Synthetic impulse and aperture radar (SIAR) is a technique that frequency diverse array (FDA) radars can imply in practice, thus overcoming some of their challenges. SIAR radars, used in various fields like transportation and defense, can detect the range, azimuth angle, elevation angle, and Doppler of the target with their 4D‐matched filter and a single receiver. However, the challenge of high‐amplitude sidelobes is a significant concern for researchers. They have attempted to reduce it through various approaches, including frequency code, range–angle coupling, and range–Doppler coupling, to accurately identify target characteristics. This paper presents the antenna place code (AP code) parameter as a significant factor in minimizing sidelobe amplitudes. The parameter specifies that, rather than having all antennas active, a certain number of antennas are active in each pulse repetition interval (PRI) to achieve a lower sidelobe. Researchers have found that using AP codes can effectively lower the amplitude of the range–angle sidelobe, the range–Doppler sidelobe, error coupling, the repetition of sidelobe strands, and the output of angle error for different target angles. All studies are conducted on a linear array for simplicity. The output of various AP codes is compared to the previously common uniform array.

OBJECTIVE: To characterize variation in clinical documentation production patterns, how this variation relates to individual resident behavior preferences, and how these choices relate to work hours. MATERIALS AND METHODS: We used unsupervised machine learning with clinical note metadata for 1265 progress notes written for 279 patient encounters by 50 first-year residents on the Hospital Medicine service in 2018 to uncover distinct note-level and user-level production patterns. We examined average and 95% confidence intervals of median user daily work hours measured from audit log data for each user-level production pattern. RESULTS: Our analysis revealed 10 distinct note-level and 5 distinct user-level production patterns (user styles). Note production patterns varied in when writing occurred and in how dispersed writing was through the day. User styles varied in which note production pattern(s) dominated. We observed suggestive trends in work hours for different user styles: residents who preferred producing notes in dispersed sessions had higher median daily hours worked while residents who preferred producing notes in the morning or in a single uninterrupted session had lower median daily hours worked. DISCUSSION: These relationships suggest that note writing behaviors should be further investigated to understand what practices could be targeted to reduce documentation burden and derivative outcomes such as resident work hour violations. CONCLUSION: Clinical note documentation is a time-consuming activity for physicians; we identify substantial variation in how first-year residents choose to do this work and suggestive trends between user preferences and work hours.

The performance of many methods of MRI-based computer-aided diagnosis of breast disease rely on accurate delineation of the breast boundary. This problem has been known to be a challenging one on the account of the complex composition of breast tissue and its extensive inter-subject variability. To address this problem, this paper introduces a new approach to whole-breast segmentation which, as opposed to many existing solutions, can operate in the absence of any prior information on the patient-specific breast anatomy. The proposed algorithm takes advantage of Dijkstra's procedure which allows accurately tracking the boundary between the pectoralis muscle and breast tissue as well as between the breast and its background. The performance of the proposed method has been tested on in vivo MRI volumes and quantified in terms of several performance metrics. The experimental results demonstrate consistent and stable performance of the proposed algorithm in terms of its accuracy and robustness to imaging artefacts.

Missing data and noisy observations pose significant challenges for reliably predicting events from irregularly sampled multivariate time series (longitudinal) data. Imputation methods, which are typically used for completing the data prior to event prediction, lack a principled mechanism to account for the uncertainty due to missingness. Alternatively, state-of-the-art joint modeling techniques can be used for jointly modeling the longitudinal and event data and compute event probabilities conditioned on the longitudinal observations. These approaches, however, make strong parametric assumptions and do not easily scale to multivariate signals with many observations. Our proposed approach consists of several key innovations. First, we develop a flexible and scalable joint model based upon sparse multiple-output Gaussian processes. Unlike state-of-the-art joint models, the proposed model can explain highly challenging structure including non-Gaussian noise while scaling to large data. Second, we derive an optimal policy for predicting events using the distribution of the event occurrence estimated by the joint model. The derived policy trades-off the cost of a delayed detection versus incorrect assessments and abstains from making decisions when the estimated event probability does not satisfy the derived confidence criteria. Experiments on a large dataset show that the proposed framework significantly outperforms state-of-the-art techniques in event prediction.

Long Term Evolution (LTE) appears to be a practical alternative to IEEE 802.11p for vehicular applications. Vehicular safety applications are based on broadcasting messages, which contain information such as location and speed to the neighboring vehicles. However, as LTE is an infrastructure-based network, all communication should pass through it, which can cause congestion and substantial delays that are unsuitable for safety applications. By introducing direct D2D communication in 3GPP Release 12, known as LTE-Advanced, User Equipments (UEs) can communicate directly if they are in close enough proximity. In this paper, we propose an approach to use direct D2D, as well as cellular communication. This approach helps to reduce the amount of resources that are used for cellular communication, while keeping information of vehicles on a central server that can be utilized for other vehicular applications such as traffic efficiency.

In this paper, we introduce possible approaches for transmission of safety messages using LTE/LTE-A network. The first solution is using only LTE cellular connections. Vehicles transmit messages to a central server and it forwards the messages to the vehicles in the awareness area of the transmitter vehicle. The second approach uses only D2D capability of LTE, allowing vehicles to communicate directly without the involvement of the infrastructure. The last approach uses both cellular and D2D connections of LTE. We compared the possible approaches using simulation results regarding the required amount of resources, central information accuracy, and successful discovery ratio of the vehicles in the awareness area of the transmitter vehicle. Each approach has advantages and disadvantages, thus the appropriate approach is chosen based on the specific vehicular applications requirements and also availability of resources.

Many classification tasks require both labeling objects and determining label associations for parts of each object. Example applications include labeling segments of images or determining relevant parts of a text document when the training labels are available only at the image or document level. This task is usually referred to as multi-instance (MI) learning, where the learner typically receives a collection of labeled (or sometimes unlabeled) bags, each containing several segments (instances). We propose a semisupervised MI learning method for multilabel classification. Most MI learning methods treat instances in each bag as independent and identically distributed samples. However, in many practical applications, instances are related to each other and should not be considered independent. Our model discovers a latent low-dimensional space that captures structure within each bag. Further, unlike many other MI learning methods, which are primarily developed for binary classification, we model multiple classes jointly, thus also capturing possible dependencies between different classes. We develop our model within a semisupervised framework, which leverages both labeled and, typically, a larger set of unlabeled bags for training. We develop several efficient inference methods for our model. We first introduce a Markov chain Monte Carlo method for inference, which can handle arbitrary relations between bag labels and instance labels, including the standard hard-max MI assumption. We also develop an extension of our model that uses stochastic variational Bayes methods for inference, and thus scales better to massive data sets. Experiments show that our approach outperforms several MI learning and standard classification methods on both bag-level and instance-level label prediction. All code for replicating our experiments is available from https://github.com/hsoleimani/MLTM .

Extracting parts of a text document relevant to a class label is a critical information retrieval task. We propose a semi-supervised multi-label topic model for jointly achieving document and sentence-level class inferences. Under our model, each sentence is associated with only a subset of the document's labels (including possibly none of them), with the label set of the document the union of the labels of all of its sentences. For training, we use both labeled documents, and, typically, a larger set of unlabeled documents. Our model, in a semisupervised fashion, discovers the topics present, learns associations between topics and class labels, predicts labels for new (or unlabeled) documents, and determines label associations for each sentence in every document. For learning, our model does not require any ground-truth labels on sentences. We develop a Hamiltonian Monte Carlo based algorithm for efficiently sampling from the joint label distribution over all sentences, a very high-dimensional discrete space. Our experiments show that our approach outperforms several benchmark methods with respect to both document and sentence-level classification, as well as test set log-likelihood. All code for replicating our experiments is available from https://github.com/hsoleimani/MLTM.

We propose a mixture of class-conditioned topic models for classifying text documents using both labeled and unlabeled training documents in a semi-supervised fashion. Most topic models incorporate documents' class labels by generating them after generating the word space. In these models, the training class labels have relatively small effect on the estimated topics, as the likelihood function is mostly dominated by the word space, whose size dwarfs a single class label per document. In this paper, we propose to increase the influence of class labels on model parameters by generating the word space in each document conditioned on the class label. We show that our specific generative process improves classification performance while maintaining the ability of the model to discover topics from the word space. Within our framework, we also provide a principled mechanism to control the contribution of the class labels and the word space to the likelihood function. Experimental results show that our approach achieves better classification performance compared to some standard semi-supervised and supervised topic models. We provide the required code to replicate our experiments at https://github.com/hsoleimani/MCCTM.

We propose an algorithm for detecting patterns exhibited by anomalous clusters in high dimensional discrete data. Unlike most anomaly detection (AD) methods, which detect individual anomalies, our proposed method detects groups (clusters) of anomalies; i.e., sets of points which collectively exhibit abnormal patterns. In many applications, this can lead to a better understanding of the nature of the atypical behavior and to identifying the sources of the anomalies. Moreover, we consider the case where the atypical patterns exhibit on only a small (salient) subset of the very high dimensional feature space. Individual AD techniques and techniques that detect anomalies using all the features typically fail to detect such anomalies, but our method can detect such instances collectively, discover the shared anomalous patterns exhibited by them, and identify the subsets of salient features. In this paper, we focus on detecting anomalous topics in a batch of text documents, developing our algorithm based on topic models. Results of our experiments show that our method can accurately detect anomalous topics and salient features (words) under each such topic in a synthetic data set and two real-world text corpora and achieves better performance compared to both standard group AD and individual AD techniques. All required code to reproduce our experiments is available from https://github.com/hsoleimani/ATD.

We propose a parsimonious topic model for text corpora. In related models such as Latent Dirichlet Allocation (LDA), all words are modeled topic-specifically, even though many words occur with similar frequencies across different topics. Our modeling determines salient words for each topic, which have topic-specific probabilities, with the rest explained by a universal shared model. Further, in LDA all topics are in principle present in every document. By contrast, our model gives sparse topic representation, determining the (small) subset of relevant topics for each document. We derive a Bayesian Information Criterion (BIC), balancing model complexity and goodness of fit. Here, interestingly, we identify an effective sample size and corresponding penalty specific to each parameter type in our model. We minimize BIC to jointly determine our entire model-the topic-specific words, document-specific topics, all model parameter values, and the total number of topics-in a wholly unsupervised fashion. Results on three text corpora and an image dataset show that our model achieves higher test set likelihood and better agreement with ground-truth class labels, compared to LDA and to a model designed to incorporate sparsity.