Performance of Three Culture Media Commonly Used for Detecting Listeria monocytogenes

Listeria monocytogenes poses a serious threat to public health, and the majority of cases of human listeriosis are associated with contaminated food. Reliable microbiological testing is needed for effective control of this pathogen by the food industry and competent authorities. The aim of this study was to determine the performance of three culture media commonly used for detecting L. monocytogenes in foods. Minced pork meat samples (n = 100) were subjected to microbiological testing for L. monocytogenes according to International Organization for Standardization methods 11290-1:1996 and 11290-2:1998 using PALCAM, ALOA, and RAPID'L. mono culture media in parallel. Presence of the pathogen was confirmed by conducting biochemical and molecular tests on the presumptive L. monocytogenes colonies. Performance attributes of sensitivity, specificity, positive and negative predictive values, positive and negative likelihood ratios, diagnostic odds ratios, error odds ratios, receiving operating characteristic (ROC) curve, and area under this curve were calculated from the presence-absence microbiological test results by combining the results obtained from the culture media and confirmative tests. PALCAM had the best performance in terms of positive predictive value (i.e., a positive result indicates high probability of L. monocytogenes presence) but not in terms of sensitivity (i.e., the ability of the medium to detect the pathogen when present). RAPID'L. mono was the most sensitive medium. None of the culture media were perfect for detecting L. monocytogenes in minced pork meat alone. The pathogen was detected in 16, 19, and 26% (apparent prevalence) of the samples by PALCAM, ALOA, and RAPID'L. mono, respectively, although the true prevalence of the pathogen was 22%. These findings indicate that the use of a single culture medium may lead to erroneous determination of the prevalence of L. monocytogenes.     

Signaling theory and information asymmetry in online commerce

An e-business environment results in information asymmetry because buyers cannot physically evaluate the quality of products and easily assess the trustworthiness of sellers. Product and seller quality are communicated through website signals. Using signaling theory, we developed a three-dimensional framework to classify website signals. We empirically tested the framework with a comparative content analysis of websites from a sample of online pharmacies. We found that low-quality sellers were likely to avoid costly and easy-to-verify signals and used fewer signals than did high-quality sellers, who used costly and difficult-to-verify signals and displayed more signals. These results provide information to online buyers and regulatory institutions in charge of online retailer evaluation.     

Cross-Shape Attention for Part Segmentation of 3D Point Clouds

We present a deep learning method that propagates point-wise feature representations across shapes within a collection for the purpose of 3D shape segmentation. We propose a cross-shape attention mechanism to enable interactions between a shape's point-wise features and those of other shapes. The mechanism assesses both the degree of interaction between points and also mediates feature propagation across shapes, improving the accuracy and consistency of the resulting point-wise feature representations for shape segmentation. Our method also proposes a shape retrieval measure to select suitable shapes for cross-shape attention operations for each test shape. Our experiments demonstrate that our approach yields state-of-the-art results in the popular PartNet dataset.     

Critical insulation thickness of a rectangular slab embedded with a periodic array of isothermal strips

We address the problem of two-dimensional heat conduction in a solid slab embedded with a periodic array of isothermal strips. The surfaces of the slab are subjected to a convective heat transfer boundary condition with a uniform heat transfer coefficient. Similar to the concept of critical insulation radius, associated with cylindrical and spherical configurations, we show that there exists a critical insulation thickness, associated with the slab, such that the total thermal resistance attains a minimum, i.e. a maximum heat transfer rate can be achieved. This result, which is not observed in one-dimensional heat conduction in a plane wall, is a consequence of the non-trivial coupling between conduction and convection that results in a 2D temperature distribution in the slab, and a non-uniform temperature on the surface of the slab. The findings of this work offer opportunities for improving the design of a broad range of engineering processes and products.     

Exploring contributions of public resources in social bookmarking systems

Our study examines whether users’ contributions of public resources to social bookmarking sites are circumstantial (a side effect of bookmarking for oneself), or motivational (intentional bookmarking for others). We develop a research model based on these two explanations and test it using survey data from users of two bookmarking sites. Our results suggest that public contributions are mainly driven by intentional bookmarking of resources for other users. In addition, we found that users deliberately bookmark resources for others when they believe that their bookmarks are valuable to other users and when they perceive that other users are contributing as well.     

Shape optimization for 2D diffusive scalar transport

A new theoretical formulation is presented for the shape optimization problem associated with maximizing or minimizing the diffusive scalar transport from a two-dimensional body. In particular, we consider the diffusive transport of heat from an isothermal body into a medium with constant temperature at the far-field. The formulation also applies to mass and momentum transport. The diffusion problem, which is governed by the Laplace equation, is addressed using conformal mapping techniques where the two-dimensional domain is mapped onto a simpler domain where an analytical solution can be readily obtained. The objective function of the optimization problem is the length of the object in the transformed domain and the variables of the optimization are the parameters of the Schwarz-Christoffel transformation. The length of the object in the transformed domain is related to the scalar displacement, which corresponds to a far-field temperature drop or rise (slip velocity in case of momentum transport), that depends on the shape of the body and it quantifies the enhancement or reduction in transport rate. The mathematical formulation is validated by addressing two fundamental shape optimization problems associated with maximizing or minimizing the transport rate (drag in case of momentum transport) from a two-dimensional body of unit span: i) for a given surface area to obtain the shape that maximizes the transport rate from a body, ii) for a given volume to obtain the shape that minimizes the transport rate from a body. For both cases we compute numerically that the cylinder is the optimal shape. The versatility of the formulation is further demonstrated by including constraints with respect to the length of the body.     

Investigation on the effect of process parameters in atmospheric pressure plasma treatment on carbon fiber reinforced polymer surfaces for bonding

Carbon Fiber Reinforced Polymer (CFRP) is used extensively in aerospace applications. Acceptance of bonded CFRP structures, mainly for aerospace applications, requires a robust surface preparation method with improved process controls to ensure high bond quality. Consistent repeatability is a factor lacking from many surface preparation processes. Atmospheric pressure plasma surface treatment is one of the robust surface preparation processes that have drawn wide attention in recent years. This process is capable of being applied in a production clean room environment that would minimize the risk of contamination and reduce cost. In plasma surface treatment the process parameters are easily controlled, documented providing a repeatable process with a high level of consistency. In this paper, the process parameters for atmospheric pressure plasma surface treatment and their effect on bonding for Out-Of-Autoclave (OOA) CFRP composite panels were fully investigated. A mechanized machine with sensory feedback to plasma treat surfaces was developed to change the process parameters for application on larger panels. By the aid of Design of Experiment (DOE) methodology critical process parameters were identified and a mathematical regression model was developed. The mathematical regression model was used to quantify the effect of process parameters on the bonding strength and the model was optimized to find the optimum settings.     

Fault Accommodation for a Class of Nonlinear Uncertain Systems With Event-Triggered Input

The event-triggered fault accommodation problem for a class of nonlinear uncertain systems is considered in this paper.The control signal transmission from the controller to the system is determined by an event-triggering scheme with relative and constant triggering thresholds.Considering the event-induced control input error and system fault threat,a novel eventtriggered active fault accommodation scheme is designed,which consists of an event-triggered nominal controller for the time period before detecting the occurrence of faults and an adaptive approximation based event-triggered fault accommodation scheme for handling the unknown faults after detecting the occurrence of faults.The closed-loop stability and inter-event time of the proposed fault accommodation scheme are rigorously analyzed.Special cases for the fault accommodation design under constant triggering threshold are also derived.An example is employed to illustrate the effectiveness of the proposed fault accommodation scheme.     

Threshold counters with increments and decrements

A threshold counter is a shared data structure that assumes integer values. It provides two operations: changes the current counter value from v to v+1, while returns the value v/w, where v is the current counter value and w is a fixed constant. Thus, the operation returns the “approximate” value of the counter to within the constant w. Threshold counters have many potential uses, including software barrier synchronization. Threshold networks are a class of distributed data structures that can be used to construct highly-concurrent, low-contention implementations of shared threshold counters. In this paper, we give the first proof that any threshold network construction of a threshold counter can be extended to support a operation that changes the counter value from v to v−1.     

Design and analysis of a fault isolation scheme for a class of uncertain nonlinear systems

This paper presents a unified fault isolation scheme for handling both process faults and sensor faults in a class of uncertain nonlinear systems. The proposed fault diagnosis architecture consists of a fault detection estimator and a bank of isolation estimators, each corresponding to a particular fault type. The design of the fault isolation decision scheme is based on the derivation of appropriate adaptive thresholds for each fault isolation estimator. Fault isolability conditions characterizing the class of process faults and sensor faults that are isolable by the proposed scheme are derived. A rigorous isolability analysis is presented via the use of the so-called fault mismatch functions, which are defined between pairs of possible faults. A simulation example is used to illustrate the proposed fault isolation scheme.