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At least 775 records · Page 43

Quantification of the epitope diversity of HIV-1-specific binding antibodies by peptide microarrays for global HIV-1 vaccine development

An effective vaccine against human immunodeficiency virus type 1 (HIV-1) will have to provide protection against a vast array of different HIV-1 strains. Current methods to measure HIV-1-specific binding antibodies following immunization typically focus on determining the magnitude of antibody responses, but the epitope diversity of antibody responses has remained largely unexplored. Here we describe the development of a global HIV-1 peptide microarray that contains 6564 peptides from across the HIV-1 proteome and covers the majority of HIV-1 sequences in the Los Alamos National Laboratory global HIV-1 sequence database. Using this microarray, we quantified the magnitude, breadth, and depth of IgG binding to linear HIV-1 sequences in HIV-1-infected humans and HIV-1-vaccinated humans, rhesus monkeys and guinea pigs. The microarray measured potentially important differences in antibody epitope diversity, particularly regarding the depth of epitope variants recognized at each binding site. Our data suggest that the global HIV-1 peptide microarray may be a useful tool for both preclinical and clinical HIV-1 research.

60 APPLIED LIFE SCIENCES↗

The triple decomposition of a fluctuating velocity field in a multiscale flow

A new method for the triple decomposition of a multiscale flow, which is based on the novel optimal mode decomposition (OMD) technique, is presented. OMD provides low order linear dynamics, which fits a given data set in an optimal way and is used to distinguish between a coherent (periodic) part of a flow and a stochastic fluctuation. The method needs no external phase indication since this information, separate for coherent structures associated with each length scale introduced into the flow, appears as the output. The proposed technique is compared against two traditional methods of the triple decomposition, i.e., bin averaging and proper orthogonal decomposition. This is done with particle image velocimetry data documenting the near wake of a multiscale bar array. It is shown that both traditional methods are unable to provide a reliable estimation for the coherent fluctuation while the proposed technique performs very well. The crucial result is that the coherence peaks are not observed within the spectral properties of the stochastic fluctuation derived with the proposed method; however, these properties remain unaltered at the residual frequencies. This proves the method’s capability of making a distinction between both types of fluctuations. The sensitivity to some prescribed parameters is checked revealing the technique’s robustness. Additionally, an example of the method application for analysis of a multiscale flow is given, i.e., the phase conditioned transverse integral length is investigated in the near wake region of the multiscale object array.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

SU-E-T-359: Measurement of Various Metrics to Determine Changes in Megavoltage Photon Beam Energy

Purpose: To examine the relationship between photon beam energy and various metrics for energy on the flattened and flattening filter free (FFF) beams generated by the Varian TrueBeam. Methods: Energy changes were accomplished by adjusting the bending magnet current ±10% from the nominal value for the 4, 6, 8, and 10 MV flattened and 6 and 10 MV FFF beams. Profiles were measured for a 30×30 cm{sup 2} field using a 2D ionization chamber array and a 3D water Scanner which was also used to measure PDDs. For flattened beams we compared several energy metrics; PDD at 10 cm depth in water (PDD(10)); the variation over the central 80% of the field (Flat); and the average of the highest reading along each diagonal divided by the CAX value, diagonal normalized flatness (FDN). For FFF beams we examined PDD(10), FDN, and the width of a chosen isodose level in a 30×30 cm{sup 2} field (W(d%)). Results: Changes in PDD(10) were nearly linear with changes in energy for both flattened and FFF beams as were changes in FDN. Changes in W(d%) were also nearly linear with energy for the FFF beams. PDD(10) was not as sensitive to changes in energy compared to the other metrics for either flattened or FFF beams. Flat was not as sensitive to changes in energy compared to FDN for flattened beams and its behavior depends on depth. FDN was the metric that had the highest sensitivity to the changes in energy for flattened beams while W(d%) was the metric that had highest sensitivity to the changes in energy for FFF beams. Conclusions: The metric FDN was found to be most sensitive to energy changes for flattened beams, while the W(d%) was most sensitive to energy changes for FFF beams.

07 ISOTOPE AND RADIATION SOURCES↗

Implementation of the LAX-Wendroff Method in Cobra-TF for Solving Two-Phase Flow Transport Equations

COBRA-TF (Coolant Boiling in Rod Arrays Two Fluid), or CTF, is a subchannel code used to conduct the reactor core thermal hydraulic (T/H) solution in both standalone and coupled multi-physics applications. CTF applies the first-order upwind spatial discretization scheme for solving two-phase flow conservation equations. In this work, the second-order Lax-Wendroff (L-W) scheme has been implemented in CTF to solve the two-phase flow transport equations to improve numerical accuracy in both temporal and spatial discretization. To avoid the oscillation issue, a non-linear flux limiter VA (Van Albada) is employed for the convective terms in the transport equations. Assessments have been carried out to evaluate the performance and stability of the implemented second-order L-W scheme. It has been found that the L-W scheme performs better than the upwind scheme for the single-phase and two-phase flow problems in terms of numerical accuracy and computational efficiency.

CTF↗

Maintaining a critical spectra within Monteburns for a gas-cooled reactor array by way of control rod manipulation

Our burnup study examined the effect of a predicted critical control rod position on the nuclide predictability of several axial and radial locations within a 4×4 graphite moderated gas cooled reactor fuel cluster geometry. To achieve this, a control rod position estimator (CRPE) tool was developed within the framework of the linkage code Monteburns between the transport code MCNP and depletion code CINDER90, and four methodologies were proposed within the tool for maintaining criticality. Two of the proposed methods used an inverse multiplication approach - where the amount of fissile material in a set configuration is slowly altered until criticality is attained - in estimating the critical control rod position. Another method carried out several MCNP criticality calculations at different control rod positions, then used a linear fit to estimate the critical rod position. The final method used a second-order polynomial fit of several MCNP criticality calculations at different control rod positions to guess the critical rod position. The results showed that consistency in prediction of power densities as well as uranium and plutonium isotopics was mutual among methods within the CRPE tool that predicted critical position consistently well. Finally, while the CRPE tool is currently limited to manipulating a single control rod, future work could be geared toward implementing additional criticality search methodologies along with additional features.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗

Machine-Learning Identification of the Sensing Descriptors Relevant in Molecular Interactions with Metal Nanoparticle-Decorated Nanotube Field-Effect Transistors

We report that carbon nanotube-based field-effect transistors (NTFETs) are ideal sensor devices as they provide rich information regarding carbon nanotube interactions with target analytes and have potential for miniaturization in diverse applications in medical, safety, environmental, and energy sectors. Herein, we investigate chemical detection with cross-sensitive NTFETs sensor arrays comprised of metal nanoparticle-decorated single-walled carbon nanotubes (SWCNTs). By combining analysis of NTFET device characteristics with supervised machine-learning algorithms, we have successfully discriminated among five selected purine compounds, adenine, guanine, xanthine, uric acid, and caffeine. Interactions of purine compounds with metal nanoparticle-decorated SWCNTs were corroborated by density functional theory calculations. Furthermore, by testing a variety of prepared as well as commercial solutions with and without caffeine, our approach accurately discerns the presence of caffeine in 95% of the samples with 48 features using a linear discriminant analysis and in 93.4% of the samples with only 11 features when using a support vector machine analysis. Lastly, we also performed recursive feature elimination and identified three NTFET parameters, transconductance, threshold voltage, and minimum conductance, as the most crucial features to analyte prediction accuracy.

36 MATERIALS SCIENCE↗

Characterization of the Impact of Soft Errors on Iterative Methods

Soft errors caused by transient bit flips have the potential to significantly impact an application’s behavior. This has motivated the design of an array of techniques to detect, isolate, and correct soft errors using microarchitectural, architectural, compilation-based, or application-level techniques to minimize their impact on the executing application. The first step towards the design of good error detection/correction techniques involves an understanding of an application’s vulnerability to soft errors. In this paper, we present the first comprehensive characterization of the impact of soft errors on the convergence characteristics of six iterative methods using application-level fault injection. In particular, we consider the use of iterative methods to incrementally solve a linear systems of equations, which constitutes the core kernel in many scientific applications. We analyze the impact of soft errors in terms of the type of error (single- vs multi-bit), the distribution and location of bits affected, the data structure and the statement impacted, and variation with time. In addition to understanding the vulnerability of iterative solvers to soft errors, this characterization can aid the design of fault injection campaigns that ensure systematic coverage.

fault injection, iterative methods, Silent data co↗

INTERFEROMETRIC UPPER LIMITS ON MILLIMETER POLARIZATION OF THE DISKS AROUND DG Tau, GM Aur, AND MWC 480

Millimeter-wavelength polarization measurements offer a promising method for probing the geometry of magnetic fields in circumstellar disks. Single dish observations and theoretical work have hinted that magnetic field geometries might be predominantly toroidal, and that disks should exhibit millimeter polarization fractions of 2%-3%. While subsequent work has not confirmed these high polarization fractions, either the wavelength of observation or the target sources differed from the original observations. Here we present new polarimetric observations of three nearby circumstellar disks at 2'' resolution with the Submillimeter Array and the Combined Array for Research in Millimeter Astronomy. We reobserve GM Aur and DG Tau, the systems in which millimeter polarization detections have been claimed. Despite higher resolution and sensitivity at wavelengths similar to the previous observations, the new observations do not show significant polarization. We also add observations of a new HAeBe system, MWC 480. These observations demonstrate that a very low ({approx}<0.5%) polarization fraction is probably common at large ({approx}>100 AU) scales in bright circumstellar disks. We suggest that high-resolution observations may be worthwhile to probe magnetic field structure on linear distances smaller than the disk scale height, as well as in regions closer to the star that may have larger MRI-induced magnetic field strengths.

79 ASTRONOMY AND ASTROPHYSICS↗

SU-F-T-430: Validation of IBEAM Evo Couch Top for Different Relative Electron Density (RED) Combination During Photon Beam Dose Calculation in Monaco− Treatment Planning System

Purpose: Validation of iBEAM™ evo couch-top for different relative electron density (RED) combination during photon beam dose calculation in Monaco− TPS. Methods: The iBEAM™ evo couch-top has two layers:outer carbon fiber (CF) and inner foam core (FC). To study the beam intensity attenuation of couch-top, measured doses were compared with doses calculated for different REDs. Measurements were performed in solid water phantom with PTW-0.125cc ion-chamber positioned at center of the phantom with 5.3cm thickness slabs placed above and below the chamber. Similarly, in TPS, iBEAM™ evo couch-top was simulated and doses were calculated for different RED combinations (0.2CF-0.2FC, 0.4CF-0.2FC, 0.6CF-0.2FC, 0.8CF-0.2FC, and 1.0CF-0.2FC) by using Monte Carlo dose calculation algorithm in Monaco TPS (V5.1). Doses were measured for every 10 degree gantry angle separation, 10×10cm{sup 2} field size and 6MV photons. Then, attenuation is defined as the ratio of output at posterior gantry angle to output of its opposed anterior gantry angle (e.g.225°/45°). output fluctuation with different gantry angle was within ±0.21%. To confirm above results, dose-planes were measured for five pelvic VMAT plans (360°arc) in PTW two-dimensional array and compared with different calculated dose-planes of above-mentioned couch REDs. Gamma pass rates<1.00) were analyzed for 3%/2mm criteria. Results: Measured and calculated attenuation was in good agreement for the RED combination of 0.2CF-0.2FC and difference was within ±0.515%. However, other density combination showed difference of ±0.9841%, ±1.667%, ±2.9241% and ±2.8832% for 0.4CF-0.2FC, 0.6CF-0.2FC, 0.8CF-0.2FC, and 1.0CF-0.2FC, respectively. Maximum couch-top attenuation was observed at 110°–120° and 240°–250° and decreases linearly as the gantry angle approaches 180°. Moreover, gamma pass rate confirmed the above results and showed maximum pass rate of 96.23% for 0.2CF-0.2FC, whereas others were 95.72%, 95.12%, 94.31% and 93.24%. Conclusion: RED value of 0.2CF-0.2FC was found to be suitable for accurate couch-top modeling for 6MV photon beam Monte Carlo calculations in Monaco TPS.

07 ISOTOPE AND RADIATION SOURCES↗

Hydrogen Adsorption, Reactivity, and Catalysis on Colloidal Iron Carbide Nanoparticles

Supported iron carbide particles have long served as catalysts for CO hydrogenation (the Fischer Tropsch synthesis, FTS) and continue to be attractive. Despite this, little is known about their chemistry. Reported here is a colloidal Fe x C nanoparticle (NP) model system that allows direct observation of surface hydrogen and CO, as well as quantification of the surface H. Dodecylamine-capped Fe x C NPs (DDA-Fe x C NPs) were synthesized through solution-phase carburization of Fe NPs and form stable colloids in low-polarity organic solvents. Treatment of these colloids with H 2 or D 2 produced highly hydrogenated materials, and FTIR spectra of DDA-Fe x C-D n showed that most of the D binds to carbides, with at least four distinct v(C-D) modes. The surface C-H(D) bonds were all reactive, transferring hydrogen to alkenes and other reagents in solution. Titration and ICP measurements showed a 0.17:1 ratio of added H:total Fe, or roughly. 40 H per 1.8 nm DDA-Fe x C NP. Conversely, CO was preferentially bound to surface Fe sites, with FTIR spectra showing a single broad v(CO) that shifted with CO coverage or co-adsorption of H 2 . The DDA-Fe x C NPs were active catalysts for both olefin hydrogenation and the FTS, under mild conditions and without catalyst pre-treatment. The CO hydrogenation reactions yielded a broad distribution of long-chain linear paraffins and olefins. Though quantitative comparisons with typical FTS results are not possible because of our use of sealed batch reactors and other factors, the observations of high catalytic reactivity demonstrate the relevance of this model system to iron-carbide catalysis. DFT calculations on model slab surfaces with varying iron carbide stoichiometries revealed that the thermodynamically preferred surface adsorption sites are C for H ads and Fe for CO ads . A variety of binding sites and binding energies were found for each adsorbate. We are unaware of previous studies indicating that a diverse array of C-H bonds is the primary source of reactive H on iron carbides. Experimentally, the diversity of *C-H sites was evident in reactions with H-atom donors and abstractors of different strengths, from both the reaction stoichiometries and IR spectra. The different surface–H binding energies correlate with the v(C-D) stretching frequencies. Furthermore, these insights into complex iron carbide surfaces and catalysis could assist catalyst design, and they showcase the importance of stoichiometric studies of reaction intermediates.

08 HYDROGEN↗

Precise magnetic field mapping of the EMPHATIC Phase 1 magnet with COMSOL

A compact Halbach array magnet is used to measure the momentum of the secondary particles in EMPHATIC(Experiment to Measure the Production ofHadrons At a Test beam InChicagoland). Hall probe data was taken for the central cylindrical bore of the magnet and a field map was constructed. COMSOL Multiphysics® Software is used for modeling the magnet and constructing the corresponding magnetic field map. Here, we present a fitting approach where the hall probe data is used to determine a 1mm-spacing map of the entire volume of the magnet using COMSOL. The new map will allow for linear interpolation within the volume, and expand the map to outside the measurement volume, thus increasing the acceptance and precision of EMPHATIC's tracking system.

47 OTHER INSTRUMENTATION↗

The repeating fast radio burst FRB 121102 as seen on milliarcsecond angular scales

The millisecond-duration radio flashes known as fast radio bursts (FRBs) represent an enigmatic astrophysical phenomenon. Recently, the sub-arcsecond localization (∼100 mas precision) of FRB 121102 using the Very Large Array has led to its unambiguous association with persistent radio and optical counterparts, and to the identification of its host galaxy. However, an even more precise localization is needed in order to probe the direct physical relationship between the millisecond bursts themselves and the associated persistent emission. Here, we report very-long-baseline radio interferometric observations using the European VLBI Network and the 305 m Arecibo telescope, which simultaneously detect both the bursts and the persistent radio emission at milliarcsecond angular scales and show that they are co-located to within a projected linear separation of ≲40 pc (≲12 mas angular separation, at 95% confidence). We detect consistent angular broadening of the bursts and persistent radio source (∼2–4 mas at 1.7 GHz), which are both similar to the expected Milky Way scattering contribution. The persistent radio source has a projected size constrained to be ≲ 0.7 pc (≲0.2 mas angular extent at 5.0 GHz) and a lower limit for the brightness temperature of T{sub b}≳5×10{sup 7} K. Together, these observations provide strong evidence for a direct physical link between FRB 121102 and the compact persistent radio source. We argue that a burst source associated with a low-luminosity active galactic nucleus or a young neutron star energizing a supernova remnant are the two scenarios for FRB 121102 that best match the observed data.

79 ASTRONOMY AND ASTROPHYSICS↗

Using SciDB to Support Photon Science Data Analysis

Array data analytic systems like SciDB hold great potential to accelerate processing data from SLAC's Linac Coherent Light Source and other experiments. SciDB is unique in its ability to integrate storage and processing of array data efficiently, providing both space-efficient storage and out-of-memory efficient parallel array processing. We describe a recent effort to leverage SciDB to store and process LCLS data. The work includes development of software to import data into SciDB, subsequent benchmarks, and interactive manipulation of data in SciDB.

43 PARTICLE ACCELERATORS↗

DNTTD (Distributed Non-Negative Tensor Train Decomposition)

The era of exascale computing opens new venues for innovations and discoveries in many scientific, engineering, and commercial fields. However, with the exa flops also come the extra-large high-dimensional data generated by high performance computing. High-dimensional data is presented as multidimensional arrays, aka tensors. The presence of latent (not directly observable) structures in the tensor allows a unique representation and compression of the data by classical tensor factorization techniques. However, the classical tensor methods are not always stable or they can be exponential in their memory requirements, which makes them not suitable for high-dimensional tensors. Tensor train (TT) is a state-of-the-art tensor network introduced for factorization of high-dimensional tensors. TT transforms the initial high-dimensional tensor in a network of three-dimensional tensors that requires only a linear storage. Many real-world data, such as, density, temperature, population, probability, etc., are non-negative and for an easy interpretation, the algorithms preserving non-negativity are preferred. Here, we introduce a distributed non-negative tensor-train and demonstrate its scalability and the compression on synthetic and real world big datasets.

Bhattarai, Manish↗

Proton and neutron contributions to the quadrupole transition strengths in 39 Ca and 39 K studied by lifetime measurements of mirror transitions

The E2 transition matrix elements of isobaric multiplets are expected to follow a linear trend as a function of isospin projection. However, measurements of the 2 + → 0 + transitions in the A = 38 triplet of Ca, K, and Ar show a deviation from this trend with an enhanced transition strength in 38 Ca with respect to its mirror 38 Ar. We have studied analogue 11/2 – → 7/2 – E2 transitions in 39 Ca and its mirror partner 39 K to determine if this enhancement persists in neighboring Ca isotopes. Recoil-distance lifetime measurements of 39 Ca and 39 K were performed utilizing a 42 Sc secondary beam, the TRIPLEX plunger, the GRETINA array, and the S800 spectrograph. Our data provide a lifetime measurement of the (11/2 – ) state in 39 Ca as well as an improved lifetime result for the (9/2 – ) state, while the 39 K data are used to validate the present analysis. Furthermore, a comparison of the present data to shell-model calculations suggests an enhanced transition strength in 39 Ca, pointing to both proton and neutron contributions to core excitations across the Z = N = 20 shell gaps in close proximity to 40 Ca.

39 ≤ A ≤ 58↗

Dislocation transmission across Σ3{112} incoherent twin boundary: a combined atomistic and phase-field study

Grain boundaries (GBs) in polycrystalline materials act as impediments to dislocation motion and result in strengthening. Understanding slip transmission through GBs, specifically twin boundaries, is essential to understand the plastic deformation behavior of polycrystalline fcc materials. Here the interaction between a glide dislocation and Σ3{112} incoherent twin boundary (ITB) in copper is investigated using a combined atomistic and mesoscale approach. The material parameters and structure of the GB in the mesoscale phase field dislocation dynamics (PFDD) model are informed from Molecular Statics (MS) simulations. The structural unit of the ITB consists of an array of three partial dislocations. The interaction between a glide dislocation impinging on each of the GB partial dislocations is investigated using both PFDD and Molecular Dynamics (MD) with two boundary conditions. Transmission planes predicted by both PFDD and MD (NVT) are in agreement, and show that not all transmission events are direct. Critical transmission stresses predicted by PFDD are in the range of 276 MPa to 1380 MPa, while MD predictions are in the range from 100 MPa to 700 MPa. The PFDD and MD predictions of slip transmission are explained using dislocation theory based on isotropic linear elasticity.

36 MATERIALS SCIENCE↗

Experimental characterization of multiscale and multifield turbulence as a critical gradient threshold is surpassed in the DIII-D tokamak

A critical gradient for long wavelength (k{sub θ}ρ{sub s}≲0.4) electron temperature fluctuations has been observed in an experiment in the DIII-D tokamak [J. L. Luxon, Nucl. Fusion 42, 614 (2002)], where below a threshold value of L{sub T{sub e}{sup −1}}=|∇T{sub e}|/T{sub e} electron temperature fluctuations are constant and above they steadily increase. Above the critical gradient, the electron heat flux inferred by power balance also increases rapidly. Critical gradients are a predicted attribute of turbulence arising from linear instabilities and are thought to be related to transport stiffness. The presented results are the first direct, systematic demonstration of critical gradient behavior in turbulence measurements in a tokamak. The experiment was performed by changing the deposition location of electron cyclotron heating shot-to-shot to locally scan L{sub T{sub e}{sup −1}} at r/a = 0.6 in L-mode plasmas; rotation was also varied by changing the momentum input from neutral beam injection. Temperature fluctuations were measured with a correlation electron cyclotron emission (CECE) radiometry system. In addition to the CECE measurements, an array of turbulence measurements were acquired to characterize fluctuations in multiple fields and at multiple scales as L{sub T{sub e}{sup −1}} and rotation were modified: long wavelength (k{sub θ}ρ{sub s}≲0.5) density fluctuations were acquired with beam emission spectroscopy, the phase angle between electron temperature and density fluctuations was measured by coupling the CECE system and a reflectometer, intermediate scale (k{sub θ}ρ{sub s}∼0.8) density fluctuations were measured with a Doppler backscattering (DBS) system, and low frequency flows were also measured with DBS. The accumulated measurements and trends constrain identification of the instability responsible for the observed critical gradient to the ∇T{sub e}-driven trapped electron mode.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

Nano-fabricated pixelated micropolarizer array for visible imaging polarimetry

Pixelated micropolarizer array (PMA) is a novel concept for real-time visible imaging polarimetry. A 320 × 240 aluminum PMA fabricated by electron beam lithography is described in this paper. The period, duty ratio, and depth of the grating are 140 nm, 0.5, and 100 nm, respectively. The units are standard square structures and the metal nanowires of the grating are collimating and uniformly thick. The extinction ratio of 75 and the maximum polarization transmittance of 78.8% demonstrate that the PMA is suitable for polarization imaging. When the PMA is applied to real-time polarization imaging, the degree of linear polarization image and the angle of linear polarization image are calculated from a single frame image. The polarized target object is highlighted from the unpolarized background, and the surface contour of the target object can be reflected by the polarization angle.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗