The Experts below are selected from a list of 75 Experts worldwide ranked by ideXlab platform
R. M. Robertson - One of the best experts on this subject based on the ideXlab platform.
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Thermal activation of Escape swimming in post-hatching Xenopus laevis frog larvae
Journal of Experimental Biology, 2009Co-Authors: Keith T. Sillar, R. M. RobertsonAbstract:SUMMARY Survival requires the selection of appropriate behavioural responses in the face of danger. With respect to the threat of predation, both the decision to Escape and the underlying neuronal mechanisms have been extensively studied, but processes that trigger evasion of abiotic stressors, which are potentially hazardous to survival, are less well understood. Here, we document the interplay between rhythmic locomotory and `C-start9 Escape swimming in Xenopus frog larvae when exposed to hyperthermic conditions. As temperature rises, swim cycle frequency increases while swim bout duration decreases, until swimming can no longer be initiated by sensory stimuli. Above a critical higher temperature, more intense Sequences of spontaneous high amplitude C-start Escape activity occur. Each C-start is followed by a few cycles of fast rhythmic swimming in which activity alternates between the two sides. The initial, high amplitude ventral root burst of an Escape Sequence propagates rostrocaudally approximately threefold faster than subsequent cycles. The high conduction velocity of this initial burst is consistent with the activation of a Mauthner neuron, one of a pair of giant reticulospinal neurons in fish and amphibians. In support of the involvement of a Mauthner neuron, unilateral lesions of the caudal hindbrain eliminated Escape activity on the operated side, but activity remained on the un-operated side. Behaviourally, tadpoles responded to temperature ramps with a Sequence of C-start responses in which the body arced through ∼130° in 22 ms, followed by high frequency swimming. These results suggest that high temperature activates the Mauthner neurons to trigger C-start Escape behaviour.
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Thermal activation of Escape swimming in post-hatching Xenopus laevis frog larvae.
The Journal of experimental biology, 2009Co-Authors: Keith T. Sillar, R. M. RobertsonAbstract:Survival requires the selection of appropriate behavioural responses in the face of danger. With respect to the threat of predation, both the decision to Escape and the underlying neuronal mechanisms have been extensively studied, but processes that trigger evasion of abiotic stressors, which are potentially hazardous to survival, are less well understood. Here, we document the interplay between rhythmic locomotory and 'C-start' Escape swimming in Xenopus frog larvae when exposed to hyperthermic conditions. As temperature rises, swim cycle frequency increases while swim bout duration decreases, until swimming can no longer be initiated by sensory stimuli. Above a critical higher temperature, more intense Sequences of spontaneous high amplitude C-start Escape activity occur. Each C-start is followed by a few cycles of fast rhythmic swimming in which activity alternates between the two sides. The initial, high amplitude ventral root burst of an Escape Sequence propagates rostrocaudally approximately threefold faster than subsequent cycles. The high conduction velocity of this initial burst is consistent with the activation of a Mauthner neuron, one of a pair of giant reticulospinal neurons in fish and amphibians. In support of the involvement of a Mauthner neuron, unilateral lesions of the caudal hindbrain eliminated Escape activity on the operated side, but activity remained on the un-operated side. Behaviourally, tadpoles responded to temperature ramps with a Sequence of C-start responses in which the body arced through approximately 130 degrees in 22 ms, followed by high frequency swimming. These results suggest that high temperature activates the Mauthner neurons to trigger C-start Escape behaviour.
Keith T. Sillar - One of the best experts on this subject based on the ideXlab platform.
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Thermal activation of Escape swimming in post-hatching Xenopus laevis frog larvae
Journal of Experimental Biology, 2009Co-Authors: Keith T. Sillar, R. M. RobertsonAbstract:SUMMARY Survival requires the selection of appropriate behavioural responses in the face of danger. With respect to the threat of predation, both the decision to Escape and the underlying neuronal mechanisms have been extensively studied, but processes that trigger evasion of abiotic stressors, which are potentially hazardous to survival, are less well understood. Here, we document the interplay between rhythmic locomotory and `C-start9 Escape swimming in Xenopus frog larvae when exposed to hyperthermic conditions. As temperature rises, swim cycle frequency increases while swim bout duration decreases, until swimming can no longer be initiated by sensory stimuli. Above a critical higher temperature, more intense Sequences of spontaneous high amplitude C-start Escape activity occur. Each C-start is followed by a few cycles of fast rhythmic swimming in which activity alternates between the two sides. The initial, high amplitude ventral root burst of an Escape Sequence propagates rostrocaudally approximately threefold faster than subsequent cycles. The high conduction velocity of this initial burst is consistent with the activation of a Mauthner neuron, one of a pair of giant reticulospinal neurons in fish and amphibians. In support of the involvement of a Mauthner neuron, unilateral lesions of the caudal hindbrain eliminated Escape activity on the operated side, but activity remained on the un-operated side. Behaviourally, tadpoles responded to temperature ramps with a Sequence of C-start responses in which the body arced through ∼130° in 22 ms, followed by high frequency swimming. These results suggest that high temperature activates the Mauthner neurons to trigger C-start Escape behaviour.
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Thermal activation of Escape swimming in post-hatching Xenopus laevis frog larvae.
The Journal of experimental biology, 2009Co-Authors: Keith T. Sillar, R. M. RobertsonAbstract:Survival requires the selection of appropriate behavioural responses in the face of danger. With respect to the threat of predation, both the decision to Escape and the underlying neuronal mechanisms have been extensively studied, but processes that trigger evasion of abiotic stressors, which are potentially hazardous to survival, are less well understood. Here, we document the interplay between rhythmic locomotory and 'C-start' Escape swimming in Xenopus frog larvae when exposed to hyperthermic conditions. As temperature rises, swim cycle frequency increases while swim bout duration decreases, until swimming can no longer be initiated by sensory stimuli. Above a critical higher temperature, more intense Sequences of spontaneous high amplitude C-start Escape activity occur. Each C-start is followed by a few cycles of fast rhythmic swimming in which activity alternates between the two sides. The initial, high amplitude ventral root burst of an Escape Sequence propagates rostrocaudally approximately threefold faster than subsequent cycles. The high conduction velocity of this initial burst is consistent with the activation of a Mauthner neuron, one of a pair of giant reticulospinal neurons in fish and amphibians. In support of the involvement of a Mauthner neuron, unilateral lesions of the caudal hindbrain eliminated Escape activity on the operated side, but activity remained on the un-operated side. Behaviourally, tadpoles responded to temperature ramps with a Sequence of C-start responses in which the body arced through approximately 130 degrees in 22 ms, followed by high frequency swimming. These results suggest that high temperature activates the Mauthner neurons to trigger C-start Escape behaviour.
Alexandre Freundlich - One of the best experts on this subject based on the ideXlab platform.
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Dependence of device performance on carrier Escape Sequence in multi-quantum-well p-i-n solar cells
Journal of Applied Physics, 2006Co-Authors: Andenet Alemu, Jose A. H. Coaquira, Alexandre FreundlichAbstract:This work is a study relating device performance and carrier Escape Sequence in a large set of InAsP∕InP p-i-n multi-quantum-well solar cells. The devices encompass nearly identical i-region thickness and built-in electric field and present similar absorption threshold energies. The Escape Sequence of the first confined electron-to-conduction band continuum and heavy/light holes-to-valence band continuum is extracted from the photoluminescence versus temperature analysis and by comparing the measured activation energies to calculated hole/electron well depths and thermionic Escape times. Light holes, as expected for most III-V nanostructure systems, are found to be the fastest escaping carriers in all samples. The Escape of electrons prior to heavy holes is shown to be a prerequisite to prevent severe open circuit voltage degradation. A possible explanation of the origin of this effect is offered. InP∕InAsP multi-quantum-well solar cells with high built-in electric field and fast electronic Escape time di...
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Correlation Between Device Performance and Photo-Generated Carriers Escape Order in III-V p-i-n Quantum Confined Solar Cells
2006 IEEE 4th World Conference on Photovoltaic Energy Conference, 2006Co-Authors: Andenet Alemu, J. A. H. Coaquira, Alexandre FreundlichAbstract:For p-i-n quantum confined solar cells, best efficiency trade-off is often achieved in the vicinity of a critical intrinsic region thickness corresponding to a critical built-in electric field. Nevertheless, even for devices satisfying such condition, the carrier Escape Sequence is shown to have a profound impact on device performance. Here, we present several correlations between photoluminescence and theoretical calculation results for studies made on specific devices. The study underlines the need to carefully consider carrier Escape processes in order to achieve the goal of highly efficient quantum confined solar cell
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Improved performance due to fast electronic Escape in MQW p-i-n solar cells
Conference Record of the Thirty-first IEEE Photovoltaic Specialists Conference 2005., 1Co-Authors: A. Alemu, L. Bhusal, Alexandre FreundlichAbstract:This study relates device performance and carrier Escape Sequence in p-i(MQW)-n solar cells and experimental and theoretical investigations are undertaken. Carrier Escape mechanisms and, in particular, the order at which holes and electrons Escape from their respective well potentials are found to have a profound impact on device performance. In these InP/InAsP MQW solar cells, the light hole was found to be the first carrier to Escape from the quantum wells. As a conSequence, a faster electronic Escape time as compared to heavy holes Escape time is found to be important in these devices. MQW solar cells with high built-in electric field and fast electron Escape time display better open circuit voltage and performance.
John Van Der Oost - One of the best experts on this subject based on the ideXlab platform.
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bacteriophage dna glucosylation impairs target dna binding by type i and ii but not by type v crispr cas effector complexes
Nucleic Acids Research, 2018Co-Authors: Marnix Vlot, Joep Houkes, Silke J A Lochs, Daan C Swarts, Peiyuan Zheng, Tim Kunne, Prarthana Mohanraju, Carolin Anders, Martin Jinek, John Van Der OostAbstract:Prokaryotes encode various host defense systems that provide protection against mobile genetic elements. Restriction–modification (R–M) and CRISPR–Cas systems mediate host defense by Sequence specific targeting of invasive DNA. T-even bacteriophages employ covalent modifications of nucleobases to avoid binding and therefore cleavage of their DNA by restriction endonucleases. Here, we describe that DNA glucosylation of bacteriophage genomes affects interference of some but not all CRISPR–Cas systems. We show that glucosyl modification of 5-hydroxymethylated cytosines in the DNA of bacteriophage T4 interferes with type I-E and type II-A CRISPR–Cas systems by lowering the affinity of the Cascade and Cas9–crRNA complexes for their target DNA. On the contrary, the type V-A nuclease Cas12a (also known as Cpf1) is not impaired in binding and cleavage of glucosylated target DNA, likely due to a more open structural architecture of the protein. Our results suggest that CRISPR–Cas systems have contributed to the selective pressure on phages to develop more generic solutions to Escape Sequence specific host defense systems.
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Bacteriophage DNA glucosylation impairs target DNA binding by type I and II but not by type V CRISPR–Cas effector complexes
Nucleic acids research, 2017Co-Authors: Marnix Vlot, Joep Houkes, Silke J A Lochs, Daan C Swarts, Peiyuan Zheng, Tim Kunne, Prarthana Mohanraju, Carolin Anders, Martin Jinek, John Van Der OostAbstract:Prokaryotes encode various host defense systems that provide protection against mobile genetic elements. Restriction–modification (R–M) and CRISPR–Cas systems mediate host defense by Sequence specific targeting of invasive DNA. T-even bacteriophages employ covalent modifications of nucleobases to avoid binding and therefore cleavage of their DNA by restriction endonucleases. Here, we describe that DNA glucosylation of bacteriophage genomes affects interference of some but not all CRISPR–Cas systems. We show that glucosyl modification of 5-hydroxymethylated cytosines in the DNA of bacteriophage T4 interferes with type I-E and type II-A CRISPR–Cas systems by lowering the affinity of the Cascade and Cas9–crRNA complexes for their target DNA. On the contrary, the type V-A nuclease Cas12a (also known as Cpf1) is not impaired in binding and cleavage of glucosylated target DNA, likely due to a more open structural architecture of the protein. Our results suggest that CRISPR–Cas systems have contributed to the selective pressure on phages to develop more generic solutions to Escape Sequence specific host defense systems.
Andenet Alemu - One of the best experts on this subject based on the ideXlab platform.
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Dependence of device performance on carrier Escape Sequence in multi-quantum-well p-i-n solar cells
Journal of Applied Physics, 2006Co-Authors: Andenet Alemu, Jose A. H. Coaquira, Alexandre FreundlichAbstract:This work is a study relating device performance and carrier Escape Sequence in a large set of InAsP∕InP p-i-n multi-quantum-well solar cells. The devices encompass nearly identical i-region thickness and built-in electric field and present similar absorption threshold energies. The Escape Sequence of the first confined electron-to-conduction band continuum and heavy/light holes-to-valence band continuum is extracted from the photoluminescence versus temperature analysis and by comparing the measured activation energies to calculated hole/electron well depths and thermionic Escape times. Light holes, as expected for most III-V nanostructure systems, are found to be the fastest escaping carriers in all samples. The Escape of electrons prior to heavy holes is shown to be a prerequisite to prevent severe open circuit voltage degradation. A possible explanation of the origin of this effect is offered. InP∕InAsP multi-quantum-well solar cells with high built-in electric field and fast electronic Escape time di...
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Correlation Between Device Performance and Photo-Generated Carriers Escape Order in III-V p-i-n Quantum Confined Solar Cells
2006 IEEE 4th World Conference on Photovoltaic Energy Conference, 2006Co-Authors: Andenet Alemu, J. A. H. Coaquira, Alexandre FreundlichAbstract:For p-i-n quantum confined solar cells, best efficiency trade-off is often achieved in the vicinity of a critical intrinsic region thickness corresponding to a critical built-in electric field. Nevertheless, even for devices satisfying such condition, the carrier Escape Sequence is shown to have a profound impact on device performance. Here, we present several correlations between photoluminescence and theoretical calculation results for studies made on specific devices. The study underlines the need to carefully consider carrier Escape processes in order to achieve the goal of highly efficient quantum confined solar cell