Explicit Asymmetric Bounds for Robust Stability of Continuous and Discrete-Time-Systems

The problem of robust stability in linear systems with parametric uncertainties is considered. Explicit stability bounds on uncertain parameters are derived and expressed in terms of linear inequalities for continuous systems and inequalities with quadratic terms for discrete-time systems. Cases where system parameters are nonlinear functions of an uncertainty are also examine

Analysis of the Genome of the Sexually Transmitted Insect Virus Helicoverpa zea Nudivirus 2

The sexually transmitted insect virus Helicoverpa zea nudivirus 2 (HzNV-2) was determined to have a circular double-stranded DNA genome of 231,621 bp coding for an estimated 113 open reading frames (ORFs). HzNV-2 is most closely related to the nudiviruses, a sister group of the insect baculoviruses. Several putative ORFs that share homology with the baculovirus core genes were identified in the viral genome. However, HzNV-2 lacks several key genetic features of baculoviruses including the late transcriptional regulation factor, LEF-1 and the palindromic hrs, which serve as origins of replication. The HzNV-2 genome was found to code for three ORFs that had significant sequence homology to cellular genes which are not generally found in viral genomes. These included a presumed juvenile hormone esterase gene, a gene coding for a putative zinc-dependent matrix metalloprotease, and a major facilitator superfamily protein gene; all of which are believed to play a role in the cellular proliferation and the tissue hypertrophy observed in the malformation of reproductive organs observed in HzNV-2 infected corn earworm moths, Helicoverpa zea

Linear plasmids and the rate of sequence evolution in plant mitochondrial genomes

Includes bibliographical references (pages 373-374).The mitochondrial genomes of flowering plants experience frequent insertions of foreign sequences, including linear plasmids that also exist in standalone forms within mitochondria, but the history and phylogenetic distribution of plasmid insertions is not well known. Taking advantage of the increased availability of plant mitochondrial genome sequences, we performed phylogenetic analyses to reconstruct the evolutionary history of these plasmids and plasmid-derived insertions. Mitochondrial genomes from multiple land plant lineages (including liverworts, lycophytes, ferns, and gymnosperms) include fragmented remnants from ancient plasmid insertions. Such insertions are much more recent and widespread in angiosperms, in which approximately 75% of sequenced mitochondrial genomes contain identifiable plasmid insertions. Although conflicts between plasmid and angiosperm phylogenies provide clear evidence of repeated horizontal transfers, we were still able to detect significant phylogenetic concordance, indicating that mitochondrial plasmids have also experienced sustained periods of (effectively) vertical transmission in angiosperms. The observed levels of sequence divergence in plasmid-derived genes suggest that nucleotide substitution rates in these plasmids, which often encode their own viral-like DNA polymerases, are orders of magnitude higher than in mitochondrial chromosomes. Based on these results, we hypothesize that the periodic incorporation of mitochondrial genes into plasmids contributes to the remarkable heterogeneity in substitution rates among genes that has recently been discovered in some angiosperm mitochondrial genomes. In support of this hypothesis, we show that the recently acquired ψtrnP-trnW gene region in a maize linear plasmid is evolving significantly faster than homologous sequences that have been retained in the mitochondrial chromosome in closely related grasses.Published with support from the Colorado State University Libraries Open Access Research and Scholarship Fund

Multicenter, observational cohort study evaluating third-generation cephalosporin therapy for bloodstream infections secondary to enterobacter, serratia, and citrobacter species

Objectives: There is debate on whether the use of third-generation cephalosporins (3GC) increases the risk of clinical failure in bloodstream infections (BSIs) caused by chromosomally-mediated AmpC-producing Enterobacterales (CAE). This study evaluates the impact of definitive 3GC therapy versus other antibiotics on clinical outcomes in BSIs due to Enterobacter, Serratia, or Citrobacter species. Methods: This multicenter, retrospective cohort study evaluated adult hospitalized patients with BSIs secondary to Enterobacter, Serratia, or Citrobacter species from 1 January 2006 to 1 September 2014. Definitive 3GC therapy was compared to definitive therapy with other non-3GC antibiotics. Multivariable Cox proportional hazards regression evaluated the impact of definitive 3GC on overall treatment failure (OTF) as a composite of in-hospital mortality, 30-day hospital readmission, or 90-day reinfection. Results: A total of 381 patients from 18 institutions in the southeastern United States were enrolled. Common sources of BSIs were the urinary tract and central venous catheters (78 (20.5%) patients each). Definitive 3GC therapy was utilized in 65 (17.1%) patients. OTF occurred in 22/65 patients (33.9%) in the definitive 3GC group vs. 94/316 (29.8%) in the non-3GC group (p = 0.51). Individual components of OTF were comparable between groups. Risk of OTF was comparable with definitive 3GC therapy vs. definitive non-3GC therapy (aHR 0.93, 95% CI 0.51–1.72) in multivariable Cox proportional hazards regression analysis. Conclusions: These outcomes suggest definitive 3GC therapy does not significantly alter the risk of poor clinical outcomes in the treatment of BSIs secondary to Enterobacter, Serratia, or Citrobacter species compared to other antimicrobial agents

Crack Propagation and Microstructural Transformation on The Friction Surface of a High-Speed Railway Brake Disc

While brake disc wear represents a significant problem in high-speed rail systems, the progressive development of fatigue cracks during successive braking cycles also plays a great role in braking integrity. The modified microstructure consisting of a white etching layer (WEL) containing nanosized ferrite was observed on the friction surface of worn brake discs. In order to analyze how sequential thermal and mechanical stress affected crack propagation and microstructure evolution in brake discs, successive braking cycles were simulated on a full-scale braking bench test rig. Crack initiation and propagation mechanisms were proposed based on the experimental results, i.e., (i) occurrence of heat checking caused by heating and cooling transients during braking; (ii) heat checking increasing the roughness of the friction surface which in turn caused a local stress concentration and (iii) localized friction stress and thermal stress driving the heat checking to propagate and coalesce with the radial main crack. Analysis of the thermal-mechanical conditions that exist at the friction surface during braking indicates that WEL formation can be attributed to severe plastic deformation caused by the repeated friction between the disc and pads. Mechanical testing also indicated that WEL formation is not detrimental to brake disc integrity

Investigation of Through Thickness Microstructure and Mechanical Properties in Friction Stir Welded 7N01 Aluminum Alloy Plate

An on-going problem in friction stir welded (FSW) joints used in the high-speed train sector is that the microstructure and mechanical properties can significantly vary in thick sections. Because inhomogeneous properties can reduce weld efficiency and degrade service performance, it is of some interest to understand how inhomogeneous properties can develop in FSW welds made from precipitation hardening alloys such as 7N01. In the current study, butt welds were made using 12 mm thick plates and then sectioned perpendicular to the weld line. Five 2.2 mm thick slices were cut from a section and used to measure tensile properties access the weld thickness. The microstructure was characterized using scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) to measure variation in grain size and second phase particle distributions over the weld zone. Results showed that, with the exception of the top slice, yield strength (σy) and ultimate tensile strength (σUTS) obtained from the slices were fairly consistent and comparable to values from the full weld. Elongation (δ) was maximum at mid-thickness decreased significantly towards the crown. Although significantly reduced elongation was found at the top of the weld, and likely limits overall weldment ductility, elongation of the full FSW weld was improved over that of the base metal and can be attributed to enhanced post-necking straining. The finest grains and second phase particles were observed at mid-thickness. In comparison, the coarsest grains were observed at the top of the nugget. This microstructural variation can be understood by considering the temperature and strain field gradients that are generated in the plasticized zone. It is expected that the findings will help to promote a better understanding of post-weld microstructure development and mechanical properties of thick plates

Investigation of Void Formation in Friction Stir Welding Of 7N01 Aluminum Alloy

Friction Stir Welding (FSW) is a solid state joining process that is widely used to produce high integrity aluminum weldments for a variety of industries. While extensive work has been conducted to understand flow behavior, much less research has been performed to identify how void defects form and how to predict them. In the present study, the relationship between rotation speed, plasticized region, and defect formation was investigated. To analyze how tunneling and cavity type void defects form during FSW, a 3-D Computational fluid dynamics(CFD) model based on the Fluent software code was used to simulate butt welding. The CFD model was validated using temperature measurements and marker materials from FSW welds made on 12 mm thick 7N01 aluminum alloy plate. Analysis of the simulation results showed that the formation of tunneling defects at lower rotation speeds correlated to a large variation in the size of the plasticized region over the plate thickness. At higher rotation speeds, analysis of material flowlines indicated an imbalance in rotational and longitudinal flow around the pin which resulted in a cavity type defect. It is considered that the results can be used to compare different weld schedules and be used to assess the likelihood of void formation in an actual weld using a CFD model

Similar ultrafast dynamics of several dissimilar Dirac and Weyl semimetals

Recent years have seen the rapid discovery of solids whose low-energy electrons have a massless, linear dispersion, such as Weyl, line-node, and Dirac semimetals. The remarkable optical properties predicted in these materials show their versatile potential for optoelectronic uses. However, little is known of their response in the picoseconds after absorbing a photon. Here we measure the ultrafast dynamics of four materials that share non-trivial band structure topology but that differ chemically, structurally, and in their low-energy band structures: ZrSiS, which hosts a Dirac line node and Dirac points; TaAs and NbP, which are Weyl semimetals; and Sr$_{1-y}$Mn$_{1-z}$Sb$_2$, in which Dirac fermions coexist with broken time-reversal symmetry. After photoexcitation by a short pulse, all four relax in two stages, first sub-picosecond, and then few-picosecond. Their rapid relaxation suggests that these and related materials may be suited for optical switches and fast infrared detectors. The complex change of refractive index shows that photoexcited carrier populations persist for a few picoseconds

N17 Modifies mutant Huntingtin nuclear pathogenesis and severity of disease in HD BAC transgenic mice.

The nucleus is a critical subcellular compartment for the pathogenesis of polyglutamine disorders, including Huntington's disease (HD). Recent studies suggest the first 17-amino-acid domain (N17) of mutant huntingtin (mHTT) mediates its nuclear exclusion in cultured cells. Here, we test whether N17 could be a molecular determinant of nuclear mHTT pathogenesis in vivo. BAC transgenic mice expressing mHTT lacking the N17 domain (BACHD-ΔN17) show dramatically accelerated mHTT pathology exclusively in the nucleus, which is associated with HD-like transcriptionopathy. Interestingly, BACHD-ΔN17 mice manifest more overt disease-like phenotypes than the original BACHD mice, including body weight loss, movement deficits, robust striatal neuron loss, and neuroinflammation. Mechanistically, N17 is necessary for nuclear exclusion of small mHTT fragments that are part of nuclear pathology in HD. Together, our study suggests that N17 modifies nuclear pathogenesis and disease severity in HD mice by regulating subcellular localization of known nuclear pathogenic mHTT species