Working with Constrained Systems: A Review of A. K. Joshi's IJCAI-97 Research Excellence Award Acceptance Lecture

This is a brief review of Joshi's award acceptance lecture published in <I>AI Magazine</I>. This review appeared in the AI Watch column in <I>Computers and Society</I>, a quarterly magazine

Acoustophoresis method and apparatus

A method and apparatus are provided for acoustophoresis, i.e., the separation of species via acoustic waves. An ultrasonic transducer applies an acoustic wave to one end of a sample container containing at least two species having different acoustic absorptions. The wave has a frequency tuned to or harmonized with the point of resonance of the species to be separated. This wave caused the species to be driven to an opposite end of the sample container for removal. A second ultrasonic transducer may be provided to apply a second, oppositely directed acoustic wave to prevent undesired streaming. In addition, a radio frequency tuned to the mechanical resonance and coupled with a magnetic field can serve to identify a species in a medium comprising species with similar absorption coefficients, whereby an acoustic wave having a frequency corresponding to this gyrational rate can then be applied to sweep the identified species to one end of the container for removal

Back to the Cave

This chapter is a call to philosophers to philosophize for their cities and not merely in them. As business-model approaches to higher education increasingly dominate, the place for philosophy within the Academy is likely to continue shrinking. It is the argument of this chapter that demonstrating the importance of philosophy demands a that we shift our focus from the problems and concerns of our colleagues to those of our neighbors. The chapter concludes with some examples of what a more urban-oriented philosophy might involve

Impact tolerant material

A material is protected from acoustic shock waves generated by impacting projectiles by means of a backing. The backing has an acoustic impedance that efficiently couples the acoustic energy out of the material

The G\mathcal{G}-invariant and catenary data of a matroid

The catenary data of a matroid $M$ of rank $r$ on $n$ elements is the vector $(\nu(M;a_0,a_1,\ldots,a_r))$, indexed by compositions $(a_0,a_1,\ldots,a_r)$, where $a_0 \geq 0$,\, $a_i > 0$ for $i \geq 1$, and $a_0+ a_1 + \cdots + a_r = n$, with the coordinate $\nu (M;a_0,a_1, \ldots,a_r)$ equal to the number of maximal chains or flags $(X_0,X_1, \ldots,X_r)$ of flats or closed sets such that $X_i$ has rank $i$,\, $|X_0| = a_0$, and $|X_i - X_{i-1}| = a_i$. We show that the catenary data of $M$ contains the same information about $M$ as its $\mathcal{G}$-invariant, which was defined by H. Derksen [\emph{J.\ Algebr.\ Combin.}\ 30 (2009) 43--86]. The Tutte polynomial is a specialization of the $\mathcal{G}$-invariant. We show that many known results for the Tutte polynomial have analogs for the $\mathcal{G}$-invariant. In particular, we show that for many matroid constructions, the $\mathcal{G}$-invariant of the construction can be calculated from the $\mathcal{G}$-invariants of the constituents and that the $\mathcal{G}$-invariant of a matroid can be calculated from its size, the isomorphism class of the lattice of cyclic flats with lattice elements labeled by the rank and size of the underlying set. We also show that the number of flats and cyclic flats of a given rank and size can be derived from the $\mathcal{G}$-invariant, that the $\mathcal{G}$-invariant of $M$ is reconstructible from the deck of $\mathcal{G}$-invariants of restrictions of $M$ to its copoints, and that, apart from free extensions and coextensions, one can detect whether a matroid is a free product from its $\mathcal{G}$-invariant.Comment: 25 page