard fixed gain condition or with selectively enhancement in the visual feedback display of intermediate (4-8 Hz) or high (8-12 Hz) frequency components of the force output. All groups reduced tracking error over practice, with the error lowest in the intermediate scaling condition followed by the high scaling and fixed gain conditions, respectively. Selective visual scaling induced persistent changes across the frequency spectrum, with the strongest effect in the intermediate scaling condition and positive transfer to novel feedback displays. The findings reveal an interdependence of the timescales in the learning and transfer of isometric force output frequency structures consistent with 1/f process models of the time scales of motor output variability.

  6. Modeling and control of non-square MIMO system using relay feedback.

    PubMed

    Kalpana, D; Thyagarajan, T; Gokulraj, N

    2015-11-01

    This paper proposes a systematic approach for the modeling and control of non-square MIMO systems in time domain using relay feedback. Conventionally, modeling, selection of the control configuration and controller design of non-square MIMO systems are performed using input/output information of direct loop, while the output of undesired responses that bears valuable information on interaction among the loops are not considered. However, in this paper, the undesired response obtained from relay feedback test is also taken into consideration to extract the information about the interaction between the loops. The studies are performed on an Air Path Scheme of Turbocharged Diesel Engine (APSTDE) model, which is a typical non-square MIMO system, with input and output variables being 3 and 2 respectively. From the relay test response, the generalized analytical expressions are derived and these analytical expressions are used to estimate unknown system parameters and also to evaluate interaction measures. The interaction is analyzed by using Block Relative Gain (BRG) method. The model thus identified is later used to design appropriate controller to carry out closed loop studies. Closed loop simulation studies were performed for both servo and regulatory operations. Integral of Squared Error (ISE) performance criterion is employed to quantitatively evaluate performance of the proposed scheme. The usefulness of the proposed method is demonstrated on a lab-scale Two-Tank Cylindrical Interacting System (TTCIS), which is configured as a non-square system.

  7. Enhanced Microwave Absorption Properties of Carbon Black/Silicone Rubber Coating by Frequency-Selective Surface

    NASA Astrophysics Data System (ADS)

    Yang, Zhaoning; Luo, Fa; Gao, Lu; Qing, Yuchang; Zhou, Wancheng; Zhu, Dongmei

    2016-10-01

    A square frequency-selective surface (FSS) design has been employed to improve the microwave absorption properties of carbon black/silicone rubber (CBSR) composite coating. The FSS is placed on the surface of the CBSR coating. The effects of FSS design parameters on the microwave absorption properties of the CBSR coating have been investigated, including the size and period of the FSS design, and the thickness and permittivity of the coating. Simulation results indicate that the absorption peak for the CBSR coating alone is related to its thickness and electromagnetic parameters, while the combination of the CBSR coating with a FSS can exhibit a new absorption peak in the reflection curve; the frequency of the new absorption peak is determined by the resonance of the square FSS design and tightly depends on the size of the squares, with larger squares in the FSS design leading to a lower frequency of the new absorption peak. The enhancement of the absorption performance depends on achievement of a new absorption peak using a suitable size and period of the FSS design. In addition, the FSS design has a stable frequency response for both transverse electromagnetic (TE) and transverse magnetic (TM) polarizations as the incident angle varies from 0° to 40°. The optimized results indicate that the bandwidth with reflection loss below -5 dB can encompass the whole frequency range from 8 GHz to 18 GHz for thickness of the CBSR coating of only 1.8 mm. The simulation results are confirmed by experiments.

  8. Broadband Tunability of Polarization-Insensitive Absorber Based on Frequency Selective Surface

    PubMed Central

    Wang, Han; Kong, Peng; Cheng, Wentao; Bao, Wenzong; Yu, Xiaowei; Miao, Ling; Jiang, Jianjun

    2016-01-01

    An innovative tunable and polarization-insensitive 1.6–8 GHz frequency selective surface (FSS) absorber was investigated in this study. The proposed FSS, which is in 4-axial symmetrical form, includes a novel array of PIN diodes with biasing lines including inductors. A gradually reduced equivalent resistor of PIN diodes can be achieved with increasing DC voltage, which characterizes tunable, multi-resonance absorption peaks. Via this simplified design, small value resistor and equivalent capacitance of the gap between patterns can improve the absorber’s performance in low frequencies; an active tunable absorber can be realized in a broad frequency range by employing adjustable devices. Changing the working state of the PIN diode allows the user to obtain strong absorption within the desired frequency. We analyzed the performance of the proposed absorber and found that it indeed shows very favorable absorption performance in low frequency (−10 dB in 1.6−4.3 GHz) and wideband (−8 dB in 4.3−5.4 GHz and −10 dB in 5.4−8.0 GHz) conditions. Calculation and simulation results also illustrated that the absorber is entirely polarization-insensitive. PMID:26983804

  9. Polarization and angle insensitive dual-band bandpass frequency selective surface using all-dielectric metamaterials

    NASA Astrophysics Data System (ADS)

    Yu, Fei; Wang, Jun; Wang, Jiafu; Ma, Hua; Du, Hongliang; Xu, Zhuo; Qu, Shaobo

    2016-04-01

    In this paper, we demonstrate a dual-band bandpass all-dielectric frequency selective surface (FSS), the building elements of which are high-permittivity ceramic particles rather than metallic patterns. With proper structural design and parameter adjustment, the resonant frequency can be tuned at will. Dual-band bandpass response can be realized due to the coupling between electric and magnetic resonances. As an example, a dual-band bandpass FSS is designed in Ku band, which is composed of two-dimensional periodic arrays of complementary quatrefoil structures (CQS) cut from dielectric plates. Moreover, cylindrical dielectric resonators are introduced and placed in the center of each CQS to broaden the bandwidth and to sharpen the cut-off frequency. Theoretical analysis shows that the bandpass response arises from impedance matching caused by electric and magnetic resonances. In addition, effective electromagnetic parameters and dynamic field distributions are presented to explain the mechanism of impedance matching. The proposed FSS has the merits of polarization independence, stable transmission, and sharp roll-off frequency. The method can also be used to design all-dielectric FSSs with continuum structures at other frequencies.

  10. Frequency-selective augmenting responses by short-term synaptic depression in cat neocortex

    PubMed Central

    Houweling, Arthur R; Bazhenov, Maxim; Timofeev, Igor; Grenier, François; Steriade, Mircea; Sejnowski, Terrence J

    2002-01-01

    Thalamic stimulation at frequencies between 5 and 15 Hz elicits incremental or ‘augmenting’ cortical responses. Augmenting responses can also be evoked in cortical slices and isolated cortical slabs in vivo. Here we show that a realistic network model of cortical pyramidal cells and interneurones including short-term plasticity of inhibitory and excitatory synapses replicates the main features of augmenting responses as obtained in isolated slabs in vivo. Repetitive stimulation of synaptic inputs at frequencies around 10 Hz produced postsynaptic potentials that grew in size and carried an increasing number of action potentials resulting from the depression of inhibitory synaptic currents. Frequency selectivity was obtained through the relatively weak depression of inhibitory synapses at low frequencies, and strong depression of excitatory synapses together with activation of a calcium-activated potassium current at high frequencies. This network resonance is a consequence of short-term synaptic plasticity in a network of neurones without intrinsic resonances. These results suggest that short-term plasticity of cortical synapses could shape the dynamics of synchronized oscillations in the brain. PMID:12122156

  11. Measuring the spatial frequency selectivity of second-order texture mechanisms.

    PubMed

    Sutter, A; Sperling, G; Chubb, C

    1995-04-01

    Recent investigations of texture and motion perception suggest two early filtering stages: an initial stage of selective linear filtering followed by rectification and a second stage of linear filtering. Here we demonstrate that there are differently scaled second-stage filters, and we measure their contrast modulation sensitivity as a function of spatial frequency. Our stimuli are Gabor modulations of a suprathreshold, bandlimited, isotropic carrier noise. The subjects' task is to discriminate between two possible orientations of the Gabor. Carrier noises are filtered into four octave-wide bands, centered at m = 2, 4, 8, and 16 c/deg. The Gabor test signals are w = 0.5, 1, 2, 4 and 8 c/deg. The threshold modulation of the test signal is measured for all 20 combinations of m and w. For each carrier frequency m, the Gabor test frequency w to which subjects are maximally sensitive appears to be approximately 3-4 octaves below m. The consistent m x w interaction suggests that each second-stage spatial filter may be differentially tuned to a particular first-stage spatial frequency. The most sensitive combination is a second-stage filter of 1 c/deg with first-stage inputs of 8-16 c/deg. We conclude that second-order texture perception appears to utilize multiple channels tuned to spatial frequency and orientation, with channels tuned to low modulation frequencies appearing to be best served by carrier frequencies 8 to 16 times higher than the modulations they are tuned to detect.

  12. Signature of forty years of artificial selection in U.S. Holstein cattle identified by long-range frequency analyses

    USDA-ARS?s Scientific Manuscript database

    Three groups of U.S. Holstein cattle were analyzed for selection signature of artificial selection since 1964 using long-range frequency measures. The three groups included Holsteins unselected since 1964, contemporary Holsteins, and an elite line of contemporary Holsteins. Long-range frequencies in...

  13. Multi-Bandwidth Frequency Selective Surfaces for Near Infrared Filtering: Design and Optimization

    NASA Technical Reports Server (NTRS)

    Cwik, Tom; Fernandez, Salvador; Ksendzov, A.; LaBaw, Clayton C.; Maker, Paul D.; Muller, Richard E.

    1998-01-01

    Frequency selective surfaces are widely used in the microwave and millimeter wave regions of the spectrum for filtering signals. They are used in telecommunication systems for multi-frequency operation or in instrument detectors for spectroscopy. The frequency selective surface operation depends on a periodic array of elements resonating at prescribed wavelengths producing a filter response. The size of the elements is on the order of half the electrical wavelength, and the array period is typically less than a wavelength for efficient operation. When operating in the optical region, diffraction gratings are used for filtering. In this regime the period of the grating may be several wavelengths producing multiple orders of light in reflection or transmission. In regions between these bands (specifically in the infrared band) frequency selective filters consisting of patterned metal layers fabricated using electron beam lithography are beginning to be developed. The operation is completely analogous to surfaces made in the microwave and millimeter wave region except for the choice of materials used and the fabrication process. In addition, the lithography process allows an arbitrary distribution of patterns corresponding to resonances at various wavelengths to be produced. The design of sub-millimeter filters follows the design methods used in the microwave region. Exacting modal matching, integral equation or finite element methods can be used for design. A major difference though is the introduction of material parameters and thicknesses that may not be important in longer wavelength designs. This paper describes the design of multi- bandwidth filters operating in the 1-5 micrometer wavelength range. This work follows on a previous design. In this paper extensions based on further optimization and an examination of the specific shape of the element in the periodic cell will be reported. Results from the design, manufacture and test of linear wedge filters built

  14. Multi-Bandwidth Frequency Selective Surfaces for Near Infrared Filtering: Design and Optimization

    NASA Technical Reports Server (NTRS)

    Cwik, Tom; Fernandez, Salvador; Ksendzov, A.; LaBaw, Clayton C.; Maker, Paul D.; Muller, Richard E.

    1999-01-01

    Frequency selective surfaces are widely used in the microwave and millimeter wave regions of the spectrum for filtering signals. They are used in telecommunication systems for multi-frequency operation or in instrument detectors for spectroscopy. The frequency selective surface operation depends on a periodic array of elements resonating at prescribed wavelengths producing a filter response. The size of the elements is on the order of half the electrical wavelength, and the array period is typically less than a wavelength for efficient operation. When operating in the optical region, diffraction gratings are used for filtering. In this regime the period of the grating may be several wavelengths producing multiple orders of light in reflection or transmission. In regions between these bands (specifically in the infrared band) frequency selective filters consisting of patterned metal layers fabricated using electron beam lithography are beginning to be developed. The operation is completely analogous to surfaces made in the microwave and millimeter wave region except for the choice of materials used and the fabrication process. In addition, the lithography process allows an arbitrary distribution of patterns corresponding to resonances at various wavelengths to be produced. The design of sub-millimeter filters follows the design methods used in the microwave region. Exacting modal matching, integral equation or finite element methods can be used for design. A major difference though is the introduction of material parameters and thicknesses tha_ may not be important in longer wavelength designs. This paper describes the design of multi-bandwidth filters operating in the I-5 micrometer wavelength range. This work follows on previous design [1,2]. In this paper extensions based on further optimization and an examination of the specific shape of the element in the periodic cell will be reported. Results from the design, manufacture and test of linear wedge filters built

  15. Multi-Bandwidth Frequency Selective Surfaces for Near Infrared Filtering: Design and Optimization

    NASA Technical Reports Server (NTRS)

    Cwik, Tom; Fernandez, Salvador; Ksendzov, A.; LaBaw, Clayton C.; Maker, Paul D.; Muller, Richard E.

    1999-01-01

    Frequency selective surfaces are widely used in the microwave and millimeter wave regions of the spectrum for filtering signals. They are used in telecommunication systems for multi-frequency operation or in instrument detectors for spectroscopy. The frequency selective surface operation depends on a periodic array of elements resonating at prescribed wavelengths producing a filter response. The size of the elements is on the order of half the electrical wavelength, and the array period is typically less than a wavelength for efficient operation. When operating in the optical region, diffraction gratings are used for filtering. In this regime the period of the grating may be several wavelengths producing multiple orders of light in reflection or transmission. In regions between these bands (specifically in the infrared band) frequency selective filters consisting of patterned metal layers fabricated using electron beam lithography are beginning to be developed. The operation is completely analogous to surfaces made in the microwave and millimeter wave region except for the choice of materials used and the fabrication process. In addition, the lithography process allows an arbitrary distribution of patterns corresponding to resonances at various wavelengths to be produced. The design of sub-millimeter filters follows the design methods used in the microwave region. Exacting modal matching, integral equation or finite element methods can be used for design. A major difference though is the introduction of material parameters and thicknesses tha_ may not be important in longer wavelength designs. This paper describes the design of multi-bandwidth filters operating in the I-5 micrometer wavelength range. This work follows on previous design [1,2]. In this paper extensions based on further optimization and an examination of the specific shape of the element in the periodic cell will be reported. Results from the design, manufacture and test of linear wedge filters built

  16. High efficiency in Mode Selective Frequency Conversion for Optical Quantum Information Processing

    NASA Astrophysics Data System (ADS)

    Quesada, Nicolas; Sipe, J. E.

    Mode selective Frequency conversion (FC) is an enabling process in many quantum information protocols. Recently, it has been observed that upconversion efficiencies in single-photon, mode-selective FC are limited to around 80%. In this contribution we show that these limits can be understood as time ordering corrections (TOCs) that modify the joint conversion amplitude of the process. Furthermore we show, using a simple scaling argument, that recently proposed cascaded FC protocols that overcome the aforementioned limitations act as ``attenuators'' of the TOCs. This observation allows us to argue that very similar cascaded architectures can be used to attenuate TOCs in photon generation via spontaneous parametric down-conversion. Finally, by using the Magnus expansion, we argue that the TOCs, which are usually considered detrimental for FC efficiency, can also be used to increase the efficiency of conversion in partially mode selective FC.

  17. Testing for Ancient Selection Using Cross-population Allele Frequency Differentiation

    PubMed Central

    Racimo, Fernando

    2016-01-01

    A powerful way to detect selection in a population is by modeling local allele frequency changes in a particular region of the genome under scenarios of selection and neutrality and finding which model is most compatible with the data. A previous method based on a cross-population composite likelihood ratio (XP-CLR) uses an outgroup population to detect departures from neutrality that could be compatible with hard or soft sweeps, at linked sites near a beneficial allele. However, this method is most sensitive to recent selection and may miss selective events that happened a long time ago. To overcome this, we developed an extension of XP-CLR that jointly models the behavior of a selected allele in a three-population tree. Our method - called “3-population composite likelihood ratio” (3P-CLR) - outperforms XP-CLR when testing for selection that occurred before two populations split from each other and can distinguish between those events and events that occurred specifically in each of the populations after the split. We applied our new test to population genomic data from the 1000 Genomes Project, to search for selective sweeps that occurred before the split of Yoruba and Eurasians, but after their split from Neanderthals, and that could have led to the spread of modern-human-specific phenotypes. We also searched for sweep events that occurred in East Asians, Europeans, and the ancestors of both populations, after their split from Yoruba. In both cases, we are able to confirm a number of regions identified by previous methods and find several new candidates for selection in recent and ancient times. For some of these, we also find suggestive functional mutations that may have driven the selective events. PMID:26596347

  18. Testing for Ancient Selection Using Cross-population Allele Frequency Differentiation.

    PubMed

    Racimo, Fernando

    2016-02-01

    A powerful way to detect selection in a population is by modeling local allele frequency changes in a particular region of the genome under scenarios of selection and neutrality and finding which model is most compatible with the data. A previous method based on a cross-population composite likelihood ratio (XP-CLR) uses an outgroup population to detect departures from neutrality that could be compatible with hard or soft sweeps, at linked sites near a beneficial allele. However, this method is most sensitive to recent selection and may miss selective events that happened a long time ago. To overcome this, we developed an extension of XP-CLR that jointly models the behavior of a selected allele in a three-population tree. Our method - called "3-population composite likelihood ratio" (3P-CLR) - outperforms XP-CLR when testing for selection that occurred before two populations split from each other and can distinguish between those events and events that occurred specifically in each of the populations after the split. We applied our new test to population genomic data from the 1000 Genomes Project, to search for selective sweeps that occurred before the split of Yoruba and Eurasians, but after their split from Neanderthals, and that could have led to the spread of modern-human-specific phenotypes. We also searched for sweep events that occurred in East Asians, Europeans, and the ancestors of both populations, after their split from Yoruba. In both cases, we are able to confirm a number of regions identified by previous methods and find several new candidates for selection in recent and ancient times. For some of these, we also find suggestive functional mutations that may have driven the selective events.

  19. Positive frequency-dependent selection on warning color in Alpine leaf beetles.

    PubMed

    Borer, Matthias; Van Noort, Tom; Rahier, Martine; Naisbit, Russell E

    2010-12-01

    Müller's theory of warning color and mimicry, despite forming a textbook example of frequency-dependent selection, has rarely been demonstrated in the wild. This may be largely due to the practical and statistical difficulties of measuring natural selection on mobile prey species. Here we demonstrate that this selection acts in alpine beetle communities by using tethered beetles exposed to natural predators. Oreina gloriosa leaf beetles (Coleoptera: Chrysomelidae) possess chemical defense in the form of cardenolides, accompanied by what appears to be warning color in bright metallic blues and greens. Individuals that match the locally predominant color morph have increased survival, with odds of week-long survival increased by a factor of 1.67 over those that do not match. This corresponds to selection of 13% against foreign morphs. Such selection, acting in concert with variation in community composition, could be responsible for geographic variation in warning color. However, in the face of this purifying selection, the within-population polymorphism seen in many Oreina species remains paradoxical.

  20. Sound Frequency and Aural Selectivity in Sound-Contingent Visual Motion Aftereffect

    PubMed Central

    Kobayashi, Maori; Teramoto, Wataru; Hidaka, Souta; Sugita, Yoichi

    2012-01-01

    Background One possible strategy to evaluate whether signals in different modalities originate from a common external event or object is to form associations between inputs from different senses. This strategy would be quite effective because signals in different modalities from a common external event would then be aligned spatially and temporally. Indeed, it has been demonstrated that after adaptation to visual apparent motion paired with alternating auditory tones, the tones begin to trigger illusory motion perception to a static visual stimulus, where the perceived direction of visual lateral motion depends on the order in which the tones are replayed. The mechanisms underlying this phenomenon remain unclear. One important approach to understanding the mechanisms is to examine whether the effect has some selectivity in auditory processing. However, it has not yet been determined whether this aftereffect can be transferred across sound frequencies and between ears. Methodology/Principal Findings Two circles placed side by side were presented in alternation, producing apparent motion perception, and each onset was accompanied by a tone burst of a specific and unique frequency. After exposure to this visual apparent motion with tones for a few minutes, the tones became drivers for illusory motion perception. However, the aftereffect was observed only when the adapter and test tones were presented at the same frequency and to the same ear. Conclusions/Significance These findings suggest that the auditory processing underlying the establishment of novel audiovisual associations is selective, potentially but not necessarily indicating that this processing occurs at an early stage. PMID:22649500

  1. Human Commercial Models' Eye Colour Shows Negative Frequency-Dependent Selection.

    PubMed

    Forti, Isabela Rodrigues Nogueira; Young, Robert John

    2016-01-01

    In this study we investigated the eye colour of human commercial models registered in the UK (400 female and 400 male) and Brazil (400 female and 400 male) to test the hypothesis that model eye colour frequency was the result of negative frequency-dependent selection. The eye colours of the models were classified as: blue, brown or intermediate. Chi-square analyses of data for countries separated by sex showed that in the United Kingdom brown eyes and intermediate colours were significantly more frequent than expected in comparison to the general United Kingdom population (P<0.001). In Brazil, the most frequent eye colour brown was significantly less frequent than expected in comparison to the general Brazilian population. These results support the hypothesis that model eye colour is the result of negative frequency-dependent selection. This could be the result of people using eye colour as a marker of genetic diversity and finding rarer eye colours more attractive because of the potential advantage more genetically diverse offspring that could result from such a choice. Eye colour may be important because in comparison to many other physical traits (e.g., hair colour) it is hard to modify, hide or disguise, and it is highly polymorphic.

  2. Selected translocation of plasmid genes: frequency and regional specificity of translocation of the Tn3 element.

    PubMed

    Kretschmer, P J; Cohen, S N

    1977-05-01

    A procedure is described that selects for the insertion of transposable antibiotic resistance elements in a variety of recipient replicons. The selected translocation procedure, which employs a plasmid having a temperature-sensitive defect in replication as a donor of transposable genetic elements, was used to investigate certain characteristics of the translocation process. Our results indicate that translocation of the Tn3 element from plasmid to plasmid occurs at a 10(3)- to 10(4)-times-higher frequency than from plasmid to chromosome. In both cases, continued accumulation of Tn3 on recipient genomes is prevented by development of an apparent equilibrium when only a small fraction of molecules in the recipient population contain Tn3. An alternative method for estimation of translocation frequency has shown that the translocation process is temperature sensitive and that its frequency is unaffected by the presence of host recA mutation. Insertions of Tn3 onto the 65 X 10(6)-dalton R6-5 plasmid in Escherichia coli are clustered on EcoRI fragments 3 (8 of 23 insertions) and 9 (7 of 23 insertions), which contain 12 and 5%, respectively, of the R6-5 genome. The occurrence of multiple insertions of Tn3 within EcoRI fragment 9, which contains the IS1 element and a terminus of the Tn4 element, is consistent with earlier evidence indicating that terminal deoxyribonucleic acid sequences of already present transposable elements may provide recognition sequences for subsequent illegitimate recombinational events.

  3. A General Model of Negative Frequency Dependent Selection Explains Global Patterns of Human ABO Polymorphism

    PubMed Central

    Villanea, Fernando A.; Safi, Kristin N.; Busch, Jeremiah W.

    2015-01-01

    The ABO locus in humans is characterized by elevated heterozygosity and very similar allele frequencies among populations scattered across the globe. Using knowledge of ABO protein function, we generated a simple model of asymmetric negative frequency dependent selection and genetic drift to explain the maintenance of ABO polymorphism and its loss in human populations. In our models, regardless of the strength of selection, models with large effective population sizes result in ABO allele frequencies that closely match those observed in most continental populations. Populations must be moderately small to fall out of equilibrium and lose either the A or B allele (Ne ≤ 50) and much smaller (Ne ≤ 25) for the complete loss of diversity, which nearly always involved the fixation of the O allele. A pattern of low heterozygosity at the ABO locus where loss of polymorphism occurs in our model is consistent with small populations, such as Native American populations. This study provides a general evolutionary model to explain the observed global patterns of polymorphism at the ABO locus and the pattern of allele loss in small populations. Moreover, these results inform the range of population sizes associated with the recent human colonization of the Americas. PMID:25946124

  4. A General Model of Negative Frequency Dependent Selection Explains Global Patterns of Human ABO Polymorphism.

    PubMed

    Villanea, Fernando A; Safi, Kristin N; Busch, Jeremiah W

    2015-01-01

    The ABO locus in humans is characterized by elevated heterozygosity and very similar allele frequencies among populations scattered across the globe. Using knowledge of ABO protein function, we generated a simple model of asymmetric negative frequency dependent selection and genetic drift to explain the maintenance of ABO polymorphism and its loss in human populations. In our models, regardless of the strength of selection, models with large effective population sizes result in ABO allele frequencies that closely match those observed in most continental populations. Populations must be moderately small to fall out of equilibrium and lose either the A or B allele (N(e) ≤ 50) and much smaller (N(e) ≤ 25) for the complete loss of diversity, which nearly always involved the fixation of the O allele. A pattern of low heterozygosity at the ABO locus where loss of polymorphism occurs in our model is consistent with small populations, such as Native American populations. This study provides a general evolutionary model to explain the observed global patterns of polymorphism at the ABO locus and the pattern of allele loss in small populations. Moreover, these results inform the range of population sizes associated with the recent human colonization of the Americas.

  5. Human Commercial Models’ Eye Colour Shows Negative Frequency-Dependent Selection

    PubMed Central

    2016-01-01

    In this study we investigated the eye colour of human commercial models registered in the UK (400 female and 400 male) and Brazil (400 female and 400 male) to test the hypothesis that model eye colour frequency was the result of negative frequency-dependent selection. The eye colours of the models were classified as: blue, brown or intermediate. Chi-square analyses of data for countries separated by sex showed that in the United Kingdom brown eyes and intermediate colours were significantly more frequent than expected in comparison to the general United Kingdom population (P<0.001). In Brazil, the most frequent eye colour brown was significantly less frequent than expected in comparison to the general Brazilian population. These results support the hypothesis that model eye colour is the result of negative frequency-dependent selection. This could be the result of people using eye colour as a marker of genetic diversity and finding rarer eye colours more attractive because of the potential advantage more genetically diverse offspring that could result from such a choice. Eye colour may be important because in comparison to many other physical traits (e.g., hair colour) it is hard to modify, hide or disguise, and it is highly polymorphic. PMID:28005995

  6. Analog nonlinear MIMO receiver for optical mode division multiplexing transmission.

    PubMed

    Spalvieri, Arnaldo; Boffi, Pierpaolo; Pecorino, Simone; Barletta, Luca; Magarini, Maurizio; Gatto, Alberto; Martelli, Paolo; Martinelli, Mario

    2013-10-21

    The complexity and the power consumption of digital signal processing are crucial issues in optical transmission systems based on mode division multiplexing and coherent multiple-input multiple-output (MIMO) processing at the receiver. In this paper the inherent characteristic of spatial separation between fiber modes is exploited, getting a MIMO system where joint demultiplexing and detection is based on spatially separated photodetectors. After photodetection, one has a MIMO system with nonlinear crosstalk between modes. The paper shows that the nonlinear crosstalk can be dealt with by a low-complexity and non-adaptive detection scheme, at least in the cases presented in the paper.

  7. Angular Stable, Dual-Polarized and Multiband Modified Circular Ring Frequency Selective Surface

    NASA Astrophysics Data System (ADS)

    Bharti, Garima; Jha, Kumud Ranjan; Singh, G.; Jyoti, Rajeev

    2015-05-01

    In this paper, a single-layer multiband slot-type frequency selective surface (FSS), which consists of a modified circular ring loaded with concentric conventional circular ring, is discussed. We have emphasized to design an angular as well as polarization stable multiband FSS structure with reflection characteristics in S-band (2-4 GHz)/Ku (12-18 GHz) and transmission characteristics in X-band (8-12 GHz)/Ka-band (24-28 GHz). A novel synthesis technique is used to obtain the geometrical parameters of the proposed multiband FSS structure, which reduces the number of iterations in the computation process. The proposed multiband FSS structure satisfies the design issues of the frequency response in chosen frequency band of the electromagnetic spectrum and provides significant frequency stability as well as 3-dB bandwidth for both the perpendicular and parallel polarized wave incidence up to 50°. The slot-type modified circular ring FSS structure has been experimentally tested at X-band to validate the synthesis approach.

  8. A transmit/reflect switchable frequency selective surface based on all dielectric metamaterials

    NASA Astrophysics Data System (ADS)

    Yu, Fei; Wang, Jun; Wang, Jiafu; Ma, Hua; Du, Hongliang; Zhuo, Xu; Qu, Shaobo

    2015-12-01

    In this paper, we propose a novel transmit/reflect switchable frequency selective surface (FSS) in millimeter wave band based on the effective medium theory under quasi-static limit, which is designed with square-hole elements cut from continuum dielectric plates. The building elements of the surface are composed of all dielectric metamaterial rather than metal material. With proper structural design and parameters tuning, the resonance frequencies can be tuned appropriately. The frequency response of the surface can be switched from that of a reflecting structure to a transmitting one by rotating the surface 90°, which means under different incident polarizations. The reflective response can be realized due to the effect of electric and magnetic resonances. Theoretical analysis shows that the reflective response arises from impedance mismatching by electric and magnetic resonances. And the transmitting response is the left-handed passband, arises from the coupling of the electric and magnetic resonances. In addition, effective electromagnetic parameters and the dynamic induced field distributions are analyzed to explain the mechanism of the responses. The method can also be used to design switchable all-dielectric FSS with continuum structures in other frequencies.

  9. Athena MIMOS II Mössbauer spectrometer investigation

    NASA Astrophysics Data System (ADS)

    Klingelhöfer, G.; Morris, R. V.; Bernhardt, B.; Rodionov, D.; de Souza, P. A.; Squyres, S. W.; Foh, J.; Kankeleit, E.; Bonnes, U.; Gellert, R.; Schröder, C.; Linkin, S.; Evlanov, E.; Zubkov, B.; Prilutski, O.

    2003-12-01

    Mössbauer spectroscopy is a powerful tool for quantitative mineralogical analysis of Fe-bearing materials. The miniature Mössbauer spectrometer MIMOS II is a component of the Athena science payload launched to Mars in 2003 on both Mars Exploration Rover missions. The instrument has two major components: (1) a rover-based electronics board that contains power supplies, a dedicated central processing unit, memory, and associated support electronics and (2) a sensor head that is mounted at the end of the instrument deployment device (IDD) for placement of the instrument in physical contact with soil and rock. The velocity transducer operates at a nominal frequency of ~25 Hz and is equipped with two 57Co/Rh Mössbauer sources. The reference source (~5 mCi landed intensity), reference target (α-Fe2O3 plus α-Fe0), and PIN-diode detector are configured in transmission geometry and are internal to the instrument and used for its calibration. The analysis Mössbauer source (~150 mCi landed intensity) irradiates Martian surface materials with a beam diameter of ~1.4 cm. The backscatter radiation is measured by four PIN-diode detectors. Physical contact with surface materials is sensed with a switch-activated contact plate. The contact plate and reference target are instrumented with temperature sensors. Assuming ~18% Fe for Martian surface materials, experiment time is 6-12 hours during the night for quality spectra (i.e., good counting statistics); 1-2 hours is sufficient to identify and quantify the most abundant Fe-bearing phases. Data stored internal to the instrument for selectable return to Earth include Mössbauer and pulse-height analysis spectra (512 and 256 channels, respectively) for each of the five detectors in up to 13 temperature intervals (65 Mössbauer spectra), engineering data for the velocity transducer, and temperature measurements. The total data volume is ~150 kB. The mass and power consumption are ~500 g (~400 g for the sensor head) and ~2 W

  10. Modafinil effects on middle-frequency oscillatory power during rule selection in schizophrenia.

    PubMed

    Minzenberg, Michael J; Yoon, Jong H; Cheng, Yaoan; Carter, Cameron S

    2014-12-01

    Control-related cognitive processes such as rule selection are associated with cortical oscillations in the theta, alpha and, beta ranges, and modulated by catecholamine neurotransmission. Thus, a potential strategy for improving cognitive control deficits in schizophrenia would be to use pro-catecholamine pharmacological agents to augment these control-related oscillations. In a double-blind, placebo-controlled (within-subjects) study, we tested the effects of adjunctive single-dose modafinil 200 mg on rule-related 4-30 Hz oscillations in 23 stable schizophrenia patients, using EEG during cognitive control task performance. EEG data underwent time-frequency decomposition with Morlet wavelets to determine the power of 4-30 Hz oscillations. Modafinil (relative to placebo) enhanced oscillatory power associated with high-control rule selection in theta, alpha, and beta ranges, with modest effects during rule maintenance. Modafinil treatment in schizophrenia augments middle-frequency cortical oscillatory power associated with rule selection, and may subserve diverse subcomponent processes in proactive cognitive control.

  11. On the application of frequency selective common mode feedback for multifrequency EIT.

    PubMed

    Langlois, Peter J; Wu, Yu; Bayford, Richard H; Demosthenous, Andreas

    2015-06-01

    Common mode voltages are frequently a problem in electrical impedance tomography (EIT) and other bioimpedance applications. To reduce their amplitude common mode feedback is employed. Formalised analyses of both current and voltage feedback is presented in this paper for current drives. Common mode effects due to imbalances caused by the current drives, the electrode connections to the body load and the introduction of the body impedance to ground are considered. Frequency selective narrowband common mode feedback previously proposed to provide feedback stability is examined. As a step towards multifrequency applications the use of narrowband feedback is experimentally demonstrated for two simultaneous current drives. Measured results using standard available components show a reduction of 62 dB for current feedback and 31 dB for voltage feedback. Frequencies ranged from 50 kHz to 1 MHz.

  12. Equivalent circuit for VO{sub 2} phase change material film in reconfigurable frequency selective surfaces

    SciTech Connect

    Sanphuang, Varittha; Ghalichechian, Nima; Nahar, Niru K.; Volakis, John L.

    2015-12-21

    We developed equivalent circuits of phase change materials based on vanadium dioxide (VO{sub 2}) thin films. These circuits are used to model VO{sub 2} thin films for reconfigurable frequency selective surfaces (FSSs). This is important as it provides a way for designing complex structures. A reconfigurable FSS filter using VO{sub 2} ON/OFF switches is designed demonstrating −60 dB isolation between the states. This filter is used to provide the transmission and reflection responses of the FSS in the frequency range of 0.1–0.6 THz. The comparison between equivalent circuit and full-wave simulation shows excellent agreement.

  13. Characterization of a diffraction grating as a simulant of a selective frequency antenna for radiometric applications

    NASA Astrophysics Data System (ADS)

    Pizzillo, Thomas J.

    1994-01-01

    This report details the study of a blazed diffraction grating as a simulant of a selective frequency antenna for radiometric applications. Specifically, the ability to direct and sweep a beam of millimeter wave (MMW) energy is explored as a potential means of munitions guidance. A grating was designed and built to direct incident energy into the negative first-order peak of the associated diffraction spectrum. A change of 1 GHz in the incident energy frequency is shown to produce a beam displacement of 0.30, a polarization dependence is shown to exist for energy in orders other than zero, and a limited scaling of the optical theory of diffraction to MMW energies is demonstrated to be feasible.

  14. Reconfigurable all-dielectric metamaterial frequency selective surface based on high-permittivity ceramics

    PubMed Central

    Li, Liyang; Wang, Jun; Wang, Jiafu; Ma, Hua; Du, Hongliang; Zhang, Jieqiu; Qu, Shaobo; Xu, Zhuo

    2016-01-01

    Based on effective medium theory and dielectric resonator theory, we propose the design of reconfigurable all-dielectric metamaterial frequency selective surfaces (FSSs) using high-permittivity ceramics. The FSS is composed of ceramic resonators with different band stop responses under front and side incidences. By mechanically tuning the orientation of the ceramic resonators, reconfigurable electromagnetic (EM) responses between two adjacent stopbands can be achieved. The two broad stopbands originate from the first two resonant modes of the ceramic resonators. As an example, a reconfigurable FSS composed of cross-shaped ceramic resonators is demonstrated. Both numerical and experimental results show that the FSS can switch between two consecutive stopbands in 3.55–4.60 GHz and 4.54–4.94 GHz. The design method can be readily extended to the design of FSSs in other frequencies for high-power applications. PMID:27052098

  15. Inferring Selective History from Multilocus Frequency Data: Wright Meets the Hamiltonian

    PubMed Central

    Fox, G. A.; Hastings, A.

    1992-01-01

    We describe a method to study characteristics of the dynamics of multilocus population genetic models without specifying the form of selection a priori. Our approach consists of specifying initial and final genotypic frequencies (either completely or partially) and then determining the minimum time to go from the initial condition to the final condition according to a continuous time genetic model, with arbitrary constraints on the strength and possibly the form of selection. In analyzing a two-locus, two-allele model with this approach, we show that-so long as r is not much larger than s-substantial linkage disequilibrium can be generated from an initial state of linkage equilibrium in a few hundred generations. We also show that unless recombination is much larger than selection, there is only weak dependence on r of the minimum time to reach a specified state. Thus, similar strengths of selection can lead to similar levels of disequilibrium over a fixed time and a range of small recombination rates. This implies that, within the level of a single gene, selection cannot in general be assumed to lead to any particular relationship between recombination rate and levels of disequilibrium. We indicate a number of other ways in which our method can be useful in asking theoretical questions and in interpreting data. PMID:1398061

  16. A guinea pig model of selective severe high-frequency hearing loss.

    PubMed

    Havenith, Sarah; Klis, Sjaak F L; Versnel, Huib; Grolman, Wilko

    2013-10-01

    Using an appropriate dose of an aminoglycoside antibiotic cotreated with a loop diuretic a guinea pig model of high-frequency loss can be obtained mimicking cochlear implant candidates with low-frequency residual hearing. We examined the stability of this model over time. A well-established method to create an animal model for profound deafness is cotreatment with an aminoglycoside antibiotic and a loop diuretic. Recent data indicated that reduction of the aminoglycoside dose might yield selective high-frequency hearing loss. Such a model is relevant for studies related to hybrid cochlear implant devices, for example, with respect to preservation of residual hearing. Guinea pigs received an electrode for chronic recording of compound action potentials to tones to assess thresholds. They were treated with a coadministration of kanamycin (200 mg/kg) and furosemide (100 mg/kg), after which, the animals were sacrificed for histologic analysis at 2, 4, or 7 weeks. After 2 to 7 weeks threshold shifts were greater than 50 dB for 8 to 16 kHz in 15 of 17 animals, whereas threshold shifts at 2 kHz or lower were less than 50 dB in 13 animals. Major threshold shifts occurred the first 2 to 4 days; subsequently, some spontaneous recovery occurred and, after 2-3 weeks thresholds, remained stable. Inner hair cell loss still progressed between 2 and 4 weeks in the most basal cochlear region; thereafter, hair cell loss was stable. An appropriate animal model for selective severe high-frequency hearing loss was obtained, which is stable at 4 weeks after ototoxic treatment.

  17. Spatial mosaic formation through frequency-dependent selection in Müllerian mimicry complexes.

    PubMed

    Sherratt, Thomas N

    2006-05-21

    Although contemporary models of Müllerian mimicry have considered the movement of interfacial boundaries between two distinct mimetic forms, and even the possibility of polymorphisms in two patch systems, no model has considered how multiple forms of Müllerian mimics might evolve and be maintained over large geographical areas. A spatially explicit individual-based model for the evolution of Müllerian mimicry is presented, in which two unpalatable species are distributed over discrete cells within a regular lattice. Populations in each cell are capable of genetic drift and experience localized dispersal as well as frequency-dependent selection by predators. When each unpalatable prey species was introduced into a random cell and allowed to spread, then mimicry evolved throughout the system in the form of a spatial mosaic of phenotypes, separated by narrow "hybrid zones". The primary mechanism generating phenotypic diversity was the occasional establishment of new mutant forms in unoccupied cells and their subsequent maintenance (and spread) through frequency-dependent selection. The mean number of discrete clusters of the same morph that formed in the lattice was higher the higher the intensity of predation, and higher the lower the dispersal rate of unpalatable prey. Under certain conditions the hybrid zones moved, in a direction dependent on the curvature of their interfacial boundaries. However, the mimetic mosaics were highly stable when the intensity of predation was high and the rate of prey dispersal was low. Overall, this model highlights how a stable mosaic of different mimetic forms can evolve from a range of starting conditions through a combination of chance effects and localized frequency-dependent selection.

  18. Experimental Verification of Multiple-input Multiple Output (MIMO) Beamforming Capabilities Using a Time-division Coherent MIMO Radar

    DTIC Science & Technology

    2015-02-01

    output (MIMO) beamforming capabilities using a time-division coherent MIMO radar P. Sévigny P.W. Moo T. Laneve Defence Research and Development Canada...time-division coherent MIMO radar P. Sévigny P.W. Moo T. Laneve Defence Research and Development Canada Scientific Report DRDC-RDDC-2015-R051 April 2015... Moo , P. W.; Laneve, T. 5. DATE OF PUBLICATION (Month and year of publication of document.) April 2015 6a. NO. OF PAGES (Total containing information

  19. Experimental Verification of Multiple-input Multiple Output (MIMO) Beamforming Capabilities Using a Time-division Coherent MIMO Radar

    DTIC Science & Technology

    2015-04-01

    output (MIMO) beamforming capabilities using a time-division coherent MIMO radar P. Sévigny P.W. Moo T. Laneve Defence Research and Development Canada...time-division coherent MIMO radar P. Sévigny P.W. Moo T. Laneve Defence Research and Development Canada Scientific Report DRDC-RDDC-2015-R051 April 2015... Moo , P. W.; Laneve, T. 5. DATE OF PUBLICATION (Month and year of publication of document.) April 2015 6a. NO. OF PAGES (Total containing information

  20. Experimental Verification of Multiple-input Multiple Output (MIMO) Beamforming Capabilities Using a Time-division Coherent MIMO Radar

    DTIC Science & Technology

    2015-03-01

    output (MIMO) beamforming capabilities using a time-division coherent MIMO radar P. Sévigny P.W. Moo T. Laneve Defence Research and Development Canada...time-division coherent MIMO radar P. Sévigny P.W. Moo T. Laneve Defence Research and Development Canada Scientific Report DRDC-RDDC-2015-R051 April 2015... Moo , P. W.; Laneve, T. 5. DATE OF PUBLICATION (Month and year of publication of document.) April 2015 6a. NO. OF PAGES (Total containing information

  1. Space-time processing for MIMO-OFDM using DFT-based complementary sequences

    NASA Astrophysics Data System (ADS)

    Lau, Chad C.; Calderbank, Robert; Zoltowski, Michael D.

    2010-04-01

    In this paper, a new space-time signaling scheme is proposed for Orthogonal Frequency Division Multiplexing (OFDM) using complementary sequences derived from the rows of the DFT matrix. The autocorrelative properties of the complementary sequences allows multiple complex data signals at the transmitter with an arbitrary number of antennas to be perfectly separated and reconstructed at the receiver without prior channel knowledge while achieving full-rate. This new method is proposed and derived for multiple MIMO-OFDM systems with multipath fading; at the receiver, symbol estimation is effected via maximum likelihood estimation (ML).

  2. Achievable degrees of freedom of MIMO two-way relay interference channel with delayed CSIT

    NASA Astrophysics Data System (ADS)

    Li, Qingyun; Wu, Gang; Li, Shaoqian

    2016-10-01

    In this paper, assuming each node has delayed channel state information at the transmitter (CSIT), we investigate the achievable degrees of freedom (DOF) of MIMO two-way relay interference channel in frequency division duplex (FDD) systems, where there are K user pairs (i.e., 2K users) and each user in a user pair exchanges messages with the other user in the same user pair simultaneously via an intermediate relay. We propose a two-stage transmission scheme and derive the closed-form expressions for its achievable DOF.

  3. Comparison of hybrid FDMA/CDMA systems in frequency selective Rayleigh fading

    NASA Astrophysics Data System (ADS)

    Eng, Thomas; Milstein, Laurence B.

    1994-06-01

    A hybrid FDMA/CDMA scheme operating over a frequency selective Rayleigh fading channel is described and analyzed. The performance of the hybrid system is then compared with that of a wideband CDMA system occupying the same total bandwidth. Both coherent and noncoherent modulation formats are investigated; it is found that, for coherent modulation with a RAKE receiver, wideband CDMA has greater capacity than does the hybrid. However, for the noncoherent modulation formats (either DPSK or square-law detected orthogonal signaling), a hybrid system can have a greater capacity if a high channel error rate can be tolerated. Otherwise, a wideband noncoherent system remains optimal.

  4. Fabrication of frequency selective surface for band stop IR-filter

    SciTech Connect

    Mishra, Akshita; Sudheer,; Tiwari, P.; Mondal, P.; Rai, V. N.; Srivastava, A. K.; Bhatt, H.

    2016-05-23

    Fabrication and characterization of frequency selective surfaces (FSS) on silicon dioxide/ silicon is reported. Electron beam lithography based techniques are used for the fabrication of periodic slot structure in tungsten layer on silicon dioxide/silicon. The fabrication process consists of growth of SiO{sub 2} on silicon, tungsten deposition, electron beam lithography, and wet etching of tungsten. The optical characterization of the structural pattern was carried out using fourier transform infrared spectroscopy (FTIR). The reflectance spectra clearly show a resonance peak at 9.09 µm in the mid infrared region. This indicates that the patterned surface acts as band stop filter in the mid-infrared region.

  5. CdTe-based Light-Controllable Frequency-Selective Photonic Crystal Switch for Millimeter Waves

    DTIC Science & Technology

    2011-09-01

    Centimeter- and Millimeter-Wave Devices,” J. Lightwave Technol., Vol. 17, No. 11, pp. 2025-2031 (1999) 7. A. A. Vikharev, G. G. Denisov , Vl. V . Kocharovskii...S. V . Kuzikov, V . V . Parshin, N. Yu . Peskov, A. N. Stepanov, D. I. Sobolev, and M. Yu . Shmelev, “A High-Speed Quasi- Optical Wave Phase Switch...10-1-3086 Final Report CdTe-based Light-Controllable Frequency-Selective Photonic Crystal Switch for Millimeter Waves V . B

  6. Frequency Selective Surfaces as Near Infrared Electro-Magnetic Filters for Thermophotovoltaic Spectral Control

    SciTech Connect

    Ryan T. Kristensen; John F. Beausang; David M. DePoy

    2003-12-01

    Frequency selective surfaces (FSS) effectively filter electromagnetic radiation in the microwave band (1mm to 100mm). Interest exists in extending this technology to the near infrared (1 {micro}m to 10 {micro}m) for use as a filter of thermal radiation in thermophotovoltaic (TPV) direct energy conversion. This paper assesses the ability of FSS to meet the strict spectral performance requirements of a TPV system. Inherent parasitic absorption, which is the result of the induced currents in the FSS metallization, is identified as a significant obstacle to achieving high spectral performance.

  7. Enantiodifferentiation through frequency-selective pure-shift (1)H nuclear magnetic resonance spectroscopy.

    PubMed

    Castañar, Laura; Pérez-Trujillo, Míriam; Nolis, Pau; Monteagudo, Eva; Virgili, Albert; Parella, Teodor

    2014-04-04

    A frequency-selective 1D (1) H nuclear magnetic resonance (NMR) experiment for the fast and sensitive determination of chemical-shift differences between overlapped resonances is proposed. The resulting fully homodecoupled (1) H NMR resonances appear as resolved 1D singlets without their typical J(HH) coupling constant multiplet structures. The high signal dispersion that is achieved is then exploited in enantiodiscrimination studies by using chiral solvating agents. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Fabrication of frequency selective surface for band stop IR-filter

    NASA Astrophysics Data System (ADS)

    Mishra, Akshita; Sudheer, Tiwari, P.; Mondal, P.; Bhatt, H.; Rai, V. N.; Srivastava, A. K.

    2016-05-01

    Fabrication and characterization of frequency selective surfaces (FSS) on silicon dioxide/ silicon is reported. Electron beam lithography based techniques are used for the fabrication of periodic slot structure in tungsten layer on silicon dioxide/silicon. The fabrication process consists of growth of SiO2 on silicon, tungsten deposition, electron beam lithography, and wet etching of tungsten. The optical characterization of the structural pattern was carried out using fourier transform infrared spectroscopy (FTIR). The reflectance spectra clearly show a resonance peak at 9.09 µm in the mid infrared region. This indicates that the patterned surface acts as band stop filter in the mid-infrared region.

  9. Feasibility of Real-Time Selection of Frequency Tables in an Acoustic Simulation of a Cochlear Implant

    PubMed Central

    Fitzgerald, Matthew; Sagi, Elad; Morbiwala, Tasnim A.; Tan, Chin-Tuan; Svirsky, Mario A.

    2013-01-01

    Objectives Perception of spectrally degraded speech is particularly difficult when the signal is also distorted along the frequency axis. This might be particularly important for post-lingually deafened recipients of cochlear implants (CI), who must adapt to a signal where there may be a mismatch between the frequencies of an input signal and the characteristic frequencies of the neurons stimulated by the CI. However, there is a lack of tools that can be used to identify whether an individual has adapted fully to a mismatch in the frequency-to-place relationship and if so, to find a frequency table that ameliorates any negative effects of an unadapted mismatch. The goal of the proposed investigation is to test the feasibility of whether real-time selection of frequency tables can be used to identify cases in which listeners have not fully adapted to a frequency mismatch. The assumption underlying this approach is that listeners who have not adapted to a frequency mismatch will select a frequency table that minimizes any such mismatches, even at the expense of reducing the information provided by this frequency table. Design 34 normal-hearing adults listened to a noise-vocoded acoustic simulation of a cochlear implant and adjusted the frequency table in real time until they obtained a frequency table that sounded “most intelligible” to them. The use of an acoustic simulation was essential to this study because it allowed us to explicitly control the degree of frequency mismatch present in the simulation. None of the listeners had any previous experience with vocoded speech, in order to test the hypothesis that the real-time selection procedure could be used to identify cases in which a listener has not adapted to a frequency mismatch. After obtaining a self-selected table, we measured CNC word-recognition scores with that self-selected table and two other frequency tables: a “frequency-matched” table that matched the analysis filters with the noisebands of

  10. Independent, extensible control of same-frequency superconducting qubits by selective broadcasting

    NASA Astrophysics Data System (ADS)

    Asaad, Serwan; Dickel, Christian; Langford, Nathan K.; Poletto, Stefano; Bruno, Alessandro; Rol, Michiel Adriaan; Deurloo, Duije; Dicarlo, Leonardo

    2016-08-01

    A critical ingredient for realising large-scale quantum information processors will be the ability to make economical use of qubit control hardware. We demonstrate an extensible strategy for reusing control hardware on same-frequency transmon qubits in a circuit QED chip with surface-code-compatible connectivity. A vector switch matrix enables selective broadcasting of input pulses to multiple transmons with individual tailoring of pulse quadratures for each, as required to minimise the effects of leakage on weakly anharmonic qubits. Using randomised benchmarking, we compare multiple broadcasting strategies that each pass the surface-code error threshold for single-qubit gates. In particular, we introduce a selective broadcasting control strategy using five pulse primitives, which allows independent, simultaneous Clifford gates on arbitrary numbers of qubits.

  11. Bards, poets, and cliques: frequency-dependent selection and the evolution of language genes.

    PubMed

    Cartwright, Reed A

    2011-09-01

    The ability of humans to communicate via language is a complex, adapted phenotype, which undoubtedly has a recently evolved genetic component. However, the evolutionary dynamics of language-associated alleles are poorly understood. To improve our knowledge of such systems, a population-genetics model for language-associated genes is developed. (The model is general and applicable to social interactions other than communication.) When an allele arises that potentially improves the ability of individuals to communicate, it will experience positive frequency-dependent selection because its fitness will depend on how many other individuals communicate the same way. Consequently, new and rare alleles are selected against, posing a problem for the evolutionary origin of language. However, the model shows that if individuals form language-based cliques, then novel language-associated alleles can sweep through a population. Thus, the origin of language ability can be sufficiently explained by Darwinian processes operating on genetic diversity in a finite population of human ancestors.

  12. LTE-advanced MIMO uplink for mobile system

    NASA Astrophysics Data System (ADS)

    Alhasson, Bader; Li, Xin; Bloul, Albe M.; Matin, M.

    2010-08-01

    By increasing multimedia communications, mobile communications are expected to reliably support high data rate transmissions. To provide higher peak rate at a better system efficiency, which is necessary to support broadband data services over Wireless links, we need to employ long term evolution Advanced (LTE-A) Multiple-input multiple-output MIMO uplink. The outline of this paper is to investigate and discuss the Long Term Evolution (LTE) for broadband wireless technologies and to discuss its functionality. We explore how LTE uses the inter-technology mobility to support a variety of access technology. This paper investigates the channel capacity and bit error rate of MIMO-OFDM system. In addition, it introduces various MIMO technologies employed in LTE and provide a brief overview on the MIMO technologies currently discussed in the LTE-Advanced forum.

  13. Multipath Propagation for Helicopter-to-Ground MIMO Links

    DTIC Science & Technology

    2011-06-02

    AFFTC-PA-11118 Multipath Propagation for Helicopter-to-Ground MIMO Links Michael Rice, Michael Jensen AIR FORCE FLIGHT TEST CENTER...EDWARDS AFB, CA June 2, 2011 A F F T C m Approved for public release; distribution is unlimited. AIR FORCE FLIGHT TEST CENTER...TITLE AND SUBTITLE Multipath Propagation for Helicopter-to-Ground MIMO Links 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM

  14. Stable Transmission in the Time-Varying MIMO Broadcast Channel

    DTIC Science & Technology

    2008-01-01

    input multiple - output ( MIMO ) wireless channel promises significant gain in performance over that offered by conventional single-antenna systems [1...Jensen, “A low-cost open-hardware wideband multiple - input multiple - output ( MIMO ) wireless channel sounder,” to appear in IEEE Transactions on...the multiple - input single- output (MISO) broadcast channel. A similar study for erroneous CSIT was also performed for the computationally simpler zero

  15. Enhancing Connectivity of Unmanned Vehicles Through MIMO Communications

    DTIC Science & Technology

    2013-09-01

    information at the transmitter . A variable rate MIMO scheme is proposed to overcome these challenges in order to realize the promising throughput gain...lead to rank deficient channel matrices, which are exacerbated due to the absence of channel state information at the transmitter . A variable rate MIMO...pair. This is further exacerbated by the lack of channel state information at the transmitter - RPAs are not only of high mobility but they may maneuver

  16. Design of Massive-MIMO-NOMA With Limited Feedback

    NASA Astrophysics Data System (ADS)

    Ding, Zhiguo; Poor, H. Vincent

    2016-05-01

    In this letter, a low-feedback non-orthogonal multiple access (NOMA) scheme using massive multiple-input multiple-output (MIMO) transmission is proposed. In particular, the proposed scheme can decompose a massive-MIMO-NOMA system into multiple separated single-input single-output NOMA channels, and analytical results are developed to evaluate the performance of the proposed scheme for two scenarios, with perfect user ordering and with one-bit feedback, respectively.

  17. Frequency response of the skin on the head and neck during production of selected speech sounds.

    PubMed

    Munger, Jacob B; Thomson, Scott L

    2008-12-01

    Vibrations within the vocal tract during speech are transmitted through tissue to the skin surface and can be used to transmit speech. Achieving quality speech signals using skin vibration is desirable but problematic, primarily due to the several sound production locations along the vocal tract. The objective of this study was to characterize the frequency content of speech signals on various locations of the head and neck. Signals were recorded using a microphone and accelerometers attached to 15 locations on the heads and necks of 14 males and 10 females. The subjects voiced various phonemes and one phrase. The power spectral densities (PSD) of the phonemes were used to determine a quality ranking for each location and sound. Spectrograms were used to examine signal frequency content for selected locations. A perceptual listening test was conducted and compared to the PSD rankings. The signal-to-noise ratio was found for each location with and without background noise. These results are presented and discussed. Notably, while high-frequency content is attenuated at the throat, it is shown to be detectable at some other locations. The best locations for speech transmission were found to be generally common to males and females.

  18. Sexual selection on male vocal fundamental frequency in humans and other anthropoids.

    PubMed

    Puts, David A; Hill, Alexander K; Bailey, Drew H; Walker, Robert S; Rendall, Drew; Wheatley, John R; Welling, Lisa L M; Dawood, Khytam; Cárdenas, Rodrigo; Burriss, Robert P; Jablonski, Nina G; Shriver, Mark D; Weiss, Daniel; Lameira, Adriano R; Apicella, Coren L; Owren, Michael J; Barelli, Claudia; Glenn, Mary E; Ramos-Fernandez, Gabriel

    2016-04-27

    In many primates, including humans, the vocalizations of males and females differ dramatically, with male vocalizations and vocal anatomy often seeming to exaggerate apparent body size. These traits may be favoured by sexual selection because low-frequency male vocalizations intimidate rivals and/or attract females, but this hypothesis has not been systematically tested across primates, nor is it clear why competitors and potential mates should attend to vocalization frequencies. Here we show across anthropoids that sexual dimorphism in fundamental frequency (F0) increased during evolutionary transitions towards polygyny, and decreased during transitions towards monogamy. Surprisingly, humans exhibit greater F0 sexual dimorphism than any other ape. We also show that low-F0 vocalizations predict perceptions of men's dominance and attractiveness, and predict hormone profiles (low cortisol and high testosterone) related to immune function. These results suggest that low male F0 signals condition to competitors and mates, and evolved in male anthropoids in response to the intensity of mating competition.

  19. [Assessment of frequency of consumption of selected sources of dietary fibre by students].

    PubMed

    Głodek, Elzbieta; Gil, Marian; Rudy, Mariusz; Pawlos, Małgorzata

    2011-01-01

    The study deals with the evaluation of the frequency of food products consumption that are a source of dietary fiber in the diet of students. Survey was conducted in May 2010 among 96 second-year students of 'Food Processing Technology and Human Nutrition' at the University of Rzeszow. The Block's questionnaire was used to assess the frequency of consumption of selected sources of dietary fiber. In order to determine the frequency of consumption of fruits, fruit juices, salads, potatoes, legumes, white bread, dark bread and other cereal products the 5-degree scale with verbal terms (less than once per week--0 points, roughly once a week--1 point, 2-3 times per week - 2 points, 4-6 times per week--3 points, every day--4 points) was used. It was found that none of the examined persons, both women and men, had a sufficient consumption of fiber in the diet. The main source of dietary fiber in the diet of the examined students were white and dark bread and potatoes. A small percentage of the examined persons consume fruits and vegetables in their daily diet.

  20. Cross-frequency power coupling between hierarchically organized face-selective areas.

    PubMed

    Furl, Nicholas; Coppola, Richard; Averbeck, Bruno B; Weinberger, Daniel R

    2014-09-01

    Neural oscillations are linked to perception and behavior and may reflect mechanisms for long-range communication between brain areas. We developed a causal model of oscillatory dynamics in the face perception network using magnetoencephalographic data from 51 normal volunteers. This model predicted induced responses to faces by estimating oscillatory power coupling between source locations corresponding to bilateral occipital and fusiform face areas (OFA and FFA) and the right superior temporal sulcus (STS). These sources showed increased alpha and theta and decreased beta power as well as selective responses to fearful facial expressions. We then used Bayesian model comparison to compare hypothetical models, which were motivated by previous connectivity data and a well-known theory of temporal lobe function. We confirmed this theory in detail by showing that the OFA bifurcated into 2 independent, hierarchical, feedforward pathways, with fearful expressions modulating power coupling only in the more dorsal (STS) pathway. The power coupling parameters showed a common pattern over connections. Low-frequency bands showed same-frequency power coupling, which, in the dorsal pathway, was modulated by fearful faces. Also, theta power showed a cross-frequency suppression of beta power. This combination of linear and nonlinear mechanisms could reflect computational mechanisms in hierarchical feedforward networks.

  1. Integrated terahertz multiparameter sensors using fiber/frequency selective surface couplers

    NASA Astrophysics Data System (ADS)

    Girard, Martin; Skorobogatiy, Maksim

    2014-09-01

    We propose using THz frequency selective surfaces interrogated with THz subwavelength optical fibers as integrated sensors for monitoring of the optical properties of thick optically non-transparent films that are brought into contact with such sensors. Changes in the test film thickness and absorption losses can be measured simultaneously by interpreting variations in the spectral resonant features in the fiber transmission and reflection spectra. In particular, changes in the film thickness induce strong shifts in the fiber transmission peaks, while changes in the film absorption induce notable amplitude variations in the fiber reflection peaks. When applied to the problem of monitoring the thickness and humidity content of paper sheets, the proposed system shows a sensitivity of 1.5 GHz/10 μm to changes in the paper’s thickness and a sensitivity of 0.6/(% of water by volume) to changes in the paper’s humidity. We estimate the detection limit of our device to be 10 μm for the paper thickness variation and 0.02% (of water by volume) for the paper humidity variation. The proposed sensor is implemented in the spirit of integrated optics, where a point device based on the frequency selective surface is interrogated with a THz fiber that is used for remote delivery of THz radiation.

  2. Increased mitochondrial mutation frequency after an island colonization: positive selection or accumulation of slightly deleterious mutations?

    PubMed

    Hardouin, Emilie A; Tautz, Diethard

    2013-04-23

    Island colonizations are excellent models for studying early processes of evolution. We found in a previous study on mice that had colonized the sub-Antarctic Kerguelen Archipelago about 200 years ago that they were derived from a single founder lineage and that this showed an unexpectedly large number of new mutations in the mitochondrial D-loop. To assess whether positive selection has played a role in the emergence of these variants, we have obtained 16 full mitochondrial genome sequences from these mice. For comparison, we have compiled 57 mitochondrial genome sequences from laboratory inbred lines that became established about 100 years ago, also starting from a single founder lineage. We find that the island mice and the laboratory lines show very similar mutation frequencies and patterns. None of the patterns in the Kerguelen mice provides evidence for positive selection. We conclude that nearly neutral evolutionary processes that assume the presence of slightly deleterious variants can fully explain the patterns. This supports the notion of time-dependency of molecular evolution and provides a new calibration point. Based on the observed mutation frequency, we calculate an average evolutionary rate of 0.23 substitutions per site per Myr for the earliest time frame of divergence, which is about six times higher than the long-term rate of 0.037 substitutions per site per Myr.

  3. Video error concealment using block matching and frequency selective extrapolation algorithms

    NASA Astrophysics Data System (ADS)

    P. K., Rajani; Khaparde, Arti

    2017-06-01

    Error Concealment (EC) is a technique at the decoder side to hide the transmission errors. It is done by analyzing the spatial or temporal information from available video frames. It is very important to recover distorted video because they are used for various applications such as video-telephone, video-conference, TV, DVD, internet video streaming, video games etc .Retransmission-based and resilient-based methods, are also used for error removal. But these methods add delay and redundant data. So error concealment is the best option for error hiding. In this paper, the error concealment methods such as Block Matching error concealment algorithm is compared with Frequency Selective Extrapolation algorithm. Both the works are based on concealment of manually error video frames as input. The parameter used for objective quality measurement was PSNR (Peak Signal to Noise Ratio) and SSIM(Structural Similarity Index). The original video frames along with error video frames are compared with both the Error concealment algorithms. According to simulation results, Frequency Selective Extrapolation is showing better quality measures such as 48% improved PSNR and 94% increased SSIM than Block Matching Algorithm.

  4. Error Probability of MRC in Frequency Selective Nakagami Fading in the Presence of CCI and ACI

    NASA Astrophysics Data System (ADS)

    Rahman, Mohammad Azizur; Sum, Chin-Sean; Funada, Ryuhei; Sasaki, Shigenobu; Baykas, Tuncer; Wang, Junyi; Harada, Hiroshi; Kato, Shuzo

    An exact expression of error rate is developed for maximal ratio combining (MRC) in an independent but not necessarily identically distributed frequency selective Nakagami fading channel taking into account inter-symbol, co-channel and adjacent channel interferences (ISI, CCI and ACI respectively). The characteristic function (CF) method is adopted. While accurate analysis of MRC performance cannot be seen in frequency selective channel taking ISI (and CCI) into account, such analysis for ACI has not been addressed yet. The general analysis presented in this paper solves a problem of past and present interest, which has so far been studied either approximately or in simulations. The exact method presented also lets us obtain an approximate error rate expression based on Gaussian approximation (GA) of the interferences. It is shown, especially while the channel is lightly faded, has fewer multipath components and a decaying delay profile, the GA may be substantially inaccurate at high signal-to-noise ratio. However, the exact results also reveal an important finding that there is a range of parameters where the simpler GA is reasonably accurate and hence, we don't have to go for more involved exact expression.

  5. Switches of stimulus tagging frequencies interact with the conflict-driven control of selective attention, but not with inhibitory control.

    PubMed

    Scherbaum, Stefan; Frisch, Simon; Dshemuchadse, Maja

    2016-01-01

    Selective attention and its adaptation by cognitive control processes are considered a core aspect of goal-directed action. Often, selective attention is studied behaviorally with conflict tasks, but an emerging neuroscientific method for the study of selective attention is EEG frequency tagging. It applies different flicker frequencies to the stimuli of interest eliciting steady state visual evoked potentials (SSVEPs) in the EEG. These oscillating SSVEPs in the EEG allow tracing the allocation of selective attention to each tagged stimulus continuously over time. The present behavioral investigation points to an important caveat of using tagging frequencies: The flicker of stimuli not only produces a useful neuroscientific marker of selective attention, but interacts with the adaptation of selective attention itself. Our results indicate that RT patterns of adaptation after response conflict (so-called conflict adaptation) are reversed when flicker frequencies switch at once. However, this effect of frequency switches is specific to the adaptation by conflict-driven control processes, since we find no effects of frequency switches on inhibitory control processes after no-go trials. We discuss the theoretical implications of this finding and propose precautions that should be taken into account when studying conflict adaptation using frequency tagging in order to control for the described confounds. Copyright © 2015 Elsevier B.V. All rights reserved.

  6. High Frequency Cluster Radio Galaxies: Luminosity Functions and Implications for SZE Selected Cluster Samples

    NASA Astrophysics Data System (ADS)

    Gupta, N.; Saro, A.; Mohr, J. J.; Benson, B. A.; Bocquet, S.; Capasso, R.; Carlstrom, J. E.; Chiu, I.; Crawford, T. M.; de Haan, T.; Dietrich, J. P.; Gangkofner, C.; Holzapfel, W. L.; McDonald, M.; Rapetti, D.; Reichardt, C. L.

    2017-01-01

    We study the overdensity of point sources in the direction of X-ray-selected galaxy clusters from the Meta-Catalog of X-ray detected Clusters of galaxies (MCXC; = 0.14) at South Pole Telescope (SPT) and Sydney University Molonglo Sky Survey (SUMSS) frequencies. Flux densities at 95, 150 and 220 GHz are extracted from the 2500 deg2 SPT-SZ survey maps at the locations of SUMSS sources, producing a multi-frequency catalog of radio galaxies. In the direction of massive galaxy clusters, the radio galaxy flux densities at 95 and 150 GHz are biased low by the cluster Sunyaev-Zel'dovich Effect (SZE) signal, which is negative at these frequencies. We employ a cluster SZE model to remove the expected flux bias and then study these corrected source catalogs. We find that the high frequency radio galaxies are centrally concentrated within the clusters and that their luminosity functions (LFs) exhibit amplitudes that are characteristically an order of magnitude lower than the cluster LF at 843 MHz. We use the 150 GHz LF to estimate the impact of cluster radio galaxies on an SPT-SZ like survey. The radio galaxy flux typically produces a small bias on the SZE signal and has negligible impact on the observed scatter in the SZE mass-observable relation. If we assume there is no redshift evolution in the radio galaxy LF then 1.8 ± 0.7 percent of the clusters with detection significance ξ ≥ 4.5 would be lost from the sample. Allowing for redshift evolution of the form (1 + z)2.5 increases the incompleteness to 5.6 ± 1.0 percent. Improved constraints on the evolution of the cluster radio galaxy LF require a larger cluster sample extending to higher redshift.

  7. Effects of unsaturated fatty acids on torpor frequency and diet selection in Djungarian hamsters (Phodopus sungorus).

    PubMed

    Diedrich, Victoria; Steinlechner, Stephan; Scherbarth, Frank

    2014-12-15

    Essential polyunsaturated fatty acids (PUFA) have been shown to play a beneficial role in hibernating mammals. High amounts of dietary PUFA led to an earlier hibernation onset, deeper and longer hibernation bouts and a higher proportion of hibernating animals in several species. In contrast, the relevance of dietary PUFA for daily heterotherms exhibiting only brief and shallow torpor bouts is less well studied. Therefore, diets differing in PUFA composition were used to examine the effects on the frequency of spontaneous daily torpor in Djungarian hamsters (Phodopus sungorus). In contrast to earlier studies, we were interested in whether the ratio of n-6 to n-3 PUFA affects torpor expression, and in comparison with a diet rich in monounsaturated fatty acids (MUFA). Although we found a positive effect on torpor frequency in hamsters fed a diet rich in n-6 PUFA compared with the groups fed diets either rich in n-3 PUFA or MUFA, the latter two groups did not show unusually low torpor frequencies. The results of the additional diet choice experiment indicated that hamsters in short photoperiod select food with only a slight excess of n-6 PUFA compared with n-3 PUFA (ratio of 1 to 1.5). However, there was no significant difference in torpor frequency between the diet choice group and hamsters fed on standard chow with a sevenfold excess of n-6 PUFA. In summary, the present data strongly indicate that the dietary composition of unsaturated fatty acids plays a minor role in the occurrence of spontaneous daily torpor in Djungarian hamsters. © 2014. Published by The Company of Biologists Ltd.

  8. Multi-band reflector antenna with double-ring element frequency selective subreflector

    NASA Technical Reports Server (NTRS)

    Wu, Te-Kao; Lee, S. W.

    1993-01-01

    Frequency selective subreflectors (FSS) are often employed in the reflector antenna system of a communication satellite or a deep space exploration vehicle for multi-frequency operations. In the past, FSS's have been designed for diplexing two frequency bands. For example, the Voyager FSS was designed to diplex S and X bands and the TDRSS FSS was designed to diplex S and Ku bands. Recently, NASA's CASSINI project requires an FSS to multiplex four frequency (S/X/Ku/Ka) bands. Theoretical analysis and experimental verifications are presented for a multi-band flat pannel FSS with double-ring elements. Both the exact formulation and the thin-ring approximation are described for analyzing and designing this multi-ring patch element FSS. It is found that the thin-ring approximation fails to predict the electrically wide ring element FSS's performance. A single screen double-ring element FSS is demonstrated for the tri-band system that reflects the X-band signal while transmitting through the S- and Ku-band signals. In addition, a double screen FSS with non-similar double-ring elements is presented for the Cassini's four-band system which reflects the X- and Ka-band signals while passing the S- and Ku-band signals. To accurately predict the FSS effects on a dual reflector antenna's radiation pattern, the FSS subreflector's transmitted/reflected field variation as functions of the polarization and incident angles with respect to the local coordinates was taken into account. An FSS transmission/reflection coefficient table is computed for TE and TM polarizations at various incident angles based on the planar FSS model. Next, the hybrid Geometric Optics (GO) and Physical Optics (PO) technique is implemented with linearly interpolating the FSS table to efficiently determine the FSS effects in a dual reflector antenna.

  9. Retail Deli Slicer Cleaning Frequency--Six Selected Sites, United States, 2012.

    PubMed

    Brown, Laura G; Hoover, E Rickamer; Ripley, Danny; Matis, Bailey; Nicholas, David; Hedeen, Nicole; Faw, Brenda

    2016-04-01

    Listeria monocytogenes (Listeria) causes the third highest number of foodborne illness deaths (an estimated 255) in the United States annually, after nontyphoidal Salmonella species and Toxoplasma gondii (1). Deli meats are a major source of listeriosis illnesses, and meats sliced and packaged at retail delis are the major source of listeriosis illnesses attributed to deli meat (4). Mechanical slicers pose cross-contamination risks in delis and are an important source of Listeria cross-contamination. Reducing Listeria contamination of sliced meats in delis will likely reduce Listeria illnesses and outbreaks. Good slicer cleaning practices can reduce this foodborne illness risk. CDC's Environmental Health Specialists Network (EHS-Net) studied how often retail deli slicers were fully cleaned (disassembled, cleaned, and sanitized) at the Food and Drug Administration (FDA) Food Code-specified minimum frequency of every 4 hours and examined deli and staff characteristics related to slicer cleaning frequency. Interviews with staff members in 298 randomly-selected delis in six EHS-Net sites showed that approximately half of delis fully cleaned their slicers less often than FDA's specified minimum frequency. Chain-owned delis and delis with more customers, more slicers, required manager food safety training, food safety-knowledgeable workers, written slicer-cleaning policies, and food safety-certified managers fully cleaned their slicers more frequently than did other types of delis, according to deli managers or workers. States and localities should require deli manager training and certification, as specified in the FDA Food Code. They should also consider encouraging or requiring delis to have written slicer-cleaning policies. Retail food industry leaders can also implement these prevention efforts to reduce risk in their establishments. Because independent and smaller delis had lower frequencies of slicer cleaning, prevention efforts should focus on these types of

  10. MIMO-OFDM equaliser for spatial multiplexing transmission modes

    NASA Astrophysics Data System (ADS)

    Beinschob, P.; Zölzer, U.

    2010-10-01

    In search for faster and more reliable communication, multiple-input multiple-output (MIMO) in conjuction with Orthogonal Frequency Division Multiplexing (OFDM) are subject of extensive research. In spatial multiplexing transmission an instantaneous rise of data rates governed by the number of transmit antennas can be realised. The system performance depends highly on signal-to-interference-plus-noise ratios (SINR) at the receiver. The receiver's equaliser is supposed to maximize the SINR by mitigating the spatial interference and thus separating the transmitted signals. For this problem several solutions exist such as linear and nonlinear, per subcarrier or OFDM symbol-based. An overview of common algorithms is given and complexity is discussed. Bit error rate (BER) performance evaluations are presented. Another aspect is the impact of the equalisation strategy on the performance of bit-interleaved soft information-based channel coding schemes. As a representative, LDPC codes are chosen. Simulation results show a significant BER performance loss for symbol decision-based equalisers compared to the uncoded performance. To overcome this problem a modification of the Maximum Likelihood algorithm is proposed which yields good performance for low SNR applications.

  11. Multi-static MIMO along track interferometry (ATI)

    NASA Astrophysics Data System (ADS)

    Knight, Chad; Deming, Ross; Gunther, Jake

    2016-05-01

    Along-track interferometry (ATI) has the ability to generate high-quality synthetic aperture radar (SAR) images and concurrently detect and estimate the positions of ground moving target indicators (GMTI) with moderate processing requirements. This paper focuses on several different ATI system configurations, with an emphasis on low-cost configurations employing no active electronic scanned array (AESA). The objective system has two transmit phase centers and four receive phase centers and supports agile adaptive radar behavior. The advantages of multistatic, multiple input multiple output (MIMO) ATI system configurations are explored. The two transmit phase centers can employ a ping-pong configuration to provide the multistatic behavior. For example, they can toggle between an up and down linear frequency modulated (LFM) waveform every other pulse. The four receive apertures are considered in simple linear spatial configurations. Simulated examples are examined to understand the trade space and verify the expected results. Finally, actual results are collected with the Space Dynamics Laboratorys (SDL) FlexSAR system in diverse configurations. The theory, as well as the simulated and actual SAR results, are presented and discussed.

  12. Performance of MIMO E-SDM Systems Using Channel Prediction in Actual Time-Varying Indoor Fading Environments

    NASA Astrophysics Data System (ADS)

    Bui, Huu Phu; Nishimoto, Hiroshi; Nishimura, Toshihiko; Ohgane, Takeo; Ogawa, Yasutaka

    In time-varying fading environments, the performance of multiple-input multiple-output (MIMO) systems applying an eigenbeam-space division multiplexing (E-SDM) technique may be degraded due to a channel change during the time interval between the transmit weight matrix determination and the actual data transmission. To compensate for the channel change, we have proposed some channel prediction methods. Simulation results based on computer-generated channel data showed that better performance can be obtained when using the prediction methods in Rayleigh fading environments assuming the Jakes model with rich scatterers. However, actual MIMO systems may be used in line-of-sight (LOS) environments, and even in a non-LOS case, scatterers may not be uniformly distributed around a receiver and/or a transmitter. In addition, mutual coupling between antennas at both the transmitter and the receiver cannot be ignored as it affects the system performance in actual implementation. We conducted MIMO channel measurement campaigns at a 5.2GHz frequency band to evaluate the channel prediction techniques. In this paper, we present the experiment and simulation results using the measured channel data. The results show that robust bit-error rate performance is obtained when using the channel prediction methods and that the methods can be used in both Rayleigh and Rician fading environments, and do not need to know the maximum Doppler frequency.

  13. Mode-Selective Photon Counting Via Quantum Frequency Conversion Using Spectrally-Engineered Pump Pulses

    NASA Astrophysics Data System (ADS)

    Manurkar, Paritosh

    Most of the existing protocols for quantum communication operate in a two-dimensional Hilbert space where their manipulation and measurement have been routinely investigated. Moving to higher-dimensional Hilbert spaces is desirable because of advantages in terms of longer distance communication capabilities, higher channel capacity and better information security. We can exploit the spatio-temporal degrees of freedom for the quantum optical signals to provide the higher-dimensional signals. But this necessitates the need for measurement and manipulation of multidimensional quantum states. To that end, there have been significant theoretical studies based on quantum frequency conversion (QFC) in recent years even though the experimental progress has been limited. QFC is a process that allows preservation of the quantum information while changing the frequency of the input quantum state. It has deservedly garnered a lot of attention because it serves as the connecting bridge between the communications band (C-band near 1550 nm) where the fiber-optic infrastructure is already established and the visible spectrum where high efficiency single-photon detectors and optical memories have been demonstrated. In this experimental work, we demonstrate mode-selective frequency conversion as a means to measure and manipulate photonic signals occupying d -dimensional Hilbert spaces where d=2 and 4. In the d=2 case, we demonstrate mode contrast between two temporal modes (TMs) which serves as the proof-of-concept demonstration. In the d=4 version, we employ six different TMs for our detailed experimental study. These TMs also include superposition modes which are a crucial component in many quantum key distribution protocols. Our method is based on producing pump pulses which allow us to upconvert the TM of interest while ideally preserving the other modes. We use MATLAB simulations to determine the pump pulse shapes which are subsequently produced by controlling the amplitude and

  14. Optimal frequency selection of multi-channel O2-band different absorption barometric radar for air pressure measurements

    NASA Astrophysics Data System (ADS)

    Lin, Bing; Min, Qilong

    2017-02-01

    Through theoretical analysis, optimal selection of frequencies for O2 differential absorption radar systems on air pressure field measurements is achieved. The required differential absorption optical depth between a radar frequency pair is 0.5. With this required value and other considerations on water vapor absorption and the contamination of radio wave transmission, frequency pairs of present considered radar system are obtained. Significant impacts on general design of differential absorption remote sensing systems are expected from current results.

  15. Performance of the IEEE 802.11a Wireless Lan Standard Over Frequency-Selective, Slow, Ricean Fading Channels

    DTIC Science & Technology

    2002-09-01

    modeled as a random variable. Typical models are the Rayleigh , Ricean, and Nakagami - m distributions. In this thesis, two widely used models for...and [2], frequency-selective, Rayleigh fading channels [3], and frequency-selective, slow, Nakagami channels [4]. Unlike the above referenced work...signal component where i qM M M = × ; therefore, the probability of symbol error for rectangular QAM can be expressed as ( )error on error on . i q i

  16. Polymorphism at a mimicry supergene maintained by opposing frequency-dependent selection pressures.

    PubMed

    Chouteau, Mathieu; Llaurens, Violaine; Piron-Prunier, Florence; Joron, Mathieu

    2017-08-01

    Explaining the maintenance of adaptive diversity within populations is a long-standing goal in evolutionary biology, with important implications for conservation, medicine, and agriculture. Adaptation often leads to the fixation of beneficial alleles, and therefore it erodes local diversity so that understanding the coexistence of multiple adaptive phenotypes requires deciphering the ecological mechanisms that determine their respective benefits. Here, we show how antagonistic frequency-dependent selection (FDS), generated by natural and sexual selection acting on the same trait, maintains mimicry polymorphism in the toxic butterfly Heliconius numata Positive FDS imposed by predators on mimetic signals favors the fixation of the most abundant and best-protected wing-pattern morph, thereby limiting polymorphism. However, by using mate-choice experiments, we reveal disassortative mate preferences of the different wing-pattern morphs. The resulting negative FDS on wing-pattern alleles is consistent with the excess of heterozygote genotypes at the supergene locus controlling wing-pattern variation in natural populations of H. numata The combined effect of positive and negative FDS on visual signals is sufficient to maintain a diversity of morphs displaying accurate mimicry with other local prey, although some of the forms only provide moderate protection against predators. Our findings help understand how alternative adaptive phenotypes can be maintained within populations and emphasize the need to investigate interactions between selective pressures in other cases of puzzling adaptive polymorphism.

  17. Consequences of selection for improving production traits on the frequency of deleterious alleles for fitness.

    PubMed

    Kearney, J F; Navarro, P; Haley, C S; Villanueva, B

    2009-03-01

    In this study the effect of artificial selection on BLUP EBV for production traits on the allele frequencies of a pleiotropic QTL affecting both production and disease susceptibility was investigated. Stochastic simulations were used to model artificial selection on a production trait that is controlled, in part, by a biallelic QTL that also controls susceptibility to disease. The QTL allele increasing production also increased susceptibility to disease. Different modes of action and proportions of variation accounted for by the QTL were assessed for the production trait. The main results indicated that alleles that confer susceptibility to the disease could be maintained in the population over a long period, depending on the mode of action of the QTL. In addition, the results of the study indicate that, under various conditions, it is possible to find pleiotropic QTL that control 2 traits despite these traits appearing to be uncorrelated. Therefore, in practice, an estimate of the genetic correlation between 2 traits may be misleading when the presence of such a QTL exists. The results of this study have implications for breeding programs. For example, if a pleiotropic QTL exists that favors heterozygotes for a production trait, it would be very difficult to remove disease susceptibility alleles via traditional selection methods.

  18. On the Implementation of Iterative Detection in Real-World MIMO Wireless Systems

    DTIC Science & Technology

    2003-12-01

    multiple - input multiple - output ( MIMO ) wireless systems can achieve...addresses the use of iterative detection in real-world multiple - input multiple - output ( MIMO ) wireless systems, which are theoretically capable of achieving...search LLR log-likelihood ratio MAP maximum a posteriori MIMO multiple - input multiple - output ML maximum likelihood MLM-ITS multilevel mapping ITS

  19. Signal Waveforms and Range/Angle Coupling in Coherent Colocated MIMO Radar

    DTIC Science & Technology

    2014-10-09

    Signal Waveforms and Range/Angle Coupling in Coherent Colocated MIMO Radar Olivier Rabaste, Laurent Savy, Mathieu Cattenoz ONERA , The French...tests with a real MIMO radar: HYCAM. A. The HYCAM platform A multifunction MIMO radar - named HYCAM - has been designed and build by ONERA . The

  20. Modeling, Simulation and Performance Analysis of Multiple-Input Multiple-Output (MIMO) Systems with Multicarrier Time Delay Diversity Modulation

    DTIC Science & Technology

    2005-09-01

    MULTIPLE - INPUT MULTIPLE - OUTPUT ( MIMO ) SYSTEMS WITH MULTICARRIER TIME DELAY DIVERSITY MODULATION by Muhammad...SUBTITLE: Modeling, Simulation and Performance Analysis of Multiple - Input Multiple - Output ( MIMO ) Systems with Multicarrier Time Delay Diversity Modulation...MISO) and multiple - input multiple - output ( MIMO ) radio communication systems with space-time codes. A MISO system and MIMO

  1. Joint Antenna Selection for Achieving Diversity in a Two-Way Relaying Channel

    NASA Astrophysics Data System (ADS)

    Xu, Kun; Gao, Yuanyuan; Yi, Xiaoxin; Yang, Weiwei

    Joint transmit and receive antenna selection (JTRAS) is proposed for the multiple-input multiple-output (MIMO) two-way relaying channel. A simple and closed-form lower bound on the outage probability of JTRAS is derived. Furthermore, asymptotic analysis reveals that JTRAS can attain the maximum achievable diversity order of the MIMO dual-hop relaying channel.

  2. High-speed photodamage cell selection using a frequency-doubled argon ion laser.

    PubMed

    Keij, J F; Groenewegen, A C; Dubelaar, G B; Visser, J W

    1995-03-01

    A flow cytometer was developed for the high-speed "sorting" of desired cells by selectively irradiating (zapping) the undesired cells from a population. After previous efforts to photoinactivate cells with photosensitizers had failed, it was decided to exploit the photosensitivity of the cell's DNA at 257 nm. It was shown that a 257 nm laser output power of 20-100 mW was sufficient to induce a 4.5 log cell kill after the cells were processed through a focused 257 nm laser beam. Experiments proved that the photodamage flow cytometer (ZAPPER) could selectively photoinactivate cells at rates over 22,000 events/s, and selection purities ranged from 81% to 100%. The yields of the desired cells depended on the selection mode. In the Enrichment mode, the zap laser was not aimed at the jet, and only undesired cells were exposed to a brief ultraviolet (UV) pulse after modulation of the UV laser beam. The yields of desired cells ranged from 95% to 105%. In the Purge mode, the zap laser beam was aimed onto the jet, and only desired cells were allowed to pass after deflection of the UV laser beam; the yields of desired cells ranged from 12% to 52%. The cause of the reduced yields in the PURGE mode was traced to the fact that the Electro-Optic Modulator was used to modulate the zap laser proved too slow for the intended application. The lifetime of the frequency-doubling crystal used for the generation of the 257 nm beam was found to be limited to several days.(ABSTRACT TRUNCATED AT 250 WORDS)

  3. A novel tunable frequency selective surface absorber with dual-DOF for broadband applications.

    PubMed

    Kong, Peng; Yu, XiaoWei; Liu, ZhengYang; Zhou, Kai; He, Yun; Miao, Ling; Jiang, JianJun

    2014-12-01

    A novel tunable frequency selective surface (FSS) with dual-degrees of freedom (DOF) is presented, and firstly applied to broadband absorber. Based on a simple prototype unit cell resonator, an approach for achieving multi-resonances is studied. A unit cell pattern with gradient edges is discussed, and variable resistor and variable capacitor are introduced to fully utilize its characteristic of multi-resonances. Bias line is designed to provide bias voltage respectively for two variable devices and provide two operational DOF for FSS. Simulation and measurement results both show that the tunable FSS absorber with dual-DOF has wideband absorption with the reflectivity below -10 dB in 1-5 GHz and with a total thickness of about 10 mm.

  4. One Dimensional Capacitive Loading in a Frequency Selective Surface for Low Profile Antenna Applications

    NASA Technical Reports Server (NTRS)

    Cure, David; Weller, Thomas; Miranda, Felix A.; Herzig, Paul

    2011-01-01

    In this paper, the impact of adding discrete capacitive loading along one dimension of a frequency selective surface for low profile antenna applications is presented for the first time. The measured data demonstrates comparable performance between a non-loaded and a capacitively-loaded FSS with a significant reduction in the number of cells and/or cell geometry size. Additionally, the provision of discrete capacitive loads reduces the FSS susceptibility to fabrication tolerances based on placement of a fixed grid capacitance. The bandwidth increased from 1.8% to 7.3% for a total antenna thickness of approx. lambda/22, and from 1.5% to 9.2% for a thickness of approx. lambda/40. The total antenna area for each case was reduced by 55% and 12%, respectively.

  5. Sibling genes as environment: Sibling dopamine genotypes and adolescent health support frequency dependent selection.

    PubMed

    Rauscher, Emily; Conley, Dalton; Siegal, Mark L

    2015-11-01

    While research consistently suggests siblings matter for individual outcomes, it remains unclear why. At the same time, studies of genetic effects on health typically correlate variants of a gene with the average level of behavioral or health measures, ignoring more complicated genetic dynamics. Using National Longitudinal Study of Adolescent Health data, we investigate whether sibling genes moderate individual genetic expression. We compare twin variation in health-related absences and self-rated health by genetic differences at three locations related to dopamine regulation and transport to test sibship-level cross-person gene-gene interactions. Results suggest effects of variation at these genetic locations are moderated by sibling genes. Although the mechanism remains unclear, this evidence is consistent with frequency dependent selection and suggests much genetic research may violate the stable unit treatment value assumption.

  6. Appropriate microwave frequency selection for biasing superconducting hot electron bolometers as terahertz direct detectors

    NASA Astrophysics Data System (ADS)

    Jiang, S. L.; Li, X. F.; Jia, X. Q.; Kang, L.; Jin, B. B.; Xu, W. W.; Chen, J.; Wu, P. H.

    2017-04-01

    Terahertz (THz) direct detectors based on superconducting niobium nitride (NbN) hot electron bolometers (HEBs) and biased by a simple microwave (MW) source have been studied. The frequency and power of the MW are selected by measuring the MW responses of the current–voltage (I–V) curves and resistance–temperature (R–T) curves of the NbN HEBs. The non-uniform absorption theory is used to explain the current jumps in the I–V curves and the resistance jumps in the R–T curves. Compared to the thermal biasing, the MW biasing method can improve the sensitivity, make the readout system much easier and consumes less liquid helium, which is important for long lasting experiments. The noise equivalent power (NEP) of 1.6 pW Hz‑1/2 and the response time of 86 ps are obtained for the detectors working at 4.2 K and 0.65 THz.

  7. A Comparison Between Jerusalem Cross and Square Patch Frequency Selective Surfaces for Low Profile Antenna Applications

    NASA Technical Reports Server (NTRS)

    Cure, David; Weller, Thomas; Miranda, Felix A.

    2011-01-01

    In this paper, a comparison between Jerusalem Cross (JC) and Square Patch (SP) based Frequency Selected Surfaces (FSS) for low profile antenna applications is presented. The comparison is aimed at understanding the performance of low profile antennas backed by high impedance surfaces. In particular, an end loaded planar open sleeve dipole (ELPOSD) antenna is examined due to the various parameters within its configuration, offering significant design flexibility and a wide operating bandwidth. Measured data of the antennas demonstrate that increasing the number of unit cells improves the fractional bandwidth. The antenna bandwidth increased from 0.8% to 1.8% and from 0.8% to 2.7% for the JC and SP structures, respectively. The number of unit cells was increased from 48 to 80 for the JC-FSS and from 24 to 48 for the SP-FSS.

  8. Near- and far-field measurements of phase-ramped frequency selective surfaces at infrared wavelengths

    SciTech Connect

    Tucker, Eric; Boreman, Glenn; D'Archangel, Jeffrey; Raschke, Markus B.

    2014-07-28

    Near- and far-field measurements of phase-ramped loop and patch structures are presented and compared to simulations. The far-field deflection measurements show that the phase-ramped structures can deflect a beam away from specular reflection, consistent with simulations. Scattering scanning near-field optical microscopy of the elements comprising the phase ramped structures reveals part of the underlying near-field phase contribution that dictates the far-field deflection, which correlates with the far-field phase behavior that was expected. These measurements provide insight into the resonances, coupling, and spatial phase variation among phase-ramped frequency selective surface (FSS) elements, which are important for the performance of FSS reflectarrays.

  9. Multilevel Concatenated Block Modulation Codes for the Frequency Non-selective Rayleigh Fading Channel

    NASA Technical Reports Server (NTRS)

    Lin, Shu; Rhee, Dojun

    1996-01-01

    This paper is concerned with construction of multilevel concatenated block modulation codes using a multi-level concatenation scheme for the frequency non-selective Rayleigh fading channel. In the construction of multilevel concatenated modulation code, block modulation codes are used as the inner codes. Various types of codes (block or convolutional, binary or nonbinary) are being considered as the outer codes. In particular, we focus on the special case for which Reed-Solomon (RS) codes are used as the outer codes. For this special case, a systematic algebraic technique for constructing q-level concatenated block modulation codes is proposed. Codes have been constructed for certain specific values of q and compared with the single-level concatenated block modulation codes using the same inner codes. A multilevel closest coset decoding scheme for these codes is proposed.

  10. Terahertz Bandpass Frequency Selective Surfaces on Glass Substrates Using a Wet Micromachining Process

    NASA Astrophysics Data System (ADS)

    Ramzan, Mehrab; Khan, Talha Masood; Bolat, Sami; Nebioglu, Mehmet Ali; Altan, Hakan; Okyay, Ali Kemal; Topalli, Kagan

    2017-08-01

    This paper presents terahertz (THz) frequency selective surfaces (FSS) implemented on glass substrate using standard microfabrication techniques. These FSS structures are designed for frequencies around 0.8 THz. A fabrication process is proposed where a 100-μm-thick glass substrate is formed through the HF etching of a standard 500-μm-thick low cost glass wafer. Using this fabrication process, three separate robust designs consisting of single-layer FSS are investigated using high-frequency structural simulator (HFSS). Based on the simulation results, the first design consists of a circular ring slot in a square metallic structure on top of a 100-μm-thick Pyrex glass substrate with 70% transmission bandwidth of approximately 0.07 THz, which remains nearly constant till 30° angle of incidence. The second design consists of a tripole structure on top of a 100-μm-thick Pyrex glass substrate with 65% transmission bandwidth of 0.035 THz, which remains nearly constant till 30° angle of incidence. The third structure consists of a triangular ring slot in a square metal on top of a 100-μm-thick Pyrex glass substrate with 70% transmission bandwidth of 0.051 THz, which remains nearly constant up to 20° angle of incidence. These designs show that the reflections from samples can be reduced compared to the conventional sample holders used in THz spectroscopy applications, by using single layer FSS structures manufactured through a relatively simple fabrication process. Practically, these structures are achieved on a fabricated 285-μm-thick glass substrate. Taking into account the losses and discrepancies in the substrate thickness, the measured results are in good agreement with the electromagnetic simulations.

  11. High–frequency cluster radio galaxies: Luminosity functions and implications for SZE–selected cluster samples

    DOE PAGES

    Gupta, Nikhel; Saro, A.; Mohr, J. J.; ...

    2017-01-15

    We study the overdensity of point sources in the direction of X-ray-selected galaxy clusters from the meta-catalogue of X-ray-detected clusters of galaxies (MCXC; < z > = 0.14) at South Pole Telescope (SPT) and Sydney University Molonglo Sky Survey (SUMSS) frequencies. Flux densities at 95, 150 and 220 GHz are extracted from the 2500 deg2 SPT-SZ survey maps at the locations of SUMSS sources, producing a multifrequency catalogue of radio galaxies. In the direction of massive galaxy clusters, the radio galaxy flux densities at 95 and 150 GHz are biased low by the cluster Sunyaev–Zel’dovich Effect (SZE) signal, which ismore » negative at these frequencies. We employ a cluster SZE model to remove the expected flux bias and then study these corrected source catalogues. We find that the high-frequency radio galaxies are centrally concentrated within the clusters and that their luminosity functions (LFs) exhibit amplitudes that are characteristically an order of magnitude lower than the cluster LF at 843 MHz. We use the 150 GHz LF to estimate the impact of cluster radio galaxies on an SPT-SZ like survey. The radio galaxy flux typically produces a small bias on the SZE signal and has negligible impact on the observed scatter in the SZE mass–observable relation. If we assume there is no redshift evolution in the radio galaxy LF then 1.8 ± 0.7 per cent of the clusters with detection significance ξ ≥ 4.5 would be lost from the sample. As a result, allowing for redshift evolution of the form (1 + z)2.5 increases the incompleteness to 5.6 ± 1.0 per cent. Improved constraints on the evolution of the cluster radio galaxy LF require a larger cluster sample extending to higher redshift.« less

  12. Low intensity and frequency pulsed electromagnetic fields selectively impair breast cancer cell viability.

    PubMed

    Crocetti, Sara; Beyer, Christian; Schade, Grit; Egli, Marcel; Fröhlich, Jürg; Franco-Obregón, Alfredo

    2013-01-01

    A common drawback of many anticancer therapies is non-specificity in action of killing. We investigated the potential of ultra-low intensity and frequency pulsed electromagnetic fields (PEMFs) to kill breast cancer cells. Our criteria to accept this technology as a potentially valid therapeutic approach were: 1) cytotoxicity to breast cancer cells and; 2) that the designed fields proved innocuous to healthy cell classes that would be exposed to the PEMFs during clinical treatment. MCF7 breast cancer cells and their normal counterparts, MCF10 cells, were exposed to PEMFs and cytotoxic indices measured in order to design PEMF paradigms that best kill breast cancer cells. The PEMF parameters tested were: 1) frequencies ranging from 20 to 50 Hz; 2) intensities ranging from 2 mT to 5 mT and; 3) exposure durations ranging from 30 to 90 minutes per day for up to three days to determine the optimum parameters for selective cancer cell killing. We observed a discrete window of vulnerability of MCF7 cells to PEMFs of 20 Hz frequency, 3 mT magnitude and exposure duration of 60 minutes per day. The cell damage accrued in response to PEMFs increased with time and gained significance after three days of consecutive daily exposure. By contrast, the PEMFs parameters determined to be most cytotoxic to breast cancer MCF-7 cells were not damaging to normal MCF-10 cells. Based on our data it appears that PEMF-based anticancer strategies may represent a new therapeutic approach to treat breast cancer without affecting normal tissues in a manner that is non-invasive and can be potentially combined with existing anti-cancer treatments.

  13. Selected low-flow frequency statistics for continuous-record streamgage locations in Maryland, 2010

    USGS Publications Warehouse

    Doheny, Edward J.; Banks, William S.L.

    2010-01-01

    According to a 2008 report by the Governor's Advisory Committee on the Management and Protection of the State's Water Resources, Maryland's population grew by 35 percent between 1970 and 2000, and is expected to increase by an additional 27 percent between 2000 and 2030. Because domestic water demand generally increases in proportion to population growth, Maryland will be facing increased pressure on water resources over the next 20 years. Water-resources decisions should be based on sound, comprehensive, long-term data and low-flow frequency statistics from all available streamgage locations with unregulated streamflow and adequate record lengths. To provide the Maryland Department of the Environment with tools for making future water-resources decisions, the U.S. Geological Survey initiated a study in October 2009 to compute low-flow frequency statistics for selected streamgage locations in Maryland with 10 or more years of continuous streamflow records. This report presents low-flow frequency statistics for 114 continuous-record streamgage locations in Maryland. The computed statistics presented for each streamgage location include the mean 7-, 14-, and 30-consecutive day minimum daily low-flow dischages for recurrence intervals of 2, 10, and 20 years, and are based on approved streamflow records that include a minimum of 10 complete climatic years of record as of June 2010. Descriptive information for each of these streamgage locations, including the station number, station name, latitude, longitude, county, physiographic province, and drainage area, also is presented. The statistics are planned for incorporation into StreamStats, which is a U.S. Geological Survey Web application for obtaining stream information, and is being used by water-resource managers and decision makers in Maryland to address water-supply planning and management, water-use appropriation and permitting, wastewater and industrial discharge permitting, and setting minimum required

  14. Low Intensity and Frequency Pulsed Electromagnetic Fields Selectively Impair Breast Cancer Cell Viability

    PubMed Central

    Crocetti, Sara; Beyer, Christian; Schade, Grit; Egli, Marcel; Fröhlich, Jürg; Franco-Obregón, Alfredo

    2013-01-01

    Introduction A common drawback of many anticancer therapies is non-specificity in action of killing. We investigated the potential of ultra-low intensity and frequency pulsed electromagnetic fields (PEMFs) to kill breast cancer cells. Our criteria to accept this technology as a potentially valid therapeutic approach were: 1) cytotoxicity to breast cancer cells and; 2) that the designed fields proved innocuous to healthy cell classes that would be exposed to the PEMFs during clinical treatment. Methods MCF7 breast cancer cells and their normal counterparts, MCF10 cells, were exposed to PEMFs and cytotoxic indices measured in order to design PEMF paradigms that best kill breast cancer cells. The PEMF parameters tested were: 1) frequencies ranging from 20 to 50 Hz; 2) intensities ranging from 2 mT to 5 mT and; 3) exposure durations ranging from 30 to 90 minutes per day for up to three days to determine the optimum parameters for selective cancer cell killing. Results We observed a discrete window of vulnerability of MCF7 cells to PEMFs of 20 Hz frequency, 3 mT magnitude and exposure duration of 60 minutes per day. The cell damage accrued in response to PEMFs increased with time and gained significance after three days of consecutive daily exposure. By contrast, the PEMFs parameters determined to be most cytotoxic to breast cancer MCF-7 cells were not damaging to normal MCF-10 cells. Conclusion Based on our data it appears that PEMF-based anticancer strategies may represent a new therapeutic approach to treat breast cancer without affecting normal tissues in a manner that is non-invasive and can be potentially combined with existing anti-cancer treatments. PMID:24039828

  15. High-frequency cluster radio galaxies: luminosity functions and implications for SZE-selected cluster samples

    NASA Astrophysics Data System (ADS)

    Gupta, N.; Saro, A.; Mohr, J. J.; Benson, B. A.; Bocquet, S.; Capasso, R.; Carlstrom, J. E.; Chiu, I.; Crawford, T. M.; de Haan, T.; Dietrich, J. P.; Gangkofner, C.; Holzapfel, W. L.; McDonald, M.; Rapetti, D.; Reichardt, C. L.

    2017-05-01

    We study the overdensity of point sources in the direction of X-ray-selected galaxy clusters from the meta-catalogue of X-ray-detected clusters of galaxies (MCXC; = 0.14) at South Pole Telescope (SPT) and Sydney University Molonglo Sky Survey (SUMSS) frequencies. Flux densities at 95, 150 and 220 GHz are extracted from the 2500 deg2 SPT-SZ survey maps at the locations of SUMSS sources, producing a multifrequency catalogue of radio galaxies. In the direction of massive galaxy clusters, the radio galaxy flux densities at 95 and 150 GHz are biased low by the cluster Sunyaev-Zel'dovich Effect (SZE) signal, which is negative at these frequencies. We employ a cluster SZE model to remove the expected flux bias and then study these corrected source catalogues. We find that the high-frequency radio galaxies are centrally concentrated within the clusters and that their luminosity functions (LFs) exhibit amplitudes that are characteristically an order of magnitude lower than the cluster LF at 843 MHz. We use the 150 GHz LF to estimate the impact of cluster radio galaxies on an SPT-SZ like survey. The radio galaxy flux typically produces a small bias on the SZE signal and has negligible impact on the observed scatter in the SZE mass-observable relation. If we assume there is no redshift evolution in the radio galaxy LF then 1.8 ± 0.7 per cent of the clusters with detection significance ξ ≥ 4.5 would be lost from the sample. Allowing for redshift evolution of the form (1 + z)2.5 increases the incompleteness to 5.6 ± 1.0 per cent. Improved constraints on the evolution of the cluster radio galaxy LF require a larger cluster sample extending to higher redshift.

  16. Simulating the maintenance of a rare fish morph experiencing negative frequency dependent selection.

    PubMed

    Horth, Lisa; Panayotova, Iordanka N

    2012-12-01

    Empirical work assessing the maintenance of rare genotypes in natural populations is difficult over very long time scales. Skirting this problematic issue is possible with theory and simulations. Major theoretical constructs, including mutation-selection balance and balancing selection, explain the theoretical maintenance of rare genotypes, and the occurrence of multiple, rare genotypes over time. Additionally, numerical simulations are valuable tools for assessing evolving biological systems because they allow for monitoring systems over long time scales, as well as for controlling model parameters, thus contributing to the exploration of system dynamics that cannot be assessed in nature. Here we employed numerical simulations to explore the importance of several biological factors that contribute to the maintenance of a fish color-pattern polymorphism. We present a numerical model of a two-morph fish polymorphism that allowed us to test the sensitivity of the rare morph's persistence and the population's stability to multiple parameters. Our simulations ran over 10,000 years (where one year is approximately one generation) and demonstrated the maintenance of a stable polymorphism with a rare morph which persisted at a frequency of ~10(-2), which is in-fact the frequency of the rare, mottled black mosquitofish morph in natural populations. This pigmentation polymorphism is stable, independent of changes in population size, but can be destabilized with very high predation when coupled with very low birth rates. Employing models with empirical fitness estimates is a valuable tool for monitoring rare vertebrate morphs in nature, however few studies exist that have accomplished this task. Our approach can be adapted for modeling rare morphs (particularly in additional live-bearing fishes like sailfin mollies) that also harbor rare, pigmentation morphs within large populations. Copyright © 2012 Elsevier Ireland Ltd. All rights reserved.

  17. Frequency-selective quantification of skin perfusion behavior during allergic testing using photoplethysmography imaging

    NASA Astrophysics Data System (ADS)

    Blanik, Nikolai; Blazek, Claudia; Pereira, Carina; Blazek, Vladimir; Leonhardt, Steffen

    2014-03-01

    Diagnosis of allergic immediate-type reactions is dependent on the visual assessment of the attending physician. With our novel non-obtrusive, camera-based photoplethysmography imaging (PPGI) setup, perfusion in the allergic testing area can be quantified and results displayed with spatial resolution in functional mappings. Thereby, each PPGI camera pixel can be assumed to be a classical (skin-based) reflective mode PPG sensor. An algorithm for post-processing of collected PPGI video sequences was developed to transfer black-and-white PPGI images into virtual 3D perfusion maps. For the first time, frequency selected perfusion quantification was assessed. For the presented evaluation, PPGI data from our clinical study were used [1]. For this purpose, different concentrations of histamine dilutions were administered to 27 healthy volunteers. Our results show clear trends in an increase in heartbeat synchronous perfusion rhythms and, simultaneously, a decrease of lower frequency vasomotor rhythms in these areas. These results, published for the first time, allow new insight into the distribution of skin perfusion dynamics and demonstrate the intuitive clinical usability of the proposed system.

  18. Two layer metamaterials for selective frequency transmission in the terahertz region (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Landau, Mayer A.

    2015-09-01

    We have fabricated a metamaterial tunable filter for dynamic frequency selection in the terahertz region. The metamaterial consists of a sandwich of two meta-surfaces grown on high resistivity silicon wafers. The first meta-surface consists of a two-dimensional array of gold double split ring resonators and the second meta-surface consisits of an array of gold cut rods. Both meta-surfaces are fabricated for a response in the terahertz region. Our terahertz pulses are produced using the standard Austin switch technique. The terahertz pulse is focused onto the two meta-surfaces which are sandwiched together to produce a transmission window. Together, with the right orientation, translation, and parallelism of the two meta-surfaces, we achieve filtering of terahertz pulses. Since the unit cells for the inclusions are on the order of 100 microns, control of the translation, orientation, and parallelism of the two meta-surfaces with respect to each other and with respect to the orientation and direction of the impinging terahertz field is a challenge. We describe our technique for doing this and present data on our frequency filtering in the terahertz.

  19. Reflective frequency selective surface based on low-permittivity dielectric metamaterials

    NASA Astrophysics Data System (ADS)

    Yu, Fei; Wang, Jun; Wang, Jiafu; Ma, Hua; Du, Hongliang; Xu, Zhuo; Qu, Shaobo

    2015-11-01

    In this letter, the design of reflective frequency selective surface (RFSS) using low-permittivity dielectrics is proposed based on effective medium theory. The effective medium approach is based on quasi-static extension of the Maxwell-Garnett model. Unlike conventional RFSSs, such RFSS is composed of low-permittivity dielectrics rather than high-permittivity or metallic materials. By drilling periodic hole arrays in multi-layer continuum dielectric plates, strong electric and magnetic resonances are introduced to produce drastic changes in effective parameters, leading to impedance mismatch and band-stop response. The band-stop response can be tailored by adjusting the size and spacing of the unit cell. As an example, an RFSS with rectangular hole element is demonstrated at K-band. The mechanism is analyzed by presenting the effective electromagnetic parameters and dynamic field distributions. A prototype was fabricated and measured. Excellent agreements between measured and simulated results were obtained. The method can also be used to design RFSS in THz and optical frequencies.

  20. All-dielectric frequency selective surface design based on dielectric resonator

    NASA Astrophysics Data System (ADS)

    Zheng-Bin, Wang; Chao, Gao; Bo, Li; Zhi-Hang, Wu; Hua-Mei, Zhang; Ye-Rong, Zhang

    2016-06-01

    In this work, we propose an all-dielectric frequency selective surface (FSS) composed of periodically placed high-permittivity dielectric resonators and a three-dimensional (3D) printed supporter. Mie resonances in the dielectric resonators offer strong electric and magnetic dipoles, quadrupoles, and higher order terms. The re-radiated electric and magnetic fields by these multipoles interact with the incident fields, which leads to total reflection or total transmission in some special frequency bands. The measured results of the fabricated FSS demonstrate a stopband fractional bandwidth (FBW) of 22.2%, which is consistent with the simulated result. Project supported by the National Natural Science Foundation of China (Grant Nos. 61201030, 61372045, 61472045, and 61401229), the Science and Technology Project of Jiangsu Province, China (Grant No. BE2015002), the Open Research Program of the State Key Laboratory of Millimeter Waves, China (Grant Nos. K201616 and K201622), and the Nanjing University of Posts and Telecommunications Scientific Foundation, China (Grant No. NY214148).

  1. Methods for estimating selected low-flow frequency statistics for unregulated streams in Kentucky

    USGS Publications Warehouse

    Martin, Gary R.; Arihood, Leslie D.

    2010-01-01

    This report provides estimates of, and presents methods for estimating, selected low-flow frequency statistics for unregulated streams in Kentucky including the 30-day mean low flows for recurrence intervals of 2 and 5 years (30Q2 and 30Q5) and the 7-day mean low flows for recurrence intervals of 5, 10, and 20 years (7Q2, 7Q10, and 7Q20). Estimates of these statistics are provided for 121 U.S. Geological Survey streamflow-gaging stations with data through the 2006 climate year, which is the 12-month period ending March 31 of each year. Data were screened to identify the periods of homogeneous, unregulated flows for use in the analyses. Logistic-regression equations are presented for estimating the annual probability of the selected low-flow frequency statistics being equal to zero. Weighted-least-squares regression equations were developed for estimating the magnitude of the nonzero 30Q2, 30Q5, 7Q2, 7Q10, and 7Q20 low flows. Three low-flow regions were defined for estimating the 7-day low-flow frequency statistics. The explicit explanatory variables in the regression equations include total drainage area and the mapped streamflow-variability index measured from a revised statewide coverage of this characteristic. The percentage of the station low-flow statistics correctly classified as zero or nonzero by use of the logistic-regression equations ranged from 87.5 to 93.8 percent. The average standard errors of prediction of the weighted-least-squares regression equations ranged from 108 to 226 percent. The 30Q2 regression equations have the smallest standard errors of prediction, and the 7Q20 regression equations have the largest standard errors of prediction. The regression equations are applicable only to stream sites with low flows unaffected by regulation from reservoirs and local diversions of flow and to drainage basins in specified ranges of basin characteristics. Caution is advised when applying the equations for basins with characteristics near the

  2. A General Design Framework for MIMO Wireless Energy Transfer With Limited Feedback

    NASA Astrophysics Data System (ADS)

    Xu, Jie; Zhang, Rui

    2016-05-01

    Multi-antenna or multiple-input multiple-output (MIMO) technique can significantly improve the efficiency of radio frequency (RF) signal enabled wireless energy transfer (WET). To fully exploit the energy beamforming gain at the energy transmitter (ET), the knowledge of channel state information (CSI) is essential, which, however, is difficult to be obtained in practice due to the hardware limitation of the energy receiver (ER). To overcome this difficulty, under a point-to-point MIMO WET setup, this paper proposes a general design framework for a new type of channel learning method based on the ER's energy measurement and feedback. Specifically, the ER measures and encodes the harvested energy levels over different training intervals into bits, and sends them to the ET via a feedback link of limited rate. Based on the energy-level feedback, the ET adjusts transmit beamforming in subsequent training intervals and obtains refined estimates of the MIMO channel by leveraging the technique of analytic center cutting plane method (ACCPM) in convex optimization. Under this general design framework, we further propose two specific feedback schemes termed energy quantization and energy comparison, where the feedback bits at each interval are generated at the ER by quantizing the measured energy level at the current interval and comparing it with those in the previous intervals, respectively. Numerical results are provided to compare the performance of the two feedback schemes. It is shown that energy quantization performs better when the number of feedback bits per interval is large, while energy comparison is more effective with small number of feedback bits.

  3. Selective addressing of solid-state spins at the nanoscale via magnetic resonance frequency encoding

    NASA Astrophysics Data System (ADS)

    Zhang, H.; Arai, K.; Belthangady, C.; Jaskula, J.-C.; Walsworth, R. L.

    2017-08-01

    The nitrogen vacancy centre in diamond is a leading platform for nanoscale sensing and imaging, as well as quantum information processing in the solid state. To date, individual control of two nitrogen vacancy electronic spins at the nanoscale has been demonstrated. However, a key challenge is to scale up such control to arrays of nitrogen vacancy spins. Here, we apply nanoscale magnetic resonance frequency encoding to realize site-selective addressing and coherent control of a four-site array of nitrogen vacancy spins. Sites in the array are separated by 100 nm, with each site containing multiple nitrogen vacancies separated by 15 nm. Microcoils fabricated on the diamond chip provide electrically tuneable magnetic field gradients 0.1 G/nm. Tailored application of gradient fields and resonant microwaves allow site-selective nitrogen vacancy spin manipulation and sensing applications, including Rabi oscillations, imaging, and nuclear magnetic resonance spectroscopy with nanoscale resolution. Microcoil-based magnetic resonance of solid-state spins provides a practical platform for quantum-assisted sensing, quantum information processing, and the study of nanoscale spin networks.

  4. Extremely Low Frequency Electromagnetic Field from Convective Air Warming System on Temperature Selection and Distance.

    PubMed

    Cho, Kwang Rae; Kim, Myoung-Hun; Ko, Myoung Jin; Jung, Jae Wook; Lee, Ki Hwa; Park, Yei-Heum; Kim, Yong Han; Kim, Ki Hoon; Kim, Jin Soo

    2014-12-01

    Hypothermia generates potentially severe complications in operating or recovery room. Forced air warmer is effective to maintain body temperature. Extremely low frequency electromagnetic field (ELF-EMF) is harmful to human body and mainly produced by electronic equipment including convective air warming system. We investigated ELF-EMF from convective air warming device on various temperature selection and distance for guideline to protect medical personnel and patients. The intensity of ELF-EMF was measured as two-second interval for five minutes on various distance (0.1, 0.2, 0.3, 0.5 and 1meter) and temperature selection (high, medium, low and ambient). All of electrical devices were off including lamp, computer and air conditioner. Groups were compared using one-way ANOVA. P<0.05 was considered significant. Mean values of ELF-EMF on the distance of 30 cm were 18.63, 18.44, 18.23 and 17.92 milligauss (mG) respectively (high, medium, low and ambient temperature set). ELF-EMF of high temperature set was higher than data of medium, low and ambient set in all the distances. ELF-EMF from convective air warming system is higher in condition of more close location and higher temperature. ELF-EMF within thirty centimeters exceeds 2mG recommended by Swedish TCO guideline.

  5. FEA modeling of CMUT with membrane stand-off structures to enable selectable frequency-mode operation.

    PubMed

    Eames, Matthew D C; Reck, Theodore J; Kilroy, Joseph P; Hossack, John A

    2011-12-01

    A selectable, dual-frequency, capacitive micro- machined ultrasonic transducer (CMUT) designed for both high-frequency imaging and low-frequency therapeutic effect is presented. A validated finite element analysis (FEA) CMUT model was used to examine the performance of the proposed dual-frequency transducer. CMUT device simulations were used to design a hybrid device incorporating stand-off structures that divide a large, low-frequency membrane into smaller, high-frequency sub-membranes when the membrane is partially collapsed so that the stand-offs contact the substrate. In low-frequency operation, simulations indicated that the peak negative pressure achieved by the hybrid device, when biased by 30.0 VDC and excited by a 2-MHz signal with 30.0 V amplitude, exceeded 190 kPa, which is sufficient for microbubble rupture. Low-frequency mode bandwidth was 93% at a center frequency of 2.1 MHz. In the high-frequency mode of operation, the device was excited by 175 Vdc and 87.5 Vac, which generated a peak negative pressure of 247 kPa. Device center frequency was 44.1 MHz with a - 6-dB fractional bandwidth of 42%.

  6. Controlling for P-value inflation in allele frequency change in experimental evolution and artificial selection experiments.

    PubMed

    Kemppainen, Petri; Rønning, Bernt; Kvalnes, Thomas; Hagen, Ingerid J; Ringsby, Thor Harald; Billing, Anna M; Pärn, Henrik; Lien, Sigbjørn; Husby, Arild; Saether, Bernt-Erik; Jensen, Henrik

    2016-11-04

    Experimental evolution studies can be used to explore genomic response to artificial and natural selection. In such studies, loci that display larger allele frequency change than expected by genetic drift alone are assumed to be directly or indirectly associated with traits under selection. However, such studies report surprisingly many loci under selection, suggesting that current tests for allele frequency change may be subject to P-value inflation and hence be anticonservative. One factor known from genomewide association (GWA) studies to cause P-value inflation is population stratification, such as relatedness among individuals. Here, we suggest that by treating presence of an individual in a population after selection as a binary response variable, existing GWA methods can be used to account for relatedness when estimating allele frequency change. We show that accounting for relatedness like this effectively reduces false-positives in tests for allele frequency change in simulated data with varying levels of population structure. However, once relatedness has been accounted for, the power to detect causal loci under selection is low. Finally, we demonstrate the presence of P-value inflation in allele frequency change in empirical data spanning multiple generations from an artificial selection experiment on tarsus length in two free-living populations of house sparrow and correct for this using genomic control. Our results indicate that since allele frequencies in large parts of the genome may change when selection acts on a heritable trait, such selection is likely to have considerable and immediate consequences for the eco-evolutionary dynamics of the affected populations.

  7. Controller certification: The generalized stability margin inference for a large number of MIMO controllers

    NASA Astrophysics Data System (ADS)

    Park, Jisang

    In this dissertation, we investigate MIMO stability margin inference of a large number of controllers using pre-established stability margins of a small number of nu-gap-wise adjacent controllers. The generalized stability margin and the nu-gap metric are inherently able to handle MIMO system analysis without the necessity of repeating multiple channel-by-channel SISO analyses. This research consists of three parts: (i) development of a decision support tool for inference of the stability margin, (ii) computational considerations for yielding the maximal stability margin with the minimal nu-gap metric in a less conservative manner, and (iii) experiment design for estimating the generalized stability margin with an assured error bound. A modern problem from aerospace control involves the certification of a large set of potential controllers with either a single plant or a fleet of potential plant systems, with both plants and controllers being MIMO and, for the moment, linear. Experiments on a limited number of controller/plant pairs should establish the stability and a certain level of margin of the complete set. We consider this certification problem for a set of controllers and provide algorithms for selecting an efficient subset for testing. This is done for a finite set of candidate controllers and, at least for SISO plants, for an infinite set. In doing this, the nu-gap metric will be the main tool. We provide a theorem restricting a radius of a ball in the parameter space so that the controller can guarantee a prescribed level of stability and performance if parameters of the controllers are contained in the ball. Computational examples are given, including one of certification of an aircraft engine controller. The overarching aim is to introduce truly MIMO margin calculations and to understand their efficacy in certifying stability over a set of controllers and in replacing legacy single-loop gain and phase margin calculations. We consider methods for the

  8. MIMO free-space optical communication employing coherent BPOLSK modulation in atmospheric optical turbulence channel with pointing errors

    NASA Astrophysics Data System (ADS)

    Prabu, K.; Kumar, D. Sriram

    2015-05-01

    An optical wireless communication system is an alternative to radio frequency communication, but atmospheric turbulence induced fading and misalignment fading are the main impairments affecting an optical signal when propagating through the turbulence channel. The resultant of misalignment fading is the pointing errors, it degrades the bit error rate (BER) performance of the free space optics (FSO) system. In this paper, we study the BER performance of the multiple-input multiple-output (MIMO) FSO system employing coherent binary polarization shift keying (BPOLSK) in gamma-gamma (G-G) channel with pointing errors. The BER performance of the BPOLSK based MIMO FSO system is compared with the single-input single-output (SISO) system. Also, the average BER performance of the systems is analyzed and compared with and without pointing errors. A novel closed form expressions of BER are derived for MIMO FSO system with maximal ratio combining (MRC) and equal gain combining (EGC) diversity techniques. The analytical results show that the pointing errors can severely degrade the performance of the system.

  9. Main-channel slopes of selected streams in Iowa for estimation of flood-frequency discharges

    USGS Publications Warehouse

    Eash, David A.

    2003-01-01

    This report describes a statewide study conducted to develop main-channel slope (MCS) curves for 138 selected streams in Iowa with drainage areas greater than 100 square miles. MCS values determined from the curves can be used in regression equations for estimating floodfrequency discharges. Multivariable regression equations previously developed for two of the three hydrologic regions defined for Iowa require the measurement of MCS. Main-channel slope is a difficult measurement to obtain for large streams using 1:24,000-scale topographic maps. The curves developed in this report provide a simplified method for determining MCS values for sites located along large streams in Iowa within hydrologic Regions 2 and 3. The curves were developed using MCS values quantified for 2,058 selected sites along 138 selected streams in Iowa. A geographic information system (GIS) technique and 1:24,000-scale topographic data were used to quantify MCS values for the stream sites. The sites were selected at about 5-mile intervals along the streams. River miles were quantified for each stream site using a GIS program. Data points for river-mile and MCS values were plotted and a best-fit curve was developed for each stream. An adjustment was applied to all 138 curves to compensate for differences in MCS values between manual measurements and GIS quantifications. The multivariable equations for Regions 2 and 3 were developed using manual measurements of MCS. A comparison of manual measurements and GIS quantifications of MCS indicates that manual measurements typically produce greater values of MCS compared to GIS quantifications. Median differences between manual measurements and GIS quantifications of MCS are 14.8 and 17.7 percent for Regions 2 and 3, respectively. Comparisons of percentage differences between flood-frequency discharges calculated using MCS values of manual measurements and GIS quantifications indicate that use of GIS values of MCS for Region 3 substantially

  10. Optimizing the wireless power transfer over MIMO Channels

    NASA Astrophysics Data System (ADS)

    Wiedmann, Karsten; Weber, Tobias

    2017-09-01

    In this paper, the optimization of the power transfer over wireless channels having multiple-inputs and multiple-outputs (MIMO) is studied. Therefore, the transmitter, the receiver and the MIMO channel are modeled as multiports. The power transfer efficiency is described by a Rayleigh quotient, which is a function of the channel's scattering parameters and the incident waves from both transmitter and receiver side. This way, the power transfer efficiency can be maximized analytically by solving a generalized eigenvalue problem, which is deduced from the Rayleigh quotient. As a result, the maximum power transfer efficiency achievable over a given MIMO channel is obtained. This maximum can be used as a performance bound in order to benchmark wireless power transfer systems. Furthermore, the optimal operating point which achieves this maximum will be obtained. The optimal operating point will be described by the complex amplitudes of the optimal incident and reflected waves of the MIMO channel. This supports the design of the optimal transmitter and receiver multiports. The proposed method applies for arbitrary MIMO channels, taking transmitter-side and/or receiver-side cross-couplings in both near- and farfield scenarios into consideration. Special cases are briefly discussed in this paper in order to illustrate the method.

  11. Experimental demonstration of high spectral efficient 4 × 4 MIMO SCMA-OFDM/OQAM radio over multi-core fiber system.

    PubMed

    Liu, Chang; Deng, Lei; He, Jiale; Li, Di; Fu, Songnian; Tang, Ming; Cheng, Mengfan; Liu, Deming

    2017-07-24

    In this paper, 4 × 4 multiple-input multiple-output (MIMO) radio over 7-core fiber system based on sparse code multiple access (SCMA) and OFDM/OQAM techniques is proposed. No cyclic prefix (CP) is required by properly designing the prototype filters in OFDM/OQAM modulator, and non-orthogonally overlaid codewords by using SCMA is help to serve more users simultaneously under the condition of using equal number of time and frequency resources compared with OFDMA, resulting in the increase of spectral efficiency (SE) and system capacity. In our experiment, 11.04 Gb/s 4 × 4 MIMO SCMA-OFDM/OQAM signal is successfully transmitted over 20 km 7-core fiber and 0.4 m air distance in both uplink and downlink. As a comparison, 6.681 Gb/s traditional MIMO-OFDM signal with the same occupied bandwidth has been evaluated for both uplink and downlink transmission. The experimental results show that SE could be increased by 65.2% with no bit error rate (BER) performance degradation compared with the traditional MIMO-OFDM technique.

  12. Downlink Training Techniques for FDD Massive MIMO Systems: Open-Loop and Closed-Loop Training With Memory

    NASA Astrophysics Data System (ADS)

    Choi, Junil; Love, David J.; Bidigare, Patrick

    2014-10-01

    The concept of deploying a large number of antennas at the base station, often called massive multiple-input multiple-output (MIMO), has drawn considerable interest because of its potential ability to revolutionize current wireless communication systems. Most literature on massive MIMO systems assumes time division duplexing (TDD), although frequency division duplexing (FDD) dominates current cellular systems. Due to the large number of transmit antennas at the base station, currently standardized approaches would require a large percentage of the precious downlink and uplink resources in FDD massive MIMO be used for training signal transmissions and channel state information (CSI) feedback. To reduce the overhead of the downlink training phase, we propose practical open-loop and closed-loop training frameworks in this paper. We assume the base station and the user share a common set of training signals in advance. In open-loop training, the base station transmits training signals in a round-robin manner, and the user successively estimates the current channel using long-term channel statistics such as temporal and spatial correlations and previous channel estimates. In closed-loop training, the user feeds back the best training signal to be sent in the future based on channel prediction and the previously received training signals. With a small amount of feedback from the user to the base station, closed-loop training offers better performance in the data communication phase, especially when the signal-to-noise ratio is low, the number of transmit antennas is large, or prior channel estimates are not accurate at the beginning of the communication setup, all of which would be mostly beneficial for massive MIMO systems.

  13. Optical frequency selective surface design using a GPU accelerated finite element boundary integral method

    NASA Astrophysics Data System (ADS)

    Ashbach, Jason A.

    Periodic metallodielectric frequency selective surface (FSS) designs have historically seen widespread use in the microwave and radio frequency spectra. By scaling the dimensions of an FSS unit cell for use in a nano-fabrication process, these concepts have recently been adapted for use in optical applications as well. While early optical designs have been limited to wellunderstood geometries or optimized pixelated screens, nano-fabrication, lithographic and interconnect technology has progressed to a point where it is possible to fabricate metallic screens of arbitrary geometries featuring curvilinear or even three-dimensional characteristics that are only tens of nanometers wide. In order to design an FSS featuring such characteristics, it is important to have a robust numerical solver that features triangular elements in purely two-dimensional geometries and prismatic or tetrahedral elements in three-dimensional geometries. In this dissertation, a periodic finite element method code has been developed which features prismatic elements whose top and bottom boundaries are truncated by numerical integration of the boundary integral as opposed to an approximate representation found in a perfectly matched layer. However, since no exact solution exists for the calculation of triangular elements in a boundary integral, this process can be time consuming. To address this, these calculations were optimized for parallelization such that they may be done on a graphics processor, which provides a large increase in computational speed. Additionally, a simple geometrical representation using a Bezier surface is presented which provides generality with few variables. With a fast numerical solver coupled with a lowvariable geometric representation, a heuristic optimization algorithm has been used to develop several optical designs such as an absorber, a circular polarization filter, a transparent conductive surface and an enhanced, optical modulator.

  14. Selective attention modulates high-frequency activity in the face-processing network.

    PubMed

    Müsch, Kathrin; Hamamé, Carlos M; Perrone-Bertolotti, Marcela; Minotti, Lorella; Kahane, Philippe; Engel, Andreas K; Lachaux, Jean-Philippe; Schneider, Till R

    2014-11-01

    Face processing depends on the orchestrated activity of a large-scale neuronal network. Its activity can be modulated by attention as a function of task demands. However, it remains largely unknown whether voluntary, endogenous attention and reflexive, exogenous attention to facial expressions equally affect all regions of the face-processing network, and whether such effects primarily modify the strength of the neuronal response, the latency, the duration, or the spectral characteristics. We exploited the good temporal and spatial resolution of intracranial electroencephalography (iEEG) and recorded from depth electrodes to uncover the fast dynamics of emotional face processing. We investigated frequency-specific responses and event-related potentials (ERP) in the ventral occipito-temporal cortex (VOTC), ventral temporal cortex (VTC), anterior insula, orbitofrontal cortex (OFC), and amygdala when facial expressions were task-relevant or task-irrelevant. All investigated regions of interest (ROI) were clearly modulated by task demands and exhibited stronger changes in stimulus-induced gamma band activity (50-150 Hz) when facial expressions were task-relevant. Observed latencies demonstrate that the activation is temporally coordinated across the network, rather than serially proceeding along a processing hierarchy. Early and sustained responses to task-relevant faces in VOTC and VTC corroborate their role for the core system of face processing, but they also occurred in the anterior insula. Strong attentional modulation in the OFC and amygdala (300 msec) suggests that the extended system of the face-processing network is only recruited if the task demands active face processing. Contrary to our expectation, we rarely observed differences between fearful and neutral faces. Our results demonstrate that activity in the face-processing network is susceptible to the deployment of selective attention. Moreover, we show that endogenous attention operates along the whole

  15. Spontaneous mutation frequency and molecular mechanisms of Shigella flexneri fluoroquinolone resistance under antibiotic selective stress.

    PubMed

    Pu, Xiao-Ying; Zhang, Qijing; Pan, Jing-Cao; Shen, Zhangqi; Zhang, Wei

    2013-02-01

    The incidence of fluoroquinolone-resistant Shigella strains has risen rapidly, presumably in response to ciprofloxacin antibiotic stress. Understanding the molecular mechanisms underlying this resistance phenotype is critical to developing novel and effective therapeutic strategies. In this study, the frequency of ciprofloxacin-induced mutation was measured in antibiotic resistance genes (gyrA, gyrB, parC, parE, marOR, and marA) of Shigella flexneri. The S. flexneri 2a strain 301 was cultured on Luria-Bertani agar plates containing one of seven different ciprofloxacin concentrations (range: 0.03125-2 μg mL(-1)). Resistant colonies were selected for gene-targeted sequencing analysis; the identified point mutations were subsequently confirmed by insertion into antibiotic cassette plasmids and growth under ciprofloxacin stress. The results demonstrated that the seven different ciprofloxacin concentrations produced dose-dependent frequencies of spontaneous mutations: 10(-8) (0.03125 and 0.0625 μg mL(-1)), 10(-9) (0.125 μg mL(-1)), and <10(-9) (0.25, 0.5, 1, 2 μg mL(-1)). PCR sequencing of the ten randomly selected resistant colonies (minimum inhibitory concentrations (MICs) of 0.125 μg mL(-1), n = 5 and 0.25 μg mL(-1), n = 5) revealed that all colonies had mutations in the gyrA gene at either codon 83 (Ser83 → Leu) or 87 (Asp87 → Tyr or → Gly), both of which were confirmed at MIC of 0.125 μg mL(-1). None of the spontaneous mutation colonies exhibited gyrB, parC, parE, marOR, or marA mutations. In conclusion, S. flexneri is normomutable under ciprofloxacin antibiotic stress and fluoroquinolone resistance by spontaneous mutation occurs at a low rate. Codon mutations gyrA 83 and/or gyrA 87 cause a 4-fold increase in the ciprofloxacin MIC, and may represent the natural mechanism of fluoroquinolone resistance.

  16. Development of inhibitory mechanisms underlying selectivity for the rate and direction of frequency-modulated sweeps in the auditory cortex.

    PubMed

    Razak, Khaleel A; Fuzessery, Zoltan M

    2007-02-14

    Although it is known that neural selectivity for species-specific vocalizations changes during development, the mechanisms underlying such changes are not known. This study followed the development of mechanisms underlying selectivity for the direction and rate of frequency-modulated (FM) sweeps in the auditory cortex of the pallid bat, a species that uses downward FM sweeps to echolocate. In the adult cortex, direction and rate selectivity arise as a result of different spectral and temporal properties of low-frequency inhibition (LFI) and high-frequency inhibition (HFI). A narrow band of delayed HFI shapes rate selectivity for downward FM sweeps. A broader band of early LFI shapes direction selectivity. Here we asked whether these differences in LFI and HFI are present at the onset of hearing in the echolocation range or whether the differences develop slowly. We also studied how the development of properties of inhibitory frequencies influences FM rate and direction selectivity. We found that adult-like FM rate selectivity is present at 2 weeks after birth, whereas direction selectivity matures 12 weeks after birth. The different developmental time course for direction and rate selectivity is attributable to the differences in the development of LFI and HFI. Arrival time and bandwidth of HFI are adult-like at 2 weeks. Average arrival time of LFI gradually becomes faster and bandwidth becomes broader between 2 and 12 weeks. Thus, two properties of FM sweeps that are important for vocalization selectivity follow different developmental time courses attributable to the differences in the development of underlying inhibitory mechanisms.

  17. The Quasar Fraction in Low-Frequency Selected Complete Samples and Implications for Unified Schemes

    NASA Technical Reports Server (NTRS)

    Willott, Chris J.; Rawlings, Steve; Blundell, Katherine M.; Lacy, Mark

    2000-01-01

    Low-frequency radio surveys are ideal for selecting orientation-independent samples of extragalactic sources because the sample members are selected by virtue of their isotropic steep-spectrum extended emission. We use the new 7C Redshift Survey along with the brighter 3CRR and 6C samples to investigate the fraction of objects with observed broad emission lines - the 'quasar fraction' - as a function of redshift and of radio and narrow emission line luminosity. We find that the quasar fraction is more strongly dependent upon luminosity (both narrow line and radio) than it is on redshift. Above a narrow [OII] emission line luminosity of log(base 10) (L(sub [OII])/W) approximately > 35 [or radio luminosity log(base 10) (L(sub 151)/ W/Hz.sr) approximately > 26.5], the quasar fraction is virtually independent of redshift and luminosity; this is consistent with a simple unified scheme with an obscuring torus with a half-opening angle theta(sub trans) approximately equal 53 deg. For objects with less luminous narrow lines, the quasar fraction is lower. We show that this is not due to the difficulty of detecting lower-luminosity broad emission lines in a less luminous, but otherwise similar, quasar population. We discuss evidence which supports at least two probable physical causes for the drop in quasar fraction at low luminosity: (i) a gradual decrease in theta(sub trans) and/or a gradual increase in the fraction of lightly-reddened (0 approximately < A(sub V) approximately < 5) lines-of-sight with decreasing quasar luminosity; and (ii) the emergence of a distinct second population of low luminosity radio sources which, like M8T, lack a well-fed quasar nucleus and may well lack a thick obscuring torus.

  18. The Quasar Fraction in Low-Frequency Selected Complete Samples and Implications for Unified Schemes

    NASA Technical Reports Server (NTRS)

    Willott, Chris J.; Rawlings, Steve; Blundell, Katherine M.; Lacy, Mark

    2000-01-01

    Low-frequency radio surveys are ideal for selecting orientation-independent samples of extragalactic sources because the sample members are selected by virtue of their isotropic steep-spectrum extended emission. We use the new 7C Redshift Survey along with the brighter 3CRR and 6C samples to investigate the fraction of objects with observed broad emission lines - the 'quasar fraction' - as a function of redshift and of radio and narrow emission line luminosity. We find that the quasar fraction is more strongly dependent upon luminosity (both narrow line and radio) than it is on redshift. Above a narrow [OII] emission line luminosity of log(base 10) (L(sub [OII])/W) approximately > 35 [or radio luminosity log(base 10) (L(sub 151)/ W/Hz.sr) approximately > 26.5], the quasar fraction is virtually independent of redshift and luminosity; this is consistent with a simple unified scheme with an obscuring torus with a half-opening angle theta(sub trans) approximately equal 53 deg. For objects with less luminous narrow lines, the quasar fraction is lower. We show that this is not due to the difficulty of detecting lower-luminosity broad emission lines in a less luminous, but otherwise similar, quasar population. We discuss evidence which supports at least two probable physical causes for the drop in quasar fraction at low luminosity: (i) a gradual decrease in theta(sub trans) and/or a gradual increase in the fraction of lightly-reddened (0 approximately < A(sub V) approximately < 5) lines-of-sight with decreasing quasar luminosity; and (ii) the emergence of a distinct second population of low luminosity radio sources which, like M8T, lack a well-fed quasar nucleus and may well lack a thick obscuring torus.

  19. Rigorous study of low-complexity adaptive space-time block-coded MIMO receivers in high-speed mode multiplexed fiber-optic transmission links using few-mode fibers

    NASA Astrophysics Data System (ADS)

    Weng, Yi; He, Xuan; Wang, Junyi; Pan, Zhongqi

    2017-01-01

    Spatial-division multiplexing (SDM) techniques have been purposed to increase the capacity of optical fiber transmission links by utilizing multicore fibers or few-mode fibers (FMF). The most challenging impairments of SDMbased long-haul optical links mainly include modal dispersion and mode-dependent loss (MDL), whereas MDL arises from inline component imperfections, and breaks modal orthogonality thus degrading the capacity of multiple-inputmultiple- output (MIMO) receivers. To reduce MDL, optical approaches include mode scramblers and specialty fiber designs, yet these methods were burdened with high cost, yet cannot completely remove the accumulated MDL in the link. Besides, space-time trellis codes (STTC) were purposed to lessen MDL, but suffered from high complexity. In this work, we investigated the performance of space-time block-coding (STBC) scheme to mitigate MDL in SDM-based optical communication by exploiting space and delay diversity, whereas weight matrices of frequency-domain equalization (FDE) were updated heuristically using decision-directed recursive-least-squares (RLS) algorithm for convergence and channel estimation. The STBC was evaluated in a six-mode multiplexed system over 30-km FMF via 6×6 MIMO FDE, with modal gain offset 3 dB, core refractive index 1.49, numerical aperture 0.5. Results show that optical-signal-to-noise ratio (OSNR) tolerance can be improved via STBC by approximately 3.1, 4.9, 7.8 dB for QPSK, 16- and 64-QAM with respective bit-error-rates (BER) and minimum-mean-square-error (MMSE). Besides, we also evaluate the complexity optimization of STBC decoding scheme with zero-forcing decision feedback (ZFDF) equalizer by shortening the coding slot length, which is robust to frequency-selective fading channels, and can be scaled up for SDM systems with more dynamic channels.

  20. Single Front-End MIMO Architecture with Parasitic Antenna Elements

    NASA Astrophysics Data System (ADS)

    Yoshida, Mitsuteru; Sakaguchi, Kei; Araki, Kiyomichi

    In recent years, wireless communication technology has been studied intensively. In particular, MIMO which employs several transmit and receive antennas is a key technology for enhancing spectral efficiency. However, conventional MIMO architectures require some transceiver circuits for the sake of transmitting and receiving separate signals, which incurs the cost of one RF front-end per antenna. In addition to that, MIMO systems are assumed to be used in low spatial correlation environment between antennas. Since a short distance between each antenna causes high spatial correlation and coupling effect, it is difficult to miniaturize wireless terminals for mobile use. This paper shows a novel architecture which enables mobile terminals to be miniaturized and to work with a single RF front-end by means of adaptive analog beam-forming with parasitic antenna elements and antenna switching for spatial multiplexing. Furthermore, statistical analysis of the proposed architecture is also discussed in this paper.

  1. Reconfigurable architecture for MIMO systems based on CORDIC operators

    NASA Astrophysics Data System (ADS)

    Wang, Hongzhi; Leray, Pierre; Palicot, Jacques

    2006-09-01

    The MIMO system is an attractive technology for wireless 3G/4G systems. In this article we propose the realization on FPGA of a MIMO 'V-BLAST Square Root' algorithm based on a variable number of CORDIC operators. The CORDIC operator is highly suitable for this implementation as it only relies on simple techniques of addition and vector offsets. This square root algorithm architecture is reconfigurable in order to adapt itself to different numbers of antennas and different data rates. The proposed architecture can achieve a data rate of 600 Mbit/s in a Virtex-II FPGA circuit from Xilinx for the MIMO system with QPSK modulation. To cite this article: H. Wang et al., C. R. Physique 7 (2006).

  2. An ICA based MIMO-OFDM VLC scheme

    NASA Astrophysics Data System (ADS)

    Jiang, Fangqing; Deng, Honggui; Xiao, Wei; Tao, Shaohua; Zhu, Kaicheng

    2015-07-01

    In this paper, we propose a novel ICA based MIMO-OFDM VLC scheme, where ICA is applied to convert the MIMO-OFDM channel into several SISO-OFDM channels to reduce computational complexity in channel estimation, without any spectral overhead. Besides, the FM is first investigated to further modulate the OFDM symbols to eliminate the correlation of the signals, so as to improve the separation performance of the ICA algorithm. In the 4×4MIMO-OFDM VLC simulation experiment, LOS path and NLOS paths are both considered, each transmitting signal at 100 Mb/s. Simulation results show that the BER of the proposed scheme reaches the 10-5 level at SNR=20 dB, which is a large improvement compared to the traditional schemes.

  3. Adaptive Optimal Control Using Frequency Selective Information of the System Uncertainty With Application to Unmanned Aircraft.

    PubMed

    Maity, Arnab; Hocht, Leonhard; Heise, Christian; Holzapfel, Florian

    2016-11-28

    A new efficient adaptive optimal control approach is presented in this paper based on the indirect model reference adaptive control (MRAC) architecture for improvement of adaptation and tracking performance of the uncertain system. The system accounts here for both matched and unmatched unknown uncertainties that can act as plant as well as input effectiveness failures or damages. For adaptation of the unknown parameters of these uncertainties, the frequency selective learning approach is used. Its idea is to compute a filtered expression of the system uncertainty using multiple filters based on online instantaneous information, which is used for augmentation of the update law. It is capable of adjusting a sudden change in system dynamics without depending on high adaptation gains and can satisfy exponential parameter error convergence under certain conditions in the presence of structured matched and unmatched uncertainties as well. Additionally, the controller of the MRAC system is designed using a new optimal control method. This method is a new linear quadratic regulator-based optimal control formulation for both output regulation and command tracking problems. It provides a closed-form control solution. The proposed overall approach is applied in a control of lateral dynamics of an unmanned aircraft problem to show its effectiveness.

  4. Mode selection and boundary conditions using MAFIA in frequency-domain

    SciTech Connect

    Jin, Y.

    1988-09-01

    The field solvers of the 3D code MAFIA in the frequency domain are R3 and E3: the former generates an eigenvalue equation, and the latter solves this equation for eigenfrequencies and eigenvectors (fields). They are usually expensive to use. In order to save memory space and CPU time, one may employ a part of a structure in calculations if there are certain symmetries that are embedded in the geometry. In this case, one must run R3 and E3 several times with different boundary conditions if one wants to get a complete set of modes of the whole structure. However, sometimes only some modes are of interest to the authors (e.g., TM{sub 01}) and they may then specify the appropriate boundary conditions for a part of a structure to obtain these modes. There are two types of boundary conditions that one may choose from in R3: either a zero tangential E-field, denoted by integer 1, or a zero tangential H-field, denoted by integer 2. This note will use a circularly cylindrical cavity as an example to discuss the relation between mode selection and boundary conditions when using a part of the cavity.

  5. A Circular Polarizer with Beamforming Feature Based on Frequency Selective Surfaces

    NASA Astrophysics Data System (ADS)

    Yin, Jia Yuan; Wan, Xiang; Ren, Jian; Cui, Tie Jun

    2017-01-01

    We propose a circular polarizer with beamforming features based on frequency selective surface (FSS), in which a modified anchor-shaped unit cell is used to reach the circular polarizer function. The beamforming characteristic is realized by a particular design of the unit-phase distribution, which is obtained by varying the scale of the unit cell. Instead of using plane waves, a horn antenna is designed to feed the phase-variant FSS. The proposed two-layer FSS is fabricated and measured to verify the design. The measured results show that the proposed structure can convert the linearly polarized waves to circularly polarized waves. Compared with the feeding horn antenna, the transmitted beam of the FSS-added horn is 14.43° broader in one direction, while 3.77° narrower in the orthogonal direction. To our best knowledge, this is the first time to realize circular polarizer with beamforming as the extra function based on FSS, which is promising in satellite and communication systems for potential applications due to its simple design and good performance.

  6. A Circular Polarizer with Beamforming Feature Based on Frequency Selective Surfaces.

    PubMed

    Yin, Jia Yuan; Wan, Xiang; Ren, Jian; Cui, Tie Jun

    2017-01-27

    We propose a circular polarizer with beamforming features based on frequency selective surface (FSS), in which a modified anchor-shaped unit cell is used to reach the circular polarizer function. The beamforming characteristic is realized by a particular design of the unit-phase distribution, which is obtained by varying the scale of the unit cell. Instead of using plane waves, a horn antenna is designed to feed the phase-variant FSS. The proposed two-layer FSS is fabricated and measured to verify the design. The measured results show that the proposed structure can convert the linearly polarized waves to circularly polarized waves. Compared with the feeding horn antenna, the transmitted beam of the FSS-added horn is 14.43° broader in one direction, while 3.77° narrower in the orthogonal direction. To our best knowledge, this is the first time to realize circular polarizer with beamforming as the extra function based on FSS, which is promising in satellite and communication systems for potential applications due to its simple design and good performance.

  7. A Circular Polarizer with Beamforming Feature Based on Frequency Selective Surfaces

    PubMed Central

    Yin, Jia Yuan; Wan, Xiang; Ren, Jian; Cui, Tie Jun

    2017-01-01

    We propose a circular polarizer with beamforming features based on frequency selective surface (FSS), in which a modified anchor-shaped unit cell is used to reach the circular polarizer function. The beamforming characteristic is realized by a particular design of the unit-phase distribution, which is obtained by varying the scale of the unit cell. Instead of using plane waves, a horn antenna is designed to feed the phase-variant FSS. The proposed two-layer FSS is fabricated and measured to verify the design. The measured results show that the proposed structure can convert the linearly polarized waves to circularly polarized waves. Compared with the feeding horn antenna, the transmitted beam of the FSS-added horn is 14.43° broader in one direction, while 3.77° narrower in the orthogonal direction. To our best knowledge, this is the first time to realize circular polarizer with beamforming as the extra function based on FSS, which is promising in satellite and communication systems for potential applications due to its simple design and good performance. PMID:28128345

  8. Adaptive switching detection algorithm for iterative-MIMO systems to enable power savings

    NASA Astrophysics Data System (ADS)

    Tadza, N.; Laurenson, D.; Thompson, J. S.

    2014-11-01

    This paper attempts to tackle one of the challenges faced in soft input soft output Multiple Input Multiple Output (MIMO) detection systems, which is to achieve optimal error rate performance with minimal power consumption. This is realized by proposing a new algorithm design that comprises multiple thresholds within the detector that, in real time, specify the receiver behavior according to the current channel in both slow and fast fading conditions, giving it adaptivity. This adaptivity enables energy savings within the system since the receiver chooses whether to accept or to reject the transmission, according to the success rate of detecting thresholds. The thresholds are calculated using the mutual information of the instantaneous channel conditions between the transmitting and receiving antennas of iterative-MIMO systems. In addition, the power saving technique, Dynamic Voltage and Frequency Scaling, helps to reduce the circuit power demands of the adaptive algorithm. This adaptivity has the potential to save up to 30% of the total energy when it is implemented on Xilinx®Virtex-5 simulation hardware. Results indicate the benefits of having this "intelligence" in the adaptive algorithm due to the promising performance-complexity tradeoff parameters in both software and hardware codesign simulation.

  9. Spatially Common Sparsity Based Adaptive Channel Estimation and Feedback for FDD Massive MIMO

    NASA Astrophysics Data System (ADS)

    Gao, Zhen; Dai, Linglong; Wang, Zhaocheng; Chen, Sheng

    2015-12-01

    This paper proposes a spatially common sparsity based adaptive channel estimation and feedback scheme for frequency division duplex based massive multi-input multi-output (MIMO) systems, which adapts training overhead and pilot design to reliably estimate and feed back the downlink channel state information (CSI) with significantly reduced overhead. Specifically, a non-orthogonal downlink pilot design is first proposed, which is very different from standard orthogonal pilots. By exploiting the spatially common sparsity of massive MIMO channels, a compressive sensing (CS) based adaptive CSI acquisition scheme is proposed, where the consumed time slot overhead only adaptively depends on the sparsity level of the channels. Additionally, a distributed sparsity adaptive matching pursuit algorithm is proposed to jointly estimate the channels of multiple subcarriers. Furthermore, by exploiting the temporal channel correlation, a closed-loop channel tracking scheme is provided, which adaptively designs the non-orthogonal pilot according to the previous channel estimation to achieve an enhanced CSI acquisition. Finally, we generalize the results of the multiple-measurement-vectors case in CS and derive the Cramer-Rao lower bound of the proposed scheme, which enlightens us to design the non-orthogonal pilot signals for the improved performance. Simulation results demonstrate that the proposed scheme outperforms its counterparts, and it is capable of approaching the performance bound.

  10. MIMO Radar System for Respiratory Monitoring Using Tx and Rx Modulation with M-Sequence Codes

    NASA Astrophysics Data System (ADS)

    Miwa, Takashi; Ogiwara, Shun; Yamakoshi, Yoshiki

    The importance of respiratory monitoring systems during sleep have increased due to early diagnosis of sleep apnea syndrome (SAS) in the home. This paper presents a simple respiratory monitoring system suitable for home use having 3D ranging of targets. The range resolution and azimuth resolution are obtained by a stepped frequency transmitting signal and MIMO arrays with preferred pair M-sequence codes doubly modulating in transmission and reception, respectively. Due to the use of these codes, Gold sequence codes corresponding to all the antenna combinations are equivalently modulated in receiver. The signal to interchannel interference ratio of the reconstructed image is evaluated by numerical simulations. The results of experiments on a developed prototype 3D-MIMO radar system show that this system can extract only the motion of respiration of a human subject 2m apart from a metallic rotatable reflector. Moreover, it is found that this system can successfully measure the respiration information of sleeping human subjects for 96.6 percent of the whole measurement time except for instances of large posture change.

  11. A coherent through-wall MIMO phased array imaging radar based on time-duplexed switching

    NASA Astrophysics Data System (ADS)

    Chen, Qingchao; Chetty, Kevin; Brennan, Paul; Lok, Lai Bun; Ritchie, Matthiew; Woodbridge, Karl

    2017-05-01

    Through-the-Wall (TW) radar sensors are gaining increasing interest for security, surveillance and search and rescue applications. Additionally, the integration of Multiple-Input, Multiple-Output (MIMO) techniques with phased array radar is allowing higher performance at lower cost. In this paper we present a 4-by-4 TW MIMO phased array imaging radar operating at 2.4 GHz with 200 MHz bandwidth. To achieve high imaging resolution in a cost-effective manner, the 4 Tx and 4 Rx elements are used to synthesize a uniform linear array (ULA) of 16 virtual elements. Furthermore, the transmitter is based on a single-channel 4-element time-multiplexed switched array. In transmission, the radar utilizes frequency modulated continuous wave (FMCW) waveforms that undergo de-ramping on receive to allow digitization at relatively low sampling rates, which then simplifies the imaging process. This architecture has been designed for the short-range TW scenarios envisaged, and permits sufficient time to switch between antenna elements. The paper first outlines the system characteristics before describing the key signal processing and imaging algorithms which are based on traditional Fast Fourier Transform (FFT) processing. These techniques are implemented in LabVIEW software. Finally, we report results from an experimental campaign that investigated the imaging capabilities of the system and demonstrated the detection of personnel targets. Moreover, we show that multiple targets within a room with greater than approximately 1 meter separation can be distinguished from one another.

  12. MIMO Sliding Mode Control for a Tailless Fighter Aircraft, An Alternative to Reconfigurable Architectures

    NASA Technical Reports Server (NTRS)

    Wells, S. R.; Hess, R. A.

    2002-01-01

    A frequency-domain procedure for the design of sliding mode controllers for multi-input, multi-output (MIMO) systems is presented. The methodology accommodates the effects of parasitic dynamics such as those introduced by unmodeled actuators through the introduction of multiple asymptotic observers and model reference hedging. The design procedure includes a frequency domain approach to specify the sliding manifold, the observer eigenvalues, and the hedge model. The procedure is applied to the development of a flight control system for a linear model of the Innovative Control Effector (ICE) fighter aircraft. The stability and performance robustness of the resulting design is demonstrated through the introduction of significant degradation in the control effector actuators and variation in vehicle dynamics.

  13. Ultra-Wideband Massive MIMO Communications Using Multi-mode Antennas

    NASA Astrophysics Data System (ADS)

    Hoeher, P. A.; Manteuffel, D.; Doose, N.; Peitzmeier, N.

    2017-08-01

    An ultra-wideband system design is presented which supports wireless internet access and similar short-range applications with data rates of the order of 100 Gbps. Unlike concurrent work exploring the 60 GHz regime and beyond for this purpose, our focus is on the 6.0 -8.5 GHz frequency band. Hence, a bandwidth efficiency of about 50 bps/Hz is necessary. This sophisticated goal is targeted by employing two key enabling techniques: massive MIMO communications in conjunction with multi-mode antennas. This concept is suitable both for small-scale terminals like smartphones, as well as for powerful access points. Compared to millimeter wave and THz band communications, the 6.0 -8.5 GHz frequency band offers more robustness in NLOS scenarios and is more mature with respect to system components.

  14. Evolutionary time-series analysis reveals the signature of frequency-dependent selection on a female mating polymorphism.

    PubMed

    Le Rouzic, Arnaud; Hansen, Thomas F; Gosden, Thomas P; Svensson, Erik I

    2015-06-01

    A major challenge in evolutionary biology is understanding how stochastic and deterministic factors interact and influence macroevolutionary dynamics in natural populations. One classical approach is to record frequency changes of heritable and visible genetic polymorphisms over multiple generations. Here, we combined this approach with a maximum likelihood-based population-genetic model with the aim of understanding and quantifying the evolutionary processes operating on a female mating polymorphism in the blue-tailed damselfly Ischnura elegans. Previous studies on this color-polymorphic species have suggested that males form a search image for females, which leads to excessive mating harassment of common female morphs. We analyzed a large temporally and spatially replicated data set of between-generation morph frequency changes in I. elegans. Morph frequencies were more stable than expected from genetic drift alone, suggesting the presence of selection toward a stable equilibrium that prevents local loss or fixation of morphs. This can be interpreted as the signature of negative frequency-dependent selection maintaining the phenotypic stasis and genetic diversity in these populations. Our novel analytical approach allows the estimation of the strength of frequency-dependent selection from the morph frequency fluctuations around their inferred long-term equilibria. This approach can be extended and applied to other polymorphic organisms for which time-series data across multiple generations are available.

  15. An Adaptive Cooperative Strategy for Underlay MIMO Cognitive Radio Networks: An Opportunistic and Low-Complexity Approach

    NASA Astrophysics Data System (ADS)

    Mazoochi, M.; Pourmina, M. A.; Bakhshi, H.

    2015-03-01

    The core aim of this work is the maximization of the achievable data rate of the secondary user pairs (SU pairs), while ensuring the QoS of primary users (PUs). All users are assumed to be equipped with multiple antennas. It is assumed that when PUs are present, the direct communications between SU pairs introduces intolerable interference to PUs and thereby SUs transmit signal using the cooperation of other SUs and avoid transmitting in the direct channel. In brief, an adaptive cooperative strategy for multiple-input/multiple-output (MIMO) cognitive radio networks is proposed. At the presence of PUs, the issue of joint relay selection and power allocation in Underlay MIMO Cooperative Cognitive Radio Networks (U-MIMO-CCRN) is addressed. The optimal approach for determining the power allocation and the cooperating SU is proposed. Besides, the outage probability of the proposed communication protocol is further derived. Due to high complexity of the optimal approach, a low-complexity approach is further proposed and its performance is evaluated using simulations. The simulation results reveal that the performance loss due to the low-complexity approach is only about 14%, while the complexity is greatly reduced.

  16. Variable Resonance Frequency Selection for Fishbone-Shaped Microelectromechanical System Resonator Based on Multi-Physics Simulation

    NASA Astrophysics Data System (ADS)

    Kuroda, Shinjiro; Suzuki, Naoya; Tanigawa, Hiroshi; Suzuki, Kenichiro

    2013-06-01

    In this paper, we present and demonstrate the principle of variable resonance frequency selection by using a fishbone-shaped microelectromechanical system (MEMS) resonator. To analyze resonator displacement caused by an electrostatic force, a multi-physics simulation, which links the applied voltage load to the mechanical domain, is carried out. The simulation clearly shows that resonators are operated by three kinds of electrostatic force exerted on the beam. A new frequency selection algorithm that selects only one among various resonant modes is also presented. The conversion matrix that transforms the voltages applied to each driving electrode into the resonant beam displacement at each resonant mode is first derived by experimental measurements. Following this, the matrix is used to calculate a set of voltages for maximizing the rejection ratio in each resonant mode. This frequency selection method is applied in a fishbone-shaped MEMS resonator with five driving electrodes and the frequency selection among the 1st resonant mode to the 5th resonant mode is successfully demonstrated. From a fine adjustment of the voltage set, a 42 dB rejection ratio is obtained.

  17. Multiuser Detectors for MIMO DS/CDMA Systems

    DTIC Science & Technology

    2005-01-01

    input vector x̃ to yield the output b̂. The weight matrix W̃ is chosen to minimize the cost function JLMS = E ·°°°CHW̃H (n) x̃ (n)ÁL− b (n)°°°2¸ = E...Multiuser Detectors for MIMO DS/CDMA Systems Fang-Biau Ueng, Shang-Chun Tsai and Jun-Da Chen EE, NCHU, Taichung, Taiwan. E-mail: fbueng...cK is the spreading sequence of each user, respectively. We consider a MIMO channel with N transmitted and M received antennas. Assuming that

  18. Performance Evaluation Of Modified V-Blast In Mimo System

    NASA Astrophysics Data System (ADS)

    Suneetha, Ch.; Harathi, N.; Sudha, K.

    2012-03-01

    The MIMO system (multiple Antennas at the transmitter and receiver)is a capable of very high theoretical capacities, the most popular architecture is so called vertical VBLAST. VBLAST is an effective detection method for MIMO communication system, but has large computational complexity due its successive iteration . In this paper we used modified VBLAST to lessen its computational complexity reducing the number of successive iterations. As a result of this simplification, the computational complexity of the detection is lowered significantly. Simulation results show that the proposed V-BLAST reduces calculation complexity by about 30% while achieving a very close BER performance s the original one.

  19. Image reconstruction and compressive sensing in MIMO radar

    NASA Astrophysics Data System (ADS)

    Sun, Bing; Lopez, Juan; Qiao, Zhijun

    2014-05-01

    Multiple-input multiple-output (MIMO) radar utilizes the flexible configuration of transmitting and receiving antennas to construct images of target scenes. Because of the target scenes' sparsity, the compressive sensing (CS) technique can be used to realize a feasible reconstruction of the target scenes from undersampling data. This paper presents the signal model of MIMO radar and derive the corresponding CS measurement matrix, which shows success of the CS technique. Also the basis pursuit method and total-variation minimization method are adopted for different scenes' recovery. Numerical simulations are provided to illustrate the validity of reconstruction for one dimensional and two dimensional scenes.

  20. MIMO decorrelation for visible light communication based on angle optimization

    NASA Astrophysics Data System (ADS)

    Zhang, Haiyong; Zhu, Yijun

    2017-03-01

    Recently, many researchers have used the normal vector tilting to solve the problems about low rate of multiplexing and channel strong correlation in Visible Light Communication Multiple-Input Multiple-Output (VLC-MIMO) system, but they all lack of the theoretical support. In this paper, we establish a channel model about 2×2 VLC-MIMO, then translate the communication problem about vector tilting optimal angle in a certain range into a mathematical problem about seeking the minimum value of function. Finally, we deduced the mathematic expressions about the optimal tilting angles of corresponding LEDs and PDs, and these expressions will provide a theoretical basis for the further study.

  1. Frequency selective surfaces and metamaterials for high-power microwave applications

    NASA Astrophysics Data System (ADS)

    Liu, Chien-Hao

    In recent years, metamaterials have received a significant amount of attention for providing engineered artificial properties which do not exist in nature such as high surface impedance, negative permittivity/permeability, and negative refractive index. However, under high-power illuminations, metamaterials tend to breakdown and alter their frequency responses. This dissertation includes two parts. First, I investigate the phenomenon of electromagnetic (EM) waves tunneling through epsilon- and mu-negative metamaterial slabs and its potential applications in designing high-power filters and frequency selective surfaces without breakdown. The second part is to investigate breakdown events in high-power microwave metamaterials. In this thesis, I examine EM waves tunneling through multi-layer structures composed of epsilon-negative (the relative permittivity is negative) materials sandwiched by double positive layers. Conventionally, EM waves can only propagate through epsilon-negative material under certain circumstance referred to as resonant tunneling. I demonstrate that this EM waves tunneling phenomenon is analogous to a well-known classic microwave filter theory. Based on this analogy, I proposed a synthesis procedure for designing this kind of structure from desired responses which are beneficial for developing high-power-capable spatial filters and microwave FSSs. To verify the proposed procedure, three prototypes of such a device are designed, fabricated and experimentally characterized and it is demonstrated that they can handle extremely high peak power levels. In the second half of my thesis, I study the impact of breakdown on the responses of metamaterials by examining several single-layer metasurfaces composed of miniaturized LC resonators. I demonstrate that the breakdown events, in atmospheric air, can be characterized with a reasonable degree of accuracy by modeling the streaming discharge as a low-impedance connection path. My recent study shows that

  2. Forward-Masked Frequency Selectivity Improvements in Simulated and Actual Cochlear Implant Users Using a Preprocessing Algorithm

    PubMed Central

    Jürgens, Tim

    2016-01-01

    Frequency selectivity can be quantified using masking paradigms, such as psychophysical tuning curves (PTCs). Normal-hearing (NH) listeners show sharp PTCs that are level- and frequency-dependent, whereas frequency selectivity is strongly reduced in cochlear implant (CI) users. This study aims at (a) assessing individual shapes of PTCs in CI users, (b) comparing these shapes to those of simulated CI listeners (NH listeners hearing through a CI simulation), and (c) increasing the sharpness of PTCs using a biologically inspired dynamic compression algorithm, BioAid, which has been shown to sharpen the PTC shape in hearing-impaired listeners. A three-alternative-forced-choice forward-masking technique was used to assess PTCs in 8 CI users (with their own speech processor) and 11 NH listeners (with and without listening through a vocoder to simulate electric hearing). CI users showed flat PTCs with large interindividual variability in shape, whereas simulated CI listeners had PTCs of the same average flatness, but more homogeneous shapes across listeners. The algorithm BioAid was used to process the stimuli before entering the CI users’ speech processor or the vocoder simulation. This algorithm was able to partially restore frequency selectivity in both groups, particularly in seven out of eight CI users, meaning significantly sharper PTCs than in the unprocessed condition. The results indicate that algorithms can improve the large-scale sharpness of frequency selectivity in some CI users. This finding may be useful for the design of sound coding strategies particularly for situations in which high frequency selectivity is desired, such as for music perception. PMID:27604785

  3. An Approach to Near Field Data Selection in Radio Frequency Identification

    NASA Astrophysics Data System (ADS)

    Winkworth, Robert D.

    Personal identification is needed in many civil activities, and the common identification cards, such as a driver's license, have become the standard document de facto. Radio frequency identification has complicated this matter. Unlike their printed predecessors, contemporary RFID cards lack a practical way for users to control access to their individual fields of data. This leaves them more available to unauthorized parties, and more prone to abuse. Here, then was undertaken a means to test a novel RFID card technology that allows overlays to be used for reliable, reversible data access settings. Similar to other proposed switching mechanisms, it offers advantages that may greatly improve outcomes. RFID use is increasing in identity documents such as drivers' licenses and passports, and with it concern over the theft of personal information, which can enable unauthorized tracking or fraud. Effort put into designing a strong foundation technology now may allow for widespread development on them later. In this dissertation, such a technology was designed and constructed, to drive the central thesis that selective detuning could serve as a feasible, reliable mechanism. The concept had been illustrated effective in limiting access to all fields simultaneously before, and was here effective in limiting access to specific fields selectively. A novel card was produced in familiar dimensions, with an intuitive interface by which users may conceal the visible print of the card to conceal the wireless emissions it allows. A discussion was included of similar technologies, involving capacitive switching, that could further improve the outcomes if such a product were put to large-scale commercial fabrication. The card prototype was put to a battery of laboratory tests to measure the degree of independence between data fields and the reliability of the switching mechanism when used under realistically variable coverage, demonstrating statistically consistent performance in

  4. Metal-dielectric frequency-selective surface for high performance solar window coatings

    NASA Astrophysics Data System (ADS)

    Toor, Fatima; Guneratne, Ananda C.; Temchenko, Marina

    2016-03-01

    We demonstrate a solar control window film consisting of metallic nanoantennas designed to reflect infrared (IR) light while allowing visible light to pass through. The film consists of a capacitive frequency-selective surface (CFSS) which acts as a band-stop filter, reflecting only light at target wavelengths. The designed CFSS when installed on windows will lower air conditioning costs by reflecting undesired wavelengths of light and thus reduce the amount of heat that enters a building. State-of-the-art commercial solar control films consist of a multilayer stack which is costly ( 13/m2 to 40/m2) to manufacture and absorbs IR radiation, causing delamination or glass breakage when attached to windows. Our solar control film consists of a nanostructured metallic layer on a polyethylene terephthalate (PET) substrate that reflects IR radiation instead of absorbing it, solving the delamination problem. The CFSS is also easy to manufacture with roll-to-roll nanoimprint lithography at a cost of <$12/m2. We design the CFSS using the COMSOL Wave Optics module to solve for electromagnetic wave propagation in optical media via the finite element method. The simulation domain is reduced to a single unit cell with periodic boundary conditions to account for the symmetries of the planar, periodic CFSS. The design is optimized using parametric sweeps around the various geometric components of the metallic nanoantenna. Our design achieves peak reflection of 80% at 1000 nm and has a broadband IR response that will allow for optimum solar control without significantly affecting the transmission of visible light.

  5. Frequency-selective control of ferromagnetic resonance linewidth in magnetic multilayers

    NASA Astrophysics Data System (ADS)

    Schäfer, S.; Pachauri, N.; Mewes, C. K. A.; Mewes, T.; Kaiser, C.; Leng, Q.; Pakala, M.

    2012-01-01

    We report on a frequency-specific linewidth broadening of the ferromagnetic resonance (FMR) mode of a NiFe free layer within a magnetic multilayer stack. The FMR studies reveal a significant broadening of the FMR linewidth of the free layer at frequencies where this resonance is degenerate with FMR modes stemming from other layers within the multilayer stack. By pinning part of the magnetic multilayer to an antiferromagnet, we tailor a ferromagnetic linewidth behavior that is anisotropic for a specific frequency.

  6. Mimo Lms-Armax Identification of Vibrating STRUCTURES—PART i: the Method

    NASA Astrophysics Data System (ADS)

    Fassois, S. D.

    2001-07-01

    A comprehensive linear multi stage autoregressive moving average with exogenous excitation (LMS-ARMAX) method for effective multiple-input multiple-output (MIMO) structural dynamics identification in the presence of noise is introduced. The method consists of (a) a vector ARMAX representation of an appropriate form, (b) effective LMS parameter estimation, (c) statistical order selection/validation, and (d) a digital dispersion analysis (DA) methodology for effective modal characterization. The LMS-ARMAX method overcomes many of the difficulties that had rendered MIMO ARMAX identification difficult in the past, featuring modest computational complexity, high accuracy, guaranteed algorithmic and model stability, and thus applicability to higher-dimensional problems and lightly damped structures, accurate modal parameter extraction, and effective distinction of structural from 'extraneous' modes. A critical assessment of the LMS-ARMAX method under various noise conditions, as well as comparisons with a simpler ARX version and the ERA (Eigensystem Realization Algorithm), are undertaken based upon experimental vibration data obtained from a scale aircraft skeleton structure. The paper is divided into two parts: The LMS-ARMAX method is presented in the first, and its critical assessment and comparisons in the second.

  7. Accurate distortion estimation and optimal bandwidth allocation for scalable H.264 video transmission over MIMO systems.

    PubMed

    Jubran, Mohammad K; Bansal, Manu; Kondi, Lisimachos P; Grover, Rohan

    2009-01-01

    In this paper, we propose an optimal strategy for the transmission of scalable video over packet-based multiple-input multiple-output (MIMO) systems. The scalable extension of H.264/AVC that provides a combined temporal, quality and spatial scalability is used. For given channel conditions, we develop a method for the estimation of the distortion of the received video and propose different error concealment schemes. We show the accuracy of our distortion estimation algorithm in comparison with simulated wireless video transmission with packet errors. In the proposed MIMO system, we employ orthogonal space-time block codes (O-STBC) that guarantee independent transmission of different symbols within the block code. In the proposed constrained bandwidth allocation framework, we use the estimated end-to-end decoder distortion to optimally select the application layer parameters, i.e., quantization parameter (QP) and group of pictures (GOP) size, and physical layer parameters, i.e., rate-compatible turbo (RCPT) code rate and symbol constellation. Results show the substantial performance gain by using different symbol constellations across the scalable layers as compared to a fixed constellation.

  8. Efficient List Extension Algorithm Using Multiple Detection Orders for Soft-Output MIMO Detection

    NASA Astrophysics Data System (ADS)

    Kim, Kilhwan; Jung, Yunho; Lee, Seongjoo; Kim, Jaeseok

    This paper proposes an efficient list extension algorithm for soft-output multiple-input-multiple-output (soft-MIMO) detection. This algorithm extends the list of candidate vectors based on the vector selected by initial detection, in order to solve the empty-set problem, while reducing the number of additional vectors. The additional vectors are obtained from multiple detection orders, from which high-quality soft-output can be generated. Furthermore, a method to reduce the complexity of the determination of the multiple detection orders is described. From simulation results for a 4×4 system with 16- and 64-quadrature amplitude modulations (QAM) and rate 1/2 and 5/6 duo-binary convolutional turbo code (CTC), the soft-MIMO detection to which the proposed list extension was applied showed a performance degradation of less than 0.5dB at bit error rate (BER) of 10-5, compared to that of the soft-output maximum-likelihood detection (soft-MLD) for all code rate and modulation pairs, while the complexity of the proposed list extension was approximately 38% and 17% of that of an existing algorithm with similar performance in a 4×4 system using 16- and 64-QAM, respectively.

  9. Description of a parametric maximum likelihood estimator in the frequency domain for multi-input, multi-output systems and its application to flight flutter analysis

    NASA Astrophysics Data System (ADS)

    Guillaume, Patrick; Pintelon, Rik; Schoukens, Johan

    1990-09-01

    The basic formula of a parametric maximum likelihood estimator (MLE) in the frequency domain for multi-input, multi-output (MIMO) systems is given. The proposed method takes into account the perturbation noise on all the measured input and output signals. It is an extension to MIMO systems of the single-input, single-output (SISO) estimation method called ELiS (Estimation of Linear Systems). The MIMO estimator will be shown to determine more accurately the natural frequencies and damping ratios of mechanical structures than the SISO estimator. The estimators are applied to very noisy flight flutter data.

  10. A note on the change in gene frequency of a selected allele in partial full-sib mating populations

    SciTech Connect

    Caballero, A.

    1996-02-01

    The change in gene frequency of a selected allele in partial full-sib mating populations was analyzed. The implications of these papers is important in terms of the fixation probability of genes because, for the same equilibrium inbreeding coefficient, fixation rates of mutant genes would be larger for partial full-sib mating than for partial selfing. 4 refs.

  11. Comparative Study on the Selection Criteria for Fitting Flood Frequency Distribution Models with Emphasis on Upper-Tail Behavior

    NASA Astrophysics Data System (ADS)

    Xiaohong, C.

    2014-12-01

    Many probability distributions have been proposed for flood frequency analysis and several criteria have been used for selecting a best fitted distribution to an observed or generated data set by some random process. The upper tail of flood frequency distribution should be specifically concerned for flood control. However, different model selection criteria often result in different optimal distributions when focus on upper tail of flood frequency distribution. In this study, with emphasis on the upper-tail behavior, 5 distribution selection criteria including 2 hypothesis tests and 3 information-based criteria are evaluated in selecting the best fitted distribution from 8 widely used distributions (Pearson 3, Log-Pearson 3, two-parameter lognormal, three-parameter lognormal, Gumbel, Weibull, Generalized extreme value and Generalized logistic distributions) by using datasets from Thames River (UK), Wabash River (USA), Beijiang River and Huai River (China), which are all within latitude of 23.5-66.5 degrees north. The performance of the 5 selection criteria is verified by using a composite criterion focus on upper tail events defined in this study. This paper shows the approach for the optimal selection of suitable flood frequency distributions for different river basins. Results illustrate that (1) Different distributions are selected by using hypothesis tests and information-based criteria for each river. (2) The information-based criteria perform better than hypothesis tests in most cases when the focus is on the goodness of predictions of the extreme upper tail events. (3) In order to decide on a particular distribution to fit the high flow, it would be better to use the combination criteria, in which the information-based criteria can be used first to rank the models and the results are inspected by hypothesis testing methods. In addition, if the information-based criteria and hypothesis tests provide different results, the composite criterion will be taken for

  12. Effect of Electroacupuncture on the NTS is modulated primarily by acupuncture point selection and stimulation frequency in normal rats.

    PubMed

    Fang, Jun-Fan; Du, Jun-Ying; Shao, Xiao-Mei; Fang, Jian-Qiao; Liu, Zhe

    2017-03-31

    The effect of electroacupuncture (EA) is affected by both the acupuncture point selection and the frequency of stimulation. However, little is known regarding acupuncture point and simulation frequency selection. Neuronal activation of the nucleus of the solitary tract (NTS) is one of the important targets of EA for modulating gastrointestinal function. This study investigated the effects of various combinations of EA frequencies and acupuncture points on NTS neurons. Rats were randomly divided into normal, 2 Hz EA, 100 Hz EA and the alternate 2/100 Hz EA groups. Then rats in each group were randomly divided into the following two subgroups according to the acupuncture point: ST 36 group and ST 25 group. All the rats underwent electrode implantation surgery. Rats in all EA groups received one treatment with EA (a constant square wave at, 2 Hz,100 Hz or 2/100 Hz frequencies with intensities ranging from 1 to 2 mA), and NTS neuronal activation was recorded before and after EA treatment. Finally, to confirm the effect of EA on the NTS, minimal acupuncture was administered and its effect on NTS was detected. ST 36 stimulated with 2 Hz EA significantly increased the population of excited NTS neurons and spike frequency. However, ST 36 stimulated with 100 Hz or 2/100 Hz EA produced only a transient effect on the activity of NTS neurons and did not induce any effect on the spike frequency. Furthermore, the excitatory effect of 100 Hz or 2/100 Hz EA on NTS neurons in the ST 36 group was lower than 2 Hz EA at the same point. When applied to ST 25, 2 Hz EA had no significant excitatory effect on NTS neurons or spike frequency. However, 100 Hz EA or 2/100 Hz EA at ST 25 decreased both NTS neuronal excitability and spike frequency. By comparing the effects of different EA combinations, it was shown 2 Hz EA applied to ST 36 had the strongest excitatory effect on NTS neurons, while 100 Hz EA applied to ST 25 had the greatest inhibitory effect. Minimal

  13. Topology optimization design of a lightweight ultra-broadband wide-angle resistance frequency selective surface absorber

    NASA Astrophysics Data System (ADS)

    Sui, Sai; Ma, Hua; Wang, Jiafu; Pang, Yongqiang; Qu, Shaobo

    2015-06-01

    In this paper, the topology design of a lightweight ultra-broadband polarization-independent frequency selective surface absorber is proposed. The absorption over a wide frequency range of 6.68-26.08 GHz with reflection below -10 dB can be achieved by optimizing the topology and dimensions of the resistive frequency selective surface by virtue of genetic algorithm. This ultra-broadband absorption can be kept when the incident angle is less than 55 degrees and is independent of the incident wave polarization. The experimental results agree well with the numerical simulations. The density of our ultra-broadband absorber is only 0.35 g cm  -  3 and thus may find potential applications in microwave engineering, such as electromagnetic interference and stealth technology.

  14. On the existence in human auditory pathways of channels selectively tuned to the modulation present in frequency-modulated tones

    PubMed Central

    Kay, R. H.; Matthews, D. R.

    1972-01-01

    1. The sensitivity of detecting modulation in a test tone sinusoidally frequency-modulated at a rate ϕtest is diminished after exposure to a conditioning tone more deeply frequency-modulated at a rate ϕcond provided that ϕcond is not very different from ϕtest, the sound amplitude being kept constant for each tone at a comfortable hearing level 40-45 dB above threshold. 2. When ϕcond = ϕtest the frequency deviation in the modulated test tone must be increased to about three times the unconditioned threshold magnitude to be detectable immediately after exposure to the conditioning tone. Detection sensitivity returns to normal in about one minute. 3. At low modulation frequencies the conditioning effects are tuned, being much diminished when ϕcond differs from ϕtest by a few cycles per second. 4. Comparing monaural with contra-aural conditioning demonstrates a considerable interaural transfer of about 60-80% of the effect, indicating that the conditioning and its selectivity are predominantly central phenomena. 5. The magnitude of the deterioration in detection sensitivity after conditioning is about 3 × at modulation frequencies between about 3/sec and 30/sec. It diminishes at lower and higher modulation frequencies and is effectively absent at 100/sec modulation. The bandwidth of the effect increases from a few cycles per second at the lower end of this range, to some tens of cycles per second at the upper end. 6. For the same modulation frequency, the conditioning is relatively insensitive to the mean `carrier' audiofrequency, f0. The band width in terms of carrier frequency is at least as wide as `critical bands'. With a test signal f0 = 250 Hz, ϕtest = 8/sec, conditioning is still appreciable for a conditioning tone of ϕcond = 8/sec but centred upon f0 = 150 Hz or = 350 Hz. Conditioning is thus not explicable in terms of coincidences between particular spectral components in the conditioning and test tones. 7. Whereas the sensitivity of detecting 8/sec

  15. Conception and realization of a semiconductor based 240 GHz full 3D MIMO imaging system

    NASA Astrophysics Data System (ADS)

    Weisenstein, Christian; Kahl, Matthias; Friederich, Fabian; Haring Bolívar, Peter

    2017-02-01

    Multiple-input multiple-output (MIMO) imaging systems in the terahertz frequency range have a high potential in the field of non-destructive testing (NDT). With such systems it is possible to detect defects in composite materials, for example cracks or delaminations in fiber composites. To investigate mass-produced products it is necessary to study the objects in close to real-time on a conveyor without affecting the production cycle time. In this work we present the conception and realization of a 3D MIMO imaging system for in-line investigation of composite materials and structures. To achieve a lateral resolution of 1 mm, in order to detect such small defects in composite materials with a moderate number of elements, precise sensor design is crucial. In our approach we use the effective aperture concept. The designed sparse array consists of 32 transmitters and 30 receivers based on planar semiconductor components. High range resolution is achieved by an operating frequency between 220 GHz and 260 GHz in a stepped frequency continuous wave (SFCW) setup. A matched filter approach is used to simulate the reconstructed 3D image through the array. This allows the evaluation of the designed array geometry in regard of resolution and side lobe level. In contrast to earlier demonstrations, in which synthetic reconstruction is only performed in a 2D plane, an optics-free full 3D recon- struction has been implemented in our concept. Based on this simulation we designed an array geometry that enables to resolve objects with a resolution smaller than 1mm and moderate side lobe level.

  16. A novel control system for automatically locking a diode laser frequency to a selected gas absorption line

    NASA Astrophysics Data System (ADS)

    Dong, Lei; Yin, Wangbao; Ma, Weiguang; Jia, Suotang

    2007-05-01

    A novel control system has been developed for avoiding manual operation during traditional frequency locking. The control system uses a computer with a commercial data acquisition card. This accomplishes the whole operation of frequency locking, including generating ramp, searching locking point, engaging a proportional-integral-differential (PID) regulator at the proper time and outputting PID compensation signal. Moreover, a new method has also been employed to make the novel control system accurately identify the locking points of all absorption lines within the scanning range, so that the laser frequency can be automatically firmly brought onto any selected absorption line centre without any adjusting time. The operation of the system, the ability to identify absorption lines and the performance of the frequency locking were discussed in detail. Successful tests were made with two different lasers: external cavity diode lasers and distributed feedback diode lasers.

  17. Narrow-band injection seeding of a terahertz frequency quantum cascade laser: Selection and suppression of longitudinal modes

    SciTech Connect

    Nong, Hanond Markmann, Sergej; Hekmat, Negar; Jukam, Nathan; Pal, Shovon; Mohandas, Reshma A.; Dean, Paul; Li, Lianhe; Linfield, Edmund H.; Giles Davies, A.; Wieck, Andreas D.

    2014-09-15

    A periodically poled lithium niobate (PPLN) crystal with multiple poling periods is used to generate tunable narrow-bandwidth THz pulses for injection seeding a quantum cascade laser (QCL). We demonstrate that longitudinal modes of the quantum cascade laser close to the gain maximum can be selected or suppressed according to the seed spectrum. The QCL emission spectra obtained by electro-optic sampling from the quantum cascade laser, in the most favorable case, shows high selectivity and amplification of the longitudinal modes that overlap the frequency of the narrow-band seed. Proper selection of the narrow-band THz seed from the PPLN crystal discretely tunes the longitudinal mode emission of the quantum cascade laser. Moreover, the THz wave build-up within the laser cavity is studied as a function of the round-trip time. When the seed frequency is outside the maximum of the gain spectrum the laser emission shifts to the preferential longitudinal mode.

  18. Efficient hierarchical list decoder for massive optical MIMO transmission.

    PubMed

    Greenberg, Maxim; Nazarathy, Moshe; Orenstein, Meir

    2008-01-21

    We propose a novel MIMO scheme over multimode fiber, acting as a distributed random code generator fed by spatial codes, using silicon photonics in the transmitter and efficient list-based hierarchical submaximum-likelihood electronic detection in the receiver, providing an alternative to CWDM for implementation of ultra-high speed parallel transmission over short-range optical interconnects.

  19. Sparse Recovery Algorithms for Pilot Assisted MIMO OFDM Channel Estimation

    NASA Astrophysics Data System (ADS)

    Qi, Chenhao; Wu, Lenan

    In this letter, the sparse recovery algorithm orthogonal matching pursuit (OMP) and subspace pursuit (SP) are applied for MIMO OFDM channel estimation. A new algorithm named SOMP is proposed, which combines the advantage of OMP and SP. Simulation results based on 3GPP spatial channel model (SCM) demonstrate that SOMP performs better than OMP and SP in terms of normalized mean square error (NMSE).

  20. Time-Domain Receiver Design for MIMO Underwater Acoustic Communications

    DTIC Science & Technology

    2008-09-01

    is also estimated with LFM signal by measuring the span of the LFM correlation main ridge [20]. It’s shown that for all MIMO subchannels , most of the...Obviously, over the de- picted delay spread of 15 ms, each of the subchannels contains two CIR peaks located at 2 ms and 6 ms, respectively, and we chose 10

  1. User-scheduling algorithm for a MU-MIMO system

    NASA Astrophysics Data System (ADS)

    Yu, Haiyang; Choi, Jaeho

    2015-12-01

    A user-scheduling algorithm for MU-MIMO systems is presented in this paper. The algorithm is a codebook based precoding method which can be suitable for the IEEE 802.16m mobile broadband standard. The proposed algorithm can effectively improve the sum capacity and fairness among the users.

  2. A multi-frequency study of an X ray selected sample of active galactic nuclei

    NASA Astrophysics Data System (ADS)

    Grossan, Bruce Alan

    1992-01-01

    The LASS (Large Area Sky Survey) experiment, which flew aboard the HEAO-1 spacecraft, carried out a 2-20 keV survey of the sky during 1977-1978. The X-ray sources from this survey make up the LASS catalog (Wood et al. 1979). Optical counterparts have been identified for greater than 86 percent of the LASS sources above a flux of approx. 0.95 microns (mu)Jy Q 5 keV (Remillard 1992b). The LASS error boxes, along with the more precise positions from the Modulation Collimator (MC) X-ray experiment (also aboard HEAO-1), subsequent X-ray imaging, and optical search techniques were all used to identify the LASS sources. From these identifications, a high-latitude (absolute value of b greater than 20 deg.), flux limited (greater than or equal to 0.95 (mu)Jy) sample of 96 emission line Active Galactic Nuclei (AGN) have been selected for study. The sample is referred to as the LMA (for the LASS/MC identified sample of AGN). The objective of this work is to produce multi-frequency spectra of this sample of objects, in order to determine and interpret the statistical properties of the sample over nearly the full range of observable wavelengths. Data were obtained for as much of the radio through hard X-ray (less than 20 keV) spectrum as possible for each object in the LMA. Radio, near infrared, and other measurements were taken from the literature, far IR fluxes were extracted from co-added observations from IRAS, UV spectra were obtained from the IUE archives, and original observations were performed (with the help of collaborators) in the radio, near IR, optical, UV, and X-ray to fulfill this goal. Correlation studies of the continuum bands found poor correlations of X-ray and radio flux, good correlations for 12 and 26 micron flux with X-ray flux, excellent correlations for optical and near IR fluxes with X-rays, and poor correlations of UV and X-ray fluxes. Correlation studies of the line and X-ray continuum flux yield a good correlation between the flux of (OIII), the

  3. Identifying the selectivity of antimicrobial peptides to cell membranes by sum frequency generation spectroscopy.

    PubMed

    Golbek, Thaddeus W; Franz, Johannes; Elliott Fowler, J; Schilke, Karl F; Weidner, Tobias; Baio, Joe E

    2017-05-05

    Cationic amphiphilic peptides have been engineered to target both Gram-positive and Gram-negative bacteria while avoiding damage to other cell types. However, the exact mechanism of how these peptides target, bind, and disrupt bacterial cell membranes is not understood. One specific peptide that has been engineered to selectively capture bacteria is WLBU2 (sequence: RRWVRRVRRWVRRVVRVVRRWVRR). It has been suggested that WLBU2 activity stems from the fact that when interacting with bacterial cell membranes the peptide assumes an α-helical structure and inserts itself into the membrane. Alternatively, in the presence of mammalian cell membranes, the peptide assumes an inert β-sheet structure. To test this hypothesis, the authors applied sum frequency generation (SFG) spectroscopy and surface tensiometry to identify the structure of WLBU2 as it interacts with model lipid monolayers that mimic mammalian and bacterial cell membranes. Model mammalian cell membranes were built upon zwitterionic 1,2-dipalmitoyl-sn-glycero-3-phosphocholine lipids while bacterial cell membranes were constructed with negatively charged 1,2-dimyristoyl-sn-glycero-3-phospho-(1'-rac-glycerol) lipids. Observed changes in surface pressure at the peptide-lipid-air interface demonstrate that the peptide has a clear binding preference toward negatively charged bacteria-like lipids. The structure of both the lipids and peptides were characterized by SFG spectra collected at the monolayer interface. Changes in monolayer structure as the peptide binds were observed by tracking the intensities of SFG vibrational modes related to the acyl chains within the lipids. Peptide structures when bound to both types of lipids were determined by SFG spectra collected within the amide I vibrational band. The SFG spectra of WLBU2 interacting with the model mammalian lipid monolayer contain two peaks near 1642 and 1678 cm(-1) indicative of an inactive β-sheet structure. SFG spectra collected from the peptide bound

  4. High frequency of donor chimerism after allogeneic transplantation of CD34+-selected peripheral blood cells.

    PubMed

    Briones, J; Urbano-Ispizua, A; Lawler, M; Rozman, C; Gardiner, N; Marín, P; Salgado, C; Féliz, P; McCann, S; Montserrat, E

    1998-05-01

    Ex vivo T cell depletion of allogeneic grafts is associated with a high (up to 80%) rate of mixed chimerism (MC) posttransplantation. The number of transplanted progenitor cells is an important factor in achieving complete donor chimerism in the T cell depletion setting. Use of granulocyte colony-stimulating factor (G-CSF) peripheral blood allografts allows the administration of large numbers of CD34+ cells. We studied the chimeric status of 13 patients who received allogeneic CD34+-selected peripheral blood progenitor cell transplants (allo-PBPCTs/CD34+) from HLA-identical sibling donors. Patients were conditioned with cyclophosphamide (120 mg/kg) and total-body irradiation (13 Gy in four fractions). Apheresis products were T cell-depleted by the immunoadsorption avidin-biotin method. The median number of CD34+ and CD3+ cells infused was 2.8x10(6)/kg (range 1.9-8.6x10(6)/kg) and 0.4x10(6)/kg (range 0.3-1x10(6)/kg), respectively. Molecular analysis of the engraftment was performed using polymerase chain reaction (PCR) amplification of highly polymorphic short tandem repeat (PCR-STR) sequences in peripheral blood samples. MC was detected in two (15%) of 13 patients. These two patients relapsed at 8 and 10 months after transplant, respectively. The remaining 11 patients showed complete donor chimerism and were in clinical remission after a maximum follow-up period of 24 months (range 6-24 months). These results were compared with those obtained in 10 patients who were treated with T cell-depleted bone marrow transplantation by means of elutriation and who received the same conditioning treatment and similar amounts of CD3+ cells (median 0.45x10(6)/kg; not significant) but a lower number of CD34+ cells (median 0.8x10(6)/kg; p = 0.001). MC was documented in six of 10 patients (60%), which was significantly higher than in the allo-PBPCT/CD34+ group (p = 0.04). We conclude that a high frequency of complete donor chimerism is achieved in patients receiving allo-PBPCT/CD34

  5. Frequency component selection for an ECoG-based brain-computer interface.

    PubMed

    Scherer, R; Graimann, B; Huggins, J E; Levine, S P; Pfurtscheller, G

    2003-01-01

    The aim of the present study was to investigate the most significant frequency components in electrocorticogram (ECoG) recordings in order to operate a brain computer interface (BCI). For this purpose the time-frequency ERD/ERS map and the distinction sensitive learning vector quantization (DSLVQ) are applied to ECoG from three subjects, recorded during a self-paced finger movement. The results show that the ERD/ERS pattern found in ECoG generally matches the ERD/ERS pattern found in EEG recordings, but has an increased prevalence of frequency components in the beta range.

  6. Frequency-selectivity of a thalamocortical relay neuron during Parkinson's disease and deep brain stimulation: a computational study.

    PubMed

    Cagnan, Hayriye; Meijer, Hil G E; van Gils, Stephan A; Krupa, Martin; Heida, Tjitske; Rudolph, Michelle; Wadman, Wytse J; Martens, Hubert C F

    2009-10-01

    In this computational study, we investigated (i) the functional importance of correlated basal ganglia (BG) activity associated with Parkinson's disease (PD) motor symptoms by analysing the effects of globus pallidus internum (GPi) bursting frequency and synchrony on a thalamocortical (TC) relay neuron, which received GABAergic projections from this nucleus; (ii) the effects of subthalamic nucleus (STN) deep brain stimulation (DBS) on the response of the TC relay neuron to synchronized GPi oscillations; and (iii) the functional basis of the inverse relationship that has been reported between DBS frequency and stimulus amplitude, required to alleviate PD motor symptoms [A. L. Benabid et al. (1991)Lancet, 337, 403-406]. The TC relay neuron selectively responded to and relayed synchronized GPi inputs bursting at a frequency located in the range 2-25 Hz. Input selectivity of the TC relay neuron is dictated by low-threshold calcium current dynamics and passive membrane properties of the neuron. STN-DBS prevented the TC relay neuron from relaying synchronized GPi oscillations to cortex. Our model indicates that DBS alters BG output and input selectivity of the TC relay neuron, providing an explanation for the clinically observed inverse relationship between DBS frequency and stimulus amplitude.

  7. MimoPro: a more efficient Web-based tool for epitope prediction using phage display libraries

    PubMed Central

    2011-01-01

    Background A B-cell epitope is a group of residues on the surface of an antigen which stimulates humoral responses. Locating these epitopes on antigens is important for the purpose of effective vaccine design. In recent years, mapping affinity-selected peptides screened from a random phage display library to the native epitope has become popular in epitope prediction. These peptides, also known as mimotopes, share the similar structure and function with the corresponding native epitopes. Great effort has been made in using this similarity between such mimotopes and native epitopes in prediction, which has resulted in better outcomes than statistics-based methods can. However, it cannot maintain a high degree of satisfaction in various circumstances. Results In this study, we propose a new method that maps a group of mimotopes back to a source antigen so as to locate the interacting epitope on the antigen. The core of this method is a searching algorithm that is incorporated with both dynamic programming (DP) and branch and bound (BB) optimization and operated on a series of overlapping patches on the surface of a protein. These patches are then transformed to a number of graphs using an adaptable distance threshold (ADT) regulated by an appropriate compactness factor (CF), a novel parameter proposed in this study. Compared with both Pep-3D-Search and PepSurf, two leading graph-based search tools, on average from the results of 18 test cases, MimoPro, the Web-based implementation of our proposed method, performed better in sensitivity, precision, and Matthews correlation coefficient (MCC) than both did in epitope prediction. In addition, MimoPro is significantly faster than both Pep-3D-Search and PepSurf in processing. Conclusions Our search algorithm designed for processing well constructed graphs using an ADT regulated by CF is more sensitive and significantly faster than other graph-based approaches in epitope prediction. MimoPro is a viable alternative to both

  8. Phonotactic selectivity in two cryptic species of gray treefrogs: effects of differences in pulse rate, carrier frequency and playback level.

    PubMed

    Gerhardt, H Carl

    2008-08-01

    The two main spectral components of the advertisement calls of two species of North American gray treefrogs (Hyla chrysoscelis and H. versicolor) overlap broadly in frequency, and the frequency of each component matches the sensitivity of one of the two different auditory inner ear organs. The calls of the two species differ in the shape and repetition rate (pulse rate) of sound pulses within trills. Standard synthetic calls with one of these spectral peaks and the pulse rate typical of conspecific calls were tested against synthetic alternatives that had the same spectral peak but a different pulse rate. The results were generalized over a wide range of playback levels. Selectivity based on differences in pulse rate depended on which spectral peak was used in some tests, and greater pulse-rate selectivity was usually observed when the low-frequency rather than the high-frequency peak was used. This effect was more pronounced and occurred over a wider range of playback levels in H. versicolor than in H. chrysoscelis when the pulse rate of the alternative was higher than that of the standard call. In tests at high playback levels with an alternative of 15 pulses s(-1), however, females of H. versicolor showed greater selectivity for the standard call when the high-frequency rather than the low-frequency spectral peak was used. This last result may reflect the different ways in which females of the two species assess trains of pulses, and the broad implications for understanding the underlying auditory mechanisms are discussed.

  9. Frequency selection mechanisms in the flow of a laminar boundary layer over a shallow cavity

    NASA Astrophysics Data System (ADS)

    Qadri, Ubaid Ali; Schmid, Peter J.

    2017-01-01

    We investigate the flow over shallow cavities as a representative configuration for modeling small surface irregularities in wall-bounded shear flows. Due to the globally stable nature of the flow, we perform a frequency response analysis, which shows a significant potential for the amplification of disturbance kinetic energy by harmonic forcing within a certain frequency band. Shorter and more shallow cavities exhibit less amplified responses, while energy from the base flow can be extracted predominantly from forcing that impacts the cavity head on. A structural sensitivity analysis, combined with a componentwise decomposition of the sensitivity tensor, reveals the regions of the flow that act most effectively as amplifiers. We find that the flow inside the cavity plays a negligible role, whereas boundary layer modifications immediately upstream and downstream of the cavity edges contribute significantly to the frequency response. The same regions constitute preferred locations for implementing active or passive control strategies to manipulate the frequency response of the flow.

  10. A Study on Trained and Differential Designs for MIMO Tactical Communications

    DTIC Science & Technology

    2008-09-29

    REPORT A Study on Trained and Differential Designs for MIMO Tactical Communications 14. ABSTRACT 16. SECURITY CLASSIFICATION OF: During the project...From - To) 6-Apr-2006 Standard Form 298 (Rev 8/98) Prescribed by ANSI Std. Z39.18 - 5-Apr-2008 A Study on Trained and Differential Designs for MIMO ...Military Communications Conference, Orlando, FL, Oct. 29-31, 2007. [4] W. Zhang and X. Ma, "A Suboptimal equalizer for MIMO systems to guarantee maximum

  11. Error Rate Improvement in Underwater MIMO Communications Using Sparse Partial Response Equalization

    DTIC Science & Technology

    2006-09-01

    multiple transmitters and receivers or MIMO ( multiple input , multiple output ) configura- tions and associated signal processing at the... input multiple output ( MIMO ) ISI channels has been proposed in [2], where the authors have designed a MIMO PRE based on the MMSE criterion. The target...soft input , soft output channel detector (usually the maximum a-posteriori probability (MAP) detector) is used to detect the channel symbols which

  12. Multi-Input Multi-Output (MIMO) Radar - Diversity Means Superiority

    DTIC Science & Technology

    2008-10-15

    SISO) radar range-Doppler imaging and multiple - input multiple - output ( MIMO ) synthetic aperture radar (SAR) imaging as well as in space time adaptive...January 2008. A multi- input multi- output ( MIMO ) radar system, unlike standard phased-array radar, can transmit via its antennas multiple probing signals...15-10-2008 Annual Report Nov. 2007 - Oct. 2008 4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER Multi- Input Multi- Output ( MIMO ) Radar - Diversity Means

  13. On the Throughput of MIMO-Empowered Multi-hop Cognitive Radio Networks

    DTIC Science & Technology

    2010-01-01

    Senior Member, IEEE, and Sastry Kompella, Member, IEEE Abstract—Cognitive radio (CR) and multiple - input multiple - output ( MIMO ) are two independent physical...2011, Issue to be determined. 14. ABSTRACT Cognitive radio (CR) and multiple - input multiple - output ( MIMO ) are two independent physical layer...1 On the Throughput of MIMO -Empowered Multi-hop Cognitive Radio Networks Cunhao Gao, Student Member, IEEE, Yi Shi, Member, IEEE, Y. Thomas Hou

  14. Multi-Input Multi-Output (MIMO) Radar - Diversity Means Superiority

    DTIC Science & Technology

    2009-10-01

    multiple - input multiple - output ( MIMO ) radar system, unlike a standard phased-array radar, can...Office of Naval Research Grant No. N00014-07-1-0293 November 2006 - October 2009 20091117236 1. Summary A multiple - input multiple - output ( MIMO ...Processing, Vol. 55, No. 6, pp. 2375-2385, June 2007. We consider a multiple - input multiple - output ( MIMO ) radar system where both the transmitter

  15. Advanced Multiple In-Multiple Out (MIMO) Antenna Communications for Airborne Networks

    DTIC Science & Technology

    2015-03-01

    ADVANCED MULTIPLE IN-MULTIPLE OUT (MIMO) ANTENNA COMMUNICATIONS FOR AIRBORNE NETWORKS SYRACUSE UNIVERSITY MARCH 2015 FINAL TECHNICAL REPORT...COMMUNICATIONS FOR AIRBORNE NETWORKS 5a. CONTRACT NUMBER FA8750-11-1-0040 5b. GRANT NUMBER N/A 5c. PROGRAM ELEMENT NUMBER 62788F 6. AUTHOR(S) Biao Chen...MIMO system with over the air transmission. 15. SUBJECT TERMS Multiple In-Multiple Out (MIMO Antenna Communications, Airborne Networks , D-BLAST

  16. Selective ensemble modeling load parameters of ball mill based on multi-scale frequency spectral features and sphere criterion

    NASA Astrophysics Data System (ADS)

    Tang, Jian; Yu, Wen; Chai, Tianyou; Liu, Zhuo; Zhou, Xiaojie

    2016-01-01

    It is difficult to model multi-frequency signal, such as mechanical vibration and acoustic signals of wet ball mill in the mineral grinding process. In this paper, these signals are decomposed into multi-scale intrinsic mode functions (IMFs) by the empirical mode decomposition (EMD) technique. A new adaptive multi-scale spectral features selection approach based on sphere criterion (SC) is applied to these IMFs frequency spectra. The candidate sub-models are constructed by the partial least squares (PLS) with the selected features. Finally, the branch and bound based selective ensemble (BBSEN) algorithm is applied to select and combine these ensemble sub-models. This method can be easily extended to regression and classification problems with multi-time scale signal. We successfully apply this approach to a laboratory-scale ball mill. The shell vibration and acoustic signals are used to model mill load parameters. The experimental results demonstrate that this novel approach is more effective than the other modeling methods based on multi-scale frequency spectral features.

  17. A scheme for noise suppression and spectral enhancement of speech to alleviate speech reception problems from loss of frequency selectivity

    NASA Astrophysics Data System (ADS)

    Lyzenga, Johannes; Festen, Joost M.; Houtgast, Tammo

    2002-05-01

    Even after sufficient amplification, hearing-impaired listeners often experience problems in understanding speech under noisy conditions. This may be caused by suprathreshold deficits such as loss of compression and reduced frequency selectivity. In this project we investigate a scheme in which speech and noise are processed before presentation to try and alleviate intelligibility problems caused by reduced frequency selectivity. The scheme contains three strategies, one in which the peak-to-valley ratios of selected modulations in the speech spectrum are enlarged, a second in which the overall speech spectrum is modified, and a third in which noise is suppressed before the two enhancement steps. An overlap-and-add (OLA) algorithm is used in the implementation. The effect of the speech processing is evaluated by measuring speech-reception thresholds (SRT) for sentences in speech noise, estimating the signal-to-noise ratio at which listeners can correctly reproduce 50% of presented sentences. Hearing-impaired and normal-hearing listeners were used. To simulate the hearing impairment resulting from a loss of frequency selectivity, we spectrally smeared the stimuli presented to the normal-hearing listeners. We found that the preprocessing scheme achieved a modest improvement of nearly 2 dB in the SRT for normal-hearing listeners. Data for hearing-impaired listeners are presently being collected.

  18. A Novel Nonlinear Precoding Detection Algorithm for VBLAST in MIMO-MC-CDMA Downlink System

    NASA Astrophysics Data System (ADS)

    Fu, Hongliang; Tao, Yong

    Considering the error propagation effect and high complexity of the Vertical Bell Labs Layered Space Time (V-BLAST), a novel nonlinear ZF-THP algorithm for VBLAST in MIMO-MC-CDMA downlink system is proposed in this paper. QR decomposition is used for precoding matrix, the nonlinear Tomlinson-Harashima Precoding (THP) is used between the sub-carrier channels of MC-CDMA to eliminate interference from other signals at the transmitter, and can obtain frequency diversity gain and eliminate effectively the error propagation effect. At the receiver, zero forcing criterion is used, and the complexity of the receiver can be reduced. Simulation results show that the proposed algorithm is better than the traditional zero forcing algorithm and the linear precoding algorithm in the system BER.

  19. PMD tolerant direct-detection polarization division multiplexed OFDM systems with MIMO processing.

    PubMed

    Wei, Chia-Chien; Lin, Chun-Ting; Wang, Chih-Yun

    2012-03-26

    This work proposes a novel direct-detection polarization division multiplexed OFDM scheme without the need of dynamic polarization control at a polarization-diverse receiver, and the proposed scheme is robust against polarization mode dispersion. Setting the frequency difference between two polarization-orthogonal reference carriers as one subcarrier spacing, possible signal fading can be avoided, and the corresponding interference from adjacent subcarriers is eliminated by a novel MIMO algorithm. The penalty caused by high channel matrix condition number can be decreased by inserting empty tones among subcarriers, and the polarization-dependent OSNR penalty at the BER of 10⁻³ is <3.6 dB with an empty tone inserted every 8 subcarriers. Moreover, the numerical results demonstrate the 16 × 10³-ps/nm chromatic dispersion and the 300-ps differential group delay will not induce additional penalty.

  20. Different spatial frequency bands selectively signal for natural image statistics in the early visual system.

    PubMed

    Hansen, Bruce C; Johnson, Aaron P; Ellemberg, Dave

    2012-10-01

    Early visual evoked potentials (VEPs) measured in humans have recently been observed to be modulated by the image statistics of natural scene imagery. Specifically, the early VEP is dominated by a strong positivity when participants view minimally complex natural scene imagery, with the magnitude of that component being modulated by luminance contrast differences across spatial frequency (i.e., the slope of the amplitude spectrum). For scenes high in structural complexity, the early VEP is dominated by a prominent negativity that exhibits little dependency on luminance contrast. However, since natural scene imagery is broad band in terms of spatial frequency, it is not known whether the above-mentioned modulation results from a complex interaction within or between the early neural processes tuned to different bands of spatial frequency. Here, we sought to address this question by measuring early VEPs (specifically, the C1, P1, and N1 components) while human participants viewed natural scene imagery that was filtered to contain specific bands of spatial frequency information. The results show that the C1 component is largely unmodulated by the luminance statistics of natural scene imagery (being only measurable when such stimuli were made to contain high spatial frequencies). The P1 and N1, on the other hand, were observed to exhibit strong spatial frequency-dependent modulation to the luminance statistics of natural scene imagery. The results therefore suggest that the dependency of early VEPs on natural image statistics results from an interaction between the early neural processes tuned to different bands of spatial frequency.