Exponential lower bounds for the pigeonhole principle

In this paper we prove an exponential lower bound on the size of bounded-depth Frege proofs for the pigeonhole principle (PHP). We also obtain an (loglogn)-depth lower bound for any polynomial-sized Frege proof of the pigeonhole principle. Our theorem nearly completes the search for the exact complexity of the PHP, as S. Buss has constructed polynomial-size, logn-depth Frege proofs for the PHP. The main lemma in our proof can be viewed as a general Håstad-style Switching Lemma for restrictions that are partial matchings. Our lower bounds for the pigeonhole principle improve on previous superpolynomial lower bounds.     

EuLisp in education

We present our experience withEuLisp as a teaching language, focussing on the level of the language which was specifically designed for this purpose (level-0).EuLisp has been used in undergraduate and postgraduate teaching since 1990, in lectures and laboratories, where in many cases it has replaced Scheme or Common Lisp. It has been used extensively in programming courses, parallelism courses, as a vehicle for advanced courses in symbolic computing and programming language design; it has also been used as a platform for final year undergraduate projects. This experience has demonstrated thatEuLisp is well suited to teaching and far reaching in its capabilities: it supports the relevant concepts in a consistent and versatile framework, so that the language serves to facilitate the educational process. The discussion is illustrated with examples, and where appropriate we draw a comparison with the Lisp dialects used previously in these courses.     

Ferrimagnetic resonance and low temperature transition in Ni- and Co-substituted powder magnetite

The effects of nickel and cobalt substitution on ferrimagnetic resonance in high-purity magnetite powder have been investigated. The low-temperature transition temperature and damping parameter, , are found to decrease with increasing solute additions. The linewidth, H, varies in proportion to the anisotropy field of the ferrites, narrowing with increasing nickel content but broadening with increasing cobalt content. Theg factor increases with the dopant concentration, passing through a maximum around room temperature. Decreasing the deviation from stoichiometry by appropriate annealing decreases the transition temperature shift but slightly increases H, g and .     

Differential effects of elevated potassium ion concentration and of theophylline on growth hormone release by rat adenohypophyses in vitro

The effects of 27 mM K+ and of 6.7 mM theophylline on the release of growth hormone (GH) by rat hemipituitaries in vitro were investigated using bioassay (rat tibia test) and radioimmunoassay (RIA). Both agents markedly increased the release of immunoreactive GH. High K+ also promoted the release of bioactive GH but to a much lesser degree than RIA-GH. Theophylline did not consistently affect the release of bioassay-detectable GH. The results suggest that these agents promote massive release of a form of immunoreactive GH (possibly "immature") that has little or no activity in the bioassay. Theophylline is relatively more effective in this regard than is elevated K+.     

Phytoplankton Productivity and Standing Crop in the Vicinity of the Lake Huron-Saginaw Bay Front

Continuous underway sampling was used in four research cruises near the mouth of Saginaw Bay in order to locate the bay-lake front, where eutrophic bay water mixes with oligotrophic Lake Huron water. Although mixing between these water masses normally occurs in outer Saginaw Bay, the distribution was variable, depending on wind force and direction as well as water temperature. Large algal crops in inner Saginaw Bay had reduced soluble nutrients, particularly silicate and nitrate-nitrogen, in the outer bay to levels lower than the adjacent lake water. Nonetheless, outer bay water supported high algal biomass (up to 14 μg/L chlorophyll a) and ¹⁴C uptake (up to 73 μg /L/h). The phytoplankton community at the nutrient front between bay and lake waters was characterized by high chlorophyll a biomass ($\overline{x}$ = 4.47 μg/L), low ¹⁴C uptake ($\overline{x}$ = 7.12 μg/L/h), and high bacterial activity (V_max$\overline{x}$ = 1.33) indicating the presence of a senescent assemblage. Decomposition and settling of phytoplankton in the vicinity of the front apparently served to remove much of the bay plankton from the water column before mixing into the open lake. But, during mid-summer, occasional large inputs of nutrients and/or phytoplankton from the bay into the open lake were observed.     

The effects of pick density on order picking areas with narrow aisles

The cost and service performance of an order fulfillment center are determined partly by how workers are organized into an order picking system. One common approach is batch picking, in which workers circumnavigate a picking area with other workers, gathering items on a pick list. In some systems with high space utilization, narrow aisles prohibit workers from passing one another when in the same aisle, and this leads to congestion. We build analytical and simulation models of these systems to investigate their behavior under different levels of activity. Among other things, our results suggest that when the system is busier and pick density is high (that is, when workers stop often to make picks) congestion is less of a problem and workers are more productive.     

Parallel implementation of time-dependent density functional theory

We present a massively parallel implementation of time-dependent density functional theory in real space, aimed at computing optical absorption spectra of realistic systems with hundreds of atoms from first principles. We provide details of the formalism and discuss its implementation, optimization, and efficient parallelization, as well as remaining limitations, in detail. The capabilities of the code are illustrated by calculations of optical properties of hydrogenated silicon quantum dots.     

Interactive Construction and Animation of Layered Elastically Deformable Characters

An interactive system is described for creating and animating deformable 3D characters. By using a hybrid layered model of kinematic and physics-based components together with an immersive 3D direct manipulation interface, it is possible to quickly construct characters that deform naturally when animated and whose behavior can be controlled interactively using intuitive parameters. In this layered construction technique, called the elastic surface layer model, a simulated elastically deformable skin surface is wrapped around a kinematic articulated figure. Unlike previous layered models, the skin is free to slide along the underlying surface layers constrained by geometric constraints which push the surface out and spring forces which pull the surface in to the underlying layers. By tuning the parameters of the physics-based model, a variety of surface shapes and behaviors can be obtained such as more realistic-looking skin deformation at the joints, skin sliding over muscles, and dynamic effects such as squash-and-stretch and follow-through. Since the elastic model derives all of its input forces from the underlying articulated figure, the animator may specify all of the physical properties of the character once, during the initial character design process, after which a complete animation sequence can be created using a traditional skeleton animation technique. Character construction and animation are done using a 3D user interface based on two-handed manipulation registered with head-tracked stereo viewing. In our configuration, a six degree-of-freedom head-tracker and CrystalEyes shutter glasses are used to display stereo images on a workstation monitor that dynamically follow the user head motion. 3D virtual objects can be made to appear at a fixed location in physical space which the user may view from different angles by moving his head. To construct 3D animated characters, the user interacts with the simulated environment using both hands simultaneously: the left hand, controlling a Spaceball, is used for 3D navigation and object movement, while the right hand, holding a 3D mouse, is used to manipulate through a virtual tool metaphor the objects appearing in front of the screen. Hand-eye coordination is made possible by registering virtual space to physical space, allowing a variety of complex 3D tasks necessary for constructing 3D animated characters to be performed more easily and more rapidly than is possible using traditional interactive techniques.