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NASA NTRS2001

A Return to Io: Science Goals and Implementation

Io remains one of the most fascinating objects in the solar system: the only place beyond Earth where we can watch hard-rock geology in action. In its high heat flow Io resembles the early Earth, providing a present-day analog to some of the processes that dominated the Earth's geology at the time that life first appeared. Io's usefulness as an early-Earth analog has been underscored recently by the detection of very high eruption temperatures, hotter than terrestrial basaltic lavas. These temperatures are most plausibly interpreted as resulting from ultramafic lava compositions, analagous to the komatiites that were common on Earth in the Precambrian but which have been virtually absent during the Phanerozoic. The large scale of many Io eruptions also provides useful analogs to Phanerozoic terrestrial eruptions, such as flood basalts, which are important for the Earth's geological and biological evolution but which occur too rarely to be witnessed by humans on our own planet. By providing living examples, Io can thus play the same role in understanding large-scale planetary volcanism that volcanically active terrestrial regions have played in understanding the results of smaller-scale volcanic processes seen in the geological record worldwide. Additional information is contained in the original extended abstract.

Spencer, J. R.↗

NASA NTRS1993

GEWEX Cloud Systems Study (GCSS)

The Global Energy and Water Cycle Experiment (GEWEX) Cloud Systems Study (GCSS) program seeks to improve the physical understanding of sub-grid scale cloud processes and their representation in parameterization schemes. By improving the description and understanding of key cloud system processes, GCSS aims to develop the necessary parameterizations in climate and numerical weather prediction (NWP) models. GCSS will address these issues mainly through the development and use of cloud-resolving or cumulus ensemble models to generate realizations of a set of archetypal cloud systems. The focus of GCSS is on mesoscale cloud systems, including precipitating convectively-driven cloud systems like MCS's and boundary layer clouds, rather than individual clouds, and on their large-scale effects. Some of the key scientific issues confronting GCSS that particularly relate to research activities in the central U.S. are presented.

Moncrieff, Mitch↗

NASA NTRS1990

Bridgman crystal growth in low gravity - A scaling analysis

The results of an order-of-magnitude or scaling analysis are compared with those of numerical simulations of the effects of steady low gravity on compositional nonuniformity in crystals grown by the Bridgman-Stockbarger technique. In particular, the results are examined of numerical simulations of the effect of steady residual acceleration on the transport of solute in a gallium-doped germanium melt during directional solidification under low-gravity conditions. The results are interpreted in terms of the relevant dimensionless groups associated with the process, and scaling techniques are evaluated by comparing their predictions with the numerical results. It is demonstrated that, when convective transport is comparable with diffusive transport, some specific knowledge of the behavior of the system is required before scaling arguments can be used to make reasonable predictions.

Alexander, J. I. D.↗

NASA NTRS2014

The Development of Stacked Core for the Fabrication of Deep Lightweight UV-Quality Space Mirrors

The 2010 Decadal Survey stated that an advanced large-aperture ultraviolet, optical, near-infrared (UVOIR) telescope is required to enable the next generation of compelling astrophysics and exoplanet science; and, that present technology is not mature enough to affordably build and launch any potential UVOIR mission concept. Under Science and Technology funding, NASA's Marshall Space Flight Center (MSFC) and Exelis have developed a more cost effective process to make 4m class or larger monolithic spaceflight UV quality, low areal density, thermally and dynamically stable primary mirrors. A proof of concept 0.43m mirror was completed at Exelis optically tested at 250K at MSFC which demonstrated the ability for imaging out to 2.5 microns. The parameters and test results of this concept mirror are shown. The next phase of the program includes a 1.5m subscale mirror that will be optically and dynamically tested. The scale-up process will be discussed and the technology development path to a 4m mirror system by 2018 will be outlined.

Matthews, Gary W.↗

NASA NTRS1994

Evaluation of water vapor distribution in general circulation models using satellite observations

This paper presents a comparison of the water vapor distribution obtained from two general circulation models, the European Centre for Medium-Range Weather Forecasts (ECMWF) model and the National Center for Atmospheric Research (NCAR) Community Climate Model (CCM), with satellite observations of total precipitable water (TPW) from Special Sensor Microwave/Imager (SSM/I) and upper tropospheric relative humidity (UTH) from GOES. Overall, both models are successful in capturing the primary features of the observed water vapor distribution and its seasonal variation. For the ECMWF model, however, a systematic moist bias in TPW is noted over well-known stratocumulus regions in the eastern subtropical oceans. Comparison with radiosonde profiles suggests that this problem is attributable to difficulties in modeling the shallowness of the boundary layer and large vertical water vapor gradients which characterize these regions. In comparison, the CCM is more successful in capturing the low values of TPW in the stratocumulus regions, although it tends to exhibit a dry bias over the eastern half of the subtropical oceans and a corresponding moist bias in the western half. The CCM also significantly overestimates the daily variability of the moisture fields in convective regions, suggesting a problem in simulating the temporal nature of moisture transport by deep convection. Comparison of the monthly mean UTH distribution indicates generally larger discrepancies than were noted for TPW owing to the greater influence of large-scale dynamical processes in determining the distribution of UTH. In particular, the ECMWF model exhibits a distinct dry bias along the Intertropical Convergence Zone (ITCZ) and a moist bias over the subtropical descending branches of the Hadley cell, suggesting an underprediction in the strength of the Hadley circulation. The CCM, on the other hand, demonstrates greater discrepancies in UTH than are observed for the ECMWF model, but none that are as clearly correlated with well-known features of the large-scale circulation.

Soden, Brian J.↗

NASA NTRS1993

Processing parameters associated with scale-up of balloon film production

A method is set forth for assessing strain-rate profiles that can be used to develop a scale-up theory for blown-film extrusion. Strain rates are evaluated by placing four ink dots on the stalk of an extruded bubble to follow the displacements of the dots as a function of time. The instantaneous Hencky strain is obtained with the displacement data and plotted for analysis. Specific attention is given to potential sources of error in the distance measurements and corrections for these complex bubble geometries. The method is shown to be effective for deriving strain-rate data related to different processing parameters for the production of balloon film. The strain rates can be compared to frostline height, blow-up ratio, and take-up ratio to optimize these processing variables.

Simpson, D. M.↗

NASA NTRS2015

The AgMIP GRIDded Crop Modeling Initiative (AgGRID) and the Global Gridded Crop Model Intercomparison (GGCMI)

Climate change is a significant risk for agricultural production. Even under optimistic scenarios for climate mitigation action, present-day agricultural areas are likely to face significant increases in temperatures in the coming decades, in addition to changes in precipitation, cloud cover, and the frequency and duration of extreme heat, drought, and flood events (IPCC, 2013). These factors will affect the agricultural system at the global scale by impacting cultivation regimes, prices, trade, and food security (Nelson et al., 2014a). Global-scale evaluation of crop productivity is a major challenge for climate impact and adaptation assessment. Rigorous global assessments that are able to inform planning and policy will benefit from consistent use of models, input data, and assumptions across regions and time that use mutually agreed protocols designed by the modeling community. To ensure this consistency, large-scale assessments are typically performed on uniform spatial grids, with spatial resolution of typically 10 to 50 km, over specified time-periods. Many distinct crop models and model types have been applied on the global scale to assess productivity and climate impacts, often with very different results (Rosenzweig et al., 2014). These models are based to a large extent on field-scale crop process or ecosystems models and they typically require resolved data on weather, environmental, and farm management conditions that are lacking in many regions (Bondeau et al., 2007; Drewniak et al., 2013; Elliott et al., 2014b; Gueneau et al., 2012; Jones et al., 2003; Liu et al., 2007; M¨uller and Robertson, 2014; Van den Hoof et al., 2011;Waha et al., 2012; Xiong et al., 2014). Due to data limitations, the requirements of consistency, and the computational and practical limitations of running models on a large scale, a variety of simplifying assumptions must generally be made regarding prevailing management strategies on the grid scale in both the baseline and future periods. Implementation differences in these and other modeling choices contribute to significant variation among global-scale crop model assessments in addition to differences in crop model implementations that also cause large differences in site-specific crop modeling (Asseng et al., 2013; Bassu et al., 2014).

climate↗

NASA NTRSDate not supplied

Assessing the Variability of Radiation, Water and Energy in the Deep Tropics Over the Last 3 Decades

Global surface energy closure and its variability depends heavily upon the surface radiative energy budget in the deep tropics. A key process observed is the change in convection regimes from disorganized convection to organized deep convection. During these periods an imbalance is observed between energy and water fluxes in terms of energy closure in some atmospheric reanalysis systems, implying that processes are not simulated well. A recent paper by Hsaio et al (2023, pre-published version) found that the transition process has wind shear and longwave cloud radiative feedback signatures. In this presentation, we assess the surface radiative budget in the deep tropics by comparing multiple data products (GEWEX SRB Rel4IP, CERES Ed4.1, ISSCP FH, etc.) and describing the variability across the deep tropics for the period from 1988 to near present. We assess this variability of the radiative flux anomalies (including the net TOA, surface and the atmospheric divergence fluxes) against water vapor divergence, cloud properties (include ISCCP “Weather States, Tselioudis et al. 2021) and larger scale wind shear. We include further analysis contrasting 6 key tropical oceanic regions (Indian Ocean east and west, tropical western, central and eastern Pacific Ocean, and Tropical Atlantic Ocean) and the sensitivity of the fluxes as a function of fluctuations in cloud types in response to various larger scale atmospheric processes (e.g. El Niño, Indian Ocean Dipole). These are contrasted against the modeled radiative fluxes from ERA-5 and MERRA-2. Ocean buoy measurements of radiative fluxes are utilized to help assess data radiative flux uncertainty over the nearly 40 year period. In general, the variability for overlap periods of these various data products agrees well, but there are significant differences in the net fluxes that vary according to the rendering of surface, atmospheric, aerosol and cloud properties. We conclude with recommendations for continuing work.

Radiation budget↗

NASA NTRS1993

Study and modeling of finite rate chemistry effects in turbulent non-premixed flames

The development of numerical models that reflect some of the most important features of turbulent reacting flows requires information about the behavior of key quantities in well defined combustion regimes. In turbulent flames, the coupling between turbulent and chemical processes is so strong that it is extremely difficult to isolate the role played by one individual physical phenomenon. Direct numerical simulation (hereafter DNS) allows us to study in detail the turbulence-chemistry interaction in some restricted but completely defined situations. Globally, non-premixed flames are controlled by two limiting regimes: the fast chemistry case, where the turbulent flame can be pictured as a random distribution of local chemical equilibrium problems; and the slow chemistry case, where the chemistry integrates in time the turbulent fluctuations. The Damkoehler number, ratio of a mechanical time scale to chemical time scale, is used to distinguish between these regimes. Today most of the industrial computer codes are able to perform predictions in the hypothesis of local equilibrium chemistry using a presumed shape for the probability density function (pdt) of the conserved scalar. However, the finite rate chemistry situation is of great interest because industrial burners usually generate regimes in which, at some points, the flame is undergoing local extinction or at least non-equilibrium situations. Moreover, this variety of situations strongly influences the production of pollutants. To quantify finite rate chemistry effect, the interaction between a non-premixed flame and a free decaying turbulence is studied using DNS. The attention is focused on the dynamic of extinction, and an attempt is made to quantify the effect of the reaction on the small scale mixing process. The unequal diffusivity effect is also addressed. Finally, a simple turbulent combustion model based on the DNS observations and tractable in real flow configurations is proposed.

Vervisch, Luc↗

NASA NTRS1992

PC-SEAPAK user's guide, version 4.0

PC-SEAPAK is designed to provide a complete and affordable capability for processing and analysis of NOAA Advanced Very High Resolution Radiometer (AVHRR) and Nimbus-7 Coastal Zone Color Scanner (CZCS) data. Since the release of version 3.0 over a year ago, significant revisions were made to the AVHRR and CZCS programs and to the statistical data analysis module, and a number of new programs were added. This new version has 114 procedures listed in its menus. The package continues to emphasize user-friendliness and interactive data analysis. Additionally, because the scientific goals of the ocean color research being conducted have shifted to larger space and time scales, batch processing capabilities were enhanced, allowing large quantities of data to be easily ingested and analyzed. The development of PC-SEAPAK was paralled by two other activities that were influential and assistive: the global CZCS processing effort at GSFC and the continued development of VAX-SEAPAK. SEAPAK incorporates the instrument calibration and support all levels of data available from the CZCS archive.

Mcclain, Charles R.↗

NASA NTRS1985

Observational requirements for the regional scale

Observational requirements are provided for the 'regional scale' (10(exp 2) to 10(exp 3) km space scale; 3 to 24 h time scale). Given this range, the regional scale represents a spatial and temporal domain in which important scale-interactive processes occur that act to concentrate large vertical wind shears, significant horizontal thermal gradients, and vertical motion patterns into narrow regions. A short review of the mass and momentum adjustments associated with jet streak-induced circulations is discussed. Evidence for the need to specify the wind field in the upper troposphere to accurately simulate forcing for the transverse circulations is also presented. The importance of specifying temperature tendency to resolve the lower tropospheric portion of the transverse circulations is highlighted. The observational requirements are then discussed, along with possible approaches for meeting the requirements on the regional scale.

Uccellini, Louis W.↗

NASA NTRS1994

Scaling effects of defects in fiber-reinforced composites

Material defects may be introduced willingly or unwillingly during material manufacturing and structural component fabrication stages. Their presence in the material plays a dominant role in determining the material's strength and the associate failure mechanisms. In the sense that the size and the number of defects may increase with the volume of the material, the effect of dimensional scaling may manifest itself in the dependence of material strength on volume. Or, alternatively, there may exist a scaling effect of material defects. In fiber-reinforced composites, manufacturing or fabrication defects may come in several forms: matrix voids, matrix microcracks, fiber misalignment, broken fibers, or interface disbonds, just to mention a few. These are interacting and competing defects in the sense that one type of defect may become dominant under one stress condition and another type of defect may become dominant under a different stress condition. This happens because the fiber reinforcement network, together with the distribution of defects, constitutes the prime microstructure of the composite, and there exist continued interactions between the evolving microstructure and the distribution of defects. In the process, the scaling effects of defects are complicated by this interaction. In this presentation, the scaling effects of defects in fiber-reinforced composites will be briefly discussed with the introduction of the concept of effective defects. It is then shown with the aid of some actual experimental and analysis results that the scaling effects are very much present, but they are regulated by the characteristic dimension of the composite microstructure due to the aforementioned microstructure-defect interaction effect.

Wang, A. S. D.↗

NASA NTRS2018

Curiosity's Investigation of the Bagnold Dunes, Gale Crater: Overview of a Two-Phase Scientific Campaign

The Mars Science Laboratory (MSL) Curiosity rover landed at Gale crater in August 2012 with the goal of unravelling the climate and habitability history of ancient Mars. On its way to higher stratigraphic levels of Aeolis Mons, the crater's central mound, Curiosity crossed an active dune field informally named the Bagnold Dune Field. Curiosity's traverse through the Bagnold Dunes between December 2015 and April 2017 constituted the first in situ investigation of an active dune field on another planet. The scientific campaign at the dunes enabled a detailed study of martian eolian processes at scales that are unachievable from orbiter-based imagery, from the scale of compound bedforms down to those of individual sand grains. The eolian-science campaign was broadly divided into two main phases - a first-phase investigation near two barchan dunes along the northern trailing edge of the dune field, Namib and High Dunes, and a second-phase investigation farther south near a linear dune, the Nathan Bridges Dune, named after our beloved colleague and friend Nathan Bridges. In addition to these two phases, the Bagnold Dunes campaign included punctual investigations of isolated ripples and ripple fields further along the rover traverse away from the Bagnold Dune Field. The main goals of the scientific investigation at the Bagnold Dunes were two-fold: (I) developing a mechanistic understanding of martian eolian processes and rates from direct in situ observations of eolian structures and their dynamics, and (II) characterizing the physical properties and the chemical and mineral composition of eolian sands and dust on Mars. Significant advances in martian eolian science resulted from Curiosity's ground investigation of the active Bagnold Dunes. Altogether, results from the Bagnold Dunes campaign are key to understanding how the martian environment affects eolian processes, and will thus prove most useful to deciphering paleoenvironments from the martian eolian sedimentary record.

Lapotre, M. G. A.↗

NASA NTRS1982

Numerical prediction of the Mid-Atlantic states cyclone of 18-19 February 1979

A series of forecast experiments was conducted to assess the accuracy of the GLAS model, and to determine the importance of large scale dynamical processes and diabatic heating to the cyclogenesis. The GLAS model correctly predicted intense coastal cyclogenesis and heavy precipitation. Repeated without surface heat and moisture fluxes, the model failed to predict any cyclone development. An extended range forecast, a forecast from the NMC analysis interpolated to the GLAS grid, and a forecast from the GLAS analysis with the surface moisture flux excluded predicted weak coastal low development. Diabatic heating resulting from oceanic fluxes significantly contributed to the generation of low level cyclonic vorticity and the intensification and slow rate of movement of an upper level ridge over the western Atlantic. As an upper level short wave trough approached this ridge, diabatic heating associated with the release of latent heat intensified, and the gradient of vorticity, vorticity advection and upper level divergence in advance of the trough were greatly increased, providing strong large scale forcing for the surface cyclogenesis.

Atlas, R.↗

NASA NTRS1985

Variation objective analyses for cyclone studies

The objectives were to: (1) develop an objective analysis technique that will maximize the information content of data available from diverse sources, with particular emphasis on the incorporation of observations from satellites with those from more traditional immersion techniques; and (2) to develop a diagnosis of the state of the synoptic scale atmosphere on a much finer scale over a much broader region than is presently possible to permit studies of the interactions and energy transfers between global, synoptic and regional scale atmospheric processes. The variational objective analysis model consists of the two horizontal momentum equations, the hydrostatic equation, and the integrated continuity equation for a dry hydrostatic atmosphere. Preliminary tests of the model with the SESMAE I data set are underway for 12 GMT 10 April 1979. At this stage of purpose of the analysis is not the diagnosis of atmospheric structures but rather the validation of the model. Model runs for rawinsonde data and with the precision modulus weights set to force most of the adjustment of the wind field to the mass field have produced 90 to 95 percent reductions in the imbalance of the initial data after only 4-cycles through the Euler-Lagrange equations. Sensitivity tests for linear stability of the 11 Euler-Lagrange equations that make up the VASP Model 1 indicate that there will be a lower limit to the scales of motion that can be resolved by this method. Linear stability criteria are violated where there is large horizontal wind shear near the upper tropospheric jet.

Achtemeier, G. L.↗

NASA NTRS1978

Characterization and properties of controlled nucleation thermochemical deposited (CNTD) silicon carbide

The microstructure of controlled nucleation thermochemical deposition (CNTD) - SiC material was studied and the room temperature and high temperature bend strength and oxidation resistance was evaluated. Utilizing the CNTD process, ultrafine grained (0.01-0.1 mm) SiC was deposited on W - wires (0.5 mm diameter by 20 cm long) as substrates. The deposited SiC rods had superior surface smoothness and were without any macrocolumnar growth commonly found in conventional CVD material. At both room and high temperature (1200 - 1380 C), the CNTD - SiC exhibited bend strength approximately 200,000 psi (1380 MPa), several times higher than that of hot pressed, sintered, or CVD SiC. The excellent retention of strength at high temperature was attributed to the high purity and fine grain size of the SiC deposit and the apparent absence of grain growth at elevated temperatures. The rates of weight change for CNTD - SiC during oxidation were lower than for NC-203 (hot pressed SiC), higher than for GE's CVD - SiC, and considerably below those for HS-130 (hot pressed Si3N4). The high purity, fully dense, and stable grain size CNTD - SiC material shows potential for high temperature structural applications; however problem areas might include: scaling the process to make larger parts, deposition on removable substrates, and the possible residual tensile stress.

Dutta, S.↗

NASA NTRS2014

Alternative, Green Processes for the Precision Cleaning of Aerospace Hardware

Precision cleaning is necessary to ensure the proper functioning of aerospace hardware, particularly those systems that come in contact with liquid oxygen or hypergolic fuels. Components that have not been cleaned to the appropriate levels may experience problems ranging from impaired performance to catastrophic failure. Traditionally, this has been achieved using various halogenated solvents. However, as information on the toxicological and/or environmental impacts of each came to light, they were subsequently regulated out of use. The solvent currently used in Kennedy Space Center (KSC) precision cleaning operations is Vertrel MCA. Environmental sampling at KSC indicates that continued use of this or similar solvents may lead to high remediation costs that must be borne by the Program for years to come. In response to this problem, the Green Solvents Project seeks to develop state-of-the-art, green technologies designed to meet KSCs precision cleaning needs.Initially, 23 solvents were identified as potential replacements for the current Vertrel MCA-based process. Highly halogenated solvents were deliberately omitted since historical precedents indicate that as the long-term consequences of these solvents become known, they will eventually be regulated out of practical use, often with significant financial burdens for the user. Three solvent-less cleaning processes (plasma, supercritical carbon dioxide, and carbon dioxide snow) were also chosen since they produce essentially no waste stream. Next, experimental and analytical procedures were developed to compare the relative effectiveness of these solvents and technologies to the current KSC standard of Vertrel MCA. Individually numbered Swagelok fittings were used to represent the hardware in the cleaning process. First, the fittings were cleaned using Vertrel MCA in order to determine their true cleaned mass. Next, the fittings were dipped into stock solutions of five commonly encountered contaminants and were weighed again showing typical contaminant deposition levels of approximately 0.00300g per part. They were then cleaned by the solvent or process being tested and then weighed a third time which allowed for the calculation of the cleaning efficiency of the test solvent or process.Based on preliminary experiments, five solvents (ethanol, isopropanol, acetone, ethyl acetate, and tert-butyl acetate) were down selected for further testing. When coupled with ultrasonic agitation, these solvents removed hydrocarbon contaminants as well as Vertrel MCA and showed improved removal of perfluorinated greases. Supercritical carbon dioxide did an excellent job dissolving each of the five contaminants but did a poor job of removing Teflon particles found in the perfluorinated greases. Plasma cleaning efficiency was found to be dependent on which supply gas was used, exposure time, and gas pressure. Under optimized conditions it was found that breathing air, energized to the plasma phase, was able to remove nearly 100% of the contamination.These findings indicate that alternative cleaning methods are indeed able to achieve precision levels of cleanliness. Currently, our team is working with a commercial cleaning company to get independent verification of our results. We are also evaluating the technical and financial aspects of scaling these processes to a size capable of supporting the future cleaning needs of KSC.

Vertrel MCA↗

NASA NTRS2005

High-Power Fiber Lasers Using Photonic Band Gap Materials

High-power fiber lasers (HPFLs) would be made from photonic band gap (PBG) materials, according to the proposal. Such lasers would be scalable in the sense that a large number of fiber lasers could be arranged in an array or bundle and then operated in phase-locked condition to generate a superposition and highly directed high-power laser beam. It has been estimated that an average power level as high as 1,000 W per fiber could be achieved in such an array. Examples of potential applications for the proposed single-fiber lasers include welding and laser surgery. Additionally, the bundled fibers have applications in beaming power through free space for autonomous vehicles, laser weapons, free-space communications, and inducing photochemical reactions in large-scale industrial processes. The proposal has been inspired in part by recent improvements in the capabilities of single-mode fiber amplifiers and lasers to produce continuous high-power radiation. In particular, it has been found that the average output power of a single strand of a fiber laser can be increased by suitably changing the doping profile of active ions in its gain medium to optimize the spatial overlap of the electromagnetic field with the distribution of active ions. Such optimization minimizes pump power losses and increases the gain in the fiber laser system. The proposal would expand the basic concept of this type of optimization to incorporate exploitation of the properties (including, in some cases, nonlinearities) of PBG materials to obtain power levels and efficiencies higher than are now possible. Another element of the proposal is to enable pumping by concentrated sunlight. Somewhat more specifically, the proposal calls for exploitation of the properties of PBG materials to overcome a number of stubborn adverse phenomena that have impeded prior efforts to perfect HPFLs. The most relevant of those phenomena is amplified spontaneous emission (ASE), which causes saturation of gain and power at undesirably low levels, and scattering of light from dopants. In designing a given fiber laser for reduced ASE, care must be taken to maintain a correct fiber structure for eventual scaling to an array of many such lasers such that the interactions among all the members of the array would cause them to operate in phase lock. Hence, the problems associated with improving a single-fiber laser are not entirely separate from the bundling problem, and some designs for individual fiber lasers may be better than others if the fibers are to be incorporated into bundles. Extensive calculations, expected to take about a year, must be performed in order to determine design parameters before construction of prototype individual and fiber lasers can begin. The design effort can be expected to include calculations to optimize overlaps between the electromagnetic modes and the gain media and calculations of responses of PBG materials to electromagnetic fields. Design alternatives and physical responses that may be considered include simple PBG fibers with no intensity-dependent responses, PBG fibers with intensity- dependent band-gap shifting (see figure), and broad-band pumping made possible by use of candidate broad-band pumping media in place of the air or vacuum gaps used in prior PBG fibers.

DiDomenico, Leo↗