Application of high-sensitivity radon monitor on walk-in type radon calibration chamber at KRISS.

This paper introduces the KRISS-Rn4, a high-sensitivity radon monitor with four detection cells, installed within a walk-in type radon calibration chamber at KRISS. The KRISS-Rn4 exhibits enhanced energy resolution through channel-by-channel signal processing and data acquisition. Results reveal that it achieves lower statistical fluctuations and faster response times in monitoring test atmospheres compared to commercial devices.

Optimal Coverage of Full Frequency Reuse in FFR Networks in Relation to Power Scaling of a Base Station.

As a strategy to coordinate inter-cell interference in cellular networks, a fractional frequency reuse (FFR) system is proposed, in which the frequency bandwidth is split into two orthogonal bands; users staying near the center of a FFR cell use the band with a frequency reuse (FR) factor of one (i.e., full FR), and users located close to the cell edge utilize the band with a FR factor greater than one (i.e., partial FR). Full FR coverage, which identifies full FR and partial FR regions (that is, near-center and near-edge regions) within a FFR cell, has a crucial effect on system performance. Some of the authors of this paper recently investigated the optimization of full FR coverage to maximize system throughput. They analytically showed that under the constraint of satisfying a specified target outage probability, the optimal full FR coverage is a non-increasing function of base station power when all base station powers in the cellular network are scaled at an equal rate. Interestingly, in this paper, it is proven that as the power of a single base station is scaled, the optimal full FR coverage in that cell is a non-decreasing function of base station power. Our results provide useful insight into the design of full FR coverage in relation to the transmit power of a base station. It gives a deeper understanding of the intricate relationship between important FFR system parameters of base station power and full FR coverage.

High-Performance γ-Al2O3 Multichannel Tube-Type Tight Ultrafiltration Membrane Using a Modified Sol-Gel Method.

We introduced a modified sol-gel method using polyvinyl alcohol (PVA) as an additive to improve the permeability of γ-Al2O3 membranes by minimizing the thickness of the selective layer and maximizing the porosity. First, the analysis revealed that the thickness of γ-Al2O3 decreased as the concentration of PVA increased in the boehmite sol. Second, the properties of the γ-Al2O3 mesoporous membranes were greatly influenced by the modified route (method B) compared to the conventional route (method A). The results showed that the porosity and surface area of the γ-Al2O3 membrane increased, and the tortuosity decreased considerably using method B. This effect was attributed to the adsorption of PVA molecules on the surface of the boehmite particles, which depended on the synthesis route. The experimentally determined pure water permeability trend and the Hagen-Poiseuille mathematical model confirmed that the modified method improved the performance of the γ-Al2O3 membrane. Finally, the γ-Al2O3 membrane fabricated via a modified sol-gel method with a pore size of 2.7 nm (MWCO = 5300 Da) exhibited a pure water permeability of over 18 LMH/bar, which is three times higher than that of the γ-Al2O3 membrane prepared using the conventional method.

Effect of the Peptization Process and Thermal Treatment on the Sol-Gel Preparation of Mesoporous α-Alumina Membranes.

Compared to traditional membrane materials, alumina membranes are particularly beneficial for industrial wastewater treatment. However, the development of mesoporous α-alumina membranes for ultrafiltration applications is still a challenge due to uncontrolled pore size. In this study, we optimized the sol-gel method for the fabrication of a high-performance mesoporous α-alumina membrane. The peptization conditions (pH and peptization time) and phase transformation of boehmite were investigated to achieve better properties of the α-alumina membrane. The surface properties of the membrane were observed to be improved by reducing the system pH to 3.5 and increasing the peptization time to 24 h. The effect of sintering temperature on the phase transformation behavior, microstructures and performance of the membranes was also elucidated. An α-alumina ultrafiltration membrane with an average thickness of 2 µm was obtained after sintering at 1100 °C. The molecular weight cut-off of the α-alumina membrane, as obtained by the filtration of aqueous PEG solution, was approximately 163 kDa (12.5 nm). This is the smallest pore size ever reported for pure α-alumina membranes.

Development of TiO2-coated YSZ/silica nanofiber membranes with excellent photocatalytic degradation ability for water purification.

Numerous reports have elucidated that TiO2 nanoparticles (TiO2-NPs) exhibit respectable photocatalytic degradation capacities due to their high specific surface areas. However, the current recovery process leads to a loss of TiO2-NPs; therefore, there is a need to immobilize TiO2-NPs on the substrate used. Herein, TiO2-coated yttria-stabilized zirconia/silica nanofiber (TiO2-coated YSZ/silica NF) was prepared by coating TiO2 on the surface of YSZ/silica NF using a sol-gel process. The TiO2 coating layer on the nanofiber surface improved the separation ability of the membrane as well as the photocatalytic degradation ability. The pore size of the TiO2-coated YSZ/silica NF membrane was less than that of the pristine YSZ/silica NF membrane, and it rejected over 99.6% of the 0.5 µm polymeric particles. In addition, the TiO2-coated YSZ/silica NF membrane showed excellent adsorption/degradation of humic acid (HA, 88.2%), methylene blue (MB, 92.4%), and tetracycline (TC, 99.5%). Six recycling tests were performed to evaluate the reusability of the TiO2-coated YSZ/silica NF membrane. The adsorption/degradation efficiency for HA, MB, and TC decreased by 3.7%, 2.8%, and 2.2%, respectively. We thus verified the high separation ability, excellent photocatalytic degradation ability, and excellent reusability of the TiO2-coated YSZ/silica NF membranes.

Performance of a segmented HPGe detector at KRISS.

A 24 segmented HPGe coaxial detector was set up with a digitized data acquisition system (DAQ). The DAQ was composed of a digitizer (5 × 107sampling/s), a Field-Programmable Gate Array (FPGA), and a real time operating system. The Full Width Half Maximum (FWHM), rise time, signal characteristics, and spectra of a 137Cs source were evaluated. The data were processed using an in-house developed gamma-ray tracking system.

Absolute measurement of (198)Au activity in gold foil using plastic scintillators and a well-type NaI(Tl) detector.

A beta-gamma coincidence system has been developed for measuring (198)Au activity in gold foils. The system was validated by Monte Carlo simulations and by measuring the activity of a (60)Co point-source. To study effects such as self-shielding of beta particles in gold foils, (198)Au activity measurements and simulations were performed for various scintillators and foil sizes. The measured (198)Au activities were ~1% above the reference activity, which might be due to self-shielding of beta particles. The measured and simulated (198)Au activities agreed, suggesting feasibility of precise activity measurement.

New method to incorporate Type B uncertainty into least-squares procedures in radionuclide metrology.

We discuss a new method to incorporate Type B uncertainty into least-squares procedures. The new method is based on an extension of the likelihood function from which a conventional least-squares function is derived. The extended likelihood function is the product of the original likelihood function with additional PDFs (Probability Density Functions) that characterize the Type B uncertainties. The PDFs are considered to describe one's incomplete knowledge on correction factors being called nuisance parameters. We use the extended likelihood function to make point and interval estimations of parameters in the basically same way as the least-squares function used in the conventional least-squares method is derived. Since the nuisance parameters are not of interest and should be prevented from appearing in the final result, we eliminate such nuisance parameters by using the profile likelihood. As an example, we present a case study for a linear regression analysis with a common component of Type B uncertainty. In this example we compare the analysis results obtained from using our procedure with those from conventional methods.

A preliminary study for the development of reference material using oyster for determination of (137)Cs, (90)Sr and plutonium isotopes.

A new reference material for the determination of (137)Cs, (90)Sr and Pu isotopes ((238)Pu and (239,240)Pu) is being developed using dried oyster matrix by Korea Research Institute of Standards and Science (KRISS). The oyster was collected from Tongyoung harbour, southern part of Korea and the artificial radionuclides ((137)Cs, (90)Sr, (238)Pu and (239,240)Pu) were spiked into the material. After pretreatment and processing, the material was tested for homogeneity and massic activities were determined by measuring (137)Cs, (90)Sr, (238)Pu and (239,240)Pu. The reference value and extended uncertainty for those isotopes will be reported later.

Effect of hydroxyapatite-containing microspheres embedded into three-dimensional magnesium phosphate scaffolds on the controlled release of lysozyme and in vitro biodegradation.

The functionality of porous three-dimensional (3D) magnesium phosphate (MgP) scaffold was investigated for the development of a novel protein delivery system and biomimetic bone tissue engineering scaffold. This enhancement can be achieved by incorporation of hydroxyapatite (HA)-containing polymeric microspheres (MSs) into a bulk MgP matrix, and a paste-extruding deposition (PED) system. In this work, the amount of MS and HA was precisely controlled when manufacturing MS-embedded MgP (MS/MgP) composite scaffolds. The main influence was researched in terms of in vitro lysozyme-release, in vitro biodegradation, mechanical properties, and in vitro calcification. The controlled release of lysozyme was indicated, while showing graded release patterns according to HA content. The composite scaffolds degraded gradually with MS content and degradation time. Due to the effect of HA inclusion, the higher HA-containing MS/MgP scaffolds could, not only delay the biodegradation process but also, compensate for the possible loss of mechanical properties. In this regard, it is reasonable to confirm the inverse relationship between biodegradation and corresponding compressive properties. In order to encourage bioactivity and osteoconductivity, the MS/MgP composite scaffolds were subjected to simulated body fluid treatment. Calcium deposition was, in turn, improved with increasing MS and HA content over time. This quantitative result was also proved using morphological and elemental analysis. In summary, a significant transformation of a monolithic MgP scaffold was directed toward a multifunctional bone tissue engineering scaffold equipped with controlled protein delivery, biodegradability, and bioactivity.

A simultaneous process of 3D magnesium phosphate scaffold fabrication and bioactive substance loading for hard tissue regeneration.

A novel room temperature process was developed to produce a 3D porous magnesium phosphate (MgP) scaffold with high drug load/release efficiency for use in hard tissue regeneration through a combination of a paste extruding deposition (PED) system and cement chemistry. MgP scaffolds were prepared using a two-step process. The first step was fabrication of the 3D porous scaffold green body to control both the morphology and pore structure using a PED system without hardening. The second step was cementation, which was carried out by immersing the scaffold green body in the binder solution for hardening instead of the typical sintering process in ceramic scaffold fabrication. Separation of the manufacturing process and cement reaction was important to secure enough time to fabricate a 3D scaffold with various sizes and architectures under homogeneous extruding conditions. Because the whole process is carried out at room temperature, the bioactive molecules, which are easily denatured by heat, may apply to scaffolds during the process. Lysozyme was selected as a model bioactive substance to demonstrate the efficiency of this process; this was directly mixed into MgP powder to introduce homogeneous distribution in the scaffold. The extruding paste for the PED system was prepared using the MgP-lysozyme blended powder as starting materials. That is, both 3D scaffold fabrication and functionalization of the scaffold with bioactive substances could be carried out simultaneously. This process significantly enhanced both drug loading efficiency and release performance compared to the typical sintering process, where the drug is generally loaded by adsorption after heat treatment. The MgP scaffold developed in this study satisfied the required conditions for scaffolding in hard tissue regeneration in an ideal manner, including 3 dimensionally well-interconnected pore structures, favorable mechanical properties, biodegradability, good cell affinity and in vitro biocompatibility; thus, it has excellent potential for application in the field of biomaterials.

Atmospheric input of ¹³7Cs and 239,240Pu isotopes in Korea after the Fukushima nuclear power plant accident.

Caesium isotopes ((134)Cs and (137)Cs) and (239,240)Pu in rainwater and dry deposition have been analyzed by Korea Research Institute of Standards and Science (KRISS) since the Fukushima nuclear power plant (NPP) accident in March 2011. The concentrations of (239,240)Pu and (137)Cs in the rainwater are 2.6±1.0 to 15±3 µBq/kg and 0.01 to 0.36 mBq/kg, respectively. The concentrations are concordant to those observed before the Fukushima NPP accident, on the other hand, the monthly depositional flux of (239,240)Pu and (137)Cs are much lower than the amounts observed after Fukushima NPP accident and in Monaco in 1998-2001. This confirms that the Fukushima NPP accident caused no significant impact in Korea.

Hydroxyapatite-containing gelatin/chitosan microspheres for controlled release of lysozyme and enhanced cytocompatibility.

A simple polymer microsphere was dramatically transformed into a novel protein delivery carrier by the incorporation of hydroxyapatite (HA) into the polymeric phase. In this study, nano-sized HA was uniformly mixed in a gelatin/chitosan solution to ultimately form composite microspheres with a well-defined spherical shape. The physicochemical properties of these microspheres were extensively characterized in terms of morphological analysis, crystalline structure, swelling properties, etc. The average sizes of the microspheres increased slightly due to a gradual increase in viscosity of the HA-containing gelatin/chitosan solution. The typical characteristics of HA used in this work were confirmed to result in the successful fabrication of composite microspheres with graded HA content (0 to 55 %). The HA-containing microspheres showed outstanding features with respect to in vitro calcification, high protein loading/controlled release, and cytocompatibility. First, the addition of HA made composite microspheres greatly facilitated in vitro calcium ion deposition while initiating nucleation in stimulated body fluid (SBF). Second, the HA-involved composite microspheres acted as a highly efficient delivery system when compared to bare polymer microspheres. These features were mostly a result of the relatively good swelling properties and protein adsorption capability of HA. Third, the HA-containing composite microspheres showed significantly improved initial cell adhesion/proliferation. The increase in HA content and surface roughness provided a favorable matrix for the attached cells, which grew extensively in elongated, spindle-like shapes. In summary, this study investigated a high protein loading/controlled release system consisting of nano-sized HA as a key component, which contributed superior features of in vitro calcification and cytocompatibility.

The effect of controlled release of PDGF-BB from heparin-conjugated electrospun PCL/gelatin scaffolds on cellular bioactivity and infiltration.

Heparin-conjugated electrospun poly(ε-caprolactone) (PCL)/gelatin scaffolds were developed to provide controlled release of platelet-derived growth factor-BB (PDGF-BB) and allow prolonged bioactivity of this molecule. A mixture of PCL and gelatin was electrospun into three different morphologies. Next, heparin molecules were conjugated to the reactive surface of the scaffolds. This heparin-conjugated scaffold allowed the immobilization of PDGF-BB via electrostatic interaction. In vitro PDGF-BB release profiles indicated that passive physical adsorption of PDGF-BB to non-heparinized scaffolds resulted in an initial burst release of PDGF-BB within 5 days, which then leveled off. However, electrostatic interaction between PDGF-BB and the heparin-conjugated scaffolds gave rise to a sustained release of PDGF-BB over the course of 20 days without an initial burst. Moreover, PDGF-BB that was strongly bound to the heparin-conjugated scaffolds enhanced smooth muscle cell (SMC) proliferation. In addition, scaffolds composed of 3.0 µm diameter fibers that were immobilized with PDGF-BB accelerated SMC infiltration into the scaffold when compared to scaffolds composed of smaller diameter fibers or scaffolds that did not release PDGF-BB. We concluded that the combination of the large pore structure in the scaffolds and the heparin-mediated delivery of PDGF-BB provided the most effective cellular interactions through synergistic physical and chemical cues.

Composite system of PLCL scaffold and heparin-based hydrogel for regeneration of partial-thickness cartilage defects.

Delivering isolated chondrocytes with matrix is a promising approach to promote the cartilage repair. The present study attempted to combine the advantages of porous scaffold and hydrogel in delivering chondrocytes to partial-thickness cartilage defects. An electrospun, gelatin-incorporated PLCL scaffold mechanically similar to natural cartilage was fabricated, and chondrocytes were seeded using an injectable heparin-based hydrogel for efficient cell seeding. The scaffold/hydrogel composite showed more enhanced expression of chondrogenic genes and production of GAGs than those prepared without hydrogel. In addition, significant cartilage formation showing good integration with surrounding, similar to natural cartilage, was observed by scaffold/hydrogel composite system in partial-thickness defects of rabbit knees while no regeneration was observed in control defects. Although no exogenous chondrogenic factors were added, it was evident that the scaffold/hydrogel composite system was highly effective and better than the scaffold alone system without hydrogel for cartilage regeneration both in vitro and in vivo.

Calibration of KRISS reference ionization chamber for key comparison of (99m)Tc measurement.

KRISS, as the national metrology institute of Korea, has used a reference ionization chamber system to certify the activity of (99m)Tc aqueous sources, but could only recently participate in a comparison exercise by the BIPM (BIPM.RI(II)-K4.Tc-99m) to secure the international equivalence of (99m)Tc radioactivity measurement by way of the BIPM transfer instrument (SIRTI). The KRISS ionization chamber system was calibrated about 100 days before the comparison with a (99m)Tc solution source standardized by the 4πß(LS)-γ(NaI(Tl)) coincidence counting method. During the comparison, beginning with a higher activity mother solution, the KRISS ionization chamber measured its specific activity without a dilution. The activity of a diluted-solution source was measured by the SIRTI at the same time.

Comparison of (99m)Tc activity measurements at the KRISS using the new SIRTI of the BIPM.

In 2010, a comparison of activity measurements of (99m)Tc was carried out at the KRISS using the BIPM's Transfer Instrument of the International Reference System (SIRTI). The transfer instrument and the KRISS coincidence measurement method are briefly described. The degrees of equivalence with the key comparison reference value and between the present KRISS result and the earlier participants in the SIRTI and SIR comparisons have been evaluated. World-wide consistency of activity measurements of (99m)Tc is demonstrated.

Enhanced regeneration of the ligament-bone interface using a poly(L-lactide-co-ε-caprolactone) scaffold with local delivery of cells/BMP-2 using a heparin-based hydrogel.

Recently, the ligament-bone (LTB) junction has been emphasized for the effective transmission of mechanical force and the reduction in stress concentration between the soft ligament and hard bone tissue. The aim of this study was to regenerate an integrated LTB interface by inoculating LTB-relevant cells, isolated from fibrocartilage (FC) or ligament (LIG), separately into each designated region in a single porous cylindrical PLCL scaffold. An injectable, heparin-based hydrogel that has proved to be effective in the culture of chondrocytes as well as the sustained release of growth factor was employed to locally deliver fibrochondrocytes and osteoinductive bone morphogenetic protein-2 (BMP-2) into the FC region, to promote FC regeneration. In in vitro experiments the hydrogel-combined FC systems produced significantly larger amounts of calcium and glycosaminoglycans (GAGs), but less collagen and DNA than FC samples without the hydrogel and all LIG samples. After in vivo subcutaneous implantation in mice for 8 weeks the secreted calcium and GAG contents of the hydrogel-containing FC samples were superior or similar to those of the in vitro hydrogel-containing FC samples at 6 weeks. As a result of the enhanced production of calcium and GAG, the in vivo hydrogel-containing FC samples produced the highest compressive modulus among all samples. Histological and immunofluorescence analysis as well as elemental analysis also confirmed a denser and more homogeneous distribution of calcium, GAG, osteocalcin and neovascularization marker in the in vitro/in vivo hydrogel-containing FC systems than those without hydrogel. These results also show the beneficial effects of BMP-2 added using the hydrogel. In summary, the use of a heparin-based hydrogel for the local delivery of fibrochondrocytes and BMP-2 could accelerate the maturation and differentiation of LTB-specific FC tissues, and it was also possible to recreate the unique stratification of calcified FC and LIG tissues in a single porous PLCL scaffold in terms of both biochemical and biomechanical properties.

Regeneration of Achilles' tendon: the role of dynamic stimulation for enhanced cell proliferation and mechanical properties.

The tissue engineering of tendon was studied using highly elastic poly(L-lactide-co-epsilon-caprolactone) (PLCL) scaffolds and focusing on the effect of dynamic tensile stimulation. Tenocytes from rabbit Achilles tendon were seeded (1.0 x 10(6) cells/scaffold) onto porous PLCL scaffolds and cultured for periods of 2 weeks and 4 weeks. This was performed in a static system and also in a bioreactor equipped with tensile modulation which mimicked the environmental surroundings of tendons with respect to tensile extension. The degradation of the polymeric scaffolds during the culture was relatively slow. However, there was an indication that cells accelerated the degradation of PLCL scaffolds. The scaffold/cell adducts from the static culture exhibited inferior strength (at 2 weeks 350 kPa, 4 weeks 300 kPa) compared to the control without cells (at 2 weeks 460 kPa, 4 weeks 340 kPa), indicating that the cells contributed to the enhanced degradation. On the contrary, the corresponding values of the adducts from the dynamic culture (at 2 weeks 430 kPa, 4 weeks 370 kPa) were similar to, or higher than, those from the control. This could be explained by the increased quantity of cells and neo-tissues in the case of dynamic culture compensating for the loss in tensile strength. Compared with static and dynamic culture conditions, mechanical stimulation played a crucial role in the regeneration of tendon tissue. In the case of the dynamic culture system, cell proliferation was enhanced and secretion of collagen type I was increased, as evidenced by DNA assay and histological and immunofluorescence analysis. Thus, tendon regeneration, indicated by improved mechanical and biological properties, was demonstrated, confirming the effect of mechanical stimulation. It could be concluded that the dynamic tensile stimulation appeared to be an essential factor in tendon/ligament tissue engineering, and that elastic PLCL co-polymers could be very beneficial in this process.

The effect of gelatin incorporation into electrospun poly(L-lactide-co-epsilon-caprolactone) fibers on mechanical properties and cytocompatibility.

Very elastic poly(L-lactide-co-epsilon-caprolactone) (PLCL) (50:50) copolymer blended with gelatin was electrospun into microfibers from a hexafluoroisopropanol solution. PLCL fiber sheet exhibited the unique soft and flexible behavior while gelatin fiber was hard and brittle. As the gelatin content of PLCL/gelatin fibers increased, Young's modulus was increased, but the elongation was decreased compared to those of PLCL. However, fibers containing 10-30 wt% gelatin demonstrated an enhanced tensile strength with still high elongation to be beneficial for tissue engineering scaffolds. The cytocompatibility of electrospun fiber sheets was evaluated by fibroblasts (NIH-3T3) cell culture. The initial cell adhesion on various fibers after 5h was somewhat similar, but in the order of PLCL>PLCL70/gelatin30 approximately PLCL50/gelatin50>PLCL90/gelatin10 approximately gelatin>PLCL30/gelatin70. However, the cell proliferation exhibited a completely different and strong dependence on the fiber composition: a very high proliferation rate on PLCL90/gelatin10, followed by PLCL>gelatin>PLCL70/gelatin30. Such an enhanced effect of gelatin, especially at 10 wt% content, on strength and cytocompatibility of PLCL/gelatin fibers would be very preferable for tissue engineering scaffolds.