RF rectifiers for EM power harvesting in a deep brain stimulating device

A passive deep brain stimulation (DBS) device can be equipped with a rectenna, consisting of an antenna and a rectifier, to harvest energy from electromagnetic fields for its operation. This paper presents optimization of radio frequency rectifier circuits for wireless energy harvesting in a passive head-mountable DBS device. The aim is to achieve a compact size, high conversion efficiency, and high output voltage rectifier. Four different rectifiers based on the Delon doubler, Greinacher voltage tripler, Delon voltage quadrupler, and 2-stage charge pumped architectures are designed, simulated, fabricated, and evaluated. The design and simulation are conducted using Agilent Genesys at operating frequency of 915 MHz. A dielectric substrate of FR-4 with thickness of 1.6 mm, and surface mount devices (SMD) components are used to fabricate the designed rectifiers. The performance of the fabricated rectifiers is evaluated using a 915 MHz radio frequency (RF) energy source. The maximum measured conversion efficiency of the Delon doubler, Greinacher tripler, Delon quadrupler, and 2-stage charge pumped rectifiers are 78, 75, 73, and 76 % at -5 dBm input power and for load resistances of 5-15 kΩ. The conversion efficiency of the rectifiers decreases significantly with the increase in the input power level. The Delon doubler rectifier provides the highest efficiency at both -5 and 5 dBm input power levels, whereas the Delon quadrupler rectifier gives the lowest efficiency for the same inputs. By considering both efficiency and DC output voltage, the charge pump rectifier outperforms the other three rectifiers. Accordingly, the optimised 2-stage charge pumped rectifier is used together with an antenna to harvest energy in our DBS device.

Prospects of renewable energy in semi-arid region

Continuous usage of fossil fuels and other conventional resources to meet the growing demand has resulted in in-creased energy crisis and greenhouse gas emissions. Hence, it is essential to use renewable energy sources for more reliable, effective, sustainable and pollution free transmission and distribution networks. Therefore, to facilitate large-scale integration of renewable energy in particular wind and solar photovoltaic (PV) energy, this paper presents the feasibility analysis for semi-arid climate and finds the most suitable places in North East region of Victoria for re-newable energy generation. For economic and environmental analysis, Hybrid Optimization Model for Electric Re-newables (HOMER) has used to investigate the prospects of wind and solar energy considering the Net Present Cost (NPC), Cost of Energy (COE) and Renewable fraction (RF). Six locations are selected from North East region of Victo-ria and simulations are performed. From the feasibility analysis, it can be concluded that Mount Hotham is one of the most suitable locations for wind energy generation while Wangaratta is the most suitable location for solar energy generation. Mount Hotham is also the best suitable locations in North East region for hybrid power systems i.e., com-bination of both wind and solar energy generation.

Lipid abundance in zebrafish embryos is regulated by complementary actions of the endocannabinoid system and retinoic acid pathway

The endocannabinoid system (ECS) and retinoic acid (RA) signaling have been associated with influencing lipid metabolism. We hypothesized that modulation of these pathways could modify lipid abundance in developing vertebrates and that these pathways could have a combinatorial effect on lipid levels. Zebrafish embryos were exposed to chemical treatments altering the activity of the ECS and RA pathway. Embryos were stained with the neutral lipid dye Oil-Red-O (ORO) and underwent whole-mount in situ hybridization. Mouse 3T3-L1 fibroblasts were differentiated under exposure to RA modulating chemicals and subsequently stained with ORO and analyzed for gene expression by qRT-PCR. ECS activation and RA exposure increased lipid abundance and the expression of lipoprotein lipase. Additionally, RA treatment increased expression of CCAAT/enhancer binding protein alpha. Both ECS receptors and RA receptor subtypes were separately involved in modulating lipid abundance. Finally, increased ECS or RA activity ameliorated the reduced lipid abundance caused by peroxisome proliferator-activated receptor gamma (PPARγ) inhibition. Therefore, the ECS and RA pathway influence lipid abundance in zebrafish embryos and have an additive effect when treated simultaneously. Furthermore, we demonstrated that these pathways act downstream or independently of PPARγ to influence lipid levels. Our study shows for the first time that the RA and ECS pathways have additive function in lipid abundance during vertebrate development.

Short note on the possible occurrence of heat stress in roosting waders on the Banc d'Arguin, Mauritania

The temperature at the Banc d'Arguin can be very high, and may cause problems of heat regulation in waders originating from the Arctic or Antarctic. A formalin-fixed bar-tailed godwit Limosa lapponica mount exposed to the sun had a temperature of 45°C. The temperature of the mount was higher when placed in a lying position than when it was placed upright. Nevertheless observed bar-tailed godwits, dunlins Calidris alpina and Kentish plovers Charadrius alexandrinus in the high water roost were often lying on the hot sand, and most birds avoided contact with humid (cold) substrates. Only the dunlins stood in the water with their bill tucked under the scapular wing feathers. This behavioral trait is thought to conserve heat, and is also observed in the other bird species in the roosts. Heat stress is apparently not a problem for birds awaiting low tide. -M.Dean

The sexual motivation of boars housed adjacent to ovariectomised gilts did not affect the efficiency of detecting hormonally induced oestrus using the back pressure test

This study tested the hypothesis that the efficiency of detecting oestrus in gilts, using the back pressure test (BPT), will be reduced when gilts are housed adjacent to a boar of high sexual motivation compared to when gilts are housed adjacent to a boar of low sexual motivation. The experiment was a 2 x 2 Latin square design with three replicates. Boars of high and low sexual motivation were selected on the basis of the total number of copulations and the mean reaction time to first mount during three mating tests. Twelve boars were observed in mating tests and the three highest and lowest ranking boars were assigned to three palm, each pair containing a boar of high and a boar of low sexual motivation. One pair was used in each replicate. In each replicate, two groups of six ovariectomised gilts were housed for 14 days, commencing 7 days prior to hormonally induced destrus, adjacent to a boar of either high or low sexual motivation. All gilts were checked twice daily for oestrus using the BPT. In the first replicate, the level of proceptive behaviour of the gilts was quantified immediately after checking for oestrus in a 3-rain test in which the amount of time that the gilts spent within 0.5 m of a pen containing a sexually mature boar was recorded. There were no effects of housing gilts adjacent to boars of high or low sexual motivation on the percentage of gilts detected in oestrus, the percentage of gilts detected in oestrus for more than I day, the duration of oestrus or the level of proceptive behaviour of gilts. These data suggest that the level of sexual motivation of boars does not influence the efficiency of detecting hormonally induced oestrus, using the BPT, in ovariectomised gilts housed adjacent to boars.