176,467 research outputs found
A Systematic Review of Mosquito Coils and Passive Emanators: Defining Recommendations for Spatial Repellency Testing Methodologies.
No full textMosquito coils, vaporizer mats and emanators confer protection against mosquito bites through the spatial action of emanated vapor or airborne pyrethroid particles. These products dominate the pest control market; therefore, it is vital to characterize mosquito responses elicited by the chemical actives and their potential for disease prevention. The aim of this review was to determine effects of mosquito coils and emanators on mosquito responses that reduce human-vector contact and to propose scientific consensus on terminologies and methodologies used for evaluation of product formats that could contain spatial chemical actives, including indoor residual spraying (IRS), long lasting insecticide treated nets (LLINs) and insecticide treated materials (ITMs). PubMed, (National Centre for Biotechnology Information (NCBI), U.S. National Library of Medicine, NIH), MEDLINE, LILAC, Cochrane library, IBECS and Armed Forces Pest Management Board Literature Retrieval System search engines were used to identify studies of pyrethroid based coils and emanators with key-words "Mosquito coils" "Mosquito emanators" and "Spatial repellents". It was concluded that there is need to improve statistical reporting of studies, and reach consensus in the methodologies and terminologies used through standardized testing guidelines. Despite differing evaluation methodologies, data showed that coils and emanators induce mortality, deterrence, repellency as well as reduce the ability of mosquitoes to feed on humans. Available data on efficacy outdoors, dose-response relationships and effective distance of coils and emanators is inadequate for developing a target product profile (TPP), which will be required for such chemicals before optimized implementation can occur for maximum benefits in disease control
A household randomized, controlled trial of the efficacy of 0.03% transfluthrin coils alone and in combination with long-lasting insecticidal nets on the incidence of Plasmodium falciparum and Plasmodium vivax malaria in Western Yunnan Province, China
No full textMosquito coils are the most commonly used household insecticidal product in the world with sales exceeding 50 billion coils, used by two billion people worldwide annually. Despite strong evidence that coils prevent mosquito bites a systematic review concluded that there is no evidence that burning mosquito coils prevents malaria acquisition. Therefore, the current trial was designed to measure and compare prevention of malaria infection by mosquito coils or long-lasting insecticidal net (LLIN) or a combination of the two in Yunnan, China in the Greater Mekong sub-region.; A four-arm single blind household-randomized design was chosen as coils emanate insecticide throughout the household. Households enrolled at baseline were randomly allocated by the lottery method to one of the four intervention arms: (i) nothing, (ii) 0.03% transfluthrin coils alone, (iii) deltamethrin long-lasting insecticide treated nets, (LLINs) alone or (iv) a combination of transfluthrin coils and deltamethrin LLINs. All household members were recruited to the study, with only those households excluded with pregnant or breastfeeding mothers, members with chest complaints or allergies or members that regularly slept away from home. The main outcome of interest was Plasmodium falciparum malaria prevalence detected by rapid diagnostic tests (RDTs) during six repeated monthly cross-sectional surveys. The secondary outcome of interest was the effect on Plasmodium vivax prevalence detected in the same way.; A total of 2,052 households were recruited into the study, comprising 7,341 individuals The odds ratios of testing positive by RDT with P. falciparum or P. vivax were <75% lower for all intervention arms compared with the control arm. Coils alone provided 77% protection (95% CI: 50%-89%), LLINs provided 91% protection (95% CI: 72%-97%) and the combination of coils and LLINs provided 94% protection (95% CI: 77%-99%) against P. falciparum compared with the control arm. There was no statistically significant difference between the protective efficacies of the different interventions.; This is the first robust clinical evaluation of transfluthrin mosquito coils as a means to reduce malaria and the high degree of infection prevented would indicate they represent a potentially highly effective tool, which could be integrated into larger vector control programmes.; ClinicalTrials.gov Identifier: NCT00442442, March 2007
Multi-component strain development in superconducting magnet coils monitored using fibre Bragg grating sensors fabricated in highly linearly birefringent fibre
No full textThe commissioning of superconducting magnet coils was monitored using embedded optical fibre Bragg grating sensors (FBG) fabricated in highly linearly birefringent (HiBi) fibre. The HiBi FBG sensors monitored the internal strain developed in the coils during the energization of the coils. The development of multiple components of strain in the coils when the magnet was energized and quenched was monitored, revealing phenomena that it had not been previously possible to measure using other sensor technologies
The development of high field magnets utilizing Bi-2212 wind & react insert coils
No full textWind & react Bi-2212 inserts have been manufactured and tested inside a wide-bore NbTi-Nb3Sn magnet providing a background field up to 20T at 4.2K. A pair of six-layer concentric coils both achieved critical currents of 350 A (JE = 200 A/mm2) in a 20T background field. A thicker 14-layer insert made from 119m of round wire had a critical quench current IQ of 287A (JE = 162 A/mm2) at the same field and contributed to a combined central field of 22.5 T. This is a record for a fully superconducting magnet at 4.2 K. The 14-layer coil, equipped with an external protective shunt, was used for an extensive series of quench measurements and endured >150 quenches without damage. Minimum quench energies were found to be in the range of 200-500mJ in background fields of 15-20T when the coil carried 70-95% of its critical quench current
Field Evaluation of the Bio-Efficacy of Three Pyrethroid Based Coils against Wild Populations of Anthropophilic Mosquitoes in Northern Tanzania.
No full textThis study aims to assess the feeding inhibition and repellency effect of three brands of mosquito coils in experimental huts (East African design). Evaluated products were all pyrethroid-based mosquito coils-Kiboko(R), Total(R) and Risasi(R). Mosfly (0.1% D-allethrin) was a positive control. Indoor resting behavior, feeding inhibition and induced exophily were measured as responses of burnt coil smoke in huts. Resting mosquitoes were collected inside the huts, in window traps and verandah traps using mechanical aspirators. Identified to species level and sex. A total of 1460 mosquitoes were collected, 58.9% (n=860) were Anopheles gambiae s.l while 41.1% (n=600) Culex quinquefasciatus. Indoor resting mosquitoes in all treated huts were significantly reduced than in negative control (DF=4, F=18.6, P < 0.001). Species found to rest indoors were not statistical different between the positive control (Mosfly coil) and other three treated huts (DF=3, F=1.068, P=0.408). Cx.quinquefasciatus had significantly higher induced exophily in all treatments comparing to An.gambiae s./ (DF=1, F=5.34, P=0.050). Comparison between species (An.gambiae s.l and Cx. quinquefasciatus) for the feeding inhibition among treated huts was not statistically significant (DF=1, F=0.062, P=0.810). Introduction of several personal protection measures will be ideal to supplement the existing gap in reducing the man vector contacts hence lowering the disease transmission
The mode of action of spatial repellents and their impact on vectorial capacity of Anopheles gambiae sensu stricto.
No full textMalaria vector control relies on toxicity of insecticides used in long lasting insecticide treated nets and indoor residual spraying. This is despite evidence that sub-lethal insecticides reduce human-vector contact and malaria transmission. The impact of sub-lethal insecticides on host seeking and blood feeding of mosquitoes was measured. Taxis boxes distinguished between repellency and attraction inhibition of mosquitoes by measuring response of mosquitoes towards or away from Transfluthrin coils and humans. Protective effective distance of coils and long-term effects on blood feeding were measured in the semi-field tunnel and in a Peet Grady chamber. Laboratory reared pyrethroid susceptible Anopheles gambiae sensu stricto mosquitoes were used. In the taxis boxes, a higher proportion of mosquitoes (67%-82%) were activated and flew towards the human in the presence of Transfluthrin coils. Coils did not hinder attraction of mosquitoes to the human. In the semi-field Tunnel, coils placed 0.3 m from the human reduced feeding by 86% (95% CI [0.66; 0.95]) when used as a "bubble" compared to 65% (95% CI [0.51; 0.76]) when used as a "point source". Mosquitoes exposed to coils inside a Peet Grady chamber were delayed from feeding normally for 12 hours but there was no effect on free flying and caged mosquitoes exposed in the semi-field tunnel. These findings indicate that airborne pyrethroids minimize human-vector contact through reduced and delayed blood feeding. This information is useful for the development of target product profiles of spatial repellent products that can be used to complement mainstream malaria vector control tools
Role of the C-terminal domain in the structure and function of tetrameric sodium channels
No full textVoltage-gated sodium channels have essential roles in electrical signalling. Prokaryotic sodium channels are tetramers consisting of transmembrane (TM) voltage-sensing and pore domains, and a cytoplasmic carboxy-terminal domain. Previous crystal structures of bacterial sodium channels revealed the nature of their TM domains but not their C-terminal domains (CTDs). Here, using electron paramagnetic resonance (EPR) spectroscopy combined with molecular dynamics, we show that the CTD of the NavMs channel from Magnetococcus marinus includes a flexible region linking the TM domains to a four-helix coiled-coil bundle. A 2.9 Å resolution crystal structure of the NavMs pore indicates the position of the CTD, which is consistent with the EPR-derived structure. Functional analyses demonstrate that the coiled-coil domain couples inactivation with channel opening, and is enabled by negatively charged residues in the linker region. A mechanism for gating is proposed based on the structure, whereby splaying of the bottom of the pore is possible without requiring unravelling of the coiled-coil
An Experimental Hut Study to Quantify the Effect of DDT and Airborne Pyrethroids on Entomological Parameters of Malaria Transmission.
No full textCurrent malaria vector control programmes rely on insecticides with rapid contact toxicity. However, spatial repellents can also be applied to reduce man-vector contact, which might ultimately impact malaria transmission. The aim of this study was to quantify effects of airborne pyrethroids from coils and DDT used an indoor residual spray (IRS) on entomological parameters that influence malaria transmission. The effect of Transfluthrin and Metofluthrin coils compared to DDT on house entry, exit and indoor feeding behaviour of Anopheles gambiae sensu lato were measured in experimental huts in the field and in the semi-field. Outcomes were deterrence - reduction in house entry of mosquitoes; irritancy or excito-repellency - induced premature exit of mosquitoes; blood feeding inhibition and effect on mosquito fecundity. Transfluthrin coils, Metofluthrin coils and DDT reduced human vector contact through deterrence by 38%, 30% and 8%, respectively and induced half of the mosquitoes to leave huts before feeding (56%, 55% and 48%, respectively). Almost all mosquitoes inside huts with Metofluthrin and Transfluthrin coils and more than three quarters of mosquitoes in the DDT hut did not feed, almost none laid eggs and 67%, 72% and 70% of all mosquitoes collected from Transfluthrin, Metofluthrin and DDT huts, respectively had died after 24 hours. This study highlights that airborne pyrethroids and DDT affect a range of anopheline mosquito behaviours that are important parameters in malaria transmission, namely deterrence, irritancy/excito-repellency and blood-feeding inhibition. These effects are in addition to significant toxicity and reduced mosquito fecundity that affect mosquito densities and, therefore, provide community protection against diseases for both users and non-users. Airborne insecticides and freshly applied DDT had similar effects on deterrence, irritancy and feeding inhibition. Therefore, it is suggested that airborne pyrethroids, if delivered in suitable formats, may complement existing mainstream vector control tools
Frosting Performance of Fin-and-Tube Evaporators with Small Copper Tubes Diameter
No full textIn modern heat pump systems, the heat exchangers use enhanced heat transfer surfaces for both air and refrigerant sides. In air conditioning applications, conventional 9.5 mm (3/8 inch) tube diameter fin-and-tube coils are slowly being replaced by microchannel heat exchangers. However, during heating mode the energy performance of heat pump systems with microchannel outdoor coils are generally lower than those of fin-and-tube direct-expansion evaporators due to a higher frequency of defrost cycles. A different approach might be to utilize fin-and-tube technology, which has proven records of excellent water drainage characteristics and good performance in frosting operating conditions, and enhance the air side heat transfer rates by introducing a larger number of small diameter copper tubes. In this paper, six fin-and-tube coils with copper tube diameter ranging from 5 mm (1/5 inch) to 7mm (8/29 inch) were experimentally investigated in frosting operating conditions. The laboratory experiments were conducted in an air flow wind tunnel at Oklahoma State University. Experimental data on heat transfer rate and air-side pressure drop across the coils were measured and the fin density and the tube diameter were varied in a parametric fashion during the experimental campaign. The performance of the fin-and-tube coils were also compared to those of a conventional 9.5 mm copper tube diameter fin-and-tube heat exchanger and of a microchannel heat exchanger that had similar air-side frontal area and at similar operating conditions of outdoor direct-expansion evaporators in heat pump systems for residential applications. The trends of the data during frosting operation suggested that reducing the tube diameter was beneficial for frosting performance at low fin density while was harmful at high fin density. The data showed that increasing the fin density increased the capacity but significantly reduced the time for heating service for the evaporator. Small copper tube diameter resulted in about 11% higher initial capacity at dry start conditions and about 4% higher average integrated capacity when considering the entire frost period. The data discussed in this paper serve as basis for future research on direct-expansion evaporators for air-source heat pump applications, in which the frosting of the outdoor heat exchangers is still one of the major concerns
Passive tracking and system interfaces for interventional MRI
No full textAbstract
One of the major pre-requisite of MR-guided interventions is the visualization and localization of interventional devices relative to the vascular system and surrounding tissues. A number of approaches have been proposed for device visualization in an MR environment that are categorized into active, passive and semi-active techniques. In spite of considerable growth of these techniques, there is a scope to investigate and develop new pulse sequences and system interfaces for these techniques to make clinically feasible. In this thesis fast and novel passive tracking approaches to efficiently visualize and track the interventional guidewire tip using positive contrast are provided and highly miniaturized active micro-coils with built-in pre-amplifier are introduced.
In passive tracking techniques, the paramagnetic markers are utilized having susceptibility differences with respect to surrounding water protons. When this marker is placed in a uniform main magnetic field B0, it cause significant field inhomogeneities leading to dual effect of local frequency shifts and local gradient induction in marker's immediate surrounding.
The first method introduced in this thesis exploit the local frequency shifts induced by paramagnetic marker to create positive contrast. The binomial spatial-spectral (SPSP) excitation pulse that selectively excites the spectral component of the off-resonant tissues in the close proximity of the marker material and within the selected spatial region is incorporated into a temporally efficient steady state free precession (SSFP)-echo sequence. In this work, the principle of off-resonance excitation of tissues using SPSP pulse is explained theoretically. The in-vitro experiments demonstrate the proper localization and feasibility of paramagnetic marker detection mounted on the interventional guidewire tip. The analysis of the signal and localization characteristics of the SPSP pulse is done theoretically and verified experimentally.
The next novel positive contrast method for passive localization and visualization of paramagnetic susceptibility markers is based on an echo-dephased SSFP sequence. Gradients dephase any signal by ±π at the centered echo-time (TE=TR/2) and induce a total dephasing of ±π per pixel within TR. This ensures that background tissues do not contribute to signal formation and thus appear dark. However, within the close vicinity of the paramagnetic marker, local gradient fields compensate for the intrinsic dephasing to form an echo. Conceptual issues of gradient compensation and its visualization characteristics are analyzed. The flow phantom experiments concluded that reliable tracking of the interventional guidewire is feasible using echo-dephased SSFP. Finally utilization of echo-dephased SSFP for positive contrast visualization of SPIO-labeled islet cells is demonstrated both in vitro and in vivo.
A novel and fast approach for passive real-time tracking of interventional devices using paramagnetic markers termed Projection Reconstruction Imaging with Echo-Dephasing (PRIDE) is also presented in this thesis. PRIDE is based on the acquisition of echo-dephased projections along all three physical axes. Dephasing is preferably set to 4π within each projection ensuring that background tissues do not contribute to signal formation and thus appear heavily suppressed. However, within the close vicinity of the paramagnetic marker, local gradient fields compensate for the intrinsic dephasing to form an echo. Successful localization of the paramagnetic marker with PRIDE is demonstrated in-vitro and in-vivo in the presence of different types of off-resonance (air/tissue interfaces, main magnetic field inhomogeneities, etc). In order to utilize the PRIDE sequence for vascular interventional applications, it was interleaved with balanced steady-state free precession (bSSFP) to provide positional updates to the imaged slice using a dedicated real-time feedback link. Active slice positioning with PRIDE is demonstrated in vitro requiring approximately 20 ms for the positional update to the imaging sequence comparable to existing active tracking methods.
The active tracking method of device visualization utilizes locally sensitive transmit/receive coils for localization and visualization of its tip. The localization of the coil is achieved in few milliseconds through acquisition of one dimensional (1D) projections along all three spatial directions (X, Y and Z). However, the dimensions of these coils are bulky in nature thereby increasing the size of normal interventional devices (for e.g. catheter). In order to overcome this disadvantage in the last part of this thesis, highly miniaturized micro coils with built-in amplifier are introduced and experimentally tested
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