Autonomy and Singularity in Dynamic Fracture

The recently developed weakly nonlinear theory of dynamic fracture predicts $1/r$ corrections to the standard asymptotic linear elastic $1/\sqrt{r}$ displacement-gradients, where $r$ is measured from the tip of a tensile crack. We show that the $1/r$ singularity does not automatically conform with the notion of autonomy (autonomy means that any crack tip nonlinear solution is uniquely determined by the surrounding linear elastic $1/\sqrt{r}$ fields) and that it does not automatically satisfy the resultant Newton's equation in the crack parallel direction. We show that these two properties are interrelated and that by requiring that the resultant Newton's equation is satisfied, autonomy of the $1/r$ singular solution is retained. We further show that the resultant linear momentum carried by the $1/r$ singular fields vanishes identically. Our results, which reveal the physical and mathematical nature of the new solution, are in favorable agreement with recent near tip measurements.Comment: 4 pages, 2 figures, related papers: arXiv:0902.2121 and arXiv:0807.486

A study of the mineral composition of pottery sherds from, Malyan, Iran

From 1971 through 1978 William M. Sumner, of the Ohio State University Department of Anthropology, conducted a five season preliminary excavation at Tal-e-Malyan, Iran. A result of his work was the discovery of a new phase of occupation, which is now known as the Banesh Phase (c. 3400-2600 B.C.). Two broad catagories of Banesh ware have been identified; one is a coarse, low fired straw tempered ware and the second is a hard grit tempered ware which occurs in several varieties, (Sumner 1980). Younger, Islamic wares (c. 800-1900 A.D.) are very similar in appearance to the older Banesh wares. Consequently the two different pottery wares can be confused. By conducting a mineral analysis on the two different wares it can now be shown that some distinguishing characteristics do exist. Twenty five Malyan sherds, ranging in size from one inch to two inches were donated for this study. In order to eliminate bias all information regarding the archaeological context of the sherds was withheld until the mineral analysis and catagorization of each sherd was completed. Only Mr. Sumner, knew that the sherds represented Banesh and Islamic pottery types. The purpose of this study was to see if textural mineral analysis of the sherds would permit catagorization. After the catagorizations were completed they were matched to Mr. Sumner's archaeological catagorizations. The results showed that the Islamic sherds characteristically contained micrite, carbonate grains, quartz, feldspar, and a low large percentage of iron oxides. The Banesh sherds contained, either large percentages of iron oxides, or else differed in composition from the characteristic Islamic sherd constituents. The polarizing microscope, Vreland Spectroscope, and x-ray analyzer were utilized in the analysis.No embarg

Some exact results for the velocity of cracks propagating in non-linear elastic models

We analyze a piece-wise linear elastic model for the propagation of a crack in a stripe geometry under mode III conditions, in the absence of dissipation. The model is continuous in the propagation direction and discrete in the perpendicular direction. The velocity of the crack is a function of the value of the applied strain. We find analytically the value of the propagation velocity close to the Griffith threshold, and close to the strain of uniform breakdown. Contrary to the case of perfectly harmonic behavior up to the fracture point, in the piece-wise linear elastic model the crack velocity is lower than the sound velocity, reaching this limiting value at the strain of uniform breakdown. We complement the analytical results with numerical simulations and find excellent agreement.Comment: 9 pages, 13 figure

Supersonic crack propagation in a class of lattice models of Mode III brittle fracture

We study a lattice model for mode III crack propagation in brittle materials in a stripe geometry at constant applied stretching. Stiffening of the material at large deformation produces supersonic crack propagation. For large stretching the propagation is guided by well developed soliton waves. For low stretching, the crack-tip velocity has a universal dependence on stretching that can be obtained using a simple geometrical argument.Comment: 4 pages, 3 figure

AMPylation: Something Old is New Again

The post-translational modification AMPylation is emerging as a significant regulatory mechanism in both prokaryotic and eukaryotic biology. This process involves the covalent addition of an adenosine monophosphate to a protein resulting in a modified protein with altered activity. Proteins capable of catalyzing AMPylation, termed AMPylators, are comparable to kinases in that they both hydrolyze ATP and reversibly transfer a part of this primary metabolite to a hydroxyl side chain of the protein substrate. To date, only four AMPylators have been characterized, though many more potential candidates have been identified through amino acid sequence analysis and preliminary in vitro studies. This modification was first discovered over 40 years ago by Earl Stadtman and colleagues through the modification of glutamine synthetase by adenylyl transferase; however research into this mechanism has only just been reenergized by the studies on bacterial effectors. New AMPylators were revealed due to the discovery that a bacterial effector having a conserved Fic domain transfers an AMP group to protein substrates. Current research focuses on identifying and characterizing various types of AMPylators homologous to Fic domains and adenylyl transferase domains and their respective substrates. While all AMPylators characterized thus far are bacterial proteins, the conservation of the Fic domain in eukaryotic organisms suggests that AMPylation is omnipresent in various forms of life and has significant impact on a wide range of regulatory processes

Velocity Fluctuations in Dynamical Fracture: the Role of Microcracks

We address the velocity fluctuations of fastly moving cracks in stressed materials. One possible mechanism for such fluctuations is the interaction of the main crack with micro cracks (irrespective whether these are existing material defects or they form during the crack evolution). We analyze carefully the dynamics (in 2 space dimensions) of one macro and one micro crack, and demonstrate that their interaction results in a {\em large} and {\em rapid} velocity fluctuation, in qualitative correspondence with typical velocity fluctuations observed in experiments. In developing the theory of the dynamical interaction we invoke an approximation that affords a reduction in mathematical complexity to a simple set of ordinary differential equations for the positions of the cracks tips; we propose that this kind of approximation has a range of usefulness that exceeds the present context.Comment: 7 pages, 7 figure

A Serendipitous Mutation Reveals the Severe Virulence Defect of a Klebsiella pneumoniae fepB Mutant

ABSTRACT Klebsiella pneumoniae is considered a significant public health threat because of the emergence of multidrug-resistant strains and the challenge associated with treating life-threatening infections. Capsule, siderophores, and adhesins have been implicated as virulence determinants of K. pneumoniae , yet we lack a clear understanding of how this pathogen causes disease. In a previous screen for virulence genes, we identified a potential new virulence locus and constructed a mutant ( smr ) with this locus deleted. In this study, we characterize the smr mutant and show that this mutation renders K. pneumoniae avirulent in a pneumonia model of infection. The smr mutant was expected to have a deletion of three genes, but subsequent genome sequencing indicated that a much larger deletion had occurred. Further analysis of the deleted region indicated that the virulence defect of the smr mutant could be attributed to the loss of FepB, a periplasmic protein required for import of the siderophore enterobactin. Interestingly, a Δ fepB mutant was more attenuated than a mutant unable to synthesize enterobactin, suggesting that additional processes are affected. As FepB is highly conserved among the members of the family Enterobacteriaceae , therapeutic targeting of FepB may be useful for the treatment of Klebsiella and other bacterial infections. IMPORTANCE In addition to having a reputation as the causative agent of several types of hospital-acquired infections, Klebsiella pneumoniae has gained widespread attention as a pathogen with a propensity for acquiring antibiotic resistance. It is capable of causing a range of infections, including urinary tract infections, pneumonia, and sepsis. Because of the rapid emergence of carbapenem resistance among Klebsiella strains, there is a dire need for a better understanding of virulence mechanisms and identification of new drug targets. Here, we identify the periplasmic transporter FepB as one such potential target

Machine Learning Groups Patients by Early Functional Improvement Likelihood Based on Wearable Sensor Instrumented Preoperative Timed-Up-and-Go Tests

© 2019 The Author(s) Background: Wearable sensors permit efficient data collection and unobtrusive systems can be used for instrumenting knee patients for objective assessment. Machine learning can be leveraged to parse the abundant information these systems provide and segment patients into relevant groups without specifying group membership criteria. The objective of this study is to examine functional parameters influencing favorable recovery outcomes by separating patients into functional groups and tracking them through clinical follow-ups. Methods: Patients undergoing primary unilateral total knee arthroplasty (n = 68) completed instrumented timed-up-and-go tests preoperatively and at their 2-, 6-, and 12-week follow-up appointments. A custom wearable system extracted 55 metrics for analysis and a K-means algorithm separated patients into functionally distinguished groups based on the derived features. These groups were analyzed to determine which metrics differentiated most and how each cluster improved during early recovery. Results: Patients separated into 2 clusters (n = 46 and n = 22) with significantly different test completion times (12.6 s vs 21.6 s, P \u3c .001). Tracking the recovery of both groups to their 12-week follow-ups revealed 64% of one group improved their function while 63% of the other maintained preoperative function. The higher improvement group shortened their test times by 4.94 s, (P = .005) showing faster recovery while the other group did not improve above a minimally important clinical difference (0.87 s, P = .07). Features with the largest effect size between groups were distinguished as important functional parameters. Conclusion: This work supports using wearable sensors to instrument functional tests during clinical visits and using machine learning to parse complex patterns to reveal clinically relevant parameters