Design of Vibration Class Laboratory Assignments: Focusing on Broader Application

Courses in vibration taught at Rose-Hulman Institute of Technology are designed to blend classroom discussion of the science of vibration with practical, hands-on applications. The laboratory portion of the undergraduate course in vibration focuses on two areas: (1) system identification for single- and multi-degree-of-freedom systems in the frequency domain through sine-sweep shake testing; and (2) identifying natural frequencies and mode shapes for continuous systems via experimental modal analysis using frequency response data collected through a roving hammer test. Modal analysis is performed using an in-house MATLAB-based program known as Easy Modal Analysis Program (EMAP). The goals of this thesis are two-fold: (1) to create new laboratory exercises to allow students to explore elements of base motion, rotating unbalance, and structural health monitoring; and (2) to expand the functionality of EMAP to allow students to explore the damping characteristics of a system via different methods. The development of these additional laboratory exercises and the expanded functionality of EMAP serve to broaden the students’ practical knowledge of topics in vibration measurement and analysis

Incredibly Fast and Extremely Cold: Development of Low-Temperature Ultrafast Microscopy

Electronic and thermal properties of nanostructures are determining factors in the performance of nanowire-based devices. Due to the inherent heterogeneity of nanostructures, the properties of one may differ dramatically from the average of a population. Pump-probe microscopy is a powerful tool for measuring spatially-resolved excited state dynamics in individual semiconductors with high-throughput and no contacts. We use this technique to directly observe photoexcited carrier recombination, carrier diffusion, and thermal transport in individual silicon nanowires. We also show significant variation in recombination rates between wires grown at the same time. The main focus of this work is on the incorporation of a low-temperature interface into the pump-probe microscope, allowing us to directly observe a variety of phenomena which are inaccessible at room temperature. Shallow energy minima which are thermally masked at room temperature become active at low temperatures, providing a more detailed picture of the nanostructure’s energetics. We will be able to observe spatial variations in the structure’s energy landscape and directly measure phenomena like ballistic transport for the first time. This new microscope is used to observe temperature-dependent excited state decay and an increase in carrier diffusivity at low temperature in silicon nanowires. We find that the dynamics do not vary uniformly with temperature over the whole structure and attribute this to spatially variant populations of deep and shallow traps in the nanowire.Doctor of Philosoph

First Report of Downy Mildew on Gynura aurantiaca Caused by Plasmopara halstedii sensu lato in Florida

Gynura aurantiaca is a member of the Senecionaea tribe of the Asteraceae, indigenous to Java. Commonly known as purple velvet plant, this tropical species is well adapted to landscapes in South Florida, but is mostly seen as a potted plant for use in the interiorscape. During February 2013, a local nursery submitted Gynura aurantiaca samples to the Florida Extension Plant Diagnostic Clinic in Homestead, FL, where 30% of 1,000 plants were affected. Downy, white mycelium was observed on the abaxial leaf surface, and the adaxial surface of affected leaves appeared darker in color. Severely affected leaves began to curl as the tissue turned necrotic. The pathogen was identified as Plasmopara halstedii (Farl.) Berl. & De Toni based on the presence of coenocytic mycelium, and right-angled, monopodially branched sporangiophores with sporangia that were hyaline, obvoid to elliptical, and measuring 21 × 29 × 17 to 21 μm (Delanoe 1972). Molecular identification was conducted by extracting pathogen DNA using the QIAGEN Plant DNA kit (QIAGEN, Gaithersburg, MD). PCR of the 5′ terminal domain of the nuclear DNA coding for the large subunit (LSU rDNA) was performed with primers NL1 and LR3 (Kurtzman et al. 1998; Vilgalys and Hester 1990). The PCR product was purified with the QIAquick kit (QIAGEN) according to the manufacturer’s instructions and sequenced bidirectionally. The sequence from our isolate (GenBank Accession No. KR028988) was nearly identical (exhibited 97% nucleotide identity; 98% query coverage; E value = 0.0) to an isolate of P. halstedii (EF553469). A phylogenetic analysis was performed using the obtained sequence data and fifteen Plasmopara sequences from GenBank and a Fusarium solani accession as an outgroup (Maximum Likelihood, Tamura-Nei model). Our isolate grouped with P. halstedii with high bootstrap support (98% bootstrap value, 1,000 replicates) further supporting identification as P. halstedii. Pathogenicity of the sequenced isolate was evaluated in shade-house experiments. Two-month-old Gynura aurantiaca plants were inoculated with a sporangial suspension (1 × 10⁶ sporangia/ml) of P. halstedii that was collected by washing sporangia from the abaxial surface of purple passion leaves using autoclaved distilled water. Inoculum or autoclaved water was sprayed over the foliage until runoff. Six plants were sprayed per treatment and the experiment was repeated twice. Inoculated plants were placed in a shade house (73% shade) when temperatures ranged from 17 to 28°C with 78 to 98% relative humidity. Plants were observed for disease development, and pathogen sporulation occurred within seven days of inoculation. No symptoms developed on the control plants. To our knowledge, this is the first report of Plasmopara halstedii causing downy mildew on Gynura aurantiaca. Gynura aurantiaca is highly valued for its stunning purple foliage and low input production costs, but a disease such as downy mildew has the potential to substantially reduce if not eliminate commercial production.This is the publisher’s final pdf. The published news item is copyrighted by American Phytopathological Society and can be found at: http://apsjournals.apsnet.org/loi/pdi

Use of a Natural Isotopic Signature in Otoliths to Evaluate Scale-Based Age Determination for American Shad

We used delta O-18 signatures in otoliths as a natural tag for hatch year to evaluate the scale-based age determination method used for adult American shad Alosa sapidissima in the York River, Virginia. Juveniles of the 2002 year-class exhibited high delta O-18 values in otolith cores that identified adult members of the cohort as they returned to spawn. Recruitment of the 2002 cohort was monitored for three consecutive years, identifying age-4, age-5, and age-6 individuals of the York River stock. The scale-based age determination method was not suitable for aging age-4, age-5, or age-6 American shad in the York River. On average, 50% of the individuals from the 2002 year-class were aged incorrectly using the scale-based method. These results suggest that the standard age determination method used for American shad is not applicable to the York River stock. Scientists and managers should use caution when applying scale-based age estimates to stock assessments for American shad in the York River and throughout their range, as the applicability of the scale-based method likely varies for each stock. This study highlights a promising new direction for otolith geochemistry to provide cohort-specific markers, and it identifies several factors that should be considered when applying the technique in the future

Recent Advances on the Multiplex Molecular Detection of Plant Viruses and Viroids

[EN] Plant viruses are still one of the main contributors to economic losses in agriculture. It has been estimated that plant viruses can cause as much as 50 billion euros loss worldwide, per year. This situation may be worsened by recent climate change events and the associated changes in disease epidemiology. Reliable and early detection methods are still one of the main and most effective actions to develop control strategies for plant viral diseases. During the last years, considerable progress has been made to develop tools with high specificity and low detection limits for use in the detection of these plant pathogens. Time and cost reductions have been some of the main objectives pursued during the last few years as these increase their feasibility for routine use. Among other strategies, these objectives can be achieved by the simultaneous detection and (or) identification of several viruses in a single assay. Nucleic acid-based detection techniques are especially suitable for this purpose. Polyvalent detection has allowed the detection of multiple plant viruses at the genus level. Multiplexing RT polymerase chain reaction (PCR) has been optimized for the simultaneous detection of more than 10 plant viruses/viroids. In this short review, we provide an update on the progress made during the last decade on techniques such as multiplex PCR, polyvalent PCR, non-isotopic molecular hybridization techniques, real-time PCR, and array technologies to allow simultaneous detection of multiple plant viruses. Also, the potential and benefits of the powerful new technique of deep sequencing/next-generation sequencing are described.This work was funded by grant BIO2017-88321-R from the Spanish Direccion General de Investigacion Cientifica y Tecnica (DGICYT) and the Prometeo Program GV2014/010 from the Generalitat Valenciana.Pallás Benet, V.; Sanchez Navarro, JÁ.; James, D. (2018). Recent Advances on the Multiplex Molecular Detection of Plant Viruses and Viroids. Frontiers in Microbiology. 9. https://doi.org/10.3389/fmicb.2018.02087S

The Value of Assurance Over Internal Controls: Evidence from Mergers and Acquisitions

In this study, I examine the value of assurance over internal controls in the mergers and acquisitions setting. Specifically, I examine the how the existence of an internal control audit mandated under Section 404(b) of SOX affects information asymmetry as proxied for by the likelihood of a company becoming the target of an acquisition. I find that companies with internal control audits are significantly more likely to receive bids than their counterparts that do not have an internal control audit. Upon further investigation, I find that the mechanism by which companies are more likely to become the target of an acquisition is the reduction in information asymmetry as the results are concentrated in the sample of companies with higher information asymmetry. I also provide some evidence that acquirers are able to reduce the length of transactional due diligence for targets with internal control audits. In additional analyses, I find that the reduction in information asymmetry attributable to internal control audits is significantly reduced when there are other intermediaries available to reduce information asymmetry for acquirers such as financial analysts, institutional owners, or larger auditors