Energy-Efficient Technologies for the Dismounted Soldier (1997) / Chapter Skim
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Appendix C
Appendix C
Pages 187-247
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From page 187... ...
This should be possible with new, more efficient techniques for DC-DC conversion, which would eliminate the problem of Army communication devices being locked into using power sources with particular voltage levels.
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From page 188... ...
The systems likely to provide the desired combination of compactness, specific energy, and specific power fall into two categories: rechargeable alkaline electrolyte systems (nickel-metal hydride, nickel-zinc, MnO2-zinc) and rechargeable lithium electrode systems (lithium metal anodes, lithium intercalating anodes, lithium alloy anodes [including the tin oxide typed.
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From page 189... ...
Zinc-air, Li/MnO2, and Li/CTX are areas of interest for the government because they have either high specific power or high specific energy or both.
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From page 190... ...
190 ENERGY-EFFICIENT TECHNOLOGIES FOR THE DISMOUNTED SOLDIER TABLE C-2 Summary of Rechargeable Portable Battery Data Theoretical Working Estimated Battery Negative Positive Production Life System Electron Electron Voltage Ah/kg Wh/kg VoltageWh/kg Wh/l Valuea (Cycles) Lead-acid Pb PbO2 2.1 83 175 2.0 35-50 85 vl 400 Nickel-iron Fe NiOOH 1.4 224 313 1.2 35-60 70 vs 500 Nickel-cadmium Cd NiOOH 1.35 181 244 1.2 35-52 75 vl 600 Nickel-zinc Zn NiOOH 1.73 215 372 1.6 65-80 150 s 400 Silver-zinc Zn AgO 1.85 283 524 1.5 90-150 180 vs 100 Nickel-hydrogen H2 NiOOH 1.5 269 434 1.4 5500 60 s 600 Nickel-metal Mhx 1.2 NiOOH 1.35 206 278 1.2 55-70 120 vl 800 hydride to 2 w/o H Silver-cadmium Cd AgO 1.4 227 318 1.2 60-80 110 vvs 200 Zinc-bromineb Zn Br 1.85 139 258 1.55 70 60 vvs 400 Complex Alkaline Zn MnO2 1.6 224 330 1.2 55 250 vl 15 manganese Zinc-air Zn O2 (air)
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From page 191... ...
Material improvements can increase cycle life of rechargeable zinc-air battery. Air cathode improvements can increase power capability and cycle life of the zinc-air system.
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From page 192... ...
introduction-activated Ag2o Li V2O5 3.3 50 100 Li SO2 3 120 200 Li SOC12 3.5 150 300 Thermal batteries Ca CaCrO4 2.4 30 40 (Not rechargeable) Mg V2Os 2.5 Li FeS2 1.8 40 100 High-temperature rechargeable batteries Lithium-iron-sulfide Li FeS 1.3 100 200 700 FeS2 1.6 180 350 1,000 Sodium-sulfur Na S 2.1 170 250 100-2,000 Sodium-nickel Na NiCl2 2.58 90 160 600-1,000 chloride aThese batteries are not designed to be weight or volume efficient.
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From page 193... ...
To achieve the projected improvements, it will be necessary to research the following areas in depth: · materials for better cycle life and low temperature performance (nano structured, catalytic MnO2, improved carbons and graphites) improved cellophane (or other separator)
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From page 194... ...
Battery Systems Present Advantages Present Disadvantages 5 Years 10 Years Higher specific energy than NiCd Maintenance free Poor overcharge recombination kinetics Higher specific power, 10% more capacity per volume 20% specific energy improvement per volume Rapid recharge Moderate charge Charge loss reduced to retention; 2% per week at 1% per week at room room temperature temperature Moderate cycle life Improved separator and Improved separator electrolytes; 500-800 and electrolytes; 800 cycles 1000 cycles
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From page 195... ...
Table C-7 shows improvements in lithium batteries with lithium metal anode structures. To achieve the projected improvements, research will be needed in the following areas: Charge control in order to eliminate safety concerns Electrolyte and separator development to improve charge morpholology Management of the film on lithiums surface for improved cycle life Lithium intercalating anodes include carbon or graphite (LiCx)
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From page 196... ...
project the developments and necessary research arid development over the next ten years. TABLE C-9 Lithium Batteries of Lithium Alloy Anode Structures Present Advantages Present Disadvantages 5 Years 10 Years Increased power density as compared to lithium carbon Reduced specific energy as compared to lithium metal Improved specific power and specific energy through materials improvements Improved specific power and specific energy through materials improvements Voltage penalty Material and electrolyte Material and electrolyte improvements improvements No tolerance of Increased tolerance of overcharge and overcharge overdischarge Rate limiting electrode
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From page 197... ...
To achieve the projected improvements, research will be necessary In: Materials research to identify higher conductivity electrolytes Charge control in order to eliminate safety concerns Electrtolyte development to improve charge morphology Electrolyte salt investigation Lithium/polymer interface reactions (a rise in cell impedance on standing andfor cycling has been observed) TABLE C-1 1 Lithium Batteries with Polymer Gel Electrolytes Present Advantages Present Disadvantages 5 Years 10 Years Stable at high voltages Polymer electrolyte and separator Encapsulates volatile and flammable electrolytes Low conductivity No tolerance of overcharge and overdischarge Material improvements improving conductivity Improved conductivity through salt research Material improvements improving conductivity Improved conductivity through salt research
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From page 198... ...
TABLE C-12 Lithium Batteries with Lithium Manganese Dioxide Spinel (LixMn2O4) Cathode Structures Present Advantages Present Disadvantages 5 Years 10 Years Inexpensive Poor cycle life High specific energy Moderate rate capability No tolerance to overcharge and overdischarge Improved cycle life and rate through material improvements Improved cycle life and rate through material improvements TABLE C-13 Lithium Batteries with Lithium Nickel Dioxide (LiXNiO2)
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From page 199... ...
Lithium batteries especially must be charged very carefully. The effects of the charging current on cycle life include the formation of lithium deposits on lithium anodes and the possibility of lithium deposits on carbon anodes.
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From page 200... ...
in the performance characteristics of the battery and hybrid systems discussed in this appendix can be achieved by improvements in the following areas: processing technology; active material composition, and morphology; reinforcing components; electrolytes; and key cycle life and rate-limiting components, such as separators. Aqueous Systems Significant improvements in specific energy, specific power, and cycle life can be achieved by optimizing the structure and particle size of reactant materials.
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From page 201... ...
Advanced charging methods can provide rapid recharging, longer cycle life, and higher performance. FUEL CELLS Improved fuel cell systems can extend mission times for the dismounted soldier because they can be designed to carry varying amounts of fuel for short or long missions without adding weight to the power generating part of the unit.
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From page 202... ...
Recent Army fuel cell project goals for small systems have been 50 W 200 Wh, and 2 kg with specific power and energy goals of 25 W/kg and 100 Wh/kg respectively.
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From page 203... ...
Note that the assumed specific energy of the advanced rechargeable battery in the figure is comparable to that of current primary batteries. For advanced fuel cells, the energy storage advantage becomes apparent at approximately 0.75 kWh.
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From page 204... ...
Problems The PEMFC has been improved significantly in the past few years, but some technical and economic issues have yet to be resolved. First, the cost of a PEMFC is around $l,000/m2, or $140/kW at a peak power density of 700 mW/cm2.
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From page 205... ...
Problems System size and complexity due to need for ancillaries Transient response (reformed fuel) Cost Lifetime Pressurized operation FIGURE C-4 State of the art of hydrogen PEMFCs.
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From page 206... ...
For small units like the ones of interest for the dismounted soldier, operating at very near atmospheric pressure (so the air feed does not need compression) will be important.
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From page 207... ...
In summary, the following focus areas are important to the development of fuel cells: · developing more efficient methods of storing and/or generating hydrogen fuel reducing the operating pressures to near atmospheric pressure improving the CO tolerance of systems that use reformed fuels reducing the cost of bipolar plates/flow fields reducing system complexity improving water management reducing the cost of proton exchange membranes improving catalysts for DMFCs reducing the rate of methanol crossover improving system-specific power to levels greater than 100 W/kg for small (< ~ 00 W) systems at atmospheric pressure HEAT ENGINES WITH ELECTROMECHANICAL ENERGY CONVERTERS The energy requirements for extended missions or power-intensive activities often exceed the capacity of the dismounted soldier's batteries.
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From page 208... ...
Technical Considerations Heat engines can be classified in a number of ways, but perhaps the distinction between internal and external combustion engines is the most appropriate discriminator for the dismounted soldier system. Internal combustion engines, such as spark-ignition and diesel engines, typically involve compressing a combustible mixture of fuel and air with a piston, igniting the mixture, which burns to produce heat, and allowing the hot gases to expand against the piston.
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From page 209... ...
For microturbines, it may be necessary to develop electrostatic generators because of the small sizes involved. The relative merits and current state of development of various heat engines for the dismounted soldier are summarized in Table C-17.
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From page 210... ...
, ~, projects but it could provide extremely attractive specific power and energy figures for dismounted soldier systems. A primary disadvantage is that the first generation system is envisioned to operate on hydrogen, although plans call for the development of versions that operate on JP-~.
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From page 211... ...
for missions requiring various" amounts of energy can be obtained from Figure C-6, which plots system mass as a function of available energy in kWh. In the figure, the data in Table C-~8 was used to plot the weight of the engine, generator, and fuel required for 50 W of electric power as a furlctionof mission energy requirements.
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From page 212... ...
Key Research Issues The most promising major power systems based on rotating machinery are miniaturized turbines driven by combustion or high-pressure gases. The key research issues are: · liquid combustion in small systems · active noise canceling techniques · microturbine fabrication techniques miniature electrostatic generators · thermal signature mitigation THERMOELECTRIC GENERATORS The thermoelectric generator is a device that uses the Pettier effect to produce electricity from any heat source (Rowe, 1988~.
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From page 213... ...
The specific power of this unit is on the order of 25 W/kg for the converter alone. Because this is a converter, specific power is determined by the basic weight of the assembly plus the weight of the filet that would be needed for a mission.
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From page 214... ...
ALKALT-METAL THERMAL-TO-ELECTRIC CONVERTER The "sodium heat engine," or alkali-metal thermal-to-electric converter (AMTEC) , is capable of converting thermal energy from any heat source to electricity with efficiency estimates as high as 35 percent (Space Power Insitute, 1990~.
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From page 215... ...
It is estimated that an AMTEC may be configured to be as high as 500 W/kg in specific power although no experimental units have demonstrated power densities approaching this value (Ivanenok and Hunt, 1994~. Experimental units have been operated in a laboratory environment for thousands of hours demonstrating the potential for Tong life.
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From page 216... ...
Figure C-9 illustrates system mass as a function of mission duration in kWh based on published estimates of efficiency and specific power (Ivanenok et al., 1993, Ivanenok and Hunt, 19941. AMTEC, like all fueled systems, has the problem of rejecting waste thermal energy at a relatively high temperature.
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From page 217... ...
Systems utilizing isotopes can be made with a wide range of specific powers. Isotopes suitable for power applications are by-products of nuclear reactor operations.
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From page 218... ...
For terrestrial use, the specific power is less important, and these units tend to be more massive, due to the use of 90Sr and 60Co. The mass increase is usually in shielding or in pressure vessels if the unit is used for deep sea submergence.
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From page 219... ...
The nuclear industry associated with small power sources has an impeccable record of addressing environmental and safety issues through extensive testing programs. Disposal is not a problem for deed space and planetary probes.
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From page 220... ...
HUMAN-POWERED SYSTEMS With sophisticated energy management and low power electronics, the energy requirements of the dismounted soldier could be reduced to a level at which the soldier could individually generate a substantial portion of the electrical energy required for a mission. It would only be necessary to convert some of the energy expended by the soldier during everyday activities to electricity.
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From page 221... ...
Rechargeable batteries, electrochemical capacitors, pneumatics, springs, and flywheels are candidates. Rechargeable batteries and electrochemical capacitors are discussed elsewhere in this chapter.
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From page 222... ...
Currently most photovoltaic cells are used on commercial satellites, more than 400 of which are planned for the next five years. About 75 percent of production is devoted to gallium arsenide (GaAs)
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From page 223... ...
In polycrystalline form, silicon solar cells have an efficiency of up to ~ 5 percent and can be produced in virtually any rectangular size up to 36 to 50 cm2. In single-crystal form, their efficiency can be as high as 25 percent.
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From page 224... ...
Several researchers have tried to deposit InP solar cells onto Si substrates with modest success. Efficiencies of about 12 percent have been achieved to date.
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From page 225... ...
. Rigid arrays have specific powers of about 25 to 30 W/kg, with similar efficiencies.
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From page 226... ...
TPV technology shows great promise for the development of portable power sources for the dismounted soldier. Figure C-10 illustrates the concept.
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From page 227... ...
These components appear to be ready for rapid development once applications have been identified. Examples include photovoTtaic cells with conversion efficiency of greater than 20 percent, black-body-like emitters, selective emitters that emit greater than 50 percent of the energy in a narrow band, burners with combustion efficiency greater than 90 percent, cavities with losses just now being defined, filters with efficiency greater than 80 percent, coolant schemes that are readily adaptable to cooling photovoltaic cells, and designs for
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From page 228... ...
The most optimistic projections for efficiency are on the order of 30 percent. Until more emphasis is placed on recuperation, it will not be possible to determine the specific power; however, specific powers greater than 100 W/kg do appear to be reasonable.
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From page 229... ...
~ illustrates the performance of TPV as extrapolated from laboratory data and goals from funded programs. 16 14 12 Y 1 0 in in Cat 8 E ID 4 2 _~ _/ , 1 7 - 7 0 1 2 / Advanced lithium /: rechargeable / battery Near-term 500-W unit 50-W design _ ~ ~ ' Far-term 50-W design _ 1 1 1 1 6 7 8 9 10 Available energy (kWh)
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From page 230... ...
In terms of both specific power and specific energy, electrochemical capacitors are intermediate between classical batteries and capacitors. They have specific energies on the order of 10 to 20 percent of batteries and specific powers at least an order of magnitude better than a conventional batteries.
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From page 231... ...
The thickness of the film is critical, and in addition to the manufacturing technology for producing the thin film, poor packing fraction results when the film thickness approaches the electrode thickness. Recently, the Army Research Laboratory has developed a version of the ruthenium technology that promises the manufacturing ease of carbon powder technology while doubling the specific energy associated with ruthenium oxidebased electrochemical capacitors.
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From page 232... ...
Because organic electrolyte CDEs can operate at higher voltage, their specific energy should be greater by the square of the ratio of the operating voltage in the organic electrolyte. In practice, however, the specific energy is less because organic electrolytes cannot wet and form double layers in small pores the ~ .
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From page 233... ...
Because an oxide coating forms on the aluminum, it is particularly stable in organic electrolytes and can be safely operated at voltages as high as 3 V In the manufacturing process, the carbon powder is mixed with a suitable binder, such as Teflon_, and processed into a tape.
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From page 234... ...
A finished device, a mixture of the particulate and carbon powder, was made using the same technique described above for carbon powder bed capacitors. The current collectors were made from graphitized rubber.
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From page 235... ...
This problem is not serious in small devices because crimp seating of a metal can under pressure is sufficient to produce a minimum ESR. Equivalent Parallel Resistance in the charged state, electrochemical capacitors, like batteries, are in a state of high energy relative to the state of minimal energy associated with discharge.
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From page 236... ...
Some laboratory prototypes can satisfy many criteria for battlefield use, but they are handmade, and the technology to mass produce devices with acceptable, reproducible results has not been established. The key areas for research are: physical phenomena that limit specific energy, specific power, internal series resistance, internal parallel resistance, degradation mechanisms, temperature dependent phenomena, and useful life of electrochemical capacitors development of a series of laboratory prototypes for evaluation in hybrid power systems development of high voltage electrolytes development of low cost materials for use in both the chemical double layer and pseudocapacitors HYBRID SYSTEMS Hybrid systems offer an alternative approach to providing portable power and energy.
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From page 238... ...
Because power sources rarely have both high specific energy and high specific power simultaneously, designers have typically designed power systems to meet the maximum demand to ensure adequate energy for the worst case. Thus, systems may be heavier than necessary, or planners may be forced to plan shorter missions or to resupply the primary eneraY sources.
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From page 239... ...
For the fueled system-battery combination, there are at least three battery chemistries that warrant further consideration: nickel-cadmium, lithium; arid leadacid. Tables C-24, C-25, arid C-26 show the specific energy, specific power, and TABLE C-25 Commercial and Developmental High-Specific-Energy Batteries as Energy Sources in Hybrid Systems Current Status Future Specific Specific Specific Specific Present Future Power Energy Power Energy Cycle Life Cycle Life State of Chemistry (W/kg)
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From page 240... ...
In most scenarios, the fueled system could maintain an intermediate store at 90 percent or more most of the time. Battery and Electrochemical Capacitor A battery-capacitor combination for an energy storage system would exploit the high specific power of a capacitor and the high specific energy of a battery.
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From page 241... ...
Meeting this requirement with a battery alone would require a battery that could provide high power pulses at ~ to ~ O times normal capacity and would still have maximum life and adequate operational time between charges. Using a capacitor to meet the peak power requirement would provide better operating performance, longer battery life, and better low temperature operation while lowering life cycle costs and a smaller, lighter weight package.
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From page 242... ...
(Wh/kg) Key Issues Laws Impact Time Batteries highly 180~360 ~400 electrodes; known major/ years developed electrolytes;seals; enabling safety; corrosion Capacitor highly 0.25-1.00 ~8.00 molecular engineering known enabling minutes developed of film; for some Film foil manufacturing systems Paper foil technology; thermal concepts stability; electrical breakdown Ceramic highly ~0.30 > 3.00 large area samples; known enabling moderate developed electrical breakdown; for some manufacturing systems technology concepts Electrolytic highly < 0.5 > 0.75 large surface area known minimal minutes developed material; suitable oxides; electrolytes Chemical double developing ~7.00 > 12.00 large surface area known major minutes layer materials; electrolytes; equivalent series resistance/equivalent parallel resistance; seals Magnetic advanced > 15.00 strength of advanced composites; known minimal milliseconds materials low resistivity limited materials Inertial highly 100.00 > 300.00 high strength known minimal hours/days developed materials; gyroscopic for some effects; safety applications Thermal evolving sensible absolute materials known uncertain days/weeks heat temperature compatibility; high depends dominated strength materials; on AT > 5000 high specific heat of battery-capacitor combinations accurately.
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From page 243... ...
A secondary battery with the specific energy and specific power of primary batteries would be highly desirable. If this technology were available, the environmental restrictions would be lessened because less frequent recycling would be required.
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From page 245... ...
There wall, however, continue to be problems associated with their disposal, inventory, safety, and availability, and wherever possible, they should be replaced. The logical evolution of the Anny power system for the dismounted soldier is toward a rechargeable battery with improved specific power and energy that would meet or exceed the power available with current primary batteries coupled with a "personal" charger that contains the primary store of energy for the mission.
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From page 246... ...
Rose, member of the Committee on Electric Power for the Dismounted Soldier. Space Power Institute.
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From page 247... ...
Sponsored by the Space Power Institute and the Army Research Office. Auburn, Alabama: Space Power Institute.
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