Biochemistry and Molecular Biology Education, 2003
This article describes the construction of a safe, programmable, automatic thermal cycler for PCR... more This article describes the construction of a safe, programmable, automatic thermal cycler for PCR that can be easily constructed by persons with basic soldering and mechanical skills for under $25 in parts and a modest computer such as IBM 486, all of which are readily available. The cycler relies on the heating provided by an incandescent light bulb and cooling by simple convection.
ABSTRACT The exposure of insulating materials to an electron beam results in the trapping of exce... more ABSTRACT The exposure of insulating materials to an electron beam results in the trapping of excess charge on the surface. We have studied the thermally and optically stimulated emission of this excess charge in an electron‐bombarded, fluorophlogopite mica glass–ceramic material (Macor). The total electron emission from the surface is measured either as a function of the sample temperature during heating or the photon wavelength. The emission as a function of temperature has four characteristic peaks whose relative intensity depends on the beam dose, energy, initial sample temperature, and history (accumulation of beam‐induced defects). One peak occurs immediately upon heating and is related to the total surface charge. Two peaks occur at fixed temperatures of 280 and 325 °C and are associated with the discrete energy trap states. The highest temperature peak is only observed after prolonged beam exposure and is due to the annihilation of defects. Illumination in the ultraviolet is required to produce photoemission for an uncharged sample. However, after electron bombardment, electron emission is observed over a broad range of visible wavelengths. In addition, two photoemission thresholds at about 2.7 and 3.1 eV suggest electron trap states which can be associated with the thermally emitted peaks. The thermally and optically stimulated emission is a valuable tool to measure the electron state distribution in charged insulating materials.
Proceedings of The National Academy of Sciences, 2004
Modifications in the strengths of synapses are thought to underlie memory, learning, and developm... more Modifications in the strengths of synapses are thought to underlie memory, learning, and development of cortical circuits. Many cellular mechanisms of synaptic plasticity have been investigated in which differential elevations of postsynaptic calcium concentrations play a key role in determining the direction and magnitude of synaptic changes. We have previously described a model of plasticity that uses calcium currents mediated by N-methyl-D-aspartate receptors as the associative signal for Hebbian learning. However, this model is not completely stable. Here, we propose a mechanism of stabilization through homeostatic regulation of intracellular calcium levels. With this model, synapses are stable and exhibit properties such as those observed in metaplasticity and synaptic scaling. In addition, the model displays synaptic competition, allowing structures to emerge in the synaptic space that reflect the statistical properties of the inputs. Therefore, the combination of a fast calcium-dependent learning and a slow stabilization mechanism can account for both the formation of selective receptive fields and the maintenance of neural circuits in a state of equilibrium.
... Ann B. Lee, Brian Blais, Harel Shouval and Leon N Cooper The Departments of Physics and Neuro... more ... Ann B. Lee, Brian Blais, Harel Shouval and Leon N Cooper The Departments of Physics and Neuroscience, The Institute for Brain and Neural Systems Box 1843, Brown University Providence, RI, 02912 (besu ... This work supported in part by the Charles A. Dana Foundation and ...
Proceedings of The National Academy of Sciences, 2004
Modifications in the strengths of synapses are thought to underlie memory, learning, and developm... more Modifications in the strengths of synapses are thought to underlie memory, learning, and development of cortical circuits. Many cellular mechanisms of synaptic plasticity have been investigated in which differential elevations of postsynaptic calcium concentrations play a key role in determining the direction and magnitude of synaptic changes. We have previously described a model of plasticity that uses calcium currents mediated by N-methyl-D-aspartate receptors as the associative signal for Hebbian learning. However, this model is not completely stable. Here, we propose a mechanism of stabilization through homeostatic regulation of intracellular calcium levels. With this model, synapses are stable and exhibit properties such as those observed in metaplasticity and synaptic scaling. In addition, the model displays synaptic competition, allowing structures to emerge in the synaptic space that reflect the statistical properties of the inputs. Therefore, the combination of a fast calcium-dependent learning and a slow stabilization mechanism can account for both the formation of selective receptive fields and the maintenance of neural circuits in a state of equilibrium.
... Ann B. Lee, Brian Blais, Harel Shouval and Leon N Cooper The Departments of Physics and Neuro... more ... Ann B. Lee, Brian Blais, Harel Shouval and Leon N Cooper The Departments of Physics and Neuroscience, The Institute for Brain and Neural Systems Box 1843, Brown University Providence, RI, 02912 (besu ... This work supported in part by the Charles A. Dana Foundation and ...
Biochemistry and Molecular Biology Education, 2003
This article describes the construction of a safe, programmable, automatic thermal cycler for PCR... more This article describes the construction of a safe, programmable, automatic thermal cycler for PCR that can be easily constructed by persons with basic soldering and mechanical skills for under $25 in parts and a modest computer such as IBM 486, all of which are readily available. The cycler relies on the heating provided by an incandescent light bulb and cooling by simple convection.
ABSTRACT The exposure of insulating materials to an electron beam results in the trapping of exce... more ABSTRACT The exposure of insulating materials to an electron beam results in the trapping of excess charge on the surface. We have studied the thermally and optically stimulated emission of this excess charge in an electron‐bombarded, fluorophlogopite mica glass–ceramic material (Macor). The total electron emission from the surface is measured either as a function of the sample temperature during heating or the photon wavelength. The emission as a function of temperature has four characteristic peaks whose relative intensity depends on the beam dose, energy, initial sample temperature, and history (accumulation of beam‐induced defects). One peak occurs immediately upon heating and is related to the total surface charge. Two peaks occur at fixed temperatures of 280 and 325 °C and are associated with the discrete energy trap states. The highest temperature peak is only observed after prolonged beam exposure and is due to the annihilation of defects. Illumination in the ultraviolet is required to produce photoemission for an uncharged sample. However, after electron bombardment, electron emission is observed over a broad range of visible wavelengths. In addition, two photoemission thresholds at about 2.7 and 3.1 eV suggest electron trap states which can be associated with the thermally emitted peaks. The thermally and optically stimulated emission is a valuable tool to measure the electron state distribution in charged insulating materials.
Proceedings of The National Academy of Sciences, 2004
Modifications in the strengths of synapses are thought to underlie memory, learning, and developm... more Modifications in the strengths of synapses are thought to underlie memory, learning, and development of cortical circuits. Many cellular mechanisms of synaptic plasticity have been investigated in which differential elevations of postsynaptic calcium concentrations play a key role in determining the direction and magnitude of synaptic changes. We have previously described a model of plasticity that uses calcium currents mediated by N-methyl-D-aspartate receptors as the associative signal for Hebbian learning. However, this model is not completely stable. Here, we propose a mechanism of stabilization through homeostatic regulation of intracellular calcium levels. With this model, synapses are stable and exhibit properties such as those observed in metaplasticity and synaptic scaling. In addition, the model displays synaptic competition, allowing structures to emerge in the synaptic space that reflect the statistical properties of the inputs. Therefore, the combination of a fast calcium-dependent learning and a slow stabilization mechanism can account for both the formation of selective receptive fields and the maintenance of neural circuits in a state of equilibrium.
... Ann B. Lee, Brian Blais, Harel Shouval and Leon N Cooper The Departments of Physics and Neuro... more ... Ann B. Lee, Brian Blais, Harel Shouval and Leon N Cooper The Departments of Physics and Neuroscience, The Institute for Brain and Neural Systems Box 1843, Brown University Providence, RI, 02912 (besu ... This work supported in part by the Charles A. Dana Foundation and ...
Proceedings of The National Academy of Sciences, 2004
Modifications in the strengths of synapses are thought to underlie memory, learning, and developm... more Modifications in the strengths of synapses are thought to underlie memory, learning, and development of cortical circuits. Many cellular mechanisms of synaptic plasticity have been investigated in which differential elevations of postsynaptic calcium concentrations play a key role in determining the direction and magnitude of synaptic changes. We have previously described a model of plasticity that uses calcium currents mediated by N-methyl-D-aspartate receptors as the associative signal for Hebbian learning. However, this model is not completely stable. Here, we propose a mechanism of stabilization through homeostatic regulation of intracellular calcium levels. With this model, synapses are stable and exhibit properties such as those observed in metaplasticity and synaptic scaling. In addition, the model displays synaptic competition, allowing structures to emerge in the synaptic space that reflect the statistical properties of the inputs. Therefore, the combination of a fast calcium-dependent learning and a slow stabilization mechanism can account for both the formation of selective receptive fields and the maintenance of neural circuits in a state of equilibrium.
... Ann B. Lee, Brian Blais, Harel Shouval and Leon N Cooper The Departments of Physics and Neuro... more ... Ann B. Lee, Brian Blais, Harel Shouval and Leon N Cooper The Departments of Physics and Neuroscience, The Institute for Brain and Neural Systems Box 1843, Brown University Providence, RI, 02912 (besu ... This work supported in part by the Charles A. Dana Foundation and ...
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