Effects of various baffle designs on acoustic characteristics in combustion chamber of liquid rocket engine

Effects of various baffle designs on acoustic characteristics in combustion chamber are numerically investigated by adopting linear acoustic analysis. A hub-blade configuration with five blades is selected as a candidate baffle and five variants of baffles with various specifications are designed depending on baffle height and hub position. As damping parameters, natural-frequency shift and damping factor are considered and the damping capacity of various baffle designs is evaluated. Increase in baffle height results in more damping capacity and the hub position affects appreciably the damping of the first radial resonant mode. Depending on baffle height, two close resonant modes could be overlapped and thereby the damping factor for one resonant mode is increased exceedingly. The present procedure based on acoustic analysis is expected to be a useful tool to predict acoustic field in combustion chamber and to design the passive control devices such as baffle and acoustic resonator.     

Electrochemical detection of ascorbic acid (vitamin C) using a glassy carbon electrode

A method for the detection of ascorbic acid (AA) was developed using square wave anodic stripping voltammetric (SWASV) analysis with a glassy carbon electrode (GCE). The results indicated a sensitive oxidation peak current of AA on the GCE. A linear curve was obtained within a concentration range of 1-130.0 microg/L with a preconcentration time of 270 s. The relative standard deviation of 30.0 microg/L observed was 0.1016% (n = 12) under optimum conditions. The low detection limit (S/N) was pegged at 0.30 microg/L. Results showed that the method developed can be used to assay biological and pharmaceutical samples, and food samples, as well as other materials requiring AA analyses.     

On-Line Construction of Two-Dimensional Suffix Trees in O(n<Superscript>2</Superscript> log n) Time

The two-dimensional suffix tree of an n × n square matrix A is a compacted trie that represents all square submatrices of A[11]. For the off-line case, i.e., A is given in advance to the algorithm, it is known how to build it in optimal time, for any type of alphabet size [11],[18]. Motivated by applications in Image Compression[22[, Giancarlo and Guaiana [14] considered the on-line version of the two-dimensional suffix tree and presented an O(n² log² n)-time algorithm, which we refer to as GG. That algorithm is a nontrivial generalization of Ukkonen's on-line algorithm for standard suffix trees [23]. The main contribution in this paper is an O(log n) factor improvement in the time complexity of the GG algorithm, making it optimal for unbounded alphabets [9]. Moreover, the ideas presented here also lead to a major simplification of the GG algorithm. Technically, we are able to preserve most of the structure of the original GG algorithm, by reducing a computational bottleneck to a primitive operation, i.e., comparison of Lcharacters, which is here implemented in constant time rather than O(log n) time as in GG. However, preserving that structure comes at a price. Indeed, in order to make everything work, we need a careful reorganization of another fundamental algorithm: Weiner's algorithm for the construction of standard suffix trees [24]. Specifically, here we provide a version of that algorithm which takes linear time and works on-line and concurrently over a set of strings.     

Electroactive Shape Memory Effect of Polyurethane Composites Filled with Carbon Nanotubes and Conducting Polymer

We report the electroactive shape memory composites obtained by shape memory polyurethane block copolymer (PU) and multi-walled carbon nanotubes (MWNTs), and polypyrrole (PPy). An addition of combined MWNTs and PPy contributed to an enhancement in conductivity of PU-MWNTs composites. PU containing 2.5% MWNTs showed better mechanical and thermal properties than other composites, but conductivity was not sufficient for showing the shape memory effect by applying electrical voltages. However, when the composite was lightly coated by PPy (2.5%), its conductivity was the highest than other composites. Such the conductivity of this composite was enough to show electroactive shape recovery by heating above transition temperature of 40-48°C due to melting of polycaprolactone soft segment domain. The good shape recovery of 90-96% could be obtained in the shape recovery test when an electric field of 25 V was applied.     

Shifting the MIMO Paradigm

Multi-user MIMO (MU-MIMO) networks reveal the unique opportunities arising from a joint optimization of antenna combining techniques with resource allocation protocols. Furthermore, it brings robustness with respect to multipath richness, allowing for compact antenna spacing at the BS and, crucially, yielding the diversity and multiplexing gains without the need for multiple antenna user terminals. To realize these gains, however, the BS should be informed with the user's channel coefficients, which may limit practical application to TDD or low-mobility settings. To circumvent this problem and reduce feedback load, combining MU-MIMO with opportunistic scheduling seems a promising direction. The success for this type of scheduler is strongly traffic and QoS-dependent, however.     

Video Service Delivery Over a Repeater-Based Optical Access Network

A low-cost and bandwidth-efficient scheme for delivering video services to customers over a long reach, large split repeater-based optical access network is proposed and experimentally demonstrated. Video channels that are on radio-frequency subcarriers are electrically combined with regenerated downstream data at the repeater and delivered to the customers on a single wavelength channel. Experimental results show that error-free transmission can be obtained for all channels with adequate power budget to support a split ratio more than 64.     

Effects of introducing silica particles on the rheological properties and crystallization behavior of poly(ethylene terephthalate)

Poly(ethylene terephthalate) (PET)/silica composites were prepared by melt compounding, and their rheological properties and isothermal crystallization were discussed. Introduction of silica particles (0.5–2 wt.%) increased the storage modulus (G′) and decreased loss tangent (tanδ). However, the effect of the particles on rheological properties became negligible at a high frequency more than ca. 70 rad/s. In the Cole–Cole plot, the PET/silica composites showed little deviation from the master curve regardless of the presence of silica particles. The particles increased the relaxation time of PET at particularly low frequency. The isothermal crystallization kinetics of PET/silica was examined using a differential scanning calorimeter (DSC). The half-time of crystallization was decreased with increasing the silica content. The incorporation of silica particles decreased the equilibrium melting temperature by ca. 5.5 °C. In addition, the composites exhibited higher average value of Avrami exponent (2.7–2.9) in comparison with that of pure PET (2.2).     

Low‐Temperature Sintering of Bi0.5(Na,K)0.5TiO3 for Multilayer Ceramic Actuators

We investigated the influence of CuO amount (0.5–3.0 mol%), sintering temperature (900°C–1000°C), and sintering time (2–6 h) on the low‐temperature sintering behavior of CuO‐added Bi_0.5(Na_0.78K_0.22)_0.5TiO₃ (BNKT22) ceramics. Normalized strain (S_max/E_max), piezoelectric coefficient (d₃₃), and remanent polarization (P_r) of 1.0 mol% CuO‐added BNKT22 ceramics sintered at 950°C for 4 h was 280 pm/V, 180 pC/N, and 28 μC/cm², respectively. These values are similar to those of pure BNKT22 ceramics sintered at 1150°C. In addition, we investigated the performance of multilayer ceramic actuators made from CuO‐added BNKT22 in acoustic sound speaker devices. A prototype sound speaker device showed similar output sound pressure levels as a Pb(Zr,Ti)O₃‐based device in the frequency range 0.66–20 kHz. This result highlights the feasibility of using low‐cost multilayer ceramic devices made of lead‐free BNKT‐based piezoelectric materials in sound speaker devices.     

A water‐developable negative photoresist based on the photocrosslinking of N‐phenylamide groups with reduced environmental impact

A water‐developable negative photoresist based on the photocrosslinking of N‐phenylamide groups was prepared by the copolymerization of 4‐styrenesulfonic acid sodium salts (SSS) with N‐phenylmethacrylamide (copolymer A) or p‐hydroxy‐N‐phenylmethacrylamide (copolymer B), and its properties such as solubility changes, photochemical reaction, and photoresist characteristics were studied. The copolymer containing a relatively higher amount of SSS units was soluble in water. Solubility changes of the copolymers in the various buffer solutions of pH 4 ～ 11 and in water upon irradiation were observed by the measurement of insoluble fraction. The copolymers were soluble in water before irradiation, whereas they became insoluble upon irradiation with the UV light of 254 nm. The photochemical reaction of the copolymer studied by the UV and IR absorption spectroscopies indicated that a photo‐Fries rearrangement was favored for copolymer A, whereas a photocrosslinking reaction was predominate for copolymer B. Resist properties of the copolymers were studied by measurement of the normalized thickness and by development of the micropattern. Negative tone images with a resolution of 1 μm were obtained with these materials that have a sensitivity (D) of ～ 1100 mJ/cm² with an aqueous developing process.© 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1172–1180, 2002     

Comfort evaluation and bed adjustment according to sleeping positions

This study explodes the relationships between the height adjustment of bed sectors and subjective comfort depending on three types of sleeping positions. An adjustable bed system that regulates the heights of 8 adjustment sectors of the bed was developed. To evaluate the comfort of 9 body areas, subjective ratings were requested from 64 subjects ranging in age from 25 to 50. The subjects included 29 males and 35 females. For an objective evaluation, the patterns of pressure distribution were investigated according to the three sleeping positions. During two separate states (before bed adjustment and after bed adjustment), measurements of the adjusted bed height and pressure distribution, and subjective ratings according to three sleeping positions were performed. Based on the results of the adjusted heights of the 8 sectors in the bed, the subjects preferred the W‐shaped sleeping posture in both the supine and side positions. However, the U‐shaped sleeping posture was preferred in the prone position. With respect to these sleeping positions, the heights of sectors significantly correlated with the subjective ratings presented by the subjects, as well as the ratios of pressure. © 2009 Wiley Periodicals, Inc.