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Several Effects (several + effects)
Selected AbstractsTheoretical evaluation of magnetoreception of power-frequency fieldsBIOELECTROMAGNETICS, Issue 5 2010Jacques Vanderstraeten Abstract Several effects of power-frequency (50/60,Hz) magnetic fields (PF-MF) of weak intensity have been hypothesized in animals and humans. No valid mechanism, however, has been proposed for an interaction between PF-MF and biological tissues and living beings at intensities relevant to animal and human exposure. Here we proposed to consider PF-MF as disrupters of the natural magnetic signal. Under exposure to these fields, an oscillating field exists that results from the vectorial summation of both the PF-MF and the geomagnetic field. At a PF-MF intensity (rms) of 0.5,µT, the peak-to-peak amplitude of the axis and/or intensity variations of this resulting field exceeds the related discrimination threshold of magnetoreception (MR) in migrating animals. From our evaluation of the 50/60,Hz responsiveness of the putative mechanisms of MR, single domain particles (Kirschvink's model) appear unable to transduce that oscillating signal. On the contrary, radical pair reactions are able to, as well as interacting multidomain iron,mineral platelets and clusters of superparamagnetic particles (Fleissner/Solov'yov's model). It is, however, not yet known whether the reception of 50/60,Hz oscillations of the natural magnetic signal might be of consequence or not. Bioelectromagnetics 31:371,379, 2010. © 2010 Wiley-Liss, Inc. [source] Impacts of Argentine ants on mealybugs and their natural enemies in California's coastal vineyardsECOLOGICAL ENTOMOLOGY, Issue 6 2007KENT M. DAANE Abstract 1.,The Argentine ant, Linepithema humile, tends honeydew-excreting homopterans and can disrupt the activity of their natural enemies. This mutualism is often cited for increases in homopteran densities; however, the ant's impact on natural enemies may be only one of several effects of ant tending that alters insect densities. To test for the variable impacts of ants, mealybug and natural enemy densities were monitored on ant-tended and ant-excluded vines in two California vineyard regions. 2.,Ant tending increased densities of the obscure mealybug, Pseudococcus viburni, and lowered densities of its encyrtid parasitoids Pseudaphycus flavidulus and Leptomastix epona. Differences in parasitoid recovery rates suggest that P. flavidulus was better able to forage on ant-tended vines than L. epona. 3.,Densities of a coccinellid predator, Cryptolaemus montrouzieri, were higher on ant-tended vines, where there were more mealybugs. Together with behavioural observations, the results showed that this predator can forage in patches of ant-tended mealybugs, and that it effectively mimics mealybugs to avoid disturbance by ants. 4.,Ant tending increased densities of the grape mealybug, Pseudococcus maritimus, by increasing the number of surviving first-instar mealybugs. Parasitoids were nearly absent from the vineyard infested with P. maritimus. Therefore, ants improved either mealybug habitat or fitness. 5.,There was no difference in mealybug distribution or seasonal development patterns on ant-tended and ant-excluded vines, indicating that ants did not move mealybugs to better feeding locations or create a spatial refuge from natural enemies. 6.,Results showed that while Argentine ants were clearly associated with increased mealybug densities, it is not a simple matter of disrupting natural enemies. Instead, ant tending includes benefits independent of the effect on natural enemies. Moreover, the effects on different natural enemy species varied, as some species thrive in the presence of ants. [source] Effects of age on the cardiac and vascular limbs of the arterial baroreflexEUROPEAN JOURNAL OF CLINICAL INVESTIGATION, Issue 1 2003C. M. Brown Abstract Background Healthy ageing has several effects on the autonomic control of the circulation. Several studies have shown that baroreflex-mediated vagal control of the heart deteriorates with age, but so far there is little information regarding the effect of ageing on sympathetically mediated baroreflex responses. The aim of this study was to assess the effects of ageing on baroreflex control of the heart and blood vessels. Materials and Methods In 40 healthy volunteers, aged 20,87 years, we applied oscillatory neck suction at 0·1 Hz to assess the sympathetic modulation of the heart and blood vessels and at 0·2 Hz to assess the effect of parasympathetic stimulation on the heart. Breathing was maintained at 0·25 Hz. Blood pressure, electrocardiographic RR intervals and respiration were recorded continuously. Spectral analysis was used to evaluate the magnitude of the low-frequency (0·03,0·14 Hz) and high-frequency (0·15,0·50 Hz) oscillations in the RR interval and blood pressure. Responses to neck suction were assessed as the change in power of the RR interval and blood pressure fluctuations at the stimulation frequency from baseline values. Results Resting low- and high-frequency powers of the RR interval decreased significantly with age (P < 0·01). However, the low-frequency power of systolic blood pressure did not correlate with age. Spontaneous baroreflex sensitivity (alpha-index) showed a significant inverse correlation with age (r = ,0·46, P < 0·05). Responses of the RR interval and systolic blood pressure to 0·1 Hz neck suction stimulation were not related to age, however, the RR interval response to 0·2 Hz neck suction declined significantly with age (r = ,0·61, P < 0·01). Conclusions These results confirm an age-related decrease in cardiovagal baroreflex responses. However, sympathetically mediated baroreflex control of the blood vessels is preserved with age. [source] Enhanced Antibacterial Activity of Nanocrystalline ZnO Due to Increased ROS-Mediated Cell InjuryADVANCED FUNCTIONAL MATERIALS, Issue 6 2009Guy Applerot Abstract An innovative study aimed at understanding the influence of the particle size of ZnO (from the microscale down to the nanoscale) on its antibacterial effect is reported herein. The antibacterial activity of ZnO has been found to be due to a reaction of the ZnO surface with water. Electron-spin resonance measurements reveal that aqueous suspensions of small nanoparticles of ZnO produce increased levels of reactive oxygen species, namely hydroxyl radicals. Interestingly, a remarkable enhancement of the oxidative stress, beyond the level yielded by the ZnO itself, is detected following the antibacterial treatment. Likewise, an exposure of bacteria to the small ZnO nanoparticles results in an increased cellular internalization of the nanoparticles and bacterial cell damage. An examination of the antibacterial effect is performed on two bacterial species: Escherichia coli (Gram negative) and Staphylococcus aureus (Gram positive). The nanocrystalline particles of ZnO are synthesized using ultrasonic irradiation, and the particle sizes are controlled using different solvents during the sonication process. Taken as a whole, it is apparent that the unique properties (i.e., small size and corresponding large specific surface area) of small nanometer-scale ZnO particles impose several effects that govern its antibacterial action. These effects are size dependent and do not exist in the range of microscale particles. [source] Androgen Receptor Expression in the Levator Ani Muscle of Male MiceJOURNAL OF NEUROENDOCRINOLOGY, Issue 10 2007J. A. Johansen The spinal nucleus of the bulbocavernosus (SNB) is a sexually dimorphic group of motoneurones that innervates the bulbocavernosus (BC) and levator ani (LA), skeletal muscles that attach to the base of the penis. In many species, including mice, rats and hamsters, the LA and BC have been found to be highly responsive to androgen and, in rats, these muscles mediate several effects of androgen on the SNB system. However, characterising the SNB system in mice is important because of the availability of genetic models in this species. In the present study, we examined AR expression in skeletal muscles of C57/BlJ6 adult male mice using immunoblotting and immunocytochemistry, comparing the BC/LA to the androgen-unresponsive extensor digitorum longus (EDL). We found similar differences in AR expression for these muscles in the mouse as previously reported for rats. In mice, the BC/LA contains more AR protein than does the EDL. At the cellular level, the LA contains a higher percentage of AR positive myonuclei and fibroblasts than does the EDL. Finally, AR expression is enriched at the neuromuscular junction of mouse LA fibres. The increased expression of AR in the LA compared to the EDL in both muscle fibres and fibroblasts indicates that each cell type may critically mediate androgen action on the SNB system in mice. [source] Effects of long-term chilling on growth and photosynthesis of the C4 gramineae Paspalum dilatatumPHYSIOLOGIA PLANTARUM, Issue 1 2003Ana M. Cavaco Dallis grass (Paspalum dilatatum Poir.) is a C4/NADP-ME gramineae, previously classified as semi-tolerant to cold, although a complete study on this species acclimation process under a long-term chilling and controlled environmental conditions has never been conducted. In the present work, plants of the variety Raki maintained at 25/18°C (day/night) (control) were compared with plants under a long-term chilling at 10/8°C (day/night) (cold-acclimated) in order to investigate how growth and carbon assimilation mechanisms are engaged in P. dilatatum chilling tolerance. Although whole plant mean relative growth rate (mean RGR) and leaf growth were significantly decreased by cold exposure, chilling did not impair plant development nor favour the investment in biomass below ground. Cold-acclimated P. dilatatum cv. Raki had a lower leaf chlorophyll content, but a higher photosynthetic capacity at optimal temperatures, its range being shifted to lower values. Associated with this higher capacity to use the reducing power in CO2 assimilation, cold-acclimated plants further showed a higher capacity to oxidize the primary stable quinone electron acceptor of PSII, QA. The activity and activation of phosphoenolpyruvate carboxylase (PEPC; EC 4.1.1.31) and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco; EC 4.1.1.39) were not significantly affected by the long-term chilling. Cold-acclimated P. dilatatum cv. Raki apparently showed a lower transfer of excitation energy from the light-harvesting complex of photosystem II to the respective reaction centre and enhancement of radiationless energy-dissipating mechanisms at suboptimal temperatures. Overall, long-term chilling resulted in several effects that comprise responses with an intermediate character of both chilling-tolerant and ,sensitive plants, which seem to play a significant role in the survival and acclimation of P. dilatatum cv. Raki at low temperature. [source] A simulation-based method for the comprehensive analysis of effective lifetime from photoconductancePROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 2 2007G. Bueno Abstract This paper presents a method for estimating recombination parameters in the volume and surface of solar cell precursors throughout the manufacturing process, taking into account several effects that are generally neglected. The technique is based on the comprehensive reconstruction of the effective lifetime assuming a set of fundamental parameters and its comparison to the experimental data obtained from the photoconductance measured under uniform generation in quasi-steady state conditions. The analysis starts from the semianalytical solution of the minority carrier profiles in the structures under test. This analysis overcomes the usual flat profile approximation and presents important advantages. It allows the asymmetry presented by the solar cell precursors to be taken into account and deals with a wide range of surface conditions: emitters, bare silicon or dielectric passivations. The model also accounts for the effect of the electric field in the volume, and implements several phenomena that are sometimes neglected but are relevant when measuring industrial solar cells precursors: the injection dependence of mobilities and recombination lifetimes, the presence of non-recombinant traps and the Depletion Region Modulation effect. The estimation technique requires uniform generation, which greatly facilitates the calculation of the carrier profiles and allows for a simple method for the auto calibration of the light absorption. Copyright © 2006 John Wiley & Sons, Ltd. [source] | |||||||||||||