Ibaraki University , Japan, is a national university located in Ibaraki Prefecture, with campuses in the cities of Mito, Ami and Hitachi. It was established on May 31, 1949, integrating these prewar institutions: Mito High School , Ibaraki Normal School , Ibaraki Juvenile Normal School , and Taga Technical Specialists' College . The initial colleges were the College of Arts and science, the College of Education, and the College of Engineering. Wikipedia.
News Article | April 17, 2017
Many young stars, as well as more middle-aged stars like our sun, have "debris disks"--like the Oort Cloud in our own solar system--that are believed to be remnants of the system's formation. Recently, radio observations have detected gas within a number of such discs, but it was not clear why the gas was there. There are two major hypotheses: either the gas is primordial gas from the original gas cloud that formed the star, or it originates from collisions between objects in the disk. In search of a solution to this problem, a team from the RIKEN Star and Planet Formation Laboratory decided to look at emissions of carbon, which are important as they can provide clues to the origin of the gas. Normally, carbon will exist mostly in a molecular form, as carbon monoxide. Ultraviolet light from the central star will "dissociate" the atoms, creating free atomic carbon, but normally a chemical reaction--mediated by hydrogen--recombines the carbon into CO. However, if there is no hydrogen, then the reaction does not take place and the carbon remains in its atomic state. Aya Higuchi, the first author of the paper, published in Astrophysical Journal Letters, was able to use the ten-meter Atacama Submillimeter Telescope Experiment (ASTE) in Chile to examine the atomic carbon line from two young star systems--49 Ceti and Beta Pictoris--that are known to have debris disks. They then compared this from data on CO taken by the Atacama Large Millimeter/submillimeter Array (ALMA), an array of telescopes in the same facility. "We were surprised," she says, "to find atomic carbon in the disk, the first time this observation has been made at sub-millimeter wavelength. But more so, we were surprised at how much there was. It was about as common as the carbon monoxide." The implication, at least for these two star systems, is that there is very little hydrogen to drive the carbon back into CO. Because hydrogen makes up most of the gas in protoplanetary clouds, this hints that the gas is not primordial, but rather is generated from some process taking place in the debris disk. Gas has been found in other debris disks, but is not found in all. Higuchi says, "If we can perform similar measurements on other young stars, it will help to clarify the origin of the gas in debris disk. Our data here suggests that the gas is secondary." Looking to the future, she continues, "This work will also help to understand how a protoplanetary disk evolves into a debris disks by distinguishing the origin of the gas in the disks." The work was done in collaboration with scientists from Ibaraki University and Nagoya University.
Ibaraki University | Date: 2017-07-05
[Problem] To achieve transmission power characteristics and a power extinction ratio in a terahertz wave band that cannot be achieved conventionally. [Solution to problem] A cutout 20b is formed between one end and an opposite end of a rectangular metal thin plate to form a plurality of grid plates 20 each having an elongated grid part 20a between the one end and the opposite end. The grid plates 20 are stacked in such a manner that the grid parts 20a of the grid plates 20 are spaced at a given interval and face each other, thereby forming a grid plate stack 2a In this case, spacers 21 are inserted between one ends and between opposite ends of adjacent ones of the grid plates 20 to form parallel flat plates configured by the grid parts 20a. The grid plate stack 2a forming the parallel flat plates operates as a polarizer for a terahertz wave band.
Ibaraki University | Date: 2015-08-21
A wire grid device having transmission power characteristics and a power extinction ratio in a terahertz wave band that cannot be achieved conventionally. A cutout is formed between one end and an opposite end of a rectangular metal thin plate to form a plurality of grid plates each having an elongated grid part between the one end and the opposite end. The grid plates are stacked in such a manner that the grid parts of the grid plates are spaced at a given interval and face each other, thereby forming a grid plate stack. In this case, spacers are inserted between one ends and between opposite ends of adjacent ones of the grid plates to form parallel flat plates configured by the grid parts. The grid plate stack forming the parallel flat plates operates as a polarizer for a terahertz wave band.
Hoshino O.,Ibaraki University
Neural Computation | Year: 2013
Multistable perception is a psychophysical phenomenon in which one unique interpretation alternates spontaneously every few seconds between two or more interpretations of the same sensory input.Well-known examples include the Necker cube and face-vase illusions in vision. Interestingly, young adults generally see more perceptual switches than do elderly people. To understand the underlying neuronal mechanism of agerelated multistable perception, we simulated a cortical neural network model that consists of multiple cell assemblies. In the network, a specific population of noncore cells and a common population of core cells form a cell assembly that represents a single object (or event). Every dynamic cell assembly, activated by a given sensory input, involves the common (overlapping) population of core cells. Ambient GABA-mediated intracortical tonic inhibition via extrasynaptic GABAa receptors destabilized the currently appearing dynamic cell assembly and terminated its burst firing. This allowed another dynamic cell assembly to emerge one after the other. Namely, multistable perception took place. Transporters, which were embedded in axon terminal membranes of interneurons, regulated levels of ambient GABA. For elderly people, we assumed a decline in transporter. This decelerated GABA augmentation and resulted in prolonging the durations of burst firing and thus in slowing perceptual switches. We suggest that poor control of ambient GABA levels due to age-related decline in GABA transporter may be responsible for the slowing of perceptual switches in elderly people. © 2013 Massachusetts Institute of Technology.
Hoshino O.,Ibaraki University
Neural Computation | Year: 2012
Activities of sensory-specific cortices are known to be suppressed when presented with a different sensory modality stimulus. This is referred to as cross-modal inhibition, for which the conventional synaptic mechanism is unlikely to work. Interestingly, the cross-modal inhibition could be eliminated when presented with multisensory stimuli arising from the same event. To elucidate the underlying neuronal mechanism of cross-modal inhibition and understand its significance for multisensory information processing, we simulated a neural network model. Principal cell to and GABAergic interneuron to glial cell projections were assumed between and within lower-order unimodal networks (X and Y), respectively. Cross-modality stimulation of Y network activated its principal cells, which then depolarized glial cells of X network. This let transporters on the glial cells export GABA molecules into the extracellular space and increased a level of ambient (extrasynaptic) GABA. The ambient GABA molecules were accepted by extrasynaptic GABAa receptors and tonically inhibited principal cells of the X network. Cross-modal inhibition took place in a nonsynaptic manner. Identical modality stimulation of X network activated its principal cells, which then activated interneurons and hyperpolarized glial cells of the X network. This let their transporters import (remove) GABA molecules from the extracellular space and reduced tonic inhibitory current in principal cells, thereby improving their gain function. Top-down signals from a higher-order multimodal network (M) contributed to elimination of the cross-modal inhibition when presented with multisensory stimuli that arose from the same event. Tuning into the multisensory event deteriorated if the cross-modal inhibitory mechanism did not work.We suggest that neuron-glia signaling may regulate local ambient GABA levels in order to coordinate cross-modal inhibition and improve neuronal gain function, thereby achieving reliable perception of multisensory events. © 2012 Massachusetts Institute of Technology.
Hoshino O.,Ibaraki University
Neural Computation | Year: 2011
Experience-dependent synaptic plasticity characterizes the adaptable brain and is believed to be the cellular substrate for perceptual learning. A chemical agent such as gamma-aminobutyric acid (GABA) is known to affect synaptic alteration, perhaps gating perceptual learning. We examined whether and how ambient (extrasynaptic)GABA affects experiencedependent synaptic alteration. A cortical neural networkmodel was simulated. Transporters onGABAergic interneurons regulate ambientGABA levels around their axonal target neurons by removing GABA from (forward transport) or releasing it into (reverse transport) the extracellular space. The ambient GABA provides neurons with tonic inhibitory currents by activating extrasynaptic GABA a receptors. During repeated exposures to the same stimulus, we modified the synaptic connection strength between principal cells in a spike-timing-dependent manner. This modulated the activity of GABAergic interneurons, and reduced or augmented ambient GABA concentration. Reduction in ambient GABA concentration led to slight depolarization (less than several millivolts) in ongoing-spontaneous membrane potential. This was a subthreshold neuronal behavior because ongoing-spontaneous spiking activity remained almost unchanged. The ongoing-spontaneous subthreshold depolarization improved a suprathreshold neuronal response. If the stimulus was long absent for perceptual learning, augmentation of ambient GABA concentration took place and the ongoing-spontaneous subthreshold depolarization was depressed. We suggest that a perceptual memory trace could be left in neuronal circuitry as an ongoing-spontaneous subthreshold membrane depolarization, which would allow that memory to be accessed easily afterward, whereas a trace of a memory that has not recently been retrieved fades away when the ongoing-spontaneous subthreshold membrane depolarization built by previous perceptual learning is depressed. This would lead that memory to be accessed with some difficulty. In the brain, ambient GABA, whose level could be regulated by transporter may have an important role in leaving memory trace for perceptual learning. © 2011 Massachusetts Institute of Technology.
Hoshino O.,Ibaraki University
Neural Computation | Year: 2011
Multisensory integration (such as somatosensation-vision, gustationolfaction) could occur even between subthreshold stimuli that in isolation do not reach perceptual awareness. For example, when a somatosensory (subthreshold) stimulus is delivered within a close spatiotemporal congruency, a visual (subthreshold) stimulus evokes a visual percept. Cross-modal enhancement of visual perception is maximal when the somatosensory stimulation precedes the visual one by tens of milliseconds. This rapid modulatory response would not be consistent with a topdown mechanism acting through higher-order multimodal cortical areas, but rather a direct interaction between lower-order unimodal areas. To elucidate the neuronal mechanisms of subthreshold cross-modal enhancement, we simulated a neural network model. In the model, lower unimodal (X, Y) and higher multimodal (M) networks are reciprocally connected by bottom-up and top-down axonal projections. The lower networks are laterally connected with each other. A pair of stimuli was presented to the lower networks, whose respective intensities were too weak to induce salient neuronal activity (population response) when presented alone. Neurons of the Y network were slightly depolarized below firing threshold when a cross-modal stimulus was presented alone to the X network. This allowed the Y network to make a rapid (within tens of milliseconds) population response when presented with a subsequent congruent stimulus. The reaction speed of the Y network was accelerated, provided that the top-down projections were strengthened. We suggest that a subthreshold (nonpopulation) response to a cross-modal stimulus, acting through interaction between lower (primary unisensory) areas, may be essential for a rapid suprathreshold (population) response to a congruent stimulus that follows. Top-down influences on cross-modal enhancement may be faster than expected, accelerating reaction speed to input, in which ongoing-spontaneous subthreshold excitation of lowerorder unimodal cells by higher-order multimodal cells may play an active role. © 2011 Massachusetts Institute of Technology.
Ibaraki University, Japan Science and Technology Agency | Date: 2016-07-06
An objective of the present invention is to easily achieve an extinction ratio in the approximate 10^(-6) class for intensity transmittance in the terahertz band with one element. Provided is a wire grid device, configured from layering a plurality of film substrates (10) each formed from a rectangular polymer film (11) wherein a narrow rectangular metal thin plate (12) is formed in the approximate center of one face thereof. By having the width (a) of the metal thin plate (12) be approximately 1.0mm, the length (1) of the metal thin plate (12) be approximately 12.0-30mm, and the thickness (d) of the film substrate (10) be approximately 0.5-50 m, it is possible to easily achieve an extinction ratio in the approximate 10^(-6) class for intensity transmittance in the terahertz band with one element.
Ibaraki University, Japan Science and Technology Agency | Date: 2014-08-21
Achieve an extinction ratio in the approximate 10^(6 )class for intensity transmittance in the terahertz band with one element. A wire grid device configured from layering a plurality of film substrates each formed from a rectangular polymer film wherein a narrow rectangular metal thin plate is formed in the approximate center of one face thereof. By having the width of the metal thin plate be approximately 1.0 mm, the length of the metal thin plate be approximately 12.0-30 mm, and the thickness of the film substrate be approximately 0.5-50 m, it is possible to easily achieve an extinction ratio in the approximate 10^(6 )class for intensity transmittance in the terahertz band with one element.
Ibaraki University | Date: 2014-12-24
To realize arrangement in place easily and to obtain a desired refractive index. A z-axis is defined as an optical axis and axes perpendicular to the z-axis are defined as an x-axis and a y-axis. Multiple metal plate pieces 10 each have multiple groove portions formed in the direction of the x-axis. An outer shape of the metal plate pieces 10 are such that the respective cross sections of the metal plate pieces 10 are parallel to x-z planes at given intervals of a lens along the y-axis from a lower edge to a center and from the center to an upper edge. A metal dielectric lens 1 is formed by laminating the metal plate pieces 10 such that the metal plate pieces 10 are arranged parallel to the x-z planes at the given intervals. As a result, a refractive index responsive to the number of the groove portions, and the width and the depth of the groove portion can be obtained. And, a resultant structure causes visible light to pass therethrough.