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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

Continuous-wave parametric oscillation in polarisation-maintaining optical fibre

Continuous-wave parametric oscillation in a polarisation-maintaining optical fibre has been achieved for the first time using polarisation phase matching. Up-conversion with a frequency shift of {approx}8.6 THz has been demonstrated experimentally. The single-pass optical power generated at 1017 nm in a 85-m-long Nufern PM980-XP fibre exceeded 40 mW. The conversion efficiency was 3.3%, which is an order of magnitude higher than that reported previously for cw parametric up-conversion in the 1-{mu}m spectral region. We compare theoretical predictions with experimental data and analyse factors that may influence output power saturation with increasing signal and pump powers.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Quasi-regenerative mode locking in a compact all-polarisation-maintaining-fibre laser

A novel technique of mode locking in erbium-doped all-polarisation-maintaining-fibre laser has been developed and preliminary investigated. The proposed quasi-regenerative technique combines the advantages of conventional active mode locking (when an intracavity modulator is driven by an independent RF oscillator) and regenerative mode locking (when a modulator is driven by an intermode beat signal from the laser itself). This scheme is based on intracavity intensity modulation driven by an RF oscillator being phase-locked to the actual intermode frequency of the laser. It features also possibilities of operation at multiple frequencies and harmonic mode-locking operation. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Amplification of dissipative solitons with a polarisation-maintaining tapered fibre amplifier

The generation of strongly chirped dissipative solitons offers great opportunities for generating high-power laser pulses of short duration. We demonstrate the possibility of amplifying such pulses in a polarisation-maintaining tapered fibre having 32 μm mode diameter at the output end. Highly chirped pulses with a repetition rate of 14.3 MHz and a duration of 10 ps at 1055 nm centre wavelength are amplified in an all-fibre circuit to 2.11 μJ energy and compressed by diffraction gratings to a duration of ∼297 fs. Reducing the pulse repetition rate to 1 MHz allows a 16.5 μJ output pulse energy to be achieved without manifestations of SRS and self-phase modulation in the spectrum. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Simulation of generation of ultrashort pulses in a laser based on the nonlinear polarisation evolution in two segments of a polarisation-maintaining fibre

A model describing generation of ultrashort optical pulses in a fibre cavity with Kerr nonlinearity and normal dispersion is constructed based on numerical solution of a nonlinear Schrödinger equation. The model makes it possible to investigate the specific features of pulsed generation of a passively mode-locked laser based on the effect of nonlinear polarisation evolution (NPE) in two segments of a polarisation-maintaining (PM) fibre. It is shown theoretically that the proposed scheme may provide generation of linearly chirped optical pulses with a spectral width of above 25 nm and a centre wavelength of 1030 nm. (generation of ultrashort laser pulses)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Critical role of Chlamydomonas reinhardtii ferredoxin-5 in maintaining membrane structure and dark metabolism

Photosynthetic microorganisms typically have multiple isoforms of the electron transfer protein ferredoxin, although we know little about their exact functions. Surprisingly, a Chlamydomonas reinhardtii mutant null for the ferredoxin-5 gene (FDX5) completely ceased growth in the dark, with both photosynthetic and respiratory functions severely compromised; growth in the light was unaffected. Thylakoid membranes in dark-maintained fdx5 mutant cells became severely disorganized concomitant with a marked decrease in the ratio of monogalactosyldiacylglycerol to digalactosyldiacylglycerol, major lipids in photosynthetic membranes, and the accumulation of triacylglycerol. Furthermore, FDX5 was shown to physically interact with the fatty acid desaturases CrΔ4FAD and CrFAD6, likely donating electrons for the desaturation of fatty acids that stabilize monogalactosyldiacylglycerol. Our results suggest that in photosynthetic organisms, specific redox reactions sustain dark metabolism, with little impact on daytime growth, likely reflecting the tailoring of electron carriers to unique intracellular metabolic circuits under these two very distinct redox conditions.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2018

Life history variation is maintained by fitness trade-offs and negative frequency-dependent selection

Significance Many populations and species have different strategies for maximizing reproductive success in changing environments. For example, some species of plants reproduce only once in their lifetime (annuals), whereas others can reproduce over multiple years (perennials). Such variation can also occur in fishes, and we examine how this variation in life history strategies is maintained in a Pacific salmonid species ( Oncorhynchus mykiss ). We find that fish that successfully migrate between the ocean and their freshwater spawning grounds multiple times (repeat spawners) have more than twice the lifetime reproductive success of fish that only spawn once (single spawners). We also find a striking pattern of negative frequency-dependent selection in which older, larger females have higher lifetime fitness when they are less abundant.

Christie, Mark R.↗
DOE OSTI2013

T-cell Receptor Specificity Maintained by Altered Thermodynamics

The T-cell receptor (TCR) recognizes peptides bound to major histocompatibility molecules (MHC) and allows T-cells to interrogate the cellular proteome for internal anomalies from the cell surface. The TCR contacts both MHC and peptide in an interaction characterized by weak affinity (K D = 100 nM to 270 M). We used phage-display to produce a melanoma-specific TCR (α24β17) with a 30,000-fold enhanced binding affinity (K D = 0.6 nM) to aid our exploration of the molecular mechanisms utilized to maintain peptide specificity. Remarkably, although the enhanced affinity was mediated primarily through new TCR-MHC contacts, α24β17 remained acutely sensitive to modifications at every position along the peptide backbone, mimicking the specificity of the wild type TCR. Thermodynamic analyses revealed an important role for solvation in directing peptide specificity. These findings advance our understanding of the molecular mechanisms that can govern the exquisite peptide specificity characteristic of TCR recognition.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2018

Collective Dispersal Leads to Variance in Fitness and Maintains Offspring Size Variation within Marine Populations

Variance in fitness is well known to influence the outcome of evolution but is rarely considered in the theory of marine reproductive strategies. In coastal environments, turbulent mesoscale eddies can collect larvae into packets, resulting in collective dispersal. Larvae in packets return to the coast or are lost offshore in groups, producing variance in fitness. Using a Markov process to calculate fixation probabilities for competing phenotypes, we examine the evolution of offspring size and spawning duration in species with benthic adults and pelagic offspring. The offspring size that provides mothers with the highest mean fitness also generates the greatest variance in fitness, but pairwise invasion plots show that bet-hedging strategies are not evolutionarily stable; maximizing expected fitness correctly predicts the unique evolutionarily stable strategy. Nonetheless, fixation can take a long time. We find that selection to increase spawning duration as a risk avoidance strategy to reduce the negative impacts of stochastic recruitment success can allow multiple offspring sizes to coexist in a population for extended periods. This has two important consequences for offspring size: (1) coexistence occurs over a broader range of sizes and is longer when spawning duration is longer because longer spawning durations reduce variation in fitness and increase the time to fixation, and (2) longer spawning durations can compensate for having a nonoptimal size and even allow less optimal sizes to reach fixation. Collective dispersal and longer spawning durations could effectively maintain offspring size variation even in the absence of good and bad years or locations. Finally, empirical comparisons of offspring size would therefore not always reflect environment-specific differences in the optimal size.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2015

Outflows and bubbles in Taurus: Star-formation feedback sufficient to maintain turbulence

We have identified outflows and bubbles in the Taurus molecular cloud based on the ∼100 deg{sup 2} Five College Radio Astronomy Observatory {sup 12}CO(1-0) and {sup 13}CO(1-0) maps and the Spitzer young stellar object catalogs. In the main 44 deg{sup 2} area of Taurus, we found 55 outflows, of which 31 were previously unknown. We also found 37 bubbles in the entire 100 deg{sup 2} area of Taurus, none of which had been found previously. The total kinetic energy of the identified outflows is estimated to be ∼3.9×10{sup 45} erg, which is 1% of the cloud turbulent energy. The total kinetic energy of the detected bubbles is estimated to be ∼9.2×10{sup 46} erg, which is 29% of the turbulent energy of Taurus. The energy injection rate from the outflows is ∼1.3×10{sup 33} erg s{sup −1}, which is 0.4–2 times the dissipation rate of the cloud turbulence. The energy injection rate from bubbles is ∼6.4×10{sup 33} erg s{sup −1}, which is 2–10 times the turbulent dissipation rate of the cloud. The gravitational binding energy of the cloud is ∼1.5×10{sup 48} erg, that is, 385 and 16 times the energy of outflows and bubbles, respectively. We conclude that neither outflows nor bubbles can provide sufficient energy to balance the overall gravitational binding energy and the turbulent energy of Taurus. However, in the current epoch, stellar feedback is sufficient to maintain the observed turbulence in Taurus.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Calibration of photoelastic modulator based dichrometers: maintaining constant phase across the spectrum

Photoelastic modulators can alter the polarization state of a beam of ultraviolet, visible or infrared photons by means of periodic stress-induced differences in the refractive index of a transparent material that forms the optical element of the device and is isotropic in the absence of stress. Furthermore, they have found widespread application in instruments that characterize or alter the polarization state of a beam in fields as diverse as astronomy, structural biology, materials science and ultraviolet lithography for the manufacture of nano-scale integrated circuits. Measurement of circular dichroism, the differential absorption of left- and right circularly polarized light, and of strain-induced birefringence of optical components are major applications. Instruments using synchrotron radiation and photoelastic modulators with CaF 2 optical elements have extended circular dichroism measurements down to wavelengths of about 130 nm in the vacuum ultraviolet. Maintaining a constant phase shift between two orthogonal polarization states across a spectrum requires that the amplitude of the modulated stress be changed as a function of wavelength. For commercially available photoelastic modulators, the voltage that controls the amplitude of modulation required to produce a specified phase shift, which is a surrogate for the stress modulation amplitude, has been shown to be an approximately linear function of wavelength in the spectral region where the optical element is transparent. But, extrapolations of such straight lines cross zero voltage at a non-zero wavelength, not at zero-wavelength. For modulators with calcium fluoride and fused silica optical elements, the zero-crossing wavelength is always in the spectral region where the optical element of the modulator strongly absorbs the incident radiation, and at a wavelength less than the longest-wavelength apparent resonance deduced from experimental values of the refractive index fit to the Sellmeier equation. Using a model that relates the refractive indices of a stressed optical element to the refractive index of its unstressed state, an expression for the modulator control voltage was derived that closely fits the experimental data. Our result provides a theoretical rational for the apparently linear constant-phase programming voltage, and thus provides theoretical backing for the calibration procedure frequently used for these modulators. Lastly there are other factors that can influence the calibration of a photoelastic modulator, including temperature and atmospheric pressure, are discussed briefly.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2023

Cooperative actin filament nucleation by the Arp2/3 complex and formins maintains the homeostatic cortical array in Arabidopsis epidermal cells

Abstract Precise control over how and where actin filaments are created leads to the construction of unique cytoskeletal arrays within a common cytoplasm. Actin filament nucleators are key players in this activity and include the conserved actin-related protein 2/3 (Arp2/3) complex as well as a large family of formins. In some eukaryotic cells, these nucleators compete for a common pool of actin monomers and loss of one favors the activity of the other. To test whether this mechanism is conserved, we combined the ability to image single filament dynamics in the homeostatic cortical actin array of living Arabidopsis (Arabidopsis thaliana) epidermal cells with genetic and/or small molecule inhibitor approaches to stably or acutely disrupt nucleator activity. We found that Arp2/3 mutants or acute CK-666 treatment markedly reduced the frequency of side-branched nucleation events as well as overall actin filament abundance. We also confirmed that plant formins contribute to side-branched filament nucleation in vivo. Surprisingly, simultaneous inhibition of both classes of nucleator increased overall actin filament abundance and enhanced the frequency of de novo nucleation events by an unknown mechanism. Collectively, our findings suggest that multiple actin nucleation mechanisms cooperate to generate and maintain the homeostatic cortical array of plant epidermal cells.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Aureochromes maintain polyunsaturated fatty acid content in Nannochloropsis oceanica

Abstract Nannochloropsis oceanica, like other stramenopile microalgae, is rich in long-chain polyunsaturated fatty acids (LC-PUFAs) such as eicosapentaenoic acid (EPA). We observed that fatty acid desaturases (FADs) involved in LC-PUFA biosynthesis were among the strongest blue light-induced genes in N. oceanica CCMP1779. Blue light was also necessary for maintaining LC-PUFA levels in CCMP1779 cells, and growth under red light led to a reduction in EPA content. Aureochromes are stramenopile-specific proteins that contain a light–oxygen–voltage (LOV)-sensing domain that associates with a flavin mononucleotide and is able to sense blue light. These proteins also contain a basic leucine zipper DNA-binding motif and can act as blue light-regulated transcription factors by associating with an E-box like motif, which we found enriched in the promoters of blue light-induced genes. We demonstrated that, in vitro, two CCMP1779 aureochromes were able to absorb blue light. Moreover, the loss or reduction of the expression of any of the three aureochrome genes led to a decrease in the blue light-specific induction of several FADs in CCMP1779. EPA content was also significantly reduced in NoAUREO2 and NoAUREO4 mutants. Taken together, our results indicate that aureochromes mediate blue light-dependent regulation of LC-PUFA content in N. oceanica CCMP1779 cells.

Plant Sciences↗
DOE OSTI2022

Why are cell populations maintained via multiple compartments?

We consider the maintenance of ‘product’ cell populations from ‘progenitor’ cells via a sequence of one or more cell types, or compartments, where each cell’s fate is chosen stochastically. If there is only one compartment then large amplification, that is, a large ratio of product cells to progenitors comes with disadvantages. The product cell population is dominated by large families (cells descended from the same progenitor) and many generations separate, on average, product cells from progenitors. These disadvantages are avoided using suitably constructed sequences of compartments: the amplification factor of a sequence is the product of the amplification factors of each compartment, while the average number of generations is a sum over contributions from each compartment. Passing through multiple compartments is, in fact, an efficient way to maintain a product cell population from a small flux of progenitors, avoiding excessive clonality and minimizing the number of rounds of division en route. We use division, exit and death rates, estimated from measurements of single-positive thymocytes, to choose illustrative parameter values in the single-compartment case. We also consider a five-compartment model of thymocyte differentiation, from double-negative precursors to single-positive product cells.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2016

Tests of constituent-quark generation methods which maintain both the nucleon center of mass and the desired radial distribution in Monte Carlo Glauber models

Here, several methods of generating three constituent quarks in a nucleon are evaluated which explicitly maintain the nucleon's center of mass and desired radial distribution and can be used within Monte Carlo Glauber frameworks. The geometric models provided by each method are used to generate distributions over the number of constituent quark participants ( N qp ) in p+p,d+Au, and Au+Au collisions. The results are compared with each other and to a previous result of N qp calculations, without this explicit constraint, used in measurements of √S NN = 200 GeV p+p,d+Au, and Au+Au collisions at the BNL Relativistic Heavy Ion Collider.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Bounded Universal Droop Control to Enable the Operation of Power Inverters Under Some Abnormal Conditions and Maintain Voltage and Frequency Within Predetermined Ranges

The universal droop control (UDC) can be applied to power inverters having an impedance angle between -pi/2 rad and pi/2 rad to achieve voltage and frequency regulation and accurate proportional power sharing without the need of knowing the type or value of impedance. However, there is an increasing need for voltage and frequency regulation within predetermined ranges even under some abnormal conditions, such as overloading, sensor faults, and large set-point changes, etc. In this paper, a bounded nonlinear dynamics is introduced into the UDC to ensure that the voltage and frequency can always stay within predetermined ranges under normal and some abnormal conditions, up to hardware limits when current protection needs to be triggered. As a result, the proposed controller can extend the operational range of power inverters in terms of voltage and frequency regulation to cover different scenarios. More importantly, the ranges for both voltage and frequency can be chosen independently from each other. Since the original structure of the UDC is kept in the proposed controller, the properties of the UDC, such as without the need of knowing the type or value of impedance, are well maintained. Furthermore, the closed-loop stability of the system is established via the Lyapunov method. Extensive simulation and experimental results are presented to validate the effectiveness of the proposed controller.

14 SOLAR ENERGY↗
DOE OSTI2024

Towards maintaining canine training aid integrity: Effects of environmental factors and operational use on the triacetone triperoxide polymer odor capture‐and‐release system

Abstract There are many factors that may affect the longevity of or guide the use of canine training aids. Literature to date has mainly focused on identifying the headspace volatiles associated with training aids or odors and only minimal research exists into how different variables may alter those volatiles. The current study examines several factors affecting canine training aids: humidity, air flow, transportation, and operational deployment, using the triacetone triperoxide polymer odor capture‐and‐release canine training aid (TATP POCR) as the target. The TATP POCR is an absorption‐based canine training aid developed to be used to safely train canines to detect the odor of the explosive TATP in operational settings. Comparisons of the TATP POCR to neat TATP are made throughout the manuscript. First, humidity increased the background components of the POCR matrix, as well as the amount of TATP recovered was above the POCR. Humidity thus affected the amount of TATP detected but did not prevent detection. Second, air flow lessened the lifetime of the TATP POCR. Third, the practice of using primary and secondary containment successfully prevented contamination, cross‐contamination, and significant target loss, thereby maintaining kit integrity. Finally, the absorption of background odors from training environments was not observed. TATP headspace concentrations between a Deployed and Control POCR kit were not significantly different at time 0 (i.e., upon opening), which suggests that the operational use does not affect the function of the TATP POCR system. This information provides pivotal evidence for explosives detection canine handlers or trainers who utilize the TATP POCR.

Legal Medicine↗
DOE OSTI2016

Rare Taxa Maintain Microbial Diversity and Contribute to Terrestrial Community Dynamics throughout Bark Beetle Infestation

A global phenomenon of increasing bark beetle-induced tree mortality has heightened concerns regarding ecosystem response and biogeochemical implications. Here, we explore microbial dynamics under lodgepole pines through the analysis of bulk (16S rRNA gene) and potentially active (16S rRNA) communities to understand the terrestrial ecosystem responses that are associated with this form of large-scale tree mortality. Here, we found that the relative abundances of bulk and potentially active taxa were correlated across taxonomic levels, but at lower levels, cladal differences became more apparent. Despite this correlation, there was a strong differentiation of community composition between bulk and potentially active taxa, with further clustering associated with the stages of tree mortality. Surprisingly, community clustering as a function of tree phase had limited correlation to soil water content and total nitrogen concentrations, which were the only two measured edaphic parameters to differ in association with tree phase. Bacterial clustering is more readily explained by the observed decrease in the abundance of active, rare microorganisms after tree death in conjunction with stable alpha diversity measurements. This enables the rare fraction of the terrestrial microbial community to maintain metabolic diversity by transitioning between metabolically active and dormant states during this ecosystem disturbance and contributes disproportionately to community dynamics and archived metabolic capabilities. Here, these results suggest that analyzing bulk and potentially active communities after beetle infestation may be a more sensitive indicator of disruption than measuring local edaphic parameters. Forests around the world are experiencing unprecedented mortality due to insect infestations that are fueled in part by a changing climate. While aboveground processes have been explored, changes at the terrestrial interface that are relevant to microbial biogeochemical cycling remain largely unknown. Here in this study, we investigated the changing bulk and potentially active microbial communities beneath healthy and beetle-killed trees. We found that, even though few edaphic parameters were altered from beetle infestation, the rare microbes were more likely to be active and fluctuate between dormancy and metabolic activity. Finally, this indicates that rare as opposed to abundant taxa contribute disproportionately to microbial community dynamics and presumably biogeochemical cycling within these types of perturbed ecosystems.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2017

Functional photosystem I maintains proper energy balance during nitrogen depletion in Chlamydomonas reinhardtii, promoting triacylglycerol accumulation

Nutrient deprivation causes significant stress to the unicellular microalga, Chlamydomonas reinhardtii, which responds by significantly altering its metabolic program. In following N deprivation, the accumulation of starch and triacylglycerols (TAGs) is significantly altered following massive reprogramming of cellular metabolism. One protein that was found to change dramatically and early to this stress was TAB2, a photosystem I (PSI) translation initiation factor, whose transcript and protein levels increased significantly after only 30 min of N deprivation. A detailed physiological and omics-based analysis of an insertional mutant of Chlamydomonas with reduced TAB2 function was conducted to determine what role the functional PSI plays in regulating the cellular response to N deprivation. The tab2 mutant displayed increased acetate assimilation and elevated starch levels during the first 6 h of N deprivation, followed by a shift toward altered amino acid synthesis, reduced TAG content and altered fatty acid profiles. Our results suggested a central role for PSI in controlling cellular metabolism and its implication in regulation of lipid/starch partitioning. Time course analyses of the tab2 mutant versus wild type under N-deprived versus N replete conditions revealed changes in the ATP/NADPH ratio and suggested that TAG biosynthesis may be associated with maintaining the redox state of the cell during N deprivation. The loss of ability to accumulate TAG in the tab2 mutant co-occurred with an up-regulation of photo-protective mechanisms, suggesting that the synthesis of TAG in the wild type occurs not only as a temporal energy sink, but also as a protective electron sink. By exploiting the tab2 mutation in the cells of C. reinhardtii cultured under autotrophic, mixotrophic, and heterotrophic conditions during nitrogen replete growth and for the first 8 days of nitrogen deprivation, we showed that TAG accumulation and lipid/starch partitioning are dynamically regulated by alterations in PSI function, which concomitantly alters the immediate ATP/NADPH demand. This occurs even without removal of nitrogen from the medium, but sufficient external carbon must nevertheless be available. Our efforts to increase lipid accumulation in algae such as Chlamydomonas need to consider carefully how the energy balance of the cell is involved in or affected by such efforts and that numerous layers of metabolic and genetic regulatory control are likely to interfere with such efforts to control oil biosynthesis. Such knowledge will enable synthetic biology approaches to alter the response to the N depletion stress, leading to rewiring of the regulatory networks so that lipid accumulation could be turned on in the absence of N deprivation, allowing for the development of algal production strains with highly enhanced lipid accumulation profiles.

09 BIOMASS FUELS↗