bluuebunny/crossref_metadata_2025_split huggingface dataset:
Temperature dependency of granule characteristics and kinetic behavior in UASB reactors
Authors: Chou Hsin‐Hsien , Huang Ju‐Sheng , Hong Wen‐Feng 
Published: May 2004

AbstractWhen an inhibitory substrate, phenol, was treated under mesophilic conditions (25, 30, 35, and 40 °C), the upflow anaerobic sludge bed (UASB) reactors at 30 °C resulted in the greatest amount of biomass and the largest granule size, while the UASB reactors at 25 °C resulted in the smallest granule size and the greatest amount of wash‐out of sludge. The granule size tended to be negatively correlated with the amount of wash‐out of sludge. With an increase in temperature, the kinetic constant k for anaerobic phenol degradation increased and the half saturation constant (Ks) decreased. The mass fraction of methanogens (f) increased with increasing operational temperature in the UASB reactors and the activation energy (Ea) for acetate methanogenesis was larger than that for phenol acidogenesis in the batch reactors, indicating that the operational temperature imposes a more influential effect on methanogens than on acidogens. From the results of the activity of acidogens and methanogens (expressed in specific COD utilization rate), the rate‐limiting step is phenol acidogenesis. Copyright © 2004 Society of Chemical Industry
Modulation of Rho GTPase activity alleviates chondroitin sulfate proteoglycan‐dependent inhibition of neurite extension
Authors: Jain Anjana , Brady‐Kalnay Susann M. , Bellamkonda Ravi V. 
Published: May 2004

AbstractThe central nervous system (CNS) fails to regenerate after injury. A glial scar forms at the injury site, contributing to regenerative failure partly resulting from the chondroitin sulfate proteoglycans (CSPGs) in the glial scar. The family of Rho GTPases, which includes Cdc42, Rac1, and RhoA, is involved in growth cone dynamics. Although the response of neural cells to the inactivation of Rho when contacting myelin‐related substrates, or CSPG, has been investigated, Rac1's and Cdc42's abilities to modulate CSPG‐dependent inhibition have yet to be explored. In this study, a stripe assay was utilized to examine the effects of modulating all three Rho GTPases on neurite extension across inhibitory CSPG lanes. Alternating laminin (LN) and CSPG lanes were created and NG108‐15 cells and E9 chick dorsal root ganglia (DRGs) were cultured on the lanes. By using the protein delivery agent Chariot, the neuronal response to exposure of constitutively active (CA) and dominant negative (DN) mutants of the Rho GTPases, along with the bacterial toxin C3, was determined by quantifying the percentage ratio of neurites crossing the CSPG lanes. CA‐Cdc42, CA‐Rac1, and C3 transferase significantly increased the number of neurites crossing into the CSPG lanes compared with the negative controls for both the NG108‐15 cells and the E9 chick DRGs. We also show that these mutant proteins require the delivery vehicle, Chariot, to enter the neurons and affect neurite extension. Therefore, activation of Cdc42 and Rac, as well as inhibition of Rho, helps overcome the CSPG‐dependent inhibition of neurite extension. © 2004 Wiley‐Liss, Inc.
Analysis of calcitonin and its analogues by capillary zone electrophoresis and matrix‐assisted laser‐desorption ionization time‐of‐flight mass spectrometry
Authors: Amini Ahmad , Olofsson Ing‐Marie 
Published: May 2004

AbstractCapillary zone electrophoretic (CZE) separations and mass spectrometric analysis of salmon calcitonin and related analogues were performed to generate electrophoresis and mass fingerprints for quality control of the recombinant polypeptide pharmaceutical salmon calcitonin. The calcitonins and their corresponding tryptic digests were successfully separated by CZE at low pH in fused silica capillaries dynamically modified with poly‐cationic polymers. The poly‐cationic modified inner surface of the fused silica capillaries generated a strong anionic electroosmotic flow (EOF). Analytes of negative, neutral, and positive charge were all swept through the capillary toward the positive electrode. Compared to Polybrene‐coated capillaries, capillaries coated with PEI showed a markedly slower but much more stable electroosmotic flow. The migration order of the analytes was predicted by comparing approximate values of the charge to (molecular mass)2/3 ratios. The predicted migration order was confirmed by off‐line analysis of CZE fractions with matrix‐assisted laser‐desorption ionization time‐of‐flight mass spectrometry (MALDI‐TOF‐MS).
Dynamics of chelation‐supercritical fluid extraction from wood fibers
Authors: Al‐Jabari Maher 
Published: May 2004

AbstractThe dynamics of supercritical fluid extraction (SFE) of the metal content of wood fibers chelated with lithium bis(trifluoroethyl) dithiocarbamate (FDDC) by supercritical (SF) CO2 was investigated experimentally by monitoring the spectra of the eluted metal complex as a function of time. The characteristic shape of the dynamic SFE curve was determined mainly by the flow conditions in the extraction vessel, the mass transfer resistance in the SF phase, and the solubility. High extraction yields of metal content were obtained in two‐stage extraction including static (batch) and dynamic (semi‐batch) stages. Increasing the length of the static stage increased the rate of dynamic elution of metal complex until it approached the dynamics of fluid displacement for a continuous stirred tank reactor (CSTR). In such cases, increasing the flow rate had no effect on the dynamic extraction curve when it was plotted using dimensionless time. Efficient chelation‐SFE from wood fibers was obtained at a pressure of 20.3 MPa and with a static time of 30 min.
Hexafluoroisopropanol as size exclusion chromatography mobile phase for Polyamide 6
Authors: Mendichi Raniero , Russo Saverio , Ricco Laura , Giacometti Schieroni Alberto 
Published: May 2004

AbstractThe present study deals with the use of hexafluoroisopropanol (HFIP) as size exclusion chromatography (SEC) mobile phase for polyamide 6 (PA6). Contradictory conclusions relating to the use of HFIP as SEC mobile phase for polyamides are found in the literature. By using a multi‐detector SEC apparatus equipped with on‐line viscometer and multi‐angle light scattering we have studied the chromatographic artifacts and the validity of the universal calibration (UC) in HFIP for different PA6 samples (hydrolytic and anionic, monofunctional or bifunctional activator). Appropriate SEC columns and optimized experimental conditions allow most of the chromatographic artifacts to be avoided, even in neat HFIP. The use of a salt in the mobile phase, namely 0.01 M tetraethylammonium nitrate (TEAN), slightly increases the elution volume for both PA6 and PMMA polymers. Under the right conditions, the UC substantially holds for PA6. The validity of the UC is not linked to the presence of TEAN in the mobile phase. With some PA6 samples, namely those anionically synthesized using a bifunctional activator, aggregation becomes a problem and the molar mass in neat HFIP is overestimated. Addition of TEAN prevents any aggregation of the above anionically synthesized PA6. In contrast, the use of a different salt, namely potassium trifluoroacetate, increases the extent of aggregation.
Polarization energies, transport gap and charge transfer states of organic molecular crystals
Authors: Soos Zoltán G. , Tsiper Eugene V. 
Published: May 2004

AbstractA self‐consistent calculation of electronic polarization in organic molecular crystals and thin films is presented in terms of charge redistribution in nonoverlapping molecules in a lattice. The polarization energies P+ and P− of a molecular cation and anion are found for anthracene and perelynetetracarboxylic dianhydride (PTCDA), together with binding energies of ion pairs and transport gaps of PTCDA films on metallic substrates. The 500 meV variation of P++P− with film thickness agrees with experiment, as do calculated dielectric tensors. Comparisons are made to submolecular calculations in crystals.
Exciton dissociation in conjugated polymers
Authors: Arkhipov Vladimir , Bässler Heinz , Emelyanova Evgenia , Hertel Dirk , Gulbinas Vidmantas , Rothberg Lewis 
Published: May 2004

AbstractIn conjugated polymers, a majority of photogenerated charges form metastable geminate pairs (GPs), of which only some fraction can dissociate completely. Both the yield of GP photogeneration and the probability of further dissociation of GPs into free charges depend upon an external electric field. In the present article we discuss several experimental methods to detect the existence of geminate pairs such as delayed field collection of charges, field quenching of fluorescence, and field‐assisted photoinduced optical absorption. It is shown that the field dependences of the exciton dissociation into GPs and of the free carrier photogeneration yield are rather similar. This is in contrast with the traditional Onsager theory, which assumes field‐independent yield of primary photoionization and disregards the field dependence of the initial separations between carriers in GPs.
Luminescence properties of PPV derivatives bearing substituted carbazole pendants
Authors: Park Jong Hyun , Kim Kyungkon , Hong Young‐Rae , Jin Jung‐Il , Sohn Byung‐Hee 
Published: May 2004

AbstractA series of PPV derivatives bearing substituted and unsubstituted carbazole and 2‐ethylhexyloxy pendants were prepared and their photo‐ (PL) and electroluminescence (EL) properties were studied. Substituted carbazole structures were N‐phenylcarbazole and 3,6‐dimethoxycarbazole. The substituents on the carbazole pendants caused little change in UV‐vis absorption, PL, and EL when compared with the polymer bearing the unsubstituted carbazole pendants. The presence of the benzene ring between the main chain and the carbazole pendant increased the threshold electric field in EL. We could obtain maximum brightness of ca. 17,000 ‐ 30,000 cd/m2 for the polymers carrying the unsubstituted and dimethoxy substituted carbazole pendants.
Manifestation of electrode surface states in molecular conduction
Authors: Fagas Giorgos , Gutierrez Rafael , Richter Klaus , Grossmann Frank , Schmidt Rüdiger 
Published: May 2004

AbstractWe present a conduction mechanism across molecular junctions which derives from conductance resonances that are not associated with particular molecular orbitals. Instead, the resonances are induced by states localized at the surface of the electrodes. To this end, we studied the conductance of a C60 molecule bridging two carbon nanotubes. A simple tight‐binding model is employed to investigate analytically the basic features of the effect.
Novel tunable optical properties of liquid crystals, conjugated molecules and polymers in nanoscale periodic structures as photonic crystals
Authors: Yoshino Katsumi , Takeda Hiroyuki , Kasano Masahiro , Satoh Shigenori , Matsui Tatsunosuke , Ozaki Ryotaro , Fujii Akihiko , Ozaki Masanori , Kose Akira 
Published: May 2004

AbstractTunability of optical properties such as transmission and reflection by temperature and applied voltage has been demonstrated in synthetic opals and inverse opals like three‐dimensional photonic crystals infiltrated with liquid crystals, conjugated molecules and polymers, in accordance with theoretical calculation. A new type of tunability based on uncoupled mode in a two‐dimensional photonic band gap influenced by the field‐dependent anisotropy in liquid crystals has also been demonstrated theoretically. Spectral narrowing and lasing have been observed in these opals infiltrated with conducting polymers and fluorescent dyes like three‐dimensional photonic crystal and fluorescent dye‐doped cholesteric and ferroelectric liquid crystal as one‐dimensional photonic crystal. These lasing wavelength can be controlled by the applied voltage. Laser emission was also realized with conducting polymer on a surface relief grating formed on an azo‐polymer film by interference optical beam.
Rough electrode surface: effect on charge carrier injection and transport in organic devices
Authors: Novikov Sergey V. 
Published: May 2004

AbstractThe effect of electrode roughness on charge carrier injection and transport is considered. An explicit formula connecting the roughness profile of an electrode with the distribution of the electric field at its surface (and the electrostatic potential in the bulk of transport layer) is derived for the case of smooth roughness, when the typical height of roughness element is small in comparison with its size across the surface (this is a very typical situation). This formula gives us an opportunity to measure the electrode surface profile (e.g., by AFM) and then to calculate various injection properties of this particular electrode for any kind of injection. General properties of the electrode ‐ organic layer interface in the case of significant (not smooth) roughness are considered and a suitable numeric procedure for the calculation of the surface electric field distribution is proposed. It is also shown that rough surface of electrodes generates an additional energy disorder in the bulk of transport layer. This principal result indicates that the electrode roughness affects not only carrier injection but carrier transport as well. Roughness‐induced energetic disorder produces a channel‐like structure in the vicinity of the electrode, thus providing separation of electrons and holes. Such separation should decrease the charge recombination rate and, hence, the emitting efficiency of light emitting devices. At the same time, the separation is favorable to solar cells.
Degradation effects in polymer light emitting devices due to heat treatment
Authors: Janssen Frank , Sturm Marco , van Ijzendoorn Leo , van der Gon Arnoud Denier , Schoo Herman , de Voigt Martien , Brongersma Hidde 
Published: May 2004

AbstractThe characteristics of polymer light emitting diodes (PLEDs) (ITO/PPV/Ca) depend strongly on the conditions during preparation and operation. We studied the effects of heat treatment (during and after preparation) of PLEDs with OC1C10‐PPV as active layer. PLEDs showed a reduction of both the current and the light output to 40 % after annealing for only 30 min at 65 °C. Effects on I‐V characteristics were studied by measuring single carrier devices (hole‐ and electron‐dominated devices). The current reduction after heat treatment can be ascribed to degradation of the ITO/PPV and the Ca/PPV interfaces.
Space charge distribution in luminescent conjugated polymers
Authors: Geschke Dieter , Feller Frank , Monkman Andy P. 
Published: May 2004

AbstractWe have used for the first time the laser intensity modulation method (LIMM) to resolve the depth profile of space charges in films of poly[(2‐(2‐ethylhexyl)‐5‐methoxy‐1,4‐phenylene)vinylene] (MEH‐PPV), poly(pyridine‐2,5‐diyl) (PPY) and poly(fluorene) (PFO). The results demonstrate that in conjugated polymers space charges can not only be created but also stored permanently.
Luminescence properties of epoxy resins modified with a carbazole derivative
Authors: Mandowska Ewa , Mazela Wojciech , Czub Piotr , Mandowski Arkadiusz , Pielichowski Jan , Świątek Józef 
Published: May 2004

AbstractLuminescence properties of a new material ‐ epoxy resin with added 9‐(2,3‐epoxypropyl)carbazole (REPK) were studied. Absorption and photoluminescence (PL) spectra of REPK are compared with those of poly(N‐vinylcarbazole) (PVK). PL in REPK is shifted to shorter wavelengths. Its intensity is higher than in PVK. REPK emits light in the range from 330 nm to 470 nm. PL spectrum of REPK could be well deconvoluted for four emission bands.
Electroluminescence and charge photogeneration in poly(9,9‐dihexadecylfluorene‐2,7‐diyl) and its blends
Authors: Cimrová Věra , Výprachtický Drahomír 
Published: May 2004

AbstractPhotoluminescence, electroluminescence (EL), charge photogeneration and transport were studied in poly(9,9‐dihexadecylfluorene‐2,7‐diyl) (PFC16), poly[(2,5‐dihexadecyl‐1,4‐phenylene)(1,4‐phenylene)] (PPPC16) and their blends. Blending of PFC16 with PPPC16 led to a significant improvement of the EL efficiency and stability compared with the devices fabricated from the neat polymers. Efficient blue and white light‐emitting devices (LEDs) were fabricated using the blends. The increase in the EL efficiency was attributed to modification of the charge injection, transport and recombination properties in the blend.
Effects of mechanical and thermal stresses on electric degradation of polyolefins and related materials
Authors: Mamedov Shaval , Alekperov Vilayet , Can Nursel , Aras Faruk , Yilmaz Gunes 
Published: May 2004

AbstractDegradation under the simultaneous effects of mechanical stress and temperature in polyolefins (PE, PP), composites on their basis (PE+PP fibre, PP+PP fibre, PP+glass fibre) and radiation low‐density polyethylene (X‐LDPE) used in high‐voltage cables obeys the thermofluctuation theory of Zhourkov (in certain σ and τ0 intervals) based on the theory of Arrhenius is presented in the following form:τσ = τ0 exp[(U0 − γσ)/ RT] (1)where τ is durability. τ0 is a constant (10−12‐10−13s) equal to period of vibrations of atoms around equilibrium position, U0 is the activation energy of the mechanical destruction process (at σ = 0), γ is a structure‐sensitive parameter, T is absolute temperature and R is universal gas constant. Electric degradation under the effects of electric field and temperature in the materials mentioned above obeys the equation:τE = τ0 exp[(W0 − χE)/ RT] (2)Here, τE, W0 and χ are analogous to τσ, U0 and γ, respectively.It is assumed that the following equation is valid under the simultaneous effects of E, σ and T:τσ,E = τ0 exp[(U0 − (γσ + χE))/ RT]. (3)electric degradation
Oxidation state and proton doping level in copolymers of 2‐aminobenzoic acid and 2‐methoxyaniline
Authors: Mav Ida , Žigon Majda , Vohlídal Jiří 
Published: May 2004

AbstractUV‐vis spectra of homopolymers and copolymers of 2‐aminobenzoic acid (OAB) and 2‐methoxyaniline (OMA) were analyzed in order to obtain information about the oxidation state and proton doping level of these polymers. Dimethyl sulfoxide (DMSO) was used as a solvent in which protonated forms of polyanilines are preserved and a mixture of N‐methyl‐2‐pyrrolidone and triethylamine (0.5 %) as a solvent (NMP/TEA) in which polyanilines are assumed to be non‐protonated. Polymers were prepared in the emeraldine salt form, externally doped with HCl. It was found that only external doping is eliminated in NMP/TEA while internal doping by carboxylate groups bound in OAB units remains operative. Since doped quinoid units do not contribute to the quinoid band (Q‐band at 630 nm), the intensity ratio of the Q‐band and benzenoid band (B‐band at 320 nm) cannot be simply correlated with the oxidation state of poly(OMA‐co‐OAB) copolymers in contrast to poly(OMA) and polyaniline. Spectra of copolymers with less than 60 % of OMA units as well as those of poly(OAB) in DMSO and NMP/TEA are almost identical due to internal doping, which is proposed to lead to structures in which main‐chain protons are coulombically bound with immobile carboxylate anions. In the spectra of copolymers with less than 60 % of OMA units, a well‐resolved band occurs at 500 nm, which can be ascribed to alternating or close‐to‐alternating sequences of OMA and OAB units.
Photoelectric properties of tetracene‐pentacene heterojunction
Authors: Signerski Ryszard , Jarosz Grażyna , Godlewski Jan 
Published: May 2004

AbstractWe investigated vacuum‐evaporated sandwich systems formed by two organic layers of pentacene and tetracene. We measured spectral dependences of photovoltaic short‐circuit currents and photocurrents as well as current‐voltage dependences. In the case of systems equipped with Au and CuI electrodes the structure of spectral characteristics is determined by exciton release of trapped charge carriers either in the bulk of tetracene or near tetracene‐pentacene interface and by photogeneration in pentacene layer. For systems with two Au electrodes we can also observe an influence of exciton injection of holes into tetracene on spectral characteristics. The measurements of dark current‐voltage characteristics allow to observe the presence of a potential barrier between tetracene and pentacene.
Studies of host‐guest thin films of corona‐poled betaine‐type polar molecules by kelvin probe technique and atomic force microscopy
Authors: Dobulans Rorijs , Cepite Daiga , Fonavs Egils , Muzikante Inta , Tokmakov Andrey , Erts Donats , Polakov Boris 
Published: May 2004

AbstractIn this work betaine‐type molecules were investigated. As a result of the asymmetry of charge distribution, molecules possess in the ground state a considerable permanent dipole moment. The decay of surface potential of poled polymer films is dependent at least on two relaxation processes. The influence of glass transition of PMMA on thermal dependence of the surface potential is shown. The transition temperature, where no changes of the surface potential appeared, is related to glass transition temperature of the host‐guest system. The topography of the film surface was obtained by AFM.
Generation of charge carrier pairs in tetracene layers
Authors: Obarowska Malgorzata , Signerski Ryszard , Godlewski Jan 
Published: May 2004

AbstractThe mechanism of negative and positive charge carrier generation by light absorption in tetracene layers has been studied. We conclude that there are different processes determining electron and hole production. Positive charge carriers are produced without recombination while the negative charge carrier generation depends strongly on the recombination process. The experimental data for charge carrier generation in tetracene layers are treated theoretically taking into account photogeneration, recombination of charge carriers, trapping and transport processes inside the sample.
Properties of optically addressed liquid crystal spatial light modulators studied by mach‐zehnder interferometry
Authors: Komorowska Katarzyna , Miniewicz Andrzej , Parka Janusz 
Published: May 2004

AbstractIn this work optically addressed liquid crystal spatial light modulators are experimentally investigated. Local reorientation of molecules in the modulator and local changes of effective refractive index neff (x,y) are induced by modulated light intensity I (x,y). We present preliminary results of measurements of phase shifts in optically addressed liquid crystal panels using a Mach‐Zehnder interferometer. Experiments were performed for the panels filled with nematic and dye‐doped nematic liquid crystals. Optical addressing was realized by Ar+ laser beam (λ = 514.5 nm) while the reading beam was supplied by He‐Ne laser (632.8 nm). The operation voltage was in the range 4 ‐ 20 V. The total phase shift under the influence of addressing light for the studied systems was 2 ‐ 6 pagr;, sensitivity to the addressing light ∼ μW/cm2 per 2π phase change and speed of response to the light was 20 ms ‐ 30 s with total recovery time 0.5 ‐ 120 s.
Optical spectroscopy of polysilylene films
Authors: Demchenko Yevhen V. , Klimovič Josef , Nešpůrek Stanislav 
Published: May 2004

AbstractLuminescence of poly[cyclohexyl(methyl)silylene] films was studied by time‐resolved emission spectroscopy at temperatures from 15 K to 300 K. The main short‐wavelength peak, shifted with rising temperature to lower energies, showed time features typical of an energy donor. Three weak emission centres were found in the visible spectral region. They decayed more slowly having the time features of an energy acceptor. The rise in temperature made both the energy transfer and extension of the effective ‐conjugation length more efficient. Model calculations of the chain conformation energy showed the close‐to‐all‐trans and gauche helix minima for iso‐ and syndiotactic sequences and barriers between them.