Verifying the Implementation of an Error Control Code

This document describes how the FORTE STE-based formal verification system was used to verify the RTL implementation of an error control code. The error control code considered is linear: its encoder and decoder proceed by matrix multiplication. Although that function is in essence combinational, its implementation in a high-performance microprocessor is done in a pipelined fashion. The additional state elements introduced by the pipelining quickly push an SMV-style model checker to its capacity limits. With the case-study presented in this document, we show that an STE-style model checker is better suited for this problem. We present two instances of the ECC verification problem. For the first we were able to combine an encoder and a decoder into one model for verification. For the second, such a combination was not possible and we resorted to verifying properties of a matrix that we extracted from the implementation.     

The dynamics of IT boundary objects,information infrastructures,and organisational identities: the introduction of 3D modelling technologies into the architecture,engineering, and construction industry

In recent years, more companies engage in collaborative cross-organisational practices to achieve their business objectives. To cooperate effectively across boundaries requires organisations to overcome the tension between their distinct backgrounds and the need to create shared understandings with their partners for collaboration. This requires the creation of shared artefacts such as boundary objects. Whereas the past work on boundary objects has highlighted their role as translation devices, we examine them in relation to the information infrastructures within which they are embedded, and the identities of the organisations that use them. We propose a model that outlines the relationships among the three concepts and illustrate its dynamics by presenting two case studies that describe the introduction of three-dimensional modelling technologies into the architecture, engineering, and construction industry. Based on the case studies we suggest that boundary objects, in addition to facilitating cross-organisational communication, also help to form organisational identities. We further suggest the occurrence of a process whereby changes in boundary objects enable changes in information infrastructures and identities in one organisation. These changes, in turn, create the conditions for change in bordering organisations through shared boundary objects and boundary practices.     

How the brain generates movement

In this study, we assume that the brain uses a general-purpose pattern generator to transform static commands into basic movement segments. We hypothesize that this pattern generator includes an oscillator whose complete cycle generates a single movement segment. In order to demonstrate this hypothesis, we construct an oscillator-based model of movement generation. The model includes an oscillator that generates harmonic outputs whose frequency and amplitudes can be modulated by external inputs. The harmonic outputs drive a number of integrators, each activating a single muscle. The model generates muscle activation patterns composed of rectilinear and harmonic terms. We show that rectilinear and fundamental harmonic terms account for known properties of natural movements, such as the invariant bell-shaped hand velocity profile during reaching. We implement these dynamics by a neural network model and characterize the tuning properties of the neural integrator cells, the neural oscillator cells, and the inputs to the system. Finally, we propose a method to test our hypothesis that a neural oscillator is a central component in the generation of voluntary movement.     

Uniform unweighted set cover: The power of non-oblivious local search

We are given $n$ base elements and a finite collection of subsets of them. The size of any subset varies between $p$ to $k$ ($p<k$). In addition, we assume that the input contains all possible subsets of size $p$. Our objective is to find a subcollection of minimum-cardinality which covers all the elements. This problem is known to be NP-hard. We provide two approximation algorithms for it, one for the generic case, and an improved one for the special case of $(p,k)=(2,4)$.The algorithm for the generic case is a greedy one, based on packing phases: at each phase we pick a collection of disjoint subsets covering $i$ new elements, starting from $i=k$ down to $i=p+1$. At a final step we cover the remaining base elements by the subsets of size $p$. We derive the exact performance guarantee of this algorithm for all values of $k$ and $p$, which is less than $H_k$, where $H_k$ is the $k$’th harmonic number. However, the algorithm exhibits the known improvement methods over the greedy one for the unweighted $k$-set cover problem (in which subset sizes are only restricted not to exceed $k$), and hence it serves as a benchmark for our improved algorithm.The improved algorithm for the special case of $(p,k)=(2,4)$ is based on non-oblivious local search: it starts with a feasible cover, and then repeatedly tries to replace sets of size 3 and 4 so as to maximize an objective function which prefers big sets over small ones. For this case, our generic algorithm achieves an asymptotic approximation ratio of $1.5+?$, and the local search algorithm achieves a better ratio, which is bounded by $1.458333\dots +?$.     

Mining students’ inquiry actions for understanding of complex systems

This study lies at an intersection between advancing educational data mining methods for detecting students’ knowledge-in-action and the broader question of how conceptual and mathematical forms of knowing interact in exploring complex chemical systems. More specifically, it investigates students’ inquiry actions in three computer-based models of complex chemical systems when their goal is to construct an equation relating physical variables of the system. The study’s participants were 368 high-school students who interacted with the Connected Chemistry (CC1¹) curriculum and completed identical pre- and post-test content knowledge questionnaires. The study explores whether and how students adapt to different mathematical behaviors of the system, examines how these explorations may relate to prior knowledge and learning in terms of conceptual and mathematical models, as well as components relating to understanding systems. Students’ data-collection choices were mined and analyzed showing: (1) In about half the cases, mainly for two out of the three models explored, students conduct mathematically-astute (fit) explorations; (2) A third of the students consistently adapt their strategies to the models’ mathematical behavior; (3) Fit explorations are associated with prior conceptual knowledge, specifically understanding of the system as complex, however, the three explorations’ fitness is predicted by the understanding of distinct sets of systems’ components; (4) Fit explorations are only somewhat associated with learning along complementary dimensions. These results are discussed with respect to 1) the importance of a conceptual understanding regarding individual system elements even when engaged in large-scale quantitative problem solving, 2) how distinct results for the different models relate to previous literature on conceptual understanding and particular affordances of the models, 3) the importance of engaging students in creating mathematical representations of scientific phenomena, as well as 4) educational applications of these results in learning environments.     

The dependence of spike field coherence on expected intensity

The coherence between neural spike trains and local-field potential recordings, called spike-field coherence, is of key importance in many neuroscience studies. In this work, aside from questions of estimator performance, we demonstrate that theoretical spike-field coherence for a broad class of spiking models depends on the expected rate of spiking. This rate dependence confounds the phase locking of spike events to field-potential oscillations with overall neuron activity and is demonstrated analytically, for a large class of stochastic models, and in simulation. Finally, the relationship between the spike-field coherence and the intensity field coherence is detailed analytically. This latter quantity is independent of neuron firing rate and, under commonly found conditions, is proportional to the probability that a neuron spikes at a specific phase of field oscillation. Hence, intensity field coherence is a rate-independent measure and a candidate on which to base the appropriate statistical inference of spike field synchrony.     

Information Filtering: A New Two-Phase Model Using Stereotypic User Profiling

Computer users often experience the lost in informationspace syndrome. Information filtering suggests a solution based onrestricting the amount of information made available to users. Thisstudy suggests an advanced model for information filtering which isbased on a two-phase filtering process. The user profiling in themodel is constructed on the basis of the user's areas of interestand on sociological parameters about him that are known to thesystem. The system maintains a database of known stereotypes thatincludes rules on their information retrieval needs and habits.During the filtering process, the system relates the user to one ormore stereotypes and operates the appropriate stereotypic rules.     

InAs Nanocrystals with Robust p-Type Doping

Robust control over the carrier type is fundamental for the fabrication of nanocrystal-based optoelectronic devices, such as the p–n homojunction, but effective incorporation of impurities in semiconductor nanocrystals and its characterization is highly challenging due to their small size. Herein, InAs nanocrystals (NCs), post-synthetically doped with Cd, serve as a model system for successful p-type doping of originally n-type InAs nanocrystals, as demonstrated in field effect transistors (FETs). Advanced structural analysis, using atomic resolution electron microscopy and synchrotron X-ray absorption fine structure spectroscopy reveal that Cd impurities reside near and on the nanocrystal surface acting as substitutional p-dopants replacing Indium. Commensurately, Cd-doped InAs FETs exhibit remarkable stability of their hole conduction, mobility, and hysteretic behavior over time when exposed to air, while intrinsic InAs NCs FETs are easily oxidized and their performance quickly declines. Therefore, Cd plays a dual role acting as a p-type dopant, and also protects the nanocrystals from oxidation, as evidenced directly by X-ray photoelectron spectroscopy measurements of air exposed samples of intrinsic and Cd-doped InAs NCs films. This study demonstrates robust p-type doping of InAs nanocrystals, setting the stage for implementation of such doped nanocrystal systems in printed electronic devices.