Defence Science and Technology Group

Increasingly, for many application areas, it is becoming important to include elements of nonlinearity and non-Gaussianity in order to model accurately the underlying dynamics of a physical system. Moreover, it is typically crucial to process data on-line as it arrives, both from the point of view of storage costs as well as for rapid adaptation to changing signal characteristics. In this paper, we review both optimal and suboptimal Bayesian algorithms for nonlinear/non-Gaussian tracking problems, with a focus on particle filters. Particle filters are sequential Monte Carlo methods based on point mass (or "particle") representations of probability densities, which can be applied to any state-space model and which generalize the traditional Kalman filtering methods. Several variants of the particle filter such as SIR, ASIR, and RPF are introduced within a generic framework of the sequential importance sampling (SIS) algorithm. These are discussed and compared with the standard EKF through an illustrative example.

Abstract Mechanisms of hydrogen embrittlement in steels and other materials are described, and the evidence supporting various hypotheses, such as those based on hydride formation, hydrogen-enhanced decohesion, hydrogen-enhanced localised plasticity, adsorption-induced dislocation emission, and hydrogen-vacancy interactions, are summarised. The relative importance of these mechanisms for different fracture modes and materials are discussed based on detailed fractographic observations and critical experiments.

This paper presents an experimental and theoretical investigation of the applicability of the time-reversal concept to guided waves in plate-like structures, where the stress waves are dispersive and of multi-modes. It is shown that temporal and spatial focusing can be achieved through time reversal, although the dispersive behaviour of the flexural waves renders it impossible to exactly reconstruct the waveform of the original excitation. Based on the principle of the time-reversal concept, a digital imaging method suitable for distributed sensor/actuator networks has been developed. This new method, which overcomes the limitation of the conventional phased array method that operates under pulse-echo mode, provides an efficient imaging method for locating and approximate sizing of structural damages. In addition, it has been shown that signal strengths can be considerably enhanced by applying the present synthetic time-reversal method, thus reducing the number of sensors and actuators required to achieve a given signal-to-noise ratio.

A fabric coating prepared from a homogeneous mixture of fluorinated-decyl polyhedral oligomeric silsesquioxane and hydrolyzed fluorinated alkyl silane shows remarkable self-healing superhydrophobic and superoleophobic properties and excellent durability against UV light, acid, repeated machine washes, and severe abrasion (see picture). Super-liquid-repellent surfaces have attracted much attention in both scientific and industrial areas.1 They are often deemed superhydrophobic or superoleophobic depending on the liquid to be repelled. Superhydrophobic surfaces have a water contact angle greater than 150°. They have interesting nonsticking, self-cleaning, and anti-contamination functions. The emerging applications include separation of oil from water,2 energy conversion,3 protection of electronic devices,4 adjusting cell/substrate adhesion in the biomedical area,5 and reducing fluid resistance for aquaculture and microfluidic devices.6 In contrast, superoleophobic surfaces can be rather complicated, but they have great potential applications in antifouling from hazard chemicals and biological contaminants.7 Although any solid surface can be characterized as superoleophobic as long as its contact angle with an oily fluid is greater than 150°, the surface properties revealed from the contact angle measurement using different contacting oils could be considerably different. For example, a surface that is superoleophobic to certain oily fluids may have lower repellency or even be wettable by other oily fluids of a lower surface tension. It is normally easy to make a surface super-repellent to oils of a high surface tension, but difficult to prepare superoleophobic surfaces against oily fluids that have a surface tension below 35 mN m−1. Most super-liquid-repellent surfaces have poor durability.8 Chemical oxidation from exposure to air, a special chemical environment, strong light, or physical rubbing could cause the surfaces to lose their super-repellency permanently. It is imperative to improve the durability for practical applications.9 Recently, great progress has been made to develop mechanically robust superhydrophobic surfaces and laundering-durable superhydrophobic fabrics.10 On the other hand, the bioinspired self-healing ability has been proposed to be a promising solution to improve the durability of synthetic superhydrophobic surfaces.11 Recently, Li et al.12 reported a self-healing superhydrophobic coating that was prepared by chemical vapor deposition (CVD) of a fluoroalkyl silane on a layer-by-layer assembled porous surface, and self-healing was derived from the reacted fluoroalkyl silane embedded in the rigidly flexible coating layer. Wang et al.13 also reported the formation of a self-healing superamphiphobic surface on anodized alumina by filling the intrinsic pores with a low-surface energy liquid. In the recent study, we have also found that fabrics coated with a hydrolysis product from fluorinated-decyl polyhedral oligomeric silsesquioxane (FD–POSS) and a fluorinated alkyl silane (FAS) have a self-healing superhydrophobic and superoleophobic surface and the coating shows excellent durability to acid, UV light, machine wash, and abrasion. Herein, we first report on its novel multiple self-healing ability and durable performance. The chemical structures of FD-POSS and FAS are shown in Figure 1 a. The coating solution was prepared by dissolving FD-POSS in five times its weight of FAS, and the resulting viscous solution was then dispersed in ethanol. After ultrasonication for 30 min, a homogeneous dispersion was obtained. Figure 1 b shows the appearance of an FD–POSS/FAS dispersion in ethanol. Such a suspension was stable at room temperature for at least 10 h. The FD–POSS/FAS suspension can be easily applied onto fabrics through a wet-chemical coating technique, such as spraying, padding, or dip-coating. In this study, a dip-coating method was used to apply the coating solution to fabrics; a plain weave polyester fabric was mainly used as a model substrate. After dip-coating, the coated fabric was dried at 135 °C for 30 min. Under the scanning electron microscope (SEM), the coated fabric looked uniform (Figure 1 c). The transmission electron microscope (TEM) image showed that a thin conformal film, with a thickness of around 100 nm, was formed on the fiber surface (Figure 1 d). Figure 1 e shows the coating prepared from the same FD–POSS/FAS suspension on a glass slide, which looks transparent. The UV/vis transmission spectrum of the coating on quartz plate revealed that the FD–POSS/FAS film was highly transparent in a wavelength range of 230-850 nm (see the Supporting Information). a) Chemical structures of FD–POSS and FAS; b) picture showing show the FD–POSS/FAS dispersion in ethanol; c) SEM images of the FD–POSS/FAS coated polyester fabric (inset SEM image of larger magnification); d) TEM image of the cross-sectional view of the coating layer; e) a photo of a glass slide coated with FD–POSS/FAS. Figure 2 a shows the colored liquid droplets (13 μL) on the coated polyester fabric (plain weave). The yellow-colored water, red-colored hexadecane, and blue-colored tetradecane all look like spheres. The contact angle (CA) measurement indicated that the coated fabric had contact angles of 171°, 155°, and 152° with water, hexadecane, and tetradecane, respectively. A series of organic solvents having different surface tensions have been used to explore the liquid repellency of the coated fabric. Figure 2 b shows the dependence of the CA on the surface tension. The CA was larger than 150° when the liquid surface tension was above 26.5 mN m−1 (tetradecane); this result clearly indicates that the treated fabric is super-liquid-repellent and has both superhydrophobic and superoleophobic properties. a) Photo of colored water (yellow), hexadecane (red), and tetradecane (blue) on the FD–POSS/FAS treated polyester fabric (for easy observation, a small amount of dyes, acid yellow 76, oil red, and oil blue, respectively, for water, hexadecane, and tetradecane, was added to the liquid droplets; the dyes had no influence on the contact angles); b) dependence of CA on the surface tension (γ) of liquids; c) photo of colored liquids on the coated fabric after plasma treatment; d) photo of colored liquids on the coated fabric after 100 cycles of plasma-and-heat treatments; e) CA changes in the first 10 cycles of plasma-and-heat treatments; f) CA changes with plasma-and-heat treatment cycles. To demonstrate the self-healing ability, the coated fabric was damaged artificially by a plasma treatment using air as gas source. After the treatment, the surface became hydrophilic with a contact angle of 0° for water, hexadecane, and tetradecane (Figure 2 c). However, when the plasma-treated fabric was heated at 135 °C for 3 min, it restored its super-liquid-repellency (Figure 2 d), with contact angles of 171°, 155°, and 151° with water, hexadecane, and tetradecane, respectively. The treated fabric can maintain the superhydrophobicity even after 100 cycles of the plasma-and-heat treatment, suggesting excellent self-healing ability. However, the superoleophobicity changed with the plasma and heat cycles to a slightly larger extent compared with the superhydrophobicity. The contact angle with hexadecane was larger than 150° after 40 plasma and self-healing cycles (Figure 2 f). For tetradecane, the plasma-and-heat treatment only enabled the surface to maintain the oleophobicity with a contact angle below 150°, and 100 plasma-and-heat cycles led to a decrease of the contact angle from 152° to 136°. This finding indicates that the FD–POSS/FAS coated fabric has a reasonable self-healing ability to recover its oil-repellent state. Besides the heat treatment, the self-healing can also be performed repeatedly at room temperature simply by leaving the plasma-treated fabric for 24 h (see the Supporting Information). Apart from plasma treatment, the coated fabric was also etched with strong acid and base solutions. Immersing the coated fabric in an aqueous KOH solution (pH 14) for 24 h resulted in reduction of the water and hexadecane contact angle, respectively, from 171° and 156° to 0° for both (Figure 3 a-1). When the KOH treated fabric was rinsed with water and heated at 135 °C for three minutes, the surface was restored to its original super-liquid repellent state (Figure 3 a-2), with water and hexadecane contact angles of 171° and 154°, respectively. Such self-healing action could be repeated several times (see the Supporting Information). When the coated fabric was immersed in an aqueous H2SO4 solution (pH 1) in the same period of time, however, the coated fabric showed no changes in water and hexadecane contact angles (Figure 3 b). This result suggests that the coating is durable enough to resist acid attacks. a) Photos of FD–POSS/FAS coated polyester fabric, 1) after 24 hr immersion in KOH solution (pH 14) and 2) the immersed fabric after rinsing with water and heating at 135 °C for 3 min; b) photos of FD–POSS/FAS coated polyester fabric before and after 24 hr immersion in H2SO4 solution (pH 1) and rinsing with water and drying in air at room temperature; c) CA of the FD–POSS/FAS coated polyester fabric before and after 200 cycles of machine wash, d) CA changes depending on the abrasion cycles. The UV stability was tested by short-distance irradiation of the coated fabric with a middle-pressure Hg lamp (450 W). After 24 h of irradiation, the fabric showed no changes in the super-liquid-repellency. For comparison, the uncoated fabric was also treated under the same condition. In just one hour of irradiation, the fabric turned hydrophilic with a water contact angle close to 0°. The washing and abrasion durability was also studied. After 200 cycles of standard machine laundry, the coated fabric was found to still maintain the superhydrophobicity and superoleophobicity (Figure 3 c). The abrasion durability was evaluated by the Martindale method using untreated fabric to simulate actual damage. During the test, 9 kPa and 12 kPa of pressure were employed, which are typically used for evaluating the coated fabrics for apparel and heavy duty upholstery usages, respectively. Figure 3 d shows the change of the contact angle with the abrasion cycles. The coated fabric can withstand at least 6000 cycles of abrasion damages without changing its super-repellent feature. More abrasion cycles led to a decrease in both water and oil repellency. Such a durable coating with self-healing super-liquid-repellent surface can also be formed on other fibrous materials such as cotton and wool. It should be noted that FD–POSS has been used with a thermoplastic elastomeric binder (Tecnoflon, BR9151) for developing oleophobic fabrics, and a hydrochlorofluorocarbon (Asahiklin AK-225) was used as solvent for preparation of the coating solution.14 However, no self-healing liquid-repellent property was reported. In our work, FD–POSS and FAS were used as the coating material, and ethanol, a commonly used environmentally friendly solvent, was used as solvent. The finding that FD–POSS is soluble in FAS is also the first of its kind, which can be presumably attributed to the strong affinity of the fluorinated alkyl chains between the two chemicals. The formation of a stable FD–POSS/FAS suspension in ethanol could derive from the high polarity of the oxysilane group in FAS. It was also observed that dissolving FD–POSS to FAS formed a clear viscous solution. However, after dispersion in ethanol for a certain period of time, the solution changed to a semisolid. Drying and heating it at 135 °C for 30 min resulted in a waxy resin. The FTIR analysis confirmed that the FAS in the FD–POSS/FAS blend after the coating treatments hydrolyzed into a silica structure (see the Supporting Information). The coating is a hydrolyzed FAS network with FD–POSS molecules embedded. Heat treatment of the coating layer resulted in surface morphological changes. AFM images of the coating showed a rough surface and the surface became rougher after heat treatment (see the Supporting Information). The rough fiber surface formed by the FD–POSS/FAS coating, plus the inherent texture structure of fabric could be an important reason for the coated fabric to show super-liquid-repellent properties. The FD–POSS molecule comprises eight fluorinated decyl groups including 136 fluorine atoms surrounding the POSS cage, making the molecule extremely low in surface free energy. The FAS also has fluorinated alkyl chains, which are often used for hydrophobic surface treatments. FD–POSS with hydrolyzed FAS contributes to a low free-energy surface. According to these results, the self-healing mechanism of the FD–POSS/FAS coating was proposed. Upon damaging the surface chemically, polar groups were normally introduced, resulting in reduced surface hydrophobicity/oleophobicity and increased surface free energy. Heating the coating layer increased the mobility of the FD–POSS molecules. As a result of molecular rotation and movement, the polar groups introduced tended to be hidden inside the coating layer, and more fluorinated alkyl chains were exposed to the surface, minimizing the surface free energy. The molecular rotation and movement could also take place at a lower temperature (e.g. room temperature) because of the low Tg (see the Supporting Information). Since the FD–POSS molecules are surrounded by hydrolyzed FAS resin, their movement is restricted considerably. As a result, the coating is stable even at the melting state. The eight flexible fluorinated alkyl chains of the FD–POSS molecule function to lubricate the molecule rotation, while the large POSS cage hinders the movement of FD–POSS molecules during melting. In summary, we have demonstrated that fabrics coated with hydrolyzed FAS containing well-dispersed FD–POSS have a remarkable self-healing super-liquid-repellent surface with excellent durability against UV, acid exposure, repeated machine washes, and severe abrasion. Such a functional coating may be useful for the development of innovative protective clothing for various applications. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

We describe an investigation into e-mail content mining for author identification, or authorship attribution, for the purpose of forensic investigation. We focus our discussion on the ability to discriminate between authors for the case of both aggregated e-mail topics as well as across different e-mail topics. An extended set of e-mail document features including structural characteristics and linguistic patterns were derived and, together with a Support Vector Machine learning algorithm, were used for mining the e-mail content. Experiments using a number of e-mail documents generated by different authors on a set of topics gave promising results for both aggregated and multi-topic author categorisation.

Mental toughness has received increased scholarly attention in recent years, yet conceptual issues related to its (a) dimensionality, (b) nomological network, and (c) traitness remain unresolved. The series of studies reported in this article were designed to examine these three substantive issues across several achievement contexts, including sport, education, military, and the workplace. Five studies were conducted to examine these research aims-Study 1: N = 30; Study 2: calibration sample (n = 418), tertiary students (n = 500), athletes (n = 427), and employees (n = 550); Study 3: N = 497 employees; Study 4: N = 203 tertiary students; Study 5: N = 115 army candidates. Collectively, the results of these studies revealed that mental toughness may be best conceptualized as a unidimensional rather than a multidimensional concept; plays an important role in performance, goal progress, and thriving despite stress; and can vary and have enduring properties across situations and time. This series of studies provides a foundation for further basic and applied research of mental toughness across various achievement contexts.

High-spectral-resolution remote-sensing data are first transformed so that the noise covariance matrix becomes the identity matrix. Then the principal components transform is applied. This transform is equivalent to the maximum noise fraction transform and is optimal in the sense that it maximizes the signal-to-noise ratio (SNR) in each successive transform component, just as the principal component transform maximizes the data variance in successive components. Application of this transform requires knowledge or an estimate of the noise covariance matrix of the data. The effectiveness of this transform for noise removal is demonstrated in both the spatial and spectral domains. Results that demonstrate the enhancement of geological mapping and detection of alteration mineralogy in data from the Pilbara region of Western Australia, including mapping of the occurrence of pyrophyllite over an extended area, are presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

We investigate the problem of bearings-only tracking of manoeuvring targets using particle filters (PFs). Three different (PFs) are proposed for this problem which is formulated as a multiple model tracking problem in a jump Markov system (JMS) framework. The proposed filters are (i) multiple model PF (MMPF), (ii) auxiliary MMPF (AUX-MMPF), and (iii) jump Markov system PF (JMS-PF). The performance of these filters is compared with that of standard interacting multiple model (IMM)-based trackers such as IMM-EKF and IMM-UKF for three separate cases: (i) single-sensor case, (ii) multisensor case, and (iii) tracking with hard constraints. A conservative CRLB applicable for this problem is also derived and compared with the RMS error performance of the filters. The results confirm the superiority of the PFs for this difficult nonlinear tracking problem.

The periodogram of a time series that contains a sinusoidal component provides a crude estimate of its frequency parameter, the maximizer over the Fourier frequencies being within O(T/sup -1/) of the frequency as the sample size T increases. In the paper, a technique for obtaining an estimator that has root mean square error of order T/sup -3/2/ is presented, which involves only the Fourier components of the time series at three frequencies, The asymptotic variance of the estimator varies between, roughly, the asymptotic variance of the maximizer of the periodogram over all frequencies (the Cramer-Rao lower bound) and three times this variance. The advantage of the new estimator is its computational simplicity.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Information communications technology systems are facing an increasing number of cyber security threats, the majority of which are originated by insiders. As insiders reside behind the enterprise-level security defence mechanisms and often have privileged access to the network, detecting and preventing insider threats is a complex and challenging problem. In fact, many schemes and systems have been proposed to address insider threats from different perspectives, such as intent, type of threat, or available audit data source. This survey attempts to line up these works together with only three most common types of insider namely traitor, masquerader, and unintentional perpetrator, while reviewing the countermeasures from a data analytics perspective. Uniquely, this survey takes into account the early stage threats which may lead to a malicious insider rising up. When direct and indirect threats are put on the same page, all the relevant works can be categorised as host, network, or contextual data-based according to audit data source and each work is reviewed for its capability against insider threats, how the information is extracted from the engaged data sources, and what the decision-making algorithm is. The works are also compared and contrasted. Finally, some issues are raised based on the observations from the reviewed works and new research gaps and challenges identified.

This paper studies the problem of tracking a ballistic object in the reentry phase by processing radar measurements. A suitable (highly nonlinear) model of target motion is developed and the theoretical Cramer-Rao lower bounds (CRLB) of estimation error are derived. The estimation performance (error mean and standard deviation; consistency test) of the following nonlinear filters is compared: the extended Kalman filter (EKF), the. statistical linearization, the particle filtering, and the unscented Kalman filter (UKF). The simulation results favor the EKF; it combines the statistical efficiency with a modest computational load. This conclusion is valid when the target ballistic coefficient is a priori known.

Recent developments in random finite sets (RFSs) have yielded a variety of tracking methods that avoid data association. This paper derives a form of the full Bayes RFS filter and observes that data association is implicitly present, in a data structure similar to multiple hypothesis tracking (MHT). Subsequently, algorithms are obtained by approximating the distribution of associations. Two algorithms result: one nearly identical to joint integrated probabilistic data association (JIPDA), and another related to the multiple target multi-Bernoulli (MeMBer) filter. Both improve performance in challenging environments.

In order to improve the efficiency of the carbon dioxide cycling process and to reduce amine emissions, a series of nonvolatile amino acid salts with sterically hindered amine groups were investigated to determine their potential as direct replacements for monoethanolamine (MEA) in submarine-based CO2 scrubbers. Absorption from atmospheres containing various levels of CO2 was measured to assess the total capacities and absorption rates of amine solutions. The regeneration rates and extent of CO2 desorption were established by heating these solutions. 13C NMR spectroscopy was used to establish reaction products and solution compositions after both absorption and desorption. Methyl groups substituted adjacent to the amine were found to increase solution absorption capacities but with an overall reduction in absorption rate. Poor absorption rates at low CO2 levels and precipitation problems would prevent the α-dimethylamines examined from being used in existing submarine scrubbers. These amines, however, show potential as replacements in industrial CO2 scrubbing processes.

Addresses the problem of stabilizing a class of nonlinear systems by using an H/sub /spl infin// fuzzy output feedback controller. First, a class of nonlinear systems is approximated by a Takagi-Sugeno (TS) fuzzy model. Then, based on a well-known Lyapunov functional approach, we develop a technique for designing an H/sub /spl infin// fuzzy output feedback control law which guarantees the L/sub 2/ gain from an exogenous input to a regulated output is less or equal to a prescribed value. A design algorithm for constructing an H/sub /spl infin// fuzzy output feedback controller is given. In contrast to the existing results, the premise variables of the H/sub /spl infin// fuzzy output feedback controller are not necessarily to be the same as the premise variables of the TS fuzzy model of the plant. A numerical simulation example is presented to illustrate the theory development.

Situation-aware technologies enabled by multitarget tracking will lead to new services and applications in fields such as autonomous driving, indoor localization, robotic networks, and crowd counting. In this tutorial paper, we advocate a recently proposed paradigm for scalable multitarget tracking that is based on message passing or, more concretely, the loopy sum-product algorithm. This approach has advantages regarding estimation accuracy, computational complexity, and implementation flexibility. Most importantly, it provides a highly effective, efficient, and scalable solution to the probabilistic data association problem, a major challenge in multitarget tracking. This fact makes it attractive for emerging applications requiring real-time operation on resource-limited devices. In addition, the message passing approach is intuitively appealing and suited to nonlinear and non-Gaussian models. We present message-passing-based multitarget tracking methods for single-sensor and multiple-sensor scenarios, and for a known and unknown number of targets. The presented methods can cope with clutter, missed detections, and an unknown association between targets and measurements. We also discuss the integration of message-passing-based probabilistic data association into existing multitarget tracking methods. The superior performance, low complexity, and attractive scaling properties of the presented methods are verified numerically. In addition to simulated data, we use measured data captured by two radar stations with overlapping fields-of-view observing a large number of targets simultaneously.

Abstract A range of probiotic and other intestinal bacteria were examined for their ability to ferment the dietary fibre carbohydrates β‐glucan, xylan, xylo‐oligosaccharides (XOS) and arabinoxylan. β‐Glucan was fermented by Bacteroides spp and Clostridium beijerinckii but was not fermented by lactobacilli, bifidobacteria, enterococci or Escherichia coli . Unsubstituted xylan was not fermented by any of the probiotic bacteria examined. However, many Bifidobacterium species and Lactobacillus brevis were able to grow to high yields using XOS. XOS were also efficiently fermented by some Bacteroides isolates but not by E coli , enterococci, Clostridium difficile, Clostridium perfringens or by the majority of intestinal Lactobacillus species examined. Bifidobacterium longum strains were able to grow well using arabinoxylan as the sole carbon source. These organisms hydrolysed and fermented the arabinosyl residues from arabinoxylan but did not substantially utilise the xylan backbone of the polysaccharide. Arabinoxylan was not fermented by lactobacilli, enterococci, E coli, C perfringens or C difficile and has potential to be an applicable carbohydrate to complement probiotic Bif longum strains in synbiotic combinations. © 2002 Society of Chemical Industry

This paper provides a detailed overview of the Digital Video Broadcasting Terrestrial (DVB-T) signal structure and the implications for passive radar systems that use these signals as illuminators of opportunity. In particular, we analyze the ambiguity function and explain its delay and Doppler properties in terms of the underlying structure of the DVB-T signal. Of particular concern for radar range-Doppler processing are ambiguities consistent in range and Doppler with targets of interest. In this paper we adopt a mismatched filtering approach for range-Doppler processing. We also recognize that while the structure of the DVB-T signal introduces ambiguities, the structure can also be exploited to better estimate the transmitted signal and channel, as well as any mismatch between transmitter and receiver (e.g., clock offsets). This study presents a scheme for pre-processing both the reference and surveillance signals obtained by the passive radar to mitigate the effects of the ambiguities and the clutter in range-Doppler processing. The effectiveness of our proposed scheme in enhancing target detection is demonstrated using real-world data from an (Australian) 8k-mode DVB-T system. A 29 dB reduction in residual ambiguity levels over existing techniques is observed, and a 36 dB reduction over standard matched filtering; with only a 1 dB reduction in the zero-delay, zero-Doppler peak.

The Z-scan technique is a popular method for measuring degenerate (single frequency) optical nonlinearities using a single laser beam. In order to perform reliable measurements, it is necessary to carefully characterize and control a number of experimental parameters, such as the beam quality, the power and temporal characteristics of the laser, the collection aperture size and position, the sample reflectivity, sample thickness and imperfections in the sample. Failure to control these parameters leads to inaccurate determinations of the nonlinearities. In this paper, we review the theory of Z-scan and examine each of these issues from experimental and theoretical viewpoints. This work will be of interest to anyone who performs Z-scan experiments and to those interested in optical power limiting and nonlinear optical propagation.

Bernoulli filters are a class of exact Bayesian filters for non-linear/non-Gaussian recursive estimation of dynamic systems, recently emerged from the random set theoretical framework. The common feature of Bernoulli filters is that they are designed for stochastic dynamic systems which randomly switch on and off. The applications are primarily in target tracking, where the switching process models target appearance or disappearance from the surveillance volume. The concept, however, is applicable to a range of dynamic phenomena, such as epidemics, pollution, social trends, etc. Bernoulli filters in general have no analytic solution and are implemented as particle filters or Gaussian sum filters. This tutorial paper reviews the theory of Bernoulli filters as well as their implementation for different measurement models. The theory is backed up by applications in sensor networks, bearings-only tracking, passive radar/sonar surveillance, visual tracking, monitoring/prediction of an epidemic and tracking using natural language statements. More advanced topics of smoothing, multi-target detection/tracking, parameter estimation and sensor control are briefly reviewed with pointers for further reading.

Visual tracking has attracted a significant attention in the last few decades. The recent surge in the number of publications on tracking-related problems have made it almost impossible to follow the developments in the field. One of the reasons is that there is a lack of commonly accepted annotated data-sets and standardized evaluation protocols that would allow objective comparison of different tracking methods. To address this issue, the Visual Object Tracking (VOT) workshop was organized in conjunction with ICCV2013. Researchers from academia as well as industry were invited to participate in the first VOT2013 challenge which aimed at single-object visual trackers that do not apply pre-learned models of object appearance (model-free). Presented here is the VOT2013 benchmark dataset for evaluation of single-object visual trackers as well as the results obtained by the trackers competing in the challenge. In contrast to related attempts in tracker benchmarking, the dataset is labeled per-frame by visual attributes that indicate occlusion, illumination change, motion change, size change and camera motion, offering a more systematic comparison of the trackers. Furthermore, we have designed an automated system for performing and evaluating the experiments. We present the evaluation protocol of the VOT2013 challenge and the results of a comparison of 27 trackers on the benchmark dataset. The dataset, the evaluation tools and the tracker rankings are publicly available from the challenge website (http://votchallenge.net).