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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 685 records · Page 38
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Frustration-guided motion planning reveals conformational transitions in proteins

Proteins exist as conformational ensembles, exchanging between substates to perform their function. Advances in experimental techniques yield unprecedented access to structural snapshots of their conformational landscape. However, computationally modeling how proteins use collective motions to transition between substates is challenging owing to a rugged landscape and large energy barriers. Here in this paper, we present a new, robotics-inspired motion planning procedure called dCCRRT that navigates the rugged landscape between substates by introducing dynamic, interatomic constraints to modulate frustration. The constraints balance non-native contacts and flexibility, and instantaneously redirect the motion towards sterically favorable conformations. On a test set of eight proteins determined in two conformations separated by, on average, 7.5Å root mean square deviation (RMSD), our pathways reduced the Cα atom RMSD to the goal conformation by 78%, outperforming peer methods. Additionally, we then applied dCC-RRT to examine how collective, small-scale motions of four side-chains in the active site of cyclophilin A propagate through the protein. dCC-RRT uncovered a spatially contiguous network of residues linked by steric interactions and collective motion connecting the active site to a recently proposed, non-canonical capsid binding site 25Å away, rationalizing NMR and multi-temperature crystallography experiments. In all, dCC-RRT can reveal detailed, all-atom molecular mechanisms for small and large amplitude motions.Source code and binaries are freely available at https://github.com/ExcitedStates/KGS/.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2011

On the relativistic classical motion of a radiating spinning particle in a magnetic field

Research Highlights: > We propose classical equations of motion for a charged particle with magnetic moment. > We account for radiation reaction as well. > Unlike previous proposals we do not have runaway solutions. > We find that the particle loses energy even in a constant magnetic field for a particular spin-polarized state. - Abstract: We propose classical equations of motion for a charged particle with magnetic moment, taking radiation reaction into account. This generalizes the Landau-Lifshitz equations for the spinless case. In the special case of spin-polarized motion in a constant magnetic field (synchrotron motion) we verify that the particle does lose energy. Previous proposals did not predict dissipation of energy and also suffered from runaway solutions analogous to those of the Lorentz-Dirac equations of motion.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Complex equations of motion for a body under gravitational influence by using a nine-parameter space–time bundle with the structural group SO(3,C)

We give equations of motion of a body under gravitational influence using a model which employs nonlinear connection adapted to 3+3+3-dimensional bundle. It is analogous to the corresponding 3+1 model with nonlinear connection in Minkowski spacetime. The equations of motion are simple complex equations whose real part gives the equations of motion previously obtained in the 3+1 model with nonlinear connection in Minkowski spacetime. They lead to the same predictions as the General Relativity, which are experimentally verified. The imaginary part of the equations of motion gives the total precession of a gyroscope (geodetic precession and frame dragging). The complex equations of motion can be used also in electrodynamics. In this case, the imaginary part corresponds to the Lorentz force, while the real part leads to the angular velocity of an electron in a magnetic field. It is obtained Ω-vector =(e/(mc)) H-vector (if E-vector =0), which fits well with the observations.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Eccentric needle motion effect on near-nozzle dynamics of diesel spray

Here, the eccentric needle motion has been regarded as an important cause of in-nozzle flow disturbances and hole-to-hole spray variations of modern fuel injectors. However, the experimental investigations on this subject have rarely been reported due to great difficulties in the direct measurements of eccentric needle motion and the flow characteristics of individual holes in an injection nozzle. In this study, the axial and eccentric needle motion and the ear-nozzle spray dynamics of 3-hole, 5-hole and 8-hole diesel injection nozzles were investigated in varied injection pressure conditions using an xray phase-contrast imaging technique. The eccentric needle motion and near-nozzle spray axial velocity showed temporal oscillations during the injection with different oscillation frequencies. The frequencies of these two oscillations were independent to the nozzle and injection pressure. To discuss the mutual dependency of these two oscillations, the time traces of the spray axial velocity were measured for individual holes. The results showed that the oscillation phase, frequency and amplitude of the spray axial velocity were almost identical for all holes, which indicated that the sac pressure variation rather than hole-to-hole flow variation can be the primary cause of the spray axial velocity oscillation by the eccentric needle motion. The adequacy of this consideration was thoroughly discussed using a mass balance model in the nozzle sac that predicted the sac pressure variation during an injection event.

42 ENGINEERING↗
DOE OSTI2010

Volumetric Imaging by Megavoltage Computed Tomography for Assessment of Internal Organ Motion During Radiotherapy for Cervical Cancer

Purpose: To assess the internal organ motion of the cervix and uterus by megavoltage computed tomography (MVCT) during intensity-modulated radiotherapy (IMRT). Methods and Materials: Ten patients with Stage IIB-IVA cervical cancer underwent daily MVCT imaging. Internal organ motion was evaluated on 150 pretreatment MVCT images by measuring shifts in their boundaries between the MVCT and kilovoltage (kV) planning CT scan in the anterior, posterior, left and right lateral, and superior and inferior direction. Additional intrafractional patient movement was evaluated on 50 posttreatment MVCT images. Results: Measured cervical motion (mean {+-} SD) was 0.4 {+-} 10.1 mm in the anterior, -3.0 {+-} 6.9 mm in the posterior direction, -3.5 {+-} 4.9 mm in the left and 0.2 {+-} 4.5 mm in the right lateral direction, 2.2 {+-} 8.0 mm in the superior and 0.5 {+-} 5.0 mm in the inferior direction. Compared to the cervix, larger uterine motion was observed. Patient movement during treatment was limited to 1.1 {+-} 1.3 mm, -0.3 {+-} 1.6 mm, and 0.2 {+-} 2.3 mm in anteroposterior, laterolateral and superoinferior direction respectively. Conclusions: MVCT imaging can be used to study patient setup accuracy and cervical and uterine motion during IMRT. This data may be used to refine treatment margins.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2010

Respiratory Organ Motion and Dosimetric Impact on Breast and Nodal Irradiation

Purpose: To examine the respiratory motion for target and normal structures during whole breast and nodal irradiation and the resulting dosimetric impact. Methods and Materials: Four-dimensional CT data sets of 18 patients with early-stage breast cancer were analyzed retrospectively. A three-dimensional conformal dosimetric plan designed to irradiate the breast was generated on the basis of CT images at 20% respiratory phase (reference phase). The reference plans were copied to other respiratory phases at 0% (end of inspiration) and 50% (end of expiration) to simulate the effects of breathing motion on whole breast irradiation. Dose-volume histograms, equivalent uniform dose, and normal tissue complication probability were evaluated and compared. Results: Organ motion of up to 8.8 mm was observed during free breathing. A large lung centroid movement was typically associated with a large shift of other organs. The variation of planning target volume coverage during a free breathing cycle is generally within 1%-5% (17 of 18 patients) compared with the reference plan. However, up to 28% of V{sub 45} variation for the internal mammary nodes was observed. Interphase mean dose variations of 2.2%, 1.2%, and 1.4% were observed for planning target volume, ipsilateral lung, and heart, respectively. Dose variations for the axillary nodes and brachial plexus were minimal. Conclusions: The doses delivered to the target and normal structures are different from the planned dose based on the reference phase. During normal breathing, the dosimetric impact of respiratory motion is clinically insignificant with the exception of internal mammary nodes. However, noticeable degradation in dosimetric plan quality may be expected for the patients with large respiratory motion.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2010

Assessment of Planning Target Volume Margins for Intensity-Modulated Radiotherapy of the Prostate Gland: Role of Daily Inter- and Intrafraction Motion

Purpose: To determine planning target volume margins for prostate intensity-modulated radiotherapy based on inter- and intrafraction motion using four daily localization techniques: three-point skin mark alignment, volumetric imaging with bony landmark registration, volumetric imaging with implanted fiducial marker registration, and implanted electromagnetic transponders (beacons) detection. Methods and Materials: Fourteen patients who underwent definitive intensity-modulated radiotherapy for prostate cancer formed the basis of this study. Each patient was implanted with three electromagnetic transponders and underwent a course of 39 treatment fractions. Daily localization was based on three-point skin mark alignment followed by transponder detection and patient repositioning. Transponder positioning was verified by volumetric imaging with cone-beam computed tomography of the pelvis. Relative motion between the prostate gland and bony anatomy was quantified by offline analyses of daily cone-beam computed tomography. Intratreatment organ motion was monitored continuously by the Calypso (registered) System for quantification of intrafraction setup error. Results: As expected, setup error (that is, inter- plus intrafraction motion, unless otherwise stated) was largest with skin mark alignment, requiring margins of 7.5 mm, 11.4 mm, and 16.3 mm, in the lateral (LR), longitudinal (SI), and vertical (AP) directions, respectively. Margin requirements accounting for intrafraction motion were smallest for transponder detection localization techniques, requiring margins of 1.4 mm (LR), 2.6 mm (SI), and 2.3 mm (AP). Bony anatomy alignment required 2.1 mm (LR), 9.4 mm (SI), and 10.5 mm (AP), whereas image-guided marker alignment required 2.8 mm (LR), 3.7 mm (SI), and 3.2 mm (AP). No marker migration was observed in the cohort. Conclusion: Clinically feasible, rapid, and reliable tools such as the electromagnetic transponder detection system for pretreatment target localization and, subsequently, intratreatment target location monitoring allow clinicians to reduce irradiated volumes and facilitate safe dose escalation, where appropriate.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2020

On the Estimation of In-Cloud Vertical Air Motion Using Radar Doppler Spectra

Measurements of in-cloud vertical air motion are key to quantitatively describe cloud dynamics and their role in cloud microphysics. Here, a retrieval technique for estimating the in-cloud vertical air motion using the upward edge of the radar Doppler spectrum is presented. An additional broadening correction factor that depends on the signal-to-noise ratio (SNR) is introduced. A variety of independent measurements are used to assess the performance of the new technique. The vertical air motion is unbiased with an uncertainty of 0.2 m s –1 for SNR <30. Here, the properties of in-cloud vertical air motion are investigated from 1 year of ground-based observations of warm marine boundary layer clouds. Clouds with higher LWP are characterized by stronger vertical air motions compared to those having lower LWP values.

42 ENGINEERING↗
DOE OSTI2012

GAIA: A WINDOW TO LARGE-SCALE MOTIONS

Using redshifts as a proxy for galaxy distances, estimates of the two-dimensional (2D) transverse peculiar velocities of distant galaxies could be obtained from future measurements of proper motions. We provide the mathematical framework for analyzing 2D transverse motions and show that they offer several advantages over traditional probes of large-scale motions. They are completely independent of any intrinsic relations between galaxy properties; hence, they are essentially free of selection biases. They are free from homogeneous and inhomogeneous Malmquist biases that typically plague distance indicator catalogs. They provide additional information to traditional probes that yield line-of-sight peculiar velocities only. Further, because of their 2D nature, fundamental questions regarding vorticity of large-scale flows can be addressed. Gaia, for example, is expected to provide proper motions of at least bright galaxies with high central surface brightness, making proper motions a likely contender for traditional probes based on current and future distance indicator measurements.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Distance and proper motion measurement of water masers in sharpless 269 IRS 2w

We present astrometric analysis of archival data of water masers in the star-forming region Sharpless 269 (S269) IRS 2w, observed with the VLBI Exploration of Radio Astrometry. An annual parallax of one of the bright maser features in this region was previously reported to be 0.189 ± 0.008 milliarcsecond (mas) using part of the same archival data as we used. However, we found that this maser feature is not the best to represent the annual parallax to S269 IRS 2w because the morphology is remarkably elongated in the east-west direction. For this study we have selected another maser feature showing simpler morphology. This makes the new annual parallax estimate more credible. Our newly obtained annual parallax is 0.247 ± 0.034 mas, corresponding to 4.05{sub −0.49}{sup +0.65} kpc. This value is well consistent with the 3.7-3.8 kpc obtained using the kinematic distance estimates and photometric distance modulus. We considered two hypotheses for the water-maser spatial distribution, a bipolar outflow and an expanding ring, in a kinematic model fitting analysis with a radially expanding flow. At this stage, any conclusions about the systemic proper motion could not be drawn from the kinematic analysis. Alternatively, we evaluated the mean proper motion to be (0.39 ± 0.92, –1.27 ± 0.90) mas yr{sup –1} eastward and northward, respectively, from the obtained proper motions of the detected water-maser features. The newly obtained annual parallax and mean proper motion give the peculiar motion of S269 IRS 2w to be (U {sub s}, V {sub s}, W {sub s}) of (8 ± 6, –21 ± 17, 1 ± 18) km s{sup –1}.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

INTERNAL PROPER MOTIONS IN THE ESKIMO NEBULA

We present measurements of internal proper motions at more than 500 positions of NGC 2392, the Eskimo Nebula, based on images acquired with WFPC2 on board the Hubble Space Telescope at two epochs separated by 7.695 yr. Comparisons of the two observations clearly show the expansion of the nebula. We measured the amplitude and direction of the motion of local structures in the nebula by determining their relative shift during that interval. In order to assess the potential uncertainties in the determination of proper motions in this object, in general, the measurements were performed using two different methods, used previously in the literature. We compare the results from the two methods, and to perform the scientific analysis of the results we choose one, the cross-correlation method, because it is more reliable. We go on to perform a ''criss-cross'' mapping analysis on the proper motion vectors, which helps in the interpretation of the velocity pattern. By combining our results of the proper motions with radial velocity measurements obtained from high resolution spectroscopic observations, and employing an existing 3D model, we estimate the distance to the nebula to be 1.3 kpc.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Proper motion and timing of two unusual pulsars: Calvera and 1E 1207.4—5209

Using pairs of images from the Chandra High Resolution Camera we examine the proper motion of the central compact object (CCO) 1E 1207.4−5209 in the supernova remnant (SNR) PKS 1209−51/52, and the unusual pulsar Calvera that is possibly a CCO descendant. For 1E 1207.4−5209, an insignificant proper motion of μ=15±7 mas yr{sup −1} is measured, corresponding to a corrected tangential velocity of v{sub ⊥,c}<180 km s{sup −1} at the distance of 2 kpc. This proves that the previously noted large offset of the pulsar from the apparent geometric center of the SNR is not due to high proper motion; evidently the symmetry of the remnant does not indicate its center of expansion. Calvera has a marginally significant proper motion of μ=69±26 mas yr{sup −1}, corresponding to v{sub ⊥,c}=86±33 km s{sup −1} for a hypothetical distance of 0.3 kpc. Notably, its vector is away from the Galactic plane, although its high Galactic latitude of b=+37{sup ∘} may be more a consequence of its proximity than its velocity. We also provide updated timing solutions for each pulsar. Spanning 14.5 years, the ephemeris of 1E 1207.4−5209 has a small and steady frequency derivative that, because of the negligible proper motion, requires no kinematic correction. The derived surface dipole magnetic field strength of 1E 1207.4−5209 thus remains B{sub s}=9.8×10{sup 10} G. Calvera has B{sub s}=4.4×10{sup 11} G, intermediate between those of ordinary young pulsars and CCOs, suggesting that it may be on a trajectory of field growth that could account for the absence of descendants in the neighborhood of CCOs in the P− P-dot diagram.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

VLBI FOR GRAVITY PROBE B. V. PROPER MOTION AND PARALLAX OF THE GUIDE STAR, IM PEGASI

We present the principal astrometric results of the very long baseline interferometry (VLBI) program undertaken in support of the Gravity Probe B (GP-B) relativity mission. VLBI observations of the GP-B guide star, the RS CVn binary IM Pegasi (HR 8703), yielded positions at 35 epochs between 1997 and 2005. We discuss the statistical assumptions behind these results and our methods for estimating the systematic errors. We find the proper motion of IM Peg in an extragalactic reference frame closely related to the International Celestial Reference Frame 2 (ICRF2) to be -20.83 {+-} 0.03 {+-} 0.09 mas yr{sup -1} in right ascension and -27.27 {+-} 0.03 {+-} 0.09 mas yr{sup -1} in declination. For each component, the first uncertainty is the statistical standard error and the second is the total standard error (SE) including plausible systematic errors. We also obtain a parallax of 10.37 {+-} 0.07 mas (distance: 96.4 {+-} 0.7 pc), for which there is no evidence of any significant contribution of systematic error. Our parameter estimates for the {approx}25 day period orbital motion of the stellar radio emission have SEs corresponding to {approx}0.10 mas on the sky in each coordinate. The total SE of our estimate of IM Peg's proper motion is {approx}30% smaller than the accuracy goal set by the GP-B project before launch: 0.14 mas yr{sup -1} for each coordinate of IM Peg's proper motion. Our results ensure that the uncertainty in IM Peg's proper motion makes only a very small contribution to the uncertainty of the GP-B relativity tests.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Fixing the reference frame for PPMXL proper motions using extragalactic sources

In this study, we quantify and correct systematic errors in PPMXL proper motions using extragalactic sources from the first two LAMOST data releases and the Vèron-Cetty & Vèron Catalog of Quasars. Although the majority of the sources are from the Vèron catalog, LAMOST makes important contributions in regions that are not well-sampled by previous catalogs, particularly at low Galactic latitudes and in the south Galactic cap. We show that quasars in PPMXL have measurable and significant proper motions, which reflect the systematic zero-point offsets present in the catalog. We confirm the global proper motion shifts seen by Wu et al., and additionally find smaller-scale fluctuations of the QSO-derived corrections to an absolute frame. Finally, we average the proper motions of 158 106 extragalactic objects in bins of 3° × 3° and present a table of proper motion corrections.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

PROPER MOTIONS AND INTERNAL DYNAMICS IN THE CORE OF THE GLOBULAR CLUSTER M71

We have used Gemini North together with the NIRI-ALTAIR adaptive optics imager in the H and K bands to explore the core of the Galactic globular cluster M71 (NGC 6838). We obtained proper motions for 217 stars and have resolved its internal proper motion dispersion. Using a 3.8 year baseline, the proper motion dispersion in the core is found to be 179 {+-} 17 {mu}as yr{sup -1}. We find no evidence of anisotropy in the motions and no radial variation in the proper motions with respect to distance from the cluster center. We also set an upper limit on any central black hole to be {approx}150 M{sub Sun} at 90% confidence level.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

OBJECTS APPEAR SMALLER AS THEY RECEDE: HOW PROPER MOTIONS CAN DIRECTLY REVEAL THE COSMIC EXPANSION, PROVIDE GEOMETRIC DISTANCES, AND MEASURE THE HUBBLE CONSTANT

Objects and structures gravitationally decoupled from the Hubble expansion will appear to shrink in angular size as the universe expands. Observations of extragalactic proper motions can thus directly reveal the cosmic expansion. Relatively static structures such as galaxies or galaxy clusters can potentially be used to measure the Hubble constant, and test masses in large scale structures can measure the overdensity. Since recession velocities and angular separations can be precisely measured, apparent proper motions can also provide geometric distance measurements to static structures. The apparent fractional angular compression of static objects is 15 μas yr{sup –1} in the local universe; this motion is modulated by the overdensity in dynamic expansion-decoupled structures. We use the Titov et al. quasar proper motion catalog to examine the pairwise proper motion of a sparse network of test masses. Small-separation pairs (<200 Mpc comoving) are too few to measure the expected effect, yielding an inconclusive 8.3 ± 14.9 μas yr{sup –1}. Large-separation pairs (200-1500 Mpc) show no net convergence or divergence for z < 1, –2.7 ± 3.7 μas yr{sup –1}, consistent with pure Hubble expansion and significantly inconsistent with static structures, as expected. For all pairs a 'null test' gives –0.36 ± 0.62 μas yr{sup –1}, consistent with Hubble expansion and excludes a static locus at ∼5-10σ significance for z ≅ 0.5-2.0. The observed large-separation pairs provide a reference frame for small-separation pairs that will significantly deviate from the Hubble flow. The current limitation is the number of small-separation objects with precise astrometry, but Gaia will address this and will likely detect the cosmic recession.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Network analysis of earthquake ground motion spatial correlation: a case study with the San Jacinto seismic nodal array

SUMMARY The spatial correlation of earthquake ground motion intensity can be measured from strong motion data; however, the data used in past studies is sparsely sampled in space, and only the interstation distance was considered as a correlation variable. These limitations mean that we have only weak constraints on the true correlation structure of ground motion and that potentially important aspects of spatial correlation are unconstrained. In this study, we combine a large-N seismic array and graph analytics to explore this issue at a local scale using small local and regional earthquakes. Our result suggests site conditions, and how they interact with the incident seismic wavefield, strongly condition the spatial correlation of ground motion. Future progress in characterizing ground motion spatial variability will require dense wavefield measurements, either through nodal deployments, or perhaps distributed acoustic sensing measurements, of seismic wavefields. Aftershock sequences of major earthquakes would provide particularly data-rich targets of opportunity.

58 GEOSCIENCES↗
DOE OSTI2015

3D delivered dose assessment using a 4DCT-based motion model

Purpose: The purpose of this work is to develop a clinically feasible method of calculating actual delivered dose distributions for patients who have significant respiratory motion during the course of stereotactic body radiation therapy (SBRT). Methods: A novel approach was proposed to calculate the actual delivered dose distribution for SBRT lung treatment. This approach can be specified in three steps. (1) At the treatment planning stage, a patient-specific motion model is created from planning 4DCT data. This model assumes that the displacement vector field (DVF) of any respiratory motion deformation can be described as a linear combination of some basis DVFs. (2) During the treatment procedure, 2D time-varying projection images (either kV or MV projections) are acquired, from which time-varying “fluoroscopic” 3D images of the patient are reconstructed using the motion model. The DVF of each timepoint in the time-varying reconstruction is an optimized linear combination of basis DVFs such that the 2D projection of the 3D volume at this timepoint matches the projection image. (3) 3D dose distribution is computed for each timepoint in the set of 3D reconstructed fluoroscopic images, from which the total effective 3D delivered dose is calculated by accumulating deformed dose distributions. This approach was first validated using two modified digital extended cardio-torso (XCAT) phantoms with lung tumors and different respiratory motions. The estimated doses were compared to the dose that would be calculated for routine 4DCT-based planning and to the actual delivered dose that was calculated using “ground truth” XCAT phantoms at all timepoints. The approach was also tested using one set of patient data, which demonstrated the application of our method in a clinical scenario. Results: For the first XCAT phantom that has a mostly regular breathing pattern, the errors in 95% volume dose (D95) are 0.11% and 0.83%, respectively for 3D fluoroscopic images reconstructed from kV and MV projections compared to the ground truth, which is clinically comparable to 4DCT (0.093%). For the second XCAT phantom that has an irregular breathing pattern, the errors are 0.81% and 1.75% for kV and MV reconstructions, both of which are better than that of 4DCT (4.01%). In the case of real patient, although it is impossible to obtain the actual delivered dose, the dose estimation is clinically reasonable and demonstrates differences between 4DCT and MV reconstruction-based dose estimates. Conclusions: With the availability of kV or MV projection images, the proposed approach is able to assess delivered doses for all respiratory phases during treatment. Compared to the planning dose based on 4DCT, the dose estimation using reconstructed 3D fluoroscopic images was as good as 4DCT for regular respiratory pattern and was a better dose estimation for the irregular respiratory pattern.

60 APPLIED LIFE SCIENCES↗