DRAM as source of randomness

Proposed is a true random number generator (TRNG) based on collision between DRAM accesses and refresh operations. The generator repeatedly executes a short code and reads a part of time counter register after each execution without an explicit post-processing. The simplicity allows the generation of true random numbers with a reasonable efficiency on commodity desktop computers without special devices and opens the possibility for simple TRNG on devices that use DRAM. Although very simple, the quality of the bit sequence is surprisingly good, as demonstrated by test results using NIST test suite.     

Evaluating longitudinal vibration characteristics of bonded strands embedded in prestressed concrete beams by a system identification approach

This study is to investigate the wire rope governing equation in order to establish the longitudinal vibration characteristics of bonded PSC strands. For this purpose, the longitudinal vibration tests have been conducted for six bonded PSC specimens with the different stress levels. Subsequently, the wave velocities of the strands have been estimated from the test results. Then, a sensitivity-based system identification algorithm has been applied to evaluate the constitutive constants of the strands using the measured wave velocities. The present study demonstrates that the longitudinal dynamic behaviour of the strands is governed by coupled extensional-torsional oscillations. The study also reveals that longitudinal elastic wave velocity of not only the bonded strands but also unbounded strands is nonlinearly increased as the applied tensile stress level increases.     

Designs of Bioreactor Systems for Solvent-Free Lipase-Catalyzed Synthesis of Fructose–Oleic Acid Esters

Fructose–oleic acid esters, biodegradable, biocompatible and biobased surfactants and value-added products were synthesized under solvent-free conditions at 65 °C in stirred-batch mode and using several different bioreactor systems. For a stirred-tank bioreactor (STBR) using fed-batch fructose addition and 5.0 wt.% immobilized Rhizomucor miehei lipase (Lipozyme^® IM, Novozymes, Franklinton, NC), the conversion yield was over 80%, and the initial rate of the reaction was comparable to previously obtained results using tert-butanol during the initial phase. The bioreactor systems contained a packed “desorption” column (DC) containing fructose crystals and silica gel for delivery of saccharide, and either a STBR or packed-bed bioreactor (PBBR). The liquid stream, initially containing oleic acid and a mixture of fructose–oleic acid esters at a ratio of 75/25 w/w, was continuously recirculated throughout the system. The PBBR system yielded the highest conversion (84.4%) and rate of reaction subsequent to the addition of 10 wt.% molecular sieves during the latter stage of reaction; however, the reaction rate was several-fold lower than the batch mode reactions due to the lower fructose concentrations provided by the DC.     

Numerical Studies on Combustion Characteristics of Interacting Pulverized Coal Particles at Various Oxygen Concentration

The two-dimensional laminar combustion characteristics of coal particles at various oxygen concentration levels of a surrounding gas have been numerically investigated. The numerical simulations, which use the two-step global reaction model to account for the surrounding gas effect, show the detailed interaction among the inter-spaced particles, undergoing devolatilization and subsequent char burning. Several parametric studies, which include the effects of gas temperature (1700 K), oxygen concentration, and variation in geometrical arrangement of the particles on the volatile release rate and the char burning rate, have been carried out. To address the change in the geometrical arrangement effect, multiple particles are located at various inter-spacings of 4–20 particle radii in both streamwise and spanwise directions. The results for the case of multiple particles are compared with those for the case of a single particle. The comparison indicates that the shift to the multiple particle arrangement resulted in the substantial change of the combustion characteristics and that the volatile release rate of the interacting coal particles exhibits a strong dependency on the particle spacing. The char combustion rate is controlled by the level of oxygen concentration and gas composition near particles during combustion. The char combustion rate is highly dependent on the particle spacing at all oxygen levels. The correlations of the volatile release rate and the change in total mass of particles are also found.     

Synthesis of polyaluminocarbosilane and reaction mechanism study

Polyaluminocarbosilane (PACS) as the precursor of high‐temperature resistant SiC fibers was synthesized by reacting polycarbosilane (PCS) with aluminum(III)acetylacetonate [Al(AcAc)₃] at 310°C in N₂ under ambient pressure. The reaction mechanism and the structure of PACS were investigated in detail by FTIR, GPC, GC/MS, ESCA, and elemental analysis. The reaction was proven complex involving the formation of Si? O? Al and Si? Al? Si bonds, which were accompanied by the evolution of 3‐methoxy‐2,2‐dimethyl‐oxirane, 2,3‐dihydro‐[1,4]dioxine, pent‐3‐en‐2‐one, and 3‐ethyl‐but‐3‐en‐2‐one, and acetylacetone. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2787–2792, 2002     

Development of virtual reality proprioceptive rehabilitation system for stroke patients

In this study, the virtual reality (VR) proprioception rehabilitation system was developed for stroke patients to use proprioception feedback in upper limb rehabilitation by blocking visual feedback. To evaluate its therapeutic effect, 10 stroke patients (onset > 3 month) trained proprioception feedback rehabilitation for one week and visual feedback rehabilitation for another week in random order. Proprioception functions were checked before, a week after, and at the end of training. The results show the click count, error distance and total error distance among proprioception evaluation factors were significantly reduced after proprioception feedback training compared to visual feedback training (respectively, p = 0.005, p = 0.001, and p = 0.007). In addition, subjects were significantly improved in conventional behavioral tests after training. In conclusion, we showed the effectiveness and possible use of the VR to recover the proprioception of stroke patients.     

Drying performance of a tumbler dryer with condenser

The effects of flow rates of hot air and cooling water on drying percentage and energy efficiency of cotton lint in a cylindrical type drum tumbler dryer (0.54m-ID×0.34m-high) have been determined. Drying of the lint is mainly affected by flow rate of hot air, which is a function of the diameter ratio (D_M/D_F) of motor and fan pulley and motor capacity. During the drying process in the tumbler dryer, temperatures and humidity before and after were measured to determine the drying characteristics. The volumetric flow rate of hot air increases with increasing the diameter ratio of the motor and fan pulley, whereas the volumetric flow rate of hot air decreases with an increase in the mass flow rate of the cooling water through the condenser. The energy consumed by the motor relied more on the diameter ratio of the motor and fan pulley as opposed to the mass flow rate of cooling water. Despite the increase in the drying percentage with increasing the diameter ratio of the motor and fan pulley and the mass flow rate of the cooling water, the energy efficiency decreased.     

Evaluation of the burst characteristics for axial notches on SG tubings

Some events of steam generator tubes have been reported in some nuclear power plants around the world. Main causes of the leakage are from various types of corrosion in the steam generator (SG) tubing. Primary water stress corrosion cracking (PWSCC) of steam generator tubing have occurred in many tubes in Korean plants, and they were repaired using sleeves or plugs. In order to develop proper repair criteria, it is necessary to ascertain the leak behavior of the tubings. A high-pressure leak and burst testing system was manufactured. Various types of electro-discharged-machined (EDM) notches having different lengths were machined on the o.d. of test tubes to study SG tube behavior. Leak rate and ligament rupture pressure as well as the burst pressure were measured for the tubes at room temperature. Rupture pressure of the part through-wall defect tubes depends on the defect depth and length. Water flow rates after the rupture were independent of the flaw types; tubes having 20–60 mm long EDM notches showed similar flow rates regardless of the initial defect depth. A fast pressurization rate generated a lower burst pressure than the case of a slow pressurization.     

Inorganic Polymer Micropillar‐Based Solution Shearing of Large‐Area Organic Semiconductor Thin Films with Pillar‐Size‐Dependent Crystal Size

It is demonstrated that the crystal size of small‐molecule organic semiconductors can be controlled during solution shearing by tuning the shape and dimensions of the micropillars on the blade. Increasing the size and spacing of the rectangular pillars increases the crystal size, resulting in higher thin‐film mobility. This phenomenon is attributed as the microstructure changing the degree and density of the meniscus line curvature, thereby controlling the nucleation process. The use of allylhybridpolycarbosilane (AHPCS), an inorganic polymer, is also demonstrated as the microstructured blade for solution shearing, which has high resistance to organic solvents, can easily be microstructured via molding, and is flexible and durable. Finally, it is shown that solution shearing can be performed on a curved surface using a curved blade. These demonstrations bring solution shearing closer to industrial applications and expand its applicability to various printed flexible electronics.     

Multicomponent aerosol mass efficiency with various mixture types for polydispersed aerosol

Based on the filter-sampled chemical composition data the seasonal variation of the optical properties of polydispersed aerosols, extinction, scattering, and absorption coefficient, are estimated for various types of aerosol mixtures. The mixtures considered in this study are the internal mixture, elemental carbon (EC)/non-EC external mixture, and fully external mixture. This study also evaluated the sensitivity of the aerosol optical properties for different size distributions. The results show that the extinction coefficient can be mostly accounted for scattering and generally shows a good agreement with each mixture type in this case study. However, the absorption coefficient shows a different tendency for internal and external mixtures. This study also shows that the aerosol optical properties vary as a function of particle diameter at the same composition and mass concentration. This means that mass extinction, scattering, and absorption efficiencies, which were considered as constants in general, should be reassessed and more specifically described as a function of particle size.