The effects of posture on suspension seat transmissibility during exposure to vertical whole-body vibration

Suspension seat is used in the off-road condition to attenuate excessive vibration exposed to the human body. The efficiency of a seat reducing vibration not only depends on the dynamic characteristics of the seat, but the dynamic characteristics of human body and the characteristics of the input vibration as well. Tractor drivers adopted different postures during their farm work activities, which may influence the dynamic characteristics of the human body. However, the influenced of the driver’s posture on suspension seat transmissibility has received less systematic attention. Thus, this study is carried out with the objective to investigate the effect of different postures on seat transmissibility when seated on a suspension seat. Three male subjects were exposed to random vibration at 2.0 m/s2 r.m.s with frequency ranging from 1-20 Hz, while seated on a vibration simulator for 60 seconds. The subjects adopted four seating postures: (i) relaxed, (ii) slouched, (iii) tensed and (iv) with backrest support. The study found that relaxed and slouched postures have a resonance frequency at 2.0 Hz. However, as the posture changed to backrest support, the resonance frequency of the seat transmissibility slightly increased by 0.25 Hz. This study suggested that changing the postures caused changes in the dynamics of human body, and thus affected the suspension seat transmissibility. It is concluded that, non-linearity in suspension seat transmissibility is influenced by the changes of body postures

Perturbation effect of noise on overall feeling of discomfort from vertical whole-body vibration in vibro-acoustic environment

The human discomfort from combined noise and vibration has been investigated with a new perspective. The concept in perturbation effect has been adopted to formulate a new novel predictive model of human discomfort from noise and vibration. A psycho-physics experiment has been designed to identify the perturbation effect which caused by noise stimulus. The subject was asked to be seated in a relaxed position, holding a handphone and used it to record all the response values after each stimulation. The finding suggested that the discomfort from vibration can be predicted with equation and the overall discomfort from noise and vibration is given by where the is the perturbation effect caused by noise stimulus

Effects Of Three-Step Magnesium Doping In p-GaN Layer On The Properties Of InGaN Based Light Emitting Diode

In this works, indium gallium nitride (InGaN) based light emitting diode (LED) was grown on a 4-inch c-plane patterned sapphire substrate using metal-organic chemical vapor deposition. Three-step magnesium (Mg) doping profile was proposed to enhance the efficiency of the LED and the attention was paid to the effects of the Mg doping concentration of the second p-GaN layer. The Mg doping levels were varied by changing the flow rates of bis-cyclopentadienyl magnesium (Cp2Mg), i.e., 150, 250, and 300 sccm. To assess the electrical, crystallographic, and optical properties of the InGaN-based LEDs, various characterization tools were used. The results showed that, the hole concentration was affected by Cp2Mg flow rate. For the light output power, it was found that LEDs with low and high hole concentration exhibit lower output power due to low conductivity and low mobility. Apart from that, it was also found that the light emission of the LED wavelength, redshifted as the hole concentration increases. Through this study, it can be deduced that the hole concentration of the second p-GaN layer has a signifcant effect on the performance of the LED

Effects Of Three-Step Magnesium Doping In p-GaN Layer On The Properties Of InGaN Based Light Emitting Diode

In this works, indium gallium nitride (InGaN) based light emitting diode (LED) was grown on a 4-inch c-plane patterned sapphire substrate using metal-organic chemical vapor deposition. Three-step magnesium (Mg) doping profile was proposed to enhance the efficiency of the LED and the attention was paid to the effects of the Mg doping concentration of the second p-GaN layer. The Mg doping levels were varied by changing the flow rates of bis-cyclopentadienyl magnesium (Cp2Mg), i.e., 150, 250, and 300 sccm. To assess the electrical, crystallographic, and optical properties of the InGaN-based LEDs, various characterization tools were used. The results showed that, the hole concentration was affected by Cp2Mg flow rate. For the light output power, it was found that LEDs with low and high hole concentration exhibit lower output power due to low conductivity and low mobility. Apart from that, it was also found that the light emission of the LED wavelength, redshifted as the hole concentration increases. Through this study, it can be deduced that the hole concentration of the second p-GaN layer has a signifcant effect on the performance of the LED

Development Of InGan Based Thin Film Solar Cells Present Status And Challenges

The Indium Gallium Nitride (InGaN) alloy has the required potentialities to be a material of choice used in the next generation high efficiency solar cells. Indeed, the mere change in its Indium composition allows its absorption to cover the whole solar spectrum. The other main advantages of InGaN, in addition to its tunable bandgap, are a high absorption coefficient, a high stability and radiation tolerance. However, challenging issues remain to address: (i) the difficulty to elaborate sufficiently thick monocrystalline InGaN layers with a high Indium content; (ii) the high defects density and the spontaneous and piezoelectric polarizations; (iii) the p-doping which remains difficult to master. A review of this promising technology for solar cells is provided and present challenges and future perspectives are presented, including the use of InGaN multijunction structures and a new InGaN Schottky Based Solar Cells (SBSC) structure

Mathematical model of suspension seat-person exposed to vertical vibration for off-road vehicles

Off-road drivers are exposed to a high magnitude of vibration at low frequency (0.5-25Hz), that can cause harm and possibly attribute to musculoskeletal disorder, particularly low-back pain. The suspension seat is commonly used on an off-road condition to isolate the vibration transmitted to the human body. Nevertheless, the suspension seat modelling that incorporates the human body is still scarce. The objective of this study is to develop a mathematical modelling to represent the suspension seat-person for off-road vehicles. This paper presents a three degrees-of-freedom lumped parameter model. A curve-fitting method is used for parameter identification, which includes the constraint variable function (fmincon()) from the optimisation toolbox of MATLAB(R2017a). The model parameters are optimised using experimentally measured of suspension seat transmissibility. It was found that the model provides a reasonable fit to the measured suspension seat transmissibility at the first peak of resonance frequency, around 2-3 Hz. The results of the study suggested that the human body forms a coupled system with the suspension seat and thus affects the overall performance of the suspension system. As a conclusion, the influence of the human body should not be ignored in the modelling, and a three-degrees degree-of-freedom lumped parameter model provides a better prediction of suspension seat transmissibility. This proposed model is recommended to predict vibration transmissibility for off-road suspension seat

Development of vibration test system to measure human biodynamic responses to hand-transmitted vibration (HTV)

Workers commonly experience hand-transmitted vibrations (HTV) especially in industries involving power tools. Vibration exposure will differ by individuals where prolonged and unmonitored exposure can lead to the development of symptoms known as hand arm vibration syndrome (HAVS). A deep understanding of human response to HTV is required to provide feasible solutions to lessen its adverse effects. Research has been extensively conducted on exploring the vibration transmission to the hand-arm system. However, there is limited study on the effects of handles mounted on a damping material or suspension systems. The objective of this study is to develop a vibration test system to measure the human biodynamic response to hand-transmitted vibration. Engineering design theory were used to formulate the essential design requirements of the system. The evaluation and selection of concepts were done. The design was modelled, and frequency analysis was performed using Computer-Aided Engineering (CAE) software. The frequency analysis results showed the first 10 modes in the frequency range of 1320 – 5088 Hz and therefore will not have resonance issues in the 25 – 1250 Hz frequency excitation range as per requirement. The prototype design was shown to comply with the product design specification and final detail design drawings were approved for fabrication. In conclusion, an instrumented handle with a modular expansion slot had been appropriately designed to measure human biodynamic responses due to hand-transmitted vibration

Inhomogeneity Of An InGaN Based Blue Led Studied By Secondary Ion Mass Spectrometry (SIMS) And Atom Probe Tomography (APT)

InGaN/GaN multiquantum wells (MQWs) grown on 2-inch c-plane patterned sapphire substrate using metal-organic chemical vapor deposition was characterized by secondary ion mass spectrometry and atom probe tomography. The average In mole fraction by APT was found to be around 16% in the InGaN well which is consistent with SIMS analysis. SIMS analysis was also performed to analyze the In distribution in the InGaN well layer, where the results were found to be nonuniform in the InGaN active layer, as opposed to the results obtained from APT measurement. Further from SIMS measurement, the upper interfaces of the QWs were slightly more diffused than the lower interfaces. Meanwhile, APT measurement showed In clustering or In rich regions based on different color distributions, indicating different In concentration. The results of APT and SIMS for average In mole fracrtion were validated by XRD measurement

Risk Factors, Radiological and Clinical Outcomes in Subclinical and Clinical Pituitary Apoplexy

Necrosis; Neurosurgery; Pituitary apoplexyNecrosis; Neurocirugía; Apoplejía de la hipófisisNecrosi; Neurocirurgia; Apoplexia de la hipòfisiBackground: Pituitary apoplexy (PA) can be symptomatic, namely acute apoplexy (APA), or asymptomatic or subclinical (SPA). Objective: To describe the clinical characteristics and evolution of the patients with APA compared to SPA Patients and methods: Retrospective, longitudinal database analysis. Results: We identified 58 patients with PA, and 37 accomplished the inclusion criteria (17 men, median age 47.7 years). A total of 29 (78.4%) had APA (17 underwent surgery, and 12 were conservatively managed), and 8 (21.6%) had SPA. The presence of non-functioning pituitary adenoma (NFPA) odds ratio (OR): 29.36 (95% confidence interval (CI): 1.86–462.36) and the largest size OR 1.10 (95% CI: 1.01–1.2) elevated the risk of having surgery. Hypopituitarism developed in 35.1% without significant differences between APA and SPA. In non-surgical patients, adenoma volume shrunk spontaneously at one year magnetic resonance imaging (MRI), without statistical differences between the conservatively treated and SPA group. Conclusions: APA is more frequent in larger NFPAs, and this subset of patients has a higher risk of surgery. Hypopituitarism is quite frequent even in patients with SPA, and, therefore, long-term follow-up is mandatory. In the non-surgical group, the pituitary tumour shrinkage is clinically relevant after one year of PA. Consequently, surgery indication in NFPA should be delayed and reassessed if patients remain asymptomatic