Towed wheel shimmy suppression through a nonlinear tuned vibration absorber

The implementation of the nonlinear tuned vibration absorber (NLTVA) for the suppression of shimmy vibration in towed wheels is addressed in this study. We adopt a modified straight tangent tyre model of a single-degree-of-freedom towed wheel system with an attached NLTVA. Stability analysis illustrated that the NLTVA can significantly improve the stability of the equilibrium of the wheel. Bifurcation analysis highlighted the existence of large bistable regions, which undermines the system’s safety. However, numerical continuation analysis, coupled with a dynamical integrity investigation, revealed that the addition of an intentional softening nonlinearity in the absorber restoring force characteristic enables the complete suppression of the bistable regions, also reducing the amplitude of shimmy oscillations in the unstable region. Quasiperiodic motions were also identified; however, their practical relevance seems marginal.

     

Automated defect detection in uniform and structured fabrics using Gabor filters and PCA

This paper describes an algorithm for texture defect detection in uniform and structured fabrics, which has been tested on the TILDA image database. The proposed approach is structured in a feature extraction phase, which relies on a complex symmetric Gabor filter bank and Principal Component Analysis (PCA), and on a defect identification phase, which is based on the Euclidean norm of features and on the comparison with fabric type specific parameters. Our analysis is performed on a patch basis, instead of considering single pixels. The performance has been evaluated with uniformly textured fabrics and fabrics with visible texture and grid-like structures, using as reference defect locations identified by human observers. The results show that our algorithm outperforms previous approaches in most cases, achieving a detection rate of 98.8% and a false alarm rate as low as 0.20–0.37%, whereas for heavily structured yarns misdetection rate can be as low as 5%.     

Novel Tyrosine Kinase Inhibitors to Target Chronic Myeloid Leukemia

This paper reports on a novel series of tyrosine kinase inhibitors (TKIs) potentially useful for the treatment of chronic myeloid leukemia (CML). The newly designed and synthesized compounds are structurally related to nilotinib (NIL), a second-generation oral TKI, and to a series of imatinib (IM)-based TKIs, previously reported by our research group, these latter characterized by a hybrid structure between TKIs and heme oxygenase-1 (HO-1) inhibitors. The enzyme HO-1 was selected as an additional target since it is overexpressed in many cases of drug resistance, including CML. The new derivatives 1a–j correctly tackle the chimeric protein BCR-ABL. Therefore, the inhibition of TK was comparable to or higher than NIL and IM for many novel compounds, while most of the new analogs showed only moderate potency against HO-1. Molecular docking studies revealed insights into the binding mode with BCR-ABL and HO-1, providing a structural explanation for the differential activity. Cytotoxicity on K562 CML cells, both NIL-sensitive and -resistant, was evaluated. Notably, some new compounds strongly reduced the viability of K562 sensitive cells.     

Red Orange and Bitter Orange IntegroPectin: Structure and Main Functional Compounds

DRIFT, HPLC-MS, and SPME-GC/MS analyses were used to unveil the structure and the main functional compounds of red (blood) orange (Citrus sinensis) and bitter orange (Citrus aurantium). The IntegroPectin samples show evidence that these new citrus pectins are comprised of pectin rich in RG-I hairy regions functionalized with citrus biophenols, chiefly flavonoids and volatile molecules, mostly terpenes. Remarkably, IntegroPectin from the peel of fresh bitter oranges is the first high methoxyl citrus pectin extracted via hydrodynamic cavitation, whereas the red orange IntegroPectin is a low methoxyl pectin. C. aurantium IntegroPectin has a uniquely high concentration of adsorbed flavonoids, especially the flavanone glycosides hesperidin, naringin, and eriocitrin.     

Natural Cryoprotective and Cytoprotective Agents in Cryopreservation: A Focus on Melatonin

Cryoprotective and cytoprotective agents (Cytoprotective Agents) are fundamental components of the cryopreservation process. This review presents the essentials of the cryopreservation process by examining its drawbacks and the role of cytoprotective agents in protecting cell physiology. Natural cryoprotective and cytoprotective agents, such as antifreeze proteins, sugars and natural deep eutectic systems, have been compared with synthetic ones, addressing their mechanisms of action and efficacy of protection. The final part of this article focuses melatonin, a hormonal substance with antioxidant properties, and its emerging role as a cytoprotective agent for somatic cells and gametes, including ovarian tissue, spermatozoa and spermatogonial stem cells.     

Four Methods to Distinguish between Fractal Dimensions in Time Series through Recurrence Quantification Analysis

Fractal properties in time series of human behavior and physiology are quite ubiquitous, and several methods to capture such properties have been proposed in the past decades. Fractal properties are marked by similarities in statistical characteristics over time and space, and it has been suggested that such properties can be well-captured through recurrence quantification analysis. However, no methods to capture fractal fluctuations by means of recurrence-based methods have been developed yet. The present paper takes this suggestion as a point of departure to propose and test several approaches to quantifying fractal fluctuations in synthetic and empirical time-series data using recurrence-based analysis. We show that such measures can be extracted based on recurrence plots, and contrast the different approaches in terms of their accuracy and range of applicability.     

Emerging Direct Targeting β-Catenin Agents

Aberrant accumulation of β-catenin in the cell nucleus as a result of deregulation of the Wnt/β-catenin pathway is found in various types of cancer. Direct β-catenin targeting agents are being researched despite obstacles; however, specific β-catenin drugs for clinical treatments have not been approved so far. We focused on direct β-catenin targeting of potential therapeutic value as anticancer agents. This review provides recent advances on small molecule β-catenin agents. Structure-activity relationships and biological activities of reported inhibitors are discussed. This work provides useful knowledge in the discovery of β-catenin agents.     

Synthesis of zigzag- and fjord-edged nanographene with dual amplified spontaneous emission

We report the synthesis of a dibenzodinaphthocoronene (DBDNC) derivative as a novel nanographene with armchair, zigzag, and fjord edges, which was characterized by NMR and X-ray crystallography as well as infrared (IR) and Raman spectroscopies. Ultrafast transient absorption (TA) spectroscopy revealed the presence of stimulated emission signals at 655 nm and 710 nm with a relatively long lifetime, which resulted in dual amplified spontaneous emission (ASE) bands under ns-pulsed excitation, indicating the promise of DBNDC as a near-infrared (NIR) fluorophore for photonics. Our results provide new insight into the design of nanographene with intriguing optical properties by incorporating fjord edges.

Dibenzo[a,m]dinaphtho[ef,hi]coronene with zigzag and fjord edges was synthesized and characterized, demonstrating a nonplanar structure with near-infrared stimulated emission with a relatively long lifetime and dual-amplified spontaneous emission.     

Controlled monodefluorination and alkylation of C(sp3)–F bonds by lanthanide photocatalysts: importance of metal–ligand cooperativity

The controlled functionalization of a single fluorine in a CF₃ group is difficult and rare. Photochemical C–F bond functionalization of the sp³-C–H bond in trifluorotoluene, PhCF₃, is achieved using catalysts made from earth-abundant lanthanides, (Cp^Me4)₂Ln(2-O-3,5-^tBu₂-C₆H₂)(1-C{N(CH)₂N(ⁱPr)}) (Ln = La, Ce, Nd and Sm, Cp^Me4 = C₅Me₄H). The Ce complex is the most effective at mediating hydrodefluorination and defluoroalkylative coupling of PhCF₃ with alkenes; addition of magnesium dialkyls enables catalytic C–F bond cleavage and C–C bond formation by all the complexes. Mechanistic experiments confirm the essential role of the Lewis acidic metal and support an inner-sphere mechanism of C–F activation. Computational studies agree that coordination of the C–F substrate is essential for C–F bond cleavage. The unexpected catalytic activity for all members is made possible by the light-absorbing ability of the redox non-innocent ligands. The results described herein underscore the importance of metal–ligand cooperativity, specifically the synergy between the metal and ligand in both light absorption and redox reactivity, in organometallic photocatalysis.

The controlled functionalization of a single fluorine in a CF₃ group is difficult and rare. Photochemical C–F bond functionalization is achieved using catalysts made from a range of earth-abundant lanthanides by using a ligand that enables M–L cooperativity.

Photoredox catalysis is a powerful synthetic method for the functionalization of inert molecules using single electron transfer (SET) reactivity^1–3 under irradiation with visible light.⁴ This has enabled challenging transformations under mild conditions including C–H activation,^5–7 radical cross-coupling,^8–11 and the valorization of lignin.^12,13 However, detailed mechanistic studies of photoredox systems are difficult due to their inherent complexity and the short lifetimes of photoexcited intermediates.Many lanthanides are more abundant in the environment than copper and their salts are less toxic than those of iron, so their potential for applications in catalysis merits exploration.^14–17 In 1990, divalent Sm, Eu, and Yb complexes Ln(Cp*)₂ (Cp* = C₅Me₅), were shown to more efficiently cleave vinylic C–F bonds when photolyzed, stoichiometrically forming Ln(iii) halide complexes, and suggesting the value of increasing the reducing power of the Ln^II excited state.¹⁸ Subsequently, analogous reactions to cleave the weaker C–Cl and C–Br bonds could be made catalytic in Ln(ii) halide (Ln = Sm, Eu, Yb), under near UV-photolysis conditions, by the addition of sacrificial reductant such as Zn or Al.^19,20 The addition of simple donor ligands enabled benzylic C–Cl cleavage by Eu^II under blue light irradiation.²¹ The addition of an organic photocatalyst or a photo-absorbing substrate to Lewis acidic LnX₃ salts (X = halide, triflate) has also been used to enhance the catalysis.²² Ln centers (Ln = Nd, Dy, Lu) with light-absorbing ligands such as porphyrins or phthalocyanins have been used to stoichiometrically dechlorinate phenols.²³Few reports of lanthanide photoredox catalysis exist with Ce^III complexes receiving the most attention. Ce possesses both an accessible III/IV redox couple and an allowed excitation from the 4f¹ ground state to the 5d¹ excited state, which can give rise to luminescent behaviour. It is also the cheapest and most readily isolated of the rare earths, offering a promising alternative to current precious metal photocatalysts.Building on the pioneering work on stoichiometric photoluminescent Ce chemistry,^24,25 in 2015 Schelter and co-workers demonstrated the utility of Ce^III in photocatalysis.^26,27 Their Ce^III amido complexes were catalysts for chlorine atom abstraction from benzyl chloride (Fig. 1, top), with both NaN(SiMe₃)₂ and additional Ce⁰ required for turnover.²⁸Open in a separate windowFig. 1Previous examples of photocatalytic C–X (X = halide) bond cleavage, and this work.They proposed an inner-sphere mechanism involving Ce⋯ClCR₃ adduct formation that provides an additional thermodynamic driving force to a bond cleavage that was otherwise out of range of the reducing power of the Ce excited state. A more sterically congested Ce^III tris(guanidinate) operates via an outer-sphere single electron transfer (SET) mechanism to cleave aryl iodides,²⁸ highlighting the mechanistic diversity that is possible in these systems.²⁹To date, ligands that support lanthanide-centered photocatalysts have been limited to halides, pseudohalides, and simple N-donors.^30,31 No organometallic lanthanide photocatalyst has yet been reported that combines the photoexcitable Ce cation with multidentate, tunable ligands. We have developed organometallic lanthanide complexes as sustainable catalysts,^16,17,32,33 and considered that those capable of forming an inner-sphere adduct, and absorbing light, could achieve the unusual and difficult, selective catalytic conversion of strong sp³ C–F bonds.Fluorine forms the strongest single bond to carbon and the C–F bond is ca. 25 kcal mol⁻¹ stronger than the C–Cl bond in monohaloalkanes, and the C–H bond in alkanes.³⁴ The selective activation and functionalization of C–F bonds is important, both due to the high bioaccumulation and toxicity of many perfluorinated compounds,³⁵ and the utility of fluorinated pharmaceuticals.³⁶ However, stoichiometric C(sp³)–F bond activation reactions are rare.^37–40 In particular, it is difficult to facilitate the controlled cleavage of a single C–F bond as the C(sp³)–F bond strength decreases as each F is removed and the remaining C–F bonds lengthen.^41,42This obstacle makes a radical methodology more attractive.^43–49 Jui and co-workers have demonstrated that some common photocatalysts can selectively activate a single C–F bond to form the putative ArCF₂˙ radical, which can either be quenched directly via H atom transfer (HAT), or coupled with an alkene followed by HAT to generate difluoroalkanes (Fig. 1, middle).^50,51 Gschwind and König have shown the photochemical functionalization of electron-poor trifluoromethylarenes.⁵² Nishimoto and Yasuda have described related C–F coupling protocols of perfluoroalkylarenes using tin reagents and an iridium photocatalyst.⁵³Here we show how selective, catalytic C–F bond functionalization can be achieved using a new family of Ln^III compounds supported by a light-absorbing aryloxide-tethered N-heterocyclic carbene, Cp^Me4, and pseudohalide ligands (Fig. 1, lower). We show that visible light-irradiated Ce complexes can selectively abstract a single fluoride from PhCF₃ and catalyze its alkylation by MgR₂ to afford PhCF₂R. The PhCF₂˙ can also be quenched to selectively form PhCF₂H or further alkylated via coupling with an alkene or other metal alkyls. We use combined experiment and density functional theory (DFT) computations to show the importance of coordination of the fluorinated substrate to the Lewis acidic metal in C–F activation, and the utility of the ligand in enabling photoredox catalysis for other lanthanide congeners.