bluuebunny/crossref_metadata_2025 huggingface dataset:
Phase‐equilibrium behavior of vinyl chloride/n‐butane and its application in determination of vinyl chloride heterogeneous polymerization kinetics
Authors: Bao Y. Z. , Brooks B. W.
Published: October 2004

Studies of the phase‐equilibrium behavior of vinyl chloride (VCM)/n‐butane mixtures and the kinetics of VCM heterogeneous polymerization, using n‐butane as a reaction medium, were carried out using a 1‐L glass autoclave. The vapor composition was measured by gas chromatography, showing that the vapor pressure of the VCM/n‐butane mixture was located above the line connecting the points for pure VCM and n‐butane. The concentration of VCM in the vapor phase was greater than that in the corresponding liquid phase. It was confirmed that the presence of poly(vinyl chloride) (PVC) resin had no significant influences on the phase equilibrium of VCM/n‐butane mixtures. Thus, the phase‐equilibrium equations were applied to determine the conversion of VCM during heterogeneous polymerization. The conversions calculated from the variations of vapor pressure or composition agreed with those determined by the weighing method. The conversion–time and polymerization rate–time curves obtained for VCM heterogeneous polymerization showed that the polymerization accelerated at low initiator concentration, but the polymerization rate decreased with an increase of conversion at relatively high initiator concentrations. The chain‐transfer reaction to n‐butane was confirmed by a decrease of the molecular weight and broadening of the molecular weight distribution of PVC. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2179–2188, 2001
A facile approach to prepare soluble side‐chain polyimides for second‐order nonlinear optics
Authors: Sui Yu , Yin Jie , Hou Zhanjia , Zhu Na , Lu Jiongxin , Liu Yangang , Zhu Zikang , Wang Zongguang
Published: October 2004

A simple and generally applicable new synthetic method to prepare second‐order nonlinear optical (NLO) polyimides has been developed. In this approach, side‐chain‐substituted polyimides were synthesized via isocyanato‐terminated prepolymers prepared directly from NLO chromophore‐containing diols Disperse Red 19. Using this technique, the tedious synthesis of the classical diamine monomers and harsh imidization process associated with polyamic acid prepolymers are avoided. The resulting polymers possessed good solubility and high glass‐transition (171–211 °C) and thermal‐decomposition temperatures. The polymers also exhibited excellent film‐forming properties, and good optical‐quality films were easily obtained by spin coating. The second‐order NLO activities of the polymer films were also studied, and several factors that might determine the growth of the second‐order NLO activity were proposed. The polymers obtained exhibit a large second‐order NLO activity (34–52.5 pm/V at 1064 nm). © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2189–2195, 2001
Radical heterogeneous polymerization behavior of N‐methyl‐α‐fluoroacrylamide in benzene
Authors: Sato Tsuneyuki , Maeda Yoshinori , Seno Makiko , Hirano Tomohiro
Published: October 2004

The polymerization of N‐methyl‐α‐fluoroacrylamide (NMFAm) initiated with dimethyl 2,2′‐azobisisobutyrate (MAIB) in benzene was studied kinetically and with electron spin resonance. The polymerization proceeded heterogeneously with the highly efficient formation of long‐lived poly(NMFAm) radicals. The overall activation energy of the polymerization was 111 kJ/mol. The polymerization rate (Rp) at 50 °C is given by Rp = k[MAIB]0.75±0.05 [NMFAm]0.44±0.05. The concentration of the long‐lived polymer radical increased linearly with time. The formation rate (Rp•) of the long‐lived polymer radical at 50 °C is expressed by Rp• = k[MAIB]1.0±0.1 [NMFAm]0±0.1. The overall activation energy of the long‐lived radical formation was 128 kJ/mol, which agreed with the energy of initiation (129 kJ/mol), which was separately estimated. A comparison of Rp• with the initiation rate led to the conclusion that 1‐methoxycarbonyl‐1‐methylethyl radicals (primary radicals from MAIB), escaping from the solvent cage, were quantitatively converted into the long‐lived poly(NMFAm) radicals. Thus, this polymerization involves completely unimolecular termination due to polymer radical occlusion. 1H NMR‐determined tacticities of resulting poly(NMFAm) were estimated to be rr = 0.34, mr = 0.48, and mm = 0.18. The copolymerization of NMFAm(M1) and St(M2) with MAIB at 50 °C in benzene gave monomer reactivity ratios of r1 = 0.61 and r2 = 1.79. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2196–2205, 2001
Amphiphilic polymer gel electrolytes. I. preparation of gels based on poly(ethylene oxide) graft copolymers containing different ionophobic groups
Authors: Gavelin Patrik , Jannasch Patric , Wesslén Bengt
Published: October 2004

Amphiphilic graft copolymers were prepared via the radical copolymerization of poly(ethylene oxide) (PEO) macromonomers with fluorocarbon or hydrocarbon acrylates in toluene with 2,2′‐azobisisobutyronitrile (AIBN) as an initiator. 1H NMR spectroscopy confirmed that the composition of the graft copolymers corresponded well to the monomer feed. For gel electrolytes prepared from the amphiphilic copolymers, the nature of the ionophobic parts of the amphiphilic graft copolymers had a great influence on the ion conductivity. Gel electrolytes based on graft copolymers containing fluorocarbon side chains showed significantly higher ion conductivity than electrolytes based on graft copolymers containing hydrocarbon groups. The ambient‐temperature ion conductivity was about 2.6 mS/cm at 20 °C for a gel electrolyte based on an amphiphilic graft copolymer consisting of an acrylate backbone carrying PEO and fluorocarbon side chains. Corresponding gels based on graft copolymers with PEO side chains and hydrocarbon groups showed an ambient‐temperature ion conductivity of about 1.2 mS/cm. The gel electrolytes contained 30 wt % copolymer and 70 wt % 1 M LiPF6 in an ethylene carbonate/γ‐butyrolactone (2/1 w/w) mixture. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2223–2232, 2001
Aromatic polybenzoxazoles containing ether–sulfone linkages
Authors: Hsiao Sheng‐Huei , Chiou Jiun‐Hsiang
Published: October 2004

A series of poly(o‐hydroxy amide)s having both ether and sulfone linkages in the main chain were synthesized via the low‐temperature solution polycondensation of 4,4′‐[sulfonylbis(1,4‐phenylene)dioxy]dibenzoyl chloride and 4,4′‐[sulfonylbis(2,6‐dimethyl‐1,4‐phenylene)dioxy]dibenzoyl chloride with three bis(o‐aminophenol)s including 4,4′‐diamino‐3,3′‐dihydroxybiphenyl, 3,3′‐diamino‐4,4′‐dihydroxybiphenyl, and 2,2‐bis(3‐diamino‐4‐hydroxyphenyl)hexafluoropropane. Subsequent thermal cyclodehydration of the poly(o‐hydroxy amide)s afforded polyethersulfone benzoxazoles. Most of the poly(o‐hydroxy amide)s were soluble in polar organic solvents such as N‐methyl‐2‐pyrrolidone; however, the polybenzoxazoles without the hexafluoroisopropylidene group were organic‐insoluble. The polybenzoxazoles exhibited glass‐transition temperatures (Tg) in the range of 219–282 °C by DSC and softening temperatures (Ts) of 242–320 °C by thermomechanical analysis. Thermogravimetric analyses indicated that most polybenzoxazoles were stable up to 450 °C in air or nitrogen. The 10% weight loss temperatures were recorded in the ranges of 474–593 °C in air and 478–643 °C in nitrogen. The methyl‐substituted polybenzoxazoles had higher Tg's but lower Ts's and initial decomposition temperatures compared with the corresponding unsubstituted polybenzoxazoles. For a comparative purpose, the synthesis and characterization of a series of sulfonyl polybenzoxazoles without the ether group that derived from 4,4′‐sulfonyldibenzoyl chloride and bis(o‐aminophenol)s were also reported. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2262–2270, 2001
Copolymers of (2‐cyclohexylidene‐1,3‐dioxolane‐4‐yl) methyl methacrylate with acrylonitrile and styrene: Synthesis, characterization, and monomer reactivity ratios
Authors: İlter Zülfi̇ye , Coşkun Mehmet , Erol İbrahi̇m
Published: October 2004

The copolymerization of (2‐cyclohexylidene‐1,3‐dioxolane‐4‐yl) methyl methacrylate monomer with styrene and acrylonitrile were carried out in 1,4‐dioxane solution at 60 °C using BPO as an initiator. The copolymers were characterized by Fourier transform infrared, 1H NMR, and 13C NMR spectroscopic techniques. Thermal properties of the polymers were also studied by thermogravimetric analysis and differential scanning calorimetry. The copolymer compositions were determined by elemental analysis. The monomer‐reactivity ratios were calculated by the application of conventional linearization methods as a result of Fineman–Ross and Kelen–Tüdős to less than 1 for both monomers. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2326–2331, 2001
Synthesis of aminosaccharide‐derived polymers with urea, urethane, and amide linkages
Authors: Bachmann Frank , Ruppenstein Marcus , Thiem Joachim
Published: October 2004

The synthesis of novel polyurethanes and polyureas based on modified glycosylamines and glucosamines has been successfully accomplished by catalytic polymerizations. Several modified glucosamine monomers were synthesized to study their reactivities during these polymerization reactions. It was found that the anomeric hydroxyl groups are more reactive than the amino groups. The resulting polymers were characterized by NMR and IR spectroscopy, elementary analysis, viscosimetry, and gel permeation chromatography. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2332–2341, 2001
Effect of ionic additives on deformation behavior of bisphenol a polycarbonate
Authors: Lee Sang‐Soo , Cho Kilwon , Kim Joonkyung
Published: October 2004

The deformation behavior of bisphenol A polycarbonate containing only a small amount of oligoionomeric additives in the range of a few parts per hundred parts of resin was examined. The impact strength of polycarbonate markedly decreased as the content of additive increased, and brittle fracture of polycarbonate was observed in tensile tests when the concentration of additive was above 2.5 phr. The ductile‐to‐brittle transition that was determined using a comparison of the critical shear yield stress and the critical craze stress appeared to exist in the range of 2.5–3.5 phr of additive. The measured entanglement density was also found to decrease significantly with the addition of a few parts per hundred parts of resin of additives, and the change of the dominant deformation mechanism from ductile to brittle failure was recognized as a result of the change of the entanglement density of polycarbonate. Therefore, it was concluded that the presence of a small amount of ionomeric additives caused the loss of entanglement density that induced transition of the deformation mechanism of polycarbonate from ductile to brittle failure and led to the corresponding deterioration of impact strength. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2635–2643, 2001
Homopolymer and small‐molecule tracer diffusion in a gyroid matrix
Authors: Milhaupt Jodi M. , Lodge Timothy P.
Published: October 2004

Forced Rayleigh scattering was used to measure the tracer diffusion coefficients of the photochromic dye tetrathioindigo (TTI) and a 1,4‐polyisoprene (PI) homopolymer (8000 g/mol) in a poly(styrene‐b‐isoprene) (SI) diblock copolymer matrix that formed a bicontinuous gyroid microstructure. The diblock copolymer contained 63% polystyrene (PS) by volume and had a total molecular weight of 21,300 g/mol. Rheology and small‐angle X‐ray scattering confirmed that the diblock copolymer microphase‐separated into the bicontinuous gyroid over the temperature range 60–230 °C, where the sample disordered. For both the TTI and PI tracers, two distinct modes of transport were observed. The faster mode displayed a temperature dependence consistent with diffusion within a PI matrix, whereas the slower mode had a temperature dependence more similar to diffusion within PS. The fast diffusivities were both over an order of magnitude lower than in a corresponding PI homopolymer matrix. For TTI, this was attributed to the preferential selectivity of the dye for PS and, therefore, an averaging of the mobility between the PS and PI domains. The slow mode was consistent with a small fraction of the TTI dye molecules becoming trapped within the much slower PS domains. For the PI tracer, the reduction in the diffusion coefficient for the fast mode was attributed to a combination of the tortuosity of the struts, the suppression of constraint release within the diblock matrix, and additional friction due to the presence of some styrene segments within the PI domains. The inevitable presence of grain boundaries or defects within the matrix interrupted the percolation of the PI struts, thereby forcing some of the PI tracers to diffuse through PS. Consequently, the slow mode was attributed to the diffusion through these defects, where the PI diffusion was retarded by both the increased segmental friction and the thermodynamic barrier to entering the PS domains. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 843–859, 2001
Effects of hydroxyl‐group end capping and branching on the physical properties of tailored polyethylene terephthalates
Authors: Oh Sung Jin , Kim Byoung Chul
Published: October 2004

Polyethylene terephthalates (PETs) with well‐defined chemical structures were prepared by molecular design, and the effect of the chemical structure on the physical properties of PET was investigated. Hydroxyl‐group end‐capped PETs with ηinh = 0.4–0.6 dL/g exhibited a viscosity behavior similar to Bingham fluids, although other PETs with similar molecular weights (MWs) showed Newtonian flow behavior. This rheological feature was more noticeable for hydroxyl‐group end‐capped branched PETs. In addition, hydroxyl‐group end‐capped branched PETs became solidlike from 80 rad/s as the frequency was increased. On the other hand, hydroxyl end‐capped linear PETs showed a noticeable viscoelastic transition peak around 20 rad/s. High MW linear and branched PETs with ηinh ≥ 0.9 prepared by multistep synthesis showed non‐Newtonian fluid behavior. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 1027–1035, 2001
Kinetically controlled phase transitions in LC polymers. I. Isokinetic range crossover for the Sm B–Sm H transition in a side‐chain polysiloxane
Authors: Kozlovsky Mikhail V.
Published: October 2004

The kinetics of smectic‐phase formation in a siloxane copolymer, as compared with the crystallization of the relating homopolymer, was studied by the Avrami analysis of DSC data. A crossover from the diffusion‐controlled kinetics (the Avrami exponent k ∼0.35) to the two‐dimensional free‐growth mode (k ∼1.5) with increasing temperature was detected. The influence of the annealing temperature on the sequence of mesophases, transition temperatures, and enthalpies of the polymers was also investigated. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 1055–1060, 2001
Viscoelastic properties and phase behavior of 12‐tert‐butyl ester dendrimer/poly(methyl methacrylate) blends
Authors: Emran S. K. , Liu Y. , Newkome G. R. , Harmon J. P.
Published: October 2004

This study used refractometry, ultraviolet–visible spectroscopy, Fourier transform infrared spectroscopy, differential scanning calorimetry, and dielectric analysis to assess the viscoelastic properties and phase behavior of blends containing 0–20% (w/w) 12‐tert‐butyl ester dendrimer in poly(methyl methacrylate) (PMMA). Dendritic blends were miscible up through 12%, exhibiting an intermediate glass‐transition temperature (Tg; α) between those of the two pure components. Interactions of PMMA CO groups and dendrimer NH groups contributed to miscibility. Tg decreased with increasing dendrimer content before phase separation. The dendrimer exhibited phase separation at 15%, as revealed by Rayleigh scattering in ultraviolet–visible spectra and the emergence of a second Tg in dielectric studies. Before phase separation, clear, secondary β relaxations for PMMA were observed at low frequencies via dielectric analysis. Apparent activation energies were obtained through Arrhenius characterization. A merged αβ process for PMMA occurred at higher frequencies and temperatures in the blends. Dielectric data for the phase‐separated dendrimer relaxation (αD) in the 20% blend conformed to Williams–Landel–Ferry behavior, which allowed the calculation of the apparent activation energy. The αD relaxation data, analyzed both before and after treatment with the electric modulus, compared well with neat dendrimer data, which confirmed that this relaxation was due to an isolated dendrimer phase. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1381–1393, 2001
Calorimetry of nanophase‐separated poly(oligoamide‐alt‐oligoether)s
Authors: Di Lorenzo M. L. , Pyda M. , Wunderlich B.
Published: October 2004

The miscibility, crystallization, vitrification, and melting behavior of multiblock copolymers consisting of alternating components of oligo[imino(1‐oxododecamethylene)] and oligo(oxytetramethylene) were investigated in their dependence of composition and molecular mass of the blocks. In all compositions studied, the copolymers present two separate glass transitions at temperatures not far from those of the corresponding homopolymers. The immiscible components are linked by chemical bonds to nanophase‐separated layers. In such a situation, the structure and mobility of each phase affect the other, causing small shifts of the glass‐transition temperatures. The enthalpy‐based crystallinity was calculated separately for each component, using the known information on heat capacities and latent heats. The crystallinity is influenced by the block lengths. The oligoamide segments crystallize from an isotropic melt with a relatively high crystallinity, whereas the oligoether blocks solidify in the presence of crystals and glass of the second component in the adjacent solid nanophases, which greatly reduces their overall long‐range chain mobility, and as a consequence, their crystallinity is rather small. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1594–1604, 2001
Evaluation methods of the longest Rouse relaxation time of an entangled polymer in a semidilute solution
Authors: Osaki K. , Inoue T. , Uematsu T. , Yamashita Y.
Published: October 2004

Estimation methods for the longest Rouse relaxation time (τR) of an entangled polymer in a semidilute solution were examined. We evaluated τR by fitting the dynamic modulus (G′) with the Rouse model theory in the power law range, where G′ was proportional to the square root of the angular frequency (ω). The τR values thus obtained for polystyrene (PS) solutions in tricresyl phosphate (TCP) were employed to derive an empirical formula for the evaluation of τR from the viscosity (η): M is the molecular weight, and c is the mass of polymer per unit volume; Me = cRT/GN is the entanglement molecular weight, where GN is the G′ value at the inflection point of the graph of log G′ versus log ω. The subscript η indicates that τR is derived from η data. The proposed equation was also applicable to bulk PS and bulk polyisoprene. Discrepancies among reported τR values in semidilute solutions seem to be mostly due to discrepancies in Me values. For PS solutions in dioctyl phthalate, a Θ solvent, the τR value derived from η was much larger than that from the G′ curve. Apart from the evaluation method of τR, we observed for PS that Me was independent of temperature for good solvent systems and melts, that Me for solutions in TCP agreed with that for solutions in another good solvent, and that Me for a Θ‐solvent system was equal to that for good solvent systems with the same M and c values. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1704–1712, 2001
Molecular dynamics studies on HIV‐1 protease: Drug resistance and folding pathways
Authors: Cecconi Fabio , Micheletti Cristian , Carloni Paolo , Maritan Amos
Published: October 2004

Drug resistance to HIV‐1 protease involves the accumulation of multiple mutations in the protein. We investigate the role of these mutations by using molecular dynamics simulations that exploit the influence of the native‐state topology in the folding process. Our calculations show that sites contributing to phenotypic resistance of FDA‐approved drugs are among the most sensitive positions for the stability of partially folded states and should play a relevant role in the folding process. Furthermore, associations between amino acid sites mutating under drug treatment are shown to be statistically correlated. The striking correlation between clinical data and our calculations suggest a novel approach to the design of drugs tailored to bind regions crucial not only for protein function, but for folding as well. Proteins 2001;43:365–372. © 2001 Wiley‐Liss, Inc.
Theoretical evidence of a salt bridge disruption as the initiating process for the α1d‐adrenergic receptor activation: A molecular dynamics and docking study
Authors: Carrieri A. , Centeno N.B. , Rodrigo J. , Sanz F. , Carotti A.
Published: October 2004

This study reports the building of the three‐dimensional structure of the rat α1d‐adrenergic receptor through a topology approach based on the structure of the rhodopsin receptor from cryoelectron microscopy. The validity and reliability of the receptor model were assessed through exhaustive molecular dynamics and docking studies. Some interesting ligand‐receptor interactions were identified along with significant differences between the binding mode of agonists and antagonists. The importance of the disruption of a salt bridge as a possible initial event leading to receptor activation is discussed on the basis of data from mutagenesis and molecular dynamics studies. Proteins 2001;43:382–394. © 2001 Wiley‐Liss, Inc.
Demographic versus genetic dispersal measures
Authors: Vandewoestijne Sofie , Baguette Michel
Published: October 2004

Quantifying dispersal, a fundamental biological process, is far from simple. Here, both direct and indirect methods were employed to estimate dispersal in an endangered butterfly species. A high and significant correlation between the dispersal patterns, generated by an inverse power function fitted to capture‐mark‐recapture (CMR) data on the one hand, and population genetic analyses on the other hand, was observed. Stepping‐stone type movements were detected by both methods, evidence for the importance of connectivity in the studied metapopulation. These results are particularly relevant to those population and conservation biology studies where quantifying dispersal is essential for the elaboration of successful management actions.
Nasopharyngeal Tuberculosis: Manifestations between 1991 and 2000
Authors: Srirompotong Somchai , Yimtae Kwanchanok , Jintakanon Darunee
Published: October 2004

OBJECTIVES/HYPOTHESIS

To present the clinical manifestation of nasopharyngeal tuberculosis.

STUDY DESIGN

Clinical analysis of 23 patients with pathologically confirmed nasopharyngeal tuberculosis was carried out retrospectively.

SETTING

Srinagarind Hospital, Khon Kaen University. Thailand.

RESULTS

The most common presenting symptom was cervical lymphadenopathy (91.3%). The common locations of nodes were the superior and middle cervical. The abnormalities of the nasopharynx were found in 16 patients. The pathological findings were caseous granuloma with positive acid‐fast bacilli (AFB) in 15 cases, caseous granuloma with negative AFB in 3 cases, and chronic granulomatous inflammation with negative AFB in 5 cases. Pulmonary tuberculosis was found in 8 of 18 patients. Sixteen patients who received complete treatment responded well.

CONCLUSION

Nasopharyngeal tuberculosis commonly presents with cervical lymphadenopathy. The differential diagnosis of tuberculosis from nasopharyngeal carcinoma is difficult. In the patients who have cervical lymphadenopathy and no other identified causes, biopsy of nasopharynx would give an additive information for diagnosis.
Starplasty: Revisiting a Pediatric Tracheostomy Technique
Authors: Solares C. Arturo , Krakovitz Paul , Hirose Keiko , Koltai Peter J.
Published: October 2004

OBJECTIVE

To determine the efficacy the “starplasty” pediatric tracheostomy technique in reducing the incidence of major complications and tracheotomy‐related death.

METHODS

Retrospective chart analysis of all the cases of starplasty performed at 2 tertiary care centers between 1990 and 2002.

RESULTS

There were 94 children in our cohort ranging in age from 2 days to 14 years. Of the patients, 47 (50%) were females and 47 (50%) were males and 60 of the children (64%) were younger than 1 year of age. Forty‐one patients (44%) had neurologically related airway problems as their primary indication for tracheostomy, 34 (36%) had upper airway obstruction, and the remainder had pulmonary diseases, prolonged intubation, or metabolic‐related airway problems. There were 41 short‐term complications including 5 cases of tracheal tube dislodgement. There were no instances of pneumothorax or tracheostomy‐related death. There were 26 long‐term complications. There were no cases of clinically relevant suprastomal collapse that compromised decannulation and no instances of tracheal stenosis. Twenty‐six patients underwent decannulation, all of whom developed a tracheocutaneous fistula (TCF). Two patients had spontaneous closure of the TCF; 9 patients underwent surgical repair of their fistulas, 53 patients remain tracheostomy‐dependent, and 8 patients died of their primary disease.

CONCLUSION

The need for pediatric tracheotomy has increased as a consequence of our success in treating chronically ill children. Starplasty reduces the incidence of major complications, including pneumothorax and death from accidental decannulation. Its major drawback is the need for secondary reconstruction of a tracheocutaneous fistula. EBM rating: C.
Phenotypic and Microarray Gene Expression Analysis of Tri‐Dimensional Raft‐Modeled Human Head and Neck Squamous Cell Carcinoma
Authors: Zanation Adam M. , Yin Xiaoying , Shores Carol , Yarbrough Wendell G.
Published: October 2004

OBJECTIVES

To describe the phenotypic and gene expression differences in monolayer and tri‐dimensional cultures systems.

METHODS

Normal oral epithelial cells (NOEC), primary head and neck squamous cell carcinoma (HNSCC), and HNSCC cell lines were used to create and study modeled tri‐dimensional tissue. Using cDNA microarray analysis, monolayer and raft‐modeled tri‐dimensional HNSCC cell lines were compared.

RESULTS

NOEC, HNSCC, and both together can be modeled with tri‐dimensional differentiation and cytokeratin characteristics analogous to in vivo tissue. Modeling of primary HNSCC resulted in a morphology of invasive HNSCC with areas of direct collagen invasion and MMP2 expression. Gene array analysis suggests that the individual cell lines themselves are the primary gene expression predictor and not the presence of tri‐dimensional tissue architecture.

CONCLUSIONS

This tissue culture modeling system approximates the differentiation and tri‐dimensional structure of in vivo tissues, and that raft modeled tri‐dimensional HNSCC does not have a significantly different gene expression profile than the corresponding monolayer culture.
Polysomnography in Children Scheduled for Adenotonsillectomy
Authors: Weatherly Robert A. , Ruzicka Deborah L. , Marriott Deanna J. , Chervin Ronald D.
Published: October 2004

OBJECTIVE

Several studies suggest that a reliable diagnosis of childhood sleep‐disordered breathing (SDB) requires polysomnography (PSG). We compared clinical and PSG‐based diagnoses in children scheduled for adenotonsillectomy (AT). Parent responses on a validated Pediatric Sleep Questionnaire were used to determine which symptoms could help identify children with clinical diagnoses of SDB but normal PSG.

STUDY DESIGN AND SETTING

Thirty‐four children aged 5.0 to 12.9 years and scheduled for AT to treat clinically diagnosed sleep‐disordered breathing underwent laboratory‐based PSG. Results were scored by 3 different criteria: 1) >1 obstructive apnea (2 breaths or longer) per hour of sleep; 2) >5 apneas or hypopneas per hour of sleep; or 3) >1 apnea, hypopnea, or respiratory event–related arousal per hour of sleep.

RESULTS

Depending on the criterion used, the PSG documented SDB from a minimum of 18/34 subjects (53%, for criterion I) to as many as 30/34 subjects (88%, for criterion III). Among symptoms studied, absence of daytime mouth breathing and habitual snoring were most helpful in identification of children who had no evidence of SDB on PSG, by criterion I (Chi‐square, P < 0.05). The absence of other common symptoms, such as “loud snoring” or “trouble breathing” at night, were not helpful.

CONCLUSION

Children with clinical diagnoses of SDB may not consistently meet PSG criteria for this disorder. Questions about daytime mouth breathing and habitual snoring might help clinicians recognize children who would not have SDB on objective testing.

SIGNIFICANCE

Clinical identification of SDB confirmable on PSG could be improved. However, available outcome data do not yet clarify whether clinical or PSG criteria best identify children likely to suffer morbidity from SDB. EBM rating: C.
Response of Lake Superior to mesoscale wind forcing: A comparison between currents driven by QuikSCAT and buoy winds
Authors: Chen Changsheng , Xu Qichun , Ralph Elise , Budd Judith Wells , Lin Huichan
Published: October 2004

The satellite scatterometer QuikSCAT wind field has been available every 12 hours on Lake Superior since 19 July 1999. The wind data cover most of the interior area of the lake with a spatial resolution of about 25 km. Driving the three‐dimensional Lake Superior circulation model by the QuikSCAT winds, we resimulated the 1999 seasonal variability of currents in Lake Superior. A comparison was made with our previous simulation results, which relied on the wind field interpolated from moored buoys and land‐based meteorological stations. The model driven by QuikSCAT winds improved the simulation of the spatial coverage area of the cold band during upwelling favorable wind events and the current jet during downwelling favorable wind events observed along the Keweenaw coast in July–October 1999. A statistical analysis shows that these improvements were mainly reflected in the low‐frequency variation of the long‐shore current, even though the overall deviation between computed and observed surface temperature and currents was measurably reduced. This study suggests that the wind field constructed from either moored buoys plus land‐based meteorological stations or QuikSCAT is not sufficient to provide a reliable and accurate simulation of coastal currents and stratification in Lake Superior. A mesoscale meteorological model assimilated with observed winds on all the available weather measurement sites or stations or QuikSCAT is needed to provide an accurate meteorological forcing for the Lake Superior physical model.
40Ar/39Ar dating of ignimbrite from Inner Mongolia, northeastern China, indicates a post‐Middle Jurassic age for the overlying Daohugou Bed
Authors: He H. Y. , Wang X. L. , Zhou Z. H. , Zhu R. X. , Jin F. , Wang F. , Ding X. , Boven A.
Published: October 2004

The 40Ar/39Ar step heating analyses of K‐feldspar derived from the ignimbrite in Inner Mongolia, China indicates that they were formed at 159.8 ± 0.8 Ma, which provides a maximum age for the overlying fossil‐bearing lacustrine deposits (Daohugou Bed). This result favors a post‐Middle Jurassic (Late Jurassic or younger), rather than the Middle Jurassic age for the Daohugou Bed. Such a result is generally consistent with vertebrate biostratigraphic evidence, providing a maximum known age for the first appearance of several major animal groups such as Cryptobranchidae of Urodela (salamanders) and Maniraptora (birds and their closest dinosaurian relatives).
Managed grasslands: A greenhouse gas sink or source?
Authors: Leahy Paul , Kiely Ger , Scanlon Todd M.
Published: October 2004

We describe a unique, one year investigation of CO2 and N2O fluxes over a fertilized grassland in Ireland using two eddy covariance systems. As the global warming potential (GWP) of N2O is 296 (100 year time horizon), relatively small N2O emissions have a potentially large impact on overall radiative forcing. Therefore nitrogen fertilizer application practices may possibly turn a site with a net CO2 uptake into a net radiative forcing source. We observed a net annual uptake of 9.45 T CO2 ha−1. N2O emissions equivalent to 5.42 T ha−1 CO2 GWP counteracted 57% of the effect of the CO2 uptake. Estimated methane emissions from ruminants (3.74 T ha−1 CO2 GWP) further counteract the CO2 uptake, making the overall GWP nearly neutral. This delicate balance of the greenhouse gas fluxes underscores the significance of fertilizer application strategies in determining whether a managed grassland is a net GWP source or sink.
Hydrogen partition coefficients between nominally anhydrous minerals and basaltic melts
Authors: Aubaud Cyril , Hauri Erik H. , Hirschmann Marc M.
Published: October 2004

We have measured hydrogen partition coefficients between nominally anhydrous minerals (olivine, pyroxenes) and basaltic melts in 13 hydrous melting experiments performed at upper mantle P‐T conditions (1–2 GPa and 1230–1380°C). Resulting liquids have 3.1–6.4 wt.% H2O and average mineral/melt partition coefficients as follows: DHol/melt = 0.0017 ± 0.0005 (n = 9), DHopx/melt = 0.019 ± 0.004 (n = 8), and DHcpx/melt = 0.023 ± 0.005 (n = 2). Mineral/mineral partition coefficients are DHol/opx = 0.11 ± 0.01 (n = 4), DHol/cpx = 0.08 ± 0.01 (n = 2) and DHcpx/opx = 1.4 ± 0.3 (n = 1). These measurements confirm that water behaves similarly to Ce during mantle melting (DHperidotite/melt is ∼0.009). For mantle water concentrations of 50–200 ppm, the onset of melting is 5–20 km deeper than the dry solidus, less than previous estimates.
Spatial and temporal multiyear sea ice distributions in the Arctic: A neural network analysis of SSM/I data, 1988–2001
Authors: Belchansky Gennady I. , Douglas David C. , Alpatsky Ilia V. , Platonov Nikita G.
Published: October 2004

Arctic multiyear sea ice concentration maps for January 1988–2001 were generated from SSM/I brightness temperatures (19H, 19V, and 37V) using modified multiple layer perceptron neural networks. Learning data for the neural networks were extracted from ice maps derived from Okean and ERS satellite imagery to capitalize on the stability of active radar multiyear ice signatures. Evaluations of three learning algorithms and several topologies indicated that networks constructed with error back propagation learning and 3‐20‐1 topology produced the most consistent and physically plausible results. Operational neural networks were developed specifically with January learning data, and then used to estimate daily multiyear ice concentrations from daily‐averaged SSM/I brightness temperatures during January. Monthly mean maps were produced for analysis by averaging the respective daily estimates. The 14‐year series of January multiyear ice distributions revealed dense and persistent cover in the central Arctic surrounded by expansive regions of highly fluctuating interannual cover. Estimates of total multiyear ice area by the neural network were intermediate to those of other passive microwave algorithms, but annual fluctuations and trends were similar among all algorithms. When compared to Radarsat estimates of multiyear ice concentration in the Beaufort and Chukchi Seas (1997–1999), average discrepancies were small (0.9–2.5%) and spatial coherency was reasonable, indicating the neural network's Okean and ERS learning data facilitated passive microwave inversion that emulated backscatter signatures. During 1988–2001, total January multiyear ice area declined at a significant linear rate of −54.3 × 103 km2 yr−1 (−1.4% yr−1). The most persistent and extensive decline in multiyear ice concentration (−3.3% yr−1) occurred in the southern Beaufort and Chukchi Seas. In autumn 1996, a large multiyear ice recruitment of over 106 km2 (mostly in the Siberian Arctic) fully replenished the previous 8‐year decline in total area, but it was followed by an accelerated and compensatory decline during the subsequent 4 years. Seventy‐five percent of the interannual variation in January multiyear sea ice area was explained by linear regression on two atmospheric parameters: the previous winter's (JFM) Arctic Oscillation index as a proxy to melt duration and the previous year's average sea level pressure gradient across the Fram Strait as a proxy to annual ice export. Consecutive year changes (1994–2001) in January multiyear ice volume were significantly correlated with duration of the intervening melt season (R2 = 0.73, −80.0 km3 d−1), emphasizing a large thermodynamic influence on the Arctic's mass sea ice balance during summers with anomalous melt durations.
Surface albedo measurements over Antarctic sites in summer
Authors: Pirazzini Roberta
Published: October 2004

Surface albedo data from several Antarctic sites were compared to determine spatial and temporal variability in albedo. The highest degree of variability was observed at Hells Gate Station on the Ross Sea coast. The temperature close to the melting point and the reduced katabatic winds during summer allowed a strong metamorphism of the snow. At Neumayer, a coastal station by the Weddell Sea, snowfall and drifting snow were more frequent, and the surface albedo was constantly high. The albedo increased by an average of 0.07 from clear days to days with snowfall and overcast sky. Surprisingly, the hourly variation in albedo at Hells Gate Station showed a trend similar to the one observed at Neumayer Station and at Dome Concordia Station on the high plateau, when only those days with fresh snow at the surface were considered. The albedo steadily decreased during the day for solar zenith angles less than 80°. Snow metamorphism, sublimation during the day, and refreezing and/or crystal formation/precipitation during the night can explain the observed trend. To represent the daily trend in albedo over ice and fresh snow, we propose two parameterizations, which can be easily applied over other Arctic and Antarctic sites in summer. Small‐ and large‐scale surface roughness elements can result in distortion in the measured albedo. The data at Reeves Névé Station show the effect produced on the albedo by changing slightly the sampling area immediately over a sastruga.
A 1500‐year El Niño/Southern Oscillation and rainfall history for the Isthmus of Panama from speleothem calcite
Authors: Lachniet Matthew S. , Burns Stephen J. , Piperno Dolores R. , Asmerom Yemane , Polyak Victor J. , Moy Christopher M. , Christenson Keith
Published: October 2004

The effect of the El Niño/Southern Oscillation (ENSO) on tropical rainfall variations of the past 2 millennia is largely unknown. High‐resolution monsoon records are sparse, despite the role of ENSO in generating global hydrologic anomalies in modern climate. To investigate the relationship between ENSO and the Central American Monsoon, we generated a high‐resolution (∼2.9 years/sample) oxygen‐isotope monsoon rainfall record from a U/Th‐dated stalagmite (180 B.C. to 1310 A.D.) from the Isthmus of Panama. We present evidence for a weakened monsoon during the “High Medieval” (1100–1200 A.D.) and the Classic Maya Collapse (750–950 A.D.). Rainfall decreased and was more variable after 550 A.D., and the period 900–1310 A.D. was drier than the preceding millennium. A weaker monsoon corresponds with increased El Niño variability, and our data display statistical variance in the ENSO band. We conclude that ENSO variation has forced isthmian rainfall and may have contributed to hemispheric climatic anomalies at this time.
Airglow imager observations of atmospheric gravity waves at Alice Springs and Adelaide, Australia during the Darwin Area Wave Experiment (DAWEX)
Authors: Hecht J. H. , Kovalam S. , May P. T. , Mills G. , Vincent R. A. , Walterscheid R. L. , Woithe J.
Published: October 2004

The Darwin Area Wave Experiment occurred in Australia from October to December 2001. An objective was to characterize the atmospheric gravity wave field produced from intense convective activity that is routinely observed around Darwin during November and December. Two airglow imagers were sited at Adelaide and at Alice Springs, each located over 1000 km south of Darwin. Waves were observed at the mesopause region propagating predominantly toward the southeast, with some going to the northwest but with none observed going from east to west. The lack of waves propagating toward the west suggests some wind filtering mechanism below 80 km altitude. Waves observed over Alice Springs were analyzed in detail on three nights. On 16 November they were seen propagating toward the northwest. It is proposed that they were generated by dynamical events associated with a cutoff low‐pressure system present over southwest Australia. On 17 and 19 November the observations are consistent with wave generation by convective activity present in the Darwin area. Thus as proposed by Walterscheid et al. [1999] and Hecht et al. [2001a], the ducting of waves from distant sources is shown to be a viable explanation for the quasi‐monochromatic waves frequently observed in airglow observations. Walterscheid et al. [1999] suggested that ducting of waves from the extensive region of deep cumulus convection over northern Australia explained the strong poleward directionality seen in the summer months. The present study suggests that propagation from northern Australia is selective, and ducted waves from this region may not be the primary source of waves over Adelaide when convection is occurring over central Australia.
Characteristics of gravity waves with short vertical wavelengths observed with radiosonde and GPS occultation during DAWEX (Darwin Area Wave Experiment)
Authors: Tsuda Toshitaka , Ratnam M. Venkat , May Peter T. , Alexander M. Joan , Vincent Robert A. , MacKinnon Andrew
Published: October 2004

We conducted radiosonde soundings during three intensive observation periods (IOP) of the Darwin Area Wave Experiment (DAWEX) campaign in October to December 2001 and measured humidity, temperature, and wind velocity up to ∼30–35 km every 3 hours for 40 times at three sites in each IOP. We analyzed height profiles of kinetic (Ek) and potential (Ep) energy per unit mass caused by gravity waves with vertical wavelengths less than 3 km. The wave energy was clearly enhanced between 15–20 km and 25–30 km, and it was considerably depressed at 20–25 km between the two height regions. This feature was seen at all the sites during the three IOPs. Different types of wave activity seem to contribute to the enhancement of Ek and Ep below 20 km and at 25–30 km. Height distribution of the wave energy at 20–30 km seems to correlate with the structure of the mean zonal wind shear. We also analyzed a latitude‐height section of Ep in October to December 2001 using GPS occultation data with the CHAMP satellite collected around the DAWEX sites (80–180°E and 30°N to 30°S). Compared with the latitude distribution of Ep with GPS, the DAWEX results were slightly smaller and larger at 20–25 km and 25–30 km, respectively. The longitude variation of Ep is also analyzed from the GPS data at 10–15°S, which generally agreed well with the DAWEX results at both 20–25 km and 25–30 km.
Ozone response to precursor controls in very complex terrains: Use of photochemical indicators to assess O3‐NOx‐VOC sensitivity in the northeastern Iberian Peninsula
Authors: Jiménez Pedro , Baldasano José M.
Published: October 2004

The kinetics of ozone (O3) chemistry and its two main precursors, nitrogen oxides (NOx) and volatile organic compounds (VOC), represents an important field of uncertainty in atmospheric chemistry and photochemical modeling. This uncertainty affects the design of control strategies to reduce tropospheric O3 production. The effect of controlling ozone precursors on sensitivity regimes was evaluated by performing simulations with MM5‐EMICAT2000‐CMAQ model to represent O3 formation in the northeastern Iberian Peninsula with baseline emission rates for VOC and NOx, and reducing anthropogenic VOC and NOx emissions on a 35%. Three different scenarios were considered in order to assess chemical sensitivity in urban, industrial, and background domains. Areas downwind of the city of Barcelona benefit from NOx reductions (reduction of 10 ppb in ground‐level O3), while the same reduction causes an important increment of O3 in Barcelona (9 ppb) and the area downwind of Tarragona (18 ppb), with a high industrial influence. The city of Barcelona benefits from VOC reductions (10 ppb of O3) as well as the industrial zone of Alcover (20 ppb). The rest of the domain is practically insensitive to VOC reductions. Diverse photochemical species derived from the air quality model were used as indicators in order to establish the chemical sensitivity regime existing in the areas, analyzing whether O3 values reacted consistently to similar changes in emissions. Results showed that NOy (total reactive nitrogen) and O3/NOy are the indicators involving a lower uncertainty when assessing sensitivity, according to the narrow transition regime between NOx‐ and VOC‐sensitive chemistry and the low uncertainty observed. Indicators performed better in VOC‐sensitive than in NOx‐sensitive domains. H2O2‐ and HNO3‐ derived indicators entailed higher uncertainties since transition regimes between NOx and VOC sensitivity covered a wide range. The extent of reaction also performed as a good indicator to separate NOx‐ and VOC‐sensitive regimes. This sensitivity analysis provides a tool for establishing hypothetical control policies for O3 precursor emissions through a comparison of simulated correlation between the species.
Squeeze air bearing based on ultrasonic oscillation: Motion error compensation using amplitude modulation
Authors: Oiwa Takaaki , Kato Masaya
Published: October 2004

This article reports an active air bearing that utilizes air films generated by ultrasonic oscillation. The films on the bearing surfaces of a horn, which is a stator, lift and restrain the rotor. Moreover, the oscillation that modulates the amplitude via the positioning signal varies the thickness of the air film. Thus, this bearing regulates the position of the rotor using a PI controller with a displacement sensor so that its runouts become zero. Furthermore, no pneumatic plant is needed in this bearing. The repetitive runouts were 0.23 μm p-p in an axial direction and 1.0 μm p-p in a radial without compensation. Nonrepetitive runouts were 0.061 μm 3σ in an axial direction and 0.065 μm 3σ in a radial without compensation. PI feedback control, in which a fiber optic displacement sensor measures the movement of a master ball mounted on the rotor, decreased repetitive axial runout from 0.232 μm p-p to 0.118 μm p-p. The settling time for 0.2 μm step positioning in an axial direction was less than 0.2 s. The positioning resolution was less than 40 nm. Infinite stiffness under a 1.2 N static load was obtained in the experiments.
Localized error bursts in estimating the state of spatiotemporal chaos
Authors: Baek Seung-Jong , Hunt Brian R. , Szunyogh Istvan , Zimin Aleksey , Ott Edward
Published: October 2004

We consider the problem of estimating the current state of an evolving spatiotemporally chaotic system from noisy observations of the system state and a model of the system dynamics. Using a simple scheme for state estimation, we show the possible occurrence of temporally and spatially intermittent large bursts in the estimation error. We discuss the similarity of these bursts with those occurring at the bubbling transition in the synchronization of low dimensional chaotic dynamical systems. We characterize the spatial and temporal behavior of the bursts and investigate how the behavior changes as we vary the number and location of the observations.