Experimental Analysis to Evaluate the Effect of Dynamic Absorber / M. Azhan Anuar...[et al.]

Passive Dynamic Absorber (PDA) is a mechanical device used to tackle unwanted vibration resonance within the operational frequency of the system. Theoretically, resonance can be avoided if the excitation (operating) frequency is far away from the natural frequencies of the structures. Hence, it is important to identify the structural natural frequencies, to ensure this condition did not occur. In this study, an experimental main system is designed and fabricated and then, tested using Operational Modal Analysis (OMA) to obtain the natural frequency. PDAs are developed based on Dunkley Method (DM) and Randy Fox Method (RFM) and applied to the main vibrating system. Frequency Response Function (FRF) for both models is obtained using OMA and its effectiveness is evaluated. It is shown that the PDA reduces the magnitude of FRF of the main system at the selected resonance frequency and splitting it into two new resonance frequencies. Hence, it can be predicted that the vibration can be effectively suppressed at a specific frequency when the PDA is attached to the main system. This study enables verification of the effectiveness of dynamic absorber to tackle resonance problem. In future, these results will be helpful to evaluate the performance of PDA based on DM and RFM methods

Performance Evaluation of Dynamic Absorbers Based on Randy Fox and Dunkerley Methods / Syafirah A. Samat ...[et al.]

Dynamic Absorber (DA) application is the method used to avoid resonance in a vibrating system. In practice, many types of DA are utilized such as active and passive DA and it depends on the cost and environmental conditions. Designers/ engineers select DA parameters and model the absorber before it is implemented and tested to the main system. Hence, it will be beneficial to have tools or templates for fast and effective selection of DA. This paper will discuss the selection parameters of a passive DA based on templates derived from Dunkerley Method (DM) and Randy Fox Method (RFM) and its accuracy is verified experimentally. It is observed that in this case, DA has reduced the vibration amplitude significantly. Furthermore, the results show the RFM absorber has performed better than the DM absorber. This study enables verification of the effectiveness of DA to tackle resonant problems. In the future, these GUI templates could be helpful for industrial application with vibrating problems

Luminescence spectra of TeO ₂-PbO-Li ₂O doped Nd ₂O ₃ glass

A tellurite glass of TeO 2-PbO-Li 2O doped with Nd 2O 3 has been successfully fabricated by using the conventional melt-quenched technique. The absorption and emission spectroscopy have been identified using UV-VIS-NIR and photoluminescence spectrometer, respectively. From the spectroscopy, ten significant spectra have been observed in the region of 400-900 nm. The absorption wavelength centered at 585 nm attributed to 4I 9/2 → 4G 5/2 transition is the predominant wavelength to be used as the excitation wavelength. Emission spectra have been determined by using 585 nm excitation wavelength at room temperature. From the emission spectra, seven distinctive upconversion bands contributed from Nd 3+ were observed in the region of 400-1500 nm. It was found that the bands were centered at 450 nm ( 4G 11/2 → 4I 9/2), 485 nm ( 4G 11/2 → 4I 11/2), 605 nm ( 4G 11/2 → 4I 15/2), 665 nm ( 4G 7/2 → 4I 13/2), 880 nm ( 4F 3/2 → 4I 9/2), 1062 nm ( 4F 3/2 → 4I 11/2) and 1340 nm ( 4F 3/2 → 4I 11/2), respectively. These emission bands showed the possibility of visible and near infrared emission spectra

Blocked, delayed, or obstructed: What causes poor white matter development in intrauterine growth restricted infants?

Poor white matter development in intrauterine growth restricted (IUGR) babies remains a major, untreated problem in neonatology. New therapies, guided by an understanding of the mechanisms that underlie normal and abnormal oligodendrocyte development and myelin formation, are required. Much of our knowledge of the mechanisms that underlie impaired myelination come from studies in adult demyelinating disease, preterm brain injury, or experimental models of hypoxia-ischemia. However, relatively less is known for IUGR which is surprising because IUGR is a leading cause of perinatal mortality and morbidity, second only to premature birth. IUGR is also a significant risk factor for the later development of cerebral palsy, and is a greater risk compared to some of the more traditionally researched antecedents - asphyxia and inflammation. Recent evidence suggests that the white matter injury and reduced myelination in the brains of some preterm babies is due to impaired maturation of oligodendrocytes thereby resulting in the reduced capacity to synthesize myelin. Therefore, it is not surprising that the hypomyelination observable in the central nervous system of IUGR infants has similarly lead to investigations identifying a delay or blockade in the progress of maturation of oligodendrocytes in these infants. This review will discuss current ideas thought to account for the poor myelination often present in the neonate's brain following IUGR, and discuss novel interventions that are promising as treatments that promote oligodendrocyte maturation, and thereby repair the myelination deficits that otherwise persist into infancy and childhood and lead to neurodevelopmental abnormalities

Human amnion epithelial cells modulate ventilation-induced white matter pathology in preterm lambs

Background: Preterm infants can be inadvertently exposed to high tidal volumes (VT) during resuscitation in the delivery room due to limitations of available equipment. High VT ventilation of preterm lambs produces cerebral white matter (WM) pathology similar to that observed in preterm infants who develop cerebral palsy. We hypothesized that human amnion epithelial cells (hAECs), which have anti-inflammatory and regenerative properties, would reduce ventilation-induced WM pathology in neonatal late preterm lamb brains. Methods: Two groups of lambs (0.85 gestation) were used, as follows: (1) ventilated lambs (Vent; n = 8) were ventilated using a protocol that induces injury (VT targeting 15 ml/kg for 15 min, with no positive end-expiratory pressure) and were then maintained for another 105 min, and (2) ventilated + hAECs lambs (Vent+hAECs; n = 7) were similarly ventilated but received intravenous and intratracheal administration of 9 × 107 hAECs (18 × 107 hAECs total) at birth. Oxygenation and ventilation parameters were monitored in real time; cerebral oxygenation was measured using near-infrared spectroscopy. qPCR (quantitative real-time PCR) and immunohistochemistry were used to assess inflammation, vascular leakage and astrogliosis in both the periventricular and subcortical WM of the frontal and parietal lobes. An unventilated control group (UVC; n = 5) was also used for qPCR analysis of gene expression. Two-way repeated measures ANOVA was used to compare physiological data. Student's t test and one-way ANOVA were used for immunohistological and qPCR data comparisons, respectively. Results: Respiratory parameters were not different between groups. Interleukin (IL)-6 mRNA levels in subcortical WM were lower in the Vent+hAECs group than the Vent group (p = 0.028). IL-1β and IL-6 mRNA levels in periventricular WM were higher in the Vent+hAECs group than the Vent group (p = 0.007 and p = 0.001, respectively). The density of Iba-1-positive microglia was lower in the subcortical WM of the parietal lobes (p = 0.010) in the Vent+hAECs group but not in the periventricular WM. The number of vessels in the WM of the parietal lobe exhibiting protein extravasation was lower (p = 0.046) in the Vent+hAECs group. Claudin-1 mRNA levels were higher in the periventricular WM (p = 0.005). The density of GFAP-positive astrocytes was not different between groups. Conclusions: Administration of hAECs at the time of birth alters the effects of injurious ventilation on the preterm neonatal brain. Further studies are required to understand the regional differences in the effects of hAECs on ventilation-induced WM pathology and their net effect on the developing brain

The optical properties of trivalent rare earth ions (Er3+) doped borotellurite glass

Erbium doped borotellurite glass has been fabricated by using conventional melting method. The density and molar volume have been calculated and analyzed while their optical properties were studied by measuring the optical absorption and luminescence spectra at room temperature. From the XRD results, since the patterns do not exhibit any diffraction line thus it confirms their amorphous nature. It is found that the density of the glass samples increased and the molar volume decreased with respect to Er ions content. Meanwhile, the upconversion emissions centered at 487, 523, 558, 642, 695 and 782 nm have been observed under the 650 nm excitation in the 4F9/2 level. Some other results will be analysed and discussed in details

Dopamine treatment during acute hypoxia is neuroprotective in the developing sheep brain

Dopamine is often used to treat hypotension in preterm infants; these infants are at risk of developing brain injury due to impaired autoregulation and cerebral hypoperfusion. However the effects of dopamine on the immature brain under conditions of cerebral hypoxia are not known. We hypothesized that pretreatment with dopamine would protect the immature brain from injury caused by cerebral hypoxia. Preterm fetal sheep were used to determine the effects of intravenous dopamine on hypoxia-induced brain injury. In 16 pregnant sheep at 90 days of gestation (0.6 of term, term = 147 days) catheters were implanted aseptically into the fetal carotid artery and jugular vein; an inflatable occluder was placed loosely around the umbilical cord for later induction of fetal hypoxemia. At 5 days after surgery, dopamine (10 μg/kg/min, n = 7 fetuses) or saline (n = 9 fetuses) was infused for 74 h. Two hours after commencing the dopamine/saline infusion, we induced umbilical cord occlusion (UCO) for up to 25 min to produce fetal asphyxia. Fetuses were allowed to recover, and brains were collected 72 h later for assessment of neuropathology. Un-operated twin fetuses were used as age-matched non-UCO controls (n = 8). In UCO + saline fetuses, microglial and apoptotic cell density in the subcortical and periventricular white matter, caudate nucleus and hippocampus was greater than that in age-matched controls; oxidative stress was elevated in the subcortical and periventricular white matter and caudate nucleus compared to that in age-matched controls. In UCO + dopamine fetuses microglial density and oxidative stress in the cerebral white matter and caudate nucleus were not different to that of age-matched controls. Apoptotic cell death was decreased in the cerebral white matter of UCO + dopamine brains, relative to UCO + saline brains. We conclude that pretreatment with dopamine does not exacerbate hypoxia-induced injury in the immature brain and may be neuroprotective because it led to decreased apoptosis, oxidative stress and neuroinflammation in the cerebral white matter and decreased neuroinflammation in the caudate nucleus

Development of physical intrusion detection system using wi-fi/zigbee RF signals

Wi-Fi is a wireless networking technology that enables computers and other devices to communicate using a RF signal enabling a lot of advanced applications to provide services. Nowadays, Wi-Fi signal coverage is almost a must in any office building or small office home office (SOHO) environment. Home and office networking concept involves the use of wireless sensors/Wi-Fi routers around the house to control and detect signals in the home-setting. In this project, however, RF signals from Wi-Fi NIC and ZigBee motes received signal strength indicators (RSSI) were used as a base feed to our system testbed to detect the human presence inside an indoor home/office environment. Then, a controller is used to switch ON/OFF appliances like air conditioning, lights …etc. The system testbed doubles as a reliable alarm for physical intrusion detection to secure an indoor perimeter as demonstrated in the paper. This simple, yet cheap, approach to home/office networking promises to save energy and cost in large numbers. It can also be used in many industrial settings including control and security applications