Missouri University of Science and Technology

About: Missouri University of Science and Technology is a education organization based out in Rolla, Missouri, United States. It is known for research contribution in the topics: Artificial neural network & Control theory. The organization has 9380 authors who have published 21161 publications receiving 462544 citations. The organization is also known as: Missouri S&T & University of Missouri–Rolla.

Saturable Absorption in 2D Ti₃C₂ MXene Thin Films for Passive Photonic Diodes

Abstract: MXenes comprise a new class of 2D transition metal carbides, nitrides, and carbonitrides that exhibit unique light-matter interactions. Recently, 2D Ti3 CNTx (Tx represents functional groups such as OH and F) was found to exhibit nonlinear saturable absorption (SA) or increased transmittance at higher light fluences, which is useful for mode locking in fiber-based femtosecond lasers. However, the fundamental origin and thickness dependence of SA behavior in MXenes remain to be understood. 2D Ti3 C2 Tx thin films of different thicknesses are fabricated using an interfacial film formation technique to systematically study their nonlinear optical properties. Using the open aperture Z-scan method, it is found that the SA behavior in Ti3 C2 Tx MXene arises from plasmon-induced increase in the ground state absorption at photon energies above the threshold for free carrier oscillations. The saturation fluence and modulation depth of Ti3 C2 Tx MXene is observed to be dependent on the film thickness. Unlike other 2D materials, Ti3 C2 Tx is found to show higher threshold for light-induced damage with up to 50% increase in nonlinear transmittance. Lastly, building on the SA behavior of Ti3 C2 Tx MXenes, a Ti3 C2 Tx MXene-based photonic diode that breaks time-reversal symmetry to achieve nonreciprocal transmission of nanosecond laser pulses is demonstrated.

Pressureless Densification of Zirconium Diboride with Boron Carbide Additions

Abstract: Zirconium diboride (ZrB 2 ) was densified (>98% relative density) at temperatures as low as 1850°C by pressureless sintering. Sintering was activated by removing oxide impurities (B 2 O 3 and ZrO 2 ) from particle surfaces. Boron oxide had a high vapor pressure and was removed during heating under a mild vacuum (∼150 mTorr). Zirconia was more persistent and had to be removed by chemical reaction. Both WC and B 4 C were evaluated as additives to facilitate the removal of ZrO 2 Reactions were proposed based on thermodynamic analysis and then confirmed by X-ray diffraction analysis of reacted powder mixtures. After the preliminary powder studies, densification was studied using either as-received ZrB 2 (surface area ∼ 1 m 2 /g) or attrition-milled ZrB 2 (surface area ∼ 7.5 m 2 /g) with WC and/or B 4 C as a sintering aid. ZrB 2 containing only WC could be sintered to ∼95% relative density in 4 h at 2050°C under vacuum. In contrast, the addition of B 4 C allowed for sintering to >98% relative density in 1 h at 1850°C under vacuum.

Border detection in dermoscopy images using statistical region merging.

Abstract: Malignant melanoma has consistently had one of the most rapidly increasing incidence of all cancers, with 59,940 new cases and 8110 deaths estimated in the United States in 2007 (1). Early diagnosis is particularly important because melanoma can be cured with a simple excision if detected early. Dermoscopy is a non-invasive skin imaging technique that uses optical magnification and either liquid immersion and low angle-of-incidence lighting or cross-polarized lighting to make the contact area translucent, making subsurface structures more easily visible when compared with conventional macroscopic (clinical) images. Dermoscopy allows the identification of dozens of morphological features such as pigment networks, dots/globules, streaks, blue-white areas, and blotches (2). This reduces screening errors, and provides greater differentiation between difficult lesions such as pigmented Spitz nevi and small, clinically equivocal lesions (3). However, it has been demonstrated that dermoscopy may actually lower the diagnostic accuracy in the hands of inexperienced dermatologists (4). Therefore, due to the lack of reproducibility and subjectivity of human interpretation, the development of computerized image analysis techniques is of paramount importance (5). The first step in the computerized analysis of skin lesion images is the detection of the lesion borders. The importance of border detection for the analysis is two-fold. First, the border structure provides important information for accurate diagnosis. Many clinical features such as asymmetry, border irregularity, and abrupt border cutoff are calculated from the border. Second, the extraction of other important clinical features such as atypical pigment networks, globules, and blue-white areas critically depends on the accuracy of border detection. Automated border detection in dermoscopy images is a challenging task due to several reasons: (i) low contrast between the lesion and the surrounding skin; (ii) irregular and fuzzy lesion borders; (iii) artifacts such as skin lines, air bubbles and hairs; and (iv) variegated coloring inside the lesion. Numerous methods have been developed for border detection in pigmented skin lesion images earlier; most of these dealt with clinical images (6). However, recent research has focused more on dermoscopy images. Gao et al. (7) proposed two methods: one based on stabilized inverse diffusion equations, a form of non-linear diffusion and another one based on Markov random fields in which the model parameters are estimated using the mean field theory. Pagadala (8) described a method based on optimized histogram thresholding. Schmid (6) developed a technique based on color clustering. First, a 2D histogram is calculated from the first two principal components of the CIE L*u*v* color space. The histogram is then smoothed and initial cluster centers are determined from the peaks using a perceptron classifier. Finally, the lesion image is segmented using a modified version of the fuzzy c-means (FCM) clustering algorithm. Donadey et al. (9) presented a supervised method based on intensity radial profiles calculated from the I (intensity) component of the HSI space. Cucchiara et al. (10) presented a recursive FCM clustering technique that augments Schmid’s method using topological information. Erkol et al. (11) proposed a method based on the gradient vector flow (GVF) snakes with an automatic initialization. Iyatomi et al. (12) described a method called the dermatologist-like tumor extraction algorithm (DTEA) that is based on thresholding followed by iterative region growing. Melli et al. (13) compared four different color clustering algorithms: median cut, k-means, FCM, and meanshift. They concluded that the meanshift algorithm gave the best results. Celebi et al. (14) developed a method based on the JSEG segmentation algorithm. Their method involves an algorithm for approximate lesion localization that reduces the computational time and improves the accuracy by focusing the border detection process on the immediate neighborhood of the lesion rather than the whole image. In this paper, we present an unsupervised approach to border detection in dermoscopy images based on the statistical region merging (SRM) algorithm (15). The SRM algorithm is adapted to this problem due to its simplicity, computational efficiency, and excellent performance in a variety of image domains.

Ceramics for Prosthetic Hip and Knee Joint Replacement

Abstract: The most commonly used bearing couple in prosthetic hip or knee joint replacements consists of a cobalt–chrome (CoCr) metal alloy articulating against ultrahigh-molecular-weight polyethylene. Ceramics have been used as an alternative to metal-on-polyethylene in joint replacement surgery of arthritic hips and knees since the 1970s. In prosthetic hip and knee bearings, ceramic surfaces offer a major benefit of drastically reduced wear rates and excellent long-term biocompatibility, which can increase the longevity of prosthetic hip and knee joints. This benefit is important clinically because hip and knee replacement has become a very common surgical procedure, particularly in the United States, and because these procedures are being increasingly performed in younger patients who place greater demands on the prosthetic bearings. However, ceramics are brittle and the risk of catastrophic bearing failure in vivo, while rare, is a major concern. Improvements in material quality, manufacturing methods, and implant design have resulted in a drastic reduction of the incidence of such failures, so that modern ceramic bearings are safe and reliable if used with components of proven design and durability. Future material improvements are actively being investigated to reduce the risk of ceramic-bearing failures even further. The purpose of this article is to review the structure, properties, applications, and limitations of the ceramics that have been used in orthopedic bearings, and to describe the new ceramic composite materials and surface treatments that will be available for joint replacement surgery in the near future.