One-dimensional and multi-dimensional substring selectivity estimation

With the increasing importance of XML, LDAP directories, and text-based information sources on the Internet, there is an ever-greater need to evaluate queries involving (sub)string matching. In many cases, matches need to be on multiple attributes/dimensions, with correlations between the multiple dimensions. Effective query optimization in this context requires good selectivity estimates. In this paper, we use pruned count-suffix trees (PSTs) as the basic data structure for substring selectivity estimation. For the 1-D problem, we present a novel technique called MO (Maximal Overlap). We then develop and analyze two 1-D estimation algorithms, MOC and MOLC, based on MO and a constraint-based characterization of all possible completions of a given PST. For the k-D problem, we first generalize PSTs to multiple dimensions and develop a space- and time-efficient probabilistic algorithm to construct k-D PSTs directly. We then show how to extend MO to multiple dimensions. Finally, we demonstrate, both analytically and experimentally, that MO is both practical and substantially superior to competing algorithms. Received April 28, 2000 / Accepted July 11, 2000     

Calculations of diffusion and diffusion-limited processes in Ni3Al using accelerated molecular dynamics

We present a systematic microscopic approach to diffusion and diffusion-limited processes in Ni₃Al. These processes have been identified as controlling the deformation of the material under specific circumstances. The embedded atom method calculations are done using kinetic Monte Carlo combined with the Dimer method of finding saddlepoints. We compute the tracer diffusivities as functions of composition and temperature. The comparison with available experiments is good. We find that at temperatures below about 1000 K, the diffusivity is a sharp function of composition, showing a pronounced dip on the Ni-rich side at 76 at.% Ni. This agrees well with experiment, except that the experiments show this structure setting in a temperatures below about 1300 K. We show that the structure arises from the composition dependence of both the vacancy formation energy and pre-exponential of the diffusivity. We also compute the mobility of an anti-phase boundary perpendicular to its plane, and conclude that vacancy-assistance is very plausible. We conclude that the kMC + Dimer method works well for these problems above 700 K but less effectively below, owing to the presence of short-range, low-energy hops that tend to localize the vacancy and lower the efficiency of the calculation.     

Self-determination and conflict in romantic relationships.

Four studies examined associations between E. L. Deci and R. M. Ryan's (1985, 2000) construct of autonomy, responses to relationship disagreements, and dissatisfaction after conflict. In Study 1, diary data showed that trait autonomy predicted relationship autonomy, which in turn predicted relative satisfaction after disagreements. In Study 2, trait autonomy predicted relationship autonomy, which was associated with less defensive and more understanding responses to conflict. Studies 3 and 4 examined whether one's partner's relationship autonomy uniquely predicted reported and observed behavior during conflict. Autonomous reasons for being in the relationship (of both self and partner) predicted both reported and observed responses to conflict and feelings of satisfaction. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Emotional Devaluation of Distracting Patterns and Faces: A Consequence of Attentional Inhibition During Visual Search?

Visual search has been studied extensively, yet little is known about how its constituent processes affect subsequent emotional evaluation of searched-for and searched-through items. In 3 experiments, the authors asked observers to locate a colored pattern or tinted face in an array of other patterns or faces. Shortly thereafter, either the target or a distractor was rated on an emotional scale (patterns, cheerfulness; faces, trustworthiness). In general, distractors were rated more negatively than targets. Moreover, distractors presented near the target during search were rated significantly more negatively than those presented far from the target. Target-distractor proximity affected distractor ratings following both simple-feature and difficult-conjunction search, even when items appeared at different locations during evaluation than during search and when faces previously tinted during search were presented in grayscale at evaluation. An attentional inhibition account is offered to explain these effects of attention on emotional evaluation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Fracture criterion for kinking cracks in a tri-material adhesively bonded joint under mixed mode loading

The fracture behavior of a composite/adhesive/steel bonded joint was investigated by using double cantilever beam specimens. A starter crack is embedded at the steel/adhesive interface by inserting Teflon tape. The composite adherend is a random carbon fiber reinforced vinyl ester resin composite while the other adherend is cold rolled steel. The adhesive is a one-part epoxy that is heat cured. The Fernlund-Spelt mixed mode loading fixture was employed to generate five different mode mixities. Due to the dissimilar adherends, crack turning into the adhesive (or crack kinking) associated with joint failure, was observed. The bulk fracture toughness of the adhesive was measured separately by using standard compact tension specimens. The strain energy release rates for kinking cracks at the critical loads were calculated by a commercial finite element analysis software ABAQUS in conjunction with the virtual crack closure technique. Two fracture criteria related to strain energy release rates were examined. These are (1) maximum energy release rate criterion (G_max) and, (2) mode I facture criterion (G_II = 0). They are shown to be equivalent in this study. That is, crack kinking takes place at the angle close to maximum G or G_I (also minimum G_II, with a value that is approximately zero). The average value of G_IC obtained from bulk adhesive tests using compact tension specimens is shown to be an accurate indicator of the mode I fracture toughness of the kinking cracks within the adhesive layer. It is concluded that the crack in tri-material adhesively bonded joint tends to initiate into the adhesive along a path that promotes failure in pure mode I, locally.     

Mapping vegetation in Yellowstone National Park using spectral feature analysis of AVIRIS data

Knowledge of the distribution of vegetation on the landscape can be used to investigate ecosystem functioning. The sizes and movements of animal populations can be linked to resources provided by different plant species. This paper demonstrates the application of imaging spectroscopy to the study of vegetation in Yellowstone National Park (Yellowstone) using spectral feature analysis of data from the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS). AVIRIS data, acquired on August 7, 1996, were calibrated to surface reflectance using a radiative transfer model and field reflectance measurements of a ground calibration site. A spectral library of canopy reflectance signatures was created by averaging pixels of the calibrated AVIRIS data over areas of known forest and nonforest vegetation cover types in Yellowstone. Using continuum removal and least squares fitting algorithms in the US Geological Survey's Tetracorder expert system, the distributions of these vegetation types were determined by comparing the absorption features of vegetation in the spectral library with the spectra from the AVIRIS data. The 0.68 μm chlorophyll absorption feature and leaf water absorption features, centered near 0.98 and 1.20 μm, were analyzed. Nonforest cover types of sagebrush, grasslands, willows, sedges, and other wetland vegetation were mapped in the Lamar Valley of Yellowstone. Conifer cover types of lodgepole pine, whitebark pine, Douglas fir, and mixed Engelmann spruce/subalpine fir forests were spectrally discriminated and their distributions mapped in the AVIRIS images. In the Mount Washburn area of Yellowstone, a comparison of the AVIRIS map of forest cover types to a map derived from air photos resulted in an overall agreement of 74.1% (kappa statistic=0.62).     

New design relations for 2-DOF PID-like control systems

Self-regulating processes can be controlled by internal model control systems where the usual three-parameter model of the process is transformed into a rational model via a parametrized first-order approximant of the apparent dead time. Using feedback and feedforward compensators leads to 2-DOF PID controllers whose time constants cancel that of the rational model. To obtain the desired sensitivity of the actual control loop, the model adaptation parameter and a gain tuning factor in the control system are determined by functions of the normalized dead time. The response to setpoint changes is selected by means of the feedforward compensator or via a prefilter. Plots of the sensitivity and the simulation of step responses to changes in the controller setpoint or to disturbances, show the validity of these design relations for transfer functions representative of typical industrial processes.     

State-space forms for higher-order discrete-time models

This paper presents a fundamental study of the connection between continuous- and discrete-time systems. Provided is a definition for discrete-time models, that is discrete-time systems with a continuous-time counterpart, whose order can be higher than that of the continuous-time system. This definition is based on a comparison in a certain sense on the time responses of continuous- and discrete-time systems. A theorem is presented for relating the higher-order discrete-time models to their continuous-time counterparts, which is an extension of a previous theorem for models with order equal to that of the continuous-time system. State-space forms are derived for models obtained through the use of a certain class of hold elements and through the use of mapping models, and these discrete-time systems are shown to be valid according to the definition. Special cases are models obtained using first-order and slewer hold devices, whose convergence to a continuous-time counterpart has not been shown mathematically before, and mapping models corresponding to two-step linear multi-step methods, which have not previously presented in the state-space form. The derived state-space forms provide a convenient way to implement these models for purposes of analysis, design, and implementation of discrete-time systems and finds applications in such areas as digital signal processing, digital simulation, and digital control.     

Hitting the wall: errors in developing and code inspecting a `simple' spreadsheet model

Field audits and experiments have found substantial error rates when students and professionals have built spreadsheet models. In this study, 102 undergraduate MIS majors and 50 MBA students developed a model from a word problem that was relatively simple and free of domain knowledge. Even so, 35% of their 152 models were incorrect. There was no significant difference in errors per model between undergraduates and MBAs. Even among the 17 MBAs with 250 h or more of experience, 24% of the models contained errors. The cell error rate (CER)—the percentage of cells with errors—was 2.0%. When 23 undergraduates attempted to audit their models through code inspection, only three with incorrect spreadsheets (15%) produced clean spreadsheets when they finished the audit.     

Oscillation and convergence behaviours exhibited in an ‘unstable’ second‐order digital filter with saturation‐type non‐linearity

This letter explains the oscillatory behaviours exhibited in a second‐order digital filter with saturation‐type non‐linearity via the Hopf bifurcation theorem. It is shown that depending on the bifurcation parameter, the state variables may converge to zero even when the eigenvalues of the system matrix are outside the unit circle. Copyright © 2004 John Wiley & Sons, Ltd. abstract