FREQUENCY SELECTIVE SURFACE WITH DUAL BAND SWITCHABLE REFLECTION AND TRANSMISSION CHARACTERISTICS

A pin diode-loaded active doubly periodic flat strip FSS is shown to act as a dynamic screen. It is shown that by means of d.c. bias control, we can utilize the screen in, (1) transmission mode as a dual band electromagnetic shutter, or with the inclusion of a ground plane in reflection mode, (is (2) it dual band refection canceller. (3) an amplitude shift keying (ASK) spatial modulator. The properties of the FSS are characterized using a specially designed parallel plate waveguide simulator that permits normal incidence excitation of the FSS under test. (C) 2009 Wiley Periodicals. Inc. Microwave Opt Technol Lett 51: 2059-2061, 2009; Published online in Wiley Inter-Science (www. interscience.wiley.com). DOI 10.1002/mop.24547

Dual-mode retrodirective/phased array

A method for producing a retrodirective (self-tracking) antenna, which can also be operated as a phased (selectively pointed) array through the addition of a simple switching circuit and DC bias offset adjustment, is presented. Phase adjustment to individual antenna elements is shown to be readily carried out by a simple frequency pushing technique, applied to a PLL circuit, thus replacing the requirement for additional phase shifters. Practical results when applied to a ten-element array operating at 2.4 GHz are shown for both modes of operation.

94 GHz dual-reflector antenna with reflectarray subreflector

The design, construction and measured performance is described of an offset parabolic reflector antenna which employs a reflectarray subreflector to tilt the focused beam from the boresight direction at 94 GHz. An analysis technique based on the method of moments (MoM) is used to design the dual-reflector antenna. Numerical simulations were employed to demonstrate that the high gain pattern of the antenna can be tilted to a predetermined angle by introducing a progressive phase shift across the aperture of the reflectarray. Experimental validation of the approach was made by constructing a 28 × 28 element patch reflectarray which was designed to deflect the beam 5° from the boresight direction in the azimuth plane. The array was printed on a 115 µm thick metal backed quartz wafer and the radiation patterns of the dual reflector antenna were measured from 92.6-95.5 GHz. The experimental results are used to validate the analysis technique by comparing the radiation patterns and the reduction in the peak gain due to beam deflection from the boresight direction. Moreover the results demonstrate that this design concept can be developed further to create an electronically scanned dual reflector antenna by using a tunable reflectarray subreflector.

Dual-task interference: Attentional and neurophysiological influences

Performing two tasks simultaneously often degrades performance of one or both tasks. While this dual-task interference is classically interpreted in terms of shared attentional resources, where two motor tasks are performed simultaneously interactions within primary motor cortex (i.e., activity-dependent coupling) may also be a contributing factor. In the present study TMS (transcranial magnetic stimulation) was used to examine the contribution of activity-dependent coupling to dual-task interference during concurrent performance of a bimanual coordination task and a discrete probe reaction time (RT) task involving the foot. Experiments 1 and 2 revealed that activity-dependent coupling within the leg corticomotor pathway was greater during dual-task performance than single-task performance, and this was associated with interference on the probe RT task (i.e., increased RT). Experiment 3 revealed that dual-task interference occurred regardless of whether the dual-task involved two motor tasks or a motor and cognitive task, however activity-dependent coupling was present only when a dual motor task was performed. This suggests that activity-dependent coupling is less detrimental to performance than attentional processes operating upstream of the corticomotor system. Finally, while prioritising the RT task reduced, but did not eliminate, dual-task interference the contribution of activity-dependent coupling to dual-task interference was not affected by task prioritisation. This suggests that although activity-dependent coupling may contribute to dual motor-task interference, attentional processes appear to be more important. It also suggests that activity-dependent coupling may not be subject to modulation by attentional processes. (C) 2009 Elsevier B.V. All rights reserved.

How many processes underline category-based induction? Effect of conclusion specificity and cognitive ability

Two studies investigated participants' sensitivity to the amount and diversity of the evidence when reasoning inductively about categories. Both showed that participants are more sensitive to characteristics of the evidence for arguments with general rather than specific conclusions. Both showed an association between cognitive ability and sensitivity to these evidence characteristics, particularly when the conclusion category was general. These results suggest that a simple associative process may not be sufficient to capture some key phenomena of category-based induction. They also support the claim that the need to generate a superordinate category is a complicating factor in category-based reasoning and that adults' tendency to generate such categories while reasoning has been overestimated.

Stable isomorphism of dual operator spaces

We prove that two dual operator spaces $X$ and $Y$ are stably isomorphic if and only if there exist completely isometric normal representations $phi$ and $psi$ of $X$ and $Y$, respectively, and ternary rings of operators $M_1, M_2$ such that $phi (X)= [M_2^*psi (Y)M_1]^{-w^*}$ and $psi (Y)=[M_2phi (X)M_1^*].$ We prove that this is equivalent to certain canonical dual operator algebras associated with the operator spaces being stably isomorphic. We apply these operator space results to prove that certain dual operator algebras are stably isomorphic if and only if they are isomorphic. We provide examples motivated by CSL algebra theory.

Nonlinear frequency coupling in dual radio-frequency driven atmospheric pressure plasmas

Plasma ionization, and associated mode transitions, in dual radio-frequency driven atmospheric pressure plasmas are governed through nonlinear frequency coupling in the dynamics of the plasma boundary sheath. Ionization in low-power mode is determined by the nonlinear coupling of electron heating and the momentary local plasma density. Ionization in high-power mode is driven by electron avalanches during phases of transient high electric fields within the boundary sheath. The transition between these distinctly different modes is controlled by the total voltage of both frequency components.