Clustering with Neighborhoods

In the standard planar $k$-center clustering problem, one is given a set $P$ of $n$ points in the plane, and the goal is to select $k$ center points, so as to minimize the maximum distance over points in $P$ to their nearest center. Here we initiate the systematic study of the clustering with neighborhoods problem, which generalizes the $k$-center problem to allow the covered objects to be a set of general disjoint convex objects $\mathscr{C}$ rather than just a point set $P$. For this problem we first show that there is a PTAS for approximating the number of centers. Specifically, if $r_{opt}$ is the optimal radius for $k$ centers, then in $n^{O(1/\varepsilon^2)}$ time we can produce a set of $(1+\varepsilon)k$ centers with radius $\leq r_{opt}$. If instead one considers the standard goal of approximating the optimal clustering radius, while keeping $k$ as a hard constraint, we show that the radius cannot be approximated within any factor in polynomial time unless $\mathsf{P=NP}$, even when $\mathscr{C}$ is a set of line segments. When $\mathscr{C}$ is a set of unit disks we show the problem is hard to approximate within a factor of $\frac{\sqrt{13}-\sqrt{3}}{2-\sqrt{3}}\approx 6.99$. This hardness result complements our main result, where we show that when the objects are disks, of possibly differing radii, there is a $(5+2\sqrt{3})\approx 8.46$ approximation algorithm. Additionally, for unit disks we give an $O(n\log k)+(k/\varepsilon)^{O(k)}$ time $(1+\varepsilon)$-approximation to the optimal radius, that is, an FPTAS for constant $k$ whose running time depends only linearly on $n$. Finally, we show that the one dimensional version of the problem, even when intersections are allowed, can be solved exactly in $O(n\log n)$ time

Current Tissue Engineering Approaches for Cartilage Regeneration

Cartilage is one of the critical tissues existed in human and animal bodies. Unlike most tissues, cartilage does not have blood vessels, nerves, and lymphatics. Most cartilage tissues in vivo are subjected to large mechanical loads, and its principal function is to provide a smooth and lubricated surface to facilitate the transmission of mechanical loads with a low frictional coefficient. As a result, cartilage tissues are easily injured. Cartilage defects are frequently caused by trauma, aging, congenital diseases (osteochondritis), and many more factors such as endocrine pathologies and cancer. The damaged cartilage has a limited capacity for healing and repairing. Thus, restoration of normal structure and function to damaged cartilage is one of the most challenging areas in orthopedic research and sports medicine. Tissue engineering provides a prospective alternative strategy by seeding chondrogenic cells into or onto biocompatible scaffolds to produce engineer cartilage for damaged cartilage repair. This book chapter has summarized recent progress in cartilage tissue engineering including stem cells, growth factors, bioactive molecules, and biomaterial scaffolds used for cartilage regeneration. The procedures for some new approaches have also been described

Clustering with Faulty Centers

In this paper we introduce and formally study the problem of k-clustering with faulty centers. Specifically, we study the faulty versions of k-center, k-median, and k-means clustering, where centers have some probability of not existing, as opposed to prior work where clients had some probability of not existing. For all three problems we provide fixed parameter tractable algorithms, in the parameters k, d, and ?, that (1+?)-approximate the minimum expected cost solutions for points in d dimensional Euclidean space. For Faulty k-center we additionally provide a 5-approximation for general metrics. Significantly, all of our algorithms have a small dependence on n. Specifically, our Faulty k-center algorithms have only linear dependence on n, while for our algorithms for Faulty k-median and Faulty k-means the dependence is still only n^(1 + o(1))

The role of peptides in reversing chemoresistance of breast cancer: current facts and future prospects

Breast cancer is the first malignant tumor in women, and its incidence is also increasing year by year. Chemotherapy is one of the standard therapies for breast cancer, but the resistance of breast cancer cells to chemotherapy drugs is a huge challenge for the effective treatment of breast cancer. At present, in the study of reversing the drug resistance of solid tumors such as breast cancer, peptides have the advantages of high selectivity, high tissue penetration, and good biocompatibility. Some of the peptides that have been studied can overcome the resistance of tumor cells to chemotherapeutic drugs in the experiment, and effectively control the growth and metastasis of breast cancer cells. Here, we describe the mechanism of different peptides in reversing breast cancer resistance, including promoting cancer cell apoptosis; promoting non-apoptotic regulatory cell death of cancer cells; inhibiting the DNA repair mechanism of cancer cells; improving the tumor microenvironment; inhibiting drug efflux mechanism; and enhancing drug uptake. This review focuses on the different mechanisms of peptides in reversing breast cancer drug resistance, and these peptides are also expected to create clinical breakthroughs in promoting the therapeutic effect of chemotherapy drugs in breast cancer patients and improving the survival rate of patients

Roadmap on energy harvesting materials

Ambient energy harvesting has great potential to contribute to sustainable development and address growing environmental challenges. Converting waste energy from energy-intensive processes and systems (e.g. combustion engines and furnaces) is crucial to reducing their environmental impact and achieving net-zero emissions. Compact energy harvesters will also be key to powering the exponentially growing smart devices ecosystem that is part of the Internet of Things, thus enabling futuristic applications that can improve our quality of life (e.g. smart homes, smart cities, smart manufacturing, and smart healthcare). To achieve these goals, innovative materials are needed to efficiently convert ambient energy into electricity through various physical mechanisms, such as the photovoltaic effect, thermoelectricity, piezoelectricity, triboelectricity, and radiofrequency wireless power transfer. By bringing together the perspectives of experts in various types of energy harvesting materials, this Roadmap provides extensive insights into recent advances and present challenges in the field. Additionally, the Roadmap analyses the key performance metrics of these technologies in relation to their ultimate energy conversion limits. Building on these insights, the Roadmap outlines promising directions for future research to fully harness the potential of energy harvesting materials for green energy anytime, anywhere

Label-Free Imaging of Single Nanoparticles Using Total Internal Reflection-Based Leakage Radiation Microscopy

Label-free, fast, and single nanoparticle detection is demanded for the in situ monitoring of nano-pollutants in the environment, which have potential toxic effects on human health. We present the label-free imaging of single nanoparticles by using total internal reflection (TIR)-based leakage radiation microscopy. We illustrate the imaging of both single polystyrene (PS) and Au nanospheres with diameters as low as 100 and 30 nm, respectively. As both far-field imaging and simulated near-field electric field intensity distribution at the interface showed the same characteristics, i.e., the localized enhancement and interference of TIR evanescent waves, we confirmed the leakage radiation, transforming the near-field distribution to far-field for fast imaging. The localized enhancement of single PS and Au nanospheres were compared. We also illustrate the TIR-based leakage radiation imaging of single polystyrene nanospheres with different incident polarizations. The TIR-based leakage radiation microscopy method is a competitive alternative for the fast, in situ, label-free imaging of nano-pollutants

An Improved Vicarious Calibration Method Based on Multi-Grayscale Targets

Vicarious calibration is a well-developed method for electro-optical (EO) sensor calibration that has been used since the early 1980s. The radiometric calibration of reflectance solar band is mainly applied to reflection inversion. In this paper, a radiometric calibration-reflectance inversion (RCRII) model is proposed as an improved vicarious calibration method. Taking the reflectance of grayscale targets with constant spectrum, suitable uniformity, and near-Lambertian characteristics as the known information, the grayscale target calibration is realized, and the initial value of calibration coefficient and offset are calculated. Then, the adjacency effect is evaluated and corrected by reflectance inversion, and the results are fed back to the calibration process to realize the iterative process of calibration inversion rescaling. The results indicate that the absolute difference between the reflectance calculated with the RCRII model and measured reflectance is less than 0.01. By comparing with Sentinel-2A images, it is cross-verified that the difference of radiance between them is within 4%, and the absolute reflectance difference is less than 0.01, in the range of 0.1~0.3 reflectance

An Improved Vicarious Calibration Method Based on Multi-Grayscale Targets

Vicarious calibration is a well-developed method for electro-optical (EO) sensor calibration that has been used since the early 1980s. The radiometric calibration of reflectance solar band is mainly applied to reflection inversion. In this paper, a radiometric calibration-reflectance inversion (RCRII) model is proposed as an improved vicarious calibration method. Taking the reflectance of grayscale targets with constant spectrum, suitable uniformity, and near-Lambertian characteristics as the known information, the grayscale target calibration is realized, and the initial value of calibration coefficient and offset are calculated. Then, the adjacency effect is evaluated and corrected by reflectance inversion, and the results are fed back to the calibration process to realize the iterative process of calibration inversion rescaling. The results indicate that the absolute difference between the reflectance calculated with the RCRII model and measured reflectance is less than 0.01. By comparing with Sentinel-2A images, it is cross-verified that the difference of radiance between them is within 4%, and the absolute reflectance difference is less than 0.01, in the range of 0.1~0.3 reflectance

Effects of single-use alfentanil versus propofol on cognitive functions after colonoscopy: A randomized controlled trial

Purpose: Colonoscopy is often accompanied by short-term postoperative cognitive decline. We aimed to explore whether single-use alfentanil for patients undergoing elective colonoscopy could reduce cognitive impairment at discharge compared with propofol. Patients and methods: 172 adult patients undergoing elective colonoscopy were randomized to receive intravenous propofol at 2 mg/kg (group P) or alfentanil at 10 μg/kg (group A); 40 healthy volunteers were included in the blank group. Cognitive function was considered the primary outcome and was measured using five neuropsychological tests before sedation and discharge. The z-score method was used to determine cognitive dysfunction according to z-score >1.96 in two types of neuropsychological tests. Other outcomes included discharge time, vital signs, associated adverse events during colonoscopy, and the satisfaction level of patients and endoscopic physicians. Results: 164 patients (78 in group A and 86 in group P) completed the study protocol. At discharge, the incidence of cognitive dysfunction in group P was 23% and was significantly lower in the alfentanil group (2.5%), with a relative risk of 0.11 (95% confidence interval: 0.03–0.46, P < 0.001). The incidence of hypotension in group A was lower than that in group P (3.8% vs 22.1%, relative risk = 0.17 [95% confidence interval: 0.05–0.46, P = 0.001]), and the discharge time in group A was shorter than that in group P (5 [(Rutter and et al., 2016; Zhang and et al., 2013; Hirsh and et al., 2006; Zhou and et al., 2021; Singh and et al., 2008; Ko and et al., 2010; Sargin et al., 2019) 3–93–9 vs 13 [(Ekmekci and et al., 2017; Eberl and et al., 2012; Eberl and et al., 2014; N'Kaoua and et al., 2002; Chung et al., 1995; Berger and et al., 2019; Quan and et al., 2019; Deng and et al., 2021; Gualtieri and Johnson, 2006) 10–1810–18 min, P < 0.001). Conclusion: For patients undergoing colonoscopy, single-use alfentanil causes less damage to postoperative cognitive function, less risk of hypotension, and shorter discharge time than propofol