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The cross sections of 89Y(n, 3n)87m,87gY and 209Bi(n, 4n)206Bi reactions at a neutron energy of 30 MeV are measured by making use of neutron beams of continuous energy spectra and a subtraction method. By impinging proton beams of 30 and 35 MeV to a thick beryllium target, neutron beams of continuous and broad energy spectra are produced and are guided to Y and Bi sample targets. The difference between the two neutron spectra generated by two neighboring proton energies is found to be peaked in a narrow energy range and thus can be regarded as quasi-monoenergetic, which can be used to extract (n, xn) cross sections. The uncertainty in the neutron fluence is reduced by analyzing the activities of aluminum and niobium reference samples placed on top of the Y and Bi samples. The use of a subtraction method by employing neutron beams of continuous energy spectra gives us the 89Y(n, 3n)87m,87gY and 209Bi(n, 4n)206Bi cross sections in fair agreement with the existing experimental data and nuclear data libraries.

A MICROMEGAS (MICRO Mesh GASeous) detector is developed to monitor neutrons with a continuous energy spectra generated by bombarding protons on a thick Be target at the MC-50 cyclotron of the Korea Institute of Radiological and Medical Sciences (KIRAMS). Two different neutron spectra are produced by protons of 20 and 40 MeV, and are detected by using the MICROMEGAS detector with a boron converter. Boron carbides (B4C) are deposited on the cathode of the detector and are used as a neutron-to-charged particle converter. α particles and 7Li nuclei produced by the 10B(n,α)7Li reaction are detected by using the MICROMEGAS detector. Monte Carlo simulations for the detector system are performed to compare the experimental data with the simulation results. For measuring the energies of the α particles and the 7Li nuclei, we vary the geometry of detector in both the simulations and the experiments to fully stop the α particles and the 7Li nuclei in the detector. The changes of the positions of the α and the 7Li peaks observed in the distribution of the deposited energy for different detector geometries agree more or less with those from the simulation results. The neutron conversion efficiency of the detector is studied.

This paper reports an increase in the optical reflectivity of two kinds of copolymers used in contact lenses, with different proportions of silicon and fluorine derivatives, when irradiated with 4.1 MeV alpha particles from an 241Am source. The fiber-optic reflectance technique showed that the lens with a higher proportion of silicon and fluorine content and a lower proportion of methyl-methacrylate is more susceptible to alpha radiation. X-Ray photoelectron spectroscopy and Raman spectroscopy have revealed the formation of silicon oxide and carbide species as a result of chain scission and recombination in the 20 μm thick irradiated regions of lens materials. It is presumed that the high (260 eV/nm) linear energy transfer of alpha particles in polymers creates trapped gas “Bubbles”, and the observed increase in the optical reflectivity with increased irradiation time is explained on the basis of diffuse reflectance caused by the scattering of light from the hard surfaces of these “Bubbles”.

Liquid crystal compounds are an important state of matter both scientifically and technologically. So we have prepared HSEO-n(n = 1,2,3,4) series shown below. In this study, in orde to acquire furt...

Objective: We evaluated the effects of tooth displacement on frictional force when conventional ligating lingual brackets (CL-LBs), CL-LBs with a narrow bracket width, and self-ligating lingual brackets (SL-LBs) were used with initial leveling and alignment wires. Methods: CL-LBs (7th Generation), CLLBs with a narrow bracket width (STb), and SL-LBs (In-Ovation L) were tested under three tooth displacement conditions: no displacement (control); a 2-mm palatal displacement (PD) of the maxillary right lateral incisor (MXLI); and a 2-mm gingival displacement (GD) of the maxillary right canine (MXC) (nine groups, n = 7 per group). A stereolithographic typodont system and artificial saliva were used. Static and kinetic frictional forces (SFF and KFF, respectively) were measured while drawing a 0.013-inch copper-nickel-titanium archwire through brackets at 0.5 mm/min for 5 minutes at 36.5 o C. Results: The In-Ovation L exhibited lower SFF under control conditions and lower KFF under all displacement conditions than the 7th Generation and STb (all p < 0.001). No significant difference in SFF existed between the In-Ovation L and STb for a 2-mm GD of the MXC and 2-mm PD of the MXLI. A 2-mm GD of the MXC produced higher SFF and KFF than a 2-mm PD of the MXLI in all brackets (all p < 0.001). Conclusions: CLLBs with narrow bracket widths exhibited higher KFF than SL-LBs under tooth displacement conditions. CL-LBs and ligation methods should be developed to produce SFF and KFF as low as those in SL-LBs during the initial and leveling stage. [Korean J Orthod 2016;46(2):87-95]

Ferromagnetic-like properties of cuprous oxide (Cu2O) are induced through its interaction with chemisorbed surfactant poly(N-vinyl-2-pyrrolidone) (PVP), which alters the intrinsic d10 configuration of Cu ions. Structural and magnetism-related properties of intact Cu2O crystals (i-Cu2O) and those capped with PVP (c-Cu2O) were examined using various analytical instruments. SEM, TEM (corresponding selected area electron diffraction (SAED)), and XRD of i-Cu2O and c-Cu2O showed cubic and hexagonal shapes of single crystallinity with facets of {200} and {111}, respectively, resulting from the differential growth rates of the original identical crystals along the facets over time. Bulk magnetic susceptibility (χ) of i-Cu2O and c-Cu2O at room temperature in field-dependent magnetization and the difference in their magnetic moment in temperature-dependent magnetization showed diamagnetic and ferromagnetic properties, respectively. The difference in the fluorescence mode of X-ray absorption near edge structure (XAN...

The latent tracks formed on CR-39 solid state track detector on exposure of alpha radiations emanating from a collimated 241 Am source were developed by a chemical etching method. Alpha track images were captured by an optical microscope and were processed by using Image Pro-Plus (6.0) software. GEANT4 simulations were carried out to obtain the angular and energy distribution profiles of the alpha particles. Apart from fluence, geometric parameters like aspect ratio (the ratio of the major to minor axis) and the depth profiles of etched tracks were measured experimentally and correlated with simulated angular and energy profile of incident radiations. Reasonable agreement was observed in the fluence and depth profile information obtained from experiments and simulations.

Single crystalline orthorhombic phase tungsten trioxide monohydrate (O-WO3·H2O, space group: Pmnb) nanoplates with a clear morphology and uniform size distribution have been synthesized by the hydrothermal method and fabricated on the surface of fluorine doped tin oxide (FTO) coated glass substrates with selective exposure of the crystal facet by the finger rubbing method. The rubbing method can easily arrange the O-WO3·H2O nanoplates along the (020) facet on the FTO substrate. The O-WO3·H2O nanoplate can be converted to monoclinic phase WO3 (γ-WO3, space group: P21/n) with dominant crystal facet of (002) without destroying the plate structure. Crystal morphologies, structures, and components of the powders and films have been determined by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman, X-ray photoelectron spectroscopy, etc. The band gap energies of the O-WO3·H2O and γ-WO3 nanoplates were determined as ca. 2.26 and 2.49 eV, respectively. Photoelectrochemical prop...

MICROMEGAS detectors have been developed for the detection and tracking of charged and neutral particles. The control parameters of MICROMEGAS include materials, the type of gases, the mixing ratio of gases and the geometry. Simulations of MICROMEGAS are conducted to optimize the characteristics and performance with respect to the nature of the gas mixture, applied voltages of drift and amplification regions. Quantities such as the equi-potential lines, electron drift lines, and avalanche process of electrons and ions are calculated. Two MICROMEGAS detectors are built and characterized by using standard X-ray sources. The voltage gains are measured against the applied voltage range for different gas pressures and are compared with our simulation results.

International audience; In this article, we report the synthesis of ultra-long carbon nanotubes (CNTs) by thermal chemical vapour deposition method. Ultra-long, individual and aligned CNTs were directly grown on a flat silicon substrate. The orientation of the nanotubes was found parallel to the gas flow direction. The ultra-long CNTs were grown with different transition metallic salts, such as nickel chloride, iron (III) chloride, cobalt acetate and ruthenium acetate, as the catalysts. The influence of the growth conditions, such as growth temperature, reactive gas flow on the length and alignment of the CNTs was studied in detail. By using different catalysts, ultra-long single-walled carbon nanotubes (SWCNTs) or multi-walled carbon nanotubes (MWCNTs) were successfully grown. These ultra-long CNTs were transferred to other substrates by two methods. (1) The first method is to use polydimethylsiloxane as a stamp. (2) The second method is to use KOH as an etching agent. The diameter and length of the CNTs were characterised by transmission electron microscope, scanning electron microscope, atomic force microscope and Raman spectroscopy. The results indicate that the length of the CNTs can reach up to 4 mm. The diameter of the SWCNTs is in the range of 0.7-2.1 nm and the diameter of the MWCNTs is approximately 150 nm.

Color, as perceived through the eye, transcends mere information in the visible range of electromagnetism and serves as an agent for communication and entertainment. Mechanochromic systems have thus far only aimed at satisfying the sense of vision and have overlooked the possibility of generating acoustic vibrations in concert with their visual color responses that would enable the simultaneous satisfaction of the auditory system. Transcending the boundaries of the two senses (i.e., sound and color), herein a strategy for their concurrent and synesthetic fulfillment is elucidated by electrically actuating an organogel photonic device, controlled by a single input signal. This new class of devices that integrate a color module with a speaker is fabricated from a mechanochromic layer that comprises close-packed photonic lattice with an organogel matrix pervading the void fraction. Exploiting a dielectric elastomer actuator, the system's mechanical response permits the simultaneous, yet independent, exploration of visible-light reflection alongside audible sound-wave generation. Large areal strains at low frequencies of actuation tune the photonic stop-band, whereas the layer remains incompressible and exhibits negligible strain when actuated at higher frequencies (e.g., tens of Hz), thereby making it amenable to modulate sound and color simultaneously yet independently.

The authors report on the optical properties of multi-dimensional ZnO hybrid structures, consisting of film (2D)/nanorods (1D)/sapphire substrate (2D), grown by metalorganic chemical vapor deposition (MOCVD). Photoluminescence investigations reveal that the sample with top layer grown at a decreased growth temperature of 240 °C and increased reactor pressure of 5 Torr exhibits superior emission properties. The presence of strong E2high optical phonon mode at 438.5 cm− 1 in the visible micro-Raman spectra demonstrates the wurtzite nature of ZnO. Although the ultraviolet Raman scattering measurements of the hybrid structures reveal the presence of in-plane tensile stress in the top ZnO layer, the sample with the improved emission performance shows the release of tensile stress.

The photolithography process has generally been used for the making of catalyst layers used for the synthesis of CNTs due to its comparative ease. However, this method results in the formation of undesirable catalyst particles, which deteriorate the quality of the devices. Therefore, we tried to form a catalyst layer without using any lift-off or wet etching process, especially for the formation of carbon nanotube interconnects. After spin coating the samples, which were previously fabricated with several vias, with an iron-acetate solution, the catalyst layer was pulled down into the bottom of the holes through the force of gravity. We were able to remove the catalyst layer which was coated over undesirable areas, by TMAH (tetramethylammonium hydroxide, N(CH3)4OH) treatment. After the catalyst deposition process, we synthesized CNTs and observed them by scanning electron microscopy (SEM). © 2007 Published by Elsevier B.V.

We have developed MICROMEGAS (MICRO MEsh GASeous) detectors for detecting {\alpha} particles emitted from an 241-Am standard source. The voltage applied to the ionization region of the detector is optimized for stable operation at room temperature and atmospheric pressure. The energy of {\alpha} particles from the 241-Am source can be varied by changing the flight path of the {\alpha} particle from the 241 Am source. The channel numbers of the experimentally-measured pulse peak positions for different energies of the {\alpha} particles are associated with the energies deposited by the alpha particles in the ionization region of the detector as calculated by using GEANT4 simulations; thus, the energy calibration of the MICROMEGAS detector for {\alpha} particles is done. For the energy calibration, the thickness of the ionization region is adjusted so that {\alpha} particles may completely stop in the ionization region and their kinetic energies are fully deposited in the region. The efficiency of our MICROMEGAS detector for {\alpha} particles under the present conditions is found to be ~ 97.3 %. We have developed MICROMEGAS (MICRO MEsh GASeous) detectors for detecting a particles emitted from an$^{241}$Am standard source. The voltage applied to the ionization region of the detector is optimized for stable operation at room temperature and atmospheric pressure. The energy of a particles from the$^{241}$Am source can be varied by changing the flight path of the a particle from the$^{241}$Am source. The channel numbers of the experimentally-measured pulse peak positions for different energies of the a particles are associated with the energies deposited by the alpha particles in the ionization region of the detector as calculated by using GEANT4 simulations, thus, the energy calibration of the MICROMEGAS detector for a particles is done. For the energy calibration, the thickness of the ionization region is adjusted so that a particles may completely stop in the ionization region and their kinetic energies are fully deposited in the region. The efficiency of our MICROMEGAS detector for a particles under the present conditions is found to be ~97.3%. We have developed MICROMEGAS (MICRO MEsh GASeous) detectors for detecting {\alpha} particles emitted from an 241-Am standard source. The voltage applied to the ionization region of the detector is optimized for stable operation at room temperature and atmospheric pressure. The energy of {\alpha} particles from the 241-Am source can be varied by changing the flight path of the {\alpha} particle from the 241 Am source. The channel numbers of the experimentally-measured pulse peak positions for different energies of the {\alpha} particles are associated with the energies deposited by the alpha particles in the ionization region of the detector as calculated by using GEANT4 simulations; thus, the energy calibration of the MICROMEGAS detector for {\alpha} particles is done. For the energy calibration, the thickness of the ionization region is adjusted so that {\alpha} particles may completely stop in the ionization region and their kinetic energies are fully deposited in the region. The efficiency of our MICROMEGAS detector for {\alpha} particles under the present conditions is found to be ~ 97.3 %.

The one-dimensional ZnO nanostructures prepared through thermal evaporation under various cooling down procedures by changing the flow rates of the carrier gas and the reactive gas were investigated. The nanorod structures were changed into the nanonail types with a broad head through the reduction of the flow rate of the carrier gas. The decrease of the reactive gas reduced the length of the nail heads due to the limited mass transport of reactive gas. The intensity ratio of the ultraviolet emission/green emission of photoluminescence was proportional to the length of the broad head showing a larger surface area. The vertically aligned nanostructures were grown along the [0 0 0 1] direction of ZnO regardless of the aligned directions. The crystal direction of the nanostructures was determined by that of the initial ZnO crystal.

The density-controlled carbon nanotubes (CNTs) were grown on the iron nanoparticles by using the freeze–dry method. The iron-acetate [Fe(II)(CH3COO)2] solution was used for the preparation of the catalytic iron nanoparticles. The density of CNTs was controlled in order to achieve the enhancement in the field emission process. Furthermore, the patterning of the iron nanoparticle catalyst layer for the fabrication of electronic devices was simply achieved by using an alkaline solution, TMAH (tetramethylammonium hydroxide). We applied this patterning process of catalyst layer to the formation of the electron emitter with under-gate type triode structure.

We studied the growth characteristics of carbon nanotubes which were grown from the uniformly dispersed iron nanoparticles prepared from iron acetate [Fe(II)(CH3COO)2]. The density of CNT was controlled from precursor concentrations. We also investigated the field emission properties of CNTs. We found that the optimization of CNT density is an important factor for field emission properties. Patterning process of iron acetate was achieved simply by alkaline solution.

The density controlled carbon nanotubes (CNTs) are grown on the iron acetate nanoparticles by using the freeze‐dry method. The iron‐acetate [Fe(||)(CH3COO)2] solution is used to prepare the catalytic iron nanoparticles. The density of CNTs is controlled in order to enhance the field emission process. Furthermore, the patterning of the iron nanoparticle catalyst‐layer for the fabrication of electronic devices is simply achieved by using alkaline solution, TMAH (tetramethylammonium hydroxide). We applied this patterning process of catalyst layer to form the electron emitter with under‐gate type triode structure.

For field emitters as a cathode of traveling wave tube–microwave power amplifiers (TWT–MPA), field-emission (FE) properties of in situ grown carbon nanotubes (CNTs) onto electrically conducting substrate were systematically characterized. CNTs grown on the Co/TiN coated Ta substrate with properly controlled process exhibited the best FE property. The maximum current density and corresponding total emission current were 3.5 mA/cm 2 and ∼1.7 mA at 21.6 V/μm, respectively. Details on the correlation between the FE properties and the morphological parameters will be discussed.

The performance and photocatalytic activity of the well-known CdS/ZnO nanorod array system were improved significantly by the layer-by-layer heterojunction structure fabrication of a transparent conductive oxide (TCO) CdO layer on the CdS/ZnO nanorods. Accordingly, a CdO layer with a thickness of approximately 5-10 nm can be formed that surrounds the CdS/ZnO nanorod arrays after annealing at 500 °C under air. At an external potential of 0.0 V vs. Ag/AgCl, the CdO/CdS/ZnO nanorod array electrodes exhibit an increased incident photon to conversion efficiency, which is significantly higher than that of the CdS/ZnO nanorod array electrodes. The high charge separation between the electrons and holes at the interfaces of the heterojunction structure results from the specific band energy structure of the photoanode materials, and the unique high conductivity of the CdO layer is attributed to the suppression of electron-hole recombination; this suppression enhances the photocurrent density of the CdO/CdS/ZnO nanorod arrays. The photoresponse of the electrodes in an electrolytic solution without sacrificial agents indicated that the CdO layer also has the ability to suppress the well-known photocorrosive behavior of CdS/ZnO nanorods.

Neutron shielding simulations by using GEANT4 and PHITS code are performed. As a neutron source, $^{252}$Cf is considered and the energy distribution of the neutrons emitted from $^{252}$Cf is assumed the Watt fission spectrum. The neutron dose equivalent rates with and without the shield are estimated for shielding materials such as graphite, iron, polyethylene, NS-4-FR and KRAFTON-HB. For the neutron shielding simulations by using GEANT4, high precision (G4HP) model with G4NDL 4.2 based on ENDF-VII data are used. And for PHITS simulations, JENDL-4.0 library are used for the same purpose. It is found that differences between the shielding calculations by using GEANT4 with G4NDL 4.2 and PHITS with JENDL-4.0 library are not significant for all cases considered in this work. We investigate the accuracy of the neutron dose equivalent rates obtained from GEANT4 and PHITS by comparing our simulation results with experimental data and other values calculated earlier. Calculated neutron dose equivalent rates agree well with the experimental dose equivalent rates within 20% errors except for polyethylene. For polyethylene material, discrepancy between the calculations and the experiments are up to 40% but all simulations show consistent features.

At room-temperature ambient, carbon nanotubes (CNTs) were selectively synthesized on each bridge of the microheater array (MHA) formed on a glass substrate. Both multiwalled (MW) and single-walled CNTs could be formed by controlling the MHA temperature, which was confirmed from Raman spectroscopy. By incorporating the selectively grown MW CNTs into the lateral-gated field-emitter arrays, high current density of electron emission was observed with low device leakage.

Membranes with nano-apertures are versatile templates that possess a wide range of electronic, optical and biomedical applications. However, such membranes have been limited to silicon-based inorganic materials to utilize standard semiconductor processes. Here we report a new type of flexible and free-standing polymeric membrane with nano-apertures by exploiting high-wettability difference and geometrical reinforcement via multiscale, multilevel architecture. In the method, polymeric membranes with various pore sizes (50-800 nm) and shapes (dots, lines) are fabricated by a hierarchical mould-based dewetting of ultraviolet-curable resins. In particular, the nano-pores are monolithically integrated on a two-level hierarchical supporting layer, allowing for the rapid (

Nano-objects would be of great interest for the development of new types of electronic circuits if one could combine their nanometer scale with original functionalities beyond the conventional transistor action. However, the associated circuit architectures will have to handle the increasing variability and defect rate intrinsic to the nanoscale. In this context, there is a very fast growing interest for memory devices, and in particular resistive memory devices, used as building blocks in reconfigurable circuits tolerant to defects and variability. It was recently shown that optically gated carbon nanotube field effect transistors (OG-CNTFETs) based on large assemblies of nanotubes covered by an organic photoconductive thin film can be operated as programmable resistors and thus used as artificial synapses in circuits with function-learning capabilities. Here, the potential of such approach is evaluated in terms of scalability by integrating and addressing several individually programmable resistances on a single carbon nanotube. In addition, the charge storage mechanism can be controlled at a length scale smaller than the device length allowing to also program the direction in which the current flows. It thus demonstrates that a single nanotube section can combine all-in-one the properties of an analog resistive memory and of a rectifying diode with tunable polarity.

Field emission properties of CNTs(carbon nanotubes) have been investigated in the various field, such as flat panel display and x-ray sources. Especially, the x-ray tube which fabricated using the CNTs can be operated with low power consumption compare with filament-based x-ray tubes. The cold cathode — CNTs- can be operated at the lower voltage and the electron which coming out from the CNTs can be controlled easilly by focus electrode. And for high emission current, the device should be stable at the high operate voltage. The gate electrode-mesh-type electrode- can be layered by using glass frit and firing process. At this point, the mesh structure can be controlled for the higher adhesion force which is for the emission stability at the high voltage. The glass frit could be act effectively between mesh electrode and insulating layer because of the designed mesh structure.

The triode-typed field emission (FE) devices using carbon nanotube (CNT) emitters for the x-ray application were fabricated. For the stability of the device, the leakage current between cathode and gate, and the emission current to the anode electrode should be controlled. We realized that the thickness of insulating layer-gap distance between cathode and gate- and the space between the gate electrodes-electron path from cathode and anode- should be controlled for the ratio of the current from cathode to anode (Ia) to the current from cathode to gate (Ig). The ratio of Ia to Ig can be represented the device efficiency. The rectangular-mesh electrode and screen printed insulating layer were controlled for Ia/Ig. When the size of gate hole was the 50 by 700 um — the electrode size is 25 by 700 um — and the thickness of insulator layer was 65 um, the maximum ratio of Ia/(Ia+Ig) was 0.63.

A (040)-crystal facet engineered BiVO4 ((040)-BVO) photoanode is investigated for solar fuel production. The (040)-BVO photoanode is favorable for improved charge carrier mobility and high photocatalytic active sites for solar light energy conversion. This crystal facet design of the (040)-BVO photoanode leads to an increase in the energy conversion efficiency for solar fuel production and an enhancement of the oxygen evolution rate. The photocurrent density of the (040)-BVO photoanode is determined to be 0.94 mA cm−2 under AM 1.5 G illumination and produces 42.1% of the absorbed photon-to-current conversion efficiency at 1.23 V (vs RHE, reversible hydrogen electrode). The enhanced charge separation efficiency and improved charge injection efficiency driven by (040) facet can produce hydrogen with 0.02 mmol h−1 at 1.23 V. The correlation between the (040)-BVO photoanode and the solar fuel production is investigated. The results provide a promising approach for the development of solar fuel production using a BiVO4 photoanode.

A custom designed optical system is reported for tissue spectroscopy over four wavelengths of 677 nm, 780 nm, 830 nm, and 977 nm. A high speed laser driver is designed with a flat frequency response using pre-emphasis circuit. The driver is employed for high current in high power lasers. Phantom and intra-lipid experiments are performed to extract optical parameters of a turbid media. Broadband measurement is used to extract optical parameters of the phantom model simulating a breast tissue using forward scattering models. The optical parameters () are extracted with a very good accuracy.

The interesting electrochemical performances and magnetic properties of hierarchical NiO hollow microspheres were investigated. A rational formation mechanism of NiO hollow spheres from Ni(OH)2 was proposed on the basis of agglomerated-mediated growth.

We investigated the optical properties of ZnO nanorods on nanosilicon-on-insulator using variable temperature photoluminescence (PL) spectroscopy, and explored the contribution of exciton–phonon coupling and surface resonance effect on the emission characteristics of the nanorods. The low-temperature (

For field emitters as an electron source of traveling wave tube microwave power amplifiers, field-emission properties of multiwalled carbon nanotubes (MWNTs) grown in situ onto an electrically conducting substrate were systematically characterized. MWNTs grown on a TiN-coated Ta substrate with NH3 plasma pre-treatment exhibited the best field-emission property. The maximum current density and corresponding total emission current were 9.4 mA/cm2 and ∼5 mA at 18.8 V/μm, respectively. These enhanced field-emission properties are caused by the highly conducting buffer layer (TiN), the optimum metal substrate (Ta) that produces high field-emission current, and the control of site density of MWNTs by NH3 plasma pre-etching. Details on the correlation between the field-emission properties and the morphological parameters will be discussed.