Impossible and ambiguous shading patterns

A smooth object depicted in a monochrome image will often exhibit brightness variation, or shading. A problem much studied in computer vision has been that of how object shape may be recovered from image shading. When the imaging conditions are such that an overhead point-source illuminates a smooth Lambertian surface, the problem may be formulated as that of finding a solution to an eikonal equation. This article will focus on the existence and uniqueness of such solutions, reporting recent results obtained. With regard to existence, shading patterns are exhibited for which there is no corresponding object shape. Specifically, a necessary and sufficient condition is presented for a circularly symmetric eikonal equation to admit exclusively unbounded solutions; additionally, a sufficient condition is given for an eikonal equation to have no solution whatsoever. In connection with uniqueness, we consider eikonal equations, defined over a disc, such that the Euclidean norm of the gradient of any solution is circularly symmetric, vanishes exactly at the disc center, and diverges to infinity as the circumference of the disc is approached. Contrary to earlier influential work, a class of such eikonal equations is shown to possess simultaneously circularly symmetric and noncircularly symmetric bounded smooth solutions.     

Parallel reduced area multipliers

As developed by Wallace and Dadda, a method for high-speed, parallel multiplication is to generate a matrix of partial products and then reduce the partial products to two numbers whose sum is equal to the final product. The resulting two numbers are then summed using a fast carry-propagate adder. This paper presents Reduced Area multipliers, which employ a modified reduction scheme that results in fewer components and less interconnect overhead than either Wallace or Dadda multipliers. This reduction scheme is especially useful for pipelined multipliers, because it minimizes the number of latches required in the reduction of the partial products. The reduction scheme can be applied to either unsigned (sign-magnitude) or two's complement numbers. Equations are given for determining the number of components and a method is presented for estimating the interconnect overhead for Wallace, Dadda, and Reduced Area multipliers. Area estimates indicate that for non-pipelined multipliers, the reduction in area achieved with Reduced Area multipliers ranges from 3.7 to 6.6 percent relative to Dadda multipliers, and from 3.8 to 8.4 percent relative to Wallace multipliers. For fully pipelined multipliers, the reduction in area ranges from 15.1 to 33.6 percent relative to Dadda multipliers, and from 2.9 to 9.0 percent relative to Wallace multipliers.     

A nonlinear operator-based speech feature analysis method withapplication to vocal fold pathology assessment

Traditional speech processing methods for laryngeal pathology assessment assume linear speech production with measures derived from an estimated glottal flow waveform. They normally require the speaker to achieve complete glottal closure, which for many vocal fold pathologies cannot be accomplished. To address this issue, a nonlinear signal processing approach is proposed which does not require direct glottal flow waveform estimation. This technique is motivated by earlier studies of airflow characterization for human speech production. The proposed nonlinear approach employs a differential Teager energy operator and the energy separation algorithm to obtain formant AM and FM modulations from filtered speech recordings. A new speech measure is proposed based on parameterization of the autocorrelation envelope of the AM response. This approach is shown to achieve impressive detection performance for a set of muscular tension dysphonias. Unlike flow characterization using numerical solutions of Navier-Stokes equations, this method is extremely computationally attractive, requiring only a small time window of speech samples. The new noninvasive method shows that a fast, effective digital speech processing technique can be developed for vocal fold pathology assessment without the need for direct glottal flow estimation or complete glottal closure by the speaker. The proposed method also confirms that alternative nonlinear methods can begin to address the limitations of previous linear approaches for speech pathology assessment     

Radiale Wärmeleitung in durchströmten Schüttungsrohren

Heat Transport to the Wall of Packed Tubes. Radial conduction of heat in packed tubes has a crucial influence on yield and selectivity of many heterogeneously catalyzed reactions. In spite of many years of intensive research in the field, there are still tremendous discrepancies between correlations of different origin. Even the standard model using two constant heat transport parameters, which was introduced in the fifties and has since become most widely accepted, has been controversially discussed and called into question. The unsatisfactory state of the art has been an incentive for several groups of researchers to take up this old topic once again. Three parallel experimental investigations on heat transport with air flowing in packed tubes of similar dimensions, electrically heated, steam-heated, or water-cooled, were completed in 1991. Comparative evaluation of the results of these three investigations, together with other data from the relevant literature, now provides the first clear answers to some of the questions so controversially discussed in the past.     

Terrorism in the 1990s

Terrorism: A Reference Handbook, Stephen Atkins, Santa Barbara, ABC-CLIO (1992), 199 pp. Terrorism: Roots, Impact, Responses, Lawrence Howard (Ed.), Prager, New York (1992), 193 pp. Hostage-Taking Terrorism: Incident Response Strategy, Alastair MacWillson, St Martins, New York (1992), 263 pp.     

Teachers' and deaf students' perceptions of communication ease and engagement.

Collected ratings of communication ease and of engagement for 95 deaf junior and senior high school students (aged 12–21 yrs) in a large, urban, multiethnic school for the deaf. Ratings were made by the students' English teachers and by the students themselves. High teacher ratings for communication ease and engagement were associated with high academic achievement as measured by the Stanford Achievement Test. High student ratings for communication ease were also associated with academic achievement. The 2 best predictors of academic achievement were student-rated communication ease and teacher-rated engagement. Findings suggest that it is important for teachers to be sensitive to the level of communication comfort of their students because students who enjoy easier communication may be more likely to be engaged, or more actively involved, in classroom learning and to demonstrate higher academic achievement. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Herd immunity to filarial infection is a function of vector biting rate

Despite the existence of an impressive body of work on human immune responses against filarial infections, the occurrence of a protective response to infection remains unclear. Here, we use a combined modelling and comparative data analysis framework to address this issue for human infections with the filarial parasite, Wuchereria bancrofti. By analogy with previous work, the analysis involves the comparison of observed field patterns of infection with epidemiological patterns predicted by a mathematical model of parasite immunity. Unlike most other human helminths, which are transmitted by ingestion or dermal penetration, exposure to infection with lymphatic filariasis can be measured explicitly in terms of vector mosquito biting rates, thereby also allowing, probably for the first time, examination of the suggested role of exposure in generating herd immunity to macroparasites. Observed field patterns in this study were derived from 19 different published studies, which gave parallel estimates of community exposure rates and the corresponding age--prevalence patterns of infection, while predictions of the epidemiological impact of herd immunity were obtained using a catalytic model framework. The results provide the first conclusive evidence to date that variations in the observed age--prevalence patterns of infection in filariasis can be effectively explained by the occurrence of an exposure-driven acquisition of herd immunity. We discuss this result in terms of implications for the new World Health Organization-led initiative for the global control of this parasitic disease.     

Ewald Hering und die Gegenfarbtheorie

Ewald Hering's color-opponent-theory is still considered one of the foundations of the visual sciences. Prior to Hering, Hermann v. Helmholtz introduced a theory of color appearance, which was based primarily on the physical aspects of the stimulus. In contrast to Helmholtz, Hering's theory strongly emphasized the subject's perception of color. As a consequence, Hering considered Helmholtz' theory inadequate. Contrary to some historical accounts, he did not object to Helmholtz's three-receptor explanation for color-mixture. Instead of Helmholtz' fundamental colors red, green, and blue, Hering suggested that the colors possess opponent character: blue-yellow; red-green; and, black-white. Helmholtz, on the other hand, refused to accept Hering's theory. Finally, a student with Helmholtz, Johannes v. Kries, developed the so-called “zone-theory”, which combines both, Young-Helmholtz's and Hering's theory at different stages of the visual information processing system.