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Array Size (array + size)

Distribution by Scientific Domains
Engineering50%

Selected Abstracts

Number sense in human infants

DEVELOPMENTAL SCIENCE, Issue 1 2005
Fei Xu
Four experiments used a preferential looking method to investigate 6-month-old infants' capacity to represent numerosity in visual-spatial displays. Building on previous findings that such infants discriminate between arrays of eight versus 16 discs, but not eight versus 12 discs (Xu & Spelke, 2000), Experiments 1 and 2 investigated whether infants' numerosity discrimination depends on the ratio of the two set sizes with even larger numerosities. Infants successfully discriminated between arrays of 16 versus 32 discs, but not 16 versus 24 discs, providing evidence that their discrimination shows the set-size ratio signature of numerosity discrimination in human adults, children and many non-human animals. Experiments 3 and 4 addressed a controversy concerning infants' ability to discriminate large numerosities (observed under conditions that control for total filled area, array size and density, item size and correlated properties such as brightness: Brannon, 2002; Xu, 2003b; Xu & Spelke, 2000) versus small numerosities (not observed under conditions that control for total contour length: Clearfield & Mix, 1999). To investigate the sources of these differing findings, Experiment 3 tested infants' large-number discrimination with controls for contour length, and Experiment 4 tested small-number discrimination with controls for total filled area. Infants successfully discriminated the large-number displays but showed no evidence of discriminating the small-number displays. These findings provide evidence that infants have robust abilities to represent large numerosities. In contrast, infants may fail to represent small numerosities in visual-spatial arrays with continuous quantity controls, consistent with the thesis that separate systems serve to represent large versus small numerosities. [source]

Cholinergic modulation of visuospatial responding in central thalamus

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 12 2007
Lori A. Newman
Abstract Central thalamus has extensive connections with basal ganglia and frontal cortex that are thought to play a critical role in sensory-guided goal-directed behavior. Central thalamic activity is influenced by cholinergic projections from mesopontine nuclei. To elucidate this function we trained rats to respond to lights in a reaction time (RT) task and compared effects of muscarinic (2.4, 7.3, 22 nmol scopolamine) and nicotinic (5.4, 16, 49, 98 nmol mecamylamine) antagonists with the GABAA agonist muscimol (0.1, 0.3, 1.0 nmol) in central thalamus. We compared this with subcutaneous (systemic) effects of mecamylamine (3.2, 9.7, 29 µmol/kg) and scopolamine (0.03, 0.09, 0.26 µmol/kg). Subcutaneous scopolamine increased omissions (failure to respond within a 3-s response window) at the highest dose tested. Subcutaneous mecamylamine increased omissions at the highest dose tested while impairing RT and per cent correct at lower doses. Intrathalamic injections of muscimol and mecamylamine decreased per cent correct at doses that did not affect omissions or RT. Intrathalamic scopolamine increased omissions and RT at doses that had little effect on per cent correct. Anatomical controls indicated that the effects of mecamylamine were localized in central thalamus and those of scopolamine were not. Drug effects did not interact with attention-demanding manipulations of stimulus duration, proximity of stimulus and response locations, or stimulus array size. These results are consistent with the hypothesis that central thalamus mediates decisional processes linking sensory stimuli with actions, downstream from systems that detect sensory signals. They also provide evidence that this function is specifically influenced by nicotinic cholinergic receptors. [source]

Fractionally spaced spatial adaptive equalization of S-UMTS mobile terminals,

INTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 8 2002
Jörgen Nordberg
Abstract In this paper we present fractionally spaced adaptive equalization techniques and space diversity combined receiver and evaluate their performance for the downlink of S-UMTS system. The conventional ,training' (or non-blind) and the ,unsupervised' (or blind) adaptive equalization algorithms are both investigated. Simulation results show that the equalizers are robust to Doppler shift and non-linearity effects due to TWT amplifiers aboard the satellite. It is also shown that even with a moderate array size of two antenna elements, a significant improvement in terminal performance is achieved. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Adaptive joint beamforming and B-MMSE detection for CDMA signal reception under multipath interference

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 7 2004
Hsiao-Hwa Chen
Abstract The combination of antenna array beamforming with multiuser detection can effectively improve the detection efficiency of a wireless system under multipath interference, especially in a fast-fading channel. This paper studies the performance of an adaptive beamformer incorporated with a block-wise minimum mean square error(B-MMSE) detector, which works on a unique signal frame characterized by training sequence preamble and data blocks segmented by zero-bits. Both beam-former weights updating and B-MMSE detection are carried out by either least mean square (LMS) or recursive least square (RLS) algorithm. The comparison of the two adaptive algorithms applied to both beamformer and B-MMSE detector will be made in terms of convergence behaviour and estimation mean square error. Various multipath patterns are considered to test the receiver's responding rapidity to changing multipath interference. The performance of the adaptive B-MMSE detector is also compared with that of non-adaptive version (i.e. through direct matrix inversion). The final performance in error probability simulation reveals that the RLS/B-MMSE scheme outperforms non-adaptive B-MMSE by 1,5 dB, depending on the multipath channel delay profiles of concern. The obtained results also suggest that adaptive beamformer should use RLS algorithm for its fast and robust convergence property; while the B-MMSE filter can choose either LMS or RLS algorithm depending on antenna array size, multipath severity and implementation complexity. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Digital imaging in transmission electron microscopy

JOURNAL OF MICROSCOPY, Issue 1 2000
G. Y. Fan
The digital revolution currently under way, as evidenced by the rapid development of the Internet and the world-wide-web technologies, is undoubtedly impacting the field of transmission electron microscopy (TEM). Digital imaging systems based on charge-coupled device (CCD) technologies, with pixel array size up to 2 k × 2 k at the present and increasing, are available for TEM applications and offer many attractions. Is it time to phase out film cameras on TEMs and close the darkrooms for good? This paper reviews digital imaging technologies for TEM at different voltages, and contrasts the performance of digital imaging systems with that of TEM film. The performance characteristics of CCD-based digital imaging systems, as well as methods for assessing them, are discussed. Other approaches to digital imaging are also briefly reviewed. [source]

Investigating the performance of MIMO systems from an electromagnetic perspective

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 7 2006
Marek E. Bialkowski
Abstract Multiple input multiple output (MIMO) wireless systems use multiple element antennas (MEAs) at the transmitter (TX) and the receiver (RX) in order to offer improved information rates (capacity) over conventional single antenna systems in rich scattering environments. In this paper, an example of a simple MIMO system is considered in which both antennas and scattering objects are formed by wire dipoles. Such a system can be analyzed in the strict electromagnetic (EM) sense and its capacity can be determined for varying array size, interelement spacing, and distributions of scatterers. The EM model of this MIMO system can be used to assess the validity of single- or double-bounce scattering models for mixed line of sight (LOS) and non-line of sight (NLOS) signal-propagation conditions. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 1233,1238, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21664 [source]