Maximum Beta Research Articles

An Empirical Investigation of the Cross‐Industry Variation in Mean Reversion of Australian Stock Betas

In this paper we empirically investigate the tendency for beta risk to mean‐revert across industries. Using a sample of Australian stocks over the ten‐year period 1989 to 1998, our key results are as follows. We generally observe evidence of a mean reversion tendency — in particular, this seems most appropriate for the Gold, Energy, Finance and Consumer industry groupings. Moreover, there is some evidence that the mean reversion of beta is different across industries. Furthermore, we see that the maximum mean reversion beta occurs for the Gold industry — a value of approximately 1.4 (1.6) for the OLS (Scholes‐Williams) beta analysis. On the other hand, the minimum mean reversion beta based on the ‘All Stocks’ OLS analysis occurs for Miscellaneous Industries with a value of 0.4, while a similar minimum mean reversion beta based on the Scholes‐Williams analysis occurs for the Consumer industry grouping.

Estimation of the radiation dose from radiotherapy for skinhaemangiomas in childhood: the ICTA software for epidemiology

Radium applicators and pure beta emitters have been widely used in the past totreat skin haemangioma in early childhood. A well defined relationship betweenthe low doses received from these applicators and radiation-induced cancersrequires accurate dosimetry. A human-based CT scan phantom has been used tosimulate every patient and treatment condition and then to calculate thesource-target distance when radium and pure beta applicators were used. Theeffective transmission factor φ(r) for the gamma spectrum emittedby the radium sources applied on the skin surface was modelled using MonteCarlo simulations. The well-known quantization approach was used to calculategamma doses delivered from radium applicators to various anatomical points.For 32P, 90Sr/90Y applicators and 90Y needles we have usedthe apparent exponential attenuation equation. The dose calculation algorithmwas integrated into the ICTA software (standing for a model that constructs anIndividualized phantom based on CT slices and Auxological data), which hasbeen developed for epidemiological studies of cohorts of patients who receivedradium and beta-treatments for skin haemangioma. The φ(r) valuesobtained for radium skin applicators are in good agreement with the availablevalues in the first 10 cm but higher at greater distances. Gamma doses can becalculated with this algorithm at 165 anatomical points throughout the body ofpatients treated with radium applicators. Lung heterogeneity and air crossedby the gamma rays are considered. Comparison of absorbed doses in water from a10 mg equivalent radium source simulated by ICTA with those measured at theRadiumhemmet, Karolinska Hospital (RAH) showed good agreement, but ICTAestimation of organ doses did not always correspond those estimated at theRAH. Beta doses from 32P, 90Sr/90Y applicators and 90Yneedles are calculated up to the maximum beta range (11 mm).

Involvement of the Proinflammatory Cytokines Tumor Necrosis Factor-α, IL-1β, and IL-6 But Not IL-8 in the Development of Heat Hyperalgesia: Effects on Heat-Evoked Calcitonin Gene-Related Peptide Release from Rat Skin

Proinflammatory cytokines contribute to the development of inflammatory and neuropathic pain and hyperalgesia in many in vivo models. The rat skin model was used to investigate the effects of proinflammatory cytokines on the basal and heat-evoked release of calcitonin gene-related peptide from nociceptors in vitro. In contrast to the excitatory effects of cytokines observed in vivo, none of the cytokines tested evoked any calcitonin gene-related peptide (CGRP) release at normal skin temperature of 32 degrees C. However, the cytokines IL-1beta, tumor necrosis factor (TNF)-alpha, and IL-6 but not IL-8 induced a pronounced and transient sensitization of the heat-evoked CGRP release from nociceptors in vitro. This heat sensitization was dose dependent, with EC(50) for IL-1 beta of 2.7 ng/ml and for TNF-alpha of 3.1 ng/ml. The maximum IL-1 beta effect reached almost 600% of the heat-evoked release, and the maximum TNF-alpha effect induced a rise in CGRP release of 350%. In contrast to IL-1 beta and TNF-alpha, IL-6 did not induce heat sensitization when applied alone but was only effective in the presence of soluble IL-6 receptor. This suggests a constitutive expression of signaling receptors for TNF and IL-1 beta and the signal transduction molecule gp130 but not IL-6 receptor or IL-8 receptor. Furthermore, the acute cytokine signaling observed in the present study was independent of transcriptional pathways because sensitization occurred on short latency in vitro and under conditions that excluded chemotactic accumulation of immune cells from blood vessels. Our results demonstrate that interleukins may play an important role in the initiation of heat hyperalgesia in inflammation and neuropathy.

Chordal force distribution determines systolic mitral leaflet configuration and severity of functional mitral regurgitation

OBJECTIVESThe purpose of this study was to investigate the impact of the chordae tendineae force distribution on systolic mitral leaflet geometry and mitral valve competence invitro.BACKGROUNDFunctional mitral regurgitation is caused by changes in several elements of the valve apparatus. Interaction among these have to comply with the chordal forcedistribution defined by the chordal coapting forces (FC) created by the transmitral pressure difference, which close the leaflets and the chordal tethering forces(FT) pulling the leaflets apart.METHODSPorcine mitral valves (n = 5) were mounted in a left ventricular model where leading edge chordal forces measured by dedicated miniature force transducers werecontrolled by changing left ventricular pressure and papillary muscle position. Chordae geometry and occlusional leaflet area (OLA) needed to cover the leaflet orifice for a givenleaflet configuration were determined by two-dimensional echo and reconstructed three-dimensionally. Occlusional leaflet area was used as expression for incomplete leafletcoaptation. Regurgitant fraction (RF) was measured with an electromagnetic flowmeter.RESULTSMixed procedure statistics revealed a linear correlation between the sum of the chordal net forces, ∑[FC−FT]s, and OLA with regression coefficient (minimum − maximum) beta = −115 to −65 [mm2/N]; p< 0.001 and RF (beta = −0.06 to −0.01 [%/N]; p < 0.001). Increasing FTby papillary muscle malalignment restrictedleaflet mobility, resulting in a tented leaflet configuration due to an apical and posterior shift of the coaptation line. Anterior leaflet coapting forces increased due to mitralleaflet remodeling, which generated a nonuniform regurgitant orifice area.CONCLUSIONSAltered chordal force distribution caused functional mitral regurgitation based on tented leaflet configuration as observed clinically.

188Re-Direct Labeling of Monoclonal Antibodies for Radioimmunotherapy of Solid Tumors: Biodistribution, Normal Organ Dosimetry, and Toxicology

The increased interest in the availability of radionuclides for therapy has resulted from the recent success and potential importance of radiolabeled antibodies for both diagnosis and therapy. There is a widespread interest in the availability of 188Re for various therapeutic applications, particularly for attachment to tumor-specific monoclonal antibodies for radioimmunotherapy. This review provides a perspective of 188Re-direct labeled MAbs for radioimmunotherapy of solid tumors, normal organ biodistribution, absorbed radiation doses to normal organs and tumors, and the toxicity to bone marrow and normal tissues. Methods for calculation of mean absorbed radiation doses to the whole body, various normal organs, and tumors have been developed using source-organ residence times and the methods developed by the Medical Internal Radiation Dose (MIRD) committee. The toxicity for 188Re-labeled antibodies is predominantly hematopoietic, with platelets and white blood cells being most sensitive to the effects of radiation. Rhenium-188 would be the isotope of choice for radioimmunotherapeutic applications because of cost, availability, and favorable radiation characteristics. Rhenium-188 has a half-life of 16.9 h and maximum beta energy of 2.118 MeV. This isotope is particularly attractive because it can be supplied conveniently from 188W/ 188Re-radionuclide generator system.

SERUM S100 beta AS A PREDICTOR OF NEUROLOGIC AND NEUROCOGNITIVE OUTCOMES AFTER CARDIAC SURGERY

S65 Introduction: The glial protein, S100 beta, has been reported to be a marker of neurologic injury in numerous clinical settings [1]. Recently, reports have described serum S100 beta elevations after cardiac surgery, suggesting its potential role as a marker for cardiac surgery-associated neurologic injury [2]. The purpose of this study was to examine the relationship between serum S100 beta and neurologic and neurocognitive outcomes after coronary artery bypass graft surgery (CABG). Methods: Under midazolam/fentanyl anesthesia, 135 patients having CABG employing CPB (non-pulsatile, alpha-stat pH, membrane oxygenator, arterial line filter, temp 32-36 [degree sign]C) were studied. Serum S100 beta was measured pre-CPB, end-CPB, then 150 and 270 min after cross-clamp release, with the maximal S100 beta level used for analysis. A battery of cognitive tests was performed preoperatively and 6 weeks postoperatively with neurologic testing performed preop and at discharge. A neurocognitive deficit was determined by the cognitive impairment index (CI index), calculated as the average % decline in each of the cognitive tests. Neurologic testing was evaluated as a change in the Western perioperative neurologic score (WPNS Delta). The maximum S100 beta was compared to the outcomes using linear regression (univariate. then multivariable, adjusting for age). Results: S100 beta showed a significant univariate association with neurocognitive and neurologic outcomes. The multivariable model (accounting for age) remained significant for neurologic outcome, but less significant for the neurocognitive outcome. (Table 1 and Figure 1)Table 1Figure 1Discussion: This is the first study examining the S100 beta association to neurocognitive and neurologic outcomes that is large enough to control for possible confounding variables, such as age [3].

Neoclassical islands on COMPASS-D

Neoclassical magnetic islands are observed to limit the achievable beta in COMPASS-D low collisionality single null divertor tokamak plasmas with ITER-like geometry (R0=0.56 m, B0=1.2 T, Ip=120-180 kA, k=1.6, epsilon =0.3). The limiting beta is typically well below that expected from ideal instabilities with maximum beta N in the range of 1.6 to 2.1. The plasma is heated with up to 1.8 MW of 60 GHz electron cyclotron resonance heating (ECRH) at the second harmonic with X mode polarization. The time history of the measured island width is compared with the predictions of neoclassical tearing mode theory, with good agreement between theory and experiment. The measured islands have a threshold width below which the mode will not grow. The density scaling of the point of onset of the measured instabilities is compared with two theories that predict a threshold island width for the onset of neoclassical tearing modes. Applied resonant helical error fields are used to induce islands in collisionality regimes wherein the neoclassical islands do not occur naturally, allowing the study of the behaviour of neoclassical tearing modes in this regime. The critical beta for the onset of neoclassical tearing modes is seen to be ~3 times higher in the naturally stable region. This observation is compared with the predictions of both threshold theories. A simple expression for the q scaling of the maximum achievable beta N in the presence of neoclassical tearing modes is derived on the basis of the assumption of a maximum allowable island width. The predicted q scaling of this beta limit is compared with data from a q scan, and the results are in good agreement

Beta particle attenuation characteristics of CaSO4.

The beta particle mass attenuation coefficient for CaSO4 in a Teflon matrix has been estimated by two methods: an experiment using collimated sources and a collimated gas flow proportional counter and simulations using the EGS4 Monte Carlo code. The attenuation coefficient has been cast in the general form of mu/rho = aE(-b), where E is the maximum beta particle energy and a and b are fitting parameters. The a and b parameters are given as a function of the atomic number of the material.

Symmetric pH dependence of buffering power in giant fused cells from frog kidney proximal tubule

This study measures the intrinsic buffering power (beta(i)) of giant fused cells from the proximal kidney tubule of the frog (Rana ridibunda) as a function of intracellular pH (pHi). We monitored pHi and transmembrane potential difference during acid or alkaline cell loading, achieved by removal of NH4Cl-containing solutions or CO2-HCO3(-)-equilibrated solutions, respectively, in the absence of extracellular Na+. Data were well fit by the equation for a single, monoprotic buffer with a maximum beta(i) at a pHi of 7.39 +/- 0.06 and a total buffer concentration of 30.7 +/- 1.6 mM (means +/- SD). From pHi measurements obtained during CO2-HCO3- exposure, we also calculated the buffering power afforded by the CO2-HCO3- pair, and we show its increasing contribution to total buffering power at increasing PCO2 and pHi. To our knowledge, this is the first report of a cell type in which intrinsic cell buffers can be adequately approximated as a single monoprotic buffer with a negative logarithm of apparent dissociation constant in the normal physiological range and essentially symmetric dependence on pHi in both acid and alkaline ranges.

High beta tokamak operation in DIII-D limited at low density/collisionality by resistive tearing modes

The maximum operational high beta in single-null divertor (SND) long pulse tokamak discharges in the DIII-D tokamak with a cross-sectional shape similar to the proposed International Thermonuclear Experimental Reactor (ITER) device is found to be limited by the onset of resistive instabilities that have the characteristics of neoclassically destabilized tearing modes. There is a soft limit due to the onset of an m/n=3/2 rotating tearing mode that saturates at low amplitude and a hard limit at slightly higher beta due to the onset of an m/n=2/1 rotating tearing mode that grows, slows down and locks. By operating at higher density and thus collisionality, the practical beta limit due to resistive tearing modes approaches the ideal magnetohydrodynamic (MHD) limit

Empirical Expressions for Beta Ray Point Source Dose Distributions

Loevinger's well-known analytic expression, plus a constant 'end-of-'range' term, has been fitted to dose distributions, calculated by Monte Carlo methods, from point sources of beta rays in an infinite water medium. Optimum parameters are given for fits to 60 individual nuclides. Addition of the end-of-range term extends the range of good fits from about 0.4Rmax to 0.65Rmax, where Rmax is the maximum beta range. For low energy emitters or those having conversion electrons, the fit is often poor at distances, rmin, less than a few mg.cm-2. The RMA error of the fit at 25 points between rmin and 0.65Rmax ranges from 1.6 to 3.3% for 41 single-component spectra, and from 1.9 to 6% for 19 multi-component spectra. This is considerably smaller than is usually assumed for Loevinger's expression or given by nearly all other expressions for point source distributions. Values of the parameters are given as functions of maximum beta energy.

257 - Radiation yield and maximum beta range of spilled radionuclide Sr-89

257 - Radiation yield and maximum beta range of spilled radionuclide Sr-89

The varying influences of gas and electron temperatures on the rates of electron attachment to some selected molecules

The rate coefficients, beta , for the attachment reactions of electrons with CCl4, CHCl3, SF6 and C7F14 have been measured in a flowing afterglow/Langmuir probe (FALP) apparatus within the range of electron temperature, Tc, from 300 to about 4000 K at a carrier gas temperature, Tg, of 300 K and for the SF6 reaction additionally at a Tg of 540 K. The above gases were chosen in the light of the results obtained from previous FALP studies under truly thermalized conditions, i.e. for Tc=Tg=T. These previous experiments showed that the beta for the CCl4 reaction (product Cl-) and SF6 reaction (products SF6-, direct attachment, and SF5-, dissociative attachment, becoming increasingly important with increasing T) were close to the maximum value beta max, and that the beta for both the CHCl3 dissociative attachment reaction and the C7F14 direct attachment reaction increased with increasing T indicating the presence of activation energy barriers in these reactions. Now the present studies indicate that (i) the beta for both CCl4 and the SF6 reactions decrease with increasing Tc at a rate predicted by s-wave capture theory, and that the SF5- product of the SF6 reaction becomes increasingly important with increasing Tc, (ii) the beta for both the CHCl3 and the C7F14 reactions increase with increasing Tc, but a much greater increase of Tc than T is required to produce a given increase in beta . To explain these experimental observations, a simple model of these attachment reactions has been constructed which is consistent with the experimental data, based on the notion that the energy of the incoming electron is distributed amongst the accessible vibrational states of the molecules, and that this vibrational excitation promotes these particular attachment reactions. A careful analysis of our data indicates that the endothermicity of the dissociative attachment reaction of SF6 producing SF5- is close to 0.12 eV which is consistent with the available thermochemical data.

Wall stabilization of high beta plasmas in DIII-D

Detailed analysis of recent high beta discharges in the DIII-D [Plasma Physics Controlled Nuclear Fusion Research, 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. I, p. 159] tokamak demonstrates that the resistive vacuum vessel can provide stabilization of low n magnetohydrodynamic (MHD) modes. The experimental beta values reaching up to βT=12.6% are more than 30% larger than the maximum stable beta calculated with no wall stabilization. Plasma rotation is essential for stabilization. When the plasma rotation slows sufficiently, unstable modes with the characteristics of the predicted ‘‘resistive wall’’ mode are observed. Through slowing of the plasma rotation between the q=2 and q=3 surfaces with the application of a nonaxisymmetric field, it has been determined that the rotation at the outer rational surfaces is most important, and that the critical rotation frequency is of the order of Ω/2π=1 kHz.

Characterization and calibration of a large area beta scintillation detector for determination of Sr-90

A large area beta scintillation detector has been developed which is currently capable of determining Sr-90/Y-90 contamination in surficial soils. The detector system employs scintillating fiber optic arrays, with active dimensions approximately 15 cm wide by 100 cm long, both ends of which are coupled to multiple photomultiplier tubes (PMTs). Electronic processing includes coincidence requirements to optimize sensitivity and selectivity for the 2.28 MeV (maximum) beta particle from Y-90. Low energy beta particles and gamma rays are discriminated against using double ended and multi-layer coincidence requirements. The detector system is personal-computer-software controlled and data restored in a format compatible with standard database software for ease of final data reduction. Experimental calibration studies have shown a linear response for Sr-90/Y-90 soil concentrations from 12 to over 500 pCi/g and a discrimination factor of 50 to 1 versus Cs-137.

Stability of high beta tokamak plasmas*

Stability at high beta (the ratio of plasma pressure to magnetic field pressure) is an important requirement for a compact, economically attractive fusion reactor. It is also important in present large tokamak experiments, where the best performance is now often limited by instabilities rather than by energy transport. The past decade has seen major advances in our understanding of the stability of high beta tokamak plasmas, as well as in the achievement of high values of beta. Ideal magnetohydrodynamic (MHD) theory has been remarkably successful in predicting the stability limits, and the scaling of maximum stable beta with the normalized plasma current predicted by Troyon and others has been confirmed in many experiments, yielding a limit βmax≊3.5 (%-m-T/MA) I/aB (where I is the plasma current, a is the minor radius, and B is the toroidal field). The instabilities which are predicted to limit beta have been observed experimentally, in good agreement with theoretical predictions, including long-wavelength kink modes and short-wavelength ballooning instabilities. Advances in understanding of tokamak stability have opened several paths to higher values of beta. The use of strong discharge shaping, approaching the limits of axisymmetric stability, has allowed beta values as high as 12% to be reached in agreement with Troyon scaling. Recent experimental results and ideal MHD modeling have shown that the beta limit depends on the form of the pressure and current density profiles, and modification of the current density to create a centrally peaked profile has allowed beta values up to 6I/aB to be achieved experimentally. Recent experiments have also begun to explore both local and global access to the predicted second stable regime for ballooning modes, with the potential for very high values of β/(I/aB). Preliminary experimental investigations of wall stabilization and radio-frequency (RF) current profile control hold the promise of further improvements in beta through passive and active control of instabilities. The developing understanding of high beta stability and the application of this understanding to present experiments and future fusion devices hold the potential for production of stable, steady state plasmas at high beta with good confinement.

The heliospheric plasma sheet

High‐resolution magnetic field and plasma data gathered by ISEE 3/ICE during several sector boundary crossings are used to investigate the narrow heliospheric current sheet (≈ 3 × 10³ km to 104 km thick), together with the heliospheric plasma sheet in which it is embedded. The heliospheric plasma sheet region is identified by a significantly enhanced plasma beta caused by density enhancements and diminished magnetic field strength and is about 20 to 30 times the thickness of the current sheet. The thickness of the heliospheric plasma sheet is found to increase exponentially with its average proton density. The heliospheric current sheet is often displaced to one edge or the other of the heliospheric plasma sheet. Further, the point of maximum plasma beta in the plasma sheet, where the magnetic field strength is at a broad local minimum, is not colocated with the heliospheric current sheet. Within the plasma sheet, changes in the magnetic pressure are balanced by corresponding changes in the plasma thermal pressure as expected for a convected solar wind feature. In addition, observations show small pressure differences between the regions upstream and downstream of the plasma sheet, which are interpreted as causing the plasma sheet to move across the spacecraft.

Effect of toroidal flow on the stability of a diffuse high-beta tokamak

The effect of toroidal flow on the stability of a diffuse current model tokamak to external kink modes is examined. For a high-β tokamak it is shown that, to leading order in the inverse aspect ratio, the effect of toroidal flow is simply to modify the kinetic pressure by adding to it the flow pressure. Then the limit on the plasma beta in the presence of toroidal flow can be obtained from the results for a static plasma. It is shown that, for a given safety factor profile and shape of the plasma boundary, the maximum plasma beta for stability to external kink modes is always lower in the presence of flow compared to a static configuration. This is true for any arbitrary profile of the toroidal flow velocity.

Ballooning-mode stability of shaped high- beta tokamaks.

The effect of elongation and triangularity of flux surfaces on the local and global stability of high-n ideal ballooning modes in a high-\ensuremath{\beta} tokamak are investigated. The equilibrium surfaces are obtained by a numerical solution of the Grad-Shafranov equation using an efficient algorithm based on a generalized variational technique. A marginal stability analysis of these surfaces is carried out in which the equilibrium shift, elongation, triangularity, and their radial variations are taken into account. The influence of the cylindrical safety factor (${\mathit{q}}_{\mathit{c}}$), as well as the variations in the shape of \ensuremath{\beta} and q profiles, on the maximum attainable beta value (${\mathrm{\ensuremath{\beta}}}_{\mathit{c}}$) are also considered. Detailed numerical results, over a wide range of parameter space, show that the effect of boundary elongation ${\mathrm{\ensuremath{\kappa}}}_{\mathit{a}}$ is always stabilizing while the effect of boundary triangularity ${\mathrm{\ensuremath{\delta}}}_{\mathit{a}}$ depends on the values of ${\mathrm{\ensuremath{\kappa}}}_{\mathit{a}}$ and ${\mathit{q}}_{\mathit{c}}$. It is found that for elongated cross section (${\mathrm{\ensuremath{\kappa}}}_{\mathit{a}}$\ensuremath{\ge}1.6), the effect of ${\mathrm{\ensuremath{\delta}}}_{\mathit{a}}$ is always stabilizing. We present an alternative scaling law that effectively captures these features of the shape parameter dependences. For a JET (Joint European Torus) -type plasma, broad \ensuremath{\beta} profiles and q profiles that tend to be flat in the interior are found to be favorable for achieving a high ${\mathrm{\ensuremath{\beta}}}_{\mathit{c}}$ value.

Dynamical scaling for spinodal decomposition - a small-angle neutron scattering study of porous Vycor glass with fractal properties

A model is developed for analysing small-angle scattering data for systems undergoing spinodal decomposition. This model is expressed as an integration of a series of Fourier components of the density fluctuation A( beta ) sin( beta r+ phi ) based on Cahn's linear theory of spinodal decomposition. Hence the time evolution of the characteristic crossover phenomenon and the width of the crossover of the scaling function of the structure factor are predicted to be associated with the maximum spinodal wavenumber beta m and the correlation length xi m, respectively. The rough surfaces and fractal network of porous materials are also considered in the model. Results of calculations based on this model are compared with small-angle neutron scattering data for dry and wet porous Vycor glass and give an excellent agreement.