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Glutamine synthetases catalyze the ATP-dependent ammonium assimilation, the initial step of nitrogen acquisition that must be tightly regulated to fit cellular needs. While their catalytic mechanisms and regulation are well-characterized in bacteria and eukaryotes, only limited knowledge exists about the archaeal representatives. Here, we natively purified the glutamine synthetases fromMethanothermococcus thermolithotrophicusandMethermicoccus shengliensis, two thermophilic methanogens belonging to different orders. Biochemical investigations combined with X-ray crystallography unveiled the first structures of archaeal glutamine synthetases and highlighted differences in their regulation. The enzyme fromM. thermolithotrophicusis inactive in its resting state and employs 2-oxoglutarate as an on-switch. The 2-oxoglutarate acts as a sensor of cellular nitrogen deficiency, and its reported cellular concentration remarkably overlays with that required for the enzyme activation. Its binding to an allosteric pocket leads to the reconfiguration of the active site and promotes a catalytically competent state. The homolog fromM. shengliensisdoes not harbor the 2-oxoglutarate binding motif and, consequently, is 2-oxoglutarate insensitive. Instead, it is directly feedback-inhibited by glutamine, as shown for bacterial homologs. The glutamine inhibition depends on a key arginine residue from the Asp50ʹ-loop. The arginine is substituted by a glycine inM. thermolithotrophicus, abolishing the inhibitory effect. While the effectors are surprisingly different, the molecular switch controlling the glutamine synthetase activity is fundamentally the same and depends on the correct positioning of the Asp50ʹ-loop and a catalytic arginine. Residue conservation suggests that both regulation mechanisms are widespread and not mutually exclusive across archaea.

PDF file - 219K, Effects of RhoB deletion on MT-myc induced mammary tumorigenesis in virgin female mice

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PDF file - 54K, RhoB is downregulated in MCF7 cells by antisense oligonucleotides

PDF file - 21K, RhoB is downregulated in MDA-MB-231 cells using lentivirus shRNA

PDF file - 34K, Level of expression of mRNA of different genes in RhoB+/+ and RhoB-/- mouse tumor cells

PDF file - 52K, Level of silencing of Akt in RhoB-/- and RhoB+/+ mouse cells

PDF file - 26K, Level of EGFR on the surface of human MDA-MB-231 cells

Microbial anaerobic oxidation of alkanes intrigues the scientific community by way of its impact on the global carbon cycle, and its biotechnological applications. Archaea are proposed to degrade short- and long-chain alkanes to CO2 by reversing methanogenesis, a theoretically reversible process. The pathway would start with alkane activation, an endergonic step catalyzed by methyl-coenzyme M reductase (MCR) homologues that would generate alkyl-thiols carried by coenzyme M. While the methane-generating MCR found in methanogens has been well characterized, the enzymatic activity of the putative alkane-fixing counterparts has not been validated so far. Such an absence of biochemical investigations contrasts with the current explosion of metagenomics data, which draws new potential alkane-oxidizing pathways in various archaeal phyla. Therefore, validating the physiological function of these putative alkane-fixing machines and investigating how their structures, catalytic mechanisms, and cofactors vary depending on the targeted alkane have become urgent needs. The first structural insights into the methane- and ethane-capturing MCRs highlighted unsuspected differences and proposed some explanations for their substrate specificity. This Perspective reviews the current physiological, biochemical, and structural knowledge of alkyl-CoM reductases and offers fresh ideas about the expected mechanistic and chemical differences among members of this broad family. We conclude with the challenges of the investigation of these particular enzymes, which might one day generate biofuels for our modern society.

Additional file 9. Peer review history.

Additional file 1: Supplementary Figures 1-11.

Objective: The objective of the present study is to determine, through phytochemical screening, the major chemical compounds and to evaluate the aphrodisiac effect of the ethanolic extract of M.acuminata stems in adult male rats. Methods :To achieve our objectives, a phytochemical study was conducted to determine the major chemical compounds present in the ethanolic extract of M. acuminatastems. The phytochemical screening was carried out following standard analytical procedures using thin layer chromatography.The aphrodisiac effect was evaluated in sexually naïve male rats. In sexually naïve male rats, a single administration of the ethanolic extract was performed at doses of 10, 20 and 40 mg/kg versus 0.5 mL/100g distilled water and 715 µg/kg Sildenafil Pfizer 50 mg in the negative and positive control rats, respectively. Female rats were induced to oestrus by sequential administration of estradiol benzoate (Sigma - Aldrich) (25 μg/rat) to make them receptive to males. Results :The results of the phytochemical screening revealed that the ethanolic extract of M. acuminata stems contains coumarins, flavonoids, tannins, triterpenes of triterpenesaponins. The biological study showed that at doses of 20 and 40 mg/kg, ethanolic extract of M. acuminatastems resulted in a significant (p < 0.05) and highly significant (p < 0.001) increase in the number of sexual mounts, the number of erections, the number of ejaculations and a significant (p < 0.01) decrease in the latency time between sexual mounts in male rats. Conclusions:The sexual stimulating effects of the ethanolic extract of M. acuminata observed in this study could be attributed to the presence of the identified chemical compounds, hence the interest in using this plant in traditional aphrodisiac medicine.

A micro-electromechanical system (MEMS) based technique is demonstrated for in situ transmission electron microscopy (TEM) measurements of stress relaxation with simultaneous observation of the underlying plastic deformation processes. True activation volumes are determined from repeated stress relaxation transients and thus provide a signature parameter of the governing mechanisms of plastic deformation. The technique is demonstrated with 100 nm-thick ultrafine-grained gold microspecimens under uniaxial tension. True activation volumes of approximately 3-5b3 (where b is the Burgers vector length) are obtained for tensile stresses ranging from 200-450 MPa. Grain boundary-dislocation interactions are observed via in situ TEM during stress relaxation measurements. The miniaturization of stress relaxation tests inside the TEM provides unique opportunities to characterize the plastic kinetics and underlying mechanisms in ultrafine-grained and nanocrystalline materials.

Background Transcription bridges genetic information and phenotypes. Here, we evaluated how changes in transcriptional regulation enable maize (Zea mays), a crop originally domesticated in the tropics, to adapt to temperate environments. Result We generated 572 unique RNA-seq datasets from the roots of 340 maize genotypes. Genes involved in core processes such as cell division, chromosome organization and cytoskeleton organization showed lower heritability of gene expression, while genes involved in anti-oxidation activity exhibited higher expression heritability. An expression genome-wide association study (eGWAS) identified 19,602 expression quantitative trait loci (eQTLs) associated with the expression of 11,444 genes. A GWAS for alternative splicing identified 49,897 splicing QTLs (sQTLs) for 7614 genes. Genes harboring both cis-eQTLs and cis-sQTLs in linkage disequilibrium were disproportionately likely to encode transcription factors or were annotated as responding to one or more stresses. Independent component analysis of gene expression data identified loci regulating co-expression modules involved in oxidation reduction, response to water deprivation, plastid biogenesis, protein biogenesis, and plant-pathogen interaction. Several genes involved in cell proliferation, flower development, DNA replication, and gene silencing showed lower gene expression variation explained by genetic factors between temperate and tropical maize lines. A GWAS of 27 previously published phenotypes identified several candidate genes overlapping with genomic intervals showing signatures of selection during adaptation to temperate environments. Conclusion Our results illustrate how maize transcriptional regulatory networks enable changes in transcriptional regulation to adapt to temperate regions.

Soft and stretchable semiconductors could enable seamless integration of wearable or implantable sensors with biological systems. We report on flexible and stretchable organic photodiodes with silicon-photodetector like performance and applications in biometric monitoring.

Description, Stretchable photodetectors for wearable electronics maintain a high level of performance when stretched by at least 60%., Stretchable optoelectronics made of elastomeric semiconductors could enable the integration of intelligent systems with soft materials, such as those of the biological world. Organic semiconductors and photodiodes have been engineered to be elastomeric; however, for photodetector applications, it remains a challenge to identify an elastomeric bulk heterojunction (e-BHJ) photoactive layer that combines a low Young’s modulus and a high strain at break that yields organic photodiodes with low electronic noise values and high photodetector performance. Here, a blend of an elastomer, a donor-like polymer, and an acceptor-like molecule yields a skin-like e-BHJ with a Young’s modulus of a few megapascals, comparable to values of human tissues, and a high strain at break of 189%. Elastomeric organic photodiodes based on e-BHJ photoactive layers maintain low electronic noise current values in the tens of femtoamperes range and noise equivalent power values in the tens of picowatts range under at least 60% strain.

This paper introduces an elliptical alert limit (or AL) to characterize horizontal positioning errors for lane-keeping applications. Equations are derived that characterize the maximum dimensions of the AL when traveling on curved roads. On curved roads, the allowable errors in the lateral and longitudinal directions are coupled, so lane-keeping requires both a limit on lateral errors and on longitudinal errors (either or both of which can carry an automated vehicle outside its lane, possibly resulting in a hazardous collision). We apply our equations for characterizing elliptical AL to relevant scenarios involving vehicles of different sizes on representative roadways; in each case, we compare the performance of the elliptical AL to that of a rectangular AL, as has been considered previously by other investigators. Our analyses indicate that the elliptical AL always outperforms the rectangular AL, allowing for larger longitudinal errors, by as much as a factor of two for passenger vehicles on narrow roadways when lateral errors are tightly constrained.

Objective: The objective of the present study is to determine, through phytochemical screening, the major chemical compounds and to evaluate the aphrodisiac effect of the ethanolic extract of M.acuminata stems in adult male rats. Methods:To achieve our objectives, a phytochemical study was conducted to determine the major chemical compounds present in the ethanolic extract of M. acuminatastems. The phytochemical screening was carried out following standard analytical procedures using thin layer chromatography.The aphrodisiac effect was evaluated in sexually naïve male rats. In sexually naïve male rats, a single administration of the ethanolic extract was performed at doses of 10, 20 and 40 mg/kg versus 0.5 mL/100g distilled water and 715 µg/kg Sildenafil Pfizer 50 mg in the negative and positive control rats, respectively. Female rats were induced to oestrus by sequential administration of estradiol benzoate (Sigma - Aldrich) (25 μg/rat) to make them receptive to males. Results:The results of the phytochemical screening revealed that the ethanolic extract of M. acuminata stems contains coumarins, flavonoids, tannins, triterpenes of triterpenesaponins. The biological study showed that at doses of 20 and 40 mg/kg, ethanolic extract of M. acuminatastems resulted in a significant (p < 0.05) and highly significant (p < 0.001) increase in the number of sexual mounts, the number of erections, the number of ejaculations and a significant (p < 0.01) decrease in the latency time between sexual mounts in male rats. Conclusions:The sexual stimulating effects of the ethanolic extract of M. acuminata observed in this study could be attributed to the presence of the identified chemical compounds, hence the interest in using this plant in traditional aphrodisiac medicine.

The fi eld of in situ nanomechanics is greatly benefi ting from microelectromechanical systems (MEMS) technology and integrated microscale testing machines that can measure a wide range of mechanical properties at nanometer scales, while characterizing the damage or microstructure evolution in electron microscopes. This article focuses on the latest advances in MEMS-based nanomechanical testing techniques that go beyond stress and strain measurements under typical monotonic loadings. Specifi cally, recent advances in MEMS testing machines now enable probing key mechanical properties of nanomaterials related to fracture, fatigue, and wear. Tensile properties can be measured without instabilities or at high strain rates, and signature parameters such as activation volume can be obtained. Opportunities for environmental in situ nanomechanics enabled by MEMS technology are also discussed.

With recent advances in computational modeling and in situ transmission electron microscopy (TEM) technologies, there have been increased efforts to apply these approaches to understand defect-based mechanisms dictating deformation mechanics. In situ TEM experiments and atomistic simulations each have their own unique limitations, including observable length and time scales and accessibility of information, motivating approaches that combine the two approaches. In this paper, we review recent studies that combine atomistic simulations and in situ TEM experiments to understand defect mechanisms associated with deformation of metals and alloys. In addition, we discuss ongoing developments in characterization and simulation capabilities that are expected to significantly advance the field of defect mechanics and allow greater integration between atomistic simulations and in situ TEM experiments.

Nanolaminates using alternating inorganic and organic layers have the potential to provide ultrabarrier with high resistance to gas permeation while also changing the crack onset strain (COS) to im...

This work investigated the effect of an 850-nm-thick electroplated Au coating on the very high cycle bending fatigue behavior of electroplated Ni microbeams tested under resonance in air at high frequencies (∼9 kHz). The S N curves show longer fatigue lives for the coated microbeams by at least a factor of 5 compared to the uncoated ones. This beneficial effect is demonstrated to be related to the delay in oxygen-assisted void formation, and therefore in void-assisted fatigue crack nucleation and growth in Ni. The improvement in fatigue life is limited by the fatigue degradation of the Au coating, which is also controlled by the formation of nanosized voids. Once a fatigue crack in the coating reaches the interface, delamination occurs, leading to exposure of the underlying Ni to air and faster, “uncoated-like”, fatigue degradation thereafter. This study highlights that thin, noble metal coatings can significantly improve the fatigue lives of metallic microbeams whose very high cycle fatigue behavior is sensitive to the environment and controlled by void formation.

Correction for ‘In situ TEM measurement of activation volume in ultrafine grained gold’ by Saurabh Gupta et al., Nanoscale, 2020, 12, 7146–7158, DOI: 10.1039/D0NR01874K.

The focus of this paper is to study the reliability of a wearable electrocardiogram sensor leadset under tight bending conditions using numerical simulations and experiments. In these simulations, appropriate material models are selected and fitted for each material layer, including a hyperelastic model for TPU, an elastic-plastic model for PET, and linear elastic models for the silver ink, carbon ink, and dielectric layers. The results from the numerical simulations are compared and validated using an analytical model as well as experimental data. Recommendations are made for acceptable operating conditions of the leadset.

Transmission electron microscopy (TEM) imaging relies on high energy electrons for atomic scale resolution, however, the electrons themselves interact with and may alter the material being imaged. Using an in situ TEM MEMS-based nanomechanical testing technique, the effect of the electron beam (e-beam) on the deformation behavior of nanocrystalline Al and ultrafine-grained Au is investigated and quantified. We show that the e-beam enhances plastic deformation, leading to an increase in plastic strain rate and a decrease in true activation volume V* in Al (28 to 21b3, with b being the Burgers vector length). The e-beam has a much weaker effect on Au. The e-beam effect is not caused by knock-on damage, but rather an effective temperature increase due to additional atomic fluctuations provided by the e-beam. The effective temperature increase is larger for Al than Au. This e-beam effect does not change the deformation mechanisms, but instead accelerates the stress-driven, thermally activated plastic deformation. These experiments provide insight into the effects of the e-beam on plastic deformation in different metals and underscore the importance of understanding and quantifying these effects for proper interpretation of measured mechanical properties during in situ TEM experiments.

This study investigated the combined effects of thickness (30 vs 100 nm) and average grain size (40 vs 70 nm for the thicker films) on the crack propagation mechanisms in ultrathin nanocrystalline gold microbeams, using a microelectromechanical system device to perform in situ transmission electron microscope (TEM) tensile experiments. Monotonic tensile tests of the two types of microbeams show similar strength levels (∼400 MPa) and ductility (∼2%). However, the thicker specimens exhibit a much more ductile behavior under repeated stress relaxation experiments, which the in situ TEM experiments revealed to be related to differences in intergranular crack propagation mechanisms. The governing crack growth process is in both cases dominated by grain boundary dislocation activities leading to grain boundary sliding. For the thinner specimens, secondary nanocracks are generated (as a result of grain boundary sliding) ahead of the main crack and coalesce together. Instead, secondary nanocracks do not form ahead of the main crack for the thicker specimens; the main crack extends as a result of sustained grain boundary sliding at the crack tip.

This work investigates the origins of electrical performance degradation under uniaxial stretching of a silver filled polyurethane ink (DuPont PE 874) screen printed onto a thermoplastic polyurethane substrate. The ink develops surface ruptures at strains of only a few percent yet remains conductive through continued elongation. We identify increasing sensitivity to surface damage beyond 10% applied strain, ɛapp, as the trace width, w, is reduced from 2 to 0.1 mm. This lowers the threshold strain for open circuit failure, from approximately 180% for w = 2 mm down to 25% for w = 0.1 mm. The damage progression remains largely consistent across trace widths: surface cracks coalesce to form longer channels, which grow perpendicular to the direction of elongation. These channels both deepen and widen with increasing ɛapp and some become laterally linked. The evolution of the network of interlinked channels is not width dependent, but a width effect manifests as a result of the channels constituting a larger fraction of specimen width for narrower traces. In addition, the narrower traces exhibit reduced cross sections due to an edge taper—an artifact of the screen printing process—which attenuates ink thickness by as much as 50% for w = 0.1 mm.

Flexible hybrid electronics rely upon compliant interconnects in order to maintain performance integrity in cases that require repeated elongation, including repeated stretching. A class of such conductive interconnects are composites of polymer with conductive particles that can be stretched at high strains without circuit failure. However, their fatigue response has so far remained largely unexplored and is essential prior to using in health monitoring applications. In this research, a stretchable silver-filled conductor is evaluated under high-strain cycling. In-situ techniques, including 4-point resistance measurement and laser profilometry, are used to correlate changes in electrical performance to the fatigue response. Surface crack formation is extensive upon stretching during the first loading cycle, forming a heavily interconnected crack network at higher strains that does not immediately result in open circuit failure. Resistance increase with cycling is attributed to a gradual deepening of these cracks until their depths approach the film thickness, eventually leading to electrical failure. Fatigue life, the number of cycles required to reach a predetermined electrical performance limit, is shown to be most influenced by the applied strain amplitude. Using a normalized resistance increase limit of R/R0=500, it is found that 500 μm wide conductive lines endure 23 cycles at 35% strain amplitude, but this becomes over 500 cycles when the amplitude is dropped to 5%. Sensitivity to mean strain, em, is relevant to strain amplitudes below 15%. In this manner, a composite conductor was shown to exhibit crack evolution behavior distinctly different from homogeneous metallic films.

Previous work demonstrated the marked effect of load ratio on the fatigue life of both mono- and poly-crystalline silicon thin films, with decreasing fatigue lives for more negative load ratios. In this paper, we investigated the role of a single compressive load on the stiffness (and therefore flaw population) of a monocrystalline Si microbeam. Specifically, we measured the resonance frequency (f 0 ~ 40 kHz) of a microresonator with ppm-level resolution before and after applying a compressive stress ranging from 1.5 to 5.5 GPa. The resolution in J 0 measurements is enough to capture the formation of subcritical penny-shaped cracks (lateral dimensions tens of nanometers), or the extension of existing cracks. No significant decrease in f 0 was measured within the resolution of the technique. This result indicates that the mechanism known for the fatigue of notched ceramics under cyclic compressive loads at the bulk scale, relying on the formation of cracks upon the first compressive cycle, does not apply to the fatigue of silicon thin films. Instead of a decrease in J 0 , the results highlighted an increase in J 0 in some specimens, which is interpreted as compression-induced crack healing (as opposed to the well documented thermally induced healing). A review of the proposed fatigue mechanisms for Si thin films is also provided.

Nanocrystalline Al thin films have been strained in situ in a transmission electron microscope using two separate nanomechanical techniques involving a push-to-pull device and a microelectromechanical system (MEMS) device. Deformation-induced grain growth was observed to occur via stress-assisted grain boundary migration with extensive grain growth occurring in the necked region, indicating that the increase in local stress drives the boundary migration. Under applied tensile stresses close to the ultimate tensile strength of 450 MPa for a nanocrystalline Al specimen, measured boundary migration speeds are 0.2 – 0.7 nm s−1 for grains outside necked region and increases to 2.5 nm s−1 for grains within the necked region where the local estimated tensile stresses are elevated to around 630 MPa. By tracking grain boundary motion over time, molecular dynamics simulations showed qualitative agreement in terms of pronounced grain boundary migration with the experimental observations. The combined in situ observation and molecular dynamics simulation results underscore the important role of stress-driven grain growth in plastically deforming nanocrystalline metals, leading to intergranular fracture through predominant grain boundary sliding in regions with large localized deformation.

A singular critical onset strain value has been used to characterize the strain limits of barrier films used in flexible electronics. However, such metrics do not account for time-dependent or environmentally assisted cracking, which can be critical in determining the overall reliability of these thin-film coatings. In this work, the time-dependent channel crack growth behavior of silicon nitride barrier films on poly(ethylene terephthalate) (PET) substrates is investigated in dry and humid environments by tensile tests with in situ optical microscopy and numerical models. The results reveal the occurrence of environmentally assisted crack growth at strains well below the critical onset crack strain and in the absence of polymer-relaxation-assisted, time-dependent crack growth. The crack growth rates in laboratory air are about 1 order of magnitude larger than those tested in dry environments (dry air or dry nitrogen). In laboratory air, crack growth rates increase from ∼200 nm/s to 60 μm/s for applied stress intensity factors, K, ranging from 1.0 to 1.4 MPa·m

Respiration on trimethylamine oxide (TMAO) allows bacterial survival under anoxia. In Shewanella oneidensis, Tor is the system involved in TMAO respiration and it is encoded by the torECAD operon. The torA and torC genes encode TorA terminal reductase and the TorC c-type cytochrome, respectively. Sequence analysis suggests that TorD is the putative specific chaperone of TorA, whereas TorE is of unknown function. The purpose of this study was to understand whether TorD and TorE are two accessory proteins that affect the efficiency of the Tor system by chaperoning TorA terminal reductase. Moreover, by deleting each gene, we established that the absence of TorD drastically affects the stability of TorA, while the absence of TorE does not affect TorA stability or activity. Since TMAO reduction was affected in the ΔtorE mutant, TorE could be an additional component of the TorC-TorA electron transfer chain during bacterial respiration. Finally, a fitness experiment indicated that the presence of TorE, as expected, confers a selective advantage in competitive environments.

We report significant improvements in the sensing scheme of a microelectromechanical system (MEMS) based nanomechanical tensile testing technique that has been previously demonstrated to allow direct microstructural observations inside a transmission electron microscope (TEM) at high magnifications while simultaneously measuring the stress and strain in the sample electronically. The particularity of the MEMS device is the presence of two capacitive sensors on either side of a specimen gap (across which nanostructures like nanowires and thin films can be manipulated and clamped), allowing independent measurement of applied load (stress) and crosshead displacement (strain). The improvement in the sensing technique lies in the independent, separate measurements of the signals from the two capacitive sensors (as opposed to the previous technique based on the differential measurement between the two sensors). The new technique (called technique 2 in this paper) provides independent electronic sensing of stress and strain without making any assumption about the material behavior and opens up the possibility of doing force controlled tests. The new sensing technique is demonstrated and compared to the previous one (called technique 1 in this paper) by performing ex-situ monotonic and stress relaxation tests on freestanding 100-nm-thick Au films. Important practical matters such as specimen clamping and signal drift are also discussed.

International audience; Molybdoenzymes play essential functions in living organisms and, as a result, in various geochemical cycles. It is thus crucial to understand how these complex proteins become highly efficient enzymes able to perform a wide range of catalytic activities. It has been established that specific chaperones are involved during their maturation process. Here, we raise the question of the involvement of general chaperones acting in concert with dedicated chaperones or not.

The fully-reversed bending fatigue behavior of 20-μm-thick electroplated Ni notched microbeams actuated at resonance (∼8 kHz) was characterized in humid air environments, in an effort to investigate the effects of extreme stress gradients (normalized stress gradients of 36%/μm over the first 2 μm at the notch root) in small-scale fatigue. Compared to our previous study, larger driving forces (stress amplitudes up to 510 MPa (60% of the ultimate tensile strength), corresponding to plastic strain amplitudes up to ∼0.1%) were applied, leading to the propagation of microstructurally small cracks ahead of the notch. The endurance limit reaches 50% of the ultimate tensile strength, and the Basquin and Coffin–Manson fits for the stress and strain-life curves, respectively, exhibit much lower (in absolute value) fatigue exponents that typical values for bulk metals. This singular behavior is explained by the ultraslow and decelerating crack growth rates, calculated based on the measured resonance frequency evolution during the fatigue tests, which appear to characterize the growth of microstructurally small cracks under extreme stress gradients. This study highlights the need to further characterize the effects of different stress gradients values on crack growth rates and fatigue lives in order to accurately predict the small-scale fatigue damage in metallic microbeams.

The failure of micron-scale metallic components presents significant variability as a result of their size being comparable to microstructural length scales. Indeed, these components do not represent the bulk of the material but correspond to statistical volume elements (SVEs). This work investigates the role of SVEs on fatigue crack nucleation with a novel comparison between microbeam experiments and microstructure-sensitive simulations. We recreate multiple microstructural computational realizations to estimate fatigue crack nucleation lives and orientations by means of physics-based crystal plasticity models. We demonstrate a unique approach to validate microstructure sensitive models and quantify the fatigue crack stochasticity associated with small volumes.

This work explores conductivity under applied uniaxial strain of two silver-based inks with similar flake volume fractions of ~50% that are screen-printed with a single pass (thickness: 10 µm) onto three different polymer substrates. The normalized resistance increases more rapidly with applied strain for the “flexible” ink (5025 with an acrylic binder), and has three times greater resistance at 35% strain when compared to the “stretchable” ink (PE874 with polyurethane binder). While resistance increase is qualitatively consistent with percolation theory, the in-situ strain map analysis and post-mortem fractography reveal drastic differences in the root causes of the inks’ electrical behavior. Both inks form strain localization bands with similar spacing. For the flexible ink (5025), strain localization is accompanied by local necking and flake fraction reduction. For the stretchable ink (PE874), strain localization is associated with surface cracking initiated by pre-existing voids, with minimal changes in the flake fraction. A model incorporating strain localization through a Gaussian distribution of flakes evolving with applied strain more closely accounts for the 5025 ink's normalized resistance increase compared to models that assume uniform strain and a uniform flake distribution. Overall, local necking and reduction of the flake fraction appear to be more detrimental to the resistance than the formation of surface cracks.

This Letter presents a quantitative in situ scanning electron microscope (SEM) nanoscale high and very high cycle fatigue (HCF/VHCF) investigation of Ni microbeams under bending, using a MEMS microresonator as an integrated testing machine. The novel technique highlights ultraslow fatigue crack growth (average values down to ∼10–14 m/cycle) that has heretofore not been reported and that indicates a discontinuous process; it also reveals strong environmental effects on fatigue lives that are 3 orders of magnitude longer in a vacuum than in air. This ultraslow fatigue regime does not follow the well documented fatigue mechanisms that rely on the common crack tip stress intensification, mediated by dislocation emission and associated with much larger crack growth rates. Instead, our study reveals fatigue nucleation and propagation mechanisms that mainly result from room temperature void formation based on vacancy condensation processes that are strongly affected by oxygen. This study therefore shows significant size effects governing the bending high/very high cycle fatigue behavior of metals at the micro- and nanoscales, whereby the stress concentration effect at the tip of a growing small fatigue crack is assumed to be greatly reduced by the effect of the bending-induced extreme stress gradients, which prevents any significant cyclic crack tip opening displacement. In this scenario, ultraslow processes relying on vacancy formation at the subsurface or in the vicinity of a crack tip and subsequent condensation into voids become the dominant fatigue mechanisms.

Tennis has been identified as an ideal context for examining the dynamics of parenting and coaching relationships (Gould et al., 2008) but coaching dual-role relationships remain unexplored in this sport and related investigations only included volunteer coaches (Jowett, 2008; Harwood & Knight, 2012). An open-ended interview approach was used to examine how female tennis players previously coached by their fathers (professional coaches) before competing in college tennis perceived their experiences with the dual-role relationship and the coaching transition. A holistic narrative approach was used to reconstruct retrospectively the stories of the participants’ experiences and understand their development. Despite some beneficial aspects, a majority of participants emphasized their challenging experiences with regards to their needs to manage blurred boundaries, receive paternal approval, and endure their fathers’ controlling and abusive behaviors. Coaching transitions helped normalize father-daughter relationships and provided insight into the respective needs that were fulfilled through the dual-role relationships.

The energy losses of a silicon lateral rotary micro-resonator operating in humid air were investigated with a three-dimensional finite volume model and compared to experiments as well as a simplified analytical model. The simulations can provide accurate modeling (within 5%) of air damping (the dominant energy loss source), unlike the analytical model capturing as little as 50% of the experimental values. The results showed that a significant portion of energy losses are associated with the complex three-dimensional path lines near the micro-resonator's edges that are not captured in the simplified analytical models. The simulations provide useful guidelines to design simple temperature and humidity sensors.

This study highlights an oxidation-assisted fatigue crack initiation mechanism in 20 μm thick electroplated Ni films under loading conditions relevant for a wide range of microelectromechanical systems, such as extreme stress gradients at the surface (50% decrease over the first micrometer from the surface). Microresonators subjected to in-plane bending at ∼8 kHz were fatigued for billions of cycles in humid air, at 30 °C, 50% relative humidity (RH), and 80 °C, 90% RH, for maximum stress amplitudes up to ∼500 MPa (∼55% of the ultimate tensile strength). Transmission electron microscopy (TEM) revealed highly localized thick oxides (∼1 μm) on specimens fatigued for several billions of cycles. These oxides are two to three orders of magnitude thicker than the regular native oxides at these low temperatures, and only form at the location of cyclic slip bands. These oxides appear to be thicker for higher partial pressures of water, based on the TEM comparison of one specimen fatigued at 30 °C, 50% RH to one fatigued at 80 °C, 90% RH. Fatigue microcracks were observed within these highly localized thick oxides. Finite element models were also employed to confirm these results based on the interpretation of the evolution of the devices’ resonance frequency. This oxidation-assisted fatigue crack initiation mechanism at low temperatures constitutes a significant departure from the established mechanisms for bulk metals and their environmental effects. A possible explanation for the different governing mechanism is the presence of extreme stress gradients in these microscale components. Under these loading conditions, the classical fatigue crack initiation mechanisms are not operational, allowing this alternative mechanism to become dominant. This study highlights the need to further understand the coupled size and environmental effects on the fatigue of metallic thin films.

Kinetics of environmentally assisted subcritical cracking in SiNx barrier films is studied by in situ optical microscopy experiments and quantum chemical molecular orbital theory simulations. The activation volume of 0.83–1.11 cm3/mol and the activation energy of 138 kJ/mol (1.43 eV) are experimentally measured for subcritical crack growth in moist air. The quantum chemical simulations reveal the molecular mechanism of stress corrosion in mechanically strained SiNx under water attack, and the predicted activation energy and activation volume are in good agreement with the experimental results. The combined experimental and modeling studies provide a fundamental understanding of subcritical crack growth in SiNx barrier films for flexible electronic device applications.Kinetics of environmentally assisted subcritical cracking in SiNx barrier films is studied by in situ optical microscopy experiments and quantum chemical molecular orbital theory simulations. The activation volume of 0.83–1.11 cm3/mol and the activation energy of 138 kJ/mol (1.43 eV) are experimentally measured for subcritical crack growth in moist air. The quantum chemical simulations reveal the molecular mechanism of stress corrosion in mechanically strained SiNx under water attack, and the predicted activation energy and activation volume are in good agreement with the experimental results. The combined experimental and modeling studies provide a fundamental understanding of subcritical crack growth in SiNx barrier films for flexible electronic device applications.

Fatigue crack formation and early growth is significantly influenced by microstructural attributes such as grain size and morphology. Although the crystallographic orientation is a primary indicator for fatigue cracking, the neighbourhood conformed by the first and second neighbour grains strongly affect the fatigue cracking driving force. Hence, two identical grains may result in different fatigue responses due to their interactions with their microstructural ensemble, which determines the fatigue variability. Naturally, macroscopic samples with millions of grains and thousands of competing microstructural neighbourhoods can effectively resemble a representative volume element in which fatigue failure may seem deterministic. However, when considering systems in which fatigue failure is controlled by hundreds or less of grains, fatigue failure is stochastic in nature and the samples are not a representative but a statistical volume. This work studies fatigue crack nucleation in micron-scale Ni beams that contain a few hundred grains. This work presents 3D crystal plasticity finite element models to compute stochastic distribution of fatigue indicator parameters that serve as proxies for crack nucleation in statistical volume elements. The integration of experiments with models provides a method to understand the irreversible deformation at the grain level that leads to fatigue cracking. Our results explain the role of grain morphology of crack nucleation distribution

Correction for ‘Quantitative in situ TEM tensile fatigue testing on nanocrystalline metallic ultrathin films’ by Ehsan Hosseinian, et al., Nanoscale, 2013, 5, 12532–12541.

In this paper, we present the results of mechanical testing that reveals the onset crack strain and fatigue crack growth of TiO2 and Al2O3 films deposited by atomic layer deposition. Data show that both films have a strong thickness dependence of the onset crack strain, with the strain reducing with increasing film thickness. Additionally, TiO2 films have a lower onset crack strain and strain for fatigue damage than Al2O3. However, TiO2 films are more resilient in harsh environments where fatigue damage in Al2O3 films grows faster.