bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fast process security assessment theory
Authors: Uygun Korkut , Huang Yinlun , Lou Helen H. 
Published: August 2004

AbstractThis communication introduces a comprehensive theory for process security assessment. The theory can quickly provide mathematically proven upper and lower bounds on minimum time to disaster (the time disaster conditions will be reached in worst‐case scenarios). Computational efficiency and reliability are achieved by performing process security assessment based on a time‐derivative–based approach, rather than conducting massive process dynamic simulations. Further, the methodology enables prioritizing the process variables critical to plant security. This facilitates pinpointing the possible reasons of a security‐threatening situation, quantifying the importance of each disturbance factor on the system's vulnerability, and creating a prioritized list of improvements/counteractions for ensuring process security. Two runaway reactor examples are studied to demonstrate the methodology for security‐threat analysis. © 2004 American Institute of Chemical Engineers AIChE J, 50: 2187–2202, 2004
Steady‐state multiplicity, flashback, and control issues in CH4 radiant burners
Authors: Bizzi M. , Saracco G. , Specchia V. 
Published: August 2004

AbstractMethane is widely employed as a source of energy in combustion systems. Among the currently available technologies, radiant heaters offer high thermal efficiency and low environmental impact in comparison with atmospheric burners. The present work deals with the modeling of methane combustion in a noncatalytic metal fiber burner, represented by means of one‐dimensional transient equations. The model accounts for a detailed reaction mechanism, radiation within the porous medium, longitudinal heat and mass transfer. After its validation, the model was employed to analyze a typical stability problem that affects these systems: under given operating conditions (low specific power inputs and excess of air) the occurrence of flashback may in fact preclude the safe operation of the system. As a consequence of energy radiation in the upstream direction, the burner upstream surface and the plenum chamber might become hot enough to heat in turn the gas feedstock, thus eventually determining flashback. In this paper, the mechanism of flashback is numerically investigated as a function of the burner structure and operating conditions by means of a model analysis so as to single out regions of flashback occurrence and a criterion for safe operation. Finally, some guidelines are outlined for a cheap and effective control of the system, paving the way for possible improvement of currently adopted control systems. © 2004 American Institute of Chemical Engineers AIChE J, 50: 2276–2286, 2004
Distributed midpoint chain scission in ultrasonic degradation of polymers
Authors: Sivalingam G. , Agarwal Nitin , Madras Giridhar 
Published: August 2004

AbstractThe ultrasonic degradation of poly(bisphenol A carbonate), poly(ε‐caprolactone), and poly(vinyl acetate) was investigated with various solvents such as benzene, monochlorobenzene, and dichlorobenzene. The time evolution of molecular weight was determined using gel permeation chromatography. A limiting molecular weight was observed for all the systems and was a function of solvent properties. The degradation rates increased with increase in viscosity and decrease in vapor pressure. The polydispersity reached a maximum before reaching a constant value at longer times. The experimental data indicate that the breakage of the polymer is around midpoint, with a distribution rather than an ideal midpoint scission. A continuous distribution model with a stoichiometric kernel based on Lorentzian probability distribution function was developed to satisfactorily model the experimental data. © 2004 American Institute of Chemical Engineers AIChE J, 50: 2258–2265, 2004
Modeling wood gasification in a countercurrent fixed‐bed reactor
Authors: Di Blasi Colomba 
Published: August 2004

AbstractA one‐dimensional, unsteady mathematical model is presented of fixed‐bed countercurrent wood gasifiers, which couples heat and mass transport with wood drying and devolatilization, char gasification, and combustion of both char and gas‐phase species. The model is used to simulate the structure of the reaction fronts and the gasification behavior of a laboratory‐scale plant as the reactor throughput and the air‐to‐wood (or char) weight ratio are varied. It is observed that a wide zone, acting essentially as a countercurrent heat exchanger, separates combustion/gasification from devolatilization/drying. Moreover, the former zone presents interesting dynamic patterns driven by the highly variable solid/gas heat transfer rates. For a constant air‐to‐wood weight ratio, the gasification process is improved by increasing the reactor throughput as a result of higher temperatures, in spite of the simultaneous reduction in the amount of char generated from wood devolatilization. In fact, an increase in the air‐to‐wood (or char) ratio always lowers the efficiency of the gasification process. Finally, good agreement is obtained between predictions and experiments for the axial temperature profiles and the composition of the producer gas. © 2004 American Institute of Chemical Engineers AIChE J, 50: 2306–2319, 2004
Analysis of the reverse flow chromatographic reactor
Authors: Caram Hugo S. , Viecco Guillermo A. 
Published: August 2004

AbstractA reverse flow chromatographic reactor with side feed (RFCR) can be used to improve the conversion and selectivity for irreversible and reversible reaction systems beyond the values obtained from conventional steady‐state reactors in the case where the reactants are more strongly adsorbed than the products. It is also simpler than conventional chromatographic, moving, and simulated moving beds and other systems that combine reaction and adsorption separation. The results of the study show the robustness and stability of the system, as well as its capacity to significantly improve conversion and selectivity for several reaction systems, including consecutive reactions. Simulation results of this mathematical model for the hydrogenation of 1,3,5‐trymethylbenzene (MES) compare well with previous studies, using countercurrent moving‐bed reactors and simulated countercurrent bed reactors. © 2004 American Institute of Chemical Engineers AIChE J, 50: 2266–2275, 2004
Formation of electric potential during the oxidation of a metal particle
Authors: Filimonov Igor , Luss Dan 
Published: August 2004

AbstractExperiments revealed that a transient electric voltage of the order of 1 V may form during the combustion of a single metal particle. We present a model showing that such an electrical field may form as a result of the different diffusion rates of the positive and negative charge carriers through a growing mixed‐ionic‐electronic‐conducting oxide shell. Simulations of the evolution of the electric charge carriers and temporal potential distribution reveal that three key parameters affect the voltage formation. The ratio of the characteristic oxygen ion diffusion rate within the particle to the maximum oxygen transport rate to the particle surface affects the formation of a diffusion layer and the carrier distributions inside the oxide shell. The ratio between the thickness of an exterior oxide layer, formed before the reaction has started, and the Debye screening length has a strong impact on the amplitude and temporal evolution of the voltage. The thinner this initial oxide shell is, the larger is the voltage amplitude. The ratio between the diffusion coefficients of the positive and negative charge carriers determines the sign of the excess electrical charge on the surface. © 2004 American Institute of Chemical Engineers AIChE J, 50: 2287–2296, 2004
On the modeling assessment of thermal styrene polymerization
Authors: López‐Serrano F. , Puig J. E. , Alvarez J. 
Published: August 2004

AbstractIn this work the problem of determining the dependencies on conversion of the initiation rate (Ri), the propagation (kp), termination (kt), and transfer to monomer (ktr) kinetic constants in the thermally initiated free‐radical polymerization of styrene is addressed. A nonlinear observability analysis establishes that the parameter groupings Ri, κ = kt/k, and Cm = ktr/kp dependencies on conversion can be determined on the basis of the species conservation balances in conjunction with conversion and (number‐ and weight‐) average molecular weight experimental measurements, without making any a priori kinetic modeling assumption. Then, the differential estimation technique associated with the observability property is applied to previously reported experimental runs at 100, 120, 170, and 200°C, yielding the following results: (1) for the two lower temperature runs, Ri exhibits a nearly quadratic dependency on monomer concentration, and for the higher temperature the overall dependency is about cubic or quartic, and this behavior differs from that of the standard cubic‐dependency model; (2) κ shows an exponential‐like decay with conversion that agrees with previous reports, and (3) Cm exhibits a quadratic‐like increase with conversion that disagrees with the linear decay assumed before. © 2004 American Institute of Chemical Engineers AIChE J, 50: 2246–2257, 2004
Crystallographic report: 1,4‐Bis(carboxymethyldiphenylphosphonio)butane dibromide, (CH2)4[(HOOCCH2)Ph2P(+)]2 ·2Br(−)
Authors: Du Miao , Zhao Xiao‐Jun 
Published: August 2004

AbstractThe centrosymmetric cation {[(HOOCCH2PPh2)]2(CH2)4}2+ adopts an extended conformation. The phosphorus atom shows a tetrahedral coordination and each OH of the carboxylic group is hydrogen bonded to a bromide ion. Copyright © 2004 John Wiley & Sons, Ltd.
Pharmacokinetics and splenic accumulation of N‐acetylamino‐3‐chloro‐N‐(2‐diethylamino‐ethyl) benzamide after a single administration to rats
Authors: Hua Jianyi , Sheng Yezhou , Olin Magnus , Pero Ronald , Edvardsen Klaus 
Published: August 2004

AbstractThe purpose of this study was to measure the pharmacokinetics and tissue accumulation of N‐acetylamino‐3‐chloro‐N‐(2‐diethylamino‐ethyl) benzamide (NACPA) after oral or intravenous administration at a single dose of 25 mg/kg to female W/Fu rats. The serum pharmacokinetics of NACPA were characterized by rapid absorption, distribution and elimination. However, in comparison with its parent compound, 4‐amino‐3‐chloro‐N‐(2‐diethylamino‐ethyl) benzamide (3‐CPA), NACPA displayed a higher Cmax (mean±SD, 201±21 vs 33.6±0.5 nmol/ml, p<0.05), and a longer elimination half‐life (50±0.8 vs 36.6±1.1 min, p<0.05) following intravenous administration. Bioavailability of NACPA was significantly greater than that of 3‐CPA (50% compared with 14%, p<0.05). The tissue accumulation of NACPA was generally higher than that of 3‐CPA. NACPA was deposited at higher concentrations in the spleen than in the kidney and liver. Cellular pharmacokinetics indicated that NACPA accumulated more readily in lymphocyte related cells than in liver related cells. Furthermore, incubation of human peripheral lymphocytes with NACPA resulted in inhibition of lymphocyte proliferation, INF‐γ production and chemotaxis. All these results suggest that NACPA may be a good candidate drug for oral administration for immune modulation. Copyright © 2004 John Wiley & Sons, Ltd.
Trafficking and signaling pathways of nuclear localizing protein ligands and their receptors
Authors: Johnson Howard M. , Subramaniam Prem S. , Olsnes Sjur , Jans David A. 
Published: August 2004

AbstractInteraction of ligands such as epidermal growth factor and interferon‐γ with the extracellular domains of their plasma membrane receptors results in internalization followed by translocation into the nucleus of the ligand and/or receptor. There has been reluctance, however, to ascribe signaling importance to this, the focus instead being on second messenger pathways, including mobilization of kinases and inducible transcription factors (TFs). The latter, however, fails to explain the fact that so many ligands stimulate the same second messenger cascades/TFs, and yet show distinct gene activation profiles. This is particularly apt in the case of the seven STAT TFs that are held to be the mediators of the distinct cellular functions of over 60 ligands. The current review focuses on five representative nuclear localizing ligands for which there is documentation of translocation into the cytosol and nucleus through well‐characterized pathways, in addition to a role in gene activation by ligand/receptor in the nucleus. BioEssays 26:993‐1004, 2004. © 2004 Wiley Periodicals, Inc.
Molecular mechanisms for organizing the neuronal cytoskeleton
Authors: Mukhopadhyay Rajendrani , Kumar Sanjay , Hoh Jan H. 
Published: August 2004

AbstractNeurofilaments and microtubules are important components of the neuronal cytoskeleton. In axons or dendrites, these filaments are aligned in parallel arrays, and separated from one another by nonrandom distances. This distinctive organization has been attributed to cross bridges formed by NF side arms or microtubule‐associated proteins. We recently proposed a polymer‐brush‐based mechanism for regulating interactions between neurofilaments and between microtubules. In this model, the side arms of neurofilaments and the projection domains of microtubule‐associated proteins are highly unstructured and exert long‐range repulsive forces that are largely entropic in origin; these forces then act to organize the cytoskeleton in axons and dendrites. Here, we review the biochemical, biophysical, genetic and cell biological data for the polymer‐brush and cross‐bridging models. We explore how the data traditionally used to support cross bridging may be reconciled with a polymer‐brush mechanism and compare the implications of recent experimental insights into axonal transport and physiology for each model. BioEssays 26:1017–1025, 2004. © 2004 Wiley Periodicals, Inc.
PML nuclear bodies: dynamic sensors of DNA damage and cellular stress
Authors: Dellaire Graham , Bazett‐Jones David P. 
Published: August 2004

AbstractPromyelocytic leukaemia nuclear bodies (PML NBs) are generally present in all mammalian cells, and their integrity correlates with normal differentiation of promyelocytes. Mice that lack PML NBs have impaired immune function, exhibit chromosome instability and are sensitive to carcinogens. Although their direct role in nuclear activity is unclear, PML NBs are implicated in the regulation of transcription, apoptosis, tumour suppression and the anti‐viral response. An emerging view is that they represent sites where multi‐subunit complexes form and where post‐translational modification of regulatory factors, such as p53, occurs in response to cellular stress. Following DNA damage, several repair factors transit through PML NBs in a temporally regulated manner implicating these bodies in DNA repair. We propose that PML NBs are dynamic sensors of cellular stress, which rapidly disassemble following DNA damage into large supramolecular complexes, dispersing associated repair factors to sites of damage. The dramatically increased total surface area available would enhance interactions between PML‐associated factors regulating DNA repair and apoptosis. BioEssays 26:963–977, 2004. © 2004 Wiley Periodicals, Inc.
VEGF: once regarded as a specific angiogenic factor, now implicated in neuroprotection
Authors: Storkebaum Erik , Lambrechts Diether , Carmeliet Peter 
Published: August 2004

AbstractBoth blood vessels and nerves are guided to their target. Vascular endothelial growth factor (VEGF)A is a key signal in the induction of vessel growth (a process termed angiogenesis). Though initial studies, now a decade ago, indicated that VEGF is an endothelial cell‐specific factor, more recent findings revealed that VEGF also has direct effects on neural cells. Genetic studies showed that mice with reduced VEGF levels develop adult‐onset motor neuron degeneration, reminiscent of the human neurodegenerative disorder amyotrophic lateral sclerosis (ALS). Additional genetic studies confirmed that VEGF is a modifier of motor neuron degeneration in humans and in SOD1G93A mice—a model of ALS. Reduced VEGF levels may promote motor neuron degeneration by limiting neural tissue perfusion and VEGF‐dependent neuroprotection. VEGF also affects neuron death after acute spinal cord or cerebral ischemia, and has also been implicated in other neurological disorders such as diabetic and ischemic neuropathy, nerve regeneration, Parkinson's disease, Alzheimer's disease and multiple sclerosis. These findings have raised growing interest in assessing the therapeutic potential of VEGF for neurodegenerative disorders. BioEssays 26:943–954, 2004. © 2004 Wiley Periodicals, Inc.
Dynamic cross‐talk between cells and the extracellular matrix in the testis
Authors: Siu Michelle K.Y. , Cheng C. Yan 
Published: August 2004

AbstractIn the seminiferous tubule of the mammalian testis, one type A1 spermatogonium (diploid, 2n) divides and differentiates into 256 spermatozoa (haploid, n) during spermatogenesis. To complete spermatogenesis and produce ∼150 × 106 spermatozoa each day in a healthy man, germ cells must migrate progressively across the seminiferous epithelium yet remain attach to the nourishing Sertoli cells. This active cell migration process involves precisely controlled restructuring events at the tight (TJ) and anchoring junctions at the cell–cell interface. While the hormonal events that regulate spermatogenesis by follicle‐stimulating hormone and testosterone from the pituitary gland and Leydig cells, respectively, are known, less is known about the mechanism(s) that regulates junction restructuring during germ cell movement in the seminiferous epithelium. The relative position of tight (TJs) and anchoring junctions in the testis is of interest. Sertoli cell TJs that constitute the blood–testis barrier (BTB) are present side by side with anchoring junctions and are adjacent to the basement membrane. This intimate physical association with the TJs, the anchoring junctions and the basement membrane (a modified form of extracellular matrix, ECM) suggests a role for the ECM in the junction dynamics of the testis. Indeed, evidence is accumulating that ECM proteins are crucial to Sertoli cell TJ dynamics. In this review, we discuss the pivotal role of tumor necrosis factor α (TNFα) on BTB dynamics via its effects on the homeostasis of ECM proteins. In addition, discussion will also be focused on the novel findings regarding the role of non‐basement‐membrane‐associated ECM proteins and components of focal adhesion (a cell–matrix anchoring junction type) in the regulation of junction dynamics in the testis. BioEssays 26:978–992, 2004. © 2004 Wiley Periodicals, Inc.
Model systems in stem cell biology
Authors: Robert Jason Scott 
Published: August 2004

AbstractStem cell scientists and ethicists have focused intently on questions relevant to the developmental stage and developmental capacities of stem cells. Comparably less attention has been paid to an equally important set of questions about the nature of stem cells, their common characteristics, their non‐negligible differences and their possible developmental species specificity. Answers to these questions are essential to the project of justly inferring anything about human stem cell biology from studies in non‐human model systems—and so to the possibility of eventually developing human therapies based on stem cell biology. After introducing and discussing these questions, I conclude with a brief discussion of the creation of novel model systems in stem cell biology: human‐to‐animal embryonic chimeras. Such novel model systems may help to overcome obstacles to extrapolation, but they are also scientifically and ethically contentious. BioEssays 26:1005‐1012, 2004. © 2004 Wiley Periodicals, Inc.
Control of asymmetric cell divisions: will cnidarians provide an answer?
Authors: Bosch Thomas C.G. 
Published: August 2004

AbstractCells in the basal metazoan phylum Cnidaria are characterized by remarkable plasticity in their differentiation capacity. The mechanism controlling asymmetric cell divisions is not understood in cnidarians or in any other animal group. PIWI proteins recently have been shown to be involved in maintaining the self‐renewal capacity of stem cells in organisms as diverse as ciliates, flies, worms and mammals. Seipel et al.1 find that, in the cnidarian Podocoryne carnea, the Piwi homolog Cniwi is transcriptionally upregulated when the polyp generates buds, which will develop into medusae. Since transdifferentiation of striated muscle cells to smooth muscle cells also activated Cniwi expression, Cniwi appears to play a crucial role in differentiation events. The discovery should facilitate elucidation of the poorly understood factors that control asymmetric cell divisions at the beginning of animal evolution. BioEssays 26:929–931, 2004. © 2004 Wiley Periodicals, Inc.
Reduced protein adsorption at solid interfaces by sugar excipients
Authors: Wendorf Janet R. , Radke Clayton J. , Blanch Harvey W. 
Published: August 2004

AbstractSugar excipients are shown to reduce the adsorption of ribonuclease A, bovine serum albumin, and hen egg white lysozyme at the liquid–solid interface. The amount of protein adsorbed decreased as the concentration of the sugar increased. At the same sugar concentration, the ability of sugars to reduce protein adsorption followed the trend: trisaccharides > disaccharides > 6‐carbon polyols > monosaccharides. This trend in adsorbed protein amounts among sugars was explained by stabilization of the protein native state in solution by the sugar excipients. The heat of solution of the amorphous saccharide was found to correlate with the amount of protein adsorbed. © 2004 Wiley Periodicals, Inc.
Biooxidation of pyrite by defined mixed cultures of moderately thermophilic acidophiles in pH‐controlled bioreactors: Significance of microbial interactions
Authors: Okibe Naoko , Johnson D. Barrie 
Published: August 2004

AbstractThe oxidative dissolution of pyrite (FeS2) by pure and mixed cultures of moderately thermophilic acidophiles was studied in shake flask cultures and in pH‐controlled bioreactors, incubated at 45°C. Various combinations of seven eubacteria (a Leptospirillum sp. (MT6), Acidimicrobium ferrooxidans, Acidithiobacillus caldus, an Alicyclobacillus sp. (Y004), and three Sulfobacillus spp.) and one archaeon (Ferroplasma sp. MT17) were examined. Pyrite dissolution was determined by measuring changes in soluble iron and generation of acidity, and microbial populations were monitored using a combined culture‐dependent (plate counts) and culture‐independent (fluorescent in situ hybridization) approach. In pure cultures, the most efficient pyrite‐oxidizing acidophile was Leptospirillum MT6, which was unique among the prokaryotes used in being obligately autotrophic. Mixed cultures of Leptospirillum MT6 and the sulfur‐oxidizer At. caldus generated more acidity than pure cultures of the iron‐oxidizer, though this did not necessarily enhance pyrite dissolution. In contrast, a mixed culture of Leptospirillum MT6 and the obligate heterotroph Alicyclobacillus Y004 oxidized pyrite more rapidly and more completely than a pure culture of Leptospirillum MT6, in synchronized bioreactors. Although the autotroph, At. caldus, and the “heterotrophically inclined” iron‐oxidizer, Am. ferrooxidans, were both ineffective at leaching pyrite in pure culture, a mixed culture of the two bacteria was able to accelerate dissolution of the mineral. Concentrations of dissolved organic carbon accumulated to >100 mg/L in some mixed cultures, and the most effective bioleaching systems were found to be consortia containing both autotrophic and heterotrophic moderate thermophiles. A mixed culture comprising the autotrophs Leptospirillum MT6 and At. caldus, and the heterotroph Ferroplasma MT17, was the most efficient of all of those examined. Mutualistic interactions between physiologically distinct moderately thermophilic acidophiles, involving transfer of organic and inorganic carbon and transformations of iron and sulfur, were considered to have critical roles in optimizing pyrite dissolution. © 2004 Wiley Periodicals, Inc.