Cultural adaptation and information design: two contrasting views

Approaches to using visual language in a cultural context can be placed on a continuum, with global (universal) on one end and culture-focused on the other. Each approach reveals contrasting assumptions about three central design issues: perception, aesthetics and pragmatics. The global approach is characterized by attempts to invent an objective, universal visual language or to define such a language through perceptual principles and empirical research. The culture-focused perspective is founded on the principle that visual communication is intimately bound to experience and hence can function only within a given cultural context, to which designers must be sensitive. While the modernist, universal approach has been losing ground to the postmodern, culture-focused approach, the two complement each other in a variety of ways and, depending on the rhetorical situation, offer pragmatic benefits and drawbacks     

Influence of the sulfonate countercation on the thermal stability of nafion perfluorosulfonate membranes

We report a strong dependence of the thermal stability of Nafion® perfluorosulfonate ionomer on the nature of the counterion associated with the fixed sulfonate site. These results were obtained using thermal gravimetric analysis on a series of alkali metal and alkyl ammonium cation-exchanged Nafion films. We have found that the temperature of decomposition of Nafion is inversely dependent on the size of the exchanged cation; i.e., Nafion films show improved thermal stability as the size of the counter cation decreases. We attribute this inverse relationship of thermal stability with counterion size to an initial decomposition reaction which is strongly influenced by the strength of the sulfonate-coun-terion interaction. © 1993 John Wiley & Sons, Inc.     

Magnetometer spacing criterion for biomagnetic source currentimaging

A criterion for determining the maximum spacing between magnetometers for measuring the magnetic field is derived. A two-dimensional (2-D) filter model is employed to determine the maximum spatial frequency component present in the magnetic field that is above the spectral noise level. This maximum frequency component is then sampled at a rate greater than twice per period as indicated by the Nyquist criterion, yielding the required magnetometer spacing. It is shown that the rule-of-thumb employed in current clinical biomagnetic array systems, that the spacing between the coils should be approximately equal to the depth of the source, is adequate when the signal-to-noise power ratio is less than 28.4 (14.5 dB). The analysis also quantitatively demonstrates that reducing the separation between the measurement and source planes has a greater effect on the resolution than decreasing the noise level by the same factor. This result is important for employing high T_c superconductor magnetometers that allow thinner thermal insulating layers at the cost of higher thermal noise     

Afterburner [network-independent card for protocols]

Many current implementations of protocols such as the Transmission Control Protocol/Internet Protocol (TCP/IP) are inefficient because data are often accessed more frequently than necessary. Three techniques that reduce the need for memory bandwidth are proposed. The techniques are copy-on-write, page remapping, and single-copy. Afterburner, a network-independent card that provides the services that are necessary for a single-copy protocol stack, is described. The card has 1 MByte of local buffers and provides a simple interface to a variety of network link adapters, including HIPPI and asynchronous transfer mode (ATM). Afterburner can support transfers to and from the link adapter card at rates up to 1 Gbit/s. An implementation of TCP/IP that uses the features provided by Afterburner to reduce the movement of data to a single copy is discussed. Measurements of the end-to-end performance of Afterburner and the single-copy implementation of TCP/IP are presented     

An improved Gaussian approximation for probability of bit-erroranalysis of asynchronous bandlimited DS-CDMA systems with BPSK spreading

This paper analyzes probability of bit-error (P_e) performance of asynchronous bandlimited direct-sequence code-division multiple-access systems with binary phase-shift keying spreading. The two present methods of P_e analysis under bandwidth-efficient pulse shaping: the often-cited standard Gaussian approximation and the characteristic function (CF) method suffer from either a low accuracy in regions of low P_e (< 10^-3) or a prohibitively large computational complexity. The paper presents an alternate method of P_e analysis with moderate computational complexity and high accuracy based on a key observation. A sequence of chip decision statistics (whose sum yields a bit statistic) forms a stationary, m-dependent sequence when conditioned on the chip delay and phase offset of each interfering signal. This observation permits the generalization of the improved Gaussian approximation previously derived for the rectangular pulse and the derivation of a numerically efficient approximation based on the CF method. Numerical examples of systems using the square-root raised-cosine and IS-95 pulses illustrate THE P _e performance, user capacity and the accuracy of the proposed method     

Modeling and CW operation of a quasi-three-level 946 nm Nd: YAG laser

A model is developed for an end-pumped quasi-three-level laser with population in the lower laser level at equilibrium such as for transitions to the manifolds⁴I9/2in Nd³⁺,⁴I15/2in Er³⁺,⁵I8in Ho³⁺and³H6in Tm³⁺. It is shown that the effect of residual lower laser level population on laser operation can be treated as a saturable loss. Room temperature operation on the⁴F3/2-⁴I9/2transition in Nd:YAG under CW dye laser pumping has been demonstrated with a threshold as low as 11.5 mW incident power and a slope efficiency of 7 percent with 0.3 percent output coupling. Performance is limited by the low output coupling and diffraction loss.