bluuebunny/crossref_metadata_2025 huggingface dataset:
Plastic energy dissipation and its role on heating/melting of single‐component polymers and multi‐component polymer blends
Authors: Qian Bainian , Todd David B. , Gogos Costas G.
Published: March 2003

Plastic energy dissipation (PED) of polymer particulates is, essentially, the energy dissipated during large and repeated plastic deformations of compacted polymer particulates while still in the solid state. PED is higher or much higher than VED, the viscous energy dissipation source of polymeric melts, because the stresses necessary to plastically deform viscoelastic polymer solids are orders of magnitude higher than the stresses needed to support viscous flow. In the last few years our group has demonstrated experimentally the dominant role which PED plays in the heating/melting of solid polymer (compacted) particulate beds in compounding processing equipment, such as twin‐screw extruders and counterrotating continuous mixers/melters, in which the deformation of solid polymers is mandatory. We have also developed simple empirical methods of predicting the total axial distance needed for melting a given polymer in specific processing/compounding machines and processing. conditions, as well as the melting rates, all based on the mechanical energy dissipated during solid particulate compression. This work explores the more complex issue of how the PED behavior of single‐component polymers may affect the PED (and the heating/melting) behavior of multi‐component polymer blends. © 2003 Wiley Periodicals, Inc. Adv Polym Techn 22: 85–95, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.10039
Synergistic effects of carbon fillers on shielding effectiveness in conductive nylon 6,6‐ and polycarbonate‐based resins
Authors: Krueger Quinton J. , King Julia A.
Published: March 2003

Electrically conductive resins can be made by adding electrically conductive fillers to typically insulating polymers. Resins with an electrical resistivity of approximately 100 Ω cm or less can be used for electromagnetic and radio frequency interference shielding applications. This research focused on performing compounding runs followed by injection molding and shielding effectiveness (SE) testing of carbon filled nylon 6,6‐ and polycarbonate‐based resins. The three carbon fillers investigated included an electrically conductive carbon black, synthetic graphite particles, and a milled pitch‐based carbon fiber. For each polymer, conductive resins were produced and tested that contained varying amounts of these single carbon fillers. In addition, combinations of fillers were investigated by conducting a full 23 factorial design and a complete replicate in each polymer. The objective of this study was to determine the effects and interactions of each filler on the SE properties of the conductive resins. Carbon black caused the largest increase in SE. Also, each single filler and each two filler interaction caused a statistically significant increase in SE. © 2003 Wiley Periodicals, Inc. Adv Polym Techn 22: 96–111, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.10040
Compatibility of polysaccharide/maleic copolymer blends. IV. Thermal behavior of hydroxypropyl cellulose‐containing blends
Authors: Bumbu Gina‐Gabriela , Vasile Cornelia , Popescu Maria Cristina , Darie Hristea , Charlotte Chiţanu Gabrielle , Singurel Gheorghe , Carpov Adrian
Published: March 2003

The compatibility of the hydroxypropyl cellulose (HPC) with maleic acid–vinyl acetate copolymer in the solid state was studied by thermogravimetry, thermo‐optical analysis, differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and optical microscopy. It was established that physical interactions are prevalent in blends with a high content of HPC, whereas chemical interactions predominate in blends with a medium and low content of HPC. By increasing the temperature, the thermochemical reactions are favored. Thermal properties are dependent on the mixing ratio of the components. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2585–2597, 2003
Low dielectric thermoset. I. Synthesis and properties of novel 2,6‐dimethyl phenol‐dicyclopentadiene epoxy
Authors: Hsuan Lin Ching , Chung Chiang Jung , Shan Wang Chun
Published: March 2003

A 2,6‐dimethyl phenol‐dicyclopentadiene novolac was synthesized from dicyclopentadiene and 2,6‐dimethyl phenol, and the resultant 2,6‐dimethyl phenol‐dicyclopentadiene novolac was epoxidized to 2,6‐dimethyl phenol‐dicyclopentadiene epoxy. The structures of novolac and epoxy were confirmed by Fourier transform infrared spectroscopy (FTIR), elemental analysis, mass spectroscopy (MS), nuclear magnetic resonance spectroscopy (NMR), and epoxy equivalent weight titration. The synthesized 2,6‐dimethyl phenol‐dicyclopentadiene epoxy was then cured with 4,4‐diaminodiphenyl methane (DDM), phenol novolac (PN), 4,4‐diaminodiphenyl sulfone (DDS), and 4,4‐diaminodiphenyl ether (DDE). Thermal properties of cured epoxy resins were studied by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), dielectric analysis (DEA), and thermal gravimetric analysis (TGA). These data were compared with those of the commercial bisphenol A epoxy system. Compared with the bisphenol A epoxy system, the cured 2,6‐dimethyl phenol‐ dicyclopentadiene epoxy resins exhibited lower dielectric constants (∼3.0 at 1 MHz and 2.8 at 1 GHz), dissipation factors (∼0.007 at 1 MHz and 0.004 at 1 GHz), glass transition temperatures (140–188°C), thermal stability (5% degradation temperature at 382–404°C), thermal expansion coefficients [50–60 ppm/°C before glass‐transition temperature (Tg)], and moisture absorption (0.9–1.1%), but higher modulus (∼2 Gpa at 60°C). © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2607–2613, 2003
Mechanical and viscoelastic behavior of natural rubber and carboxylated styrene‐butadiene rubber latex blends
Authors: Stephen Ranimol , Raju K. V. S. N. , Nair Sobha V. , Varghese Siby , Oommen Zachariah , Thomas Sabu
Published: March 2003

The morphology, mechanical and viscoelastic behavior of latex blends of unvulcanized natural rubber (NR) with carboxylated styrene‐butadiene rubber (XSBR) were investigated, with special reference to the effect of the blend ratio, temperature, and frequency. Mechanical properties like tensile strength, modulus, and elongation at break were also studied. As the XSBR content increased, the tensile strength increased up to a 50:50 NR/XSBR ratio and then decreased as a result of the self‐curing nature of XSBR. The dynamic mechanical properties of these latex blends were analyzed for loss tangent, storage modulus, and loss modulus. The entire blend yielded two glass‐transition temperatures, which corresponded to the transitions of individual components, indicating that the system was immiscible. To determine the change in modulus with time, a master curve of 50:50 NR/XSBR blends was plotted. Time–temperature superposition and Cole–Cole analysis were done to understand the phase behavior of the latex blends. The experimental and theoretical values of storage modulus of blends were compared using the Kerner and Halpin–Tsai models. With the help of optical micrographs, attempts were made to correlate the morphology and viscoelastic behavior of these blends. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2639–2648, 2003
Modeling of poly(L‐lactide) thermal degradation: Theoretical prediction of molecular weight and polydispersity index
Authors: Yu Hengxing , Huang Nanxun , Wang Chaosheng , Tang Zhilian
Published: March 2003

A mathematical model to describe the molecular weight and polydispersity index (Q) in poly(L‐lactide) (PLLA) thermal degradation has been developed. Based on the random chain scission mechanism, effects of temperature and time on the molecular weight and polydispersity index are included in this model. It incorporates the degradation and recombination reaction of PLLA thermal degradation, while taking into account the equal probability assumption. The developments of molecular weight and polydispersity index of PLLA polymer in the thermal degradation process were investigated at temperature ranging from 180–220°C, the experimental data show PLLA reaches its thermal degradation equilibrium in 2 h. The simulated results of this model are compared with the measured molecular weight and polydispersity index of the PLLA polymer. The changes of the molecular weight and polydispersity index in the PLLA thermal degradation can be predicted by this model. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2557–2562, 2003
Thermal characteristics of IPNs composed of poly(propylene glycol) and poly(acrylic acid)
Authors: Jeong Kim Seon , Jung Lee Ki , Min Lee Sang , Young Kim In , Moo Lee Young , Kim Sun I.
Published: March 2003

Interpenetrating polymer networks (IPNs) based on poly(propylene glycol) (PPG) and poly(acrylic acid) (PAAc) were prepared by UV irradiation and characterized using fourier transform infrared (FTIR), differential scanning calorimetry (DSC), dielectric analysis (DEA), and thermogaravimetry (TGA). The glass transition temperatures (Tgs) of these IPNs exhibited a relatively higher temperature with an increased PAAc content. The decomposition temperature of PAAc is lower than that of PPG. PAAc affects the thermal stability of IPN more than PPG. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2570–2574, 2003
Preparation of a novel poloxamer hydrogel
Authors: Kweon HaeYong , Yoo Mi‐Kyong , Lee Jin‐Hak , Wee Won‐Ryang , Han Young‐Gun , Lee Kwang‐Gill , Cho Chong‐Su
Published: March 2003

Poloxamer hydrogels were prepared by photopolymerization from poloxamer macromer, which was synthesized by reaction of poloxamer 407 with acryloyl chloride. The synthesis of poloxamer macromer was confirmed using NMR and FTIR spectrometry. The gelation behavior and crystalline structure of poloxamer macromer was similar to those of poloxamer 407 itself; however, the amorphous scattering of poloxamer macromer was higher than that of poloxamer itself. Differential scanning calorimetric analysis showed that the melting temperature and enthalpy of poloxamer hydrogel were also lower than those of poloxamer itself. The compressive modulus of poloxamer hydrogels were similar (92.6–101.7 kPa), regardless of the concentration of poloxamer macromer. Equilibrium water uptake of poloxamer hydrogels decreased with an increase of concentration of poloxamer macromer. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2670–2676, 2003
Reactivity, chemical structure, and molecular mobility of urea–formaldehyde adhesives synthesized under different conditions using FTIR and solid‐state 13C CP/MAS NMR spectroscopy
Authors: Park Byung‐Dae , Kim Yoon Soo , Singh Adya P. , Lim Kie Pyo
Published: March 2003

This study was conducted to investigate the effects of reaction pH condition and hardener type on the reactivity, chemical structure, and molecular mobility of urea–formaldehyde (UF) resins. Three different reaction pH conditions, such as alkaline (7.5), weak acid (4.5), and strong acid (1.0), were used to synthesize UF resins, which were cured by adding four different hardeners (ammonium chloride, ammonium sulfate, ammonium citrate, and zinc nitrate) to measure gel time as the reactivity. FTIR and 13C‐NMR spectroscopies were used to study the chemical structure of the resin prepared under three different reaction pH conditions. The gel time of UF resins decreased with an increase in the amount of ammonium chloride, ammonium sulfate, and ammonium citrate added in the resins, whereas the gel time increased when zinc nitrate was added. Both FTIR and 13C‐NMR spectroscopies showed that the strong reaction pH condition produced uronic structures in UF resin, whereas both alkaline and weak‐acid conditions produced quite similar chemical species in the resins. The proton rotating‐frame spin–lattice relaxation time (T1ρH) decreased with a decrease in the reaction pH of UF resin. This result indicates that the molecular mobility of UF resin increases with a decrease in the reaction pH used during its synthesis. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2677–2687, 2003
Permselectivities of 2,2′‐dimethyl‐4,4′‐bis(aminophenoxyl)biphenyl diphenyl methane–based aromatic polyamide membranes for aqueous alcohol mixtures in pervaporation and evapomeation
Authors: Fan Shu‐Chin , Wang Yi‐Chieh , Li Chi‐Lan , Lee Kueir‐Rarn , Liaw Der‐Jang , Lai Juin‐Yih
Published: March 2003

The separation of aqueous alcohol mixtures was carried out by use of a series of novel aromatic polyamide membranes. The aromatic polyamides were prepared by the direct polycondensation of 2,2′‐dimethyl‐4,4′‐bis(aminophenoxyl)biphenyl (DBAPB) with various aromatic diacids, such as terephthalic acid (TPAc), 5‐tert‐butylisophthalic acid (TBPAc), and 4,4′‐hexafluoroisopropylidenedibenzoic acid (FDAc). The pervaporation and evapomeation performance of these novel aromatic polyamide membranes for dehydrating aqueous alcohol solution were investigated. The solubility of ethanol in the aromatic polyamide membranes is higher than that of water, but the diffusivity of water through the membrane is higher than that of ethanol. The effect of diffusion selectivity on the membrane separation performances plays an important role in the evapomeation process. Compared with pervaporation, evapomeation effectively increases the permselectivity of water. Moreover, the effect of aromatic diacids on the polymer chain packing density, pervaporation, and evapomeation performance were investigated. It was found that the permeation rate could be increased by introduction of a bulky group into the polymer backbone. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2688–2697, 2003
Optical properties of injection‐molded polystyrene scintillators. I. Processing and optical properties
Authors: Martins J. A. , Seixas J. , Silva J. , Esteves V. , Oliveira M. J. , Gomes J. , Maio A. , Pouzada A. S.
Published: March 2003

Scintillating tiles for the Tilecal/Atlas calorimeter can be produced by injection molding, an alternative to mold casting via in situ polymerization. This new production method, which leads to a much faster production rate, introduces a number of additional variables that affect the optical yield of the scintillators and that have not yet been reported in the literature. In this work, the effect of processing‐induced orientation on the optical properties of the scintillators is analyzed and discussed. For this purpose, the birefringence across the thickness of the scintillator has been measured. The variations of the birefringence may be correlated with the orientation and, therefore, related to the optical performance, that is, the average light output and its nonuniformity. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2706–2713, 2003
Synthesis and polymerization of a new iodine‐containing monomer
Authors: Lakshmi S. , James Nirmala R. , Nisha V. S. , Jayakrishnan A.
Published: March 2003

A new iodine‐containing methacrylate monomer, 3,4,5‐triiodobenzoyloxyethyl methacrylate (TIBEM), was synthesized by coupling 2‐hydroxyethyl methacrylate (HEMA) with 3,4,5‐triiodobenzoic acid. The monomer was characterized by 1H nuclear magnetic resonance, infrared (IR), and ultraviolet spectra. Homopolymerization and copolymerization of the monomer with methyl methacrylate (MMA) were carried out using 2,2′‐azobis isobutyronitrile as the initiator. A terpolymer of TIBEM, MMA, and HEMA was also synthesized. The copolymers were characterized by IR, gel permeation chromatography, differential thermal analysis, and thermogravimetric analysis (TGA). High molecular weight polymers were produced with MMA at different feed compositions of TIBEM. The polymers were found to be freely soluble in common solvents for acrylic polymers. TGA showed little decomposition of the copolymer below 280°C. Copolymers showed good radiopacity at 25 wt % of TIBEM in the feed. These copolymers could find applications in medical and dental areas where radiopacity is a desirable feature of the implants. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2580–2584, 2003
Pulsed electromagnetic fields prevent osteoporosis in an ovariectomized female rat model: A prostaglandin E2‐associated process
Authors: Chang Kyle , Chang Walter Hong‐Shong
Published: March 2003

With the use of Helmholtz coils and pulsed electromagnetic field (PEMF) stimulators to generate uniform time varying electromagnetic fields, the effects of extremely low frequency electromagnetic fields on osteoporosis and serum prostaglandin E2 (PGE2) concentration were investigated in bilaterally ovariectomized rats. Thirty‐five 3 month old female Sprague–Dawley rats were randomly divided into five different groups: intact (INT), ovariectomy (OVX), aspirin treated (ASP), PEMF stimulation (PEMF + OVX), and PEMF stimulation with aspirin (PEMF + ASP) groups. All rats were subjected to bilateral ovariectomy except those in INT group. Histomorphometric analyses showed that PEMF stimulation augmented and restored proximal tibial metaphyseal trabecular bone mass (increased hard tissue percentage, bone volume percentage, and trabecular number) and architecture (increased trabecular perimeter, trabecular thickness, and decreased trabecular separation) in both PEMF + OVX and PEMF + ASP. Trabecular bone mass of PEMF + OVX rats after PEMF stimulation for 30 days was restored to levels of age matched INT rats. PEMF exposure also attenuated the higher serum PGE2 concentrations of OVX rats and restored it to levels of INT rats. These experiments demonstrated that extremely low intensity, low frequency, single pulse electromagnetic fields significantly suppressed the trabecular bone loss and restored the trabecular bone structure in bilateral ovariectomized rats. We, therefore, conclude that PEMF may be useful in the prevention of osteoporosis resulting from ovariectomy and that PGE2 might relate to these preventive effects. Bioelectromagnetics 24:189–198, 2003. © 2003 Wiley‐Liss, Inc.
Effects of high power microwave pulses on synaptic transmission and long term potentiation in hippocampus
Authors: Pakhomov Andrei G. , Doyle Joanne , Stuck Bruce E. , Murphy Michael R.
Published: March 2003

Effects of short, extremely high power microwave pulses (EHPP) on neuronal network function were explored by electrophysiological techniques in the isolated rat hippocampal slice model. Population spikes (PS) in the CA1 area were evoked by repeated stimulation (1 per 30 s) of the Schaffer collateral pathway. A brief tetanus (2 s at 50 Hz) was used to induce long term potentiation (LTP) of synaptic transmission. In three different series of experiments with a total of 160 brain slices, the EHPP irradiation was performed before, during, or after the tetanus. The EHPP carrier frequency was 9.3 GHz, the pulse width and repetition rate were from 0.5 to 2 μs and from 0.5 to 10 Hz, respectively, and the peak specific absorption rate (SAR) in brain slices reached up to 500 MW/kg. Microwave heating of the preparation ranged from 0.5 °C (at 0.3 kW/kg time average SAR) to 6 °C (at 3.6 kW/kg). The experiments established that the only effect caused by EHPP exposure within the studied range of parameters was a transient and fully reversible decrease in the PS amplitude. Recovery took no more than a few minutes after the cessation of exposure and return to the initial temperature. This effect's features were characteristic of an ordinary thermal response: it was proportional to the temperature rise but not to any specific parameter of EHPP, and it could also be induced by a continuous wave (CW) irradiation or conventional heating. Irradiation did not affect the ability of neurons to develop LTP in response to tetanus or to retain the potentiated state that was induced before irradiation. No lasting or delayed effects of EHPP were observed. The results are consistent with the thermal mechanism of EHPP action and thus far provided no indication of EHPP‐specific effects on neuronal function. Bioelectromagnetics 24:174–181, 2003. Published 2003 Wiley‐Liss, Inc.
Whole body exposure of rats to microwaves emitted from a cell phone does not affect the testes
Authors: Dasdag Suleyman , Zulkuf Akdag M. , Aksen Feyzan , Yılmaz Fahri , Bashan Mehmet , Mutlu Dasdag M. , Salih Celik M.
Published: March 2003

The objective of this study was to investigate the effects of radiofrequency radiation emitted from cellular phones on the lipid composition, malondialdehyde concentration, p53 immune reactivity, sperm count, morphology, histological structure of testes, and on rectal temperature of rats exposed to microwave radiation emitted from cellular phones. Sixteen Spraque–Dawley rats were separated into two groups of eight, sham exposed (control) and experimental. The rats were confined in plexiglas cages specially designed for this study, and cellular phones were placed 0.5 cm under the cages. For the experimental group, cellular phones were activated 20 min per day (7 days a week) for 1 month. For the control group, the cellular phones were placed beneath the cages for 20 min a day, but the phones were turned off. Rectal temperatures were measured weekly. For 250 mW radiated power, the whole body average SAR (rms) is 0.52 W/kg and 1 g averaged peak SAR (rms) is 3.13 W/kg. The Mann–Whitney U‐test was used for statistical comparisons of groups. No statistically significant alteration in any of the endpoints was noted. This study found no evidence suggesting an adverse effect of cell phone exposure on measures of testicular function or structure. Bioelectromagnetics 24:182–188, 2003. © 2003 Wiley‐Liss, Inc.
Extracellular currents alter gap junction intercellular communication in synovial fibroblasts
Authors: Marino Andrew A. , Kolomytkin Oleg V. , Frilot Clifton
Published: March 2003

We studied the effect of extremely low frequency (ELF) currents on gap junction intercellular communication (GJIC) mediated by connexin43 protein. Confluent monolayers of synovial fibroblasts (HIG‐82) and neuroblastoma cells (5Y) were exposed in bath solution to 0–75 mA/m2 (0–56 mV/m), 60 Hz. Single channel conductance, cell membrane current‐voltage (I‐V) curves, and Ca2+ influx were measured using the nystatin single and double patch methods. The conductances of the closed and open states of the gap junction channel in HIG‐82 cells were each significantly reduced (by 0.76 and 0.39 pA, respectively) in cells exposed to 20 mA/m2. Current densities as low as 10 mA/m2 significantly increased Ca2+ influx in HIG‐82 cells. No effects were seen in 5Y cells. The I‐V curves of the plasma membranes of both types of cells were independent of 60 Hz electric fields and current densities, 0–75 mA/m2, indicating that the effect of the 60 Hz fields on GJIC in HIG‐82 cells was not mediated by a change in membrane potential. We conclude that ELF electric fields can alter GJIC in synovial cells via a mechanism that does not depend on changes in membrane potential, but may depend on Ca2+ influx. The results open the possibility that GJIC mediated responses in synovial cells, such as for example, their secretory responses to proinflammatory cytokines, could be antagonized by the application of ELF electric fields. Bioelectromagnetics 24:199–205, 2003. © 2003 Wiley‐Liss, Inc.
Elevated residential exposure to power frequency magnetic field associated with greater average age at diagnosis for patients with brain tumors
Authors: Li Chung‐Yi , Lin Ruey S. , Sung Fung‐Chang
Published: March 2003

To explore whether the age at cancer diagnosis was associated with residential exposure to magnetic field, we compared average ages at diagnosis for cases of leukemia, brain tumor, or female breast cancer with elevated exposure (magnetic flux density ≥ 0.2 μT, or residential distance from major power lines ≤ 100 m) to average ages at diagnosis for cancer cases with same diagnoses but with a background exposure (< 0.2 μT or > 100 m from major power lines). Comparing with brain tumor cases with background magnetic field exposure (n = 506), brain tumor cases with elevated exposure (n = 71) were 6 years older on average at diagnosis (P = 0.01). The difference was greater for males (45.2 vs. 52.1 years, P = 0.01) than for females (44.3 vs. 48.2 years, P = 0.27). No such phenomena at a significant level was observed for leukemia, female breast cancer, or a random sample of general population. We noted an association between magnetic field exposure and a greater mean age at diagnosis for brain tumors. Whether or not these phenomena suggest a delayed occurrence of brain tumors following a higher than background residential magnetic field exposure deserves further investigation. Bioelectromagnetics 24:218–221, 2003. © 2003 Wiley‐Liss, Inc.
Effect of coexposure to 50 Hz magnetic fields and an aneugen on human lymphocytes, determined by the cytokinesis block micronucleus assay
Authors: Verheyen G.R. , Pauwels G. , Verschaeve L. , Schoeters G.
Published: March 2003

Interference of 50 Hz extremely low frequency magnetic fields (ELF‐MF) with the known aneugen vinblastine (VBL) on micronucleus formation was tested with the in vitro cytokinesis block micronucleus assay in human lymphocyte cultures. Isolated lymphocyte cultures were prepared from 18 individuals. Three groups of quadruplicate cultures from six unrelated individuals were exposed to 50 Hz ELF‐MF of background (bkg), 80 and 800 μT, respectively, during the complete incubation period (72 h). Twenty‐four hours after culture initiation, one replicate culture from each individual within each ELF‐MF group was exposed to 0, 5, 10, or 15 ng/ml VBL. The isolated lymphocyte cultures were scored for the presence of micronuclei, the nuclear division index (NDI), and apoptosis. As expected, increased VBL concentration resulted in an increased micronucleus and apoptosis frequency and in a decreased NDI. In the presence of VBL, there was a systematic tendency for increased micronucleus and apoptosis frequency in the ELF‐MF exposed groups compared to the bkg group. In the absence of VBL, we observed no statistically significant effect of ELF‐MF on micronucleus induction or apoptosis frequency, but the NDI was significantly higher in the 800 μT group compared to the other groups, suggesting an effect of ELF‐MF on cell proliferation. An interaction between ELF‐MF and VBL on NDI was observed. This interaction reflected the drastic decrease in NDI due to coexposure to VBL. Bioelectromagnetics 24:160–164, 2003. © 2003 Wiley‐Liss, Inc.
Role of C‐terminal domain phosphorylation in RNA polymerase II transcription through the nucleosome
Authors: Liu Y. V. , Clark D. J. , Tchernajenko V. , Dahmus M. E. , Studitsky V. M.
Published: March 2003

End‐initiated transcription of a 256 base‐pair (bp) template containing a single uniquely positioned nucleosome by yeast and calf thymus nuclear RNA polymerases II (pol II) was analyzed in vitro. The nucleosome‐specific pausing pattern is similar to the pattern observed in the case of transcription of the same nucleosome by yeast RNA polymerase III. However, the pausing pattern is clearly different from the patterns observed previously during transcription by promoter‐initiated and assembled pol II. This suggests that end‐initiated and promoter‐initiated RNA polymerases differ in the way they progress through the nucleosome. The rates of transcription through the nucleosome by pol II are significantly lower than the rates observed in the case of SP6 polymerase and RNA polymerase III. Using calf thymus pol II, we have investigated the possibility that phosphorylation of the C‐terminal domain (CTD) facilitates transcription through the nucleosome. The rates of transcription through the nucleosome by phosphorylated (IIO) and nonphosphorylated (IIA) forms of calf thymus pol II are very similar. This suggests that CTD phosphorylation is not sufficient to facilitate transcription through the nucleosome by end‐initiated pol II. © 2003 Wiley Periodicals, Inc. Biopolymers 68: 528–538, 2003
Structure and dynamics of nucleosomal DNA
Authors: Muthurajan Uma M. , Park Young‐Jun , Edayathumangalam R. S. , Suto Robert K. , Chakravarthy Srinivas , Dyer Pamela N. , Luger Karolin
Published: March 2003

The last five years have seen exciting advances in our understanding of the structure of the nucleosome core particle, the basic repeating unit in all eukaryotic chromatin. A picture emerges in which nucleosomal DNA, while distorted and compacted fivefold by tight interactions with the histone octamer core, is at the same time highly dynamic and adaptable. Here, we summarize the salient features from recent structural studies of nucleosome core particles (both published and unpublished) that concern the structure and dynamics of nucleosomal DNA, and the nature of protein–DNA interactions. Current mechanisms for chromatin remodeling and nucleosome sliding are discussed in light of new structural evidence. Finally, techniques to study nucleosome stability and ultimately dynamics are introduced. © 2003 Wiley Periodicals, Inc. Biopolymers 68: 547–556, 2003
Mechanisms for nucleosome mobilization
Authors: Flaus Andrew , Owen‐Hughes Tom
Published: March 2003

Nucleosomes are the ubiquitous and fundamental packaging for eukaryotic genomes, and are the substrate for many processes in the nucleus. Nucleosomes are not static entities but can readily be moved by thermal energy and ATP‐dependent chromatin remodeling complexes in a process known as sliding or shifting. We summarize from a mechanical perspective the twist defect and bulge diffusion mechanisms proposed as the most likely pathway for nucleosome mobilization. We then consider the elastic properties of DNA and how this affects the potential for each mechanism, concentrating on kinetic aspects of twist diffusion and possible planar bulge sizes and summarize the experimental evidence reflecting on each. Either, or both, mechanisms could occur, and careful experimentation focusing on their uniquely distinguishing features will be required to determine their relative contributions to chromatin dynamics. © 2003 Wiley Periodicals, Inc. Biopolymers 68: 563–578, 2003
Comparison of the conformation and electrostatic surface properties of magainin peptides bound to sodium dodecyl sulfate and dodecylphosphocholine micelles
Authors: Hicks Rickey P. , Mones Erin , Kim Hanah , Koser Brandon W. , Nichols Daniel A. , Bhattacharjee Apurba K.
Published: March 2003

The role played by noncovalent interactions in inducing a stable secondary structure onto the sodium dodecyl sulfate (SDS) and dodecylphosphocholine (DPC) micelle‐bound conformations of (Ala8,13,18)magainin 2 amide and the DPC micelle bound conformation of magainin 1 were determined. Two‐dimensional NMR and molecular modeling investigations indicated that (Ala8,13,18)magainin 2 amide bound to DPC micelles adopts a α‐helical secondary structure involving residues 2–16. The four C‐terminal residues converge to a lose β‐turn structure. (Ala8,13,18)magainin 2 amide bound to SDS miscelles adopts a α‐helical secondary structure involving residues 7–18. The C‐ and N‐terminal residues exhibited a great deal of conformational flexibility. Magainin 1 bound to DPC micelles adopts a α‐helical secondary structure involving residues 4–19. The C‐terminal residues converge to a lose β‐turn structure. The results of this investigation indicate hydrophobic interactions are the major contributors to stabilizing the induced helical structure of the micelle‐bound peptides. Electrostatic interactions between the polar head groups of the micelle and the cationic side chains of the peptides define the positions along the peptide backbone where the helical structures begin and end. Published 2003 Wiley Periodicals, Inc. Biopolymers 68: 459–470, 2003
Conformational analysis of endomorphin‐2 by molecular dynamics methods
Authors: Leitgeb Balázs , Ötvös Ferenc , Tóth Géza
Published: March 2003

Endomorphin‐2 (EM2, H–Tyr–Pro–Phe–Phe–NH2) is a highly potent and selective μ‐opioid receptor agonist. A conformational analysis of EM2 was carried out by simulated annealing (SA) and molecular dynamics (MD) methods. Molecular modeling was conducted on both neutral (N‐terminal NH2) and charged (N‐terminal NH) molecules. Based on the results of NMR investigations showing an equilibrium mixture of cis and trans Tyr1–Pro2 peptide bonds for EM2 in solution, simulations were performed with restrained cis‐Pro and trans‐Pro peptide bonds, too. A separate SA study with unrestrained Pro peptide bonds was also conducted. Preferred conformational states are presented in Ramachandran plots. The g(+), g(‐), and trans populations of the aromatic amino acid residue side chains were determined in χ1 space. The distances between the N‐terminal N atom and the other backbone N and O atoms, and the distances between the centers of the aromatic rings and the Pro2 ring, were determined. The energy distribution of the structures obtained by SA was calculated. The preferred secondary structural elements were different kinds of β‐turns, an inverse γ‐turn located in the N‐terminal region, and regular and inverse γ‐turns located in the C‐terminal region. These turns were stabilized by intramolecular H‐bonds and bifurcated H‐bonds. © 2003 Wiley Periodicals, Inc. Biopolymers 68: 497–511, 2003
Experimental studies of direction of arrivals using a smart antenna testbed in wireless communication systems
Authors: Jeng Shiann‐Shiun , Lin Hsin‐Piao , Tsung Chen‐Wan
Published: March 2003

This paper presents some preliminary results from experimental studies on space‐division‐multiple‐access (SDMA) for wireless communications. A smart antenna system utilizing direction‐of‐arrival (DOA)‐based beamforming techniques can enhance signal quality by reducing co‐channel interference from mobiles located at angles spatially distinct from the base station. Adopting both smart uplink and downlink beamforming, a communication system with an antenna array can increase the cell coverage of a base station and significantly boost capacity compared with conventional antenna systems. However, successful implementation of DOA‐based beamforming techniques depends on the DOA characteristics. This paper presented the feasibility of direction finding and DOA variation with respect to frequency. Furthermore, the angle spread was studied for selected environments. The results demonstrate the feasibility of applying proposed smart antenna system utilizing DOA‐based beamforming algorithm for increasing channel capacity and improving system performance in frequency‐division‐duplex (FDD) wireless communication systems. Copyright © 2003 John Wiley & Sons, Ltd.
Identification and characterization of Grainyhead‐like epithelial transactivator (GET‐1), a novel mammalian Grainyhead‐like factor
Authors: Kudryavtseva Elena I. , Sugihara Tod M. , Wang Ning , Lasso Ronan J. , Gudnason Janus F. , Lipkin Steven M. , Andersen Bogi
Published: March 2003

LMO‐4 is an LIM‐only factor that is highly expressed in many epithelial cells, including those of the epidermis and hair follicles. Because LMOs may function by interacting with DNA‐binding proteins, we have used the yeast two‐hybrid system to screen mouse skin libraries for LMO‐4–interacting DNA‐binding proteins. In this screen, we isolated a novel LMO‐4–interacting factor highly related to the Drosophila gene Grainyhead. Grainyhead is epidermally expressed and carries out important functions in cuticular formation in the fly embryo. With the identification of this novel mammalian Grainyhead‐like gene, referred to as Grainyhead‐like epithelial transactivator 1 (GET‐1), the known members of the mammalian Grainyhead‐like gene family are extended to six, falling into two classes based on sequence homology. Of interest, the expression pattern of GET‐1 is similar to that of Drosophila Grainyhead with highest expression in the somatic ectoderm/epidermis, but GET‐1 is additionally expressed in epithelial cells of gastrointestinal, genitourinary, and respiratory tracks. The GET‐1 protein localizes to the nucleus and binds to at least one Grainyhead DNA‐binding site. The GET‐1 DNA‐binding domain maps to a region containing homology to the Drosophila Grainyhead DNA‐binding domain. GET‐1 homodimerizes in solution by means of a short C‐terminally located domain that is homologous to other Grainyhead‐like genes. A short domain located between amino acids 100 and 190, which bears no homology to known transactivation domains, is sufficient to confer transactivation to the heterologous GAL4 DNA‐binding domain. In addition, GET‐1 appears to contain repression domains consistent with the observation that Grainyhead and other mammalian Grainyhead‐like genes can act both as activators and repressors. These data suggest that GET‐1 is a transcriptional regulator that may perform important functions in epithelial tissues of mammals. Developmental Dynamics 226:604–617, 2003. © 2003 Wiley‐Liss, Inc.
Alternative splicing of papilin and the diversity of Drosophila extracellular matrix during embryonic morphogenesis
Authors: Kramerova Irina A. , Kramerov Andrei A. , Fessler John H.
Published: March 2003

Papilins are extracellular matrix proteins that share a particular, common order of types of protein domains. They occur widely, from nematodes to man, and can differ in the number of repeats of a given type of domain. Protein variety is increased by differential splicing of pre‐mRNA. We report that Drosophila, which has a compact genome, expresses three splice variants of papilin during embryogenesis in developmentally defined patterns. These isoforms have different numbers of Kunitz and IgC2 domains. The papilin isoforms are expressed in specific cell types and contribute to different extracellular matrices in gastrulation folds, early mesoderm, heart formation, basement membranes, and elaboration of the excorporeal peritrophic membrane that lines the gut. This finding indicates an unexpectedly broad spectrum of different pericellular matrices in Drosophila embryos. Such papilin‐containing matrices have developmental as well as functional significance, as we previously showed that both suppression of papilin synthesis and ectopic overexpression lethally disrupt organogenesis. Developmental Dynamics 226:634–642, 2003. © 2003 Wiley‐Liss, Inc.
Apparent mitochondrial asymmetry in Xenopus eggs
Authors: Volodina Natalia , Denegre James M. , Mowry Kimberly L.
Published: March 2003

Cell polarity is manifest along the animal/vegetal axis in eggs of the frog, Xenopus laevis. Along this axis, maternal cytoplasmic components are asymmetrically distributed and are thought to underlie specification of distinct cell fates. To ascertain the molecular identities of such cytoplasmic components, we have used a monoclonal antibody that specifically stains the vegetal hemisphere of Xenopus eggs. The antigenic protein Vp67 (vegetal protein of 67 kDa) was identified through purification and cloning as a Xenopus homolog of the mitochondrial protein dihydrolipoamide acetyltransferase, a component of the pyruvate dehydrogenase complex. The identification of Vp67 as a mitochondrial protein could indicate that populations of mitochondria are asymmetrically distributed in Xenopus eggs. Developmental Dynamics 226:654–662, © 2003 Wiley‐Liss, Inc.
Spontaneous mutation in mice provides new insight into the genetic mechanisms that pattern the seminal vesicles and prostate gland
Authors: Marker Paul C. , Dahiya Rajvir , Cunha Gerald R.
Published: March 2003

The seminal vesicles and prostate gland are anatomically adjacent male sex‐accessory glands. Although they arise from different embryonic precursor structures and express distinct sets of secretory proteins, these organs share common features in their developmental biology. A key shared developmental feature is the elaboration of complex secretory epithelia with tremendous surface area from simple precursor structures with juxtaposed epithelial and mesenchymal cells. In this study, new insight into the nature of the biological processes that underlie glandular morphogenesis is achieved by analyzing the phenotypes present in mice that harbor a spontaneous mutation, seminal vesicle shape (svs), previously identified for causing altered seminal vesicle morphology in adults. An examination of seminal vesicle development in svs mice provides the first evidence that the concurrent processes of epithelial branching and epithelial infolding are distinct processes under separate genetic control. It also provides the first direct evidence that the thickness and topology of the smooth muscle layer in the seminal vesicles are determined by interaction with the glandular epithelium during the branching process. In addition, the seminal vesicle phenotype in svs mice is shown to phenocopy the morphologic form present in certain other mammals such as the guinea pig, raising the possibility that the svs mutation is the sort of variant that arises during evolution. By also including an investigation of the prostate gland, this study also identifies previously unrecognized phenotypes in svs prostates, including increased gland size and dramatically reduced levels of branching morphogenesis. Finally, this study advances the goal of identifying the svs gene by mapping the svs mutation relative to known molecular markers and testing Fgfr2 as a candidate gene. The finding that the svs mutation maps to a genomic region syntenic to a region frequently deleted in human prostate tumors, together with the prostatic phenotype present in svs mice, further raises the interesting possibility that the svs mutation will identify a candidate prostate tumor suppressor gene. Developmental Dynamics 226:643–653, 2003. © 2003 Wiley‐Liss, Inc.
Origin of directionality in the fish stripe pattern
Authors: Shoji Hiroto , Mochizuki Atsushi , Iwasa Yoh , Hirata Masashi , Watanabe Tsuyoshi , Hioki Syozo , Kondo Shigeru
Published: March 2003

The formation of stripe patterns in animal skin has been explained by the reaction‐diffusion (RD) system, a hypothetical chemical reaction proposed by A. Turing. Although animal stripes usually have directionality, the RD model alone cannot explain how the direction is specified. To investigate the mechanism regulating the direction of stripes, we studied stripe pattern formation in two species of Genicanthus during sexual conversion. These species share almost identical morphologic properties, except for their stripe direction. In both species, spots transiently arise at random positions and then combine and rearrange to form directional stripes. Computational analysis has shown that diffusion anisotropy is very effective at specifying the direction of stripes formed by the RD system. Model simulations reproduce the transient dynamics of directional pattern formation observed in fish as well as the resulting stripes. In cases where the magnitude and direction of diffusion anisotropy of the substances are identical, the resulting stripes are not directional. However, if they differ, stripes become directional. As only a small difference in anisotropy is required for this effect, any kind of structure with directional conformation might cause a marked change in stripe direction. Scales are the most likely candidate structure for generating anisotropic interactions in skin. Developmental Dynamics 226:627–633, 2003. © 2003 Wiley‐Liss, Inc.
Hes1 but not Hes5 regulates an astrocyte versus oligodendrocyte fate choice in glial restricted precursors
Authors: Wu Yuanyuan , Liu Ying , Levine Edward M. , Rao Mahendra S.
Published: March 2003

To determine the role of Hes genes in the differentiation process of neuroepithelial (NEP) cells to glial restricted precursor cells (GRPs) and subsequently GRPs to oligodendrocytes and astrocytes, we have examined the effects of Hes1 and Hes5 on glial differentiation. We find that both Hes1 and Hes5 are expressed by GRPs and that Hes1 can drive GRPs to an astrocyte cell fate at the expense of oligodendrocyte differentiation. Overexpression of Hes1 in GRPs results in the up‐regulation of the astrocyte markers glial fibrillary acidic protein and CD44 and the down‐regulation of oligodendrocyte markers myelin proteolipid protein/DM20, GalC, and CNPase. Transcription factors involved in oligodendrocyte differentiation, such as Nkx2.2, Olig1, and Mash1, are also down‐regulated in Hes1‐overexpressing cells. The effect of Hes1 on gliogenesis is stage‐specific as Hes1 does not direct NEP cells to an astrocytic fate. In contrast to Hes1, Hes5 does not promote astrocyte differentiation. Instead, it inhibits both astrocyte and oligodendrocyte differentiation. Overexpression of Notch1 has an effect on gliogenesis similar to that of Hes1 and the mRNA levels of Hes1 are up‐regulated in cells overexpressing Notch1, suggesting that Notch1 could be an upstream activator of Hes1. Developmental Dynamics 675–689, 2003. © 2003 Wiley‐Liss, Inc.
Appearance of neurons and glia with respect to the wavefront during colonization of the avian gut by neural crest cells
Authors: Connor Paul J. , Focke Paul J. , Noden Drew M. , Epstein Miles L.
Published: March 2003

The original article to which this Erratum refers was published in Developmental Dynamics 226:91–98Developmental Dynamics(2000) 226(1) 91–98
Performance evaluation of TCP throughput with consideration of lower‐layer protocols for wireless cellular networks
Authors: Miyoshi Masahiro , Sugano Masashi , Murata Masayuki
Published: March 2003

We propose an analytical method for performance evaluation of TCP in a wireless cellular network, where the slotted ALOHA protocol is adopted as the data link layer. By using our method, we show that improving throughput at the data link layer level does not necessarily lead to TCP throughput improvement. Furthermore, we evaluate TCP throughput by considering communication errors on the radio link. When we introduce FEC as an error correcting method, we show that TCP throughput can be improved by selecting an appropriate error correction code with careful consideration of the overhead and the error correction capability according to the quality of the wireless channel. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(8): 29–39, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10086
Development of tabular broadband antenna for UHF‐TV
Authors: Okano Yoshinobu
Published: March 2003

A tabular loop antenna is proposed that can be matched to the characteristic impedance of a coaxial cable without using complex parasitic elements or expensive matching elements while maintaining the broadband character and superior gain of the loop antenna. Specifically, modification of the aperture shape inside the loop is attempted without changing the external shape. In this way, the control of the input impedance becomes possible and the bandwidth for VSWR ≤ 2 can reach about 40% at the center frequency of 620 MHz for UHF‐band TV. An antenna with a unidirectional radiation pattern with a reflector was fabricated for trial and was studied both by experiments and by FDTD analysis. It was confirmed that the bandwidth for VSWR ≤ 2 reaches about 50% at 620 MHz. Further, with regard to the dynamic gain, a stable gain of 7.6 to 8.2 dBi was attained for the entire UHF band. This antenna will be useful for ground wave digital broadcasting. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(8): 1–8, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10112