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At least 1,063 records · Page 59
All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

Phase transitions in colloids under microgravity

Research on colloids is motivated by several factors. They can be used to answer fundamental questions related to the assembly of materials, and they have many potential applications in electronics, photonics, and life sciences. However, the rich variety of colloidal structures observed on the Earth can be influenced by the effects of gravity, which leads to particles settling and the motion of the surrounding fluid. To suppress the gravity effects, experiments on concentrated colloids of spherical and ellipsoidal fluorescent particles were carried out aboard the International Space Station. The particles were suspended in a decalin/tetralin mixture to match the particle refractive index. Confocal microscopy was used to visualize the particle behavior.

microgravity↗
NASA NTRSDate not supplied

On the Emitted Dust Size Distribution and Its Variability: Insights From A Field Campaign in an Ephemeral Lake of the Lower Drâa Valley, Moroccan Sahara

During the last decades the emitted particle size distribution (PSD) of dust and its variability have been actively discussed due to their effects on the Earth System. Some frameworks support a higher proportion of aggregate’s fragmentation as wind speed increases, while others suggest the PSD independence of wind speed and soil properties, at least up to ~10 µm. Constraining the size-resolved dust emission and its variability is key to reduce the uncertainty of Earth system models, but still requires further analysis. The ERC project FRAGMENT addresses these and other issues related to dust emission, dust mineralogical composition and its effects upon climate. In this context we conducted a one month field campaign in September 2019 at L’Bour, an ephemeral lake located in the Lower Drâa Valley, resulting in a detailed description of the soil, dust emission and meteorology. During the campaign saltation and dust emission were very frequent under two prevailing wind directions. Friction velocity varied around 0.15 ms⁻¹, with peaks close to 0.4 ms⁻¹, except for a peak of 0.6 ms⁻¹ coinciding with the arrival of one of the moist convective storms or haboobs that occurred during this period. We study the near-surface concentration and diffusive flux PSDs along with their variability up to ~19 µm in optical diameter (~21 µm in geometric dust diameter). As expected, we find significant differences between the concentration and diffusive flux PSDs, with the latter showing a higher proportion of coarse and super-coarse particles. Our results also highlight dependencies of the PSDs with friction velocity, wind direction, and type of event (regular events vs haboob outflow events). We first discuss the potential origin of the variations and dependencies, which include 1) differences in fetch and surface between directions, 2) dry deposition of coarse and super-coarse dust depending on friction velocity, 3) more disaggregation with increasing friction velocity, and 4) the effect of the haboob gust front. Our calculations show the influence of dry deposition upon the diffusive flux PSDs. We finally compare our PSDs with brittle fragmentation theory, both with the original 2011 formulation using optical diameters, and with the more recent 2022 formulation including the emission of super-coarse dust and using geometric diameters.

particle size distribution↗
NASA NTRSDate not supplied

Identifying Indicators of Harmful Algal Blooms in Coastal Atacama Using Satellite Image Processing Techniques to Improve Industry and Authority Response

Over the past decade, Chile has experienced a significant rise in both the frequency and intensity of coastal Harmful Algal Blooms (HABs). These bloom events are a growing concern for the Atacama Region especially, with potential impacts on human health, aquaculture, and the environment. HABs are caused by an excess proliferation of microalgae, with certain algae species commonly found in Chilean HABs capable of producing toxins which can poison fish, toxify shellfish, and cause illness or death when ingested by humans. Collaborating with the Ministry of Health of Chile, Centro de Información de Recursos Naturales, the University of Atacama, and the Embassy of Chile’s Agricultural Office, this study identifies potential indicators of HABs in the Coastal Atacama Region using NASA Earth observations. Satellite imagery from the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument onboard NASA’s Aqua satellite was used for the identification of chlorophyll-a which provides direct estimates of the algae pigment’s concentration in water bodies. In addition, the spatiotemporal patterns of several other parameters were examined to identify correlations with occurrences of HABs, including sea surface temperature and normalized fluorescence line height using Aqua MODIS, Normalized Difference Turbidity Index (NDTI) using Landsat 8, and ocean wind speed measurements from the NOAA Joint Polar Satellite System. Analysis of these patterns revealed hotspots of high chlorophyll-a concentrations from the years 2014 to 2022, the most major of which occurring in the coastal zones of Chañaral, Bahía Inglesa, and Huasco. Also, through the use of a similarity search conducted, the seasonal variation of these indicators was mapped to highlight areas with great likelihood of experiencing HABs in the future. The results can guide future efforts for in-situ water sampling, toxin analysis and assessment, and HAB monitoring and prevention.

Cody O'Ferrall↗
NASA NTRS1977

Evaluation of solar cells for potential space satellite power applications

The evaluation focused on the following subjects: (1) the relative merits of alternative solar cell materials, based on performance and availability, (2) the best manufacturing methods for various solar cell options and the effects of extremely large production volumes on their ultimate costs and operational characteristics, (3) the areas of uncertainty in achieving large solar cell production volumes, (4) the effects of concentration ratios on solar array mass and system performance, (5) the factors influencing solar cell life in the radiation environment during transport to and in geosynchronous orbit, and (6) the merits of conducting solar cell manufacturing operations in space.

Source record↗
NASA NTRS1977

Solar power satellite concepts and potential related space systems

Recent parametric studies of alternate SPS design concepts have shown that the concept appears technically feasible. The parametric studies were based on the use of advanced technology silicon solar cells for solar energy conversion. Solar array blanket unit masses of 0.31 to 0.46 kg/sq m were investigated. Conversion efficiencies of 15 to 17 percent air mass zero (AMO at 247 K) with a concentration ratio of two were considered. The systems were sized for a ground power output of 10 GW. To the level of detail studied, no design or operational problems were encountered that did not appear amenable to solution; however, the economic viability of the SPS concepts studied is obviously dependent upon a combination of technology advancement and/or the costs of competitive sources.

Redding, T. E.↗
NASA NTRS2014

Retrieval of Methane Source Strengths in Europe Using a Simple Modeling Approach to Assess the Potential of Spaceborne Lidar Observations

We investigate the sensitivity of future spaceborne lidar measurements to changes in surface methane emissions. We use surface methane observations from nine European ground stations and a Lagrangian transport model to infer surface methane emissions for 2010. Our inversion shows the strongest emissions from the Netherlands, the coal mines in Upper Silesia, Poland, and wetlands in southern Finland. The simulated methane surface concentrations capture at least half of the daily variability in the observations, suggesting that the transport model is correctly simulating the regional transport pathways over Europe. With this tool we can test whether proposed methane lidar instruments will be sensitive to changes in surface emissions. We show that future lidar instruments should be able to detect a 50% reduction in methane emissions from the Netherlands and Germany, at least during summer.

surface fluxes↗
NASA NTRS1992

Oxygen isotopes implanted in the LDEF spacecraft

Depth profiles of O-16 and O-18/O-16 were measured on stainless steel nuts and copper sheet (from a grounding strap) recovered from the leading edge of LDEF (Tray E10). The measurements were obtained by dynamic SIMS (secondary ion mass spectrometry) using a VG Isolab 54 ion microprobe. Plots of O-18/O-16 against time, show large depletions of up to a factor of 2 compared to the O-18/O-16 value at sea level. The O-16 current decreases by 2 orders of magnitude in the interior of the metal, and the corresponding profile of anomalous O-16 is strongly peaked in the outer few tens of nanometers of the surface. This depth scale is a tentative one based on estimated sputtering rates. Plots of O-18/O-16 against 1/O-16 should be linear if two isotopically distinct components, one of variable concentration (orbital component) and one of fixed concentration (normal oxygen), are mixed. Data to be presented at the meeting show departures from linearity which result from variability in the concentration of normal oxygen, but may also arise from the implantation of oxygen with a range of fractionation due to the decaying orbit of the LDEF, sputtering of the surface by atomic oxygen, and the different momenta of the two isotopes due to their equal velocities. The potential for using this method as a means of identifying exposure to low-Earth orbit, de-convoluting the effects of space exposure from terrestrial contamination, and using the implanted anomolous oxygen as a means of studying the atomic oxygen density and upper atmosphere temperature height profile will be discussed at the meeting.

Saxton, J. M.↗
NASA NTRS1992

The Prebiotic Synthesis of Ethylenediamine Monoacetic Acid, The Repeating Unit of Peptide Nucleic Acids

The polymerization of ribonucleic acids or their precursors constitutes an important event in prebiotic chemistry. The various problems using ribonucleotides to make RNA suggest that there may have been a precursor. An attractive possibility are the peptide nucleic acids (PNA). PNAs are nucleotide analogs that make use of a polymer of ethylenediamine monoacetic acid (EDMA or 2-amninoethyl glycine) with the bases attached by an acetic acid. EDMA is an especially attractive alternative to the ribose phosphate or deoxyribose phosphate backbone because it contains no chiral centers and is potentially prebiotic, but there is no reported prebiotic synthesis. We have synthesized both EDMA and ethylenediamine diacetic acid (EDDA) from the prebiotic compounds ethylenediamine, formaldehyde, and hydrogen cyanide. The yields of EDMA range from 11 to 79% along with some sEDDA and uEDDA. These reactions work with concentrations of 10(exp -1)M and as low as 10(exp -4)M, and the reaction is likely to be effective at even lower concentrations. Ethylenediamine is a likely prebiotic compound, but it has not yet been demonstrated, although compounds such as ethanolamine and cysteamine have been proven to be prebiotic. Under neutral pH and heating at l00 C, EDMA is converted to the lactam, monoketopiperazine (MKP). The cyclization occurs and has an approximate ratio of MKP/EDMA = 3 at equilibrium. We have measured the solubilities of EDMA center dot H20 as 6.4 m, EDMA center dot HCl center dot H20 as 13.7 m, and EDMA center dot 2HCl center dot H20 as 3.4 m. These syntheses together with the high solubility of EDMA suggest that EDMA would concentrate in drying lagoons and might efficiently form polymers. Given the instability of ribose and the poor polymerizability of nucleotides, the prebiotic presence of EDMA and the possibility of its polymerization raises the possibility that PNAs are the progenitors of present day nucleic acids. A pre-RNA world may have existed in which PNAs or polymers with related peptide backbones were the dominant information macromolecules.

Nelson, Kevin E.↗
NASA NTRS1996

NASA Space Missions to Asteroids: Protecting the Earth from NEO Impacts

There is now a general recognition of the hazard of impacts on Earth by comets and asteroids, but there is yet no consensus concerning international actions that should be taken to protect the planet from such impacts. An essential step in the analysis of the situation involves estimating the relative hazard posed by comets and asteroids of different sizes and orbits. All recent studies agree that the larger impacts pose the greater danger, and that our primary concern from the perspective of total risk should be on impacts that are large enough to cause global ecological catastrophe. These global catastrophes are also of special interest, since they (alone among natural disasters) have the potential to destroy civilization. Studies of the sensitivity of the Earth's environment suggest that the energy threshold energy for causing a global catastrophe is at about 1 million megatons, corresponding to impactor diameters of 1.5 to 2 km. This information leads naturally to a strategy of concentrating on the larger NEOs, say those 1 km or more in diameter. This is the rationale for the Spaceguard Survey, which must be the highest priority in mitigation efforts. The second question concerns the value of developing standing defensive systems that could deflect or destroy an incoming NEO. In the case of the asteroids larger than 1 km in diameter, no such system is needed, since there will be ample time (at least several decades) between the discovery of the threatening object by Spaceguard and the requirement to take action against it. In the case of objects smaller than 1 km diameter, development of defensive systems is not cost-effective; there are many greater dangers to persons and property that are much more urgent. Only in the case of large long-period comets is there a rationale for standing defense systems. The question is also raised whether the risks inherent in developing and maintaining a defense system might be greater than the impact risks it is intended to guard against. These and related issues are the focus of much current international debate on defense of the planet against NEO impacts. Meanwhile, the most critical issue remains the expansion of the telescopic search for NEOs.

Morrison, David↗
NASA NTRS2004

Wavelength-Agile Optical Sensor for Exhaust Plume and Cryogenic Fluid Interrogation

Two optical sensors developed in UW-Madison labs were evaluated for their potential to characterize rocket engine exhaust plumes and liquid oxygen (LOX) fluid properties. The plume sensor is based on wavelength-agile absorption spectroscopy A device called a chirped white pulse emitter (CWPE) is used to generate the wavelength agile light, scanning, for example, 1340 - 1560 nm every microsecond. Properties of the gases in the rocket plume (for example temperature and water mole fraction) can be monitored using these wavelength scans. We have performed preliminary tests in static gas cells, a laboratory GOX/GH2 thrust chamber, and a solid-fuel hybrid thrust chamber, and these initial tests demonstrate the potential of the CWPE for monitoring rocket plumes. The LOX sensor uses an alternative to wavelength agile sensing: two independent, fixed-wavelength lasers are combined into a single fiber. One laser is absorbed by LOX and the other not: by monitoring the differential transmission the LOX concentration in cryogenic feed lines can be inferred. The sensor was successful in interrogating static LOX pools in laboratory tests. Even in ice- and bubble-laden cryogenic fluids, LOX concentrations were measured to better than 1% with a 3 microsec time constant.

Sanders, Scott T.↗
NASA NTRS2001

Adenovirus-mediated gene delivery to cells of the magnocellular hypothalamo-neurohypophyseal system

The objective of the present study was to define the optimum conditions for using replication-defective adenovirus (Ad) to transfer the gene for the green fluorescent protein (GFP) to the hypothalamic paraventricular (PVN) and supraoptic (SON) nuclei and cells of the neurohypophysis (NH). As indicated by characterizing cell survival over 15 days in culture and in electrophysiological whole cell patch-clamp studies, viral concentrations up to 2 x 10(7) pfu/coverslip did not affect viability of transfected PVN and NH cultured cells from preweanling rats. At 2 x 10(7) pfu, GFP gene expression was higher (40% of GFP-positive cells) and more sustained (up to 15 days). Using a stereotaxic approach in adult rats, we were able to directly transduce the PVN, SON, and NH and visualize gene expression in coronal brain slices and in the pituitary 4 days after injection of Ad. In animals receiving NH injections of Ad, the virus was retrogradely transported to PVN and SON neurons as indicated by the appearance of GFP-positive neurons in cultures of dissociated cells from those brain nuclei and by polymerase chain reaction and Western blot analyses of PVN and SON tissues. Adenoviral concentrations of up to 8 x 10(6) pfu injected into the NH did not affect cell viability and did not cause inflammatory responses. Adenoviral injection into the pituitary enabled the selective delivery of genes to the soma of magnocellular neurons. The experimental approaches described here provide potentially useful strategies for the treatment of disordered expression of the hormones vasopressin or oxytocin. Copyright 2000 Academic Press.

Non-NASA Center↗
NASA NTRS1997

1,25 (OH)2D3 enhances PTH-induced Ca2+ transients in preosteoblasts by activating L-type Ca2+ channels

We previously demonstrated electrophysiologically that 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] shifts the activation threshold of L-type Ca2+ channels in osteoblasts toward the resting potential and prolongs mean open time. Presently, we used single-cell Ca2+ imaging to study the combined effects of 1,25(OH)2D3 and parathyroid hormone (PTH) during generation of Ca2+ transients in fura 2-loaded MC3T3-E1 cells. Pretreatment with 1,25(OH)2D3 concentrations, which alone did not produce Ca2+ transients, consistently enhanced Ca2+ responses to PTH. Enhancement was dose dependent over the range of 1 to 10 nM and was blocked by pretreatment with 5 microM nitrendipine during pretreatment. A 1,25(OH)2D3 analog that activates L-type channels and shifts their activation threshold also enhanced PTH responses. In contrast, an analog devoid of membrane Ca2+ effects did not enhance PTH-induced Ca2+ transients. The PTH-induced Ca2+ transient involved activation of a dihydropyridine-insensitive cation channel that was inhibited by Gd3+. Together, these data suggest that 1,25(OH)2D3 increases osteoblast responsiveness to PTH through rapid modification of L-type Ca2+ channel gating properties, whose activation enhances Ca2+ entry through other channels such as the PTH-responsive, Gd(3+)-sensitive cation channel.

Non-NASA Center↗
NASA NTRS2004

High Temperature VARTM with LaRC Polyimides

Recent work at NASA Langley Research Center (LaRC) has concentrated on developing new polyimide resin systems for advanced aerospace applications that can be processed without the use of an autoclave. Polyimide composites are very attractive for applications that require a high strength to weight ratio and thermal stability. Vacuum assisted resin transfer molding (VARTM) has shown potential to reduce the manufacturing cost of composite structures. In VARTM, the fibrous preform is infiltrated on a rigid tool surface contained beneath a flexible vacuum bag. Both resin injection and fiber compaction are achieved under pressures of 101.3 KPa or less. Recent studies have demonstrated the feasibility of the VARTM process for fabrication of void free structures utilizing epoxy resin systems with fiber volume fractions approaching 60%. In this work, the VARTM process has been extended to the fabrication of composite panels from polyimide systems developed at the Langley Research Center. This work has focused on processing LARC(trademark) PETI-8 (Langley Research Center Phenylethynyl Terminated Imide- 8), an aromatic polyimide based on 3,3',4,4' -biphenyltetracarboxylic dianhydride, a 50:50 molar ratio of 3,4'-oxydianiline and 1,3-bis(3-aminophenoxy)benzene, with 4-phenylethynylphthalic anhydride as the endcapping agent. Various molecular weight versions were investigated to determine their feasibility of being processed by VARTM at elevated temperatures. An injection temperature of approximately 280 C was required to achieve the necessary viscosity (<5 Poise) for flow at VARTM pressures. Laminate quality and initial mechanical properties are presented for LARC(trademark) PETI-8 and 6k IM7 uniweave fabric.

Cano, Roberto J.↗
NASA NTRS2018

Atmospheric Chemistry Modeling Using a Regression Forest Model

Atmospheric chemistry is central to many environmental issues such as air pollution, climate change, and stratospheric ozone loss. Chemistry Transport Models (CTM) are a central tool for understanding these issues, whether for research or for forecasting. These models split the atmosphere in a large number of grid-boxes and consider the emission of compounds into these boxes and their subsequent transport, deposition, and chemical processing. The chemistry is represented through a series of simultaneous ordinary differential equations, one for each compound. Given the difference in life-times between the chemical compounds (milli-seconds for O1D to years for CH4) these equations are numerically stiff and solving them consists of a significant fraction of the computational burden of a CTM. We have investigated a machine learning approach to solving the differential equations instead of solving them numerically. From an annual simulation of the GEOS-Chem model we have produced a training dataset consisting of the concentration of compounds before and after the differential equations are solved, together with some key physical parameters for every grid-box and time-step. From this dataset we have trained a machine learning algorithm (regression forest) to be able to predict the concentration of the compounds after the integration step based on the concentrations and physical state at the beginning of the time step. We have then included this algorithm back into the GEOS-Chem model, bypassing the need to integrate the chemistry. This machine learning approach shows many of the characteristics of the full simulation and has the potential to be substantially faster. There are a wide range of application for such an approach - generating boundary conditions, for use in air quality forecasts, chemical data assimilation systems, centennial scale climate simulations etc. We discuss our approches' speed and accuracy, and highlight some potential future directions for improving this approach.

Keller, Christoph A.↗
NASA NTRS2019

Atmospheric Chemistry Modeling Using Machine Learning

Atmospheric chemistry models are a central tool to study the impact of chemical constituents on the environment, vegetation and human health. These models split the atmosphere in a large number of grid-boxes and consider the emission of compounds into these boxes and their subsequent transport, deposition, and chemical processing. The chemistry is represented through a series of simultaneous ordinary differential equations, one for each compound. Given the difference in life-times between the chemical compounds (milli-seconds for O1D to years for CH4) these equations are numerically stiff and solving them consists of a significant fraction of the computational burden of a chemistry model. We have investigated a machine learning approach to emulate the chemistry instead of solving the differential equations numerically. From a one-month simulation of the GEOS-Chem model we have produced a training dataset consisting of the concentration of compounds before and after the differential equations are solved, together with some key physical parameters for every grid-box and time-step. From this dataset we have trained a machine learning algorithm (regression forest) to be able to predict the concentration of the compounds after the integration step based on the concentrations and physical state at the beginning of the time step. We have then included this algorithm back into the GEOS-Chem model, bypassing the need to integrate the chemistry. This machine learning approach shows many of the characteristics of the full simulation and has the potential to be substantially faster. There are a wide range of application for such an approach - generating boundary conditions, for use in air quality forecasts, chemical data assimilation systems, etc. We discuss speed and accuracy of our approach, and highlight some potential future directions for improving it.

Keller, Christoph A.↗
NASA NTRS2019

Machine Learning Application to Atmospheric Chemistry Modeling

Atmospheric chemistry models are a central tool to study the impact of chemical constituents on the environment, vegetation and human health. These models split the atmosphere in a large number of grid-boxes and consider the emission of compounds into these boxes and their subsequent transport, deposition, and chemical processing. The chemistry is represented through a series of simultaneous ordinary differential equations, one for each compound. Given the difference in life-times between the chemical compounds (milli-seconds for O (sup 1) D (Deuterium) to years for CH4) these equations are numerically stiff and solving them consists of a significant fraction of the computational burden of a chemistry model. We have investigated a machine learning approach to emulate the chemistry instead of solving the differential equations numerically. From a one-month simulation of the GEOS-Chem model we have produced a training dataset consisting of the concentration of compounds before and after the differential equations are solved, together with some key physical parameters for every grid-box and time-step. From this dataset we have trained a machine learning algorithm (regression forest) to be able to predict the concentration of the compounds after the integration step based on the concentrations and physical state at the beginning of the time step. We have then included this algorithm back into the GEOS-Chem model, bypassing the need to integrate the chemistry. This machine learning approach shows many of the characteristics of the full simulation and has the potential to be substantially faster. There are a wide range of application for such an approach - generating boundary conditions, for use in air quality forecasts, chemical data assimilation systems, etc. We discuss speed and accuracy of our approach, and highlight some potential future directions for improving it.

Keller, Christoph A.↗
NASA NTRS2024

Helium Reservoirs in Iron Nanoparticles on the Lunar Surface

The Moon’s surface is directly exposed to the space environment and subject to alteration by space weathering. One agent of space weathering, the solar wind, enriches the lunar surface with helium. Although we understand how helium is delivered to the Moon, certain aspects of helium concentration processes on the surface remain unknown, such as why impact-generated glass aggregates contain more helium than equally sized soil grains of other types. Here we have analyzed the contents of vesicular iron nanoparticles in lunar impact glasses using aberration-corrected scanning transmission electron microscopy and electron energy loss spectroscopy and show that the nanoparticles contain high concentrations of helium (10-24 atoms/nm3). The widespread occurrence of vesicular iron nanoparticles among lunar samples suggests that they may be an important helium reservoir. These results also suggest that space weathering of iron-rich minerals plays a role in helium sequestration on the Moon and potentially on other airless bodies.

Brittany A. Cymes↗
NASA NTRS2015

Analysis of Process Gases and Trace Contaminants in Membrane-Aerated Gaseous Effluent Streams.

In membrane-aerated biofilm reactors (MABRs), hollow fibers are used to supply oxygen to the biofilms and bulk fluid. A pressure and concentration gradient between the inner volume of the fibers and the reactor reservoir drives oxygen mass transport across the fibers toward the bulk solution, providing the fiber-adhered biofilm with oxygen. Conversely, bacterial metabolic gases from the bulk liquid, as well as from the biofilm, move opposite to the flow of oxygen, entering the hollow fiber and out of the reactor. Metabolic gases are excellent indicators of biofilm vitality, and can aid in microbial identification. Certain gases can be indicative of system perturbations and control anomalies, or potentially unwanted biological processes occurring within the reactor. In confined environments, such as those found during spaceflight, it is important to understand what compounds are being stripped from the reactor and potentially released into the crew cabin to determine the appropriateness or the requirement for additional mitigation factors. Reactor effluent gas analysis focused on samples provided from Kennedy Space Center's sub-scale MABRs, as well as Johnson Space Center's full-scale MABRs, using infrared spectroscopy and gas chromatography techniques. Process gases, such as carbon dioxide, oxygen, nitrogen, nitrogen dioxide, and nitrous oxide, were quantified to monitor reactor operations. Solid Phase Microextraction (SPME) GC-MS analysis was used to identify trace volatile compounds. Compounds of interest were subsequently quantified. Reactor supply air was examined to establish target compound baseline concentrations. Concentration levels were compared to average ISS concentration values and/or Spacecraft Maximum Allowable Concentration (SMAC) levels where appropriate. Based on a review of to-date results, current trace contaminant control systems (TCCS) currently on board the ISS should be able to handle the added load from bioreactor systems without the need for secondary mitigation.

Gaseous Effluent Streams↗