Nonexistence of Global Solutions to Time-Fractional Damped Wave Inequalities in Bounded Domains with a Singular Potential on the Boundary

We first consider the damped wave inequality ∂2u∂t2−∂2u∂x2+∂u∂t≥xσ|u|p,t>0,x∈(0,L), where L>0, σ∈R, and p>1, under the Dirichlet boundary conditions (u(t,0),u(t,L))=(f(t),g(t)),t>0. We establish sufficient conditions depending on σ, p, the initial conditions, and the boundary conditions, under which the considered problem admits no global solution. Two cases of boundary conditions are investigated: g≡0 and g(t)=tγ, γ>−1. Next, we extend our study to the time-fractional analogue of the above problem, namely, the time-fractional damped wave inequality ∂αu∂tα−∂2u∂x2+∂βu∂tβ≥xσ|u|p,t>0,x∈(0,L), where α∈(1,2), β∈(0,1), and ∂τ∂tτ is the time-Caputo fractional derivative of order τ, τ∈{α,β}. Our approach is based on the test function method. Namely, a judicious choice of test functions is made, taking in consideration the boundedness of the domain and the boundary conditions. Comparing with previous existing results in the literature, our results hold without assuming that the initial values are large with respect to a certain norm.

Fluorinated Dibenzo[a,c]-phenazine-Based Green to Red Thermally Activated Delayed Fluorescent OLED Emitters

Purely organic thermally activated delayed fluorescence (TADF) emitting materials for organic light-emitting diodes (OLEDs) enable a facile method to modulate the emission color through judicious choice of donor and acceptor units. Amongst purely organic TADF emitters, the development of TADF molecules that emit at longer wavelengths and produce high-efficiency devices that show low efficiency roll-off remains a challenge. We report a modular synthesis route that delivers three structurally related fluorinated dibenzo[a,c]-phenazine-based TADF molecules, each bearing two donor moieties with different electron-donating strengths, namely 3,6-bis(3,6-di-tert-butyl-9H-carbazol-9-yl)-10-fluorodibenzo[a,c]phenazine (2DTCz-BP-F), 3,6-bis(9,9-dimethylacridin-10(9H)-yl)-10-fluorodibenzo[a,c]phenazine (2DMAC-BP-F) and 10,10'-(10-fluorodibenzo[a,c]phenazine-3,6-diyl)bis(10H-phenoxazine) (2PXZ-BP-F). They exhibit donor strength-controlled color-tuning over a wide color range from green to deep-red with photoluminescence maxima, PL, of 505 nm, 589 nm, and 674 nm in toluene solution. OLED devices using these TADF materials showed excellent to moderate performance with an EQEmax of 21.8% in the case of 2DMAC-BP-F, 12.4% for 2PXZ-BP-F and 2.1% with 2DTCZ-BP-F, and associated electroluminescence (EL) emission maxima, EL, of 585 nm, 605 nm and 518 nm in mCBP host, respectively.

Production and Surface Modification of Cellulose Bioproducts

Petroleum-based synthetic plastics play an important role in our life. As the detrimental health and environmental effects of synthetic plastics continue to increase, the renewable, degradable and recyclable properties of cellulose make subsequent products the “preferred environmentally friendly” alternatives, with a small carbon footprint. Despite the fact that the bioplastic industry is growing rapidly with many innovative discoveries, cellulose-based bioproducts in their natural state face challenges in replacing synthetic plastics. These challenges include scalability issues, high cost of production, and most importantly, limited functionality of cellulosic materials. However, in order for cellulosic materials to be able to compete with synthetic plastics, they must possess properties adequate for the end use and meet performance expectations. In this regard, surface modification of pre-made cellulosic materials preserves the chemical profile of cellulose, its mechanical properties, and biodegradability, while diversifying its possible applications. The review covers numerous techniques for surface functionalization of materials prepared from cellulose such as plasma treatment, surface grafting (including RDRP methods), and chemical vapor and atomic layer deposition techniques. The review also highlights purposeful development of new cellulosic architectures and their utilization, with a specific focus on cellulosic hydrogels, aerogels, beads, membranes, and nanomaterials. The judicious choice of material architecture combined with a specific surface functionalization method will allow us to take full advantage of the polymer’s biocompatibility and biodegradability and improve existing and target novel applications of cellulose, such as proteins and antibodies immobilization, enantiomers separation, and composites preparation.

Phoretic self-propulsion of helical active particles

Chemically active colloids self-propel by catalysing the decomposition of molecular ‘fuel’ available in the surrounding solution. If the various molecular species involved in the reaction have distinct interactions with the colloid surface, and if the colloid has some intrinsic asymmetry in its surface chemistry or geometry, there will be phoretic flows in an interfacial layer surrounding the particle, leading to directed motion. Most studies of chemically active colloids have focused on spherical, axisymmetric ‘Janus’ particles, which (in the bulk, and in absence of fluctuations) simply move in a straight line. For particles with a complex (non-spherical and non-axisymmetric) geometry, the dynamics can be much richer. Here, we consider chemically active helices. Via numerical calculations and slender body theory, we study how the translational and rotational velocities of the particle depend on geometry and the distribution of catalytic activity over the particle surface. We confirm the recent finding of Katsamba et al. (J. Fluid Mech., vol. 898, 2020, p. A24) that both tangential and circumferential concentration gradients contribute to the particle velocity. The relative importance of these contributions has a strong impact on the motion of the particle. We show that, by a judicious choice of the particle design parameters, one can suppress components of angular velocity that are perpendicular to the screw axis, or even select for purely ‘sideways’ translation of the helix.

Cooperative Rh(II)/Pd(0) Dual Catalysis for the Synthesis of Carbo- and Heterocyclic Compounds

Dual transition-metal catalysis has been introduced as a robust tool to synthesize a diverse range of organic compounds which are not able to be accessed by traditional single metal catalysis. In this context, we have recently developed the cooperative Rh(II)/Pd(0) dual catalytic systems, which have been utilized for the preparation of carbo- and heterocyclic compounds through the reaction between Rh(II)-carbenoid and π-allyl Pd(II)-complex intermediates in either synergistic or tandem relay catalysis. In synergistic Rh(II)/Pd(0) dual catalysis, the two reactive intermediates are generated simultaneously, which then undergo formal [6+3] dipolar cycloaddition to afford medium-sized N,O-heterocyclic compounds. On the other hand, tandem relay dual catalysis can be enabled through judicious choice of reaction parameters, which proceed through the insertion of Rh(II)-carbenoid into O–H or C–H bonds, followed by Pd(0)-catalyzed allylation to provide allylated benzofused cyclic compounds or chiral β-lactam derivatives.

Arbitrary stability for a Hopfield neural network problem with discrete and distributed delays

We consider a Hopfield neural network system containing discrete as well as distributed delays. A stability result of arbitrary type is proved under weaker assumptions than the used ones so far. This result includes exponential and polynomial (or power type) stability as special cases. Our proof relies on a judicious choice of Lyapunov-type functionals and some appropriate manipulations.

Hydrodynamic Entrance Length for Laminar Flow in Microchannels with Rectangular Cross Section

This work presents a detailed numerical investigation on the required development length (L=L/B) in laminar Newtonian fluid flow in microchannels with rectangular cross section and different aspect ratios (AR). The advent of new microfluidic technologies shifted the practical Reynolds numbers (Re) to the range of unitary (and even lower) orders of magnitude, i.e., creeping flow conditions. Therefore, accurate estimations of L at Re≤O(1) are important for microsystem design. At such low Reynolds numbers, in which inertial forces are less dominant than viscous forces, flow characteristics become necessarily different from those at the macroscale where Re is typically much larger. A judicious choice of mesh refinement and adequate numerical methods allowed obtaining accurate results and a general correlation for estimating L, valid in the ranges 0≤Re≤2000 and 0.1≤AR≤1, thus covering applications in both macro and microfluidics.

Task-Based Design Approach: Development of a Planar Cable-Driven Parallel Robot for Upper Limb Rehabilitation

This paper deals with the optimal design of a planar cable-driven parallel robot (CDPR), with three degrees of freedom, intended for assisting the patient’s affected upper limb along a prescribed movement. A Qualisys motion capture system was used to record the prescribed task performed by a healthy subject. For each pose taken by the center of mass of the end-effector, the cable tensions, the elastic stiffness and the dexterity were optimized while satisfying a set of constraints. First, a multiobjective formulation of the optimization problem was adopted. Since selecting a single solution among the multiple ones given by the Pareto front presents an issue, a mono-objective formulation was chosen, where the objective function was defined as a weighted sum of the chosen criteria. The appropriate values of the weighted coefficients were studied with the aim of identifying their influence on the optimization process and, thus, a judicious choice was made. A prototype of the optimal design of the CDPR was developed and validated experimentally on the prescribed workspace using the position control approach for the motors. The tests showed promising reliability of the proposed design for the task.

Skin and Bones—and Muscle Too

This chapter recounts bioprinting studies of skin, bone, skeletal muscle, and neuromuscular junctions. The chapter begins with a study of bioprinted skin designed to enable the creation of skin with a uniform pigmentation. The chapter relates two very different approaches to bioprinted bone: a synthetic bone called hyperelastic bone and a strategy that prints cartilage precursors to bone and then induces the conversion of the cartilage to bone by judicious choice of bioinks. Muscles move bone, and the chapter discusses an investigation of bioprinted skeletal muscle. Finally, the chapter considers an attempt to bioprint a neuromuscular junction, a synapse—a minute gap—of about 20 billionths of a meter between a motor neuron and the cell membrane of a skeletal muscle cell. A motor neuron is a nerve in the central nervous system that sends signals to the muscles of the body.

Effect of three types of oils and their level of incorporation on sensory quality of sorghum cookies

Lipid (oil and fat) is one of the basic and important components used in the production of cookies. It plays several roles in their composition and a judicious choice of this ingredient makes it possible to have cheap, delicious and very nutritious cookies. This study aimed to evaluate the effect of refined cottonseeds oil (RCO), refined palm oil (RPO) and red (or crude) palm oil (CPO) on sorghum (Sorghum bicolour var. Gampela) cookies. Oils were incorporated at levels of 16%, 20% and 24%. Cookies quality were evaluated based on quantitative sensory profile, sensory acceptability, preference classification and paired-comparison test. The results of sensory profile tests showed that the sensory descriptors ranged from very low to medium intensity (1.33 to 3.83 on a scale of 5). Both acceptability and classification tests showed that cookies produced with 20% of refined oil (RCO and RPO) and those with 16% of CPO were the most preferred and RCO and RPO with 20% of the oil were appreciated as control cookies produced with 20% of margarine. The colour, texture and fat impression had most influenced the consumers’ preferences. RCO, RPO and CPO exhibit the potential to be used as substitutes to margarine to produce sorghum cookies.