Used cot mattresses as potential reservoirs of bacterial infection: nutrient availability within polyurethane foam

Aim: To evaluate possible source of nutrients for bacterial growth within polyurethane (PU) foam of used cot mattresses as determinants of bacterial population density. Methods and Results: Used infant mattresses (n = 30) were analysed for bacteria capable of degrading colloidal PU and for aqueous soluble chemical components (aromatic amines, ammonium ions, phosphates and protein). Mattress type (waterproof cover vs exposed PU foam at the infant‐head region), mattress age and previous use by another child were evaluated as factors that could influence the measured parameters. The levels of protein extracted from PU foam were (i) significantly (P = 0·0019) higher for mattresses lacking a waterproof cover at the infant‐head region and (ii) positively correlated with both culturable bacterial population densities of the PU foams and extent of growth of Staphylococcus aureus on aqueous leachates. No statistically significant (P > 0·05) associations between other measured parameters and mattress type/use factors were identified. Conclusions: Infant use of cot mattresses with exposed PU foam leads to accumulation of proteins within the PU, which can promote bacterial growth. Significance and Impact of the Study: The study provides a mechanistic explanation for increased levels of bacteria associated with exposed PU of cot mattresses. In the context of the common bacterial toxins hypothesis for the sudden infant death syndrome (SIDS), this could explain the lowered risk of SIDS associated with use of a waterproof cover above the mattress.     

Mechanical properties of polyurethane foams prepared from liquefied corn stover with PAPI

Corn stover was liquefied by using ethylene carbonate (EC) as liquefying solvent and 97% sulfur acid as catalyst at 170 degrees C for 90 min. Polyurethane (PU) foams were prepared from liquefied corn stover (LCS) with variable amount of polymethylene polyphenylisocyanate (PAPI) by one-shot method, with water as blowing agent, silicone as surfactant and triethylamine and dibutyltine dilaurate as co-catalyst. The mechanical properties of LCS-PU foam with different [NCO]/[OH] ratio were studied on a universal tensile tester. With the increase of [NCO]/[OH] ratio from 0.4 to 1.0, the tensile strength and Young's modulus of the LCS-PU foam first raised, reached their maximum values at [NCO]/[OH] ratio of 0.8, and then declined; while the elongation at break decreased from 117% to 3.6%. The results indicated that by changing the [NCO]/[OH] ratio, mechanical properties of LCS-PU foams could be adjusted for various end uses.     

Structure and properties of starch-based foams prepared by microwave heating from extruded pellets

The physical properties of microwave-foamed starch-based pellets, including density, porosity, cell structure, water absorption characteristics and mechanical properties were characterized. It was found that the physical properties of these starch-based foams produced by microwave heating are highly dependent on the raw materials and additives. Foam density decreased significantly after addition of 5.5–10.5% w/w salts, while foams containing nucleation agent (talc) were denser than the control with reduced cell size. A proprietary blowing agent did not affect the foam density markedly. Addition of salts also increased the water sorption of foams and plasticized cell walls. Mechanical behaviour of foamed pellets can be adjusted effectively by controlling the cell structure through using different additives. Mechanical properties of the foamed pellets in the elastic region as well as under large deformation (up to 40% strain) all follow a power–law relationship with foam density.     

Growth and survival of bacteria implicated in sudden infant death syndrome on cot mattress materials

AIMS: To compare growth and survival of selected bacteria implicated in sudden infant death syndrome (SIDS) on cot mattress polyurethane (PU) inner-foams and on different types of cot mattress cover materials. METHODS AND RESULTS: Escherichia coli, Staphylococcus aureus or Streptococcus pyogenes were inoculated onto swatches of new-unused cot mattress PU inner-foam and onto three types of cot mattress covers (polyvinyl chloride, cotton and polyester). The influence of inoculation cell density, relative humidity (RH) and temperature of incubation on survival was assessed by recovery of cells in 0.85% NaCl, with viable cell enumeration by plate counting on selective and differential media. Utilization of carbon and nitrogen sources within cot mattress PU was assessed by following growth on aqueous leachate from PU, and by colorimetric determination of aromatic amines. Good survival capability (>206 d) was shown by all three test species on PU inner-foam and on polyester mattress cover at high RH (75%), but only by Staph. aureus on PU at low RH (25%). Aqueous soluble material from PU foam supports bacterial growth; removal of aromatic amines from aqueous leachate from PU accompanies growth of Staph. aureus. CONCLUSIONS: Staphylococcus aureus has good survival capability on cot mattress PU foam, even at low RH. Soluble material within PU can serve as carbon and nitrogen sources for bacterial growth. SIGNIFICANCE AND IMPACT OF THE STUDY: Prolonged survival of Staph. aureus on PU at low RH could explain, in the context of the common bacterial toxins hypothesis, an increased risk of SIDS associated with used infant mattresses.     

Biodegradation of gas-phase styrene in a high-performance biotrickling filter using porous polyurethane foam as a packing medium

A biotrickling filter (BTF) packed with porous polyurethane (PU) foam sheets was developed and operated for removal of gas-phase styrene. The specific surface area and void fraction of the PU foam sheet were determined to be 497 m²/m³ and 0.92, respectively, by using mathematical modeling and experimental measurement. The effects of gas flow direction (co-current and counter-current), styrene loading rate and empty bed residence time on the efficiency of the BTF were analyzed. The BTF achieved a high elimination capacity of 4.0 ∼ 5.0 kg styrene/m³ day due to the high specific surface area of the PU foam. The BTF could be operated repeatedly when excessively-grown biomass was periodically removed, using circulating NaOH solution for 2 h every four days.     

Removal of nitrate from water by foam-immobilizedPhormidium laminosum in batch and continuous-flow bioreactors

Cells of the non-N₂-fixing cyanobacteriumPhormidium laminosum were immobilized in polyurethane (PU) foams either by absorption or by entrapment in the PU prepolymer followed by polymerisation and by adsorption onto polyvinyl (PV) foams. Although entrapment caused toxicity problems which lead to rapid death of the immobilized cells, they were immobilized successfully by adsorption onto PU or PV foams and maintained their photosynthetic electron transport activities (PS I, II, I + II) for at least 7 weeks. Changes in the morphology resulting from immobilization, as revealed by scanning electron microscopy (SEM) and low temperature-SEM, were investigated. Batch cultures and a continuous-flow packed bed photobioreactor were used to study nitrate removal from water. The effects of light intensity and CO₂ concentration on bioreactor performance were studied with respect to the nitrate uptake efficiency of the system. It was concluded thatP. laminosum immobilized on polymer foams is of potential value for biological nitrate removal in a continuous-flow system. author for correspondence     

Characterization of the polyurethanolytic activity of two Alicycliphilus sp. strains able to degrade polyurethane and N-methylpyrrolidone

Two bacterial strains (BQ1 and BQ8) were isolated from decomposed soft foam. These were selected for their capacity to grow in a minimal medium (MM) supplemented with a commercial surface-coating polyurethane (PU) (Hydroform) as the carbon source (MM-PUh). Both bacterial strains were identified as Alicycliphilus sp. by comparative 16S rRNA gene sequence analysis. Growth in MM-PUh showed hyperbolic behavior, with BQ1 producing higher maximum growth (17.8 +/- 0.6 mg.ml(-1)) than BQ8 (14.0 +/- 0.6 mg.ml(-1)) after 100 h of culture. Nuclear magnetic resonance, Fourier transform infrared (IR) spectroscopy, and gas chromatography-mass spectrometry analyses of Hydroform showed that it was a polyester PU type which also contained N-methylpyrrolidone (NMP) as an additive. Alicycliphilus sp. utilizes NMP during the first stage of growth and was able to use it as the sole carbon and nitrogen source, with calculated K(s) values of about 8 mg.ml(-1). Enzymatic activities related to PU degradation (esterase, protease, and urease activities) were tested by using differential media and activity assays in cell-free supernatants of bacterial cultures in MM-PUh. Induction of esterase activity in inoculated MM-PUh, but not that of protease or urease activities, was observed at 12 h of culture. Esterase activity reached its maximum at 18 h and was maintained at 50% of its maximal activity until the end of the analysis (120 h). The capacity of Alicycliphilus sp. to degrade PU was demonstrated by changes in the PU IR spectrum and by the numerous holes produced in solid PU observed by scanning electron microscopy after bacterial culture. Changes in the PU IR spectra indicate that an esterase activity is involved in PU degradation.     

Using growth factor conditioning to modify the properties of human cell derived extracellular matrix

We have recently reported on a bench‐top approach for isolating extracellular matrix (ECM) from pure populations of cells grown in culture using sacrificial, open‐celled foams to concentrate and capture the ECM. To increase both the accumulation and the strength of the ECM harvested, cell‐seeded polyurethane (PU) foams were cultured in media supplemented with either transforming growth factor β‐1 (TGFβ1) or hepatocyte growth factor (HGF). At the end of a 3‐week culture period, ECM yield was significantly increased for samples conditioned in supplemented media. Control foams yielded 48 ± 12 mg of material for every gram of PU foam seeded. Yield values increased to 102 ± 21 and 243 ± 25 mg for HGF and TGFβ1‐treated samples, respectively. HGF supplementation increased the modulus by 59%, while TGFβ1 treatment increased the elastic modulus by 204%. TGFβ1‐stimulated material was organized into a network that was markedly denser than control material, with HGF‐stimulated network density intermediate to TGFβ1 and controls. Our study showed that TGFβ1‐treated samples were collagen enriched while HGF samples had an increased gylcosaminoglycan concentration. The results demonstrate that growth factor supplementation, particularly with TGFβ1, can significantly alter the biomechanical properties of cell‐derived ECM that may be used for therapeutic applications. © 2012 American Institute of Chemical Engineers Biotechnol. Prog., 2012     

Activity and batch operational stability of Candida rugosa lipase immobilized in different hydrophilic polyurethane foams during hydrolysis in a biphasic medium

The aim of this study was to investigate eventual relationships between some physico-chemical properties (e.g. porosity, aquaphilicity, partition coefficient for oleic acid and drying curves) of relatively hydrophilic polyurethane foams and the activity and batch operational stabiliy of Candida rugosa lipase immobilized within these foams. Two biocompatible polyurethane pre-polymers ("HYPOL FHP 2002^TM" and "Hypol FHP X4300^TM" from Hampshire Chemical GmbH, Germany) were tested as immobilization supports. The model reaction was the hydrolysis of crude olive residue oil in a biphasic aqueous/n-hexane medium. Drying curves under normal and reduced pressures suggested that water molecules are more strongly bound to the "FHP 2002" than to "FHP X4300" foams. This is in agreement with the higher aquaphilicity value estimated for the "FHP 2002" foam (3.7 vs 2.8). For every enzyme loading tested, hydrolysis efficiency was considerably higher for the lipase in "FHP X4300" foam when compared to the other counterpart. However, internal mass transfer limitations seem to be more severe with "FHP X4300" foams. Operational stability was evaluated in 10 consecutive batches (1 batch = 23 hours) for both immobilized preparations. A fast deactivation was observed for both biocatalysts. However, a slightly higher operational stability was observed for the lipase in "FHP 2002" foam. For the lipase in "FHP X4300" foam, the activity decay can be explained by a dramatic lipase leakage from the foam observed along successive batches. For the lipase in "FHP 2002" foam, no significant enzyme loss was observed along the reutilizations probably due to a higher number of multi-point attachment between the lipase and its support. In fact, activity and operational stability of Candida rugosa lipase in "FHP 2002" and "FHP X4300" foams appear to be related with the strength and/or the number of covalent binding between the enzyme and the support rather than to the physico-chemical properties evaluated in this work.     

Effects of polyurethane foams on microbial growth in fuel-water systems

Four, open-cell, ester-base polyurethane foams were examined for their effect on growth of fuel-utilizing organisms in jet fuel-water systems. Three foams contained a potential biocide, tetraethylthiuram E (0.66%), sodium omadine (0.07%), or zinc omadine (0.07%), all w/v. These were compared with a control foam which did not contain an additive. Each foam was examined in fuel-water systems containing JP-4 fuel, JP-4 fuel plus 0.1% anti-icing additive (AIA), or JP-5 fuel. Pure cultures of a fuel-grown bacterium, Pseudomonas aeruginosa, and of a fuel-grown fungus, Hormodendrum (Cladosporium) sp., served as test organisms. In control cultures without foam and in cultures containing control foam, P. aeruginosa achieved maximum stationary-phase populations of approximately 10⁸ viable cells per ml, and Hormodendrum sp. produced an extensive mycelial mat. In the three fuel systems examined, tetraethylthiuram E- and sodium omadine-containing foams had little effect on growth of the bacterium; foam with zinc omadine decreased the rate of bacterial growth but had little effect on total populations. Tetraethylthiuram E decreased the rate of fungal growth and showed its greatest effect in JP-4 plus AIA. Foam with sodium omadine or zinc omadine markedly decreased fungal growth in all three fuel systems. The data suggest that either sodium omadine or zinc omadine in polyurethane foam may be a useful antifungal agent; and that tetraethylthiuram E and AIA could exert a synergistic effect, particularly at AIA concentrations which have been reported to occur in some field situations.     

Calibration of crushable foam plasticity models for synthetic bone material for use in finite element analysis of acetabular cup deformation and primary stability

Polyurethane (PU) foam is a material often used in biomechanical experiments and demands for the definition of crushable foam plasticity (CFP) in numerical simulations of the primary stability and deformation of implants, to describe the crushing behaviour appropriately. Material data of PU foams with five different densities (10–40 pounds per cubic foot were ascertained experimentally in uniaxial compression test and used to calibrate CFP models for finite element modelling. Additionally, experimental and numerical deformation, push-out and lever-out tests of press-fit acetabular cups were carried out to assess the influence of the chosen material definition (linear elastic and CFP) on the numerical results. Comparison of the experimentally and numerically determined force–displacement curves of the uniaxial compression test showed a mean deviation of less than 3%. In primary stability testing, the deviation between the experimental and numerical results was in a range of 0%–27% for CFP modelling and 64%–341% for the linear elastic model. The material definition selected, highly influenced the numerical results in the current study. The use of a CFP model is recommended for further numerical simulations, when a deformation of the foam beyond the yield strength is likely to occur.     

Mechanisms for enhanced biodegradation of petroleum hydrocarbons by a microbe-colonized gas-liquid foam

AIMS: A microbe-colonized gas-liquid foam formulation has been previously shown to provide enhanced biodegradation capabilities in soil microcosms. The present study considers the reservoir properties of this foam and how this affects hydrocarbon degradation rates. METHODS AND RESULTS: Oxygen solubility in protein hydrolysate solutions draining from aerated and oxygenated foams was measured. The suitability of oxygenated foam to enhance the degradation of n-hexadecane in soil microcosms was assessed. Sorption of bacterial isolates at the gas-liquid interface was also investigated using a range of microscopy techniques. CONCLUSIONS: Oxygenated bioactive foam enhanced biodegradation rates by improving oxygen availability and transfer. Biodegradation of n-hexadecane was also stimulated by the protein hydrolysate used and by the inclusion of known bacterial hydrocarbon-degrading bacteria. The interaction of bacteria with the gas-liquid interface was shown to be a significant factor governing the drainage of the bacteria from the bioactive foam. SIGNIFICANCE AND IMPACT OF THE STUDY: Protein hydrolysate-based bioactive foam may be a suitable treatment technology to enhance the biodegradation of petroleum hydrocarbons in soil.     

Hierarchically Structured 3D Integrated Electrodes by Galvanic Replacement Reaction for Highly Efficient Water Splitting

A NiFe‐based integrated electrode is fabricated by the spontaneous galvanic replacement reaction on an iron foam. Driven by the different electrochemical potentials between Ni and Fe, the dissolution of surface Fe occurs with electroless plating of Ni on iron foam with no need to access instrumentation and input energy. A facile cyclic voltammetry treatment is subsequently applied to convert the metallic NiFe to NiFeO_x . A series of analytical methods indicates formation of a NiFeO_x film of nanosheets on the iron foam surface. This hierarchically structured three dimensional electrode displays high activity and durability against water oxidation. In 1 m KOH, a current density of 1000 mA cm^?2 is achieved at an overpotential of only 300 mV. This method is readily extended to fabricate CoFe or NiCoFe‐based integrated electrodes for water oxidation. Phosphorization of the bimetallic oxide (NiFeO_x ) generates the bimetallic phosphide (NiFe‐P), which can act as an excellent electrocatalyst for hydrogen production in 1 m KOH. An alkaline electrolyzer is constructed using NiFeO_x and NiFe‐P coated iron foams as anode and cathode, which can realize overall water splitting with a current density of 100 mA cm^?2 at an overpotential of 630 mV.     

Bioanode of polyurethane/graphite/polypyrrole composite in microbial fuel cells

Polyurethane (PU) foams were coated with graphite, and pyrrole monomer was subsequently polymerized onto its surface by chemical oxidization to obtain nanostructured polyurethane/graphite/polypyrrole (PU/Graph/PPy) composites, which were used for anaerobic microorganisms grown and tested as anodes in microbial fuel cells (MFC) using municipal wastewater as fuel. The effects of oxidizing agent type (ammonium persulfate and FeCl3) used in pyrrole polymerization on the performance of electrodes in MFC were studied. Composites were characterized by Fourier Transform Infrared (FTIR) spectroscopy, Scanning Electron Microscopy (SEM), and by the four-point probes to determine conductivity. It was observed from SEM analysis that globular nanostructures of PPy were formed onto PU surface with average diameters between 120 and 450 nm, which are typical of aqueous polymerization of pyrrole monomer. The highest output power density observed in MFCs was 305.5 mW/m³ for the composite synthesized using FeCl₃ as the oxidant, and 128.6 mW/m³ using the composite obtained with ammonium persulfate as oxidizing; the corresponding chemical oxygen demand (COD) removal were 48.2 and 45.5%, respectively. The calculated coulombic efficiency for PU/Graph/PPy composite obtained with FeCl₃ as oxidant was of 9.4%. Internal resistance of MFC using the composite obtained with FeCl₃ as oxidant was determined by linear sweep voltammetry (LSV) and the variable resistance (VR) methods, giving 4.8 and 2.9 kO, respectively, with average maximum power density of 237.5 mW/m³.     

Low-cost acoustic design of a bat test room

Experiments with captive bats need a flight room that is acoustically neutral, especially when recording and analysing bat calls or the response of bats to certain sound stimuli. Our aim was to identify an isolation material with the best quality–price relationship to acoustically coat such a flight room. For this, we built a flight room divided into two compartments that were to be acoustically isolated from one another. Audible and infrasonic waves are difficult to attenuate with low-cost materials but the attenuation of ultrasounds is rather straightforward. We evaluated the absorbing capacities of different low-cost materials – felt fabric, polystyrene, egg boxes, egg boxes coated with felt fabric, absorbing pyramidal foams, polyurethane foams and cork. The material that showed the best quality–price relationship was the polyurethane foam of open cells (5 cm thickness), which was able to attenuate approximately 20 dB at ultrasonic frequencies.     

Extruding foams from corn starch acetate and native corn starch

Because of the hydrophilic characteristics of native starch foams and the cost of modifying starch, the uses of starch and modified starch foams are hindered. To decrease hydrophilicity and cost of starch foams, native corn starch was blended with starch acetate and extruded. A twin-screw mixing extruder was used to produce the foams. Native starch content, screw speed, and barrel temperature had significant effects on molecular degradation of starches during extrusion. The melting temperature of extruded starch acetate/native starch foam was higher (216 degrees C) than that for starch acetate (193.4 degrees C). Strong peaks in the X-ray diffractograms of extruded starch acetate/native starch foam suggested new crystalline regions were formed. Optimum conditions for high radial expansion ratio, high compressibility, low specific mechanical energy requirement, and low water absorption index were 46.0% native starch content, 163 rpm screw speed, and 148 degrees C barrel temperature.     

Nitrogen removal in moving bed sequencing batch reactor using polyurethane foam cubes of various sizes as carrier materials

The performance of moving bed sequencing batch reactors (MBSBRs) added with 8 % (v/v) of polyurethane (PU) foam cubes as carrier media in nitrogen removal was investigated in treating low COD/N wastewater. The results indicate that MBSBR with 8-mL cubes achieved the highest total nitrogen (TN) removal efficiency of 37% during the aeration period, followed by 31%, 24% and 19 % for MBSBRs with 27-, 64- and 125-mL cubes, respectively. The increased TN removal in MBSBRs was mainly due to simultaneous nitrification and denitrification (SND) process which was verified by batch studies. The relatively lower TN removal in MBSBR with larger PU foam cubes was attributed to the observation that larger PU foam cubes were not fully attached by biomass. Higher concentrations of 8-mL PU foam cubes in batch reactors yielded higher TN removal.     

Production and characterization of biopolyols and polyurethane foams from crude glycerol based liquefaction of soybean straw

The feasibility of using crude glycerol to liquefy soybean straw for the production of biopolyols and polyurethane (PU) foams was investigated in this study. Liquefaction conditions of 240 °C, >180 min, 3% sulfuric acid loading, and 10-15% biomass loading were preferred for the production of biopolyols with promising material properties. Biopolyols produced under preferential conditions showed hydroxyl numbers from 440 to 540 mg KOH/g, acid numbers below 5 mg KOH/g, and viscosities from 16 to 45 Pa.s. PU foams produced under preferential conditions showed densities from 0.033 to 0.037 g/cm³ and compressive strength from 148 to 227 kPa. These results suggest that crude glycerol can be used as an alternative solvent for the liquefaction of lignocellulosic biomass such as soybean straw for the production of biopolyols and PU foams. The produced biopolyols and PU foams showed material properties comparable to their analogs from petroleum solvent based liquefaction processes.     

Characterization of the Polyurethanolytic Activity of Two Alicycliphilus sp. Strains Able To Degrade Polyurethane and N-Methylpyrrolidone

Two bacterial strains (BQ1 and BQ8) were isolated from decomposed soft foam. These were selected for their capacity to grow in a minimal medium (MM) supplemented with a commercial surface-coating polyurethane (PU) (Hydroform) as the carbon source (MM-PUh). Both bacterial strains were identified as Alicycliphilus sp. by comparative 16S rRNA gene sequence analysis. Growth in MM-PUh showed hyperbolic behavior, with BQ1 producing higher maximum growth (17.8 ± 0.6 mg·ml⁻¹) than BQ8 (14.0 ± 0.6 mg·ml⁻¹) after 100 h of culture. Nuclear magnetic resonance, Fourier transform infrared (IR) spectroscopy, and gas chromatography-mass spectrometry analyses of Hydroform showed that it was a polyester PU type which also contained N-methylpyrrolidone (NMP) as an additive. Alicycliphilus sp. utilizes NMP during the first stage of growth and was able to use it as the sole carbon and nitrogen source, with calculated K_s values of about 8 mg·ml⁻¹. Enzymatic activities related to PU degradation (esterase, protease, and urease activities) were tested by using differential media and activity assays in cell-free supernatants of bacterial cultures in MM-PUh. Induction of esterase activity in inoculated MM-PUh, but not that of protease or urease activities, was observed at 12 h of culture. Esterase activity reached its maximum at 18 h and was maintained at 50% of its maximal activity until the end of the analysis (120 h). The capacity of Alicycliphilus sp. to degrade PU was demonstrated by changes in the PU IR spectrum and by the numerous holes produced in solid PU observed by scanning electron microscopy after bacterial culture. Changes in the PU IR spectra indicate that an esterase activity is involved in PU degradation.     

Decreased astroglial cell adhesion and proliferation on zinc oxide nanoparticle polyurethane composites

Nanomaterials offer a number of properties that are of interest to the field of neural tissue engineering. Specifically, materials that exhibit nanoscale surface dimensions have been shown to promote neuron function while simultaneously minimizing the activity of cells such as astrocytes that inhibit central nervous system regeneration. Studies demonstrating enhanced neural tissue regeneration in electrical fields through the use of conductive materials have led to interest in piezoelectric materials (or those materials which generate a transient electrical potential when mechanically deformed) such as zinc oxide (ZnO). It has been speculated that ZnO nanoparticles possess increased piezoelectric properties over ZnO micron particles. Due to this promise in neural applications, the objective of the present in vitro study was, for the first time, to assess the activity of astroglial cells on ZnO nanoparticle polymer composites. ZnO nanoparticles embedded in polyurethane were analyzed via scanning electron microscopy to evaluate nanoscale surface features of the composites. The surface chemistry was characterized via X-ray photoelectron spectroscopy. Astroglial cell response was evaluated based on cell adhesion and proliferation. Astrocyte adhesion was significantly reduced on ZnO nanoparticle/polyurethane (PU) composites with a weight ratio of 50:50 (PU:ZnO) wt.%, 75:25 (PU:ZnO) wt.%, and 90:10 (PU:ZnO) wt.% in comparison to pure PU. The successful production of ZnO nanoparticle composite scaffolds suitable for decreasing astroglial cell density demonstrates their potential as a nerve guidance channel material with greater efficiency than what may be available today.