bluuebunny/crossref_metadata_2025 huggingface dataset:
Post–Dural Puncture Headache and other Complications after Lumbar Puncture
Authors: Chordas Christine
Published: August 2002

In pediatric hematology and oncology specialties, lumbar punctures are frequently performed for diagnostic and therapeutic purposes. Lumbar puncture is a procedure that is generally well tolerated with minimal adverse effects. However, adverse effects do occur. Post–dural puncture headache (PDPH) is the most common adverse effect after lumbar puncture. A better understanding of the pathophysiology of PDPH and attention to needle selection and technique may lessen the occurrence of PDPH. A review of the literature that addresses the variables associated with PDPH and its prevention are presented. Other adverse effects after lumbar puncture include dysesthesias, backache, transient radicular irritation, nerve palsies, infectious processes, herniation, and bleeding disorders. Although most adverse effects are mild and resolve without intervention, others require astute diagnosis and management. This review discusses the general principles in the clinical presentation of adverse effects after lumbar puncture and offers interventions for management. The prevention and the recognition and treatment of adverse effects is the role of the entire health care team that cares for children who require lumbar puncture. As such, implications for the role of nursing are essential before, during, and after a lumbar puncture and are briefly discussed.
An in vitro biomechanical investigation of an intramedullary nailing technique for repair of third metacarpal and metatarsal fractures in neonates and foals
Authors: Fitch Gareth L. , Galuppo Larry D. , Stover Susan M. , Willits Neil H.
Published: August 2002

Objective—To evaluate a dorsoproximal extra‐articular approach for insertion of 8.25‐mm, solid‐titanium, intramedullary (IM) interlocking nails into ostectomized foal third metacarpal (MC3) and third metatarsal (MT3) bones; to compare the monotonic mechanical properties of IM nail constructs with paired intact bones; and to determine the effects of age, body weight, fore‐ or hindlimb, and left or right limb on the mechanical testing variables.

Animal or Sample Population—Twenty bone pairs (10 MC3, 10 MT3) collected from 10 foals of various weights and ages.

Methods—One bone from each pair was randomly selected to be ostectomized and stabilized using an 8.25‐mm, solid‐titanium IM nail, and four 3.7‐mm titanium interlocking screws (construct). Constructs and contralateral intact bone specimens were tested in axial compression and palmaro‐/plantarodorsal (PD) 4‐point bending. Monotonic mechanical properties were compared between intact specimens and constructs with an ANOVA; significance was set atP< .05.

Results—Nail insertion caused bone failure in 6 MC3 and 2 MT3. In general, mean mechanical testing values indicated that intact specimens were significantly stronger and stiffer than constructs for all age and weight ranges when tested in compression and PD 4‐point bending (P< .05). Bone strength and stiffness of intact specimens tested in compression and bending tended to increase linearly with age and weight.

Conclusions—IM interlocking nail fixation of gap‐ostectomized MC3 and MT3 with 8.25‐mm IM nails and 3.7‐mm interlocking screws did not achieve sufficient strength or stiffness to be recommended as the sole means of repair for comminuted MC3 and MT3 fractures in young foals.

Clinical Relevance—IM interlocking nail fixation of foal cannon bone fractures may be useful to decrease soft‐tissue disruption at the fracture site; however, there is a risk of bone failure associated with extra‐articular insertion. This method should be combined with other forms of external coaptation for added stability in axial compression and PD bending.
Modelling of a laser plasma source of amorphic diamond
Authors: J Stevefelt  , C B Collins
Published: August 2002

Recently, attention has been focused upon laser plasma sources of thin-film diamond. The paper reports a model of an expanding carbon plasma ablated from graphite feedstock by a focused laser beam. The model includes as essential ingredients adiabatic cooling of plasma electrons and electron-ion recombination through both collisional and radiative processes. It is shown that, under experimental conditions that have been proven relevant for producing hard amorphic diamond films characterized by a high percentage of sp3 bonds, the plasma is composed of multiple-charged carbon ions with kinetic energies of the order of 1 keV. This ionization can readily survive plasma transport to substrates positioned a few centimetres from the graphite target.
DC glow discharge in air flow at atmospheric pressure in connection with waste gases treatment
Authors: Yu S Akishev  , A A Deryugin  , I V Kochetov  , A P Napartovich  , N I Trushkin
Published: August 2002

The results of an experimental investigation of a DC glow discharge in fast air flow at a pressure of up to two atmospheres are presented. A high efficiency in the production of chemically active particles is achieved in this kind of discharge. For dry air the ozone yield was as high as 80 g kWh-1at a concentration of 0.05%. The results of a successful application of this discharge for SO2and NO removal from polluted air are described. A full kinetic model for the glow discharge at atmospheric pressure of dry air has been developed which explains experimental results with satisfactory accuracy.
Thermal transport properties of D-Er2Si22O7at room temperature
Authors: A Maqsood  , M Arshad  , M Maqsood
Published: August 2002

The compound Er2Si2O7exists in three modifications-a triclinic low-temperature phase (type B), a monoclinic modification (type C) and a high-temperature monoclinic modification (type D). The thermal transport properties of single crystals of D-Er2Si2O7have been measured by the transient hot strip method. The average thermal conductivity was found to be about 1 W m-1K-1. By using the calorimetric method the heat capacity per unit mass of D-Er2Si2O7at room temperature was found to be 0.52+or-0.04 J g-1K-1, corresponding to the molecular heat capacity of 31.4 R. The calculated molecular heat capacity at room temperature is 33 R.
High-resolution X-ray optics for third-generation synchrotron radiation
Authors: T Ishikawa
Published: August 2002

Novel high-resolution X-ray optics for the use of the extremely high brilliance of the undulator X-radiation from the third-generation synchrotron light sources are presented. These include plane-wave X-ray optics to produce a 40 nrad collimated beam, multiple flat-crystal monochromators with milli-electron-volt and sub-milli-electron-volt resolution, a nuclear Doppler monochromator with 50 neV resolution and interface-selective X-ray topography with 30 nm depth resolution.
Atomic hydrogen and argon ground state density determination in a recombining plasma using visible light absorption spectroscopy
Authors: D K Otorbaev  , A J M Buuron  , M C M van de Sanden  , R F G Meulenbroeks  , D C Schram
Published: August 2002

The atomic radical density in the first excited state, obtained by the technique of optical absorption spectroscopy, and a simple kinetic model are used to determine the radical ground state density in a recombining expanding plasma. The kinetic model used does not require knowledge of the shape of the electron energy distribution function. The information on electron density and electron temperature has been derived from the Thomson-Rayleigh scattering diagnostic. The method is demonstrated for the determination of the absolute ground state densities of atomic hydrogen H(n=1) and argon Ar(3p6) in a freely expanding plasma jet.
The determination of the neutral atom density in a high-pressure mercury discharge from the 253.7 nm self-reversed resonance line
Authors: H Elloumi  , M Aubès  , F Simonet  , J J Damelincourt
Published: August 2002

In this work the broadening of the red wing of the 253.7 nm resonance mercury line is used to determine the radial distribution of the neutral atom density in a high-pressure mercury discharge. Abel inversion allows resolution of the integral relation between the wavelength at the maximum intensity of the red-wing resonance line and the square of the neutral atom density. This method, which does not require the assumption of local thermodynamic equilibrium, is applied to the pressure range 0.2 - 5 bar. Results are compared with those obtained from the broadening of the 491.6 nm mercury line.
Theoretical model for thermally stimulated luminescence, conductivity and exoelectronic emission
Authors: S Guissi  , R Bindi  , P Iacconi  , D Jeambrun  , D Lapraz
Published: August 2002

A theoretical model which takes into account thermally stimulated luminescence (TSL), conductivity (TSC) and exoelectronic emission (TSEE) is proposed in this article. The model is established for the case of a single type of electron trap, a single type of recombination centre and in the presence of thermally disconnected traps. It generalizes the model of Lewandowski and McKeever by taking the TSEE phenomenon into consideration. TSEE is described as resulting from the thermionic effect and so the model applies only to a thin solid film about 10 nm thick. As an application example, the influence of various parameters involved in the model on peak shape and position is investigated.
Structural and optical properties of thin films of
Authors: H S Soliman
Published: August 2002

Thin films ofof various thicknesses (94-400 nm) were prepared either on glass or on quartz substrates. X-ray diffractograms show thatin a powder form or annealed samples in thin film form have a single-phase chalcopyrite tetragonal structure with lattice parametersandwithand distortion parameter. However, the as-depositedfilms may have a polycrystalline nature with very fine crystallites. The optical constants (the refractive indexn, the absorption indexkand the absorption coefficient) of thin films ofeither as deposited or after being annealed for 2 h at 673 K were determined using the transmissionTand reflectionRat normal incidence of light in the wavelength range 400-2500 nm. The refractive index in both cases (as deposited and after being annealed) exhibits anomalous dispersion in the wavelength range 400-600 nm. The permittivitywas found to be 6.12 and 6.02 foras deposited and after being annealed respectively. A plot ofshows that these films, whether as deposited or after being annealed, have two direct allowed optical transitions which are attributable to the splitting of the valence band.
The diffusion cooling coefficient for thermal neutrons in Plexiglas
Authors: Krzysztof Drozdowicz
Published: August 2002

The thermal neutron diffusion cooling coefficient is a macroscopic material parameter which is needed for a description of the decay of the thermal neutron pulse in a medium and gives information on the diffusion cooling of the thermal neutron spectrum in a bounded volume. Experimental results from various measurements for Plexiglas (a hydrogenous substance) are overviewed in the paper. A method for a theoretical calculation of the parameter is presented. The formula used utilizes other thermal neutron parameters and a cooling function which describes the deviation of the neutron spectrum in a bounded system from the distribution in an infinite one. The energy dependence of the function is obtained numerically from relations which result from the eigenvalue problem of the scattering operator when both the decay constant and the spectrum of the thermal neutron flux are developed in powers of the geometrical buckling. The calculation utilizes Granada's synthetic scattering function. The obtained value of the diffusion cooling coefficient for Plexiglas isat the temperature ofC. The uncertainty is estimated to bewithin the physical model of the scattering kernel used. Results obtained using the same type of kernel in other theoretical methods are also included.
RF discharge modelling in a N2O/SiH4mixture for SiO2deposition and comparison with experiment
Authors: K Radouane  , L Date  , M Yousfi  , B Despax  , H Caquineau
Published: August 2002

The present work concerns the experimental and theoretical analysis of the electrical behaviour and N2O/SiH4dissociation of a classical RF discharge used for SiO2thin-film deposition. Electric and deposition rate measurements are undertaken at 0.5 and 1 Torr gas pressures. The reactor modelling involves electrical, hydrodynamic and mass transfer models. The electrical model enables the calculation of the electron impact dissociation rates required for the mass transfer model, while the gas velocities are determined by the hydrodynamic model. Only an electrical discharge model accounting for the negative-ion conversion reactions O-/SiH4and NO-/SiH4allows good agreement between the measured and calculated power densities particularly at 1 Torr. Furthermore, a simplified chemical scheme which includes 16 species (N2O, N2, O2, NO, NO2, N, O(3P), O(1D), SiH4, SiH3, SiH3O, H2SiO, H, H2, OH and H2O) is used in the mass transfer model. The corresponding results (deposition rates) are quite consistent with the measurements.
Measurement of the ultrafast third-order optical nonlinearity of multi-adducts C70(NH2CN)5and C70(NH2CNNCNH2)5
Authors: Ruisheng Liang  , Shufeng Wang  , Wentao Huang  , Qihuang Gong  , Hongbo Li  , Huiying Chen  , Di Qiang
Published: August 2002

The second-order hyperpolarizability of two multi-adducts of fullerene, C705-aminonitrile and C705-dicyandiamide, was measured by using a femtosecond time-resolved optical Kerr effect at 810 nm wavelength. The magnitude was estimated to be as large as 4.1×10-32 esu for C705-aminonitrile and 5.8×10-32 esu for C705-dicyandimide. This showed that the optical nonlinearity of C70was strongly enhanced by forming a multi-addition charge-transfer complex.
Pressure effect on the electrical ageing of polyethylene
Authors: F-Benlizidia Lalam  , Hoang-The-Giam
Published: August 2002

The purpose of this study is to show the effect of hydrostatic pressure on the electrical ageing, by a dc voltage, on polyethylene used in submarine cables. Experimental results are obtained at 1 and 300 bar, for a temperature of 70 °C in the range of an electrical field of 1.1-4.5 MV cm-1and for up to 1500 h of ageing. By using the Weibull statistic and the estimation of confidence bounds of 90%, the results have shown an increase of lifetime with pressure. The time dependence of the breakdown behaviour of the two materials (HDPE and XLPE) is consistent with the inverse power law model. The pressure effect may be explained by changes in the activation free energy for the formation of submicrocavities.
Removal of cyclohexanone in transition electric discharges at atmospheric pressure
Authors: Zdenko Machala  , Marcela Morvová  , Emmanuel Marode  , Imrich Morva
Published: August 2002

Two new types of streamer-induced electric discharges operating in a non-uniform electric field in air at atmospheric pressure were applied to the removal of volatile organic compounds (VOCs). The first type is a pulseless dc discharge with physical properties corresponding to the glow discharge. The second, also supplied by a dc high voltage of both polarities, is a spontaneously pulsing discharge operating in the regime of the streamer-to-spark transition, the spark phase being too short to reach local thermodynamic equilibrium conditions. Both discharges are able to generate a non-thermal plasma, as resolved from their rotational and vibrational temperatures.

The influences of these discharges on the removal of cyclohexanone at various gas flow rates and concentrations (600-6000 ppm) were compared. The removal efficiencies achieved were about 50-60%, and the energy costs were 16-100 eV/molecule at various energy densities. Special conditions where CO2and other gaseous products are minor and dominant products appear in the condensed phase can be obtained, especially in the spontaneously pulsing transition discharge.

We explain some plasmochemical processes induced by the discharges by considering heterogeneous effects of the copper electrode surface. The role of active nitrogen and the formation of the NCO radical are probably key factors leading to the formation of the condensation product based on amino acids, here produced for the first time from VOCs, as well as in the overall energy cycle resulting in low energy costs of the process.

The small pilot-scale reactor based on the spontaneously pulsing transition discharge has been successfully applied to the removal of cyclohexanone in the mixture with other VOCs with no noxious gas output. This validates the possibility of the application of such a type of reactor for larger scales.
Role of photoionization processes in propagation of cathode-directed streamer
Authors: S V Pancheshnyi  , S M Starikovskaia  , A Yu Starikovskii
Published: August 2002

The effect of the electron distribution in front of the cathode-directed streamer head on the characteristics of the discharge itself has been analysed in this paper. Both the process of gas photoionization in front of the streamer head and the effect of spatially uniform `background' pre-ionization have been taken into consideration. It is shown that the substitution of the actual photoelectron distribution in front of the streamer head for uniform `background' pre-ionization makes it possible, by the variation of this parameter, to attain the coincidence of some characteristics of the streamer discharge (streamer velocity, conduction current, electron distribution in the streamer head and channel), not allowing for coincidence of all the characteristics simultaneously in this case. The analytical model that allows us, with the use of the known streamer head potential, to obtain associated values of the head radius and peak electric field strength has been proposed and verified.
NO formation in a pulsed spark discharge in
N2/O2/Ar mixture at atmospheric pressure
Authors: Ryo Ono  , Tetsuji Oda
Published: August 2002

Nitrogen monoxide (NO) formation in a pulsed spark discharge is studied in
N2/O2/Ar mixture at atmospheric pressure. For monitoring NO
formation, vibrationally excited NO(X,v = 3) is
measured by laser-induced fluorescence (LIF) with a tunable KrF excimer laser. The
LIF with a KrF laser has an advantage that it can also monitor vibrationally excited
oxygen O2(X,v = 6) along with
NO(X,3). The generation of the
O2(X,6) is closely related with the production of O
radical or excited oxygen O2* that is generally responsible for NO
formation. Therefore, LIF can observe NO formation associated with O and
O2* production. LIF analysis shows a similarity between
NO(X,3) and O2(X,6) formation when
O2 content changes. NO(X,3) and
O2(X,6) are not formed at O2 content less
than 9%, whereas both molecules increase linearly with O2 concentration
when the O2 content exceeds 9%. The similarity between
NO(X,3) and O2(X,6) formation
suggests that NO is mainly formed by reaction with O or O2*. With the
result, the possible NO production processes are discussed. It is concluded that NO
is mainly produced by reactions N2* + O or N2* +
O2*, where N2* represents an excited nitrogen molecule.
Atomic Evolutions of a Single Atom in a High-Q Cavity
Authors: Ge Guo-Qin  , P. T. Leung
Published: August 2002

Atomic evolutions in a single atom laser system are studied for different preparations of the initial atomic state and cavity field. Both the analytical and the numerical results are in very good agreement with the experiment carried out by Brune et al. [Phys. Rev. Lett.76(1996) 1800], if we choose the same parameters as the experiment. The research justified that the spontaneous emission rates are enhanced in the high-Qcavity.
Deep Ultraviolet Harmonic Generation with
KBe2BO3F2 Crystal
Authors: Chen Chuang-Tian  , Lü Jun-Hua  , Wang Gui-Ling  , Xu Zu-Yan  , Wang Ji-Yang  , Zhang Cheng-Qian  , Liu Yao-Gang
Published: August 2002

A special prism coupling technique with the KBe2BO3F2 crystal is
adopted to produce deep ultraviolet light including the fourth harmonic from
an Nd:YAG laser, for which a conversion efficiency as high as 10% has been
obtained.
Electrical Conductivity of ε-Iron under Shock Compression up to 208G Pa
Authors: Bi Yan  , Tan Hua  , Jing Fu-Qian
Published: August 2002

The electrical conductivity of shock-compressed iron was measured up to 208 GPa by using an improved design in experiment assembly in which the iron sample was encapsulated in a single-crystal sapphire cell. High-pressure shock compressions were generated by the plate impact technique with the two-stage light-gas gun. The measured conductivity of iron varies from 1.45×104 Ω-1 cm-1at 101 GPa and 2010 K to 7.65×103 Ω-1 cm-1at 208 GPa and 5220 K. After examining these data together with those reported, we found that the Bloch-Grüneisen expression is still valid at high pressures and temperatures, even up to 208 GPa and 5220 K, at least for ε-iron, which is significant in the field of condensed matter physics and deep interior earth science.
Siloxane Modified Polyimides for Microelectronics Coating Applications
Authors: Yamada Yasuharu
Published: August 2002

Two types of siloxane modified polyimide were prepared as coating materials for microelectronics applications and their thermal, mechanical, electrical, adhesive and coating properties were characterized. The coatings prepared were classified as polysiloxane block (type A) polyimides and disiloxane modified (type B) polyimides. All of the polyimides showed excellent thermal, mechanical, electrical, adhesive and coating properties suitable for use in microelectronics coating applications. The type A polyimides have lower dielectric constants and good stress relaxation capability as compared with typical aromatic polyimides. The type B polyimides have excellent adhesive properties to silicon wafers. The polyimide prepared from 2, 2-bis[4-aminophenoxyphenyl]hexafluoropropane exhibited the lowest dielectric constant due to the presence of trifluoromethyl groups in the polymer backbone. Model encapsulated semiconductor devices coated with various polyimides were assembled, and the interface adherence between the polyimide and the encapsulant along with the reliability of the semiconductor devices were examined. Superior interface adherence between the polyimide passivant and the encapsulant was exhibited, resulting in improved reliability of integrated circuit chips. With the incorporation of siloxane moieties into the polyimide backbone these siloxane modified polyimides were shown to be good candidate materials for microelectronics coatings.
Smectic Characteristics of Main-Chain Polyesters as Elucidated from a Variation of Layer Thickness with Carbon Number of Aliphatic Spacer in a Wide Range, 5 to 20
Authors: Nakata Yasukazu , Hayashi Manabu , Tokita Masatoshi , Osada Kensuke , Watanabe Junji
Published: August 2002

We prepared the main-chain type of TP- n polyesters, which are based on the terphenyl dicarboxylic acid and alkane diols with the carbon number of n = 5–20. All the TP- n polyesters form a smectic liquid crystal, exhibiting the well known odd–even oscillation with respect to the thermodynamic parameters of transitions and smectic structure. From the x-ray patterns of the oriented fibres, the SA and SCA structures were identified for the even and odd series of TP- n respectively. The structural characteristics of the polymeric SA and SCA phases are presented by examining the variation of layer spacing with n in a wide range of n = 5 to 20.
IM7/LARC™-IAX-3 Polyimide Composites
Authors: Hou T H , St Clair T L
Published: August 2002

LARC™-IAX-3 (Langley Research Center™-improved adhesive experimental resin-3) aromatic polyimide, based on oxydiphthalic anhydride, 3,′4-oxydianiline (3,′4-ODA) and 1,4-phenylenediamine ( p-PDA), was evaluated as a matrix for high-performance composites. Four poly(amide acid) solutions in either N-methypyrrolidone or γ-butyrolactone, end-capped with phthalic anhydride to various theoretical molecular weights, were synthesized. Unidirectional prepreg was fabricated from each of the four resins utilizing NASA-Langley’s multipurpose prepreg machine. The temperature-dependent volatile depletion rates, the thermal crystallization behaviour and the resin rheology were characterized. Based on this information, a composite moulding cycle was developed which consistently yielded well consolidated void-free laminate parts. Composite mechanical properties such as short beam shear strength, longitudinal and transverse flexural strength and flexural modulus, longitudinal tensile strength and notched and unnotched compression strengths were measured at room temperature (RT) and elevated temperatures. Similar properties were obtained independent of the carrier solvent used during matrix resin synthesis. These mechanical properties were superior to those previously measured for IM7/LARC™-IA and IM7/LARC™-IAX composites. The enhanced mechanical properties were attributed to the substitution of 25% 3,′4-ODA by p-PDA in the LARC™-IA imide backbones.
Investigation of Thin Films Made from Silicon-Containing Polyphenylquinoxaline-Amides
Authors: Bruma M , Schulz B , Köpnick T , Dietel R , Stiller B , Mercer F , Reddy V N
Published: August 2002

Thin films in the range of 50 nm to 10 μm thickness have been prepared from NMP solutions of silicon-containing polyphenylquinoxaline-amides which had been synthesized by the polycondensation reaction of aromatic diaminophenylquinoxalines with bis( p-chlorocarbonylphenyl)diphenylsilane. A spin-coating technique onto glass plates or onto silicon wafers was used to make the films, followed by gradual heating to remove the solvent. The resulting films were very smooth and free of pinholes when studied by atomic force microscopy (AFM). They showed a strong adhesion to silicon wafers, were thermally stable in air to above 400 °C and their dielectric constant was in the range of 3.5–3.7. Thermal treatment of the films was performed in order to induce crosslinking. Such treated films became completely insoluble in organic solvents, maintained their smoothness and strong adhesion to the silicon substrate, and did not show any Tg in DSC experiments. Their FTIR spectra in reflection mode did not show any changes compared with the untreated films, meaning on the one hand that the polymers maintain their structural integrity at high temperature and on the other hand that the number of crosslinks was very low and could not be detected by IR spectroscopy.
Imide Oligomers Containing Pendent and Terminal Phenylethynyl Groups—II
Authors: Connell J W , Smith J G , Hergenrother P M
Published: August 2002

As part of a programme to develop high-performance/high-temperature structural resins for aeronautical applications, imide oligomers containing pendent and terminal phenylethynyl groups were prepared, characterized and the cured resins evaluated as composite matrices. The oligomers were prepared at a calculated number-average molecular weight of 5000 g mol−1 and contained 15–20 mol% pendent phenylethynyl groups. In previous work, an oligomer containing pendent and terminal phenylethynyl groups exhibited a high glass transition temperature (∼313 °C), and laminates therefrom exhibited high compressive properties, but processability, fracture toughness, microcrack resistance and damage tolerance were less than desired. In an attempt to improve these deficiencies, modifications in the oligomeric backbone involving the incorporation of 1,3-bis(3-aminophenoxy)benzene were investigated as a means of improving processability and toughness without detracting from the high glass transition temperature and high compressive properties. The amide acid oligomeric solutions were prepared in N-methyl-2-pyrrolidinone and were subsequently processed into imide powder, thin films, adhesive tape and carbon fibre prepreg. Neat resin plaques were fabricated from imide powder by compression moulding. The maximum processing pressure was 1.4 MPa and the cure temperature ranged from 350 to 371 °C for 1 h for the mouldings, adhesives, films and composites. The properties of the 1,3-bis(3-aminophenoxy)benzene modified cured imide oligomers containing pendent and terminal phenylethynyl groups are compared with those of previously prepared oligomers containing pendent and terminal phenylethynyl groups of similar composition and molecular weight.
Synthesis and Characterization of Poly(Propylene Imine)-Based Liquid Crystalline Dendrimers
Authors: Yonetake Koichiro , Suzuki Kazuhiro , Morishita Takashi , Nagahata Ritsuko , Ueda Mitsuru
Published: August 2002

Poly(propylene imine)-based liquid crystalline dendrimers (PPILCDs) with a relatively flexible dendritic scaffold were successfully synthesized by reaction of poly(propylene imine) dendrimers with 4′-cyanobiphenyl hydrogen glutarate in the presence of condensing agent, diphenyl(2,3-dihydro-2-thioxo-3-benzoxazolyl)phosphonate. The structures of PPILCDs were characterized by IR, 1H NMR and MALDI-TOF mass spectroscopies and elemental analysis. These LCDs did not show a thermotropic liquid crystalline nature, but exhibited the liquid crystalline textures in the samples sheared at 70 °C. Furthermore, they showed a lyotropic liquid crystalline property in the 80 wt% DMF solutions.
Hubble Space Telescope Metallized Teflon ® FEP thermal Control Materials: On-Orbit Degradation and Post-Retrieval Analysis
Authors: Townsend Jacqueline A , Hansen Patricia A , Dever Joyce A , de Groh Kim K , Banks Bruce A , Wang Len , He Charles
Published: August 2002

During the Hubble Space Telescope (HST) second servicing mission (SM2), degradation of unsupported Teflon® FEP (fluorinated ethylene propylene), used as the outer layer of the multilayer insulation (MLI) blankets, was evident as large cracks on the telescope light shield. A sample of the degraded outer layer was retrieved during the mission and returned to Earth for ground testing and evaluation. The results of the Teflon® FEP sample evaluation and additional testing of pristine Teflon® FEP led the investigative team to theorize that the HST damage was caused by thermal cycling with deep-layer damage from electron and proton radiation which allowed the propagation of cracks along stress concentrations, and that the damage increased with the combined total dose of electrons, protons, ultraviolet and x-ray radiation along with thermal cycling. This paper discusses the testing and evaluation of the retrieved Teflon® FEP.
Protection of Polymeric Materials from Atomic Oxygen
Authors: Tennyson R C
Published: August 2002

The erosion of polymers and polymer-based materials (such as composites and paints) due to atomic oxygen (AO) present in the low Earth orbit (LEO) environment is described. Since many polymers are used extensively to fabricate spacecraft structures and components, a method of protecting them from AO erosion was developed. This process involves surface activation of the polymer by UV radiation and subsequent silylation treatment to produce an outer layer (not a coating) of silicon-dioxide based material. Experiments conducted in the UTIAS AO beam facility provide comparative test data for a wide range of polymers, including composites and polyurethane paints. A predictive model is also presented for estimating the AO erosion rates for hydrocarbon polymers based on their polymer repeat unit structure.
Novel Vinyl Ester Resin and its Urethane Derivatives
Authors: Patel Sanjay V , Thakkar Jatin R , Patel Harshad A
Published: August 2002

The epoxy resin, triglycidyl m-amino phenol, was reacted with acrylic acid to afford the vinyl ester resins. These vinyl ester resins were then reacted with toluenediisocyanate and hexamethylenediisocyanate to procure urethanized derivatives abbreviated as UTATGMAP and UTATGMAP* respectively. All these resins were characterized by their viscosity, number average molecular weight and infrared spectrophotometry. Curing characteristics for these resins were established by differential scanning calorimetry. The synthesized vinyl ester resin (TATGMAP) and urethane resins (UTATGMAP and UTATGMAP*) were polymerized on mild steel panels at 120 °C for 1 h. The resulting coated panels were characterized by scratch hardness, flexibility, impact strength and chemical resistance. The incorporation of styrene in the resin systems improves the properties of the coatings remarkably.
Development of a Pneumatic Spreading System for Kevlar-Based Sic-Precursor Carbon Fibre Tows
Authors: Newell James A , Puzianowski Allan A
Published: August 2002

A novel spreading system based upon the Venturi principle was designed and constructed. The system was used to spread Kevlar-based carbon fibres and to maintain that spread for sufficient time to facilitate chemical vapour deposition of an SiC coating. The Kevlar-based carbon fibres were shown to possess excellent thermal stability and a combination of properties that make them an ideal silicon carbide precursor fibre. Through a combination of pinch-rollers and two distinct axial Venturi spreaders, a highly chaotic and effective spread was achieved and maintained. This work provides a novel process for producing potentially excellent silicon carbide precursor fibres as well as providing a novel use for a high-performance polymer.
Synthesis and Properties of Aromatic Polyamides Containing 5-(4-Acetoxybenzoylamino) Side Groups
Authors: Sava I , Hamciuc E , Hamciuc C , Bruma M , Mercer F W , Reddy V N
Published: August 2002

New aromatic polyamides containing 5-(4-acetoxybenzoylamino) side groups have been synthesized by low-temperature solution polycondensation reaction of equimolar amounts of aromatic diamines having ether bridges with 5-(4-acetoxybenzoylamino)isophthaloyl chloride, in N-methylpyrrolidinone (NMP) as a solvent and in the presence of pyridine as acid acceptor. These polyamides were characterized by IR spectra, viscometry, differential scanning calorimetry (DSC), thermogravimetric analyses and dielectric measurements. These polymers show improved solubility in polar aprotic solvents such as NMP and dimethylacetamide (DMA) and good thermal stability comparable with traditional aromatic polyisophthalamides, with initial decomposition temperature being between 270 and 320 °C and glass transition temperature in the range of 230-270 °C.
Amine Reactivity Changes in Imide Formation from Heterocyclic Bases
Authors: Hawthorne D G , Hodgkin J H
Published: August 2002

The inclusion of aza-heterocyclic di- or tri-amines in aromatic polyimide formulations can hinder the formation of high molecular weight products. Model studies using the reactions of pyridine, pyrimidine and triazine polyamines with phthalic anhydride and substituted phthalic anhydrides have shown that the combined deactivating effects of multiple aza-substitution and successive imidization of the amino groups can be sufficient to seriously impede or even prevent the formation of fully imidized derivatives. Model co-polyimides incorporating 2, 4, 6-triamino-pyrimidine were found to have lowered molecular weights and to contain persistent free amino groups. Other polyimides containing these amines could be expected to have similar non-ideal structures (defects), which could extend into the structures of products formed from these resins, thereby potentially lessening the extent of any beneficial effects arising from use of the heterocyclic amines.
Semiaromatic Polyimides based on Bis(Aminomethyl)Bicyclo[2.2.1]Heptane
Authors: Matsumoto Toshihiko
Published: August 2002

Semiaromatic polyimides with a polyalicyclic structure were prepared by the polycondensation of bis(aminomethyl)bicyclo[2.2.1]heptane (BBH) with aromatic dianhydrides. The corresponding poly(amic acid)s possessed an inherent viscosity range of 0.60–1.00 dl g−1. The polyimides were soluble in organic polar solvents and most of them formed flexible, free-standing films. The polyimides had good thermal stability with no significant weight loss up to approximately 400 °C and possessed a 5% weight loss temperature range of 428–465 °C. These polyimide films showed a tensile modulus range of 1.4–3.0 GPa, a tensile strength range of 62–115 MPa, and an elongation at break range of 5.4–6.1%. The semiaromatic polyimide films exhibit a cut-off wavelength around 322–362 nm and are entirely colourless, while the cut-off wavelengths of PI(PMDA-DDE) and PI(BPDA-DDE) films were 426 and 376 nm respectively. The origin of coloration in the aromatic polyimides and the lack of colour in the semiaromatic polyimides were elucidated from the standpoint of molecular orbital (MO) calculations of the model compounds using semiempirical AM1 and INDO/S methods. The calculated λmax of the M(PMDA-BBH) was 371 nm, and the first excited state is mainly characterized by an n−π* transition. Based on both the MOs and the difference in electron density between the ground and the first excited states, the first excited state is attributable to light-induced polarization in the five-membered imide ring. The λmax of the M(PMDA-DDE) model for a representative aromatic polyimide was calculated to be 392 nm. From the charge difference map, it is theoretically evident that the coloration in the aromatic polyimides caused intramolecular charge transfer between the diamine and dianhydride moieties.
The Formulation of Polymers by Polymerization–Polycondensation Processes: Polyimide Based Systems
Authors: Vygodskii Yakov S , Sakharova Antonina A , Matieva Aza M
Published: August 2002

Radical chain (co)polymerization of a set of acrylates containing dissolved high performance polymers, namely fluoropolyimide, is performed. Based on the study of the structure and properties of the polymers (elemental composition, solubility, molecular weight parameters, etc) it is proposed that the copolymer formation reaction takes place due to a transfer chain reaction on the polyimide. The influence of acrylate (ethyl-, n-butyl-, methyl-α- fluoro-, ethyl-α-fluoro-, methyl-glycidyl-, butyl-, hexafluoro- iso-propylmethacrylate) and polyimide content on the properties of the copolymers obtained is studied. Clear and opaque, hard and elastic materials are obtained. These polymers differ in their characteristics from the relevant polyacrylates and their blends with polyimide prepared by the usual method of mixing. One-step catalytic polycondensation of diamines and tetracarboxylic acid dianhydrides in a solution of preformed polyimide is studied. It is shown that such a procedure influences the structure and properties of polyimides formed in situ.
Low-Temperature Route to 1, 2-Benzoylenebenzimidazole Ladder Structure
Authors: Likhatchev D , Granados-Fócil S , Gaviño R , Canseco M , Alexandrova L
Published: August 2002

Low-temperature catalytic conversion of N-( o-aminophenyl)phthalamic acid (I) was studied as a model reaction for the synthesis of ladder poly(aroylenebenzimidazole)s. The treatment of I with acetic anhydride/pyridine or trifluoroacetic anhydride resulted in the selective and quantitative cyclodehydration to yield either imide or isoimide structures respectively. The imidization was accompanied by acylation of the ortho amino group to form lateral acetamide or trifluoroacetamide substitutes. Thermodynamically unstable N-( o-trifluoroacetamidophenyl)phthalisoimide (III) underwent secondary cyclization to yield ladder 1, 2-benzoylenebenzimidazole (V) between 130 and 150 °C. The conversion of this reaction did not exceed 35% because it competed with the thermal isomerization of III to the stable N-( o-trifluoroacetamido-phenyl)phthalimide (IV). The cyclization of N-( o-trifluoroacetamidophenyl)phthalisoimide (III) was found to be possible even at room temperature. The formation of 30–35% of the ladder 1, 2-benzoylene-benzimidazole (V) was observed after III was dissolved in DMF and stored at room temperature for 4–10 h. This also was accompanied by the catalytic isoimide-to-imide isomerization. The obtained data may be useful for the further development of novel low-temperature approaches to the synthesis of ladder poly(aroylenebenzimidazole)s. Synthesis of aromatic polyimides and polyisoimides with lateral alkylamide or trifluoroalkylamide from available aromatic dianhydrides and tetraamines may also be of practical interest.
Volume Diffusion of Atomic Oxygen in α-SiO2 Protective Coating
Authors: Tagawa Masahito , Yokota Kumiko , Ohmae Nobuo , Kinoshita Hiroshi
Published: August 2002

The minimum thickness for an amorphous silicon dioxide (α-SiO2) protective coating required to prevent volume diffusion of atomic oxygen in a low Earth orbit (LEO) was evaluated by measuring the oxide thickness formed on Si(001) wafers in a hyperthermal atomic oxygen beam. The thickness of oxide film was measured by x-ray photoelectron spectroscopy. The diffusion length of atomic oxygen in α-SiO2 at temperatures between 297 K and 493 K, where exterior surfaces of a spacecraft may be heated in LEO, shows temperature and flux dependences, i.e. the diffusion length of atomic oxygen increases with increasing temperature and beam flux. It was also demonstrated that the atomic oxygen fluence is not a primary factor of the diffusion length since the oxide growth obeys a parabolic law. The ground-based testing condition to evaluate performances of protective coatings are also discussed, based on the experimental data obtained in the experiments.
Environmental Exposure Conditions for Teflon® Fluorinated Ethylene Propylene on the Hubble Space Telescope
Authors: Dever Joyce A , de Groh Kim K , Banks Bruce A , Townsend Jacqueline A , Barth Janet L , Thomson Shaun , Gregory Teri , Savagek William
Published: August 2002

The outer layer of Teflon® fluorinated ethylene propylene (FEP) multi-layer insulation (MLI) on the Hubble Space Telescope (HST) was observed to be significantly cracked at the time of the Second HST Servicing Mission (SM2), 6.8 years after HST was launched into low Earth orbit (LEO). Comparatively minor embrittlement and cracking were also observed in the FEP materials retrieved from solar-facing surfaces on the HST at the time of the First Servicing Mission (3.6 years exposure). After SM2, a failure review board was convened to address the problem of degradation of MLI on the HST. In order for this board to determine possible degradation mechanisms, it was necessary to consider all environmental constituents to which the FEP MLI surfaces were exposed. Based on measurements and various models, the environmental exposure conditions for the FEP surfaces on the HST were estimated, including: the number and temperature ranges of thermal cycles; equivalent sun hours; fluence and absorbed radiation dose of x-rays, trapped protons and electrons and plasma electrons and protons; and atomic oxygen (AO) fluence. This paper presents the environmental exposure conditions for FEP on the HST, briefly describing the possible roles of the environmental factors in the observed FEP embrittlement and providing references to the published works which describe in detail testing and analysis related to FEP degradation on the HST.
A Novel Photosensitive Polyimide: A Polyimide Containing the Hydroxytriphenylamine Structure with Diazonaphthoquinone
Authors: Akimoto Satoshi , Jikei Mitsutoshi , Kakimoto Masa-aki
Published: August 2002

A novel photosensitive polyimide based on a polyimide containing the hydroxytriphenylamine structure (HTA-PI) and 2, 3, 4-tris[1-oxo-2-diazonaphthoquinone-4-sulfonyloxy] benzophenone (D4SB) as a photoreactive compound has been developed. The HTAPI was prepared by the ring-opening polyaddition of 4, 4′-hexafluoroisopropylidenebis(phthalic anhydride) (6FDA) and 4,4′-diamino-4″-hydroxytriphenylamine (DHTA), followed by thermal cyclization in refluxing N-methyl-2-pyrrolidone (NMP). The resulting polyimide film showed excellent transparency to 436 nm light. Photosensitive polyimide containing 30 wt% of D4SB showed a sensitivity of 800 mJ cm−2 and a contrast of 0.8 when it was exposed to 436 nm light followed by development with 5% tetramethylammonium hydroxide (TMAH) aqueous solution at 45°C.
Synthesis and Properties of Poly(Amide-Imide-Hydrazide)s and Poly(Amide-Imide-1,3,4-Oxadiazole)s
Authors: Hsiao Sheng-Huei , Chang Li-Min
Published: August 2002

A series of new wholly aromatic and aromatic-aliphatic poly(amide-imide-hydrazide)s were prepared by the direct polycondensation from p-aminobenzhydrazide with various imide ring-containing dicarboxylic acids by means of diphenyl phosphite and pyridine. These polymers had inherent viscosities between 0.60 and 1.17 dl g−1. Most of the poly(amide-imide-hydrazide)s were readily soluble in polar aprotic solvents such as N-methyl-2-pyrrolidone (NMP) and dimethyl sulfoxide (DMSO) and could be solution cast into light yellow, transparent, flexible, and tough films. These poly(amide-imide-hydrazide)s had Tg in the range 122–211 °C and could be thermally cyclodehydrated in the solid state to the corresponding poly(amide-imide-1,3,4-oxadiazole)s approximately in the range 250–400 °C, as evidenced by the differential scanning calorimetry thermograms. The thermally converted oxadiazole copolymers exhibited Tg in the range 120–271 °C and did not show significant weight loss before 380 °C in air or nitrogen. Effects of structural changes such as polymethylene length and the nature of the diacid monomers on the properties of polymers were studied.
Methylnadimide End-Capped Polyimides for Use in High Temperature Composites—A New Approach to Their Synthesis
Authors: Morton T , Dao B
Published: August 2002

Two methylnadimide end-capped polyimides have been prepared by a new water synthesis procedure and their properties compared to similar polyimides synthesized in the conventional solvents, cresol and NMP. The water method has been shown to be a practical alternative for the synthesis of a wide range of polyimides with no evidence of contaminating polyamic acids. The present results showed that with appropriate adjustment of the synthesis conditions very useful methylnadimide end-capped polyimides could be obtained. It was found that the amount of methylnadimide end-cap was reduced under 180°C synthesis conditions, and even at lower temperatures with prolonged heating, and that the water reaction is best carried out at 165°C for these polyimides. One of the uncured resins, Polyimide 1 was quite soluble in common solvents allowing complete characterization. It was found that the amount of endcap introduced by either conventional or water synthesis procedures was less than the theoretical maximum. Examination of the cured neat resin from polyimide 1 showed it to consist of a portion of insoluble, possibly cross-linked, material and a considerable amount of soluble polymer of wide molecular weight distribution. The potential usefulness of these polymers as high-temperature composite matrices was indicated by the excellent tensile properties of polyimide 2B, which on curing produced a tough voidless polymer with a tensile strength of 120 MPa, a modulus of 3.9 GPa and a strain at break of 9.7%.
Novel Propargylether-Terminated Ester-Imide Prepolymers: II. Matrix Resins for High-Temperature-Use composites
Authors: Furutani Hiroyuki , Ida Junya , Nagano Hirosaku
Published: August 2002

Glass-cloth-reinforced composites were prepared from the state-of-the-art propargyl-ether-terminated ester-imide prepolymers developed in our laboratory. The composites demonstrated excellent initial mechanical properties and chemical properties, as well as electrical properties. The storage stability of the varnish of the prepolymer was evaluated at 0 °C and 20 °C. The flexural strength after ageing at various severe temperature levels in air was also demonstrated as a typical composite property. The initial flexural strength was well maintained even after 1000 h at 200 °C, 220 °C, and 240 °C.
Modelling Micelle Formation in Confined Geometries
Authors: Gersappe D
Published: August 2002

We use numerical self consistent field calculations to determine the effect confinement has on the critical micelle concentration for diblock copolymers. Our studies show that increasing the confinement increases the free energy of micelle formation. As the confinement increases, the micelle undergoes a decrease in its size, until finally the entropic losses associated with packing the copolymer into a smaller micelle become too large and the micelle structure becomes unstable. Our results have important implications when diblock copolymers are used as compatibilizers in thin films, as our studies indicate that micelle formation will be suppressed in thin films.