bluuebunny/crossref_metadata_2025 huggingface dataset:
Detection and phylogenetic analysis ofWolbachiain Collembola
Authors: Czarnetzki Alice B. , Tebbe Christoph C.
Published: December 2004

Wolbachiaare obligatory, cytoplasmatically inherited α‐Proteobacteria which are known for infecting the reproductive tissues of many arthropods. Their prevalence in the large group of Collembola, however, is not known, except for PCR detection in the parthenogenetically reproducing speciesFolsomia candida(Order: Entomobryomorpha; Family: Isotomidae). In this study, fluorescencein situhybridization on microscopic sections ofF. candidaspecimens indicated thatWolbachia‐related bacteria were restricted to tissues of the ovary and brain. PCR with primers designed to detect 16S rRNA genes ofWolbachiawere positive with specimens from all of five geographically independentF. candidabreeding stocks and with three parthenogenetic species from another order (Poduromorpha; Family Tullbergiidae), i.e.Mesaphorura italica,M. macrochaetaandParatullbergia callipygos. In contrast, negative results were obtained with the two sexually reproducing species,Isotoma viridis(Isotomidae) andProtaphorura fimata(Poduromorpha; Onychiuridae). TheftsZgene ofWolbachiacould be PCR‐amplified from allWolbachia‐positive hosts with the exception ofM. macrochaeta. The phylogenetic distances of theftsZand 16S rRNA gene sequences reflected the phylogenetic distances of the host organisms but the sequences ofWolbachiawere relatively closely related, indicating thatWolbachiainfections took place after the Collembola had diversified. Our study confirms a monophyletic branch (supergroup E) of Collembola colonizingWolbachiaand indicates that this group is a sister group of supergroup A, the latter harbouring a high diversity of host organisms within the group of insects.
A novel approach to investigate biofilm accumulation and bacterial transport in porous matrices
Authors: Dunsmore Braden C. , Bass Catherine J. , Lappin‐Scott Hilary M.
Published: December 2004

Knowledge of bacterial transport through, and biofilm growth in, porous media is vitally important in numerous natural and engineered environments. Despite this, porous media systems are generally oversimplified and the local complexity of cell transport, biofilm formation and the effect of biofilm accumulation on flow patterns is lost. In this study, cells of the sulphate‐reducing bacterium, Desulfovibrio sp. EX265, accumulated primarily on the leading faces of obstructions and developed into biofilm, which grew to narrow and block pore throats (at a rate of 12 µm h−1 in one instance). This pore blocking corresponded to a decrease in permeability from 9.9 to 4.9 Darcy. Biofilm processes were observed in detail and quantitative data were used to describe the rate of biofilm accumulation temporally and spatially. Accumulation in the inlet zone of the micromodel was 10% higher than in the outlet zone and a mean biofilm height of 28.4 µm was measured in a micromodel with an average pore height of 34.9 µm. Backflow (flow reversal) of fluid was implemented on micromodels blocked with biofilm growth. Although biofilm surface area cover did immediately decrease (∼5%), the biofilm quickly re‐established and permeability was not significantly affected (9.4 Darcy). These results demonstrate that the glass micromodel used here is an effective tool for in situ analysis and quantification of bacteria in porous media.
PET visualization of microglia in multiple sclerosis patients using [11C]PK11195
Authors: Debruyne J. C. , Versijpt J. , Van Laere K. J. , De Vos F. , Keppens J. , Strijckmans K. , Achten E. , Slegers G. , Dierckx R. A. , Korf J. , De Reuck J. L.
Published: December 2004

Activated microglia are involved in the immune response of multiple sclerosis (MS). The peripheral benzodiazepine receptor (PBR) is expressed on microglia and up‐regulated after neuronal injury. [11C]PK11195 is a positron emission tomography (PET) radioligand for the PBR. The objective of the present study was to investigate [11C]PK11195 imaging in MS patients and its additional value over magnetic resonance imaging (MRI) concerning the immuno‐pathophysiological process. Seven healthy and 22 MS subjects were included. Semiquantitative [11C]PK11195 uptake values were assessed with normalization on cortical grey matter. Uptake in Gadolinium‐lesions was significantly increased compared with normal white matter. Uptake in T2‐lesions was generally decreased, suggesting a PBR down‐regulation. However, uptake values increased whenever a clinical or MR‐relapse was present, suggestive for a dynamic process with a transient PBR up‐regulation. During disease progression, an increase of normal‐appearing white matter (NAWM) uptake was found, propagating NAWM as the possible real burden of disease. In conclusion, [11C]PK11195 and PET are able to demonstrate inflammatory processes with microglial involvement in MS.
Clinical characteristics of the alpha‐synuclein mutation (G209A)‐associated Parkinson's disease in comparison with other forms of familial Parkinson's disease in Greece
Authors: Papapetropoulos S. , Ellul J. , Paschalis C. , Athanassiadou A. , Papadimitriou A. , Papapetropoulos T.
Published: December 2004

An Ala53Thr mutation of the α‐synuclein has been recently identified as a rare cause of familial Parkinson's disease (fPD). In the present study, the clinical characteristics of Parkinson's disease (PD) patients with Ala53Thr α‐synuclein mutation (α‐synPD) were compared with fPD patients without any known mutation. An investigator blinded to the results of the genetic analysis examined 15 α‐synPD patients and 43 consecutive fPD patients. Demographic data, age at onset of the illness, duration of the disease and modality of presentation were collected. Segregation ratios for both sexes in individuals at risk of developing α‐synPD were estimated. The Unified Parkinson's disease rating scale (UPDRS) was also completed. The 15 α‐synPD patients were matched for duration of the disease and age at onset with 15 of the 43 fPD patients (MfPD). Comparisons were also made between 14 patients belonging to three multicase families with patterns of inheritance similar to α‐synPD. The α‐synPD patients were significantly younger (mean difference 11.8 years) and showed the first sign of the disease earlier in life (mean difference 12.7 years) as compared with the fPD patients. Tremor at onset was present in only one (6.7%) of the α ‐synPD patients compared with 18 (41.9%) of the fPD patients (P = 0.01). At the time of examination rigidity, postural instability, orthostatic hypotension and the overall clinical severity did not differ significantly either between α‐synPD and fPD or between α‐synPD and MfPD groups. Nevertheless, some clinically relevant trends concerning the psychiatric symptoms and complications of therapy were recognized. The overall clinical severity and the progression of the disease in patients with α‐synPD did not differ from that of the fPD patients. The α‐synPD patients presented the illness at a younger age and also had lower prevalence of tremor when compared with the fPD patients.
Acute stroke treatment in Europe: a questionnaire‐based survey on behalf of the EFNS Task Force on acute neurological stroke care
Authors: Thomassen L. , Brainin M. , Demarin V. , Grond M. , Toni D. , Venables G. S. ,   for the EFNS Task Force on Acute Neurological Stroke Care
Published: December 2004

In 1997 the EFNS Task Force on Acute Neurological Stroke Care published its recommendations for acute stroke care (Brainin et al., 1997), which, in 1999, was followed by a stroke care inventory (Brainin et al., 2000) assessing the development of acute stroke care. In 2000 all 33 members of the EFNS Stroke Scientist Panel were asked to complete a questionnaire on the treatment of acute stroke in their country as of 2000. Data were based either on national surveys or a personal estimate of national practice, together with data from the personal practice of the panel member. Data from 22 countries were received. One of the principal findings is the lack of systematic evidence about practice in a significant number of European countries. Results illustrate that neurologists have a leading role in implementing acute stroke treatment guidelines and in adopting new therapeutic methods in most countries, but there is a wide variation in the application of different therapeutic procedures.
A Proton Magnetic Resonance Spectroscopy Study of Metabolites in the Occipital Lobes in Epilepsy
Authors: Simister Robert J. , McLean Mary A. , Barker Gareth J. , Duncan John S.
Published: December 2004

Summary: Purpose:γ‐Amino butyric acid (GABA) and glutamate, respectively the principal inhibitory and excitatory neurochemicals in the brain, are visible to proton magnetic resonance spectroscopy (MRS). We report a study of GABA+ (GABA plus homocarnosine) and GLX (glutamate plus glutamine) concentrations in the occipital lobes in patients with idiopathic generalised epilepsy (IGE) and in patients with occipital lobe epilepsy (OLE).

Methods:Fifteen patients with IGE, 15 patients with OLE, and 15 healthy volunteers were studied. A single voxel was prescribed in the occipital lobes for each subject. PRESS localised short‐echo‐time MRS was performed to measure GLX by using LCModel. A double quantum GABA filter was used to measure GABA+. Segmented T1‐weighted images gave the tissue composition of the prescribed voxel.

Results:Grey‐matter proportion, GLX, and GABA+ were all elevated in IGE. However, analysis using grey‐matter proportion as a covariable showed no significant group differences. No correlation was observed between GABA+ concentration and either seizure frequency or time since last seizure.

Conclusions:GLX and GABA+ were elevated in IGE. Elevated grey‐matter content in the IGE group despite normal MRI appearance can be expected to account for some or all of this observed elevation of GLX and GABA+. GABA+ concentration did not correlate with seizure control or duration since most recent seizure.
Tolerability and Pharmacokinetics of Oral Loading with Lamotrigine in Epilepsy Monitoring Units
Authors: Lardizabal David V. , Morris Harold H. , Hovinga Collin A. , Del Mar Carreño Maria
Published: December 2004

Summary:  Purpose: To investigate the tolerability and pharmacokinetics of oral loading with lamotrigine (LTG) among epilepsy patients after temporary drug discontinuation in an epilepsy monitoring unit.

Methods: We conducted a pilot study among epilepsy patients (18 years or older) receiving maintenance doses of LTG. LTG was discontinued on admission and restarted at the end of epilepsy monitoring. LTG was given as a single oral dose calculated based on the population expected volume of distribution (Vd, 1.0 L/kg) and target blood level on admission. Baseline and serial blood levels of LTG were determined hourly for 10 to 12 h after the loading dose. Outcome measures: (a) frequency of patients with side effects; (b) time to maximum concentration (Tmax), maximum concentration (Cmax), actual volume of distribution, and half‐life.

Results: Twenty‐four patients received a single oral load of LTG (mean, 6.5 ± 2.7 mg/kg). Overall, LTG loading was well tolerated with no serious adverse events or skin rash observed. Two patients had transient and mild nausea 1 to 2 h after the oral load. The mean estimated pharmacokinetic parameters are as follows: Tmax, 3.1 ± 2.1 h; Cmax, 8.2 ± 6.5 mg/L; Vd, 1.1 ± 1.0 L/kg; clearance, 0.08 ± 0.08 mg/L/h; half‐life, 22 ± 30 h. All patients reached their target blood levels.

Conclusions: Epilepsy patients temporarily discontinued from LTG can be restarted with a single oral loading dose. This was well tolerated, and therapeutic levels can be achieved within 1 to 3 h.
Prolonged Low‐dose Caffeine Exposure Protects Against Hippocampal Damage but Not Against the Occurrence of Epilepsy in the Lithium‐pilocarpine Model in the Rat
Authors: Rigoulot Marie‐Aude , Leroy Claire , Koning Estelle , Ferrandon Arielle , Nehlig Astrid
Published: December 2004

Summary:  Purpose: Acute caffeine exposure has proconvulsant effects and worsens epileptic and ischemic neuronal damage. Surprisingly, prolonged caffeine exposure decreases the susceptibility to seizures and the extent of ischemic damage. We explored whether the exposure to a low long‐term dose of caffeine could protect the brain from neuronal damage and epileptogenesis in the lithium‐pilocarpine model of temporal lobe epilepsy.

Methods: Rats received either plain tap water or water containing caffeine (0.3 g/L) for 15 days before the induction of status epilepticus (SE) by lithium‐pilocarpine and for 7 days after SE. The extent of neuronal damage was assessed in the hippocampus and piriform and entorhinal cortices in brain sections stained with thionine and obtained from animals killed 7 days after SE. The latency to spontaneous recurrent seizures was controlled by video monitoring.

Results: Caffeine treatment induced a marked, almost total neuroprotection in CA1 and a very limited protection in the hilus of the dentate gyrus, whereas damage in layers III–IV of the piriform cortex was slightly worsened by the treatment. All rats, whether they received caffeine or plain tap water, became epileptic after the same latency (17–19 days).

Conclusions: Thus these data extend the neuroprotective effects of low long‐term caffeine exposure to epileptic damage and confirm that the sole protection of the Ammon's horn has no influence on the genesis of spontaneous recurrent seizures in this model.
An In Vitro Study of New Antiepileptic Drugs and Astrocytes
Authors: Pavone Antonino , Cardile Venera
Published: December 2004

Summary:  Purpose: The aim of our research was to study some biochemical modifications elicited in primary rat astrocyte cultures by treatment with gabapentin (GBP), carbamazepine (CBZ), lamotrigine (LTG), topiramate (TPM), oxcarbazepine (OXC), tiagabine (TGB), and levetiracetam (LEV), commonly used in the treatment of epilepsy. We investigated the biologic effects of these anticonvulsants (AEDs) at concentrations of 1, 10, 50, and 100 μg/ml.

Methods: The study was performed by examining cell viability (MTT assay), cell toxicity [lactate dehydrogenase (LDH) release in the medium], glutamine synthetase (GS) activity, reactive oxygen species (ROS) production, lipoperoxidation level (malondialdehyde; MDA), and DNA fragmentation (COMET assay). The level of the expression of 70‐kDa heat‐shock protein (HSP70) and inducible nitric oxide synthase (iNOS) as oxidative stress–modulated genes also was determined.

Results: Our experiments indicate that CBZ, TPM, and OXC induce stress on astrocytes at all concentrations. GBP, LTG, TGB, and LEV, at low concentrations, do not significantly change the metabolic activities examined and do not demonstrate toxic actions on astrocytes. They do so at higher concentrations.

Conclusions: Most AEDs have effects on glial cells and, when used at an appropriate cell‐specific concentrations, may be well tolerated by cortical astrocytes. However, at higher concentrations, GBP, LTG, TGB, and LEV seem to be better tolerated than are CBZ, TPM, and OXC. These findings may reveal novel ways of producing large numbers of new AEDs capable of reducing the extent of inflammation, neuronal damage, and death under pathological conditions such as epilepsy and/or traumatic brain injury.
Risk Factors for Posttraumatic Seizures in Adults
Authors: Temkin Nancy R.
Published: December 2004

Summary:  Purpose: Traumatic brain injury has long been known to be a cause of epilepsy. Most information on risk factors for developing posttraumatic seizures is from before computed tomography (CT) scanning became universal. This article looks at factors about the injury or individual that put people at especially high risk of developing posttraumatic seizures.

Methods: We considered 783 cases at high risk of developing seizures, followed up for 2 years as part of seizure prophylaxis studies. Cumulative incidence of seizures in subgroups and standardized incidence ratios were used to identify factors related to unprovoked seizure risk.

Results: Subgroups with significantly elevated risk include those with evacuation of a subdural hematoma; surgery for an intracerebral hematoma; Glasgow Coma Scale in the severe range of 3 to 8; early seizures, especially delayed early seizures; time to following commands of a week or more; depressed skull fracture that was not surgically elevated; dural penetration by injury; at least one nonreactive pupil; and parietal lesions on CT scan.

Conclusions: Both the risk factors and the time course of the risk are important for designing seizure‐prophylaxis studies and, if an effective prophylactic regimen is identified, for deciding on appropriate candidates for prophylaxis.
Newer Antiepileptic Drugs and Cognitive Issues
Authors: Aldenkamp Albert P. , Krom Marc De , Reijs Rianne
Published: December 2004

Summary:  Although the causes of cognitive impairment in patients with epilepsy have not been completely elucidated, three factors are clearly involved: the underlying etiology of epilepsy, the effects of seizures themselves, and the central nervous system effects of antiepileptic drugs (AEDs). All commonly used AEDS have some effect on cognitive function, and the effect may be substantial when crucial functions are involved, such as learning in children or driving ability in adults, or when already‐vulnerable functions are involved, such as memory in elderly patients. The available evidence is insufficient to support definite conclusions about the cognitive effects of three of the newer AEDs, tiagabine, gabapentin, and levetiracetam. Better evidence is available for lamotrigine (LTG), topiramate (TPM), and, to a lesser degree, oxcarbazepine (OXC). OXC appears not to affect cognitive function in healthy volunteers or adults with newly diagnosed epilepsy, but its cognitive effects in children and adolescents have not been systematically studied. A relatively large number of studies are available for LTG, which has demonstrated a favorable cognitive profile overall, both in volunteers and in patients with epilepsy. Although dose and titration speed may be confounding factors in some of the studies of TPM, there is clear evidence that this agent does affect cognitive function, with specific effects on attention and verbal function. For LTG, attempts have been made to correlate cognitive effects with what is known of the drug's mechanism of action; this is an area of research that deserves further exploration with regard to other AEDs as well, especially TPM.
Inverse Relation Between Input Resistance and Threshold Current in Canine Cardiac Syncytium
Authors: MENDEZ CARLOS , HERNANDEZ VICENTE
Published: December 2004

Input Resistance and Threshold Current. Introduction: The present study was designed to examine the extent to which differences in input resistance contribute to the heterogeneity of excitability in canine endocardium.

Methods and Results: The experiments were performed in isolated canine right anterior papillary muscles. The preparations were superfused with oxygenated Tyrode's solution at 36° to 37°C. Conventional methods were used for recording and stimulation. To obtain pertinent data, two microelectrodes were inserted into the same cell or into two contiguous cells. One microelectrode injected intracellular hyperpolarizing current to polarize the membrane; the second microelectrode recorded the changes in transmembrane potential. The two micreoelectrodes were separated by 8 to 10 μm. The procedure used provided input resistance and threshold current values for the doubly impaled cell or the two contiguous cell units. The same procedure was repeated at different sites of the preparation. The plot of input resistance versus threshold current showed a good fit (R2= 0.97) between the experimental data and the curve for the rectangular hyperbola XY = 30 mV; therefore, the input resistance and the threshold current are inversely related.

Conclusion: The results indicate that the canine cardiac syncytium is nonhomogeneous with respect to input resistance and that input resistance is inversely related to the minimal current needed to reach threshold. Accordingly, the electrical excitability of the cells studied also is inhomogeneous.
Radiofrequency Ablation of Atrial Flutter Using Large‐Tip Electrode Catheters
Authors: FELD GREGORY K.
Published: December 2004

The use of large‐tip ablation catheters in both animal and clinical studies has been documented in work conducted over the last 10 years. These studies have demonstrated the safety and efficacy of the use of 8‐ and 10‐mm tip ablation catheters in the treatment of type I isthmus‐dependent atrial flutter. Shorter procedure times are reported with the larger‐tip ablation catheters compared to standard 4‐ or 5‐mm tip ablation catheters, with comparable or greater efficacy, no significant increase in complications, and an improved quality of life. Larger‐tip ablation electrodes do require the use of higher‐power radiofrequency generators up to 100 W. The benefits of large‐tip ablation catheters are thus well documented for the treatment of type I isthmus‐dependent atrial flutter.
Expanded characterization of the social interaction abnormalities in mice lacking Dvl1
Authors: Long J. M. , LaPorte P. , Paylor R. , Wynshaw‐Boris A.
Published: December 2004

Dvl1 is one of three murine Dishevelled genes widely expressed in embryonic development and in the adult central nervous system. Dishevelled proteins are a necessary component of the Wnt and planar cell polarity developmental signaling pathways. We reported previously that mice deficient in Dvl1 exhibited abnormal social interaction and sensorimotor gating. To assess the validity of our earlier findings, we replicated the previous behavioral tests and included several new assays. The behaviors assessed included: social interaction, sensorimotor reflexes, motor activity, nociception, prepulse inhibition of acoustic startle (PPI) and learning and memory. Assessments with an explicit social component included: social dominance test, whisker trimming, nest building, home‐cage huddling and ultrasonic vocalization rate analysis in pups. In addition, separate cohorts of wildtype and Dvl1‐null mice were assessed for social recognition of a conspecific. Replicating the original report, Dvl1‐null mice were impaired in several tasks containing an explicit social component. However, no impairment was obser‐ ved in the social memory task. A previously observed deficit in PPI did not replicate in two institutions. In conclusion, we provide evidence that the social interaction phenotype of Dvl1‐deficient mice has a strong genetic influence, but the sensorimotor gating deficit was subject to environmental influences. The specificity of observed social interaction deficits also suggests that lack of Dvl1 is associated with deficits in the recognition of social hierarchy and dominance.
Caries and periodontal disease of the elderly in Pomerania, Germany: results of the Study of Health in Pomerania
Authors: Mack Florian , Mojon Philippe , Budtz‐Jørgensen Ejvind , Kocher Thomas , Splieth Christian , Schwahn Christian , Bernhardt Olaf , Gesch Dietmar , Kordaß Bernd , John Ulrich , Biffar Reiner
Published: December 2004

Objective:  The aim of this study was to describe the oral health status of older adults living in north‐eastern Germany.

Materials and Methods:  Representative samples of adults aged 60 years or older were examined as part of Study of the Health in Pomerania, a cross‐sectional, population‐based study. Data on 1446 subjects aged 60–79 years were evaluated for coronal caries using the decayed/missing/filled teeth (DMFT) index, root caries using the root caries index (RCI), calculus, plaque, bleeding on probing, pocket depth and attachment loss.

Results:  The prevalence of edentulousness varied from 16% in the 60–65‐year‐old group to 30% in the 75–79‐year‐old group, whereas the median number of remaining natural teeth per subject varied from 14 in the youngest age group (60–65 years) to one in the oldest (75–79 years). Among subjects aged 60–69 years, a quarter (26%) of the teeth examined had coronal restoration against 17% in the oldest age group (70–79 years). Coronal caries was found in 2% of the teeth in both age groups. Among teeth with gingival recession, 6% had fillings on root surfaces and 2% had root caries, irrespective of age. In all, 11% of the subjects had at least one untreated coronal lesion and 27% had at least one untreated root caries lesion. Plaque score, calculus score and bleeding on probing were higher in the oldest age group (70–79 years). The prevalence of periodontal disease expressed as the presence of at least one periodontal pocket of 4 mm and more, was higher in men and among the younger subjects (men aged 60–69 years: 85% vs. 71% in 70–79‐year‐old men; women aged 60–69 years: 71% vs. 62% in 70–79‐year‐olds). The prevalence of attachment loss of 3 mm or more followed a similar pattern.

Conclusions:  It seems therefore that in this population, the major oral health concern is related to caries and the small number of teeth retained among the dentate subjects.
Theory of Electrostatic Probes in a Low-Density Plasma
Authors: Bernstein Ira B. , Rabinowitz Irving N.
Published: December 2004

The theory of sperical and cylindrical probes immersed in plasmas of such low density that collisions can be neglected is formulated. The appropriate Boltzmann equation is solved, yielding the particle density and flux as functionals of the electrostatic potential, the situation in the body of the plasma, and the properties of the probe. This information when inserted in Poisson's equation serves to determine the potential, and hence the probe characteristic. No a priori separation into sheath and plasma regions is required. Though amenable to a determination of the full probe characteristic, the method is applied in detail and numerical results are presented only for the collection of monoenergetic ions, for the case of negligible electron current. These results indicate that the potential is not so insensitive to ion energy as has been believed, and that if the probe radius is sufficiently small, there enters the possibility of a class of ions which are trapped near the probe in troughs of the effective radial potential energy. The population of these trapped ions is determined by collisions, however infrequent. It is difficult to calculate, and conceivably can have a marked effect on the local potential.
Onset of Convection in Liquids Subjected to Transient Heating from Below
Authors: Soberman Robert K.
Published: December 2004

Experimental studies have been made of the onset of natural convection in liquids subjected to heating from below while insulated above. The temperature gradient necessary for convection to start was measured with a thermopile immersed in the liquid. When the liquids were not rotating, it was found that the temperature difference between the top and bottom surfaces required to initiate convection can be related with the heat input by the formula Ra=90.7 (Ra·Nu)0.394, Ra>1700,where Ra is the Rayleigh number, and Nu is the Nusselt number, both specially defined for the transient case. Mercury and silicone oil were used in the experiments without rotation. It was found in experiments with mercury, that in the range of Taylor numbers covered, the presence of spin increased the temperature difference required to initiate convection. The Rayleigh number necessary for the onset of fluid motion in spinning mercury is plotted as a function of the Taylor number for several values of the heat flux.
Blast Wave from a Spherical Charge
Authors: Brode Harold L.
Published: December 2004

The blast wave from the detonation of a spherical charge of TNT is described based on results of a numerical calculation. The equations of motion and the equations of state for TNT and for air are described. The pressures, densities, temperatures, and velocities are detailed as functions of time and radius. Space-time relations and energy and impulse histories are shown. A second shock is seen to originate as an imploding shock following the inward rarefaction into the explosion product gases and a series of subsequent minor shocks are seen to appear in a similar manner, moving out in the negative phase behind the main shock.
Theory of Flames Produced by Unimolecular Reactions. II. Ignition Temperature and Other Types of Approximations
Authors: Hirschfelder Joseph O.
Published: December 2004

An ignition temperature approximation is used to explain many of the properties of flames, including the effect of heat transfer to the flame-holder. The Corner, Adams, Wilde, and Klein treatments are explained. Finally, a new approximation scheme (based on the Adams and Wilde) is developed which is extremely accurate.
Irreversible Processes in Ionized Gases
Authors: Balescu R.
Published: December 2004

The general theory of irreversible processes, developed by Prigogine and Balescu, is applied to the case of long range interactions in ionized gases. A similar diagram technique permits the systematic selection of all the contributions to the evolution of the distribution function, to an order of approximation equivalent to Debye's equilibrium theory. The infinite series which appear in this way can be summed exactly. The resulting evolution equations have a clear physical significance: they describe interactions of ``quasi particles,'' which are electrons or ions ``dressed'' by their polarization clouds. These clouds are not a permanent feature, as in equilibrium theory, but have a nonequilibrium, changing shape, distorted by the motions of the particles. From the mathematical point of view, these equations exhibit a new type of nonlinearity, which is very directly related to the collective nature of the interactions.
Diagram Expansions in Quantum Statistics
Authors: Levine Howard B.
Published: December 2004

The Montroll-Ward-Lee-Yang approach to quantum statistics is generalized to multicomponent systems. It is also generalized so as to include external fields. The formalism is constructed in a volume-dependent manner, and includes internal coordinates, such as spin, from the beginning. It is rigorously proved that the quantum-mechanical volume-dependent cluster integral may be expressed in terms of connected diagrams only. The rules for drawing these diagrams are given. By simply generalizing the meaning of the word ``determinant,'' all arguments are made to apply to both Fermi-Dirac and Bose-Einstein statistics simultaneously. A statistics factor, γ = ±1, for bosons (fermions) is introduced, in terms of which single formulas apply to both statistics. Rules are stated, by means of which the γ dependence of the contribution to the pressure for any diagram is given in terms an elementary topological property of the diagram.
New Variational Principle for Incompressible Non-Newtonian Flow
Authors: Bird R. Byron
Published: December 2004

A variational principle is given which describes the steady laminar motion of simple non-Newtonian fluids, for which the viscosity is a function of the second invariant of the rate of deformation tensor. This principle simplifies to von Helmholtz's principle for the Newtonian fluid, and to Tomita's principle for the Ostwald-de Waele fluid. For the latter two types of fluids, the equations of continuity and motion are equivalent to the statement that the rate of entropy production in the system is a minimum; for more general fluids, the variational principle does not admit this simple interpretation.
Analysis of Steady-State Supported One-Dimensional Detonations and Shocks
Authors: Wood W. W. , Salsburg Z. W.
Published: December 2004

Consideration is given to the possible steady one-dimensional flows which can occur in a medium in which an arbitrary number of chemical reactions proceed behind an initiating shock, and the stability of solutions to the chemical rate equations is investigated. The theoretical apparatus is that of irreversible thermodynamics and nonlinear mechanics, with neglect of transport processes. Most of the discussion is concerned with detonations, but the analysis applies to all such reacting systems. For detonations, it is shown that under suitable conditions on the rate functions, there are stable solutions resulting in an equilibrium final state for detonation velocities equal to or greater than the ``equilibrium Chapman-Jouguet (C-J)'' value corresponding to tangency of the Rayleigh line and the equilibrium Hugoniot. The final state in such a flow is the high-pressure intersection of the Rayleigh line and the equilibrium Hugoniot. We suggest that these solutions correspond to piston-supported detonations after decay of initiation transients, and we further suggest that the equilibrium C-J detonation is stable with respect to removal of the piston support at sufficiently late times.

The ``normal frozen C-J condition,'' corresponding to attainment of chemical equilibrium at a point where the flow velocity is sonic with respect to the ``frozen'' or high frequency sound speed, is shown to result in an unstable solution. Solutions corresponding to ``pathological detonations,'' in which the region of steady flow terminates at a point of incomplete reaction, are identified, but the conditions necessary or sufficient for their realization have not been obtained, nor has the nature of the subsequent time-dependent flow been elucidated. Thus their physical significance remains somewhat doubtful.
Statistical Mechanics of Relativistic Streams. II
Authors: Bludman S. A. , Watson K. M. , Rosenbluth M. N.
Published: December 2004

The stability of a uniform relativistic beam of particles injected into a plasma is studied using the previously developed linear transport theory. Velocity distribution in the beam and electron-ion collisions in the plasma are considered. For wave propagation in the beam direction, an exact treatment is given, while for oblique angles between plasma waves and the beam two kinds of perturbation theory are developed. We find that the two electromagnetic modes of beam-plasma oscillation are always stable, but that growing electrostatic oscillations are possible for long enough wavelengths. For short wavelengths or high temperatures this mode is also stable. Boundary effects and the effects of static fields are not considered.
Drift Instabilities in a Maxwellian Plasma
Authors: Jackson E. Atlee
Published: December 2004

The stability of two Maxwellian components of a plasma, which have different drift velocities, is investigated by means of a graphical solution of the dispersion relation. The graphical technique has the advantage of exhibiting the content of the dispersion relation in a transparent manner. By this method we determine the region of instability as a function of the perturbation wavelength λ and the relative velocity of the components, and show how this region depends on the ratio of the Debye lengths and plasma frequencies. In the case of an electron-proton plasma we obtain the maximum growth rate as a function of λ and the critical drift velocity as a function of the temperature ratios. The structure of the unstable region is also indicated by a few lines of constant growth rate.
Leading Edge of a Shock-Induced Boundary Layer
Authors: Sichel Martin
Published: December 2004

The boundary layer which is formed as a shock wave propagates down a shock tube causes both shock attenuation and shock curvature. Hartunian studied the curvature effect; however, as he points out, because of the singularities at the leading edge of the boundary layer his solution is not valid where the shock wave touches the tube wall. A detailed study is now made of the flow near the leading edge of this shock-induced boundary layer for a weak shock wave. The leading-edge flow can be divided into a shear layer near the wall, and into a free stream or shock region. By expanding the Navier—Stokes equations in the small parameter M1* — 1 and stretching the coordinates, simplified equations for the shear layer and shock region are obtained. The shear layer and shock region flows interact and it is found that the shock region must be a zone of non-Hugoniot flow where the shock structure is two dimensional. An approximate solution of the shock shape is obtained by replacing the shock region by an oblique shock which is approximately matched to the shear layer.
Stagnation-Point Heat Transfer in a High-Temperature Inert Gas
Authors: Bade W. L.
Published: December 2004

Stagnation-point similarity solutions of the laminar boundary-layer equations are calculated for a thermally and calorically perfect gas with Prandtl number ⅔ and viscosity proportional to a power of the absolute temperature (μ ∝ T1−α). The parameter α is varied from 0 to 0.5, and the enthalpy ratio across the boundary layer from 0.01 to 0.80. The results are closely applicable to high-temperature flows of the five inert gases. Heat-flux values predicted using these results and Amdur and Mason's viscosity calculations are compared with Rutowski's shock-tube measurements for argon. The agreement is excellent up to a stagnation temperature of 5400 °K. At higher temperatures, the experimental values gradually rise above the theoretical curve, indicating possible onset of electronic excitation and ionization effects upon the heat transfer.
Two-Stream Instability in Finite Beams
Authors: Frieman E. A. , Goldberger M. L. , Watson K. M. , Weinberg S. , Rosenbluth M. N.
Published: December 2004

The streaming instabilities of a finite beam of charged particles passing through a zero-temperature plasma are studied. It is shown that there are no eigenmodes associated with the instabilities. Nevertheless, by constructing wave-packet disturbances one is led to instabilities similar to those for a beam of infinite extent.
Pair Correlation in a Plasma
Authors: Wolff P. A.
Published: December 2004

A technique due to Dupree is used to investigate the pair correlation function in a dilute, uniform, quiescent plasma. It is demonstrated that his formal expression for the pair function may be evaluated in many cases of physical interest. In equilibrium one obtains the usual Debye-Hückel result, which may be generalized to the case of a plasma having different temperatures in different directions. A Lorentzian-type velocity distribution gives rise to a correlation function containing less than unit screening charge. It is shown that such behavior is only to be expected for velocity distributions that approach zero rather slowly in the limit of large velocity. Finally, a Druyvesteyn-type distribution is investigated and shown to lead to a pair function that falls off somewhat more slowly, and has a different form, from that of the Debye-Hückel theory.
Macroscopic Instability of the Positive Column in a Magnetic Field
Authors: Paulikas George A. , Pyle Robert V.
Published: December 2004

The positive column of a glow discharge has previously been shown to become unstable when immersed in a longitudinal magnetic field of the order of 1 kgauss, the instability transforming the azimuthally symmetric column into a constricted rotating helical stage. The measurements have been extended, with emphasis on the properties and growth of the instability, to permit a quantitative comparison between experiment and the theory of Kadomtsev and Nedospasov. The properties of the helical state have been measured in H2, D2, He, and Ne as functions of gas pressure and tube radius. The dependence of the critical magnetic field, and the frequency and wavelength of the oscillation on the kind of gas, pressure, and the tube radius are in fairly good agreement with the predictions made by the perturbation theory of Kadomtsev and Nedospasov. It is interesting that the onset of the instability is also fairly well predicted by the simple sheath-instability theory of Hoh, but the agreement is not as good as in the previous case, nor is the nature or appearance of the instability specified.
Solution of the Boltzmann Equations for Strong Shock Waves by the Two-Fluid Model
Authors: Glansdorff P.
Published: December 2004

The structure of a plane shock wave is studied by an extension to the gas dynamics of the two-fluid model already introduced in the superfluidity theory. The classical form is used for the linearization of two Boltzmann equations, and restricted to the first approximation. This is different from Mott-Smith's solutions which cannot be derived by linearization from a single Boltzmann equation, and as a result has to be introduced arbitrarily. Six equations of change for conservative quantities (mass, momentum, energy) are obtained which makes possible the solution of the wave problem without having to introduce other equations of change. Calculations are made using the elastic-sphere model. Comparison with observations made on argon gives very satisfactory results. The solutions tend asymptotically to a stationary solution corresponding to a Mach number equal to infinity, and to a shock wave thickness 11.4 times the mean free path ahead of the shock for all monatomic gases. This establishes the possibility of coexistence of two fluids in nonequilibrium, even thermal, in shock waves with large gradients.
Collision Integrals for the Transport Properties of Dissociating Air at High Temperatures
Authors: Yun K. S. , Mason E. A.
Published: December 2004

Collision integrals (transport cross sections) for atomic and molecular interactions of importance in high-temperature air are calculated based on accurate force laws which have recently become available. The tabulations include the collision integrals for diffusion, viscosity, and thermal conductivity, and the collision integral ratios A*, B*, and C* needed for mixture calculations, and cover the range from 1000° to 15 000°K for the major interactions N–N, O–O, N–O, N–N2, O–O2, O–N2, N2–N2, O2–O2, and N2–O2. Average potential energy functions, but no collision integrals, are given for the minor interactions O–NO, O2–NO, N2–NO, and NO–NO. The calculations all refer to atoms and molecules in their ground states only. Calculational errors are estimated to be about 5% over the temperature range, but may occasionally rise as high as 10%. The relative magnitudes of the average collision integrals are discussed briefly for their bearing on the qualitative behavior of the corresponding gas mixtures, and on the assessment of the errors involved in some approximations commonly used in calculations of transport properties of air.
Plasma Stability in an Inhomogeneous Magnetic Field
Authors: Lehnert B.
Published: December 2004

The problem of flute instabilities earlier discussed by Rosenbluth and Longmire and by the author is reconsidered. The theory is extended to include the influence of a mass velocity in the unperturbed state as well as compression and expansion effects arising from the inhomogeneity of the magnetic field. According to the latter effects, surfaces of constant density will not move with the fluid velocity. A description of the dynamics of density perturbations is made in terms of the fluid equations under the assumption of negligible Ohmic and viscous dissipation. Adiabatic and isothermal changes of state are discussed for a plasma with adiabatic and isothermal distributions of pressure and density in the unperturbed state. The plasma is found to be stable against flute disturbances of any wavelength, not only for cusped geometry, but also for mirror geometry under certain conditions. This is the case when the characteristic length B/|∇B| of the magnetic field is less than twice the characteristic length N/|∇N| of the unperturbed density distribution. The approximations of the present theory exclude a treatment of perturbations which extend across the whole plasma body. The compression mechanism which is responsible for the stabilization is a zero-order effect which is independent of the assumptions of isotropy and of the special forms of the unperturbed density and pressure distributions.
One-Dimensional Plasma Model
Authors: Dawson John
Published: December 2004

A one-dimensional plasma model consisting of a large number of identical charge sheets embedded in a uniform fixed neutralizing background is investigated by following the sheet motions on a high-speed computer. The thermalizing properties and ergodic behavior of the system are examined and found to be in agreement with the assumption that one is equally likely to find the system in equal volumes of the available phase space. The velocity distribution, Debye shielding, drag on fast and slow sheets, diffusion in velocity space, the Landau damping of the Fourier modes, the amplitude distribution function for the Fourier modes, and the distribution of electric fields felt by the sheets were obtained for the plasma in thermal equilibrium and compared with theoretically predicted values. In every case, except one, the drag on a slow sheet, the numerical results agreed with theory to within the statistical accuracy of the results. The numerical results for the drag on a slow sheet were about a factor of 2 lower than the theory predicated indicating that the approximations made in the theory are not entirely valid. An understanding of the cause of the discrepancy might lead to a better understanding of collisional processes in plasmas.
Hydromagnetic Turbulent Flow between Parallel Plates
Authors: Kapur J. N. , Jain R. K.
Published: December 2004

Turbulent flow of an incompressible, electrically conducting fluid between two parallel plates in the presence of an external, uniform magnetic field parallel to the plates is discussed. Starting with the Reynolds equations for hydromagnetics which are eventually reduced to three equations in seven unknowns, some conclusions about the mean pressure distribution and turbulent fluctuations are drawn. Unlike the case of laminar flow, the mean velocity distribution is found to be affected by the magnetic field through turbulent fluctuations and the mean magnetic field distribution does not remain uniform.
Asymptotic Theory of the Boltzmann Equation
Authors: Grad Harold
Published: December 2004

The precise mathematical relation that the Hilbert and Chapman-Enskog expansions bear to the manifold of solutions of the Boltzmann equation is described. These expansions yield inherently imprecise descriptions of a gas in terms of macroscopic fluid variables instead of a molecular distribution function. It is shown that these expansions are asymptotic to a very special class of solutions of the Boltzmann equation for sufficiently small mean free path. Next, a generalization of the Hilbert and Chapman-Enskog expansions is described in terms of extended sets of macroscopic state variables, each governed by partial differential equations similar to those found in fluid dynamics, but sufficiently general to approximate an arbitrary distribution function. The generalized expansions are shown to be asymptotic to quite arbitrary solutions of the Boltzmann equation. It is then shown that the ordinary Hilbert and Chapman-Enskog expansions can also be made asymptotic to very general solutions of the Boltzmann equation by reinterpreting the variables that enter these expansions as certain well-defined replacements for the actual fluid state of the gas. In this way the scope of the Euler, Navier-Stokes, Burnett equations, etc., is greatly extended by interpreting them as governing the artificial variables. Not only are general solutions of the Boltzmann equation shown to be approximated by fluid dynamics (in the limit of small mean free path), but the rapid decay of an arbitrary initial distribution function to a special Hilbert distribution function is also governed by sets of partial differential equations similar to those found in fluid dynamics.