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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Isolation and characterization of endothelial colony-forming cells from mononuclear cells of rat bone marrow

Highlights: • BM-ECFCs are isolated from rat bone marrow with high purity by an optimized method. • Primary colony BM-ECFCs highly display CD34{sup +}/CD133{sup +}/VEGFR2{sup +}. • BM-ECFCs possess and maintain pronounced angiogenic abilities during the expansion. • BM-ECFCs spontaneously form tube-like structures during culture without Matrigel. Transplantation of bone marrow-derived endothelial progenitor cells (BM-EPCs) has been used as a therapeutic strategy for vascular repair. However, it remains controversial whether BM-EPCs exhibit clonal endothelial colony-forming cell (ECFC) capacity, a characteristic of true EPCs. The aim of this study was to isolate and explore the cellular properties of BM-ECFCs. We isolated BM-ECFCs from rat bone marrow with high purity via an optimized method. This approach involved the removal of selective colonies based on the conventional differential adhesive culture method used to isolate ECFCs from peripheral and umbilical cord blood. Our results indicate that primary colony BM-ECFCs display a panel of surface antigen markers consistent with endothelial cells. These BM-ECFCs coexpress CD34, CD133, and VEGFR2 at high levels, and these levels decrease with passaging. These cells have high potential for proliferation, migration, and formation of capillary-like structures on Matrigel, and these abilities are retained during ex vivo expansion. Furthermore, BM-ECFCs cultured with 10% or 20% fetal bovine serum demonstrated two different patterns of spontaneous capillary-like structure formation. These results provide a foundation for isolation of ECFCs from human bone marrow for autologous cell transplantation and tissue engineering applications in the future.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2022

Do Genetic Drift and Gene Flow Affect the Geographic Distribution of Female Plants in Gynodioecious Lobelia siphilitica?

Variation in population sex ratio is particularly pronounced in gynodioecious angiosperms. Extremely high female frequencies in gynodioecious populations cannot be readily explained by selective forces alone. To assess the contributions of drift and gene flow to extreme sex-ratio variation, we documented sex ratio and population size in 92 populations of Lobelia siphilitica across its range and genotyped plants using plastid and nuclear genetic markers. Similarity in spatial patterns of genetic and demographic variables may suggest that drift and/or gene flow have contributed to population sex-ratio variation in L. siphilitica. We found strong spatial structuring of extremely high female frequencies: populations with >50% female plants are restricted to the south–central portion of the range. However, we did not detect any spatial structuring in population size nor metrics of genetic diversity, suggesting that extreme variation in female frequency is not strongly affected by drift or gene flow. Extreme sex-ratio variation is frequently observed in gynodioecious plants, but its causes are difficult to identify. Further investigation into mechanisms that create or maintain the spatial structure of sex ratios in gynodioecious species will provide much needed insight.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

Cdkn1a transcript variant 2 is a marker of aging and cellular senescence

Cellular senescence is a cell fate response characterized by a permanent cell cycle arrest driven primarily the by cell cycle inhibitor and tumor suppressor proteins p16 Ink4a and p21 Cip1/Waf1 . In mice, the p21 Cip1/Waf1 encoding locus, Cdkn1a , is known to generate two transcripts that produce identical proteins, but one of these transcript variants is poorly characterized. We show that the Cdkn1a transcript variant 2, but not the better-studied variant 1, is selectively elevated during natural aging across multiple mouse tissues. Importantly, mouse cells induced to senescence in culture by genotoxic stress (ionizing radiation or doxorubicin) upregulated both transcripts, but with different temporal dynamics: variant 1 responded nearly immediately to genotoxic stress, whereas variant 2 increased much more slowly as cells acquired senescent characteristics. Upon treating mice systemically with doxorubicin, which induces widespread cellular senescence in vivo , variant 2 increased to a larger extent than variant 1. Variant 2 levels were also more sensitive to the senolytic drug ABT-263 in naturally aged mice. Thus, variant 2 is a novel and more sensitive marker than variant 1 or total p21 Cip1/Waf1 protein for assessing the senescent cell burden and clearance in mice.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2022

Sporophyte Stage Genes Exhibit Stronger Selection Than Gametophyte Stage Genes in Haplodiplontic Giant Kelp

Macrocystis pyrifera (giant kelp), a haplodiplontic brown macroalga that alternates between a macroscopic diploid (sporophyte) and a microscopic haploid (gametophyte) phase, provides an ideal system to investigate how ploidy background affects the evolutionary history of a gene. In M. pyrifera , the same genome is subjected to different selective pressures and environments as it alternates between haploid and diploid life stages. We assembled M. pyrifera gene models using available expression data and validated 8,292 genes models using the model alga Ectocarpus siliculosus . Differential expression analysis identified gene models expressed in either or both the haploid and diploid life stages while functional annotation identified processes enriched in each stage. Genes expressed preferentially or exclusively in the gametophyte stage were found to have higher nucleotide diversity (π = 2.3 × 10 –3 and 2.8 × 10 –3 , respectively) than those for sporophytes (π = 1.1 × 10 –3 and 1 × 10 –3 , respectively). While gametophyte-biased genes show faster sequence evolution, the sequence evolution exhibits less signatures of adaptations when compared to sporophyte-biased genes. Our findings contrast the standing masking hypothesis, which predicts higher standing genetic variation at the sporophyte stage, and support the strength of expression theory, which posits that genes expressed more strongly are expected to evolve slower. We argue that the sporophyte stage undergoes more stringent selection compared with the gametophyte stage, which carries a heavy genetic load associated with broadcast spawning. Furthermore, using whole-genome sequencing, we confirm the strong population structure in wild M. pyrifera populations previously established using microsatellite markers, and estimate population genetic parameters, such as pairwise genetic diversity and Tajima’s D , important for conservation and domestication of M. pyrifera .

Molano, Gary↗
DOE OSTI2016

SU-F-T-202: An Evaluation Method of Lifetime Attributable Risk for Comparing Between Proton Beam Therapy and Intensity Modulated X-Ray Therapy for Pediatric Cancer Patients by Averaging Four Dose-Response Models for Carcinoma Induction

Purpose: To examine how much lifetime attributable risk (LAR) as an in silico surrogate marker of radiation-induced secondary cancer would be lowered by using proton beam therapy (PBT) in place of intensity modulated x-ray therapy (IMXT) in pediatric patients. Methods: From 242 pediatric patients with cancers who were treated with PBT, 26 patients were selected by random sampling after stratification into four categories: a) brain, head, and neck, b) thoracic, c) abdominal, and d) whole craniospinal (WCNS) irradiation. IMXT was re-planned using the same computed tomography and region of interest. Using dose volume histogram (DVH) of PBT and IMXT, the LAR of Schneider et al. was calculated for the same patient. The published four dose-response models for carcinoma induction: i) full model, ii) bell-shaped model, iii) plateau model, and ix) linear model were tested for organs at risk. In the case that more than one dose-response model was available, the LAR for this patient was calculated by averaging LAR for each dose-response model. Results: Calculation of the LARs of PBT and IMXT based on DVH was feasible for all patients. The mean±standard deviation of the cumulative LAR difference between PBT and IMXT for the four categories was a) 0.77±0.44% (n=7, p=0.0037), b) 23.1±17.2%,(n=8, p=0.0067), c) 16.4±19.8% (n=8, p=0.0525), and d) 49.9±21.2% (n=3, p=0.0275, one tailed t-test), respectively. The LAR was significantly lower by PBT than IMXT for the the brain, head, and neck region, thoracic region, and whole craniospinal irradiation. Conclusion: In pediatric patients who had undergone PBT, the LAR of PBT was significantly lower than the LAR of IMXT estimated by in silico modeling. This method was suggested to be useful as an in silico surrogate marker of secondary cancer induced by different radiotherapy techniques. This research was supported by the Translational Research Network Program, JSPS KAKENHI Grant No. 15H04768 and the Global Institution for Collaborative Research and Education (GI-CoRE), Hokkaido University, founded by the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2024

Literature Review of Recycling Polypropylene and Polyamide 12 Powders for Selective Laser Sintering

Additive manufacturing (AM) is the creation of three-dimensional parts by adding material layer-by-layer based on two dimensional “slices” of a CAD file, without molds or tooling. AM has broken the relationship between part complexity and manufacturing cost. As a general rule, for conventional manufacturing, the more complex the part produced, the more costly its manufacturing. For example, in the production of a bracket for a satellite, moving from conventional manufacturing to AM allowed the part to be consolidated from 4 parts to just one, as well as reducing the weight of the part by 35%. A further benefit, AM can be more cost effective for small lot sizes. To illustrate, consider a case study of white board marker caps presented by Klahn et al. The cost to produce 1,000 units of a new design using SLS was about an order of magnitude lower than conventional manufacturing, as shown in Figure 1.

36 MATERIALS SCIENCE↗
DOE OSTI2018

The 5T4 oncofetal glycoprotein does not act as a general organizer of the CXCL12 system in cancer cells

Highlights: • The response of cancer cells to CXCL12 either depends on CXCR7 and/or CXCR4. • 5T4 does not dictate the use CXCL12 receptors in most cancer cell lines. • 5T4 does not generally affect subcellular distribution of CXCL12 receptors. • 5T4 per se modulates migration and proliferation of distinct cancer cells. The chemokine, CXCL12, promotes cancer growth and metastasis through interaction with either CXCR4 and/or CXCR7. This tumor-specific organization of the CXCL12 system obscures current therapeutic approaches, aiming at the selective inactivation of CXCL12 receptors. Since it has been previously suggested that the cellular use of CXCR4 or CXCR7 is dictated by the 5T4 oncofetal glycoprotein, we have now tested whether 5T4 would represent a general and reliable marker for the organization of the CXCL12 system in cancer cells. The CXCR4 antagonist, AMD3100, as well as the CXCR7 antagonist, CCX771, demonstrated that the cancer cell lines A549, C33A, DLD-1, MDA-231, and PC-3 use either CXCR7 and/or CXCR4 for mediating CXCL12-induced chemotaxis and cell proliferation. The use of CXCL12 receptors as well as their subcellular localization remained unchanged in most cell lines following siRNA-mediated depletion of 5T4. In distinct cell lines, inhibition of 5T4 expression, however, modulated tumor cell migration and proliferation per se. Collectively our analyses fail to demonstrate general organizational influences of 5T4 of the CXCL12 system in different cancer cell lines, and, hence, dismiss its future use as a diagnostic marker.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2017

In vitro neuroprotective potential of lichen metabolite fumarprotocetraric acid via intracellular redox modulation

The lichen-forming fungi Cetraria islandica has been largely used in folk medicines, and it has recently showed promising in vitro antioxidant effects in glial-like cells. Current work aimed at investigating the neuroprotective potential of its major isolated secondary metabolite: the depsidone fumarprotocetraric acid (FUM). H{sub 2}O{sub 2} was used herein to induce oxidative stress (OS)-mediated cytotoxicity in two models of neurons and astrocytes cells (SH-SY5Y and U373-MG cell lines). We found that a pre-treatment with FUM significantly enhanced cell viability compared to H{sub 2}O{sub 2}-treated cells, and we selected the optimal concentrations in each model (1 and 25 μg/ml, respectively) for assessing its cytoprotective mechanisms. FUM, which exerted effective peroxyl radical scavenging effect in the chemical oxygen radical antioxidant capacity (ORAC) assay, alleviated the alterations in OS markers provoked by H{sub 2}O{sub 2}. It attenuated intracellular ROS formation, lipid peroxidation and GSH depletion. At mitochondrial level, FUM prevented from the dissipation of mitochondrial membrane potential and the increase in mitochondrial calcium, implying a protective role against oxidative damage in mitochondrial membrane. Similarly, FUM pre-treatment diminished H{sub 2}O{sub 2}-induced apoptosis, as evidenced by the reduction in caspase-3 activity and expression; inmunoblot analysis also revealed a decrease in Bax and an increase in Bcl-2 proteins levels. Furthermore, FUM up-regulated the expression of the antioxidant enzymes catalase, superoxide dismutase-1, and hemeoxigenase-1. These findings and the activation of Nrf2 binding activity in nuclear extracts suggest a plausible involvement of Nrf2 signaling pathway in the cytoprotection by FUM. In conclusion, FUM emerges as a potential drug candidate in the therapy of OS-related diseases, such as the neurodegenerative disorders. - Highlights: • FUM pre-treatment exerts significant cytoprotection against H{sub 2}O{sub 2}-mediated apoptosis. • ROS scavenger and mitochondria-targeted effects mediate its antioxidant properties. • A plausible involvement for the cytoprotective Nrf2 pathways is suggested.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2023

Discovering useful genetic variation in the seed parent gene pool for sorghum improvement

Multi-parent populations contain valuable genetic material for dissecting complex, quantitative traits and provide a unique opportunity to capture multi-allelic variation compared to the biparental populations. A multi-parent advanced generation inter-cross (MAGIC) B-line (MBL) population composed of 708 F 6 recombinant inbred lines (RILs), was recently developed from four diverse founders. These selected founders strategically represented the four most prevalent botanical races (kafir, guinea, durra, and caudatum) to capture a significant source of genetic variation to study the quantitative traits in grain sorghum [Sorghum bicolor (L.) Moench]. MBL was phenotyped at two field locations for seven yield-influencing traits: panicle type (PT), days to anthesis (DTA), plant height (PH), grain yield (GY), 1000-grain weight (TGW), tiller number per meter (TN) and yield per panicle (YPP). High phenotypic variation was observed for all the quantitative traits, with broad-sense heritabilities ranging from 0.34 (TN) to 0.84 (PH). The entire population was genotyped using Diversity Arrays Technology (DArTseq), and 8,800 single nucleotide polymorphisms (SNPs) were generated. A set of polymorphic, quality-filtered markers (3,751 SNPs) and phenotypic data were used for genome-wide association studies (GWAS). We identified 52 marker-trait associations (MTAs) for the seven traits using BLUPs generated from replicated plots in two locations. We also identified desirable allelic combinations based on the plant height loci (Dw1, Dw2, and Dw3), which influences yield related traits. Additionally, two novel MTAs were identified each on Chr1 and Chr7 for yield traits independent of dwarfing genes. We further performed a multi-variate adaptive shrinkage analysis and 15 MTAs with pleiotropic effect were identified. The five best performing MBL progenies were selected carrying desirable allelic combinations. Since the MBL population was designed to capture significant diversity for maintainer line (B-line) accessions, these progenies can serve as valuable resources to develop superior sorghum hybrids after validation of their general combining abilities via crossing with elite pollinators. Further, newly identified desirable allelic combinations can be used to enrich the maintainer germplasm lines through marker-assisted backcross breeding.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2018

Two Photon Spectroscopy Can Serve as a Marker of Protein Denaturation Pathway

Rhodamine group of molecules are widely used dyes for imaging of biological molecules. Application of these dyes however includes a limitation that these molecules absorb in the visible range of the spectrum, which does not fall in the ‘biologically transparent window’ (BTW). Two photon absorption (TPA) process could come up with an alternate solution to this as these dyes could be excited in the near infrared (NIR) window to extract similar information. To validate this we have investigated TPA cross section (TPACS, σ{sub 2}) of two rhodamine dyes, namely Rhodamine 6G (R6G), Rhodamine B (RhB), site selectively bound with a model protein, bovine serum albumin (BSA), by exciting at 800 nm. Two photon spectroscopy and imaging confirms the binding of the dye to the protein. The decreases in TPACS with increasing temperature at a fixed BSA concentration excellently follows the temperature induced structural transition of BSA as the protein transforms from a molten globule to unfolded conformation beyond 60 °C, which has previously been established through circular dichroism (CD) measurements. The thus established resemblance in TPACS and CD measurement trends thus strongly affirms the suitability of TPA process in protein imaging and as an alternative marker to tracking its conformational transformations using NIR radiation.

74 ATOMIC AND MOLECULAR PHYSICS↗
NASA NTRS1974

Omega flight-test data reduction sequence

Computer programs for Omega data conversion, summary, and preparation for distribution are presented. Program logic and sample data formats are included, along with operational instructions for each program. Flight data (or data collected in flight format in the laboratory) is provided by the Ohio University Omega receiver base in the form of 6-bit binary words representing the phase of an Omega station with respect to the receiver's local clock. All eight Omega stations are measured in each 10-second Omega time frame. In addition, an event-marker bit and a time-slot D synchronizing bit are recorded. Program FDCON is used to remove data from the flight recorder tape and place it on data-processing cards for later use. Program FDSUM provides for computer plotting of selected LOP's, for single-station phase plots, and for printout of basic signal statistics for each Omega channel. Mean phase and standard deviation are printed, along with data from which a phase distribution can be plotted for each Omega station. Program DACOP simply copies the Omega data deck a controlled number of times, for distribution to users.

Lilley, R. W.↗
DOE OSTI2016

The Quest for Evidence for Proton Therapy: Model-Based Approach and Precision Medicine

Purpose: Reducing dose to normal tissues is the advantage of protons versus photons. We aimed to describe a method for translating this reduction into a clinically relevant benefit. Methods and Materials: Dutch scientific and health care governance bodies have recently issued landmark reports regarding generation of relevant evidence for new technologies in health care including proton therapy. An approach based on normal tissue complication probability (NTCP) models has been adopted to select patients who are most likely to experience fewer (serious) adverse events achievable by state-of-the-art proton treatment. Results: By analogy with biologically targeted therapies, the technology needs to be tested in enriched cohorts of patients exhibiting the decisive predictive marker: difference in normal tissue dosimetric signatures between proton and photon treatment plans. Expected clinical benefit is then estimated by virtue of multifactorial NTCP models. In this sense, high-tech radiation therapy falls under precision medicine. As a consequence, randomizing nonenriched populations between photons and protons is predictably inefficient and likely to produce confusing results. Conclusions: Validating NTCP models in appropriately composed cohorts treated with protons should be the primary research agenda leading to urgently needed evidence for proton therapy.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2022

Electricity Costs and Carbon Implications for CO 2 -to-Fuels in Selected Locations in 2030

With the growing interest in converting carbon dioxide (CO 2 ) to fuels and products to reduce overall greenhouse gas emissions and extend carbon from biogenic and other sources, the development of carbon capture and utilization (CO2U) technologies and industry is crucial. The Markets, Resources, and Environmental and Energy Justice of CO 2 -to-Fuels Technologies (short title: MarkeRs & EEJ) project supports this goal by assessing the resource and market potential and infrastructure requirements for mid-term (-2030) and long-term (-2050) deployment of CO2U technologies. The overall project analyzes CO2U economic and resource requirements as well as sustainability and environmental and energy justice (EEJ) metrics. This report focuses on short-term (-2030) aspects of the project. It identifies three CO2U locations in the Midwestern United States and quantifies the costs for potential electricity resources and marginal emissions for each site in the near term (e.g., 2030). We focus on four electricity purchase options, including retail rate, physical power purchase agreement (PPA), financial PPA, and real-time pricing (RTP), for each of the three sites and consider potential policies such as production tax credits (PTCs). We also assess time-dependent hourly marginal electricity costs and the marginal emission rates using modeled scenarios from Cambium (Gagnon et al. 2021).The results of the analysis are expected to inform other projects within the U.S. Department of Energy's CO 2 -to-Fuels Consortium, especially the Economics and Sustainability of CO 2 Utilization Technologies with Techno-Economic Analysis and Life Cycle Analysis (TEA/LCA) project, led by Michael Wang of Argonne National Laboratory and Ling Tao of the National Renewable Energy Laboratory. The project results are also expected to inform the investment and technology communities and policymakers at the U.S. Department of Energy, state, and regional levels and guide investment by government and industry in research and development portfolios.

09 BIOMASS FUELS↗
DOE OSTI2017

Cytokines and {sup 90}Y-Radioembolization: Relation to Liver Function and Overall Survival

BackgroundTo evaluate the course of pro- and anti-inflammatory cytokines after {sup 90}Y-radioembolization (RE) of liver malignancies and to identify prognosticators for liver-related adverse events and survival.MethodsIn 34 consecutive patients with secondary or primary liver tumors scheduled for RE, the following cytokines were measured prior to and 2 h, 3 days, and 6 weeks after RE: interleukin (IL) -1, IL-2, IL-4, IL-6, IL-8, tumor necrosis factor alpha (TNF-α), and interferon-γ. Liver function impairment was defined as an elevation of liver-related laboratory values as graded by CTCAE ≥ 2 and/or serum bilirubin ≥30 µmol/l and/or development of ascites at 6-week follow-up.ResultsSignificant changes over time were seen in IL-1 (increase from 0.4 pg/ml (±0.7) at baseline to 1.1 pg/ml (±1.4) 3 days after RE (p = 0.02)), and in IL-6 (increase from 16.8 pg/ml (±21.8) at baseline to 54.6 pg/ml (±78.2) 3 days after RE (p = 0.003)). Baseline values of IL-6 and IL-8 were independently associated with liver function impairment at follow-up as well as decreased survival with an optimal cutoff at 6.53 and 60.8 pg/ml, respectively.ConclusionExpected changes in pro- and anti-inflammatory cytokines after RE were shown. Furthermore, baseline values of IL-6 and IL-8 were associated with later liver dysfunction and survival. We hypothesize that these biomarkers are potential prognosticators and might help in patient selection for RE.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
NASA NTRS1990

A study of murine bone marrow cells cultured in bioreactors which create an environment which simulated microgravity

Previous research indicated that mouse bone marrow cells could be grown in conditions of simulated microgravity. This environment was created in rotating bioreactor vessels. On three attempts mouse cells were grown successfully in the vessels. The cells reached a stage where the concentrations were doubling daily. Phenotypic analysis using a panel of monoclonal antibodies indicated that the cell were hematopoietic pluripotent stem cells. One unsuccessful attempt was made to reestablish the immune system in immunocompromised mice using these cells. Since last summer, several unsuccessful attempts were made to duplicate these results. It was determined by electron microscopy that the cells successfully grown in 1989 contained virus particles. It was suggested that these virally parasitized cells had been immortalized. The work of this summer is a continuation of efforts to grow mouse bone marrow in these vessels. A number of variations of the protocol were introduced. Certified pathogen free mice were used in the repeat experiments. In some attempts the medium of last summer was used; in others Dexture Culture Medium containing Iscove's Medium supplemented with 20 percent horse serum and 10-6 M hydrocortisone. Efforts this summer were directed solely to repeating the work of last summer. Plans were made for investigations if stem cells were isolated. Immortalization of the undifferentiated stem cell would be attempted by transfection with an oncogenic vector. Selective differentiation would be induced in the stem cell line by growing it with known growth factors and immune response modulators. Interest is in identifying any surface antigens unique to stem cells that would help in their characterization. Another goal was to search for markers on stem cells that would distinguish them from stem cells committed to a particular lineage. If the undifferentiated hematopoietic stem cell was obtained, the pathways that would terminally convert it to myeloid, lyphoid, erythroid, or other cell lines would be studied. Transfection with a known gene would be attempted and then conversion to a terminally identifiable cell.

Lawless, Brother Desales↗
NASA NTRS1993

Do it yourself remote sensing: Generating an inexpensive, high tech, real science lake mapping project for the classroom

The utilization of modest equipment and software revealed bottom contours and water column conditions of a dynamic water body. Classroom discussions of field techniques and equipment capabilities followed by exercises with the data sets in cause-and-effect analysis all contributed to participatory education in the process of science. This project is presented as a case study of the value of engaging secondary and collegiate level students in planning, executing and appraising a real world investigation which they can directly relate to. A 1 km wide bay, experiencing marsh inflow, along an 8 km long lake situated 120 km north of Ottawa, Canada, on the glaciated Canadian Precambrian Shield was mapped in midsummer for submerged topography, bottom composition, temperature profile, turbudity, dissolved oxygen and biota distribution. Low level aerial photographs scanned into image processing software are permitting spatial classification of bottom variations in biology and geology. Instrumentation consisted of a portable sport fishing SONAR depth finder, an electronic lead line multiprobe with photocell, thermistor and dissolved oxygen sensors, a selective depth water sampler, portable pH meter, an underwater camera mounted on a home-made platform with a bottom-contact trigger and a disposable underwater camera for shallow survey work. Sampling transects were referenced using a Brunton hand transit triangulating several shore markers.

Metzger, Stephen M.↗
DOE OSTI2016

Molecular Characterization of Brown Carbon in Biomass Burning Aerosol Particles

Emissions from biomass burning are a significant source of brown carbon (BrC) in the atmosphere. In this study, we investigate the molecular composition of freshly-emitted biomass burning organic aerosol (BBOA) samples collected during test burns of selected biomass fuels: sawgrass, peat, ponderosa pine, and black spruce. We characterize individual BrC chromophores present in these samples using high performance liquid chromatography coupled to a photodiode array detector and a high-resolution mass spectrometer. We demonstrate that both the overall BrC absorption and the chemical composition of light-absorbing compounds depend significantly on the type of biomass fuels and burning conditions. Common BrC chromophores in the selected BBOA samples include nitro-aromatics, polycyclic aromatic hydrocarbon derivatives, and polyphenols spanning a wide range of molecular weights, structures, and light absorption properties. A number of biofuel-specific BrC chromophores are observed, indicating that some of them may be used as potential markers of BrC originating from different biomass burning sources. On average, ~50% of the light absorption above 300 nm can be attributed to a limited number of strong BrC chromophores, which may serve as representative light-absorbing species for studying atmospheric processing of BrC aerosol. The absorption coefficients of BBOA are affected by solar photolysis. Specifically, under typical atmospheric conditions, the 300 nm absorbance decays with a half-life of 16 hours. A “molecular corridors” analysis of the BBOA volatility distribution suggests that many BrC compounds in the fresh BBOA have low volatility (<1 g m-1) and will be retained in the particle phase under atmospherically relevant conditions.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2023

Polaritonic Chern Insulators in Monolayer Semiconductors

Systems with strong light-matter interaction open up new avenues for studying topological phases of matter. Examples include exciton polaritons, mixed light-matter quasiparticles, where the topology of the polaritonic band structure arises from the collective coupling between matter wave and optical fields strongly confined in periodic dielectric structures. Distinct from light-matter interaction in a uniform environment, the spatially varying nature of the optical fields leads to a fundamental modification of the well-known optical selection rules, which were derived under the plane wave approximation. Here, in this study, we identify polaritonic Chern insulators by coupling valley excitons in transition metal dichalcogenides to photonic Bloch modes in a dielectric photonic crystal slab. We show that polaritonic Dirac points, which are markers for topological phase transition points, can be constructed from the collective coupling between valley excitons and photonic Dirac cones in the presence of both time-reversal and inversion symmetries. Lifting exciton valley degeneracy by breaking time-reversal symmetry leads to gapped polaritonic bands with nonzero Chern numbers. Through numerical simulations, we predict polaritonic chiral edge states residing inside the topological gaps. Our Letter paves the way for the further study of strong exciton-photon interaction in nanophotonic structures and for exploring polaritonic topological phases and their practical applications in polaritonic devices.

74 ATOMIC AND MOLECULAR PHYSICS↗