Constructing cities,deconstructing scaling laws

Cities can be characterized and modelled through different urban measures. Consistency within these observables is crucial in order to advance towards a science of cities. Bettencourt et al. have proposed that many of these urban measures can be predicted through universal scaling laws. We develop a framework to consistently define cities, using commuting to work and population density thresholds, and construct thousands of realizations of systems of cities with different boundaries for England and Wales. These serve as a laboratory for the scaling analysis of a large set of urban indicators. The analysis shows that population size alone does not provide us enough information to describe or predict the state of a city as previously proposed, indicating that the expected scaling laws are not corroborated. We found that most urban indicators scale linearly with city size, regardless of the definition of the urban boundaries. However, when nonlinear correlations are present, the exponent fluctuates considerably.     

Electromagnetic scattering analysis using a model of dipoleslocated in complex space

Fictitious current-models have been applied extensively in recent years to a variety of time-harmonic electromagnetic wave scattering problems. This paper is introducing an extension of the current-model technique which facilitates the solution to problems subsuming metallic scatterers whose periphery contains a variety of length-scales features. This extension is in tune with the current-model technique philosophy of using simple current sources the fields of which are analytically derivable. It amounts to letting the coordinates of part of the source centers assume complex values. Positioned in complex space, the simple current sources radiate beam-type fields which are more localized and are better approximations of the scattering by the smooth expanses of the structure. The coordinates of the other source centers can retain their conventional real values or have only a relatively small imaginary constituent. These latter current sources are used to approximate the fields in the vicinity of the more rapidly varying regions of the structure. The new approach is applied to analyze electromagnetic scattering by a perfectly conducting oblate spheroid. It is found to render the solution computationally more effective at the expense of only a slight increase in its complexity     

Nested linear/lattice codes for structured multiterminal binning

Network information theory promises high gains over simple point-to-point communication techniques, at the cost of higher complexity. However, lack of structured coding schemes limited the practical application of these concepts so far. One of the basic elements of a network code is the binning scheme. Wyner (1974, 1978) and other researchers proposed various forms of coset codes for efficient binning, yet these schemes were applicable only for lossless source (or noiseless channel) network coding. To extend the algebraic binning approach to lossy source (or noisy channel) network coding, previous work proposed the idea of nested codes, or more specifically, nested parity-check codes for the binary case and nested lattices in the continuous case. These ideas connect network information theory with the rich areas of linear codes and lattice codes, and have strong potential for practical applications. We review these developments and explore their tight relation to concepts such as combined shaping and precoding, coding for memories with defects, and digital watermarking. We also propose a few novel applications adhering to a unified approach     

Capacity and lattice strategies for canceling known interference

We consider the generalized dirty-paper channel Y=X+S+N,E{X/sup 2/}/spl les/P/sub X/, where N is not necessarily Gaussian, and the interference S is known causally or noncausally to the transmitter. We derive worst case capacity formulas and strategies for "strong" or arbitrarily varying interference. In the causal side information (SI) case, we develop a capacity formula based on minimum noise entropy strategies. We then show that strategies associated with entropy-constrained quantizers provide lower and upper bounds on the capacity. At high signal-to-noise ratio (SNR) conditions, i.e., if N is weak relative to the power constraint P/sub X/, these bounds coincide, the optimum strategies take the form of scalar lattice quantizers, and the capacity loss due to not having S at the receiver is shown to be exactly the "shaping gain" 1/2log(2/spl pi/e/12)/spl ap/ 0.254 bit. We extend the schemes to obtain achievable rates at any SNR and to noncausal SI, by incorporating minimum mean-squared error (MMSE) scaling, and by using k-dimensional lattices. For Gaussian N, the capacity loss of this scheme is upper-bounded by 1/2log2/spl pi/eG(/spl Lambda/), where G(/spl Lambda/) is the normalized second moment of the lattice. With a proper choice of lattice, the loss goes to zero as the dimension k goes to infinity, in agreement with the results of Costa. These results provide an information-theoretic framework for the study of common communication problems such as precoding for intersymbol interference (ISI) channels and broadcast channels.     

Approximate belief updating in max-2-connected Bayes networks is NP-hard

A max-2-connected Bayes network is one where there are at most 2 distinct directed paths between any two nodes. We show that even for this restricted topology, null-evidence belief updating is hard to approximate.     

Unitary and non-unitary manipulations of qubit-bath entanglement: non-Markov qubit cooling

Initialization of quantum logic operations makes it imperative to cool down the information-carrying qubits as much and as fast as possible, so as to purify their state, or at least their ensemble average. Yet, the limit on the speed of existing cooling schemes is either the duration of the qubit equilibration with its bath or the decay time of an auxiliary state to one of the qubit states. Here we show that highly-frequent phase-shifts or measurements of the state of thermalized qubits can be designed to affect the qubit-bath entanglement so that the qubits undergo cooling, well before they re-equilibrate with the bath and without resorting to auxiliary states. These processes can be used in principally novel, advantageous, cooling schemes to assist quantum logic operations.     

Liking and attributions of motives as mediators of the relationships between individuals' reputations, helpful behaviors and raters' reward decisions.

Two studies investigated the mediating effects of liking and attributions of motives on the relationship between a ratee's reputation and helpful behaviors and raters' reward decisions. During managerial simulations, raters evaluated individuals after watching videotapes in which the individual's reputation and helpful behaviors were manipulated. Results indicated an interaction effect between reputation and helpful behaviors such that a helpful person with a good reputation received more rewards than did a helpful person with a bad reputation. In contrast, an unhelpful person with a good reputation did not receive better rewards than an unhelpful person with a bad reputation. Moreover, raters' liking of ratees and the motives raters attributed to ratees' helpful behaviors mediated the relationship between the manipulations and raters' reward decisions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The influence of positive affect on the components of expectancy motivation.

The influence of positive affect on expectancy motivation was investigated in 2 studies. The results of Study 1 indicated that positive affect improved people's performance and affected their perceptions of expectancy and valence. In Study 1, in which outcomes depended on chance, positive affect did not influence people's perceptions of instrumentality. In Study 2, in which the link between performance and outcomes was specified, positive affect influenced all 3 components of expectancy motivation. Together, the results of Studies 1 and 2 indicated that positive affect interacts with task conditions in influencing motivation and that its influence on motivation occurs not through general effects, such as response bias or general activation, but rather through its influence on the cognitive processes involved in motivation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of goal acceptance on the relationship of goal difficulty to performance.

Tested the hypotheses that goal acceptance moderates the relationship of goal difficulty to task performance as follows: (a) The relationship is positive and linear for accepted goals; (b) it is negative and linear if the goal is rejected; and thus, (c) slope reversal from positively to negatively linear relationships is associated with transition from positive to negative values of goal acceptance. The experiment was a within-S design, allowing for high variance in acceptance, with technicians and engineers (21–50 yrs of age) divided at random into a 2-phase experimental condition (n?=?104) with specific goal difficulty gradually increasing from Trial 1 to 7 and a control group (n?=?36) with the general instructions to "do your best." Instructions for Phase 2 differed from Phase 1 in that Ss were instructed to reassess their acceptance of difficult goals. The task consisted of determining, within 2-min trials, how many digits or letters in a row were the same as the circled one to the left of each row. Results support the hypotheses. (16 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)