Learning in Real-Time Search: A Unifying Framework

Real-time search methods are suited for tasks in which the agent is interacting with an initially unknown environment in real time. In such simultaneous planning and learning problems, the agent has to select its actions in a limited amount of time, while sensing only a local part of the environment centered at the agents current location. Real-time heuristic search agents select actions using a limited lookahead search and evaluating the frontier states with a heuristic function. Over repeated experiences, they refine heuristic values of states to avoid infinite loops and to converge to better solutions. The wide spread of such settings in autonomous software and hardware agents has led to an explosion of real-time search algorithms over the last two decades. Not only is a potential user confronted with a hodgepodge of algorithms, but he also faces the choice of control parameters they use. In this paper we address both problems. The first contribution is an introduction of a simple three-parameter framework (named LRTS) which extracts the core ideas behind many existing algorithms. We then prove that LRTA*, epsilon-LRTA*, SLA*, and gamma-Trap algorithms are special cases of our framework. Thus, they are unified and extended with additional features. Second, we prove completeness and convergence of any algorithm covered by the LRTS framework. Third, we prove several upper-bounds relating the control parameters and solution quality. Finally, we analyze the influence of the three control parameters empirically in the realistic scalable domains of real-time navigation on initially unknown maps from a commercial role-playing game as well as routing in ad hoc sensor networks

Molecular and cellular mechanisms underlying the evolution of form and function in the amniote jaw.

The amniote jaw complex is a remarkable amalgamation of derivatives from distinct embryonic cell lineages. During development, the cells in these lineages experience concerted movements, migrations, and signaling interactions that take them from their initial origins to their final destinations and imbue their derivatives with aspects of form including their axial orientation, anatomical identity, size, and shape. Perturbations along the way can produce defects and disease, but also generate the variation necessary for jaw evolution and adaptation. We focus on molecular and cellular mechanisms that regulate form in the amniote jaw complex, and that enable structural and functional integration. Special emphasis is placed on the role of cranial neural crest mesenchyme (NCM) during the species-specific patterning of bone, cartilage, tendon, muscle, and other jaw tissues. We also address the effects of biomechanical forces during jaw development and discuss ways in which certain molecular and cellular responses add adaptive and evolutionary plasticity to jaw morphology. Overall, we highlight how variation in molecular and cellular programs can promote the phenomenal diversity and functional morphology achieved during amniote jaw evolution or lead to the range of jaw defects and disease that affect the human condition

Utility Of Shear Wave Elastography In Breast Cancer Diagnosis: A Systematic Review And Meta-Analysis

In the United States, breast cancer is one of the most diagnosed cancers in women. Early detection, often via mammography, and intervention have been shown to reduce mortality. However, not all cancers are mammographically evident in early stages, if at all. As a result, ultrasound has been increasingly used to supplement mammography for breast cancer detection and assessment, particularly in dense breasts. Recent advancements in ultrasonography include the ability to characterize the stiffness of biological tissues. Shear Wave Elastography (SWE) is one such development used to quantify tissue stiffness within a region of interest. The resistance of soft tissue to deformation depends on the molecular makeup of the tissue components as well as elements of tissue structure, such as stromal and connective tissue. As tumor growth often involves architectural changes that cause increased stiffness compared to normal neighboring tissue, SWE has the potential to compliment mammography and B-mode ultrasound for breast lesion characterization. Studies establishing the clinical value of SWE may aid in its incorporation into diagnostic guidelines. This study aimed to quantify the performance of 2D SWE for differentiating benign and malignant breast lesions in women with abnormal mammography via a systematic review of the literature and meta-analysis. A systematic search of PubMed, Scopus, Embase, Ovid-Medline, Cochrane Library and Web of Science was performed. Studies of diagnostic accuracy published prior to June 2021 using SWE to evaluate abnormal breast tissue with at least 50 lesions that reported quantitative shear wave speed (SWS) parameters (the mean (SWSmean), maximum (SWSmax), minimum (SWSmin), or standard deviation (SWSSD) of the SWS) and thresholds and included a reference standard of either biopsy or 2-year stability were included in the analysis. The QUADAS- 2 tool was used to assess possible bias within studies as well as their applicability. 87 studies of diagnostic accuracy were included, encompassing 17,810 women (47) with 19,043 lesions (7,623 malignant). A hierarchical summary receiver operating characteristic model produced the following summary sensitivities and specificities: 0.86 [0.83, 0.88] / 0.87 [0.84, 0.88] for SWSmean, 0.83 [0.80, 0.85]/ 0.88 [0.86, 0.90] for SWSmax, 0.86 [0.74, 0.93]/ 0.81 [0.69, 0.89] for SWSmin, and 0.82 [0.77, 0.86] / 0.88 [0.85, 0.91] for SWSSD, respectively. By calculating and utilizing the resulting likelihood ratios, SWE was shown capable of downgrading BI-RADS 4a and upgrading BI-RADS 3 lesions. Thus, SWE has the potential to provide increased discriminative power in the diagnosis of breast cancer if used synergistically with mammography and B-mode ultrasound. Current society guidelines do not provide definitive recommendations about the role of SWE in screening and diagnosis, nor its counterpart strain elastography (SE). The literature suggests that a combination of SE and SWE may provide better discriminatory power than SWE alone and serve as an adjunct to current diagnostic techniques, opening an avenue for future study