Group dynamics and record signals in the ant Temnothorax albipennis

Many purely physical complex systems, in which there are both stochasticity and local interactions between the components, exhibit record dynamics. The temporal statistics of record dynamics is a Poisson process operating on a logarithmic rather than a linear time scale (i.e. a log-Poisson process). Record dynamics often drive substantial changes in complex systems when new high water marks in partially stochastic processes trigger new events. Social insect colonies are exemplary complex biological systems in which many of the local interactions of the components have been moulded by natural selection for the common good. Here, we combine experimental manipulation of ant colony demography with modelling to test the hypothesis that social interactions are the mechanism underlying the record dynamics. We found that compared with the control, log-Poisson statistics were disrupted in colonies in which the pattern of interactions was modified by the removal of the brood, and disappeared completely in ‘callow’ colonies composed entirely of very young workers from the same age cohort. We conclude that a subtle interplay between the demography of the society and the pattern of the interactions between the ants is crucial for the emergence of record dynamics. This could help identify what makes an ant colony a cohesive society.     

Fractal modeling techniques for spatial data

The paper presents convolutional linear data models for the processing of one-dimensional (1D) and two-dimensional (2D) spatial data. The models assume that the measured data is the superposition of a stochastic innovation process and a deterministic system function. The innovation process is described by a fractal scaling noise, which has a power spectral density proportional to some power (-β) of the frequency. The system function is assumed to be symmetric and is constructed using autoregressive (AR) filtering procedures. Iterative deconvolution procedures are developed to recover the fractal innovation from the data. For computational convenience, these procedures assume a spectrally white (β=0) innovation, but modify the data prior to inversion by prewhitening the a priori assumed fractal innovation. The filter coefficients recovered by inverting the modified data are then applied to the original data to recover the fractal innovation. The ability of the deconvolution procedures to recover the fractal innovation is demonstrated using 1D and 2D synthetic data sets. As a practical example, the 2D deconvolution technique is applied to an aeromagnetic map from northeastern Ontario, Canada, and is shown to be effective in enhancing magnetic field anomalies     

EEG complexity as a measure of depth of anesthesia for patients

A new approach for quantifying the relationship between brain activity patterns and depth of anesthesia (DOA) is presented by analyzing the spatio-temporal patterns in the electroencephalogram (EEG) using Lempel-Ziv complexity analysis. Twenty-seven patients undergoing vascular surgery were studied under general anesthesia with sevoflurane, isoflurane, propofol, or desflurane. The EEG was recorded continuously during the procedure and patients' anesthesia states were assessed according to the responsiveness component of the observer's assessment of alertness/sedation (OAA/S) score. An OAA/S score of zero or one was considered asleep and two or greater was considered awake. Complexity of the EEG was quantitatively estimated by the measure C(n), whose performance in discriminating awake and asleep states was analyzed by statistics for different anesthetic techniques and different patient populations. Compared with other measures, such as approximate entropy, spectral entropy, and median frequency, C(n) not only demonstrates better performance (93% accuracy) across all of the patients, but also is an easier algorithm to implement for real-time use. The study shows that C(n) is a very useful and promising EEG-derived parameter for characterizing the (DOA) under clinical situations.     

Dynamic modelling of service delivery

Planning to deliver excellent service by balancing demand and supply in the context of a set of business policies is not an easy task. How an organisation dynamically deploys its resources and people in response to external demand determines how quickly an organisation can deliver service to its customers. To model this you need to represent the flows of work through the organisation, the resources available and the relationships between intake of work, outputs, workstacks and time-to-deliver. You also need to understand how flexible the organisation is in dealing with uncertain and fluctuating intakes and the policies the organisation adopts in deploying this flexibility. We have constructed a model of the operations of a telecommunications company that incorporates all of these elements using the system dynamics approach. This paper describes how the model is constructed and gives examples of how it can be used to explain observed behaviours. It also explains how it has been used to guide decision making on resource requirements and the optimum mix between proactive and reactive approaches to service assurance.     

Highly birefringent index-guiding photonic crystal fibers

Photonic crystal fibers (PCFs) offer new possibilities of realizing highly birefringent fibers due to a higher intrinsic index contrast compared to conventional fibers. In this letter, we analyze theoretically the levels of birefringence that can be expected using relatively simple PCF designs. While extremely high degrees of birefringence may be obtained for the fibers, we demonstrate that careful design with respect to multimode behavior must be performed. We further discuss the cutoff properties of birefringent PCFs and present experimental results in agreement with theoretical predictions on both single- and multimode behavior and on levels of birefringence     

Thermally induced variation in barrier height and ideality factor of Ni/Au contacts to p-GaN

In this paper, we describe the change in barrier heights (ϕ_B) and ideality factors (n) of Ni/Au contacts to p-GaN determined from current-voltage measurements as a result of (a) rapid thermal annealing between 400–700°C under flowing nitrogen, and (b) testing at temperatures of 20–300°C. The lowest barrier height and ideality factor values were obtained from samples annealed at 500–600°C. These results provide supporting evidence that thermal processing helps to remove contaminants at the contact-GaN interface, thus decreasing effective barrier height and consequently, contact resistance.     

Quantitative secretion and maximal secretion capacity of retinol, beta-carotene and alpha-tocopherol into cows' milk

Changes in the contents of retinol, alpha-tocopherol and beta-carotene in plasma, milk and milk fat from 38 Holstein-Friesian cows were followed during their first lactation, and the quantitative and kinetic relationships for secretion of alpha-tocopherol and beta-carotene from blood into milk were determined. The cows were assigned to three groups such that all cows in the same group had the same sire. Milk yield and milk fat content differed with stage of lactation, but not according to sire. The plasma concentrations of retinol, alpha-tocopherol and beta-carotene differed with stage of lactation; in addition, retinol and beta-carotene concentration also differed according to sire. The concentrations of all three vitamins in milk and milk fat differed according to sire and stage of lactation. Furthermore, the total secretion of retinol, alpha-tocopherol and beta-carotene into milk (expressed as mg/d) differed with sire and stage of lactation. The quantitative secretion of alpha-tocopherol and beta-carotene from blood into milk followed Michaelis-Menten kinetics for active transport across membranes. Values of maximum secretory capacity Vmax and the half-rate constant K(m) for both alpha-tocopherol and beta-carotene varied according to sire. Overall means for Vmax for alpha-tocopherol and beta-carotene were 32.4 and 2.5 mg/d. Thus, the daily secretion of alpha-tocopherol and beta-carotene is limited in quantity, and is independent of the yields of milk and milk fat. It follows that continuing breeding and management systems that focus solely on increasing milk and milk fat yield will result in a steady dilution in the milk fat of these vitamins and antioxidants important for the immune defence of the cows and oxidative stability of milk products. The genetic variation found offers the possibility of utilizing these variations in breeding systems.     

UTRA/FDD RF Transceiver Requirements

Unified RF requirements are derived for an UMTS Terrestrial RadioAccess/Frequency Division Duplex (UTRA/FDD) compliant mobile transceiver. Aset of transceiver requirements are proposed with consideration to systemissues including duplex aspects. From these design-compatible requirements areproposed for each functional block in the transceiver.     

Fabrication and characterization of two-color midwavelength/long wavelength HgCdTe infrared detectors

High-performance 20-μm unit-cell two-color detectors using an n-p⁺-n HgCdTe triple-layer heterojunction (TLHJ) device architecture grown by molecular beam epitaxy (MBE) on (211)-oriented CdZnTe substrates with midwavelength (MW) infrared and long wavelength (LW) infrared spectral bands have been demonstrated. Detectors with nominal MW and LW cut-off wavelengths of 5.5 μm and 10.5 μm, respectively, exhibit 78 K LW performance with >70 % quantum efficiency, reverse bias dark currents below 300 pA, and RA products (zero field of view, 150-mV bias) in excess of 1×10³ Ωcm². Temperature-dependent current-voltage (I–V) detector measurements show diffusion-limited LW dark current performance extending to temperatures below 70 K with good operating bias stability (150 mV ± 50 mV). These results reflect the successful implementation of MBE-grown TLHJ detector designs and the introduction of advanced photolithography techniques with inductively coupled plasma (ICP) etching to achieve high aspect ratio mesa delineation of individual detector elements with benefits to detector performance. These detector improvements complement the development of high operability large format 640×480 and 1280×720 two-color HgCdTe infrared focal plane arrays (FPAs) to support third generation forward looking infrared (FLIR) systems.     

Ku-band subsampling track-and-hold amplifier with 8 ENOB resolution

A wideband subsampling track-and-hold amplifier has been designed for input frequencies up to Ku-band and clock rates up to 2.5 GS/s. Circuits were fabricated in 1 /spl mu/m InP SHBT technology. Spur-free dynamic range measured with two-tone input frequencies of 12.6 and 12.602 GHz and a 2.5 GS/s clock rate ranges from 53-69 dB at an input level of -1 dBFS for each tone. Signal-to-noise ratio (SNR) test results show that the master/slave (M/S) track-and-hold design provides 59 dB of SNR in a 1 GHz bandwidth at input frequencies up to at least 2.6 GHz. A single track-and-hold dissipates 1.5 W while the M/S configuration dissipates 2.5 W.