Stress evolution during molecular-beam epitaxy of AIN films was monitored with in situ curvature measurements. Changes in the growth rate produced large stress variations, with more tensile stress observed at higher growth rates. For example, at a growth temperature of 750°C the instantaneous steady-state stress in films with similar grain sizes varied from −0.15GPa at a growth rate of 90nm∕h, to approximately 1.0GPa at a growth rate of 300nm∕h. To explain these results, we develop a kinetic model of stress evolution that describes both tensile and compressive mechanisms. The tensile component is based on a mechanism which is proposed here as an inherent feature of grain-boundary formation. The compressive component is based on our recent model of atom insertion, driven by the excess chemical potential of surface adatoms that is created by the growth flux. The combined model predicts that the stress is largely governed by the competition between tensile and compressive mechanisms, which can be conveniently described with a single parameter, α. The limiting values α→0 and α→+∞ correspond to previous models of compressive and tensile stresses, respectively.
Distributed Denial of Service (DDoS) attacks are the intimidation trials on the Internet that depletes the network bandwidth or exhausts the victim's resources. Researchers have introduced various defense mechanisms (such as attack prevention, traceback, reaction, detection, and characterization) against DDoS attacks, but such attacks are still growing year by year, and the ideal solutions of this problem are eluded so far. In the past, various signature-based and anomaly-based approaches were introduced for the detection of DDoS attacks, but only a few of them have focused on the nature of anomalies. Most of the detection approaches do not provide efficient real-time detection with high detection rate and low faux pas. In this paper, a classification of detection approaches against DDoS attacks has been presented with an aim to go deep insight into the DDoS problem for the beginners in this research area. The detection approaches have been explained along with their pluses and minuses. Further, this review paper includes the different functional classes to which the detection approaches belong to. In the end, a comparison of signature-based, anomaly-based and hybrid detection approaches is depicted in tabular form. ARTICLE HISTORY
Various analytical models have been proposed to predict the tensile stress created when discrete islands contact during a Volmer-Weber thin film growth. Past efforts to experimentally validate these models have been hindered by the stochastic nucleation of islands, which results in coalescence over a large distribution of times and length scales. To avoid this we systematically varied island geometries using electrodeposition of Ni islands on lithographically patterned conductive substrates (Au film on Si), which allowed for independent control of island size and growth rate. Using this technique, we previously demonstrated that most of the coalescence stress occurred after the initial contact of the neighboring islands, reaching a steady state when the film surface became nearly planar. In this work, we expand on these initial results to examine the kinetics of the coalescence process and to systematically evaluate the stress transition from discrete islands to a planar film. The steady state stress in planar films increased with growth rate, but asymptotically approached a limiting value for higher growth rates that depended on the island size. We attribute this to the competition between the kinetically limited compressive stress generation and tensile coalescence stress processes. The interaction of these mechanisms is consistent with both the observed transient stress evolution during the initial stages of island coalescence and the steady state stress evolution later in the process. The instantaneous stress at both the initial contact and at longer times decreased with increasing island size, as predicted in the literature. However, the existing models predict significantly larger grain size effects than those observed in these experiments.
In this work, we provide direct evidence of the fundamental mechanism through which saccharin, a standard industrial Ni electroplating additive, reduces stress in electrodeposited Ni. This was accomplished using real-time in situ stress measurements taken during through-mask electrodeposition of Ni films from a bath where the saccharin concentration was varied. This technique facilitated the direct measure of the effect of saccharin on the stress created at the Ni island boundaries. We demonstrated that increased saccharin concentration in a Ni-sulfamate-based bath resulted in a systematic reduction in the tensile grain-boundary coalescence stress. Based on this and ex situ S concentration measurements of the Ni films, we propose that the reduction in tensile stress was the result of a reduction in the grain-boundary energy due to S incorporation at the island boundaries.The majority of high strength electrodeposited Ni films are formed with large tensile intrinsic stress. 1 To reduce the tensile stress and increase the engineering yield strength, millimole per liter concentrations of sulfur containing additives are included in the electroplating baths. 1 These additives have been studied extensively and have been shown to also impact the film's brightness, grain size, and sulfur content. Sulfur causes embrittlement in nickel due to the segregation of the S at the grain boundary, resulting in a decrease in the fracture toughness of the metal. 2,3 In this work, we provide direct observations that elucidate the fundamental mechanism through which saccharin reduces the deposition stress in electrodeposited Ni. We report in situ measurements of the stress evolution during plating of a series of samples where the saccharin concentration was systematically varied. By performing these measurements using a through-mask plating technique, we were able to decouple the island size effects from the plating conditions and thus separate the morphological effects of the stress creation processes from the kinetically limited processes. ExperimentalNi films were potentiostatically electrodeposited through a photoresist defined periodic array of trenches on Au-coated 100-250 m thick Si͑001͒ substrates. Electrodeposition through the patterned photoresist produced an array of identical semicylindrical islands where the island radius at the initial moment of coalescence was dependent on the trench pitch. The details of this technique were discussed elsewhere, 4 but in short the technique allowed for the decoupling of the geometric stress effects from the kinetically limited stress processes. In this study, films were grown with a fixed island radius ͑10.6 m͒ using seven different growth rates ranging from 0.5 to 4.5 nm/s and saccharin concentrations of 0.25, 0.5, and 0.75 mmol/L. Figure 1a shows a cross-sectional image of a patterned island ͑before island coalescence͒, where the shape and polycrystalline character of the island is clearly visible. Also, in the top-view image in Fig. 1b, the well-defined boundaries between neighboring...
In the information age where Internet is the most important means of delivery of plethora of services, distributed denial‐of‐service (DDoS) attacks have emerged as one of the most serious threat. Strategic, security, social, and financial implications of these attacks have ceaselessly alarmed the entire cyber community. To obviate a DDoS attack and mitigate its impact, there is an irrevocable prerequisite to accurately detect them promptly. An inherent challenge in addressing this issue is to efficiently distinguish these attacks from characteristically analogous flash events (FEs) which are bona fide occurrences generated by legitimate users. Most of the studies have focused on finding out the unique characteristics of DDoS attacks in isolation, with the peril of false alarms heuristically. To preclude this, it is pertinent to fundamentally focus on identifying the unique characteristics of FE vis‐a‐vis DDoS attacks ab initio which has been the basis of this work. The aim of this paper is to formulate the taxonomy of FEs and compare the characteristics of FEs and DDoS attacks to segregate these using several empirical metrics. Real and emulation datasets have been used to validate the characteristics of both. The extensive analysis in this study establishes that there are numerous technical dissimilarities that can be exploited to separate these similar looking events. Copyright © 2016 John Wiley & Sons, Ltd.
Diseases should be treated well and on time. If they are not treated on time, they can lead to many health problems and these problems may become the cause of death. These problems are becoming worse due to the scarcity of specialists, practitioners and health facilities. In an effort to address such problems, studies made attempts to design and develop expert systems which can provide advice for physicians and patients to facilitate the diagnosis and recommend treatment of patients. This review paper presents a comprehensive study of medical expert systems for diagnosis of various diseases. It provides a brief overview of medical diagnostic expert systems and presents an analysis of already existing studies.
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