Positive Drift Research Articles

Analysis of Thermal-Conductivity Measurement Data from International Comparison of National Laboratories

For the first time under the auspices of the Bureau International des Poids et Mesures (BIPM), seven national metrology institutes (NMIs) participated in an international interlaboratory comparison on thermal-conductivity measurements by the guarded hot-plate method. Measurements were conducted successively by all participants on the same set of specimens of insulating materials (mineral wool and expanded polystyrene) at temperatures ranging from 10 °C to 40 °C, according to the International Standard ISO 8302. This protocol aims to minimize issues of material variability by circulating the same pairs of specimens among the laboratories following the strict format of a round-robin test program. This comparison is a pilot study which is intended as a first stage for future key comparisons between NMIs. The descriptive analysis of obtained results shows good agreement between laboratories for the mineral wool (MW) specimens and the thicker specimens of expanded polystyrene (EPS), with relative deviations within the uncertainties of measurement. A positive drift of thermal-conductivity values, which has appeared progressively during the comparison process, seems to be correlated with the size of the metering area of the guarded hot plates used. A statistical analysis was applied to repeated thermal-conductivity measurements at 23 °C, to identify anomalous and outlying data, to assess the within- and between-laboratory variability, and to evaluate the participant laboratories’ performance.

Probing the Inhomogeneous Universe with Gravitational Wave Cosmology

If we assume that we live in the center of a spherical inhomogeneous universe, we can explain the apparent accelerating expansion of the universe without introducing the unknown dark energy or modifying gravitational theory. Direct measurement of the cosmic acceleration can be a powerful tool in distinguishing ΛCDM and the inhomogeneous models. If ΛCDM is the correct model, we have shown that DECIGO/BBO has sufficient ability to detect the positive redshift drift of the source by observing gravitational waves from neutron star binaries for 5-10 years. This enables us to rule out any Lemaître-Tolman-Bondi (LTB) void model with monotonically increasing density profile. Furthermore, by detecting the positive redshift drift at z ~ 0, we can even rule out generic LTB models unless we allow unrealistically steep density gradient at z ~ 0. We also show that the measurement accuracy is slightly improved when we consider the joint search of DECIGO/BBO and the third generation Einstein Telescope. This test can be performed with GW observations alone without any reference to electromagnetic observations.

Particle trajectories in extreme Stokes waves

We give a qualitative description of the particle paths in extreme Stokes waves, showing that all particle paths are looping curves with a positive drift. We also prove that the wave crest is only an apparent stagnation point: although in the frame moving at the wave speed, the velocity field is zero at this point, a particle can never rest at this location.

Impact of Interfacial Trap Density of States on the Stability of Amorphous InGaZnO-Based Thin-Film Transistors

The impact of interfacial trap states on the stability of amorphous indium-gallium-zinc oxide thin film transistors is studied under positive gate bias stress. With increasing stress time, the device exhibits a large positive drift of threshold voltage while maintaining a stable sub-threshold swing and a constant field-effect mobility of channel electrons. The threshold voltage drift is explained by charge trapping at the high-density trap states near the channel/dielectric interface, which is confirmed by photo-excited charge-collection spectroscopy measurement.

Empirical analysis of air traffic controller dynamics

This paper addresses an empirical analysis of air traffic controller’s activities using a human dynamics and complex systems approach. Recent studies on human dynamics show several empirical evidences that, different from common belief respecting random-based Poisson distributions, patterns of human activities fit into power law distribution with heavy tail patterns. Our hypothesis lies upon the question whether or not controller’s dynamics obeys the same power law pattern. The analysis based on a 2-weeks simulation dataset is first performed to examine the interaction between traffic activities and controller’s communication activities. Two widely studied complexity metrics, the Dynamic Density (DD) and the complexity based on dynamical system modeling (C-DSM) approach, have been constructed from the aircraft trajectory data. It is, however, found that neither the DD nor the C-DSM has significant influence on the controller’s communication temporal behavior, except that few approach sectors show close relationships between the DD and communication. Beside this simulation dataset, three other datasets which include another simulation dataset and two operational datasets are also investigated to study the temporal characteristics of controller activities. The use of detrended fluctuation analysis (DFA) found that the inter-communication times of controller are long-rang correlated, showing a heavy tailed pattern. We show that the Inverse Gaussian distribution is better than the Power-law distribution to describe the temporal data. This indicates that the mechanism underlying controller’s activities is different from the general one proposed by Barabasi (2005). The Lévy process with positive drift may be capable of explaining the adaptive behavior of the controller.

Complete Mitochondrial Genome Sequencing Reveals Novel Haplotypes in a Polynesian Population

The high risk of metabolic disease traits in Polynesians may be partly explained by elevated prevalence of genetic variants involved in energy metabolism. The genetics of Polynesian populations has been shaped by island hoping migration events which have possibly favoured thrifty genes. The aim of this study was to sequence the mitochondrial genome in a group of Maoris in an effort to characterise genome variation in this Polynesian population for use in future disease association studies. We sequenced the complete mitochondrial genomes of 20 non-admixed Maori subjects using Affymetrix technology. DNA diversity analyses showed the Maori group exhibited reduced mitochondrial genome diversity compared to other worldwide populations, which is consistent with historical bottleneck and founder effects. Global phylogenetic analysis positioned these Maori subjects specifically within mitochondrial haplogroup - B4a1a1. Interestingly, we identified several novel variants that collectively form new and unique Maori motifs – B4a1a1c, B4a1a1a3 and B4a1a1a5. Compared to ancestral populations we observed an increased frequency of non-synonymous coding variants of several mitochondrial genes in the Maori group, which may be a result of positive selection and/or genetic drift effects. In conclusion, this study reports the first complete mitochondrial genome sequence data for a Maori population. Overall, these new data reveal novel mitochondrial genome signatures in this Polynesian population and enhance the phylogenetic picture of maternal ancestry in Oceania. The increased frequency of several mitochondrial coding variants makes them good candidates for future studies aimed at assessment of metabolic disease risk in Polynesian populations.

Direct measurement of the positive acceleration of the universe and testing inhomogeneous models under gravitational wave cosmology

One possibility for explaining the apparent accelerating expansion of the universe is that we live in the center of a spherically inhomogeneous universe. Although current observations cannot fully distinguish ΛCDM and these inhomogeneous models, direct measurement of the acceleration of the universe can be a powerful tool in probing them. We have shown that, if ΛCDM is the correct model, DECIGO/BBO would be able to detect the positive redshift drift (which is the time evolution of the source redshift z) in 3–5 year gravitational wave (GW) observations from neutron-star binaries, which enables us to rule out any Lemaître-Tolman-Bondi (LTB) void model with monotonically increasing density profile. We may even be able to rule out any LTB model unless we allow unrealistically steep density profile at z ∼ 0. This test can be performed with GW observations alone, without any reference to electromagnetic observations, and is more powerful than the redshift drift measurement using Lyman α forest.

DDD: A New Ensemble Approach for Dealing with Concept Drift

Online learning algorithms often have to operate in the presence of concept drifts. A recent study revealed that different diversity levels in an ensemble of learning machines are required in order to maintain high generalization on both old and new concepts. Inspired by this study and based on a further study of diversity with different strategies to deal with drifts, we propose a new online ensemble learning approach called Diversity for Dealing with Drifts (DDD). DDD maintains ensembles with different diversity levels and is able to attain better accuracy than other approaches. Furthermore, it is very robust, outperforming other drift handling approaches in terms of accuracy when there are false positive drift detections. In all the experimental comparisons we have carried out, DDD always performed at least as well as other drift handling approaches under various conditions, with very few exceptions.

Ventilatory long‐term facilitation following acute intermittent or continuous hypoxaemia in awake humans: the role of carotid chemoreceptors and ventilatory drift to sustained hypercapnia

In awake humans, acute intermittent hypoxaemia (IH) causes a sustained increase in ventilation upon reoxygenation, known as ventilatory long‐term facilitation (vLTF), but only if combined with mild hypercapnia. It is not known if mild hypercapnia also unmasks vLTF following continuous hypoxia (CH). Carotid chemoreceptor (CC) sensitisation has been proposed as a mechanism for vLTF. We hypothesised that silencing the CC with 100% O2 would transiently abolish vLTF.12 males undertook 3 trials. Mild hypercapnia was maintained in all trials and one minute exposures to 100% O2 occurred at baseline and recovery. Trials differed only in their hypoxic exposure; Trial 1‐Acute IH, Trial 2‐Acute CH, Trial 3‐Euoxia. Ventilation in Trial 1 and 2 increased from baseline to recovery (T1: 20.1 ± 1.1 vs. 25.1 ± 1.6, T2: 20.0 ± 1.2 vs. 25.1 ± 1.4 L/min).Ventilation also increased in Trial 3 but to a lesser extent (19.8 ± 1.17 vs. 22.4 ± 1.84 L/min). Ventilation during 100% O2 increased from baseline to recovery in all trials (T1: 17.1 ± 1.2 vs. 21.8 ± 1.6, T2: 18.0 ± 1.5 vs. 22.5 ± 1.5, T3: 17.6 ± 1.4 vs. 20.2 ± 2.1).In awake humans, during mild hypercapnia, CH induces a similar magnitude of vLTF as IH. However, a gradual positive drift in ventilation to mild hypercapnia accounts for ~50% of the vLTF. Silencing of the CC with 100% O2 exposure does not transiently abolish vLTF following acute IH or CH, suggesting CC sensitisation may not mediate vLTF.

Do Buy-Side Recommendations Have Investment Value

We examine a dataset consisting of comprehensive investment recommendations paired with analyst-specific information for over 1,100 buy-side analysts (predominantly analysts from hedge funds). Short recommendations from these analysts generate an immediate and significant decline in price, whereas long recommendations for small firms have positive short-term returns and exhibit a positive drift. The evidence suggests buy-side recommendations provide information to market participants and that buy-side firms front-run their own information events. We also explore institutional ownership changes and document a wealth transfer between the broader institutional market and buy-side firms in the sample.

Sequential maximum likelihood estimation for reflected generalized Ornstein–Uhlenbeck processes

In this paper, we investigate a sequential maximum likelihood estimator of the unknown drift parameter for a class of reflected generalized Ornstein–Uhlenbeck processes driven by spectrally positive Lévy processes. In both of the cases of negative drift and positive drift, we prove that the sequential maximum likelihood estimator of the drift parameter is closed, unbiased, normally distributed and strongly consistent. Finally a numerical test is presented to illustrate the efficiency of the estimator.

Optimal dividend distribution under Markov regime switching

We investigate the problem of optimal dividend distribution for a company in the presence of regime shifts. We consider a company whose cumulative net revenues evolve as a Brownian motion with positive drift that is modulated by a finite state Markov chain, and model the discount rate as a deterministic function of the current state of the chain. In this setting, the objective of the company is to maximize the expected cumulative discounted dividend payments until the moment of bankruptcy, which is taken to be the first time that the cash reserves (the cumulative net revenues minus cumulative dividend payments) are zero. We show that if the drift is positive in each state, it is optimal to adopt a barrier strategy at certain positive regime-dependent levels, and provide an explicit characterization of the value function as the fixed point of a contraction. In the case that the drift is small and negative in one state, the optimal strategy takes a different form, which we explicitly identify if there are two regimes. We also provide a numerical illustration of the sensitivities of the optimal barriers and the influence of regime switching.

Comparison of Mediterranean sea level variability as given by three baroclinic models

We compare the results of three baroclinic models with the aim of evaluating their skills in reproducing Mediterranean long‐term sea level variability. The models are an ocean‐ice coupled forced global model (ORCA), a regional forced ocean model (OM8) and a regional coupled atmosphere‐ocean model (MITgcm). Model results are compared for the period 1961–2000 against hydrographic observations for water mass properties and steric sea level, and against satellite altimetry data and a reconstruction for sea level. All models represent the temperature variability of the upper layers reasonably well, but exhibit a considerable positive drift in the temperature of the deep layers due to an imbalance between the surface heat flux and the heat flux through Gibraltar. OM8 and MITgcm simulate the process of dense water formation better than ORCA thanks to their higher resolution in the model grid and in the atmospheric forcings. Concerning sea level variability, MITgcm is the only model that simulates well the inter‐annual sea level variability associated with the Eastern Mediterranean Transient. However, none of the models is able to reproduce other features that have clear signatures on sea level. The inter‐annual variability of Mediterranean mean sea level is better reproduced by the ORCA model because it is the only one considering the mass contribution from the Atlantic. The lack of that component in the regional models is a major shortcoming to reproduce Mediterranean sea level variability. Finally, mean sea level trends are overestimated by all models due to the spurious warming drift in the deep layers.

DIA Solitary and Shock Waves in Dusty Multi-Ion Dense Plasma with Arbitrary Charged Dust

The nonlinear propagation of the DIA (dust ion-acoustic) waves in multi-ion dense plasma system containing degener- ate electrons, both positive and negative ions, arbitrary charged dust grains has been investigated by employing the reductive perturbation method. The nonlinear waves (solitary and shock waves) have been observed to be formed in case of both positive and negative charged dust grains from the stationary solution of the Korteweg de-Vries (K-dV) equation and Burger’s equation. The fundamental properties of such nonlinear waves have been theoretically analyzed by comparing system potential for both positive and negative dust grains. It has been shown that the basic features of these waves are significantly modified by the positive and negative ions drift speed and polarities of dust grains. The implications of our results in space and laboratory plasmas are briefly discussed.

Simulation of Islanding Detection for Photovoltaic Grid-Connected Inverters Based on Positive Feedback Intermittent Frequency Drift

Islanding detection is a absolutely necessary function for Photovoltaic Grid-Connected Inverters and it is very important to detect the islanding accurately and quickly with less adverse impact on power quality. This paper proposes a positive feedback intermittent active frequency drift method which can decrease the adverse impact of frequency disturbance effectively within the time restrict of islanding detection according to that of traditional islanding detection methods. The theoretical analysis and simulation results show that this algorithm which is simple, effective, fast and have less adverse impact on power quality and has certain application value.

Optimal Dividend Policy When Cash Reserves Follow a Jump-Diffusion Process Under Markov-Regime Switching

We study the problem of optimal dividend payments for a company of limited liability whose cash reserves in the absence of dividends follow a Markov-modulated jump-diffusion process with positive drifts, where parameters and the discount rate are modulated by a finite-state irreducible Markov chain and governed by a deterministic function of the current state of the chain. In this setup, our main purpose is to maximize the expected cumulative discounted dividend payments until the moment of bankruptcy, the first time that cash reserves are nonpositive. Along the lines of Jiang and Pistorius \cite [23], we extend their results to our setup by using fixed point theorem and stochastic control to prove that it is also optimal to adopt a modulated barrier strategy at certain positive regime-dependent levels and that value function can be explicitly characterized as the fixed point of a contraction.

Pressure Sensor Drifts in Argo and Their Impacts

Abstract In recent years, autonomous profiling floats have become the prime component of the in situ ocean observing system through the implementation of the Argo program. These data are now the dominant input to estimates of the evolution of the global ocean heat content and associated thermosteric sea level rise. The Autonomous Profiling Explorer (APEX) is the dominant type of Argo float (~62%), and a large portion of these floats report pressure measurements that are uncorrected for sensor drift, the size and source of which are described herein. The remaining Argo float types are designed to automatically self-correct for any pressure drift. Only about 57% of the APEX float profiles (or ~38% Argo profiles) can be corrected, but this typically has not been done by the data centers that distribute the data (as of January 2009). A pressure correction method for APEX floats is described and applied to the Argo dataset. A comparison between estimates using the corrected Argo dataset and the publically available uncorrected dataset (as of January 2009) reveals that the pressure corrections remove significant regional errors from ocean temperature, salinity, and thermosteric sea level fields. In the global mean, 43% of uncorrectable APEX float profiles (or ~28% Argo profiles) appear to largely offset the effect of the correctable APEX float profiles with positive pressure drifts. While about half of the uncorrectable APEX profiles can, in principle, be recovered in the near future (after inclusion of technical information that allows for corrections), the other half have negative pressure drifts truncated to zero (resulting from firmware limitations), which do not allow for corrections. Therefore, any Argo pressure profile that cannot be corrected for biases should be excluded from global change research. This study underscores the ongoing need for careful analyses to detect and remove subtle but systematic errors in ocean observations.

Coating thickness measurement of thin gold and palladium coatings on printed circuit boards using X‐ray fluorescence

PurposeThe purpose of this paper is to compare the performance of X‐ray fluorescence (XRF) instruments with different detector systems (proportional counter, positive intrinsic negative and Si drift detectors) for measuring thin Au and Pd coatings on printed circuit boards and to investigate different ways of background treatment. It also aims to provide and certify suitable reference materials which are similar to samples used in production.Design/methodology/approachXRF measurements were performed with different instruments and detector types. The quantification of the reference materials is based on XRF, gravimetric analysis and Rutherford backscattering (RBS).FindingsThe well‐established X‐ray instrumentation for coating thickness measurement, with proportional counter detectors, are not very suitable for measuring thin ( < approx. 100 nm) coatings of gold and palladium due to the poor energy resolution of the proportional counter‐tubes. Systems with semiconductor detectors achieve results that are more reliable with a significantly higher accuracy. A correct background treatment is especially important for very thin coatings. The composition of the base material has to be taken into account by the software evaluation algorithm for each measurement. A global base subtraction performed prior to the measurement can achieve better repeatability, but can also lead to incorrect absolute values.Research limitations/implicationsIf small measuring spots (e.g. 150 μm) have to be realized with semiconductor detector systems, special X‐ray optics (polycapillaries) have to be used to obtain an intensity comparable to that offered by proportional counter devices. This will be the subject of a further publication.Originality/valueThe paper provides an overall review and results for different types of instruments (detectors) and compares different background treatments. Suitable reference materials have been developed for precise and traceable measurements. Their quantification is based on gravimetric analysis and RBS. The standard‐free energy dispersive X‐ray fluorescence (ED‐X‐ray fluorescence analysis (XRFA)) was used for interpolation of the gravimetric data for thin coatings. For the region below 100 nm, measurement uncertainties of less than 1 nm can be achieved.

Millisecond Radio Spikes in the Decimetric Band

We present the results of the analysis of thirteen events consisting of dm-spikes observed in Torun between 15 March 2000 and 30 October 2001. The events were obtained with a very high time resolution (80 microseconds) radio spectrograph in the 1352 – 1490 MHz range. These data were complemented with observations from the radio spectrograph at Ondřejov in the 0.8 – 2.0 GHz band. We evaluated the basic characteristics of the individual spikes (duration, spectral width, and frequency drifts), as well as their groups and chains, the location of their emission sources, and the temporal correlations of the emissions with various phases of the associated solar flares. We found that the mean duration and spectral width of the radio spikes are equal to 0.036 s and 9.96 MHz, respectively. Distributions of the duration and spectral widths of the spikes have positive skewness for all investigated events. Each spike shows positive or negative frequency drift. The mean negative and positive drifts of the investigated spikes are equal to −776 MHz s−1 and 1608 MHz s−1, respectively. The emission sources of the dm-spikes are located mainly at disk center. We have noticed two kinds of chains, with and without frequency drifts. The mean durations of the chains vary between 0.067 s and 0.509 s, while their spectral widths vary between 7.2 MHz and 17.25 MHz. The mean duration of an individual spike observed in a chain was equal to 0.03 s. While we found some agreement between the global characteristics of the groups of spikes recorded with the two instruments located in Torun and Ondřejov, we did not find any one-to-one relation between individual spikes.

(Non)Differentiability and Asymptotics for Potential Densities of Subordinators

For subordinators with positive drift we extend recent results on the structure of the potential measures and the renewal densities. Applying Fourier analysis a new representation of the potential densities is derived from which we deduce asymptotic results and show how the atoms of the Levy measure translate into points of (non)differentiability of the potential densities.