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LAYERED METAMATERIAL BEAM STRUCTURE WITH LOCAL RESONATORS FOR VIBRATION ATTENUATION: MODEL AND EXPERIMENT
Get PDFLayered metamaterial beam structures are gaining attention in a variety of fields including vibration attenuation and energy harvesting. Exhaustive research on single-beam metamaterial vibration attenuation structures using local resonators exists in literature. Moreover, there are recent attempts at modelling double-layered beams with different kinds of constraints. The double-layered beam models in literature are limited to simple beams and not extended to metamaterials with local resonators. This research is primarily focused on developing a design criterion and a modelling platform for layered metamaterial structures with multiple beams and local resonators for vibration isolation. The model is developed using Euler-Bernoulli beam equations, superposition of mode shapes and Galerkin methods. A prototype layered metamaterial structure is fabricated and characterized experimentally. The prototype consists of horizontal beams, local resonators forming unit cells, and vertical beams linkages. Each local resonator consists of cantilevers with tip masses. Results show good agreement between model and experiment. Two major bandgaps are observed at 190 Hz – 410 Hz and 550 Hz – 710 Hz. Results reveal that the low frequency bandgap can be further reduced through the design of the local resonators. Results also show that alternating the length of the local resonators causes a shift in the first frequency bandgap. An increase in the number of local resonators opens up extra frequency bandgaps at lower frequencies with the drawback of reducing the depth in vibration transmissibility. Moreover, the higher frequency bandgaps are mostly affected by the horizontal beams. An increase in the length of the horizontal beams, while the number and design of the local resonators are fixed, broadens the second frequency bandgap and shifts it to lower frequency values. Additionally, the ability of the fabricated metamaterial structure to harvest electric power in these bandgaps is examined. Results show that vibration attenuation and energy harvesting characteristics of the metamaterial structure are coupled. Stronger vibration attenuation within the first bandgap has led to enhanced energy harvesting capabilities within this bandgap. Power measurements at optimum load resistance of 15 Ω reveal that maximum power generated within the first bandgap reaches 5.2 µW at 245 Hz. Compared to state-of-the-art, the metamaterial structure presented here shows a significant improvement in electric power generation, at considerably lower load resistance, while maintaining the ability to attenuate undesired vibrations within the frequency bandgap. Lastly, the comparative advantages of layered-beam structures over single-beam metamaterial structures is studied. A beam prototype and dimension studied by multiple articles in literature is used in simulating the comparative study. Results show that in cases where spacing and design of the local resonators are desired to remain fixed, layering the horizontal beams offers a significant pathway for both lowering the bandgap and developing additional bandgaps. Results also suggest that increasing the number of resonators per horizontal beam further generates multiple lower bandgaps in layered metamaterial beams. In situations where the number of local resonators per beam are desired to remain constant, increasing the length of the unit-cells offers an alternative technique for lowering the bandgaps. This comparative study is particularly useful to engineers and researchers designing applications of beam-type metamaterial structures
Synthesis and Analysis of Short Antimicrobial Peptides: RR, RIKA IGR, and HQ
Get PDFA significant impending threat to the public health system is the rise of multidrug resistant bacteria. An attractive potential option to combat this is antimicrobial peptides (AMPs). AMPs are peptide chains with lengths that range from 10 to 70 amino acid residues that show antimicrobial activity. AMPs tend to have less toxicity than other antibiotic therapies, have a broader range of activity, and have a decreased resistance development by the target cells. Short AMPs are especially attractive due to their stability as well as their ability to penetrate cell membranes. With a wide range of possible AMPs available, further characterization of these molecules is needed before using AMPs in a clinical setting. For this study, 4 previously identified AMPs (WLRRIKAWLRR [RR], WLRRIKAWLRRIKA [RIKA], IIGGR [IGR], and HPQYNQR [HQ]) were synthesized using solid phase peptide synthesis and evaluated for antimicrobial activity. Previous studies regarding MIC assay methods indicate that special considerations, such as test vessel material and growth media, are required for AMPs to obtain accurate MIC data. Therefore, a resazurin colorimetric assay was conducted in a 96-well polypropylene microtiter plate with iso-sensitest broth. Eight species were challenged with these 4 peptides, many for the first time. Peptides RR and RIKA demonstrated antimicrobial activity in 6 and 7 species, respectively. RIKA consistently demonstrated more antimicrobial activity than RR. IGR and HQ showed no antibiotic activity in this study. This novel study involved synthesizing four AMPs, designing a novel experimental method for antibiotic activity of AMPs, and expanding antimicrobial activity testing to eight bacterial species to allow for a comprehensive comparison of these potential novel antibiotic therapies. This comparison could renew interest in these AMPs and possible combination therapies
Impact Of Biodegradable Materials On Healthy And Diseased Brain Cells: Function And Viability
Get PDFWith the recent creation of Metal Organic Biohybrids (MOBs) from the DeCoster lab group at Louisiana Tech University, a new class of nano and micro particles needs to be investigated. The amalgamation of metals such as copper and an amino acid have already shown promise for biomedical applications such as delayed drug delivery or time delayed anti-microbial effects1. In this study the effects of cobalt, copper, and zinc-based MOBs have been compared against silicon dioxide nanoparticles, a negative control, and copper oxide nanoparticles, a positive control, in order to observe their effects on cancerous glioma cells and healthy astrocyte cells. The cellular health was examined in terms of cell metabolism, calcium response intensity and nuclear morphology via MTT assay, DAPI staining and calcium imaging. The study showed that all MOBs tested had desired negative effects on both the astrocyte and glioma cell lines. Of exception were CuHARs which were able to successfully decrease the astrocyte metabolism by 21% and the glioma was more harshly affected at 29%. Calcium imaging data of glioma also showed an initial suppression followed by agitation concluded by suppression when compared to control cells. When CuHARs were compared to CuNPs by concentration of copper mass present in the total dose of the material. the metabolism was 89 ± 0% CuNPs and 94 ± 0% CuHARs at 24Hrs. In summary, all MOBs tested showed promise and with alterations to dosages, amounts, and loadings they may be a key to a new cancer treatment method
Quality of Life in Persons with Type 2 Diabetes Mellitus Who Also Have Depression as Defined by the Beck Depression Inventory
Get PDFRegistered Dietitian Nutritionists (RDN) are an essential part of type 2 diabetes disease management. This study assessed whether self-reported symptoms of depression, glycemic control, and reported intervention by a RDN had an impact on the quality-of-life in person diagnosed with type 2 diabetes mellitus. An online survey was created using Qualtics software which was distributed to a convenience sample of online support groups for people diagnosed with diabetes as well as the personal pages of the researchers. The survey was available for 10 weeks and collected demographic data, information regarding the RDN intervention and assessed participant diabetes related quality-of-life using the Appraisal of Diabetes Scale and depressive symptoms using the Beck Depression Inventory-II. A total of 95 participants’ responses were used for data analysis. Frequencies and measures of central tendency were used to describe the demographic data. A positive correlation was found between the Beck Depression Inventory-II scores and Appraisal of Diabetes Scale scores (quality-of-life) (p\u3c.01). There was significant difference found in mean Appraisal of Diabetes Scale scores for those having glucose monitoring checks outside of the recommended range greater ≥50% of the time when compared to those outside of the range for ≤ 25% of the time (p=.001). The results suggest that RDN’s who can help achieve glucose control can also improve a person’s diabetes related quality-of-life and decrease depressive symptoms. Further research is needed to validate these results
Security-Related Technostress Trifecta on Employees’ Security Counterproductive Behaviors
Get PDFInformation security technology has become more important in preventing and protecting organizational digital assets, and employees are often considered the last line of defense. However, employees at all levels have to face and deal with the complexity, overload, and uncertainty of information security technology in their jobs every day. Although information security technology could benefit the organization and individual employees as it is critical to building and strengthening protection mechanisms for organizational digital assets and employees’ data, it could also negatively affect employees’ emotions and work accomplishments.
This study examines the two effects of psychological techno-stress responses (security-techno distress and security-techno eustress) are caused by information security techno-stressors, which eventually influence security counterproductive behavior. In addition, a quantitative investigation with a cross-sectional survey design to collect data that measured items reflect the constructs discussed in the above section will be considered to evaluate the hindrance and challenge security techno-stressors that predict emotional security-techno distress and security techno-eustress response that may lead to the security counterproductive behavior. The findings suggested that security job demands are positively associated with security-techno distress and security-techno eustress, suggesting that if there is no demand, there is no challenge or motivation for employees to improve their security best practice. Meanwhile, security job resources This study has theoretical and practical implications for information security scholars and practitioners. It had negative significant impacts on security-techno distress and positive significant effects on eustress, which suggested that these factors encourage employees to prepare well for challenges interacting with information security technology. Overall, this research increases the understanding of information security technostress and the essential role of distress and eustress on security counterproductive behavior
