Intermittent Observations Research Articles

Kalman Filtering Over a Packet-Dropping Network: A Probabilistic Perspective

We consider the problem of state estimation of a discrete time process over a packet-dropping network. Previous work on Kalman filtering with intermittent observations is concerned with the asymptotic behavior of E[Pk], i.e., the expected value of the error covariance, for a given packet arrival rate. We consider a different performance metric, Pr[Pk ? M], i.e., the probability that Pk is bounded by a given M. We consider two scenarios in the paper. In the first scenario, when the sensor sends its measurement data to the remote estimator via a packet-dropping network, we derive lower and upper bounds on Pr[Pk ? M]. In the second scenario, when the sensor preprocesses the measurement data and sends its local state estimate to the estimator, we show that the previously derived lower and upper bounds are equal to each other, hence we are able to provide a closed form expression for Pr[Pk ? M]. We also recover the results in the literature when using Pr[Pk ? M] as a metric for scalar systems. Examples are provided to illustrate the theory developed in the paper.

Stochastic Stability of the Extended Kalman Filter With Intermittent Observations

In this technical note, we analyze the error behavior of the discrete-time extended Kalman filter for nonlinear systems with intermittent observations. Modelling the arrival of the observations as a random process, we show that, given a certain regularity of the system, the estimation error remains bounded if the noise covariance and the initial estimation error are small enough. We also study the effect of different measurement models on the bounds for the error covariance matrices.

Evaluation of the safety of time-lapse observations for human embryos

To assess the effects of light from an integrated optical microscope and evaluate the safety of time-lapse observations using a built-in microscope incubator. We prospectively compared the fertilization rate and embryonic morphology after intracytoplasmic sperm injection between embryos cultured with time-lapse observations every 15 min in an incubator with an integrated optical microscope and embryos with intermittent observations (once a day) in conventional incubators. No significant differences were observed in the fertilization rate (57.5% vs. 57.5%) or the rate of excellent-good cleavage embryos (36.0% vs. 36.0%). These results suggest that time-lapse observations using an incubator with an integrated optical microscope may therefore be safely utilized in clinical practice.

Random-Set-Based Estimation in Networked Environments and a Relationship to Kalman Filtering with Intermittent Observations

Firstly, an exposition of random-set-based estimation in general networked control systems is examined. This provides a background for the work introduced in this paper. This exposition is also aimed at highlighting the advantages of the random-set-based estimator formulation. Then, the case of state estimation across packet-dropping networks (but with instantaneous transmission times) is shown to be a special case of the standard random-set-based system/measurement model. A well-known result in the control literature concerning the convergence of the Kalman filter's covariance estimate is related to a simplified random-set-based algorithm for this packet-dropping scenario. Finally, a novel algorithm for random-set-based estimation across general networks with irregular measurement sequences (delayed and out-of-sequence measurements) is developed. This is the first attempt to extend random-set-based estimation to accommodate realistic, networked, scenarios.

後方散乱電子回折(EBSD)付属の走査電子顕微鏡を用いた間歇的観察

後方散乱電子回折(EBSD)付属の走査電子顕微鏡を用いた間歇的観察

Stability in the Pseudo-state Formalism of Discrete Systems Controlled in the Presence of Intermittent Sensor Faults

This paper presents sufficient conditions for the stabilization of open-loop unstable discrete time invariant systems, with nonlinear actuators, described in the pseudo-state formalism, stabilized by state feedback, when intermittent observations due to sensor faults occur. It is shown that the closed-loop system with feedback through a reconstructed signal, when, at least, one of the sensors is unavailable, remains uniformly exponentially stable, provided that the intervals of unavailability satisfy a certain time bound, even in the presence of state vanishing perturbations. The result is proved for a class of Hammerstein systems.

Alternative approaches to ‘enhanced observations’ in acute inpatient mental health care: a review of the literature

Formal 'enhanced observations' involving allocating one or two nurses to place an patient under continuous observation when acutely ill and at risk of self-harm are ineffective, contribute to impersonal care, are stressful to practitioners and reinforce the perception of a custodial environment. The aim of this literature review was to systematically bring together published studies and research that identified alternative approaches to 'enhanced observations' from those proposed in the Standing Nursing and Midwifery Advisory Committee guidelines on individuals receiving care on open acute inpatient settings. The literature search strategy resulted in the retrieval of five empirical studies, with further analysis revealing six potential interventions relating to the development of an alternative approach to observations. These are: (1) assessment; (2) nurse autonomy; (3) ward management initiatives (4) engagement and collaboration; (5) a team approach; and (6) intermittent observations. The review emphasized how enhanced observations and the development of alternative approaches are a complex activity requiring planning and consideration to facilitate appropriate implementation. The review also highlights a dearth in empirical evidence for alternatives, and a need to revise current practices because of the dissatisfaction from clients and practitioners involved in this intervention.

Consensus based overlapping decentralized estimation with missing observations and communication faults

In this paper a new algorithm for discrete-time overlapping decentralized state estimation of large scale systems is proposed in the form of a multi-agent network based on a combination of local estimators of Kalman filtering type and a dynamic consensus strategy, assuming intermittent observations and communication faults. Under general conditions concerning the agent resources and the network topology, conditions are derived for the convergence to zero of the estimation error mean and for the mean-square estimation error boundedness. A centralized strategy based on minimization of the steady-state mean-square estimation error is proposed for selection of the consensus gains; these gains can also be adjusted by local adaptation schemes. It is also demonstrated that there exists a connection between the network complexity and efficiency of denoising, i.e., of suppression of the measurement noise influence. Several numerical examples serve to illustrate characteristic properties of the proposed algorithm and to demonstrate its applicability to real problems.

Investigation of radio astronomical windows between 1 MHz and 2060 MHz in Universiti Malaya, Malaysia

An indoor and an outdoor radio frequency survey was conducted in Universiti Malaya, Malaysia, as a test site, for the purpose of developing radio astronomy research in Malaysia. This is the first radio astronomical survey of any such done in Malaysia. Observation and analysis were done in the radio frequency spectrum between 1 MHz and 2060 MHz. In this paper, the experimental setup and procedure of surveying are outlined and the measured data are interpreted. The eight radio astronomical windows were investigated from a 24 h observation, with the emphasis on two of the most important radio astronomical windows which are protected by the Malaysian Communications and Multimedia Commission (MCMC). Some intermittent observations were also done for referencing purposes. The radio frequency interferences (RFIs) are found to be relatively low. The overall relative Interference-to-Noise ratio (INR) at this test site ranges between 5.72% and 11.74%. The average strength of RFI in the eight focused radio astronomical windows at this site ranges between −100 dBm and −90 dBm (equivalently between 9.23 × 10 4 Jy and 93.29 × 10 4 Jy at resolution bandwidth of 125 kHz).

Composition of energetic particles in the Jovian magnetotail

The New Horizons spacecraft offered a unique opportunity to explore the distant Jovian magnetotail to over 2565 Jovian Radii. Previous observations of ion abundances were available only out to ∼150 Jovian Radii. During the 100+‐day exploration of the magnetotail, New Horizons observed a number of energetic particle bursts, similar to particle bursts observed by Galileo much closer to Jupiter. We examine the composition of these dynamic structures and compare the ion abundances with those found in more quiescent regions. We show that the composition of these energetic bursts is Iogenic and suggest it is within these bursts that Jupiter releases the bulk of its energetic material. We report on the ion composition ratios as a function distance down the Jovian magnetotail, finding an increasing intrusion of interplanetary He into the tail with distance from the planet. These observations show that the radial gradients in particle flux observed by Galileo in the magnetotail close to Jupiter extend deep into the magnetotail. We observed large electron intensities at the noon magnetopause crossing and continuous strong 10‐h modulations in electron intensity to nearly 500 Jovian Radii toward the tail. Our current hypothesis is that Jupiter enforces azimuthal rotation on some fields to distances of over a few hundred Jovian Radii. At distances greater than 500 Jovian Radii we observed long‐duration periods of strong electron anisotropy beaming down the magnetotail. Intermittent observations of 10‐h electron modulations continue into distant regions of the magnetotail and we suggest these are a signature of occasional field line connection to the magnetosphere.

Pore evolution during high pressure atomic vapor deposition

The development of physical vapor deposition systems that employ inert gas jets to entrain and deposit atomic and molecular fluxes have created an interest in the atomic assembly of thin films under high pressure (10–500 Pa) deposition conditions. Thin films grown under elevated pressure and low surface mobility conditions can contain a higher volume fraction of porosity and a different pore morphology to coatings created by conventional, low pressure (<10−4 Pa) deposition processes. A recent direct simulation Monte Carlo simulation analysis of binary vapor–gas jet atom interactions has shown that the incident angle distribution (IAD) for vapor atom impacts with a substrate is strongly effected by the background pressure. Here, these results are combined with a kinetic Monte Carlo technique to simulate the high pressure growth of vapor deposited nickel films and identify the mechanisms of pore formation. We find that when the surface atom mobility is low, shadowing of oblique angle arrivals by features on the substrate result in the incorporation of porosity with a hierarchical size distribution that includes elongated, inter-columnar pores and finer scale intra-columnar pores. The nucleation of the inter-columnar pores is related not only to the IAD, but also to the height and spacing of the initial asperities on the substrate and to those that subsequently evolve during deposition. The volume fraction of the inter-columnar pores is found to increase as both the fraction of oblique atom arrivals and the height of the asperities increase. For each prescribed IAD and asperity height, an asperity spacing is found that maximizes the inter-columnar pore fraction. By varying the IAD for a given substrate surface topology, in conjunction with intermittent observations of the coating structure during the growth process, the flux shadowing mechanisms that govern the inter-columnar pore nucleation have been determined.

Composite Hypothesis Testing with Intermittent Observations

In this paper, we consider the detection problem with intermittent observations, due to the unreliable shared communication link between local sensors and the fusion center. Detection performance is analyzed using Neyman-Pearson criterion of maximizing the probability of detection, for a given probability of false alarm. The detector performance is compared, with and without intermittent observations, and a formal approach is presented to restore the original detector performance.

SEM-EBSD analysis on early stage of recrystallization in Al–0.7%Mg–0.4%Si–0.2%Cr alloy

Intermittent observations have been carried out on an early stage of recrystallization in Al–Mg–Si–Cr alloy with using an SEM-EBSD system. The specimen of Al–0.7%Mg–0.4%Si–0.2%Cr alloy was solution heat treated at 813 K for 3.6 ks, and then mechanically polished and finished by electropolishing. Vickers indentations were applied on the surface for landmarks. The specimen was cold-rolled at R. T. with about 30% of a reduction rate. After an EBSD observation, the specimen was cut into about 5×5×2 mm in size. Annealing the specimen at 673 K with using a molten salt bath, ion-polishing of the surface of the specimen for 180 s, and observing with the SEM-EBSD system were repeated. Intermittent observations on the same area were carried out during annealing up to 60 s. All the grains were rotated by cold-rolling. Deformation was inhomogeneity even in the same grain. Recovery was observed as formation of subgrains after annealing for 3 s. Subgrains having a similar orientation to the mother grain showed subgrain growth with annealing out of heavily deformed region. Such a subgrain growth was followed by formation of small grain without subgrains and surrounded by large angle grain boundary. Stress induced boundary migration was also observed.

THE ENGLISH BEECH MASTING SURVEY 1980–2007: VARIATION IN THE FRUITING OF THE COMMON BEECH (FAGUS SYLVATICA L.) AND ITS EFFECTS ON WOODLAND ECOSYSTEMS

Summary 1. Study of annual production of beech mast at twelve main sites including closed canopy beechwood, shelter belts, avenues and an isolated tree in a park, as well as intermittent observations at others, has now continued for twenty-eight years. 2. During this period beech mast was sampled from up to 100 trees by seven-minute samples collected from the ground. Aerial samples have also been collected from low-growing branches. 3. Production of full seed varies greatly from year to year, and all trees produce empty pericarps as well as full mast, especially on lower or shaded branches. 4. The proportion of full nuts consumed or damaged by the moth Cydia fagiglandana Z., birds and small mammals, in English sites, can become significant especially in non-mast years. 5. Good masting occurred in 1980, 1982, 1984, 1987, 1990, 1995, 1997, 2000, 2002, 2004 and 2006: after each of these good years, one year of very poor masting normally followed. The best year recorded so far was 1990. In both 1981 and 2005, no full mast was found, and singularly very little in 1991 and 2001. 6. Regional variation within England is much less than the annual variation, but over the period the northern trees have produced on average fewer full nuts but rather more empty and total nuts. In 2007, however, northern trees produced markedly less full and total nuts than their southern counterparts. 7. Over such a long period it was inevitable that site changes would occur. In some instances the substrate beneath particular trees is now less favourable for rapid nut collection. As some trees have died, additional younger trees are now being assessed. In 1996, far more viable seed was formed in certain Scottish sites than at those we observed in England, so it is highly desirable that Scottish and Welsh sites be monitored in the future.

Consensus Based Overlapping Decentralized Estimation With Missing Observations and Communication Faults

In this paper a new algorithm for discrete-time overlapping decentralized state estimation of large scale systems is proposed in the form of a multi-agent network based on a combination of local Kalman filters and a dynamic consensus strategy, assuming intermittent observations and communication faults. Conditions are derived for the algorithm to provide, under general conditions concerning the agent resources and the network topology, asymptotic stability in the sense of bounded mean-square estimation error. It is also demonstrated how the consensus gains can be chosen by minimizing the total steady-state mean-square estimation error. Numerical examples illustrate some properties of the proposed algorithm.

Mood‐management dynamics: The interrelationship between moods and behaviours

People actively attempt to create and maintain positive moods and to escape from negative moods by engaging in various activities. The principle of homeostasis explains the essence of the mood-management system: adjustments of individuals' moods and activities help maintain constant their conditions of life. We model the dynamics of mood and mood-management behaviour through a pair of interdependent, linear differential equations and estimate the equations using mood and behaviour data collected from an adult panel. Because empirically fitting continuous-time differential equations to intermittent observations is uncommon in the literature, we show how to transform differential equations into equations that can be estimated using simultaneous-equation regression methods. Our adult panel shows strong homeostasis in mood management with mood episodes of several hours and no evidence of endogenous mood cycles.

Spatial Association among Soil Hydraulic Properties, Soil Texture, and Geoelectrical Resistivity

Spatial variability of soil hydraulic properties causes considerable variations in water and solute flow and transport processes. It remains a difficult task to determine and describe the spatial pattern of soil physical properties for modeling landscape‐scale vadose zone processes. Strategies that involve measurements of relevant variables and appropriate spatial modeling tools need to be identified for this purpose. The objective of this study was to investigate a nested sampling approach for soil hydraulic properties and associated variables, such as soil texture, in a highly variable soil landscape in northeastern Germany dominated by soils derived from glacial till. Additionally, spatially highly resolved and nondestructive measurements of geoelectrical resistivity were examined for their spatial relation to soil physical and transport properties and their applicability in spatial process models of soil hydraulic property coefficients. Two pedotransfer function (PTF) approaches were applied to gain insight into their capacity to estimate the mean and the spatial variation of soil hydraulic property coefficients, although pedotransfer functions are originally not developed for this purpose. State‐space models estimated the spatial process of hydraulic conductivity at a soil water pressure head of −50 cm and the van Genuchten parameter n with relatively narrow confidence bands, whereas for α confidence was larger. Geoelectrical resistivity supported the estimation of the spatial distribution of soil hydraulic property coefficients. Despite the fact that without calibration, pedotransfer variable estimates did not always represent the mean of the respective variable, there was generally little spatial fluctuation reflected. However, considerable horizontal and vertical variability in soil textural properties existed within the investigated landscape. The findings suggest that state‐space models incorporating intermittent observations and spatial autocovariance behavior provide more flexibility in the estimation of the spatial process of hydraulic functional coefficients than regression type functions only.

Kalman Filtering With Intermittent Observations

Motivated by navigation and tracking applications within sensor networks, we consider the problem of performing Kalman filtering with intermittent observations. When data travel along unreliable communication channels in a large, wireless, multihop sensor network, the effect of communication delays and loss of information in the control loop cannot be neglected. We address this problem starting from the discrete Kalman filtering formulation, and modeling the arrival of the observation as a random process. We study the statistical convergence properties of the estimation error covariance, showing the existence of a critical value for the arrival rate of the observations, beyond which a transition to an unbounded state error covariance occurs. We also give upper and lower bounds on this expected state error covariance.

Earthshine and the Earth's albedo: 1. Earthshine observations and measurements of the lunar phase function for accurate measurements of the Earth's Bond albedo

We have been making sustained observations of the earthshine from Big Bear Solar Observatory in California since late 1998. We also have intermittent observations from 1994–1995. We have reinvigorated and modernized a nearly forgotten way of measuring the Earth's albedo, and hence its energy balance, previously studied by A. Danjon and his followers for about 25 years early in the last century using their observations of the earthshine from France. This is the first in a series of papers covering observations and simulations of the Earth's reflectance from photometric and spectral observations of the Moon. Here, we develop a modern method of measuring, instantaneously, the large‐scale reflectance of the Earth. From California we see the Moon reflecting sunlight from the third of the Earth to the west of us in our evening (before midnight, which is during the Moon's rising phase) and from the third of the Earth to our east in our morning (after midnight, which is during the Moon's declining phase). We have precisely measured the scattering from the Moon as a function of lunar phase, which enables us to measure, in a typical night's observations, the Earth's reflectance to an accuracy of 2.0% (equivalent to measuring the Earth's emission temperature to ∼0.8 K). We have also identified the lunar phase function as the major source of discrepancy between Danjon's estimates of the albedo and more recent measurements. The albedo is due to the interplay of cloud cover and different landscapes.

Statistical characteristics of low-latitude ionospheric field-aligned irregularities obtained with the Piura VHF radar

Abstract. We present a summary of the statistical characteristics of echoes from ionospheric (E- and F-region) field-aligned irregularities obtained with the Piura VHF radar. This radar is located at ~ 7.0° dip latitude, just outside the equatorial electrojet (EEJ) region. Our results are based on (1) intermittent observations made between 1991 and 1999 just few days a year, and (2) continuous observations made between January 2000 and June 2001. During most of the intermittent observations, simultaneous measurements of EEJ and equatorial spread F (ESF) irregularities were performed with the Jicamarca VHF radar. From the continuous measurements, we have obtained the diurnal and seasonal characteristics of a variety of parameters (percentage of occurrence, signal-to-noise ratio and/or Doppler velocities) from the lower and upper E-region irregularities and also from F-region irregularities over Piura. For example, we have found that (1) the E-region echoes are stronger and occur more frequently during local summer (i.e. between December and March); (2) between May and June, the E-region echoes are weaker and occur less frequently; moreover, during these months, a semidiurnal wave with large amplitudes is observed in the meridional wind (&gt; 100 ms- 1); (3) there is vertical wavelength of about 20 km in the Doppler velocity, particularly after midnight; (4) the lower (upper) E-region Doppler velocities are influenced mainly by meridional winds (equatorial F-region vertical drifts). In addition, we have observed that the seasonal and daily occurrences of Piura F-region irregularities are similar to the occurrence of topside ESF irregularities over Jicamarca. The likelihood of occurrence of F-region irregularities over Piura and, therefore, topside ESF over Jicamarca is greater when there are no E-region irregularities over Piura. On the other hand, there is more probability of observing bottomtype/bottomside ESF irregularities over Jicamarca when E-region irregularities are observed over Piura.Key words. Ionosphere (ionospheric irregularities; equatorial ionosphere; instruments and techniques)