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At least 1,657 records · Page 92

Measurements of differential charged-current cross sections on argon for electron neutrinos with final-state protons in MicroBooNE

This work presents single-differential electron-neutrino charged-current cross sections on argon measured using the MicroBooNE detector at the Fermi National Accelerator Laboratory. The analysis uses data recorded when the Neutrinos at the Main Injector beam was operating in both neutrino and antineutrino modes, with exposures of $2 \times 10^{20}$ and $5 \times 10^{20}$ protons on target, respectively. A selection algorithm targeting electron-neutrino charged-current interactions with at least one proton, one electron, and no pions in the final topology is used to measure differential cross sections as a function of outgoing electron energy, total visible energy, and opening angle between the electron and the most energetic proton. The interaction rate as a function of proton multiplicity is also reported. The total cross section is measured as [4.1 $\pm$ 0.4 (stat.) $\pm$ 1.2 (syst.)]$ $$\times 10^{-39} \mathrm{cm}^{2}/ \mathrm{nucleon}$. The unfolded cross-section measurements are compared to predictions from neutrino event generators commonly employed in the field. Good agreement is seen across all variables within uncertainties.

Abratenko, P. [Tufts U. (main)]↗

Dynamics of Global Gene Expression and Regulatory Elements in Growing Brachypodium Root System

Root systems are dynamic and adaptable organs that play critical roles in plant development. However, how roots grow and accumulate biomass during plant life cycle and in relation to shoot growth phenology remains understudied. A comprehensive time-dependent root morphological analysis integrated with molecular signatures is then required to advance our understanding of root growth and development. Here we studied Brachypodium distachyon rooting process by monitoring root morphology, biomass production, and C/N ratios during developmental stages. To provide insight into gene regulation that accompanies root growth, we generated comprehensive transcript profiles of Brachypodium whole-root system at four developmental stages. Our data analysis revealed that multiple biological processes including trehalose metabolism and various families of transcription factors (TFs) were differentially expressed in root system during plant development. In particular, the AUX/IAA, ERFs, WRKY, NAC, and MADS TF family members were upregulated as plant entered the booting/heading stage, while ARFs and GRFs were downregulated suggesting these TF families as important factors involved in specific phases of rooting, and possibly in regulation of transition to plant reproductive stages. We identified several Brachypodium candidate root biomass-promoting genes and cis -regulatory elements for further functional validations and root growth improvements in grasses.

59 BASIC BIOLOGICAL SCIENCES↗

Multiple ferroelectric nematic phases of a highly polar liquid crystal compound

Ferroelectric nematic liquid crystals represent not only fascinating, fundamental science, but they also hold promise for new technologies including high-density power storage or sub-millisecond switching information displays. In this work, we describe the synthesis and measurements of the physical properties of a new compound, 4-nitrophenyl 4-[(2,4-dimethoxylbenzoyl)oxy]-2-fluorobenzoate (RT11001). This material exhibits multiple, highly polar, ferroelectric nematic phases that have not been previously reported. Here we employ a wide range of physical characterisation methods including differential scanning calorimetry (DSC), mass density measurement, optical birefringence, polarising optical microscopy (POM), dielectric spectroscopy, electric current analysis, electro-optical switching, small-angle and wide-angle x-ray scattering measurements to show that RT11001 has multiple, distinct ferroelectric phases. We argue that the highest temperature phase is a polar nematic fluid with non-polar smectic clusters. Directly below appears to be a transition to another polar nematic phase containing polar positionally ordered clusters. Lastly, there are indications of an additional, polar biaxial liquid crystal phase at lower temperatures.

36 MATERIALS SCIENCE↗

Differentiable stochastic halo occupation distribution

ABSTRACT In this work, we demonstrate how differentiable stochastic sampling techniques developed in the context of deep reinforcement learning can be used to perform efficient parameter inference over stochastic, simulation-based, forward models. As a particular example, we focus on the problem of estimating parameters of halo occupation distribution (HOD) models that are used to connect galaxies with their dark matter haloes. Using a combination of continuous relaxation and gradient re-parametrization techniques, we can obtain well-defined gradients with respect to HOD parameters through discrete galaxy catalogue realizations. Having access to these gradients allows us to leverage efficient sampling schemes, such as Hamiltonian Monte Carlo, and greatly speed up parameter inference. We demonstrate our technique on a mock galaxy catalogue generated from the Bolshoi simulation using a standard HOD model and find near-identical posteriors as standard Markov chain Monte Carlo techniques with an increase of ∼8× in convergence efficiency. Our differentiable HOD model also has broad applications in full forward model approaches to cosmic structure and cosmological analysis.

79 ASTRONOMY AND ASTROPHYSICS↗

Circulating unmethylated CHTOP and INS DNA fragments provide evidence of possible islet cell death in youth with obesity and diabetes

Circulating unmethylated DNA fragments arising from the human INS gene have been proposed as biomarkers of islet beta-cell death and diabetes risk, but this gene alone does not yield sufficiently specific information to report ß-cell death. We employed an unbiased approach to identify the CHTOP gene as a new candidate biomarker whose CpGs show a greater frequency of unmethylation in human islets. Although both INS and CHTOP contained unmethylated CpG sites in several human tissues, they occurred in a non-overlapping pattern. Based on Naïve Bayes classifier analysis, the two genes used together, however, report 100% specificity for islet damage. Compared to healthy controls, differentially methylated CHTOP and INS levels were higher in youth with new onset type 1 diabetes (T1D) and, unexpectedly, in healthy autoantibody-negative youth who have first-degree relatives with T1D. When tested in youth at risk for type 2 diabetes (T2D), increased levels of unmethylated INS and CHTOP were observed in obese individuals. Our data suggest that concurrent measurement of circulating unmethylated INS and CHTOP detects islet death in youth at risk for both T1D and T2D, and support the use of multiple parameters to increase the confidence of detecting islet damage in at-risk individuals.

59 BASIC BIOLOGICAL SCIENCES↗

Thermal analysis of non-actinide bearing salt

The Netzsch STA 409 CD 403/5/G STA-MS Skimmer Coupling System was used to perform thermal analysis on FLiNaK to establish a method for characterizing vapor pressures over molten salts. The measurements include differential scanning calorimetry, thermogravimetry, and mass spectrometry to generate comprehensive thermochemical property data as stand-alone information to aid in MSR design and licensing as well as inputs into the Molten Salt Thermodynamic Database (MSTDB). The FY20 focus is to establish procedures and quantify uncertainty levels for measurements of non-actinide compositions for moving toward actinide bearing salt measurements in FY21.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Burnup Monitoring for Pebble Bed Reactor Systems

A pebble burnup monitoring system is a required component for domestic reactor safety and safeguards applications associated with pebble bed reactors (PBRs). One of the main requirements of a PBR burnup monitoring system is that it needs to be capable of rapid measurements to assess the burnup of each individual pebble to determine whether to recirculate it in the reactor or discard it as spent fuel. This report considers three different approaches for a burnup monitoring system for pebbles discharged from the reactor core in a pebble bed modular reactor-400: • passive gamma spectrometry measurement, • passive neutron coincidence measurement, and • active neutron counter based on the differential die-away technique. Conceptual designs have been created for each of these detectors, and preliminary analysis has been performed using Monte Carlo N-Particle and Oak Ridge Isotope Generation code simulations. The advantages and practical limitations (e.g., high radiation background) of each system were identified. Simulations suggest that each of the three measurement techniques can be successfully employed to distinguish between pebbles based on their number of passes through the core and to quantify the burnup of pebbles.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗

Experiment M409: Bremsstrahlung spectrometer

Spectrometric data were used to gain information for computation of the flux-energy spectra of bremsstrahlung inside the Gemini spacecraft and to determine if energetic electrons are able to penetrate the vehicle walls. The spectra were compared with computer predicted bremsstrahlung spectra by the use of data from beta spectrometers flown on Gemini 10 and 12 missions. The calculations of bremsstrahlung radiation involved uncertainties because of the small amount of information available on cross-section interaction and because of the complex, heterogeneous composition of the spacecraft. The bremsstrahlung detector was designed for time-differentiated measurement of the electron-induced gamma rays over a large section of the vehicle. Preliminary analysis of the data obtained during the missions was indicative that electrons did penetrate the spacecraft wall.

Lindsey, R. S., Jr.↗

Attitude control of a spinning Skylab.

Active attitude control of a spinning Skylab is analyzed to determine a simple control law that will provide a satisfactory response, considering the dynamics of attached flexible appendages. A simplified model of the complex Skylab vehicle is selected to make it analytically tractable. The vehicle is modeled as a single rigid-core body with two attached flexible massless booms having masses on their tips. The equations of motion describing the attitude dynamics of the model are presented as a linear matrix-differential equation. The states of the vehicle are small perturbations about its steady-state spin. An analysis is performed to determine the domain of stability. Next, attitude dynamics are analyzed; both frequency domain (parameter plane) and time domain (an optimal linear quadratic loss program) techniques are compared. An analysis of the nonlinear effect of control torque saturation of Skylab's control moment gyroscopes is discussed. The results of the analysis compare favorably with a large-scale digital simulation of the Skylab.

Seltzer, S. M.↗

Theory of flux anisotropies in a guiding center plasma

The one particle distribution function f on the scale of the bounce motion of particles in a magnetic field B is considered. The Vlasov equation is expanded through O(epsilon) in the adiabatic parameter which is the ratio of particle gyroradius to scale length of the magnetic field. Because f is directly proportional to particle flux differential in kinetic energy and solid angle, f is in principle measurable in space experiments, and the analysis is tailored to be explicitly applicable to space problems. To O(1), f is gyrotropic; its first velocity moment is (if non-vanishing) parallel to B, and hence macroscopic parallel flow is included in this term. The O(epsilon) contribution is non-gyrotropic and macroscopic flow parallel to B plus additional parallel flow results from these terms. The degree of non-gyrotropy and the amount of cross-field macroscopic flow depend on the perpendicular component of the electric field, on curvature and shear in the magnetic field, and on the spatial gradient, pitch angle derivative, and speed derivative of the lowest order distribution function.

Birmingham, T. J.↗

FAA navigation program

The FAA navigation program, which includes two major activity areas: those associated with certification of navigation systems to meet current requirements and those associated with building the data base needed to define future system improvements is examined. The near term activities, including the VORTAC upgrading program, the development of the technical data base needed for certification of LORAN C and OMEGA as a part of the current air navigation system, and the development of area navigation standards are examined in regard to cost factors and user requirements. Future system activities discussed include analysis of alternative system configurations made up of system elements including VORTAC VOR-DME, OMEGA and differential OMEGA, LORAN C, and GPS. The interrelationships between the near and far term programs are discussed. A helicopter IFR program which includes an assessment of the operational suitability of several navigation system alternatives for meeting helicopter navigation requirements for CONUS and offshore operations is reported.

Blake, N. A.↗

Metal ion-containing epoxies

A variety of metallic and organometallic complexes to be used as potential additives for an epoxy used by the aerospace industry as a composite matrix resin were investigated. A total of 9 complexes were screened for compatibility and for their ability to accelerate or inhibit the cure of a highly crosslinkable epoxy resin. Methods for combining the metallic complexes with the resin were investigated, gel times recorded, and cure exotherms studied by differential scanning calorimetry. Glass transition temperatures of cured metal ion containing epoxy castings were determined by thermomechanical analysis. Thermal stabilities of the castings were determined by thermogravimetric analysis. Mechanical strength and stiffness of these doped epoxies were also measured.

Stoakley, D. M.↗

Thermal-stress analysis for a wood composite blade

A thermal-stress analysis of a wind turbine blade made of wood composite material is reported. First, the governing partial differential equation on heat conduction is derived, then, a finite element procedure using variational approach is developed for the solution of the governing equation. Thus, the temperature distribution throughout the blade is determined. Next, based on the temperature distribution, a finite element procedure using potential energy approach is applied to determine the thermal-stress distribution. A set of results is obtained through the use of a computer, which is considered to be satisfactory. All computer programs are contained in the report.

Fu, K. C.↗

The spectrum of high energy cosmic-ray electrons - Results and interpretation

Results of a measurement of high energy cosmic-ray electrons that was performed with a balloon-borne transition radiation/shower detector telescope are presented. The data cover the energy range from 5 to 300 GeV. The interstellar spectrum below 10 GeV, which is affected by solar modulation, is derived through analysis of the nonthermal galactic radio emission, and extended to lower energies (about 300 MeV). The interstellar differential spectrum is described by a power law dependence on E with an index of -1.4 below 2 GeV, but attaining a slope of -2.6 at 2-10 GeV, and steepening further to almost -3.6 at 30-300 GeV. The features of this spectrum are interpreted in the context of galactic propagation models, assuming that the spectrum at the acceleration site has the form of a single power law. It is concluded that: (1) regions outside the galactic disk contribute to the confinement volume of electrons, (2) the containment time of electrons is of the order 10 to the 7th years and is independent of energy, (3) the spectrum at the acceleration site has a power law exponent equal to -2.65, and (4) a specific mechanism is responsible for the apparent flattening of the electron spectrum below 2 GeV.

Muller, D.↗

Two dimensional tethered satellite attitude dynamics

This paper discusses a simplified dynamical model of two-dimensional tethered satellite attitude motion (coning). The tether is assumed massless, inextensible, and long relative to the satellite dimension, and has no flexural rigidity. The satellite is assumed rigid, is constrained to planar motion, and the model includes a tension augmentation thruster. Problem formulation results in one second order differential equation which has one integral of motion that is not the system energy. Results of the analysis include methods of changing satellite rotational energy, the effects of changing the tether tension, and frequency/amplitude information.

Humble, Ronald W.↗

Research highlights: June 1990 - May 1991

Linear instability calculations at MSFC have suggested that the Geophysical Fluid Flow Cell (GFFC) should exhibit classic baroclinic instability at accessible parameter settings. Interest was in the mechanisms of transition to temporal chaos and the evolution of spatio-temporal chaos. In order to understand more about such transitions, high resolution numerical experiments for the physically simplest model of two layer baroclinic instability were conducted. This model has the advantage that the numerical code is exponentially convergent and can be efficiently run for very long times, enabling the study of chaotic attractors without the often devastating effects of low-order trunction found in many previous studies. Numerical algorithms for implementing an empirical orthogonal function (EOF) analysis of the high resolution numerical results were completed. Under conditions of rapid rotation and relatively low differential heating, convection in a spherical shell takes place as columnar banana cells wrapped around the annular gap, but with axes oriented along the axis of rotation; these were clearly evident in the GFFC experiments. The results of recent numerical simulations of columnar convection and future research plans are presented.

Source record↗

On determining the spectrum of primordial inhomogeneity from the COBE DMR sky maps: Results of two-year data analysis

A new technique of Fourier analysis on a cut sky has been applied to the two-year Cosmic Background Explorer (COBE) Differential Microwave Radiometer (DMR) 53 and 90 GHz sky maps. The Bayesian power spectrum estimation results are consistent with the Harrison-Zel'dovich n = 1 model. The maximum likelihood estimates of the usual parameters defining the power spectrum of primordial perturbations are n = 1.22 (1.02) and Q(sub rms-PS) = 17 (20) microK including (excluding) the quadrupole. A spectral-index-independent normalization is naturally expressed for the two-year maps in terms of the multipole amplitude a(sub 9) = 8.2 (8.3) microK (to approximately 12 sigma significance). The marginal likelihood function on n obtained by intergration with respect to a(sub 9) renders n = 1.17 +/- 0.31 (0.96 +/- 0.36).

Gorski, K. M.↗

Influence of cross-flow on nonlinear Tollmien-Schlichting/vortex interaction

The transition of an incompressible three-dimensional boundary layer with strong cross-flow is considered theoretically and computationally in the context of vortex/wave interactions. Specifically the work centers on two lower-branch Tollmien-Schlichting waves which mutually interact nonlinearly to induce a longitudinal vortex flow. The vortex motion in turn gives rise to significant wave modulation via wall-shear forcing. The characteristic Reynolds number is large and, as a consequence, the waves' and the vortex motion are governed primarily by triple deck theory. The nonlinear interaction is captured by a viscous partial-differential system for the vortex coupled with a pair of amplitude equations for each wave pressure. Following analysis and computation over a wide range of parameters, three distinct responses are found to emerge in the nonlinear behavior of the flow solution downstream: an algebraic finite-distance singularity, far-downstream saturation or far-downstream wave decay leaving pure vortex flow. These depend on the input conditions, the wave angles and the size of the cross flow.

Davis, D. A. R.↗