human
***task***
the task is to summarize an input biomedical literature in six sentences

***input***
the input is a biomedical literature

***output***
the output is the summary of an input biomedical literature in six sentences

***documentation***

***examples***

input: development of high explosives for military use involves extensive safety considerations and resource limitations due to test facility requirements . at the us army armament research and development and engineering command ( ardec ) , picatinny arsenal , new explosives that are safer for handling , storage , and loading are continuously evaluated in an effort to provide effective and safe munitions for the warfighter . recent law dictates that whenever possible , insensitive munitions ( i m ) guidelines and requirements are followed . therefore , whenever new explosives are synthesized and formulated , performance testing is paramount to ensure they meet user requirements . in this context , the measurement of detonation properties of newly developed pax - 30 is compared with the pbxn - 5 , a traditional high performance explosive . in particular , measurement of its detonation velocity and detonation pressure , which are important for verification of theoretical models and performance calculations , the pax - 30 was developed to replace legacy explosives such as pbxn - 5 by using reactive aluminum . aluminum possesses a high enthalpy of oxidation as aluminum on a per molar basis : 2al + 3/2 o2 - al2o3 ( 1,670 kj / mol ) by adding aluminum in place of the shock sensitive explosive ingredients , the formulation is rendered more safe to external shock and hazard insults . this effectively helps fulfill insensitive munition ( i m ) united nation requirements while at the same time maintaining the performance necessary for military applications . the facilities to test such items are unique and highly specialized . these tests include thermal characterization with differential scanning calorimetry ( dsc ) and impact and friction tests . for the dsc tests , a small test sample is heated at a constant rate in an inert atmosphere , and the amount and direction of heat flow is monitored . for impact and friction tests , the sample is subjected to insults from a standardized falling weight ( bundesanstalt fur materialprufung , or bam impact ) , and for the friction test a standardized ceramic pin and plate ( bundesanstalt fur materialprufung , or bam friction ) . once the formulations are deemed safe for handling , further scale - up is accomplished by proprietary mixing technologies . in short , high explosives fall into three categories : melt - cast , in which the binder is a melt - phase material like a wax , trinitrotoluene ( tnt ) , dintroanisole ( dnan ) , or other meltable material . energetic or fuel solids can be incorporated with careful consideration of particle size and compatibility . cast - cure , in which the binder is a castable polymer , such as hydroxyl - terminated polybutadiene ( htpb ) , polyacrylate , or other epoxy - type plastic that is liquid in its unreacted state , but upon initiation solidifies to a solid . pressed , in which the solids loading is very high , often approaching nearly 95 % by weight , with a binder that is added to coat the solids using a lacquer or extrusion process . once pressed or cast , the materials are machined using standard methodologies to obtain proper geometry for a desired test . in this paper , pax - 30 and pbxn - 5the formulations are made through a slurry - coating process , in which energetic nitramine crystals ( hmx , rdx , or cl - 20 ) and aluminum particles are suspended in an aqueous solution . a lacquer with the proprietary binder is then added . upon lacquer addition , the polymer coats the explosive crystals , the suspension is heated under vacuum to drive off the solvent , and the particles are then filtered and dried . the granule - like particles are then pressed to the configuration desired . in order to determine the detonation velocitya detonation is defined as a self - sustaining instantaneous rise in pressure and temperature that is faster than the sound speed in the material . it becomes self - sustaining once the temperature and pressure are sufficient to provide exothermic reactions behind the propagating reaction front . such behavior is realized by incorporating oxidizing moieties such as nitrate groups in certain materials of the formation . two examples known as rdx ( cyclo -1,3,5-trimethylene-2,4,6-trinitramine ) and hmx ( cyclotetramethylenetetranitramine ) are shown in figure 1 , which by and large are the most used energetic materials in the us dod ( department of defense ) . note the oxygen balance of the molecules , which results in the self - propagating exothermic reaction behind the shock front . figure 1 . rdx ( cyclo -1,3,5-trimethylene-2,4,6-trinitramine , left ) and hmx ( cyclotetramethylenetetranitramine , right ) . one way to determine the speed of the detonation front is to monitor its position as a function of time . fiber - optic detonation velocity ( fodv ) testing is performed to determine the detonation velocity of an explosive material . an acrylic fixture was designed to hold the explosive sample , and locate the optical fibers at known distances down the charge length . the standard test uses a 5 - inch long by 0.75 - inch diameter explosive sample with five total optical fibers ; the bottom fiber is located 0.50 - inch from the bottom of the charge and each successive fiber is located 1 - inch above the next . the larger diameter hole is sized to fit the core and cladding of the optical fiber and the smaller diameter hole serves as a confined air space . as the detonation progresses through the explosive sample , the shock wave produced excites the confined air space producing a short , bright flash that can be observed with the fiber - optics . the fiber - optics used for this test possess an inexpensive plastic core . due to the destructive nature of the test and the consistency of the air shock , higher quality fibers were not found to be necessary to maintain high quality velocity data . the test facility at picatinny arsenal uses summed photodiodes to translate the light from the detonation into voltage . a 1 - ghz oscilloscope is connected to the photodiode summing box , although that sampling rate is far beyond what is necessary for this test . the optical fiber peaks can be either determined by first rise of the signal or peak values . given the distance between optical fibers and the time difference between detonation arrival , detonation velocity is then determined . detonation pressure is estimated by measuring the dent depth in a standard steel plate resultant from the explosive s detonation . dent depths are well correlated to known pressure values for a variety of explosive compounds . usually , since most explosives satisfy the chapman - jouguet ( cj ) condition for a detonation to occur , the detonation pressure is typically referred to as cj pressure , and it will be from this point forward in this article . the charge assembly is placed on top of a steel plate , called a witness plate , and the detonation results in a dent in the plate . the dent depth at the standard 0.75 - inch charge diameter for numerous explosive materials with known detonation pressures is then compared to the test dent depth . detonation pressure by the plate dent is a reliable method with many years of documented data for acceptable correlations . however , a detonation is a dynamic , fast chemical reaction , and in recent years it has become desirable to utilize tools with higher resolution to observe the pressure - time history . to directly measure the detonation pressure of an explosive , photonic doppler velocimetry ( pdv ) this laser interferometer system was developed by lawrence livermore national laboratory and utilizes a 1,550 nm cw laser source . by directing the laser at a moving target and collecting the doppler - shifted light , the resulting beat frequency can be analyzed to provide a velocity trace of the target . unlike traditional high - speed photographic techniques , these velocity traces provide a continuous record of the target s velocity as a function of time . this measurement technique has gained significant attention in the last few years and is becoming ubiquitous in dod and department of energy ( doe ) explosive characterization labs . in order to calculate the cj pressure of a new explosive , a pdv system can be used to measure the particle velocity between the explosive and a polymethyl methacrylate ( pmma ) window . a very thin foil , usually aluminum or copper , is placed at this interface to act as a reflective surface . in these studies , this foil should be thin enough to prevent significant shock wave attenuation while being thick enough to prevent detonation light from passing through . typically , a foil thickness of 1,000 angstroms is ideal for most experimental setups . given the particle velocity in the pmma and the detonation velocity of the explosive , the detonation pressure can be calculated with hugoniot shock matching equations . while the fodv test at 0.75 charge diameter is an established standard at ardec , pdv - based tests are continually undergoing refinement . depending on the explosive formulation , either one or both tests can be used to characterize detonation velocity and detonation pressure . caution ! the processing , handling , and testing of high explosives ( hazard division class 1 materials ) should only be carried out by trained and qualified personnel . high explosives are sensitive to impact , friction , electrostatic discharge , and shock . only use approved research and development facilities that can handle large quantities of class 1 materials . cut optical - fiber to length using fiber - optic cutters and bundle in sets of five cables . based on site - specific test chamber geometries , 15 meter lengths are typically used . strip cable jacket material back 15 mm on one end of the bundle and 5 mm on the other end of the bundle . polish the cut ends of the fiber - optics with p800 grit sandpaper to remove any burrs . note : due to the destructive nature of this test , plastic optical fiber is preferred . optical fiber properties are as follows ; polymethyl methacrylate resin ( pmma ) core material ( 980 m diameter ) , fluorinated polymer cladding material ( 1,000 m diameter ) , 1.49 core refractive index , 0.5 numerical aperture . measure test sample and composition a-3 type ii booster pellet diameters , lengths , and masses using a high accuracy caliper and balance . note : while the typical test uses 1.905 cm diameter by 2.54 cm length pellets , the test procedure can be used with any size pellet provided the plastic fixture holds the fiber - optic cable centered on each pellet . for the tests in this study , the 1.905 cm diameter pellets were used . load the explosive pellets , one by one , into the plastic fixture by expanding the tube s inner diameter via prying the slot open . record explosive pellet numbers and locations in the fixture . then load the booster pellet into the tube from the top of the fixture . other detonators could be substituted , although re - calibration of the test would be necessary . insert the shorter exposed ends ( 5 mm ) of the optical fibers into the two - stepped holes in the detonation velocity test fixture . note : the two - step holes ensure there is sufficient air for ionization upon passage of the detonation front which leads to a strong signal . the holes for the fixture should have a 0.021 - inch diameter by 0.020 length inner hole against the explosive and a 0.042 - inch diameter hole for insertion of the fiber - optic . if plastic fibers are used , light sanding of the outer diameter of the optical fiber may be necessary depending on both fiber diameter and test fixture tolerances . ensure that the optical fiber is fully inserted ( seated on the step in the two - stepped hole ) . glue / epoxy the fibers in place . when the epoxy holding the fibers in has fully cured , position the acrylic tube containing the explosive pellets on top of the steel witness plate . secure the text fixture to the steel plate with either a weight on top of it or tape . ensure that there is not an air gap between the bottom surface of the last explosive pellet and the steel witness plate . after the epoxy has fully cured , place the detonator in the detonator holder that is at the top of the test fixture and secure it in place with tape . transport the test fixture to the test chamber and insert longer exposed ends ( 15 mm ) of the optical fibers into the photodiode summing box . connect the photodiode summing box , or other data acquisition method , as appropriate , to an oscilloscope ( 1 ghz bandwidth is more than sufficient ) . close all required doors / ports / etc . and conduct area lockdown operations per facility s explosive test firing ( standard operating procedures ) sops . confirm oscilloscope trigger , voltage / division , time / division settings . connect the trigger out from the high - voltage fireset with a trigger threshold of 3.0 v to one channel on the oscilloscope . connect the photodiode summing box to a second channel on the oscilloscope . set both channels to 5 v / division and the timebase to 5 sec / division , with a delay setting of -20 sec . measure the peaks corresponding to time from the output of the photodiode summing box . from the oscilloscope screen trace , use peak voltages to determine specific times , although first rise may be a better indicator depending on the equipment used . since the spacing of each fiber - optic is known , calculate the detonation velocity by dividing the distance between each pin by the time between each peak ( distance / time = velocity ) . calculate the depth of the dent in the steel witness plate by placing a calibrated steel bearing in the dent to find the minimum level , and then a depth gauge used to determine the depth . machine a pmma window sized to the diameter of the explosive charge approximately 6.5 mm thick . ensure that the window is optically clear and free of any machining defects . to accomplish thistake an optically clear sheet of cast acrylic and machining out the disks using a laser cutter or similar machining process . if the foil surface is pristine ( specular ) , roll over the surface with a sanded stainless steel ball bearing . a diffuse surface results in optimal laser back reflection , even when alignment is slightly off . use a thin , optically clear , acrylic - based adhesive tape to affix the aluminum foil to the pmma window . ensure that there are no air bubbles between the pmma and the aluminum . use high - accuracy calipers and balance . affix the explosive test sample pellets to each other to form a continuous charge , including any boosters ( if necessary ) . apply grease at each explosive interface during assembly to minimize air gaps at pellet interfaces . typically , the fiber / pin locations are nearest the bottom of the explosive charge such that steady state detonation may be observed . invert the assembled charge and stabilize it in this orientation to prepare for affixing the pmma window . place a small amount of grease on the explosive face to prevent air bubbles at the aluminum / explosive interface . if the window and charge are concentric , use tape circumferentially . if not , tape down the axis of the explosive chargeonce the pmma window is securely attached to the explosive charge , affix the acrylic pdv probe holder to the pmma window with tape . insert the pdv probe into the pdv probe holder . align the pdv probe in the holder with a back - reflection meter . this device outputs a low power laser beam and measures the back - reflection amplitude . epoxy the pdv probe in place once the back reflection has been determined to be optimal . place the test item in the chamber and attach both the detonation velocity wires ( fiber - optic or piezoelectric ) and the pdv fiber . close all required doors / ports / etc . and conduct area lockdown operations per facility s explosive test firing sops . confirm oscilloscope trigger , voltage / division , time / division settings . save oscilloscope traces for both pdv data and detonation velocity data . analyze the pdv data in relevant data analysis program . the raw pdv signal must be processed using an fast fourier transform ( fft ) based analysis package . note : by looking at the frequency content of this raw signal , and knowing the initial frequency of the light source ( 1,550 nm ) , the fft analysis package produces a velocity spectrogram that plots the recorded velocity as a function of time . in this case , plotdata , a proprietary united states department of energy graphical user interface ( gui ) , is used in conjunction with labview software to carry out the fft . however , many commercially available analysis packages exist that are capable of performing these tasks . since the spacing of each fiber - optic is known , the detonation velocity is calculated by dividing the distance between each pin by the time between each peak ( distance / time = velocity ) . cut optical - fiber to length using fiber - optic cutters and bundle in sets of five cables . based on site - specific test chamber geometries , 15 meter lengths are typically used . strip cable jacket material back 15 mm on one end of the bundle and 5 mm on the other end of the bundle . polish the cut ends of the fiber - optics with p800 grit sandpaper to remove any burrs . note : due to the destructive nature of this test , plastic optical fiber is preferred . optical fiber properties are as follows ; polymethyl methacrylate resin ( pmma ) core material ( 980 m diameter ) , fluorinated polymer cladding material ( 1,000 m diameter ) , 1.49 core refractive index , 0.5 numerical aperture . measure test sample and composition a-3 type ii booster pellet diameters , lengths , and masses using a high accuracy caliper and balance . note : while the typical test uses 1.905 cm diameter by 2.54 cm length pellets , the test procedure can be used with any size pellet provided the plastic fixture holds the fiber - optic cable centered on each pellet . for the tests in this study , the 1.905 cm diameter pellets were used . load the explosive pellets , one by one , into the plastic fixture by expanding the tube s inner diameter via prying the slot open . record explosive pellet numbers and locations in the fixture . then load the booster pellet into the tube from the top of the fixture . other detonators could be substituted , although re - calibration of the test would be necessary . insert the shorter exposed ends ( 5 mm ) of the optical fibers into the two - stepped holes in the detonation velocity test fixture . note : the two - step holes ensure there is sufficient air for ionization upon passage of the detonation front which leads to a strong signal . the holes for the fixture should have a 0.021 - inch diameter by 0.020 length inner hole against the explosive and a 0.042 - inch diameter hole for insertion of the fiber - optic . if plastic fibers are used , light sanding of the outer diameter of the optical fiber may be necessary depending on both fiber diameter and test fixture tolerances . ensure that the optical fiber is fully inserted ( seated on the step in the two - stepped hole ) . glue / epoxy the fibers in place . when the epoxy holding the fibers in has fully cured , position the acrylic tube containing the explosive pellets on top of the steel witness plate . secure the text fixture to the steel plate with either a weight on top of it or tape . ensure that there is not an air gap between the bottom surface of the last explosive pellet and the steel witness plate . after the epoxy has fully cured , place the detonator in the detonator holder that is at the top of the test fixture and secure it in place with tape . transport the test fixture to the test chamber and insert longer exposed ends ( 15 mm ) of the optical fibers into the photodiode summing box . connect the photodiode summing box , or other data acquisition method , as appropriate , to an oscilloscope ( 1 ghz bandwidth is more than sufficient ) . close all required doors / ports / etc . and conduct area lockdown operations per facility s explosive test firing ( standard operating procedures ) sops . confirm oscilloscope trigger , voltage / division , time / division settings . connect the trigger out from the high - voltage fireset with a trigger threshold of 3.0 v to one channel on the oscilloscope . . set both channels to 5 v / division and the timebase to 5 sec / division , with a delay setting of -20 sec . measure the peaks corresponding to time from the output of the photodiode summing box . from the oscilloscope screen trace , use peak voltages to determine specific times , although first rise may be a better indicator depending on the equipment used . since the spacing of each fiber - optic is known , calculate the detonation velocity by dividing the distance between each pin by the time between each peak ( distance / time = velocity ) . calculate the depth of the dent in the steel witness plate by placing a calibrated steel bearing in the dent to find the minimum level , and then a depth gauge used to determine the depth . machine a pmma window sized to the diameter of the explosive charge approximately 6.5 mm thick . ensure that the window is optically clear and free of any machining defects . to accomplish thistake an optically clear sheet of cast acrylic and machining out the disks using a laser cutter or similar machining process . if the foil surface is pristine ( specular ) , roll over the surface with a sanded stainless steel ball bearing . a diffuse surface results in optimal laser back reflection , even when alignment is slightly off . use a thin , optically clear , acrylic - based adhesive tape to affix the aluminum foil to the pmma window . use high - accuracy calipers and balance . affix the explosive test sample pellets to each other to form a continuous charge , including any boosters ( if necessary ) . apply grease at each explosive interface during assembly to minimize air gaps at pellet interfaces . typically , the fiber / pin locations are nearest the bottom of the explosive charge such that steady state detonation may be observed . invert the assembled charge and stabilize it in this orientation to prepare for affixing the pmma window . place a small amount of grease on the explosive face to prevent air bubbles at the aluminum / explosive interface . if the window and charge are concentric , use tape circumferentially . if not , tape down the axis of the explosive charge . once the pmma window is securely attached to the explosive charge , affix the acrylic pdv probe holder to the pmma window with tape . insert the pdv probe into the pdv probe holder . align the pdv probe in the holder with a back - reflection meter . this device outputs a low power laser beam and measures the back - reflection amplitude . epoxy the pdv probe in place once the back reflection has been determined to be optimal . place the test item in the chamber and attach both the detonation velocity wires ( fiber - optic or piezoelectric ) and the pdv fiber . close all required doors / ports / etc . and conduct area lockdown operations per facility s explosive test firing sops . confirm oscilloscope trigger , voltage / division , time / division settings . the raw pdv signal must be processed using an fast fourier transform ( fft ) based analysis package . note : by looking at the frequency content of this raw signal , and knowing the initial frequency of the light source ( 1,550 nm ) , the fft analysis package produces a velocity spectrogram that plots the recorded velocity as a function of time . in this case , plotdata , a proprietary united states department of energy graphical user interface ( gui ) , is used in conjunction with labview software to carry out the fft . however , since the spacing of each fiber - optic is known , the detonation velocity is calculated by dividing the distance between each pin by the time between each peak ( distance / time = velocity ) . the average and standard deviation is reported . a typical setup for pdv is shown in figures 2 and 3 , while the fodv setup is shown in figure 4 . upon detonation , the resulting dent plates from traditional fodv shots are shown in figure 5 , with the position / time results of pax - 30 and pbxn - 5 in figure 6 . both materials possess similar detonation velocities ( the slope of the line ) , with pax - 30 ~ 0.4 sec / mm slower . while it may not seem to be a significant difference , it is indeed in light of the fact that pax - 30 possesses nearly 20 % less by weight explosive fill . detonation velocity is not the conclusive test to quantify the aluminum reaction in the or immediately after the detonation front , but it can give a preliminary assessment of aluminum reaction . the stick is epoxied on the steel witness plate to ensure a solid contact and upright stance during setup . each data point is from the fiber - optic pins in the fodv setup . pax - 30r = 0.999717 , rmse ( root mean square error ) = 0.519693 ; pbxn - 5 r = 0.998778 , rmse = 1.342272 . the output from the pdv trace of the flyer plate from the bottom of the explosive charge of figures 2 - 3 is shown in figure 7 . the oscillations arise from the ringing in the plate from the rapid acceleration to nearly 4 - 5 km / sec . the cj pressure is calculated from modeling the product gas hugoniot with cooper s approximation , and then extrapolating the cj point once the aluminum - explosive hugoniot is matched . a typical screen print from such a calculationthe technique still has some limitations since the calculations assume a linear acceleration extrapolation from the beginning of the flyer velocity . this results in slightly underestimating the pressure , as evidenced by the results ( table 1 ) . work is ongoing to develop new equations to fit the early acceleration of the flyer plate . figure 7 . plate velocity as a function of time for the measurement of cj pressure in the pbxn - 5 explosive . note the excellent agreement between two different shots , where the traces practically fall on one another . calculation of the cj pressure from the copper flyer plate data on the pdv experiment . note that the extrapolation assumes a linear acceleration in the initial push of the flyer plate which currently leads to an underestimation of the cj pressure . the blue straight lines are the tangent solutions that are proportional to the detonation velocity . note the reacted al products solution force the detonation velocity to be lower than the unreacted al solution . the aluminized explosive exhibits less pressure , partially due to less nitramine ( hmx ) loading , but also because the aluminum reacts with oxygen in the expanding detonation gases , which results in a smaller dent from a lower detonation pressure . the pbxn - 5 exerts a higher detonation pressure due to its higher gas content upon detonation compared to pax - 30 ( 36.2 moles / kg for pbxn - 5 versus 33.1 moles / kg for pax - 30 ) . more advanced equations of state ( eos ) derived from wall velocity measurements are used to describe the conditions of the explosive products at such extreme temperatures and pressures . it was apparent that when early reaction of a metal in an explosive occurs , the detected detonation velocity is lower than if the metal does not react . this is somewhat counterintuitive ; one would expect the velocity to increase if more energy deposits into the expanding detonation front due to exothermic reaction of aluminum . the specific volume ( inverse density ) - pressure isentrope denotes changes in as products from the detonation expand ( from left to right in figure 9 ) . the expansion isentrope represents those detonation products that can thermodynamically form and expand along the pressure - specific volume curve . during the course of expansion , if the aluminum reacts to form oxidized species , it results in an overall decrease in density of gas and leads to a lower velocity . this is manifested in an expansion isentrope below the solution for the non - reactive aluminum ( figure 9 ) . since the detonation velocity is the tangent line intersecting the isentrope from the starting density on the x - axis , it is apparent the detonation velocity must decrease when the aluminum in the formulation reacts . in summary , the united states department of defense continues to actively pursue applied research and characterization of new energetic materials with both traditional and novel technologies . in the case of pdv , it is a valuable tool that characterizes explosives with extreme accuracy and provides the researchers with valuable insight into the explosive effectiveness . this rapid test cycle greatly decreases cost and the time needed for formulation optimization and requirements verification .
output:

agent
developmental testing of high explosives for military applications involves small - scale formulation , safety testing , and finally detonation performance tests to verify theoretical calculations . small - scale for newly developed formulations , the process begins with small - scale mixes , thermal testing , and impact and friction sensitivity . only then do subsequent larger scale formulations proceed to detonation testing , which will be covered in this paper . recent advances in characterization techniques have led to unparalleled precision in the characterization of early - time evolution of detonations . the new technique of photo - doppler velocimetry ( pdv ) for the measurement of detonation pressure and velocity will be shared and compared with traditional fiber - optic detonation velocity and plate - dent calculation of detonation pressure . in particular , the role of aluminum in explosive formulations will be discussed . recent developments led to the development of explosive formulations that result in reaction of aluminum very early in the detonation product expansion . this enhanced reaction leads to changes in the detonation velocity and pressure due to reaction of the aluminum with oxygen in the expanding gas products .
***task***
the task is to summarize an input biomedical literature in six sentences

***input***
the input is a biomedical literature

***output***
the output is the summary of an input biomedical literature in six sentences

***documentation***

***examples***

input: development of high explosives for military use involves extensive safety considerations and resource limitations due to test facility requirements . at the us army armament research and development and engineering command ( ardec ) , picatinny arsenal , new explosives that are safer for handling , storage , and loading are continuously evaluated in an effort to provide effective and safe munitions for the warfighter . recent law dictates that whenever possible , insensitive munitions ( i m ) guidelines and requirements are followed . therefore , whenever new explosives are synthesized and formulated , performance testing is paramount to ensure they meet user requirements . in this context , the measurement of detonation properties of newly developed pax - 30 is compared with the pbxn - 5 , a traditional high performance explosive . in particular , measurement of its detonation velocity and detonation pressure , which are important for verification of theoretical models and performance calculations , the pax - 30 was developed to replace legacy explosives such as pbxn - 5 by using reactive aluminum . aluminum possesses a high enthalpy of oxidation as aluminum on a per molar basis : 2al + 3/2 o2 - al2o3 ( 1,670 kj / mol ) by adding aluminum in place of the shock sensitive explosive ingredients , the formulation is rendered more safe to external shock and hazard insults . this effectively helps fulfill insensitive munition ( i m ) united nation requirements while at the same time maintaining the performance necessary for military applications . the facilities to test such items are unique and highly specialized . these tests include thermal characterization with differential scanning calorimetry ( dsc ) and impact and friction tests . for the dsc tests , a small test sample is heated at a constant rate in an inert atmosphere , and the amount and direction of heat flow is monitored . for impact and friction tests , the sample is subjected to insults from a standardized falling weight ( bundesanstalt fur materialprufung , or bam impact ) , and for the friction test a standardized ceramic pin and plate ( bundesanstalt fur materialprufung , or bam friction ) . once the formulations are deemed safe for handling , further scale - up is accomplished by proprietary mixing technologies . in short , high explosives fall into three categories : melt - cast , in which the binder is a melt - phase material like a wax , trinitrotoluene ( tnt ) , dintroanisole ( dnan ) , or other meltable material . energetic or fuel solids can be incorporated with careful consideration of particle size and compatibility . cast - cure , in which the binder is a castable polymer , such as hydroxyl - terminated polybutadiene ( htpb ) , polyacrylate , or other epoxy - type plastic that is liquid in its unreacted state , but upon initiation solidifies to a solid . pressed , in which the solids loading is very high , often approaching nearly 95 % by weight , with a binder that is added to coat the solids using a lacquer or extrusion process . once pressed or cast , the materials are machined using standard methodologies to obtain proper geometry for a desired test . in this paper , pax - 30 and pbxn - 5the formulations are made through a slurry - coating process , in which energetic nitramine crystals ( hmx , rdx , or cl - 20 ) and aluminum particles are suspended in an aqueous solution . a lacquer with the proprietary binder is then added . upon lacquer addition , the polymer coats the explosive crystals , the suspension is heated under vacuum to drive off the solvent , and the particles are then filtered and dried . the granule - like particles are then pressed to the configuration desired . in order to determine the detonation velocitya detonation is defined as a self - sustaining instantaneous rise in pressure and temperature that is faster than the sound speed in the material . it becomes self - sustaining once the temperature and pressure are sufficient to provide exothermic reactions behind the propagating reaction front . such behavior is realized by incorporating oxidizing moieties such as nitrate groups in certain materials of the formation . two examples known as rdx ( cyclo -1,3,5-trimethylene-2,4,6-trinitramine ) and hmx ( cyclotetramethylenetetranitramine ) are shown in figure 1 , which by and large are the most used energetic materials in the us dod ( department of defense ) . note the oxygen balance of the molecules , which results in the self - propagating exothermic reaction behind the shock front . figure 1 . rdx ( cyclo -1,3,5-trimethylene-2,4,6-trinitramine , left ) and hmx ( cyclotetramethylenetetranitramine , right ) . one way to determine the speed of the detonation front is to monitor its position as a function of time . fiber - optic detonation velocity ( fodv ) testing is performed to determine the detonation velocity of an explosive material . an acrylic fixture was designed to hold the explosive sample , and locate the optical fibers at known distances down the charge length . the standard test uses a 5 - inch long by 0.75 - inch diameter explosive sample with five total optical fibers ; the bottom fiber is located 0.50 - inch from the bottom of the charge and each successive fiber is located 1 - inch above the next . the larger diameter hole is sized to fit the core and cladding of the optical fiber and the smaller diameter hole serves as a confined air space . as the detonation progresses through the explosive sample , the shock wave produced excites the confined air space producing a short , bright flash that can be observed with the fiber - optics . the fiber - optics used for this test possess an inexpensive plastic core . due to the destructive nature of the test and the consistency of the air shock , higher quality fibers were not found to be necessary to maintain high quality velocity data . the test facility at picatinny arsenal uses summed photodiodes to translate the light from the detonation into voltage . a 1 - ghz oscilloscope is connected to the photodiode summing box , although that sampling rate is far beyond what is necessary for this test . the optical fiber peaks can be either determined by first rise of the signal or peak values . given the distance between optical fibers and the time difference between detonation arrival , detonation velocity is then determined . detonation pressure is estimated by measuring the dent depth in a standard steel plate resultant from the explosive s detonation . dent depths are well correlated to known pressure values for a variety of explosive compounds . usually , since most explosives satisfy the chapman - jouguet ( cj ) condition for a detonation to occur , the detonation pressure is typically referred to as cj pressure , and it will be from this point forward in this article . the charge assembly is placed on top of a steel plate , called a witness plate , and the detonation results in a dent in the plate . the dent depth at the standard 0.75 - inch charge diameter for numerous explosive materials with known detonation pressures is then compared to the test dent depth . detonation pressure by the plate dent is a reliable method with many years of documented data for acceptable correlations . however , a detonation is a dynamic , fast chemical reaction , and in recent years it has become desirable to utilize tools with higher resolution to observe the pressure - time history . to directly measure the detonation pressure of an explosive , photonic doppler velocimetry ( pdv ) this laser interferometer system was developed by lawrence livermore national laboratory and utilizes a 1,550 nm cw laser source . by directing the laser at a moving target and collecting the doppler - shifted light , the resulting beat frequency can be analyzed to provide a velocity trace of the target . unlike traditional high - speed photographic techniques , these velocity traces provide a continuous record of the target s velocity as a function of time . this measurement technique has gained significant attention in the last few years and is becoming ubiquitous in dod and department of energy ( doe ) explosive characterization labs . in order to calculate the cj pressure of a new explosive , a pdv system can be used to measure the particle velocity between the explosive and a polymethyl methacrylate ( pmma ) window . a very thin foil , usually aluminum or copper , is placed at this interface to act as a reflective surface . in these studies , this foil should be thin enough to prevent significant shock wave attenuation while being thick enough to prevent detonation light from passing through . typically , a foil thickness of 1,000 angstroms is ideal for most experimental setups . given the particle velocity in the pmma and the detonation velocity of the explosive , the detonation pressure can be calculated with hugoniot shock matching equations . while the fodv test at 0.75 charge diameter is an established standard at ardec , pdv - based tests are continually undergoing refinement . depending on the explosive formulation , either one or both tests can be used to characterize detonation velocity and detonation pressure . caution ! the processing , handling , and testing of high explosives ( hazard division class 1 materials ) should only be carried out by trained and qualified personnel . high explosives are sensitive to impact , friction , electrostatic discharge , and shock . only use approved research and development facilities that can handle large quantities of class 1 materials . cut optical - fiber to length using fiber - optic cutters and bundle in sets of five cables . based on site - specific test chamber geometries , 15 meter lengths are typically used . strip cable jacket material back 15 mm on one end of the bundle and 5 mm on the other end of the bundle . polish the cut ends of the fiber - optics with p800 grit sandpaper to remove any burrs . note : due to the destructive nature of this test , plastic optical fiber is preferred . optical fiber properties are as follows ; polymethyl methacrylate resin ( pmma ) core material ( 980 m diameter ) , fluorinated polymer cladding material ( 1,000 m diameter ) , 1.49 core refractive index , 0.5 numerical aperture . measure test sample and composition a-3 type ii booster pellet diameters , lengths , and masses using a high accuracy caliper and balance . note : while the typical test uses 1.905 cm diameter by 2.54 cm length pellets , the test procedure can be used with any size pellet provided the plastic fixture holds the fiber - optic cable centered on each pellet . for the tests in this study , the 1.905 cm diameter pellets were used . load the explosive pellets , one by one , into the plastic fixture by expanding the tube s inner diameter via prying the slot open . record explosive pellet numbers and locations in the fixture . then load the booster pellet into the tube from the top of the fixture . other detonators could be substituted , although re - calibration of the test would be necessary . insert the shorter exposed ends ( 5 mm ) of the optical fibers into the two - stepped holes in the detonation velocity test fixture . note : the two - step holes ensure there is sufficient air for ionization upon passage of the detonation front which leads to a strong signal . the holes for the fixture should have a 0.021 - inch diameter by 0.020 length inner hole against the explosive and a 0.042 - inch diameter hole for insertion of the fiber - optic . if plastic fibers are used , light sanding of the outer diameter of the optical fiber may be necessary depending on both fiber diameter and test fixture tolerances . ensure that the optical fiber is fully inserted ( seated on the step in the two - stepped hole ) . glue / epoxy the fibers in place . when the epoxy holding the fibers in has fully cured , position the acrylic tube containing the explosive pellets on top of the steel witness plate . secure the text fixture to the steel plate with either a weight on top of it or tape . ensure that there is not an air gap between the bottom surface of the last explosive pellet and the steel witness plate . after the epoxy has fully cured , place the detonator in the detonator holder that is at the top of the test fixture and secure it in place with tape . transport the test fixture to the test chamber and insert longer exposed ends ( 15 mm ) of the optical fibers into the photodiode summing box . connect the photodiode summing box , or other data acquisition method , as appropriate , to an oscilloscope ( 1 ghz bandwidth is more than sufficient ) . close all required doors / ports / etc . and conduct area lockdown operations per facility s explosive test firing ( standard operating procedures ) sops . confirm oscilloscope trigger , voltage / division , time / division settings . connect the trigger out from the high - voltage fireset with a trigger threshold of 3.0 v to one channel on the oscilloscope . connect the photodiode summing box to a second channel on the oscilloscope . set both channels to 5 v / division and the timebase to 5 sec / division , with a delay setting of -20 sec . measure the peaks corresponding to time from the output of the photodiode summing box . from the oscilloscope screen trace , use peak voltages to determine specific times , although first rise may be a better indicator depending on the equipment used . since the spacing of each fiber - optic is known , calculate the detonation velocity by dividing the distance between each pin by the time between each peak ( distance / time = velocity ) . calculate the depth of the dent in the steel witness plate by placing a calibrated steel bearing in the dent to find the minimum level , and then a depth gauge used to determine the depth . machine a pmma window sized to the diameter of the explosive charge approximately 6.5 mm thick . ensure that the window is optically clear and free of any machining defects . to accomplish thistake an optically clear sheet of cast acrylic and machining out the disks using a laser cutter or similar machining process . if the foil surface is pristine ( specular ) , roll over the surface with a sanded stainless steel ball bearing . a diffuse surface results in optimal laser back reflection , even when alignment is slightly off . use a thin , optically clear , acrylic - based adhesive tape to affix the aluminum foil to the pmma window . ensure that there are no air bubbles between the pmma and the aluminum . use high - accuracy calipers and balance . affix the explosive test sample pellets to each other to form a continuous charge , including any boosters ( if necessary ) . apply grease at each explosive interface during assembly to minimize air gaps at pellet interfaces . typically , the fiber / pin locations are nearest the bottom of the explosive charge such that steady state detonation may be observed . invert the assembled charge and stabilize it in this orientation to prepare for affixing the pmma window . place a small amount of grease on the explosive face to prevent air bubbles at the aluminum / explosive interface . if the window and charge are concentric , use tape circumferentially . if not , tape down the axis of the explosive chargeonce the pmma window is securely attached to the explosive charge , affix the acrylic pdv probe holder to the pmma window with tape . insert the pdv probe into the pdv probe holder . align the pdv probe in the holder with a back - reflection meter . this device outputs a low power laser beam and measures the back - reflection amplitude . epoxy the pdv probe in place once the back reflection has been determined to be optimal . place the test item in the chamber and attach both the detonation velocity wires ( fiber - optic or piezoelectric ) and the pdv fiber . close all required doors / ports / etc . and conduct area lockdown operations per facility s explosive test firing sops . confirm oscilloscope trigger , voltage / division , time / division settings . save oscilloscope traces for both pdv data and detonation velocity data . analyze the pdv data in relevant data analysis program . the raw pdv signal must be processed using an fast fourier transform ( fft ) based analysis package . note : by looking at the frequency content of this raw signal , and knowing the initial frequency of the light source ( 1,550 nm ) , the fft analysis package produces a velocity spectrogram that plots the recorded velocity as a function of time . in this case , plotdata , a proprietary united states department of energy graphical user interface ( gui ) , is used in conjunction with labview software to carry out the fft . however , many commercially available analysis packages exist that are capable of performing these tasks . since the spacing of each fiber - optic is known , the detonation velocity is calculated by dividing the distance between each pin by the time between each peak ( distance / time = velocity ) . cut optical - fiber to length using fiber - optic cutters and bundle in sets of five cables . based on site - specific test chamber geometries , 15 meter lengths are typically used . strip cable jacket material back 15 mm on one end of the bundle and 5 mm on the other end of the bundle . polish the cut ends of the fiber - optics with p800 grit sandpaper to remove any burrs . note : due to the destructive nature of this test , plastic optical fiber is preferred . optical fiber properties are as follows ; polymethyl methacrylate resin ( pmma ) core material ( 980 m diameter ) , fluorinated polymer cladding material ( 1,000 m diameter ) , 1.49 core refractive index , 0.5 numerical aperture . measure test sample and composition a-3 type ii booster pellet diameters , lengths , and masses using a high accuracy caliper and balance . note : while the typical test uses 1.905 cm diameter by 2.54 cm length pellets , the test procedure can be used with any size pellet provided the plastic fixture holds the fiber - optic cable centered on each pellet . for the tests in this study , the 1.905 cm diameter pellets were used . load the explosive pellets , one by one , into the plastic fixture by expanding the tube s inner diameter via prying the slot open . record explosive pellet numbers and locations in the fixture . then load the booster pellet into the tube from the top of the fixture . other detonators could be substituted , although re - calibration of the test would be necessary . insert the shorter exposed ends ( 5 mm ) of the optical fibers into the two - stepped holes in the detonation velocity test fixture . note : the two - step holes ensure there is sufficient air for ionization upon passage of the detonation front which leads to a strong signal . the holes for the fixture should have a 0.021 - inch diameter by 0.020 length inner hole against the explosive and a 0.042 - inch diameter hole for insertion of the fiber - optic . if plastic fibers are used , light sanding of the outer diameter of the optical fiber may be necessary depending on both fiber diameter and test fixture tolerances . ensure that the optical fiber is fully inserted ( seated on the step in the two - stepped hole ) . glue / epoxy the fibers in place . when the epoxy holding the fibers in has fully cured , position the acrylic tube containing the explosive pellets on top of the steel witness plate . secure the text fixture to the steel plate with either a weight on top of it or tape . ensure that there is not an air gap between the bottom surface of the last explosive pellet and the steel witness plate . after the epoxy has fully cured , place the detonator in the detonator holder that is at the top of the test fixture and secure it in place with tape . transport the test fixture to the test chamber and insert longer exposed ends ( 15 mm ) of the optical fibers into the photodiode summing box . connect the photodiode summing box , or other data acquisition method , as appropriate , to an oscilloscope ( 1 ghz bandwidth is more than sufficient ) . close all required doors / ports / etc . and conduct area lockdown operations per facility s explosive test firing ( standard operating procedures ) sops . confirm oscilloscope trigger , voltage / division , time / division settings . connect the trigger out from the high - voltage fireset with a trigger threshold of 3.0 v to one channel on the oscilloscope . . set both channels to 5 v / division and the timebase to 5 sec / division , with a delay setting of -20 sec . measure the peaks corresponding to time from the output of the photodiode summing box . from the oscilloscope screen trace , use peak voltages to determine specific times , although first rise may be a better indicator depending on the equipment used . since the spacing of each fiber - optic is known , calculate the detonation velocity by dividing the distance between each pin by the time between each peak ( distance / time = velocity ) . calculate the depth of the dent in the steel witness plate by placing a calibrated steel bearing in the dent to find the minimum level , and then a depth gauge used to determine the depth . machine a pmma window sized to the diameter of the explosive charge approximately 6.5 mm thick . ensure that the window is optically clear and free of any machining defects . to accomplish thistake an optically clear sheet of cast acrylic and machining out the disks using a laser cutter or similar machining process . if the foil surface is pristine ( specular ) , roll over the surface with a sanded stainless steel ball bearing . a diffuse surface results in optimal laser back reflection , even when alignment is slightly off . use a thin , optically clear , acrylic - based adhesive tape to affix the aluminum foil to the pmma window . use high - accuracy calipers and balance . affix the explosive test sample pellets to each other to form a continuous charge , including any boosters ( if necessary ) . apply grease at each explosive interface during assembly to minimize air gaps at pellet interfaces . typically , the fiber / pin locations are nearest the bottom of the explosive charge such that steady state detonation may be observed . invert the assembled charge and stabilize it in this orientation to prepare for affixing the pmma window . place a small amount of grease on the explosive face to prevent air bubbles at the aluminum / explosive interface . if the window and charge are concentric , use tape circumferentially . if not , tape down the axis of the explosive charge . once the pmma window is securely attached to the explosive charge , affix the acrylic pdv probe holder to the pmma window with tape . insert the pdv probe into the pdv probe holder . align the pdv probe in the holder with a back - reflection meter . this device outputs a low power laser beam and measures the back - reflection amplitude . epoxy the pdv probe in place once the back reflection has been determined to be optimal . place the test item in the chamber and attach both the detonation velocity wires ( fiber - optic or piezoelectric ) and the pdv fiber . close all required doors / ports / etc . and conduct area lockdown operations per facility s explosive test firing sops . confirm oscilloscope trigger , voltage / division , time / division settings . the raw pdv signal must be processed using an fast fourier transform ( fft ) based analysis package . note : by looking at the frequency content of this raw signal , and knowing the initial frequency of the light source ( 1,550 nm ) , the fft analysis package produces a velocity spectrogram that plots the recorded velocity as a function of time . in this case , plotdata , a proprietary united states department of energy graphical user interface ( gui ) , is used in conjunction with labview software to carry out the fft . however , since the spacing of each fiber - optic is known , the detonation velocity is calculated by dividing the distance between each pin by the time between each peak ( distance / time = velocity ) . the average and standard deviation is reported . a typical setup for pdv is shown in figures 2 and 3 , while the fodv setup is shown in figure 4 . upon detonation , the resulting dent plates from traditional fodv shots are shown in figure 5 , with the position / time results of pax - 30 and pbxn - 5 in figure 6 . both materials possess similar detonation velocities ( the slope of the line ) , with pax - 30 ~ 0.4 sec / mm slower . while it may not seem to be a significant difference , it is indeed in light of the fact that pax - 30 possesses nearly 20 % less by weight explosive fill . detonation velocity is not the conclusive test to quantify the aluminum reaction in the or immediately after the detonation front , but it can give a preliminary assessment of aluminum reaction . the stick is epoxied on the steel witness plate to ensure a solid contact and upright stance during setup . each data point is from the fiber - optic pins in the fodv setup . pax - 30r = 0.999717 , rmse ( root mean square error ) = 0.519693 ; pbxn - 5 r = 0.998778 , rmse = 1.342272 . the output from the pdv trace of the flyer plate from the bottom of the explosive charge of figures 2 - 3 is shown in figure 7 . the oscillations arise from the ringing in the plate from the rapid acceleration to nearly 4 - 5 km / sec . the cj pressure is calculated from modeling the product gas hugoniot with cooper s approximation , and then extrapolating the cj point once the aluminum - explosive hugoniot is matched . a typical screen print from such a calculationthe technique still has some limitations since the calculations assume a linear acceleration extrapolation from the beginning of the flyer velocity . this results in slightly underestimating the pressure , as evidenced by the results ( table 1 ) . work is ongoing to develop new equations to fit the early acceleration of the flyer plate . figure 7 . plate velocity as a function of time for the measurement of cj pressure in the pbxn - 5 explosive . note the excellent agreement between two different shots , where the traces practically fall on one another . calculation of the cj pressure from the copper flyer plate data on the pdv experiment . note that the extrapolation assumes a linear acceleration in the initial push of the flyer plate which currently leads to an underestimation of the cj pressure . the blue straight lines are the tangent solutions that are proportional to the detonation velocity . note the reacted al products solution force the detonation velocity to be lower than the unreacted al solution . the aluminized explosive exhibits less pressure , partially due to less nitramine ( hmx ) loading , but also because the aluminum reacts with oxygen in the expanding detonation gases , which results in a smaller dent from a lower detonation pressure . the pbxn - 5 exerts a higher detonation pressure due to its higher gas content upon detonation compared to pax - 30 ( 36.2 moles / kg for pbxn - 5 versus 33.1 moles / kg for pax - 30 ) . more advanced equations of state ( eos ) derived from wall velocity measurements are used to describe the conditions of the explosive products at such extreme temperatures and pressures . it was apparent that when early reaction of a metal in an explosive occurs , the detected detonation velocity is lower than if the metal does not react . this is somewhat counterintuitive ; one would expect the velocity to increase if more energy deposits into the expanding detonation front due to exothermic reaction of aluminum . the specific volume ( inverse density ) - pressure isentrope denotes changes in as products from the detonation expand ( from left to right in figure 9 ) . the expansion isentrope represents those detonation products that can thermodynamically form and expand along the pressure - specific volume curve . during the course of expansion , if the aluminum reacts to form oxidized species , it results in an overall decrease in density of gas and leads to a lower velocity . this is manifested in an expansion isentrope below the solution for the non - reactive aluminum ( figure 9 ) . since the detonation velocity is the tangent line intersecting the isentrope from the starting density on the x - axis , it is apparent the detonation velocity must decrease when the aluminum in the formulation reacts . in summary , the united states department of defense continues to actively pursue applied research and characterization of new energetic materials with both traditional and novel technologies . in the case of pdv , it is a valuable tool that characterizes explosives with extreme accuracy and provides the researchers with valuable insight into the explosive effectiveness . this rapid test cycle greatly decreases cost and the time needed for formulation optimization and requirements verification .
output:
