Energy release rate based dynamic crack propagation

An energy release rate based simulation method for dynamic fracture mechanics is developed to model crack initiation and propagation in elastic–plastic solid. Potential crack surface is modeled by a series of paired nodes bonded together by nodal constraint forces before crack propagation. The nodal constraint force of the paired nodes at the current crack tip is linearly decreased to zero in a specified time interval to mimic the crack propagation with a corresponding crack speed. During this process, the nodal force vectors and the nodal displacement vectors of the paired nodes are obtained. Based on the force-displacement curve, energy release rate can be calculated. It is found that energy release rate is monotonically decreasing with crack speed, a physical phenomenon predicted by Freund [1]. In this study, we hypothesize that the energy release rate is equal to a constant critical value during the entire crack propagation process. Hence, we may find the variable crack speed as a function of time. It is noticed that crack initiation is a special case of crack propagation with the crack speed approaching zero. The direction of crack propagation is determined by an iterative routine that adjusts the mesh such that the crack path is perpendicular to the nodal force of the paired nodes. The constitutive theory of the material is formulated based on large strain plasticity with return mapping algorithm. Notice that small strain elasticity is a special case of large strain plasticity. Hence we can verify our numerical results with those in linear elastic fracture mechanics. It is found that (1) the magnitude of crack tip stress decreases when large strain, instead of small strain, is considered; (2) node releasing method is adequate to determine the critical stress intensity factor with very high accuracy; (3) node releasing method enables one to simulate the fracture phenomenon with no initial crack—therefore ideally a simple tension test is sufficient to determine the critical energy release rate of a material; (4) crack speed asymptotically approaches to Rayleigh wave speed in case of elasticity, mode I, plain stress, and fixed grip; (5) crack speed asymptotically approaches to approximately half of Rayleigh wave speed if plasticity is considered; (6) plasticity affects the direction of crack propagation. REFERENCE [1] Freund, L.B. Dynamic Fracture Mechanics. Cambridge University Press: New York, 1990

Segregation and expression of transgenes in the progenies of Bt transgenic rice crossed to conventional rice varieties

β-Glucuronidase (GUS) activity bioassay, western blotting and polymerase chain reaction (PCR) analysis demonstrated that the cry1Ab gene was closely inherited and expressed with reporter gene gus in the progenies of Bacillus thuringiensis (Bt) transgenic rice (Oryza sativa L.) crossed to conventional rice varieties. Therefore, it is feasible using GUS-assisted-selection to preliminarily identify the Bt gene and study the inheritance of transgenes in breeding program. Mendelian segregation was observed in BC1F1, BC1F2 and F2 populations derived from Bt rice crossed to japonica rice respectively which indicated that the cry1Ab gene was inherited as a single dominant locus. PCR, Southern blotting and Western dot blotting analysis confirmed that cry1Ab gene was transferred to the genome of conventional rice varieties and it was highly expressed in the different progenies of Bt rice crossed to conventional rice varieties. Among these lines, the highest Bt toxin protein content reached 2.88% of total soluble proteins, even though the amount of Bt toxin protein in leaves of some GUS positive plants was higher than that detected in the original Bt rice. Meanwhile, the variances in Bt toxin protein between crosses and its parents were significant at 0.05 or 0.01 levels, respectively. Therefore, foreign cry1Ab gene with native insect resistant trait can be easily transferred to other rice varieties with higher yield potential and good quality through classical breeding.Keywords: Oryza sativa L., transgenes, inheritance, expressio

SCAPER, a novel cyclin A–interacting protein that regulates cell cycle progression

Cyclin A/Cdk2 plays an important role during S and G2/M phases of the eukaryotic cell cycle, but the mechanisms by which it regulates cell cycle events are not fully understood. We have biochemically purified and identified SCAPER, a novel protein that specifically interacts with cyclin A/Cdk2 in vivo. Its expression is cell cycle independent, and it associates with cyclin A/Cdk2 at multiple phases of the cell cycle. SCAPER localizes primarily to the endoplasmic reticulum. Ectopic expression of SCAPER sequesters cyclin A from the nucleus and results specifically in an accumulation of cells in M phase of the cell cycle. RNAi-mediated depletion of SCAPER decreases the cytoplasmic pool of cyclin A and delays the G1/S phase transition upon cell cycle re-entry from quiescence. We propose that SCAPER represents a novel cyclin A/Cdk2 regulatory protein that transiently maintains this kinase in the cytoplasm. SCAPER could play a role in distinguishing S phase– from M phase–specific functions of cyclin A/Cdk2

DICER-ARGONAUTE2 Complex in Continuous Fluorogenic Assays of RNA Interference Enzymes

Mechanistic studies of RNA processing in the RNA-Induced Silencing Complex (RISC) have been hindered by lack of methods for continuous monitoring of enzymatic activity. “Quencherless” fluorogenic substrates of RNAi enzymes enable continuous monitoring of enzymatic reactions for detailed kinetics studies. Recombinant RISC enzymes cleave the fluorogenic substrates targeting human thymidylate synthase (TYMS) and hypoxia-inducible factor 1-α subunit (HIF1A). Using fluorogenic dsRNA DICER substrates and fluorogenic siRNA, DICER+ARGONAUTE2 mixtures exhibit synergistic enzymatic activity relative to either enzyme alone, and addition of TRBP does not enhance the apparent activity. Titration of AGO2 and DICER in enzyme assays suggests that AGO2 and DICER form a functional high-affinity complex in equimolar ratio. DICER and DICER+AGO2 exhibit Michaelis-Menten kinetics with DICER substrates. However, AGO2 cannot process the fluorogenic siRNA without DICER enzyme, suggesting that AGO2 cannot self-load siRNA into its active site. The DICER+AGO2 combination processes the fluorogenic siRNA substrate (Km=74 nM) with substrate inhibition kinetics (Ki=105 nM), demonstrating experimentally that siRNA binds two different sites that affect Dicing and AGO2-loading reactions in RISC. This result suggests that siRNA (product of DICER) bound in the active site of DICER may undergo direct transfer (as AGO2 substrate) to the active site of AGO2 in the DICER+AGO2 complex. Competitive substrate assays indicate that DICER+AGO2 cleavage of fluorogenic siRNA is specific, since unlabeled siRNA and DICER substrates serve as competing substrates that cause a concentration-dependent decrease in fluorescent rates. Competitive substrate assays of a series of DICER substrates in vitro were correlated with cell-based assays of HIF1A mRNA knockdown (log-log slope=0.29), suggesting that improved DICER substrate designs with 10-fold greater processing by the DICER+AGO2 complex can provide a strong (~2800-fold) improvement in potency for mRNA knockdown. This study lays the foundation of a systematic biochemical approach to optimize nucleic acid-based therapeutics for Dicing and ARGONAUTE2-loading for improving efficacy

Delivery Efficiency of miR-21i-CPP-SWCNT and Its Inhibitory Effect on Fibrosis of the Renal Mesangial Cells

MicroRNA 21 (miR-21) was proved to cause renal fibrosis and the inhibition of miR-21 would improve the poor prognosis in renal cell carcinoma diseases. The complementary oligonucleotide of mature miR-21 was considered to be an effective intracellular miR-21 inhibitor (miR-21i). The directly effective delivery of miR-21i into fibrotic cell is a facile method for treatment of renal fibrosis. Herein, the miR-21i-CPP-SWCNT delivery system, synthesized via single-walled carbon nanotube (SWCNT) and cell-penetrating peptide (CPP), was taken as a novel fibrosis-targeting therapeutic carrier. The miR-21i and CPP firstly bind together via electrostatic forces, and subsequently miR-21i-CPP binds to the surface of SWCNTs via hydrophobic forces. CPP could endow the delivery system with targeting property, while SWCNT would enhance its penetrating ability. The exogenous miR-21i released from the designed miR-21i-CPP-SWCNTs had successfully inhibited the expression of fibrosis-related proteins in renal mesangial cells (RMCs). We found that the expression of TGF-β1 proteins was more sensitive to miR-21i-CPP-SWCNT than the expression of α-SMA proteins

Ultrasmall Organic Nanoparticles with Aggregation-Induced Emission and Enhanced Quantum Yield for Fluorescence Cell Imaging

The use of fluorescence probes for biomedical imaging has attracted significant attention over recent years owing to their high resolution at cellular level. The probes are available in many formats including small particle size based imaging agents which are considered to be promising candidates, due to their excellent stabilities. Yet, concerns over the potential cytotoxicity effects of inorganic luminescent particles have led to questions about their suitability for imaging applications. Exploration of alternatives inspired us to use organic fluorophores with aggregation-induced emission (AIE), prepared by functionalizing the amine group on tetraphenylethene with 3,5-bis­(trifluoromethyl)­phenyl isocyanate. The as-synthesized novel AIE fluorophore (TPE-F) display enhanced quantum yield and longer lifetime as compared with its counterparts (4,4′,4″,4‴-(ethene-1,1,2,2-tetrayl)­tetraaniline, TPE-AM). Furthermore, the TPE-F was encapsulated into small-size organic nanoparticles (NPs; dynamic light scattering size, ∼10 nm) with polysuccinimide (PSI). The biocompatibility, excellent stability, bright fluorescence, and selective cell targeting of these NPs enable the as-prepared TPE-F NPs to be suitable for specific fluorescence cell imaging

Ethical Challenges of Virtual Reality Technology Interventions for the Vulnerabilities of Patients With Chronic Pain: Exploration of Technician Responsibility

Chronic pain, a common disease, is a crucial global public health concern. Approximately 20% of the worldwide population is affected by chronic pain, which accounts for 15% to 20% of hospital visits. In Canada, approximately 7.6 million people—or 1 in 5 people—experience chronic pain. Among this population, 60% has either lost their employment or experienced a reduction in income as a result of their pain. The proportion of older people (aged ≥65 years) with chronic pain is high, comprising one-third of the total older population. In addition, the causes of chronic pain and its cures are unknown, and treatment is limited by these unknowns and the dangers of opioids. These essential factors make patients with chronic pain one of the most vulnerable populations. The use of emerging virtual reality (VR) technology as an intervention for chronic pain has consistently demonstrated early effectiveness and has been termed as a “nonpharmacological analgesic.” Nevertheless, we must remain vigilant about the potential ethical risks of VR interventions, as inappropriate VR interventions may exacerbate the vulnerabilities of patients. Currently, a central challenge for VR developers is the ambiguity of patient vulnerability and the unpredictability of ethical dilemmas. Therefore, our paper focused on the vulnerability and ethical dilemmas faced by patients with chronic pain in VR interventions. Through an experience-based, prospective ethical examination, we have identified both existing and potential new vulnerabilities and specific manifestations that patients with chronic pain may encounter in VR interventions. Our aim was to highlight the ethical risks that may be present in VR interventions. On one hand, this can help raise awareness among technology developers regarding the vulnerabilities of patients with chronic pain and mitigate technological ethical risks. In addition, it can assist technology developers in determining the priorities for VR technology interventions. These efforts collectively lay a solid foundation for the comprehensive realization of responsible VR technology interventions

Work conjugate strain of virial stress

Certain stress tensor and strain tensor form a conjugate pair if there exists a scalar valued strain energy function such that the stress tensor is equal to the derivative of strain energy function with respect to the strain tensor. Virial stress is widely accepted as the stress measurement in molecular dynamics (MD). However, its conjugate strain is not yet identified. An atomic logarithmic strain is proposed and numerically verified as the conjugate strain of virial stress at $$0\ {\rm{K}}$$ temperature. The strain energy is calculated by virial stress and the proposed atomic logarithmic strain equals to the interatomic potential energy density. This conclusion is numerically verified with (1) Coulomb-Buckingham potential, Lenard-Jones potential, or arbitrary nonlinear pair potential and (2) randomly generated atomic configurations and deformation gradients. Examples are given in determining the stress–strain relation for magnesium oxide with MD simulation. The result shows that the atomic logarithmic strain is identical to engineering strain when deformation is small