19,619 research outputs found
A high resolution silicon-on-glass Z Axis Gyroscope Operating at Atmospheric Pressure
No full textThis paper describes a high-resolution silicon-on-glass z axis gyroscope operating at atmospheric pressure. The mechanical structure is designed in such a way that it exhibits low cross coupling between drive and sense mode of less than 0.5% simulated using finite-element method and 1.35% verified by experimental measurements. Due to a symmetrically designed structure, the specified bandwidth can be maintained despite of fabrication imperfections. The fabrication process flow is based on a combination of silicon on glass bonding and deep reactive ion etching which results in a large proof mass and capacitances. A closed loop self-oscillation drive interface is used to resonate the gyroscope in the drive mode, which reaches steady-state after 150 ms. Using area-varying capacitors, large quality factors of 217 and 97 for drive and sense mode, respectively, were achieved operating at atmospheric pressure. A low drive voltage, with a 1 Vpeak-peak AC drive amplitude and 10 V DC bias was used to excite the drive mode. The measured scale factor was 10.7 mV/º/s in a range of ±300 º/s with a R2-nonlinearity of 0.12%. The noise equivalent angular rate is 0.0015 º/s/Hz1/2 (=5.4 º/h/Hz1/2) in a 50 Hz bandwidth. The measured SNR was 34 dB at an angular rate input signal with an amplitude of 12.5 º/ s and a frequency of 10 Hz. Without any active temperature control, zero bias stability of 1 was achieved for long-term measurements over six hours and 0.3 º/s for short-term measurements over 120 seconds (1-σ)
A metawindow with optimised acoustic and ventilation performance
No full textFeatured ApplicationA new AMM window simultaneously allows a tunable dual performance of natural ventilation and noise mitigation.Crucial factors in window performance, such as natural ventilation and noise control, are generally conceived separately, forcing users to choose one over the other. To solve this dualism, this study aimed to develop an acoustic metamaterial (AMM) ergonomic window design to allow noise control without dependence on the natural ventilation duration and vice versa. First, the finite element method (FEM) was used to investigate the noise control performance of the acoustic metawindow (AMW) unit, followed by anechoic chamber testing, which also served as the validation of the FEM models. Furthermore, FEM analysis was used to optimise the acoustic performance and assess the ventilation potential. The numerical and experimental results exhibited an overall mean sound reduction of 15 dB within a bandwidth of 380 to 5000 Hz. A good agreement between the measured and numerical results was obtained, with a mean variation of 30%. Therefore, the AMW unit optimised acoustic performance, resulting in a higher noise reduction, especially from 50 to 500 Hz. Finally, most of the AMW unit configurations are suitable for natural ventilation, and a dynamic tuned ventilation capacity can be achieved for particular ranges by adjusting the window's ventilation opening. The proposed designs have potential applications in building acoustics and engineering where natural ventilation and noise mitigation are required to meet regulations simultaneously
Better late than never: on epistemic diagnosability of discrete event systems
No full textWe investigate the diagnosability verification problem in the framework of discrete-event systems. Most of the existing works on this topic assume that faults are related to the internal behaviors of the system such as occurrences of particular events. In this work, motivated by information-flow security considerations, we model faults as some critical information leakages of the system to an intruder, which may have different observations from the system user. Specifically, we say that a fault occurs if the intruder knows that the system has passed by a secret state. We present a formal notion called epistemic diagnosability to capture whether or not the system user can always detect, based on its own observation, the critical information leakage to an intruder within a bounded delay. We show that this new notion subsumes the standard notion of event-based diagnosability. Furthermore, an effective algorithm is provided to verify this new notion
Solid-state stability of Z′ < 1 and Z′ = 2 polymorphs of N,N,N′,N′-tetrabenzylethylenediamine: a combined experimental and theoretical study
No full textThe synthesis and structural analysis by means of single crystal X-ray diffraction (SC-XRD) and DFT calculations, of two additional new polymorphs of the flexible organic molecule N,N,N′,N′-tetrabenzylethylenediamine (L) which is used as first sphere ligand in outer sphere adducts are reported. Slow crystallization of L in the solution-state yields two polymorphs (Lα-phase and Lβ-phase) with Z′ = 0.5, while fast crystallization by rapid cooling from solution and directly from melt, allows a third, less stable polymorph with Z′ = 2 (Lγ-phase). The latter structure can be seen as a low-density metastable phase obtained by trapping L molecules after they reached high mobility by thermal treatment (i.e., high energy state). The three L polymorphs have been also studied using quantum mechanical (QM) calculations specific for the solid state by comparing the sublimation energy for each polymorph, and by comparing the experimental X-ray structures against the optimized structures from DFT, showing that Lβ-phase is the most stable and Lγ-phase is the least stable phase. The high Z′ structure can be considered as a “crystal on the way” of a more stable form. These results provide insights about crystallization mechanisms and polymorphism in organic crystals. The potential use of conformational polymorphs of flexible ligands to prepare second sphere adducts with marked polymorphism is commented
Fatigue failure investigation of thick plate butt-welded joints with incomplete penetration effect
No full textThe objective of this paper was to investigate the fatigue performance of the thick plate structural steel butt-welded joints influenced by its geometrical factors, such as the notch angles, incomplete penetration length, and plate thickness. Utilizing experimental tests, finite element calculations, and analytical models, the fatigue behavior of various weld joint shapes and dimensions was analyzed, and the discrepancy of fatigue strength for different incomplete penetration lengths was evaluated using the nominal stress method. Meanwhile, the local approaches, including notch stress intensity factor (NSIF), averaged strain energy density (SED), effective notch stress (ENS) method, peak stress method (PSM), and implicit gradient effective stress (IGES) method, are employed to assess the fatigue life of thick plate welded joints. According to the results, incomplete penetration ratios in butt-welded joints led to a decrease in fatigue strength. The analytical solutions of butt-welded joints in high cycle regime based on SED results were obtained to estimate the fatigue characteristic values for different plate thickness and incomplete penetration ratios. The proposed equations could illustrate the relationship between the nominal stress and local SED dealing with the variations of incomplete penetration length and geometrical dimensions. Moreover, the results obtained by the analysis of ENS, PSM, and IGES could be deduced by the analytical models to determine the fatigue life of welded joints
Navigating the landscape of global sustainable livelihood research: past insights and future trajectory
No full textSustainable livelihoods (SL) have emerged as a crucial area of focus in global environmental change research, aligning with the Sustainable Development Goals (SDGs). This field is rapidly gaining prominence in sustainability science and has become one of the primary research paradigms. In our study, we conducted scientometrics analysis using the ISI Web of Science core collection database to examine research patterns and frontier areas in SL research. We selected 6441 papers and 265,759 references related to SL published from 1991 to 2020. To achieve this, we employed advanced quantitative analysis tools such as CiteSpace and VOSviewer to quantitatively analyze and visualize the evolution of literature in the SL research field. Our overarching objectives were to understand historical research characteristics, identify the knowledge base, and determine future research trends. The results revealed an exponential increase in SL research documentation since 1991, with the Consortium of International Agricultural Research Center (CGIAR) contributing the highest volume of research documents and citations. Key journals in this field included World Development, Global Environmental Change, Ecological Economics, and Ecology and Society. Notably, Singh RK and Shackleton CM emerged as prolific authors in SL research. Through our analysis, we identified six primary clusters of research areas: livelihoods, conservation, food security, management, climate change, and ecosystem services. Additionally, we found that tags such as rural household, agricultural intensification, cultural intensification, and livelihoods vulnerability remained relevant and represented active research hotspots. By analyzing keyword score relevance, we identified frontier areas in SL research, including mass tourism, solar home systems, artisanal and small-scale mining, forest quality, marine-protected areas, agricultural sustainability, sustainable rangeland management, and indigenous knowledge. These findings provide valuable insights to stakeholders regarding the historical, current, and future trends in SL research, offering strategic opportunities to enhance the sustainability of livelihoods for farmers and rural communities in alignment with the SDGs
Increased nonstationarity of stormflow threshold behaviors in a forested watershed due to abrupt earthquake disturbance
No full textExtreme earthquake disturbances to the vegetation of local and regional landscapes could swiftly impair the former hydrologic function, significantly increasing the challenge of predicting threshold behaviors of rainfall-runoff processes as well as the hydrologic system's complexity over time. It is still unclear how alternating catchment hydrologic behaviors under an ongoing large earthquake disruption are mediated by long-term interactions between landslides and vegetation evolution. In a well-known watershed affected by the Wenchuan earthquake, the nonlinear hydrologic behavior is examined using two thresholds with intervening linear segments. A lower rising threshold (THr) value (210.48ĝmm) observed in post-earthquake local landslide regions exhibited a faster stormflow response rate than that in undisturbed forest and grassland-shrubland regions, easily triggering huge flash-flood disasters. Additionally, an integrated response metric pair (integrated watershed average generation threshold THg-IWA and rising threshold THr-IWA) with areas of disparate land use, ecology, and physiography was proposed and efficiently applied to identify emergent catchment hydrologic behaviors. The interannual variation in the two integrated hydrologic thresholds before and following the earthquake was assessed to detect the temporal nonstationarity in hydrologic extremes and nonlinear runoff response. The year 2011 was an important turning point along the hydrologic disturbance-recovery timescale following the earthquake, as post-earthquake landslide evolution reached a state of extreme heterogeneity in space. At that time, the THr-IWA value decreased by ĝ1/4ĝ9ĝmm compared with the pre-earthquake level. This is closely related to the fast expansion of landslides, leading to a larger extension of variable source area from the channel to neighboring hillslopes, and faster subsurface stormflow, contributing to flash floods. Finally, we present a conceptual model interpreting how the short- and long-term interactions between earthquake-induced landslides and vegetation affect flood hydrographs at event timescale that generated an increased nonstationary hydrologic behavior. This study expands our current knowledge of threshold-based hydrologic and nonstationary stormflow behaviors in response to abrupt earthquake disturbance for the prediction of future flood regimes
Nanoimprint lithography for planar chiral photonic meta-materials
No full textRoom temperature nanoimprint lithography has successfully been applied to the fabrication of planar chiral photonic meta-materials. For dielectric chiral structures a single layer of thick HSQ was used while for metallic chiral structures a bi-layer technique using PMMA/hydrogen silsequioxane (HSQ) was applied. The polarization conversion capabilities of planar chiral structures imprinted in dielectric materials have experimentally been observed. This indicates that the developed processes in this work have the prospect of manufacturing planar photonic meta media in high volume at low cost
Growth Strategy and Physical Properties of the High Mobility P-Type CuI Crystal
No full textAcquiring stable binary wide band-gap semiconductor (WBS) materials with high p-type mobility is essential for the development of WBS optoelectronic devices. CuI is-a p-type WBS material with a large band gap (3.1 eV) and high exciton binding energy (62 meV). However, the semiconductor-characteristics of the CuI single crystal are unknown due to the lack of a large sized and high quality crystal. Our approach focuses on the design of the mineralizer for the hydrothermal method to effectively control the growth habit and the impurity concentration in the crystal. A large size (15 mm x 10 mm x 1 mm) and high quality CuI single crystal is obtained by using a new mineralizer (NH4I + KI). The crystal shows high p-type mobility (43.9 cm(2).V-1.S1-). The strong and sharp band-edge emission at 410 nm indicates that the interband excitonic transition dominates the optical response in the spectrum. Such a binary crystalline material may open the way to new applications in optoelectronic devices
Influence of ac ageing on space charge dynamics in LDPE
No full textPolymeric materials have been widely used as insulation in power industry due to their excellent electrical properties. However, these properties deteriorate in time irreversibly when the material is subjected to electric stress. Although space charge is believed to play an important role in ac ageing, exact mechanisms are poorly understood due to very limited experimental data. In the present work efforts have been made to investigate the influence of ac ageing on space charge dynamics in low-density polyethylene (LDPE). LDPE films with 200mm were aged at 50 kV/mm at 50 Hz for various times at ambient temperature. Space charge dynamics in the samples prior to and after ageing were monitored using the pulsed electroacoustic (PEA) technique under dc electric stress. The results indicate that there is a significant amount of homocharge accumulation in the unaged sample due to charge injection. These injected charges are the captured by the deep traps originated from the interface between crystalline and amorphous regions in LDPE. Ageing under ac condition does not necessarily lead to an increase in amount of charge in the bulk but leads to an increase in mobility of charge carriers. Chemical analysis by infrared spectroscope (FTIR) reveals there are chemical changes taken place in the bulk of the material after ac ageing. It is believed that the chemical changes introduce shallow traps which promote the movement of charge carriers in the bulk. Consequently, the injected charges spread across the sample
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