Aeromechanical stability of a hingeless rotor in hover and forward flight: Analysis and wind tunnel tests

A research effort of analysis and testing was conducted to investigate the ground resonance phenomenon of a soft in-plane hingeless rotor. Experimental data were obtained using a 9 ft. (2.74 m) diameter model rotor in hover and forward flight. Eight model rotor configurations were investigated. Configuration parameters included pitch flap coupling, blade sweep and droop, and precone of the blade feathering axis. An analysis based on a comprehensive analytical model of rotorcraft aerodynamics and dynamics was used. The moving block was used to experimentally determine the regressing lead lag mode damping. Good agreement was obtained between the analysis and test. Both analysis and experiment indicated ground resonance instability in hover. An outline of the analysis, a description of the experimental model and procedures, and comparison of the analytical and experimental data are presented

Wind-Tunnel Survey of an Oscillating Flow Field for Application to Model Helicopter Rotor Testing

A survey was conducted of the flow field produced by the Airstream Oscillator System (AOS) in the Langley Transonic Dynamics Tunnel (TDT). The magnitude of a simulated gust field was measured at 15 locations in the plane of a typical model helicopter rotor when tested in the TDT using the Aeroelastic Rotor Experimental System (ARES) model. These measurements were made over a range of tunnel dynamic pressures typical of those used for an ARES test. The data indicate that the gust field produced by the AOS is non-uniform across the tunnel test section, but should be sufficient to excite a model rotor

An experimental investigation of the aeromechanical stability of a hingeless rotor in hover and forward flight

Analysis and testing were conducted in the Langley Transonic Dynamics Tunnel to investigate the aeromechanical stability of a soft inplane hingeless rotor model. Rotor stability data were obtained in hover and in forward flight up to an advance ratio of 0.35. Model rotor parameters evaluated were blade sweep and droop, pre-cone of the blade feathering axis, and blade pitch-flap coupling. Data obtained during these tests are presented without analysis

Aeroelastic model helicopter rotor testing in the Langley TDT

Wind-tunnel testing of a properly scaled aeroelastic model helicopter rotor is considered a necessary phase in the design development of new or existing rotor systems. For this reason, extensive testing of aeroelastically scaled model rotors is done in the Transonic Dynamics Tunnel (TDT) located at the NASA Langley Research Center. A unique capability of this facility, which enables proper dynamic scaling, is the use of Freon as a test medium. A description of the TDT and a discussion of the benefits of using Freon as a test medium are presented. A description of the model test bed used, the Aeroelastic Rotor Experimental System (ARES), is also provided and examples of recent rotor tests are cited to illustrate the advantages and capabilities of aeroelastic model rotor testing in the TDT. The importance of proper dynamic scaling in identifying and solving rotorcraft aeroelastic problems, and the importance of aeroelastic testing of model rotor systems in the design of advanced rotor systems are demonstrated

Vibratory Loads Data from a Wind-Tunnel Test of Structurally Tailored Model Helicopter Rotors

An experimental study was conducted in the Langley Transonic Dynamics Tunnel to investigate the use of a Bell Helicopter Textron (BHT) rotor structural tailoring concept, known as rotor nodalization, in conjunction with advanced blade aerodynamics as well as to evaluate rotor blade aerodynamic design methodologies. A 1/5-size, four-bladed bearingless hub, three sets of Mach-scaled model rotor blades were tested in forward flight from transition up to an advance ratio of 0.35. The data presented pertain only to the evaluation of the structural tailoring concept and consist of fixed-system and rotating system vibratory loads. These data will be useful for evaluating the effects of tailoring blade structural properties on fixed-system vibratory loads, as well as validating analyses used in the design of advanced rotor systems

A rapid staining technique for the detection of the initiation of germination of bacterial spores

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75645/1/j.1472-765x.2002.01047.x.pd

Impact of the COVID-19 pandemic and associated non-pharmaceutical interventions on other notifiable infectious diseases in Germany: An analysis of national surveillance data during week 1–2016 – week 32–2020

Background The COVID-19 pandemic and associated non-pharmaceutical interventions (NPIs) affect healthcare seeking behaviour, access to healthcare, test strategies, disease notification and workload at public health authorities, but may also lead to a true change in transmission dynamics. We aimed to assess the impact of the pandemic and NPIs on other notifiable infectious diseases under surveillance in Germany. Methods We included 32 nationally notifiable disease categories with case numbers >100/year in 2016–2019. We used quasi-Poisson regression analysis on a weekly aggregated time-series incorporating trend and seasonality, to compute the relative change in case numbers during week 2020–10 to 2020–32 (pandemic/NPIs), in comparison to week 2016–01 to 2020–09. Findings During week 2020–10 to 2020–32, 216,825 COVID-19 cases, and 162,942 (-35%) cases of other diseases, were notified. Case numbers decreased across all ages and notification categories (all p<0•05), except for tick-borne encephalitis, which increased (+58%). The number of cases decreased most for respiratory diseases (from -86% for measles, to -12% for tuberculosis), gastro-intestinal diseases (from -83% for rotavirus gastroenteritis, to -7% for yersiniosis) and imported vector-borne diseases (-75% dengue fever, -73% malaria). The less affected infections were healthcare associated pathogens (from -43% infection/colonisation with carbapenem-non-susceptible Acinetobacter, to -28% for Methicillin-resistant Staphylococcus aureus invasive infection) and sexually transmitted and blood-borne diseases (from -28% for hepatitis B, to -12% for syphilis). Interpretation During the COVID-19 pandemic a drastic decrease of notifications for most infectious diseases and pathogens was observed. Our findings suggest effects of NPIs on overall disease transmission that require further investigation.Peer Reviewe

Polylactic Acid (PLA) Reinforced with Date Palm Sheath Fiber Bio-Composites: Evaluation of Fiber Density, Geometry, and Content on the Physical and Mechanical Properties

Copyright © 2022 The Author(s). Significant interest for utilizing and processing natural fibers (NF) to develop sustainable and fully biodegradable composites evolved as the global environmental concerns upsurge. Date palm tree (DPT) accounts for more than 2.8 million tons of waste annually, making it the most abundant agricultural biomass waste in the MENA region. This study investigates the effect of date palm fiber (DPF) density, diameter size and content on both the mechanical and physical properties of polylactic acid (PLA) reinforced DPF bio-composite. The bio-composites are developed using melt-mixing technique which is followed by compression molding. The influence of the mechanical properties is investigated by evaluating the tensile, flexural and impact strengths. Meanwhile bio-composite thickness swelling (TS), moisture content (MC) and water absorption (WA) characteristics are evaluated. Bio-composite microstructures are examined using SEM to investigate the interfacial bonding between PLA matrix and DPF. Results showed that at 40 wt.% DPF, the TS, MC, and WA were the highest demonstrating an increase of 4.10%, 4.95%, and 8.22%, respectively. Although the results demonstrated a decrease in mechanical properties as DPF content increased (depending on DPF geometry), the results indicate that the developed technologies could be commercialized under the waste management scheme for non-structural applications. 摘要 随着全球环境问题的加剧，人们对利用和加工天然纤维（NF）开发可持续和完全生物降解的复合材料产生了极大的兴趣. 椰枣树（DPT）每年产生280多万吨废弃物，是中东和北非地区最丰富的农业生物质废弃物. 本研究研究了椰枣纤维（DPF）密度、直径大小和含量对聚乳酸（PLA）增强DPF生物复合材料力学和物理性能的影响. 生物复合材料是使用熔融混合技术开发的，然后是压缩成型. 通过评估拉伸、弯曲和冲击强度来研究力学性能的影响. 同时，评估了生物复合材料的厚度膨胀（TS）、水分含量（MC）和吸水率（WA）特性. 使用SEM检查生物复合材料微观结构，以研究PLA基质和DPF之间的界面结合. 结果表明，在40重量%的DPF下，TS、MC和WA最高，分别增加了4.10%、4.95%和8.22%. 尽管结果表明，随着DPF含量的增加（取决于DPF的几何形状），机械性能有所下降，但结果表明，开发的技术可以在非结构应用的废物管理计划下商业化.This research did not receive any public or private grants and funds

Photoaffinity Labeling the Agonist Binding Sites of Torpedo and α4β2 Nicotinic Acetylcholine Receptors and Acetylcholine Binding Proteins (AChBPs) with [3H]Cytisine

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Estimating the regional distribution of men who have sex with men (MSM) based on Internet surveys

<p>Abstract</p> <p>Background</p> <p>Measurement of prevalence and incidence of infections in a hard to reach population like men who have sex with men (MSM) is hampered by its unknown size and regional distribution. Population-based surveys have recently been used to estimate the total number of MSM, but these surveys are usually not large enough to measure regional differences in the proportion of MSM in the population. We explored the use of the proportional regional distribution of participants of large internet-based surveys among MSM from Germany to estimate the regional distribution of MSM in Germany.</p> <p>Methods</p> <p>We compared participants from two separate MSM behavioural surveys with each other and with the distribution of user profiles of the largest contact and dating website for gay and other MSM in Germany in terms of the representativeness of the regional distribution. In addition, we compared the regional distribution of reportedly HIV positive survey participants with the regional distribution of HIV notifications within the national surveillance system that can be attributed to transmission through homosexual contacts.</p> <p>Results</p> <p>Regional distribution of survey participants was almost identical in both surveys, despite little overlap between survey participants. Slight discrepancies between surveys and user profiles could be observed. Proportional regional distribution of survey participants with HIV diagnosis resembled national surveillance data.</p> <p>Conclusion</p> <p>Considering the difficulties to obtain representative data by other sampling methods for "hidden" populations like MSM, internet-based surveys may provide an easy and low cost tool to estimate the regional population distribution – at least in Western post-industrialized countries. Some uncertainties remain about the exact place of residence of MSM in larger cities or catchment areas of these cities. Slightly different results from different datasets may be due to unequal popularity of MSM websites in different regions. The total population size of the MSM population can be estimated based on e.g. data from representative national population surveys. Both estimates can then be combined to calculate the absolute size of regional MSM populations.</p