Browsing by Subject "density"

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Anomalous structure and dynamics of the Gaussian-core fluid
(2009-04) Krekelberg, William P.; Kumar, Tanuj; Mittal, Jeetain; Errington, Jeffrey R.; Truskett, Thomas M.; Krekelberg, William P.; Kumar, Tanuj; Truskett, Thomas M.
It is known that there are thermodynamic states for which the Gaussian-core fluid displays anomalous properties such as expansion upon isobaric cooling (density anomaly) and increased single-particle mobility upon isothermal compression (self-diffusivity anomaly). Here, we investigate how temperature and density affect its short-range translational structural order, as characterized by the two-body excess entropy. We find that there is a wide range of conditions for which the short-range translational order of the Gaussian-core fluid decreases upon isothermal compression (structural order anomaly). As we show, the origin of the structural anomaly is qualitatively similar to that of other anomalous fluids (e.g., water or colloids with short-range attractions) and is connected to how compression affects static correlations at different length scales. Interestingly, we find that the self-diffusivity of the Gaussian-core fluid obeys a scaling relationship with the two-body excess entropy that is very similar to the one observed for a variety of simple liquids. One consequence of this relationship is that the state points for which structural, self-diffusivity, and density anomalies of the Gaussian-core fluid occur appear as cascading regions on the temperature-density plane; a phenomenon observed earlier for models of waterlike fluids. There are, however, key differences between the anomalies of Gaussian-core and waterlike fluids, and we discuss how those can be qualitatively understood by considering the respective interparticle potentials of these models. Finally, we note that the self-diffusivity of the Gaussian-core fluid obeys different scaling laws depending on whether the two-body or total excess entropy is considered. This finding, which deserves more comprehensive future study, appears to underscore the significance of higher-body correlations for the behavior of fluids with bounded interactions.
Binder Saturation, Layer Thickness, Drying Time and Their Effects on Dimensional Tolerance and Density of Cobalt Chrome - Tricalcium Phosphate Biocomposite
(University of Texas at Austin, 2019) Ruprecht, John; Agarwal, Kuldeep; Ahmed, Shaheen
Traditional metals such as stainless steel, titanium and cobalt chrome are used in biomedical applications (implants, scaffolds etc.) but suffer from issues such as osseointegration and compatibility with existing bone. One way to improve traditional biomaterials is to incorporate ceramics with these metals so that their mechanical properties can be similar to cortical bones. Tricalcium phosphate is such a ceramic with properties so that it can be used in human body. This research explores the use of binder jetting based additive manufacturing process to create a novel biocomposite made of cobalt chrome and tricalcium phosphate. Experiments were conducted and processing parameters were varied to study their effect on the printing of this biocomposite. Layer thickness, binder saturation and drying time affected the dimensional tolerance and the density of the green samples. This effect is important to understand so that the material can be optimized for use in specific applications.
The Black Hole Mass And Extreme Orbital Structure In NGC 1399
(2007-12) Gebhardt, Karl; Lauer, Tod R.; Pinkney, Jason; Bender, Ralf; Richstone, Douglas; Aller, Monique; Bower, Gary; Dressler, Alan; Faber, S. M.; Filippenko, Alexei V.; Green, Richard; Ho, Luis C.; Kormendy, John; Siopis, Christos; Tremaine, Scott; Gebhardt, Karl; Kormendy, John
The largest galaxies, and in particular central galaxies in clusters, offer unique insight into understanding the mechanism for the growth of nuclear black holes. We present Hubble Space Telescope kinematics for NGC 1399, the central galaxy in Fornax. We find the best-fit model contains a black hole of (5.1 +/- 0: 7) x 10(8) M-circle dot (at a distance of 21.1 Mpc), a factor of over 2 below the correlation of black hole mass and velocity dispersion. We also find a dramatic signature for central tangential anisotropy. The velocity profiles on adjacent sides 0.5 '' away from the nucleus show strong bimodality, and the central spectrum shows a large drop in the dispersion. Both of these observations point to an orbital distribution that is tangentially biased. The best-fit orbital model suggests a ratio of the tangential to radial internal velocity dispersions of 3. This ratio is the largest seen in any galaxy to date and will provide an important measure for the mode by which the central black hole has grown.
Challenges during laser Powder Bed Fusion of a Near-Alpha Titanium Alloy - Ti-6242Si
(University of Texas at Austin, 2021) Patel, Sagar; Keshavarz, Mohsen; Vlasea, Mihaela
Ti-6Al-2Sn-4Zr-2Mo-Si (Ti-6242Si) is a near-α phase titanium alloy that has a greater strength up to 565 °C compared to the workhorse Ti-6Al-4V alloy with a typical service temperature of up to 400 °C. While there is a wealth of literature to help understand the laser powder bed fusion (LPBF) of Ti-6Al-4V, only a few research articles about LPBF of Ti-6242Si are available in the open literature. In this work, LPBF processing diagrams and temperature prediction models were used to investigate the impact of process parameters such as laser power, scan speed, and beam spot radius on macroscale characteristics of the builds such as density and surface roughness. The use of processing diagrams allowed for exploration of density ranges between 99.55-99.98 %, and surface roughness, Sa, ranges between 8-16 μm in Ti-6242Si processed by LPBF. Cracking in Ti-6242Si manufactured by LPBF is reported for the first time. Cracking during LPBF of Ti-6242Si was observed to strongly depend upon the predicted melting mode (conduction, transition, and keyhole) for a given set of LPBF process parameters.
Characterizing the Influence of Print Parameters on Porosity and Resulting Density
(University of Texas at Austin, 2019) Brackett, James; Cauthen, Dakota; Condon, Justin; Smith, Tyler; Gallego, Nidia; Kunc, Vlastamil
Extrusion deposition additive manufacturing produces parts with inherent porosity, which typically manifests as easily accessible voids between beads. This open porosity can also be accompanied by voids within the beads themselves, and both types can impact a part’s desired performance. Porosity is influenced by a variety of factors, including infill percentage, layer height, nozzle diameter, print speed, and raster orientation. While their influence on mechanical properties and porosity have been studied previously, there has been minimal work connecting print parameters to porosity and subsequently to mechanical performance. This study investigates the relationships between print parameters, volumetric porosity, and mechanical performance. In addition, this study measures both open and closed porosity through use of a helium pycnometer rather than image analysis of a cross-section. Thus, this study will identify correlations between the volumetric density of parts and the resulting mechanical performance as a function of print parameters.
GEMS : Galaxy Fitting Catalogs and Testing Parametric Galaxy Fitting Codes : GALFIT and GIM2D
(2007-10) Haeussler, Boris; McIntosh, Daniel H.; Barden, Marco; Bell, Eric F.; Rix, Hans-Walter; Borch, Andrea; Beckwith, Steven V. W.; Caldwell, John A. R.; Heymans, Catherine; Jahnke, Knud; Jogee, Shardha; Koposov, Sergey E.; Meisenheimer, Klaus; Sanchez, Sebastian F.; Somerville, Rachel S.; Wisotzki, Lutz; Wolf, Christian; Caldwell, John A. R.
In the context of measuring the structures of intermediate-redshift galaxies with HST ACS surveys, we tune, test, and compare two widely used fitting codes (GALFIT and GIM2D) for fitting single-component Sersic models to both simulated and real galaxy data. Our study focuses on the GEMS survey with the sensitivity of typical HST survey data, and we include our final catalog of fit results for all 41,495 objects detected in GEMS. Using simulations, we find that fitting accuracy depends sensitively on galaxy profile shape. Exponential disks are well fit and have small measurement errors, whereas fits to de Vaucouleurs profiles show larger uncertainties owing to the large amount of light at large radii. Both codes provide reliable fits with little systematic error for galaxies with effective surface brightnesses brighter than that of the sky; the formal uncertainties returned by these codes significantly underestimate the true uncertainties (as estimated using the simulations). We find that GIM2D suffers significant systematic errors for spheroids with close companions owing to the difficulty of effectively masking out neighboring galaxy light; there appears to be no work-around to this important systematic in GIM2D's current implementation. While this crowding error affects only a small fraction of galaxies in GEMS, it must be accounted for in the analysis of deeper cosmological images or of more crowded fields with GIM2D. In contrast, GALFIT results are robust to the presence of neighbors because it can simultaneously fit the profiles of multiple companions as well as the galaxy of interest. We find GALFIT's robustness to nearby companions and factor of greater than or similar to 20 faster runtime speed are important advantages over GIM2D for analyzing large HST ACS data sets.
GEMS Survey Data and Catalog
(2008-01) Caldwell, John A. R.; McIntosh, Daniel H.; Rix, Hans-Walter; Barden, Marco; Beckwith, Steven V. W.; Bell, Eric F.; Borch, Andrea; Heymans, Catherine; Haeussler, Boris; Jahnke, Knud; Jogee, Shardha; Meisenheimer, Klaus; Peng, Chien Y.; Sanchez, Sebastian F.; Somerville, Rachel S.; Wisotzki, Lutz; Wolf, Christian; Caldwell, John A. R.
We describe the data reduction and object cataloging for the GEMS survey, a large-area (800 arcmin(2)) two-band (F606W and F850LP) imaging survey with the Advanced Camera for Surveys on the Hubble Space Telescope, centered on the Chandra Deep Field-South.
High Density Ti6Al4V via Slim Processing: Microstructure and Mechanical Properties
(University of Texas at Austin, 2011-08-17) Kong, Chang-Jing; Tuck, Christopher J.; Ashcroft, Ian A.; Wildman, Ricky D.; Hague, Richard
This paper investigates a density improvement method for Ti6Al4V alloy processed by the selective laser melting method. A modified inert gas inlet baffle has been employed to develop improved mechanical properties for these materials. Comparisons of the top surface and cross-section porosities of solid blocks processed by the original and modified gas inlet baffles indicate that the modified baffle greatly increases the properties of the processing blocks. Results showed that the porosity of the Ti6Al4V alloy was lower than 0.1% by area. The microstructure of the SLM Ti6Al4V alloy exhibited martensitic α' phase. The UTS tensile strength was 920-960MPa and the elongation at the fracture was 3-5%. The fracture surfaces of the tensile samples demonstrated a mixture of ductile and brittle fracture.
High Resolution Laser Melting with Brilliant Radiation
(University of Texas at Austin, 2014) Streek, A.; Regenfuss, P.; Exner, H.
Since the discovery of selective laser sintering/melting, numerous modifications have been made to upgrade or customize this technology for industrial purposes. Laser micro sintering (LMS) is one of those modifications: Powders with particles in the range of a few micrometers are used to obtain products with highly resolved structures. Pulses of a q-switched laser had been considered necessary in order to generate sinter layers from these µm-scaled metal powders. However, despite the high resolution, the process repeatability of LMS and the material property of the products have never been completely satisfactory. Recent technological and theoretical progress and the application of brilliant continuous laser radiation have now allowed for efficient laser melting of µm-scaled metal powders. Thereby, it is remarkable that thin sinter layers are generated with a very high laser power. The resulting product resolution is comparable to the one achieved by the LMS regime with q-switched pulses. From the experimental results the performance and potential of this high resolution laser melting regime is demonstrated and the limits of the applicable parameters are deduced.
Physical And Morphological Properties Of O II Emitting Galaxies In The HETDEX Pilot Survey
(2015-02) Bridge, Joanna S.; Gronwall, Caryl; Ciardullo, Robin; Hagen, Alex; Zeimann, Greg; Malz, A. I.; Acquaviva, Viviana; Schneider, Donald P.; Drory, Niv; Gebhardt, Karl; Jogee, Shardha; Drory, Niv; Gebhardt, Karl; Jogee, Shardha
The Hobby-Eberly Dark Energy Experiment pilot survey identified 284 [O II] lambda 3727 emitting galaxies in a 169 arcmin(2) field of sky in the redshift range 0 < z < 0.57. This line flux limited sample provides a bridge between studies in the local universe and higher-redshift [O II] surveys. We present an analysis of the star formation rates (SFRs) of these galaxies as a function of stellar mass as determined via spectral energy distribution fitting. The [O II] emitters fall on the "main sequence" of star-forming galaxies with SFR decreasing at lower masses and redshifts. However, the slope of our relation is flatter than that found for most other samples, a result of the metallicity dependence of the [O II] star formation rate indicator. The mass-specific SFR is higher for lower mass objects, supporting the idea that massive galaxies formed more quickly and efficiently than their lower mass counterparts. This is confirmed by the fact that the equivalent widths of the [O II] emission lines trend smaller with larger stellar mass. Examination of the morphologies of the [O II] emitters reveals that their star formation is not a result of mergers, and the galaxies' half-light radii do not indicate evolution of physical sizes.
Population Mobility in Austin, Texas 1929-1931
(University of Texas at Austin, 1941-07-15) University of Texas at Austin
The Relation Between Star Formation Rate And Stellar Mass For Galaxies At 3.5 <= Z <= 6.5 In CANDELS
(2015-02) Salmon, Brett; Papovich, Casey; Finkelstein, Steven L.; Tilvi, Vithal; Finlator, Kristian; Behroozi, Peter; Dahlen, Tomas; Dave, Romeel; Dekel, Avishai; Dickinson, Mark; Ferguson, Henry C.; Giavalisco, Mauro; Long, James; Lu, Yu; Mobasher, Bahram; Reddy, Naveen; Somerville, Rachel S.; Wechsler, Risa H.; Finkelstein, Steven L.
Distant star-forming galaxies show a correlation between their star formation rates (SFRs) and stellar masses, and this has deep implications for galaxy formation. Here, we present a study on the evolution of the slope and scatter of the SFR-stellar mass relation for galaxies at 3.5 <= z <= 6.5 using multi-wavelength photometry in GOODS-S from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) and Spitzer Extended Deep Survey. We describe an updated, Bayesian spectral-energy distribution fitting method that incorporates effects of nebular line emission, star formation histories that are constant or rising with time, and different dust-attenuation prescriptions (starburst and Small Magellanic Cloud). From z = 6.5 to z = 3.5 star-forming galaxies in CANDELS follow a nearly unevolving correlation between stellar mass and SFR that follows SFR similar to M-a* with a = 0.54 +/- 0.16 at z similar to 6 and 0.70 +/- 0.21 at z similar to 4. This evolution requires a star formation history that increases with decreasing redshift (on average, the SFRs of individual galaxies rise with time). The observed scatter in the SFR-stellar mass relation is tight, sigma(log SFR/M-circle dot yr(-1)) < 0.3-0.4 dex, for galaxies with log M*/M-circle dot > 9 dex. Assuming that the SFR is tied to the net gas inflow rate (SFR similar to M-circle dot gas), then the scatter in the gas inflow rate is also smaller than 0.3-0.4 dex for star-forming galaxies in these stellar mass and redshift ranges, at least when averaged over the timescale of star formation. We further show that the implied star formation history of objects selected on the basis of their co-moving number densities is consistent with the evolution in the SFR-stellar mass relation.
Relativistic Ab initio Study On PtF and HePtF
(2010-01) Zou, Wenli L.; Liu, Yang; Boggs, James E.; Zou, Wenli L.; Liu, Yang; Boggs, James E.
The electronic structures and spectroscopic constants of the first three low-lying electronic states (Omega = 1/2, 3/2, and 5/2) of the linear HePtF complex were investigated by highly accurate relativistic ab initio methods, in which the spin-orbit coupling was taken into account, and compared with the results of PtF. It shows that the complex is significantly different from the typical van der Waals systems because of short He-Pt bond distances (1.80 similar to 1.87 angstrom), large He-Pt stretching frequencies (500 similar to 600 cm(-1)), considerable binding energies (1400 similar to 2500 cm(-1) with corrections), and a small electron transfer from helium (about 0.06). However, the topological analysis of the electron density distribution indicates that there is strong van der Waals interaction in the He-Pt bond instead of weak covalent one.
Third-Order Perturbation Theory With Nonlinear Pressure
(2009-07) Shoji, Masatoshi; Komatsu, Eiichiro; Shoji, Masatoshi; Komatsu, Eiichiro
We calculate the nonlinear matter power spectrum using the third-order perturbation theory without ignoring the pressure gradient term. We consider a semirealistic system consisting of two matter components with and without pressure, and both are expanded into the third order in perturbations in a self-consistent manner, for the first time. While the pressured component may be identified with baryons or neutrinos, in this paper we mainly explore the physics of the nonlinear pressure effect using a toy model in which the Jeans length does not depend on time, i.e., the sound speed decreases as a(-1/2), where a is the scale factor. The linear analysis shows that the power spectrum below the so-called filtering scale is suppressed relative to the power spectrum of the cold dark matter. Our nonlinear calculation shows that the actual filtering scale for a given sound speed is smaller than the linear filtering scale by a factor depending on the redshift and the Jeans length. A similar to 40% change is common, and our results suggest that, when applied to baryons, the temperature of the intergalactic medium inferred from the filtering scale observed in the flux power spectrum of Ly alpha forests would be underestimated by a factor of 2, if one used the linear filtering scale to interpret the data. The filtering mass, which is proportional to the filtering scale cubed, can also be significantly smaller than the linear theory prediction especially at low redshift, where the actual filtering mass can be smaller than the linear prediction by a factor of 3. Finally, when applied to neutrinos, we find that neutrino perturbations deviate significantly from linear perturbations even below the free-streaming scales, and thus neutrinos cannot be treated as linear perturbations.
Understanding the Influence of Energy-Density of the Layer Dependent Part Properties in Laser-Sintering of PA12
(University of Texas at Austin, 2019) Wörz, A.; Wudy, K.; Drummer, D.
As the demand for individualization and complex parts is continuously growing, laser-sintering of polymers is on the edge from a pure prototyping technology to manufacturing parts for applications in series production. The influences on resulting parts and layer depending part properties are well known in the literature but the understanding of the interaction between process parameters and layer dependent properties is missing and limiting the dimensioning. Within this study, tensile bars with different amounts of layers and energy densities were produced and investigated for the resulting mechanical properties, roughness, density and the degree of particle melt. The results showed a strong interaction between the energy density and amount of layers, which results in differences in the fracture behavior as well as the mechanical properties. Therefore, the presented results enable the prediction of necessary part thickness for dimensioning thin parts with laser-sintering.
μ-SLS of Metals: Physical and Thermal Characterization of Cu- Nanopowders
(University of Texas at Austin, 2015) Roy, N.K.; Yuksel, A.; Cullinan, M.A.
Micro-scale selective laser sintering(μ-SLS) requires the use of nanoparticles(NPs) since the particle size needs to be an order of magnitude smaller than the melt pool in order to accurately sinter particles together to form a part. Most NPs properties are dependent upon size and thus, an exhaustive study of the physical and thermal properties of these NPs is required in order to successfully model and simulate the sintering process. In this paper we will present particle size characterization using Scanning electron microscopy (SEM), density measurements using He pycnometry, and X-ray Energy Dispersive Spectroscopy that were carried out to characterize the copper(Cu) nanopowder samples. Furthermore, the samples were sintered with different powers to estimate optimum power and exposure times and the results have been discussed along with further scope of work for fully characterizing the particles.