Condensed matter systems with topological defects in the ground states range from the Abrikosov phases in superconductors, to various blue phases and twist grain boundary phases in liquid crystals, and to phases of sk...
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Condensed matter systems with topological defects in the ground states range from the Abrikosov phases in superconductors, to various blue phases and twist grain boundary phases in liquid crystals, and to phases of skyrmion lattices in chiral ferromagnets and Bose-Einstein condensates. In nematic and chiral nematic liquid crystals, which are true fluids with long-range orientational ordering of constituent molecules, point and line defects spontaneously occur as a result of symmetry-breaking phase transitions or due to flow, but they are unstable, hard to control, and typically annihilate with time. Here we describe the optical generation of two-dimensional crystalline, quasicrystalline, and arbitrary ensembles of particlelike structures manifesting both skyrmionlike and Hopf fibration features—dubbed “torons”—composed of looped double twist cylinders and point defects embedded in a uniform director field. In these two-dimensional lattices, we then introduce various dislocations, defects in positional ordering of the torons. We show that the periodic defect lattices with and without dislocation are light- and voltage-tunable reconfigurable two-dimensional diffraction gratings and can be used to generate various controlled phase singularities in the diffracted laser beams. The results of computer simulations of optical images, diffraction patterns, and phase distributions with optical vortices are in a good agreement with the corresponding experimental findings.
The paper presents a case report of the therapy by neurofeedback training of a chronic female schizophrenia outpatient. The purpose of the neurofeedback training was to enhance cognition, memory and behavioral perform...
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The paper presents a case report of the therapy by neurofeedback training of a chronic female schizophrenia outpatient. The purpose of the neurofeedback training was to enhance cognition, memory and behavioral performance. We used an intensive approach. All the training sessions were performed during 4 consecutive days. The results showed that the patient learnt to increase individual alpha amplitude and simultaneously decrease beta2 (20-30 Hz) amplitude at P4 site during active state over sessions. The individual alpha increased 74.73% and beta2 decreased 13.73%. The short term memory was enhanced after training. Her mood had positive change and her speech was much clearer than before. She started to associate the meaning of her life and illness. These results support that neurofeedback is not only a feasible therapy for schizophrenia but also positive results could be obtained using a much more intensive training sessions than the one reported in the literature.
In order to approach human hand performance levels, artificial anthropomorphic hands/fingers have increasingly incorporated human biomechanical features. However, the performance of finger reaching movements to visual...
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ISBN:
(纸本)9781424441198
In order to approach human hand performance levels, artificial anthropomorphic hands/fingers have increasingly incorporated human biomechanical features. However, the performance of finger reaching movements to visual targets involving the complex kinematics of multijointed, anthropomorphic actuators is a difficult problem. This is because the relationship between sensory and motor coordinates is highly nonlinear, and also often includes mechanical coupling of the two last joints. Recently, we developed a cortical model that learns the inverse kinematics of a simulated anthropomorphic finger. Here, we expand this previous work by assessing if this cortical model is able to learn the inverse kinematics for an actual anthropomorphic humanoid finger having its two last joints coupled and controlled by pneumatic muscles. The findings revealed that single 3D reaching movements, as well as more complex patterns of motion of the humanoid finger, were accurately and robustly performed by this cortical model while producing kinematics comparable to those of humans. This work contributes to the development of a bioinspired controller providing adaptive, robust and flexible control of dexterous robotic and prosthetic hands.
The low-frequency 1/f noise in graphene transistors has been studied extensively owing to the proposed graphene applications in analog devices and communication systems [1-5]. The studies were motivated by the fact th...
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The low-frequency 1/f noise in graphene transistors has been studied extensively owing to the proposed graphene applications in analog devices and communication systems [1-5]. The studies were motivated by the fact that the low-frequency noise can be up-converted by device nonlinearity and contribute to the phase noise of the system. Similarly, the sensor sensitivity is often limited by the electronic low-frequency noise. Therefore, noise is usually considered as one of the main limiting factors for the device or overall system operation. However, the electronic noise spectrum itself can be used as a sensing parameter increasing the sensor sensitivity and selectivity. Here, we show that vapors of different chemicals produce distinguishably different effects on the low-frequency noise spectra of the graphene-on-Si transistor. Our study showed that some gases change the electrical resistance of pristine graphene devices without changing their low-frequency noise spectra while other gases modify the noise spectra by inducing Lorentzian components with distinctive features. The characteristic corner frequency f C of the Lorentzian noise bulges in graphene devices is different for different chemicals and varies from f C =10 - 20 Hz for tetrahydrofuran to f C =1300 - 1600 Hz for chloroform. We tested the selected set of chemicals vapors on different graphene device samples and alternated different vapors for the same samples. The obtained results indicate that 1/f noise in combination with other sensing parameters can allow one to achieve the selective gas sensing with a single pristine graphene transistor. Our method of gas sensing with graphene does not require graphene surface functionalization or fabrication of an array of the devices with each tuned to a certain chemical. The observation of the Lorentzian components in the vapor-exposed graphene can also help in developing an accurate theoretical description of the noise mechanism in graphene.
In this work, we show that molecularly-sensitive contrast can be generated in OCT using targeted multifunctional magnetic microspheres. These microspheres were engineered to target the ΑvΒ3 integrin for the localiza...
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We describe a soft matter system of self-organized oblate micelles and plasmonic gold nanorods that exhibit a negative orientational order parameter. Because of anisotropic surface anchoring interactions, colloidal go...
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We describe a soft matter system of self-organized oblate micelles and plasmonic gold nanorods that exhibit a negative orientational order parameter. Because of anisotropic surface anchoring interactions, colloidal gold nanorods tend to align perpendicular to the director describing the average orientation of normals to the discoidal micelles. Helicoidal structures of highly concentrated nanorods with a negative order parameter are realized by adding a chiral additive and are further controlled by means of confinement and mechanical stress. Polarization-sensitive absorption, scattering, and two-photon luminescence are used to characterize orientations and spatial distributions of nanorods. Self-alignment and effective-medium optical properties of these hybrid inorganic-organic complex fluids match predictions of a simple model based on anisotropic surface anchoring interactions of nanorods with the structured host medium.
Because of its ability to study specifically labeled structures, fluorescence microscopy is the most widely used technique for investigating live cell dynamics and function. Fluorescence correlation spectroscopy is an...
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Because of its ability to study specifically labeled structures, fluorescence microscopy is the most widely used technique for investigating live cell dynamics and function. Fluorescence correlation spectroscopy is an established method for studying molecular transport and diffusion coefficients at a fixed spatial scale. We propose a new approach, dispersion-relation fluorescence spectroscopy (DFS), to study the transport dynamics over a broad range of spatial and temporal scales. The molecules of interest are labeled with a fluorophore whose motion gives rise to spontaneous fluorescence intensity fluctuations that are analyzed to quantify the governing mass transport dynamics. These data are characterized by the effective dispersion relation. We report on experiments demonstrating that DFS can distinguish diffusive from advection motion in a model system, where we obtain quantitatively accurate values of both diffusivities and advection velocities. Because of its spatially resolved information, DFS can distinguish between directed and diffusive transport in living cells. Our data indicate that the fluorescently labeled actin cytoskeleton exhibits active transport motion along a direction parallel to the fibers and diffusive in the perpendicular direction.
We have developed and characterized ultrafast and highly sensitive photodetectors based on GaAs nanowhiskers fabricated with an improved top-down etching method. We evaluated the material properties of the etched nano...
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We have developed and characterized ultrafast and highly sensitive photodetectors based on GaAs nanowhiskers fabricated with an improved top-down etching method. We evaluated the material properties of the etched nanowhiskers by micro photoluminescence measurements and studied the effect of post annealing on nanowhiskers' luminescence. The nanowhiskers were integrated into the coplanar striplines for device testing using DC and time-resolved electro-optic characterization techniques. Our photodetectors exhibit a very low dark current below 500 pA at 10 V bias as well as a high responsivity of 0.19 A/W at 30 V, and a cut-off frequency of 1.3 THz. These characteristics make the GaAs nanowhisker photodetectors very promising candidates for high-speed optoelectronics and efficient THz emitters.
Micro-electrode arrays (MEAs) have been used in a variety of intracortical neural prostheses. While intracortical MEAs have demonstrated their utility in neural prostheses, in many cases MEA performance declines after...
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ISBN:
(纸本)9781424441198
Micro-electrode arrays (MEAs) have been used in a variety of intracortical neural prostheses. While intracortical MEAs have demonstrated their utility in neural prostheses, in many cases MEA performance declines after several months to years of in vivo implantation. The application of carbon nanotubes (CNTs) may increase the functional longevity of intracortical MEAs through enhanced biocompatibility and charge injection properties. An MEA metalized with platinum (Pt) on all electrodes had a CNT coating applied to the electrodes on half of the array. This Pt/Pt-CNT MEA was implanted into feline motor cortex for >1 year. Recordings of action potentials and 1 kHz impedance measurements were made on all electrodes to evaluate device functionality. Additionally, electromyogram (EMG) responses were evoked using micro-stimulation via the MEA to measure device performance. These metrics were compared between Pt and Pt- CNT electrodes. There was no significant difference in the data acquisition or micro-stimulation performance of Pt and the Pt- CNT electrodes. However, impedances were lower on the Pt- CNT electrodes. These results demonstrate the functionality of CNT coatings during chronic in vivo implantation. The lower impedances suggest that for microstimulation applications CNT coatings may impart enhanced interface properties.
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