Low-frequency seismic properties of olivine-orthopyroxene mixtures

2020 ◽  
Author(s):  
Tongzhang Qu ◽  
Ian Jackson ◽  
Ulrich Faul
Keyword(s):  
Shear Modulus ◽  
Upper Mantle ◽  
Forced Oscillation ◽  
Low Frequency ◽  
Secondary Phase ◽  
Confining Pressure ◽  
Creep Function ◽  
Seismic Properties ◽  
New Findings

<p>Although the seismic properties of polycrystalline olivine have been the subject of systematic and comprehensive study at seismic frequencies, the role of orthopyroxene as the major secondary phase in the shallow parts of the Earth’s upper mantle has so far received little attention. Accordingly, we have newly prepared synthetic melt-free polycrystalline specimens containing different proportions of olivine (Ol, Fo<sub>90</sub>) and orthopyroxene (Opx, En<sub>90</sub>) by the solution-gelation method. The resulting specimens, ranging in composition between Ol<sub>95</sub>Opx<sub>5</sub> and Ol<sub>5</sub>Opx<sub>95</sub> composition, were mechanically tested by torsional forced oscillation at temperatures of 1200 ºC to 400 ºC accessed during staged cooling under a confining pressure of 200 MPa. The microstructures of tested specimens were evaluated by BSE, EBSD and TEM. The forced-oscillation data, i.e. shear modulus and associated strain-energy dissipation at 1-1000 s period, were closely fitted by a model based on an extended Burgers-type creep function. This model was also required to fit data from previous ultrasonic and Brillouin spectroscopic measurements at ns-µs periods. Within the observational window (1-1000 s), the shear modulus and dissipation vary monotonically with period and temperature for each of the tested specimens, which is broadly comparable with that previously reported for olivine-only samples. There is no evidence of the superimposed dissipation peak reported by Sundberg and Cooper (2010) for an Ol<sub>60</sub>Opx<sub>40</sub> specimen prepared from natural precursor materials and containing a melt fraction of 1.5%. The higher orthopyroxene concentrations are associated with systematically somewhat lower levels of dissipation and corresponding weaker modulus dispersion. The new findings suggest that the olivine-based model for high-temperature viscoelasticity in upper-mantle olivine requires only modest modification to accommodate the role of orthopyroxene, including appropriate compositional dependence of the unrelaxed modulus and its temperature derivative.</p>

Low-frequency seismic properties of thermally cracked and argon-saturated granite

Geophysics ◽  
2006 ◽  
Vol 71 (6) ◽  
pp. F147-F159 ◽  
Author(s):  
Cao Lu ◽  
Ian Jackson
Keyword(s):  
Shear Modulus ◽  
Transient Flow ◽  
Crack Density ◽  
Fluid Pressure ◽  
Low Frequency ◽  
Confining Pressure ◽  
Seismic Properties ◽  
Aspect Ratios ◽  
In Situ Permeability

Torsional forced-oscillation techniques have been used to measure the shear modulus and strain-energy dissipation on cylindrical specimens of a fine-grained granite, Delegate aplite. The specimens were subjected to thermal cycling and associated microcracking under varying conditions of confining pressure [Formula: see text] and argon pore-fluid pressure [Formula: see text] within the low-frequency saturated isobaric regime. Complementary transient-flow studies of in-situ permeability and volumetric measurements of connected crack porosity allowed the modulus measurements to be interpreted in terms of the density and interconnectivity of the thermally generated cracks. The modulus measurements indicate that newly generated thermal cracks are closed by a differential pressure, [Formula: see text], which ranges from [Formula: see text] for temperatures of [Formula: see text]. This suggests crack aspect ratios on the order of [Formula: see text]. The covariation of in-situ permeability [Formula: see text] and thermal crack density [Formula: see text] that we infer from the modulus deficit is consistent with percolation theory. There is a well-defined threshold at [Formula: see text], beyond which [Formula: see text] increases markedly as [Formula: see text], with [Formula: see text]. At lower crack densities, it is difficult to measure the sensitivity of shear modulus to variations of confining and pore pressures because pore-pressure equilibrium is approached so sluggishly. At temperatures beyond the percolation threshold, the modulus variation is a function of the effective pressure, [Formula: see text], with the value of [Formula: see text] increasing toward one with increasing crack connectivity.

Calculation-and-experimental estimation of the role of the frequency ratio in changing the endurance at two-frequency deformation modes

2019 ◽  
Vol 85 (1(I)) ◽  
pp. 64-71 ◽  
Author(s):  
M. M. Gadenin
Keyword(s):  
High Frequency ◽  
Experimental Studies ◽  
Low Frequency ◽  
Reduction Factor ◽  
Single Frequency ◽  
Cyclic Loads ◽  
Small Ratio ◽  
Harmonic Components ◽  
Deformation Modes

The cycle configuration at two-frequency loading regimes depends on the number of parameters including the absolute values of the frequencies and amplitudes of the low-frequency and high-frequency loads added during this mode, the ratio of their frequencies and amplitudes, as well as the phase shift between these harmonic components, the latter having a significant effect only with a small ratio of frequencies. Presence of such two-frequency regimes or service loading conditions for parts of machines and structures schematized by them can significantly reduce their endurance. Using the results of experimental studies of changes in the endurance of a two-frequency loading of specimens of cyclically stable, cyclically softened and cyclically hardened steels under rigid conditions we have shown that decrease in the endurance under the aforementioned conditions depends on the ratio of frequencies and amplitudes of operation low-frequency low-cycle and high-frequency vibration stresses, and, moreover, the higher the level of the ratios of amplitudes and frequencies of those stacked harmonic processes of loading the greater the effect. It is shown that estimation of such a decrease in the endurance compared to a single frequency loading equal in the total stress (strains) amplitudes can be carried out using an exponential expression coupling those endurances through a parameter (reduction factor) containing the ratio of frequencies and amplitudes of operation cyclic loads and characteristic of the material. The reduction is illustrated by a set of calculation-experimental curves on the corresponding diagrams for each of the considered types of materials and compared with the experimental data.

scholarly journals High Ripple-Density Resolution for Discriminating Between Rippled and Nonrippled Signals: Effect of Temporal Processing or Combination Products?

2021 ◽  
Vol 25 ◽  
pp. 233121652110101
Author(s):  
Dmitry I. Nechaev ◽  
Olga N. Milekhina ◽  
Marina S. Tomozova ◽  
Alexander Y. Supin
Keyword(s):  
Low Frequency ◽  
Noise Signal ◽  
Density Variation ◽  
Choice Procedure ◽  
Masker Level ◽  
Reference Signals ◽  
Forced Choice Procedure ◽  
The Mean ◽  
Density Resolution

The goal of the study was to investigate the role of combination products in the higher ripple-density resolution estimates obtained by discrimination between a spectrally rippled and a nonrippled noise signal than that obtained by discrimination between two rippled signals. To attain this goal, a noise band was used to mask the frequency band of expected low-frequency combination products. A three-alternative forced-choice procedure with adaptive ripple-density variation was used. The mean background (unmasked) ripple-density resolution was 9.8 ripples/oct for rippled reference signals and 21.8 ripples/oct for nonrippled reference signals. Low-frequency maskers reduced the ripple-density resolution. For masker levels from −10 to 10 dB re. signal, the ripple-density resolution for nonrippled reference signals was approximately twice as high as that for rippled reference signals. At a masker level as high as 20 dB re. signal, the ripple-density resolution decreased in both discrimination tasks. This result leads to the conclusion that low-frequency combination products are not responsible for the task-dependent difference in ripple-density resolution estimates.

Activation of bovine oocytes by protein synthesis inhibitors: new findings on the role of MPF/MAPKs†

2021 ◽  
Author(s):  
Cecilia Valencia ◽  
Felipe Alonso Pérez ◽  
Carola Matus ◽  
Ricardo Felmer ◽  
María Elena Arias
Keyword(s):  
Protein Synthesis ◽  
Kinase Activity ◽  
Cyclin B1 ◽  
Protein Synthesis Inhibitors ◽  
Vitro Fertilization ◽  
New Findings ◽  
Bovine Oocytes ◽  
Dependent Pathway

Abstract The present study evaluated the mechanism by which protein synthesis inhibitors activate bovine oocytes. The aim was to analyze the dynamics of MPF and MAPKs. MII oocytes were activated with ionomycin (Io), ionomycin+anisomycin (ANY) and ionomycin+cycloheximide (CHX) and by in vitro fertilization (IVF). The expression of cyclin B1, p-CDK1, p-ERK1/2, p-JNK, and p-P38 were evaluated by immunodetection and the kinase activity of ERK1/2 was measured by enzyme assay. Evaluations at 1, 4, and 15 hours postactivation (hpa) showed that the expression of cyclin B1 was not modified by the treatments. ANY inactivated MPF by p-CDK1Thr14-Tyr15 at 4 hpa (P < 0.05), CHX increased pre-MPF (p-CDK1Thr161 and p-CDK1Thr14-Tyr15) at 1 hpa and IVF increased p-CDK1Thr14-Tyr15 at 17 hours postfertilization (hpf) (P < 0.05). ANY and CHX reduced the levels of p-ERK1/2 at 4 hpa (P < 0.05) and its activity at 4 and 1 hpa, respectively (P < 0.05). Meanwhile, IVF increased p-ERK1/2 at 6 hpf (P < 0.05); however, its kinase activity decreased at 6 hpf (P < 0.05). p-JNK in ANY, CHX, and IVF oocytes decreased at 4 hpa (P < 0.05). p-P38 was only observed at 1 hpa, with no differences between treatments. In conclusion, activation of bovine oocytes by ANY, CHX, and IVF inactivates MPF by CDK1-dependent specific phosphorylation without cyclin B1 degradation. ANY or CHX promoted this inactivation, which seemed to be more delayed in the physiological activation (IVF). Both inhibitors modulated MPF activity via an ERK1/2-independent pathway, whereas IVF activated the bovine oocytes via an ERK1/2-dependent pathway. Finally, ANY does not activate the JNK and P38 kinase pathways.

scholarly journals Current trends in leather science

2020 ◽  
Vol 2 (1) ◽  
Author(s):  
Anthony D. Covington ◽  
William R. Wise
Keyword(s):  
Ionic Liquids ◽  
Potential Role ◽  
Solid Medium ◽  
Leather Industry ◽  
Chromium Vi ◽  
Current Trends ◽  
New Findings ◽  
Vegetable Tanning ◽  
Sulfide Species

Abstract In preparing the second edition of ‘Tanning Chemistry. The Science of Leather.’, the literature was updated and the content was revised and reviewed. Here, the new findings are presented and discussed. Notable developments include the necessary rethinking of the mechanism of sulfide unhairing because of new understanding of the aqueous chemistry of sulfide species. Revision upwards of the value of the second pKa for sulfide species ionisation means that S2− cannot exist in an aqueous medium, so the unhairing species in hair burn reactions is HS−. Although the technology remains the same, this means the mechanisms of associated reactions such as immunisation must be revised. Rawstock preservation has benefitted from studies of the potential role of materials from plants which accumulate salt, but which also contribute terpene compounds. There is also further discussion on the continuing issue of chromium (VI) in the leather industry. The application to processing of new solvents, ionic liquids and deep eutectics, is the coming technology, which offers transforming options for new chemistries and products. Renewed interest in vegetable tanning and methods of wet white processing are current trends. Also, within the topic of reagent delivery is processing in a solid medium of plastic beads. Graphical abstract

scholarly journals From Exosome Glycobiology to Exosome Glycotechnology, the Role of Natural Occurring Polysaccharides

2021 ◽  
Vol 2 (2) ◽  
pp. 311-338
Author(s):  
Giulia Della Rosa ◽  
Clarissa Ruggeri ◽  
Alessandra Aloisi
Keyword(s):  
State Of The Art ◽  
Cell Communication ◽  
Pathological Conditions ◽  
New Findings ◽  
Cell Type Specific ◽  
New Perspective ◽  
And Function ◽  
And Personalized Medicine ◽  
Innate Ability

Exosomes (EXOs) are nano-sized informative shuttles acting as endogenous mediators of cell-to-cell communication. Their innate ability to target specific cells and deliver functional cargo is recently claimed as a promising theranostic strategy. The glycan profile, actively involved in the EXO biogenesis, release, sorting and function, is highly cell type-specific and frequently altered in pathological conditions. Therefore, the modulation of EXO glyco-composition has recently been considered an attractive tool in the design of novel therapeutics. In addition to the available approaches involving conventional glyco-engineering, soft technology is becoming more and more attractive for better exploiting EXO glycan tasks and optimizing EXO delivery platforms. This review, first, explores the main functions of EXO glycans and associates the potential implications of the reported new findings across the nanomedicine applications. The state-of-the-art of the last decade concerning the role of natural polysaccharides—as targeting molecules and in 3D soft structure manufacture matrices—is then analysed and highlighted, as an advancing EXO biofunction toolkit. The promising results, integrating the biopolymers area to the EXO-based bio-nanofabrication and bio-nanotechnology field, lay the foundation for further investigation and offer a new perspective in drug delivery and personalized medicine progress.

scholarly journals Moduli and modes in the Mikado model

Soft Matter ◽  
2021 ◽  
Author(s):  
Brian Tighe ◽  
Karsten Baumgarten
Keyword(s):  
Shear Modulus ◽  
Mechanical Model ◽  
Low Frequency ◽  
Vibrational Modes ◽  
Prior Work ◽  
Fiber Networks ◽  
Elastic Shear Modulus ◽  
Flexible Fiber ◽  
Elastic Shear

We determine how low frequency vibrational modes control the elastic shear modulus of Mikado networks, a minimal mechanical model for semi-flexible fiber networks. From prior work it is known that...

Role of secondary phase particles in fatigue behavior of high-speed railway gearbox material

2020 ◽  
Vol 131 ◽  
pp. 105336 ◽  
Author(s):  
Yinan Jiao ◽  
Yifan Zhang ◽  
Shiqing Ma ◽  
Deli Sang ◽  
Yang Zhang ◽  
...  
Keyword(s):  
High Speed ◽  
Fatigue Behavior ◽  
Secondary Phase ◽  
High Speed Railway

scholarly journals Shoot–root carbon allocation, sugar signalling and their coupling with nitrogen uptake and assimilation

2016 ◽  
Vol 43 (2) ◽  
pp. 105 ◽  
Author(s):  
Lu Wang ◽  
Yong-Ling Ruan
Keyword(s):  
Growth And Development ◽  
Carbon Allocation ◽  
Dynamic Balance ◽  
Shoot Development ◽  
Long Distance ◽  
Root Carbon ◽  
Organ Systems ◽  
New Findings ◽  
Sugar Signalling

Roots and shoots are distantly located but functionally interdependent. The growth and development of these two organ systems compete for energy and nutrient resource, and yet, they keep a dynamic balance with each other for growth and development. The success of such a relationship depends on efficient root-shoot communication. Aside from the well-known signalling processes mediated by hormones such as auxin and cytokinin, sugars have recently been shown to act as a rapid signal to co-ordinate root and shoot development in response to endogenous and exogenous clues, in parallel to their function as carbon and energy resources for biomass production. New findings from studies on vascular fluids have provided molecular insights into the role of sugars in long-distance communications between shoot and root. In this review, we discussed phloem- and xylem- translocation of sugars and the impacts of sugar allocation and signalling on balancing root–shoot development. Also, we have taken the shoot–root carbon–nitrogen allocation as an example to illustrate the communication between the two organs through multi-layer root–shoot–root signalling circuits, comprising sugar, nitrogen, cytokinin, auxin and vascular small peptide signals.

scholarly journals NMDA Receptor-Dependent Synaptic Activity in Dorsal Motor Nucleus of Vagus Mediates the Enhancement of Gastric Motility by Stimulating ST36

2012 ◽  
Vol 2012 ◽  
pp. 1-11 ◽  
Author(s):  
Xinyan Gao ◽  
Yongfa Qiao ◽  
Baohui Jia ◽  
Xianghong Jing ◽  
Bin Cheng ◽  
...  
Keyword(s):  
Synaptic Transmission ◽  
Gastric Motility ◽  
Low Frequency ◽  
Synaptic Activity ◽  
Motor Nucleus ◽  
Dorsal Motor Nucleus ◽  
Vagal Reflex ◽  
Precise Molecular Mechanism ◽  
Lines Of Evidence

Previous studies have demonstrated the efficacy of electroacupuncture at ST36 for patients with gastrointestinal motility disorders. While several lines of evidence suggest that the effect may involve vagal reflex, the precise molecular mechanism underlying this process still remains unclear. Here we report that the intragastric pressure increase induced by low frequency electric stimulation at ST36 was blocked by AP-5, an antagonist of N-methyl-D-aspartate receptors (NMDARs). Indeed, stimulating ST36 enhanced NMDAR-mediated, but not 2-amino-3-(5-methyl-3-oxo-1,2-oxazol-4-yl)propanoic-acid-(AMPA-) receptor-(AMPAR-) mediated synaptic transmission in gastric-projecting neurons of the dorsal motor nucleus of the vagus (DMV). We also identified that suppression of presynapticμ-opioid receptors may contribute to upregulation of NMDAR-mediated synaptic transmission induced by electroacupuncture at ST36. Furthermore, we determined that the glutamate-receptor-2a-(NR2A-) containing NMDARs are essential for NMDAR-mediated enhancement of gastric motility caused by stimulating ST36. Taken together, our results reveal an important role of NMDA receptors in mediating enhancement of gastric motility induced by stimulating ST36.

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