Low Stretch Research Articles

Terminal regions of a protein are a hotspot for low complexity regions and selection.

Volatile low complexity regions (LCRs) are a novel source of adaptive variation, functional diversification and evolutionary novelty. An interplay of selection and mutation governs the composition and length of low complexity regions. High %GC and mutations provide length variability because of mechanisms like replication slippage. Owing to the complex dynamics between selection and mutation, we need a better understanding of their coexistence. Our findings underscore that positively selected sites (PSS) and low complexity regions prefer the terminal regions of genes, co-occurring in most Tetrapoda clades. We observed that positively selected sites within a gene have position-specific roles. Central-positively selected site genes primarily participate in defence responses, whereas terminal-positively selected site genes exhibit non-specific functions. Low complexity region-containing genes in the Tetrapoda clade exhibit a significantly higher %GC and lower ω (dN/dS: non-synonymous substitution rate/synonymous substitution rate) compared with genes without low complexity regions. This lower ω implies that despite providing rapid functional diversity, low complexity region-containing genes are subjected to intense purifying selection. Furthermore, we observe that low complexity regions consistently display ubiquitous prevalence at lower purity levels, but exhibit a preference for specific positions within a gene as the purity of the low complexity region stretch increases, implying a composition-dependent evolutionary role. Our findings collectively contribute to the understanding of how genetic diversity and adaptation are shaped by the interplay of selection and low complexity regions in the Tetrapoda clade.

Automatic Detection and Analysis of the Shoreline Change Rate at Maravanthe Coast, India

Maravanthe Beach has been witnessing erosion due to waves caused by tidal forces, destroying vegetation, and causing enormous damage to people’s lives, livestock, and property. Hence, an attempt has been made to understand the shoreline change analysis using the automatic shoreline extraction method and determine the rate of change in terms of erosion and accretion rate before and after the construction of coastal structures during the period from 2014 to 2023. The SWAT model was applied to analyze the influence of surface runoff on shoreline changes near Maravanthe Beach for the periods 2004–2014 and 2012–2023. Also, runoff was chosen as one of the parameters for validation of the analysis. It was noticed that the shoreline stretch had experienced significant erosion prior to the construction of shore protection infrastructure. Soon after the deployment of certain shore structures, the shoreline progressed from a high erosion stretch to a low erosion stretch. This study reveals that Maravanthe Beach witnessed greater erosion during the period 2014–2018 than it did from 2019–2023 and also observed a decrease in erosion from 11% to 3% and an increase in the accretion zones from 2 to 9%.

#2450 Alternative splicing in podocytes under mechanical stress: a new perspective for the pathogenic effect of glomerular hypertension

Abstract Background and Aims High blood pressure is considered one of the most important risk factors leading to chronic kidney disease. The pathogenesis of hypertension-induced damage to podocytes remains still elusive. Since recent reports have shown that alternative splicing (AS) has a significant impact on disease progression, we investigated alternative splicing of mechanically stretched podocytes, a well-established model for glomerular hypertension, in the Sys_CARE (Systems Medicine Investigation of AS in Cardiac and Renal Diseases) project. Our results provide new insights into the molecular mechanisms that might drive the progression of hypertensive nephropathy. Method Differentiated murine podocytes were exposed to mechanical stretch for 3 days under low and high stretch conditions. Subsequently, mRNA and proteins were analyzed by RNA-Seq and LC-MS/MS, respectively. Enrichment analysis identified transcripts which were classified according to the related biological processes, molecular function, and cellular components. Splicing and transcript expression were evaluated with bioinformatical tools such as MAJIQ, Multivariate Analysis of Transcript Splicing (rMATS), leafcutter, Whippet and IsoformSwitchAnalyzeR. Results Transcriptome analyses of mechanically stretched podocytes by RNA sequencing showed that mechanical stress leads to a high number of differentially expressed genes (1323 with log2 fc ± 1) compared to unstretched podocytes. Detailed gene set enrichment analysis for GO-Terms showed an enrichment among up-regulated transcripts related to mRNA processing and RNA splicing. In contrast, most transcripts with decreased expression upon stretch are associated with cytoskeleton function. To identify AS events, different AS tools were used. We found a wide variety of splice events. The most frequent event was exon skipping (between 63-82% of all AS events), followed by intron retention and alternative 5′ or 3′ splice site. 290 alternatively spliced genes were detected after mechanical stretch by three different splice analysis tools (rMATS, leafcutter, Whippet). Out of these candidates, the IsoformSwitchAnalyzeR identified 17 genes exhibiting significant isoform switches. To prioritize the candidates, we performed a screening that included only those genes that were identified by proteomic analysis and that are expressed in podocytes in vivo or showed an altered expression pattern in glomerular disease. This screening led to the two candidates Shroom3 and Myl6. Shroom3, an actin-binding protein, is crucial for podocyte morphology and function. Genetic variants of Shroom3 have been linked with chronic kidney disease by GWAS. Here we found that two of four Shroom3 isoforms showed significant expression changes due to mechanical stretch. Isoform 2 which showed the highest expression in cultured podocytes, significantly decreased, but the shorter isoform X1 was significantly up-regulated after mechanical stretch. Both changes were verified by qRT-PCR as well as by in situ hybridization in mouse tissue. Myosin light chain 6 (Myl6), a component of the myosin motor protein complex, has two isoforms which are detected in cultured podocytes as well as in vivo. We found an expression switch from isoform 1 to 2 due to mechanical stretch. Our analysis showed that this is accompanied by a change of the amino acid sequence AFVRHILS to ELVRMVLN, sequences that are well conserved in mice, rat, and human. The analysis of the protein structure by FoldX revealed that this change in the amino acid sequence could lead to an impairment of the binding of the motor protein complex to actin and might therefore influence the functionality of the actin cytoskeleton, which is highly important for proper podocyte foot process morphology. Conclusion Mechanical stretch of cultured mouse podocytes, which is an excellent model to simulate hypertensive nephropathy, leads to alterations in isoform expression due to alternative splicing. These changes in the expression of isoforms, such as Shroom 3 and Myl6, have the potential to play a key role in the pathophysiology of hypertension-induced nephropathy.

Muscle function and structure in a mouse model of dysfunctional central nervous system myelin

INTRODUCTION. Claudin-11(CLDN11)-deficient mice have been reported to have dysfunctional central nervous system myelin, and altered motor control and muscle tone in their hindlimbs. OBJECTIVE. We compared CLDN11-deficient mice with strain-, age-, and sex-matched controls (CLDN11-suffent mice). We hypothesized that CLDN11-deficient mice will have reduced muscle strength and will show a greater resistance to high stretch velocities compared to their CLDN11-suffcient counterparts. METHODS. We studied the ankle dorsiflexor and plantarflexor muscles in a convenience sample of ten CLDN11-deficient and four CLDN11-suffcient mice (3-4 months, males). We recorded the maximum isometric contractile torque of the ankle plantarflexor and dorsiflexor muscles measured in milli-Newton-millimeter (mNmm), and the maximum contractile torque at low (100 °/s) and high (1200 °/s) muscle stretch velocities during eccentric contractions to assess spasticity. We also studied structural changes in muscle cross sections stained with hematoxylin and eosin. RESULTS. Data are reported as mean ± SD. Maximum plantarflexor contractile torque was 7800 ± 1651 mNmm and 9646 ± 2637 mNmm in CLDN11-deficient and -suffcient mice, respectively. Maximum dorsiflexor contractile torque was 1956 ± 347 mNmm and 2975 ± 195 mNmm in CLDN11-deficient and -suffcient mice, respectively. Spasticity assessed as the ratio of maximum eccentric torque measured at 1200 °/s to 100 °/s was 0.94 ± 0.07 and 0.93 ± 0.01 in the plantarflexors of CLDN11-deficient and -suffcient mice, respectively, and 1.41 ± 0.19 and 2.1 ± 0.33 in the dorsiflexors of CLDN11-deficient and -suffcient mice, respectively. One-way ANOVAs indicated that CLDN11-deficient and -suffcient mice were not statistically different (p>0.05) in maximum torque production and spasticity. CLDN11-deficient mice showed no remarkable alterations in muscle structure. CONCLUSION. Claudin 11 deficiency in mice does not affect maximum contractile torque and stretch-velocity-dependent muscle tone when studied by robotic dynamometry under general anesthesia, nor does it prominently affect muscle structure. We thank the WSU UROP funding mechanism for supporting Ms. Iman Manzoor’s involvement on this project. We thank the Wayne State University Doctor of Physical Therapy (DPT) Program for supporting student research and providing research training through coursework and research experiences. We thank Dr. Alexander Gow for sharing mice and mentorship. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Ultrasparse Ultrasparsifiers and Faster Laplacian System Solvers

In this paper we provide an O ( m loglog O (1) n log (1/ϵ))-expected time algorithm for solving Laplacian systems on n -node m -edge graphs, improving upon the previous best expected runtime of \(O(m \sqrt {\log n} \mathrm{log log}^{O(1)} n \log (1/\epsilon)) \) achieved by (Cohen, Kyng, Miller, Pachocki, Peng, Rao, Xu 2014). To obtain this result we provide efficient constructions of low spectral stretch graph approximations with improved stretch and sparsity bounds. As motivation for this work, we show that for every set of vectors in \(\mathbb {R}^d \) (not just those induced by graphs) and all integer k > 1 there exist an ultra-sparsifier with d − 1 + O ( d / k ) re-weighted vectors of relative condition number at most k 2 . For small k , this improves upon the previous best known multiplicative factor of \(k \cdot \tilde{O}(\log d) \) , which is only known for the graph case. Additionally, in the graph case we employ our low-stretch subgraph construction to obtain n − 1 + O ( n / k )-edge ultrasparsifiers of relative condition number k 1 + o (1) for k = ω (log δ n ) for any δ > 0: this improves upon the previous work for k = o (exp (log 1/2 − δ n )).

Measurement of Laminar Burning Speed of Methane/Hydrogen/Air Mixtures at High Pressures and Temperatures

Abstract Green hydrogen which could be produced from renewable sources by solar water splitting or photovoltaic electrolysis will play an important role in achieving net-zero in the near future. One possible approach will be to mix hydrogen with natural gas for power generation in gas turbine systems. It is necessary to know the physical properties of burning speed of the mixture of natural gas and hydrogen. Since natural gas is mainly made up of methane, the burning speed of mixtures of methane and hydrogen has been measured and reported in this paper. Adding hydrogen gas during the combustion of methane enhances flame stability, expands the lean flammability range, decreases pollutant emissions, and boosts the burning speed. Burning speed measurement is performed in a cylindrical and spherical chamber. The pressure rise due to combustion was measured by a pressure transducer on the top of cylindrical and spherical chambers. The Z-shaped Schlieren system, equipped with a high-speed complementary metal oxide semiconductor (CMOS) camera, obtains pictures of flame propagation. Laminar burning speed is measured exclusively for flames that have a smooth and spherical shape. In addition, burning speed is only measured for large flame radii with low stretch rates. Burning speed is calculated by a thermodynamic model with the pressure rise data as an input. Measurements cover a wide range of operating conditions. The hydrogen mole fraction is 0%, 20%, and 40%, with temperatures of 298–400 K, pressures between 0.5 and 5.5 atmospheres and equivalence ratios of 0.8, 1, and 1.2.

Direct measurements of collagen fiber recruitment in the posterior pole of the eye

Collagen is the main load-bearing component of the peripapillary sclera (PPS) and lamina cribrosa (LC) in the eye. Whilst it has been shown that uncrimping and recruitment of the PPS and LC collagen fibers underlies the macro-scale nonlinear stiffening of both tissues with increased intraocular pressure (IOP), the uncrimping and recruitment as a function of local stretch have not been directly measured. This knowledge is crucial to understanding their functions in bearing loads and maintaining tissue integrity. In this project we measured local stretch-induced collagen fiber bundle uncrimping and recruitment curves of the PPS and LC. Thin coronal samples of PPS and LC of sheep eyes were mounted and stretched biaxially quasi-statically using a custom system. At each step, we imaged the PPS and LC with instant polarized light microscopy and quantified pixel-level (1.5 μm/pixel) collagen fiber orientations. We used digital image correlation to measure the local stretch and quantified collagen crimp by the circular standard deviation of fiber orientations, or waviness. Local stretch-recruitment curves of PPS and LC approximated sigmoid functions. PPS recruited more fibers than the LC at the low levels of stretch. At 10% stretch the curves crossed with 75% bundles recruited. The PPS had higher uncrimping rate and waviness remaining after recruitment than the LC: 0.9º vs. 0.6º and 3.1º vs. 2.7º. Altogether our findings support describing fiber recruitment of both PPS and LC with sigmoid curves, with the PPS recruiting faster and at lower stretch than the LC, consistent with a stiffer tissue. Statement of significancePeripapillary sclera (PPS) and lamina cribrosa (LC) collagen recruitment behaviors are central to the nonlinear mechanical behavior of the posterior pole of the eye. How PPS and LC collagen fibers recruit under stretch is crucial to develop constitutive models of the tissues but remains unclear. We used image-based stretch testing to characterize PPS and LC collagen fiber bundle recruitment under local stretch. We found that fiber-level stretch-recruitment curves of PPS and LC approximated sigmoid functions. PPS recruited more fibers at a low stretch, but at 10% bundle stretch the two curves crossed with 75% bundles recruited. We also found that PPS and LC fibers had different uncrimping rates and non-zero waviness's when recruited.

Near-extinction transient behaviors of counterflow nonpremixed flames in a porous spherical burner at very low stretch rate

Near extinction transient behaviors of CH4/N2 versus O2/N2 counterflow nonpremixed flames were investigated by adopting a porous spherical burner with a large radius of curvature to achieve a very low buoyant stretch rate. By varying the oxygen concentrations in the oxidizer stream, four regimes were identified by three limits of sooting, instability, and extinction. The sooting limit was sensitive to flame temperature, and was characterized by two indexes of fuel injection velocity uF and oxygen concentration XO2. When decreasing uF, the sooting limit was different from high stretch flames because of appreciable heat loss toward the burner surface. In the instability regime, periodic holes were observed whose frequency decreased with XO2. Periodic holes were also found to occur with N2 dilution in the fuel stream, which were more regular with larger frequencies compared with the periodic holes in the diluted oxidizer streams. The edge propagation behaviors for periodic holes in diluted fuel streams were analyzed. The statistical average of the propagation speed of advancing edge (hole closing) Se decreased with increasing fuel concentration gradient, and the ratio of Se with the stoichiometric laminar burning velocity SLst of Se/SLst was larger than unity. Also, the stretch rate significantly affected the propagation speed of advancing edge flames. Determination of the propagation speed of the retreating edge (hole opening) had intrinsic difficulty in estimating the transient radial flow velocity, however, the approximated |Se/SLst| was larger than unity and decreased with the fuel mole fraction. Nitrogen dilution in the oxidizer stream was proven to be more effective than in the fuel stream for flame suppression of methane. This study could enrich the understanding of very low-stretch nonpremixed flames in a counterflow burner and provide information regarding low-stretch flame suppression, which may be relevant to microgravity flame behaviors.

Spherically expanding flame simulations using Cantera coupled to an unsteady Lagrangian formulation

A Lagrangian-based one-dimensional approach has been applied, using Cantera libraries, to study the dynamics of spherically expanding flames. Detailed reaction models have been employed to examine spherical flame propagation in hydrogen-air mixtures. In the first part, our approach was validated against laminar flame speed and Markstein number data from the literature. It was shown that the laminar flame speed was predicted within 5% on average but that significant discrepancies were observed for the Markstein number, especially for rich mixtures. This suggests that even application of detailed reaction models can lead to inaccurate prediction of the stability of rich flames, which can be detrimental to the prediction of flame acceleration and the deflagration to detonation transition process. In the second part, a detailed analysis of the thermo-chemical dynamics along the path of Lagrangian particles propagating in stretched flames was performed. For mixtures with negative Markstein lengths, it was found that at high stretch rates, the mixture entering the reaction-dominated period is less lean with respect to the initial mixture than at low stretch rates. This induces faster rates of chemical heat release and active radical production which results in higher flame propagation speed. Opposite effects were observed for mixtures with positive Markstein lengths, for which slower flame propagation was observed at high stretch rates compared to low stretch rates.

Structure and extinction of methane and propane nonpremixed counterflow flames at extremely low stretch rates in buoyant flowfields

This study experimentally investigated the structures and extinction behaviors of methane-air and propane-air counterflow nonpremixed flames influenced by individually controlled fuel injection velocity uF at extremely low stretch rates, which were induced by natural convection alone. A sooting limit fuel injection velocity (SLFIV) index was introduced, which increased with stretch rate in the low stretch rate region. Methane had higher SLFIV than propane. Quasi-one-dimensional blue flames appeared for both methane and propane within a certain uF range. The range for methane was higher than that for propane. The steady flame standoff distances yf had a relationship with uF and low stretch rate ab of yf∝uFabλ∞1/2, which differed from high-stretch flames. Different flame instabilities occurred for methane and propane by changing uF only without fuel or oxidizer dilutions. At low uF near extinction limit of methane, periodic flame holes appeared, which was due to large heat loss. This instability finally caused flame extinction by keeping retreating edges. At high uF, simultaneous cellular and wave flame instability appeared for propane, which differed from cellular flames occurred alone in highly diluted oxy-fuel flames. By modulating uF alone in this experiment, the cellular/wave flame was due to Rayleigh-Taylor and hydrodynamic instabilities. Flame extinction at the lowest uF for propane was through outer edge shrinking, where the displacement speed increased with stretch rate. Flammability maps of limit uF versus low ab were established for both methane and propane. Both maps were divided into four regions by sooting, instability and extinction limits. The three limits uF all increased with ab. This changing tendency was opposite with high-stretch flames reported previously. For propane, the instability limit uF approached infinity at higher ab. This work provided knowledge of extremely low stretch flame combustion, which can be applied to microgravity flames, because the combustion characteristics of microgravity forced low stretch flames were identical to those of low stretch flame induced by natural convection alone.

#6118 ALTERNATIVE SPLICING IN MECHANICALLY STRETCHED PODOCYTES AS A MODEL OF GLOMERULAR HYPERTENSION

Abstract Background and Aims It has been shown that mRNA splicing plays a relevant role in disease pathophysiology. However, the possible role of alternative splicing (AS) in hypertensive nephropathy (HN) has not been investigated. The purpose of the Sys_CARE (Systems Medicine Investigation of AS in Cardiac and Renal Diseases) project is to investigate the possible implication of AS events in HN development and progression. Method Differentiated murine podocytes were seeded on a flexible silicone membrane, and mechanically stretched using the Stretchy apparatus (NIPOKA GmbH, Greifswald). Cells were stretched for 3 days under low and high stretch conditions with a frequency of 0.5 Hz. The mRNA and proteins were isolated and analyzed using RNA_Seq and LC-MS/MS techniques. Enrichment analysis identified proteins which were classified according to the related biological processes, molecular function and cellular components. Splicing and transcript expression were evaluated with bioinformatical tools (rMATS, leafcutter, Whippet, MAJIQ, IsoformSwitchAnalyzeR). Results Proteomic analysis of cultured podocytes revealed significant different expression levels for 135 proteins (54 increased and 81 decreased) and 424 proteins (195 increased and 229 decreased) under low and high stretch conditions, respectively, compared to unstretched conditions. Interestingly, most of the proteins with decreased intensity upon stretch are cytoskeleton and actin-binding proteins. In contrast, the up-regulated proteins are more associated in clusters affecting mRNA processing and splicing. By RNA_Seq we identified over 1000 different splicing events including all types of alternative splicing events. We screened for candidates that showed an alternative splicing event in multiple tools, were found in the proteomics, were podocyte-specific, or showed altered expression in glomerulopathies such as diabetic nephropathy. In this regard, we found an isoform switch of Myl6 and Shroom3 after mechanical stretch. Conclusion Using mechanically stretched podocytes as a model of HN, we found significant up- and down-regulated proteins. In addition, by RNA_Seq we identified an isoform switch of Myl6 and Shroom3 that might be essential for the development of HN.

Ovariectomy with simulated vaginal delivery to establish a rat model for pelvic organ prolapse

ABSTRACT The widespread prevalence of Pelvic Organ Prolapse (POP) and the paucity of ongoing treatments prompted us to develop a unique rat model combining ovariectomy and simulated vaginal delivery. We hypothesized that the tissue changes caused by low hormone levels and mechanical stretch could complement each other. Thus, the combined model can potentially mimic the collagen metabolism of vaginal wall tissue as well as mechanical stretch properties to complement disease progression in POP. Ovariectomy with sequential simulated vaginal delivery was performed on rats in the modeling group. Sham surgeries were performed as control. At 2, 4, and 12 weeks after modeling, the vaginal tissues of rats were evaluated by Masson’s trichrome staining, Picro-Sirius red staining, immunohistochemistry, western blotting, and uniaxial tensile tests. Compared to the control group, the vaginal tissues of the model rats showed an atrophic epithelial layer and loose collagen fibers. The smooth muscle fibers were ruptured, smaller in diameter, and disorganized. The ratio of collagen type I/III significantly increased, but the contents of both Collagen I and III decreased. The expression of metalloproteinases 2 and 9 in the tissues increased, and the expression of tissue inhibitors of metalloproteinases 1 and 2 decreased. The tangent modulus of the tissues was significantly increased in the model rats. We verified a novel method to establish a pelvic organ prolapse model in rats. This approach combined the advantages of low hormone levels and mechanical stretch effects.

Ammonia and hydrogen blending effects on combustion stabilities in optical SI engines

Ammonia is a promising energy carrier and carbon-free fuel, which is getting more attention today when fossil energy is increasingly exhausted. However, ammonia combustion in the IC engine suffers from combustion instabilities and misfiring issues. Hydrogen is also carbon-free energy and can be directly obtained by ammonia catalytic reforming. The addition of a small amount of hydrogen can effectively alleviate the weakness of ammonia combustion, while ammonia and hydrogen blending effects on combustion stabilities and their critical conditions remain unclear. In this work, the effects of hydrogen addition on ammonia combustion characteristics were experimentally investigated in an optical SI engine with high compression ratios. The results show that the indicated thermal efficiency first increases and then decreases with the elevation of hydrogen-ammonia energy ratios (χ), with an optimal value at χ≈7.5 %. Further hydrogen addition can aggravate indicated thermal efficiency due to the large heat transfer loss caused by high-temperature hydrogen combustion. Combustion visualizations show that there is a critical threshold of hydrogen-ammonia energy ratio (χ=10.0–12.5 %), around which engine combustion characteristics are changed significantly. When χ < 10 %, the effect of hydrogen addition on the ammonia flame speed becomes more pronounced since the hydrogen substantially improves the stability of the early-stage combustion. When χ > 12.5 %, hydrogen shows an obvious influence on the initial flame formation of ammonia, which is attributed to the low flame stretch sensitivity, facilitating early flame development. In addition, flame propagation when χ < 10 % is more sensitive to temperature than flame propagation with χ > 12.5 %. The current research demonstrates that proper ammonia-hydrogen energy ratios are important for stable combustion and thermal efficiency improvement.

Magnetic resonance imaging-based hemodynamic wall shear stress alters aortic wall tissue biomechanics in bicuspid aortic valve patients

ObjectiveIn this study we aimed to conclusively determine whether altered aortic biomechanics are associated with wall shear stress (WSS) independent of region of tissue collection. Elevated WSS in the ascending aorta of patients with bicuspid aortic valve has been shown to contribute to local maladaptive aortic remodeling and might alter biomechanics. MethodsPreoperative 4-dimensional flow magnetic resonance imaging was performed on 22 patients who underwent prophylactic aortic root and/or ascending aorta replacement. Localized elevated WSS was identified in patients using age-matched healthy atlases (n = 60 controls). Tissue samples (n = 78) were collected and categorized according to WSS (elevated vs normal) and region. Samples were subjected to planar biaxial testing. To fully quantify the nonlinear biomechanical response, the tangential modulus (local stiffness) at a low-stretch (LTM) and high-stretch (HTM) linear region and the onset (TZo) and end stress of the nonlinear transition zone were measured. A linear mixed effect models was implemented to determine statistical relationships. ResultsA higher LTM in the circumferential and axial direction was associated with elevated WSS (P = .007 and P = .018 respectively) independent of collection region. Circumferential TZo and HTM were higher with elevated WSS (P = .024 and P = .003); whereas the collection region was associated with variations in axial TZo (P = .013), circumferential HTM (P = .015), and axial HTM (P = .001). ConclusionsThis study shows strong evidence that biomechanical changes in the aorta are strongly associated with hemodynamics, and not region of tissue collection for bicuspid valve aortopathy patients. Elevated WSS is associated with tissue behavior at low stretch ranges (ie, LTM and TZo).

Structure and Extinction of Methane-Air and Propane-Air Counterflow Nonpremixed Flames at Very Low Buoyancy-Induced Stretch Rates

Structure and Extinction of Methane-Air and Propane-Air Counterflow Nonpremixed Flames at Very Low Buoyancy-Induced Stretch Rates

Effects of radiation, curvature, and preferential diffusion on the extinction of laminar non-premixed flames

The combined effects of radiative heat loss, curvature, and preferential diffusion on laminar non-premixed flames (or flamelets) are investigated in this work by using asymptotic analysis. A general theoretical description of flame temperature and extinction is derived for curved flames with non-unity Lewis numbers and radiative heat loss. Special attention is paid to the effects of curvature and radiative heat loss on the flammability limits. The results show that (1) a curved flamelet always has two extinction limits: one is the kinetic extinction limit, and the other is the curvature-induced extinction limit for the adiabatic case or the radiative extinction limit for the radiative case; (2) the curvature exerts a different influence on the adiabatic and radiative flames. Specifically for the adiabatic flame, it is found that both flame temperature and flame position significantly decrease as the curvature increases and that a new extinction limit at a low stretch rate occurs due to the existence of curvature. Furthermore, a higher curvature coupled with the increase in the Lewis number results in a lower flammability limit and narrower flammable zone. Therefore, the presence of curvature has a negative impact on the adiabatic flame. On the contrary, for the radiative flame, the results show that the increase in curvature has a positive effect on the flammability limit and thereby increases the flammable zone. It is expected that curved flamelets hold smaller (larger) flammable zones than planar flamelets under the adiabatic (radiative) condition. All results show that the change in flame curvature has a stronger effect on the flame structure and extinction than the deviation of the Lewis number from unity.

Fracture of dual crosslink gels with permanent and transient crosslinks: Effect of the relaxation time of the transient crosslinks

We investigate the fracture properties of poly(acrylamide-co-1-vinylimidazole) dual crosslink hydrogels [P(AAm-co-VIm)-M2+ gels] containing a small fraction of covalent bonds and a majority of dynamic bonds based on metal coordination bonds (Ni2+ or Zn2+). Unlike a previous study on a different dual crosslink hydrogel system having slower dynamic bonds based on poly(vinylalcohol) and borate ions (PVA-Borax gels), the presence of these faster dynamic coordination bonds has two main effects: They significantly toughen the P(AAm-co-VIm)-M2+ gels even at high stretch rates, where the dynamic bonds should in principle behave as covalent bonds at the crack tip, and they toughen the gels at very low stretch rates, where the dynamic bonds are invisible during the loading stage. We propose two additional molecular mechanisms to rationalize this behavior of P(AAm-co-VIm)-M2+ gels: we hypothesize that fast exchanging dynamic bonds remain slow compared to the characteristic time of bond scission and are, therefore, able to share the load upon covalent bond scission even at low loading rates. We also argue of the existence of longer-lived clusters of dynamic bonds that introduce a stretch rate-dependent strain hardening in uniaxial tension and stabilize and increase the size of the dissipative zone at the crack tip, thereby introducing a strain-dependent dissipative mechanism.

Biomechanical Assessment of Macro-Calcification in Human Carotid Atherosclerosis and Its Impact on Smooth Muscle Cell Phenotype.

Intimal calcification and vascular stiffening are predominant features of end-stage atherosclerosis. However, their role in atherosclerotic plaque instability and how the extent and spatial distribution of calcification influence plaque biology remain unclear. We recently showed that extensive macro calcification can be a stabilizing feature of late-stage human lesions, associated with a reacquisition of more differentiated properties of plaque smooth muscle cells (SMCs) and extracellular matrix (ECM) remodeling. Here, we hypothesized that biomechanical forces related to macro-calcification within plaques influence SMC phenotype and contribute to plaque stabilization. We generated a finite element modeling (FEM) pipeline to assess plaque tissue stretch based on image analysis of preoperative computed tomography angiography (CTA) of carotid atherosclerotic plaques to visualize calcification and soft tissues (lipids and extracellular matrix) within the lesions. Biomechanical stretch was significantly reduced in tissues in close proximity to macro calcification, while increased levels were observed within distant soft tissues. Applying this data to an in vitro stretch model on primary vascular SMCs revealed upregulation of typical markers for differentiated SMCs and contractility under low stretch conditions but also impeded SMC alignment. In contrast, high stretch conditions in combination with calcifying conditions induced SMC apoptosis. Our findings suggest that the load bearing capacities of macro calcifications influence SMC differentiation and survival and contribute to atherosclerotic plaque stabilization.

Effect of Gleno-humeral-capsulo-Ligamentous Stretch Maneuvers on Range of motion in Bilateral Frozen Shoulder

Background: Painful restriction of shoulder movement, without an underlying cause, which results in complete loss of motion of the glenohumeral joint is called Frozen Shoulder. The process is started with an inflammation of the lining of the joint within the shoulder. Gradually this area thickens and results in the shoulder becoming stiffer and more painful. It is seen commonly at the age of 40-65 years and more often in women. Overall, this condition affects work, leisure, and quality of life. Frozen shoulder often progresses in three stages: the freezing, frozen and thawing phases. Risk factors for frozen shoulder are diabetes, thyroid, history of shoulder trauma, cervical radiculopathy, post-operative immobilization, and shoulder surgery. Cyriax described the typical capsular patterns of the gle¬no humeral joint in the frozen shoulder with abduction more limited than external rotation, and external rota¬tion more limited than internalrotation. This study aims to establish the effect of gleno humeral capsulo ligamentous stretch maneuvers on bilateral frozen shoulder. Methods: A total of 40 subjects diagnosed with bilateral frozen shoulder were selected for the study. Subjects received low load prolonged stretching, mobilization and shoulder range of motion exercises. Each session was conducted for 30 minutes duration, 5 days per week for 4 weeks. Outcome measures used were Numerical pain rating scale (NPRS), Goniometer and Shoulder Pain and Disability Index (SPADI). Results: The results of the study demonstrate that there was a significant effect of gleno humeral capsulo ligamentous stretch on numerical pain rating scale (p&lt;0.0001), range of motion (Shoulder flexion, abduction, internal rotation and external rotation (p&lt;0.0001), Shoulder pain and disability index (p&lt;0.0001) during the pre and post intervention assessment. Conclusion: It is concluded that that the use of low load prolonged stretch and mobilization was very effective in reducing pain and improving range of motion. Shoulder range of motion exercises was effective in improving strength and flexibility of shoulder musculature. KEYWORDS: Low load prolonged stretch, mobilization, numerical pain rating scale, Shoulder pain and disability index, Bilateral frozen shoulder.

A mechanical evaluation of polyvinyl alcohol hydrogels for temporomandibular joint disc replacement

The temporomandibular joint (TMJ) is a bilateral ginglymoarthroidal joint containing a fibrocartilaginous disc which distributes compressive stress and reduces friction on the articulating surfaces of the joint. Initially, conservative treatments can address disorders of the TMJ, but surgical procedures such as discectomy may be employed if dysfunction persists. Unfortunately, discectomy increases friction and alters the mechanical behavior of the TMJ when the disc is not replaced. An ideal replacement for the TMJ disc would restore healthy function of the joint and prevent further degeneration. Rigorous evaluation of materials is necessary to ensure the safety and efficacy of novel implants. Poly(vinyl) alcohol (PVA) hydrogels have been suggested as a good candidate for artificial cartilage replacement in other applications and are promising for replacing the TMJ disc due to their biocompatibility, low friction, and biomimetic levels of hydration. The objective of this study was to mechanically characterize hydrogel formulations of 15, 20, and 25% PVA and to compare them with the ovine TMJ disc to investigate the appropriateness of PVA hydrogels for TMJ disc replacement in a translational model. Experimental evaluations were conducted in indentation, unconfined compression, friction, and uniaxial tension. There were no statistically significant differences in the coefficient of friction between the PVA hydrogels and ovine TMJ disc. No statistically significant differences were found between at least one PVA hydrogel group and the TMJ disc for the indentation properties or the unconfined compression properties at low stretch magnitudes. The 20% PVA and 25% PVA hydrogels exhibited significantly higher failure stretch as compared to the ovine TMJ disc, and they were not statistically different in ultimate tensile strength from the TMJ disc in the mediolateral direction. However, the ovine TMJ disc tensile elastic moduli were 630 times larger in the anteroposterior direction and 53 times larger in the mediolateral direction than the stiffest PVA hydrogel. Ultimately, the 25% PVA hydrogel was the best candidate for TMJ disc replacement, demonstrating the most similarity to the ovine TMJ disc compressive properties; however, tensile reinforcement of the hydrogels would be necessary to approach the tensile modulus of the native TMJ disc.