bluuebunny/crossref_metadata_2025 huggingface dataset:
Induction of CB2 receptor expression in the rat spinal cord of neuropathic but not inflammatory chronic pain models
Authors: Zhang Ji , Hoffert Cyrla , Vu Huy Khang , Groblewski Thierry , Ahmad Sultan , O'Donnell Dajan
Published: December 2004

Cannabinoids have been considered for some time as potent therapeutic agents in chronic pain management. Central and systemic administration of natural, synthetic and endogenous cannabinoids produce antinociceptive and antihyperalgesic effects in both acute and chronic animal pain models. Although much of the existing data suggest that the analgesic effects of cannabinoids are mediated via neuronal CB1 receptors, there is increasing evidence to support a role for peripheral CB2 receptors, which are expressed preferentially on immune cells. As yet, little is known about the central contribution of CB2 in neuropathic pain states. We report here that chronic pain models associated with peripheral nerve injury, but not peripheral inflammation, induce CB2 receptor expression in a highly restricted and specific manner within the lumbar spinal cord. Moreover, the appearance of CB2 expression coincides with the appearance of activated microglia.
Limited functional redundancy in high diversity systems: resilience and ecosystem function on coral reefs
Authors: Bellwood David R. , Hoey Andrew S. , Choat J. Howard
Published: December 2004

Abstract Biodiversity is frequently associated with functional redundancy. Indo‐Pacific coral reefs incorporate some of the most diverse ecosystems on the globe with over 3000 species of fishes recorded from the region. Despite this diversity, we document changes in ecosystem function on coral reefs at regional biogeographical scales as a result of overfishing of just one species, the giant humphead parrotfish (Bolbometopon muricatum). Each parrotfish ingests over 5 tonnes of structural reef carbonates per year, almost half being living corals. On relatively unexploited oceanic reefs, total ingestion rates per m2 balance estimated rates of reef growth. However, human activity and ecosystem disruption are strongly correlated, regardless of local fish biodiversity. The results emphasize the need to consider the functional role of species when formulating management strategies and the potential weakness of the link between biodiversity and ecosystem resilience.
Natural enemy specialization and the period of population cycles
Authors: Rohani P. , Wearing H.J. , Cameron T. , Sait S.M.
Published: December 2004

The dynamical consequences of multiple‐species interactions remain an elusive and fiercely debated topic. Recently, Murdoch and colleagues proposed a general rule for the dynamics of generalist natural enemies: when periodic, they exhibit single generation cycles (SGCs), similar to single species systems. This contrasts markedly with specialists, which tend to show classic (longer period) consumer–resource cycles. Using a well‐studied laboratory system, we show that this general rule is contradicted when we consider resource age‐structure.
Tree size frequency distributions, plant density, age and community disturbance
Authors: Niklas Karl J. , Midgley Jeremy J. , Rand Richard H.
Published: December 2004

We show that explicit mathematical and biological relationships exist among the scaling exponents and the allometric constants (α and β, respectively) of log–log linear tree‐community size frequency distributions, plant density NT, and minimum, maximum and average stem diameters (Dmin, Dmax, and , respectively). As individuals grow in size and Dmax increases, NT is predicted to decrease as reflected by a decrease in the numerical value of α and an increase in the value of β. Our derivations further show that NT decreases as increases even if Dmin or Dmax remain unchanged. Because Dmax and the age of the largest individuals in a community are correlated, albeit weakly, we argue that the interdependent relationships among the numerical values of α, β, NT, and shed light on the extent to which communities have experienced recent global disturbance. These predicted relationships receive strong statistical support using two large datasets spanning a broad spectrum of tree‐dominated communities.
A developmental bottleneck in dispersing larvae: implications for spatial population dynamics
Authors: Schneider Daniel W. , Stoeckel James A. , Rehmann Chris R. , Douglas Blodgett K. , Sparks Richard E. , Padilla Dianna K.
Published: December 2004

We found evidence for a critical population bottleneck at a developmental‐stage transition in larvae of the zebra mussel Dreissena polymorpha Pallas from field estimates of mortality. Identification of this critical period in the field was made possible by closely tracking cohorts of larvae over 5 days of development as they dispersed 128 km in a river system. The presence of a survival bottleneck during development was confirmed in laboratory studies of zebra mussel larvae. Development‐specific mortality has important implications for spatial population dynamics of the zebra mussel in particular, and all species with indirect development in general. Marine reserves that do not take development‐specific mortality into account may dramatically underestimate reserve size needed to protect rare and/or exploited marine populations. Conversely, for the zebra mussel, the lower contribution of dispersing individuals to population growth downstream of reserves can lead to more feasible control through the blocking of dispersal.
Variable reporting and quantitative reviews: a comparison of three meta‐analytical techniques
Authors: Lajeunesse Marc J. , Forbes Mark R.
Published: December 2004

Variable reporting of results can influence quantitative reviews by limiting the number of studies for analysis, and thereby influencing both the type of analysis and the scope of the review. We performed a Monte Carlo simulation to determine statistical errors for three meta‐analytical approaches and related how such errors were affected by numbers of constituent studies. Hedges’dand effect sizes based on item response theory (IRT) had similarly improved error rates with increasing numbers of studies when there was no true effect, but IRT was conservative when there was a true effect. Log response ratio had low precision for detecting null effects as a result of overestimation of effect sizes, but high ability to detect true effects, largely irrespective of number of studies. Traditional meta‐analysis based on Hedges’dare preferred; however, quantitative reviews should use various methods in concert to improve representation and inferences from summaries of published data.
Environmental variation and the maintenance of polymorphism: the effect of ambient light spectrum on mating behaviour and sexual selection in guppies
Authors: Gamble Shenagh , Lindholm Anna K. , Endler John A. , Brooks Robert
Published: December 2004

The intensity of sexual selection is influenced by environmental conditions because these conditions influence signal propagation and the risks of the signal being exploited by predators and parasites. We explore the possibility that spatial or temporal heterogeneity in environmental signalling conditions (in this case light spectrum) may induce fluctuating sexual selection on male behaviour and ornamentation in guppies. We used shade cloth and filters to experimentally manipulate light spectrum, mimicking conditions found naturally: early morning/late afternoon light (SC treatment), midday forest shade (F89 filter treatment) and midday woodland shade (F55 filter treatment). Females were more responsive to male courtship and males were less likely to attempt sneak copulations under F55 light than the other two treatments. By contrast, male display rate was not influenced by treatment. Females tended to prefer the same males under SC and F55 light, but attractiveness in these treatments was unrelated to attractiveness under F89 light. There were similarities among treatments in the traits that females preferred: females preferred males with larger areas of orange in all three treatments. There were, however, also some differences, including preference for larger males under F89 light and for smaller males under the other treatments. Overall, the influence of ambient light spectrum on the relative importance of mate choice and male sneak copulation may have important implications for the mode and strength of sexual selection in different environments. The findings on attractiveness and preference functions, however, suggest that light spectrum only weakly affects the direction of sexual selection by female choice.
Regulation of moth–yucca mutualisms: mortality of eggs in oviposition‐induced ‘damage zones’
Authors: Shapiro Judith M. , Addicott John F.
Published: December 2004

Pollination–seed predation mutualisms such as moth–yucca interactions are important model systems for studying mechanisms that limit exploitation when mutualistic partners have strong conflicts of interest. In many moth–yucca interactions, oviposition leads to the failure of some ovules to develop normally. Here, we demonstrate that moth eggs almost always perish if they are inside these oviposition‐induced ‘damage zones’ of developing fruit. Moreover, because more ovipositions result both in larger damage zones and in higher proportions of eggs within damage zones, this source of mortality is strongly density‐dependent. Therefore, mortality of eggs in oviposition‐induced damage zones may be an important process for limiting seed consumption and regulating moth densities in many moth–yucca mutualisms.
Analysis and comparison of the microbial community structures of two enrichment cultures capable of reductively dechlorinating TCE and cis‐DCE
Authors: Gu April Z. , Hedlund Brian P. , Staley James T. , Strand Stuart E. , Stensel H. David
Published: December 2004

In order to study the effect of different chloroethenes (electron acceptors) on the bacterial composition of dechlorinating communities, two reductive dechlorinating enrichment cultures were developed that were able to reduce trichloroethene (TCE) and cis‐1,2‐dichloroethene (cis‐DCE) to ethene using hydrogen as electron donor, respectively. The inoculum for the cultures was material from a methanogenic fluidized bed reactor (FBR), which was originally seeded with digester sludge and showed a stable capacity for tetrachloroethene (PCE) reduction to ethene for over six years. Molecular methods were used to determine and compare the microbial communities of these two enrichment cultures. A clone library of bacterial 16S rRNA genes was generated for each enrichment. The clones were screened into different groups by restriction fragment length polymorphism (RFLP) analysis using two different four base pair recognition restriction enzymes. A total of 12 sequence types were identified by phylogenetic analysis of nearly complete 16S rDNA sequences (∼1450 bp). The sequences were affiliated with six recognized phyla of the domain Bacteria: Firmicutes (low G+C Gram‐positives), Chloroflexi (green non‐sulphur bacteria), Actinobacteria (high G+C Gram‐positives), Bacteroidetes (Cytophaga‐Flexibacter‐Bacteroides), Nitrospira and Spirochaetes. The results led to the identification of an organism closely related to Dehalococcoides ethenogenes to be the presumptive dechlorinator in both enrichments. Different electron acceptors affected the bacterial diversity and the community profiles of the two enrichments. Most of the sequences identified in our dechlorinating enrichments shared high similarities with sequences previously obtained from other enriched dechlorinating cultures and chlorinated‐compound‐contaminated sediments or aquifers, suggesting these bacteria may have direct or indirect roles in reductive dechlorination.
Comorbidity in post‐stroke rehabilitation
Authors: Giaquinto S.
Published: December 2004

Patients referred to rehabilitation centers often suffer from associated comorbidity, which might negatively influence the effective outcome of the treatment program. The study was aimed at evaluating the impact of comorbidity on functional independence and gain after stroke. Ninety‐three patients admitted to rehabilitation were enrolled. The disability was evaluated, both at time of admission and at discharge. The functional independence measure (FIM) was used. Comorbidity was evaluated by means of the Cumulative Illness Rating Scale (CIRS), that generates two indexes, the cumulative index (CI) and the severity index (SI). A logistic model could discriminate patients who were regularly discharged from the others (dead or transferred to acute care) pooled together (P ≤ 0.02). The CI and SI were significantly correlated with FIM at admission. The r‐values were −0.24 (P ≤ 0.02) and −0.32 (P < 0.002). Recovery was not even influenced in the most severe patients. In conclusion, the CIRS appears to be a sensitive tool for the evaluation of comorbidity in stroke patients. The comorbidity is correlated to dependence in stroke patients but does not affect functional gain. However, comorbidity is of actual interest in view of new payment systems in rehabilitation, because it is included among the variables leading to costs.
East–west differences in the organization of botulinum toxin use in nine Central European countries
Authors: Homann C. N. , Suppan K. , Wenzel K. , Homann B. , Pluta‐Fürst A. , Crevenna R. , Schinagl D. , Ruzicka E. , Dressle D. , Ivanic G.
Published: December 2004

Availability and quality of expensive treatment modalities such as botulinum toxin (BTX) largely depend on organizational aspects such as costs, reimbursement by insurance companies, expertise and facilities for expert training, and the propagation of research. To investigate which determinants influence the organization of BTX' use throughout nine Central European countries (Austria, Croatia, Czech Republic, Germany, Hungary, Italy, Slovakia, Slovenia and Switzerland) we sent out questionnaires to leading BTX experts and consulted data banks of manufacturers and bulletins of international organizations. In Western European countries, there is a tendency for users to organize themselves in formal groups and to concentrate on research whereas the way how BTX is provided is diverse regarding qualifications of specialists and institutions. In the post‐communist Eastern European countries, we found a tendency towards a centralized system of reimbursement and BTX treatment seems to be more in the hands of neurologists than any other specialists. Strong correlations were observed between the number of BTX centres, degree of organization of user groups and number of scientific publications, on the one hand, and parameters of healthcare performance and socioeconomic determinants, on the other. Our study suggests that in the nine countries surveyed, organizational aspects of BTX use vary considerably, whilst similarities are based mainly on socioeconomic rather than socio‐demographic determinants.
Mortality in a Population‐based Cohort of Epilepsy Surgery Patients
Authors: Nilsson Lena , Ahlbom Anders , Farahmand Bahman Y. , Tomson Torbjōrn
Published: December 2004

Summary:  Purpose: To investigate mortality and especially the incidence of sudden unexpected death in epilepsy (SUDEP) in a population‐based cohort of epilepsy surgery patients.

Methods: All patients who underwent epilepsy surgery treatment between January 1990 and December 1998 (surgery patients) or whose presurgical evaluation started, although not leading to an operation, during the same period (nonsurgery patients) were identified through the Swedish National Epilepsy register. All subjects were followed up through the Cause of Death Register until December 1998. Standardized mortality ratios (SMRs) for all causes of death and incidence of SUDEP were calculated.

Results: During the study period, 651 surgical operations were carried out on 596 patients (316 male). Of those, 14 patients died (six in SUDEP), rendering a total SMR of 4.9 [95% confidence interval (CI), 2.7–8.3]. SUDEP incidence was 2.4 per 1,000 person years. No major differences were found in SMRs or SUDEP rates between subgroups when stratifying for type of operation and for seizure outcome 2 years after surgery. SMR and SUDEP rates were higher in right‐sided temporal lobe resections for gliosis than in left‐sided, but the number of deaths was small. Among 212 nonsurgery patients, five died (four in SUDEP). The SMR for all causes was 7.9 (2.6–18.4), and SUDEP incidence, 6.3 per 1,000 person years.

Conclusions: In this large and strictly population‐based cohort, SMR for all causes and SUDEP incidence among surgery patients were similar to those of other studies. No differences in overall mortality emerged by seizure outcome, but none of the SUDEP cases was seizure free at the time of death. Four of five deaths in the nonsurgery group occurred during the surgery evaluation period. Mortality appeared to be lower for surgery than for nonsurgery patients, and the interpretation of this finding is discussed.
Epidemiology of Posttraumatic Epilepsy: A Critical Review
Authors: Frey Lauren C.
Published: December 2004

Summary:  Problem: Traumatic brain injury (TBI) is a major cause of epilepsy. We need to understand its frequency and its contribution to the total spectrum of the convulsive disorders.

Methods: A review of selected articles dealing with epilepsy after brain trauma was undertaken.

Results: The number of epidemiologic studies of posttraumatic seizures has increased substantially over the past 40–50 years, offering steadily increasing knowledge of the frequency, natural history, and risk factors of this well‐recognized complication of TBI. In general, the incidence of posttraumatic seizures varies with the time period after injury and population age range under study, as well as the spectrum of severity of the inciting injuries, and has been reported to be anywhere from 4 to 53%. As high as 86% of patients with one seizure after TBI will have a second in the next 2 years. Longer‐term remission rates of 25–40% have been reported. Significant risk factors for the development of seizures in the first week after injury include acute intracerebral hematoma (especially subdural hematoma), younger age, increased injury severity, and chronic alcoholism. Significant risk factors for the development of seizures >1 week after TBI include seizures within the first week, acute intra‐cerebral hematoma (especially subdural hematoma), brain contusion, increased injury severity, and age >65 years at the time of injury.

Conclusions: Epilepsy is a frequent consequence of brain injury in both civilian and military populations. We understand some factors associated with its development, but there remain many unanswered questions.
Current Trends in Antiepileptic Drug Therapy
Authors: Perucca Emilio
Published: December 2004

Summary:  Over the last two decades, drug therapy for epilepsy has improved substantially. This can be ascribed to a large extent to three factors, including the demonstration of the advantages of monotherapy; the realization of the need for dosage tailoring, coupled [for some antiepileptic drugs (AEDs)] with control of pharmacokinetic variability through therapeutic drug monitoring; and the introduction of newer agents with improved tolerability profiles. What further advances should we expect for the future? Current trends that are expected to increasingly affect our prescribing patterns include greater reliance on evidence‐based medicine and treatment guidelines, a trend that will be facilitated by completion of therapeutically meaningful randomized trials (including cost‐effectiveness studies) and high‐quality observational studies (including multinational pregnancy registries), as well as initiatives from scientific societies and government organizations aimed at condensing the most relevant information into therapeutic guidelines. The explosion in communication technology will accelerate dissemination of this information and its application to clinical practice. Other factors include a more rational patient‐tailored AED selection and dose individualization, aided by characterization of predictors of outcome as defined by clinical parameters (sex, age, epilepsy syndrome, and etiology), pathophysiological mechanisms, and newly discovered genetic markers of outcome; improved definition of the role of new AEDs, resulting in their increased use in newly diagnosed epilepsy; and reappraisal of the value of combination therapy in refractory epilepsies, based on evidence produced by experimental and clinical studies designed to identify favorable pharmacodynamic interactions. Additional important developments may come from the discovery of novel, more efficacious AEDs and from exploration of potential new targets, such as prevention of epileptogenesis.
Biophysics of Ablation:
Authors: HAINES DAVID
Published: December 2004

Introduction: The question of what happens to tissue during radiofrequency (RF) catheter ablation continues to be asked as we evolve into the use of newer delivery systems.

Methods and Results: Three assumptions are made about RF ablation. (1) Tissue injury is thermally mediated; (2) heat transfer in tissue should be a predictable biophysical phenomenon; and (3) large lesion technologies have more or less equivalent efficacies. Based on these assumptions, predictions are made and discussed. Many of the predictors were proven to be true while some surprisingly were not.

Conclusion: In conclusion, tissue‐area injury occurs reproducibly at a temperature of about 50°C. Heat transfer in tissue is a predictable phenomenon. And finally, new technologies for large lesions are all effective, but greater surface area of ablation was achieved with a 10‐mm tip and greater depth was achieved with a Chilli® cooled ablation catheter.
Inhibition of Hydrodynamic Instability by an Electric Current
Authors: Yih Chia-Shun
Published: December 2004

The inhibition of instability of a viscous fluid contained in a circular cylinder and heated from below by an electric current is investigated. Previous results indicate that, for a thermally nonconducting wall, the critical Rayleigh number is 452.1 for symmetric convection, and 67.9 for the first (and critical) mode of unsymmetric convection. It has been found in this investigation that unsymmetric convections can be delayed or completely inhibited by an electric current, whereas symmetric convection is not at all affected. This indicates a very interesting physical situation at Rayleigh number 452.1, for an electric current just strong enough to inhibit unsymmetric convection. If the current is slightly increased, only symmetric motion will occur. If it is slightly decreased, unsymmetric convection, being more unstable, will prevail. Thus the physically significant solution of a differential system may have a sudden change of behavior at certain critical values of its parameters.
Equilibrium Statistical Mechanics of Dissociating Diatomic Gases
Authors: Heller Leon
Published: December 2004

For the diatomic molecule AB in thermal and chemical equilibrium with its dissociated atoms, the pressure, density, specific entropy, and specific enthalpy are written as functions of the temperature and the fractional dissociation, with the approximations that the rotation is fully excited and there is no electronic excitation. These approximations are very good for many molecules over a large range of the variables. Atoms A and B can be either identical or distinct provided there is no excess of one atom over the other. For molecules composed of the isotopes of hydrogen, because of their large vibrational energies, it is possible to have considerable dissociation without vibration being important. If vibration is neglected, then the thermodynamic variables (written in dimensionless form) are related by equations which do not involve any properties of the species under consideration. Curves of constant pressure, density, specific entropy, and specific enthalpy are presented in the temperature-dissociation plane. The errors introduced by neglecting vibration are proportional to exp (−TV/T), where TV is the vibrational temperature.
Thermodynamics of Viscoelasticity in Liquids
Authors: Nettleton R. E.
Published: December 2004

A tensorial ordering parameter, obeying a linear relaxation equation, is introduced to describe the elastic shearing strain exhibited by a liquid at high frequencies. The coefficients in the relaxation-rate equation and the shear modulus in the stress tensor are linked by the Onsager-Casimir reciprocal relations with the result that the total rate of deformation is divided into elastic and viscous parts, in agreement with a hypothesis made by Frenkel to derive the viscoelastic stress relaxation equation of Maxwell. The hypersound wave velocity is computed from the thermal conductivity by an adaptation of a theory of Debye and from it the shear modulus and shear relaxation time are computed, effects of thermal relaxation being taken into account. In three nonassociated liquids, order-of-magnitude agreement is found with values calculated from a theory by Mooney.
Collisionless Plasma Shock
Authors: Colgate Stirling A.
Published: December 2004

The structure of an extremely strong magnetohydrodynamic shock is discussed in the limit of no particle collisions. It is tentatively concluded that the shock transition takes place through the mechanism of a strong electric field produced by charge separation. The pressure in the shocked plasma is due primarily to a very high electron temperature. The entropy increase occurs by Landau damping of the coherent electron oscillation. The ions, on the other hand, undergo an irreversible temperature change of only 3.
Mutual Reflection of Two Shock Waves of Arbitrary Strengths
Authors: Smith W. R.
Published: December 2004

Experiments were performed in air on the mutual reflection of a pair of weak shock waves of strength ξ = 0.915. The strengths of the shock waves were measured interferometrically. The regular reflection data agreed with the weak shock regular reflection solution for the flow. Regular reflection terminated at the extreme angle αe, and Mach reflection was found for larger angles. Four sets of experiments were performed in air with pairs of mutually reflecting shock waves of unequal strengths. The strengths of these shock waves were also measured interferometrically. The regular data agreed with the weak shock regular reflection solution for the flow. Mach reflection was found to occur for angles larger than the extreme angle. The experiments failed to resolve any of the difficulties concerned with Mach reflection.
Head-On Collision of Spherical Shock Waves
Authors: Glass I. I. , Heuckroth L. E.
Published: December 2004

Some experimental results are presented of colliding shock waves and the associated spherical flows generated by the blasts from two high-pressure gas spheres. Glass spheres, 2 in. in diam, with their centers located 9 in. apart, containing air or helium up to 500 psi were used to produce the explosions. Instantaneous spark shadowgrams, multi-spark schlieren photographs, and wave-speed schlieren records of the radius-time plane indicate that this method can be used successfully to study such interactions.
High-Speed Shock Waves in a Magnetic Annular Shock Tube
Authors: Patrick Richard M.
Published: December 2004

Experiments were carried out with two magnetic field configurations ahead of the shock front, the first with a magnetic field ahead of the shock front in the direction of motion of the shock. In the second configuration the magnetic field ahead of the shock had its principal component in the plane of the shock front and a small component in the direction of the shock motion. The continuum radiation emitted by the shock-heated plasma was measured with photomultipliers. Use of probes to measure the change in the local magnetic field in the shock front was investigated. With the second configuration, shock velocities in excess of 4 × 107 cm/sec were measured in hydrogen. For these high-speed shock waves, shock thicknesses, obtained from measured rise times of the emitted visible radiation, are thinner than the mean free path in the shock-heated plasma, an observation which agrees with a theoretical prediction.
Thermal and Electrical Properties of an Argon Plasma
Authors: Olsen H. N.
Published: December 2004

Temperatures ranging from 10 000 to 25 000°K have been measured spectroscopically in thermal plasmas of atmospheric pressure argon arcs at currents in the range of 200 to 800 amp. Electrical properties of the plasmas have been derived from measured radial temperature distributions using Spitzer's theory for the temperature dependence of electrical conductivity of a completely ionized gas. Existence of local thermal equilibrium has been demonstrated by the agreement between excitation temperatures determined from both atomic and ionic spectral line intensities. Agreement between values of electrical quantities obtained by direct measurement and those derived from measured temperatures based on the assumption of thermal equilibrium demonstrates the internal consistency of the experimental and analytical methods.
Turbulent Boundary Layer Measurements at Mach Numbers from 8 to 10
Authors: Hill F. K.
Published: December 2004

Data are presented showing the properties of hypersonic boundary layers at Mach numbers from 8 to 10. The measurements extend experimental data on skin friction and heat transfer previously reported in the literature, and provide a basis for comparison with theory. Significant results of the investigation include the relatively rapid growth of the laminar sublayer at high Mach numbers, the increase in the momentum thickness with heat transfer, the decrease in the heat transfer coefficient, and the skin friction dependence on heat transfer and pressure gradient at high Mach numbers. The velocity profiles in the turbulent portion of the boundary layer are found to extend the trend evidenced at lower Mach numbers of a fit to a power profile, but with a somewhat lower velocity index (n = 5 as compared to 7 and 9 at lower supersonic Mach numbers). On the other hand an exponential fit to the experimental points provides equally good agreement, and satisfies better the physical conditions at the edge of the boundary layer.
Growth of Instabilities on Displacement Fronts in Porous Media
Authors: Scheidegger A. E.
Published: December 2004

The problem investigated is that of the penetration of a fluid into a porous medium containing a more viscous liquid. In order to do this, the flow potentials for a displacement front which is just about to become unstable are calculated. For such a displacement front it is possible to linearize the differential equations, and to give a description in terms of Fourier analysis. The law of growth for each spectral component of the front is deduced, and it is shown how the time dependence of the whole front can be represented by a superposition of elemental solutions. Subsequently, the effect of the heterogeneities contained in the porous medium is accounted for by introducing a random velocity perturbation term into the differential equation for each spectral component. In this fashion one arrives at an equation describing the growth of each spectral component of the fingers with time. It is shown that, under given external conditions, fingering should be independent of the speed with which the displacement proceeds. This is, in fact, what has been observed experimentally.
Stability of an Idealized Atmosphere. I. Discussion of Results
Authors: Case K. M.
Published: December 2004

The stability of an idealized atmosphere with constant shear flow and exponentially decreasing density is considered. In no case does an initial perturbation increase with time. The decrease is, in general, not faster than a small fractional power of the time.
Expansion of a Rarefield Gas Cloud into a Vacuum
Authors: Molmud Paul
Published: December 2004

Analytical solutions are obtained describing the expansion into a vacuum of gas clouds having simple initial configurations. The assumptions employed are free molecular flow and local Maxwellian distribution of velocities initially. By means of a simple transformation in time, equivalence is shown between these solutions and the solutions of some elementary problems in transient heat flow. The initially uniform spherical gas cloud expanding into a vacuum is solved by two methods: (1) by the assumption of free molecular flow; and (2) by programming the conventional equations of gas dynamics. Good agreement is observed between the solutions resulting from the two treatments.
Hydrodynamic Model of Diffusion Effects on Shock Structure in a Plasma
Authors: Greenberg O. W. , Sen H. K. , Trève Y. M.
Published: December 2004

Diffusion effects on the structure of a steady, plane shock in a proton-electron plasma have been studied using a simplified, two-fluid, hydrodynamic model in which diffusion is the only shock broadening mechanism. Charge separations occur inside the shock because of the mass difference between protons and electrons. The shock is shown to have electric field and density oscillations as a function of distance through the shock. The peak electric fields are large; the peak electric field inside a weak shock of Mach 1.169 reaches 41 700 v/cm for typical quiescent plasma conditions. The distance in which electric field changes occur is of the order of ten Debye lengths of the quiescent plasma. The present work is limited to shocks of Mach number less than 2.
Shear and Heat Flow for Maxwellian Molecules
Authors: Ziering S.
Published: December 2004

In previous studies treating the problems of linear shear and heat flow in parallel plate geometry, a half-range moment expansion of the distribution function was given for arbitrary values of the Knudsen number. The half-range collision integrals for Maxwellian molecules are now evaluated numerically. The inverse fifth law of molecular interaction can be regarded as a lower bound for neutral gases. The problems of shear and heat flow are reconsidered in this light.
Influence of Pressure History on Momentum Transfer in Rarefied Gas Flows
Authors: Hurlbut F. C.
Published: December 2004

The coefficient for tangential momentum transfer σ between the boundary and a flow of rarefied gas has been investigated by the rotating cylinder technique. Systematic perturbation of the pressure history of the active surfaces were made and correlated with observed variation of σ. A high-pressure history is found to result in a lowering of σ with time (order of days) from values in the range 0.9 to 1.0 values approaching 0.6. A low-pressure history is found to result in constant values of σ in the range 0.9 to 1.0. The observations were of the same character for all gases.
Experiments on Plasmoid Motion along Magnetic Fields
Authors: Wetstone David M. , Ehrlich Melvin P. , Finkelstein David
Published: December 2004

Time-integrated photographs are presented of collimated plasmoid motion parallel to magnetic fields, into and around magnetic flux diverters, into and out of magnetic mirrors, and along curved fields. Field strengths up to 3 weber/m2 were employed. The material projected along the field lines was substantially copper plasma, created by short vacuum spark bursts (plasmoids), and injected into a vacuum chamber. Flux diverters and nonuniform solenoids expanded or compressed the plasmoid, which followed the field lines. In the case of curved fields, at least parts of the plasmoid appeared to be guided by the field lines, the guidance improving with decrease in plasmoid density. In general the behavior was more complicated than with straight geometries because of the presence of internal polarization fields. Photomultiplier studies were employed with some geometries to estimate center of mass and expansion velocities which, in later experiments, reached 5.5 and 1.9 cm/μsec. The latter figure gives an upper bound to ion temperature of 120 ev for copper. This ion energy is considerably higher than those normally encountered in spark channels and is a substantial fraction (0. 12) of the axial energy. A mechanism is described for achieving such a thermal energy through the interaction of a strong shock wave with the initial discharge channel, thermalizing a large fraction of the axial energy. The upper bound for ion Larmor radius was that of the plasmoid. In order to extend the well-known treatment of the mirror reflection phenomenon to such a dynamical plasma, a theoretical total reflection coefficient is derived for a plasmoid entering a magnetic mirror. The experimental equipment is described, and a machine-computational method is outlined for mapping the flux distribution and density in a wide variety of solenoid geometries and combinations.
Observation of Ion Cyclotron Waves
Authors: Stix Thomas H. , Palladino Richard W.
Published: December 2004

The existence of ion cyclotron waves had been inferred from theoretical calculations and indirectly from experimental observations. In this paper direct experimental observations are reported of phenomena appropriate to these waves in a hot plasma. An induction coil energized at 11.5 Mc with approximately 200 000 w of rf power surrounds a deuterium plasma confined in a 16-kilogauss magnetic field. A single-turn rf magnetic probe located in the plasma about 50 cm down the axis from the center of the induction coil is used to detect the propagated wave. The probe is movable. Radial motion of the probe shows the expected penetration of the transverse rf field into the center of the plasma. Axial motion of the probe shows a 300-cm damping length, and an oscillation wavelength 64% longer than the calculated value. The probe signals disappear when the ion cyclotron frequency is less than the induction coil frequency, which is a result predicted from the ion cyclotron wave dispersion relation.
Approximations in the Theory of Dense Fluids
Authors: Stillinger Frank H.
Published: December 2004

A fluid of rigid spheres in equilibrium is considered from a viewpoint which allows the deduced equation of state to reflect very sensitively the accuracy of two approximations to the triplet distribution function. Specifically, these approximations are: (1) the usual Kirkwood superposition scheme, and (2) assumption that the correlation of excess particles near a fixed particle pair is additively composed of the excesses induced individually by each member of the pair (linear correlation field hypothesis). Granted only these hypotheses, each in turn, the rigorous statistical mechanical relations between rigid-sphere distribution functions and the thermodynamic pressure and compressibility lead unambiguously to nonlinear first-order differential equations for the pressure as a function of density. The simply obtained numerical solutions clearly demonstrate that assumption (1) is considerably superior to (2).
On the Boltzmann Equation and the Structure of Shock Waves
Authors: Gustafson W. A.
Published: December 2004

The methods of Mott-Smith and Rosen for the shock structure problem are correlated. It is found that the application of Rosen's restricted variational technique to the Boltzmann equation yields the transport equation used by Mott-Smith, and in addition determines a transport function. The expression for the average translational temperature profile, as derived by Mott-Smith, is examined for the existence of relative minima or maxima. For a monatomic gas the temperature profiles have no relative extrema inside the shock wave for any Mach number. For a diatomic gas the temperature profiles are smooth for Mach numbers below 1.89, but above that a hump appears.
Statistical Mechanics of Relativistic Streams. I
Authors: Watson K. M. , Bludman S. A. , Rosenbluth M. N.
Published: December 2004

The small-amplitude motion of a relativistic beam passing through plasma is studied using transport theory. For the equilibrium state, a relativistic Maxwellian velocity distribution is obtained. The linearized Boltzmann equation is used to relate beam and plasma density and current perturbations to perturbations in the electromagnetic field. Approximate criteria are obtained to justify the neglect of static fields. Finally, these general results are specialized to those of a uniform beam.
Sound Velocity, Phase Separation, and Lambda Transitions of He3–He4 Mixtures
Authors: Roberts Thomas R. , Sydoriak Stephen G.
Published: December 2004

The velocity of first sound has been measured in saturated liquid He3–He4 mixtures ranging in composition from 20 to 90% He3 between 0.5° and 2.3°K. The velocities decrease with increasing He3 concentration due to the large increase in compressibility. The temperature Ts at which a liquid mixture first begins to separate into two layers of different composition is identified by a break in the temperature derivative of the sound velocity. The values of Ts are compared with and found to agree well with all other recent direct measurements. Breaks also occur in the temperature derivatives of first sound velocity and signal amplitude at temperatures which are in good agreement with most recent determinations of lambda transition temperatures for concentrations up to 30%. For higher concentrations, the values obtained are in good agreement with λ points determined from second sound measurements but differ markedly from results based on the disappearance of boiling. Possible reasons for the differences are discussed. A smoothed table of λ temperature as a function of concentration is given up to the intersection of the λ line and the phase separation region at 68% He3 and 0.86°K. The vapor pressure of pure He4 at its lambda point is 37.80 ± 0.01 mm Hg (at 0°C and standard gravity) based on the measured vapor pressure at the minimum sound signal and a calculated displacement of the sound minimum from the lambda point.
Dynamic Stabilization of a Plasma Column
Authors: Weibel Erich S.
Published: December 2004

A cylindrical plasma column is confined by a magnetic field whose z component is constant while the φ component oscillates sinusoidally. The skin depth is assumed to be negligible so that the boundary can be considered as sharp and the interior of the plasma as field free. The plasma itself is treated as an assembly of noncolliding particles which are specularly reflected at the plasma surface. The oscillating pressure of the applied field causes the plasma surface to execute a small periodic motion independent of φ and z. All other components of the displacement decay in time. Thus the plasma is positively stable against all deformations. For magnetostatic confinement this treatment yields the usual instabilities, but, in contrast to earlier work, the growth rates are bounded as the deformation wavelength approaches zero. This appears to be in better agreement with experiment.
Laminar Boundary Layer behind Strong Shock Moving with Nonuniform Velocity
Authors: Mirels Harold , Hamman Jesse
Published: December 2004

The laminar wall boundary layer behind a strong shock moving with nonuniform velocity into a stationary fluid has been investigated. In particular, two-dimensional and axisymmetric boundary layers behind plane, cylindrical, and spherical shocks which move according to the power law xs = Ctm have been considered. The wall boundary layers associated with blast waves are special cases of the class of problems treated herein. It was assumed that the fluid is a perfect gas, that viscosity is proportional to temperature, and that the wall surface temperature is small relative to the temperature in the free stream. The resulting boundary-layer equations were simplified by expanding the dependent variables in powers of a nondimensional distance measured from the shock. The zero-order flow corresponds, at each instant, to a two-dimensional boundary layer behind a shock wave moving with uniform velocity. Numerical solutions of the first-order equations have been found for several cases of interest, and the results for wall shear and heat transfer have been tabulated and discussed.
Stability of a Rotating Liquid Column
Authors: Gillis J. , Suh K. S.
Published: December 2004

The stability of a rotating cylindrical column of liquid with a concentric solid core is discussed. The critical value of the surface tension is determined for the case of a viscous liquid while, for a nonviscous liquid, the problem is solved for axisymmetric and plane perturbations. The physical significance of the results is also discussed.
Stability of Nonrotationally Symmetric Disturbances for Inviscid Flow between Rotating Cylinders
Authors: Krueger E. R. , DiPrima R. C.
Published: December 2004

The stability of an inviscid fluid between two concentric rotating cylinders to nonrotationally symmetric disturbances is investigated. The limiting form of the disturbance equations for small gap-to-radius ratios is derived. Computations of the growth rate of unstable disturbances are carried out for the case in which the cylinders rotate in the same direction. It is found that the growth rate of rotationally symmetric disturbances is greater than that of nonrotationally symmetric disturbances.
Trapping Instabilities in a Slightly Inhomogeneous Plasma
Authors: Krall Nicholas A. , Rosenbluth Marshall N.
Published: December 2004

The stability of an infinite collisionless plasma with a small density gradient in the x direction (using the collisionless Boltzmann equation and Maxwell's equations) confined by a static magnetic field in the z direction, is studied. Unstable modes are found at frequencies near multiples of the ion-cyclotron frequency Ωi. These modes are electrostatic oscillations transverse to the magnetic field, and have very short wavelengths λ ∼ vd/Ωi, where vd is the (small) drift occasioned by the magnetic-field inhomogeneity. The phase velocity of the wave is comparable to vd, and resonant interaction leads to the growth. Typical growth rates are large, α ∼ (me/mi) Ωi, but the effect of the instability is minimized by the extremely short wavelength.
Simple Waves and Shocks in Magnetohydrodynamics
Authors: Bohachevsky Ihor O.
Published: December 2004

A theorem due to P. Lax asserts that transition across a weak shock, when expanded in powers of a suitable shock-strength parameter, agrees with the transition across the simple wave of the same kind up to the terms of second order, inclusive. This theorem, however, does not apply to the shock velocity v; it is shown that v can also be determined up to second-order terms from the simple-wave relations. The above result is used to extend Friedrichs' theory of simple wave-weak shock interactions from gas dynamics to a general system of conservation laws. To illustrate the general theory, the treatment of a special system of conservation laws, namely, the Lundquist equations, and an explicit description of simple magnetohydrodynamic waves are given. The latter includes construction of Riemann invariants and the expansion of simple-wave relations into power series up to quadratic terms, inclusive. In connection with this work, a special approximation is proposed to describe the switch-on waves. Shocks are described by analogy with simple waves. To illustrate the necessary modifications of gas-dynamic formulas, the above results are used to discuss in detail the location of the point at which the shock forms. In particular, conditions are given under which the magnetohydrodynamic shocks develop sooner or later than the gas-dynamic.