Irreversible Breakdown Research Articles

Electrical Breakdown of Suspended Mono- and Few-Layer Tungsten Disulfide via Sulfur Depletion Identified by in Situ Atomic Imaging.

The high-bias and breakdown behavior of suspended mono- and few-layer WS2 was explored by in situ aberration-corrected transmission electron microscopy. The suspended WS2 devices were found to undergo irreversible breakdown at sufficiently high biases due to vaporization of the WS2. Simultaneous to the removal of WS2 was the accompanying formation of few-layer graphene decorated with W and WS2 nanoparticles, with the carbon source attributed to organic residues present on the WS2 surface. The breakdown of few-layer WS2 resulted in the formation of faceted S-depleted WS2 tendrils along the vaporization boundary, which were found to exhibit lattice contraction indicative of S depletion, alongside pure W phases incorporated into the structure, with the interfaces imaged at atomic resolution. The combination of observing the graphitization of the amorphous carbon surface residue, W nanoparticles, and S-depleted WS2 phases following the high-bias WS2 disintegration all indicate a thermal Joule heating breakdown mechanism over an avalanche process, with WS2 destruction promoted by preferential S emission. The observation of graphene formation and the role the thin amorphous carbon layer has in the prebreakdown behavior of the device demonstrate the importance of employing encapsulated heterostructure device architectures that exclude residues.

Breakdown of antiferromagnet order in polycrystalline NiFe/NiO bilayers probed with acoustic emission

Magnetization reversal of polycrystalline NiFe/NiO bilayers was investigated using magneto-optical indicator film imaging and acoustic emission techniques. Sporadic acoustic signals were detected in a constant magnetic field after the magnetization reversal. It is suggested that they are related to elastic waves excited by sharp shocks in the NiO layer with strong magnetostriction. Their probability depends on the history and number of repetitions of the field cycling, thus testifying the thermal-activation nature of the long-time relaxation of an antiferromagnetic order. These results provide evidence of spontaneous thermally activated switching of the antiferromagnetic order in NiO grains during magnetization reversal in ferromagnet/antiferromagnet (FM/AFM) heterostructures. The respective deformation modes are discussed in terms of the thermal fluctuation aftereffect in the Fulcomer and Charap model which predicts that irreversible breakdown of the original spin orientation can take place in some antiferromagnetic grains with disordered anisotropy axes during magnetization reversal of exchange-coupled FM/AFM structures. The spin reorientation in the saturated state may induce abrupt distortion of isolated metastable grains because of the NiO magnetostriction, leading to excitation of shock waves and formation of plate (or Lamb) waves.

Nano-second time resolved investigations on thermal implications of high-field transport through MWCNTs

The high-current carrying capacity of Multi-walled Carbon Nanotubes (MWCNTs) is the central idea behind their possible applications as interconnects. Joule-heating due to transport of high current through constricted quasi-1D electron channel results in various temperature-driven phenomena. Two such phenomena are current annealing and irreversible breakdown, which play vital roles in deciding electron transport and interconnect reliability, respectively. These phenomena occur at the time scale of 1–100 ns and hence cannot be precisely captured by conventional steady-state or DC measurement techniques. In this work, we explore these two phenomena by investigating electro-thermal transport through the inner and outer shells of MWCNTs, both suspended and substrate-supported, at the time scale of nano-seconds.

Sustained inflammation after pericyte depletion induces irreversible blood-retina barrier breakdown.

In the central nervous system, endothelial cells (ECs) and pericytes (PCs) of blood vessel walls cooperatively form a physical and chemical barrier to maintain neural homeostasis. However, in diabetic retinopathy (DR), the loss of PCs from vessel walls is assumed to cause breakdown of the blood-retina barrier (BRB) and subsequent vision-threatening vascular dysfunctions. Nonetheless, the lack of adequate DR animal models has precluded disease understanding and drug discovery. Here, by using an anti-PDGFRβ antibody, we show that transient inhibition of the PC recruitment to developing retinal vessels sustained EC-PC dissociations and BRB breakdown in adult mouse retinas, reproducing characteristic features of DR such as hyperpermeability, hypoperfusion, and neoangiogenesis. Notably, PC depletion directly induced inflammatory responses in ECs and perivascular infiltration of macrophages, whereby macrophage-derived VEGF and placental growth factor (PlGF) activated VEGFR1 in macrophages and VEGFR2 in ECs. Moreover, angiopoietin-2 (Angpt2) upregulation and Tie1 downregulation activated FOXO1 in PC-free ECs locally at the leaky aneurysms. This cycle of vessel damage was shut down by simultaneously blocking VEGF, PlGF, and Angpt2, thus restoring the BRB integrity. Together, our model provides new opportunities for identifying the sequential events triggered by PC deficiency, not only in DR, but also in various neurological disorders.

Cytokine-induced MMP13 Expression in Human Chondrocytes Is Dependent on Activating Transcription Factor 3 (ATF3) Regulation

Irreversible breakdown of cartilage extracellular matrix (ECM) by the collagenase matrix metalloproteinase 13 (MMP13) represents a key event in osteoarthritis (OA) progression. Although inflammation is most commonly associated with inflammatory joint diseases, it also occurs in OA and is thus relevant to the prevalent tissue destruction. Here, inflammation generates a cFOS AP-1 early response that indirectly affects MMP13 gene expression. To ascertain a more direct effect on prolonged MMP13 production we examined the potential molecular events occurring between the rapid, transient expression of cFOS and the subsequent MMP13 induction. Importantly, we show MMP13 mRNA expression is mirrored by nascent hnRNA transcription. Employing ChIP assays, cFOS recruitment to the MMP13 promoter occurs at an early stage prior to gene transcription and that recruitment of transcriptional initiation markers also correlated with MMP13 expression. Moreover, protein synthesis inhibition following early FOS expression resulted in a significant decrease in MMP13 expression thus indicating a role for different regulatory factors modulating expression of the gene. Subsequent mRNA transcriptome analyses highlighted several genes induced soon after FOS that could contribute to MMP13 expression. Specific small interfering RNA-mediated silencing highlighted that ATF3 was as highly selective for MMP13 as cFOS. Moreover, ATF3 expression was AP-1(cFOS/cJUN)-dependent and expression levels were maintained after the early transient cFOS response. Furthermore, ATF3 bound the proximal MMP13 AP-1 motif in stimulated chondrocytes at time points that no longer supported binding of FOS Consequently, these findings support roles for both cFOS (indirect) and ATF3 (direct) in effecting MMP13 transcription in human chondrocytes.

Treatment decision, death and the value of life.

The ontological status of patients—i.e. whether they are alive or dead—doesn’t usually influence treatment decisions. That most patients are alive is self-evident and irrelevant, and treatment decisions are no longer required for the clearly deceased. But the appropriate treatment of a minority of troubling patients turns on their ontological status. For example, that a brain dead patient artificially maintained on life-support is legally dead permits the retrieval of transplant organs. Treatment should be based on ontological status only if two questions can be compellingly answered: first, is the patient alive or dead; and second, if the patient is alive, what is the value of their life? But both questions are notoriously controversial. The first requires a definition of death whilst the latter requires ascertaining what makes life valuable. This review article clarifies why the prospects of answering each question remain poor. It is well established that the definition of death—and the criteria and tests to determine whether death, thus defined, has occurred—is controversial (Youngner et al. 1999).1 Less obvious is the root cause of the problem, which is that our ordinary concept of death is too complex to be reduced to one simple definition. This will be illustrated by considering patients in the Permanent Vegetative State (PermVS). There are two main approaches to defining death. On the first, death is a biological phenomenon which is the same for all (and only) organisms.2,3 Organisms are alive when they function in a holistic fashion, their components integrating to form a coherent organic whole; they die when they undergo irreversible breakdown in the functioning of the organism as a whole. There are two main candidates for determining when a human has undergone organismic breakdown. One is cardio-centric: death has occurred when the cardiorespiratory system is defunct. The other is …

Investigation of metastable Na2FeSiO4 as a cathode material for Na-ion secondary battery

Li2FeSiO4 has been widely investigated as a promising cathode material due to its high theoretical capacity of 330 mAh g−1 via two electron reactions. However, its Na-equivalent was not reported yet even it could considerably reduce the potential product costs due to the abundance of sodium resources in nature. In this study, sodium iron silicate with an empirical formula unit, Na2FeSiO4, was synthesized via solvothermal synthesis with two unavoidable impurities, Na2SiO3 and Fe3O4, for the first time. Galvanostatic charge/discharge test vs. Na/Na+ showed an initial discharge capacity of 126 mAh g−1 at 1/40 C in a voltage range of 1.0–4.1 V (1C = 138 mA g−1). However, during the initial charge, sodium iron silicate underwent irreversible crystal lattice breakdown and became amorphous.

β-Hydrogen Elimination Reactions of Nickel and Palladium Methoxides Stabilised by PCP Pincer Ligands.

Nickel and palladium methoxides [((iPr)PCP)M-OMe], which contain the (iPr)PCP pincer ligand, decompose upon heating to give products of different kinds. The palladium derivative cleanly gives the dimeric Pd(0) complex [Pd(μ-(iPr)PCHP)]2 ((iPr)PCHP = 2,6-bis(diisopropylphosphinomethyl)phenyl) and formaldehyde. In contrast, decomposition of [((iPr)PCP)Ni-OMe] affords polynuclear carbonyl phosphine complexes. Both decomposition processes are initiated by β-hydrogen elimination (BHE), but the resulting [((iPr)PCP)M-H] hydrides undergo divergent reaction sequences that ultimately lead to the irreversible breakdown of the pincer units. Whereas the Pd hydride spontaneously experiences reductive C-H coupling, the decay of its Ni analogue is brought about by its reaction with formaldehyde released in the BHE step. Kinetic measurements showed that the BHE reaction is reversible and less favourable for Ni than for Pd for both kinetic and thermodynamic reasons. DFT calculations confirmed the main conclusions of the kinetic studies and provided further insight into the mechanisms of the decomposition reactions.

Light modulated activity of root alkaline/neutral invertase involves the interaction with 14-3-3 proteins.

Alkaline/neutral invertases (A/N-Invs) are now recognized as essential proteins in plant life. They catalyze the irreversible breakdown of sucrose into glucose and fructose and thus supply the cells with energy as well as signaling molecules. In this study we report on a mechanism that affects the activity of the cytosolic invertase AtCINV1 (At-A/N-InvG or AT1G35580). We demonstrate that Ser547 at the extreme C-terminus of the AtCINV1 protein is a substrate of calcium-dependent kinases (CPK3 and 21) and that phosphorylation creates a high-affinity binding site for 14-3-3 proteins. The invertase as such has basal activity, but we provide evidence that interaction with 14-3-3 proteins enhances its activity. The analysis of three quadruple 14-3-3 mutants generated from six T-DNA insertion mutants of the non-epsilon family shows both specificity as well as redundancy for this function of 14-3-3 proteins. The strong reduction in hexose levels in the roots of one 14-3-3 quadruple mutant plant is in line with the activating function of 14-3-3 proteins. The physiological relevance of this mechanism that affects A/N-invertase activity is underscored by the light-induced activation and is another example of the central role of 14-3-3 proteins in mediating dark/light signaling. The nature of the light-induced signal that travels from the shoot to root and the question whether this signal is transmitted via cytosolic Ca(++) changes that activate calcium-dependent kinases, await further study.

Model of current-limited negative differential resistance in oxide-based resistance-switching devices

Resistance-switching devices such as resistive random access memories (RRAMs) exhibit the ability to rapidly reduce resistance upon exceeding a threshold voltage, as part of the SET operation. For oxide-based RRAMs, the progressive generation of defects during SET requires strict regulation of the current, e.g., by a transistor, in order to avoid irreversible breakdown. In doing so, the current-limiting device itself takes some voltage burden. The observed negative differential resistance for both the initial (forming) and regular SET operations can be analytically explained with a basic circuit model for the current-limited switching element, linking the voltage transfer to the current-limiting device with the degree of current rise. Consequently, it is found that RRAM operation current is a vital consideration for the reliability of the current-limiting device.

Isoprenoid lipid chains increase membrane resistance to pore formation

The process of electroporation of bilayer lipid membranes made of diphytanoylphosphatidylcholine (DPhPC) has been studied. DPhPC combines a polar part typical for lipids of eukaryotic cells and branched isoprenoid chains forming the hydrophobic “tails” of archaea lipids. From the experimental dependence of the average lifetime on the magnitude of the applied transmembrane potential difference we evaluated line tension of the pore edge in DPhPC bilayers (Γ) and the diffusion coefficient of the defect in the space of the pore radii (D). Line tension Γ was 5.5 ± 0.2 pN and diffusion coefficient D, (6 ± 2) × 10−19 m2/s. Comparison of these values with the values typical for eukaryotic lipids suggests that the critical radius of the pore, further growth of which results in an irreversible electrical breakdown of the lipid bilayer, is less in the case of DPhPC than for conventional membranes of phosphatidylcholines, but the probability of the defect emergence and the increase of its radius is also lower for the DPhPC membranes. Apparently, these peculiarities can be accounted for by high hydrophobicity of the branched isoprenoid chains of DPhPC.

Construction and evaluation of a genetic construct for specific detection and measurement of propionate by whole-cell bacteria.

Anaerobic digestion is a microbiological technology that converts biomass wastes into biogas, achieving both waste treatment and bioenergy production. Accumulation of volatile fatty acids (VFA) during acidogenesis, particularly propionate, often causes upset or failure of digesters. Early detection and monitoring of propionate concentration in digesters allow for just-in-time interventions to prevent irreversible costly process breakdown. In an attempt to develop a rapid method of measuring propionate concentration and bioavailability, we constructed a genetic construct for specific detection of bioavailable propionate. The genetic construct was constructed by transcriptional fusion of the regulatory gene (prpR) and the promoter of the prp operon (PprpB ) of Escherichia coli W3110 with the reporter gene cassette luxCDABE. When the genetic construct was carried on a plasmid and transformed into E. coli (referred to as plasmid-based biosensor), it resulted in stronger emission of luminescence than when it was inserted into the chromosome of E. coli (referred to as chromosome-based biosensor). The biosensor responded specifically to propionate. The luminescence signal increased linearly with increasing concentration of propionate from 1 to 10 mM. The utility of the biosensor was evaluated using samples collected from anaerobic digesters. Once instrumented in future studies, the whole-cell bacterial biosensor developed in this study may provide an alternative technology for real-time detection and measurement of propionate in digesters.

Field-programmable optical devices based on resonance elimination.

Optical switches are among the essential building blocks in optical networks due to their unique role in routing data. In this Letter, for the first time to our knowledge, we have exploited a high-quality factor (Q) optical microresonator combined with the well-known irreversible dielectric breakdown phenomenon to introduce a simple field-programmable on/off optical switch. This simple unit can be thought of as a building block for more complex optical systems with different functionalities. By using this simple unit we have demonstrated an optical field-programmable 2×2 switch. After the device is programmed by the user, no external electrical signal is needed to maintain the state of the device. The same approach can readily be adopted to design a field-programmable arbitrary N×N optical switch.

Molecular dynamics simulations of lipid membranes with lateral force: Rupture and dynamic properties

Membranes' response to lateral tension, and eventual rupture, remains poorly understood. In this study, pure dipalmitoylphosphatidylcholine (DPPC) lipid bilayers, under tension/pressure, were studied using molecular dynamics (MD) simulations. The irreversible membrane breakdown is demonstrated to depend on the amplitude of lateral tension, loading rate, and the size of the bilayer. In all of our simulations, −200bar lateral pressure was found to be enough to rupture lipid membrane regardless of the loading rate or the membrane size. Loading rate and membrane size had a significant impact on rupture. A variety of dynamic properties of lipid molecules, probability distribution of area per lipid particularly, have been determined, and found to be fundamental for describing membrane behavior in detail, thus providing the quantitative description for the requirement of membrane rupture.

Interactions of peptide triazole thiols with Env gp120 induce irreversible breakdown and inactivation of HIV-1 virions

BackgroundWe examined the underlying mechanism of action of the peptide triazole thiol, KR13 that has been shown previously to specifically bind gp120, block cell receptor site interactions and potently inhibit HIV-1 infectivity.ResultsKR13, the sulfhydryl blocked KR13b and its parent non-sulfhydryl peptide triazole, HNG156, induced gp120 shedding but only KR13 induced p24 capsid protein release. The resulting virion post virolysis had an altered morphology, contained no gp120, but retained gp41 that bound to neutralizing gp41 antibodies. Remarkably, HIV-1 p24 release by KR13 was inhibited by enfuvirtide, which blocks formation of the gp41 6-helix bundle during membrane fusion, while no inhibition of p24 release occurred for enfuvirtide-resistant virus. KR13 thus appears to induce structural changes in gp41 normally associated with membrane fusion and cell entry. The HIV-1 p24 release induced by KR13 was observed in several clades of HIV-1 as well as in fully infectious HIV-1 virions.ConclusionsThe antiviral activity of KR13 and its ability to inactivate virions prior to target cell engagement suggest that peptide triazole thiols could be highly effective in inhibiting HIV transmission across mucosal barriers and provide a novel probe to understand biochemical signals within envelope that are involved in membrane fusion.

Approaching the limits of dielectric breakdown for SiO2 films deposited by plasma-enhanced atomic layer deposition

This study explores the ultimate limit in dielectric breakdown of SiO2 thin films deposited by gas-phase, plasma-enhanced atomic layer deposition. Thickness-dependent breakdown behaviors similar to conventional, thermally grown SiO2 thin films were observed for the first time on ALD films, where the dominant breakdown mechanisms were impact ionization, trap creation and anode hole injection, respectively. By suppressing these mechanisms, we show a reversible degradation in SiO2 after the onset of Fowler–Nordheim tunneling before permanent dielectric damage occurs. The reversible window was only observable in films thinner than 10nm. The SiO2 thin films ultimately reached irreversible breakdown at a field strength of 2.7Vnm−1, where Si–O bonds were destroyed due to impact ionization and accelerated electrons.

Temozolomide chemical degradation to 5-aminoimidazole-4-carboxamide – Electrochemical study

The evaluation of the chemical degradation of temozolomide (TMZ), a potential anti-cancer drug, to its major metabolite 5-aminoimidazole-4-carboxamide (AIC), in aqueous solution with different pH values, was investigated at a glassy carbon electrode using cyclic and differential pulse voltammetry, and UV–Vis spectrophotometry. TMZ was incubated in aqueous solution, for different periods of time, and the changes in TMZ electrochemistry behaviour detected. The TMZ reduction is a pH-dependent irreversible process on the tetrazinone ring causing its irreversible breakdown. TMZ oxidation is a pH-dependent irreversible process that occurs in two consecutive charge transfer reactions. TMZ chemical degradation was electrochemically detected by the increase of the TMZ anodic peak current and the disappearance of the TMZ cathodic peak. The rate of chemical degradation increases with increasing pH and the mechanism corresponds to TMZ chemical degradation to AIC. The electrochemical behaviour of AIC over a wide pH range, was also investigated using cyclic, differential pulse and square wave voltammetry, AIC oxidation is an irreversible, diffusion-controlled process, pH-dependent up to a pH close to the pKa, and occurs in two consecutive charge transfer reactions, with the formation of two reversible redox products. A mechanism for AIC oxidation is proposed.

The effect of recycled polymer addition on the thermorheological behavior of modified lubricating greases

AbstractThis article deals with the influence of temperature on the rheological behavior of lithium lubricating greases modified with three different types of recycled polymers, high‐density polyethylene (HDPE), low‐density polyethylene, and polypropylene (PP), all deriving from waste plastic recycling plants. Grease formulations containing diverse polymers were manufactured and rheologically characterized. Small‐amplitude oscillatory shear and viscous flow measurements over a temperature range of 25–175°C were carried out. The experimental results obtained suggest that a blend of HDPE and PP could be considered a suitable potential viscosity modifier for lithium lubricating greases in a wide range of in‐service temperature. Thus, the lubricating greases studied modified by HDPE or PP show quite promising results at low or high temperature, respectively. In addition, thermomechanical reversibility has been studied by applying different combined stress–temperature protocols. Lubricating greases containing any of the recycled polymers studied show a significant irreversible structural breakdown when the sample is submitted to temperatures and stresses higher than 75°C and 200 Pa, respectively. Regarding lubricating grease viscous flow behavior, a minimum in the shear stress versus shear rate plots appeared at temperatures above 50°C, more pronounced as temperature increased, resulting from material flow instabilities. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers.

Electrical properties of new tin dioxide varistor ceramics at high currents

New dense SnO 2 -based varistor ceramics with high nonlinear current–voltage characteristics (nonlinearity coefficients are of approximately 50) in a system of SnO 2 –CoO–Nb 2 O 5 –Cr 2 O 3 –Y 2 O 3 –SrO–MgO are reported. The current–voltage behaviour at high currents is studied by using exponential voltage pulses. The obtained SnO 2 varistor ceramics exhibit low grain resistivity values of 0.23–0.64 ohm cm. To date, such values are the lowest known for SnO 2 varistors, and are closely approaching the grain resistivity of the ZnO varistor. The current–voltage characteristics of the obtained SnO 2 -based varistor materials are reproducible in a wide current range from 10 −11 to approximately 10 4 A cm −2 . The minimum current density and the minimum electric field necessary to cause the irreversible electrical breakdown are measured. It is established that a decrease in the grain resistivity leads to an increase in the minimum current density necessary for irreversible electrical breakdown to occur.

Modelling the degradation kinetics of vitamin C in fruit juice in relation to the initial headspace oxygen concentration

Abstract In the presence of oxygen, ascorbic acid (AA) is readily degraded to dehydroascorbic acid (DHA), which is prone to further degradation, hereby losing its vitamin C activity. In this study, the influence of different initial headspace O 2 concentrations on the oxidation of AA and the subsequent formation and breakdown of DHA was investigated in a model fruit juice. Kinetic rate constants for solely AA degradation were estimated using zero and first order kinetics, while first order irreversible and reversible consecutive models were used to describe the degradation kinetics of AA combined with the oxidative formation and irreversible breakdown of DHA. A linear relationship was found between the first order AA degradation constants and the initial headspace oxygen concentrations. Further, a similar relationship was found for a commercial fruit juice. In this way a tool is provided to predict the AA content in fruit juices at different stages during storage, knowing the residual headspace oxygen concentration after packaging, the O 2 -permeability of the packaging material and the initial AA and DHA concentration.