Unified approach to crack growth and fracture

Unified approach connects the behavior of a smooth specimen, of a notched specimen and of the fracture-mechanics specimen, under inert and corrosive environments, using the unifying principles and the Modified Kitagawa-Takahashi Diagram. The unifying principles are based on the fact that the behavior of short cracks is not different from that of long cracks, and the same thresholds govern the crack growth. Cracks being high energy defects, local internal stresses are required to initiate and grow the cracks in all cases. The internal stresses can be pre-existing as in the case of long cracks or in situ generated or augmented in the case of smooth and notched specimens. Observed variations in the crack growth rates of short cracks from those of long cracks arise due to variations in the types and degrees of pre-existing internal stresses. In aggressive environments, chemical forces provide additional driving forces over and above the mechanical forces. Chemical forces come from the chemical and/or electro chemical potential gradients which may be difficult to determine as they depend on the nature and the extent of the local chemical reactions in the changing compositional gradients. From practical considerations, we show that they can be quantified using the inert medium as a reference. Cyclic loads provides additional factors since crack tip driving forces come from both monotonic and cyclic loads leading to load-ratio R dependence. We provide here a systematic analysis of these factors using our Unified Approach to help in quantification and codification of the kinetics of the crack growth and fracture

Initiation and growth of corrosion fatigue cracks from corrosion pits using elasto-plastic notch analysis

Corrosion pits are known to act as precursors for fatigue crack initiation under corrosive environment. The transition from pit to crack growth under corrosion fatigue is of considerable interest for many engineering structures. Several predictive methodologies have been developed. As the Pits grow with large aspect ratio, they behave like local stress/strain concentrations accentuating the crack initiation and growth. In this paper, we extend our recent analysis of crack initiation at the elastic-plastic notch tip stress fields* to evaluate its applicability to pit to crack transition. Ref: K. Sadananda, A. Arcari, A.K. Vaudevan, Eng. Frac. Mech., 2017, 176 pp.144-16

Association of Chlamydia pneumoniae IgG and IgA antibody in coronary artery disease

Background:Cardiovascular disease, resulting from atherosclerosis, is a leading cause of global morbidity and mortality. Classical risk factors explain much of the attributable risk for cardiovascular events, but other risk factors for the development and progression of atherosclerosis, which can be identified, may be important therapeutic targets. Infectious agents, such as Chlamydia pneumoniae, have been proposed as contributory factors in the pathogenesis of atherosclerosis. The present study was conducted to determine the seroprevalence of C. pneumoniae antibodies and to study the association of chronic C. pneumoniae infection with Coronary Artery Disease (CAD).Methods:The study group included 90 angiographically proven CAD patients and age and sex matched 90 normal coronaries as control group. With total aseptic precaution 3 ml blood was collected. Enzyme linked immunosorbant assay was performed for all subjects to detect the presence of IgG and IgA antibodies to Chlamydia pneumoniae (Cp).  Results:IgG and IgA Cp antibodies were detected in 67.8% and 58.9% CAD patients compared to 45.6% and 11.1%   controls. IgG + IgA Cp antibodies were detected in 88.9% CAD patients when compared to 50.0% controls. Seroprevalence of IgG and IgA Cp antibodies were high among CAD patients compared to controls and was found statistically significant. A significant presence of Chlamydia pneumoniae antibodies was detected in smokers, diabetes mellitus, hypertension, and dyslipidemia.  Conclusion:In the present study, the seroprevalence of IgG and IgA Cp antibodies was found to be higher in CAD patients compared to controls. The present study supports the   association between Chlamydia pneumoniae infection and Coronary artery disease.

External Urethral Sphincter Pressure Measurement: An Accurate Method for the Diagnosis of Detrusor External Sphincter Dyssynergia?

Combined pelvic floor electromyography (EMG) and videocystourethrography (VCUG) during urodynamic investigation are the most acceptable and widely agreed methods for diagnosing detrusor external sphincter dyssynergia (DESD). Theoretically, external urethral sphincter pressure (EUSP) measurement would provide enough information for the diagnosis of DESD and could simplify the urodynamic investigation replacing combined pelvic floor EMG and VCUG. Thus, we evaluated the diagnostic accuracy of EUSP measurement for DESD. PATIENTS #ENTITYSTARTX00026;A consecutive series of 72 patients (36 women, 36 men) with neurogenic lower urinary tract dysfunction able to void spontaneously was prospectively evaluated at a single university spinal cord injury center. Diagnosis of DESD using EUSP measurement (index test) versus combined pelvic floor EMG and VCUG (reference standard) was assessed according to the recommendations of the Standards for Reporting of Diagnostic Accuracy Initiative.Using EUSP measurement (index test) and combined pelvic floor EMG and VCUR (reference standard), DESD was diagnosed in 10 (14%) and in 41 (57%) patients, respectively. More than half of the patients presented discordant diagnosis between the index test and the reference standard. Among 41 patients with DESD diagnosed by combined pelvic floor EMG and VCUR, EUSP measurement identified only 6 patients. EUSP measurement had a sensitivity of 15% (95% CI 5%-25%), specificity of 87% (95% CI 76%-98%), positive predictive value of 60% (95% CI 30%-90%), and negative predictive value of 56% (95% CI 44%-68%) for the diagnosis of DESD.For diagnosis of DESD, EUSP measurement is inaccurate and cannot replace combined pelvic floor EMG and VCUR

Neurophysiological modeling of bladder afferent activity in the rat overactive bladder model

The overactive bladder (OAB) is a syndrome-based urinary dysfunction characterized by “urgency, with or without urge incontinence, usually with frequency and nocturia”. Earlier we developed a mathematical model of bladder nerve activity during voiding in anesthetized rats and found that the nerve activity in the relaxation phase of voiding contractions was all afferent. In the present study, we applied this mathematical model to an acetic acid (AA) rat model of bladder overactivity to study the sensitivity of afferent fibers in intact nerves to bladder pressure and volume changes. The afferent activity in the filling phase and the slope, i.e., the sensitivity of the afferent fibers to pressure changes in the post-void relaxation phase, were found to be significantly higher in AA than in saline measurements, while the offset (nerve activity at pressure ~0) and maximum pressure were comparable. We have thus shown, for the first time, that the sensitivity of afferent fibers in the OAB can be studied without cutting nerves or preparation of single fibers. We conclude that bladder overactivity induced by AA in rats is neurogenic in origin and is caused by increased sensitivity of afferent sensors in the bladder wall

TRPV1 enhances the afferent response to P2X receptor activation in the mouse urinary bladder

Both TRPV1 and P2X receptors present on bladder sensory nerve fibres have been implicated in mechanosensation during bladder filling. The aim of this study was to determine possible interactions between these receptors in modulating afferent nerve activity. In wildtype (TRPV1+/+) and TRPV1 knockout (TRPV1−/−) mice, bladder afferent nerve activity, intravesical pressure, and luminal ATP and acetylcholine levels were determined and also intracellular calcium responses of dissociated pelvic DRG neurones and primary mouse urothelial cells (PMUCs). Bladder afferent nerve responses to the purinergic agonist αβMethylene-ATP were depressed in TRPV1−/− mice (p ≤ 0.001) and also in TRPV1+/+ mice treated with the TRPV1-antagonist capsazepine (10 µM; p ≤ 0.001). These effects were independent of changes in bladder compliance or contractility. Responses of DRG neuron to αβMethylene-ATP (30 µM) were unchanged in the TRPV1−/− mice, but the proportion of responsive neurones was reduced (p ≤ 0.01). Although the TRPV1 agonist capsaicin (1 µM) did not evoke intracellular responses in PMUCs from TRPV1+/+ mice, luminal ATP levels were reduced in the TRPV1−/− mice (p ≤ 0.001) compared to wildtype. TRPV1 modulates P2X mediated afferent responses and provides a mechanistic basis for the decrease in sensory symptoms observed following resiniferatoxin and capsaicin treatment for lower urinary tract symptoms

Adult Male Mice Emit Context-Specific Ultrasonic Vocalizations That Are Modulated by Prior Isolation or Group Rearing Environment

Social interactions in mice are frequently analysed in genetically modified strains in order to get insight of disorders affecting social interactions such as autism spectrum disorders. Different types of social interactions have been described, mostly between females and pups, and between adult males and females. However, we recently showed that social interactions between adult males could also encompass cognitive and motivational features. During social interactions, rodents emit ultrasonic vocalizations (USVs), but it remains unknown if call types are differently used depending of the context and if they are correlated with motivational state. Here, we recorded the calls of adult C57BL/6J male mice in various behavioral conditions, such as social interaction, novelty exploration and restraint stress. We introduced a modulator for the motivational state by comparing males maintained in isolation and males maintained in groups before the experiments. Male mice uttered USVs in all social and non-social situations, and even in a stressful restraint context. They nevertheless emitted the most important number of calls with the largest diversity of call types in social interactions, particularly when showing a high motivation for social contact. For mice maintained in social isolation, the number of calls recorded was positively correlated with the duration of social contacts, and most calls were uttered during contacts between the two mice. This correlation was not observed in mice maintained in groups. These results open the way for a deeper understanding and characterization of acoustic signals associated with social interactions. They can also help evaluating the role of motivational states in the emission of acoustic signals