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NASA NTRS2000

A Passive Method for Detecting Vegetation Stress from Orbit: Chlorophyll Fluorescence Spectra from Fraunhofer Lines

Solar-stimulated chlorophyll fluorescence measured with the Fraunhofer line depth method has correlated well with vegetation stress in previous studies. However, the instruments used in those studies were limited to a single solar absorption line (e.g. 656.3 nm), obviating the red/far-red ratio (R/FR) method. Optics and detector technology have reached the level whereby multiple, very narrow Fraunhofer lines are resolvable. Thirteen such lines span the visible spectrum in the red to far-red region where chlorophyll fluorescence occurs. Fluorescence intensities at the 13 Fraunhofer line wavelengths were used to model emission spectra. The source data were collected for summer and fall bean crops (Phaseolus vulgaris L.) subjected to various levels of nitrogen fertilization. The intensities were adjusted to account for Fraunhofer line depth and atmospheric transmittance. Multiple R/FR fluorescence ratios, calculated from the modeled fluorescence spectra, correlated strongly with leaf chlorophyll concentration and well with applied nitrogen. The ratio yielding the best correlation with chlorophyll utilized red fluorescence at the 694.5 nm Fraunhofer line and farred fluorescence at the 755.6 nm Fraunhofer line. Twenty R/FR ratios, each evaluated for the maximum differential between low and high (optimal) nitrogen treatments, ranked higher in some cases and lower in others, possibly related to the time of year the crops were grown and the stage of growth of the crops. Ratios with 728.9 nm and 738.9 nm in the denominator consistently ranked in the lowest and next lowest quartile, respectively. Ratios of the 656.3 nm Fraunhofer line and the 755.6 nm line consistently ranked highest for the summer crop. Ratios with 755.6 nm in the denominator ranked in the upper quartile for 10 out of 12 measurement dates. Differences in ratio ranking indicate that physiological conditions may be estimated using selected ratios of Fraunhofer lines within the context of R/FR analysis. A passive instrument designed to monitor R/FR chlorophyll fluorescence (i.e. vegetation stress) from orbit could be built today.

Theisen, Arnold F.↗

NASA NTRS2010

The Hot Horizontal-Branch Stars in omega Centauri

Context. UV observations of some massive globular clusters have revealed a significant population of stars hotter and fainter than the hot end of the horizontal branch (HB), the so-called blue hook stars. This feature might be explained either by the late hot flasher scenario where stars experience the helium flash while on the white dwarf cooling curve or by the progeny of the helium-enriched sub-population recently postulated to exist in some clusters. Previous spectroscopic analyses of blue hook stars in co Cen and NGC 2808 support the late hot flasher scenario, but the stars contain much less helium than expected and the predicted C, N enrichment could not be verified. Aims. We compare observed effective temperatures, surface gravities, helium abundances, and carbon line strengths (where detectable) of our targets stars to the predictions of the two scenarios. Methods. Moderately high resolution spectra of hot HB stars in the globular cluster omega-Cen were analysed for radial velocity variations, atmospheric parameters and abundances using LTE and non-LTE model atmospheres. Results. We find no evidence for close binaries among our target stars. All stars below 30 000 K are helium-poor and very similar to HB stars observed in that temperature range in other globular clusters. In the temperature range 30000 K to 50000 K we find that 28% of our stars are helium-poor (log ((sup n)He/(sup n )H)< - 1.6), while 72% have roughly solar or super-solar helium abundance (log ((sup n)He/(sup n )H) >/= -1.5). We also find carbon enrichment strongly correlated with helium enrichment, with a maximum carbon enrichment of 3% by mass. Conclusions. The strong carbon enrichment in tandem with helium enrichment is predicted by the late hot flasher scenario, but not by the helium-enrichment scenario. We conclude that the helium-rich HB stars in omega-Cen cannot be explained solely by the helium-enrichment scenario invoked to explain the blue main sequence.

Moehler, S.↗

DOE OSTI2024

Strain tuning of vestigial three-state Potts nematicity in a correlated antiferromagnet

Electronic nematicity is a state of matter in which rotational symmetry is spontaneously broken and translational symmetry is preserved. In strongly correlated materials, nematicity often emerges from fluctuations of a multicomponent primary order, such as spin or charge density waves, and is termed vestigial nematicity. One widely studied example is Ising nematicity, which arises as a vestigial order of collinear antiferromagnetism in the tetragonal iron pnictide superconductors. Because nematic directors in crystals are restricted by the underlying crystal symmetry, recently identified quantum materials with three-fold rotational symmetry offer a new platform to investigate nematic order with three-state Potts character. Here, in this study, we demonstrate strain control of three-state Potts nematicity as a vestigial order of zigzag antiferromagnetism in FePSe 3 . Optical linear dichroism measurements reveal the nematic state and demonstrate the rotation of the nematic director by uniaxial strain. We show that the nature of the nematic phase transition can also be controlled by strain, inducing a smooth crossover transition between a Potts nematic transition and an Ising nematic flop transition. Elastocaloric measurements demonstrate the signatures of two coupled phase transitions, indicating that the vestigial nematic transition is separated from the antiferromagnetic transition. This establishes FePSe 3 as a system to explore three-state Potts vestigial nematicity.

Hwangbo, Kyle↗

DOE OSTI2025

Mott transition and correlation effects on strictly localized states in an octagonal quasicrystal

Flat-band systems have attracted significant attention as platforms for studying strongly correlated electron physics, where the dominance of electron-electron interactions over kinetic energy gives rise to a variety of emergent phenomena. Quasicrystals are compelling systems for studying these phenomena as they host degenerate strictly localized states at zero energy due to perfect destructive interference patterns. In this study, we use the slave-rotor mean-field approach to investigate the effects of electron interactions within the Hubbard model on the Ammann-Beenker quasicrystal. The phase diagram characterizing metallic and Mott insulator regions indicates a first-order phase transition. Our analysis shows that the local coordination number affects the local quasiparticle weight, displaying varying metallicity across the sites. Furthermore, we focus on the strictly localized states that arise in the noninteracting limit. We find that interactions and deviation from particle-hole symmetry induce spectral splitting, broadening, and partial delocalization of the localized states, depending on the local environment. In particular, certain localized states with higher coordination numbers remain more robust compared to others. Finally, our results highlight the critical role of local geometry in shaping correlation effects in flat-band quasicrystals.

Mott insulators↗

NASA NTRS1986

Spatial and temporal variability of infrared-observable properties of the Jovian atmosphere: A partial survey

Examination of infrared characteristics of the Jovian atmosphere are made using Voyager IRIS mapping from 1979, groud based scanning from 1979-1983, and ground based mapping from 1983 to the present. In general, there is a strong correlation between tropospheric thermal properties and the visual cloud albedo for all observations. The Voyager IRIS maps show no strong evidence for day/night differences. Temperature differences diminish with depth in the troposphere. Temporal changes over several weeks indicate a high correlation between thermal and visual properties, although no changes in the distribution of para H2 and ortho H2 are seen. Stratospheric banded organization is different from the troposphere, and there is a temperature enhancement near the north magnetic pole. The spatial distributions of ammonia gas and ammonia ice absorption are different. Stratospheric temperatures exhibit seasonal hemispheric asymmetry. Other temperature changes at and below the 150-mb level correlate with changes in the Jovian visual structure. The stratospheric temperature field is uncorrelated with visual features or temperatures below the 150-mb level. Elevated temperatures are observed near both north and south magnetic pole positions. Both the meridional positions and the relative intensities of stratospheric banded organization change significantly, especially after 1982. Ground based mapping confirms a correlation between temperatures and various measures of cloud distribution. Complex and unexpected characteristics are observed in the stratospheric temperature field; these include dramatic temporal changes on short time scales.

Orton, Glenn S.↗

NASA NTRS1990

Correlation of X-ray burst properties with source state in the 'atoll' source 4U/MXB 1636 - 53

A series of Exosat observations of the 'atoll' source 4U/MXB 1636 - 53 shows that duration and temperature of the X-ray bursts strongly correlate with the X-ray spectral and fast variability characteristics of the persistent emission of the source. This implies that spectral shape, fast variability, and burst duration and temperature all correlate well with accretion rate M. This provides a strong argument that in the atoll sources, source-state is determined by M, just as in the Z sources. These observations also show that the persistent X-ray intensity can vary independently from the other mentioned characteristics. Therefore, intensity is probably not a good measure for the accretion rate.

Van Der Klis, M.↗

NASA NTRS1987

The effects of interactions on spiral galaxies. II - Disk star-formation rates

H-alpha emission-line and IRAS far-IR observations of interacting spiral and irregular galaxies are here used to assess the influence of interactions on their global star-formation rates. Two samples of interacting galaxies were observed: a complete sample of close pairs, and an Arp atlas sample of peculiar systems. When compared to a control sample of single galaxies, both samples of interacting systems exhibit systematically higher levels of H-alpha and infrared emission on average, and a larger dispersion in emission properties. Emission levels in the very active system are much more strongly correlated with the properties of the interaction than with the internal properties of the galaxies themselves. Strong disk emission is almost always accompanied by unusually strong nuclear activity. Simple star-formation burst models can reproduce the observed H-alpha equivalent widths and broadband colors of most of the galaxies. The bursts are relatively short (few times 10 million yr) and rarely involve more than 1-2 percent of a galaxy's total mass.

Kennicutt, Robert C., Jr.↗

NASA NTRS1990

Pre-mixed flame simulations for non-unity Lewis numbers

A principal effect of turbulence on premixed flames in the flamelet region is to wrinkle the flame fronts. For non-unity Lewis numbers (Le), the local flame structure is altered in curved regions. This effect is examined using direct numerical simulations of the three dimensional, constant density, decaying isotropic turbulence with a single step, finite rate chemical reaction. Simulations of Lewis numbers 0.8, 1.0, and 1.2 are compared. The turbulent flame speed, S(sub T), increases as Le decreases. The correlation between S(sub T) and u prime found in previous Le = 1 simulations has a strong Lewis number dependency. The variance of the pdf of the flame curvature increases as Le decreases, indicating that the flames become more wrinkled. A strong correlation between local flame speed and curvature was found. For Le greater than 1, the flame speed increases in regions concave towards the products and decreases in convex regions. The opposite correlation was found for Le less than 1. The mean temperature of the products was also found to vary with Lewis number. For Le = 0.8, it is less than the adiabatic flame temperature and for Le = 1.2 it is greater.

Rutland, C. J.↗

NASA NTRS2010

Application of Reflected Global Navigation Satellite System (GNSS-R) Signals in the Estimation of Sea Roughness Effects in Microwave Radiometry

In February-March 2009 NASA JPL conducted an airborne field campaign using the Passive Active L-band System (PALS) and the Ku-band Polarimetric Scatterometer (PolSCAT) collecting measurements of brightness temperature and near surface wind speeds. Flights were conducted over a region of expected high-speed winds in the Atlantic Ocean, for the purposes of algorithm development for salinity retrievals. Wind speeds encountered were in the range of 5 to 25 m/s during the two weeks deployment. The NASA-Langley GPS delay-mapping receiver (DMR) was also flown to collect GPS signals reflected from the ocean surface and generate post-correlation power vs. delay measurements. This data was used to estimate ocean surface roughness and a strong correlation with brightness temperature was found. Initial results suggest that reflected GPS signals, using small low-power instruments, will provide an additional source of data for correcting brightness temperature measurements for the purpose of sea surface salinity retrievals.

Voo, Justin K.↗

NASA NTRS2011

Changing Snow Cover and Stream Discharge in the Western United States - Wind River Range, Wyoming

Earlier onset of springtime weather has been documented in the western United States over at least the last 50 years. Because the majority (>70%) of the water supply in the western U.S. comes from snowmelt, analysis of the declining spring snowpack has important implications for the management of water resources. We studied ten years of Moderate-Resolution Imaging Spectroradiometer (MODIS) snow-cover products, 40 years of stream discharge and meteorological station data and 30 years of snow-water equivalent (SWE) SNOw Telemetry (SNOTEL) data in the Wind River Range (WRR), Wyoming. Results show increasing air temperatures for.the 40-year study period. Discharge from streams in WRR drainage basins show lower annual discharge and earlier snowmelt in the decade of the 2000s than in the previous three decades. Changes in streamflow may be related to increasing air temperatures which are probably contributing to a reduction in snow cover, although no trend of either increasingly lower streamflow or earlier snowmelt was observed within the decade of the 2000s. And SWE on 1 April does not show an expected downward trend from 1980 to 2009. The extent of snow cover derived from the lowest-elevation zone of the WRR study area is strongly correlated (r=0.91) with stream discharge on 1 May during the decade of the 2000s. The strong relationship between snow cover and streamflow indicates that MODIS snow-cover maps can be used to improve management of water resources in the drought-prone western U.S.

Hall, Dorothy K.↗

NASA NTRS2022

Leaf-level chlorophyll fluorescence and reflectance spectra of high latitude plants

Little is known about the chlorophyll fluorescence spectra for high latitude plants. A FluoWat leaf clip was used to measure leaf-level reflectance and chlorophyll fluorescence spectra of leaves of common high latitude plants to examine general spectral characteristics of these species. Fluorescence yield (Fyield) was calculated as the ratio of the emitted fluorescence divided by the absorbed radiation for the wavelengths from 400 nm up to the wavelength of the cut-off for the FluoWat low pass filter (either 650 or 700 nm). The Fyield spectra grouped into distinctly different patterns among different plant functional types. Black spruce (Picea mariana) Fyield spectra had little red fluorescence, which was reabsorbed in the shoot, but displayed a distinct far-red peak. Quaking aspen (Populus tremuloides) had both high red and far-red Fyield peaks, as did sweet coltsfoot (Petasites frigidus). Cotton grass (Eriophorum spp.) had both red and far-red Fyield peaks, but these peaks were much lower than for aspen or coltsfoot. Sphagnum moss (Sphagnum spp.) had a distinct Fyield red peak but low far-red fluorescence. Reindeer moss lichen (Cladonia rangiferina) had very low fluorescence levels, although when damp displayed a small red Fyield peak. These high latitude vegetation samples showed wide variations in Fyield spectral shapes. The Fyield values for the individual red or far-red peaks were poorly correlated to chlorophyll content, however the ratio of far-red to red Fyield showed a strong correlation with chlorophyll content. The spectral variability of these plants may provide information for remote sensing of vegetation type but may also confound attempts to measure high latitude vegetation biophysical characteristics and function using solar induced fluorescence (SIF).

K Fred Huemmrich↗

NASA NTRSDate not supplied

Evaluating The Relationships Between Supine Propriorception Assessments with Upright Functional Mobility and Balance Tests

INTRODUCTION Upon return to Earth, spaceflight sensorimotor adaptations can result in impaired posture and locomotion [1], [2], and current exercise countermeasures in the International Space Station are not sufficient to maintain sensorimotor function. In-flight countermeasures and assessment tools for sensorimotor function are needed to mitigate risks associated with mission-critical task performance upon return to Earth or arrival to 0.38 G on Mars. One proposed countermeasure for proprioceptive deconditioning includes training on a tilt board device [3], which will be tested in an upcoming bed rest study. In preparation for the said study, the objective of this pilot study is to compare performance in supine proprioceptive assessments to performance in functional upright activities. The results are intended to guide the selection of supine assessment tools for the upcoming bedrest study and the development of future inflight proprioceptive training and assessment tools for exploration missions. METHODS Seventeen healthy participants (8 males and 9 females, 27.9 ± 8.5 years) provided informed consent as approved by the Institutional Review Board (IRB) at NASA. A horizontal air-bearing sled was used to provide a proprioceptive challenge in a supine body orientation, allowing for mediolateral motion with minimal friction during supine stance [4]. Participants were loaded axially (30 to 60% body weight) with their feet on a vertically oriented tilt board and instructed to perform supine assessment activities using custom software that displays a cursor controlled by tilting the tilt board. In a single-leg static activity on the tilt board (TB-St), performance was measured as the percent time spent on a center target during a 30-second trial. During a two-feet dynamic activity on the tilt board (TB-Dy), performance was measured as the number of targets captured in 30 seconds. These supine tasks were compared to performance during two upright activities used to represent upright performance: completion time for a functional mobility task (FMT) [2],[5] and a performance score from force plate sway data during 30-second single-leg upright standing (USL). RESULTS AND DISCUSSION A Spearman's rank-order correlation was run to assess the relationship between upright and supine assessments. There were statistically significant, strong correlations between scores for the FMT and each TB activity, including TB-St, rs(17) = 0.50, p<0.05, TB-Dy3, rs(17) = 0.73, p<0.001, and TB-Dy9, rs(15) = 0.53, p<0.05. There were no statistically significant correlations between USL and each TB activity. Despite a lack of correlation with upright single-leg balance, the ability of the TB to indicate upright performance in the FMT is promising, as this task is a standard post-flight measure designed to characterize locomotor dysfunction [2], [5]. CONCLUSION These efforts will inform the selection of an appropriate sensorimotor assessment method for the upcoming bed rest study and similar future studies. While current work uses a bed rest analog to develop these technologies, future work aims to prepare capabilities for future in-flight sensorimotor training and assessment to mitigate the risks of proprioception impairment after spaceflight. ACKNOWLEDGEMENTS This work was supported by the University Space Research Association Internship Program. REFERENCES [1] Mulavara A.P. et al (2018) Med Sci Sports Exerc, 50(9), 1961-1980. [2] Mulavara A.P. et al (2010) Exp Brain Res, 202(3), 649-659. [3] Macaulay T.R. et al (2021) Front. Syst. Neurosci., 15, 658-985. [4] Goel R. et al (2017) Front. Syst. Neurosci, 11. [5] Koppelmans V. et al (2013) BMC Neurology, 12.

R Bellisle↗

DOE OSTI2025

Scalable Implementation of Mean-Field and Correlation Methods Based on Lie-Algebraic Similarity Transformation of Spin Hamiltonians in the Jordan–Wigner Representation

Recent work has highlighted that the strong correlation inherent in spin Hamiltonians can be effectively reduced by mapping spins to Fermions via the Jordan−Wigner transformation (JW). The Hartree−Fock method is straightforward in the Fermionic domain and may provide a reasonable approximation to the ground state. Correlation with respect to the Fermionic mean field can be recovered based on Lie-algebraic similarity transformation (LAST) with two-body correlators. Specifically, a unitary LAST variant eliminates the dependence on site ordering, while a nonunitary LAST yields size-extensive correlation energies. Whereas the first recent demonstration of such methods was restricted to small spin systems, we present efficient implementations using analytical gradients for the optimization with respect to the mean-field reference and the LAST parameters, thereby enabling the treatment of larger clusters, including systems with local spins s > $\frac{1}{2}$.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2025

Towards excitations and dynamical quantities in correlated lattices with density matrix embedding theory

Density matrix embedding theory (DMET) provides a framework to describe ground-state expectation values in strongly correlated systems, but its extension to dynamical quantities is still an open problem. We show one route to obtaining excitations and dynamical spectral functions by using the techniques of DMET to approximate the matrix elements that arise in a single-mode inspired excitation ansatz. We demonstrate this approach in the one-dimensional Hubbard model, comparing the neutral excitations, single-particle density of states, charge, and spin dynamical structure factors to benchmarks from the Bethe ansatz and density matrix renormalization group. Finally, our work highlights the potential of these ideas in building computationally efficient approaches for dynamical quantities.

1-dimensional systems↗

DOE OSTI2024

Downfolding from ab initio to interacting model Hamiltonians: comprehensive analysis and benchmarking of the DFT+cRPA approach

Abstract Model Hamiltonians are regularly derived from first principles to describe correlated matter. However, the standard methods for this contain a number of largely unexplored approximations. For a strongly correlated impurity model system, here we carefully compare a standard downfolding technique with the best possible ground-truth estimates for charge-neutral excited-state energies and wave functions using state-of-the-art first-principles many-body wave function approaches. To this end, we use the vanadocene molecule and analyze all downfolding aspects, including the Hamiltonian form, target basis, double-counting correction, and Coulomb interaction screening models. We find that the choice of target-space basis functions emerges as a key factor for the quality of the downfolded results, while orbital-dependent double-counting corrections diminish the quality. Background screening of the Coulomb interaction matrix elements primarily affects crystal-field excitations. Our benchmark uncovers the relative importance of each downfolding step and offers insights into the potential accuracy of minimal downfolded model Hamiltonians.

Chemistry↗

DOE OSTI2025

Investigation of magnetic fluctuations in L-H and H-L transition dynamics on DIII-D

The dynamics of the L-H transition is not fully understood, with many parameters changing the threshold power to enter H-mode and the self-regulation between zonal flows and turbulence in the plasma edge. This paper is primarily a presentation of experimental results for DIII-D L-H and H-L transitions and speculation on the observations made. Power threshold analysis and measurements of pedestal temperatures for these transitions are presented. A comparison is made between an L-H transition and H-L transition of comparable Psep exhibiting oscillatory behaviour, showing symmetry between forward and backward transition dynamics. This paper shows the first observations of magnetic fluctuations during L-H and H-L transitions on DIII-D, and shows that L-H and H-L transitions have similar magnetic fluctuation dynamics. Information geometry analysis has been performed on measurements of plasma density fluctuations, perpendicular plasma velocity fluctuations, and magnetic field fluctuations to investigate the self-regulation and evolution of these variables during the transitions. Perpendicular flow evolution is shown to dominate the transition dynamics in both directions, but self-regulation behaviour is observed between all three variables. A strong correlation between magnetic fluctuation information rate and density fluctuation information rate for these two shots shows the strong influence of magnetic behaviour on both the L-H and H-L transition, and that these transition dynamics necessarily include electromagnetic effects.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2024

Properties of Nb x Ti (1–x) N thin films deposited on 300 mm silicon wafers for upscaling superconducting digital circuits

Scaling superconducting digital circuits requires fundamental changes in the current material set and fabrication process. The transition to 300 mm wafers and the implementation of advanced lithography are instrumental in facilitating mature CMOS processes, ensuring uniformity, and optimizing the yield. Here, this study explores the properties of Nb x Ti (1–x) N films fabricated by magnetron DC sputtering on 300 mm Si wafers. As a promising alternative to traditional Nb in device manufacturing, Nb x Ti (1–x) N offers numerous advantages, including enhanced stability and scalability to smaller dimensions, in both processing and design. As a ternary material, Nb x Ti (1–x) N allows engineering material parameters by changing deposition conditions. The engineered properties can be used to modulate device parameters through the stack and mitigate failure modes. We report characterization of Nb x Ti (1–x) N films at less than 2% thickness variability, 2.4% T c variability and 3% composition variability. Film resistivity (140–375 Ωcm) shows a strong correlation with the film oxygen content, while the critical temperature T c (4.6 K–14.1 K) is strongly affected by film stoichiometry and its microstructure has only a moderate effect on modifying T c . Our results offer insights about the interplay between film stoichiometry, film microstructure and critical temperature.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

NASA NTRS1995

A multiparametric analysis of the Einstein sample of early-type galaxies. 2: Galaxy formation history and properties of the interstellar medium

We have conducted bivariate and multivariate statistical analysis of data measuring the integrated luminosity, shape, and potential depth of the Einstein sample of early-type galaxies (presented by Fabbiano et al. 1992). We find significant correlations between the X-ray properties and the axial ratios (a/b) of our sample, such that the roundest systems tend to have the highest L(sub x) and L(sub x)/L(sub B). The most radio-loud objects are also the roundest. We confirm the assertion of Bender et al. (1989) that galaxies with high L(sub x) are boxy (have negative a(sub 4)). Both a/b and a(sub 4) are correlated with L(sub B), but not with IRAS 12 um and 100 um luminosities. There are strong correlations between L(sub x), Mg(sub 2), and sigma(sub nu) in the sense that those systems with the deepest potential wells have the highest L(sub x) and Mg(sub 2). Thus the depth of the potential well appears to govern both the ability to reatin an ISM at the present epoch and to retain the enriched ejecta of early star formation bursts. Both L(sub x)/L(sub B) and L(sub 6) (the 6 cm radio luminosity) show threshold effects with sigma(sub nu) exhibiting sharp increases at log sigma(sub nu) approximately = 2.2. Finally, there is clearly an interrelationship between the various stellar and structural parameters: The scatter in the bivariate relationships between the shape parameters (a/b and a(sub 4)) and the depth parameter sigma(sub nu) is a function of abundance in the sense that, for a given a(sub 4) or a/b, the systems with the highest sigma(sub nu) also have the highest Mg(sub 2). Furthermore, for a constant sigma(sun nu), disky galaxies tend to have higher Mg(sub 2) than boxy ones. Alternatively, for a given abundance, boxy ellipticals tend to be more massive than disky ellipticals. One possibility is that early-type galaxies of a given mass, originating from mergers (boxy ellipticals), have lower abundances than 'primordial' (disky) early-type galaxies. Another is that disky inner isophotes are due not to primordial dissipation collapse, but to either the self-gravitating inner disks of captured spirals or the dissipational collapse of new disk structures from the premerger ISM. The high measured nuclear Mg(sub 2) values would thus be due to enrichment from secondary bursts of star formation triggered by the merging event.

Eskridge, Paul B.↗