Variable temperature, variable-gap Otto prism coupler for use in a vacuum environment

The field of surface polariton physics really took off with the prism coupling techniques developed by Kretschmann and Raether, and by Otto. This article reports on the construction and operation of a rotatable, in vacuo, variable temperature, Otto coupler with a coupling gap that can be varied by remote control. The specific design attributes of the system offer additional advantages to those of standard Otto systems of (i) temperature variation (ambient to 85 K), and (ii) the use of a valuable, additional reference point, namely the gap-independent reflectance at the Brewster angle at any given, fixed temperature. The instrument is placed firmly in a historical context of developments in the field. The efficacy of the coupler is demonstrated by sample attenuated total reflectance results on films of platinum, niobium, and yttrium barium copper oxide and on aluminum/gallium arsenide (Al/GaAs) Schottky diode structures. (C) 2000 American Institute of Physics. [S0034-6748(00)02411-4].

Tact training versus bi-directional intraverbal training in teaching a foreign language

The current study involved an evaluation of the emergence of untrained verbal relations as a function of between three different foreign-language teaching strategies. Two Spanish-speaking adults received foreign-language (English) tact-training as well as native-to-foreign and foreign-to-native intraverbal training. The results indicated that tact training and native-to-foreign intraverbal training are more likely to result in the emergence of untrained relations, and may thus be more efficient compared to foreign-to-native intraverbal training.

Directional Modulation Transmitter Synthesis using Particle Swarm Optimization

Phased DM transmitter array synthesis using particle swarm optimization (PSO) is presented in this paper. The PSO algorithm is described in details with key parameters provided for 1-D four-element half-wavelength spaced QPSK DM array synthesis. A DM transmitter array for boresight and 30º direction secure communications are taken as examples to validate the proposed synthesis approach. The optimization process exhibits good convergence performance and solution quality.

Assessment of the effectiveness of the guard ring in obtaining a uni-directional flow in an in situ water permeability test

The non-destructive evaluation of the water permeability of concrete structures is a long standing challenge, principally due to the difficulty of achieving a uni-direction flow for computing the water permeability coefficient. The use of a guard ring (GR) was originally proposed for the in situ sorptivity test, but little information can be found for the water permeability test. In this study, the effect of a GR was carefully examined through the flow simulation, which was verified by carrying out experiments. It was observed that the GR can confine the flow near the surface, but cannot achieve a uni-directional flow across the whole depth of flow. To achieve a better performance, it is essential to consider the effects of the size of the inner seal and the GR and the significant interaction between these two. The analysis of the experimental data has indicated that the GR influences the flow for porous concretes, but there is no significant effect for dense concretes. Further investigation, validated using the flow-net theory, has shown a strong correlation between the water permeability coefficients obtained with the GR (K w-GR) and without it (K w-No GR), suggesting that one dimensional flow is not essential for interpreting data for site tests. Another practical issue was that more than 30 % of the tests with GR failed due to the difficulty of achieving a good seal between the inner and the outer chambers. Based on the work reported in this paper, a new water permeability test is proposed.

A Vector Approach for the Analysis and Synthesis of Directional Modulation Transmitters

In order to formalize and extend on previous ad-hoc analysis and synthesis methods a theoretical treatment using vector representations of directional modulation (DM) systems is introduced and used to achieve DM transmitter characteristics. An orthogonal vector approach is proposed which allows the artificial orthogonal noise concept derived from information theory to be brought to bear on DM analysis and synthesis. The orthogonal vector method is validated and discussed via bit error rate (BER) simulations.

Directional modulation transmitter radiation pattern considerations

A pattern synthesis approach is applied to a directional modulation (DM) system. A systematic synthesis procedure is suggested which ensures optimal constellation patterns production along pre-specified communication directions, whereas simultaneously conserving energy dispersal in other directions. In this study, the properties of DM systems synthesised from Gaussian magnitude far-field radiation pattern templates are used to illustrate performance benefits with regards to DM bit error rate response compared with those achieved by a conventional steered array.

BER Driven Synthesis for Directional Modulation Secured Wireless Communication

Directional modulation (DM) is a recently introduced technique for secure wireless transmission using direct physical layer wave-front manipulation. This paper provides a bit error rate (BER)-based DM array synthesis method. It is shown for the first time that the standard constellation mappings in In-phase and Quadrature (IQ) space to a pre-specified BER can be exactly achieved along a given specified spatial direction. Different receiver capabilities are investigated and different assessment metrics for each case are discussed. The approach is validated for a 1 × 4 element dipole array operating at 1 GHz.

Establishing Metrics for Assessing the Performance of Directional Modulation Systems

In this paper metrics for assessing the performance of directional modulation (DM) physical-layer secure wireless systems are discussed. In the paper DM systems are shown to be categorized as static or dynamic. The behavior of each type of system is discussed for QPSK modulation. Besides EVM-like and BER metrics, secrecy rate as used in information theory community is also derived for the purpose of this QPSK DM system evaluation.

Vector representation of directional modulation transmitters

Directional Modulation (DM) is a recently proposed technique for securing wireless communication. In this paper we point out that modulation-directionality is a consequence of varying the beamforming network, either in baseband or in the RF stage, at the information rate In order to formalize and extend on previous analysis and synthesis methods a new theoretical treatment using vector representations of directional modulation (DM) systems is introduced and used to obtain the necessary and sufficient con