Group B Streptococcus Surface Protein[beta]: Structural Characterization of a Complement Factor H?Bi
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Xu, Xin↗
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Thermal Emission Spectroscopy of 1 Ceres: Evidence for Olivine
Thermal emission spectra of the largest asteroid 1 Ceres obtained from the Kuiper Airborne Observatory display features that may provide information on its surface mineralogy. A plot of the Ceres spectrum (calibrated using alpha Boo as a standard) divided by a standard thermal model (STM) is shown. Also shown is the emissivity spectrum deduced from reflectivity measurements for olivine grains <5 microns in diameter. The general shape of the Ceres and the olivine curves agree in essential details, such as the maxima from 8 to 12 microns, the minimum between 12 and 14 microns, the broad peak near 17.5 micron, and the slope beyond 22 micron. (Use of the 10 to 15-micron grain reflectivities provides a better match to the 12- to 14-micron dip. We used a value of unity for beta, the beaming factor associated with small-scale surface roughness in our STM. Adjustment of beta to a lower value raises the long-wavelength side of the Ceres spectrum, providing an even better match to the olivine curve.) The emissivity behavior roughly matches the emission coefficients which were calculated for olivine particles with a particle radius of 3 microns. Their calculations show not only the negative slope from 23 to 25 pm, but a continued decrease past 30 micron. The Ceres emissivity is thus similar to that of small olivine grains from 8 to 30 micron, but olivine's emissivity is lower from 5 to 8 pm.
Witteborn, F. C.↗
On the electromagnetic fields, Poynting vector, and peak power radiated by lightning return strokes
The initial radiation fields, Poynting vector, and total electromagnetic power that a vertical return stroke radiates into the upper half space have been computed when the speed of the stroke, nu, is a significant fraction of the speed of light, c, assuming that at large distances and early times the source is an infinitesimal dipole. The initial current is also assumed to satisfy the transmission-line model with a constant nu and to be perpendicular to an infinite, perfectly conducting ground. The effect of a large nu is to increase the radiation fields by a factor of (1-beta-sq cos-sq theta) exp -1, where beta = nu/c and theta is measured from the vertical, and the Poynting vector by a factor of (1-beta-sq cos-sq theta) exp -2.
Krider, E. P.↗
Modelling atmospheric aerosol backscatter at CO2 laser wavelengths. I - Aerosol properties, modeling techniques, and associated problems. II - Modeled values in the atmosphere. III - Effects of changes in wavelength and ambient conditions
The various methods of calculating the atmospheric aerosol backscattering function, beta(CO2), both from measured aerosol characteristics and from optical measurements made at other wavelengths, are discussed in detail, with limits placed on their accuracy. The most significant factor in determining beta(CO2) is found to be the aerosol size distribution and concentration; this should be known accurately for particle radii up to at least 1 micron for stratospheric particles and 5 microns for tropospheric particles. Results are then presented from the modeling of the aerosol backscattering function at a wavelength of 10.6 microns in the lowest 20 km of the atmosphere. It is found that beta(CO2) varies from 10 to the -6th per m per sr in the planetary boundary layer to less than 10 to the -11th per m per sr in the stratosphere. It is next shown that, with the exception of (NH4)2SO4-containing aerosols, whose size distributions have relatively large numbers of small particles, the variation of backscattering with CO2 wavelength is less than a factor of approximately 3. For such (NH4)2SO4 aerosol distributions, however, the variation of backscatter function with CO2 wavelengths between 9.1 and 11.1 microns may reach one order of magnitude.
Kent, G.S.↗
Forbidden Mass Ranges for Shower Meteoroids
Burns et al. (1979) use the parameter beta to describe the ratio of radiation pressure to gravity for a particle in the Solar System. The central potential that these particles experience is effectively reduced by a factor of (1- beta ), which in turn lowers the escape velocity. Burns et al. (1979) derived a simple expression for the value of beta at which particles ejected from a comet follow parabolic orbits and thus leave the Solar System; we expand on this to derive an expression for critical beta values that takes ejection velocity into account, assuming geometric optics. We use our expression to compute the critical value and corresponding mass for cometary ejecta leading, trailing, and following the parent comet's nucleus for 10 major meteor showers. Finally, we numerically solve for critical beta values in the case of non-geometric optics. These values determine the mass regimes within which meteoroids are ejected from the Solar System and therefore cannot contribute to meteor showers.
Moorhead, Althea V.↗
Advances in the steady-state hybrid regime in DIII-D – a fully non-inductive, ELM-suppressed scenario for ITER
Here, the hybrid regime with beta, collisionality, safety factor and plasma shape relevant to the ITER steady-state mission has been successfully integrated with ELM suppression by applying an odd parity n=3 resonant magnetic perturbation (RMP). Fully non-inductive hybrids in the DIII-D tokamak with high beta (< β> ≤ 2.8%) and high confinement (H 98y2 ≤ 1.4) in the ITER similar shape have achieved zero surface loop voltage for up to two current relaxation times using efficient central current drive from ECCD and NBCD. The n=3 RMP causes surprisingly little increase in thermal transport during ELM suppression. Poloidal magnetic flux pumping in hybrid plasmas maintains q above 1 without loss of current drive efficiency, except that experiments show that extremely peaked ECCD profiles can create sawteeth. During ECCD, Alfvén eigenmode (AE) activity is replaced by a more benign fishbone-like mode, reducing anomalous beam ion diffusion by a factor of 2. While the electron and ion thermal diffusivities substantially increase with higher ECCD power, the loss of confinement can be offset by the decreased fast ion transport resulting from AE suppression. Extrapolations from DIII-D along a dimensionless parameter scaling path as well as those using self-consistent theory-based modeling show that these ELM-suppressed, fully non-inductive hybrids can achieve the Q fus = 5 ITER steady-state mission.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Search for neutrino transitions to sterile states using an intense beta source
The results of beta spectrum calculations for two {sup 144}Pr decay branches are presented, which are of interest for reconstructing the spectrum of antineutrinos from the {sup 144}Ce–{sup 144}Pr source to be used in the SOX experiment on the search for sterile neutrinos. The main factors affecting the beta spectrum are analyzed, their calculation methods are given, and calculations are compared with experiment.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Factorization and resummation of QED radiative corrections for neutron beta decay
Details of the two-loop analysis of long-distance QED radiative corrections to neutron beta decay are presented. Explicit expressions are given for hard, jet, and soft functions appearing in the factorization formula that describes the limit of small electron mass and large electron energy. Numerical enhancements from the infrared region are resummed using renormalization group methods. Power corrections, cancellation of singularities in the small-mass expansion, renormalization scheme dependence, and bound-state effects are also discussed. These results provide the most precise determination of long-distance radiative corrections to neutron beta decay and impact the determination of |𝑉 𝑢𝑑 | from the measured neutron lifetime and thus set a target for uncertainty reductions in the experimental and short-distance inputs.
Beta decay↗
Advanced surrogate model for electron-scale turbulence in tokamak pedestals
We derive an advanced surrogate model for predicting turbulent transport at the edge of tokamaks driven by electron temperature gradient (ETG) modes. Our derivation is based on a recently developed sensitivity-driven sparse grid interpolation approach for uncertainty quantification and sensitivity analysis at scale, which informs the set of parameters that define the surrogate model as a scaling law. Our model reveals that ETG-driven electron heat flux is influenced by the safety factor q, electron beta β e and normalized electron Debye length λ D , in addition to well-established parameters such as the electron temperature and density gradients. To assess the trustworthiness of our model's predictions beyond training, we compute prediction intervals using bootstrapping. The surrogate model's predictive power is tested across a wide range of parameter values, including within-distribution testing parameters (to verify our model) as well as out-of-bounds and out-of-distribution testing (to validate the proposed model). Overall, validation efforts show that our model competes well with, or can even outperform, existing scaling laws in predicting ETG-driven transport.
fusion plasma↗
Beam emittance preservation using Gaussian density ramps in a beam-driven plasma wakefield accelerator
A current challenge that is facing the plasma wakefield accelerator (PWFA) community is transverse beam emittance preservation. This can be achieved by balancing the natural divergence of the beam against the strong focusing force provided by the PWFA plasma source in a scheme referred to as beam matching. One method to accomplish beam matching is through the gradual focusing of a beam with a plasma density ramp leading into the bulk plasma. Here, the beam dynamics in a Gaussian plasma density ramp are considered, and an empirical formula is identified that gives the ramp length and beam vacuum waist location needed to achieve near-perfect matching. The method uses only the beam vacuum waist beta function as an input. Numerical studies show that the Gaussian ramp focusing formula is robust for beta function demagnification factors spanning more than an order of magnitude with experimentally favourable tolerances for future PWFA research facilities. This article is part of the Theo Murphy meeting issue ‘Directions in particle beam-driven plasma wakefield acceleration’.
43 PARTICLE ACCELERATORS↗
Streamer Brightness Boundary
Flow tubes adjacent to closed magnetic field lines on the boundaries of streamers can have spreading factors which change rapidly with height. Numerical models in this thin layer are subject to uncertainties. Here we use an analytic model of magnetically closed and adjacent open regions to analyze the spreading factor close to the closed field lines. The model is based on the one-temperature, isothermal flow model of Pneuman (1968), extended to calculate spreading factors and plasma beta, and to better explain streamer evolution with increasing temperature.
Suess, S. T.↗
Protein Crystal Growth Dynamics and Impurity Incorporation
The general concepts and theories of crystal growth are proven to work for biomolecular crystallization. This allowed us to extract basic parameters controlling growth kinetics - free surface energy, alpha, and kinetic coefficient, beta, for steps. Surface energy per molecular site in thermal units, alpha(omega)(sup 2/3)/kT approx. = 1, is close to the one for inorganic crystals in solution (omega is the specific molecular volume, T is the temperature). Entropic restrictions on incorporation of biomolecules into the lattice reduce the incorporation rate, beta, by a factor of 10(exp 2) - 10(exp 3) relative to inorganic crystals. A dehydration barrier of approx. 18kcal/mol may explain approx. 10(exp -6) times difference between frequencies of adding a molecule to the lattice and Brownian attempts to do so. The latter was obtained from AFM measurements of step and kink growth rates on orthorhombic lysozyme. Protein and many inorganic crystals typically do not belong to the Kossel type, thus requiring a theory to account for inequivalent molecular positions within its unit cell. Orthorhombic lysozyme will serve as an example of how to develop such a theory. Factors deteriorating crystal quality - stress and strain, mosaicity, molecular disorder - will be reviewed with emphasis on impurities. Dimers in ferritin and lysozyme and acetylated lysozyme, are microheterogeneous i.e. nearly isomorphic impurities that are shown to be preferentially trapped by tetragonal lysozyme and ferritin crystals, respectively. The distribution coefficient, K defined as a ratio of the (impurity/protein) ratios in crystal and in solution is a measure of trapping. For acetylated lysoyzme, K = 2.15 or, 3.42 for differently acetylated forms, is independent of both the impurity and the crystallizing protein concentration. The reason is that impurity flux to the surface is constant while the growth rate rises with supersaturation. About 3 times lower dimer concentration in space grown ferritin and lysozyme crystals might be examples explaining higher quality of the space grown protein crystal. Depletion of solution with respect to isomorphic impurities around a growing crystal may be K times deeper than with respect to the crystallizing protein.
Chernov, Alex A.↗
Comparison of fluence-rate determination techniques for the Advanced Test Reactor-Critical Facility
The Advanced Test Reactor (ATR) at the Idaho National Laboratory (INL) is a unique, water-cooled, high-flux test reactor capable of performing tests prototypical of PWR operating conditions. The design and safe operation of experiments in ATR is aided by the operation of the ATR-Critical Facility (ATR-C), a lower-power reactor with the same size and geometry of the ATR. Short, low-power irradiations at the ATR-C are used to study the effects of control devices and test assemblies on the overall power distribution of various core loadings and to compare calculated data for reactor models. A technique was developed at INL to measure fission rates in fuel plate assembly reactors utilizing small, enriched uranium-aluminum (U-Al) alloy monitors, and to support ATR-C irradiations for forty years. Several hundred monitor wires placed throughout the reactor provide fine spatial resolution of the fission rates. A direct correlation exists between the fission rates of the U-Al monitors and the immediately adjacent reactor region. Extensive calibration was previously performed to determine the conversion factor for beta-particle activity of the irradiated U-Al monitors. The fission rate in the U-Al monitors can thus be determined by measuring the beta-particle decay of fission-products following irradiation of the monitors. The American Society for Testing and Materials (ASTM International) has established a standard practice for determining neutron fluence rate by radioactivation of depleted uranium. The ASTM standard practice also measures the concentration of fission-products in the uranium monitors. Rather than measuring the beta-particle decay from fission-products, the decay rate of fission-products is determined by gamma-ray spectroscopy. The feasibility of the ASTM standard practice was investigated for ATR-C irradiations and compared to the present method. The need to analyze hundreds of samples for each irradiation posed several challenges. Therefore, practical considerations such as expected fluence-rates, sample activity, and counting-time were compared between the two methods and the expected sources of error for each method were investigated.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Europium and samarium separation using ion exchange between molten salts and beta“-alumina
Here, a new approach to separating europium and samarium using ion exchange reactions between molten salts and a solid electrolyte, beta"-alumina, has been demonstrated. Separations were achieved by both ion exchange of europium and samarium into and out of beta"-alumina. A small separation factor of 1.07 was achieved from the ion exchange of europium into beta"-alumina. A much larger separation was achieved from ion exchange of europium out of beta"-alumina, with noticeable dependencies on the molten salt and experimental parameters (temperature, atmosphere, etc.) used. The highest separation factor achieved was greater than 30. However, the europium extraction efficiency was low. The highest europium extraction efficiency achieved was 51.8% ± 2.6 with a separation factor of 4.70 ± 0.46. The selective ion exchange of europium out of the beta"-alumina material is achieved based upon the higher conductivity of Eu 2+ compared to Ln 3+ (Ln = Eu, Sm) species also present in the beta"-alumina.
36 MATERIALS SCIENCE↗
Vascular endothelial growth factor receptor-1 (FLT1) interactions with amyloid-beta in Alzheimer’s disease: A putative biomarker of amyloid-induced vascular damage
We have identified FLT1 as a protein that changes during Alzheimer's disease (AD) whereby higher brain protein levels are associated with more amyloid, more tau, and faster longitudinal cognitive decline. Given FLT1's role in angiogenesis and immune activation, we hypothesized that FLT1 is upregulated in response to amyloid pathology, driving a vascular-immune cascade resulting in neurodegeneration and cognitive decline. We sought to determine (1) if in vivo FLT1 levels (CSF and plasma) associate with biomarkers of AD neuropathology or differ between diagnostic staging in an aged cohort enriched for early disease, and (2) whether FLT1 expression interacts with amyloid on downstream outcomes, such as phosphorylated tau levels and cognitive performance. Additionally, we sought to replicate FLT1 interactions in the brain. The results showed that higher levels of FLT1 in CSF and post-mortem brain tissue related to increased tau, particularly among amyloid positive individuals. These analyses help clarify the potential utility of FLT1 as a biomarker among individuals with evidence of brain amyloidosis.
60 APPLIED LIFE SCIENCES↗
Enablement or Suppression of Collisionless Magnetic- Reconnection By the Background Plasma Beta and Guide Field
How magnetic reconnection is triggered or suppressed is an important outstanding problem. By considering pinching of a current sheet that has formed at non-equilibrium, we show that the background plasma beta is a major controlling factor in the onset and nature of magnetic reconnection. A high plasma beta inhibits a current sheet from pinching down to kinetic scales required for collisionless reconnection, while a low beta facilitates it. A simple adiabatic model provides a good prediction for the reconnection-enabled regions in thickness versus peak plasma beta space, which are confirmed by a series of particle-in-cell simulations with varying initial parameters. A strong dependency of the peak reconnection rate on the plasma beta is clearly predicted with reconnection being favored in low beta conditions. A finite guide field is an additional source of reconnection suppression, consistent with previous observations that reconnection requires a large enough magnetic shear angle for high-beta situations.
Young-Dae Yoon↗
Electron and Proton Heating in Transrelativistic Magnetic Reconnection
Hot collisionless accretion flows, such as the one in Sgr A* at our Galactic center, provide a unique setting for the investigation of magnetic reconnection. Here protons are nonrelativistic, while electrons can be ultrarelativistic. By means of 2D particle-in-cell simulations, we investigate electron and proton heating in the outflows of transrelativistic reconnection (i.e., ${\sigma }_{w}\sim 0.1\mbox{--}1$, where the magnetization ${\sigma }_{w}$ is the ratio of magnetic energy density to enthalpy density). For both electrons and protons, we find that heating at high ${\beta }_{{\rm{i}}}$ (here ${\beta }_{{\rm{i}}}$ is the ratio of proton thermal pressure to magnetic pressure) is dominated by adiabatic compression ("adiabatic heating"), while at low ${\beta }_{{\rm{i}}}$ it is accompanied by a genuine increase in entropy ("irreversible heating"). For our fiducial ${\sigma }_{w}=0.1$, the irreversible heating efficiency at ${\beta }_{{\rm{i}}}\lesssim 1$ is nearly independent of the electron-to-proton temperature ratio ${T}_{{\rm{e}}}/{T}_{{\rm{i}}}$ (which we vary from 0.1 up to 1), and it asymptotes to $\sim 2 \% $ of the inflowing magnetic energy in the low-${\beta }_{{\rm{i}}}$ limit. Protons are heated more efficiently than electrons at low and moderate ${\beta }_{{\rm{i}}}$ (by a factor of ~7), whereas the electron and proton heating efficiencies become comparable at ${\beta }_{{\rm{i}}}\sim 2$ if ${T}_{{\rm{e}}}/{T}_{{\rm{i}}}=1$, when both species start already relativistically hot. We find comparable heating efficiencies between the two species also in the limit of relativistic reconnection (${\sigma }_{w}\gtrsim 1$). Finally, our results have important implications for the two-temperature nature of collisionless accretion flows and may provide the subgrid physics needed in general relativistic MHD simulations.
79 ASTRONOMY AND ASTROPHYSICS↗
Latent transforming growth factor beta1 activation in situ: quantitative and functional evidence after low-dose gamma-irradiation
The biological activity of transforming growth factor beta1 (TGF-beta) is controlled by its secretion as a latent complex in which it is noncovalently associated with latency-associated peptide (LAP). Activation is the extracellular process in which TGF-beta is released from LAP, and is considered to be a primary regulatory control. We recently reported rapid and persistent changes in TGF-beta immunoreactivity in conjunction with extracellular matrix remodeling in gamma-irradiated mouse mammary gland. Our hypothesis is that these specific changes in immunoreactivity are indicative of latent TGF-beta activation. In the present study, we determined the radiation dose response and tested whether a functional relationship exists between radiation-induced TGF-beta and collagen type III remodeling. After radiation exposures as low as 0.1 Gy, we detected increased TGF-beta immunoreactivity in the mammary epithelium concomitant with decreased LAP immunostaining, which are events consistent with activation. Quantitative image analysis demonstrated a significant (P=0.0005) response at 0.1 Gy without an apparent threshold and a linear dose response to 5 Gy. However, in the adipose stroma, loss of LAP demonstrated a qualitative threshold at 0.5 Gy. Loss of LAP paralleled induction of collagen III immunoreactivity in this tissue compartment. We tested whether TGF-beta mediates collagen III expression by treating animals with TGF-beta panspecific monoclonal antibody, 1D11.16, administered i.p. shortly before irradiation. Radiation-induced collagen III staining in the adipose stroma was blocked in an antibody dose-dependent manner, which persisted through 7 days postirradiation. RNase protection assay revealed that radiation-induced elevation of total gland collagen III mRNA was also blocked by neutralizing antibody treatment. These data provide functional confirmation of the hypothesis that radiation exposure leads to latent TGF-beta activation, support our interpretation of the reciprocal shift in immunoreactivity as evidence of activation, and implicate TGF-beta as a mediator of tissue response to ionizing radiation. The sensitivity of activation to low radiation doses points to a potential role for TGF-beta in orchestrating tissue response to oxidative stress. As such, radiation may be useful as a probe to delineate the consequences of latent TGF-beta activation in situ.
NASA Discipline Radiation Health↗