Implementation of a Matrix Crack Spacing Parameter in a Continuum Damage Mechanics Finite Element Model

Continuum Damage Mechanics (CDM) based progressive damage and failure analysis (PDFA) methods have demonstrated success in a variety of finite element analysis (FEA) implementations. However, the technical maturity of CDM codes has not yet been proven for the full design space of composite materials in aerospace applications. CDM-based approaches represent the presence of damage by changing the local material stiffness definitions and without updating the original mesh or element integration schemes. Without discretely representing cracks and their paths through the mesh, damage in models with CDM-based materials is often distributed in a region of partially damaged elements ahead of stress concentrations. Having a series of discrete matrix cracks represented by a softened region may affect predictions of damage propagation and, thus, structural failure. This issue can be mitigated by restricting matrix damage development to discrete, fiber-aligned rows of elements; hence CDM-based matrix cracks can be implemented to be more representative of discrete matrix cracks. This paper evaluates the effect of restricting CDM matrix crack development to discrete, fiber-aligned rows where the spacing of these rows is controlled by a user-defined crack spacing parameter. Initially, the effect of incrementally increasing matrix crack spacing in a unidirectional center notch coupon is evaluated. Then, the lessons learned from the center notch specimen are applied to open-hole compression finite element models. Results are compared to test data, and the limitations, successes, and potential of the matrix crack spacing approach are discussed

Impaired Hyperemic Response to Exercise Post Stroke

Individuals with chronic stroke have reduced perfusion of the paretic lower limb at rest; however, the hyperemic response to graded muscle contractions in this patient population has not been examined. This study quantified blood flow to the paretic and non-paretic lower limbs of subjects with chronic stroke after submaximal contractions of the knee extensor muscles and correlated those measures with limb function and activity. Ten subjects with chronic stroke and ten controls had blood flow through the superficial femoral artery quantified with ultrasonography before and immediately after 10 second contractions of the knee extensor muscles at 20, 40, 60, and 80% of the maximal voluntary contraction (MVC) of the test limb. Blood flow to the paretic and non-paretic limb of stroke subjects was significantly reduced at all load levels compared to control subjects even after normalization to lean muscle mass. Of variables measured, increased blood flow after an 80% MVC was the single best predictor of paretic limb strength, the symmetry of strength between the paretic and non-paretic limbs, coordination of the paretic limb, and physical activity. The impaired hemodynamic response to high intensity contractions was a better predictor of lower limb function than resting perfusion measures. Stroke-dependent weakness and atrophy of the paretic limb do not explain the reduced hyperemic response to muscle contraction alone as the response is similarly reduced in the non-paretic limb when compared to controls. These data may suggest a role for perfusion therapies to optimize rehabilitation post stroke

Stability, Persistence and Habitat Associations of the Pearl Darter \u3ci\u3ePercina aurora\u3c/i\u3e in the Pascagoula River System, Southeastern USA

The southeastern United States represents one of the richest collections of aquatic biodiversity worldwide; however, many of these taxa are under an increasing threat of imperilment, local extirpation, or extinction. The pearl darter Percina aurora is a small-bodied freshwater fish endemic to the Pearl and Pascagoula river systems of Mississippi and Louisiana (USA). The last collected specimen from the Pearl River drainage was taken in 1973, and it now appears that populations in this system are likely extirpated. This reduced the historical range of this species by approximately 50%, ultimately resulting in federal protection under the US Endangered Species Act in 2017. To better understand the current distribution and general biology of extant populations, we analyzed data collected from a series of surveys conducted in the Pascagoula River drainage from 2000 to 2016. Pearl darters were captured at relatively low abundance (2.4 ± 4.0 ind. per collection) from 57% of 308 collections. We identified strong relationships between local habitat variables and occurrence and catch-per-unit-effort (CPUE) of pearl darters. Pearl darters were frequently encountered and in greater abundance in depositional areas characterized by low-velocity habitats and finer substrates. Patterns of occurrence and CPUE were spatiotemporally variable across years; however, repeated collections from a subset of localities collected across a decade or more indicated long-term persistence and stability, suggesting population resilience throughout the Pascagoula River drainage

Directed Fusion of Mesenchymal Stem Cells with Cardiomyocytes via VSV-G Facilitates Stem Cell Programming

Mesenchymal stem cells (MSCs) spontaneously fuse with somatic cells in vivo, albeit rarely, and the fusion products are capable of tissue-specific function (mature trait) or proliferation (immature trait), depending on the microenvironment. That stem cells can be programmed, or somatic cells reprogrammed, in this fashion suggests that stem cell fusion holds promise as a therapeutic approach for the repair of damaged tissues, especially tissues not readily capable of functional regeneration, such as the myocardium. In an attempt to increase the frequency of stem cell fusion and, in so doing, increase the potential for cardiac tissue repair, we expressed the fusogen of the vesicular stomatitis virus (VSV-G) in human MSCs. We found VSV-G expressing MSCs (vMSCs) fused with cardiomyocytes (CMs) and these fusion products adopted a CM-like phenotype and morphology in vitro. In vivo, vMSCs delivered to damaged mouse myocardium via a collagen patch were able to home to the myocardium and fuse to cells within the infarct and peri-infarct region of the myocardium. This study provides a basis for the investigation of the biological impact of fusion of stem cells with CMs in vivo and illustrates how viral fusion proteins might better enable such studies

Hubble Space Telescope Astrometry of the Procyon System

The nearby star Procyon is a visual binary containing the F5 IV-V subgiant Procyon A, orbited in a 40.84 yr period by the faint DQZ white dwarf Procyon B. Using images obtained over two decades with the Hubble Space Telescope, and historical measurements back to the 19th century, we have determined precise orbital elements. Combined with measurements of the parallax and the motion of the A component, these elements yield dynamical masses of 1.478 +/- 0.012 Msun and 0.592 +/- 0.006 Msun for A and B, respectively. The mass of Procyon A agrees well with theoretical predictions based on asteroseismology and its temperature and luminosity. Use of a standard core-overshoot model agrees best for a surprisingly high amount of core overshoot. Under these modeling assumptions, Procyon A's age is ~2.7 Gyr. Procyon B's location in the H-R diagram is in excellent agreement with theoretical cooling tracks for white dwarfs of its dynamical mass. Its position in the mass-radius plane is also consistent with theory, assuming a carbon-oxygen core and a helium-dominated atmosphere. Its progenitor's mass was 1.9-2.2 Msun, depending on its amount of core overshoot. Several astrophysical puzzles remain. In the progenitor system, the stars at periastron were separated by only ~5 AU, which might have led to tidal interactions and even mass transfer; yet there is no direct evidence that these have occurred. Moreover the orbital eccentricity has remained high (~0.40). The mass of Procyon B is somewhat lower than anticipated from the initial-to-final-mass relation seen in open clusters. The presence of heavy elements in its atmosphere requires ongoing accretion, but the place of origin is uncertain.Comment: Accepted by Astrophysical Journa

Star-Crossed Lovers DI Tau A and B: Orbit Characterization and Physical Properties Determination

The stellar companion to the weak-line T Tauri star DI Tau A was first discovered by the lunar occultation technique in 1989 and was subsequently confirmed by a speckle imaging observation in 1991. It has not been detected since, despite being targeted by five different studies that used a variety of methods and spanned more than 20 years. Here, we report the serendipitous rediscovery of DI Tau B during our Young Exoplanets Spectroscopic Survey (YESS). Using radial velocity data from YESS spanning 17 years, new adaptive optics observations from Keck II, and a variety of other data from the literature, we derive a preliminary orbital solution for the system that effectively explains the detection and (almost all of the) non-detection history of DI Tau B. We estimate the dynamical masses of both components, finding that the large mass difference (q $\sim$0.17) and long orbital period ($\gtrsim$35 years) make DI Tau system a noteworthy and valuable addition to studies of stellar evolution and pre-main-sequence models. With a long orbital period and a small flux ratio (f2/f1) between DI Tau A and B, additional measurements are needed for a better comparison between these observational results and pre-main-sequence models. Finally, we report an average surface magnetic field strength ($\bar B$) for DI Tau A, of $\sim$0.55 kG, which is unusually low in the context of young active stars.Comment: 21 pages, 10 figures. Accepted to Ap

Metagenomic analysis of DNA viruses with targeted sequence capture of canine lobular orbital adenomas and normal conjunctiva

Our study aims are: (1) to evaluate phenotypically normal canine conjunctival and orbital tissue and tissue from canine lobular orbital adenomas (CLOAs) for the presence of viral genomic material and (2) phylogenetically classify detected DNA viruses to determine if a DNA virus is associated with CLOAs. A total of 31 formalin fixed paraffin embedded CLOA tissue samples, 4 papillomas or sarcoid, and 10 fresh clinically normal conjunctival tissues were included in this study. Genomic DNA was isolated from all samples and sequencing libraries were prepared. The libraries were molecularly indexed and pooled and viral DNA was enriched via targeted sequence capture utilizing ViroCap. The libraries were sequenced on the Illumina HiSeq platform and compared to known viral DNA reference genomes to identify viral DNA. Carnivore parvovirus was identified in 6.4% and 20% of CLOA tissue and normal conjunctival samples, respectively. This study showed that conjunctival tissue from healthy dogs and CLOAs uncommonly harbor DNA viruses, and no DNA virus was associated with these tumors. Further studies are needed to evaluate the etiologic cause of CLOAs