Node counting in wireless ad-hoc networks

We study wireless ad-hoc networks consisting of small microprocessors with limited memory, where the wireless communication between the processors can be highly unreliable. For this setting, we propose a number of algorithms to estimate the number of nodes in the network, and the number of direct neighbors of each node. The algorithms are simulated, allowing comparison of their performance

Coherent versus incoherent excitation dynamics in dissipative many-body Rydberg systems

We study the impact of dephasing on the excitation dynamics of a cloud of ultracold two-level Rydberg atoms for both resonant and off-resonant laser excitation, using the wave function Monte Carlo (MCWF) technique. We find that while for resonant laser driving, dephasing mainly leads to an increase of the Rydberg population and a decrease of the Mandel Q parameter, at off-resonant driving strong dephasing toggles between direct excitation of pairs of atoms and subsequent excitation of single atoms, respectively. These two excitation mechanisms can be directly quantified via the pair correlation function, which shows strong suppression of the two-photon resonance peak for strong dephasing. Consequently, qualitatively different dynamics arise in the excitation statistics for weak and strong dephasing in off-resonant excitation. Our findings show that time-resolved excitation number measurements can serve as a powerful tool to identify the dominating process in the system's excitation dynamics.Comment: 10 pages, 10 figure

Semi-analytical model for nonlinear light propagation in strongly interacting Rydberg gases

Rate equation models are extensively used to describe the many-body states of laser driven atomic gases. We show that the properties of the rate equation model used to describe nonlinear optical effects arising in interacting Rydberg gases can be understood by considering the excitation of individual super-atoms. From this we deduce a simple semi-analytic model that accurately describes the Rydberg density and optical susceptibility for different dimensionalities. We identify the previously reported universal dependence of the susceptibility on the Rydberg excited fraction as an intrinsic property of the rate equation model that is rooted in one-body properties. Benchmarking against exact master equation calculations, we identify regimes in which the semi-analytic model is particularly reliable. The performance of the model improves in the presence of dephasing which destroys higher order atomic coherences.Comment: 7 pages, 4 figure

BURNOUT AMONG DUTCH REFORMED PASTORS

research articleThe present study examined the degree of burnout among Dutch reformed pastors and aspects that may be conducive to the onset of burnout. They were asked to report how difficult they found their tasks and what options they had to alleviate the pressure of work they experienced. Compared with other human service professionals the results show that pastors have relatively high scores on emotional exhaustion and relatively low scores on depersonalization. Pastors have relatively low scores on personal accomplishment. Those who say they are experiencing severe pressure of work appear to have high scores on the three burnout dimensions. Role ambiguity and lack of social support appear to intensify reported feelings of burnout. This article concludes by discussing some of the pastor's own suggestions as to how to relieve work pressure

Statistics of Conductances and Subleading Corrections to Scaling near the Integer Quantum Hall Plateau Transition

We study the critical behavior near the integer quantum Hall plateau transition by focusing on the multifractal (MF) exponents $X_q$ describing the scaling of the disorder-average moments of the point contact conductance $T$ between two points of the sample, within the Chalker-Coddington network model. Past analytical work has related the exponents $X_q$ to the MF exponents $\Delta_q$ of the local density of states (LDOS). To verify this relation, we numerically determine the exponents $X_q$ with high accuracy. We thereby provide, at the same time, independent numerical results for the MF exponents $\Delta_q$ for the LDOS. The presence of subleading corrections to scaling makes such determination directly from scaling of the moments of $T$ virtually impossible. We overcome this difficulty by using two recent advances. First, we construct pure scaling operators for the moments of $T$ which have precisely the same leading scaling behavior, but no subleading contributions. Secondly, we take into account corrections to scaling from irrelevant (in the renormalization group sense) scaling fields by employing a numerical technique ("stability map") recently developed by us. We thereby numerically confirm the relation between the two sets of exponents, $X_q$ (point contact conductances) and $\Delta_q$ (LDOS), and also determine the leading irrelevant (corrections to scaling) exponent $y$ as well as other subleading exponents. Our results suggest a way to access multifractality in an experimental setting.Comment: 7 pages and 4 figures, plus Supplemental materia

A hybrid model for Rydberg gases including exact two-body correlations

A model for the simulation of ensembles of laser-driven Rydberg-Rydberg interacting multi-level atoms is discussed. Our hybrid approach combines an exact two-body treatment of nearby atom pairs with an effective approximate treatment for spatially separated pairs. We propose an optimized evolution equation based only on the system steady state, and a time-independent Monte Carlo technique is used to efficiently determine this steady state. The hybrid model predicts features in the pair correlation function arising from multi-atom processes which existing models can only partially reproduce. Our interpretation of these features shows that higher-order correlations are relevant already at low densities. Finally, we analyze the performance of our model in the high-density case.Comment: significantly expanded and revised version (more observables, high-density regime); 9 pages, 8 figure

Exploring multivariate data structures with local principal curves.

A new approach to find the underlying structure of a multidimensional data cloud is proposed, which is based on a localized version of principal components analysis. More specifically, we calculate a series of local centers of mass and move through the data in directions given by the first local principal axis. One obtains a smooth ``local principal curve'' passing through the "middle" of a multivariate data cloud. The concept adopts to branched curves by considering the second local principal axis. Since the algorithm is based on a simple eigendecomposition, computation is fast and easy

Cost methods in a hosiery mill

During the past three or four years hosiery manufacturers with an effective cost system have had many occasions to rejoice. With the excessive fluctuations of materials and supplies, labor and overhead, and high taxes, it is small wonder that many mills have gone bankrupt. Without a cost system it was next to impossible to determine a financial condition without a general inventory, and even then, in many cases, it was too late to recover. And now when conditions are gradually getting back to normal, competition becoming keener, and buyers demanding honest quality, there is all the more reason why a manufacturer requires an effective cost system. This article deals with the cost methods in a hosiery mill employing 1,200 operatives, having a daily capacity of 4,000 dozen pairs, making twenty different styles of seamless hosiery of pure silk, fibre silk and cotton, and a combination of these materials

Reducing Soil Phosphorus Buildup from Animal Manure Application

Animal manure is an excellent plant nutrient source for pastures but increasing soil P level over time is a major environmental problem (Sims et al., 1998). The increase in residual soil P is due to the difference in N-P ratio in the manure and forage crop requirements (Robinson, 1996). All the N in animal manure is normally utilised but only from 20 to 40% of the P is taken up. With moderate rates of manure application, nitrogen becomes the limiting nutrient for grasses. The objective of this study was to see if combining commercial N fertiliser with broiler litter would enhance forage yield and P uptake sufficiently to reduce residual soil P levels