bluuebunny/crossref_metadata_2025 huggingface dataset:
Migraine Disability Assessment (MIDAS) Score: Relation to Headache Frequency, Pain Intensity, and Headache Symptoms
Authors: Stewart Walter F. , Lipton Richard B. , Kolodner Ken
Published: December 2004

Objective.—To determine the extent to which variation in the Migraine Disability Assessment (MIDAS) score is associated with headache frequency, pain intensity, headache symptoms, gender, and employment status.

Background.—The MIDAS questionnaire is a 7‐item questionnaire (with 5 scored items) designed to measure headache‐related disability, to improve physician‐patient communication, and to identify patients with high treatment needs.

Methods.—Data from 3 population‐based studies (total sample, n  =  397) conducted in the United States and the United Kingdom were used to evaluate the relationship between headache features (attack frequency, pain intensity, pain quality, and associated symptoms) and MIDAS score. Data on headache features were collected by telephone using a standardized interview. The MIDAS questionnaire was completed shortly after the telephone interview. General linear models were used to determine the extent to which population variation in the MIDAS score was explained by headache features.

Results.—Using linear regression, variables for all headache features (ie, headache frequency, pain intensity, pain quality, and associated symptoms) and demographic characteristics explained only 22% of the variation in MIDAS scores. Almost all (19.9%) the explained variance was accounted for by average pain intensity (12.0%), number of headache days (6.1%), and exacerbation of pain with movement (1.8%). When pain intensity and headache frequency were included in the model, no statistically significant differences in MIDAS scores were observed by gender or employment status. Although explaining only 2.1% of the variance, age was significantly associated with MIDAS scores, with those under 25 years demonstrating higher MIDAS scores than other age groups. No other variables (ie, frequency of occurrence of associated symptoms and other measures of quality of pain) were associated with MIDAS scores.

Conclusions.—Challenges to the utility of the MIDAS as a measure include whether headache‐related disability is largely a function of other routine headache features and whether MIDAS is inherently biased based on work status and gender. While the MIDAS score was associated with headache frequency and average pain score, these two headache features explain only a modest proportion of the variation in MIDAS scores. Additionally, gender and work status were not related to MIDAS scores. These findings suggest that the MIDAS score captures information about disability that is not inherent to other headache features and is independent of gender and work status.
Academic Headache Medicine in America: Report of Academic Membership Survey of the American Headache Society Special Interest Section on Academic Affairs
Authors: Finkel Alan G.
Published: December 2004

Background.—What constitutes the typical clinical experience of an academic headache specialist in America is unknown.

Purpose.—To clarify this issue, we undertook a survey of academic headache specialists who are members of the American Headache Society.

Methods.—In June 2000, 181 surveys including questions regarding academic rank, departmental and institutional affiliation, and time distribution were sent to members drawn from the 1999‐2000 Membership Directory of the American Headache Society whose primary addresses were recognized academic institutions or who, by reputation, had extensive academic affiliation. Additional questions about headache teaching, research, and practice were included.

Results.—Seventy‐two (39.7%) of the surveys were returned. Forty‐nine (40%) of the 122 American medical schools were represented. The most prevalent academic rank was professor (38%). Included were 2 departmental chairs, 1 division chief, 1 vice dean, and 1 residency training director. The majority (70.8%) were neurologists. Seventy‐two percent of respondents spent at least 50% of their time in a clinic, 79% spent 25% or less of their time on research, and 78% spent 25% or less time in teaching. The average number of new patients seen per week was 9.0  ±  7.6, with each visit lasting 62.4  ±  20.8 minutes. Clinicians saw 22.7  ±  14.6 patients for follow‐up per week, with the average visit lasting 24.7  ±  6.8 minutes. Although it appears that at least informal instruction in headache is provided to medical students, interns, and residents, 19.7% (12 of 61) of respondents reported that no formal medical school lecture on the topic of headache was offered at their institutions.

Conclusion.—This preliminary survey offers some insight into the clinical experience of academic headache specialists in the American medical system. Suggestions for future studies are discussed.
Electrophysiological evidence for trigeminal neuron sensitization in patients with migraine.
Authors: Sandrini G , Proietti Cecchini A , Milanov I , Tassorelli C , Buzzi MG , Nappi G
Published: December 2004

Neurosci Lett. 2002 Jan 14;317(3):135‐138

The electrically elicited corneal reflex is a useful tool for exploring the trigeminal system in humans and it may provide additional evidence pointing to a dysfunction of this system in migrainous patients. Tactile perception, corneal reflex and pain thresholds were studied in 48 migraine without aura patients during pain‐free periods and compared with those observed in 24 controls. Twenty‐eight of the patients had strictly unilateral headache, while the other 20 had bilateral or side‐shifting pain during attacks. Both migraine subgroups (bilateral and unilateral) showed significantly lower thresholds compared with controls. The lowest values were observed on the symptomatic side of unilateral migraine patients. These findings suggest that sensorimotor mechanisms and/or pain control systems at the trigeminal level are impaired in migraine. The bilateral location of these abnormalities seems to point to a centrally located dysfunction.

Comment: This is an important paper which describes a noninvasive method of studying sensorimotor/pain control mechanism in humans. This approach may help in the development of potential prophylactic agents, to establish likely clinically effective doses and duration of treatments in small‐scale phase II trials, before exposing larger numbers of subjects to potentially ineffective doses in phase III trials. DSM
Linking olfaction with nausea and vomiting of pregnancy, recurrent abortion, hyperemesis gravidarum, and migraine headache.
Authors: Heinrichs L
Published: December 2004

Am J Obstet Gynecol. 2002 May;185(5 Suppl Understanding):S215‐S219

Objective: The experience of women was sought about nausea and vomiting, its relation to olfaction, its occurrence among pregnant women with anosmia, and the potential association of hyperemesis gravidarum and migraine headache.

Methods: We performed a community‐based study with a physician/patient‐directed questionnaire, and a retrospective analysis of hospital records.

Results: Nearly all women (n  =  163 parous women) experience nausea (98%) and vomiting (97%). The highest frequency causes of nausea and vomiting were “food poisoning” (65%), “flu” (58%), pregnancy (54%), and offensive odors (52%); vomiting occurred as frequently as nausea for the first 2 causes, and one half as often for the latter causes. Most women reported that the pain experienced during vomiting exceeded that of parturition. Among 9 women with hypogonadotropic anosmia with advanced reproductive technology‐induced pregnancies, 2 experienced nausea and vomiting, one from “food poisoning.” Among 37 women with migraine headache, 10 (27%) had experienced hyperemesis gravidarum, and among 16 who experienced hyperemesis gravidarum, 5 (37%) had migraine headaches.

Conclusions: The frequency of nausea and vomiting, caused most often by nonpregnancy‐related triggers, is high among women. In a small sample of women with congenital anosmia, nausea and vomiting of pregnancy occurred in only 1 pregnancy, suggesting that olfaction is a highly selected trigger for nausea and vomiting of pregnancy. The shared nausea and vomiting experience of hyperemesis gravidarum and migraine headache among women suggests a common mechanism, possibly based on allelic variations within the DRD2 (dopaminergic receptor) gene. Because olfactory receptors, odor types, and MHC antigens are closely integrated, and because olfactory stimuli often incite episodes of pregnancy, nausea, and vomiting, hyperemesis gravidarum, and migraine headache, these genes and their products invite further scrutiny. The pregnancy‐conserving effect of PNV and the MHC antigen overlap in couples with recurrent abortion are important clues possibly relating olfaction, MHC antigens, and reproductive success or failure.

Comment: Dr Stephen Peroutka described a group of patients with migraine with DRD2 gene abnormalities that he thought might predict for antidopamine medication efficacy in treating their migraines. He felt these patients had prominent dopaminergic manifestations in their migraine presentations: yawning and severe nausea and vomiting. (Peroutka SJ. Dopamine and migraine. Neurology. 1997;49:650‐656). The current study suggests that we may be able to look for other comorbid illnesses, such as hyperemesis gravidarum, to find patients with “dopaminergic migraine,” if this entity exists. SJT
Sinus headache or migraine? Considerations in making a differential diagnosis.
Authors: Cady RK , Schreiber CP
Published: December 2004

Neurology. 2002 May 14;58(9 Suppl 6):S10‐S14

Sinus headache is commonly diagnosed, and patients with headache often cite sinus pain and pressure as a cause of their headaches. A high frequency of diagnosis of sinus headache, which specialists consider to be relatively rare, among patients meeting International Headache Society (IHS) diagnostic criteria for migraine raises the possibility that migraine and perhaps other headache types are sometimes mistaken for sinus headache. This article considers clinical, epidemiologic, and pathophysiologic relationships between sinus headache and migraine and discusses the implications for clinical management of headache. Both historic and new data show that nasal symptoms frequently accompany migraine, although these symptoms are not part of the IHS diagnostic criteria for migraine. Parasympathetic activation, as well as the hypothesized mechanism of neurogenic or immunogenic switching (i.e., crossover interactions of neurogenic and immunogenic inflammation), may account for both the frequent occurrence of nasal symptoms in migraine and the possibility that sinus inflammation can sometimes act as a migraine trigger. Considered in aggregate, the data show that the occurrence of nasal symptoms associated with a headache should neither trigger a diagnosis of sinus disease nor exclude a diagnosis of migraine. It should, in fact, prompt diagnostic consideration of both conditions.

Comment: This article summarizes a small pilot study performed in the United States, in which patients with self‐diagnosed “sinus headache” were evaluated as to International Headache Society (IHS) diagnosis. Ninety‐six percent met IHS criteria for migraine or migrainous headache, suggesting that this entity, at least in the United States, is most frequently migraine with accompanying cranial parasympathetic activation. The article is worth tracking down and reading in its entirety, as the section of the article on pathophysiology is quite original and thought provoking. SJT
Cluster headache: the challenge of clinical trials.
Authors: Moore K
Published: December 2004

Curr Pain Headache. Rep 2002 Feb;6(1):52‐56

The design and execution of clinical trials poses special problems for cluster headache. Although there is less inter‐individual and intra‐individual variability of attacks than seen with migraine, the brevity of attacks, spontaneous remissions unrelated to treatment, and the relative rarity of cluster headaches challenge investigators. The International Headache Society has developed guidelines that represent a compromise between scientific rigor and practicality. Only injectable sumatriptan for acute attacks and verapamil for prophylaxis have demonstrated a robust therapeutic effect in controlled clinical trials.

Comment: Kenneth Moore raises important methodological considerations. It is possible to undertake crossover trials comparing different active treatments? He is correct in his assertion that few agents show robust efficacy. A major issue relates to the proportion of patients with episodic versus chronic cluster headache where efficacy of active treatments can vary. For example, oral zolmitriptan was effective against placebo only in those patients with episodic disease (Bahra A, Gawel MJ, Hardebo JE, Millson DS, Breen SA, Goadsby PJ. Oral zolmitriptan is effective in the acute treatment of cluster headache. Neurology. 2000;54:1832‐1839). And a set of small studies on melatonin and cluster demonstrate the problems Dr. Moore describes. In one study (Leone M, D'Amico D, Moschiano F, Fraschini F, Busonne G. Metalonin versus placebo in the prophylaxis of cluster headache: a double‐blind pilot study with parallel groups. Cephalalgia. 1996;16:494‐496), the melatonin worked only in episodic, not chronic cluster patients. In the second study (Prinsheim T, Magnoux E, Dobson CF, Hamel E, Aube M. Melatonin as adjuctive therapy in the prophylaxis of cluster headache: a pilot study. Headache. 2002;42:787‐792), melatonin did not work better than placebo in either episodic or chronic cluster patients. Furthermore, the paper abstracted above by Torelli and Manzoni suggests that episodic cluster may progress to chronic cluster as a result of extrinsic factors such as smoking. Finally, there are ethical issues in placebo‐controlled cluster studies, given the severity of the pain and the availability of effective acute and chronic treatments. As noted above, Dr. Peter Goadsby points out the need to persevere with these studies to find nonvasoactive treatments for patients with cluster headache. DSM and SJT
In vivo evidence of altered skeletal muscle blood flow in chronic tension‐type headache.
Authors: Ashina M , Stallknecht B , Bendtsen L , Pedersen JF , Galbo H , Dalgaard P , Olesen J
Published: December 2004

Brain. 2002 Feb;125(Pt 2):320‐326

Painful impulses from tender pericranial muscles may play a major role in the pathophysiology of chronic tension‐type headache. Firm evidence for peripheral muscle pathology as a cause of muscle pain and chronic headache is still lacking. Using a microdialysis technique, we aimed to estimate in vivo blood flow and interstitial lactate concentrations in the trapezius muscle at rest and during static exercise in patients with chronic tension‐type headache and in healthy subjects. We recruited 16 patients with chronic tension‐type headache and 17 healthy control subjects. Two microdialysis catheters were inserted into the trapezius muscle (on the non‐dominant side) of subjects, and dialysates were collected at rest, 15 and 30 min after the start of static exercise (10% of maximal force) and 15 and 30 min after the exercise was completed. All samples were coded and analysed blind. The primary endpoints were to detect a difference between patients and controls in changes of muscle blood flow and the interstitial lactate concentration from baseline to exercise and post‐exercise periods. The increase in muscle blood flow from baseline to exercise and post‐exercise periods was significantly lower in patients than controls (P  =  0.03). There was no difference in resting blood flow between patients and controls (P  =  0.43). Resting interstitial concentration of lactate did not differ between patients (2.51  ± *T0.18 mM; mean ± standard error of the mean) and controls (2.35  ±  0.23 mM, P  =  0.57). There was no difference in change in interstitial lactate from baseline to exercise and post‐exercise periods between patients and controls (P  =  0.38). The present study provides in vivo evidence of decreased blood flow in response to static exercise in a tender muscle in patients with chronic tension‐type headache. We suggest that, because of increased excitability of neurones in the CNS, the central interpretation and response to normal sensory input are altered in patients with chronic tension‐type headache. This may lead to enhanced sympathetically mediated vasoconstriction and thereby a decreased blood flow in response to static exercise.

Comment: An important study which links decreased blood flow in statically exercised trapezius muscle in patients with chronic tension‐type headache (CTTH) with muscle tenderness. A better understanding of the pathophysiology of CTTH may provide a clue to novel therapeutic maneuvers. DSM
Cost savings in migraine associated with less chest pain on new triptan therapy.
Authors: Wang JT , Barr CE , Torigoe Y , Wang E , Rowland CR , Goldfarb SD
Published: December 2004

Am J Manag Care. 2002 Feb;8(3 Suppl):S102‐S107

Objectives: This article constructs an economic model to estimate cost of chest‐pain‐related care in migraine patients receiving almotriptan 12.5 mg compared with those receiving sumatriptan 50 mg.

Study Design: This population‐based, retrospective cohort study used data from the MEDSTAT Marketscan database (Ann Arbor, Michigan) to quantify incidence and costs of chest‐pain‐related diagnoses and procedures. After a 6‐month exclusion period, the study used a pre‐post design, with baseline and treatment periods defined, respectively, as 5 months before and after receiving sumatriptan therapy. An economic model was constructed to estimate annual cost savings per 1,000 patients receiving almotriptan instead of sumatriptan as a function of differing rates of chest pain. Annual direct medical cost avoided was calculated for a hypothetical health plan covering 1 million lives.

Results: Among a cohort of 1,390 patients, the incidence of chest‐pain‐related diagnoses increased significantly (43.6%) with sumatriptan, from 110 during the baseline period to 158 during the treatment period (P  =  .003). Aggregate costs for chest‐pain‐related diagnoses and procedures increased 33.1%, from $22,713 to $30,234. Payments for inpatient hospital services rose 10‐fold; costs for primary care visits and outpatient hospital visits rose 53.1% and 14.4%, respectively. Payments for angiography increased from $0 to $462, and costs for chest radiographs and electrocardiograms increased 58.7% and 31.2%, respectively. Sumatriptan treatment was associated with a 3‐fold increase in payments for services for painful respiration and other chest pain. The model predicted $11,215 in direct medical cost savings annually per 1000 patients treated with almotriptan instead of sumatriptan. Annual direct medical costs avoided for the health plan totaled $195,913.

Conclusion: Using almotriptan instead of sumatriptan will likely reduce the cost of chest‐pain‐related care for patients with migraine headaches.

Comment: In my view, this study takes conjecture a step too far. The lower reported chest adverse events (AEs) reported in clinical trials where all AEs are scrutinized will not necessarily lead to lower reporting in the clinic. This hypothesis remains to be proven in a well‐designed post‐marketing surveillance program, untarnished by commercial sponsorship. Until such an independent prospective study is carried out, the extrapolations described here and in similar papers are pure conjecture and should be classed as the lowest grade of evidence on a par with uncorroborated clinical opinion. DSM
Mutation analysis of the CACNA1A calcium channel subunit gene in 27 patients with sporadic hemiplegic migraine.
Authors: Terwindt G , Kors E , Haan J , Vermeulen F , Van den Maagdenberg A  , Frants R , Ferrari M
Published: December 2004

Arch Neurol. 2002 Jun;59(6):1016‐1018

Background: Familial hemiplegic migraine is a rare autosomal dominant subtype of migraine with aura that in half of the families is caused by mutations in the CACNA1A gene on chromosome 19p13. In sporadic hemiplegic migraine (SHM), that is, hemiplegic migraine without affected family members, the contribution of the CACNA1A gene is unknown.

Objective: To investigate the involvement of the CACNA1A calcium channel subunit gene in SHM.

Methods: We screened 27 patients with SHM for mutations in the CACNA1A gene by a combination of single‐strand conformational polymorphism analysis and sequence analysis.

Results: One patient with SHM also had ataxia, nystagmus, and cerebellar atrophy on computed tomography and carried a T666M mutation. Another patient with SHM who had no cerebellar signs carried an R583Q mutation. No mutations or interictal neurological abnormalities were found in the remaining 25 patients with SHM.

Conclusions: Most patients with SHM do not have a CACNA1A mutation. The results of this study, combined with the findings reported in the literature, show that the presence of cerebellar symptoms in addition to the hemiplegic attacks increases the chance of finding a CACNA1A mutation. In addition, to our knowledge, we have found a first patient with SHM without cerebellar signs with a mutation.

Comment: The story on calcium channelopathies and neurologic disorders becomes ever more complex, as multiple neurologic disorders appear linked to varying forms of calcium‐channel mutations. Professor Ferrari has described links to cerebellar disorders, to a peculiar and severe response to head trauma, and to epilepsy, as well as to familial hemiplegic migraine. Now his group finds that the most frequently found calcium channelopathy mutations are not found in most patients with spontaneous hemiplegic migraine. Does this just mean that other mutations, not yet described, cause a common phenotypic expression? Or are there multiple causes for the hemiplegic migraine syndrome, and not all of them due to calcium channelopathies? SJT
Kinetic Equation to Higher Orders in the Plasma Parameter
Authors: Weinstock Jerome
Published: December 2004

A kinetic equation for a homogeneous electron gas is derived to all orders in the plasma parameter λ (the reciprocal number of electrons per Debye sphere). It has the form ∂φ1∂t= ∑ n=1∞ (e2)n(R̄(n)+β̄n−R̄n(n)),where R̄(n) is a Fokker-Planck type collision integral which rigorously describes distant collisions between (n+1) electrons and diverges logarithmically at small impact parameter; β̄n is a Boltzmann-like collision integral for close collisions between (n+1) electrons and diverges at large impact parameter; and R̄n(n) accounts for intermediate collisions between (n+1) electrons and diverges at both large and small impact parameter. Whether or not the various divergent parts of (R̄(n) + β̄n − R̄n(n)) exactly cancel each other out has not yet been proven for all n. The infinite sum, however, is a direct consequence of Liouville's equation and is exact at all t. The first term (R̄(1) + β̄1 − R̄1(1)) has been proven convergent elsewhere. The second-order term (R̄(2) + β̄2 − R̄2(2)), which corresponds to ternary correlations (ternary collisions), is examined in detail and found to have its order of magnitude given by O(λ2 log λ) + O(λ2).
Intermolecular Forces in Globular Molecules. III. A Comparison of the Spherical Shell and Kihara Models
Authors: Spurling T. H. , De Rocco A. G.
Published: December 2004

A series expansion for the second virial coefficient of the spherical shell potential is used to show that this model, in contrast to the Kihara model, does not inadvertently include terms which can represent contributions due to multipolar interactions.
Hydromagnetic Wake around a Nonconducting Sphere
Authors: Chow Chuen-Yen
Published: December 2004

Flow around a nonconducting sphere moving slowly through a current-carrying fluid along an arbitrary direction is considered. Standing eddies are found under certain conditions and a wake ahead of the sphere is possible.
Possibility of Ion-Wave Amplification in a Plasma
Authors: Schulz Michael
Published: December 2004

The ion-acoustic dispersion relation for a two-component plasma, calculated in the presence of intercomponent energy transfer but in the absence of ion-acoustic losses, exhibits amplification in this mode if the election gas is assumed to behave isothermally.
Turbulence of the Positive Column in a Large Longitudinal Magnetic Field
Authors: Woehler Karlheinz E.
Published: December 2004

At large longitudinal magnetic fields the positive column assumes a turbulent state due to helical instability. The correlation of potential fluctuation and current fluctuation at two probes as function of the distance and the density profile have been measured.
Time-Varying Weight Functions and the Convergence of Polynomial Expansions
Authors: Holway Lowell H.
Published: December 2004

Expansions are given for isotropic distribution functions in a series of polynomials orthogonal with respect to a time-dependent Maxwellian weight function. It is shown that the choice of the weight function can affect the rate of convergence or, indeed, whether the expansion will converge at all. For the case of the Fokker-Planck equation describing the relaxation of electrons in a Lorentz gas, the infinite matrix determining the time dependence of the expansion coefficients is diagonalized by an appropriate choice of the weight function. The equilibrium expansion of Kahalas and Kashian and Osipov's result for an initial Maxwellian are special cases of our more general formulation. An alternative expansion method is discussed which can be expected to converge for all realistic distribution functions. Applications to the theory of plane shock waves are suggested.
On Boltzmann Equation with Cutoff Potentials
Authors: Cercignani Carlo
Published: December 2004

After showing that the existence of a cutoff in the two-body interaction follows from consistency in the frame of assumptions upon which the Boltzmann equation is based, the collision operators for such cutoff potentials are studied in detail. It is proved that the essential properties required to build up a rigorous mathematical theory of the linearized Boltzmann equation are possessed by the collision with cutoff potentials. In particular, results of basic importance for existence, uniqueness, and approach to equilibrium are proved.
Solutions Illustrating the Decay of Dissipation Layers in Burgers' Nonlinear Diffusion Equation
Authors: Benton Edward R.
Published: December 2004

Two exact viscous and nonsteady solutions of Burgers' nonlinear diffusion equation are derived which show how sawtooth discontinuities or dissipation layers broaden and decay. One solution is in the ``physical space''; the other is a discrete spatial Fourier series. Spectral coefficients of the second solution satisfy (exactly) an infinite set of coupled nonlinear ordinary differential equations. Energetics of the two solutions are briefly discussed.
Two-Dimensional, Time-Independent Solutions for Plasma Moving through a Uniform Transverse Magnetic Field
Authors: Poukey James W.
Published: December 2004

If particle gyroradii and drift velocities are small in a collisionless plasma which is infinite and uniform in the direction of the straight magnetic field B, it may be shown in the time-independent case that particle densities and B are constant on any surface of constant electrostatic potential. Using the magnetohydrodynamic equation of motion, it follows that the particles move very nearly along these equipotential surfaces, and an expression for the charge density may be derived. From the resulting Poisson equation, solutions for plasma crossing a uniform B0 field may be obtained; collectively these solutions may appropriately be termed the ``double-vortex'' model from their drift velocity patterns.
Discontinuities in an Anisotropic Plasma
Authors: Lynn Y. M.
Published: December 2004

Chew-Goldberger-Low theory is used to investigate discontinuities in an anisotropic plasma. Average ion magnetic moment is assumed to be conserved. Transition solutions and their properties for compressive shocks, contact and rotational discontinuities are given.
Class of Exact Magnetohydrodynamic Solutions
Authors: O'Brien Vivian , Weinbaum Sheldon
Published: December 2004

Exact magnetohydrodynamic solutions for incompressible fluids, valid for all values of conductivity and viscosity, are found. These collinear magnetohydrodynamic fields have magnetic surfaces corresponding to stream surfaces.
Stability of a Dense Plasma Confined by a Rotating Magnetic Field
Authors: Troyon Francis
Published: December 2004

The stability of a dense plasma (negligible skin depth) confined by a rotating magnetic field which is parallel to the surface is analyzed for plane and cylindrical geometries. This analysis culminates in an integrodifferential equation for each mode of deformation. Specific properties of the plasma enter only through the normal acoustic impedance. The concept of average stability is introduced. Very general restrictions on the acoustic impedance of the plasma are introduced which allow the derivation of various stability criteria. These criteria are applied to different cases of interest. The plasma is described successively by a fluid model and a free particle model. Numerical estimates of the frequency needed to achive stability for each mode are given.
Radiation Losses from a Test Particle in a Plasma
Authors: McKenzie J. F.
Published: December 2004

A formula is derived for the average rate of energy loss suffered by a charged particle moving in a helical orbit in a homogeneous medium. In a cold, magnetized plasma it is shown that the Čerenkov excitation of the whistler and ion cyclotron waves depends critically on certain characteristic wave speeds relative to the component of the particle's velocity parallel to the magnetic field. The power spectrum of Čerenkov radiation exhibits sharp peaks not only at the frequencies of the lower and upper hybrid resonances but also at those frequencies at which the ray phase velocity equals the particle's velocity, v∥, parallel to the magnetic field. An intriguing feature of this radiation is that the more slowly the particle moves along the magnetic field, the greater is the emitted radiation; the power emitted in the whistler mode also becomes large when v∥ equals the group speed of those waves that are beamed along the magnetic field. By using a simple graphical construction one can readily locate those directions in which the angular distribution of synchrotron radiation is sharply peaked.
Interaction of an Electron Beam with a Collisionless Plasma
Authors: Carnevale M. , Crosignani B. , Engelmann F.
Published: December 2004

The growth of electrostatic wave excitation in a collisionless plasma, interacting with an electron beam of finite length, as well as the simultaneous modification of the beam are studied for weakly unstable situations. Using quasi-linear theory, explicit results as a function of space, of time, and of the plasma and beam parameters are obtained for the surface layer where the relaxation of the beam effectively takes place. The effect on the beam of both unstable modes and resonant stable modes of thermal excitation is considered.
Plasma Diagnostics using Electrostatic Probes under Short Mean Free Path Conditions
Authors: Weissman D. E. , Scharfman W. E. , Guthart H.
Published: December 2004

The properties of a medium pressure plasma were inferred from electrostatic probe measurements using the theory of Zakharova et al. The results were compared with microwave measurements and the agreement was within a factor of 3.
Bubble Dynamics on a Hot Surface
Authors: Skinner L. A.
Published: December 2004

A theory of surface nucleate boiling complying with recent evidence of significant heat extraction from the ebullition surface during bubble growth, but not presuming an evaporating liquid film at the bubble base.
Solution of the Born-Green-Yvon Equation for a High Density One-Component Plasma
Authors: Hirt C. W.
Published: December 2004

Recent Monte Carlo calculations of the radial distribution function of a one-component, classical, plasma are shown to be well approximated by solutions of the Born-Green-Yvon integral equation, almost up to densities where there is definite short range order. The Born-Green-Yvon solutions appear to be somewhat better than the corresponding solutions of the Percus-Yevick and convolution-hypernetted-chain equations. The Born-Green-Yvon equation is further shown to be related to the original Debye-Hückel equation for an ionic solution. It differs from the latter equation by accounting for more short range correlations, a feature that makes it more accurate at higher densities. The special methods used to obtain numerical solutions of the Born-Green-Yvon equation at high density are briefly discussed.
Cyclotron Wave Instabilities in a Plasma
Authors: Scharer J. E. , Trivelpiece A. W.
Published: December 2004

Transverse electromagnetic waves that propagate along a uniform magnetic field in an unbounded, thermally anisotropic plasma are investigated. The linearized Vlasov equation is solved to obtain the dispersion relation for the electron- and ion-cyclotron waves. This dispersion relation is used to determine the critical frequencies and wavenumbers below which the wave is unstable. The electron-cylotron wave is unstable for T⊥e > Tze. Numerical solutions for the growth and damping rates of the waves obtained from the dispersion relation show that the maximum growth rate occurs at a frequency slightly below the marginally stable frequency. For the ion-cyclotron wave, both ion and electron thermal anisotropy are included, and cold electrons are shown to have a stabilizing influence on an unstable ion-cyclotron wave; however, when the electrons are thermally anisotropic, they have a destabilizing effect for T⊥e > Tze.
Helical Configuration Produced in Gaseous Magnetoplasmas by the Gyro-Resonance Absorption of Microwaves
Authors: Cherrington B. E. , Goldstein L.
Published: December 2004

The nonuniform absorption of gyro-resonant microwave energy by an electron gas is used to produce the helical configuration in gaseous magnetoplasmas. This configuration is examined both theoretically and experimentally. Stability criteria for the existence of the helix and the dependence of the properties of the helix on the plasma parameters are derived from the two-fluid mangetohydrodynamic equations for electrons and ions. The experimental examination of the instability is accomplished by the use of a suitable diagnostic procedure using low power (≈ 50 μW), nonresonant microwave sensing signals. The detailed examination of the properties of the helical configuration verifies the theoretical predictions. Where it has been possible to measure the properties of the plasma discharge exactly, such as helix rotational frequency and discharge tube radius, excellent quantitative agreement between theory and experiment is found. Where it has only been possible to estimate the plasma parameters, such as electron temperature and longitudinal gradients, good qualitative agreement between theory and experiment is found.
Elastic Collisions in Simulating One-Dimensional Plasma Diodes on the Computer
Authors: Burger Peter
Published: December 2004

The inclusion of electron-neutral collisions in computer simulation calculations is demonstrated. Only one-dimensional fields are considered in diodes with plane-parallel symmetry. The method used is to change the velocities of particles in a random manner according to their probabilities of suffering a collision. The method is applied to the hard-sphere type of collisions between electrons and neutrals. Three examples are shown, and in two of them comparison between analytical and computer simulation results are possible. Reasonably good agreements are obtained. It is demonstrated that the inclusion of electron-neutral collisions into computer simulation procedures could be used for finding the damping effect of these collisions on the oscillatory behavior of unstable plasma diodes. With this method we can compute the large-signal, time-dependent characteristics of diodes at intermediate pressures in which the mean-free path is comparable to the diode distance.
Composition Dependence of the Thermal Diffusion Factor of the Xe–Ne System
Authors: Taylor William L. , Weissman Stanley
Published: December 2004

Due to inconsistencies in earlier data for αT for Xe–Ne mixtures, this system was reinvestigated. The present results show that one of the earlier sets of data is in error and that the composition dependence of αT agrees with theoretical expectations.
Invariant of the Higher-Order Chew-Goldberger-Low Theory
Authors: Davidson Ronald C.
Published: December 2004

In the context of the higher-order Chew-Goldberger-Low theory an expression for the magnetic moment invariant μj is obtained correct to first order in the expansion parameter.
Uniformly Valid Asymptotic Theory of Collisionless Electrostatic Probes
Authors: Bienkowski George
Published: December 2004

Extensions and corrections to Lam's theory of collisionless electrostatic probes are presented. A sheath is shown to exist for all finite potentials. The leading correction of O′(he/Rp)2/3 to the saturation current is determined.
Effects of a Density Gradient on the Magneto-Kerr Effect at the Boundary of a Collisional Plasma
Authors: Heckenberg N. R. , Robinson L. C. , Rothman G. P.
Published: December 2004

Results are presented of calculations showing the effects of collision frequency and surface density gradient on the polarization of microwaves reflected from a plasma surface. Experimental observations are compared with these results and estimates made of collision frequency and density gradient.
Fourier-Hermite Solutions of the Vlasov Equations in the Linearized Limit
Authors: Grant Frederick C. , Feix Marc R.
Published: December 2004

The properties of the Fourier-Hermite transformation of the one-dimensional Vlasov equation for the motion of electrons against a uniform positive neutralizing background are examined in the linearized limit. The general dispersion relation is presented for the transformed equations. Numerical and analytical results are given which show the recovery of Landau damping for Maxwell's distribution even though the corresponding eigenfrequencies are always real. An example of double streaming is treated to show the appearance of imaginary eigenfrequencies in the analysis. Introduction of a small number of collisions is shown to improve the long-term behavior. Nonlinear numerical results for the nearly cold plasma are shown to agree with the exact treatment of Kalman.
Anomalous Skin Effect in a Plasma
Authors: Weibel Erich S.
Published: December 2004

The theory of the skin effect in a plasma is developed for the case in which the relation between current and electric field is not local.
Stability of an Elastico-Viscous Liquid Film Flowing down an Inclined Plane
Authors: Lai Wei
Published: December 2004

The stability of a layer of elastico-viscous liquid (Oldroyd's liquid B) flowing down an inclined plane under the action of gravity is investigated. An eigenvalue problem governing the stability of the flow against wave formation is formulated and solved for small values of wave number. It is found that the presence of elasticity in the liquid lowers the value of the critical Reynolds number.
Penetrative Convective Instabilities
Authors: Rintel Lionel
Published: December 2004

An approximate method for finding the critical conditions for stability with respect to penetrative cellular perturbation is proposed. The method is tested by finding the critical conditions for stability of flow between counter-rotating cylinders and by comparing them with those obtained by more rigorous methods and by experiments. The same method is later applied for Bénard convection arising in a horizontal layer of fluid with constant unstable density gradient and penetrating into a layer of fluid with constant stable density gradient situated above the unstable layer. It is found that the classical rigid-free boundary solution corresponds to the limiting case of infinite stability on top of the unstable layer. For small stability on top the solutions have some of the features of Chandra's columnar perturbations and the build up of cumulus towers in the tropics. The critical value of the Rayleigh number in this case is found to be much smaller than that obtained by not taking penetration into account.
Growth of Turbulent Magnetic Fields
Authors: Kraichnan Robert H. , Nagarajan S.
Published: December 2004

The evolution of a weak, random initial magnetic field in a highly conducting, isotropically turbulent fluid is discussed with the aid of the exact expression for initial growth of the magnetic energy spectrum. Equipartition arguments, the vorticity analogy, and the known turbulence approximations all are found inadequate for predicting whether the magnetic energy eventually dies away or grows exponentially. This is true for any ratio of magnetic diffusivity λ to kinematic viscosity ν. The possibilities of eventual growth and eventual decay are therefore both admitted, and, for each, the shape of the magnetic-energy spectrum in the case λ » ν is estimated by simple dynamical arguments. If there is growth, it is concluded that the magnetic spectrum below the Ohmic cut-off eventually reaches equipartition with the kinetic-energy spectrum roughly in the fashion predicted by Biermann and Schlüter, with the principal exceptions that the spectrum of kinetic energy in the equipartition inertial range evolves to the form k−3/2 and that equipartition is maintained, with rapidly falling spectrum, through part of the Ohmic dissipation range. The evolution of the magnetic spectrum in the weak-field λ » ν regime is also computed numerically with a simplified transfer approximation suggested by the Lagrangian-history direct-interaction equations. This calculation turns out to yield an eventual very weak exponential growth of magnetic energy.
Current-Carrying Fluid Past a Nonconducting Sphere at Low Reynolds Number
Authors: Chow Chuen-Yen , Billings Dana F.
Published: December 2004

The problem of a nonconducting sphere moving slowly through a current-carrying, incompressible, viscous fluid is re-examined by taking fluid inertia into consideration. Stokes and Oseen expansions appropriate for flow near and far from the sphere are constructed and matched properly. The result shows that a standing eddy first appears behind the sphere at a Reynolds number Re = 24(3+4 Rh)−1, Rh being the magnetic pressure number. The effect of current is to hasten flow separation and to enlarge the reverse-flow region. The drag of the sphere is found to be 1 + Re (3 + Rh)/8 times the Stokes value.
Magneto-Fluid-Mechanic Channel Flow. II. Theory
Authors: Lykoudis P. S. , Brouillette E. C.
Published: December 2004

A semi-empirical theoretical analysis is presented describing the fully established turbulent channel flow of an electrically conducting fluid in the presence of a transverse and uniform magnetic field. The channel is assumed to be electrically insulated and of such geometry that two-dimensional flow prevails. The magnetic Reynolds number is assumed to be small so that the distortion of the externally imposed magnetic field is negligible. The paper establishes that a straightforward generalization of Prandtl's mixing length concept providing for the damping of the turbulent fluctuation is sufficient in predicting skin friction coefficients and velocity profiles over the whole range of Reynolds and Hartmann numbers for which experimental data are available.
New Approach to Plasma Turbulence
Authors: Galeev A. A.
Published: December 2004

An attempt is made to go beyond the framework of conventional weak turbulence theory. A simple dispersion equation for the stability of a steady turbulent state can be found by selective summation of higher-order terms from perturbation theory. The main contribution in the model to be considered here comes from particle motion in the turbulent electric field. In the limit of small wave amplitude, the usual equations of the weakly turbulent plasma can be obtained easily. The theory is applied to the drift-cyclotron instability of a nonuniform plasma to find the steady-state level of drift-cyclotron turbulence. The growth rate of the instability changes essentially at the nonlinear stage, so the usual dimensional arguments to find the turbulent diffusion coefficient cannot be applied using the linear description only.
Space-Charge Waves and the Isotropy of the Galactic Cosmic Ray Plasma
Authors: Lerche I.
Published: December 2004

Linearized equations are set up to describe the effect of an electrostatic wave on an anisotropic relativistic proton plasma embedded in a homogeneous magnetic field. It is assumed that a cold background plasma of protons and electrons co-exists with the relativistic plasma. It is shown that instability arises whenever the relativistic proton plasma is anisotropic in the right sense. It is also shown that the growth rates are physically significant for galactic cosmic rays and thus space-charge waves are a mechanism for producing some measure of isotropy in an anisotropic cosmic ray distribution. For instance, 10% anisotropy yields an e-folding time of about 103 years.
Motion and Decay of a Vortex Ring
Authors: Tung C. , Ting L.
Published: December 2004

In the classical inviscid theory of a vortex ring, the velocity at a point near the vortex ring becomes singular due to terms of r−1 and ln r where r is the shortest distance from the point to the vortex ring. Also the velocity of the vortex ring depends on the logarithm of the effective radius of the cross section of the vortex ring and is infinite for zero radius. The effect of the viscosity in the inner core of the vortex ring is now included and the inner viscous solution is matched with the classical inviscid solution of the outer region by the boundary layer technique. By means of the systematic matching, the singularities of r−1 and ln r in the classical inviscid theory is removed. By the requirement that the velocity at the center of the viscous core is finite, a unique and finite value is obtained for the velocity of the translation of the vortex ring which is decreasing with respect to time as − ln (ντ), where ν is the kinematic viscosity. From this analysis, the effective radius of the cross section of the vortex ring can be identified as 2(ντ)½. The variable τ is transformed from the time variable t by the relationship τ = ∫0t R(t′)dt′/R(t), where R(t) is the radius of the ring.
Stability of the Plane Incompressible Viscous Wall Jet Subjected to Small Disturbances
Authors: Chun D. H. , Schwarz W. H.
Published: December 2004

The hydrodynamic stability of a plane, two-dimensional, incompressible wall jet subjected to small disturbances was examined by a linearized theory. The critical Reynolds number Rδc was determined to be about 57. The eigenvalues and eigenfunctions were numerically calculated for neutral stability (ci = 0) as well as for several cases of amplification of the wave (ci > 0).
Boundary Layer Oscillations over a Resonant Surface
Authors: Rhines Peter B. , Mollo-Christensen Erik L.
Published: December 2004

The boundary layer is observed in low-speed flow over a dispersively-coupled system of acoustic resonators. It is found that oscillations in the laminar layer are strongly excited by this model of a passive, flexible wall. The ``geometry'' of this process differs from that expected with a real membrane, however, due to the details of the wall construction. A different set of laminar oscillations dominates the flow over the middle of the surface, producing turbulence in a manner controlled by the spanwise variations in the wall. The importance of the nature of this transition process to other shearing flows is discussed.